Radiant energy – Electrically neutral molecular or atomic beam devices and...
Reexamination Certificate
2001-11-14
2004-08-31
Weber, Jon P. (Department: 1651)
Radiant energy
Electrically neutral molecular or atomic beam devices and...
C435S173100
Reexamination Certificate
active
06784420
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to methods and apparatus for the selection, identification, characterization, and/or sorting of materials utilizing at least optical or photonic forces. More particularly, the inventions find utility in biological systems, generally considered to be the use of optical forces for interaction with bioparticles having an optical dielectric constant.
BACKGROUND OF THE INVENTION
Separation and characterization of particles has a wide variety of applications ranging from industrial applications, to biological applications, to environmental applications. For example, in the field of biology, the separation of cells has numerous applications in medicine and biotechnology. Historically, sorting technologies focused on gross physical characteristics, such as particle size or density, or to utilize some affinity interaction, such as receptor-ligand interactions or reactions with immunologic targets.
Electromagnetic response properties of materials have been utilized for particle sorting and characterization. For example, dielectrophoretic separators utilize non-uniform DC or AC electric fields for separation of particles. See, e.g., U.S. Pat. No. 5,814,200, Pethig et al., entitled “Apparatus for Separating By Dielectrophoresis”. The application of dielectrophoresis to cell sorting has been attempted. In Becker (with Gascoyne) et al., PNAS USA, Vol. 92, pp. 860-864, January 1995, Cell Biology, in the article entitled “Separation of Human Breast Cancer Cells from Blood by Differential Dielectric Affinity”, the authors reported that the dielectric properties of diseased cells differed sufficiently to enable separation of the cancer cells from normal blood cells. The system balanced hydrodynamic and dielectrophoretic forces acting on cells within a dielectric affinity column containing a microelectrode array. More sophisticated separation systems have been implemented. See, e.g., Cheng, et al., U.S. Pat. No. 6,071,394, “Channel-Less Separation of Bioparticles on a Bioelectronic Chip by Dielectrophoresis”. Yet others have attempted to use electrostatic forces for separation of particles. See, e.g., Judy et al., U.S. Pat. No. 4,440,638, entitled “Surface Field-Effect Device for Manipulation of Charged Species”, and Washizu “Electrostatic Manipulation of Biological Objects”, Journal of Electrostatics, Vol. 25, No. 1, June 1990, pp. 109-103.
Light has been used to sort and trap particles. One of the earliest workers in the field was Arthur Ashkin at Bell Laboratories, who used a laser for manipulating transparent, &mgr;m-size latex beads. Ashkin's U.S. Pat. No. 3,808,550 entitled “Apparatuses for Trapping and Accelerating Neutral Particles” disclosed systems for trapping or containing particles through radiation pressure. Lasers generating coherent optical radiation were the preferred source of optical pressure. The use of optical radiation to trap small particles grew within the Ashkin Bell Labs group to the point that ultimately the Nobel Prize was awarded to researchers from that lab, including Steven Chu. See, e.g., Chu, S., “Laser Trapping of Neutral Particles”, Sci. Am., p. 71 (February 1992), Chu, S., “Laser Manipulation of Atoms and Particles”, Science 253, pp. 861-866 (1991).
Generally, the interaction of a focused beam of light with dielectric particles or matter falls into the broad categories of a gradient force and a scattering force. The gradient force tends to pull materials with higher relative dielectric constants toward the areas of highest intensity in the focused beam of light. The scattering force is the result of momentum transfer from the beam of light to the material, and is generally in the same direction as the beam. The use of light to trap particles is also sometimes referred to as an optical tweezer arrangement. Generally, utilizing the Rayleigh approximation, the force of trapping is given by the following equation:
F
g
=
2
π
·
r
3
ϵ
B
c
(
ϵ
-
ϵ
B
ϵ
+
2
ϵ
B
)
(
∇
·
I
)
where F
g
is the optical gradient force on the particle in the direction toward the higher intensity, r is the radius of the particle, ∈
B
is the dielectric constant of the background medium, ∈ is the dielectric constant of the particle, I is the light intensity in watts per square centimeter and ∇ is the spatial derivative.
FIG. 1
shows a drawing of a particle in an optical tweezer. The optical tweezer consists of a highly focused beam directed to the particle.
As shown in
FIG. 1
, the focused beam
12
first converges on the particle
10
and then diverges. The intensity pattern
14
relates to the cross-section of the intensity of the beam in the horizontal dimension, and the intensity pattern
16
is the cross-section of intensity in the vertical dimension. As can be seen from the equation, the trapping force is a function of the gradient of the intensity of the light. Thus, the force is greater where the light intensity changes most rapidly, and contrarily, is at a minimum where the light intensity is uniform.
Early stable optical traps levitated particles with a vertical laser beam, balancing the upward scattering force against the downward gravitational force. The gradient force of the light served to keep the particle on the optical axis. See, e.g., Ashkin, “Optical Levitation by Radiation Pressure”, Appl. Phys. Lett., 19(6), pp. 283-285 (1971). In 1986, Ashkin disclosed a trap based upon a highly focused laser beam, as opposed to light propagating along an axis. The highly focused beam results in a small point in space having an extremely high intensity. The extreme focusing causes a large gradient force to pull the dielectric particle toward that point. Under certain conditions, the gradient force overcomes the scattering force, which would otherwise push the particle in the direction of the light out of the focal point. Typically, to realize such a high level of focusing, the laser beam is directed through a high numerical aperture microscope objective. This arrangement serves to enhance the relative contribution from the high numerical aperture illumination but decreases the effect of the scattering force.
In 1987, Ashkin reported an experimental demonstration of optical trapping and manipulation of biological materials with a single beam gradient force optical trap system. Ashkin, et al., “Optical Trapping and Manipulation of Viruses and Bacteria”, Science, Mar. 20, 1987, Vol. 235, No. 4795, pp. 1517-1520. In U.S. Pat. No. 4,893,886, Ashkin et al., entitled “Non-Destructive Optical Trap for Biological Particles and Method of Doing Same”, reported successful trapping of biological particles in a single beam gradient force optical trap utilizing an infrared light source. The use of an infrared laser emitting coherent light in substantially infrared range of wavelengths, there stated to be 0.8 &mgr;m to 1.8 &mgr;m, was said to permit the biological materials to exhibit normal motility in continued reproductivity even after trapping for several life cycles in a laser power of 160 mW. The term “opticution” has become known in the art to refer to optic radiation killing biological materials.
The use of light to investigate biological materials has been utilized by a number of researchers. Internal cell manipulation in plant cells has been demonstrated. Ashkin, et al., PNAS USA, Vol. 86, 7914-7918 (1989). See also, the summary article by Ashkin, A., “Optical Trapping and Manipulation of Neutral Particles Using Lasers”, PNAS USA, Vol. 94, pp. 4853-4860, May 1997, Physics. Various mechanical and force measurements have been made including the measurement of torsional compliance of bacterial flagella by twisting a bacterium about a tethered flagellum. Block, S., et al., Nature (London), 338, pp. 514-518 (1989). Micromanipulation of particles has been demonstrated. For example, the use of optical tweezers in combination with a microbeam technique of pulsed laser cutting, sometimes also referred to as laser scissors or sca
Butler William F.
Lykstad Kristie L.
O'Connell James P.
Tu Eugene
Wang Mark M.
Genoptix, Inc.
O'Melveny & Myers LLP
Weber Jon P.
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