An innovative electrochemical approach for selective and sensitive urea sensing using NiNPs modified GCE

Urea contamination from waste and sewage sources necessitates a simple, selective, and sensitive method for its detection in food and environmental samples. In this work, an innovative electrochemical approach is presented for urea sensing using a NiNPs modified GCE in 0.1 M NaOH electrolyte. A highly stable colloidal solution of NiNPs was synthesized using tris base as a capping agent and ascorbic acid as a reducing agent, followed by drop-casting onto the GCE surface. The formation of NiNPs was confirmed by surface plasmon resonance (SPR) observed in UV-Visible spectroscopy, while FTIR and Raman analysis validated effective capping by tris base. Structural and morphological characterization using XRD, SEM, and TEM revealed a face-centered cubic (fcc) crystalline structure and oval-shaped nanoparticles with smooth surfaces and an average size of 50-90 nm, dispersed heterogeneously across the GCE surface. The enhanced electrochemical charge transfer properties of NiNPs/GCE were demonstrated using [Fe(CN)₆]^-3/-4, NaOH, and urea in NaOH. The distinct catalytic activity of NiNPs for the electrochemical oxidation of urea, facilitated by the catalytically active NiOOH form, was clearly exhibited through cyclic voltammetry (CV), highlighting the enhanced performance of the NiNPs/GCE in urea sensing, with tris-capped NiNPs outperforming malic acid-capped counterparts. Square wave voltammetry (SWV) effectively decoupled urea oxidation from the reversible oxidation of Ni(OH)₂ to NiOOH, enabling selective detection of urea. As a result, a linear detection range of 0.0625-1.25 mM for urea with a regression coefficient (R²) of 0.9972 and a detection limit of 28.8 µM (S/N = 3) was established. Aside from NH₃, other interferences were well tolerated, with urea recovery exceeding 98.7% in municipal and 94% in agricultural wastewater.