Chitosan-based improved stability of gold nanoparticles for the study of adsorption of dyes using SERS

SERS spectroscopy is a sensitive technique for the detection of molecules adsorbed on the surface of metallic nanoparticles; the molecules induce changes on the aggregation of the colloidal suspension and on the Localized Surface Plasmon Resonance (LSPR) band. Owing to the analytical sensitivity, the surface nanoparticles are protected to avoid the aggregation/sedimentation and false-positive results. Citrate ions are a very common stabilizing agent for metal nanoparticles, but the interaction of citrate with Au surfaces is insufficient to avoid exchanges with molecules in solution, requiring a more efficient surface stabilizer protection. Chitosan is a protonated biopolymer, which has been used to modify the surfaces of gold nanoparticles. This work aims to improve the stability of preformed spherical Au nanoparticles by adding chitosan, and to study the anionic and cationic dyes using SERS; chitosan protects the metal surface by avoiding the aggregation of the nanoparticles that is induced by the dyes.