A simple three component array of host-fluorophore complexes is capable of sensitive and selective discrimination of heavy metal ions, including lanthanide and actinide salts in aqueous solution. Instead of applying optical sensors that only use "single-mode" detection, i.e., coordination of the metal to a specific ligand and monitoring the change in emission of an appended fluorophore, we exploit a series of host-fluorophore complexes that are affected by the presence of small amounts of metal ions in aqueous solution in different ways. Variable host-metal and host-guest-metal interactions lead to both turn-on and turn-off fluorescence sensing mechanisms, enhancing the discriminatory properties of the array. The limit of detection for certain metals is as low as 70 nM, and highly similar metals such as lanthanides and actinides can be easily distinguished at low micromolar concentrations in complex salt mixtures.