Information

Has any research lab done serious work to engineer new bacteria which assemble graphene wafers?

Has any research lab done serious work to engineer new bacteria which assemble graphene wafers?


We are searching data for your request:

Forums and discussions:
Manuals and reference books:
Data from registers:
Wait the end of the search in all databases.
Upon completion, a link will appear to access the found materials.

I was thinking about crazy uses for engineered bacteria. Nano-assembly of Graphene seems like a potentially excellent target for the technology. Have any research/full-blown labs worked on this? Any papers on it? What would be some of the difficulties?


Surprisingly, the answer is yes. In 2012 Tanizawa et al published a paper titled Microorganism mediated synthesis of reduced graphene oxide films. The gist of it is that most of the steps (including the structuring of the graphene sheet) were carried out with chemical synthesis, but a final reduction step from graphene oxide to graphene was carried out using bacteria from a local river.

Probably not quite what you were thinking of, but I imagine this is the closest you'll get for right now.


Water quality monitoring of drinking, waste, fresh and seawaters is of great importance to ensure safety and wellbeing for humans, fauna and flora. Researchers are developing robust water monitoring microfluidic devices but, the delivery of a cost-effective, commercially available platform has not yet been achieved. Conventional water monitoring is mainly based on laboratory instruments or sophisticated and expensive handheld probes for on-site analysis, both requiring trained personnel and being time-consuming. As an alternative, microfluidics has emerged as a powerful tool with the capacity to replace conventional analytical systems. Nevertheless, microfluidic devices largely use conventional pumps and valves for operation and electronics for sensing, that increment the dimensions and cost of the final platforms, reducing their commercialization perspectives. In this review, we critically analyze the characteristics of conventional microfluidic devices for water monitoring, focusing on different water sources (drinking, waste, fresh and seawaters), and their application in commercial products. Moreover, we introduce the revolutionary concept of using functional materials such as hydrogels, poly(ionic liquid) hydrogels and ionogels as alternatives to conventional fluidic handling and sensing tools, for water monitoring in microfluidic devices.

Janire Saez is a Marie Curie Fellow and Research Associate in the Bioelectronic Systems and Technology group at the University of Cambridge working on bioelectronics and microfluidics. She has a degree in Chemistry and a Master’s degree in Pharmacology from the University of the Basque Country (UPV/EHU). In 2017, she obtained her PhD in Environment and Marine Resources from the same university. During this time, she studied the integration of smart materials into microfluidic devices for environmental water monitoring, fluidic handling and sensing.

Raquel Catalán-Carrio studied Chemistry in the University of Valencia and completed her master studies in Electrochemistry in the Department of Physical Chemistry in 2014. Then, she worked in the Polytechnic University of Valencia (UPV) studying the corrosion of hip prosthesis, for six months. In 2018 she finished another master degree in Environmental Contamination and Toxicology at the Basque Country University (UPV/EHU) on microfluidics for the detection of nitrite and nitrate in water. Now, she’s doing her PhD in the generation of innovative detection systems based on microfluidics and optical fibers to monitor water analytes at the point of need.

Róisín M. Owens is a University Lecturer at the Dept. of Chemical Engineering and Biotechnology in the University of Cambridge and a Fellow of Newnham College. She received her BA in Natural Sciences (Mod. Biochemistry) at Trinity College Dublin, and her PhD in Biochemistry and Molecular Biology at Southampton University. From 2009 to 2017 she was a group leader in the dept. of bioelectronics at Ecole des Mines de St. Etienne, on the microelectronics campus in Provence. Her current research centers on application of organic electronic materials for monitoring biological systems in vitro, with a specific interest in enhancing the biological complexity and adapting the electronics to be fit for purpose. She currently serves as co-I and co-director for the EPSRC CDT in Sensor Technologies, renewed in 2019. She is a 2019 laureate of the Suffrage Science award. From 2014 to 2020, she was principle editor for biomaterials for MRS communications (Cambridge University Press), and she serves on the advisory board of Advanced BioSystems and Journal of Applied Polymer Science (Wiley). In 2020 she became Scientific Editor for Materials Horizons (RSC). She is author of 80+ publications and 2 patents and her work has been cited more than 4000 times.

Lourdes Basabe-Desmonts is an IKERBASQUE Research Professor and the group leader of BIOMICS microfluidics Research Group at the University of the Basque Country (UPV/EHU). Her team is focused on the development of microtechnologies for lab-on-a-chip applications for biology and medicine, comprising areas such as chemistry, micro and nano engineering of surfaces, optical sensing, microfluidics, microsystems for single cell studies and point of care diagnostics. She is co-founder of the Microfluidics Cluster UPV/EHU. Lourdes studied Chemistry at the Universidad Autónoma de Madrid, then she did a PhD at the University of Twente in Supramolecular Chemistry and Nanotechnology. Following she joined the Biomedical Diagnostics Institute in Dublin where after a postdoc in polymer microfluidics she became a team leader on “microtechnologies for platelet biology”. In June 2012 she was appointed Research Professor by IKERBASQUE the Basque Foundation of Spain in Spain.

Fernando Benito-Lopez studied chemistry at the Universidad Autonoma de Madrid and completed his master studies in the Department of Inorganic Chemistry in 2002. He obtained his PhD at the University of Twente, The Netherlands in 2007. He carried out his postdoctoral research in the group of Prof. Dermot Diamond at Dublin City University, Dublin, where in 2010, he became Team Leader in polymer microfluidics. In 2012 he moved to CIC microGUNE a Research Center working in Microtechnology in Spain. In 2015 he became Ramón y Cajal Fellow at the University of the Basque Country, Spain. He is currently Assoc. Prof. of the Microfluidics Cluster UPV/EHU at the University of the Basque Country.


Development of DNA Nanotechnology and Uses in Molecular Medicine and Biology

*Corresponding Author: Dr. Asit Kumar Chakraborty
Department of Biotechnology and Biochemistry
Oriental Institute of Science and Technology (OIST)
Vidyasagar University, Medinipur
West Bengal 721102, India
Tel: 919339609268
E-mail: [email protected]

Received date: October 25, 2016 Accepted date: November 16, 2016 Published date: November 21, 2016

Citation: Chakraborty AK, Roy T, Mondal S. (2016) Development of DNA nanotechnology and uses in molecular medicine and biologyy. Insights in Biomed. 2016, 1:2.

Abstract

DNA is hereditary material with simple and stable building blocks of phosphate- 2&rsquodeoxy ribose-organic nitrogenous base with unique 3-D structure with AT-GC paring of two anti-parallel strands. DNA in solid or solution is a good carrier of electrons and biocompatable with binding efficiency to many proteins, organic molecules and metal ions. With the advent of nanotechnology in silver-gold nanoparticles and carbon nanoparticles, DNA has now been utilized as good source of nanotechnology material. In DNA nanotechnology, Watson-Crick DNA molecules are arranged into variety of nanostructures in the range of 10-100 nm size under special physical conditions due to electrostatic attraction among free electrons of sugar and phosphate oxygen and base nitrogen. However, different cohesive or sticky ends or loop structures among oligonucleotide staple strands have helped to make 3-D DNA nanostructures with various shapes. Holiday junction formation during crossover of chromosomes is the basis of DNA nanotechnology as millions fold compacted 3-D DNA structure is inherited in DNA itself. DNA tiles are hydrogen bonded few oligonucleotides which have cross sharing among themselves at the both ends. DNA-origami is principle when one big single stranded circular DNA crossovers with hundreds of short antisense oligonucleotide staple strands at different positions giving different shapes. In principle, when DNA tiles or DNA origami are allowed to crystal formation at 90°C to 4°C transition in presence of 10-20 mM MgCl2, DNA nanocrystals are formed. Thus, gold and silver as well as many drugs were impregnated in the DNA nanocages that were targeted to many pathogens and cancer cells. Such co-crystallised nano-drug delivery system also has been integrated to antisense/ribozyme/dicer molecular medicine. Recently, solid DNA nanotechnology applications combining DNA with proteins or cellulose and cross-linked with streptavidin-biotin are used in nanochip, nanosensor and nano-robotic technologies.

Keywords

DNA tiles DNA nanotubes DNA origami DNA-nanocages Drug delivery

The term "nanotechnology" was first defined by Dr. Norio Taniguchi in 1974 as process and utilization of materials made of single atom or molecule [1]. The nanomaterial exists in a very small scale (10-6 of a millimetre) as exemplified, a human hair is about 80000 nanometers and our hereditary DNA molecule (chromosome) is about only 5-10 nanometers. Nano-particles or nano-medicines are 100-10000 times smaller than a human cell (

20-50 &mum) and much smaller than microorganisms (

1-5 &mum) that to be targeted or to be modified (Figure 1).

Figure 1: Size of nanoparticles.
Note: Nanoparticles are compared with different sizes of the cells and large particles like tennis ball including atomic particles like glucose and water molecules.

DNA nanotechnology was started due to the development of Cluster science and Scanning tunneling microscope followed by discovery of fullerenes in 1985 that had demonstrated how wonder properties of single cell carbon film (200x strength than steel) could exist in nature [2]. Nano-materials prepared from transition metals like silver or gold were complexed with drugs that eradicated many untreatable MDR diseases and metastasis cancer in human. The basis for nano-medicine approaches were pioneered by the earlier discoveries: (i) liposomes in drug delivery and in DNA transfection, (ii) controlled release system of macromolecules [3], (iii) circulating stealth polymeric nanoparticles [4], (iv) quantum dot bio-conjugate system [5] and (v) nanowire nano-sensor dates [6].

Success of Silver-Gold Nano-Particles and Graphenes

Most published nano-particles today are silver and gold nanoparticles. Silver (Ag) is a transition metal element having atomic number-47 (1s2, 2s2, 2p6, 3s2, 3p6, 3d10, 4s2, 4p6, 4d10, 5s) and atomic mass-107.87 whereas gold (Au) has an atomic number-79 (Ag.5s2, 5p6, 5d10, 6s) and atomic mass 170.23. Inert gas condensation or co-condensation techniques are used where evaporation of metal into an inert atmosphere with the subsequent cooling for the nucleation and growth of the nanoparticles are done. For the biosynthesis silver/gold nanoparticles, 1.5 ml of plant extract was mixed with 30 ml of 1 mM AgNO3 or 1 mM HAuCl2 solution and was incubated at 28˚C for 24 hrs until colourless silver nitrate solution turned brown colour or pale yellowish HAuCl2 [7]. The mixture was centrifuged at 6000rpm for 10 min and the pellet was re-suspended in sterilized double distilled water and then sprayed on glass slide to make thin film. The thin film was kept in hot air oven to dry and then the thin film was used for the TEM/SEM analysis (Figure 2). The antibacterial efficiency of the nano-particles was determined by introducing the particles into a media containing bacteria in petridisc. The nanoparticles were found to be completely cytotoxic to bacteria like Escherichia coli and Pseudomonas aeruginosa for surface concentrations as low as 8 &mug of Ag/cm 2 [8-10].

Figure 2: Ultra-structures of gold nanoparticles.
Note: 0.5 gm dry plant extract was added to 50 ml of 1 mM aqueous HAuCl4 solution in conical flasks of 100 ml content at room temperature and was shaked at 150 rpm in the dark at 30°C. The solutions were dried at 60°C and examined by an X&rsquoPert Pro x-ray diffractometer (PANalytical BV, The Netherlands) operated at a voltage of 40 kV and a current of 30 mA with Cu K&alpha radiation.

DNA Nano-Technology

DNA is a chain of phosphate-pentose sugar which attached to different organic bases (adenine, cytosine, guanine and thymidine) and ds-DNA (genetic material in living cells) means two monomeric chains of DNA intertwined in opposite directions in Watson-Crick Model (Figure 3). Solid DNA is thread like whitish stable structure which is very soluble in water giving viscous opaque solution and could be detected in ng quantities by fluorescence banding of ethidium bromide stained agarose gel or 260 nm UV spectrometry. Biological synthesis of DNA by enzyme, DNA polymerase or in vitro synthesis of DNA by automated oligo-synthesizer is easy task. Similarly, topological inter-conversions of circular DNA molecules (plasmids) by enzyme DNA topoisomerases are now easy to see the inter-conversion of coiled-relaxed, monomer-catenenes, knotted-unknotted DNA topological isomers. Interestingly, DNA ligase could arrange head to tail joining of small ds-DNA molecules into massive DNA structure as seen in the chromosomes 2000000-20000000 [11,12]. In nature, similar chain structure also have been found in other systems like (i) cellulose is chains of hexose sugar (&beta1- >4 linkage) and in starch (&alpha1->4 linkage),, (ii) proteins are chains (up to few thousands) of 20 different amino acids joined by &ndashCO-NH- peptide bonds and (iii) in RNA which is very similar to monomeric DNA except in place of thymidine usually uracil present. Important thing, such chains could form complex 2-D and 3-D structures naturally and their roles in biology inevitably were emerging out recently. ds-DNA presents in bacterial genome (usually 1-2 molecules in bacteria, few in fungi and yeast and more than twenty in parasites and 46 in human diploid cells). The bacterial chromosome contains 3000000-5000000 bases but circular plasmids exist in many copies as only few thousand bases carrying drug resistant genes (amp, tet, neo, str, cat) but could be larger as conjugative MDR plasmids (

100-500 kb) containing 10- 15 mdr genes and few dozen of Tra and Tnp genes [13,14]. Such DNA could form topological isomers with difference in linking number or form knot and catenenes as exemplified in (Figure 4) [15]. It is noteworthy to say that now all enzymes have been purified and available and you could test how such enzymes (DNA topoisomerases, DNA ligase, Taq DNA polymerase) could form complex structures from monomer substrates.

