Direct biosensor coating with a photopolymerised microlayer through a controllable step-procedure

Biosensors are based on the intimate association of a transducer and of a sensing layer. The latter can be a preformed membrane further connected to the transducer, or a thin film directly deposited on its surface. As the stability is a key parameter to be considered, a polymer with high potentialities for this purpose was chosen to form a direct surface coating: a poly(vinyl alcohol) bearing styrylpyridinium groups (PVA-SbQ). Choline oxidase was entrapped in this photo-cross-linkable gel for making an enzyme electrode through controllable steps. The influence of the ratio PVA-SbQ/enzyme was studied and the stability of the resulting modified electrodes was determined. After deposition of minute volumes (10-45 mu l) including no more than one unit of choline oxidase and 0.3 mg of polymer, an efficient choline sensor was obtained. It exhibited a fast response time lower than 30 s, a low detection limit of 2.5 nM choline, a wide linear range extending up to ca. 10(-4) M and good stability, both operational and on storage. This method appears promising for making miniaturized biosensors.