A new homogeneous assay for a fast, selective and sensitive detection and elimination of lead ions has been developed using copper clusters as novel fluorescent probes in aqueous solutions. At the same time, their elimination is achieved using the efficient photocatalytic activity of such clusters. Both effects are explained in terms of an efficient electron transfer due to the LUMO energy of the cluster overlapping with the ion redox potential. The mechanism, which allows the explanation of previously reported results for different types of metal clusters, is further confirmed using smaller and larger Cu clusters displaying non-selective and non-quenching luminescence in the presence of different cations.