Figure 3: Structure of ds-DNA and base-paring.
Note: DNA is composed of two anti-parallel phosphate-sugar-base backbones with A-T and G-C base paring between two strands and 10.5 base pairs are required for every turn requiring 34AO or 3.4 nm length along the axis.

Figure 4: (A) Agarose gel electrophoresis of different topological forms of plasmid DNA and KDNA. (B) Part of the catenated structure of kDNA. (C) EM of decatenated KDNA. (D) Linking number changes by step-1 or step-2.
Note: (A) Lane 1, 4063bp supercolied plasmid pBR322 but also present nicked relaxed contaminant lane 2, treated with topoisomerase I causing slow moving topological isomers, lanes 3 and 4, high molecular weight DNA catenenes formation by topoisomerase in presence of histone H1 or spermidine lane 5, kDNA of Leishmania donovani and lane 6, kDNA treated with topoisomerase II which releases monomer kDNA minicircles (Chakraborty and Majumder, 1987). (B) kDNA is composed of thousands of mini-circles canenated with maxi-circles (

30 kb) or within mini-circles (

860bp). (C) The super-coiled, relaxed and linear minicircles were shown that were obtained by digestion of kDNA with topoisomerase II. (D) Plasmid DNA (lane 1) treated with topoisomerase I (lane 2), isolated unique topoisomer from lane 2 was treated with topoisomerase I (lane 3) or topoisomerase II (lane 4) showing linking number changes. All reactions support that DNA has inherent property to make many topological isomers and hence forms nanostructures (Chakraborty et al., 1994).

Watson-Crick ds-DNA has minor groove and major groove and free electron of sugar oxygen and phosphate oxygen providing centres of electrostatic attractions facilitating the formation of nano-particles of different shape and size. The field of structural DNA nanotechnology could be traced back to the words written by Nadrian Seeman in 1982 &ldquoIt is possible to generate sequences of oligomeric nucleic acids which will preferentially associate to form migrationally immobile junctions, rather than linear duplexes, as they usually do [16] and further advanced by Seeman and co-workers with the construction of relatively flexible branched junction structures and topological structures [17,18] and progressing to the fabrication of crossover DNA tiles with greater rigidity. These DNA tiles could be used to assemble higher-order periodic and aperiodic crystal lattices as the basics of DNA nano-technology [19-23].

One of the most important developments in structural DNA nanotechnology since the introduction of the crossover tile DNA nano-particles was the use of a &lsquoscaffold&rsquo DNA strand for the assembly of aperiodic structures. It had been previously demonstrated that a long single-stranded DNA chain could be used to organize double-crossover tiles into barcode-patterned lattices, and that a 1.7-kb single-stranded DNA chain could serve as a scaffold for the assembly of a 3-D wire-frame octahedron (Figure 5). The breakthrough came with the concept of &lsquoDNA origami&rsquo, where a long scaffold strand (single-stranded DNA from the M13 phage genome,

7,429 nucleotides long) was folded with the help of hundreds of short &lsquostaple&rsquo strands into defined two-dimensional (2-D) shapes [24,25].

Figure 5: Simple demonstration of DNA nano-crystal formation by 3% PAGE.
Note: About 0.25 mM ss-DNA (300-7000 bases), 1.5 mM DNA staple strand oligonucleotides (30-40 bases), 20 mM MgCl2, 40 mM Tris-acetate P H 8.0, 2 mM EDTA and 90°C to 20°C temperature are mixed and samples are withdrawn at different time intervals and run 3% polyacrylamide gel electrophoresis in 1x TAE buffer for 4 hrs. The autoradiograph positions of DNA nanostructures are shown as very slow moving DNAs. High molecular weight crystal 3-D nanostructures are formed at 2 hrs to 48 hrs (Zhang et al. in 2008).

Preparation of DNA Nanoparticles

Solid DNA is thread like whitish stable structure which is very soluble in water giving viscous opaque solution and could be detected in ng quantities by fluorescence banding of ethidium bromide stained agarose gel or 260 nm UV spectrometry. Large genomic DNA is hard to handle as it breaks into parts due to high viscosity. The starting material for DNA nano-particles was made by synthesising short oligo-nucleotides (two dozen to few dozen phosphate-sugar-base units), called oligonucleotides primer or staple strands which have cross AT/GC pairing with parent single stranded cccDNA strand which is usually M13 viral DNA (

7400bases). Such DNA mixture (1:5 at 1-5 mM concentrations) when heated to 90°C and then slowly cooled 20˚C in presence of

20 mM MgCl2, 2-D and 3-D ds-DNA nano-structures were formed.

Bacterial genomic DNA could be isolated by digesting bacteria in SDS-Proteinase-K overnight followed by phenol-chloroformisoamyl alcohol (25:24:1) extraction and ethanol precipitation (2 vol., 99% pure) in presence of salt (300 mM NaCl). Then sonicate the genomic DNA to get smaller DNA which could be further purified by agarose gel electrophoresis followed by elution of specified length ds-DNA from gel using DNA Gel extraction kit from Promega or Qiagen. As the genome sequence is known, any DNA staple strands could be synthesized which could form double cross over (DX) or triple cross over (TX) with parent ssDNA giving nano-crystals. Single stranded bacteriophage DNA (M13) was used with success and design of staple strands would be easy and DNA origami of different shapes could be prepared using few to hundred staple strands (30-40 bases 1-5 mM solution 10 mM MgCl2) from different part of the M13 genome [26]. Now, different softwares were available which could predict the main DNA (200- 300 bases) and 32 bases long different oligonucleotides straple strands to produce 3-D DNA nano-tubes or DNA nano-cages. One can design many sticky strands like cohesive ends of EcoRI and PstI restriction enzymes digested DNAs or different nob like hairpin structures between AT/GC pairing complementary staple strands which favours the DNA crystal formation at the range 10- 50 nm (Figure 5).

DNA Holiday Junction

Holliday Junction was produced as a DNA recombination intermediate in cells and was proposed by Dr. Rabin Holiday in 1965. Dr. N. C. Seeman in 1980 had shown a number of DNA nanostructures using PX DNA branched staple strands very similar to holiday junction of chromosome recombination (Figure 6). In other words, DNA assembly was the inherent property of DNA itself of B-DNA or Z-DNA and was favoured by Mg++ ions and proteins which could be histones and transcription factors.

Figure 6: Four staple strands complex and chromosome holiday junction.
Note: Holiday junction formation during chromosomes crossover in cells (panel A) and similar structure was formed in DNA nanotiles (panel B) and original compressed chromosome structure in mammalian cells (Panel C) were presented. In DNA tile four cross sharing oligonucleotides are used shown in different colour. Note that human DNA

1.5 meter long in 46 chromosomes (3x109 bases) but compacted into 5 micrometer diameter nucleus where each metaphase chromosome DNA appeared as 10-20 nanometer length due to histone assembly, helical structures and electrostatic interactions with non-histone proteins (Chen et al., 2004).

DNA Tiles and DNA Nanotubes

DNA tiles defined as ds-DNA fragments with sticky ends composed from few synthetic oligonucleotides (30-100 bases) with multiple complementary hydrogen bonding motifs among themselves and forms variety programmable DNA lattice structures in presence of 10-20 mM Mg++ ion at 90˚C to 20˚C program in a thermostat for 2 hrs [26,27]. Self-assembled 2D DNA tiling lattices composed of tens of thousands of tiles had been demonstrated by Seeman, Winfree, and Reif groups and visualized by molecular imaging techniques such as atomic force microscopy (Figure 7). There are at least three major strategies for the formation of patterned DNA tiling lattice with DX and TX self-assemblies: (i) Unmediated algorithmic self-assembly is the simplest method for 2D pattern formation using 3-10 sets of DNA tiles that self-assemble in a predictable manner. Unmediated algorithmic self-assembly of complex patterns requires delicate control of physical phenomena, which includes nucleation rates, crystal growth rates, spontaneous nucleation, and error rates in solutions containing many distinct DNA tile types but hardly requires patterned oligonucleotides. (ii) 2 nd Sequential stepwise assembly of DNA tiles was started with molecular building blocks (MBBs) attached to a solid support, to enable removal of excess reactants after each step. Such sequential assembly might allow for the synthesis of complex molecular structures, while extensively reusing a small number of MBB types. (iii) Directed nucleation assembly is the 3rd method used for selfassembly of complex patterned lattice. It uses a preassembled input DNA strand that encodes the required pattern information other oligonucleotides then assemble into specified tiles around this input scaffold strand, forming the desired 1D or 2D pattern of DNA tiles. Karina et al. produced Rolling Circle Amplification nanotubes (RCA) using circular phage M13 or phage 29 and 31 base primers (0.4-1.5 mM) led to nanotubes formation in 1x TAE + Mg++ (20 mM) buffer at buffer at 95°->4°C thermostat thermostat [28-31].

Figure 7: 2-D DNA nano-tiles formation principles.
Note: Representative four ssDNA oligonucleotides with sharing AT-GC base pairing and sticky ends were mixed and allowed crystal formation as in Figure 5 (Seeman, 2010).

DNA Origami

Origami means to a Japanese art of transforming a flat sheet of paper into an arbitrarily shaped object through folding and sculpting techniques. In DNA origami, a long single strand of DNA (scaffold) is folded into various shapes by hundreds of synthetic oligonucleotides, referred to as staple strands targeted to bind to different places along the scaffold anti-parallel DNA strand, giving a precise size and shape of the final DNA nano-structure, called DNA origami structures or origami nanotiles (Figure 8) [32]. As for example 7249 bp M13mp18 DNA with 225 oligonucleotides of 32 nt long could assembled within 2 hrs into 90 nm × 60 nm rectangular origami with 32 helices [19,33,34]. Sugiyama et al. have also reported box structures with similar design features and Yan et al. have used a related strategy to construct a hollow 3-D DNA origami tetrahedron. Shih and co-workers also have reported a new set of design principles for 3D origami construction [34]. Rather than hollow structures, the origami was denser with a design based on the parallel arrangement of helices into a honeycomb lattice. Further, Yan and co-workers have reported a strategy to design and construct 3D DNA origami structures that contain highly curved surfaces providing DNA into under wound or over wound as compared to B-DNA with 10.5 bp per helical turn as well as 3-D tensegrity origami [35-37]. Tensegrity means to construct light weight structures from compressed (rigid) beams connected by stress-bearing wires. When applied to DNA origami, the scaffold is used to generate the rigid beams, together with the staple strands, but also as the stress-bearing wires and is very stable DNA structures [38].

Figure 8: 3-D DNA origami formation principles.
Note: One circular ssDNA (large) and other few staple oligonucleotides are assembled (Zhang et al. 2008 with permission) as in Figure 5 and 3-D nano-tubes are formed (Zheng et al. 2009).

DNA Aptamer

Aptamers are ss-DNA or ss-RNA oligonucleotides that can selectively bind certain targets such as proteins/ nucleic acids/ small organic compounds with high specificity. Selective thrombin DNA aptamer (5&rsquo-GGTTGGTGTGGTTGG-3&rsquo) binding as tool to position proteins in the self-assembled DNA arrays [38]. Polystyrene adaptamer (PS13-DNA) nanotubes has been characterized at 36 nm when annealed at 95˚C to 4˚C in a thermostat coupling and polymer ultra-structure were confirmed by 3% PAGE and TEM [25,39-42].

DNA Walker

Concept of DNA walker is branched DNA strands located on the parental strand hybrids could be hybridised repeatedly by walking mobile staple strand following strand displacement method and sequestering a move of electrical signal which could be utilized as barcode [43-45]. Green mobile strand could move one hairpin nob into another due to AT-GC pairing and greater strand homology (Figure 9).

Figure 9: Concept of DNA walker.
Note: Watson-Crick DNA make 2-D structure with base paring. Different staple strands with sticky ends when assembled in a base ss-DNA periodically, then a mobile linker staple strand (green) could be designed to move one knob DNA into nearby nob DNA due to preferential and greater hydrogen bonding (Zhang and Winfree, 2009).

Problems of DNA-Nanoparticles

Working with Ag-nano-particles is quite easy but using DNA, you need a DNAase, RNAase and Protease free environment, and otherwise you will see no result. DNase present in every organism from bacteria to fungus to yeast. So all reagent and chemicals are used in preparing DNA-nanoparticles must be aseptic conditions and must be free from DNase enzyme. Simple way to do it, autoclave at 121˚C for 15 min or heat at 250˚C for 2 hrs or wash with ethanol repeatedly (whatever applies to your system) and possibly keep 1-10 mM EDTA in buffer and use gloves during work. So handling with RNA like in ribozyme technology is more serious because RNaseH/T/A also present in every organism and is very stable and active [46]. Similarly protease could cleave proteins used in DNA-nanotechnology. Thus during use of polymer biomolecules like DNA, RNA and protein excess heat and hydrolytic enzymes contaminations must be avoided [47]. Similarly, during each experiment you have to check the preparation by atomic force microscopy to TEM/ SEM as oligonucleotides form crystal structures. However, 3% polyacrylamide gel could be easy to see the slow moving crystals by EtBr staining or autoradiography in case of radiolablled oligonucleotides. Biotin-labelled oligonucleotides could be used using non-radioactive labelling method involving streptavidineconjugated peroxidise.

