FRET between CdSe quantum dots in lipid vesicles and water- and lipid-soluble dyes

Because of the coatings needed to solubilize and passivate quantum dots for biological applications, their use in fluorescent resonance energy transfer (FRET) has been limited. However, hydrophobic particles without polymer coatings may be embedded into lipid membranes, as demonstrated here with biomimetic vesicles. FRET is seen to a lipid-soluble dye (DiD) and a water-soluble dye (Cy3.5) in which the vesicles are suspended. The degree of energy transfer to each dye suggests that most of the QDs are located deep within the lipid, as confirmed by electron microscopy of whole mounts and thin sections of vesicles. Energy transfer is also seen to a voltage-sensitive, lipid-soluble dye (di-4-ANEPPS) only when the potassium ionophore valinomycin is present in the membrane. The effect is dependent upon potassium ion concentration rather than absolute membrane potential.