Preparation of an enzymatic glucose sensor based on hybrid organic–inorganic Langmuir–Blodgett films: Adsorption of glucose oxidase into positively charged molecular layers

The adsorption of glucose oxidase (GOx) into positively charged Langmuir–Blodgett (LB) films has been studied to obtain an insight into the adsorption mechanism. Glucose oxidase was immobilized in hybrid organic–inorganic Langmuir–Blodgett films consisting of positively charged octadecyltrimethylammonium (ODTA) and nano-sized Prussian blue (PB) clusters. These ODTA/PB/GOx LB films showed a glucose sensor action at a very low operating potential of 0.0 V (vs. Ag/AgCl), a potential which has been determined as being effective in inhibiting the responses from interferents such as ascorbic and uric acids. We investigated the response current density of the glucose sensor as a function of the pH of GOx adsorption solution. It was found that the current density depended strongly on the pH. The maximum current density, whose values were some four times greater than that of a typical current density for these systems, was obtained at pH 4, which is near the isoelectric point of GOx. Infrared absorption spectra revealed that such dependence of the current density was caused by the pH dependence of the amount of adsorbed GOx. A series of models based on the electrostatic attractive forces between GOx and ODTA can well explain the observed pH effect on the GOx adsorption. These findings are useful for immobilizing GOx through electrostatic interaction with positively charged molecules.