Modified Colpitts Oscillator With Lossy Fractor for the Biosensors With Single Cole Model and Its Application in Water Urea Sensing

A single Cole model, which comprises of a lossy fractor (fractor with a parallel resistor), is a commonly reported model for several biosensors. The parameters of the model are often the measurand of the biomolecules present in the sensing media. However, due to the lack of suitable signal conditioning circuit for fractional order (FO) systems, such sensing often relies upon bioimpedance spectroscopy followed by offline analysis. This article presents a compact real-time solution for this by presenting a modified Colpitts oscillator. The proposed oscillator is designed with lossy fractor, such that Cole-modeled sensing devices can act as one of its constituent elements. Consequently, the response of the oscillator becomes the measure of the parameters of the Cole model or, in turn, the measure of the bioelement. In this work, the designed Colpitts oscillator has been applied for detecting urea concentration in aqueous medium. A paper-urease disposable sensor in urea solution can be modeled with single Cole dispersion and, hence, can be used in association with the designed oscillator. Together, the system acts as urea sensing device for the range 1 mg/dL to 1 g/dL. This article presents various case studies to find out optimal mode of operation, optimal response time, linearity, sensitivity, and repeatability of the designed system.