Noninvasive Urea Monitoring Using a Flexible Electrochemical Sweat Based Sensor

With the development of technology in healthcare systems, interest in a wearable, portable, and even implantable device is growing, allowing health indicators to be read by direct skin contact [1], [2]. The non-invasive sensing platform overcomes the inconvenience of the conventional monitoring system and enabling easy and quick medical diagnosis in real time [3]. Urea is a major metabolite of the human body in a form of nitrogen, a key biomarker above the renal failure, dehydration, and hepatic issues [4], [5]. Urea detection is conceivable from serum, urine, and sweat in the body. The concentration of urea in the sweat is higher than that of serum so sweat based urea sensor can substitute the current pricking test method [6]. Higher levels of urea in sweat are also essential notices because they are correlated with uremia [7]. To sense the non-electric active of urea, the present method uses an enzyme in electrochemical sensors. The enzyme-based sensor consists of an enzyme (urease) and a mediator, which distinguishes the urease-catalyzed hydrolysis products [8]. However, the enzymatic sensor is complex, unstable, and costly, so non-enzyme sensors are better suited for wearable sensor devices. Nickel-based catalysts with nanostructures, large surface area, good electrical conductivity, and low cost are the best nominees for urea detection as they oxidize urea without enzymes [9]. Recently, a polymer-type substrate has been utilized for the flexible and wearable sensor device which requires porous and conductive polymers. Herein, we investigated a facile approach to form nickel oxyhydroxide with metal (metal-NiOOH) based flexible electrochemical sensor by electrospinning method. The morphology and the structure of the metal-NiOOH catalysts were observed using transmission electron microscopy, scanning electron microscopy, and X-ray diffraction. The metal-NiOOH catalysts with polymer showed excellent flexibility and competent linear sensitivity to urea electrooxidation in the physiological concentration area. A comprehensive investigation of the performances regarding metal-NiOOH as a catalyst in a sweat-based sensor will be presented. References Feiner, Ron, et al. "Engineered hybrid cardiac patches with multifunctional electronics for online monitoring and regulation of tissue function." Nature materials 15.6 (2016): 679. Liu, Yuhao, Matt Pharr, and Giovanni Antonio Salvatore. "Lab-on-skin: a review of flexible and stretchable electronics for wearable health monitoring." ACS nano 11.10 (2017): 9614-9635. Pickup, John C., et al. "In vivo glucose monitoring: the clinical reality and the promise." Biosensors and Bioelectronics 20.10 (2005): 1897-1902. D'Apolito, Maria, et al. "Urea-induced ROS cause endothelial dysfunction in chronic renal failure." Atherosclerosis 239.2 (2015): 393-400. Thudichum, J. L. W. "On the analysis of urea in urine for clinical purposes." British medical journal 1.38 (1857): 788 Stefaniak, Aleksandr B., and Christopher J. Harvey. "Dissolution of materials in artificial skin surface film liquids." Toxicology in Vitro 20.8 (2006): 1265-1283. Kazory, Amir. "Emergence of blood urea nitrogen as a biomarker of neurohormonal activation in heart failure." The American journal of cardiology 106.5 (2010): 694-700. Liu, Yan-Ling, et al. "Flexible electrochemical urea sensor based on surface molecularly imprinted nanotubes for detection of human sweat." Analytical chemistry 90.21 (2018): 13081-13087. Mahshid, Sahar Sadat, et al. "Template-based electrodeposition of Pt/Ni nanowires and its catalytic activity towards glucose oxidation." Electrochimica Acta 58 (2011): 551-555. Acknowledgement This work was supported by Agency for Defense Development (ADD) as global cooperative research for high performance and light weight bio-urine based fuel cell (UD160050BD) and the Ocean University of China-Auburn University (OUC-AU) Grants program.