A novel double target fluorescence probe for Al3+/Mg2+ detection with distinctively different responses and its applications in cell imaging.

The metal cations, Al3+ and Mg2+, could affect human health and cell biological processes. Their fast and selective detection using one probe remains a challenge. A novel fluorescence probe, N'-((1-hydroxynaphthalen-2-yl)methylene)isoquinoline-3-carbohydrazide (NHMI), was developed for selectively monitoring Al3+ and Mg2+. The probe NHMI showed a distinctive "turn-on" fluorescence signal towards Al3+ and Mg2+ (cyan for Al3+ with 2556-folds enhancement and yellow for Mg2+ with 88-folds enhancement), which is quite distinct from other metal cations and allows for naked-eye detection. This interesting response was attributed to the influence of PET, ESIPT process and CHEF effect, when Al3+ or Mg2+ chelated with NHMI. Furthermore, the fluorescence titration experiments manifested that the detection limit of probe NHMI for Al3+/Mg2+ was as low as 1.20 × 10-8 M and 7.69 × 10-8 M, respectively. The formed complexes NHMI-Al3+ and NHMI-Mg2+ were analyzed by Job's plot, ESI-MS, 1H NMR and FT-IR. The coordination pockets and fluorescence mechanisms of two metal complexes were explored by density functional theory calculation. Moreover, NHMI showed low cytotoxicity and good cell permeability. Fluorescence bioimaging of Al3+/Mg2+ in MCF-7 cells with NHMI indicated its potential application in biological diagnostic analysis.