A FRET ratiometric fluorescence sensing system for mercury detection and intracellular colorimetric imaging in live Hela cells.

The detection of mercury in biological systems and its imaging is of highly importance. In this work, a ratiometric fluorescence sensor is developed based on fluorescence resonance energy transfer (FRET) with N-acetyl-L-cysteine functionalized quantum dots (NAC-QDs) as donor and Rhodamine 6G derivative-mercury conjugate (R6G-D-Hg) as acceptor. Mercury annihilates the fluorescence of NAC-QDs at 508 nm and meanwhile interacts with R6G derivative to form a fluorescent conjugate giving rise to emission at 554 nm. Resonance energy transfer from NAC-QDs to R6G-D-Hg is triggered by mercury resulting in concentration-dependent variation of fluorescence ratio F508/F554. A linear calibration of F508/F554 versus mercury concentration is obtained within 5-250 μg L(-1), along with a detection limit of 0.75 μg L(-1) and a RSD of 3.2% (175 μg L(-1)). The sensor generates colorimetric images for mercury within 0-250 μg L(-1), facilitating visual detection of mercury with a distinguishing ability of 50 μg L(-1). This feature is further demonstrated by colorimetric imaging of intracellular mercury. On the other hand, the NAC-QDs/R6G-D FRET sensing system is characterized by a combination of high sensitivity and selectivity. The present study provides an approach for further development of ratiometric sensors dedicated to selective in vitro or in vivo sensing some species of biologically interest.