Surface-enhanced Raman scattering (SERS) spectra were recorded for p-mercaptobenzoic acid (PMBA) monolayers on Ag and Au surfaces. As evidenced by the relative intensities of the bands corresponding to the symmetric stretching COO − vibration and to the out-of-plane vibration of the phenyl ring, the molecules are at least tilted with respect to the surface and simultaneously bonded through the sulfur atom and COO − groups. This situation takes place when modification is carried out from aqueous solutions at natural or alkaline pH and at low concentrations of monomer. At higher concentration of the monomer (>10 −3 ) and/or at acidic pH, carboxylic groups are protonated and PMBA molecules adopt a more vertical configuration. It was also found that rough Ag and Au surfaces that are applied in SERS experiments promote partial decarboxylation of PMBA.

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The chemisorption of cysteamine (2-aminoethanethiol) on silver, giving monolayers often used for adsorption of proteins, was studied using surface-enhanced Raman scattering (SERS). Raman measurements revealed that the ratio of gauche-trans conformers of adsorbed cysteamine molecules significantly changed during the incubation. Layers with a higher ratio of trans conformers are formed when the time of incubation is relatively short (less than 1 h). Long incubation leads to reconstructed layers with a higher portion of cysteamine molecules in gauche conformation. The results of SERS experiments reveal that cysteamine molecules during chemisorption do not replace the large part of preadsorbed Clanions and that the structure of the obtained monolayer strongly depends on the surface concentration of preadsorbed chlorides. The effect of prolonged treatment of cysteamine layers by various electrolytes was also investigated. Raman spectroscopy revealed that after the transfer of the monolayer of cysteamine on silver to the solution containing ClO4or SO4 2anions, a relatively large amount of these anions is coadsorbed. However, after about 1 day, the bands of ClO4and SO4 2anions disappear, whereas the spectrum of adsorbed cysteamine is still well visible. Possible explanations for these experimental findings are discussed. Our results provide some suggestions that may help to obtain more uniform monolayers, terminated by amino groups, which are desired for various applications.

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A simple thiolipid molecule was synthesized by covalent linking of mercaptopropionic acid with phosphatidylethanolamine. The integrity of thiolipid self-assembled monolayers supported on gold and mercury electrodes was tested by electrochemical techniques both in the absence and in the presence of hydrophilic redox couples. The organization of the thiolipid monolayer supported on gold was also assessed by surface-enhanced Raman spectroscopy both in air and in aqueous solution. The thiolipid monolayer was then covered with a phospholipid monolayer to form a bilayer lipid membrane tethered to the electrode surface (t-BLM), and the electrochemical tests were repeated using cyclic voltammetry, differential capacitance, impedance spectroscopy (IS), and chronocoulometry. These bilayers possess an exceptionally good mechanical stability while exhibiting electrochemical properties similar to those of conventional BLMs. However, no substantial “ionic reservoir” separating the t-BLM from the electrode surface was observed by IS. Most probably, this is due to the insufficient length of the mercaptopropionic spacer and its gauche conformation related to the electrode surface.