SERS Surfaces Modified with a 4-(2-Pyridylazo)resorcinol Disulfide Derivative: Detection of Copper, Lead, and Cadmium

Abstract

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

FT‐IR, FT‐Raman and DFT calculations of 3‐{[(4‐fluorophenyl)methylene]amino}‐2‐phenylquinazolin‐4(3H)‐one

“…In the present case, the υC 25 -N 26 , and υC 23 -N 26 stretching bands are observed at 1273, 1109 cm −1 in the IR spectrum and at 1257, 1110 cm −1 theoretically. υN-N has been reported at 1115 cm −1 by Crane et al, [47] at 1121 cm −1 by Bezerra et al [48] and at 1130 cm −1 by El-Behery and El-Twigry. [49] The band observed at ∼1093 cm −1 in both spectra is assigned to the υ N 26 -N 27 mode.…”

Ab initio and density functional theory studies on vibrational spectra of 3-{[(4-methoxyphenyl)methylene]amino}-2-phenylquinazolin-4(3H)-one

“…For similar quinzoline derivatives, the C-N stretching modes are reported at 1109, 1232, 1246, 1273, 1283 cm -1 in the IR spectrum, 1243, 1250, 1286, 1295 cm -1 in the Raman spectrum and at 1110, 1119, 1235, 1240, 1248, 1257, 1283, 1288 cm -1 theoretically [17,18]. υN-N has been reported at 1115 cm -1 by Crane et al [34] at 1121 cm -1 by Bezerra et al [35] and at 1130 cm -1 by El-Behery and El-Twigry [36]. The band observed at 1119 (DFT) cm -1 is assigned to the υN15-N16 mode.…”

FT‐IR and FT‐Raman spectra and ab initio calculations of 3‐{[(2‐hydroxyphenyl) methylene]amino}‐2‐phenylquinazolin‐4(3H)‐one

“…In the present case, the υC 14 -N 15 and υC 11 -N 15 stretching bands are observed at 1283 cm −1 in the IR spectrum and at 1286, 1243 cm −1 in the Raman spectrum, and at 1283, 1240, 1119 cm −1 theoretically. υN-N has been reported at 1115 cm −1 by Crane et al, [60] at 1121 cm −1 by Bezerra et al [61] and at 1130 cm −1 by El-Behery and El-Twigry. [62] The band observed at 967 (HF) and 960 cm −1 (IR) is assigned to the υN 15 -N 16 mode.…”