DNA-Nanotechnology in Medicine

Nanotechnology uses for the treatment, diagnosis and control of diseases has been referred to as &ldquonano-medicine&rdquo [48-50]. The work of N. C. Seeman and co-workers have established DNA structures as versatile building blocks for complex nano-scale assembly including immobile holiday junctions, cubic cages, and two dimensional lattices to the vision of a three dimensional DNA crystals. Such DNA-nanoparticles could carry drugs and gene medicines [51]. Although the application of nanotechnology to medicine appears new, the basic nanotechnology approaches for medical application was known for decades. The first example of lipid vesicles or liposomes in drug delivery and DNA transfection were described in 1960s and the first controlled release polymer system of macromolecules was described in 1976 [3] and the first quantum dot bio-conjugate was described in 1998 [5] and the first nanowire nanosenser dates back to 2001 [6]. DNA nanostructures are biocompatible and very potential in drug delivery with no toxicity [52-54]. Carbon monolayer (fullerenes) nanotubes have been increasingly used to deliver plasmids and DNA-conjugates in gene therapy and gene targeting [55].

Uses of DNA nano-particles to cure bacterial infections

The medicinal uses of silver have been documented since 1000 B.C. Silver is a health additive in traditional Chinese and Indian Ayurvedic medicine. Silver nanoparticles broadly accomplish its activities in three ways against Gram-negative bacteria: (1) nanoparticles (

2&ndash8 nm) attach to the surface of the cell membrane disrupting permeability and respiration (2) inside the bacteria they cause further damage by interacting DNA and, (3) nanoparticles release silver ions which could bind cysteine residues. ROS and free radical production is one of the primary mechanisms of nanoparticle toxicity it may result in oxidative stress, inflammation, and consequent damage to proteins, membranes and DNA for bactericidal activities [56]. Studies demonstrated the potential for nano-materials to cause DNA mutation and induce major structural damage to mitochondria resulting in cell death [57]. The development of drug resistance in bacteria has become a serious problem in public health and alternative methods are welcomed by medical authorities [13]. The structural differences in gram(+) and gram(-) bacteria lie in the organization of the peptidoglycan layer as a thin layer (

2&ndash3 nm) between the cytoplasmic membrane and the outer membrane, in contrast to Gram-positive bacteria lack the outer membrane but have a rigid peptidoglycan layer of about 30 nm thick. A multi-drug resistant strain of gram-negative (Salmonella typhus, resistant to chloramphenicol, amoxicillin and trimethoprim) bacteria was also subjected to analysis to examine the antibacterial effect of the nanoparticles [58]. Silver and gold nanoparticles with Cinnamomum plant extract show very potent antibacterial activities and also cure multi-drug resistant bacterial infections [59,60]. Such advantage when combined with DNA nanotubes, immobilized gold with DNA nanostructures were found more effective in killing pathogens and no toxicity to the host was detected [61,62].

Uses of DNA nano-particles to cure cancer

DNA nanostructures are ideal vehicles to deliver toxic drugs into tumour sites less affecting normal cells. Thus, DNA is genetic material, possesses high biocompatibility and low cytotoxicity, ideal for applications in the biomedical field [63-66]. Its remarkable molecular recognition properties, and GC/AT base pairing with mechanical rigidity, nano-dimensions of the repeating unit, easily custom synthesis with any length of strands allow the formation of any shape of 2-D and 3-D nanostructures with versatile highly nontoxic drug nano-carriers (Figure 10) [67,68]. In 2004, the National Cancer Institute (NCI) in the USA created the Alliance for Nanotechnology in Cancer, which spearheads the integration of nanotechnology into biomedical research through the coordinated effort of a network of investigators from diverse institutions and organizations. The Centres of Cancer Nanotechnology Excellence (CCNEs) integrate discovery and tool development for nanotechnology applications into clinical oncology. CCNEs link physical scientists, engineers, and technologists working at the nanoscale with cancer biologists and oncologists. The Cancer Nanotechnology Platform Partnerships are engaged in directed, product-focused research that aims to translate cutting-edge science and technology into the next generation of diagnostic and therapeutic tools. These platforms serve as core technologies for a wide array of applications. Doxorubicin coupled with isosahedral and hexagonal DNA origami and also with SiRNA used to deliver cancer cells with success [69-72]. Small interfering RNAs of VEGF, XLAP, PGP, MRP-1, BCL-2 and cMyc genes have shown immense promise to knockout drug resistance genes as well as to recover the sensitivity of resistant tumours to anticancer therapy [73-76]. Combinatorial anticancer effects of curcumin and 5-fluorouracil loaded thiolated chitosan nanoparticles towards colon cancer also has been developed [65].

Figure 10: Doxurubicin drug packaging in DNA nanotubes.
Note: The association of single strand oligonucleotides (shown in different colours) in DNA are shown and forms DNA nanotubes carring drug doxorubicin. Such DNA nano-structures exceptionally could deliver drugs into cancer cells which then go apoptosis (Klippstein et al., 2015).

DNA nanostructures used against viral diseases

Versatile nature of DNA nanotubes as carrier of drugs, antisense RNA, enzymes to the target sites also have been utilized to control virus penetration and elimination [77].

Discussion

Pinheiro et al. beautifully have explained in an research article in Nature Nanotechnology in 2011, the advanced nano-chips in modern mobile phone vs. in an ancient calculator and also in a biology context,

40 proteins and few RNA molecules complexed to form ribosome where protein synthesis occur [9]. Such examples satisfied the future of DNA nanotechnology and to design many advanced technologies with biological particles as well as biophysical particles. The essence is that DNA is also very stable and a good carrier of electrons if protected from heat and nuclease enzyme. Thus, a device like cellulose fibre or like fullerene carbon sheet nanoparticles could be assembled with DNA molecules to increase the stability of DNA nano-particles or DNA nano-transistors [78]. As for example, graphene oxide has been utilized as a veritable wonder material, when incorporated into nano-cellulose foam (as the lab-created bacterial product) conducting heat and electricity quickly and efficiently. The cellulose at the bottom of the bi-layered bio-foam acts as a sponge, drawing water up to the graphene oxide where rapid evaporation occurs and a system for easy water purification was also prepared [59].

Recently, nano-technology has been utilized in many nanomaterials with negative Poisson's ratios with shear resistance and fracture toughness as has been representatively used as vanes for aircraft gas-turbine engines and also applicable to ultrathin oxides films, carbon nano-tube, ferroelectrics, bucklicrystal and fluorides [55]. Boriskina et al. explore different regimes of hybrid optical-thermal antenna operation that depend on the intensity of the light illumination and thermal resistances between the nano-antennas and the rest of the optical nano-chips. The authors also demonstrate how hybrid optical-thermal antennas can be used to achieve strong localized heating of nanoparticles while keeping the rest of the optical chip at low temperature, which can be useful for applications in thermal and thermally assisted catalysis. Plasmonic nanoantennas have opened new horizons in bio-chemical sensing and nanoscale imaging and use of NA nanoparticles could be in the door [79,80]. Recently, Sleiman et al. has integrated a RNA antisense strand of Luciferase in DNA tiles which has reduced the luc gene expression in HeLa cells up to 48 hrs suggesting the use of DNA nano-chips in future molecular biology techniques [81]. DNA nanoparticles mediated vaccine delivery could be a good promise [82].

Conclusion

DNA nanotechnology has given good promise in drug delivery and preparation of biochips and biosensors. However, heat and nuclease sensitivities are much problem and many conjugated adaptamer methods have been formulated like locked nucleotides, peptide nucleic acids, L-DNA, DNA-RNA hybrids, PEG-nucleic acids, Cellulose/Cholesterol/polystyrene-adaptamer oligonucleotides and so many more. UNIQUIMER 3D software has been tested on the design of both existing motifs (holiday junction, 4 × 4 tile, double crossover, DNA tetrahedron, DNA cube, etc.) and non-existing motifs (soccer ball) and other complex DNA nanostructures [72]. We foresee a challenging golden era of DNA nanotechnology in medicine and biology. Use of DNA nanostructures in DNA Walker, DNA Chips, DNA Robotics, DNA Transistors are other applications where we will see tremendous success in the future [52,53].

Acknowledgement

We thank Dr. Bidyut Bandhopadhyay for help during the study and Dr. J. B. Medda for financial support.


Bacterial extracellular electron transfer

The earliest observation of microbial capacity to exchange electrons with extracellular environments was observed by Potter in the early 1900s [35], while the research upsurge started after the discoveries of two typical DMRB (Shewanella and Geobacter spp.) three decades ago [15, 17]. Since then, extensive studies have devoted to molecular mechanisms by which DMRB cells exchange electrons with extracellular redox-active substances, particularlly solid electrodes and inorganic minerals, as well as their functions on the earth's ecology and geochemical element cycle [11]. Meanwhile, a series of microbial electrochemical technologies, such as microbial fuel cell, microbial electrolysis cells, microbial desalination cell and microbial electrosynthesis, have also emerged on the basis of electron exchange between electroactive microorganisms and solid electrodes [13, 36].

As shown in Fig. 2, the bacterial EET process can carry out either directly or indirectly [11, 13, 36]. For the model strain of S. oneidensis MR-1, its direct EET relies on a metal-reducing (Mtr) conduit consisting of six multi-heme c-type cytochromes (c-Cyts): CymA, Fcc3, MtrA, MtrC, OmcA and small tetraheme cytochrome (STC), and a porin-like MtrB located on the outer-membrane, which work together for electron trans-membrane transport [11]. In detail, CymA oxidizes the menaquinol pool located in the cytoplasmic membrane wherein the electrons come from reducing equivalents produced during intracellular energy metabolism, and transfers electrons to the periplasmic redox proteins Fcc3 and STC. Proteins MtrA, MtrB and MtrC form a ternary complex across the outer-membrane responsible for transporting electrons from the periplasmic space to bacterial cell surface [37,38,39,40]. Then MtrC and OmcA can interact with each other and deliver electrons to extracellular electron acceptors (e.g. solid electrodes and insoluble minerals) directly contacted with bacterial surfaces [41,42,43,44]. Notably, the direct physical contact between extracellular electron acceptors and bacterial out-membrane c-Cyts (MtrC and OmcA) is necessary for this EET mode. The Mtr pathway of S. oneidensis MR-1 is the best-characterized EET route so far, and its homologues are found in all sequenced Shewanella species [11, 45]. In the case of indirect pattern, S. oneidensis MR-1 secretes small redox-active molecules such as flavins or other quinones to execute electron shuttling back and forth between cells and external electron acceptors [46, 47]. The indirect EET mode relies on the abilities of these endogenous electron shuttles to effectively pass through the cell membrane barrier. However, the two EET pathways seem to be not independent. For instance, out-membrane c-Cyts have been evidenced to serve as terminal reductases for the extracellular reduction of electron shuttles [45, 48]. Besides, some studies have demonstrated that the flavins can act as the co-factors for outer-membrane MtrC and OmcA to accelerate interfacial electron transfer rate [49, 50].

Mechanistic diagram for the bacterial EET. a Shewanella oneidensis MR-1, and b Geobacter sulfurreducens

Multiheme c-Cyts, especially diverse types of Omc proteins, are also identified to play key roles in the EET process of G. sulfurreducens, and these c-Cyts work collectively to transfer electrons from the quinol pool existed in the cytoplasmic membrane, across the periplasm and outer membrane to the bacterial outside [11, 51, 52]. For example, the deletion of OmcZ (an out-membrane c-Cyts of G. sulfurreducens) resulted in alomost failure in EET capacity [53, 54]. Moreover, it should be pointed out that G. sulfurreducens can generate specific conductive pili that are referred to as bacterial nanowires with metal-like conductivity. The bio-nanowires serve as an alternative direct pathway to achieve more effective electron transport especially in biofilms [55, 56].

There are convincible evidences to indicate that extracellular polymeric substances (EPS), a complex biopolymer mixture produced by bacterial cells, are involved in the EET process [57]. For example, about 20 redox proteins including c-Cyts of MtrC and OmcA were detected in EPS from Shewanella sp. HRCR-1 biofilms [58]. Moreover, EPS matrices extracted from S. oneidensis MR-1 have been confirmed to be electrochemically active with the clear observation of redox peaks of c-Cyts by voltammetry measurement [59, 60]. On account of the existence of vast functional groups like carboxyl, phosphoric, amine and hydroxyl groups, the EPS matrices are expected to be relevant to the formation of MNPs because of their electrostatic affinity for metal ions.

For more details about mechanisms underlying EET, refer to some previous reviews [11,12,13, 19, 36].


Affiliations

Department of Biochemistry and Biomedical Sciences, McMaster University, 1280 Main Street West, Hamilton, Ontario, L8S 4K1, Canada

Meng Liu, John D. Brennan & Yingfu Li

Biointerfaces Institute, McMaster University, Hamilton, Ontario, L8S 4O3, Canada

Meng Liu, Qiang Zhang, John D. Brennan & Yingfu Li

School of Environmental Science and Technology, Key Laboratory of Industrial Ecology and Environmental Engineering (Ministry of Education), Dalian University of Technology, Dalian, 116024, China

School of Life Science and Biotechnology, Dalian University of Technology, Dalian, 116024, China


Using machine learning for wireless communication systems with emphasis on intelligent collaborative spectrum access and interference management. Tasks include source identification, analyzing peer behavior, and context understanding.

