Development of a conductometric phosphate biosensor based on tri-layer maltose phosphorylase composite films

A conductometric biosensor for phosphate detection was developed using maltose phosphorylase (MP) from recombinant Escherichia coli immobilized on a planar interdigitated electrode by cross-linking with saturated glutaraldehyde (GA) vapour in the presence of bovine serum albumin (BSA). The process parameters for the fabrication of the mono-enzymatic sensor and various experimental variables such as the enzyme loading, time of immobilization in saturated GA vapour, working buffer solution and temperature were investigated with regard to their influence on sensitivity, detection limit, dynamic range, operational and storage stability. The biosensor can work well at the temperature between 20 °C and 50 °C, and reach 90% of steady-state conductance in about 10 s. The sensor has two linear ranges, one is from 1.0 μM to 20 μM phosphate with a detection limit of 1.0 μM, and the other is between 20 μM and 400 μM phosphate. When stored in citrate buffer (0.1 M, pH 6.0) at 4 °C, the biosensor showed good stability over two months. No obvious interference from other anionic species like SO42−, Cl−, NO3−, NO2− and HCO3− was detected. The biosensor is suitable for use in real water samples.