Boosting Copper Biocidal Activity by Silver Decoration and Few-Layer Graphene in Coatings on Textile Fibers.

The outbreak of the Coronavirus disease 2019 (COVID-19) pandemic has highlighted the importance of developing antiviral surface coatings that are capable of repelling pathogens and neutralizing them through self-sanitizing properties. In this study, a novel coating design based on few-layer graphene (FLG) is proposed and silver-decorated micro copper flakes (CuMF) that exhibit both antibacterial and antiviral properties. The role of sacrificial anode surfaces and intrinsic graphene defects in enhancing the release of metal ions from CuMF embedded in water-based binders is investigated. In silico analysis is conducted to better understand the molecular interactions of pathogen-repelling species with bacterial or bacteriophage proteins. The results show that the optimal amount of CuMF/FLG in the coating leads to a significant reduction in bacterial growth, with reductions of 3.17 and 9.81 log for Staphylococcus aureus and Escherichia coli, respectively. The same coating also showed high antiviral efficacy, reducing bacteriophage phi6 by 5.53 log. The antiviral efficiency of the coating is find to be doubled compared to either micro copper flakes or few-layer graphene alone. This novel coating design is versatile and can be applied to various substrates, such as personal protective clothing and face masks, to provide biocidal activity against both bacterial and viral pathogens.

A Unique Interactive Nanostructure Knitting based Passive Sampler Adsorbent for Monitoring of Hg2+ in Water.

This work reports the development of ultralight interwoven ultrathin graphitic carbon nitride (g-CN) nanosheets for use as a potential adsorbent in a passive sampler (PAS) designed to bind Hg2+ ions. The g-CN nanosheets were prepared from bulk g-CN synthesised via a modified high-temperature short-time (HTST) polycondensation process. The crystal structure, surface functional groups, and morphology of the g-CN nanosheets were characterised using a battery of instruments. The results confirmed that the as-synthesized product is composed of few-layered nanosheets. The adsorption efficiency of g-CN for binding Hg2+ (100 ng mL-1) in sea, river, rain, and Milli-Q quality water was 89%, 93%, 97%, and 100%, respectively, at natural pH. Interference studies found that the cations tested (Co2+, Ca2+, Zn2+, Fe2+, Mn2+, Ni2+, Bi3+, Na+, and K+) had no significant effect on the adsorption efficiency of Hg2+. Different parameters were optimised to improve the performance of g-CN such as pH, contact time, and amount of adsorbent. Optimum conditions were pH 7, 120 min incubation time and 10 mg of nanosheets. The yield of nanosheets was 72.5%, which is higher compared to other polycondensation processes using different monomers. The g-CN sheets could also be regenerated up to eight times with only a 20% loss in binding efficiency. Overall, nano-knitted g-CN is a promising low-cost green adsorbent for use in passive samplers or as a transducing material in sensor applications.

Nanomaterial resistant microorganism mediated reduction of graphene oxide.

In this study, soil bacteria were isolated from nanomaterials (NMs) contaminated pond soil and enriched in the presence of graphene oxide (GO) in mineral medium to obtain NMs resistant bacteria. The isolated resistant bacteria were biochemically and genetically identified as Fontibacillus aquaticus. The resistant bacteria were allowed to interact with engineered GO in order to study the biotransformation in GO structure. Raman spectra of GO extracted from culture medium revealed decreased intensity ratio of ID/IG with subsequent reduction of CO which was consistent with Fourier transform infrared (FTIR) results. The structural changes and exfoliatied GO nanosheets were also evident from transmission electron microscopy (TEM) images. Ultraviolet-visible spectroscopy, high resolution X-ray diffraction (XRD) and current-voltage measurements confirmed the reduction of GO after the interaction with resistant bacteria. X-ray photoelectron spectroscopy (XPS) analysis of biotransformed GO revealed reduction of oxygen-containing species on the surface of nanosheets. Our results demonstrated that the presented method is an environment friendly, cost effective, simple and based on green approaches for the reduction of GO using NMs resistant bacteria.

Determining the fate of fluorescent quantum dots on surface of engineered budding S. cerevisiae cell molecular landscape.

In this study, we surface engineered living S. cerevisiae cells by decorating quantum dots (QDs) and traced the fate of QDs on molecular landscape of single mother cell through several generation times (progeny cells). The fate of QDs on cell-surface was tracked through the cellular division events using confocal microscopy and fluorescence emission profiles. The extent of cell-surface QDs distribution among the offspring was determined as the mother cell divides into daughter cells. Fluorescence emission from QDs on progeny cells was persistent through the second-generation time (~240min) until all of the progeny cells lost their cell-bound QDs during the third generation time (~360min). The surface engineered yeast cells were unaffected by the QDs present on their molecular landscapes and retained their normal cellular growth, architecture and metabolic activities as confirmed by their viability, scanning electron microscopy (SEM) examinations and cytotoxicity tests, respectively. Our results demonstrated that QDs on mother cell landscape tend to distribute among its progeny cells that accompanied with concomitant reduction in QDs' fluorescence, which can be quantified. We suggest that surface engineered cells with QDs will enable investigating the cellular behavior and monitoring cell growth patterns as nanobiosensors for screening of drugs/chemicals at single cell level with fewer side effects.

Whole-cell based label-free capacitive biosensor for rapid nanosize-dependent toxicity detection.

