Axicon-based annular laser trap for studies on sperm activity

1
A ring-shaped laser trap based on axicons
Bing Shao University of California, San
Diego Del Mar Photonics August 3rd, 2005
San Diego, CA Optics Photonics 2005 The
International Society for Optical Engineering
2
Photonics in Cell Based Bio-Chip Platforms
Photonics to augment m-fluidics chips e.g., for
sample purification or sorting
Photonics to augment cell array chips e.g., for
pharmacological data extraction

• Key features of Photonics
• Remote manipulation
• reduces cross-contamination
• wireless connectivity
• Individual selectivity of single cells or
  particles
• Fast, highly parallel processing
• Independent of environment of cells or medium
• Essentially harmless to bio-molecules

3
Background on Optical Trapping

• Discovered in 1970 1 and demonstrated in 1986
  2 both by Ashkin, optical tweezers have been
  applied effectively for
• Manipulation of biological cells, organelles and
  beads
• Characterization and sorting of microparticles
  including cells
• Generating and measuring molecular-scale forces
  for single molecule study

Scanning laser line optophoresis 4
Kinesin Moving on a Microtubule5
Multiple-step yeast manipulation 3

1. A. Ashkin, Physical Review Letters, v24,
   p154-159, 1970.
2. A. Ashkin, et al., Optics Letters, v11, n5,
   p288-291, 1986.
3. B. Shao et al., accepted for publication, Sensors
   Actuators B Chemical,, 2005.
4. A. Forster et al., Analytical biochemistry, v327,
   p 14-22, 2004.
5. Koen Visscher, et al., Nature, v400, p184-189,
   1999.

4
Optical Trapping Theory

• Optical tweezers form a stable three-dimensional
  trap that is created by the optical forces that
  arise in highly focused laser beams.
• These optical forces can be attributed to the
  transfer of momentum of a photon that occurs
  while undergoing a scattering event such as
  reflection or refraction.

Photon Momentum

• Ray Optics Analysis for Large Particles (D gtgtl)
• Refraction at boundary transfers photon momentum
  to particle
• Force due to refraction (FD) is higher than that
  due to reflection (FR)
• Restorative trapping force pushes particle
  toward z axis
• Arises from the gradient in the Gaussian
  envelope of the beam such that a gt b.
• For a high NA lens, the gradient force will be in
  z direction and acts to restore the object to
  the focal point as well as to the z axis
  resulting in a Single Beam Optical Trap

After A. Ashkin, Phys. Rev. Lett., 24, 156
(1970)
5
A Ring trap

• When studying self-propelling cells (e.g., sperm,
  algae, etc.) with single point trap, interference
  from untrapped cells need to be avoided.
• A Ring trap based speed bump could be used as a
  force shield to protect analysis area from other
  cells.
• Parallel sorting / separation of the cells based
  on their motility and response to attractants can
  be accomplished.
• Only winners will make it to the attractant

stimuli
Facilitate single sperm study by preventing
interference/competition
High efficiency bio-tropism study under
equal-distance condition
6
Generating a uniform Ring Trap!

• Mechanical scanning---moving part, speed
  limitation (especially for fast moving target),
  reduced average exposure time, tangential drag
  force introduced by scanning focus
• Diffractive optics/Holography---lower efficiency,
  not suitable for power limiting system,
  dynamically adjustment of ring size and depth
  needs SLM.
• Axicon---low cost, high efficiency, easy
  implementation, ring size dynamically adjustable

Axicon (rotationally symmetric prism), is a lens
composed of a flat surface and a conical surface.
7
History of Axicon for Trapping

• 1. Diffraction-free Bessel beam13(GaussianAxico
  n)

Non-diffractive propagation distance for a
quasi-Bassel beam
2. Hollow laser beam for atom trapping14(Gaussia
nLensAxicon)
Provide a large and dark inner region and the
available laser power is used in an optimum way
for creating the repulsive optical wall.
13. D. McGloin,et al., Spies oemagazine, p42-45,
Jan 2003. 14. I. Manek, et al., Optics
Communicatons, 147, p67-70, 1998.
8
How to use Axicons to trap particles in a ring?

