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

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

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

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

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]

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]

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

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]

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

System Design 100 X Magnification 7000 X Magnification

System Design

Particle Tracking & Force Determination 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

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

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

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

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

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