Nagappan Rajendiran

Biological synthesis of silver and gold nanoparticles using apiin as reducing agent

We report a novel strategy for the biological synthesis of anisotropic gold and quasi-spherical silver nanoparticles by using apiin as the reducing and stabilizing agent. The size and shape of the nanoparticles can be controlled by varying the ratio of metal salts to apiin compound in the reaction medium. The resultant nanoparticles were characterized by UV-vis-NIR, transmission electron microscopy (TEM), FT-IR spectroscopy, X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The interaction between nanoparticles with carbonyl group of apiin compound was confirmed by using FT-IR analysis. TEM photograph confirming the average size of the gold and silver nanoparticles were found to be at 21 and 39 nm. The NIR absorption of the gold nanotriangles is expected to be of application in hyperthermia of cancer cells and in IR-absorbing optical coatings.

Spectroscopic investigations of nanohydroxyapatite powders synthesized by conventional and ultrasonic coupled sol-gel routes

In the present work, the synthesis and characterization of nano-HAP powders by a novel ultrasonic coupled sol-gel synthesis is reported. The obtained powders were sintered by conventional means at different temperatures. In addition to this, HAP powders prepared through the sol-gel method without the aid of the ultrasonic waves is also studied. The obtained nano-HAP powders were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and scanning electron microscopic (SEM) techniques. The results have proved that the nano-HAP powders synthesized by ultrasonic coupled sol-gel synthesis showed remarkable reduction in the particle size when compared with the conventional sol-gel method and hence these powders could be used as a coating material in biomedical applications.

Functionalization of silver and gold nanoparticles using amino acid conjugated bile salts with tunable longitudinal plasmon resonance

The vital bioactivities of bile salts are physiologically important molecules. The concept of using bile acids and their conjugates in nanoscience is a novel idea, which opens up fascinating prospects and gives way for various versatile properties. Here in, we report novel strategy for the synthesis of aqueous stable, silver and gold nanoparticles (Ag & AuNPs) using naturally occurring amino acid conjugated sodium salt of taurocholate (NaTC) and glycocholate (NaGC) as reducing and capping agents. The formation of nanoparticles was kinetically monitored using UV-vis spectroscopy at different time intervals. It was noticed, that the rate of reduction of AgNO(3) is much faster than the HAuCl(4) at fixed concentration of bile salts. Furthermore, the size and shape of the NPs are controlled and achieved by changing the nature of bile salts. The synthesized nanoparticles were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD) techniques for morphological studies. The interaction between nanoparticles with bile salts was investigated using FT-IR spectroscopy, cyclic voltammetry (CV) and thermogravimetric analysis (TGA).

Green synthesis of gold nanoparticles under sunlight irradiation and their colorimetric detection of Ni2+ and Co2+ ions

The present work describes the preparation of gold nanoparticles (AuNPs) under natural sunlight irradiation and their use in colorimetric detection of heavy metal ions. The AuNPs were prepared by an environmentally benign method using N-cholyl-l-valine (NaValC) as a self-reducing as well as stabilizing agent in aqueous medium. The size and shape of the particles were systematically controlled by varying the ratio of NaValC and Au3+ ions. The pH of the solution medium, sunlight irradiation and reaction time also influence the size and shape selectivity. The prepared NPs were thoroughly characterized by using UV-visible spectroscopy, TEM, DLS, EDX, XRD, XPS, FT-IR, cyclic voltammetry and TGA techniques. Natural solar energy acting as a driving force for the generation of AuNPs in aqueous medium makes the process eco-friendly, attractive and economical. As these NPs are highly reactive towards the surrounding environment the prepared AuNPs were effectively utilized for the colorimetric detection of Co2+ and Ni2+ ions in environmental samples.

A sunlight-induced rapid synthesis of silver nanoparticles using sodium salt of N-cholyl amino acids and its antimicrobial applications

Aqueous solution containing two additives, silver nitrate (AgNO(3)) and sodium salt of N-cholyl amino acid were irradiated by sunlight for the synthesis of spherical shaped AgNPs without the need for an additional stabilizer or capping agent. Variations of N-cholyl amino acid concentration provided good control over the morphology of the AgNPs, while the carboxylate group of bile salt reduced the Ag(+) ions and the amide group binds strongly to the surface of the NPs. The optical properties, morphology of the AgNPs were characterized by UV-visible, transmission electron microscopy (TEM) and dynamic light scattering (DLS) studies. The interaction of N-cholyl amino acid on the AgNPs surface was studied using cyclic voltammetry and FT-IR techniques. The reduction process was completed within 5 min and the synthesized AgNPs were stable for more than 6 months. The possible mechanism of N-cholyl amino acid on the reduction and stabilization of AgNPs is also discussed. The antimicrobial activity of N-cholyl amino acid capped AgNPs against Escherichia coli, Staphylococcus aureus and Pseudomonas aeroginosa using Mueller Hinton broth and the antifungal activity against Candida albicans, Candida krusei and Candida tropicalis using RPMI broth were determined by MIC studies as per CLSI guidelines.

Sodium cholate-templated blue light-emitting Ag subnanoclusters: in vivo toxicity and imaging in zebrafish embryos.

