Expanding the optical trapping range of lipid vesicles to the nanoscale.

Small unilamellar lipid vesicles with diameters down to 50 nm enclosing high refractive index sucrose cores can be optically trapped individually in three dimensions using a focused laser beam. Combined optical trapping and confocal microscopy allows for simultaneous quantitative measurements of the forces exerted on individual vesicles and of their size and shape. The position of individual vesicles in three dimensions is measured with nanometer spatial and ∼10 μs temporal resolution.