CRITICAL FACTORS DRIVING FOSTER RESONANT ENERGY TRANSFER BETWEEN QUANTUM DOTS

Förster Resonant Energy Transfer (FRET) is a physical phenomenon involving the non-radiative energy transfer between two fluorescent species. More precisely, such a dipole-dipole energy transfer occurs from the excited state of a donor to a lower-energy state of an acceptor. One of the most interesting application of FRET relies on the development of highly sensitive optical biosensors. In such FRET-based biomedical devices, the donor entity is usually an organic fluorophore or a semiconductor quantum dot (QD) while the acceptor entity is always an organic fluorophore. There is only a few works where QDs are used as acceptors. The reason stems in their broad absorption spectrum which is responsible of an important emission background signal hindering the FRET detection.
We recently showed the possibility to use QDs both as donors and acceptors to achieve efficient FRET and fabricate efficient biosensors based on this phenomenon.1 Figure 1 highlights the proof of concept. Especially, we studied both experimentally and theoretically the FRET mechanism occurring within pairs of QDs having different emission wavelengths in order to determine the critical factors driving the process. First, using fluorescence spectroscopy, we determined the donor fluorescence quenching rates (DFQR) and the acceptor fluorescence enhancement factors (AFEF). Second, we developed a mathematical model based on the energy diagrams of two coupled QDs and their relaxation paths. The model fits well the DFQR and AFEF experimental values and allowed us to identify the key parameters driving FRET in the specific case of QDs: the number of donors per acceptor, their absorption cross sections, the dissipative coupling of the QDs with their surrounding medium and the difference between the QDs fluorescence wavelengths.
Our work opens new ways for the development of efficient all-QD based biosensors.