Studies towards an amperometric phosphate ion biosensor for urine and water analysis

An amperometric biosensor for phosphate ion is described that is based on a cobalt phthalocyanine modified screen-printed carbon electrode (CoPC-SPCE). The biosensor operation is based on the enzyme pyruvate oxidase (PyOd) which catalyses the oxidative decarboxylation of pyruvate, in the presence of inorganic phosphate and O₂, to acetyl phosphate, hydrogen peroxide (H₂O₂) and CO₂. The transducer allows the electrocatalytic oxidation of H₂O₂ in order to generate the analytical signal. The enzyme was immobilised onto the CoPC-SPCE using a sandwich format. The inner membrane was formed in situ by depositing an acetone solution containing cellulose acetate first onto the transducer surface. The enzyme and cofactors were then deposited onto this layer and allowed to dry; finally a second aliquot of the cellulose acetate solution was deposited onto the enzyme layer and allowed to dry. The biosensor was characterised by amperometry in stirred solution to produce current-voltage curves and for calibration studies. From these it was deduced that a reliable electrocatalytic response was obtained for phosphate ion; an operating potential of +0.4 V was selected for the analysis of urine samples. The precision of the response for urine analysis and recovery data for potable water suggests that the biosensor could have applications in clinical and environmental monitoring.