The red (nanodisk I) silver colloid was prepared using a similar
process. Trisodium citrate (100 mM, 3.6 mL), PVP (0.24 g), and
hydrogen peroxide (30 wt.%, 0.48 mL) were added into an aqueous
solution of AgNO3 (0.1 mM, 200 mL) and NaBH4 (100 mM, 0.8 mL)
under vigorous stirring