US 20060060767 A1
Apparatus and methods are provided for interacting light with particles, including but not limited to biological matter such as cells, in unique and highly useful ways. Optophoresis consists of subjecting particles to various optical forces, especially optical gradient forces, and more particularly moving optical gradient forces, so as to obtain useful results. In biology, this technology represents a practical approach to probing the inner workings of a living cell, preferably without any dyes, labels or other markers. In one aspect, a particle may be characterized by determining its optophoretic constant or signature. For example, a diseased cell has a different optophoretic constant from a healthy cell, thereby providing information, or the basis for sorting. In the event of physical sorting, various forces may be used for separation, including fluidic forces, such as through the use of laminar flow, or optical forces, or mechanical forces, such as through adhesion. Various techniques for measuring the dielectric constant of particles are provided.
1. A method for separating particles comprising the steps of:
subjecting particles to optical gradient force,
analyzing, based at least in part on the relative motion of the particles, and
separating desired particle from other particles.
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This application is a continuation of U.S. application Ser. No. 09/845,245, filed Apr. 27, 2001, entitled “Methods and Apparatus for Use of Optical Forces for Identification, Characterization and/or Sorting of Particles”, and is related to application Ser. No. 09/843,902, filed on Apr. 27, 2001, entitled “System and Method for Separating Micro-Particles”, with named inventor Osman Kibar, which claims priority from provisional Application Ser. No. 60/248,451, entitled “Method and Apparatus for Sorting Cells or Particles”, filed Nov. 13, 2000. Those applications are incorporated herein by reference as if fully set forth herein.
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.
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, μm-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, the force of trapping is given by the following equation:
As shown in
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, 20 Mar. 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 μm to 1.8 μm, 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 scalpel, for cutting moving cells and organelles was demonstrated. Seeger, et al., Cytometry, 12, pp. 497-504 (1991). Optical tweezers and scissors have been used in all-optical in vitro fertilization. Tadir, Y., Human Reproduction, 6, pp. 1011-1016 (1991). Various techniques have included the use of “handles” wherein a structure is attached to a biological material to aid in the trapping. See, e.g., Block, Nature (London), 348, pp. 348-352 (1990).
Various measurements have been made of biological systems utilizing optical trapping and interferometric position monitoring with subnanometer resolution. Svoboda, Nature (London), 365, pp. 721-727 (1993). Yet others have proposed feedback based systems in which a tweezer trap is utilized. Molloy, et al., Biophys. J., 68, pp. 2985-3055 (1995).
A number of workers have sought to distort or stretch biological materials. Ashkin in Nature (London), 330 pp. 769-771 (1987), utilized optical tweezers to distort the shape of red blood cells. Multiple optical tweezers have been utilized to form an assay to measure the shape recovery time of red blood cells. Bronkhorst, Biophys. J., 69, pp. 1666-1673 (1995). Kas, et al., has proposed an “optical stretcher” in U.S. Pat. No. 6,067,859 which suggests the use of a tunable laser to trap and deform cells between two counter-propagating beams generated by a laser. The system is utilized to detect single malignant cancer cells. Yet another assay proposed colliding two cells or particles under controlled conditions, termed the OPTCOL for optical collision. See, e.g., Mammer, Chem & Biol., 3, pp. 757,763 (1996).
Yet others have proposed utilizing optical forces to measure a property of an object. See, e.g., Guanming, Lai et al., “Determination of Spring Constant of Laser-Trapped Particle by Self-Mining Interferometry”, Proc. of SPIE, 3921, pp. 197-204 (2000). Yet others have utilized the optical trapping force balanced against a fluidic drag force as a method to calibrate the force of an optical trap. These systems utilize the high degree of dependence on the drag force, particularly Stokes drag force.
Yet others have utilized light intensity patterns for positioning materials. In U.S. Pat. No. 5,245,466, Burnes et al., entitled “Optical Matter”, arrays of extended crystalline and non-crystalline structures are created using light beams coupled to microscopic polarizable matter. The polarizable matter adopts the pattern of an applied, patterned light intensity distribution. See also, “Matter Rides on Ripples of Lights”, reporting on the Burns work in New Scientist, 18 Nov. 1989, No. 1691. Yet others have proposed methods for depositing atoms on a substrate utilizing a standing wave optical pattern. The system may be utilized to produce an array of structures by translating the standing wave pattern. See, Celotta et al., U.S. Pat. No. 5,360,764, entitled “Method of Fabricating Laser Controlled Nanolithography”.
Yet others have attempted to cause motion of particles by utilizing light. With a technique termed by its authors as “photophoresis”, Brian Space, et al., utilized a polarized beam to induce rotary motion in molecules to induce translation of the molecules, the desired goal being to form a concentration gradient of the molecules. The technique preferably utilizes propeller shaped molecules, such that the induced rotary motion of the molecules results in translation.
Various attempts have been made to form microfluidic systems, put to various purposes, such as sample preparation and sorting applications. See, e.g., Ramsey, U.S. Pat. No. 6,033,546, entitled “Apparatus and Method for Performing Microfluidic Manipulations for Chemical Analysis and Synthesis”. Numerous companies, such as Aclara and Caliper, are attempting to form micro-systems comprising a ‘lab on a chip’.
Others have attempted to combine microfabricated devices with optical systems. In “A Microfabricated Device for Sizing and Sorting DNA Molecules”, Chou, et al., PNAS USA, Vol. 96, pp. 11-13, January 1999, Applied Physical Sciences, Biophysics, a microfabricated device is described for sizing and sorting microscopic objects based upon a measurement of fluorescent properties. The paper describes a system for determining the length of DNA by measuring the fluorescent properties, including the amount of intercalated fluorescent dye within the DNA. In “A Microfabricated Fluorescence-Activated Cells Sorter”, Nature Biotechnology, Vol. 17, November 1999, pp. 1109-1111, a “T” microfabricated structure was used for cell sorting. The system utilized a detection window upstream of the “T” intersection and based upon the detected property, would sort particles within the system. A forward sorting system switched fluid flow based upon a detected event. In a reverse sorting mode, the fluid flow was set to route all particles to a waste collection, but upon detection of a collectible event, reversed the fluid flow until the particle was detected a second time, after which the particle was collected. Certain of these systems are described in Quake et al., PCT Publication WO 99/61888, entitled “Microfabricated Cell Sorter”.
Yet others have attempted to characterize biological systems based upon measuring various properties, including electromagnetic radiation related properties. Various efforts to explore dielectric properties of materials, especially biological materials, in the microwave range have been made. See, e.g., Larson et al., U.S. Pat. No. 4,247,815, entitled “Method and Apparatus for Physiologic Facsimile Imaging of Biologic Targets Based on Complex Permittivity Measurements Using Remote Microwave Interrogation”, and PCT Publication WO 99/39190, named inventor Hefti, entitled “Method and Apparatus for Detecting Molecular Binding Events”.
Despite the substantial effort made in the art, no comprehensive, effective, sensitive and reliable system has been achieved.
The methods and apparatus of this relate generally to the use of light energy to obtain information from, or to apply forces to, particles. The particles may be of any form which have a dielectric constant. The use of light for these beneficial purposes is the field of optophoresis. A particle, such as a cell, will have a Optophoretic constant or signature which is indicative of a state, or permits the selection, sorting, characterization or unique interaction with the particle. In the biological regime, the particles may include cells, organelles, proteins, or any component down to the atomic level. The techniques also apply in the non-biological realm, including when applied to all inorganic matter, metals, semiconductors, insulators, polymers and other inorganic matter.
Considering the biological realm, the cell represents the true point of integration for all genomic information. Accessing and deciphering this information is important to the diagnosis and treatment of disease. Existing technologies cannot efficiently and comprehensively address the enormous complexity of this information. By unlocking the fundamental properties of the cell itself, the methods and apparatus described herein create new parameters for cellular characterization, cellular analysis and cell-based assays.
