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By connecting 1,8-naphthalimide and indole sulfonate, a ratio fluorescent probe capable of differential detection of hydrogen sulfite and hypochlorite was synthesized for the first time. It was able to achieve the qualitative detection of HSO3− and ClO− with high sensitivity and selectivity, respectively. It provides a multi-purpose probe and is based on different emission channels without mutual interference. The probe has the advantages of larger Stokes shift (ClO−: 115 nm, HSO3−: 88 nm), longer λem (ClO−: 515 nm, HSO3−: 548 nm) and better water solubility (DMF/PBS = 1:99, v/v). In addition, the probe is a ratio fluorescence probe, which can detect fluorescence intensity with two different emission waves. It provides internal self-calibration, reduces interference from the background and increases detection accuracy. In vitro cytotoxicity and imaging experiments show that the probe can effectively perform the detection of exogenous HSO3− and ClO− in cells. It can also achieve the detection of HSO3− and ClO− in the plasma environment. Because the probe can detect endogenous ClO−, it also has a good prospect for biological application in identifying tumor cells.

Copper is an essential element in living systems and plays an important role in human physiology; therefore, methods to detect the concentration of copper ions in living organisms are important. Herein, we report a highly water-soluble naphthalimide-based fluorescent probe that can be used for the detection of Cu2+. The probe, BNQ, has high selectivity and sensitivity. The fluorescence intensity of the probe at 520 nm was visible to the naked eye under a UV lamp; upon the gradual addition of Cu2+, there was a colour change from green to nearly colourless. Furthermore, the detection limit of BNQ for Cu2+ was 45.5 nM. The detection mechanism was investigated using a Job's plot and density functional theory (DFT) calculations. In addition, owing to great biocompatibility, we were able to successfully use BNQ to detect Cu2+ in living HeLa cells with low toxicity.

A novel highly active fluorescence chemical sensor (TBQN) for HSO3− was synthesized by the Knoevenagel reaction based on triphenylamine–benzothiazole as a new fluorophore. The probe possessed good selectivity toward HSO3− and anti-interference ability with common ions. The fluorescence and UV-vis spectra of the TBQN probe were significantly changed after the addition of HSO3−. At the same time, the probe solution released obvious green fluorescence. Moreover, the limit of detection for HSO3− was calculated to be 3.19 × 10–8 M. The TBQN probe displayed a rapid response to HSO3− and it took about 3 min to complete the recognition. The detection mechanism is the nucleophilic addition reaction between HSO3− and –CC– in the probe molecule. The π-conjugation and ICT (intramolecular charge transfer) transition in the TBQN molecule were destroyed by this addition, which resulted in the change of the fluorescence before and after the addition of HSO3−. Then, the mechanism was verified by theoretical calculations, 1H NMR measurements and mass spectroscopy. In addition, the probe showed low cytotoxicity and could be used for biological imaging in RAW264.7 cells.