The role of nitric oxide (NO) as a putative mediator of neuronal death can be understood best if NO is detected directly. 1,2-Diaminonaphthalene (DAN) is a fluorogenic probe that is used to detect nitric oxide (NO) productions in live cell and animals. The reaction product of DAN with NO is a triazole with blue fluorescence. The DAN-based methodology of NO assessment is convenient and applicable to numerous living systems both in vivo and in vitro. As low as 10 nM nitrite can be detected using DAN.