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Amperometric biosensor based on a functionalized gold electrode for the detection of antioxidants
(2002)
Superoxide sensor based on cytochrome c immobilized on mixed-thiol SAM with a new calibration method
(2002)
The combination of the biocatalytic features of enzymes with the unique physical properties of nanoparticles in a biohybrid system provides a promising approach for the development of advanced bioelectrocatalytic devices. This study describes the construction of photoelectrochemical signal chains based on CdSe/ZnS quantum dot (QD) modified gold electrodes as light switchable elements, and low molecular weight redox molecules for the combination with different biocatalysts. Photoelectrochemical and photoluminescence experiments verify that electron transfer can be achieved between the redox molecules hexacyanoferrate and ferrocene, and the QDs under illumination. Since for both redox mediators a concentration dependent photocurrent change has been found, light switchable enzymatic signal chains are built up with fructose dehydrogenase (FDH) and pyrroloquinoline quinone-dependent glucose dehydrogenase ((PQQ) GDH) for the detection of sugars. After immobilization of the enzymes at the QD electrode the biocatalytic oxidation of the substrates can be followed by conversion of the redox mediator in solution and subsequent detection at the QD electrode. Furthermore, (PQQ) GDH has been assembled together with ferrocenecarboxylic acid on top of the QD electrode for the construction of a funtional biohybrid architecture, showing that electron transfer can be realized from the enzyme over the redox mediator to the QDs and subsequently to the electrode in a completely immobilized fashion. The results obtained here do not only provide the basis for light-switchable biosensing and bioelectrocatalytic applications, but may also open the way for self-driven point-of-care systems by combination with solar cell approaches (power generation at the QD electrode by enzymatic substrate consumption).
The layer-by-layer adsorption technique based on the consecutive deposition of oppositely charged species is for the preparation of protein multilayers with fully electro-active protein molecules. The methodology was established with cytochrome c and the polyelectrolyte sulfonated polyaniline (PASA). The technique is also useful for the construction of bi-protein architectures confining protein-protein communication to an electrode. Following natural examples of protein complexes with defined signal transfer, cytochrome c was arranged with enzymes such as xanthine oxidase, bilirubin oxidase, laccase, and sulfite oxidase in self-assembled multilayer architectures. Thus, biomimetic signal chains from the enzyme substrate via the enzyme and cytochrome c towards the electrode can be established. Communication between proteins immobilised in multiple layers on the electrode can be achieved by in situ generation of small shuttle molecules or more advantageously by direct interprotein electron transfer. This allows the construction of new sensing electrodes, the properties of which can be tuned by the number of deposited protein layers. The mechanism of electron transfer within such protein assemblies on gold electrodes will be discussed.