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Nanotechnology-based disinfectants and sensors for SARS-CoV-2

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Diagnostics is a critical weapon in the fight against this pandemic, as it is pivotal to isolate infected individuals as early as possible, preventing dissemination17. Several nanotechnology-based approaches for SARS-CoV-2 tagging and detection are being developed (Fig. 2).

Fig. 2: Nanotechnology-based sensors for SARS-CoV-2 detection, involved in the development of platforms for viral tagging and nano-diagnostic assays.
figure2

Nanomaterials functionalized with nucleic acids or antibodies represent the main lines of nano-based detection, via colorimetric or antigen-binding assays, as well as light and photothermal platforms. Ab, antibody; FRET, Förster resonance energy transfer; LSPR, localized surface plasmon resonance; NPs, nanoparticles; PNA, peptide nucleic acid; PPT, photothermal therapy.

Generally, testing kits operate based on detection of antibodies (by enzyme-linked immunosorbent assay, or enzyme-linked immunosorbent assay (ELISA)) or RNA (by polymerase chain reaction, or PCR) associated with the virus (from nasopharyngeal swabs taken from individuals’ noses and throats). This relies on their surface interactions with a complementary detection ligand or strand in the kit18. However, these testing kits are generally associated with problems such as false-negative results, long response times and poor analytical sensitivity19. To this end, due to their extremely large surface-to-volume ratios, nanosized materials can instigate highly efficient surface interactions between the sensor and the analyte, allowing faster and more reliable detection of the virus20. Accordingly, a group of researchers have developed a colloidal gold-based test kit that enables easy conjugation of gold nanoparticles to IgM/IgG antibodies in human serum, plasma and whole blood samples21. However, the targeted IgM/IgG antibodies in this kit were not specific to COVID-19, and as a result in some cases produced false results associated with patients who were suffering from irrelevant infections. Consequently, researchers from the University of Maryland, USA, developed a colorimetric assay based on gold nanoparticles capped with suitably designed thiol-modified DNA antisense oligonucleotides specific for N-gene (nucleocapsid phosphoprotein) of SARS-CoV-2, which were used for diagnosing positive COVID-19 cases within 10 min from the isolated RNA samples22. Such testing kits could potentially produce promising results, however their performance would still be affected by quantity of the viral load. To address this shortcoming, researchers from ETH, Switzerland, have recently reported a unique dual-functional plasmonic biosensor combining the plasmonic photothermal effect and localized surface plasmon resonance (LSPR) sensing transduction to provide an alternative and promising solution for clinical COVID-19 diagnosis23. The two-dimensional gold nano-islands functionalized with complementary DNA receptors provide highly sensitive detection of the selected sequences from SARS-CoV-2 through nucleic acid hybridization. For better sensing performance, thermoplasmonic heat is generated on the same gold nano-islands chip when illuminated at their plasmonic resonance frequency. Remarkably, this dual-functional LSPR biosensor exhibited high selectivity towards the SARS-CoV-2 sequences with a detection limit as low as 0.22 pM. In other work, to achieve rapid and accurate detection of SARS-CoV-2 in clinical samples, researchers from the Korea Basic Science Institute developed an ultra-sensitive field-effect transistor (FET)-based biosensing device24. The sensor was produced by coating graphene sheets of the FET with a specific antibody against SARS-CoV-2 spike protein. The FET device could detect the SARS-CoV-2 spike protein at concentrations of 1.31×10–5 pM in phosphate-buffered saline and 1.31×10–3 pM in clinical transport medium. Remarkably, the device exhibited no measurable cross-reactivity with Middle East respiratory syndrome coronavirus (MERS-CoV) antigen, indicating the extraordinary capability of this sensor to distinguish the SARS-CoV-2 antigen protein from those of MERS-CoV.

Another approach that can be used for SARS-CoV-2 and that was successfully used with MERS-CoV, Mycobacterium tuberculosis and human papillomavirus consists of a paper-based colorimetric sensor for DNA detection based on pyrrolidinyl peptide nucleic acid (acpcPNA)-induced silver nanoparticle aggregation25. Briefly, in the absence of complementary DNA, silver nanoparticles aggregate due their electrostatic interactions with the acpcPNA probe. However, in the presence of target DNA, a DNA–acpcPNA duplex starts to form which leads to dispersion of the silver nanoparticles as a result of electrostatic repulsion, giving rise to a detectable colour change25. The use of aptamers and molecular beacons instead of PNA can also represent a potential alternative.

