The use of layer-by-layer techniques for immobilizing several types of enzymes, e.g., glucose oxidase, horse radish oxidases, and choline oxidase, on carbon nanotubes (CNTs) and the applications of these techniques for biosensing are presented. The enzyme is immobilized on the negatively charged CNT surface by alternatively assembling a cationic polydiallyl-dimethyl-ammonium chloride (PDDA) layer and an enzyme layer The sandwich-like layer structure (PDDA/enzyme/ PDDA/CNT) formed by electrostatic assembly provides a favorable microenvironment to retain the bioactivity of the enzyme and to prevent enzyme molecule leakage. The morphologies and electrocatalytic activity of the resulting enzyme films were characterized using transmission electron microscopy and electrochemical techniques, respectively It was found that these enzyme-based biosensors are very sensitive and selective for the detection of biomolecules, e.g., glucose, choline.
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