Silver-Based Supramolecular Hydrogel for the Development of Smartphone-Enabled Alkaline Phosphatase Sensor

Alkaline phosphatase (ALP) is an important protein responsible for various conditions related to hepatobiliary, osteopenia, pregnancy, and certain cancers. Developing an easy-to-use paper-based sensor for ALP would provide a point-of-care diagnostic device. A silver-coordinated cytidine hydrogel is a potential candidate to show responses under different concentrations of ALP. Herein, we prepared and characterized a three-component hydrogel system comprising cytidine, boric acid, and silver nitrate. The gelation occurs rapidly within a minute at room temperature and atmospheric pressure, which makes the system more convenient to use. Reduction of Ag+ by the in situ generated ascorbic acid by ALP allows the development of colorimetric sensor based on the gel-coated paper, enabling quantification of ALP concentration. This portable sensor works efficiently on a smartphone color-scanning app, making point-of-care detection easier. RGB values obtained from scanning indicate the ALP concentration in the range of 1-100 nM, which is independent of mobile cameras. The hydrogel exhibits excellent solvo-reversibility and enables naked-eye colorimetric detection of ALP with a detection limit of 0.23 nM (0.016 U/L). The sensing strategy works well in spiked human serum with a detection limit of 0.34 nM (0.023 U/L) in solution and paper-based sensors. Overall, the cytidine-based gel system presents an effective point-of-care diagnostic system for detecting ALP with high sensitivity.