A Practical Non-Enzymatic Urea Sensor Based on Nico(OH)2 nanorods
Authors: Yoon Jaesik , Lee Doohee , Yoon Young Soo , Kim Dong-Joo 
Published: May 2020

Urea is an essential biomarker for the diagnosis of healthy kidneys because urea, a protein metabolite, is formed by the function of kidneys and is excreted into the urine. The urea level in human blood is between 10.2 and 49.8 mg/dL (equivalent to 3mM-7mM) [1]. When the concentration of urea in serum increases up to 720–900 mg/dL, kidney dialysis is required [2]. Since the early diagnosis of kidney disease is a useful way to stop or delay kidney dysfunction [3], selective and sensitive urea sensing through economic methods is very important.
For urea detection, various methods such as infrared spectrometry [4], gas chromatography [5], and calorimetry [6] have been proposed as analytical methods. Another technique is the electrochemical process, which is most effective in the economic aspect [7]. Typical electrochemical urea sensing is based on the use of urease as an enzyme. Enzyme-based urea sensing, however, has limited practical applications due to its limited working conditions depending on the temperature, pH, and humidity. Non-enzymatic urea sensors with nickel-based catalysts have been mainly used due to their high stability, biocompatibility, and nontoxicity. However, the issues such as low electrical conductivity, a narrow range of urea reactions, and a high limit of detection require the investigation of new catalysts in non-enzymatic techniques for urea sensor application. The nanostructured Ni(OH)2 has a relatively high electrical conductivity [8]. Also, the bimetallic types of catalysts help to improve the issue of low electrical conductivity and sluggish charge transfer processes [7].
Within, we studied a form of nickel hydroxide with cobalt (NiCo(OH)2) based on the nonenzymatic electrochemical sensor by hydrothermal method. The morphology and the structure of the NiCo(OH)2 catalysts were examined using transmission electron microscopy, scanning electron microscopy, and X-ray diffraction. The NiCo(OH)2 catalysts showed excellent electrochemical performance with competent linear sensitivity and selectivity to urea oxidation. Comprehensive knowledge of the performances regarding NiCo(OH)2 as a catalyst in non-enzyme based urea sensor will be given.
References
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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.