Irshad A. Wani

Biosynthesis, structural characterization and antimicrobial activity of gold and silver nanoparticles

An eco friendly simple biosynthetic route was used for the preparation of monodisperse and highly crystalline gold and silver nanoparticles using cell free extract of fungus, Candida albicans. Transmission electron microscopic studies show the formation of gold and silver nanocrystals of average size of 5 nm and 30 nm with the specific surface areas of 18.9 m(2)/g and 184.4 m(2)/g respectively. The interaction of gold and silver nanoparticles with proteins has been formulated by FT-IR spectroscopy and thermal gravimetric analysis. The formation of gold and silver nanoparticles was also confirmed by the appearance of a surface plasmon band at 540 nm and 450 nm respectively. The antimicrobial activity of the synthesized gold and silver nanoparticles was investigated against both Staphylococcus aureus and Escherichia coli. The results suggest that these nanoparticles can be used as effective growth inhibitors against the test microorganisms. Greater bactericidal activity was observed for silver nanoparticles. The E. coli, a gram negative bacterium was found to be more susceptible to gold and silver nanoparticles than the S. aureus, a gram positive bacterium.

Size and shape dependant antifungal activity of gold nanoparticles: A case study of Candida

A simple and economical sonochemical approach was employed for the synthesis of gold nanoparticles. The effect of the reducing agents has been studied on the particle size, morphology and properties at the same ultrasonic frequency under ambient conditions. Gold nanodiscs of average diameter of 25 nm were obtained using tinchloride (SnCl(2)) as a reducing agent, while sodium borohydride (NaBH(4)) produced polyhedral structures of the average size of 30 nm. The time evolution of the UV-visible absorption spectra of the gold nanostructures shows the origin of peaks due to higher order quadrupolar modes apart from the peaks of the in plane and out plane dipolar surface plasmon modes. Surface area studies reveal the much higher surface area of the gold nanodiscs (179.5 m(2)/g), than the gold nanoparticles (150.5m(2)/g) prepared by the sodium borohydride as the reducing agent. The gold nanoparticles exhibit excellent antifungal activity against the fungus, Candida. We investigated the effect of the gold nanoparticles on the H(+)-ATPase mediated H(+) pumping by various Candida species. Gold nanodiscs displayed the stronger fungicidal activity compared to the gold polyhedral nanoparticles. The two types of gold nanoparticles inhibit H(+)-ATPase activity at their respective MIC values.

Structural characterization and antimicrobial properties of silver nanoparticles prepared by inverse microemulsion method

Silver nanoparticles have been synthesized in the inverse microemulsions formed using three different surfactants viz., cetyl-trimethyl ammonium bromide (CTAB), Tergitol and Triton X-100. We have done a systematic study of the effect of the surfactants on the particle size and properties of the silver nanoparticles. Microscopic studies show the formation of spheres, cubes and discs shaped silver nanostructures with the size in the range from 8 to 40 nm. Surface plasmon resonance (SPR) peak was observed around 400 nm and 500 nm. In addition to SPR some extra peaks have also been observed due to the formation of silver metal clusters. The surface area increases from 3.45 to 15.06 m(2)/g with decreasing the size of silver nanoparticles (40-8 nm). To investigate the antimicrobial activity of silver nanoparticles, the nanoparticles were tested against the yeast, Candida albicans and the bacterium, E. coli. The results suggest very good antimicrobial activity of the silver nanoparticles against the test microbes. The mode of action of the antimicrobial activity was also proposed.

Chemistry of reverse micelles: a versatile route to the synthesis of nanorods and nanoparticles

Nanostructured wires and rods are expected to have interesting optical, electrical, magnetic and mechanical properties as compared to micron sized whiskers and fibers. We have explored a versatile route for the synthesis of nanorods of transition metal (Cu, Ni, Mn, Zn, Co and Fe) oxalates, succinates of few metals (Co and Fe) and SnO2 nanoparticles using reverse micelles. The aspect ratio of the nanorods copper oxalate could be modified by changing the solvent. The aspect ratio of the cobalt oxalate nanorods could be modified by controlling the temperature. The nanorods of metal (Cu, Ni, Mn, Zn, Co and Fe) oxalates were found to be suitable precursors to obtain a variety of transition metal oxide nanoparticles. Our studies show that the grain size of CuO nanoparticles is highly dependent on the nature of non-polar solvent used to initially synthesize the oxalate rods. All the commonly known manganese oxides could be obtained as single phases from the manganese oxalate precursor by decomposing in different atmosphere (air, vaccum or nitrogen). In order to see the templating effect of the ligand we have changed the dicarboxylate ligand by using succinate (4 carbon chain) instead of oxalate (2 carbon chain).We found spherical nanoparticles for iron succinate where the oxidation state of Fe is in +3. Shorter rods of cobalt succinate were observed. Monophasic tin dioxide (SnO2) nanoparticles with an average size of 6-8 nm was obtained at 500°C by the reverse micellar route using liquor NH3 as precipitating agent.