Infrared photoelectrochemical sensing of urea with silicon photoanodes

Abstract

Urea is an essential molecule for life and the environment. In particular, in biological fluids, the urea concentration can be indicative of several pathologies. Herein, we propose a photoelectrochemical system activated by infrared irradiation (850 nm) for the detection of urea. Our sensor is made of a photoactive Si photoanode protected by a silicon oxide/Ni thin film and is coated with a Ni–Mo–O film that catalyzes the urea oxidation reaction. This approach is employed for the sensitive quantification of urea, and the operation of the system in a wide range of concentrations (from μM to 10 mM) is demonstrated, revealing a sub-μM limit of detection. Sensing is performed at a constant potential of 0.24 V vs Hg/HgO under infrared illumination, and the photocurrent output depends on the urea concentration. This new device has good reliability for urea analysis in alkaline aqueous solutions. The method is tested in the determination of the urea concentration in human urine samples, and the results are compared with a reference enzymatic photochemistry assay. The method is promising for the analysis of urine samples and can open new doors in biosensing and environmental analysis.