Near-field waveguide trapping and tracking of particles using fluorescence imaging

The evanescent field from an optical waveguide is used for near-field trapping and transporting of fluorescent microspheres. Out-of-focus fluorescence imaging is used to track the trapped particle in 3-D with nanometer precision (<100 nm). A prior calibration is done to determine the relationship between the z-coordinate and the radius of the outermost diffraction ring in the image of the sphere. This gives precise information about how much the particle moves up and down during propulsion along the waveguide. Results are presented for trapping and tracking a 1 m fluorescent particle on a strip waveguide.