Rhodamine derivatives as selective“naked-eye” colorimetric and fluorescence off-on sensor for Hg2+ in aqueous solution and its applications in bioimaging

Abstract

Three new rhodamine based probes 1, 2, 3 were synthesized and acted as fluorescence probes for Hg2+ detection in Tris - HCl/C2H5OH (v: v = 3: 7, 10 mM, pH = 7.2). Hg2+ induced a colorless solution of probes 1, 2, 3 to turn to naked-eye visible pink with a 44 - fold fluorescence enhancement at 576 nm. Probes 1, 2, 3 are highly selective to Hg2+ over other tested cations with the detection limits are 18 nM, 16 nM, 56 nM, respectively. What's more, the binding constants between probes 1, 2, 3 and Hg2+ are 5.0 × 106 M−1, 1.8 × 106 M−1, 1.5 × 106 M−1, respectively. The different detection limits and binding constants of probes 1, 2, 3 and Hg2+ may depend on the coordination of probes 1, 2, 3. The recognition mechanism of probes 1, 2, 3 towards Hg2+ is determinated by ESI - MS, DFT and indicates that a ring-opening of the spirolactam unit and formed complexes between probes 1, 2, 3, resulting in chromogenic and fluorogenic changes. The probes 1, 2, 3 could be applied in both environmental and Hg2+ polluted samples due to the instantly and reversible ‘‘off-on’’ Hg2+ response, well cell permeability, cell imaging ability.