Despite intensive studies on examining the toxicity of nanomaterials (NMs), our current understanding on potential toxicity in relation to size and cellular responses has remained limited. In this work, we have developed a whole-cell based capacitive biosensor (WCB) to determine the biological toxicity of nanoparticles (NPs) using iron oxide (Fe3O4) NPs as models. This WCB chip comprised of an array of capacitor sensors made of gold interdigitated microelectrodes on which living Escherichia coli cells were immobilized. Cells-on-chip was then allowed to interact with different sizes of Fe3O4 NPs (5, 20 and 100 nm) and concentration-depended cellular-responses were measured in terms of change in dielectric properties (capacitance) as a function of applied AC frequency. The WCB response showed smaller-sized Fe3O4 NPs (5 nm) induced maximum change in surface capacitance because of their effective cellular interaction with E. coli cells-on-chip indicating that the cells suffered from severe cellular deformation, which was confirmed by scanning electron microscopic (SEM) examination. Further our results were validated through their cell viability and E. coli responses at the interface of cell-membrane and NPs as a proof-of-concept. WCB response showed a size-dependent shift in maximum response level from 2 µg/ml of 5 nm sized NPs to 4 µg/ml with NP-sizes greater than 20 nm. The developed WCB offered real-time, label-free and noninvasive detection of cellular responses against Fe3O4 NPs' toxicity with speed, simplicity and sensitivity that can be extended to toxicity screening of various other NPs.

Quantum dot conjugated S. cerevisiae as smart nanotoxicity indicators for screening the toxicity of nanomaterials.

In this study, we have evaluated the toxicity of different forms of carbon nanotubes (CNTs) using S. cerevisiae-QD (SQD) bioconjugates as a novel fluorescent biological nanotoxicity indicator. A CNT mediated effect in SQD bioconjugates was used as an indicator for the changes occurring at the cell-membrane interfaces that induced disruption of membrane bound QDs resulting in the loss of fluorescence. Single, double and multiwalled carbon nanotubes (SWCNTs, DWCNTs and MWCNTs) were tested for their toxicities imposed on SQD bioconjugates. Bioconjugates exposed to varying concentrations of different forms of CNTs exhibited different modes of toxicities on SQD bioconjugates. SQD bioconjugates were highly responsive in the 0.1-10 µg mL-1 CNT concentration range after 1 h of exposure. The toxicity of CNTs was linked to the number of CNT walls. These results were further confirmed by SEM analysis and cell-viability tests that were consistent with the toxicity assays using fluorescent bioconjugates with different types of CNTs. SWCNTs imposed more severe cellular toxicity followed by MWCNTs and DWCNTs and the order of increasing cellular-damage by CNTs followed DWCNTs < MWCNTs < SWCNTs. This study speculates that the cell-injury by CNTs depends on their physical properties, such as layers of walls, non-covalent forces and dispersion states. Our results demonstrated a facile optical strategy that enables rapid and real-time cytotoxicity screening with yeast as model living-cells for engineering nanomaterials.

E. coli-quantum dot bioconjugates as whole-cell fluorescent reporters for probing cellular damage.

A quantum dot (QD) conjugated whole-cell E. coli biosensor (E. coli-QD bioconjugates) was developed as a new molecular tool for probing cellular damage. The E. coli-QD bioconjugates were viable and exhibited fluorescence emission at 585 nm. Scanning electron microscopy (SEM) analysis of E. coli-QD bioconjugates revealed that the QDs were immobilized on the cell-surfaces and the fluorescence emission from QDs present on cell-surfaces was visualized by confocal microscopic examination. The E. coli-QD bioconjugates were employed as whole-cell fluorescent reporters that were designed to function as fluorescence switches that turn-off when cellular damage occurs. In this study, multi-walled carbon nanotubes (CNTs) were utilized as a model nanomaterial to probe cellular damage. Fluorescence spectra were recorded after the exposure of E. coli-QD bioconjugates with CNTs. We observed a strong correlation between fluorescence emission spectra, SEM and confocal microscopic analysis demonstrating that CNTs induced a dose and exposure time-dependent cellular toxicity. This toxicity mainly occurred by the physical interaction and cellular trafficking mechanisms that led to the collapse of the cellular structure and thus loss of fluorescence. The responses of E. coli-QD bioconjugates against CNTs were also visualized by simply exposing the cells to UV light and therefore rapid toxicity analysis and screening can be made. Our study demonstrated an easy and simple method to determine an important mechanistic perspective for the biological toxicity of chemicals or nanomaterials (NMs).

Trace-level detection of atrazine using immuno-chemiluminescence: dipstick and automated flow injection analyses formats.

A sensitive chemiluminescence (CL)-based immunoassay technique based on both dipstick and flow injection analytical formats is reported for the detection of atrazine. In the dipstick-based immunoassay technique, antibody (anti-atrazine) was first immobilized on the nitrocellulose membranes. The dipstick was then treated with atrazine and atrazine-horseradish peroxidase conjugate (atra-HRP) to facilitate the competitive binding. The dipstick was further treated with urea-hydrogen peroxide (U-H202) and luminol to generate photons. The number of photons generated was inversely proportional to the atrazine concentration. In the flow injection analysis (FIA) format, the antibody was immobilized on protein-A sepharose matrix and packed in a glass capillary column, which functioned as an immunoreactor. Competitive binding of antigen and antibody occurred. The CL signals generated during the biochemical reactions were correlated with atrazine concentrations in the analytical samples. By using dipstick technique, it was possible to detect atrazine concentration down to 0.1 ng/mL; with the FIA format, the detection of atrazine was down to 0.01 ng/mL.