Preparation of antimicrobial gold and silver nanoparticles from tea leaf extracts

Gold and silver nanoparticles were prepared from the green tea and black tea extracts of the leaves of Camellia sinensis. The metal nanoparticle solutions were obtained by reacting HAuCl4 or AgNO3 aqueous solutions with aqueous NaHCO3 and tea leaf extracts, which were obtained from used tea leaves at low temperature, under ambient conditions. The nanoparticles were stable at room temperature and had a uniform particle size (Au: similar to 10 nm, Ag: similar to 30 nm). Nanoparticle-immobilized cotton cloths were then prepared, which displayed high antibacterial activity and a characteristic color, thereby showing potential application as antimicrobial pigments. This study provides a means of utilizing used tea leaves, which would otherwise be considered waste products.