Optical Tweezers

Researcher: Alexei Faustov, Michael Webb

We present a method to generate and regenerate arrays of microspheres by optically trapping through optical imaging fiber bundles. In this method, a laser beam is coupled into the proximal end of an optical fiber bundle, and the light energy is distributed across the face of the fiber. Each illuminated individual fiber in the array propagates light to the distal face of the bundle, where light focusing elements at the end of each fiber focus the laser light and form optical traps. These optical traps are capable of capturing and arraying microspheres in parallel. The number of optical traps is determined by the number of fibers in the optical fiber bundle and is capable of creating a dense array (~5x10 4 traps/mm 2 ) of optical tweezers.

Figure 1 (a) Schematic for an imaging fiber-based optical tweezer array system. (b) Region of optical tweezer array system shown in more detail. Depending on the magnification of the objective lens, light illuminates a specific number of optical fibers in the array. Light travels down the length of the fiber, and lens elements at the end of each illuminated fiber focus the laser light into optical traps. Microparticles flowing into these regions become trapped by these fibers. (c) Consecutive images of trapped 4.5 micron silica microspheres using the apparatus in Fig. 1a.

Figure 2 Trapping an array of silica microspheres with the imaging fiber-based optical tweezer array (individual beads enhanced). Flow is from the 4 o'clock position. Frames a-e show progressive trapping of beads. Frame f shows the beads flowing away after the trap is turned off.

“Fabrication and Optical Characterization of Imaging Fiber Based Nanoarrays”, J. Tam, L. Song, D.R. Walt. Talanta , 2005 67 (3), 498-502

“An imaging fiber-based optical tweezer array for microparticle array assembly,” J. Tam, I. Biran, D.R. Walt, Applied Physics Letters , 2004 , 84 (24) 4289-4291.