A Cobalt Coordination Polymer Enabling Ratiometric Detection of Al ³⁺ and Fluorescence Quenching of Nitroimidazole Antibiotics with Logic Gate Integration and Portable Hydrogel Sensing

Fluorescent sensing platforms capable of reporting both heavy-metal ions and antibiotic residues are valuable for environmental analysis and food-safety surveillance. Here, a cobalt-based coordination polymer, {[Co(SBDC)(L1)]·2H 2 O} n ( 1 ), was assembled from 4,4′-stilbenedicarboxylic acid (H 2 SBDC) and 1,1′-((2,4,6–trimethyl-1,3-phenylene)bis(methylene))bis(2-methyl-1 H -imidazole) (L1). Upon a specific interaction with Al 3+, complex 1 exhibits a large Stokes shift of approximately 145 nm between the UV absorption and fluorescence emission, enabling ratiometric recognition of Al 3+ based on an emission red-shift feature. In terms of analytical performance, complex 1 provides selective and sensitive ratiometric output for Al 3+, while dimetridazole (DTZ), metronidazole (MDZ), and ornidazole (ODZ) are effectively identified via fluorescence quenching with similarly high selectivity and responsiveness. The limits of detection (LODs) for Al 3+, DTZ, MDZ, and ODZ are 0.266, 0.657, 0.356, and 0.0738 μM, respectively. Validation using rice as a model sample further supports its applicability, where Al 3+ contamination produces discernible fluorescence differences under UV light. Moreover, by employing Al 3+ and nitroimidazole antibiotics as two independent inputs, the distinct fluorescence responses of complex 1 enable the construction of a three-output combinatorial logic gate that generates unique output codes for different chemical states. Complex 1 was also immobilized in an agarose hydrogel to fabricate a flexible and portable sensing chip, allowing direct visual readout and smartphone-assisted quantification. Overall, this work integrates molecular recognition with device-level implementation, offering a visualization-oriented material basis and a practical route for instrument-light monitoring in food-safety and environmental contexts.