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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...

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.