Impedimetry-Based Disposable Sensor for the Detection of Urea in Aqueous Media

Abstract

The article presents a novel, disposable paper–dielectric urea sensor that uses adhesive copper tapes as electrodes. The electrodes are coated with layers of wax, urease, and poly(methyl methacrylate) (PMMA). The wax layer keeps the paper–dielectric sensor dry even in aqueous media, whereas the urease–PMMA layer improves the sensitivity. An ac impedimetry-based sensing technique is presented, which is developed from the electrical impedance spectroscopy (EIS) of the sensing system. Several case studies are performed to determine a suitable operating frequency, measurement time, and primary sensing variable. A precalibration before the measurement is proposed for each sensor for quality check and grading of the sensor to improve its accuracy. Separate sensing equations are proposed for different groups of sensors using linear regression in a semilog plane (with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}^{{2}} \ge {0.89}$ </tex-math></inline-formula> ). An electronic interface is also presented to design a prototype of a portable, inexpensive urea detection meter. As per the experimental data, the fabricated sensor has a detection range of 0.16–175 mM (1–1050 mg/dL), an accuracy of ±2.8%, a yield rate of 91%, and a shelf life of more than three months. It has a minimum sensitivity of 0.83 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{k}\Omega $ </tex-math></inline-formula> for one decade change in concentration.