Förster resonance energy transfer between quantum dots and dye immobilized in biopolymer particles

We used high adsorption properties of the cationic biopolymer chitosan to synthesize colloidal polymer particles (average size about 0.3 μm) with immobilized CdTe quantum dots (QDs) and organic dye (erythrosin B). A high local concentration of fluorophores bound to the particles (about 10 mM), as well as a wide overlap of their optical spectra result in an efficient (up to 80%) Förster resonance energy transfer (FRET) from QDs ensembles to dye molecules. The FRET was registered by both steady-state (quenching of the donor and enhancement of the acceptor fluorescence) and time-resolved methods (decreasing of donor lifetime). The dependence of the transfer efficiency on acceptor concentration was analyzed within the scope of the Förster theory extended for the case of multiple energy transfer configuration. The average distances between the donor and acceptor as well as local concentration of fluorophores within particles were determined. It was demonstrated that the synthesized particles can be used as FRET-based sensitive probes for inter-fluorophore distance calculation within the range of 4 ÷ 9 nm