Application of AIE-active probes in fluorescence sensing

Fluorescent probes that exhibit distinct advantages of high sensitivity, good selectivity, fast response speed, etc., have been widely applied in diverse sensing areas. However, the fluorescence of traditional organic probes tends to decrease or be quenched at high concentration or in aggregate state due to the aggregation-caused quenching (ACQ) effect, which limits their application in sensing areas. In 2001, our group coined the concept of aggregation-induced luminescence (AIE), which is exactly opposite to the ACQ effect and refers to a unique phenomenon that a kind of non- or weakly emissive luminogens in dilute solutions are induced to emit intensely upon aggregation or in solid state. Thus, the AIE-active luminogens (AIEgens) provide an alternative to solve this difficulty. Thanks to their intrinsic advantages, the fluorescent sensors based on AIEgens show lower background, higher signal-to-noise ratio and more outstanding resistance to photobleaching etc. Moroever, the AIE probes not only could overcome the problem encountered by ACQ ones, but also achieve faster and more sensitive detection of the targets. Thus, using AIE probes to detect a wide varity of targets is one of the hot research areas. To highlight the progress in this area, herein, we briefly summarize the sensing applications of AIEgens. First, we introduced the AIE probes used in the detection of ions, including K+, Hg2+, Fe3+, CN−, ClO−, PO43−, etc. Notably, the fluorescent probes based on AIEgen could realize the selective detection of various ions not only in the organic solutions, but also in aqueous solutions. Next, we discussed the detection of low mass molecules using AIE probes for they play a very important role in life activities and their content can reflect the health status and life information of an organism. The used low mass molecules include gas (NH3, CO2, H2S), explosive (PA, TNT), biothiol (Gys, GSH), and ATP and so on. Third, we summarized the qualitative and quantitative sensing of biomacromolecules, such as DNA, proteins, enzyme, by AIE probes, which is critical to the life sciences, biotechnology, and pharmaceutical industries. Fourth, the application of AIE probes in the fields like pH response, cell membrane imaging, mitochondrial imaging and fungal detection are reviewed. Finally, the prospects for the design and application of AIE probes are presented. We hope that this review will stimulate interests in AIE-based sensors and provide some new ideas for researchers working in this area.