Empirical analysis of adversarial deep learning.

Information theoretic approaches to adversarial machine learning.

Machine learning for wireless network security.

Data analysis for soccer players' wearable for promoting physical wellness in training sessions.


4 Common Imaging Problems (and how to fix them)

How frustrating is it to have spent time carefully preparing your sample and setting up the AFM only to find that you’re not getting the images you expected?

Having problems acquiring accurate images is incredibly common, especially if working with the AFM is reasonably new to you.

In most instances it will be due to one of three main things - your sample, the probe you’re using, or because someone else has fiddled with the AFM default settings.

To help navigate some of the common causes of imaging problems you may come across we’ve compiled a short and simple guide to the main problems, what causes them and how you can fix them.

Problem: Unexpected patterns in images

Cause: Tip artefacts

Structures appearing duplicated or irregular shaped features repeating across the image can indicate a broken tip or contamination on the tip. With a blunt tip, structures will appear larger and trenches will appear smaller. If you are seeing either of those things try using a new probe to see if that makes the problem disappear. At NuNano we understand this frustration first hand! We inspect every probe to guarantee tip sharpness, to ensure no contaminated or broken probes which could produce unexpected shapes.

For some more information on probe artefacts, take a look at this blog on ‘Lamentation of Arti(e)facts’ by Dalia Yablon and Philip Moriarty in Microscopy & Analysis: https://analyticalscience.wiley.com/do/10.1002/was.00020100

Problem: Difficulty imaging vertical structures and/or deep trenches

Cause A: Side-wall from pyramidal or tetrahedral shaped probe

Particularly with samples with high aspect ratio features you may be using the wrong type of probe. Check which probe you are using including what shape it is. Conical tips are superior to pyramidal and tetrahedral types in many ways. They can be fabricated with higher aspect ratio (because etching along a particular crystal orientation is not required for their fabrication). As you can see from the image below the trace of a conical tip over a surface with steep-edged features more closely resolves the “real” profile of this surface.

Cause B: Side-wall from low aspect ratio probes

The aspect ratio is defined as the ratio between the height and width of an AFM tip. Conventional probes are unable to accurately resolve the topography of highly non-planar features such as deep and narrow trenches, common in semiconductor device processing. The tip apex is unable to reach the bottom of the trench. Using HAR probes with high aspect ratio tips would resolve this issue as they can fit inside the trenches and produce high-resolution images of these types of features as shown in the image below.

Problem: Repetitive lines appearing across the image

Cause A: Electrical noise.

Electrical noise is easiest to identify first, since its frequency is likely to be 50 Hz. You can compare the frequency of the noise in the image to the scan rate. If your scan rate is 1 Hz, you will see 25 lines on the image, i.e. 25 lines in the trace direction and 25 lines on the retrace, totalling 50 lines in 1 second (50 Hz). If you halve the scan rate, you should see twice as many lines in the image.

In many cases electrical noise can be out of your control, since it’s likely governed by the quality of the electrical circuits in the building, other instrumentation etc. Sometimes it’s possible to identify periods (e.g. early mornings/late evenings) when this problem doesn’t persist, albeit necessitating a change in working habits…)

Cause B: Interference of the laser reflecting off the sample.

A more common cause is laser inference: On most AFM systems some portion of the laser spot will spill off the sides of the cantilever. If the sample is highly reflective, there may be some reflection of the laser light from the sample surface that enters the photodetector, interfering with the light reflecting off the cantilever. Additional interference can occur with light reflecting off the front (tip) side of the cantilever, since thin cantilevers are semi-transparent to typical wavelengths of the laser.

Using a probe with a reflective coating, typically aluminium or gold, can eliminate both of these problems. The metal coating acts to prevent interference between the primary laser signal and reflected light from other surfaces.

For more information about advantages and drawbacks of reflective coatings, different types of metal coatings, and what coatings should and should not be used download our AFM guide: Reflective coating of the cantilever in atomic force microscopy (AFM)

Problem: Streaks on your images

Cause A: Environmental noise/vibration

Environmental vibrations from people moving around the building, open/closing doors, or traffic outside on the street, can affect your images (especially when you’re working on images requiring high resolution). Most AFMs are sold with some form of anti-vibration table and, less commonly, an acoustic box. Make sure the AV table is working, e.g. if it requires a gas supply, it hasn’t run out. Again, carrying out your imaging at a quiet time where possible or even relocating your instrument to a basement room can reduce this.

Sometimes the people around you are simply unaware that there’s vibration sensitive work going on in the lab. We’ve created a ‘STOP AFM in progress’ poster which you’re free to download here. Just letting people know you are imaging a sample could be the easiest and simplest solution. Most fellow researchers will be understanding about your need for them to keep the noise down to decrease chances of noise vibration affecting your images.

Cause B: Surface contamination

Surface contamination causing these streaks can be harder to identify. Loose particles on the sample surface can interact with the AFM tip and either be moved around, or worse, adhere to the tip (see problem 1). The streaks are caused by the instability in the tip-sample interaction, combined with the AFM control trying to react to it.

The only solution here is to ensure your sample preparation protocols minimise loosely adhered material.

For more information on suitable sample prep see our blog: ‘From one AFM user to another …’

These top 4 are the ones you’re most likely to come across. If you’ve come across other issues (especially if you’ve identified the cause) please do get in touch and share with us and the rest of the AFM Community. Sharing is caring after all and seriously, we all need to get those images just right so we can crack on with that other messy business of analysing our data…

Some great places to get more information:

Atomic Force Microscopy, By Peter Eaton and Paul west

Dalia Yablon’s blogs in Microscopy & Analysis:

As always we’re happy to help, if you’re having problems with your imaging that you can’t get your head around get in touch: [email protected]

And make sure to sign up for our newsletter to get NuNano AFM Community emails and hear about our latest blogs, news and products.


Materials Science News

An innovative approach to synthesizing a novel crystalline form of silicon with a hexagonal structure has been developed by researchers at the Carnegie Institution for Science, RMIT University and the Australian National University. The new form could lead to electronic and energy devices with enhanced properties that improve upon the standard cubic form of silicon currently being used.

With the global drive to advance semiconductor technology for both renewable energy conversion and new electronics, it is hoped enhanced forms of silicon, both allotropes and compounds, will offer more effective optoelectronic properties that compliment and/or exceed those of diamond-cubic(DC)-Si. Although silicon can take different crystalline forms, the standard form used in electronic devices such as computers and solar panels is not fully optimized for these new applications.

New synthetic methods are therefore needed, and here a team led by Thomas Shiell and Timothy Strobel applied novel pressure/temperature processing pathways to access these materials. Strobel&rsquos lab had previously developed a new form of silicon called Si24 with an open framework comprising a series of one-dimensional channels. As reported in Physical Review Letters [Shiell et al. Phys. Rev. Lett. (2021) DOI: 10.1103/PhysRevLett.126.215701], here they used Si24 in a multi-stage synthesis pathway. This allowed highly oriented crystals in a form called 4H-silicon, as hexagonal silicon has the potential for tunable electronic properties that could improve performance beyond the cubic form.

While hexagonal forms of silicon have already been synthesized, this was only achieved by the deposition of thin films or as nanocrystals that coexist with disordered material. However, the newly demonstrated Si24 pathway offers the first high-quality, bulk crystals, while the 4H-Si structure opens up new opportunities for semiconductor devices.

Their findings provide a bulk path to the 4H-Si structure and also show the importance of metastability for discovering new phases beyond DC-Si. The application of anisotropic stress could lead to new direct-gap semiconductors for photovoltaic and transistor devices, while the improved elastic properties could help advance micro-electromechanical systems.

As Thomas Shiell said, &ldquoIn addition to expanding our fundamental control over the synthesis of novel structures, the discovery of bulk 4H-silicon crystals opens the door to exciting future research prospects for tuning the optical and electronic properties through strain engineering and elemental substitution&rdquo. There is also potential for using the approach to develop seed crystals to grow large volumes of the 4H structure with beneficial properties.

The team hope the work will encourage further research to scale-up and produce usable devices, and now plan to perform detailed characterization to gain a better understanding of the fundamental optoelectronic and mechanical properties of the 4H structure.

This image shows a trion trapped in a moiré potential well the plane represents the moiré superlattice with a simplified moiré pattern. Three moiré cells are highlighted in color above them is the potential energy profile. The sphere with three glowing 'balls' represents the moiré trion. Image: Ella Maru Studio, with contributions from Hongyi Yu and Wang Yao at the University of Hong Kong, and Wangxiang Li and Joshua Lui at UC Riverside.

When two similar atomic layers with mismatching lattice constants &ndash the constant distance between a layer's unit cells &ndash and/or orientation are stacked together, the resulting bilayer can exhibit a moiré pattern and form a moiré superlattice.

Moiré patterns are interference patterns that typically arise when one object with a repetitive pattern is placed over another with a similar pattern. Moiré superlattices, formed by atomic layers, can exhibit fascinating phenomena not found in the individual layers, opening the door to technological revolutions in many areas, including electricity transmission, information engineering and quantum computing.

Now, by shining laser light on semiconducting moiré superlattices formed by stacking two atomically thin materials &ndash monolayer tungsten diselenide (WSe2) and monolayer molybdenum diselenide (MoSe2) &ndash a team led by researchers at the University of California (UC) Riverside and Academia Sinica in Taiwan have found a new class of electronic excited states called 'moiré trions'.

"These trions, which are confined trion states in moiré potential wells &ndash dips in potential energy &ndash of the WSe2/MoSe2 structure, exhibit novel characteristics that differ markedly from those of conventional trions," said Chun Hung (Joshua) Lui, an assistant professor in the Department of Physics and Astronomy at UC Riverside, who led the research.

The study, reported in a paper in Nature, opens up new opportunities for developing trion-based quantum optical emitters and offers new approaches for exploring moiré physics.

A trion is a bound state of two electrons and one hole, or one electron and two holes, where a hole is the vacancy of an electron. Trions are the dominant light emitters and energy carriers in atomically thin semiconductors with extra charges. By applying external voltages, or electric or magnetic fields, many characteristics of trions, such as their population, emission polarization and motion, can be controlled. The trions' versatile tunability makes them useful for light emission, energy transport and, potentially, information transmission.

In homogeneous semiconductors, trions are free to move and scatter, resulting in broad optical spectra. However, in moiré superlattices, trions get trapped near moiré potential wells and become moiré trions. Their confinement there prevents random scattering.

"We find the emission lines of moiré trions are more than 10 times sharper than those of free trions," Lui said. "As the moiré trions are spatially isolated, they can emit single photons, making them a feasible optical source for quantum information technology."

"Our work points to the possibility of generating two-dimensional arrays of trions in the periodic moiré potential wells," said Erfu Liu, a postdoctoral researcher in Lui's lab and the first author of the paper. "Such 2D trion arrays may exhibit spatial coherence, reveal new physics and find applications in laser technology."

This research on moiré trions also reveals some new physics that could be useful for the further study of moiré superlattices.

"Moiré superlattices are known to host many 'minibands' in their electronic energy band structure," Lui said. "Such minibands are crucial for fascinating phenomena, such as superconductivity, in moiré superlattices. Due to the small energy spacing between these minibands, it is challenging to probe their detailed structure. Moiré trions inspire a new approach to probe the minibands."

Liu explained that in conventional semiconductors with relatively simple electronic bands, a trion decays into the same final electronic state and shows just one emission line. But in moiré superlattices with multiple electronic minibands, a trion can decay into states in different minibands.

"This will produce multiple emission lines, and the energy separation of these lines reflects the energy spacing of the minibands," he said. "Our results support such novel behavior of moiré trions and suggest that moiré trion spectroscopy can be developed to probe electrons in moiré superlattices."

Given the novel characteristics of moiré trions, Lui expects research on them will attract much attention.

"Indeed, related studies of moiré trions were also recently reported by researchers at Heriot-Watt University in the United Kingdom, Nanyang Technological University in Singapore and Tsinghua University in China," he said. "I believe moiré trion research will surge and lead to many exciting discoveries in the future."

This story is adapted from material from the University of California, Riverside, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.

Biodegradable battery made from cellulose nanofibers and nanocrystallites

Researchers from the Swiss Federal Laboratories for Materials Science and Technology (Empa) have developed a biodegradable battery made from a modified and commercially available 3D printer. The printing process, based on a combination of gelatinous inks produced from cellulose nanofibers and nanocrystallites, as well as carbon black, graphite and activated carbon, ensures the device is biodegradable, and can be left to decompose.

The battery has potential uses in biodegradable inks for sustainable electronics, energy storage devices for low power applications in the Internet of Things, integrated health monitoring, and environmental or agricultural sensing. Expanded use of the Internet of Things for wearables, packaging and powering sensors in environmental monitoring has helped a new class of electronics to emerge, with the number of connected devices expected to rise rapidly over the next few years. However, standard lithium-ion and alkaline batteries are still powering most smart devices that require dedicated collection and recycling of their non-renewable and toxic materials.

This has all helped promote the field of sustainable electronics. In this study, reported in the journal Advanced Materials [Aeby et al. Adv. Mater. (2021) DOI: 10.1002/adma.202101328], a combination of digital material assembly, stable performance operation, and non-toxicity could offer a path to innovative and sustainable electronics.