• Size---Trapping spot deviation from the optical
  axis d ? input beam inclination q 7.
• Uniformity---MO input is a cone of collimated
  beam intersecting at the back aperture with
  inclination angle q.
• Strength---filling MO back aperture completely to
  ensure tight focusing ? input light cone
  thickness diameter of MO back aperture

7. B. Shao et al., Proceedings of the SPIE,
v5514, p62-72, 2004.
9
Ray Tracing Simulation
ZEMAX simulation with 40x NA 1.3 oil immersion
lens shows a ring-shaped focus at the sample
plane whose diameter agrees with the theoretical
calculation220mm.
40x Oil WD0.2 fFL100mm fTL400mm
Water 0.077mm
Immersion Oil 0.20mm
Coverglass 0.17mm
sample plane spot diagram
Cross-section of annular focus
10
Ray Tracing Simulation
11
Experimental Setup
Ytterbium l1064nm P0
Axiovert 200M
12
Experimental Setup
13
Experimental Results
Experiment with microspheres verified the
feasibility of the annular laser trap.
40 MO NA1.3 Oil (Zeiss) PpostMO80mW 15 micron
polystyrene beads (Duke Scientific) Buffer Water
Rring105mm
Formation of the ring of microspheres
Leftwards stage translation
P2.4mW/microsphere
14
Experimental Results
Preliminary experiment with sperm shows an
annular reaction zone
(a)
(b)
Rring105mm Ptrap30mW/sperm
(c)
(d)
Average trapping power 100200mW/sperm
6
6. J. Vinson, et al., Poster 5930-79, Optics
Photonics, SPIE 50th Annual Meeting, Jul.
31-Aug.4, San Diego, 2005.
15
Dynamically Adjustable Annular Trap?

• With fixed total power, changing the size of the
  ring trap leads to a change of trapping power per
  spot. This could be used for quantitative
  evaluating and sorting self-propelling cells with
  different swimming forces, motility patterns, and
  chemotaxis responses to chemo-attractants.
• The size of self-propelling cells varies
  dramatically. A variable annular trap enables
  study of different species without redesigning
  the system.

16
Optical System Design

• Only q should be changed (normal telescope lens
  pair also changes Din)!
• Introducing an axicon telescope pair in between
  the focusing lens and the tube lens
• Shift axicon2 along the optical axis while fixing
  other optics
• The incident angle q is varied correspondingly
  while the filling of the objective back aperture
  is almost not changed.

Dd?Dq?Drring
Din
17
Simulation Results
80 mm
D486mm
D84mm
18
Experimental Setup
Ytterbium l1064nm P0
P0
D130430mm
l66126mm
40x oil NA1.3
Power throughput
19
Experimental Results
40x Oil NA1.3 15mm polystyrene beads
Pout0.3W PpostMO55mW
da2-a389mm
da2-a368mm
Pout0.5W PpostMO90mW
20
Experimental Results
P012W, Rring55mm Ptrap70mW/sperm, 5
P012W, Rring55mm Ptrap70mW/sperm, 3
Fast sperm not affected, swim across Slow sperm
drawn to the ring and scattered out of the focus
plane Dead sperm and red blood cells stably
trapped to the ring and can freely move along the
circumference.
21
Conclusions

• Traditional applications of axicons lies in
  generating diffraction-free Bessel beam for
  communication or longitudinal partical
  confinement, and create central dark region for
  atom trapping
• A new application of axicon has been explored to
  build an annular laser trap which confines
  particles into a ring-shaped pattern.
• By adding two more axicons, and simply
  translating one of them along the optical axis,
  the diameter of the annular trap can be
  dynamically adjusted.
• Although further optimization of the system is
  needed to improve the strength and stability of
  the annular trap, this system provides a
  prototype of an objective, automated,
  quantitative, and parallel tool for, cell
  motility and bio-tropism study.

22
Acknowledgements

• Scripps Institute of Oceanography
• Beckman Laser Institute
• Beckman Center for
• Conservation and Research for Endangered Species
  (CRES)
• Zoological Society of San Diego

23
References

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6. M. Eisenbach et al., BioEssays, v21, p203-210,
   1999.
7. J. Vinson, et al., Poster 5930-79, Optics
   Photonics, SPIE 50th Annual Meeting, Jul.
   31-Aug.4, San Diego, 2005.
8. B. Shao et al., Proceedings of the SPIE, v5514,
   p62-72, 2004.
9. A. Ashkin, Physical Review Letters, v24,
   p154-159, 1970.
10. A. Ashkin, et al., Optics Letters, v11, n5,
    p288-291, 1986.
11. Koen Visscher, et al., Nature, v400, p184-189,
    1999.
12. A. Forster et al., Analytical biochemistry, v327,
    p 14-22, 2004.
13. A. Birkbeck, et al., Biomedical Microdevices, v5,
    n1, p47-54, 2003.
14. D. McGloin,et al., Spies oemagazine, p42-45, Jan
    2003.
15. I. Manek, et al., Optics Communicatons, v147,
    p67-70, 1998.