| The ability to control the placement of molecules onto substrates is an important challenge for advancing the development of sensor technologies. Although self-assembled monolayers (SAMs) of alkyl thiolates on gold have been rigorously studied, achieving regiochemical control in this system is more challenging. Using alkyl thiosulfates, SAM formation can be directed electrochemically, thereby alleviating potential difficulties associated with approaches that use thiol chemistry. The first challenge of this research was to determine which u-functionalities are compatible with the electrosynthesis of monolayers from alkyl thiosulfates. The elemental compositions of methyl-, perfluoroalkyl-, carboxylic acid-, amide-, and methyl ester-terminated SAMs derived from alkyl thiosulfates were similar to those measured for analogous SAMs derived from thiols. In contrast, x-ray photoelectron spectroscopy (XPS) revealed that by-products of the electrosynthesis react with the terminal functionality of the hydroxyl- and vinyl-terminated SAMs.;Mixed monolayers formed from solutions containing two-different alkyl thiosulfates allowed enhanced flexibility in controlling the surface properties of electrodes. The surface composition of these two-component systems was determined kinetically and was therefore linearly related to the solution composition from which they were derived. To demonstrate the selectivity of the electrosynthesis, different monolayers were directed onto individually addressable electrodes in arrays. Initially, four different monolayers were placed on four adjacent electrodes on a single substrate. To gain insight into the applicability of this technology at the microscale, an array containing three microelectrodes was functionalized sequentially with a different monolayer on each electrode. Using XPS and measurements of wettability, the presence of u-functionalized SAMs was detected only on electrodes to which they were directed. |