Other avenue where nanomaterials can contribute to detection of SARS-CoV-2 is the extraction and purification of targeted molecules from biological fluids (blood and nasal/throat samples). Thus, nanomaterials with magnetic properties can be decorated with specific receptors of the virus, leading to attachment of virus molecules to the nanoparticles that will allow their magnetic extraction using an external magnetic field.

In this way nanomaterial-based detection can facilitate faster and more accurate detection of the virus even at early stages of the infection, in large due to versatility of surface modification of nanoparticles.

Source: https://www.nature.com/articles/s41565-020-0751-0

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A shapeshifting material based on inorganic matter

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Nov 30, 2020 (Nanowerk News) By embedding titanium-based sheets in water, a group led by scientists from the RIKEN Center for Emergent Matter Science has created a material using inorganic materials that can be converted from a hard gel to soft matter using temperature changes. Science fiction often features inorganic life forms, but in reality, organisms and devices that respond to stimuli such as temperature changes are nearly always based on organic materials, and hence, research in the area of “adaptive materials” has almost exclusively focused on organic substances. However, there are advantages to using inorganic materials such as metals, including potentially better mechanical properties. Considering this, the RIKEN-led group decided to attempt to recreate the behavior displayed by organic hydrogels, but using inorganic materials. The inspiration for the material comes from an aquatic creature called a sea cucumber. Sea cucumbers are fascinating animals, related to starfishes (but not to cucumbers!) that have the ability to morph their skin from a hard layer to a kind of jelly, allowing them to throw out their internal organs – which are eventually regrown—to escape from predators. In the case of the sea cucumbers, chemicals released by their nervous systems trigger the change in the configuration of a protein scaffold, creating the change. To make it, the researchers experimented with arranging nanosheets—thin sheets of titanium oxide in this case—in water, with the nanosheets making up 14 percent and water 86 percent of the material by weight. schematic illustration of unilamellar titanate nanosheet a A schematic illustration of unilamellar titanate (IV) nanosheet (TiNS). Countercations are omitted for clarity. Open square indicates vacant sites. b–g Schematic illustrations of the hydrogel of TiNS (TiNS-Gel) in a repulsion-dominant state (TiNS-GelRepuls; b–d) and an attraction-dominant state (TiNS-GelAttract; e–g). When the electrostatic repulsion between TiNSs in an aqueous dispersion is strong enough, TiNSs spontaneously self-assemble into a long-periodicity lamellar architecture (c) in which their mobility is mutually restricted (d). As a result, their aqueous dispersion can exhibit a gel-like behavior, denoted as TiNS-GelRepuls. When TiNS-GelRepuls is heated above a critical temperature, the electrostatic repulsion becomes weaker than the competing van der Waals attraction, so that TiNSs abruptly stack tightly (g) to form an interconnected 3D network that can hold large quantities of water (f), denoted as TiNS-GelAttract. Because of the large difference in the topology of the internal structure between TiNS-GelRepuls and TiNS-GelAttract, this gel-to-gel transition is accompanied by drastic changes in the optical and mechanical properties. (© Nature Communications) (click on image to enlarge) According to Koki Sano of RIKEN CEMS, the first author of the paper (Nature Communications, “A mechanically adaptive hydrogel with a reconfigurable network consisting entirely of inorganic nanosheets and water”), “The key to whether a material is a soft hydrogel or a harder gel is based on the balance between attractive and repulsive forces among the nanosheets. If the repulsive forces dominate, it is softer, but if the attractive ones are strong, the sheets become locked into a three-dimensional network, and it can rearrange into a harder gel. By using finely tuned electrostatic repulsion, we tried to make a gel whose properties would change depending on temperature.” The group was ultimately successful in doing this, finding that the material changed from a softer repulsion-dominated state to a harder attraction-dominated state at a temperature of around 55 centigrade. They also found that they could repeat the process repeatedly without significant deterioration. “What was fascinating,” he continues, “is that this transition process is completed within just two seconds even though it requires a large structural rearrangement. This transition is accompanied by a 23-fold change in the mechanical elasticity of the gel, reminiscent of sea cucumbers.” To make the material more useful, they next doped it with gold nanoparticles that could convert light into heat, allowing them to shine laser light on the material to heat it up and change the structure. According to Yasuhiro Ishida of RIKEN CEMS, one of the corresponding authors of the paper, “This is really exciting work as it greatly opens the scope of substance that can be used in next-generation adaptive materials, and may even allow us to create a form of ‘inorganic life’.”

