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

In modern biology, hydrogen polysulfides (H₂S_n, 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 H₂S_n level in organisms. We designed and synthesized a ratiometric fluorescent probe for highly selective detection of H₂S_n 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 H₂S_n. In the absence of H₂S_n, the rhodol receptor existed in the non-fluorescent spirolactone state and FRET process was disabled. In the presence of H₂S_n, 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 (I_537nm/I_460nm) of the probe exhibited a good linear relationship toward H₂S_n 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 H₂S_n over other biologically related species. Moreover, the probe displayed little cell toxicity and had been successfully used to the confocal imaging of H₂S_n in HepG2 cells by dual emission channels.