3.1. Biosynthesis of silver and gold nanoparticles
When the extract was subjected to AgNO3 and HAuCl2, the
biosynthesis reaction started within few minutes and the color
reaction was observed in which clear AgNO3 solution changed into
brown color whereas pale yellowish HAuCl4 solution turned to ruby
red colored solution which indicates that formation of corresponding
nanoparticles (Fig. 1). The UV–Vis spectra of silver and gold
nanoparticles synthesized by M. piperita are shown in Fig. 2. The
distinct peak observed at 450 nm, that is surface plasmon resonance
of the silver nanoparticles (Fig. 2a). Whereas, after the addition of
M. piperita extract, the color of HAuCl4 changed from light yellow
to pink indicated the synthesis of gold nanoparticles in the
aqueous solution. A broad peak was observed at 530 nm in gold
nanoparticles (Fig. 2b).