跨键能量转移（TBET）用于构建高效比率型荧光探针

FRET strategy has been widely applied in designing ratiometric probes for bio-imaging applications. Unfortunately, for FRET systems, sufficiently large spectral overlap is necessary between the donor emission and the acceptor absorption, which would limit the resolution of double-channel images. Through-bond energy transfer (TBET) system does not need spectral overlap between donor and acceptor, and could afford large wavelength difference between the two emissions with improved imaging resolution and higher energy transfer efficiency than that of classic FRET system. It seems to be more favorable for designing ratiometric probes for bio-imaging applications. In this paper, we have designed and synthesized a coumarin-rhodamine (CR) TBET system, and demonstrated that TBET is a convenient strategy to design efficient ratiometric fluorescent bio-imaging probe for metal ions. As a proof-of-concept, Hg2+ was chosen as a model metal ion. By combining TBET strategy with dual-switch design, the proposed sensing platform shows two well-separated emission peaks with a wavelength difference of 110 nm, high energy transfer efficiency and a large signal-to-background ratio, which affords a high sensitivity for the probe with a detection limit of 7 nM for Hg2+. Moreover, by employing an Hg2+-promoted desulfurization reaction as recognition unit, the probe also shows a high selectivity to Hg2+. It has been preliminarily used for ratiometric image of Hg2+ in living cells and practical detection of Hg2+ in river water samples with satisfying results.