Creating stable and versatile monolayer systems on carbon substrates for sensors and other applications

The aim of this project is to develop strategies for fabrication of carbon electrode surfaces with a view to creating stable and versatile monolayersystems for sensing and other applications. Glassy carbon (GC) electrodes have been successfully modified with versatile monolayers via theelectrochemical reduction of aryl diazonium salts. The surfaces modified with diazonium salt monolayers were properly characterised byelectrochemistry, AFM and XPS. The rates of heterogeneous electron transfer through organic monolayers on GC, Pyrolysed Photoresist Films(PPF) and gold surfaces have been studied using ferrocene as the redox probe.The diazonium salt monolayers created on GC surfaces demonstrated very stable ability and can serve as a good alternative to alkanethiol selfassembledmonolayers on gold electrodes for sensing purposes. Tripeptide Gly-Gly-His modified GC electrodes have been successfully used asthe electrochemical copper sensors and were found to be extremely stable. PPF has proved to be a good alternative to the GC electrode for thecommercialisation of the fabricated electrochemical sensors.The most important and difficult task of this project is to fabricate glucose biosensors and immunosensors on carbon electrodes. The rigid andconjugated molecular wires (MW) as the efficient conduit for electron transfer, and a molecule with poly(ethylene glycol) chains (PEG) as aninsulator for reducing the non-specific protein adsorption were successfully synthesised and introduced in the sensing systems. MW modified onGC electrodes can be used to explore the deeply buried active site of glucose oxidase to achieve direct electron transfer of GOx from the activecentre FAD through the MW to the underlying GC electrode, and to fabricate third generation biosensors.The interface comprising mixed monolayers of MW and PEG has the ability to facilitate efficient electron transfer. A label-free immunosensorsystem has been successfully developed for electrochemical detection of biomolecular pairs such as biotin/antibiotin with low detection limitationbased on mixed monolayers of MW and PEG modified GC electrode surfaces. In addition, a displacement assay has shown that the free biotincan compete with the attached biotin for binding antibiotin. SWNTs can be used as an alternative to MW to fabricate another label-freeimmunosensor system due to the high efficiency of electron transfer that SWNTs have demonstrated