Led by Gustav Nyström, the team focused on identifying new ways to create high performance materials from renewable resources. Here, they examined the multifunctional use of nanocellulose as a structural material, dispersing agent for inks and as active component in the electrodes of a fully 3D printed supercapacitor. As Nyström told Materials Today, &ldquoBy combining nanocellulose with various forms of carbon particles we were able to create a highly functional device containing non-toxic and biodegradable materials&rdquo.

Glycerin, water and two types of alcohol were used to liquefy the gelatinous inks, with some table salt to ensure ionic conductivity. These ingredients were processed in four layers &ndash a flexible substrate, a conductive layer, the electrode and then the electrolyte &ndash which were 3D printed in succession in a single procedure. This combination was then folded up with the electrolyte in the middle.

The resulting mini-capacitor can store electricity for hours, and there would be no need to collect these batteries as they could be left in nature to degrade. The battery can also endure thousands of charge and discharge cycles and years of storage, even in freezing temperatures, and is resistant to pressure and shock. The team now hope to further develop their fully green printed energy storage approach, as well as to enhance its performance and investigate ways to interface with biodegradable sensing concepts.

A scanning tunnelling microscope image of the photopolymerization process that produces the 2D polymer. Image: Markus Lackinger.

The quest for new two-dimensional (2D) materials has rapidly intensified after the discovery of graphene &ndash a supermaterial whose excellent properties include high conductivity and strength, making it incredibly versatile.

Two main approaches are used to create ultrathin 2D materials. In the first, a continuous layer of molecules or atoms is 'peeled off' from the bulk of the material. Graphene can be derived from graphite using such a process.

The other approach, in contrast, involves constructing the material molecule-by-molecule by producing bonds between the molecules in various ways. The problem is that the materials are often small and fragile, and can contain many defects, which limits their potential areas of application.

An international research team with members from Linköping University in Sweden, and the Technical University of Munich and the Deutsches Museum in Germany, among others, has now developed a new method for manufacturing 2D polymers. Their discovery, which they report in a paper in Nature Chemistry, makes it possible to develop new ultrathin functional materials with highly defined and regular crystalline structures.

The manufacture, or polymerization, of this novel 2D material takes place in two steps. The researchers use a molecule known as 'fantrip' &ndash a contraction of 'fluorinated anthracene triptycene' &ndash which is a merger of two different hydrocarbons, anthracene and triptycene. The specific properties of fantrip cause the molecules to spontaneously arrange themselves into a pattern suitable for photopolymerization when they are placed onto a graphite surface covered with an alkane.

The next step is the photopolymerization itself, when the pattern is fixed with the aid of light. The molecules are illuminated by a violet laser that excites the electrons in the outermost electron shells of their component atoms, causing strong and durable covalent bonds to form between the molecules. The result is a porous 2D polymer, half a nanometre thick, consisting of several hundred thousand molecules identically linked. In other words, a material with nearly perfect order, right down to the atomic level.

"Creating covalent bonds between molecules requires a lot of energy," says Markus Lackinger, research group leader at the Deutsches Museum and the Technical University of Munich. "The most common way of supplying energy is to raise the temperature, but this also causes the molecules to start moving. So it won&rsquot work with self-organized molecules, since the pattern would blur. Using light to create covalent bonds preserves the pattern and fixes it precisely as we want it.

Since the photopolymerization is carried out on a surface of solid graphite, it is possible to follow the process at the molecular scale using scanning tunnelling microscopy. This shows the newly formed bonds creating a persistent network. In order to confirm this structure, the research group simulated the appearance of the molecular networks in the microscope at different stages of the reaction.

Jonas Björk, assistant professor in the Materials Design Division at the Department of Physics, Chemistry and Biology at Linköping University, used high-performance computing resources at the National Supercomputer Centre in Linköping to validate the experiments and understand the key factors that make the method successful.

"We see that the simulations agree well with reality down to the tiniest detail, and we can also understand why our specific system gives such useful results," says Björk. "The next step of the research will be to see whether the method can be used to link other molecules for new two-dimensional and functional materials. By improving the method, we will also be able to control and tailor the type of ultrathin materials we aim to manufacture."

The polymerization takes place in a vacuum to ensure the 2D material is not contaminated. However, the final 2D polymer film is stable under atmospheric conditions, which is an advantage for future applications.

Lackinger believes that the material will find many conceivable applications. "The most obvious application is to use the material as filter or membrane, but applications that we have no idea of at the moment in entirely different contexts may appear on the horizon, also by chance. This is why basic research is so exciting," he says.

This story is adapted from material from Linköping University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.

MIT engineers have discovered a way to generate electricity using tiny carbon particles that can create an electric current simply by interacting with an organic solvent in which theyre floating. The particles are made from crushed carbon nanotubes (blue) coated with a Teflon-like polymer (green). Image: Jose-Luis Olivares, MIT. Based on a figure courtesy of the researchers.

Engineers at Massachusetts Institute of Technology (MIT) have discovered a new way of generating electricity using tiny carbon particles that can create a current simply by interacting with liquid surrounding them. The liquid, an organic solvent, draws electrons out of the particles, generating a current that could be used to drive chemical reactions or to power micro- or nanoscale robots.

"This mechanism is new, and this way of generating energy is completely new," says Michael Strano, a professor of chemical engineering at MIT. "This technology is intriguing because all you have to do is flow a solvent through a bed of these particles. This allows you to do electrochemistry, but with no wires."

In a new study, the researchers showed they could use this electric current to drive a reaction known as alcohol oxidation &ndash an organic chemical reaction that is important in the chemical industry. Strano and his colleagues report their findings in a paper in Nature Communications.

This discovery grew out of Strano's research on carbon nanotubes &ndash hollow tubes made of a lattice of carbon atoms, which have unique electrical properties. In 2010, Strano demonstrated, for the first time, that carbon nanotubes can generate 'thermopower waves'. When a carbon nanotube is coated with layer of fuel, moving pulses of heat, or thermopower waves, travel along the tube, creating an electrical current.

That work led Strano and his students to uncover a related feature of carbon nanotubes. When part of a nanotube is coated with a Teflon-like polymer, it creates an asymmetry that makes it possible for electrons to flow from the coated to the uncoated part of the tube, generating an electrical current. Those electrons can be drawn out by submerging the particles in a solvent that is hungry for electrons.

To harness this special capability, the researchers created electricity-generating particles by grinding up carbon nanotubes and forming them into a sheet of paper-like material. They then coated one side of each sheet with a Teflon-like polymer and cut out small particles, which could be any shape or size. For this study, they made particles that were 250µm by 250µm.

When these particles are submerged in an organic solvent such as acetonitrile, the solvent adheres to the uncoated surface of the particles and begins pulling electrons out of them.

"The solvent takes electrons away, and the system tries to equilibrate by moving electrons," Strano says. "There's no sophisticated battery chemistry inside. It's just a particle and you put it into solvent and it starts generating an electric field."

The current version of the particles can generate about 0.7 volts of electricity per particle. In this study, the researchers also showed that they can form arrays of hundreds of particles in a small test tube. This 'packed bed' reactor generates enough energy to power a chemical reaction called an alcohol oxidation, in which an alcohol is converted to an aldehyde or a ketone. Usually, this reaction is not performed using electrochemistry because it would require too much external current.

"Because the packed bed reactor is compact, it has more flexibility in terms of applications than a large electrochemical reactor," says MIT graduate student Ge Zhang. "The particles can be made very small, and they don't require any external wires in order to drive the electrochemical reaction."

In future work, Strano hopes to use this kind of energy generation to build polymers using only carbon dioxide as a starting material. In a related project, he has already created polymers that can regenerate themselves using carbon dioxide as a building material, in a process powered by solar energy. This work is inspired by carbon fixation, the set of chemical reactions that plants use to build sugars from carbon dioxide, using energy from the Sun.

In the longer term, this approach could also be used to power micro- or nanoscale robots. Strano's lab has already begun building robots at that scale, which could one day be used as diagnostic or environmental sensors. The idea of being able to scavenge energy from the environment to power these kinds of robots is appealing, he says.

"It means you don't have to put the energy storage on board," he says. "What we like about this mechanism is that you can take the energy, at least in part, from the environment."

This story is adapted from material from MIT, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.

(Left) Scanning tunnelling microscope image of bottom-up zigzag graphene nanoribbons. (Right) Spin-density in the vicinity of a 'bite' defect in a zigzag graphene nanoribbon. Image: Empa/EPFL (adapted with permission from J. Phys. Chem. Lett. 2021,12, 4692-4696, Copyright 2021 American Chemical Society).

Graphene nanoribbons (GNRs) are narrow strips of single-layer graphene that possess interesting physical, electrical, thermal and optical properties because of the interplay between their crystal and electronic structures. These novel characteristics have pushed GNRs to the forefront in the search for ways to advance next-generation nanotechnologies.

While bottom-up fabrication techniques now allow the controlled synthesis of a broad range of graphene nanoribbons that feature various edge geometries, widths and other atoms, the question of whether or not structural disorder is present in these atomically precise GNRs, and to what extent, is still subject to debate. The answer to this riddle is of critical importance for any potential applications or resulting devices.

A collaboration between Oleg Yazyev's Chair of Computational Condensed Matter Physics theory group at the Ecole Polytechnique Fédérale de Lausanne (EPFL) and Roman Fasel's experimental [email protected] laboratory at the Swiss Federal Laboratories for Materials Science and Technology (Empa), both in Switzerland, has now produced two papers that look at this issue in armchair-edged and zigzag-edged graphene nanoribbons.

"In these two works, we focused on characterizing 'bite-defects' in graphene nanoribbons and their implications on GNR properties," explains Gabriela Borin Barin from Empa's [email protected] lab. "We observed that even though the presence of these defects can disrupt GNRs' electronic transport, they could also yield spin-polarized currents. These are important findings in the context of the potential applications of GNRs in nanoelectronics and quantum technology."

The paper in 2D Materials specifically looks at nine-carbon-atom-wide armchair graphene nanoribbons (9-AGNRs). The mechanical robustness, long-term stability under ambient conditions, easy transferability onto target substrates, scalability of fabrication and suitable band-gap width of these GNRs has made them one of the most promising candidates for integration as active channels in field-effect transistors (FETs). Indeed, among the graphene-based electronic devices realized so far, 9-AGNR-FETs display the highest performance.

The detrimental role of defects in GNRs on electronic devices is well known. But so-called Schottky barriers, which are potential energy barriers for electrons formed at metal-semiconductor junctions, both limit the performance of current GNR-FETs and also prevent experimental characterization of the impact of defects on device performance. In the 2D Materials paper, the researchers report combining experimental and theoretical approaches to investigate defects in bottom-up AGNRs.

Using scanning-tunnelling and atomic-force microscopies, the researchers were first able to determine that missing benzene rings at the edges are a very common defect in 9-AGNRs, and to estimate both the density and spatial distribution of these imperfections, which they have dubbed 'bite' defects. They quantified the density and found that these defects have a strong tendency to aggregate. Using first-principles calculations, they then explored the effect of such defects on quantum charge transport, finding that these imperfections significantly disrupt charge transport at the band edges by reducing conductance.

By generalizing these theoretical findings to wider nanoribbons in a systematic manner, the researchers were able to establish practical guidelines for minimizing the detrimental role of these defects on charge transport, an instrumental step towards the realization of novel carbon-based electronic devices.

In a paper in the Journal of Physical Chemistry Letters, the same team of researchers reports combining scanning probe microscopy experiments and first-principles calculations to examine structural disorder and its effect on magnetism and electronic transport in so-called bottom-up zigzag GNRs (ZGNRs).

ZGNRs are unique because of their unconventional metal-free magnetic order that, according to predictions, is preserved up to room temperature. They possess magnetic moments that are coupled ferromagnetically along their edges and antiferromagnetically across them, and it has been shown that their electronic and magnetic structures can be modulated to a large extent, such as via charge doping, electric fields, lattice deformations or defect engineering.

This combination of tunable magnetic correlations, sizable band gap width and weak spin-orbit interactions has made these ZGNRs promising candidates for spin-logic operations. This study specifically looked at six-carbon-atom-wide zigzag graphene nanoribbons (6-ZGNRs), the only width of ZGNRs that has been produced with a bottom-up approach so far.

Again using scanning-tunnelling and atomic-force microscopies, the researchers first identified the presence of ubiquitous carbon vacancy defects located at the edges of the nanoribbons and then resolved their atomic structure. Their results indicated that each vacancy comprises a missing m-xylene unit, producing a similar 'bite' defect to those seen in AGNRs. This defect is created by the scission of carbon-carbon bonds during the synthesis reaction. The researchers estimate that the density of 'bite' defects in 6-ZGNRs is larger than in bottom-up AGNRs.

The researchers again theoretically examined the effect of these bite defects on the electronic structure and quantum transport properties of 6-ZGNRs. Similar to the case with AGNRs, they found that the defects cause a significant disruption to the conductance. However, in this nanostructure, these unintentional defects also induce sublattice and spin imbalance, causing a local magnetic moment. This, in turn, gives rise to spin-polarized charge transport that makes defective zigzag nanoribbons optimally suited for applications in all-carbon logic spintronics at the ultimate limit of scalability.

