Integration of Axial Displacement in Optical Tweezers

Dy, Mary-Clare Clarin (1051138)

 Optical tweezers is an optical manipulation technique wherein tiny particles can be trapped and manipulated using a highly focused laser beam. It has become an integral part of learning the mechanics of biomolecules and bio-molecular processes because aside from being able to move particles in the nanometer-scale, it also has the capability to measure pico- and nanoNewton forces of objects. Recent researches consider three-dimensional manipulation and force measurement by incorporating acousto-optics deflectors, spatial light modulators, among others. Although, these devices can enable other applications such as creation of multitraps, these devices are also expensive and require complicated modifications. Thus, this thesis propose a simple, yet sensitive, scheme that can integrate the axial displacement in optical tweezers: by moving one lens, called L1, which is a component found in any typical optical tweezers set-up, a microbead can be displaced in the axial direction.

 In this research, two L1 translation programs will be utilized to observe the relationship of moving the L1 with the axial displacement of the microbead. Moreover, the corresponding change in axial movement of the bead will be computed. The feasibility of bead attachment was also examined using the proposed scheme. Experiments reveal that a microbead with 4.26-micron diameter can be axially displaced for approximately 4-micron with a 15mm-L1 translation, and a short L1-translation of 6mm can move a 2.1-micron diameter bead in less than 2-micron. The bead-to-gel attachment using the said microbeads are also shown.

 Future work includes improvement of the image processing system and refinement of the particle position estimation, as well as application of the bead-to-cell attachment. Finally, this technique will be incorporated in the Cell Palpation System, a technique that can measure the mechanical forces of cells, to enable three-dimensional particle manipulation and cell-force measurement.