The excessive sulfur dioxide and bisulfites in the environment can not only cause aquatic and terrestrial ecosystems damage like acid rain, but also impact the respiratory system of human and even cause severe adverse effects and acute symptoms. In biosystems, bisulfite and sulfur dioxide can be endogenously generated through the oxidation of intracellular hydrogen sulfide or sulfur containing amino acids. Pathological studies report that the concentrations of bisulfites would rise significantly in pneumonia and chronic renal failure patients. Therefore, it is of great importance to develop a selective and sensitive fluorescent probe for the detection of sulfur dioxide and its derivatives bisulfite in the point view of environmental protection, food safety and some related diseases study.

To develop an analytical method to quickly and selectively monitor the SO₂/ROS redox cycle and visual detection of environmental sulfur dioxide, a study team led by Prof. WANG Suhua in Institute of Intelligent Machines (IIM), Hefei Institutes of Physical Science, designed and synthesized a reversible and ratiometric fluorescent probe HBT-Cy for bisulfites.

In aqueous solution, the probe can react with bisulfites through nucleophilic addition and lead to the fluorescence color changes from rose red to blue, which can be clearly observed under a 365 nm UV lamp. Upon treatment with hydrogen peroxide, the original probe HBT-Cy can be restored, causing a turn-on of the red fluorescence. The reversible reduction-oxidation cycle can be repeated and maintains the reactivity and spectral properties.

The cell imaging experiments suggest that HBT-Cy could sense exogenous and endogenous bisulfite as well as possess the redox activity in biological system. This is indicative of its potential application to monitor cell oxidative stress in the process of imaging research.

Cooperated with Institute of Chemistry and National University of Singapore, this study was mainly performed by ZHANG Yajiao, YU Huan, SUN Mingtai, etc. Their study was published in Analytical Chemistry with title Reversible Fluorescent Probe for Selective Detection and Cell Imaging of Oxidative Stress Indicator Bisulfite. 

The schematic diagram of probe with its structure, recognition principle and reversible fluorescence signal changes in cell imaging. (Image by ZHANG Yajiao)