Synthesis of quinoline-based fluorescence probe for Zn(II) sensing and its applications in anti-counterfeiting ink and imaging in plants and living cells

Zn(II) plays a crucial role in various biological processes. Notably, its homeostatic imbalance has been linked to the pathogenesis of neurodegenerative disorders and metabolic syndromes. Therefore, it is important to develop fluorescent probes for detecting Zn2+ in environmental and biological systems. In this study, a quinoline-based fluorescent probe (QP2) was synthesized by combining a qa-active 8-hydroxyquinoline moiety with a rotatable pyridine amine group via the -CH=N unit. In a dimethyl sulfoxide (DMSO)/H2O (fw = 95%) solution, QP2 exhibited turn-on fluorescence, selectively detecting Zn2+ among a wide variety of competing metal ions. Detailed experiments and theoretical calculations confirmed that the response mechanism was related to the formation of a 2:1 rigid hydrophobic complex between QP2 and Zn2+, which inhibited the excited-state intramolecular proton transfer (ESIPT) process. Notably, the QP2-Zn2+ complex had an X-shaped spatial structure, which was formed via π-π stacking between the adjacent quinoline ring and the pyridine ring, resulting in aggregation-induced emission (AIE). Probe QP2 detected Zn2+ with excellent selectivity and rapid response over a broad pH range. Moreover, it exhibited a low detection limit (17.7 nM). Furthermore, an anti-counterfeiting ink and portable test strips were prepared using QP2 and used to detect Zn2+, on the basis of the formation of AIE-active Zn(II) complex. Additionally, QP2 was successfully used in the fluorescence imaging of Zn2+ in plants and HepG2 cells. This study demonstrates the design of a probe based on a complex exhibiting AIE and ESIPT mechanisms.