An Amperometric Oxalate Biosensor Based on Polypropylene Tip Bound Sorghum Oxalate Oxidase

An oxalate oxidase electrode was constructed by immobilizing sorghum oxalate oxidase covalently on the surface of a polypropylene (PP) tip inserted in a Pt wire. Determination of oxalic acid was performed by oxidation of enzymatically generated H₂O₂ at 0.4 V Versus Ag/AgCl. The biosensor showed optimal response within 30 s at pH 5.0 and 35 °C with a linear range of 0.028 to 0.4 mM. Biosensor measured oxalate in urine of healthy persons and urinary stone formers. The detection limit was 0.028 mM. Analytic recoveries of exogenously added oxalate in urine (5 mg/L and 10 mg/L) were 94.5% and 90.2% respectively. Within and between batch coefficients of variation for urinary oxalate determination were < 5.1% and < 5.34% respectively. There was a good correlation (r = 0.96) between urinary oxalate values by standard enzymic method and present method Enzyme electrode was used for more than 150 assays and had a storage life of 100 days at 4 °C. These results also conclude that polypropylene tube/sheet could be used as a solid support for immobilization of biomolecules for fabrication of biosensors.