Biosynthesis, Characterization and Biological Application of Gold Nanoparticles

Abstract

Nanotechnology is an interdisciplinary science that deals with development and manipulation of functional systems at atomic and molecular level. Nanoparticles are objects that range in size from 1 - 100nm and may differ from their bulk material in chemical and physical properties. Among a variety of nanomaterials, metallic nanoparticle such as gold nanoparticles have gained significant importance in past due to their administration in the field of material and manufacturing industry, cosmetics, therapeutic and pharmaceutical industries. Nanoparticles can be synthesized using physic-chemical and biological approaches. Physico-chemical methods provide nanoparticles of definite size but synthesis process is toxic and expensive. Biological methods are preferred because they provide ease of handling, synthesis and no toxic material by products formation. In this study, Lactobacillus rhamnosus is used for synthesis of gold nanoparticles. Bacteria provide bioactive oxidoreductase enzymes that act as catalyst in bio-reduction reaction and reduces gold ions in solution to gold nanoparticles. Synthesis of these nanoparticles is evaluated by change in color of reaction mixture. These nanoparticles were further verified by UV/Vis spectrophotometer that shows peak for AuNPs at 540nm. Comparison of Ultraviolet/Visible spectra of bacterial biomass and AuNPs showed characteristic change in absorbance. Their elemental composition, evaluated by Element Disspersive Spectroscopy analysis, indicated presence of 4% gold element in the sample mixture. Crystallinity of nanoparticles were analyzed by X-Ray Diffractogram, whereas Fourier Transformed Infrared spectrum indicated the presence of amine groups depicting that particles are stable in nature. Morphology and diameter were measured by microscopic analysis such as Scanning Electron Microscopy. Newly synthesized AuNPs were spherical with varying size of 50-70nm. Bactericidal activity of nanoparticles was performed against strains of Salmonella enterica, Escherichia coli, Pseudomonas nitroreducens Pseudomonas aeruginosa, and Bacillus subtilis. Antibacterial results showed that AuNPs can be used as an alternative to antibiotic. DPPH inhibition assay revealed scavenging ability of biogenic AuNPs compared with ascorbic acids at different concentrations. 500g/ml of biogenic AuNPs show 70% free radical scavenging ability.