Multifunctional Fluorescent Nanoprobe for Sequential Detections of Hg²⁺ Ions and Biothiols in Live Cells

Herein, we report an amphiphilic fluorescent probe consisting of a dansyl fluorophore as a reporter and a hydrophobic cetyl chain bridged by a triazole unit. The cetyl-based probe can self-assemble to form nanoaggregates in aqueous solution, as confirmed by Tyndall effect, dynamic light scattering (DLS), and transmission electron microscopy (TEM) measurements. This probe exhibited an "on-off" fluorescence quenching response toward Hg²⁺ ions in aqueous solution over other tested metal ions. In contrast, the analogous methyl-based probe barely exhibits Hg²⁺ ion sensing behavior under the same conditions. Moreover, the resulting complex of the cetyl-based probe and Hg²⁺ (1-Hg²⁺, 1:1 stoichiometry) exhibited an efficient fluorescence "off-on" sensing for thiol-containing amino acids, including cysteine (Cys), homocysteine (Hcy), and glutathione (GSH). This nanoprobe exhibited minimal cytotoxicity with excellent cell permeability and was efficiently tested for the imaging of intracellular Hg²⁺ and cysteine in live cells.