Self-assembled super-small AIEgen nanoprobe for highly sensitive and selective detection of protamine and trypsin

Amphiphilic aggregation-induced emission (AIE) molecules show superior potential for fabricating novel ultrasmall nanoprobes. Here, an anionic dipyridyl tetraphenylethene (TPE) derivative is rationally designed and a super-small self-assembled AIEgen nanoprobe (TPE-2Py-SO₃NaNPs, ca. 2.48 nm) is thus conveniently constructed for the supersensitive detection of protamine and trypsin. In HEPES/DMSO solution (8 : 2, v/v, pH = 7.4), negatively charged TPE-2Py-SO₃NaNPs exhibited an AIE effect in the presence of positively charged protamine, presenting a fluorescence enhancement at 498 nm together with a large Stokes shift of 150 nm and a low detection limit of 8.0 ng mL^-1. In addition, the in situ formed TPE-2Py-SO₃Na/protamine nanocomposite can be dissociated by trypsin due to the highly selective degradation of protamine via enzymatic hydrolysis, achieving a detection limit for trypsin as low as 5.0 ng mL^-1.