A novel fluorescent probe with high sensitivity for sequential detection of CN− and Al3+ in highly aqueous medium and its applications in living cell bioimaging

Benzothiazole refers to a type of heteroaromatic compound constituted by electron rich nitrogen and sulphur atoms from molecular level, and presents powerful fluorescence in solutions, resulting its widely application in fluorescent whitening agents, fluorescent dyes and functional coordination. In this paper, we focused on designing and synthesizing a benzothiazole-functionalized naphthalimide fluorescent probe NIB for sequentially detecting CN− and Al3+ in DMSO/H2O (1:9, v/v) solution using these fluorescence properties of benzothiazole. When the fluorescent probe NIB interacts with CN−, the fluorescence of the probe is quenched, indicating that NIB can specifically respond to CN−. According to the anti-interference experiment, NIB possesses strong anti-interference ability toward CN−, and its detection limit of CN− is 6.31 × 10−7 M. Interestingly, the fluorescence of the NIB-CN− system was turned back on again by adding Al3+ ions which has good anti-interference performance against other cations. The lowest detection limit of NIB-CN− system for Al3+ is 2.85 × 10−6 M. After 10 cycles, NIB still has good sequential detection performance for CN− and Al3+, which can serve as a highly sensitive logic gate for the detection of CN− and Al3+, and the “On-Off-On” switches of this fluorescence can be observed under UV light megascopically. The mechanism of sequential detection of CN− and Al3+ was further discussed by experimental and theoretical methods. The detection mechanism is not the traditional coordination competition mechanism, but the sequential addition of CN− and Al3+ changes the aggregation mode of probe molecules in the system. In addition, the potential application of this probe was fully confirmed by the preparation of probe NIB test paper and the realization of sequential detection of CN− and Al3+ in living cells (HeLa).