Silver-Nanoparticle-Decorated NiOOH Nanorods for Electrocatalytic Urea Sensing

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