This technology represents a practical approach to probing the inner workings of a particle, such as a living cell, preferably without any dyes, labels or other markers. The “Optophoretic Constant” of a cell uniquely reflects the physiological state of the cell at the exact moment in which it is being analyzed, and permits investigation of the inner workings of cells. These techniques allow simple and efficient gathering of a wide spectrum of information, from screening new drugs, to studying the expression of novel genes, to creating new diagnostic products, and even to monitoring cancer patients. This technology permits the simultaneous analysis and isolation of specific cells based on this unique optophoretic parameter. Stated otherwise, this technology is capable of simultaneously analyzing and isolating specific particles, e.g. cells, based on their differences at the atomic level. Used alone or in combination with modern molecular techniques, the technology provides a useful way to link the intricate mechanisms involving the living cell's overall activity with uniquely identifiable parameters.
In one aspect, the invention is a method for the characterization of a particle by the steps of observing a first physical position of a particle, optically illuminating the particle to subject it to an optical force, observing the second physical position of the particle, and characterizing the particle based at least in part upon reaction of the particle to the optical force. The characterization may be that the particle, e.g., a cell, has a certain disease state based upon the detected optophoretic constant or signature.
While characterization may be done with or without physical separation of multiple particles, a method for separating particles may consist of, first, subjecting particles to optical gradient force, second, moving the particle, and third, separating desired particle from other particles. The particle may be separate from the others by further optical forces, by fluidic forces, by electromagnetic forces or any other force sufficient to cause the required separation. Separation may include segregation and sorting of particles.
In yet another aspect, the invention includes a method for analyzing particles by electrokinetically moving the particles, and subjecting the particles to optical forces for sorting. The electrokinetic forces may include, for example, eletroosmosis, electrophoresis and dielectrophoresis.
In addition to the use of the dielectric aspects of the particle for characterization and sorting, certain of the inventive methods may be used to determine the dielectric constant of a particle. One method consists of subjecting the particle to an optical gradient force in a plurality of media having different dielectric constants, monitoring the motion of the particle when subject to the optical gradient force in the various media, and determining the dielectric constant of the particle based upon the relative amount of motion in the various media.
Yet other methods permit the sorting of particles according to their size. One method includes the steps of subjecting the particles to a optical fringe pattern, moving the fringes relative to the particles, wherein the improvement comprises selecting the period of the fringes to have a differential effect on differently sized particles. An allied method sorts or otherwise separates particles based upon the particles flexibility when subject to a optical force. One set of exemplary steps includes: subjecting the particles to an optical pattern having fringes, the fringe spacing being less than the size of the particle in an uncompressed state, moving the fringes relative to the medium containing the particles, and whereby particles having relatively higher flexibility are separated from those with relatively lower flexibility.
In addition to the use of optical gradient forces, the systems and methods may use, either alone or in combination with other forces, the optical scattering force. One method for separation in an optophoresis set up consists of providing one or more particles, subjecting the particles to light so as to cause a scattering force on the particles, and separating the particles based upon the reaction to at least the scattering force.
Various techniques are described for enhancing the sensitivity and discrimination of the system. For example, a sensitive arrangement may be provided by separating the particles in a medium having a dielectric constant chosen to enhance the sensitivity of the discrimination between the particles, and changing the medium to one having a dielectric constant which causes faster separation between the particles. One option for enhancing the sensitivity is to choose the dielectric constant of the medium to be close to the dielectric constant of the particles.
Accordingly, it is an object of this invention to provide a method of identification, characterization, selection and/or sorting of materials having an optical dielectric constant.
It is yet a further object of this invention to provide a system for sorting or identifying particles without labeling or otherwise modifying the particle.
It is yet another object of this invention to provide a system in which uncharged or neutral particles may be sorted or otherwise characterized.
Yet another object of this invention is to provide a system in which particles may be manipulated remotely, thereby reducing the contamination to the system under study.
It is yet another object of this invention to provide a system for characterizing, moving and/or sorting particles that may be used in conjunction with other forces, without interference between the optical forces and the other forces.
The following definitions are provided for an understanding of the invention disclosed herein.
“Dielectric constant” is defined to be that property which determines the electrostatic energy stored per unit volume for unit potential gradient. (See, e.g., the New IEEE Standard Dictionary Of Electrical And Electronics Terms,© 1993).
The “optical dielectric constant” is the dielectric constant of a particle or thing at optical wavelengths. Generally, the optical wavelength range is from 150 Å to 30,000 Å.
An “optical gradient field” is an optical pattern having a variation in one or more parameters including intensity, wavelength or frequency, phase, polarization or other parameters relating to the optical energy. When generated by an interferometer, an optical gradient field or pattern may also be called an optical fringe field or fringe pattern, or variants thereof.
A “moving optical gradient field” is an optical gradient field that moves in space and/or time relative to other components of the system, e.g., particles or objects to be identified, characterized, selected and/or sorted, the medium, typically a fluidic medium, in contact with the particles, and/or any containment or support structure.
An “optical scattering force” is that force applied to a particle or thing caused by a momentum transfer from photons to material irradiated with optical energy.
An “optical gradient force” is one which causes a particle or object to be subject to a force based upon a difference in dielectric constant between the particle and the medium in which it is located.
“Optophoresis” or “Optophoretic” generally relates to the use of photonic or light energy to obtain information about or spatially move or otherwise usefully interact with a particle.
“Optophoretic constant” or “optophoretic signature” or “optophoretic fingerprint” refer to the parameter or parameters which distinguish or characterize particles for optical selection, identification, characterization or sorting.
An “optical tweezer” is a light based system having a highly focused beam to a point in space of sufficiently high intensity that the gradient force tends to pull a dielectric particle toward the point of highest intensity, typically with the gradient force being sufficiently strong to overcome the scattering force. Most typically, the laser beam is directed through a microscope objective with a high numerical aperture, with the beam having a diffraction limited spot size of approximately the wavelength of the light, 5,000 to 20,000 Å, though more typically 10,000 Å. Generally, an optical tweezer has a beam width in the focal plane of 2 μm or less, and typically about 1 μm.
“Separation” of two objects is the relative spatial distancing over time of a particle from some other reference point or thing.
“Sorting” involves the separation of two or more particles in a meaningful way.
Optical Components—Generation of Moving Optical Gradient Field.
The points raised in discussions of specific embodiments may be considered to be generally applicable to descriptions of the other embodiments, even if not expressly stated to be applicable.
The light source for use with systems has certain generally desirable properties. As to wavelength, the wavelength will generally be chosen based upon one or more considerations. In certain applications, it may be desirable to avoid damage to biological materials, such as cells. By choosing wavelengths in ranges where the absorption by cellular components, mostly water, are minimized, the deleterious effects of heating may be minimized. Wavelengths in the range from approximately 0.3 μm to approximately 1.8 μm, and more preferably, from substantially 0.8 to substantially 1.8 μm, aid in reducing biological damage. However, even for biological applications, a laser having a wavelength generally considered to be damaging to biological materials may be used, such as where the illumination is for a short period of time where deleterious absorption of energy does not occur. In yet other applications, it may be desirable to choose a wavelength based upon a property of the particle or object under consideration. For example, it may be desirable to choose the wavelength to be at or near an absorption band in order to increase (or decrease) the force applied against a particle having a particular attribute. Yet another consideration for wavelength choice may be compatibility with existing technology, or a wavelength naturally generated by a source. One example would be the choice of the wavelength at 1.55 μm. Numerous devices in the 1.55 μm wavelength region exist commercially and are used extensively for telecommunications applications.
Generally, the light sources will be coherent light sources. Most typically, the coherent light source will consist of a laser. However, non-coherent sources may be utilized, provided the system can generate the forces required to achieve the desired results. Various laser modes may be utilized, such as the Laguerre-Gaussian mode of the laser. Furthermore, if there is more than one light source in the system, these sources can be coherent or incoherent with respect to each other.
The spot size or periodicity of the intensity pattern is preferably chosen to optimize the effective results of the illumination. In certain applications, it is desirable to have the periodicity of the illumination in the range from substantially 1 to substantially 2 times the size (diameter or average size) of the particle or object. For many biological applications, a periodicity of from substantially 5 μm to 25 μm, and more preferably from 10 μm to 20 μm. In yet other applications, it may be desired to utilize a spot size smaller than the particle or object, such as where interrogation of a sub-cellular region is desired.
