Polypyrrole based amperometric and potentiometric phosphate biosensors: A comparative study B

The preparation of two electrochemical (potentiometric and amperometric) phosphate biosensors is described and compared. Purine nucleoside phosphorylase (PNP) and xanthine oxidase (XOD) were co-immobilized via entrapment into polypyrrole (PPy) films by galvanostatic polymerization. Polypyrrole entrapment was achieved with 0.5 M pyrrole by using a polymerization time of 200 s and a mole ratio of 1:8 (6.2 U/mL XOD: 49.6 U/mL PNP) in amperometric phosphate biosensor. Potentiometric bi-layer biosensor PPy-NO3/BSA-GLA-PNP-XOD is made of an inner electropolymerized PPy-NO3 layer and an outer layer of PNP and XOD cross-linked with a mixture of bovine serum albumen (BSA) and gultaraldehyde (GLA).The optimum conditions for potentiometric bi-layer 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 MTris-HCl. Sensitive amperometric measurements obtained from PPy-PNP-XOD-Fe(CN)64− biosensors were compared with those of potentiometric measurements obtained from PPy-NO3/BSA/GLA-PNP-XOD bi-layer biosensor. A minimum detectable concentration of 20.0 μM phosphates and a linear concentration range of 20-200 μM were achieved with potentiometric PPy-NO3/BSA/GLA-PNP-XOD biosensor. In comparison, a minimum detectable concentration of 10 μM and a linear concentration range of 0.1-1 mM were achieved with amperometric biosensor. The presence of uric and ascorbic acids had the least effect on the performance of the PPy-PNP-XOD-Fe(CN)64− amperometric and PPy-NO3/BSA/GLA-PNP-XOD potentiometric bi-biosensors, therefore, they will not have any effect on phosphate measurement in both biosensors at levels normally present in water. PPy-NO3/BSA-GLA-PNP-XOD potentiometric biosensor was used to analyse phosphate in real samples.