Urease-free Ni microwires-intercalated Co-ZIF electrocatalyst for rapid detection of urea in human fluid and milk samples in diverse electrolytes

Abstract

Urea plays an important biological role in metabolism to determine the protein levels in the human body. The surplus limit of its prescribed level causes heart failure, dehydration, cachexia, and hepatic failure. Thus, accurate determination of urea is very important from the medical point of view. In this study, cobalt zeolitic imidazolate framework (Co-ZIF)-nickel microwires (NiMWs) were synthesized through a simple one-pot solvothermal method. The microstructures and composition of the synthesized material were analysed by various spectral and microscopic techniques. The SEM images exhibited a well-defined spherical-like structure for Co-ZIF with a diameter of 3 μm and NiMWs with a diameter of 1 μm. XPS results clearly confirmed that the composite material contains both Co²⁺ and Ni⁰ in its lattice. The composite material was then drop cast on GCE and the EIS analysis displayed lower R_CT = 7845 Ω and higher kinetic rate constant (k_et = 4.844 × 10⁻⁴ cm² s⁻¹) than those for bare GCE, Co-ZIF and NiMWs/GCEs. Electrochemical oxidation of urea was evaluated in various electrolytes at the composite fabricated electrode and the response in Tris–HCl (pH 8.0) was better than that in KOH, acetate and phosphate buffer solutions. The fabricated sensor exhibited a wide range for urea determination from 0.5 × 10⁻⁶ M to 0.5 × 10⁻³ M with the lowest LOD of 0.3 × 10⁻⁶ M. Subsequently, the present sensor was successfully exploited to determine urea in human biological fluid and milk samples, and the results were confirmed with the enzymatic method used in the clinical laboratory. The proposed non-enzymatic urea sensor exhibited a wide linear range, lowest detection limit, good selectivity and sensitivity.