The examples of systems for generating intensity patterns, described below, as well as other systems for generating intensity patterns useful for the subject inventions include various optical components, as well as a control system to generate the desired pattern, intensity profile or other gradient, such as a moving optical field gradient. Various optical systems may be adapted for use in the systems of the invention, so as to effectively carry out the methods and achieve the results described herein. Exemplary systems which may be adapted in whole or in part include: Young's slits, Michelson interferometer, Mach-Zender interferometer, Haidinger circular fringe systems, Fresnel mirror interferometer, plane-parallel plate interferometer, Fabry-Perot interferometer and any other system for generating an optical gradient intensity pattern or fringe pattern.
Turning now to a detailed description of exemplary systems for use with the subject inventions.
The objective 104 is directed toward the sample plate 106. Optionally, a mirror 108, most preferably a planar mirror, may be disposed beneath the sample plate 106. The mirror 108 is oriented so as to provide reflected light onto the sample plate 106 bearing or containing the particles or objects under analysis or action of the system 80. The scattering force caused by the beam 102 as initially illuminates the sample plate 106 may be counteracted, in whole or in part, by directing the reflected radiation from mirror 108 back toward the sample. As discussed more in the section relating to surface effects, below, the reflected light and the upward scattering force reduce the overall effects of the scattering forces, such that the gradient forces may be more effectively utilized.
A control system 118 controls the modulator 92 so as to generate the desired optical force pattern within the system 80. Optionally, the imaging system 116 may be coupled to the control system 118. A feedback system may be created whereby the action of the particles on the sample plate 106 may be imaged through the system 116 and then utilized in the control system analysis to control the operation of the overall system 80.
As shown in
Beam 150 exits the interferometer 140 and is directed toward objective 152 and imaged at or near the sample plate 154. As shown, a dichroic mirror 170 serves to reflect the light 150, but to also permit passage of light from source 168, such as a fiber providing radiation from a source through the dichroic mirror 170 and objective 152 to illuminate the operative regions of the sample plate 154.
Optionally, a detection system may be disposed to image the operative portions of the sample plate 154. As shown, objective 156 is disposed beneath the sample plate 154, with the output radiation being transferred via mirror 158 to an imaging apparatus 164, such as a charge couple device (CCD). Optionally, an infrared filter 160 may be disposed within the optical path in order to select the desired wavelengths for detection. The output of the detector 164 is provided to an imaging system 166. As described in connection with other figures, the imaging system 166 may include image enhancement and image analysis software and provide various modes of display to be user. Optionally, the imaging system 166 is coupled to the control system 172 such as when used for feedback.
The microscope objective 232 serves to both provide the optical radiation to the sample plate 222 as well as to provide the imaging of the system. A light source 238, such as a laser, or more particularly, a laser diode, generates light which may be imaged by optics 240. A dichroic beam splitter 236 directs the radiation to the microscope objective 232. As shown, the objective has a magnification power of 100. For the biological applications, a magnification range of from 1 to 200 is desired, and more preferably, from 10 to 100. The objective 232 has a 1.25 numerical aperture. The preferable range of numerical apertures for the lenses is from 0.1 to 1.50, and more preferably from 0.4 to 1.25. The output from the objective 232 passes through the beam splitter 236, reflects from optional mirror 242 through optics (e.g., lens) 244, through the optional filter 246 to the imaging device 280. The imaging device, shown as a CCD, is connected to the imaging system 282. The output of the imaging system 282 is optionally coupled to the control system 284. As shown, the control system 284 controls both the translation stage 232 connected to the sample plate 212, as well as to the light source 238.
Yet another mirror arrangement consists of utilizing a micromirror arrangement. One such micromirror structure consists of an array of mirrors, such as utilized in the Texas Instrument Digital Micromirror product.
Arrays of sources 290 may be fabricated in many ways. One preferable structure is a vertical cavity surface emitting laser (VCSEL) array. VCSEL arrays are known to those skilled in the art and serve to generate optical patterns with control of the various lasers comprising the VCSELs. Similarly, laser diode bars provide an array of sources. Alternatively, separate light sources may be coupled, such as through fiber optic coupling, to a region directed toward the surface 294.
The imaging system may serve function beyond the mirror imaging of the system. In addition to monitoring the intensity, size and shape of the optical fringes, it may be used for purposes such as calibration.
The apparatus and methods of the instant inventions utilize, at least in part, forces on particles caused by light. In certain embodiments, a light pattern is moved relative to another physical structure, the particle or object, the medium containing the particle or object and/or the structure supporting the particle or object and the medium. Often times, a moving optical pattern, such as moving optical gradient field moves relative to the particles. By moving the light relative to particles, typically through a medium having some degree of viscosity, particles are separated or otherwise characterized based at least in part upon the optical force asserted against the particle. While most of the description describes the light moving relative to other structures, it will be appreciated that the relative motion may be achieved otherwise, such as by holding the light pattern stationary and moving the subject particle, medium and/or support structure relative to the optical pattern.
The profiles of
In one implementation of the system, the position of particles A and B in
By utilizing a property of the particle, such as the optical dielectric constant, the light forces serve to identify, select, characterize and/or sort particles having differences in those attributes. Exposure of one or more particles to the optical force may provide information regarding the status of that particle. No separation of that particle from any other particle or structure may be required. In yet other applications, the application of the optical force causes a separation of particles based upon characteristics, such that the separation between the particles may result in yet further separation. The modes of further separation may be of any various forms, such as fluidic separation, mechanical separation, such as through the use of mechanical devices or other capture structures, or optically, such as through the use of an optical tweezer as shown in
The apparatus and methods of these inventions utilize optical forces, either alone or in combination with additional forces, to characterize, identify, select and/or sort material based upon different properties or attributes of the particles. The optical profiles may be static, though vary with position, or dynamic. When dynamic, both the gradient fields as well as the scattering forces may be made to move relative to the particle, medium containing the particle, the support structure containing the particle and the medium. When using a moving optical gradient field, the motion may be at a constant velocity (speed and direction), or may vary in a linear or non-linear manner.
The optical forces may be used in conjunction with other forces. Generally, the optical forces do not interfere or conflict with the other forces. The additional forces may be magnetic forces, such as static magnetic forces as generated by a permanent magnet, or dynamic magnetic forces. Additional electric forces may be static, such as electrostatic forces, or may be dynamic, such as when subject to alternating electric fields. The various frequency ranges of alternating electromagnetic fields are generally termed as follows: DC is frequencies much less than 1 Hz, audio frequencies are from 1 Hz to 50 kHz, radio frequencies are from 50 kHz to 2 GHz, microwave frequencies are from 1 GHz to 200 GHz, infrared (1R) is from 20 GHz to 400 THz, visible is from 400 THz to 800 THz, ultraviolet (UV) is from 800 THz to 50 PHz, x-ray is from 5 PHz to 20 EHz and gamma rays are from 5 EHz and higher (see, e.g., Physics Vade Mecum).) The frequency ranges overlap, and the boundaries are sometimes defined slightly differently, but the ranges are always substantially the same. Dielectrophoretic forces are generated by alternating fields generally being in the single Hz to 10 MHz range. For the sake of completeness, we note that dielectrophoretic forces are more electrostatic in nature, whereas optophoretic forces are electromagnetic in nature (that is, comparing the frequency ranges is not meant to imply that they differ only in their frequency.) Gravitational forces may be used in conjunction with optical forces. By configuring the orientation of the apparatus, the forces of gravity may be used to affect the actions of the particle. For example, a channel may be disposed in a vertical direction so as to provide a downward force on a particle, such as where an optical force in the upward direction has been generated. When a channel is disposed in the horizontal direction, other forces, e.g., frictional forces, may be present. Fluidic forces (or Fluidics) may be advantageously utilized with optical forces. By utilizing an optical force to effect initial particle separation, a fluidic force may be utilized as the mechanism for further separating the particles. As yet another additional force, other optical forces may be applied against the particle. Any or all of the aforementioned additional forces may be used singly or in combination. Additionally, the forces may be utilized serially or may be applied simultaneously.
The techniques of this invention may be utilized in a non-guided, i.e., homogeneous, environment, or in a guided environment. A guided environment may optionally include structures such as channels, including microchannels, reservoirs, switches, disposal regions or other vesicles. The surfaces of the systems may be uniform, or may be heterogeneous.
