Implementing both short- and long-working-distance optical trappings into a commercial microscope
Résumé
Optical tweezers are now a widespread tool based on three-dimensional trapping by a tightly focused single laser beam. This configuration only works with large numerical aperture and short-working-distance (SWD) objectives, restricting optical manipulation to the high magnification end of the microscope nosepiece. Certain applications of optical trapping demand long-working distances (LWDs) at moderate magnification, imposing a more complex two-beam trapping configuration. In this article, we describe a complete setup that incorporates both SWD and LWD optical trapping functionalities into a single Axiovert 200M Zeiss microscope. We evaluate the performance of the setup in both trapping modes with latex particles, either fluorescent or not, of different sizes, in the 1-20 μm range. We provide practical information allowing for optimal configuration of the two-beam geometry, in relation with longitudinal and lateral stabilities of the trap.