A dual-mode fluorescence "turn-on" biosensor based on an aggregation-induced emission luminogen.

A novel dual-mode fluorescence "turn-on" probe is developed based on a phosphorylated tetraphenylethene (TPE) derivative bearing aggregation-induced emission (AIE) characteristics. The probe is weakly emissive in aqueous solution but its fluorescence is significantly enhanced in the presence of protamine or alkaline phosphatase (ALP). The cationic protamine interacted with the anionic phosphate group of the amphiphilic probe via electrostatic interaction and induced micelle formation. This micelle aggregates the hydrophobic TPE core and results in fluorescence enhancement. The detection limit for the protamine assay reached as low as 12 ng mL-1. On the other hand, ALP hydrolysed the fluorescent probe and led to self-aggregation of insoluble fluorescent residues. The linear light-up response of the probe enables ALP quantification in the range of 10-200 mU mL-1, which covers the physiological level of ALP activity in human serum. Moreover, the two activation modes could be differentiated by distinct responses to protamine and ALP.