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Polyvinylpyrrolidone (PVP)-based silver nanoprisms (AgNPrs) show an initial stacking geometry because of their low zeta potential and electrostatic interaction between face-to-face energetically stable {111} surface-bound pyrrolidone groups through the Na+-ion-induced cation−π interaction. Congested interplanar space between AgNPrs allows As(III) to react differentially with silver atoms from facial {111} and peripheral {110} facets to result in smaller stackings and finally nanoseeds. Above this critical concentration of As(III), PVP leached out from nanoparticles to form nanoseed-engulfed emulsions and induced controlled aggregation. This entire morphological transition has been decoded by recording their surface plasmon and surface-enhanced Raman scattering tuning and confirmed by the transmission electron microscopy study. Strong affinity and selectivity of As(III) toward the Ag atom (verified and estimated by the HF/3-21g* level of density functional theory calculation) coupled with low-cost colorime...

The actin cytoskeleton is required for the maintenance of the cell shape and viability of bacteria. It remains unknown to which extent nanoparticles (NPs) can orchestrate the mechanical instability by disrupting the cytoskeletal network in bacterial cells. Our work demonstrates that Au–Ag NPs disrupt the bacterial actin cytoskeleton specifically, fluidize the inner membrane and lead to killing of bacterial cells. In this study, we have tried to emphasize on the key parameters important for NP–cell interactions and found that the shape, specific elemental surface localization and enhanced electrostatic interaction developed due to the acquired partial positive charge by silver atoms in the aggregated NPs are some of the major factors contributing towards better NP interactions and subsequent cell death. In vivo studies in bacterial cells showed that the NPs exerted a mild perturbation of the membrane potential. However, its most striking effect was on the actin cytoskeleton MreB resulting in morphological changes in the bacterial cell shape from rods to predominantly spheres. Exposure to NPs resulted in the delocalization of MreB patches from the membrane but not the tubulin homologue FtsZ. Concomitant with the redistribution of MreB localization, a dramatic increase of membrane fluid regions was observed. Our studies reveal for the first time that Au–Ag NPs can mediate bacterial killing and disrupt the actin cytoskeletal functions in bacteria.

We report an effective method to produce surface-enhanced Raman scattering (SERS) substrates with improved enhancement efficiency, high uniformity, greater chemical and physical stability, and absolute synthetic reproducibility. Nanobipyramidal gold (Au) core and silver (Ag) shell nanorods (NRs) with variable length were prepared simply by varying the Ag precursor amount during growth, and we successfully prepared NRs of lengths from 200 to 1200 nm and studied their formation mechanism and morphology using transmission electron microscopy (TEM) and their optical properties by using UV–vis–near-IR (NIR) and Raman spectroscopy. Here we have utilized the properties of both Au and Ag nanoparticles by synthesizing Au@Ag core–shell NRs for high SERS enhancement. NRs have stronger absorption and large scattering cross sections for electromagnetic radiation, and variation of the aspect ratios of these NRs leads to a broad-band surface plasmon tuning in the vis–NIR region. The relative SERS enhancement efficiencie...

The role of the single-domain ferrimagnetic nanostructure and the associated surface for many fold magnetic-field-induced surface enhanced transient spin-trajectory modulation is a new venture in m...

Triplet-triplet (T-T) absorption spectroscopy has been used successfully as a molecular ruler to understand the actual release process of sanguinarine as a drug molecule from a gold nanoparticle surface in the presence of cell components, that is, DNA and chromatin. The obtained results have been verified by fluorescence and surface-enhanced Raman spectroscopy (SERS), and a plausible explanation has been put forward to describe the underestimation and overestimation of the percentage (%) of the release of drug molecules measured by fluorescence- and SERS-based techniques, respectively, over the highlighted T-T absorption spectroscopy. Because of the intrinsic nature of absorption, the reported T-T absorption spectroscopic assay overpowers fluorescence- and SERS-based assays, which are limited by the long-range interaction and nonlinear dependence of the concentration of analytes, respectively.

Understanding and exploring the decisive factors responsible for superlative catalytic efficiency is necessary to formulate active electrode materials for improved electrocatalysis and high-throughput sensing. This research demonstrates the ability of bud-shaped gold nanoflowers (AuNFs), intermediates in the bud-to-blossom gold nanoflower synthesis, to offer remarkable electrocatalytic efficiency in the oxidation of ascorbic acid (AA) at nanomolar concentrations. Multicomponent sensing in a single potential sweep is measured using differential pulse voltammetry while the kinetic parameters are estimated using electrochemical impedance spectroscopy. The outstanding catalytic activity of bud-structured AuNF [iAuNFp(Bud)/iGCp ≅ 100] compared with other bud-to-blossom intermediate nanostructures is explained by studying their structural transitions, charge distributions, crystalline patterns, and intrinsic irregularities/defects. Detailed microscopic analysis shows that density of crystal defects, such as edges, terraces, steps, ledges, kinks, and dislocation, plays a major role in producing the high catalytic efficiency. An associated ab initio simulation provides necessary support for the projected role of different crystal facets as selective catalytic sites. Density functional theory corroborates the appearance of inter- and intra-molecular hydrogen bonding within AA molecules to control the resultant fingerprint peak potentials at variable concentrations. Bud-structured AuNF facilitates AA detection at nanomolar levels in a multicomponent pathological sample.