The channels may be formed in a substrate or built upon some support or substrate. Generally, the depth of the channel would be on the order of from substantially 1 to substantially 2 diameters of the particle. For many biological cell sorting or characterization applications, the depth would be on the order of 10 to 20 μm. The width of the channels generally would be on the order of from substantially 2 to substantially 8 diameters of the particle, to allow for at least one optical gradient maximum with a width of the order of the particle diameter up to four or more optical gradient maxima with a width of the order of the particle diameter. For many biological cell sorting or characterization applications, the width would be of the order of 20 to 160 micrometers. The channels may have varying shapes, such as a rectangular channel structure with vertical walls, a V-shaped structure with intersecting non-planar walls, a curved structure, such as a semicircular or elliptical shaped channel. The channels, or the substrate or base when the channel was formed within it, may be made of various materials. For example, polymers, such as silicon elastomers (e.g., PDMS), gels (e.g., Agarose gels) and plastics (e.g., TMMA) may be utilized: glass, and silica are other materials. For certain applications, it may be desirable to have the support material be optically transparent. The surfaces may be charged or uncharged. The surface should have properties which are compatible with the materials to be placed in contact therewith. For example, surfaces having biological compatibility should be used for biological arrays or other operations.
Various forms of motive force may be used to cause the particles, typically included within a fluid, to move within the system. Electroosmotic forces may be utilized. As known in the art, various coatings of the walls or channels may be utilized to enhance or suppress the electroosmotic effect. Electrophoresis may be used to transport materials through the system. Pumping systems may be utilized such as where a pressure differential is impressed across the inlet and outlet of the system. Capillary action may be utilized to cause materials to move through the system. Gravity feeding may be utilized. Finally, mechanical systems such as rotors, micropumps, centrifugation may be utilized.
The systems described herein, and especially a more complex system, may include various additional structures and functionalities. For example, sensors, such as cell sensors, may be located adjacent various channels, e.g., channel 742. Various types of sensors are known to those skilled in the art, including capacitive sensors, optical sensors and electrical sensors. Complex systems may further include various holding vessels or vesicles, being used for source materials or collection materials, or as an intermediate holding reservoir. Complex systems may further include amplification systems. For example, a PCR amplification system may be utilized within the system. Other linear or exponential biological amplification methods known to those skilled in the art may be integrated. Complex systems may further include assays or other detection schemes. Counters may be integrated within the system. For example, a counter may be disposed adjacent an output to tally the number of particles or cells flowing through the output. The systems of the instant invention are useable with microelectromechanical (MEMs) technology. MEMs systems provide for microsized electrical and mechanical devices, such as for actuation of switches, pumps or other electrical or mechanical devices. The system may optionally include various containment structures, such as flow cells or cover slips over microchannels.
A computerized workstation may include a miniaturized sample station with active fluidics, an optical platform containing a laser (e.g., a near infrared laser for biological applications) and necessary system hardware for data analysis and interpretation. The system may include real-time analysis and testing under full computer control.
The inventions herein may be used alone, or with other methods of cell separation. Current methods for cell separation and analysis include flow cytometry, density gradients, antibody panning, magnetic activated cell sorting (“MACS™”), microscopy, dielectrophoresis and various physiological and biochemical assays. MACS separations work only with small cell populations and do not achieve the purity of flow cytometry. Flow cytometry, otherwise known as Fluorescent Activated Cell Sorting (“FACS™”) requires labeling.
In yet another aspect, the systems of the present invention may optionally include sample preparation steps and structure for performing them. For example, sample preparation may include a preliminary step of obtaining uniform size, e.g., radius, particles for subsequent optical sorting.
The systems may optionally include disposable components. For example, the channel structures described may be formed in separable, disposable plates. The disposable component would be adapted for use in a larger system that would typically include control electronics, optical components and the control system. The fluidic system may be included in part in the disposable component, as well as in the non-disposable system components.
Methods for Reducing or Modifying Forces
The system and methods may include various techniques for reducing or otherwise modifying forces. Certain forces may be desirable in certain applications, but undesirable in other applications. By selecting the technique to reduce or minimize the undesired forces, the desired forces may more efficiently, sensitively and specifically sort or identify the desired particles or conditions. Brownian motion of particles may be an undesired condition for certain applications. Cooling of the system may result in a reduced amount of Brownian motion. The system itself may be cooled, or the fluidic medium may be cooled.
Yet another force which may be undesired in certain applications is friction or other form of sticking force. If surface effects are to be minimized, various techniques may be utilized. For example, a counterpropagating beam arrangement may be utilized to capture particles and to remove them from contact with undesired surfaces. Alternatively, the particles may be levitated, such as through the use of reflected light (see, e.g.,
Yet other techniques exist for addressing friction, stiction, electrostatic and other surface interactions which may interfere with the mobility of cells and/or particles. For example, surfaces may be treated, such as through the use of covalent or non-covalent chemistries, which may moderate the frictional and/or adhesion forces. Surfaces may be pretreated to provide better starting surfaces. Such pretreatments may include plasma etching and cleaning, solvent washes and pH washes, either singly or in combination. Surfaces may also be functionalized with agents which inhibit or minimize frictional and adhesive forces. Single or multi-step, multi-layer chemistries may be utilized. By way of example, a fluorosilane may be used in a single layer arrangement which renders the surface hydrophobic. A two-step, two-layer chemistry may be, for example, aminopropylsilane followed by carboxy-PEG. Teflon formal coating reagents such as CYTOP™ or Parylene™ can also be used. Certain coatings may have the additional benefit of reducing surface irregularities. Functional groups may, in certain cases, be introduced into the substrate itself. For example, a polymeric substrate may include functional monomers. Further, surfaces may be derivitized to provide a surface which is responsive to other triggers. For example, a derivatized surface may be responsive to external forces, such as an electric field. Alternatively, surfaces may be derivatized such that they selectively bind via affinity or other interactions.
Yet another technique for reducing surface interactions is to utilize a biphasic medium where the cells or particles are kept at the interface. Such aqueous polymer solutions, such as PEG-dextran partition into two phases. If the cells partitioned preferentially into one of the layers, then under an optical gradient the cells would be effectively floating at the interface.
Methods for Enhancing or Changing the Dielectric Constant
Optionally, the particles to be subject to the apparatus and methods of these inventions may be either labeled or unlabeled. If labeled, the label would typically be one which changes or contributes to the dielectric constant of the particle or new particle (i.e., the initial particle and the label will act as one new particle). For example, a gold label or a diamond label would effectively change most typical dielectric constants of particles.
Yet other systems may include an expressible change in dielectric constant. For example, a genetic sequence may exist, or be modified to contain, an expressible protein or other material which when expressed changes the dielectric constant of the cell or system. Another way to tune the dielectric constant of the medium is to have a single medium in a fluidic chamber where the dielectric constant can be changed by changing the temperature, applying an electric field, applying an optical filed, etc. One example of this would be to dope the medium with a highly bi-refringent molecule such as a water-soluble liquid crystal. In this case, the index of refraction that the optical beam will see can be altered by changing the amplitude and direction of an electric field.
Methods for Increasing Sensitivity
Maximizing the force on a particle for a given intensity gradient suggests that the difference in dielectric constant between the particle and medium should be maximized. However, when sensitivity is required in an application, the medium should be selected such that the dielectric constant of the medium is close to the dielectric constant of the particle or particles to be sorted. By way of example, if the particle population to be sorted has dielectric constants ranging from 1.25 to 1.3, it would be desirable to choose a dielectric constant which is close to (or even within) that range. By close, a dielectric constant within 10% or, more particularly, within 5%, would be advantageous. While the absolute value of the magnitude of the force on the particle population may be less than in the case where the dielectric constant differs markedly from the dielectric constant of the medium, the difference in resulting motion of the particles may be larger when the dielectric constant of the medium is close to the range of dielectric constants of the particles in the population. While utilizing the increased sensitivity of this technique at the outset, once the separation begins, the force may be increased by changing the dielectric constant of the medium to a more substantial difference from the dielectric constants of the particle or particle collection. As indicated, it is possible to choose the dielectric constant of the medium to be within the range of dielectric constants of the particle population. In that instance, particles having a dielectric constant above the dielectric constant of the medium will feel a force in one direction, whereas those particles having a dielectric constant less than the dielectric constant of the medium will feel a force moving in the opposite direction.
