Biosensors based on direct electron transfer of proteins cytochrome

Biosensors based on direct electron transfer of proteins cytochrome c... 

Carbon nanotubes (CNTs), as a new class of nanomaterial, were discovered in 1991 by Iijima [55] and have also been employed in biosensors. Such an application is attributed to their unique electrical properties, which make a redox active close to the surface of proteins, and enable direct electron transfer between proteins and electrode [56]. CNTs are highly conductive (rapid electron transfer) nanomaterials with great promise for applications in biochemical sensing [57-59], Several successful sensors based on CNTs have been reported for the detection of substances, including for NADH [58], glucose [59], cytochrome c [60] and thymine [61]. 

The application of direct electrochemistry of small redox proteins is not restricted to cytochrome c. For example, the hydroxylation of aromatic compounds was possible by promoted electron transfer from p-cresol methylhydroxylase (a monooxygenase from Pseudomonas putida) to a modified gold electrode [87] via the blue copper protein azurin. All these results prove that well-oriented non-covalent binding of redox proteins on appropriate electrode surfaces increases the probability of fast electron transfer, a prerequisite for unmediated biosensors. Although direct electron-transfer reactions based on small redox proteins and modified electrode surfaces are not extensively used in amperometric biosensors, the understanding of possible electron-transfer mechanisms is important for systems with proteins bearing catalytic activity. 

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