RB-OPD (NO-red) is a o-phenylenediamine (OPD)-locked rhodamine nitric oxide (NO) fluorescent probe with great sensitivity and selectivity (Λex=550 nm, Λem=590 nm)[1].
RB-OPD (compound 1) exhibits "turn-on" type fluorogenic and chromogenic behavior toward NO in aqueous solution with great sensitivity and selectivity, and it can be used for the sensing of NO under normal physiological conditions. NO-red is composed of two moieties: rhodamine B spirolactam as the potential strong fluorophore and chromophore, and o-phenylenediamine as an NO-reactive group in a lactam form as a "masked" NO-sensitive modulator[1].
[1]. Hong Zheng, et al. Fluorogenic and chromogenic rhodamine spirolactam based probe for nitric oxide by spiro ring opening reaction. Org Lett. 2008 Jun 19;10(12):2357-60.