Urea is one of the major adulterants in milk which is added to increase the Solid-Not-Fat and protein contents in adulterated milk, as well as its shelf-life. Prolong consumption of excess urea beyond the permissible limit (70 mg/dL) leads to kidney disease and renal failure. As mostly run through unorganized sectors, reliable quality check of milk in India can only be done in the consumer end. That requires an in-home, portable device with simple test protocol. A disposable urea sensor is designed in this work from this motivation. It adopts impedimetry based enzymatic technique which is integrable with smart devices. Its disposable nature avoids any calibration shift resulted by the fat contents present in milk. The presence of urease makes the sensor sensitive to urea and tells the exact concentration in the range of 20−250 mg/dL. The response is linear and sensitivity is 1.36 Ω/mg/dL.

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 systems such sensing often relies upon bioimpedance spectroscopy followed by offline analysis. This paper 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-modelled sensing devices can act as one of its constituent element. Consequently, the response of the oscillator becomes the measure of the parameters of the Cole model or in turn, the measure of the bio-element. 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 modelled 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 paper presents the design of a fractional order (FO) Hartley oscillator (FOHO) using a practical, non-ideal op-amp and investigates the optimal position of the FO inductor within the circuit. Three key non-idealities of the op-amp are considered: finite gain bandwidth product, non-zero output resistance, and finite open-loop DC gain. A generic mathematical relationship is developed to account for these non-idealities, describing both the oscillation frequency and conditions for the proposed FOHO. The effects of these non-idealities on oscillation frequency and critical resistance ratio are analyzed, with four different configurations explored to determine the optimal inductor placement. The parametric variation of the oscillator is studied, and based on this, design guidelines are provided for determining the values of L, F, alpha, and R for a specified oscillation frequency. These guidelines, demonstrated through a design example, are validated using LTspice simulations, and case studies are presented to achieve the highest possible oscillation frequency.