Analytical methods for detecting neurotransmitters (NTs) and organophosphorus (OP) pesticides with high sensitivity are vitally necessary for the rapid identification of physical, mental, and neurological illnesses, as well as to ensure food safety and safeguard ecosystems. In this work, we developed a supramolecular self-assembled system (SupraZyme) that exhibits multi-enzymatic activity. SupraZyme possesses the ability to show both oxidase and peroxidase-like activity, which has been employed for biosensing. The peroxidase-like activity was used for the detection of catecholamine NTs, epinephrine (EP), and norepinephrine (NE) with a detection limit of 6.3 µM and 1.8 µM, respectively, while the oxidase-like activity was utilized for the detection of organophosphate pesticides. The detection strategy for OP chemicals was based on the inhibition of acetylcholine esterase (AChE) activity: a key enzyme that is responsible for the hydrolysis of acetylthiocholine (ATCh). The corresponding limit of detection of paraoxon-methyl (POM) and methamidophos (MAP) was measured to be 0.48 ppb and 15.8 ppb, respectively. Overall, we report an efficient supramolecular system with multiple enzyme-like activities that provide a versatile toolbox for the construction of sensing platforms for the colorimetric point-of-care detection of both NTs and OP pesticides.

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.