Ligand 1, bearing two ethylenediamine groups, was designed to form a hydrophobic cavity upon binding to metals. The shape of its nonpolar cavity depends on the metal: a reversal in binding preference for naphthalene or biphenyl groups is found when the metal is changed from zinc to copper, with a selectivity change of 260-fold. In the presence of dansylated amino acids, the new ligand constitutes a fluorescent sensor for zinc ion. Variations are seen in affinity for dansylamino acid with minor structural changes, and organic selectivity changes with complexes of variant metals. These findings suggest that sensor tuning of affinity and selectivity for metal is possible by choice of simple organic guest and for organic guest by choice of metal.