Nanometer-Scale Resolution Achieved with Nonradiative Excitation
American Chemical Society
Nonradiative excitation fluorescence microscopy (NEFM) is a promising technique allowing the observation of biological samples beyond the diffraction limit. By coating a substrate with an homogeneous monolayer of quantum dots (QDs), NEFM is achieved through a nonradiative energy transfer from QDs (donors) to dye molecules located in the sample (acceptors). The excitation depth of the sample is then given by the Förster radius, which corresponds to a few nanometers above the surface. The powerful axial resolution of NEFM is highlighted by observing the adhesion of giant unilamellar vesicles (GUVs) on strong interaction with coated surfaces. In this paper, we demonstrate that the QD-quenching level is valuable to calculate and map the distance between the membrane and the surface with a high precision along the optical axis. By tuning the electrostatic interactions between the membrane and the substrate, we have been able to measure a height displacement of ≈1 nm of the lipid membrane. The experimental results were discussed according to simulations, which take into account all the common forces appearing between lipid membranes and surfaces.