To assess the usefulness of the sensor, it was applied to the determination of zinc in serum of diabetic patients. The serum samples were obtained from medical diagnostic laboratory (MDL). Glucose determination of all serum samples was previously performed by MDL. The serum samples were deproteinized before measurementas follows: 4 mL of serum and 2 mL of a mixture of 0.1 mol L−1hydrochloric acid and 10% trichloroacetic acid were mixed in a cen-trifuge tube and heated for 15 min. After cooling, the mixture wascentrifuged for 10 min. The supernatant liquid was removed andthe zinc contents were then determined as described in analyticalprocedure. For evaluating the accuracy of the method, a compari-son between results obtained by proposed method and ICP-OES wasperformed. The results are shown in Table 2. It can be seen that theresults measured by the present sensor are in good agreement withthose measured by ICP-OES as a reference technique.In this study, although no relationship (correlation) wasobserved between serum Zn (II) concentrations and serum glucose in diabetic patients, but there seems to be a rational decrease inserum Zn (II) for patients with higher glucose levels.