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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 energy-dispersive 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 ( $R^{2}=0.91$ ) 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.

A method of describing systems by sets of second-order differential equations is suggested. In this second-order state-space formulation the states are defined in a manner slightly different from the conventional one. It is shown that this modified procedure reduces the order of matrices, renders easier the evaluation of the characteristic equation and the system solution, and provides some additional insight into the relative stability of system states. Procedures of characterization and analysis of systems by this modified method are indicated, and an example is considered to illustrate the advantageous features of the method in contrast with the normal procedure.