Trx-red (NBL-SS perchlorate) is a red-emitting fluorescent probe derived from the nile blue fluorophore. It is specifically designed for imaging thioredoxin (Trx) in live cells and in vivo, with excitation and emission wavelengths of 615 nm and 661 nm, respectively.

Trx-red (NBL-SS) displayed multiple favorable properties, such as red emission, fast response, and high fluorescence signal. Thioredoxin (Trx) is a ubiquitous redox-regulating protein essentially involved in cell growth, differentiation, and death[1]. When HeLa cells are incubated with Trx-red (NBL-SS; 5 μM; 0-30 min), a clear time-dependent increase of the fluorescence is observed[1].

Trx-red (NBL-SS; 10 μM; 30 min) is also suitable to image thioredoxin in 6 day-old zebrafish larvae[1].