Green chemistry approach for gold nanoparticles synthesis using plant extracts: a potential material towards catalysis and biology

Plant extracts of amla (Phyllanthus emblica), tea (Camellia sinensis) and coffee (Coffea) are prepared and used for the green synthesis of stable gold nanoparticles. The approach is simple, cost effective and environmentally friendly. The various gold nanoparticles (AuNPs-Amla, AuNPs-Tea and AuNPs-Coffee) are characterised by various spectroscopic and microscopic techniques. The borohydride mediated reduction of 4-nitrophenol is used as a model system to study the catalytic activity of the resulting AuNPs. The reaction rates are quite high following the first order kinetics with first order rate constant of 5.4 × 10⁻¹ min⁻¹, 8.7 × 10⁻¹ min⁻¹, and 2.8 × 10⁻¹ min⁻¹ respectively for AuNP-amla, AuNP-tea and AuNP-coffee. The in vitro cytotoxicity study by MTT assay reveals that the various green synthesised AuNPs are not cytotoxic to living cells and their IC₅₀ values towards two cancer cell lines, MCF-7 and HCT-116 are within the permissible doses. Moreover, IC₅₀ values for AuNPs are in good agreement with direct treatment of aqueous plant extracts. (paper)