The tetrakisquinoline ligand HT(6-McO8Q)-HPN (N,N,N',N'-tetrakis(6-methoxy-8-quinolylmethyl)-2-hydroxy-1,3-propariediamine) exhibited Zn2+-induced fluorescence enhancement with high specificity and sensitivity (I-Zn/I-0 = 57 and I-Cd/I-Zn = 6% in the presence of 2 equiv of Zn2+; LOD (limit of detection) = 15 nM). This ligand also exhibited fluorescence enhancement specific to inorganic phosphate (PO43-) in DMF-HEPES buffer (50 mM HEPES, 100 mM KCl, pH = 7.5) (1:1) in the presence of 2 equiv of Zn2+. The structure of the unprecedented tetranuclear zinc complex with a mu(4)-PO4 bridge was elucidated by X-ray crystallography as the key species responsible for fluorescence enhancement.