An A–π–A′ structural ratiometric fluorescent probe 1 bearing a benzo[e]indolium moiety was developed for the detection of HSO3− in PBS buffer solution. HSO3− was expected to react with probe 1 via a Michael addition reaction, causing dramatic changes in its emission spectrum (from 578 nm to 466 nm) and an obvious color change from orange red to blue which could be observed by the naked eye. The reaction could be complete in 30 seconds in the sensing system, and displayed a high selectivity and sensitivity for HSO3− with a detection limit of 15 nM. The practical value of the probe was confirmed for application to detect the level of HSO3− in sugar samples with good recovery and in living cells.

A turn-on fluorescent probe based on terthienyl for CN− has been constructed and CN− was detected by taking advantage of aggregation-induced emission (AIE) behavior of terthienyl units in aqueous solutions. The probe displayed a high selectivity and sensitivity for CN− against other analytes, and the detection limit was measured to be 0.1 μM. The aggregation behavior confirmed by DLS and SEM caused fluorescence enhancement in the sensing environment. A simple paper test strip system for the rapid monitoring of CN− was developed. Moreover, the probe could be employed to detect CN− in biological samples.

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.

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.

A new ratiometric fluorescent cyanide probe bearing a benzo [e] indolium moiety as a fluorophore and binding site was developed. The detection of cyanide was performed via the nucleophilic attack of cyanide toward the benzo [e] indolium group of the probe, resulting in a prominent fluorescence ratiometric change and a color change. The probe was invested in water with high selectivity and sensitivity for cyanide. A simple paper test strip system for the rapid monitoring of cyanide was developed.