Scattering Force Systems
It is possible to utilize the scattering force, either alone or in combination with the optical gradient force, such as supplied by a moving optical field gradient, for separation of particles.
The first setup is a moving fringe workstation for optophoresis experiments. A high power, 2.5 watt, Nd-YAG laser (A) is the near IR, 1064 nm wavelength, light source. The fringe pattern is produced by directing the collimated laser beam from the mirror (1) through the Michelson interferometer formed by the prism beam splitter (2) and the carefully aligned mirrors (3). A variable phase retarder (4) causes the fringe pattern to continuously move. This fringe pattern is directed by the periscope (5) through the telescope (5 a) and (5 b) to size the pattern to fill the back focal plane of the microscope objective, and then is directed by the dichroic beam splitter (6) through a 20× microscope objective (7) to produce an image of the moving fringe pattern in the fluidic chamber holding the sample to be sorted. A second, 60× microscope objective (8) images the flow cell onto a CCD camera to provide visualization of the sorting experiments. A fiber-optic illuminator (9) provides illumination, through the dichroic beam splitter (6), for the sample in the fluidic chamber. The fluidic chamber is positioned between the two microscope objectives by means of an XYZ-translation stage.
It will be appreciated by those skilled in the art that there are any number of additional or different components which may be included. For example, additional mirrors or other optical routing components may be used to ‘steer’ the beam where required. Various optical components for expanding or collimating the beam may be used, as needed. In the set-up implementing
The second setup is a workstation for measuring and comparing the dielectric properties of cells and particles at near IR optical frequencies, using a 600 mW, ultra-low noise Nd-YAG laser (B) as a light source. The remainder of the optical setup is similar to the moving fringe workstation, except there is no interferometer to produce moving fringes. Instead a single, partially focused illumination spot is imaged within the fluidic chamber. The interaction of cells with this illumination field provides a measurement of the dielectric constant of the cells at near IR optical frequencies.
High Throughput Biology
The methods and apparatus herein permit a robust cell analysis system suitable for use in high throughput biology in pharmaceutical and life sciences research. This system may be manufactured using higher performance, lower cost optical devices in the system. A fully integrated high throughput biology, cell analysis workstation is suitable for use in drug discovery, drug discovery, toxicology and life science research.
These systems may utilize advanced optical technologies to revolutionize the drug discovery process and cellular characterization, separation and analysis by integrating optophoresis technology into devices for the rapid identification, selection and sorting of specific cells based on their innate properties, including their innate optical dielectric properties. In addition, since the technology is based on the recognition of such innate properties, labels are not required, greatly simplifying and accelerating the testing process. The lasers employed are preferably in the biologically-compatible infrared wavelengths, allowing precise cell characterization and manipulation with little or no effect on the cell itself. The technology is suited to the post-genomics era, where the interaction of the cell's molecular design/make-up (DNA, RNA and proteins) and the specific cellular changes (growth, differentiation, tissue formation and death) are of critical importance to the basic understanding of health and disease.
The Optophoresis technology changes the nature of cell-based assays. Applications would include all methods of cellular characterization and sorting. The technology also offers diverse applications in the areas of molecular and cellular physiology. Optophoresis technology addresses fundamental properties of the cell itself, including its optical dielectric properties. The optophoretic properties of the cell change from cell type to cell type, and in response to external stimuli. These properties are reflective of the overall physiologic status of the cell. Active cells have dielectric properties that are different from resting cells of the same type. Cancer cells have different optophoretic properties than their normal counterparts. These cellular properties can also be used effectively in drug discovery and pharmaceutical research, since nearly all drugs are targeted ultimately to have direct effects on cells themselves. In other words, drugs designed to effect specific molecular targets will ultimately manifest their effects on cellular properties as they change the net dielectric charge of the cell. Therefore, rapid screening of cells for drug activity or toxicity is an application of the technology, and may be referred to as High Throughput Biology. Other main applications include drug discovery and pharmaceutical research.
The Human Genome Project and other associated genome programs will provide enormous demand for improved drug development and screening technologies. Sophisticated cellular approaches will be needed for cost-effective and functional screening of new drug targets. Likewise, information from the genome projects will create demand for improved methods of tissue and organ engineering, each requiring access to well characterized cellular materials. Moreover, optical technology from the information and telecommunications industry will provide the system hardware for improved optical cell selection and sorting. The price/performance ratios for high powered near infrared and infrared lasers originally developed for telecommunications applications continue to improve significantly. In addition, solid-state diode lasers may be used having a variety of new wavelengths, with typically much higher power output than older versions. Vertical Cavity Surface Emitting Lasers (“VCSELs”) provide arrays of diode lasers at very reasonable costs with increasing power output.
A computerized Workstation may be composed of a miniaturized sample station with active fluidics, an optical platform containing a near infrared laser and necessary system hardware for data analysis and interpretation. The system includes real-time analysis and testing under full computer control. Principal applications of the technology include cell characterization and selection, particularly for identifying and selecting distinct cells from complex backgrounds.
Importantly, unlabelled, physiologically normal, intact test cells will be employed in the system. The sample is quickly analyzed, with the cells classified and sorted by the optical field, thereby allowing characterization of drug response and identify toxicity or other measures of drug efficacy. Characterizing the cellular optophoretic properties uniquely associated with various drug testing outcomes and disease states is a part of this invention. Identification of these novel parameters constitutes useful information.
An integrated system may, in various aspects, permit: the identification, selection and separation of cells without the use of labels and without damaging the cells; perform complex cell analysis and separation tasks with ease and efficiency; observe cells in real time as they are being tested and manipulated; establish custom cell sorting protocols for later use; isolate rare cells from complex backgrounds; purify and enrich rare cells (e.g. stem cells, fragile cells, tumor cells); more easily link cell phenotype to genotype; study cell-cell interactions under precise and optical control; and control sample processing and analysis from start to finish.
The technology offers a unique and valuable approach to building cellular arrays that could miniaturize current assays, increase throughput and decrease unit costs. Single cell (or small groups of cells) based assays will allow miniaturization, and could allow more detailed study of cell function and their response to drugs and other stimuli. This would permit cellular arrays or cell chips to perform parallel high-throughput processing of single cell assays. It could also permit the standardization of cell chip fabrication, yielding a more efficient method for creation of cell chips applicable to a variety of different cells types.
Mammalian cell culture is one of the key areas in both research (e.g., discovery of new cell-produced compounds and creation of new cell lines capable of producing specific proteins) and development (e.g., developing monoclonal cell lines capable of producing highly specific proteins for further research and testing). Mammalian cell culture is also a key technology for the production of new biopharmaceuticals on a commercial scale.
Once researchers have identified drug targets, compounds or vaccines, mammalian cell culture is an important technology for the production of quantities necessary for further research and development. There are currently more than 70 approved biotechnology medicines and more than 350 such compounds in testing, targeting more than 200 diseases.
Optical cell characterization, sorting and analysis technologies could be useful in selecting and separating lines of mammalian cells according to whether they produce a new protein or biopharmaceutical compound and according to the yield of the protein or compound. Cell yield is a key factor in determining the size of the plant a manufacturer must build to produce commercial quantities of a new biotechnology drug.
We turn now to more specific discussions of applications. First, we address separation applications, and second, address monitoring applications.
White cells from red cells. White blood cells are the constituents of blood which are responsible for the immune response as compared with red cells which transport oxygen through the body. White cells need to be removed from red cells prior to transfusion for better tolerance and to decrease infection risks. It is also often important to remove red cells in order to obtain enriched populations of white cells for analysis or manipulation. Optophoresis can allow the separation of these two distinct cell populations from one another for use in applications where a single population is required.
Reticulocytes from mature red blood cells. Reticulocytes, which are immature red blood cells normally found at very low levels can be indicators of disease states when they are found at increased levels. This application would use optophoresis for the separation and enumeration of the levels of reticulocytes from whole blood.
