Silver-Nanoparticle-Decorated NiOOH Nanorods for Electrocatalytic\nUrea Sensing

Abstract

Nickel\n(Ni)-based urea biosensors have been proven to be a useful\nprescreening technology because of their excellent electrocatalyst\nactivities on urea. However, the behavior of Ni-based nonenzymatic\nurea biosensors showed limitations in identifying the presence of\nurea molecules in biomarkers such as urine and serum because the catalytic\nresponse of the Ni element is only applicable to an alkaline or OH^– environment. To use Ni-based catalysts as urea biosensors\nin a physiological situation, pH-independent functioning for urea\nelectrooxidation is necessary. This paper presents Ni-based catalysts\nthat exhibit electrocatalytic activity toward urea oxidation reaction\nin a neutral pH environment. The silver (Ag)/NiOOH nanorod composite\ncatalysts were prepared by a cyclic voltammetry (CV) treatment of\nthe Ni­(OH)₂ precursor and sputter deposition of Ag. Their\nproperties were characterized by scanning electron microscopy, energy-dispersive\nspectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy.\nGood electrochemical performances by CV and chronoamperometry showed\na high sensitivity of 233.7 μA mM^–1 cm^–2, a wide linear range of 0.2–26.0 mM, a fast\nresponse time of approximately 3.0 s, and a detection limit of 5.0\nμM (S/N = 3) at an applied potential of 0.35 V (vs Ag/AgCl)\nin a neutral phosphate-buffered saline solution. The performances\nof the new electrochemical electrode provide a promising platform\nto distinguish the presence of urea in human serum via nonenzymatic\nroutes.