We investigated the chemosignaling of Au(3+) by the selective desulfurization of thiocoumarin. In the presence of a heavy metal ion chelator N,N,N',N'-tetrakis-(2-pyridylmethyl)ethylenediamine, thiocoumarin was selectively converted to its oxo analogue by reaction with Au(3+), resulting in a pronounced chromogenic and fluorescent signaling. Selective signaling of Au(3+) was possible in the presence of common alkali, alkaline earth, and transition metal ions, as well as Au(+) in a mixed aqueous environment. The colorimetric determination of Au(3+) was possible by the color change from pink to yellowish green of the designed probe. The detection limit for the determination of Au(3+) in 50% aqueous acetonitrile was 1.1 × 10(-7) M.