| Since the discovery by Iijima in 1991, carbon nanotubes (CNTs) have attracted much attention and opened up a new way to material sciences and nanotechnology because of their fascinating and extraordinary structural, mechanical, electrical, and electrochemical properties as well as promiseing applications in various research fields, including physics, chemistry, energy conversion technologies and materials sciences. Recent efforts have also revealed that the unique properties of CNTs have endowed them with excellent electrochemical properties that are useful for electrochemical studies and electroanalytical applications, e.g., electrocatalysis, electrochemical sensors and biosensors. We are interested in the uses of CNTs to construct nanostructure-based electrochemical biosensors, of which the direct electron transfer between proteins and enzymes and CNTs is the key point. To circumvent such a key problem, we have conducted several works, mainly through non-covalent and covalent functionalization of CNTs. The possible applications of the direct electron transfer of proteins at the CNTs are also demonstrated for development of third-generation electrochemical biosensors and enzymatic biofuel cells. The works undertaken can be summarized as follows.i) We have tried to chemically functionalize the CNTs through both covalent and noncovalent ways. In the covalent way, we intentionally introduce oxygenated groups such as hydroxyl and carboxyl groups on the sidewall of the CNTs since the sidewall functionalization of covalently bound moieties, (-OH and -COOH groups in this case) can substantially improve the hydrophilic property and may enhance the biocompatibility with biomacromolecles of the CNTs. In the noncovalent way, poly(ethylene oxide)-poly(propylene oxide)-poly-(ethylene oxide) (PEO-PPO-PEO) block copolymers, (i.e., Plurioue F127 and P123) are used to functionalize the CNTs through a hydrophobic interaction. We find that the...
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