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. How experiments using an optical fiber probe indicated instantaneous response to changes in metal concentration.We have recently demonstrated the ability to detect ionic species1-4 and organic compounds in aqueous solutions using chemically modified silver surfaces.* 12345•6 The approach we have developed combines surface-enhanced Raman spectroscopy (SERS), analyte-specific affinity coatings, and fiber-optic sensors. The coatings vary from simple alkanes to complex macrocycles with the common theme of containing a thiol or disulfide group to anchor the coating to a silver substrate. Long-chain alkyl disulfides and thiols have been shown to form self-assembled monolayers (SAM) at noble metal surfaces.7•8 These surfaces mimic reversed-phase HPLC coatings and provide excellent surfaces for the detection of hydrophobic organic analytes. The same types of intermolecular interactions responsible for selfassembly may not be present in some of the complex metal ion chelating and macrocyclic coatings that we have synthesized for metal ion detection. However, it has been found that these
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