Intermolecular sensitization of lanthanide ions was effectively implemented in the development of fluorescent sensors targeting cyclin A. A chelating unit has been conjugated to peptides containing a known cyclin A binding motif (CBM). Upon interaction of the modified terbium-chelating peptides with the cyclin A substrate recruitment groove, the Tb3+ ion is placed in the vicinity of the Trp(217) side chain, which results in efficient intermolecular terbium sensitization and specific long wavelength fluorescent emission from the metal center.