Characterization of a 1,4-dithiane gold self-assembled monolayer:: an electrochemical sensor for the cyt-c redox process

Electrochemical desorption and spectroscopic investigations of the gold electrode surface modified with 1,4-dithiane (1,4-dt) organothiol species were performed. The wave observed at -0.87 V versus Ag \ AgCl in the LSV (linear sweep voltammetry) reductive curve of the 1,4-dt compared to that for a similar 4-mercaptopyridine (pyS) system (-0.56 V) is indicative of a most effectively chemisorbed monolayer. The evaluation of the capability of the 1,4-dt self-assembled monolayer (SAM) in assessing the direct electron transfer (ET) of cytochrome c (cyt c) metalloprotein was investigated by cyclic voltammetry. The electrochemical response of the cyt c (E-1/2 approximate to0.0 V vs. Ag \ AgCl, DeltaE(p) approximate to 50 mV) showed the characteristics of a reversible redox process. The cyt c voltammetric parameters acquired with the 24-h air exposure modified electrode, and after 100 cycles suggest a considerable improvement of the 1,4-dt electrode performance. The surface enhanced Raman spectroscopy (SERS) spectra revealed that 1,4-dt species is in a mixed gauche and trans orientation on the gold surface. The shift for higher wavenumbers observed for the C-S stretching modes in the SERS spectra, comparatively to the normal Raman spectrum, is assigned to the 1,4-dt coordination to surface gold atoms via a pi interaction with the sulfur p-orbitals. The data collected suggest that this pi interaction plays an important role on the stability of the 1,4-dt adlayer, improving the assessment of the cyt c heterogeneous electron transfer reaction. (C) 2003 Elsevier Science B.V. All rights reserved.