We report the rational design of a 20-mer basic peptide, derived from the transcriptional antitermination protein N of bacteriophage P22, equipped with a luminescent DOTA[Tb3+] macrocyclic complex and a sensitizing tryptophan antenna. Folding of this peptide into an a helical conformation, which occurs upon binding to its target boxB RNA hairpin, results in a large increase in luminescence emission. Therefore, the peptide construct works as a highly sensitive and selective probe for this RNA hairpin.