A novel structural specific creatinine sensing scheme for the determination of the urine creatinine

In this work, a highly structural dependent amperometric scheme was proposed for the determination of creatinine without enzymatic assistance. The principle of this novel method is based upon the formation of a soluble copper-creatinine complex on the copper electrode surface. Subsequently, an oxidative current from the regeneration of the surface oxide layer is monitored and it is proportional to the concentration of the creatinine. This scheme can be conducted at potential of -0.1 V (vs. Ag/AgCl, 3 M) in phosphate buffer (pH 7). A typical calibration plot from 25 μg/dL to 1.5 mg/dL (R(2)=0.997) with a detection limit of 6.8 μg/dL (S/N=3) is achieved. The relative standard deviation of 21 successive injections of 0.2 mg/dL creatinine is 0.018. Under the optimal conditions, the frequently encountered biological interferences at physiological or higher concentration were investigated. Only uric acid revealed an obvious interference (298.1%). However, a Nafion(®) coated copper plating electrode shows a successful decrement of the interference of the uric acid with slightly decreased sensitivity of creatinine. The feasibility of this scheme for further clinical application is demonstrated by both HPLC and FIA to evaluate the creatinine concentration in a urine sample.