Resultant inward imbalanced seeding force (RIISF)-induced concave gold nanostar (CAuNS) for non-enzymatic electrocatalytic detection of serotonin and Kynurenine in human serum.

CTAC-based gold nanoseed-induced concave curvature evolution of surface boundary planes from concave gold nanocube (CAuNC) to concave gold nanostar (CAuNS) has been achieved by a novel synthetic methodology simply by controlling the extent of seed used and hence the generated 'Resultant Inward Imbalanced Seeding Force (RIISF)'. The resultant CAuNS shows an excellent enhancement in catalytic activity compared to CAuNC and other intermediates as a function of curvature-induced anisotropy. Detailed characterization evaluates the presence of an enhanced number of multiple defect sites, high energy facets, larger surface area, and roughened surface which ultimately results in an increased mechanical strain, coordinately unsaturation, and multifacet-oriented anisotropic behavior suitable for positive influence on the binding affinity of CAuNSs. While different crystalline and structural parameters improve their catalytic activity, the resultant uniform three-dimensional (3D) platform shows comparatively easy pliability and well absorptivity on the glassy carbon electrode surface for increased shelf life, a uniform structure to confine a large extent of stoichiometric systems, and long-term stability under ambient conditions for making this newly developed material a unique nonenzymatic scalable universal electrocatalytic platform. With the help of various electrochemical measurements, the ability of the platform has been established by performing highly specific and sensitive detection of the two most important human bio messengers: Serotonin (STN) and Kynurenine (KYN) which are metabolites of L-Tryptophan in the human body system. The present study mechanistically surveys the role of seed-induced RIISF-modulated anisotropy in controlling the catalytic activity which offers a universal 3D electrocatalytic sensing tenet by an electrocatalytic approach.

Bimetallic gold-silver nanoparticles mediate bacterial killing by disrupting the actin cytoskeleton MreB.

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.

Correction: Crystal-defect-induced facet-dependent electrocatalytic activity of 3D gold nanoflowers for the selective nanomolar detection of ascorbic acid.

Correction for 'Crystal-defect-induced facet-dependent electrocatalytic activity of 3D gold nanoflowers for the selective nanomolar detection of ascorbic acid' by Sandip Kumar De, et al., Nanoscale, 2018, 10, 11091-11102.

Crystal-defect-induced facet-dependent electrocatalytic activity of 3D gold nanoflowers for the selective nanomolar detection of ascorbic acid.

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.

Decoupled in-plane Dipole Resonance Modulated Colorimetric Assay-Based Optical Ruler for Ultra-Trace Gold (Au) Detection.

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.

Development of a Triplet-Triplet Absorption Ruler: DNA- and Chromatin-Mediated Drug Molecule Release from a Nanosurface.

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.