Smartphone-enabled detection of urea in animal feed based on a disposable electrode modified with silver nanoparticles decorated on nitrogen-doped graphene nanoplatelets.

A flow injection amperometric sensing method was developed for the detection of urea in animal feed. A screen-printed electrode was modified with a nanocatalyst comprising silver nanoparticles anchored on nitrogen-doped graphene nanoplatelets. The nanocatalyst was synthesized via a two-step hydrothermal procedure and used to modify an electrode as a non-enzymatic electrochemical urea sensing platform. The morphology and structure of the as-synthesized nanocatalyst were investigated, and its electrochemical properties were characterized through electrochemical impedance spectroscopy, cyclic voltammetry, chronocuolometry, and chronoamperometry. The nanocatalyst exhibited good charge transfer ability and electrocatalytic activity for urea oxidation. The sensor fabrication and flow injection amperometric parameters were optimized. Under optimal conditions, the anodic current exhibited a linear correlation with urea concentration from 0.01 to 40 mM (0.6 to 2400 mg L^-1) with a detection limit of 0.0036 mM (0.22 mg L^-1). The developed system was highly sensitive (4.0 ± 0.3 μA mM^-1 cm^-2), showed good repeatability (RSD of 1.4%, n = 10), reproducibility (RSD of 2.5%, n = 10), and operational stability (RSD of 1.01%, n = 100), with a throughput of 60 samples per hour. Furthermore, the proposed system showed resilience against potential interferences commonly found in animal feeds. A strong correlation coefficient between results obtained from the flow injection amperometric sensor and a standard spectrophotometric method underscored the accuracy of the proposed system, ensuring its suitability for urea detection in animal feedstuffs.