An Easy Detection of Sulfide by an Imine-Bond Cleavage-Based Fluorescence Chemosensor: Smartphone and Paper-Strip Applications

We designed an imine-bond cleavage-based fluorescent chemosensor CDH ((E)-(5-chloro-2-((3,5-dichloro-2-hydroxybenzylidene)amino)phenyl)(phenyl)methanone) for detecting S²⁻. The sensor CDH selectively sensed S²⁻ among various anions through fluorescent change. The fluorescent change was cyan turn-on from colorless with a high quantum yield (λ_ex = 427 nm, Φ = 0.486), resulting in strong fluorescent intensity. With the result of Job plot, the reaction of S²⁻ and CDH turned out to be a 1:1 interaction. The detection limit for S²⁻ of CDH was 2.85 µM. The reaction process of S²⁻ by CDH was demonstrated to be imine-bond cleavage through ESI-mass, ¹H NMR titration, and theoretical calculations. Additionally, test-strip and smartphone applications were successfully constructed for S²⁻ detection, and these findings revealed that CDH could be effectively utilized for sulfide sensing without sophisticated instruments.