Sequential pH-Dependent Adsorption of Ionic Amphiphilic Diblock Copolymer Micelles and Choline Oxidase Onto Conductive Substrates: Toward the Design of Biosensors

This work examines the fabrication regime and the properties of polymer-enzyme thin-films adsorbed onto conductive substrates (graphite or gold). The films are formed via two-steps, sequential adsorption of poly(n-butylmethacrylate)-block-poly(N,N-dimethylaminoethyl methacrylate) (PnBMA-b-PDMAEMA) diblock copolymer micelles (1st step of adsorption), followed by the enzyme choline oxidase (ChO) (2nd step of adsorption). The solution properties of both adsorbed components are studied and the pH-dependent step-by-step fabrication of polymer-enzyme biosensor coatings reveals rather drastic differences in their enzymatic activities in dependence on the pH of both adsorption steps. The resulting hybrid thin-films represent highly active biosensors for choline with a low detection limit of 30 nM and a good linearity in a range between 30 nM and 100 mM. The sensitivity is found to be 175 mu A mM(-1) cm(-2) and the operational stability of the polymer-enzyme thin-films can be additionally improved via enzyme-to-enzyme crosslinking with glutaraldehyde.