DAF-2 is a highly sensitive fluorescent indicator commonly used for the detection of nitric oxide (NO). It reacts with NO in the presence of oxygen to yield the highly fluorescent triazolofluorescein (DAF-2T). Fluorescence is monitored using excitation and emission wavelengths of 485 and 538 nM, respectively. At neutral pH the detection limit for NO is 2-5 nM. This sensitive fluorescent probe has been used to identify individual nitric oxide-producing neurons in brain slices, in mitochondria and in living plant cells.