New fluorescent sensors for aqueous copper ions were developed via screening of metal ligand libraries. Identified ionophores were linked to a dansyl fluorophore reporter, affording copper ion sensors based on fluorescence quenching. Simple chemical. modification of identified ionophores generated sensors responsive to a broad range of copper ion concentrations (10 nM-35 muM). (C) 2000 Elsevier Science Ltd. All rights reserved.