Formation of Self-Assembled Nanowires from Copper Nanoparticles Synthesized by the Electro-Explosion of Wires Technique-Study of the Time-Dependent Structural and Functional Evolution.

We report here the formation of Cu nanowires (CuNWs) from Cu nanoparticles (CuNPs) by a self-assembly process. The CuNPs were synthesized by the electro-explosion of wire (EEW) technique that included nonequilibrium processes for the synthesis. Structural evolution in terms of aggregation or nanowire formation in the samples was observed when the CuNPs were kept for a month after synthesis in a glass vial without the application of any external driving force. The emergence of tangled CuNWs was noticed at the bottom of the vials only when no agitation or aeration was allowed. The nanowires were characterized using transmission electron microscopy (TEM) and X-ray diffraction (XRD). Thermal oxidation of the nanowire samples implied that they could convert into rod-shaped structures. Loss of functionality was also observed in the hemoglobin precipitation study conducted to compare the activity of freshly prepared CuNPs and CuNWs. From the above observations, we conclude that the CuNP, after synthesis, possesses a huge amount of energy, and attainment of equilibrium occurs through either aggregation (clustering) or ordered self-assembly, depending on the conditions applied.

Limit-Defying µ-Total Analysis System: Achieving Part-Per-Quadrillion Sensitivity on a Hierarchical Optofluidic SERS Sensor.

Optofluidic sensors have accelerated the growth of smart sensor platforms with improved sensitivity, reliability, and innovation. In this article, we report the integration of a surface-enhanced Raman scattering (SERS) material consisting of silver nanoparticle-decorated diatomaceous earth (AgNPs-DE) with a flow-through microfluidic device, building up a hierarchical structured micro-total analysis system (µ-TAS) capable of achieving part-per-quadrillion (ppq)-level sensitivity. By the synergic integration of millimeter-scale microfluidic devices and porous laboratory filter paper with a micrometer-sized crosslinked cellulosic network that carries SERS-active AgNPs-DE, which possesses submicron to nanometer regimes of photonic crystals and plasmonic nanostructures, we achieved enhanced mass-transfer efficiency and unprecedented detection sensitivity. In our experiment, fentanyl as the testing analyte at different concentrations was measured using a portable Raman spectrometer. The limit of detection (LOD) was estimated to be 10 ppq from a small detection volume of 10 mL with an ultrafast time of sensing (TOS) of 3 min. To attain comparable signals, the traditional soaking method took more than 90 min to detect 10 part-per-trillion fentanyl from a 10 mL sample. Compared with existing SERS sensing results of fentanyl, the limit-defying µ-TAS reduced the LOD-TOS product by almost 4 orders of magnitude, which represents a new stage of ultrafast sensing of extremely low concentration analytes.

Quantitative Sensing of Domoic Acid from Shellfish Using Biological Photonic Crystal Enhanced SERS Substrates.

Frequent monitoring of sea food, especially shellfish samples, for the presence of biotoxins serves not only as a valuable strategy to mitigate adulteration associated health risks, but could also be used to develop predictive models to understand algal explosion and toxin trends. Periodic toxin assessment is often restricted due to poor sensitivity, multifarious cleaning/extraction protocols and high operational costs of conventional detection methods. Through this work, a simplistic approach to quantitatively assess the presence of a representative marine neurotoxin, Domoic acid (DA), from spiked water and crab meat samples is presented. DA sensing was performed based on surface-enhanced Raman scattering (SERS) using silver nanoparticle enriched diatomaceous earth­a biological photonic crystal material in nature. Distinctive optical features of the quasi-ordered pore patterns in diatom skeleton with sporadic yet uniform functionalization of silver nanoparticles act as excellent SERS substrates with improved DA signals. Different concentrations of DA were tested on the substrates with the lowest detectable concentration being 1 ppm that falls well below the regulatory DA levels in seafood (>20 ppm). All the measurements were rapid and were performed within a measurement time of 1 min. Utilizing the measurement results, a standard calibration curve between SERS signal intensity and DA concentration was developed. The calibration curve was later utilized to predict the DA concentration from spiked Dungeness crab meat samples. SERS based quantitative assessment was further complemented with principal component analysis and partial least square regression studies. The tested methodology aims to bring forth a sensitive yet simple, economical and an extraction free routine to assess biotoxin presence in sea food samples onsite.

Antibacterial and antiviral high-performance nanosystems to mitigate new SARS-CoV-2 variants of concern.

The increased severity of the COVID-19 infection due to new SARS-CoV-2 variants has resonated pandemic impact which made health experts to re-evaluate the effectiveness of pandemic management strategies. This becomes critical owing to the infection in large population and shortcomings in the existing global healthcare system worldwide. The designing of high-performance nanosystems (NS) with tunable performances seems to be the most efficient method to tackle infectious SARS-CoV-2 variants including recently emerged omicron mutation. In this direction, experts projects the versatile functionalized NS and their capabilities to mitigate SARS-CoV-2 propagation pathways by sensitization, antipathogenicity, photocatalysis, photothermal effects, immune response, developing efficient diagnostics assays or associated, selective biomarkers detection, and targeted drug delivery systems. To achieve these tasks, this opinion article project the importance of the fabrication of nano-enabled protective gear, masks, gloves, sheets, filtration units, nano-emulsified disinfectants, antiviral/bacterial paints, and therangostics to facilitate quarantine strategies via protection, detection, and treatment needed to manage COVID-19 pandemic in personalized manners. These functional protective high-performance antibacterial and antiviral NS can efficiently tackle the SARS-CoV-2 variants transmission through respiratory fluids and pollutants within water droplets, aerosols, air, and particulates along with their severe infection via neutralizing or eradicating the virus.

