Creatinine-Iron Complex and Its Use in Electrochemical Measurement of Urine Creatinine

A non-enzymatic electrochemical technique for creatinine sensing is presented, exploiting iron binding property of creatinine. Disposable carbon printed electrodes layered with FeCl₃ coated cotton fiber membranes are used to sense creatinine from 10 to 245 mg/dl, on clinical urine samples. The energydispersive X-ray spectroscopy analysis confirms the presence of Fe(III) dry chemistry on cotton membrane. Creatinine binding with Fe(III) is verified with UV analysis, with a corresponding decrease in Fe(III) reduction current in cyclic voltammetry. The disposable test strips are interfaced with multi-potentiostat point of care (POC) hand-held device, working in amperometry mode. The results obtained on POC biosensors demonstrate good correlation (R² = 0.91) with Jaffe method laboratory gold standard. The intra-assay variability is less than 7.1%. The statistical bias as revealed from the Bland-Altman analysis indicates that the POC results are within 95% confidence interval. This POC device does not require any sample preparation step and provides sample to result in less than a minute. FeCl₃ sensing chemistry is robust against urine albumin interference, which is especially significant for accurate estimation of albumin to creatinine ratio. The non-enzymatic nature of disposable test strips results in highly stable and robust operation of the POC device over a large range of temperature variations.

I. Introduction

Although the research publications in biosensor have grown exponentially in the last few decade after the invention of blood glucometer, the commercialization has alarmingly lagged behind. Point of care (POC) biosensor market is growing rapidly but the reality is that only glucose biosensor is the major contributor in this growth and we are still waiting for other biosensors which are robust and cost effective. Many critical reviews and editorials have stressed the need for new strategies for biomolecule recognition, with an emphasis on novel receptors for robust and reliable biosensing. Before the advent of immunoassays, the clinical pathology mainly relied on the analytical techniques, without sophisticated instrumentations, for various pathology tests. Though it has been possible to miniaturize the bulky biochemistry analyzers of pathology lab into a table-top device, the receptor element has remained the same, either antibody or enzyme. Immunoassays are very sensitive when used in controlled environmental conditions but the use of POC device should not be dependent on environmental and operator conditions. In this scenario, it is worthwhile to analyze the possibilities of novel receptors for POC biosensors using simple analytical chemistry that can be easily integrated with today’s advanced engineering [1]–[6].