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 Hg 2+ detection in Tris - HCl/C 2 H 5 OH ( v : v = 3: 7, 10 mM, pH = 7.2). Hg 2+ 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 Hg 2+ 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 Hg 2+ are 5.0 × 10 6 M −1 , 1.8 × 10 6 M −1 , 1.5 × 10 6 M −1 , respectively. The different detection limits and binding constants of probes 1 , 2 , 3 and Hg 2+ may depend on the coordination of probes 1 , 2 , 3 . The recognition mechanism of probes 1 , 2 , 3 towards Hg 2+ 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 Hg 2+ polluted samples due to the instantly and reversible ‘‘off-on’’ Hg 2+ response, well cell permeability, cell imaging ability.