A comparison between ZGNRs and AGNRs of equal width shows that transport across the former is less sensitive to the introduction of both single and multiple defects than the latter. Overall, this research provides a global picture of the impact of these ubiquitous 'bite' defects on the low-energy electronic structure of bottom-up graphene nanoribbons. According to the researchers, future research might focus on investigating other types of point defects experimentally observed at the edges of such nanoribbons.

This story is adapted from material from Empa, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.

I am pleased to announce some exciting developments on the Materialia editorial team. Having now completed its second year, our youngest journal has enjoyed a welcome response from the Materials community and has taken some cues from it. We have listened and observed, and believe that this response has helped us come to a clearer understanding of future direction and how best to meet the ever-changing, growing needs of researchers in the broader materials field.

For its first few years, Materialia has developed under the leadership of its two Editors, Baptiste Gault and Zhengwei Mao. Presently, Dr. Mao has been asked to serve a sister journal in the family, Acta Biomaterialia, and will therefore move on from his role at Materialia. Moving forward, Dr. Gault will take the title of Principal Editor for Materialia, and will be complemented by some new experts on his team. https://www.journals.elsevier.com/materialia/editorial-board

First, Dr. Evelyn Yim will join as Editor, taking over the biomaterials area and the soft matter content for Materialia. Dr. Yim is a faculty member in the Department of Chemical Engineering, University of Waterloo, Canada. https://www.journals.elsevier.com/materialia/editorial-board/dr-evelyn-yim

Second, Dr. Sylvain Deville CNRS Research Director at the Institut Lumière Matière in Lyon, France, will also join as an Editor of Materialia, strengthening the team&rsquos expertise in areas such as ceramics, solidification, and materials processing. https://www.journals.elsevier.com/materialia/editorial-board/dr-sylvain-deville

Third, Dr. Sophie Le Cann, CNRS Research Scientist at the Laboratoire Modélisation et Simulation Multi Echelle, Créteil, France, will join the Materialia editorial team alongside Dr. Philip Rodenbough both are Associate Editors for the journal. https://www.journals.elsevier.com/materialia/editorial-board/dr-sophie-le-cann https://www.journals.elsevier.com/materialia/editorial-board/dr-philip-rodenbough

Please join me in sending a welcome to our new editors, and congratulations to all!

Coordinating Editor - Acta Journals

The novel cellulose aerogels are nearly as light as air. Photo: Andrew Marais.

A new low-cost and sustainable synthesis technique could expand the opportunities for hospitals and clinics to deliver therapeutics with aerogels, a foam-like material now found in high-tech applications such as insulation for spacesuits and breathable plasters.

With the help of an ordinary kitchen freezer, this newest form of aerogel was made from all-natural ingredients, including plant cellulose and algae, says Jowan Rostami, a researcher in fiber technology at KTH Royal Institute of Technology in Stockholm, Sweden. The aerogel's low density and favorable surface area make it ideal for a wide range of uses, including timed release of medication and wound dressing. Rostami, together with colleagues at KTH and Lund University in Sweden, reports this new aerogel in a paper in Materials Today.

The aerogel's density can be pushed down to as low as 2kg per cubic meter, which Rostami and her colleagues believe is among the lowest recorded densities for similar materials. "To give you an idea of how light that is &ndash the density of air is 1.23kg per cubic meter," she says.

To demonstrate that the material can be used for controlled delivery of therapeutics, the researchers attached proteins to the aerogel via a water-based self-assembly process. "The aerogel is designed for biointeractivity, so it can for example be used to treat wounds or other medical problems," Rostami explains.

With an air volume of up to nearly 99.9%, aerogels are super-lightweight yet durable (the KTH aerogel is nearly 99% air). They have been used in a wide range of products since the mid-20th century, from skin care to paint, and numerous materials for building construction. Technical advances have recently allowed aerogels to be produced from the cellulose nanofibrils in plant cells, and these aerogels have generated interest for environmental applications such as water purification and home insulation.

The usual process for synthesizing nanocellulose-based aerogels involves dispersing the cellulose nanofibrils in water and then drying out the mixture. But the steps required to do this are energy-intensive and time-consuming, in part because they require freeze drying or critical-point drying with carbon dioxide gas.

"We use a sustainable approach instead," Rostami says. "It's simple yet sophisticated."

The nanofibrils are mixed in water with alginate &ndash a naturally occurring polymer derived from seaweed &ndash and then calcium carbonate is added. In the freezer, the water turns to ice and compresses these components together, producing a frozen hydrogel.

This frozen hydrogel is removed from the freezer and placed in acetone. Not only does the acetone remove the water and evaporate quickly, but by adding a bit of acid, it also dissolves the calcium carbonate particles, thereby releasing carbon dioxide bubbles that make the material more porous.

The dissolution of calcium carbonate produces yet another benefit: it releases calcium ions that crosslink with the alginate and cellulose nanofibrils, giving the aerogel wet-stability and the ability to recover its shape after being suffused with liquid.

Rostami says this quality further adds to the aerogel's usefulness in a greater range of applications, "without using costly, time and energy-consuming processes, toxic chemicals or complicated chemistry".

This story is adapted from material from KTH Royal Institute of Technology, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.

This image shows how the new ultrathin carbon nanotube films optically rotate polarized light output by 90°, but only when the input light's polarization is at a specific angle with respect to the nanotube alignment direction. Image: Kono Laboratory/Rice University.

Ultrathin, highly aligned carbon nanotube films, first made by Rice University physicist Junichiro Kono and his students a few years ago, have turned out to have a surprising phenomenon waiting within: an ability to make highly capable terahertz polarization rotation possible.

This rotation doesn't mean the films are spinning. Rather, polarized light from a laser or other source can now be manipulated in ways that were previously out of reach.

The unique optical rotation happens when linearly polarized pulses of light pass through the 45nm carbon nanotube film and hit the silicon surface on which it sits. The light bounces between the substrate and the film before finally reflecting back, but with its polarization turned by 90°. This only occurs, Kono said, when the input light's polarization is at a specific angle with respect to the nanotube alignment direction: the 'magic angle'.

This discovery by lead author Andrey Baydin, a postdoctoral researcher in Kono's lab, is reported in a paper in Optica. The phenomenon, which can be tuned by changing the refractive index of the substrate and the film thickness, could lead to robust, flexible devices that manipulate terahertz waves.

Kono said easy-to-fabricate, ultrathin broadband polarization rotators that stand up to high temperatures will address a fundamental challenge in the development of terahertz optical devices. The bulky devices available up to now only work with limited polarization angles, so compact devices with more capability are highly desirable.

Because terahertz radiation easily passes through materials like plastics and cardboard, these polarization rotators could be particularly useful for manufacturing, quality control and process monitoring. They could also prove handy in telecommunications systems and for security screening, because many materials have unique spectral signatures in the terahertz range.

"The discovery opens up new possibilities for waveplates," Baydin said. A waveplate alters the polarization of light that travels through it. In devices like terahertz spectrometers, which are used to analyze the molecular composition of materials, being able to adjust polarization up to a full 90° would allow for data gathering at a much finer resolution.

"We found that specifically at far-infrared wavelengths &ndash in other words, in the terahertz frequency range &ndash this anisotropy is nearly perfect," Baydin said. "Basically, there's no attenuation in the perpendicular polarization, and then significant attenuation in the parallel direction.

"We did not look for this. It was completely a surprise."

Baydin said theoretical analysis showed the effect is entirely due to the nature of the highly aligned nanotube films, which were vanishingly thin but about two inches in diameter. The researchers both observed and confirmed this giant polarization rotation with experiments and computer models.

"Usually, people have to use millimeter-thick quartz waveplates in order to rotate terahertz polarization," said Baydin, who joined the Kono lab in late 2019 and discovered the phenomenon soon after that. "But in our case, the film is just nanometers thick."

"Big and bulky waveplates are fine if you're just using them in a laboratory setting, but for applications, you want a compact device," Kono said. "What Andrey has found makes it possible."

This story is adapted from material from Rice University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.

This image shows the oscillating chemical wave on a rhodium nanoparticle. Image: TU Wien.

Most commercial chemicals are produced using catalysts. Usually, these catalysts consist of tiny metal nanoparticles on an oxidic support. Similar to a cut diamond, which has a surface consisting of different facets oriented in different directions, a catalytic nanoparticle also possesses crystallographically different facets &ndash and these facets can have different chemical properties.

Until now, these differences haven't often been considered in catalysis research, because it's very difficult to simultaneously obtain information about the chemical reaction and the surface structure of the catalyst. But this has now been achieved by researchers at the Vienna University of Technology (TU Wien) in Austria by combining different microscopic methods.

Utilizing field electron microscopy and field ion microscopy, the researchers were able to visualize the oxidation of hydrogen on a single rhodium nanoparticle in real time at nanometer resolution. This revealed surprising effects that will have to be taken into account in the search for better catalysts in the future. They report their findings in a paper in Science.

"In certain chemical reactions, a catalyst can periodically switch back and forth between an active and an inactive state," says Günter Rupprechter from the Institute of Materials Chemistry at TU Wien. "Self-sustaining chemical oscillations can occur between the two states &ndash the chemist Gerhard Ertl received the Nobel Prize in Chemistry for this discovery in 2007."

These chemical oscillations happen on rhodium nanoparticles, which are used as a catalyst for hydrogen oxidation &ndash the basis of every fuel cell. Under certain conditions, the rhodium nanoparticles can oscillate between a state in which oxygen molecules dissociate on the surface of the particle and a state in which hydrogen is bound.

"When a rhodium particle is exposed to an atmosphere of oxygen and hydrogen, the oxygen molecules are split into individual atoms at the rhodium surface," explains Yuri Suchorski, the first author of the paper. "These oxygen atoms can then migrate below the uppermost rhodium layer and accumulate as the subsurface oxygen there."

Through interaction with hydrogen, these stored oxygen atoms can then be brought out again to react with hydrogen atoms, which creates room for more oxygen atoms inside the rhodium particle and the cycle starts again. "This feedback mechanism controls the frequency of the oscillations", says Suchorski.

Until now, it was thought that these chemical oscillations always took place in the same rhythm over the entire nanoparticle. After all, the chemical processes on the different facets of the nanoparticle surface are spatially coupled, as the hydrogen atoms can easily migrate from one facet to the adjacent facets.

However, the results of the research groups of Rupprechter and Suchorski show that things are actually much more complex. Under certain conditions, the spatial coupling breaks and adjacent facets suddenly oscillate with significantly different frequencies &ndash and in some regions of the nanoparticle, these oscillating 'chemical waves' do not propagate at all.

"This can be explained on an atomic scale," says Suchorski. "Under the influence of oxygen, protruding rows of rhodium atoms can emerge from a smooth surface." These rows of atoms can then act as a kind of 'wave breaker' and hamper the migration of hydrogen atoms from one facet to another &ndash the facets become decoupled.

If this happens, the individual facets can form oscillations with different frequencies. "On different facets, the rhodium atoms are arranged differently on the surface," says Rupprechter. "That's why the incorporation of oxygen under the differing facets of the rhodium particle also proceeds at different rates, and so oscillations with different frequencies result on crystallographically different facets."

The key to unravelling this complex chemical behaviour lay in using a fine rhodium tip as a model for a catalytic nanoparticle. Applying an electric field to the tip caused electrons to leave due to the quantum mechanical tunnelling effect. These electrons are then accelerated by the electric field towards a screen, creating a projection image of the tip with a resolution of around 2nm.

In contrast to scanning microscopies, where the surface sites are scanned one after the other, such parallel imaging visualizes all surface atoms simultaneously &ndash otherwise it would not be possible to monitor the synchronization and desynchronization of the oscillations.

These new insights into the interaction of individual facets of a nanoparticle can now lead to more effective catalysts, and provide deep atomic insights into mechanisms of non-linear reaction kinetics, pattern formation and spatial coupling.

This story is adapted from material from TU Wien, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.

We are delighted to announce that Composites Part C: Open Access - the sister journal to the Composites Part A and B family of Journals - is now accepted for inclusion in Scopus.

Being indexed for Scopus demonstrates that a Journal has been found to be a reliable source of information in the Composites field. Papers published will be fully discoverable by many communities of researchers, as well as institutions, worldwide.

On this important occasion for the development of the Journal, we would like to highlight the following recently-published papers:

If you find these articles of interest, we hope you&rsquoll consider publishing your next paper with Composites Part C: Open Access. Key areas covered by the Journal include Sustainable Composites, Multi-functional Composites, and Composite Structures.

POSS-peptoid molecules self-assemble into rhomboid-shaped nanocrystals. Image: Stephanie King/Pacific Northwest National Laboratory.

Inspired by nature, researchers at Pacific Northwest National Laboratory (PNNL), along with collaborators at Washington State University, have created a novel material capable of capturing light energy. The material could form the basis of a highly efficient, artificial light-harvesting system with potential applications in photovoltaics and bioimaging.

This research provides a foundation for overcoming the difficult challenges involved in creating hierarchical functional organic-inorganic hybrid materials. Nature provides beautiful examples of hierarchically structured hybrid materials, such as bones and teeth. These materials typically showcase a precise atomic arrangement that confers many exceptional properties, such as great strength and toughness.

PNNL materials scientist Chun-Long Chen and his collaborators created a new material that reflects the structural and functional complexity of natural hybrid materials. This material combines the programmability of a protein-like synthetic molecule with the complexity of a silicate-based nanocluster to create a new class of highly robust 2D nanocrystals. Chen and his collaborators programmed this 2D hybrid material to create a highly efficient artificial light-harvesting system.

