SARS-CoV-2 Virus Detection Via a Polymeric Nanochannel-Based Electrochemical Biosensor.

The development of simple, cost-effective, rapid, and quantitative diagnostic tools remains critical to monitor infectious COVID-19 disease. Although numerous diagnostic platforms, including rapid antigen tests, are developed and used, they suffer from limited accuracy, especially when tested with asymptomatic patients. Here, a unique approach to fabricate a nanochannel-based electrochemical biosensor that can detect the entire virion instead of virus fragments, is demonstrated. The sensing platform has uniform nanoscale channels created by the convective assembly of polystyrene (PS) beads on gold electrodes. The PS beads are then functionalized with bioreceptors while the gold surface is endowed with anti-fouling properties. When added to the biosensor, SARS-CoV-2 virus particles block the nanochannels by specific binding to the bioreceptors. The nanochannel blockage hinders the diffusion of a redox probe; and thus, allows quantification of the viral load by measuring the changes in the oxidation current before and after virus incubation. The biosensor shows a low limit of detection of ≈1.0 viral particle mL-1 with a wide detection range up to 108 particles mL-1 in cell culture media. Moreover, the biosensor is able to differentiate saliva samples with SARS-CoV-2 from those without, demonstrating the potential of this technology for translation into a point-of-care biosensor product.

Electrochemical Biosensors Based on Convectively Assembled Colloidal Crystals.

Rapid, sensitive, selective and portable virus detection is in high demand globally. However, differentiating non-infectious viral particles from intact/infectious viruses is still a rarely satisfied sensing requirement. Using the negative space within monolayers of polystyrene (PS) spheres deposited directly on gold electrodes, we fabricated tuneable nanochannels decorated with target-selective bioreceptors that facilitate the size-selective detection of intact viruses. Detection occurred through selective nanochannel blockage of diffusion of a redox probe, [Fe(CN)6]3/4-, allowing a quantifiable change in the oxidation current before and after analyte binding to the bioreceptor immobilised on the spheres. Our model system involved partial surface passivation of the mono-assembled PS spheres, by silica glancing angle deposition, to confine bioreceptor immobilisation specifically to the channels and improve particle detection sensitivity. Virus detection was first optimised and modelled with biotinylated gold nanoparticles, recognised by streptavidin immobilised on the PS layer, reaching a low limit of detection of 37 particles/mL. Intact, label-free virus detection was demonstrated using MS2 bacteriophage (~23-28 nm), a marker of microbiological contamination, showing an excellent limit of detection of ~1.0 pfu/mL. Tuneable nanochannel geometries constructed directly on sensing electrodes offer label-free, sensitive, and cost-efficient point-of-care biosensing platforms that could be applied for a wide range of viruses.

Porous polymeric membranes: fabrication techniques and biomedical applications.

Porous polymeric membranes have shown great potential in biological and biomedical applications such as tissue engineering, bioseparation, and biosensing, due to their structural flexibility, versatile surface chemistry, and biocompatibility. This review outlines the advantages and limitations of the fabrication techniques commonly used to produce porous polymeric membranes, with especial focus on those featuring nano/submicron scale pores, which include track etching, nanoimprinting, block-copolymer self-assembly, and electrospinning. Recent advances in membrane technology have been key to facilitate precise control of pore size, shape, density and surface properties. The review provides a critical overview of the main biological and biomedical applications of these porous polymeric membranes, especially focusing on drug delivery, tissue engineering, biosensing, and bioseparation. The effect of the membrane material and pore morphology on the role of the membranes for each specific application as well as the specific fabrication challenges, and future prospects of these membranes are thoroughly discussed.

Solution processed polydimethylsiloxane/gold nanostar flexible substrates for plasmonic sensing.

Gold nanostars can display tunable optical properties in the visible and near IR, which lead to strong electromagnetic field enhancement at their tips. We report generalized application of gold nanostars for ultrasensitive identification of molecules, based on both localized surface plasmon resonance (LSPR) and surface enhanced Raman scattering (SERS). We address the requirements of plasmonic sensors, related to sufficiently large areas where nanoparticles are uniformly immobilized with high density, as well as mechanical flexibility, which offers additional advantages for real-world applications. Gold nanostar monolayers were thus immobilized on transparent, flexible polydimethylsiloxane substrates, and their refractive index sensitivity and SERS performance were studied. The application of such substrates for LSPR based molecular sensing is demonstrated via detection of a model analyte, mercaptoundecanoic acid. We further demonstrate SERS-based pesticide detection on fruit skin, by simply covering the fruit surface with the flexible plasmonic substrate, at the area where the target molecule is to be detected. The transparency of the substrate allows SERS detection through backside excitation, thereby facilitating practical implementation.

Sized controlled synthesis, purification, and cell studies with silicon quantum dots.

This article describes the size control synthesis of silicon quantum dots with simple microemulsion techniques. The silicon nanocrystals are small enough to be in the strong confinement regime and photoluminesce in the blue region of the visible spectrum and the emission can be tuned by changing the nanocrystal size. The silicon quantum dots were capped with allylamine either a platinum catalyst or UV-radiation. An extensive purification protocol is reported and assessed using (1)H NMR to produce ultra pure silicon quantum dots suitable for biological studies. The highly pure quantum dots were used in cellular uptake experiments and monitored using confocal microscopy. The results showed that the amine terminated silicon nanocrystals accumulated in lysosome but not in nuclei and could be used as bio-markers to monitor cancer cells over long timescales.

Chemical reactions on surface molecules attached to silicon quantum dots.

This Article describes research on chemical reactions on molecules attached to the surface of silicon quantum dots that have been performed to produce quantum dots with reactive surface functionalities such as diols and epoxides. Characterization of the surface reactions includes NMR and FT-IR studies, and the quantum dots were characterized by transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). Cytotoxicity and cell viability assay conducted on silicon dots capped with polar molecules indicated low toxicity with quantum dots with more reactive functionalities found to be more toxic. The silicon quantum dots photoluminesce and have been used as a blue chromophore for the biological imaging of cells.

On the cyto-toxicity caused by quantum dots.

Quantum dots (QDs) such as CdSe QDs have been introduced as new fluorophores. The QDs conjugated with antibody are starting to be widely used for immunostaining. However there is still not sufficient analysis of the toxicity of QDs in the literature. Therefore we evaluated the cell damage caused by the quantum dots for biological applications. We performed cell viability assay to determine the difference in cell damage depending on the sizes and colors of mercapto-undecanoic acid (MUA) QDs and the cell types. The results showed that the cell viability decreased with increasing concentration of MUA-QDs. But in the case of Vero cell (African green monkey's kidney cell) with red fluorescence QD (QD640), the cell damage was less than for the others. Furthermore through the flow cytometry assay we found that this cell damage caused by MUA-QD turned out to be cell death after 4-6-hr incubation. From the two assays described above, we found that there is a range of concentration of MUA-QDs where the cell viability decreased without cell death occurring and thus we conclude that attention should be given when MUAQDs are applied to living organisms even in low concentrations.

Regioselective hydroxylation of the xylyl linker in a diiron(III) complex having a carboxylate-rich ligand with H2O2.

Reaction of a diiron(III) complex having a xylta4- ligand (N,N,N',N'-m-xylylenediamine tetraacetate) with H2O2 resulted in regioselective hydroxylation of the m-xylyl linker. The reaction mimics the self-hydroxylation of a phenylalanine side chain found for ribonucleotide reductase (R2-W48F/D84E).