Reagentless biosensors based on co-entrapment of a soluble redox polymer and an enzyme within an electrochemically deposited polymer film

Abstract

A novel biosensor architecture, which is based on the combination of a manual and a non-manual deposition technique for sensor components on the electrode surface is reported. A water-soluble Os-poly(vinyl-imidazole) redox hydrogel is deposited on a graphite electrode by drop-coating (i.e. manually) followed by the electrochemically-induced deposition of an enzyme-containing non-conducting polymer film. The local polymer deposition is initiated by electrochemical generation of H 3O + exclusively at the electrode surface causing a pH-shift to be established in the diffusion zone around the electrode (i.e. non-manually). This pH-shift leads to the protonation of a dissolved polyanionic polymer which in consequence changes significantly its solubility and is hence precipitating on the electrode surface. In the presence of a suitable enzyme, such as quinohemoprotein alcohol dehydrogenase (QH-ADH), the polymer precipitation leads to an entrapment of the redox enzyme within the polymer film. Simultaneously, the water-soluble Os-poly(vinyl-imidazole) redox hydrogel, which is slowly dissolving from the electrode surface after addition of the electrolyte, is co-entrapped within the precipitating polymer layer. This provides the pre-requisite for an efficient electron-transfer pathway from the redox enzyme via the polymer-bound redox centres to the electrode surface. The sensor preparation protocol has been optimised aiming on a high mediator concentration in the polymer film and an effective electron transfer.