A prototype luminescent turn-on probe for Cu(+) (and Ag(+)) is described, harnessing a selective binding site (log Kass = 9.4 and 7.3 for Cu(+) and Ag(+), respectively) based on the coordinating environment of the bacterial metallo-chaperone CusF, integrated with a terbium-ion-signaling moiety. Cation-π interactions were shown to enhance tryptophan triplet population, which subsequently sensitized, on the microsecond timescale, the long-lived terbium emission, offering a novel approach in bioinspired chemosensor design.