Adsorption of dipeptide L-alanyl-L-tryptophan on gold colloidal nanoparticles studied by surface-enhanced Raman spectroscopy

Surface adsorption of a dipeptide L-alanyl-L-tryptophan (Ala-Trp) on gold nanoparticles reduced by citrate (CT) and borohydride (BH) ions was investigated by a surface-enhanced Raman scattering (SERS) technique. Two distinct SERS spectra of Ala-Trp depending on the types of gold nanoparticles were observed, and the vibrational assignments were based on the density functional theory simulations and the previous SERS results of Trp. Ala-Trp mainly adsorbs through the amine group on CT gold nanoparticles with a perpendicular orientation of the indole ring to the surface. In contrast, the adsorption occurs via the pi electrons of the indole ring on the BH gold surfaces while maintaining a flat geometry of the indole ring to the surface. The amide I band of Ala-Trp was observed only with the CT gold colloids in acidic and neutral conditions where partial surface adsorption via the amide group is expected. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

In this study, the surface adsorption of dipeptide L-alanyl-L-tryptophan (Ala-Trp) on gold nanoparticles reduced by citrate (CT) and borohydride (BH) ions was investigated using surface-enhanced Raman scattering (SERS) technique. Different adsorption modes of Ala-Trp were observed on CT and BH gold nanoparticles, with Ala-Trp mainly adsorbing through the amine group on CT gold nanoparticles and via the pi electrons of the indole ring on BH gold surfaces. The amide I band of Ala-Trp was only observed on CT gold colloids under acidic and neutral conditions.