Comparative Performance of Citrate, Borohydride, Hydroxylamine and β-Cyclodextrin Silver Sols for Detecting Ibuprofen and Caffeine Pollutants by Means of Surface-Enhanced Raman Spectroscopy

The detection of emerging contaminants in the aquatic environment, such as ibuprofen and caffeine, was studied by means of surface-enhanced Raman spectroscopy (SERS) using Ag nanoparticles (AgNPs) synthesized with beta-cyclodextrin (beta CD) as a reducing agent. The effect on the SERS signal of different molar ratios of Ag+/beta CD in the synthesis route and the aging process of AgNPs were investigated by using trans-cinnamic as a test molecule. The SERS effectiveness of these beta-cyclodextrin colloids (Ag@beta CD) was also checked and compared with that of other silver sols usually employed in SERS synthesized by using other reducing agents such as citrate, borohydride and hydroxylamine. All the synthesized SERS substrates were characterized by different techniques. The experimental results indicate that Ag@beta CD with the more diluted Ag+/beta CD molar ratio showed the best SERS signal, enabling detection at trace concentrations of 0.5 mu M in the case of trans-cinnamic acid. The Ag@beta CD sols also showed the best sensitivity for detecting ibuprofen and caffeine, reaching the lowest limit of detection (0.1 mM). The proposed synthetic route for Ag@beta CD sols provides an improved SERS substrate for detecting organic pollutants with better performance than other standard silver sols.