MTS-CR110 (MTS-5-(and-6)-carboxyrhodamine 110, mixed isomers) is a green fluorescent thiol-reactive dye. CR110 (5-(and-6)-carboxyrhodamine 110) has absorption and emission spectra (502/524 nm) similar to those of fluorescein (495/519 nm) but its photostability is far better than that of the latter.