Cascading chemiresistive paper-based enzymatic biosensor for urea detection

• Cascade based enzymatic sensor system for rapid detection of urea. • Detection range encompasses urea levels found in healthy and diseased individuals. • Sensor offers rapid, selective detection of urea under different test conditions. • Potential as a POCT device for frequent non-invasive monitoring of urea. The conventional approach for diagnosing high risk metabolic disorders, such as chronic kidney disease (CKD), involves drawing a blood sample, which necessitates access to a centralized facility, making it undesirable for frequent urea monitoring. Alternative biological fluids, such as saliva, have demonstrated potential as non-invasive mediums for CKD monitoring due to the strong correlation between blood urea and salivary urea levels, indicating their suitability for point-of-care test kits. In this study, we present an innovative chemiresistive paper-based enzymatic sensor that utilizes a combination of urease and polystyrene sulfonate (PSS) to measure urea. This sensor detects urea over a broad concentration range (10–110 mg/dl), encompassing the salivary urea levels found in both healthy (20±10 mg/dl) and diseased (100±10 mg/dl) individuals. Furthermore, the sensor’s response to urea remains unaffected by the presence of interfering molecules in saliva such as metabolites, proteins, sugars and acids. The stability and response time of the sensor were also assessed under various temperatures, as encountered during storage. Overall, the sensor developed in this study offers a promising solution for creating a rapid, scalable, cost-effective, and user-friendly point-of-care monitoring test kit for urea screening in resource-limited setting with restricted access to healthcare facilities. This article presents the development of a cascading chemiresistive paper-based sensor that utilizes urease (enzyme) and polystyrene sulfonate (negatively charged polymer) for the detection of urea. The sensor was optimised to detect urea in biofluids such as saliva requiring only 25 µl of analyte.