DAF-FM diacetate is a cell-permeable, fluorescent probe for the detection and bioimaging of nitric oxide (NO) with excitation/emission maxima of 495/515 nm. It passively diffuses across cellular membranes and, once inside cells, is deacetylated by intracellular esterases to become DAF-FM. The fluorescence quantum yield of DAF-FM is ~0.005, but increases about 160-fold, to ~0.81, after reacting with NO. DAF-FM is advantageous over the NO probe, DAF-2 for several reasons: 1) the spectra of the NO adduct of DAF-FM are independent of pH above pH 5.5; 2) the NO adduct of DAF-FM is significantly more photostable than that of DAF-2; 3) the NO detection limit of DAF-FM (~3 nM) is more sensitive than that of DAF-2 (~5 nM).
