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Abstract: Rhodamin 6G (Rh6G) functionalized Au nanoparticles (AuNPs) are being used as efficient fluorescence probe for selective sensing of heavy metal ions. It has been observed that the quenching of fluorescence of Rh6G in presence of AuNPs takes place through fluorescence resonance energy transfer (FRET). Recovery of fluorescence of Rh6G emission in presence of Hg (II) in AuNPs–Rh6G coupled system has been explained as the increasing affinity of heavy metal ions to form shell and thereby reduced the FRET rate. In presence of heavy metal ions such as Hg (II), Rh6G molecules are released from the AuNPs surface and the fluorescence of Rh6G is restored. The modulation of photoluminescence quenching efficiency of Rh6G–AuNPs in the presence of Hg (II) ions can achieve a large turn on fluorescence enhancement. Our experiment using marcapto propanoic acid (MPA) caped AuNPs show much less fluorescence enhancement in presence of Hg2+ compares to tri sodium citrate (TSC) stabilized AuNPs. [Copyright &y& Elsevier]

Synthesis of core @ shell (Au @ Ag) nanoparticle with varying silver composition has been carried out in aqueous poly vinyl alcohol (PVA) matrix. Core gold nanoparticle (~15 nm) has been synthesized through seed-mediated growth process. Synthesis of silver shell with increasing thickness (~1-5 nm) has been done by reducing Ag over the gold sol in the presence of mild reducing ascorbic acid. Characterization of Au @ Ag nanoparticles has been done by UV-Vis, High resolution transmission electron microscope (HRTEM) and energy dispersive X-ray (EDX) spectroscopic study. The blue shift of surface plasmon resonance (SPR) band with increasing mole fraction of silver has been interpreted due to dampening of core, i.e. Au SPR by Ag. The dependence of nonlinear optical response of spherical core @ shell nanoparticles has been investigated as a function of relative composition of each metal. Simulation of SPR extinction spectra based on quasi-static theory is done. A comparison of our experimental and the simulated extinction spectra using quasi-static theory of nanoshell suggests that our synthesized bimetallic particles have core @ shell structure rather than bimetallic alloy particles. [ABSTRACT FROM AUTHOR]

Present investigation demonstrates a very simple seed-mediated route for the synthesis of silver nanorods in aqueous solution. Central to the concept of seed-mediated growth of nanoparticles is that small nanoparticle seeds serve as nucleation centres to grow nanoparticles to a desired size and shape. Hydroxypropyl methyl cellulose (HPMC) has been used as soft template for one-dimensional growth of silver particles. Morphological, structural and spectral changes that are associated with the seed-mediated growth of the nanoparticles in presence of HPMC are characterized using UV-vis and HR-TEM spectroscopic study. Simulation of UV-vis extinction spectra of our synthesized silver nanorods has been carried out using discrete dipole approximation methodology. The broad red-shifted longitudinal extinction band of green-coloured silver sol has been explained, due to the presence of silver nanorods of different aspect ratios. [ABSTRACT FROM AUTHOR]

Abstract: Here, we report synthesis of star shape gold nanoparticles using seed mediated growth process. Ag+ ions have been used to catalyze the anisotropic growth of gold particles in the growth solution. Star like gold nanoparticles are characterized using UV–vis and TEM study. Excitation of localized surface plasmon of star shaped gold nanoparticles by the visible radiation results broad and intense localized surface plasmon resonance excitation band. Emission spectra of nanostars upon excitation at 230nm and 480nm has been explained due to localized plasmon at the edge of star like particle and the longitudinal mode of these anisotropically grown gold nanoparticles. [ABSTRACT FROM AUTHOR]

Abstract: Spherical, hexagonal, triangular and bar shaped silver nanostructures have been synthesized at large scale in aqueous media using methyl cellulose (MC) as soft template. Synthesis is based on the reduction of Ag+ by hydrogen at different temperatures. Morphology of particles is mostly spherical at 60°C with an average diameter 4–8nm, whereas hexagonal, triangular and truncated hexagon silver nanostructures are obtained at 80°C. On the other hand bar shaped silver nanoparticles are formed as the reaction is carried out at 90°C. Silver nanoparticles are characterized using UV–Vis and TEM study. Formation of silver nanostructures of variable morphologies has been explained in terms of different shaped template formed by MC at different temperature due to its thermogelation properties. [Copyright &y& Elsevier]

Abstract: Solution-phase synthesis of nanometer-sized silver particles is reported by sodium borohydride reduction of AgNO3. Two isomeric dicarboxylates (sodium maleate and sodium fumarate) have been used as stabilizing agents. The dicarboxylate-stabilized silver nanoparticles are characterized by UV–vis spectroscopy, high-resolution transmission electron microscopy (HR-TEM) and fourier transform infrared (FT-IR) spectroscopy. A qualitative comparison is made between the UV–vis spectral characteristic of the SPR band and the simulated curve obtained from modified Mie''s theory. Silver nanoparticles prepared using these two isomeric dicarboxylates show intense fluorescence in the visible region. DFT with hybrid functional (B3LYP)-based frequency (IR) calculation of both the dicarboxylates and the respective nanoparticles are in good agreement with the experimental IR frequency. On the basis of this calculation a model has been proposed for the stabilization of silver nanoparticles by these two isomeric dicarboxylate anions. [Copyright &y& Elsevier]

Abstract: A method for the size-controlled synthesis of silver nanoparticles is proposed and described. Synthesis is based on the reduction of AgNO3 in aqueous SDS solution by hydrogen. These nanoparticles are poly-disperse in size and shape and their dimensions can be easily controlled in the range of 20 to 60 nm by varying the concentration of AgNO3. Silver nanoparticles are analyzed using transmission electron microscope (TEM) and UV–vis spectroscopic technique. A comparison between the experimentally observed UV–vis spectra and the simulated one obtained from the modified Mie''s theory, are made to understand the nature of shift of the SPR band. [Copyright &y& Elsevier]