News Column

Patent Issued for Separation of Colloidal Suspensions Using Laser Optical Pressure Fluidic Devices

July 2, 2014



By a News Reporter-Staff News Editor at Journal of Engineering -- According to news reporting originating from Alexandria, Virginia, by VerticalNews journalists, a patent by the inventors Hart, Sean J. (Keswick, VA); Terray, Alexander V. (Alexandria, VA), filed on August 8, 2013, was published online on June 17, 2014.

The assignee for this patent, patent number 8753891, is The United States of America, as represented by the Secretary of the Navy (Washington, DC).

Reporters obtained the following quote from the background information supplied by the inventors: "This invention relates in general to a particle separator for fluids, and in particular to a particle separator for fluids using optical pressure.

"The invention of the laser has made possible many new areas of research and technology. Unique optical properties allowing a laser to be highly focused have made detailed studies of radiation pressure possible. Most important is the laser's ability to focus down to a tiny spot size, resulting in a large photon density. This large number of photons translates into a significant amount of radiation force applied to a particle in the beam path. Radiation pressure has been used to trap and direct particles caught in the focus of a laser beam. Manipulation of the beam focus and beam position can be used to move particles into desired positions and configurations. The types of objects that have been optically trapped include glass and polymer spheres, viruses, bacteria, and biological cells. Recently, size-based separation of particles flowing in a fluid opposite to the direction of laser propagation has been achieved.

"In recent years, a technique has been developed, termed optical chromatography, which involves laser separation of differently sized particles in the 1-10 micron range. When particles in a liquid flowing within a capillary encounter a laser beam propagating in the opposite direction, the particles are subjected to optical pressure near the beam focal point (i.e., the region of highest photon density) intense enough to impart momentum sufficient to overcome fluid drag forces. The result is that particles in the fluid become trapped and move against the fluid flow until the beam diverges and the photon density decreases. The particles remain stationary when the optical pressure equals the force exerted on the particles by the liquid flow (i.e., Stoke's force).

"For a sphere of refractive index n.sub.2 in a medium of lower refractive index, n.sub.1, the force due to optical pressure of the laser, F.sub.optical.sub.--.sub.pressure, is given by equation 1:

".times..times..times..times..times..times..omega..times. ##EQU00001## where P is the power of the laser, c is the speed of light, a is the sphere radius, .omega. is the beam radius, and Q* is the conversion efficiency of optical radiation pressure to Newtonian force on the particle. The term (n.sub.1P/c) defines the incident momentum per second in a medium of refractive index n.sub.1. The dimensionless parameter, Q* defines the conversion efficiency of optical pressure transfer arising from light reflection and refraction based upon geometrical considerations and is calculated using the Fresnel reflection and transmission coefficients, which in turn depend upon n.sub.2, the refractive index of the particle.

"Separation in a liquid flow is measured by the distance particles travel away from the focal point against the fluid flow. This distance traveled is the optical retention distance, z: the point at which the optical pressure equals the force exerted on the spheres by the liquid molecules and is defined, according to Equation 2:

".pi..times..times..omega..lamda..times..times..times..times..pi..times..t- imes..eta..times..times..times..times..omega. ##EQU00002## where P is the power of the TEM.sub.00 mode laser, c is the speed of light, a is the sphere radius, is the beam radius at the focal point, .lamda. is the wavelength of light, .nu. is the velocity of the particle in the water flow, and n.sub.1 is the viscosity of water. The refractive index of the particle is used in the calculation of the efficiency of optical pressure transfer, Q.

"Optical pressure has been used extensively in research and industry for biological size-based micromanipulation. The chemical effect on optical pressure in bacteria has been observed: small chemical differences in the surface coatings have been shown to result in large force differentials on different strains of the same species of non-pathogenic bacteria. However, the theoretical chemical dependence, development, and use of optical pressure chemical differentials for separation have not yet been demonstrated."

In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventors' summary information for this patent: "An embodiment of the invention includes a device having a collimated light source operable to generate a collimated light source beam, the collimated light source beam comprising a beam cross-section. The device further includes at least one body defining a first channel in a first plane, the first channel comprising a first channel cross-section, the first channel being oriented to receive the collimated light source beam such that the beam cross-section completely overlaps the first channel cross-section. Optionally, the body defines a second channel in a second plane orthogonal to the first plane, wherein the body defines a third channel in a third plane orthogonal to the first plane.

"Optionally, the device includes a fluid input reservoir communicating with the second channel. Optionally, the device includes a pump communicating with the fluid input reservoir. For example, the pump includes, for example, a pump having a fixed flow rate or a pump having a dynamically changeable flow rate. For example, the pump includes a gravity-feed pump, a pneumatic pump, a syringe pump, a piezo-electric pump, a peristaltic pump, an electro-osmotic flow pump, or a photophoresis pump.

"Optionally, the first channel includes a first end and a second end, the first channel defining a bulge at the first end, at the second end, or between the first end and the second end. Optionally, the shape of the bulge is, for example, a circular shape, an oval shape, a rectangular shape, a triangular shape, a venturi shape, a diamond-bulge shape, a tapered shape, a pentagonal shape, a hexagonal shape, and/or a helical shape. These two-dimensional shapes are optionally used in one of two ways: a 2-D shape that is lofted (i.e., raised to create 3-D shape) or a 2-D shape that is lathed (i.e., rotated 360 degrees to create a 3-D shape).