Sunlight mediated enhanced photocatalytic activity of TiO2 nanoparticles functionalized CuO-Cu2O nanorods for removal of methylene blue and oxytetracycline hydrochloride.

Metal free heterojunctions have shown promising applicability as potential photocatalyst materials. Like the commonly explored metal-non metal heterojunctions, semiconductor-semiconductor junctions are also capable of facilitating charge separation and improved lifetimes, leading to augmented surface reaction efficacy. However, unlike the metal carrying heterojunctions, they are much economical and easier to fabricate and tune. Through this study, we present a facile one step hydrothermal route to synthesize CuO-Cu2O nanorods/TiO2 nanoparticles heterostructures (CTHS) with their potential application as a low cost photocatalytic alternative. The average size of the synthesized heterojunction components, as estimated from transmission electron microscopy (TEM) evaluation was 13 and 5 nm respectively for the nanorod length and width, while the functionalizing TiO2 nanoparticles were averaged around 10 nm. Heterojunction formation was confirmed using Raman spectroscopy, X-ray diffraction, high resolution TEM, and elemental mapping. X-ray photoelectron spectroscopy data marked with presence of Cu+ and Cu+2 state of CuO in CuXO-TiO2 also supported junction formation. Optical characteristics of the heterojunction were studied using UV-vis diffuse reflectance spectroscopy and photoluminescence spectroscopy. Compared to TiO2 nanoparticles, CTHS exhibited superior sunlight-induced photodegradation activity. CuXO/TiO2 heterojunction could also remediate toxic waste water containing model antibiotic residue (Oxytetracycline hydrochloride, 0.4 mg/mL) and organic pollutant (methylene blue, 10 µM) in 20 and 60 min respectively. Ultra-fast degradation using a nonmetal heterojunction nanohybrid, like ours, finds negligible mention in literature. Improved visible light absorption and reduction in recombination rate for CuXO-TiO2 nanohybrids were ascribed as major contributing factors towards their enhanced photocatalytic potential. The charge separation mechanism for nanohybrids has been studied and elaborated in detail.

UV Lithography-Assisted Fabrication of Low-Cost Copper Electrodes Modified with Gold Nanostructures for Improved Analyte Detection.

An in-house UV lithography setup has been optimized to fabricate low-cost disposable electrochemical sensing Cu electrodes using a copper clad board. In view of the high oxidation probability of copper, the low-cost electrodes were modified using different gold nanostructures and a conducing polymer PEDOT:PSS to attain maximal signal output and improved shelf-life. Zero-dimensional (0D) gold nanoparticles (∼40 nm) and three-dimensional (3D) gold nanoflowers (∼38 nm) mixed with PEDOT:PSS were used as signal-enhancing conductors for the ultrasensitive detection of our model contaminant, methylene blue dye (MB). The bare copper electrode was sensitive to MB, linearly within the range of 4-100 µM, with a limit of detection of 3.49 µM. While for gold nanoparticle-PEDOT:PSS-modified electrode, the sensitivity of the electrode was found to increase linearly in the range of 0.01-0.1 µM, and for gold nanoflowers-PEDOT:PSS, the sensitivity achieved was 0.01-0.1 µM with the LOD as 0.0022 µM. For a PEDOT:PSS-modified Cu electrode, used as a comparative to study the contributing role of gold nanostructures towards improved sensitivity, the linearity was found to be in the range of 0.1-1.9 µM with the LOD as 0.0228 µM. A 6 times improvement in signal sensitivity for the nanoflower-PEDOT:PSS electrode compared to the nanoparticle-PEDOT:PSS-modified electrode indicates the influence of nanoparticle shape on the electrode efficiency. 3D gold nanoflowers with a large surface area-to-volume ratio and a high catalytic activity prove to be a superior choice for electrode modification.

Growth Kinetics of Gold Nanoparticle Formation from Glycated Hemoglobin.

Gold nanostructures have always been a subject of interest to physicists, chemists, and material scientists. Despite the extensive research associated with gold nanoparticles, their actual formation mechanism is still debatable. The nanoscale rearrangements leading to the formation of gold nanostructures of definite size and shape are contradictory. The study presented in here details out a mechanism for gold nanoparticle formation in the presence of a biological template. The kinetics of gold nanostructure formation was studied using glycated hemoglobin as a biological template as well as the reducing agent. Particle formation was studied in a time- and temperature-dependent manner using different biophysical techniques. Here, we report for the first time spontaneous formation of gold nanoflowers which gradually dissociates to form smaller spherical particles. In addition, our experiments conclusively substantiate the existing postulations on gold nanoparticle formation from relatively larger precursor structures of gold and contradict with the popular nucleation growth mechanism.

