1-(3',6'-Bis(ethylamino)-2',7'-dimethyl-3-oxospiro-2-yl)-3-phenylurea
1-(3',6'-Bis(ethylamino)-2',7'-dimethyl-3-oxospiro[isoindoline-1,9'-xanthen]-2-yl)-3-phenylurea (compound 1a) can be used as a fast-responsive fluorescent gold ion probe for detection of gold ions in water and synthetic products.