Characterisation of electrode microarrays produced photolithographically and with thiol self-assembled monolayers on gold electrodes

Abstract

The macroscale electrochemical theory breaks down with microstructures smaller than the dimensions of the diffusion layer, showing that such electrodes have significant quantitative effects and qualitative advantages.
The great advantage of microelectrodes over macroelectrodes is the minimisation of interference, which gives rise to much lower detection limits. Microelectrodes have much reduced ohmic drops and capacitive effects and can be used in the absence of supporting electrolyte. These features have opened a growing interest in the fabrication and application of microelectrodes in various areas. There are different microelectrode geometries, but disc type is the most used.
Microelectrode arrays have been proposed as a way of increasing the magnitude of the current (produced for a single microelectrode), while maintaining the advantages of the single microelectrode. Although the inlaid microdisc microelectrode can be considered as one the most popular microelectrode geometry, there is also a need to consider conical recessed, recessed and protruding microdiscs as photolithographic microfabrication techniques often result in non-ideal geometries. It has been proved using surface imaging techniques such as scanning Kelvin nanoprobe (SKN), scanning electron microscopy (SEM) and white light interferometer microscopy that conical recessed electrodes with gradient potential along the recessed walls are formed during standard photolithographic methods for producing microelectrode arrays.
Microarrays are ubiquitously used for high-throughput measurements using various signal transduction techniques. Ideally each sensor in a microarray platform should perform optimally to ensure an error free response. In this thesis, a simple method for designing a microelectrode array platform (MEA) is described, allowing a ‘defective’ cluster of sensing arrays to be easily identified. It is possible to extend this concept for multiple analyses on a single chip. Molecular electronic is a promising technology which would be an alternative. The concept of molecular electronics is the use of single molecules or arrays, or layers of molecules for the fabrication of electronic components such as wires, switches, and storage elements. Indeed, functionalised thiol monolayer-based microelectrode array may provide unique possibilities, facilitating electrochemical measurements involving electron transfer via electron tunnelling. The conjugated structure of rigid, linear molecule increases greatly the rate of electron transfer across the monolayer.
Charge transfer and self-assembly characteristics of novel fully conjugated molecules molecular wires (synthesised at the Department of Chemistry and Centre for Molecular and Nanoscale Electronics, Durham University) assembled on flat gold electrodes are evaluated using Marcus model of electron-transfer and tunnelling theory. The behaviour of these wires is compared with heptanethiol and dodecanethiol SAMs.
A preliminary study for application of self-assembled monolayer of molecular wires in microelectrode arrays for multiple analyses on a single chip has been successfully reached.