Water-soluble TREN-amino-1,8-naphthalimide fluorescent probes for selective, reversible Cu(II) detection and live-cell imaging.

Two water-soluble amino-1,8-naphthalimide-based fluorophores, TREN-Nap-1 and TREN-Nap-2, incorporating a tris(2-aminoethyl)amine (TREN) receptor unit, were synthesized through a straightforward single-step protocol and investigated as selective fluorescent chemosensors with high sensitivity for Cu(II) ions in aqueous media. Both probes exhibit strong intrinsic fluorescence that is significantly quenched upon coordination to Cu(II) and display negligible interference from competing metal ions. The sensing process is rapid (response time < 2 min) and highly sensitive, affording detection limits in the nanomolar range. The practical utility of these sensors was validated by the successful detection of Cu(II) in real water samples, including pond and tap water. In addition, cytotoxicity assessments using human MDA-MB-231 (triple-negative breast cancer) and L929 (mouse fibroblast) cell lines confirmed their good biocompatibility. Furthermore, both probes demonstrated efficient intracellular fluorescence imaging of Cu(II) ions in these cell lines, highlighting their potential for biological applications.