Biogenic synthesis of Au and Ag nanoparticles using aqueous solutions of Black Tea leaf extracts

We explored the application of three different aqueous solutions derived from Black Tea leaf extracts in the synthesis of Au and Ag nanoparticles. The plain tea leaf broth, as well as that containing the ethyl acetate extract of tea leaves, were found to be extremely efficient, leading to rapid formation of stable nanoparticles of various shapes: spheres, trapezoids, prisms and rods. For a given metal ion precursor, the kinetics of particle synthesis were remarkably similar in these two solutions, as evidenced from their absorption spectroscopy monitored over time. Moreover, they exhibited similar redox behavior. In contrast, with the other solution, containing the dichloromethane (CH2Cl2) extract of tea leaves, we failed to detect any nanoparticle generation under similar reaction conditions. Our results suggest that the reduction of metal ions and stabilization of the resultant particles in the first two solutions involved the same class of biomolecules. We identified these biomolecules as the tea polyphenols, including flavonoids, which were present in comparable amounts in both the tea leaf broth and ethyl acetate extract, but are absent in the CH2Cl2 extract of tea leaves. The efficiency of the tea leaf extracts towards Au and Ag nanoparticle synthesis were compared with that of a naturally occurring hydroxyflavonoid, quercetin.