We report a novel green chemical approach for the synthesis of blue light-emitting and water-soluble Ag subnanoclusters, using sodium cholate (NaC) as a template at a concentration higher than the critical micelle concentration (CMC) at room temperature. However, under photochemical irradiation, small anisotropic and spherically shaped Ag nanoparticles (3-11 nm) were obtained upon changing the concentration of NaC from below to above the CMC. The matrix-assisted laser desorption ionization time-of-flight and electrospray ionization mass spectra showed that the cluster sample was composed of Ag4 and Ag6. The optical properties of the clusters were studied by UV-visible and luminescence spectroscopy. The lifetime of the synthesized fluorescent Ag nanoclusters (AgNCs) was measured using a time-correlated single-photon counting technique. High-resolution transmission electron microscopy was used to assess the size of clusters and nanoparticles. A protocol for transferring nanoclusters to organic solvents is also described. Toxicity and bioimaging studies of NaC templated AgNCs were conducted using developmental stage zebrafish embryos. From the survival and hatching experiment, no significant toxic effect was observed at AgNC concentrations of up to 200 μL/mL, and the NC-stained embryos exhibited blue fluorescence with high intensity for a long period of time, which shows that AgNCs are more stable in living system.

Antipyrilquinoneimine dye formation by coupling aniline derivatives with 4-aminoantipyrine in the presence of ruthenium nanoparticles

The coupling of 4-aminoantipyrine (4-AAP) with aniline derivatives catalyzed by ruthenium nanoparticles (Rnp) has been studied by UV-Vis spectroscopy in aqueous medium. The rate constant for antipyrilquinoneimine dye formation depends on the nature of the aniline substituent and the pH, ionic strength and temperature of the reaction medium. The maximum rate constant of the dye formation reaction is observed at pH 3.6. Aniline derivatives with electron donating substituents show higher rate constant values than those with electron withdrawing substituents, with increasing rate constant values in the order: N,N-dimethyl aniline > o-toluidine > o-chloroaniline > m-chloroaniline. With pseudo first order kinetics, the total order is 1.0 + 1.0 + 1.0 = 3.0, which includes the orders with respect to amine, 4-AAP and Rnp. Studies on these effects help to complete the kinetic analysis as well as propose the reaction pathway. Furthermore, TEM measurement confirms that the nanoscalar size of the Rnp is 7 nm.

Interaction of sulfur dioxide with zinc(II) tetrasulfo phthalocyanine in aqueous medium: steady state fluorescence quenching studies

Abstract A sensitive fluorimetric method of determination of SO 2 dissolved in solvents using the steady state fluorescence of tetrasulfonated zinc(II) phthalocyanine and SO 2 in the concentration range (0.1–1.0 mM) was carried out. Effects of various solvents, pH, and salt on the interaction properties of ZnPcTsSO 2 are determined, based on the quenchings by SO 2 . Linear and non-linear Stern–Volmer plots have been analysed. Modified non-linear Stern–Volmer analysis produced best fits for a 1:2 stoichiometry. The association constant values of the ZnPcTsSO 2 complex in various environments have been determined adopting single stage and two step equilibria processes. Stern–Volmer deviations are attributed to solvent extraplanar coordinations, a 20% DMSO–water mixture seems to produce a stability constant value higher than the other effects. A cyclic voltammogram in DMSO–water medium shows significantly suppressed redox processes of the central Zinc metal ion in ZnPcTs in the presence of SO 2 (1×10 −3 M). Axial coordination leading to the formation of bis sulfonato ZnPcTs is envisaged.

Gold nanoparticles assisted characterization of amine functionalized polystyrene multiwell plate and glass slide surfaces

We demonstrated citrate-capped gold nanoparticles assisted characterization of amine functionalized polystyrene plate and glass slide surfaces through AuNPs staining method. The effect of AuNPs concentration on the characterization of amine modified surfaces was also studied with different concentration of AuNPs (ratios 1.0–0.0). 3-Aminopropylyl triethoxy silane has been used as amine group source for the surface modification. The interactions of AuNPs on modified and unmodified surfaces were investigated using atomic force microscopy and the dispersibility, and the aggregation of AuNPs was analyzed using UV–visible spectrophotometer. Water contact angle measurement and X-ray photoelectron spectroscopy (XPS) were used to further confirmation of amine modified surfaces. The aggregation of AuNPs in modified multiwell plate leads to the color change from red to purple and they are found to be adsorped on the modified surfaces. Aggregation and adsorption of AuNPs on the modified surfaces through the electrostatic interactions and the hydrogen bonds were revealed by XPS analysis. Remarkable results were found even in the very low concentration of AuNPs (ratio 0.2). This AuNPs staining method is simple, cost-effective, less time consuming, and required very low concentration of AuNPs. These results can be read out through the naked eye without the help of sophisticated equipments.

Role of Surface Hydrophobicity of Dicationic Amphiphile-Stabilized Gold Nanoparticles on A549 Lung Cancer Cells

Herein, we report the surface functionality of dicationic cysteamine conjugated cholic acid (DCaC), dicationic cysteamine conjugated deoxycholic acid (DCaDC), and dicationic cysteamine conjugated lithocholic acid (DCaLC) templated gold nanoparticles (AuNPs) on mammalian cells. The haemocompatibility of the synthesized NPs was evaluated by in vitro hemolysis and erythrocyte sedimentation rate using human red blood cells (RBCs). In all of the systems, no toxicity was observed on human erythrocytes (RBCs) up to the concentration of 120 μg/mL. The anticancer activity of these dicationic amphiphile-stabilized AuNPs on A549 lung cancer cells was demonstrated by in vitro cell viability assay, intracellular reactive oxygen species estimation by DCFH-DA, apoptosis analysis using AO-EtBr fluorescence staining, DNA fragmentation analysis by agarose gel electrophoresis, and western blot analysis of caspase-3 expression. These results suggest that the cytotoxicity of AuNPs to A549 cells increase with the dose and hydrophobicity of amphiphiles and were found to be in the order: DCaLC-AuNPs > DCaDC-AuNPs > DCaC-AuNPs.