Improved performance of the potentiometric biosensor for the determination of creatinine

Contemporary methods of analyzing creatinine engage chemicals harmful to the environment and generate large volumes of waste disposals. By introducing a membrane-based potentiometric biosensor with immobilized creatinine deaminase, the measurements can be performed by miniaturized portable devices that are easy to handle and allow rapid analysis with minimum consumption of chemicals. Thus, the enzymatic creatinine biosensors were revisited and optimized with respect to repeatability, sensitivity, limit of detection (LOD), and response time. A detection limit of 0.3 mu M and a sensitivity of 58.78 +/- 0.03 mV (23.58 degrees C) were obtained in tris buffer at pH = 7.4 after introduction of shielding of all electronics and software filtering. Measurements performed by flow injection analysis (FIA) showed that the response time could be lowered to approximately 30 sec using sample volumes of 30 mu l. Interferences were corrected for by application of the Nicolsky-Eisenman equation, thus allowing determination of creatinine in matrices resembling those of clinical measurements. Investigations of sandwich structures showed that the sensitivity decreased as a function of the number of membranes on top of the immobilized layer of active creatinine deaminase. It was thus shown that the sensitivity depends on the distance of diffusion of species from the sample solution through the membranes to the enzyme.