A fluorescent τ-probe: quantitative imaging of ultra-trace endogenous hydrogen polysulfide in cells and in vivo

Hydrogen sulfide (H(2)S) has been recognized as an important endogenous gasotransmitter associated with biological signaling transduction. However, recent biological studies implied that the H(2)S-related cellular signaling might actually be mediated by hydrogen polysulfides (H(2)S(n), n > 1), not H(2)S itself. Unraveling such a mystery strongly demanded the quantification of endogenous H(2)S(n) in living systems. However, endogenous H(2)S(n) has been undetectable thus far, due to its extremely low concentration within cells. Herein, we demonstrated a strategy to detect ultra-trace endogenous H(2)S(n)via a fluorescent τ-probe, through changes of fluorescence lifetime instead of fluorescence intensity. This τ-probe exhibited an ultrasensitive response to H(2)S(n), bringing about the lowest value of the detection limit (2 nM) and a lower limit of quantification (10 nM) to date. With such merits, we quantified and mapped endogenous H(2)S(n) within cells and zebrafish. The quantitative information about endogenous H(2)S(n) in cells and in vivo may have a significant implication for future research on the role of H(2)S(n) in biology. The methodology of the τ-probe established here might provide a general insight into the design and application of any fluorescent probes, beyond the limit of utilizing fluorescence intensity.