Design and development of an azo dye‐based ultra‐sensitive chemosensor for the ubiquitous organic anion in aqueous solutions

Oxalate plays a crucial role in various biological and industrial applications. Its involvement in diseases, drug‐ and toxin‐induced disorders, and disruption of industrial processes makes it a high‐priority chemical for the development of more precise, selective, and straightforward analytical methods. Herein, an innovative and efficient strategy for sequentially measuring Cu 2+ and oxalate ions is reported. During an indicator displacement process, where Cu 2+ and azo dye, ArsenazoIII (AAIII), are used as receiver and indicator, respectively, oxalate (C 2 O 4 2− ) is measured by a colorimetric method. Proof of concept results from UV–visible spectroscopy, naked eye, and signal reset of the indicator revealed a more robust interaction of the Cu 2+ receptor with C 2 O 4 2− than the AAIII indicator with high selectivity, good sensitivity, and lower detection limit(4.01 × 10 −8 and 3.04 × 10 −9 mol L −1 , for Cu 2+ and C 2 O 4 2− , respectively). The results of measuring C 2 O 4 2− in actual samples (urine, mushrooms, and spinach) showed the applicability of the existing method. Most importantly, the colorimetric system based on molecular exchange in the indicator dislocation proceeding can serve as a colorimetric INHIBIT logic‐gate. It works like a molecular keypad lock system that can be controlled by two users with two different sets of chemical passwords (inputs) that can be identified through optical paths.