The ThioStar® Thiol Detection Reagent allows users to accurately determine the extent of free thiol content in samples. ThioStar is converted to a brightly fluorescent product upon reaction with the thiol in the sample. The thiol in the sample can either be one that is generated by a reaction, like the end product of an enzymatic reaction such as glutathione, or can be the cysteine content of the protein to be measured.

Free thiols in biological systems have important roles. Oxidatively modified thiol groups of cysteine residues are known to modulate the activity of a growing number of proteins. One of the most pressing problems with this approach is to accurately determine the extent of modification of specific amino acids, such as cysteine residues, in a complex protein sample.