A large-Stokes-shift fluorescent probe for Zn²⁺ based on AIE, and application in live cell imaging

A fluorescence-enhanced sensor based on aggregation-induced emission (AIE) was synthesized using a di(2-picolyl)amine (DPA) group as a highly selective metal chelating agent for Zn²⁺. The combination of the probe and Zn²⁺ was achieved in an environment where the volume fraction of water was 90%, giving the probe good biocompatibility, and a large Stokes shift (100 nm) occurred after Zn²⁺ was combined with the probe. The obvious color change makes the probe visible to the naked eye, and gives it a high signal-to-noise ratio, and high contrast, and minimizes self-absorption. Because of the high selectivity of the DPA group to Zn²⁺, the sensitivity of the probe to detect Zn²⁺ has been improved. The mechanism of the formation of complexes between the probe and Zn²⁺ was confirmed by nuclear magnetic resonance spectroscopy (NMR), high-resolution mass spectrometry (HRMS), and particle size distribution. Under the optimal experimental conditions, the linear fluorescence reaction of Zn²⁺ was good, between 0.2 and 18 μM, and the detection limit was 1.3 × 10^-7 M. The low toxicity and excellent membrane permeability of the probe in living cells enable it to be efficiently applied for Zn²⁺ imaging in cells. Graphical abstract.