Abstract
This study presents an innovative urea detection method utilizing pH-controlled Fenton etching of gold nanobipyramids (AuNBPs), offering a multicolor visual response. By leveraging the urease-catalyzed hydrolysis of urea, which releases ammonia and raises pH, the Fenton reaction is inhibited, reducing the etching of AuNBPs. This approach enables a highly sensitive and distinct multichromatic response across a wide range of urea concentrations, particularly at low target levels. The solution-based sensor achieved an exceptionally low detection limit of 0.098 μM, surpassing existing colorimetric urea biosensors. Furthermore, embedding the sensor in an agarose hydrogel matrix to create a solid-state format resulted in a detection limit of 0.2 μM. Real-world validation demonstrated high recovery rates in urine samples, further affirming the sensor's reliability. This multicolor biosensing platform offers a robust tool for point-of-care diagnostics, facilitating accurate and user-friendly urea detection.