1,2-diaminoanthraquinone sulfate (DAA) is a nitric oxide probe that is nonfluorescent until it reacts with nitric oxide (NO) to produce a red-fluorescent precipitate. This probe has been used to detect changes in NO levels in rat retinas after injury to the optic nerve. However, preliminary experiments performed by Molecular Probes' scientists indicate that this reagent may not be useful for detecting NO activity in cells due to the probe's limited membrane permeability and low solubility in aqueous buffers at proposed working concentrations.