A ratiometric fluorescent probe based on a positively charged benzo[e]indolium moiety for bisulfite is reported. The bisulfite underwent a 1,4-addition reaction with the C-4 atom in the ethylene group. This reaction resulted in a large emission wavelength shift (Δλ = 106 nm) and an observable fluorescent color change from orange to cyan. The reaction could be completed in 90 s in a PBS buffer solution and displayed high selectivity and sensitivity for bisulfite. A simple paper test strip system was developed to detect bisulfite rapidly. Probe 1 was used to detect bisulfite in real samples with good recovery.

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A highly selective fluorescent turn-on probe for CN(-) bearing a benzo [e] indolium group as a fluorophore and binding site was reported. The detection of CN(-) was performed via the nucleophilic attack of CN(-) toward the benzo [e] indolium group of the probe, resulting in a prominent fluorescence enhancement and an obvious color change. The probe shown a highly selectivity in water and could be performed in a range of pH value between 6 and 9. The detection limit was 4.6 × 10(-8) M, which could be detected CN(-) in drinking water. A simple paper test strip system for the rapid monitoring of CN(-) was developed.