Spectroscopic analysis of L-histidine adsorbed on gold and silver nanoparticle surfaces investigated by surface-enhanced Raman scattering

The adsorption of L-histidine on gold (An) and silver (Ag) nanoparticle surfaces has been comparatively analyzed by means of surface-enhanced Raman scattering (SERS). The SERS spectra of L-histidine on Ag were found to be quite different from those on Au, indicating dissimilar adsorption structures depending on metal substrates. Most peaks of L-histidine on Ag appeared to be due to coordination via the carboxylate (COO-) group with an imidazole ring of fairly upright geometry, whereas on An it was assumed to adsorb with a rather flat geometry. A density functional theory (DFT) calculation was performed at the level of B3LYP/LANL2DZ to estimate the energetic stability of the binding of the imidazole ring and the carboxylate group of L-histidine with the Ag and An atoms, respectively. Based on the DFT calculation, the carboxylate group of L-histidine was predicted to bind more favorably to Ag than to Au, and this was in line with our SERS spectral analysis. (C) 2007 Elsevier B.V. All rights reserved.