Detection of alkaline phosphatase via a paper-based flow sensor constructed by cytidine-H3BO3 supramolecular hydrogels

Alkaline phosphatase (ALP) is a critical biomarker for blood-related diseases, with significant implications in the fields of medicine and biological research; hence, precise detection of ALP is indispensable. Herein, we report the development of a novel paper-based flow sensor for detecting ALP by utilizing Ag⁺ as a cross-linking agent to create cytidine-boric acid (H₃BO₃) supramolecular hydrogels that immobilize water within the gel matrix. Upon introduction of l-ascorbic acid-2-phosphate (AAP), ALP specifically catalyzes the hydrolysis of AAP to ascorbic acid (AA), triggering the reduction of Ag⁺ to Ag⁰. This reaction disrupts the hydrogel system, enabling water to flow along the pH indicator strip. The quantification of both the coverage area of water flow on the pH indicator strip and the volume of the upper aqueous solution after centrifugation enables for the execution of an ALP assay. Notably, this method employing pH indicator strips eliminates the need for complex equipment, achieves a low detection threshold as low as 3.1 mU/mL, and exhibits high specificity levels. Furthermore, the method's applicability has been validated through the effective detection of ALP in serum samples. To summarize, this approach presents a straightforward, cost-effective, and user-friendly system for ALP detection without requiring sophisticated sensors or costly equipment and it holds significant promise for future uses.