In Situ Photoreduced Silver Nanoparticles on Cysteine: An Insight into the Origin of Chirality

An experiment was conducted to demonstrate that Ag + complexes with L- or D-isomers of cysteine (Ag + Cys) could be in situ photoreduced to form Ag NPs without the assistant of any other reducing agents or protecting ligands. Ag + Cys complexes of defined stoichiometry were first formed by mixing different amounts of AgNO 3 and L or D-cysteine with final concentrations of 0.5 mm. Upon mixing, the formation of Ag + Cys complexes at r=1.1 was instantaneous, witnessed from both a dramatic increase in the UV absorbance and the significant CD signals of Ag + Cys complexes. The most interesting is that the in situ photoreduction of Ag + bound to cysteine generated an intense CD signal around the SPR frequency of Ag NPs centered at about λ=405 nm, which is completely different from that of Ag + Cys complexes and that of presynthesized large Ag NPs modified with cysteines.