AMPEROMETRIC BIENZYME BASED BIOSENSOR FOR THE DETERMINATION OF LACTOSE WITH AN EXTENDED LINEAR RANGE

Amperometric biosensors were developed for the determination of lactos e using beta-galactosidase and glucose oxidase. The enzymes were co-im mobilized under mild conditio ns in a poly(carbamoyl)sulphonate-hydrog el matrix onto the surface of low-cost-screen-printed platinum working electrodes for the amperometric detection of the enzymatically genera ted hydrogen peroxide which was monitored at + 600 mV versus Ag/AgCl/3 M KCl. The basic sensors showed linearity over a concentration range of 0.0035-2 mM (correlation coefficient, r = 0.99992). They were used in a batch system to determine the lactose content in milk. As sample pre-treatment, only dilution was necessary. Data for the determination of lactose with the enzyme electrodes were compared to those obtained using a soluble enzyme test kit (the Boehringer Mannheim UV method). The linear range of the sensors could be increased by applying additio nal membranes to the top of the planar sensor surface. Commercially av ailable polycarbonate membranes with reduced pore densities and pore s izes supplied best results when fixed using double-sided tape. As an a lternative approach, an extended linear range could also be accomplish ed by spray-coating the sensor surface using a water-based polymer dis persion.