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 measurement as follows: 4 mL of serum and 2 mL of a mixture of 0.1 mol L−1 hydrochloric acid and 10% trichloroacetic acid were mixed in a centrifuge tube and heated for 15 min. After cooling, the mixture was centrifuged for 10 min. The supernatant liquid was removed and the zinc contents were then determined as described in analytical procedure. For evaluating the accuracy of the method, a comparison between results obtained by proposed method and ICP-OES was performed. The results are shown in Table 2. It can be seen that the results measured by the present sensor are in good agreement with those measured by ICP-OES as a reference technique. In this study, although no relationship (correlation) was observed between serum Zn (II) concentrations and serum glucose in diabetic patients, but there seems to be a rational decrease in serum Zn (II) for patients with higher glucose levels.