Two water-soluble two-photon fluorescence probes for ratiometric imaging endogenous SO2 derivatives in mitochondria

Rational and convenient design water-soluble two-photon excited fluorescence (TPEF) probes for monitoring SO2 derivatives with specificity at subcellular level remain a challenge. Herein, two low molecular weight, ratiometric fluorescence probes, bearing alpha, beta-unsaturated benzoindolium moiety (EIM and EIS), are designed for monitoring endogenously SO2 derivatives in mitochondria using two-photon microscopy (TPM). The two probes not only showed >100 nm blue-shift emission with two well-resolved bands upon addition of HSO3-/SO32-, but also displayed rapid response, high selectivity and sensitivity for monitoring and quantifying HSO3-/SO32- over other species in living cells. Further studies indicated that probes EIM and EIS can highly discern HSO3-/SO32- with two different nucleophilic addition mechanisms, respectively, just by structural fine-tuning, which were confirmed by both theoretical calculation and experimental technique. It is suggested that probes EIM/EIS with two-photon absorption property in the NIR region, large Stocks shift, high selectivity and signal ratio, are promising molecular tool for bisulfite/sulfite biology. (C) 2017 Published by Elsevier B.V.