Fluorescence "turn-on" sensor for highly selective recognition of Cu2+ ion and its application to living cell imaging

A new, bis-thiophene based Schiff base receptor A2 has been synthesized and rationally designed as rapid and highly selective fluorescence sensor for Cu2+ ion in a semi-aqueous medium. Structural characterization of A2 was confirmed by NMR, FT-IR and HRMS spectral techniques. The receptor A2 shows the colorimetric response from yellow to colorless and fluorescence "turn-on" with Cu2+ ions under visible and UV light. Both the UV-Vis and fluorescence studies were confirmed the formation of 1:1 stoichiometry complex with an estimated association constant of 1.07 x 10(-5) M-1. The sensor could work in the pH range of 4.0-8.0 without interference in the presence of other interfering ions. The lowest detection limits by colorimetric and fluorescence techniques were found to be 1.18 x 10(-7 )M and 8.8 x 10(-8) M respectively. Further, the probe was applied to image the intracellular Cu2+ ions in the HeLa cell line. The sensing mechanism was studied by ESI-mass analysis and DFT calculations.