Surface enhanced Raman spectroscopic readout on heavy metal ions based on surface self assembly



A new method is reported for detecting heavy metal ions by using the self assembled monolayer (SAM) technique and surface enhanced Raman spectroscopy (SERS). The p-mercaptobenzoic acid (MBA) served as the SERS readout molecule and the modified tag to attach on the smooth gold substrate as well as the tag of nanoparticles by the SAM method. Two carboxyl groups from MBA molecules which were attached respectively to gold substrate and gold nanoparticles were linked through the heavy metal ions (Cu2+, Pb2+ and Zn2+) as bridge, and thus sandwich structure of ‘MBA modified gold substrate/heavy metal ions/MBA modified gold nanoparticles’ was built for detection. The observation of the oxidation peak of metal nanoparticles from cyclic voltammetry (CV) curve, gold nanoparticles from scanning electron microscopy (SEM) images and SERS signal of MBA from the sandwich structure indicated the existence of heavy metal ions. The difference in the wavenumbers of vibrational modes from MBA in the sandwich structure constructed by different could be used to identify different heavy metal ions. The assembled structure was rinsed by strong chelator of EDTA solution to remove the heavy metal ions from the sandwich structure and thus to obtain a fresh gold substrate modified with MBA for the cyclic detection. Copyright © 2007 John Wiley & Sons, Ltd.