RT-AM is a pro-drug real thiol. Real Thiol is a reversible reaction-based fluorescent probe.

The carboxylic acid groups is converted to acetoxymethyl (AM) esters to enhance the cell permeability of Real Thiol, which are hydrolysed by esterases to regenerate Real Thiol inside cells. For cells treated with the RT-AM, real-time ratiometric images of rapid changes in intracellular GSH concentrations can be generated by dividing fluorescence intensity values of the 405 nm channel by the 488 nm channel at each corresponding pixel.