Electron transfer (ET) mechanism of redox-active self-assembled molecular monolayers (SAMs) and enzymes is of great interest in (bio)electrochemical studies. The combination of SAMs and nanomaterials has gained increasing attention in improving the ET rate, catalytic activity and operational stability. This Ph.D. project includes three main parts.
In the first part, the electrochemistry of a novel anthraquinone (AQ) derivative SAM on nanoporous gold (NPG) and Au(111) electrodes is investigated. AQ SAMs exhibit a pH-dependent electrochemical behavior and the electrochemically addressable surface coverage on the NPG electrode is higher than that on the single-crystal Au(111) electrode due to the larger surface area. In the second part, direct ET (DET) of fructose dehydrogenase (FDH) on SAM-modified gold electrodes is studied. The first section is to study the surface orientation and ET mechanism of FDH on Au(111) electrodes modified with variable length and variably terminated SAMs. The second section is a systematic comparison of FDH performance on Au(111) and NPG electrodes. FDH exhibits the best DET activity on the Au(111) electrode modified with 2-mercaptoethanol (BME) SAMs. NPG is crucial to improve the catalytic performance and operational stability. In the final part, graphene-modified carbon paper is prepared to immobilize Myriococcum thermophilum cellobiose dehydrogenase (MtCDH) for efficient DET. Electrochemical reduction of graphene oxide (GO) and simultaneous electrodeposition of polyethylenimine (PEI) are essential to prepare well-dispersed carbon electrodes. The optimal MtCDH bioelectrode is further used as a bioanode in an EBFC assembled with a Myrothecium verrucaria bilirubin oxidase (MvBOD) biocathode. A self-powered biosupercapacitor/EBFC hybrid is also fabricated with higher power densities and stability than the EBFC alone.
The AQ derivative SAM with unique redox properties provides novel prospects as linkers or mediators in bioelectrocatalysis. The FDH bioelectrode can be employed in fructose biosensors due to its high catalytic performance and long-term stability. In addition, the biosupercapacitor/EBFC hybrid holds promise for developing self-powered wearable and implantable devices. Overall, this Ph.D. project contributes a considerable step to further in-depth understanding of the ET mechanism in bioelectrocatalysis and the rational development of advanced bioelectronic devices for practical applications.