Clinical Care Applications, e.g., Fetal stem cells from maternal circulation. The Clinical Care applications include cell-based treatments and clinical diagnostics. The successful isolation of fetal cells from maternal blood represents a source of fetal DNA obtainable in a non-invasive manner. A number of investigators worldwide have now demonstrated that fetal cells are present in the maternal circulation and can be retrieved for genetic analysis. The major current challenges in fetal cell isolation include selection of the target fetal cell type, selection and isolation of the cells and the means of genetic analysis once the cells are isolated. Using a maternal blood sample, the system can identify the rare fetal cells circulating within the mother's blood and to permit the diagnosis of genetic disorders that account for up to 95% of prenatal genetic abnormalities, e.g., Down's Syndrome. Cell-based treatments refer to procedures similar to diagnostic procedures, but for which the clinical purpose is somewhat broader. During pregnancy, a small number of fetal cells enter the maternal circulation. By purifying these cells using optophoresis prenatal diagnosis of a variety of genetic abnormalities would be possible from a single maternal blood sample.
Clinical Care Applications, e.g., Stem Cell Isolation. The purpose of stem cell isolation is to purify stem cells from stem cell grafts for transplantation, i.e., to remove T-cells in allogeneic grafts (where the donor and the recipient are not the same person) and cancer cells in autologous grafts (where the donor and the recipient are the same person). Currently stem cell technologies suffer from several drawbacks. For example, the recovery efficiency of stem cells obtained using currently available systems is on the order of 65-70%. In addition, current methods do not offer the 100% purity which is beneficial in transplant procedures.
Tumor cells from blood. Minimal Residual Disease (MRD) Testing The National Cancer Institute (NCI) estimates that approximately 8.4 million Americans alive today have a history of cancer, and that over 1.2 million new cancer cases were diagnosed in 2000. The NCI also estimates that since 1990 approximately 13 million new cancer cases were diagnosed, excluding noninvasive and squamous cell skin cancers. Optophoresis technology addresses some of the key unmet needs for better cancer screening, including: accurate, reproducible and standardized techniques that can detect, quantify and characterize disseminated cancer cells; highly specific and sensitive immunocytological techniques; faster speed of cell sorting; and techniques that can characterize and isolate viable cancer cells for further analysis.
Cancer cells may be found in low numbers circulating in the blood of patients with various forms of that disease, particularly when metastasis has occurred. The presence of tumor cells in the blood can be used for a diagnosis of cancer, or to follow the success or failure of various treatment protocols. Such tumor cells are extremely rare, so a means of enrichment from blood such as optophoresis would need to be employed in order to have enough cells to detect for accurate diagnosis. Another application for optophoresis in this regard would be to remove tumor cells from blood or stem cell products prior to them being used to perform an autologous transplant for a cancer patient.
Fetal stem cells from cord blood. The umbilical cord from a newborn generally contains blood which is rich in stem cells. The cord blood material is usually discarded at birth; however, there are both academic and private concerns who are banking cord blood so that such discarded material can be used for either autologous or allogenic stem cell replacement. Enrichment of the cord blood stem cells by optophoresis would allow for a smaller amount of material to be stored, which could be more easily given back to the patient or another host.
Adult stem cells from liver, neural tissue, bone marrow, and the Like. It is becoming increasingly clear that many mature tissues have small subpopulations of immortal stem cells which may be manipulated ex vivo and then can be reintroduced into a patient in order to repopulate a damaged tissue. Optophoresis can be used to purify these extremely rare adult stem cells so that they may be used for cell therapy applications.
Islet cells from pancreas. It has been proposed that for persons with diabetes resulting from lack of insulin production, the insulin producing beta islet cells from a healthy pancreas could be transplanted to restore that function to the diabetic person. These cells make up only a small fraction of the total donor pancreas. Optophoresis provides a method to enrich the islet cells and would be useful for preparation of this specific type of cell for transplantation.
Activated B or T cells. During an immune response either T or B white cell subsets which target a specific antigen become active. These specific activated cells may be required as separate components for use in ex vivo expansion to then be applied as immunotherapy products or to be gotten rid of, since activated B or T cells can cause unwanted immune reactions in a patient such as organ rejection, or autoimmune diseases such as lupus or rheumatoid arthritis. Optophoresis provides a method to obtain activated cells either to enrich and give back to a patient or to discard cells which are causing pathological destruction.
Dendritic cells. Dendritic cells are a subset of white blood cells which are critical to establishing a T-cell mediated immune response. Biotech and pharmaceutical companies are working on ways to harvest dendritic cells and use them ex vivo in conjunction with the appropriate antigen to produce a specific activated T cell response. Optophoresis would allow isolation of large numbers of dendritic cells for such work.
HPRT− cells. Hypoxanthine-guanine phosphoribosyltransferase (HPRT) is an enzyme which exits in many cells of the blood and is involved in the nucleoside scavenging pathway. Persons who have high mutation rates due to either endogenous genetic mutations or exogenous exposure to mutagens can be screened for HPRT lacking cells (HPRT−) which indicate a mutation has occurred in this gene. Optophoresis following screening by compounds which go through the HPRT system can be used to easily select HPRT minus cells and quantitate their numbers.
Viable or mobile sperm cells. Approximately 12% of couples are unable to initiate a pregnancy without some form of assistance or therapy. In about 30% these cases, the male appears to be singularly responsible. In an additional 20% of cases, both male and female factors can be identified. Thus, a male factor is partly responsible for difficulties in conception in roughly 50% of cases. The number of women aged 15-44 with impaired ability to have children is well over 6 million. Semen analysis is currently performed using a variety of tests and is based on a number of parameters including count, volume, pH, viscosity, motility and morphology. At present, semen analysis is a subjective and manual process. The results of semen analysis do not always clearly indicate if the male is contributing to the couple's infertility. Gradient centrifugation to isolate motile sperm is an inefficient process (10 to 20% recovery rate). Sperm selection is accomplished using either gradient centrifugation to isolate motile sperm used in In Utero Insemination (IUI) and In Vitro Fertilization (IVF) or visual inspection and selection to isolate morphologically correct sperm used in IVF and Intracytoplasmic Sperm Injection (ICSI). Each year in the U.S., 600,000 males seek medical assistance for infertility.
One of the reasons for male infertility is the lack of high enough percentages of viable and/or mobile sperm cells. Viable and/or mobile sperm cells can be selected using optophoresis and by enriching their numbers, higher rates of fertilization can be achieved. This application could also be used to select X from Y bearing sperm and vice versa, which would then be used selectively to induce pregnancies in animal applications where one sex of animal is vastly preferred for economic reasons (dairy cows need to be female, while it is preferable for meat producing cattle to be male for example).
Liposomes loaded with various compounds. A recent mode of therapeutic delivery of pharmaceutical products is to use liposomes as the delivery vehicle. It should be possible using optophoresis to separate liposomes with different levels of drug in them and to enrich for those liposomes in which the drugs are most concentrated.
Tissue Engineering, e.g., Cartilage precursors from fat cells. Tissue engineering involves the use of living cells to develop biological substitutes for tissue replacements which can be used in place of traditional synthetic implants. Loss of human tissue or organ function is a devastating problem for a patient and family. The goal of tissue engineering is to design and grow new tissue outside the body that could then be transplanted into the body.
A recent report has demonstrated that cells found in human adipose tissue can be used ex vivo to generate cartilage which can be used as a transplant material to repair damage in human joints. Optophoresis can be used to purify the cartilage forming cells from the other cells in adipose tissue for ex vivo expansion and eventual tissue engineering therapy.
Nanomanipulation of small numbers of cells. Recent miniaturization of many lab processes have resulted in many lab analyses being put onto smaller and smaller platforms, evolving towards a “lab-on-a-chip” approach. While manipulation of biomolecules in solution has become routine in such environments, manipulation of small numbers of cells in microchannel and other nano-devices has not been widely achieved. Optophoresis will allow cells to be moved in microchannels and directed into the region with the appropriate processes on the chip.
Cellular organelles; mitochondria, nucleus, ER, microsomes. The internal constituents of a cell consists of the cytoplasm and many organelles such as the mitochondria, nucleus, etc. Changes in the numbers or physical features of these organelles can be used to monitor changes in the physiology of the cell itself. Optophoresis can allow cells to be selected and enriched which have particular types, morphologies or numbers of a particular organelle.
