Win–Win Integration Strategy to Construct Multifunctional Fluorescence Hydrogels for On-Site Monitoring of Food Freshness Via Nucleophilic Substitution

Abstract Fluorescence hydrogels have become attractive candidates for monitoring food freshness; however, the ability to improve anti-interference, broaden the color variation range, and introduce multifunctionality remains limited. Here, an ingenious fluorescence hydrogel design strategy for monitoring food freshness is proposed via integrating an OH–-responsive dye into functional matrices. By adjusting the intermolecular charge transfer and π–π stacking effect, nitrobenzoxadiazaole-based dye BOD-R1 was prepared and responded to biogenic amines via nucleophilic substitution. Embedding BOD-R1 in benzene-1,4-diboronic acid, poly(vinyl alcohol) (PVA), agarose (AG), and carboxymethyl cellulose (CMC) produced hydrogel R1@BAPC, which exhibited antifreezing ability, self-repairing function, high adhesion, and interface self-adaptability. Notably, the fluorescence color of R1@BAPC progressively changed from blue to yellow, as the amount of target putrescine (Put) increased, and then extracted into RGB values, in which G/B acted as the quantitative output. The hydrogel achieved a limit of detection (LOD) of 0.26 ppm for Put and completed detection within 85 s. Real sample analyses with shrimp, chicken, and pork suggested that the test results aligned well with those of the standard method, supporting excellent practical usability. The BOD-R1/BAPC design not only provides a distinct route for the synthesis of multifunctional hydrogels but also provides a portable platform for monitoring food freshness, with potential benefits for healthy food supply.