SERS surfaces modified with a 4-(2-pyridylazo)resorcinol disulfide derivative: Detection of copper, lead, and cadmium

Article abstract of DOI:10.1021/ac00098a021

We have developed a surface-enhanced Raman spectroscopic technique for the determination of Pb²⁺, Cd²⁺, and Cu²⁺ concentration using a 4-(2-pyridylazo)resorcinol (PAR) coating modified with a disulfide. The disulfide provided a strong anchor to a roughened silver substrate. Atomic specificity was demonstrated by the distinct spectral changes that occurred through the interaction of Pb²⁺, Cd²⁺, and Cu²⁺ ions with the indicator. The absorption of these metals by the coating was followed with SERS and could be fit to a Frumkin isotherm. Langmuirian behavior was not observed; this is most likely due to the electrostatic repulsions as the metal cations are absorbed. The detection limits at pH 6 for Pb²⁺, Cd²⁺, and Cu²⁺ were 522, 50.3, and 1.49 ppb, respectively. Flow experiments using an optical fiber probe indicated instantaneous response to changes in metal concentration.