"Optionally, the body includes a substrate, a first plate, and a second plate. The substrate defines the first channel, the first plate defining the second channel, and the second plate defining the third channel.

"Optionally, the device also includes, for example, a lens, a beam chopper, an acousto-optic modulator, a phase-shifting optic, a holographic element, and/or a mirror located between the collimated light source and the first channel, and communicating with the collimated light source such that the beam cross-section overlaps the channel cross-section.

"Optionally, the first channel includes a liquid core waveguide.

"Optionally, the collimated light source includes, for example, a tunable laser, a continuous wave laser, a fiber laser, a pulsed laser, a femtosecond laser, a near infrared laser, a visible light laser, an ultraviolet light laser, a diode laser, or a vertical cavity surface emitting laser.

"Optionally, the collimated light source includes, for example, a collimated light source having dynamically changeable power and/or a dynamically moveable collimated light source.

"Optionally, the at least one body includes a plurality of bodies, each body comprising a respective channel, each respective channel comprising a respective channel cross-section, each respective channel being oriented to receive the collimated light source beam such that the beam cross-section completely overlaps the respective channel cross-section.

"Optionally, the collimated light source beam includes, for example, a polarized beam, a Bessel beam, or one of several Hermite-Gauss beam types: HG.sub.00, HG.sub.01, HG.sub.10, and HG.sub.11, and higher order modes, or one of several Laguerre-Gauss beam types: LG.sub.0.sup.0, LG.sub.0.sup.+1, LG.sub.0.sup.-1, or higher order modes which possess angular momentum. Acceptable Hermite-Gauss Beams have the form HG.sub.nm where n and m are coefficients describing the beam order. For example, n and m are greater than 1. Acceptable Laguerre-Gauss beams have the form LG.sub.n.sup.m, where n and m are coefficients describing the beam order. For example, n and m are greater than 1.

"Another embodiment of the invention includes a method. A collimated light source operable to generate a collimated light source beam is provided. The collimated light source beam includes a beam cross-section. A body is provided, wherein the body defines a wall and a first channel in a first plane. The first channel includes a first channel cross-section, the first channel being oriented to receive the collimated light source beam such that the beam cross-section completely overlaps the channel cross-section. The collimated light source beam is transmitted through the channel. A fluid sample is transmitted through the channel, fluid sample including a plurality of particles of a same type. All of the particles of the plurality of particles are separated axially along the collimated light source beam. All of the particles of the plurality of particles are retained against the wall in the collimated light source beam.

"Optionally, the fluid sample includes a colloidal sample and/or a biological sample. Optionally, the biological sample includes the fluid sample including one of a plurality of viruses and a plurality of macrophages; the fluid sample including a plurality of spores; the fluid sample including a plurality of vegetative bacterial cells; the fluid sample including a plurality of yeast cells; the fluid sample including a plurality of eukaryotic cells; the fluid sample including a plurality of cancer cells; the fluid sample including a plurality of sperm cells; and/or the fluid including a plurality of pluripotent stem cells.

"Optionally, a fluid sample product comprising a greater concentration of particles than the fluid sample is produced.

"Optionally, a fluid sample product free of the plurality of particles in the fluid sample is produced.

"Separating chemically different particles offers important new possibilities for analysis and possible purified collection of colloidal samples such as organic particulates, inorganic particles (glass and metal particles), and biological species such as cells, bacteria, and viruses. Differentiation of biological samples such as bacteria is based upon chemical differences in their capsules. Polysaccharides, lectins, lipoteichoic acids, and proteins are examples of the biomolecules present in various bacterial species and strains. There is a substantial range of refractive indices in bacterial and viral samples due to their different chemical compositions. The ability to separate biological species based upon physical and chemical properties using only light interaction with samples in a simple fluid flow has great potential benefits when applied, for example, to bio-warfare detection and biomedical analysis. In an embodiment of the invention, not only are samples physically separable using light, but from their position in the separation field one can determine their refractive index. That is, from a predicted location, an embodiment of the invention permits identification of specific entities in an unknown mixture.

"In an embodiment of the invention, when samples are optically retained against a glass wall of a bulge, such as when occurs using the microfluidic step function type device, the extent to which they are deformed against the glass wall by the force of the laser is related to their composition and mechanical structure. This has beneficial implications for biological cells that are affected by disease such as cancer, which is known to directly affect the cytoskeleton of cells. For example, cancerous cells are known to have a more rigid cell structure than their non-cancerous counterparts. Through observation of their deformation either in the channel or against the wall, an estimate of disease state is optionally obtained, in an embodiment of the invention. As another example, erythrocytes undergo stretching and compression which depends on their age; older erythrocytes being less flexible. This stretching/compression is visible in the channel or against the wall. With this understanding, an embodiment of the invention has application in analysis of disease states in biological systems (e.g., cells and small tissue samples)."

For more information, see this patent: Hart, Sean J.; Terray, Alexander V.. Separation of Colloidal Suspensions Using Laser Optical Pressure Fluidic Devices. U.S. Patent Number 8753891, filed August 8, 2013, and published online on June 17, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8753891.PN.&OS=PN/8753891RS=PN/8753891

Keywords for this news article include: Bacterial Infections and Mycoses, The United States of America as represented by the Secretary of the Navy.

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Source: Journal of Engineering


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