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

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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 0.5M pyrrole by using a polymerization time of 200s and a mole ratio of 1:8 (6.2U/mL XOD: 49.6U/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 300s for the inner layer at an applied current density of 0.25mAcm−2, a drying time of 30min for the outer layer, pH 7, and 0.025MTris–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 20.0μM phosphates and a linear concentration range of 20–200μM were achieved with potentiometric PPy–NO3/BSA/GLA–PNP–XOD biosensor. In comparison, a minimum detectable concentration of 10μM and a linear concentration range of 0.1–1mM 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.