A FRET-based ratiometric fluorescent probe for highly selective detection of hydrogen polysulfides based on a coumarin-rhodol derivative.

In modern biology, hydrogen polysulfides (H2Sn, n > 1) are members of reactive sulfur species (RSS), with anti-oxidation, cell protection and redox signals in tissues and organs. Therefore, it is crucial to develop a method to monitor the changes of H2Sn level in organisms. We designed and synthesized a ratiometric fluorescent probe for highly selective detection of H2Sn based on the fluorescence resonance energy transfer (FRET) process. In this work, a coumarin derivative was chosen as an energy donor, a rhodol derivative was used as an energy acceptor and a 2-fluoro-5-nitrobenzoate group was applied as a recognition unit for H2Sn. In the absence of H2Sn, the rhodol receptor existed in the non-fluorescent spirolactone state and FRET process was disabled. In the presence of H2Sn, the closed spirolactone form was converted to a conjugated fluorescent xanthenes form to invoke the occurrence of FRET which resulted in a 77 nm red-shift of fluorescence emission from 460 nm to 537 nm. The ratio value of the fluorescence intensity between 537 nm and 460 nm (I537nm/I460nm) of the probe exhibited a good linear relationship toward H2Sn in the range of 3.0 × 10-6-1.0 × 10-4 mol·L-1, and the detection limit was estimated to be 8.0 × 10-7 mol·L-1. In addition, the ratiometric fluorescent probe showed high specificity for H2Sn over other biologically related species. Moreover, the probe displayed little cell toxicity and had been successfully used to the confocal imaging of H2Sn in HepG2 cells by dual emission channels.