An Electrochemical Sensor with Graphene–Graphene Oxide Nanocomposite and Ammonium Molybdate for Phosphate Determination

This paper presents an electrochemical sensor for the quantitative determination of phosphate. The sensor’s working electrode was modified with a layer of graphene–graphene oxide nanocomposite and ammonium molybdate. The reaction of phosphate and ammonium molybdate forms a phosphomolybdate complex on the electrode. Furthermore, the nanocomposite with a proper mixing ratio can immobilize the phosphomolybdate for cyclic voltammetry (CV) measurement since it possesses both the high conductivity of graphene and the polyfunctional groups of graphene oxide. The experimental results show that the absolute value of peak reduction current at -0.21 V increased with the increase of phosphate concentration and exhibited a linear relationship in the concentration range of 0.2–5 mM. This proposed sensor is suitable for detecting phosphate levels in the physiological and higher concentration ranges. Moreover, all possible interfering substances in both urethral calculus and human blood, except for copper ions, do not influence the detection of phosphate using this proposed sensor. Therefore, it can be used to detect the content of phosphate in urethral calculus or human blood.