Second harmonic generation of chiral-modified silver nanoparticles

Various approaches for the optical detection of chiral compounds have been developed due to their natural optical activity. Since the advantages of second harmonic generation (SHG) on noble-metal nanoparticles (NPs) have been observed, it would be interesting to study the nonlinear phenomena from chiral compounds attached Ag NPs. In the present work, we fabricated chiral-modified Ag NPs based on the self-assembly process of cysteine and Ag, and carried out the investigation on SHG on modified and unmodified Ag NPs. For modified Ag NPs, either L-Cysteine (L-C) or D-Cysteine (D-C), as a pair of enantiomers, was applied on top of the Ag NPs. The resulting chiral-modified monolayers of L-C/Ag NPs and D-C/Ag NPs exhibit a reversed optical rotation difference (ORD) at linearly ±45° polarization of SH, where no such difference exists for Ag NPs alone. SHG efficiently probes and discriminates L-C from D-C monolayers on the modified Ag NPs, which constitutes a simple and sensitive optical diagnostic of chiral molecules.