A pH responsive AIE probe for enzyme assays.

By combining leucine (Leu) and tetraphenylethene (TPE), a pH-sensitive aggregation induced emission (AIE) probe TPE-Leu was developed. The aliphatic amine in TPE-Leu was more easily protonated under acidic conditions, which made TPE-Leu more water soluble. Therefore, the protonated AIE probe showed weak fluorescence under acidic conditions. When the pH was changed to basic conditions, it showed strong fluorescence due to the hydrophobic nature of TPE-Leu. We demonstrated that the probe showed high selectivity toward pH changes with the coexistence of other potential species such as metal ions, redox agents, and biomolecules. In contrast, TPE-NH2 did not exhibit obvious pH-sensitive properties. Moreover, TPE-Leu was further utilized to develop a sensitive and selective sensing platform for urease and acetylcholinesterase (AChE) detection. The current study not only provides a new strategy for designing pH-sensitive fluorescent probes for bioassays but also broadens the applications of AIE probes.