Comparative electrochemical and impedance studies of self-assembled rigid-rod molecular wires and alkanethiols on gold substrates.

A study of the charge transfer and self-assembly characteristics of two new rigid-rod molecular wires 1 and 2 assembled on polycrystalline gold electrodes was carried out using electrochemical impedance spectroscopy and cyclic voltammetry. This class of wires have precisely controlled (ca. 1.5-2.5 nm) lengths of π-conjugation, with extended HOMO and LUMO wavefunctions. While rotations can occur around the C-C single bonds, the molecules cannot isomerise or fold due to their rigid backbone structures. The behaviour of these wires was compared with SAMs of heptanethiol (HPT) and dodecanethiol (DDT). It was found that SAMs of 1, which bears flexible hexyloxy sidechains, had randomly distributed pinholes which show microelectrode behaviour even when diluted with DDT. SAMs of 2, which do not have any sidechains, were well-organised at open-circuit potentials enabling evaluation of electron transfer kinetics assuming an average film thickness. However, impedance studies show that deviations from open circuit potentials resulted in an exponential decrease in charge transfer resistance, whereas capacitance remained constant, possibly attributable to conformational changes of the SAM. The syntheses and characterisation of the molecules is described.

Towards multifunctional microelectrode arrays.

A single microelectrode array platform, divided into groups of microelectrodes with flexible multiplexing can enable a 'defective' cluster of microelectrodes to be readily identified, by comparing normalised currents with the numbers of microelectrodes in the groups of arrays. This generic design principle may be extended for integrating multiple analyte sensing in a single microarray platform. The calibration of the microelectrode arrays, using white light interferometry and electrochemistry is described. The application for multianalyte detection is discussed.