"The Sun is the most important energy source we have," said Chen. "We wanted to see if we could program our hybrid nanocrystals to harvest light energy &ndash much like natural plants and photosynthetic bacteria can &ndash while achieving a high robustness and processibility seen in synthetic systems." Chen and his collaborators report their work in a paper in Science Advances.

Though these types of hierarchically structured materials are exceptionally difficult to create, Chen's multidisciplinary team of scientists combined their expert knowledge to synthesize a sequence-defined molecule capable of forming such a structured arrangement. The researchers created an altered protein-like structure, called a peptoid, and attached a precise silicate-based cage-like structure (termed POSS) to one end of it.

Under the right conditions, they were able to induce these molecules to self-assemble into perfectly shaped crystals of 2D nanosheets. This created another layer of cell-membrane-like complexity similar to that seen in natural hierarchical structures while retaining the high stability and enhanced mechanical properties of the individual molecules.

"As a materials scientist, nature provides me with a lot of inspiration," said Chen. "Whenever I want to design a molecule to do something specific, such as act as a drug delivery vehicle, I can almost always find a natural example to model my designs after."

Once the team successfully created the POSS-peptoid nanocrystals and demonstrated their unique properties, including high programmability, they set out to exploit these properties by programming the material to include special functional groups at specific locations. Because these nanocrystals combine the strength and stability of POSS with the variability of the peptoid building block, the programming possibilities ae endless.

Once again looking to nature for inspiration, the scientists used their nanocrystals to create a system that could capture light energy much in the way the pigments in plants do. They added pairs of special 'donor' molecules and cage-like structures that could bind an 'acceptor' molecule at precise locations within the nanocrystal. The donor molecules absorb light at a specific wavelength and transfer the light energy to the acceptor molecules, which then emit light at a different wavelength. This newly created system displayed an energy transfer efficiency of over 96%, making it one of the most efficient aqueous light-harvesting systems of its kind reported thus far.

To showcase the use of this system, the researchers then inserted the nanocrystals into live human cells as a biocompatible probe for live-cell imaging. When light of a certain color shines on the cells and the acceptor molecules are present, the cells emit light of a different color. When the acceptor molecules are absent, the color change is not observed. Though the team has so far only demonstrated the usefulness of this system for live-cell imaging, the enhanced properties and high programmability of this 2D hybrid material leads them to believe this is just one of many applications.

"Though this research is still in its early stages, the unique structural features and high energy transfer of POSS-peptoid 2D nanocrystals have the potential to be applied to many different systems, from photovoltaics to photocatalysis," said Chen. He and his colleagues will continue to explore avenues for application of this new hybrid material.

This story is adapted from material from Pacific Northwest National Laboratory, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.

This image shows the stringlike particles formed by iron (Fe) and nickel (Ni) and the more globular clusters formed by copper (Cu). Image: Abbaschian, Zachariah, et. al. 2021.

In order for metal nanomaterials to deliver on their promise to energy and electronics, they need to shape up &ndash literally.

To deliver reliable mechanical and electric properties, nanomaterials must have consistent, predictable shapes and surfaces, as well as scalable production techniques. Engineers at the University of California (UC) Riverside are meeting this challenge by vaporizing metals within a magnetic field to direct the reassembly of the metal atoms into predictable shapes. They report their work in a paper in the Journal of Physical Chemistry Letters.

Nanomaterials comprising particles measuring 1&ndash100nm are typically created within a liquid matrix, which is expensive for bulk production and in many cases cannot produce nanoparticles made of pure metals, such as aluminum or magnesium. More economical production techniques typically involve vapor-phase approaches, in which a a cloud of particles condenses from a vapor, but they suffer from a lack of control.

Reza Abbaschian, professor of mechanical engineering, and Michael Zachariah, professor of chemical and environmental engineering, joined forces to develop a novel technique for creating nanomaterials from iron, copper and nickel in a gas phase. Their technique involves placing solid metal within a powerful electromagnetic levitation coil to heat the metal beyond its melting point, vaporizing it.

The resulting metal droplets levitate in the gas within the coil and move in directions determined by their inherent interactions with the magnetic forces. When the droplets bond, they do so in an orderly fashion that the researchers found could be predicted from the type of metal and how and where they applied the magnetic fields.

Iron and nickel nanoparticles formed string-like aggregates, while copper nanoparticles formed globular clusters. When deposited on a carbon film, the iron and nickel aggregates gave the film a porous surface, while the carbon aggregates gave it a more compact, solid surface. The qualities of the materials on the carbon film mirrored at larger scales the properties of each type of nanoparticle.

Because the magnetic field can be thought of as an 'add-on', this approach could be applied to any vapor-phase technique for generating nanomaterials where structure is important, such as the fillers used in polymer composites for magnetic shielding. It could also help to improve the electrical and mechanical properties of nanomaterials.

"This 'field directed' approach enables one to manipulate the assembly process and change the architecture of the resulting particles from high fractal dimension objects to lower dimension string-like structures. The field strength can be used to manipulate the extent of this arrangement," said Zachariah.

This story is adapted from material from the University of California, Riverside, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.

We are excited to share some of the first papers published from BBA Advances, an open access journal that complements the existing BBA journals. BBA Advances publishes high quality research showing novel results in all aspects of biochemistry, biophysics and related areas like molecular and cell biology.

BBA Advances will waive the Article Publishing Charge for any submissions received before 31 October 2021, which are accepted for publication after peer review. Find out more.

Are you ready to take your research to the next level? ?Publish open access in BBA Advances where it will be discoverable on ScienceDirect, the world&rsquos leading source of scientific research accounting for 18% of global research output.

Drug-loaded piezoelectric polymer nanoparticles can cross the blood-brain barrier to deliver anticancer drugs and electrical stimulation to tumor cells in the brain.

Researchers have developed new nanoparticles for the treatment of glioblastoma, one of the most aggressive, invasive, and difficult to treat brain cancers [Pucci et al., Acta Biomaterialia (2021), https://doi.org/10.1016/j.actbio.2021.04.005 ].

&ldquoGlioblastoma cells are highly aggressive and require multi-modality treatments,&rdquo explains Gianni Ciofani of the Istituto Italiano di Tecnologia for Smart Bio-Interfaces, who led the work. &ldquo[This] aggressiveness is associated with the ability [of glioblastoma cells] to invade brain tissue, so it is important to inhibit their motility, invasiveness, and proliferation to avoid progression.&rdquo

Together with colleagues from the IRCCS Istituto Giannina Gaslini, University of Florence, European Laboratory for Non-linear Spectroscopy, and Istituto Italiano di Tecnologia for Electron Microscopy, Ciofani has developed nanoparticles composed of a piezoelectric polymeric core, into which drugs can be encapsulated, and a lipid shell that is highly biocompatible.

&ldquoThe delivery of a drug or a drug-loaded nanomaterial [to the brain] represents a huge challenge because of the presence of the blood-brain barrier (BBB), a biological barrier that protects the brain by preventing the passage of toxic compounds and microorganisms,&rdquo says Ciofani. &ldquoIt is difficult to deliver chemotherapy drugs from blood capillaries to brain tumors [so] drugs cannot be used in high concentrations because of their strong side effects on healthy tissue.&rdquo

To overcome this problem, the researchers functionalized the nanoparticles&rsquo surface with a peptide known to facilitate the movement of chemical species through the BBB. Using a biomimetic microfluidic model of the BBB, the researchers demonstrate that the novel nanoparticles can indeed pass through the barrier. Once in the brain, the same peptide helps the nanoparticles target tumor cells and deliver a double blow. When stimulated with ultrasound, the piezoelectric nanoparticles not only release their drug cargo but also produce an electrical signal in response to the mechanical deformation.

&ldquoSince electrical stimuli are known to induce the inhibition of cell proliferation and the reduction of chemotherapy resistance, we have used [piezoelectric nanoparticles] to deliver anticancer electrical cues to glioblastoma cells,&rdquo says Ciofani.

The nanoparticles offer a potential multimodal treatment of glioblastoma, delivering both anticancer drugs in a controlled manner to kill cancer cells while minimizing effects on healthy tissue and electrical stimulation to inhibit cell mobility.

&ldquoThe combined piezoelectrical stimulation and chemotherapy treatment was able to induce glioblastoma cell death, inhibit cell division, and reduce both glioblastoma cell invasiveness and epithelial-mesenchymal transition, [which is] associated with glioblastoma progression,&rdquo says Ciofani. &ldquoThese polymeric nanomaterials display a high potential for approval in clinical applications.&rdquo

The approach could provide on-demand, non-invasive, and more efficacious anticancer treatment in highly sensitive areas like the brain, improving outcomes for patients, which are currently very poor.

The award committee is pleased to announce that Ying Wang, University of Manchester, has been selected the recipient of the 2021 CSTE Outstanding Young Researcher Award. The award was established in 2017 to recognize young scientists with research excellence in composite materials, with special consideration for those who have made outstanding contributions to the journal of CSTE.

Dr. Ying Wang received her B.Eng. in Materials from Shanghai Jiao Tong University in 2011, followed by a Ph.D. degree in Composite Materials from The University of Manchester in 2015, under the supervision of Regius Prof. Philip Withers and Prof. Costas Soutis. At present, she is engaged in post-doctoral research work on fibre-reinforced composite materials at the Henry Moseley X-ray Imaging Facility, Henry Royce Institute, The University of Manchester, UK.

The award ceremony will be held online and included in the program of ICFC8, the 8th International Conference of Fatigue of Composites (June 23-25) www.gest.unipd.it/ICFC8.

The award committee would also like to thank all applicants and readers for their attention and support to this award.

The following publications authored by the winner in 2019 and 2020 are accessible to view on Science Direct:

We would like to congratulate Ying on this achievement.

On behalf of the CSTE Journal Editors, Judging Panel and Publishing Team.

A team from the University of Bath in the UK have demonstrated modified energy landscapes at the intersection of 2D materials. By nanoengineering a number of defects in 2D materials that induce intra-bandgap energy levels, these characteristics establish nanomeshes with enhanced optical and electronic properties as useful for the next generation of ultrathin devices in energy, communications, imaging and quantum computing.

2D materials such as graphene and transition metal dichalcogenides, including tungsten disulfide (WS2), are made up of layers of single atoms, with electrons able to move in two dimensions while their motion in the third dimension is restricted. Most applications using 2D materials involve sheets that are lying flat, but they are so thin that, on being illuminated, light only interacts with them for a small thickness, limiting their usefulness. To increase the interaction length with light, studies have been investigating ways to stack and fold 2D materials into &ldquothicker&rdquo complex 3D shapes.

As reported in Laser & Photonics Reviews [Murphy et al. Laser Photonics Rev. (2021) DOI: 10.1002/lpor.202100117], the researchers here designed an approach to making intricate 3D networks of 2D sheets of WS2 that retain their 2D characteristics, offering a strongly modified energy landscape compared to the flat-lying WS2 sheets. This 3D arrangement, called a &ldquonanomesh&rdquo, is a webbed network of randomly distributed and densely packed stacks.

The WS2 sheets have finite dimensions with irregular edges, with the sheets intersecting and fusing together, and even twist on top of each other and lean against each other, which alters the energy landscape of the materials and brings new physical properties. This energy landscape is evidence that assembling 2D materials into a 3D arrangement goes beyond making 2D materials &ldquothicker&rdquo to produce completely new materials.

As team leader Ventsislav Valev told Materials Today, &ldquoWe illustrated how 2D materials can be reassembled into new types of 3D networks with unique physical properties. Practically, we have shown that our materials have very strong and unusual nonlinear optical properties &ndash they efficiently convert light from one color into another.&rdquo The materials are also more broadband than other 2D materials, allowing for a broader spectrum of colors that can be converted into other colors.

The nanomesh is relatively easy to make, and as the material grows on silicon and is therefore compatible with quantum optical technologies, it could be deposited on Si waveguides and used to process optical signals for innovative light-based computing chips. The team now hope to demonstrate how efficiently the material can convert light of one color into another, and are looking to apply their approach to other types of 2D materials.

Stacked 2D nanosheets with enhanced optical and electronic properties

A team of researchers at Penn State has developed a new hardware security device that takes advantage of microstructure variations in graphene to generate secure keys. Image: Jennifer McCann, Penn State.

As more private data is stored and shared digitally, researchers are exploring new ways to protect data against attacks from bad actors. Current silicon technology exploits microscopic differences between computing components to create secure keys, but artificial intelligence (AI) techniques can be used to predict these keys and gain access to data. Now, researchers at Penn State have designed a way to make the encrypted keys harder to crack.

Led by Saptarshi Das, assistant professor of engineering science and mechanics, the researchers used graphene &ndash a layer of carbon one atom thick &ndash to develop a novel low-power, scalable, reconfigurable hardware security device with significant resilience to AI attacks. The researchers report their work in a paper in Nature Electronics.

"There has been more and more breaching of private data recently," Das said. "We developed a new hardware security device that could eventually be implemented to protect these data across industries and sectors."

The device is called a physically unclonable function (PUF), and the researchers says this is the first demonstration of a graphene-based PUF. The physical and electrical properties of graphene, as well as the fabrication process, make this novel PUF more energy-efficient, scalable and secure against AI attacks that can pose a threat to silicon PUFs.

