Improved Performance of the Potentiometric Biosensor for the Determination of Creatinine

The development of potentiometric biosensors for the determination of creatinine is attractive because it is a frequently analysed species in clinical chemistry. Contemporary methods of analysing creatinine engage chemicals harmful to the environment and generate large volumes of waste disposals. By introducing a membrane-based potentiometric biosensor with immobilised creatinine deaminase, the measurements can be performed by miniaturised portable devices that are easy to handle and allow rapid analysis at a minimum consumption of chemicals. Thus, the enzymatic creatinine biosensors was revisited and optimised with respect to repeatability, sensitivity, limit of detection (LOD) and response time. A detection limit of 0.3 M and a sensitivity of 58.78 ± 0.03 mV (23.5 0C) 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 approx. 30 sec. using sample volumes of 30 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 immobilised 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.