Source: https://feeds.nanowerk.com/~/639407215/0/nanowerk/agwb~A-shapeshifting-material-based-on-inorganic-matter.php

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Nanoscopic barcodes set a new science limit

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Nov 29, 2020 (Nanowerk News) Using barcodes to label and identify everyday items is as familiar as a trip to the supermarket. Imagine shrinking those barcodes a million times, from millimetre to nanometre scale, so that they could be used inside living cells to label, identify and track the building blocks of life or, blended into inks to prevent counterfeiting. This is the frontier of nanoengineering, requiring fabrication and controlled manipulation of nanostructures at atomic level – new, fundamental research, published in Nature Communications (“Nanorods with multidimensional optical information beyond the diffraction limit”), shows the possibilities and opportunities ahead. Schematic diagram to illustrate the route that leads to the formation of the nanorods a Schematic diagram to illustrate the route that leads to the formation of the nanorods. Conditions, including the well-controlled amount of surfactant concentration (OA-) and the relatively low concentration of shell precursor, have to be met, otherwise, nanoplates, nanodumbbells, and small nanoparticles from precursor self-nucleation, will form. b High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images of three typical heterogeneous nanorods, scale bar is 50 nm. c Large area HAADF-STEM image of 18-segment heterogeneous nanorods, scale bar is 100 nm. d Distance statistics of five pairwise NaErF4 segments (center-to-center of each pairwise with different color markers) of the heterogeneous nanorods in c. (© Nature Communications) (click on image to enlarge) The University of Technology Sydney (UTS) led collaboration developed a nanocrystal growth method that controls the growth direction, producing programmable atomic thin layers, arbitrary barcoded nanorods, with morphology uniformity. The result is millions of different kinds of nanobarcodes that can form a “library” for future nanoscale sensing applications. The researchers anticipate that such barcode structures will attract broad interests in a range of applications as information nanocarriers for bio-nanotechnology, life sciences, data storage, once they are incorporated into a variety of matrixes. Lead author Dr Shihui Wen said the research provides a benchmark that will open up the potential for engineering smaller nanophotonics devices. “The inorganic nanobarcode structures are rigid, and it is easy to control the composite, thickness and distance accuracy between different functional segments for geometrical barcoding beyond the optical diffraction limit. Because they are chemically and optically stable, the nanoscopic barcodes can be used as carriers for drug delivery and tracking into the cell, once the surface of the barcode structures is further modified and functionalized with probe molecules and cargos,” Dr Wen, from the UTS Institute of Biomedical Materials and Devices (IBMD), said. The team also had an additional breakthrough with the development of a novel, tandem decoding system, using super-resolution nanoscopy to characterize different optical barcodes within the diffraction limit. Senior author, UTS IBMD Director, Professor Dayong Jin said there was no commercial system available for this type of super resolution imaging. “We had to build the instrumentation to diagnose the sophisticated functions that can be intentionally built into the tiny nanorod. These together allow us to unlock the further potential for placing atomic molecules where we want them so we can continue to miniaturise devices. This was the first time we were able to use super resolution system to probe, activate and readout the specific functional segment within the nanorod. “Imagine a tiny device, smaller than one thousandth the width of a human hair, and we can selectively activate a particular region of that device, see the optical properties, quantify them. This is the science now showing many new possibilities,” he said. Professor Jin is also the co-director of UTS-SUStech Joint Research Centre. The researchers envisage the developed nanoscale optical devices could be simultaneously used for tagging different cellular species. “These devices are also readily applicable for high-security-level anticounterfeiting when different batches of them are blended with inks and can be readily printed on high-value products for authentication.’ Dr Wen said

Source: https://feeds.nanowerk.com/~/639384579/0/nanowerk/agwb~Nanoscopic-barcodes-set-a-new-science-limit.php

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Freeze like a star! Web exhibition explores the mysteries of the quantum world