Evidence of oxygen defects mediated enhanced photocatalytic and antibacterial performance of ZnO nanorods.

Defect engineered one-dimensional (1D) ZnO nanostructures have found great interest in diverse fields, including water detoxification and environmental remediation. In this article, we report a facile, low-temperature hydrothermal synthesis of defect enriched ZnO nanorods at different pH conditions. The dimension of all the synthesized ZnO nanostructures was restricted to 1D with changes only in their aspect ratios, unlike previous reports where change in morphology accompanies the effect of pH. With an increment in the pH value of the reaction mixture, oxygen defect concentration was controlled and confirmed using XPS and Raman spectroscopy. Considerable increase in optical light absorption and reduction in the bandgap, as inferred from the UV-vis study, corroborating the pH-dependent enrichment of defect states in 1D ZnO. Superior photosensitivity of oxygen defect rich ZnO nanorods was utilized to study their sunlight-induced photocatalytic and bactericidal activity towards its application in wastewater treatment. Within 4 h and 30 min of sunlight exposure (900 W/cm2), a 100% bacterial population (S.aureus, 106 cells/m) killing and complete degradation of methylene blue dye (10µM) were achieved. Enhanced reactive oxidative species (ROS) formation due to the presence of additional oxygen defect states is ascribed to be the prime factor facilitating improved degradation efficiency. Additionally, during the optimization study, ZnO nanorods were found to be active against bacterial cells even in the absence of light opening avenues in antimicrobial food packaging and protective surface coatings.

Coffee ring effect assisted improved S. aureus screening on a physically restrained gold nanoflower enriched SERS substrate.

Proactive water pathogen identification process holds significance in view of increasing bioterrorism prospects, quantification of virulence properties and water supply regulation for human welfare. Strikingly, pathogen concentration is rather low in water bodies to be identified using conventional methods and usually involves three typical steps: 1) concentration 2) purification and 3) characterization and assay. Surface enhanced Raman scattering (SERS) analysis on other hand could easily surpass these steps to give a rather robust identification owing to its exceptionally high specificity and sensing abilities. In this article we use SERS as a diagnostic tool to identify low concentrations of noxious pathogens from water, using a two level confinement that results in a superlative SERS analytical assay, capable of analyte identification down to single molecule level. Unlike the regular dip coat process, we restrict the nanostructure deposition only to a very small area of the larger substrate, by restricting its application volume. In this way, we limit our data processing time, increase our probability of target interaction and also reduce nanostructure/analyte sample quantities for analysis. To enhance the signal intensities further, we use natural three phase pinning or the coffee ring effect to pre-concentrate the analytes on our spatially confined nanostructure pocket, allowing maximal deposition at the edges and subsequently higher signal intensities. The methodology was employed to measure the presence of S. aureus and R6 G in spiked drinking water. LOD achieved for R6 G and S. aureus is 10-12 M and 103 CFU/ml respectively. The increasing signal intensities share a linear relationship with analyte concentration. The acquired signals were reproducible and non-degenerate, overcoming the drawback of irregular data patterns associated with conventional metal nanostructure based SERS systems. Estimated RSD value for physical confinement and coffee ring effect measured was 11.6% and 8.37% respectively. This simple, low cost, robust and reproducible method can be useful for increasing the sensitivity of SERS based detection devices with capability to be developed into a micro total analysis system (µTAS).

Synthesis of graphenized Au/ZnO plasmonic nanocomposites for simultaneous sunlight mediated photo-catalysis and anti-microbial activity.

Sunlight mediated photo-degradation and anti-bacterial activity of hetero junctioned plasmonic binary (Au/ZnO, RGO/ZnO) and ternary (RGO/Au/ZnO) nanocomposites (NC) have been reported. Higher photo-charge carrier generation, increased charge separation, improved active sites for catalysis, enhanced LSPR and larger photo-response regions have been achieved. Decoration with Au nanoparticles (ca. 11 ±â€¯3 and 48 ±â€¯5 nm) and RGO of ZnO (3D/1D) microstructures (aspect ratio 15.18) provides ternary NCs an edge over mono/bi component catalysts. The ternary NC have shown improved dye degradation capacity with 100% efficiency (5 µM MB solution) and average adsorption degradation capacity (Q°) of 83.34 mg/g within 30 min of sunlight exposure (900 ±â€¯30 Wm-2). Elaborated studies by varying reaction parameters like initial dye concentration, contact time, type of NCs and initial loading of NCs reveals pseudo first order degradation kinetics. 100% microbial killing of Gram positive S.aureus strain with 60 µg/ml of NC using sunlight as activator has proven the simultaneous multiple functionality of the NC. Further, facile green one pot hydrothermal synthesis with water as reaction medium, absence of photo-corrosion of NCs, regeneration ability (ca. 90% for 10 µM solution) of NCs, projects a broader potential application of the synthesized NCs and could reduce the continuous requirement of such material, limiting the environmental toxicity.