Biosensing of Urea with a Functionalized Gold Electrode for Health and Food Monitoring

Urea monitoring in biological fluids is of crucial significance, since urea is a key indicator of liver and kidney physiological functioning, a marker for hemodynamic treatments, and has been used for food adulteration. Therefore, we have covalently anchored the urease enzyme (Ur) to a screen-printed gold electrode (SPGE) using the 3,3'-dithiodipropionic acid di(<i>N</i>-hydroxysuccinimide ester) (DSP) bifunctional linker that allowed optimal electronic communication between urease and gold electrode and developed a selective urea biosensor (Ur-DSP/SPGE). The Ur-DSP/SPGE was characterized by infrared spectroscopy (FTIR), cyclovoltammetry (CV), and electrical impedance spectroscopy (EIS). Open-circuit potentiometry (OCP) was also used to detect urea at different concentrations (0-600 μM) in water. The biosensor showed a urea limit of detection (LOD) of 5.0 μM, as well as excellent temporal stability and selectivity. Urea sensing was also investigated in caw's milk, human saliva, and tap water with excellent results and recoveries.