The team first fabricated nearly 2000 identical graphene transistors, which switch current on and off in a circuit. Despite their structural similarity, the transistors' electrical conductivity varied due to the inherent randomness arising from the production process. While such variation is typically a drawback for electronic devices, it's a desirable quality for a PUF, and one not shared by silicon-based devices.

After the graphene transistors were implemented into PUFs, the researchers modeled their characteristics to create a simulation of 64 million graphene-based PUFs. To test the PUFs' security, Das and his team turned to machine learning, a method that allows AI to study a system and find new patterns. The researchers trained the AI with the graphene PUF simulation data, testing to see if the AI could use this training to make predictions about the encrypted data and reveal system insecurities.

"Neural networks are very good at developing a model from a huge amount of data, even if humans are unable to," Das said. "We found that AI could not develop a model, and it was not possible for the encryption process to be learned."

According to Das, this resistance to machine-learning attacks makes the PUF more secure because potential hackers could not use breached data to reverse engineer a device for future exploitation. Even if the key could be predicted, the graphene PUF could generate a new key through a reconfiguration process requiring no additional hardware or replacement of components.

"Normally, once a system's security has been compromised, it is permanently compromised," said Akhil Dodda, an engineering science and mechanics graduate student conducting research under Das's mentorship. "We developed a scheme where such a compromised system could be reconfigured and used again, adding tamper resistance as another security feature."

With these features, as well as the capacity to operate across a wide range of temperatures, the graphene-based PUF could be used in a variety of applications. Further research could open pathways for its use in flexible and printable electronics, household devices and more.

This story is adapted from material from Penn State, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.

This image shows 2D materials intersecting and twisting on top of each other, which modifies the energy landscape of the materials. Image: Ventsislav Valev.

In 1884, Edwin Abbott wrote the novel Flatland: A Romance in Many Dimensions as a satire of Victorian hierarchy. He imagined a world that existed in only two dimensions, where the beings are 2D geometric figures. The physics of such a world are somewhat akin to that of modern 2D materials such as graphene and the transition metal dichalcogenides, which include tungsten disulfide (WS2), tungsten diselenide (WSe2), molybdenum disulfide (MoS2) and molybdenum diselenide (MoSe2).

In modern 2D materials, which consist of single-atom layers, electrons can move in two dimensions but their motion in the third dimension is restricted. Due to this 'squeeze', 2D materials have enhanced optical and electronic properties that show great promise as next-generation, ultrathin devices in the fields of energy, communications, imaging and quantum computing, among others.

Typically, for all these applications, the 2D materials are envisioned in flat-lying arrangements. Unfortunately, however, the strength of these materials is also their greatest weakness &ndash they are extremely thin. This means that when they are illuminated, light can only interact with them over a tiny thickness, which limits their usefulness. To overcome this shortcoming, researchers are starting to look for new ways to fold 2D materials into complex 3D shapes.

In our 3D universe, 2D materials can be arranged on top of each other. To extend the Flatland metaphor, this arrangement would represent parallel worlds inhabited by people who are destined never to meet.

Now, scientists from the Department of Physics at the University of Bath in the UK have found a way to arrange 2D sheets of WS2 (previously created in their lab) into a 3D configuration with an energy landscape that is strongly modified when compared to that of the flat-laying WS2 sheets. This particular 3D arrangement is known as a 'nanomesh' &ndash a webbed network of densely packed, randomly distributed stacks, containing twisted and/or fused WS2 sheets &ndash and is described in paper in Laser & Photonics Reviews.

In Flatland, modifications of this kind would allow people to step into each other's worlds. "We didn't set out to distress the inhabitants of Flatland," said Ventsislav Valev, who led the research, "But because of the many defects that we nanoengineered in the 2D materials, these hypothetical inhabitants would find their world quite strange indeed.

"First, our WS2 sheets have finite dimensions with irregular edges, so their world would have a strangely shaped end. Also, some of the sulphur atoms have been replaced by oxygen, which would feel just wrong to any inhabitant. Most importantly, our sheets intersect and fuse together, and even twist on top of each other, which modifies the energy landscape of the materials. For the Flatlanders, such an effect would look like the laws of the universe had suddenly changed across their entire landscape."

"The modified energy landscape is a key point for our study," explained Adelina Ilie, who developed the new material together with her former PhD student and post-doc Zichen Liu. "It is proof that assembling 2D materials into a 3D arrangement does not just result in 'thicker' 2D materials &ndash it produces entirely new materials. Our nanomesh is technologically simple to produce, and it offers tunable material properties to meet the demands of future applications."

"The nanomesh has very strong nonlinear optical properties &ndash it efficiently converts one laser color into another over a broad palette of colours," added Valev. "Our next goal is to use it on Si waveguides for developing quantum optical communications."

"In order to reveal the modified energy landscape, we devised new characterization methods and I look forward to applying these to other materials," said PhD student Alexander Murphy, who was also involved in the research. "Who knows what else we could discover?"

This story is adapted from material from the University of Bath, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.

Simplified schematic of the magnetic graphene-based spintronic device, showing electrical and thermal generation of spin currents in the bilayer graphene/CrSBr heterostructure. Magnetic cobalt electrodes are used to determine the degree of proximity-induced spin polarization in the bilayer graphene, where the magnetization of the outer-most layer of CrSBr (MCSB) allows for higher conductivity of the spin-up electrons (red arrows). Image: Talieh Ghiasi, University of Groningen.

Experiments by physicists at the University of Groningen in the Netherlands and Colombia University suggest that magnetic graphene could be an ideal material for producing ultra-compact spintronic devices. This follows their discovery that magnetic graphene can efficiently convert charge to spin current and transfer this strong spin-polarization over long distances, which they report in a paper in Nature Nanotechnology.

Spintronic devices are promising high-speed and energy-saving alternatives for current electronics. These devices use the magnetic moment of electrons, known as spin, which can be 'up' or 'down', to transfer and store information. The ongoing scaling down of memory technology requires ever smaller spintronic devices, and thus researchers have been looking for atomically thin materials that can actively generate large spin signals and transfer the spin information over micrometer-long distances.

For over a decade, graphene has been the most favourable 2D material for the transport of spin information. However, graphene cannot generate spin current by itself unless its properties are appropriately modified. One way to achieve this is to make it act as a magnetic material. This magnetism would favour the passage of one type of spin and thus create an imbalance in the number of electrons with spin-up versus spin-down, resulting in a highly spin-polarized current.

This idea has now been experimentally confirmed by scientists in the Physics of Nanodevices group at the University of Groningen, led by Bart van Wees. When the physicists brought graphene in close proximity to a 2D layered antiferromagnet, CrSBr, they were able to directly measure a large spin-polarization of current, generated by the magnetic graphene.

In conventional graphene-based spintronic devices, ferromagnetic (cobalt) electrodes are used for injecting and detecting the spin signal into graphene. In contrast, in circuits built from magnetic graphene, the injection, transport and detection of the spins can all be done by the graphene itself.

"We detect an exceptionally large spin-polarization of conductivity of 14% in the magnetic graphene that is also expected to be efficiently tuneable by a transverse electric field," says Talieh Ghiasi, first author of the paper, This, together with the outstanding charge and spin transport properties of graphene, allows for the realization of all-graphene 2D spin-logic circuitries where the magnetic graphene alone can inject, transport and detect spin information.

Moreover, the unavoidable heat dissipation that happens in any electronic circuitry becomes an advantage in these spintronic devices. "We observe that the temperature gradient in the magnetic graphene due to the Joule heating is converted to spin current," Ghiasi explains. "This happens by the spin-dependent Seebeck effect that is also observed in graphene for the first time in our experiments." The efficient electrical and thermal generation of spin currents by magnetic graphene promises substantial advances for both 2D spintronic and spin-caloritronic technologies.

In addition, because the spin transport in graphene is highly sensitive to the magnetic behaviour of the outer-most layer of the neighbouring antiferromagnet, these spin transport measurements could offer a way to probe the magnetization of a single atomic layer. Thus, these magnetic graphene-based devices could not only address the most technologically relevant aspects of magnetism in graphene for 2D memory and sensory systems, but could also provide further insight into the physics of magnetism.

This story is adapted from material from the University of Groningen, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.


Physics

Cosmic ray muon computed tomography of spent nuclear fuel in dry storage casks

Radiography with cosmic ray muon scattering has proven to be a successful method of imaging nuclear material through heavy shielding. Development of the technique to monitor spent nuclear fuel sealed in dry storage casks would have useful international safeguards applications. These casks are heavily shielded to prevent radiation leakage to the environment. This precludes monitoring using typical radiographic probes such as neutrons or photons. Subatomic Physics (P- 25) researchers and collaborators have demonstrated a novel approach to image these casks using cosmic ray muon imaging and computed tomography algorithms typically used in medical imaging. The team used a cylindrical muon-tracking detector surrounding a typical spent fuel cask to demonstrate that cask contents could be confirmed with high confidence with less than two days of exposure.

Cosmic ray muons are produced through interactions of protons and nuclei from space with atoms in the upper atmosphere. Collisions of these primary cosmic rays with atmospheric gas produce showers of pions, many of which decay to muons. These muons arrive on the Earth’s surface at a rate of approximately 1/cm2/min with an average energy of approximately 4 GeV. They form a naturally occurring probe that can be used to radiograph objects from multiple views simultaneously. Due to their high energies, ubiquitous availability, and highly penetrating nature, comic ray muons are being explored as a tool for a variety of difficult imaging scenarios.

Monitoring spent nuclear fuel that is sealed in dry storage casks is of particular interest for international safeguards applications to detect diversion. Muon radiography offers a standalone method to determine a cask’s contents and recover from a loss of continuity of knowledge.

Previous muon radiography measurements on a fuel cask used drift tube tracking detectors to measure the areal density between the two detectors. This method showed that missing fuel assemblies could be located, but the single measurement of integrated density left ambiguity in the exact location of the missing fuel elements in the direction orthogonal to the two detectors.

Figure 10. (Top): Top down view and (bottom) side view of the simulated cask and detector geometries. The fuel assembly loading configuration is shown with six fuel assembly compartments left empty.

This new work describes the first application of filtered back projection algorithms, typically used in medical imaging, to cosmic ray muon imaging. The team developed the specific application to monitor spent nuclear fuel in dry storage casks via GEANT4 simulations. The investigators used a cylindrical muon tracking detector fitting around the outside of a partially loaded Westinghouse MC-10 cask of the type used at Idaho National Laboratory. The detector completely surrounded the cask. This geometry increased the detector’s active area and enabled simultaneous measuring of muon scattering through all azimuthal angles of the cask. With this continuum of areal density measurements, computed tomography image reconstruction algorithms could be applied to produce full images of the cask interior. The team utilized a filtered back-projection algorithm on the data. The resulting simulations of muon imaging of a partially loaded dry storage cask demonstrate that the missing fuel assemblies could be located with high confidence in a process that took less than two days.

Figure 11. Process used to analyze data and obtain a volume density image of the cask with fuel rods and empty slots.

Figure 11 depicts the process that the team used. The images clearly reveal the structures of the cask including the cooling fins, steel shielding shell, and the loading configuration of the fuel assemblies. The new technique, which fulfills an NA-22 milestone and solves a three decades-old safeguard challenge, shows that the diversion of spent fuel assemblies could be determined without opening the cask and on a time scale well within the International Atomic Energy Agency’s timeliness goals. The team concludes that this technique and a dedicated instrument could be a useful tool for international nuclear safeguards inspectors.

This work, which is funded by the National Nuclear Security Administration’s Office of Defense Nuclear Nonproliferation Research and Development (LANL Program Manager, Roger Petrin), supports the Laboratory’s Global Security mission area and the Science of Signatures pillar. Researchers include: Daniel Poulson (P-25 and University of New Mexico, Albuquerque), J. Matthew Durham, Elena Guardincerri, Christopher L. Morris, Jeffrey D. Bacon, Kenie Plaud- Ramos, and Deborah Morley (P-25) and Adam Hecht (University of New Mexico, Albuquerque). Technical contact: Chris Morris


Nanobiotechnology: An Engineer's Foray into Biology

This book chapter concentrates on applications of nanotechnologies in the field of biological/medical research. The chapter is presented in two parts. In the first part, a brief overview of state-of-the-art nanofabrication technologies is provided, including bottom–up methods, top–down methods, and replication-based methods. The working principles, advantages and limitations of each technology are presented and discussed. The commonly-used nanomaterials for these nanofabrication technologies are also reviewed. Considering the increasingly rapid growth of this interdisciplinary field, several representative emerging nanofabrication technologies are demonstrated and the future direction is commented. The second part of the chapter focuses on applications of nanotechnologies in typical biomedical research fields, including biosensing, bioactuating, drug delivery and therapeutics. Since the nanodevices and nanosystems are similarly in size with many biological entities and possess a number of unique characteristics different from their micro/meso/macroscale counterparts, they can be used to address many unsolved problems in the biological/medical field. Several successful nanoengineered devices and systems are elucidated. The fabrication, characterization and measurement of the nanosystems are demonstrated, with an emphasis of the interaction between these nanosystems and the subject biological entities. These nanosystems are drawn from the technologies reported in scientific literatures, which are being used in research or under the way of commercialization. These examples are expected to provide the readers a big picture of current development and potential perspective of nanobiotechnology. Meanwhile, we would convey via this book chapter the importance of technologies fusion among different research disciplines upon development of the interdisciplinary field.