Ethyl 4-[(3-amino-2-naphthyl)aminomethyl]benzoate hydrochloride is Ethyl 4-[(3-amino-2-naphthyl)aminomethyl]benzoate hydrochloride (DAN-1 EE), a membrane permeable ester of DAN-1, is used as a fluorescent indicator (sensor dye) for bioimaging of nitric oxide within cells in vivo.