Polypyrrole-based bilayer biosensor for potentiometric determination of phosphate in natural waters

A method is described for the fabrication of a novel polypyrrole-based potentiometric bilayer biosensor for phosphate, as PPy-NO₃/BSA-GLA- PNP-XOD, consisting of an inner electropolymerized PPy-NO₃ layer and an outer layer of PNP and XOD cross-linked with a mixture of BSA and GLA. The optimum conditions for reliable utilization of the biosensor include a polymerization time of 300 s for the inner layer at an applied current density of 0.25 mA cm^-2, a drying time of 30 min for the outer layer, pH 7, and 0.025 M Tris-HCl. As little as 20 μM of phosphate was detected with the PPy-NO₃/BSA-GLA-PNP-XOD biosensor and the response was linear between 20 and 200 μM. Excellent recoveries (98.5-100.5%) of phosphate in lake, swamp and river water samples were obtained with the biosensor.