Fluorescence Resonance Energy Transfer Enhanced Luminescence (FRETEL) of Quantum Dyes®

Methods for increasing the luminescence intensity of lanthanide macrocycles, Quantum Dyes®, by the Fluorescence Res-onance Energy Transfer Enhanced Luminescence (FRETEL) effect in the solid state have been developed. A homoge-neous solution containing the europium or terbium Quantum Dye and an excess of selected energy transfer species is evaporated to dryness, resulting in a thin film that surrounds and embeds the Quantum Dye or its conjugates. Under these conditions, in the presence of the gadolinium-thenoyltrifluoroacetonate complex as the energy transfer species, the lumi-nescence of the europium Quantum Dye increased approximately 6-fold upon drying. However, the presence of a non-emitting lanthanide such as gadolinium is not always required for this effect. In studies employing the 2,6-pyridinedicar-boxylate ion as the energy transfer species, where both the terbium and the europium Quantum Dyes could be simulta-neously excited at 280 nm, the presence of gadolinium actually decreased the luminescence compared to that obtained with the 2,6-pyridinedicarboxylate alone. The simplest explanation for the FRETEL effect is that fluorescence resonance energy transfer occurs between the photo-trapping energy transfer species, either unbound or complexed with the non-luminescent gadolinium ion. The energy being finally transferred to the luminescent lanthanide ion complexes with con-sequent increase in emission intensity. This new method for the enhancement of luminescence intensity in the solid state has the significant advantage of eliminating the need for the previously required aqueous emulsion, which was difficult to make and transport. 1