Detection of Urea in Water using Disposable Paper Sensor with FO Colpitts Oscillator

This work presents a paper based disposable planar sensor to detect the amount of urea present in an aqueous solution using fractional order (FO) impedimetry. The presented sensor uses Cu tape as electrodes and wax-urea coating as a urea sensitive layer. The electrical impedance spectroscopy (EIS) of the sensor show a variation in Nyquist plots with varying sample urea concentrations. In the equivalent electrical model of the sensor, such variation is manifested in the change of model parameters. A FO Colpitts oscillator is designed as the primary signal conditioning element for the proposed sensor: It uses the sensor as one of its constituent element and the change in model parameters of the sensor results in a change in the oscillator frequency. Eventually, the oscillator frequency becomes a measure of the sample urea concentration. The proposed device show a linear response in semi-log plane in the range 3 mg/dL to 330 mg/dL with a limit of detection 3 mg/dL and sensitivity 160 kHz/decade. The presented FO oscillator capture entire impedimetric response of the sensor in a single circuit.