Quantitative recognition and ratiometric cell imaging of HSO3− inspired of confined-space based FRET system within human serum albumin

A ratiometric fluorescent probe for HSO3− was assembled using a pair of Förster resonance energy transfer (FRET)-matchable fluorescent dyes within a single human serum albumin (HSA). In this work, the micro-environment-sensitive dyes B1 and HE were designed and synthesized, wherein B1 located in site II as the FRET donor while HE located in site I as the FRET acceptor and receptor for HSO3−. This B1−HE FRET system exhibited a good efficiency in the sensitive, selective, and ratiometric recognition of HSO3− with a detection limit of 99 nM in aqueous media. Furthermore, this B1−HE system could realize the ratiometric imaging of HSO3− in human breast cancer cells.