Herein, we report the design and preparation of a benzothiazolium hemicyanine derivative that exhibits
red emission at 585 nm. Its complex with Hg2þ may be used for selective and sensitive sensing of thiol
biomolecules through the reversible visual color and florescence changes they induce in the complex.
This complex was used to detect three test thiol biomolecules, and exhibited sensitivity in the order
cysteine > glutathione > homocysteine. Furthermore, the complex allowed the detection of cysteine at
0.2 mM, lower than the normal human intracellular cysteine concentration (30e200 mM), and was found
to be useable over at least five cycles upon alternate addition of cysteine and Hg2þ.