Cow reticulocytes for BSE assays. It has been reported that a cellular component of the reticulocyte, EDRF, is found at elevated levels in the reticulocytes of cows infected with BSE (bovine spongiform encephalopathy). Reticulocytes are generally found at low levels in the blood and therefore the use of optophoresis would allow their enrichment and would increase the accuracy of diagnostic tests based on the quantitation of the EDRF mRNA or protein.
Growing/dividing cells vs. resting cells. Cells may be stimulated to grow by various growth factors or growth conditions. Most assays which exist for cell growth require the addition of external labeling reagents and/or significant time in culture before cell growth can be demonstrated. By using optophoresis, cells which have begun to divide will be identified, providing a rapid method for calculating how much of a given cell population is in the growth phase. Cells in different parts of the cell cycle should have different optical properties and these may be used to either sort cells based on where in the cycle they are as well as to determine what fraction of the total cell population is in each stage of the cell cycle.
Apoptotic cells. Cells which are undergoing programmed cell death or apoptosis can be used to identify specific drugs or other phenomenon which lead to this event. Optophoresis can be used to identify which cells are undergoing apoptosis and this knowledge can be used to screen novel molecules or cell conditions or interactions which promote apoptosis.
Cells with membrane channels open; change in membrane potentials. The outer membrane of many types of cells contain channels which facilitate the passage of ions and small molecules into and out of the cell. Movement of such molecules can lead to further changes in the cell such as changes in electrical potential, changes in levels of second messengers, etc. Knowledge of these changes can be useful in drug screening for compounds which modulate membrane channel activity. Optophoresis can be used to indicate when membrane channels are being perturbed by exogenous compounds.
Live vs. dead cells. Many applications exist which require the identification and quantitation of live versus dead cells. By using optophoresis dead cells can be identified and counted.
Virally infected cells. There are many diagnostic applications where it is important to measure cells which contain virus, including ones for CMV, HIV, etc. Optophoresis can be used to differentiate cells which contain virus from cells which do not.
Cells with abnormal nucleus or elevated DNA content. One of the hallmarks of a tumor cell is that it will contain either excess DNA, resulting in an abnormal size and/or shape to it's nucleus. By using optophoresis tuned to the nuclear content of a cell populations with abnormal amounts of DNA and/or nuclear structure may be identified and this information can be used as a diagnostic or prognostic indicator for cancer patients.
Cells decorated with antibodies. A large selection of commercially available antibodies exists which have specificities to cellular markers which define unique proteins and/or types of cells. Many diagnostic applications rely on the characterization of cell types by identifying what antibodies bind to their surface. Optophoresis can be used to detect when a cell has a specific antibody bound to it.
Cells with bound ligands, peptides, growth factors. Many compounds and proteins bind to receptors on the surface of specific cell types. Such ligands may then cause changes inside the cell. Many drug screens look for such interactions. Optophoresis provides a means to monitor binding of exogenous large and small molecules to the outside of the cell, as well as measurement of physiological changes inside the cell as a result of compound binding.
Bacteria for viability after antibiotic exposure. Microorganisms are often tested for sensitivity to a spectrum of antibiotics in order to determine the appropriate therapy to pursue to kill an infectious organism. Optophoresis can be used to monitor bacterial cells for viability and for cessation of growth following antibiotic exposure.
Drug screening on the NCI 60 panel. A panel of 60 tumor cell lines has been established by the National Cancer Institute as a screening tool to determine compounds which may have properties favorable to use as chemotherapeutic agents. It should be possible to use optophoresis to array all 60 lines and then to challenge them with known and novel chemicals and to monitor the cell lines for response to the chemicals.
Cells for cytoskeletal changes. The cytoskeleton is a complex of structural proteins which keeps the internal structure of the cell intact. Many drugs such as taxol, vincristine, etc . . . as well as other external stimuli such as temperature are known to cause the cytoskeleton to be disrupted and breakdown. Optophoresis provides a means to monitor populations of cells for perturbations in the cytoskeleton.
Beads with compounds bound to them, to measure interactions with the cell surface or with other beads. The interactions of microspheres with cells or other compounds has been used in a number of in vitro diagnostic applications. Compounds may be attached to beads and the interactions of the beads with cells or with beads with other compounds on them can be monitored by optophoresis.
Progenitor cell/colony forming assays. Progenitors are cells of a given tissue which can give rise to large numbers of more mature cells of that same tissue. A typical assay for measuring progenitor cells is to allow these cells to remain in culture and to count how many colonies of the appropriate mature cell type they form in a given time. This type of assay is slow and cumbersome sometimes taking weeks to perform. By using optophoresis to monitor the growth of a single cell, progenitor proliferation can be measured on a nano-scale and results should be obtained within a much shorter length of time.
Dose limiting toxicity screening. Almost all compounds are toxic at some level, and the specific levels of toxicity of compounds are identified by measuring at what concentration they kill living cells and organisms. By monitoring living cells with optophoresis as the dose of a compound is slowly increased, the level at which optical properties indicative of cell damage and/or death can be ascertained.
Monitor lipid composition/membrane fluidity in cells. The membranes of all cells are composed of lipids which must maintain both the proper degree of membrane fluidity at the same time that they maintain basic cell membrane integrity. Optophoresis should be able to measure the fluidity of the membrane and to provide information on compounds and conditions which can change membrane fluidity, causing membranes to be either more or less fluid.
Measure clotting/platelet aggregation. Components found in the blood such as platelets and clotting proteins are needed to facilitate blood clot formation under the appropriate circumstances. Clotting is often monitored in order to measure disease states or to assess basic blood physiology. Optophoresis can provide information on platelet aggregation and clot formation.
Certain of the data reported herein were generated with the following setup. Optical gradient fields were generated using a Michelson interferometer and either a 150 mW, 812 nm laser (812 system) or a 2.5 W, 1064 nm laser (1064 system). The 812 system used a 100× (1.25 NA) oil immersion lens to focus the fringe pattern and to visualize the sample. The 1064 system used a 20× objective to focus the fringes and a 60× objective to visualize the sample. In general the sample cell was a coated microscope slide and/or coverslip that was sealed with Vaseline. Coverslip spacers controlled the height of the cell at approximately 150 micrometers
Coating Of Surfaces; Rain-X™, Agarose, CYTOP, Fluorosilane Scattering forces tend to push the particles or cells against the surface of the sample cell. Therefore, a number of surface coatings were evaluated to minimize nonspecific adhesion and frictional forces. Hydrophobic/hydrophilic and covalent/noncovalent surface treatments were evaluated.
Covalent/Hydrophobic Glass slides and coverslips were treated with perfluoro-octyltrichlorosilane (Aldrich, Milwaukee, Wis.) using solution or vapor deposition. Solution deposition was as follows: a 2-5% silane solution in ethanol, incubate 30 minutes at room temperature, rinse 3 times in ethanol and air dry. Vapor deposition involved applying equal volumes of silane and water in separate microcentrifuge tubes and sealing in a vacuum chamber with the substrate to be treated. Heat to 50° C., 15 hrs.
Noncovalent/Hydrophobic—A commercial water repellent containing polysiloxanes, Rain-X, was applied according to the manufacturer's instructions.
A liquid Teflon, CYTOP (CTL-107M, Wilmington, Del.) was spun coated using a microfuge. The CYTOP was diluted to 10% in fluorooctane (v/v) and 50 microliters was pipetted and spun for 5 seconds. This was repeated a second time and then air dried.
Noncovalent/Hydrophilic—Agarose hydrogel coatings were prepared as follows: melt 2% agarose in water, pipette 100 microliters to the substrate, spin for 5 seconds, bake at 37° C. for 30 minutes.
All of the coatings were effective when working with particles. The CYTOP was more effective at preventing adhesion when working with biological cells.
Separation By Size—Polystyrene particles (Bangs Labs, Fishers, Ind.) of different sizes (1, 3 and 5 micrometer diameter) were separated using moving optical gradient fields. Three and five micrometer diameter particles were diluted 1/500 in distilled water and ten microliters was pipetted onto a Rain-X coated slide. The 812 system was used to generate a spot size of 25-30 micrometers consisting of 4-5 fringe periods and moving at 15 micrometers/second.