Decoupling of different plasmon resonance modes (in-plane, and out-of-plane dipole and quadrupole resonances) by tuning nanoparticle’s size and shape offers a new field of plasmonics as colorimetric assay-based optical-ruler for ultra-trace sensing. Driven by its low cost, easy to perform and efficient way to measure trace level (up to 30 ppt in presence of common mining elements in natural gold ore) abundance, this study develops a highly selective and ultrasensitive turn-on colorimetric sensor to detect gold-ion from environmental samples. Different level of gold-ion tracer makes size variable spherical- and disc-shaped silver nanoparticles when added to a ‘growth solution’ which results decoupling of in-plane dipole resonance from in-plane quadrupole and out-of-plane dipole resonances with a wide range of in-plane dipole plasmon tunability to generate different colors. This color-coded sensing of gold-ion shows high selectivity and ultrasensitivity over other metal ions in the ppt level with an impurity aberration limit of 1 ppm. A plausible explanation explains the possible role of catalytic gold-ion to initiate unfavorable silver ion (Ag+) reduction by ascorbic acid to generate silver nanoparticles. Proposed technology has been applied in real mining sample (Bugunda Gold Deposit, Tajikistan) to detect gold concentration from ores to find potential application in mining technology.

We report a simple method for measuring the inelastic mean free path of nanostructures of known geometry using energy filtered transmission electron microscopy imaging. The mean free path of inelastic electrons was measured by using systems having known symmetry, such as cylindrical or cubic, combined with Poisson statistics without employing the knowledge of microscope parameters, namely the convergence angle and the collection angle. Having inherent symmetry of such systems, their absolute thickness can be measured from their two-dimensional projection images. We have calculated mean free path of inelastic scattering of electrons in gold, silver and nickel doing case study research by employing gold nanorod, silver nanocube and nickel nanorod lying on a carbon-coated TEM grid at two different electron energies (viz. 200 and 300 keV) following this alternative approach. Results obtained using such alternative approach were verified using microscope parameters.

Understanding and exploring the decisive factors responsible for superlative catalytic efficiency is necessary to formulate active electrode materials for improved electrocatalysis and high-throughput sensing. This research demonstrates the ability of bud-shaped gold nanoflowers (AuNFs), intermediates in the bud-to-blossom gold nanoflower synthesis, to offer remarkable electrocatalytic efficiency in the oxidation of ascorbic acid (AA) at nanomolar concentrations. Multicomponent sensing in a single potential sweep is measured using differential pulse voltammetry while the kinetic parameters are estimated using electrochemical impedance spectroscopy. The outstanding catalytic activity of bud-structured AuNF [iAuNFp(Bud)/iGCp ≅ 100] compared with other bud-to-blossom intermediate nanostructures is explained by studying their structural transitions, charge distributions, crystalline patterns, and intrinsic irregularities/defects. Detailed microscopic analysis shows that density of crystal defects, such as edges, terraces, steps, ledges, kinks, and dislocation, plays a major role in producing the high catalytic efficiency. An associated ab initio simulation provides necessary support for the projected role of different crystal facets as selective catalytic sites. Density functional theory corroborates the appearance of inter- and intra-molecular hydrogen bonding within AA molecules to control the resultant fingerprint peak potentials at variable concentrations. Bud-structured AuNF facilitates AA detection at nanomolar levels in a multicomponent pathological sample.

The gene coding for outer capsid protein, VP7 of rotaviruses detected among the children suffering from watery diarrhea in the eastern part of India was studied. The full length gene, coding for VP7 was synthesized from a local strain, WD33, by combined reverse transcriptase–polymerase chain reaction. A total of 42 fecal RNA out of 93 rotavirus-positive samples hybridized with this DNA, indicating the prevalence of this strain in the community. Comparison of the nucleotide and deduced amino acid sequence with the VP7 gene of other serotypes revealed that the local strain,WD33, resembled closely with G1 serotype, the homology being 94 and 97%, respectively. Multiplex PCR using the specific oligonucleotide primers also amplified the G1 specific DNA fragment. The overall change of 16 amino acids was noticed when compared with G1 specific prototype Wa strain of which nine amino acids are within the neutralization domain. However, the phylogenetic tree constructed by comparing the G1 strains from different countries demonstrated that this strain WD33 clustered as a distinct sub-lineage of lineage IV and not with Wa strain, that clustered with lineage III.