DAN-1 EE is a fluorescent indicator for the bioimaging of NO. DAN-1 EE is a cell permeable derivative of DAN, a molecule which has been used extensively in the quantitation of nitrate and nitrite using fluorescence spectroscopy. Upon entry into the cell, DAN-1 EE is transformed into the less cell permeable DAN-1 by cellular esterases thus preventing loss of signal due to diffusion of the molecule from the cell. Intracellular formation of NO can be monitored using excitation and emission wavelengths of 360-380 nm and 420-450 nm, respectively.