Effects of the type of polycation in the coating films prepared by a layer-by-layer deposition technique on the properties of amperometric choline sensors

A layer-by-layer deposition technique was employed for fabricating choline sensors with different polycations. We used two kinds of choline oxidase (ChOx)/polycation thin films to modify platinum (Pt) electrodes, each having the same enzyme (ChOx) but with different polycations, poly(ethyleneimine) (PEI) and poly(diallyldimethylammonium chloride) (PDDA). The Pt electrodes coated with a ChOx/PEI or ChOx/PDDA thin film were used successfully as choline sensors. The ChOx/PEI film-modified sensor showed a higher response, wider dynamic range and shorter response time than those of the ChOx/PDDA film-based sensor. The results were rationalized based on the different permeability of the thin films due to the different structure of the polycationic materials. The assembly processes of the thin films were monitored by quartz crystal microbalance (QCM) measurements.