A ratiometric fluorescence probe for imaging sulfur dioxide derivatives in the mitochondria of living cells

Abstract

Although sulfur dioxide (SO₂) plays an essential role in several physiological processes, monitoring of intracellular SO₂ at subcellular levels remains challenging due to the lack of rapid and sensitive methods for its quantification in a 100% aqueous solution. Herein, a new hemicyanine dyes-based fluorescence probe, NBD-Id, was designed and synthesized for the detection of SO₂ derivatives in pure aqueous solution and living cells. By virtue of a specific 1,4-addition reaction of SO₃²⁻HSO₃⁻ and the polymethine chain of hemicyanine, significant changes in the absorption and fluorescence emission spectra were observed in less than 20 seconds. The ratiometric fluorescence (F₄₆₇/F₅₉₃) detection of SO₂ derivatives was then obtained with high sensitivity (detection limit 3.6 nM). It was noted that NBD-Id has a specific response towards SO₂ derivatives without interference from other anions and biomolecules. Intracellular fluorescence imaging indicated that NBD-Id is cell membrane permeable and mainly distributed within the mitochondria. Therefore, ratiometric fluorescence imaging of SO₂ derivatives in the mitochondria of MCF-7 cells was successfully demonstrated.