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

Abstract

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 × 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 × 10−7 M and 8.8 × 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.