A bis-hydrazone Schiff base chemosensor for highly selective and sensitive colorimetric and fluorometric detection of nitrite for environmental, biological, and food sample applications

. The proposed sensing mechanism involves hydrogen-bond-assisted host-guest adduct formation, which enhances intramolecular charge transfer (ICT) and hydrogen-bond-induced fluorescence enhancement, leading to pronounced optical responses. Furthermore, the sensor demonstrated excellent analytical performance in spiked water and food samples as well as a real sample spinach extract affording good recoveries, confirming its reliability for practical nitrite determination. In addition, the probe L showed promising applications in bovine serum albumin (BSA) recognition, azithromycin detection, and the development of a reversible molecular logic gate, demonstrating its multifunctional sensing capability.