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Development of a 3-D Fibre Based Laser Light Force Optical Trap

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Development of a 3-D Fibre Based Laser Light Force Optical Trap

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  1. Development of a 3-D Fibre Based Laser Light Force Optical Trap Steven Ross GERI-CEORG Supervisors: Prof. D. Burton, Dr. F. Lilley and Dr. M. Murphy

  2. Introduction • Objective of the project • Optical Trapping Theory • Why Fibre Based Trapping? • Shaping Fibre For 3-D Optical Trapping • System Design • Results • Particle Tracking and Force Determination • Future Work • Summary

  3. Objective of the project • To aid current investigations of the mechanical properties of cells • Normal cells like to attach themselves • Pathological cells, such as cancer are not so friendly • OT can also be used to apply forces • LASER scanning confocal and holographic Microscopy

  4. Optical Trapping Theory • Scattering force • Propels particles in the direction of the beams propagation • Gradient force • Pulls particles into the high intensity region of the beams axis

  5. Optical Trapping Theory Counter propagating dual beam trap Net opposing scattering force at E Optical levitation trap Scattering force balanced with gravity at E Images taken from [1]

  6. Optical Trapping Theory • Single beam gradient force optical trap - “optical tweezers” • Gradient force greater than scattering force • Tightly focusing laser through high NA microscope objective lens • Gradient force F slightly below focal point f Image taken from [1]

  7. Why Fibre Based Trapping? • Advantages • Reduced size and costs • Decoupled from the microscope • Light delivered to sample chamber via optical fibre • No need for position detection • Disadvantages • System complexity increases with additional trap • Fibre ends prone to damage require maintenance

  8. Shaping Fibre for 3-D Optical Trapping • Focused ion beam milling [2] • Fibre polishing [3] • Laser micro-machining [4 ] • Chemical etching [5] • Heating and drawing [6] 4 Axis lapping [3] Chemical etching [5]

  9. System Design • Heating & Drawing • Fibre heated with 20W CO2 laser • Microcontroller controlled allowing a wide range of tapers • Simple, rapid & repeatable fabrication of taper • Core/cladding ratio maintained Sutter P-2000/F Micropipette Puller

  10. System Design 100 X Magnification 7000 X Magnification

  11. System Design

  12. IDL Doesn’t like working with video Allows the user to track a specified particle Records specific particle data LabView Does like working with video Tracks multiple particles simultaneously Records data for all particles Particle Tracking & Force Determination

  13. Particle Tracking & Force Determination

  14. Particle Tracking & Force Determination • Trapping force determination-dynamic measurement method • Obtained as a function of the beads displacement

  15. Particle Tracking & Force Determination • Newton's second law and the stokes law fopt = 6∏nrŚ +mŜ [7] • Trapping force-1st & 2nd derivatives of the beads position as a function of time • Displacement-in a certain time can be calculated from the beads position

  16. Further Work • Develop particle tracking software • Define optical trap parameters • Trap strength • Trap stiffness • Continue to find the optimum optical fibre taper • Trapping of non adhered cells • Integrate laser trap with other microscopy systems

  17. Summary • Objective of the project • Optical Trapping Theory • Why Fibre Based Trapping? • Shaping Fibre For 3-D Optical Trapping • System Design • Results • Particle Tracking and Force Determination • Future Work • Summary

  18. References [1] Ashkin A 1997 Optical trapping and manipulation of neutral particles using lasers proc. Natl. Acad. Sci. 19 (8) pp.283-285 [2] Minzioni P, Bragheri F, Liberale C, Di Fabrizio E and Crisiani I 2008 A novel approach to fibre-optic tweezers: numerical analysis of the trapping efficiency IEEE journal of selected topics in quantum electronics 14 (1) pp.151-157 [3] I-En Lin S A lensed fibre workstation based on the elastic polishing plate method Precision Engineering 29 pp.146-150 [4] Presby H M, Benner A F and Edwards C A 1990 Laser micromachining of efficient fiber microlenses Applied Optics 29 (18) pp.2692-2695 [5] Luo J, Fan Y, Zhou H, Gu W and Xu W 2007 fabrication of different fine fibre tips for near field scanning optical microscopy by simple chemical etching technique Chineese Optics Leters 5 pp. S232-S234 [6] Liu Z, Guo C, Yang J and Yuan L 2006 Tapered fiber optical tweezers for microscopic particle trapping: fabrication and application Optics Express 14 (25) pp.12510-12516 [7] Hu Z, Wang J and Liang J 2006 Experimental measurement and analysis of the optical trapping force acting on a yeast cell with a lensed optical fiber probe optics and laser technology 39 pp. 475-480