AND-logic-gate measurement of bisulfite and viscosity using a dual-lock-and-key fluorescent probe

This study presents an innovative dual-lock-and-key fluorescent probe engineered for the simultaneous detection of bisulfite and viscosity. The functionalized probe, (E)-2-(1-ethyl-2-(N-methylquinolinevinyl)quinolin-4(1H)-ylidene)malononitrile (QC-QNM), was strategically synthesized by conjugating the quinolylmalononitrile and N-melhylquinolinium through an ethylene bridge. Within this construction, the N-methylquinolinium selectively targets bisulfite, while the vinyl moiety serves as a responsive rotor for viscosity. Notably, the presence of either sulfite or viscosity alone cannot elicit significant fluorescent responses from the probe. Conversely, concurrent exposure to both bisulfite and viscosity triggers enhanced fluorescent signals, indicative of an "AND" logic gate characteristic. Quantum chemical calculations were further applied to rationalize the working mechanism of the probe. Additionally, the excellent biocompatibility of this probe in cellular imaging experiments highlights its potential for specific mitochondrial imaging by modulating both exogenous/endogenous bisulfite levels alongside viscosity induced by monensin. This novel approach thereby offers a distinctive analytical tool for monitoring the coexistence of viscosity and bisulfite in specific metabolic and physiological contexts.