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Sorting Cells by Size, Refractive Index, or Antigen Presentation
Optical separation of cell populations is possible using a variety of beam configurations (collectively referred to as optical landscapes) in either a static or dynamic fluid flow environment. In the fluid flow example shown, colloids of differing sizes are separated using an optical landscape that deflects larger particles more strongly than smaller particles. Using this landscape, the separation of lymphocytes and erythrocytes has also been demonstrated. As an extension of this concept, cells may be separated based on the presentation of surface antigens by tagging them with monoclonal antibody doped dielectric spheres. An acousto optic deflector is often used to generate the optical landscapes, such as in the example here.
A further separation technology under investigation is that of optical chromatography, which separates particles or cells based on a competing drag force from a fluid flow and radiation pressure from a laser. As particles flow in solution towards a weakly focussed beam, they are trapped by the beam. Depending on their size and refractive index, they will be trapped in different positions along the length of the light field, allowing extremely sensitive separation to occur. In this technique, stokes drag is balanced by radiation pressure – particles with a higher refractive index and a larger size will be affected more strongly by the radiation pressure than the stokes drag.
Key References
Optical chromatography using a photonic crystal fiber with on-chip fluorescence excitation P. C. Ashok, R. F. Marchington, P. Mthunzi, T. F. Krauss and K. Dholakia, Optics Express 18(6) 6396-6407
Intracellular Dielectric Tagging for Improved Optical Manipulation of Mammalian Cells P. Mthunzi, W. M. Lee, A. C. Riches, C.T.A. Brown, F. J. Gunn-Moore, and K. Dholakia. Published online ahead of print (IEEE Journal of Selected Topics in Quantum Electronics). (2009)
Optical redistribution of microparticles and cells between microwells, Jörg Baumgartl, Gregor M. Hannappel, David J. Stevenson, Daniel Day, Min Gu, and K. Dholakia. Lab Chip 9, 1334 - 1336 (2009) (video 1) (video 2) (highlighted in the magazine Chemical Technology)
(If desired, all references and pdfs may be downloaded en masse in an Endnote formatted zip file)