A logic gate-based fluorogenic probe for Hg2+ detection and its applications in cellular imaging

A new colorimetric and fluorogenic probe (RN3) based on rhodamine-B has been successfully designed and synthesized. It displays a selective response to Hg2+ in the aqueous buffer solution over the other competing metals. Upon addition of Hg2+, the solution of RN3 exhibits a 'naked eye' observable color change from colorless to red and an intensive fluorescence with about 105-fold enhancement. The changes in the color and fluorescence are ascribed to the ring-opening of spirolactam in rhodamine fluorophore, which is induced by a binding of the constructed receptor to Hg2+ with the association and dissociation constants of 0.22 x 10(5) M-1 and 25.2 mM, respectively. The Job's plot experiment determines a 1: 1 binding stoichiometry between RN3 and Hg2+. The resultant turn-on fluorescence in buffer solution, allows the application of a method to determine Hg2+ levels in the range of 4.0-15.0 mu M, with the limit of detection (LOD) calculated at 60.7 nM (3 sigma/slope). In addition, the fluorescence 'turn-off' and color 'fading-out' happen to the mixture of RN3-Hg2+ by further addition of I- or S2-. The reversible switching cycles of fluorescence intensity upon alternate additions of Hg2+ and S2- demonstrate that RN3 can perform as an INHIBIT logic gate. Furthermore, the potential of RN3 as a fluorescent probe has been demonstrated for cellular imaging. (C) 2016 Elsevier B.V. All rights reserved.