Separation By Refractive Index—Polystyrene, polymethylmethacrylate and silica particles of similar size (˜5 micrometer diameter, Bangs Labs) and refractive indexes of 1.59, 1.49 and 1.37, respectively, were sorted by moving optical gradient fields. Observed escape velocities for polystyrene, PMMA and silica were 44, 47 and 32 micrometers/second, respectively. Briefly, a particle is aligned in the fringe and the fringes are moved at increasing speed until the particle slips. This results in a semi-quantitative measurement of the total forces experienced by the particle, i.e. photonic, hydrodynamic and frictional. It will be appreciated by those skilled in the art that the absolute value of the escape velocity will differ depending upon system conditions, e.g., laser power. The numerical results provided herein are meant to provide measured data for the system actually used, and are not to be considered a limitation on the values which might exist in a different system.
Particles were diluted 1/500 in distilled water (n=1.33). The 812 system was used to generate a gradient field with a fringe period of 10 micrometers. Polystyrene and PMMA particles were sorted from silica particles by moving the gradient field at a threshold value of approximately 40 micrometers/second.
Separation By Surface Functionalization and Doping—Polystyrene particles (˜6 micrometer diameter) colored with blue or pink dye were purchased from Polysciences, Inc. The pink particles also had carboxyl groups on the particle surface. The particles were diluted 1/500 in distilled water and 10 microliters was pipetted onto a Rain-X coated slide. The 812 system was used to generate a moving optical gradient field with a fringe period of approximately 12 micrometers. In the fringes, the pink particle moved preferentially.
In another experiment, 1 micrometer latex beads labeled with biotin were used to determine changes in escape velocity when different ligands were attached. The biotin labeled beads were diluted 1/100 in PBS buffer. A 50 ul aliquot was incubated with an excess of streptavidin or 10 nanometer colloidal gold-streptavidin conjugate for 10 minutes. The beads were pelleted by centrifugation and resuspended in PBS buffer. Measured escape velocities, using the 1064 system, were 5.3, 4.3 and 3.6 micrometers/second for biotin labeled beads, beads with streptavidin and beads with streptavidin-colloidal gold, respectively.
Separation By Wavelength Resonance (812 vs. 1064 nm)—The above experiment with colored polystyrene particles was repeated using the 1064 system and the results were reversed. The blue particle was preferentially moved. Similar results were obtained when the 1064 system was set at 150 mW rather than 2.5 W. This suggests that wavelength tuning could enhance the discrimination process.
Separation By Index Matching—Silica and polystyrene particles (3 and 5 micrometer diameter, respectively) were diluted 1/500 in hydrophilic silicone (dimethylsiloxane-ethylene oxide block copolymer, Gelest, Inc., Tullytown, Pa.). The refractive index of the medium (n=1.44) was intermediate between the silica (n=1.37) and polystyrene (n=1.59) particles. The particle size was not important in this experiment.
Using the 1064 system, the gradient force was focused into a diffuse spot approx. 15 micrometers in diameter. The polystyene particle moved towards the gradient field while the silica particle moved away from it. This demonstrated that the suspending medium could be changed to optimize separation. Separation Red Blood Cells vs. Retic
A reticulocyte control (Retic-Chex) was obtained from Streck Labs. A sample containing 6% reticulocytes was stained for 15 minutes with New Methylene Blue for 15 minutes, a nucleic acid stain that differentially stains the reticulocytes versus the unnucleated red blood cells. The sample was diluted 1/200 in PBS and mounted on a fluorosilane coated slide The 812 system was used to generate optical gradient fields. The fringe period was adjusted to 15 micrometers and was moved at 15 micrometers/second. The reticulocytes were preferentially moved relative to red blood cells.
Separation of White Blood Cells vs. Red Blood Cells
A whole blood control (Para12 Plus) was obtained from Streck Labs. The sample was stained for 15 minutes with New Methylene Blue, a nucleic acid stain that differentially stains the nucleated white blood cells versus the unnucleated red blood cells. The sample was diluted 1/200 in PBS and mounted on a fluorosilane coated slide. The 812 system was used to generate optical gradient fields. The fringe period was adjusted to 15 micrometers and was moved at 22 micrometers/second. The white blood cells were moved by the fringes while the red blood cells were not. Separation of Leukemia vs. Red Blood Cells
One milliliter of the leukemia cell line U937 suspension was pelleted and resuspended in 100 microliters PBS containing 1% BSA. Equal volumes of U937 and a 1/200 dilution of red blood cells were mixed together and 10 microliters was placed on a CYTOP coated slide. Separate measurements with moving fringe fields showed that the escape velocity for U937 cells was significantly higher than the escape velocity for red blood cells, 60 and 23 micrometers/second, respectively. The 1064 system was used to generate optical gradient fields with a fringe period of approximately 30 micrometers and moving at 45 micrometers/second, an intermediate fringe velocity. As expected the U937 cells move with the fringes and the red blood cells do not.
Sorting of Red Blood Cells vs. Polystyrene Particles in Microchannels
Glass microchannels with an “H” configuration (see
A 1/200 mixture of red blood cells and particles in PBS buffer, 1% BSA was added to an inlet reservoir and an equal volume of PBS buffer, 1% BSA was added to the other inlet reservoir. The gradient field was positioned in the crossbar of the “H” near the downstream junction. The 1064 system was fitted with a cylindrical lens to increase the aspect ratio of the gradient field. The resultant gradient field was approximately 40 micrometers wide by 80 micrometers long with a fringe period of 12 ums and moving at 30 micrometers/second.
In the absence of or with a nonmoving optical gradient field, the cells and particles remain in the top half of the “H” channel and exit via the upper outlet. In the presence of a moving optical gradient field, the particles are diverted to the lower outlet arm and are sorted from the red blood cells.
The flow rate was adjusted to approximately 80 micrometers/second. The sorting process was digitally recorded and subsequently analyzed. Out of 132 possible sorting events (121 red blood cells and 11 particles), 2 red blood cells and no particles were mis-sorted. The sort rate was approximately 2/second.
Sorting of Red Blood Cells vs. White Blood Cells in Microchannels
Gradient Force Manipulation of Liposomes
Fluorescently labeled liposomes, approximately 0.2 micrometers in diameter, were obtained from a B-D Qtest Strep kit. Ten microliters was placed in a Rain-X coated slide and the 1064 system was used to generate an optical gradient field. A 15 mW 532 nm diode laser was also focused through the objective to visualize the liposome fluorescence. When a standing gradient field was projected onto the sample, fluorescence was more intense in this area. This suggests that the liposomes were moving towards the gradient field.
Differential Motion Imaging
Polystyrene and silica particles were diluted in distilled water. A “before” image was captured using a CCD camera and Image Pro Express software. A moving optical gradient field generated by the 1064 system was scanned over the particles. Another image was captured and the “before” image was subtracted. The resultant image clearly identifies that the polystyrene particle had moved. Escape Velocities of Different Cell Types
Escape velocities were measured using a gradient field generated by the 1064 system on CYTOP coated coverslips.
Separation of Treated and Untreated Leukemia Cells
PMA was dissolved in ethanol at a concentration of 5 mg/mL. 3 mls of U937 cells grown in RPMI 1640 media with supplements were removed from the culture flask and 1 ml was placed into each of three eppendorf tubes. Cells from the first tube were pelleted for 4 minutes at 10,000 rpm and resuspended in 250 uL PBS/1% BSA buffer for escape velocity measurements. PMA was added to the remaining two tubes of U937 cells to a final concentration of 5 ug/mL. These tubes were vortexed and placed in a 37° C. water bath for either one hour or six hours. At the end of the time point, the tube was removed, cells were pelleted and then resuspended as described above and escape velocity measurements taken. The cells treated for 6 hours had a significantly higher escape velocity as compared to the untreated cells.
While preferred embodiments and methods have been shown and described, it will be apparent to one of ordinary skill in the art that numerous alterations may be made without departing from the spirit or scope of the invention. Therefore, the invention is not limited except in accordance with the following claims.