Amperometric bi-enzyme based biosensor for the determination of lactose with an extended linear range

Abstract

 Amperometric biosensors were developed for the determination of lactose using β-galactosidase and glucose oxidase. The enzymes were co-immobilized under mild conditions in a poly(carbamoyl)sulphonate-hydrogel matrix onto the surface of low-cost-screen-printed platinum working electrodes for the amperometric detection of the enzymatically generated 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 additional membranes to the top of the planar sensor surface. Commercially available polycarbonate membranes with reduced pore densities and pore sizes supplied best results when fixed using double-sided tape. As an alternative approach, an extended linear range could also be accomplished by spray-coating the sensor surface using a water-based polymer dispersion.