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(Nanowerk News) Colder than in outer space, higher pressure than 30 sperm whales on a stamp, and super magnets that could hold two Eiffel Towers: The search for new quantum materials – the materials of the day after tomorrow – is taking place today under extreme conditions.
Yet it is often difficult to understand what the researchers actually do in their high-performance laboratories.
The Würzburg-Dresden Cluster of Excellence ct.qmat–Complexity and Topology in Quantum Matter has now taken a big step towards popular science communication.
The web exhibition SHOWCASE–Insight into our Research provides information about the goals, current activities, and research achievements of over 250 international cluster researchers – with easy-to-understand texts, catchy illustrations and entertaining videos.
“No less than three exhibitions were opened this year, all explaining our research themes. The positive response inspired us to prepare these topics in a multimedia format and make them accessible on our website. Now you can navigate through our mysterious quantum world from the comfort of your sofa anywhere in the world. This is an enormous advantage, not the least during the coronavirus pandemic,” emphasizes Prof. Matthias Vojta, spokesperson of the Dresden branch of the Cluster of Excellence.
Available in German and English, the web exhibition explains in an easily understandable way the extreme conditions that prevail in the high-performance laboratories, why researchers design quantum materials atom by atom, and what topological quantum physics has to do with hairy donuts.
An outlook on future applications leads from “cold chips” to “QuBits” and quantum computers. For those who want to know more, there are links to background information.
“In Germany we are leaders in the field of topological quantum materials and we play in the top league of our research field worldwide. But we also want to communicate to the general public outside our scientific community how exciting our experiments are, what groundbreaking results we have achieved and what this means for the society as a whole. This is particularly important to us, because we are convinced that quantum technologies will decisively shape the high-tech of the 21st century and lead to new applications,” explains Prof. Ralph Claessen, spokesperson of the Würzburg branch of the Cluster.
Source: Technische Universität Dresden
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Source: https://feeds.nanowerk.com/~/639374679/0/nanowerk/agwb~Freeze-like-a-star-Web-exhibition-explores-the-mysteries-of-the-quantum-world.php

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Game-changer in thermoelectric materials: decoupling electronic and thermal transport

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Nov 29, 2020 (Nanowerk News) A new University of Wollongong study (Advanced Energy Materials,“Ultra-High Thermoelectric Performance in Bulk BiSbTe/Amorphous Boron Composites with Nano-Defect Architectures”) overcomes a major challenge of thermoelectric materials, which can convert heat into electricity and vice versa, improving conversion efficiency by more than 60%. Current and potential future applications range from low-maintenance, solid-state refrigeration to compact, zero-carbon power generation, which could include small, personal devices powered by the body’s own heat. “The decoupling of electronic (electron-based) and thermal (phonon-based) transport will be a game-changer in this industry,” says the UOW’s Prof Xiaolin Wang.

Thermoelectric applications and challenges

Bismuth telluride-based materials (Bi2Te3, Sb2Te3 and their alloys) are the most successful commercially-available thermoelectric materials, with current and future applications falling into two categories: converting electricity into heat, and vice versa:
  • Converting electricity into heat: reliable, low-maintenance solid-state refrigeration (heat pump) with no moving parts, no noise, and no vibration.
  • Converting heat into electricity including fossil-free power generation from a wide range of heat sources or powering micro-devices ‘for free’, using ambient or body temperature.
  • Heat ‘harvesting’ takes advantage of the free, plentiful heat sources provided by body heat, automobiles, everyday living, and industrial process. Without the need for batteries or a power supply, thermoelectric materials could be used to power intelligent sensors in remote, inaccessible locations. An ongoing challenge of thermoelectric materials is the balance of electrical and thermal properties: In most cases, an improvement in a material’s electrical properties (higher electrical conductivity) means a worsening of thermal properties (higher thermal conductivity), and vice versa. “The key is to decouple thermal transport and electrical transport”, says lead author, PhD student Guangsai Yang.

    Better efficiency through decoupling

    The three-year project at UOW’s Institute of Superconductivity and Electronic Materials (ISEM) found a way to decouple and simultaneously improve both thermal and electronic properties.
    cover image Advanced Energy Materials
    The new paper was selected as the cover story for the November edition of Wiley’s Advanced Energy Materials

    The team added a small amount of amorphous nano-boron particles to bismuth telluride-based thermoelectric materials, using nano-defect engineering and structural design.

    Amorphous nano boron particles were introduced using the spark plasma sintering (SPS) method.

    “This reduces the thermal conductivity of the material, and at the same time increases its electron transmission”, explains corresponding author Prof Xiaolin Wang.

    “The secret of thermoelectric materials engineering is manipulating the phonon and electron transport,” explains Professor Wang.

    Because electrons both carry heat and conduct electricity, material engineering based on electron transport alone is prone to the perennial tradeoff between thermal and electrical properties.

    Phonons, on the other hand, only carry heat. Therefore, blocking phonon transport reduces thermal conductivity induced by lattice vibrations, without affecting electronic properties. “The key to improving thermoelectric efficiency is to minimize the heat flow via phonon blocking, and maximize electron flow via (electron transmitting),” says Guangsai Yang. “This is the origin of the record-high thermoelectric efficiency in our materials.” The result is record-high conversion efficiency of 11.3%, which is 60% better than commercially-available materials prepared by the zone melting method. As well as being the most successful commercially-available thermoelectric materials, bismuth telluride-based materials are also typical topological insulators.

    Source: https://feeds.nanowerk.com/~/639374601/0/nanowerk/agwb~Gamechanger-in-thermoelectric-materials-decoupling-electronic-and-thermal-transport.php

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