Abstract:
A portable apparatus for extracting and concentrating bioagents within a fluid medium includes a container with sample solution inlet port and traveling wave grids patterned on surfaces of the container. The traveling wave grids cause bioagents to migrate to a specified surface within the container and then to an extraction port. The traveling wave grids include a substrate, across which extend a collection of closely spaced and parallel electrically conductive electrodes, and a collection of buses providing electrical communication with the collection of conductive electrodes. A voltage controller provides a multiphase electrical signal to the collection of buses and electrodes of the traveling wave grids.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     The following copending applications, Attorney Docket Number D/A3104, U.S. application Ser. No. 10/460,137, filed Jun. 12, 2003, titled “Traveling Wave Algorithms to Focus and Concentrate Proteins in Gel Electrophoresis”, Attorney Docket Number D/A3105, U.S. application Ser. No. 10/459,799, filed Jun. 12, 2003, titled “Distributed Multi-segmented Reconfigurable Traveling Wave Grids for Separation of Proteins in Gel Electrophoresis”, Attorney Docket Number D/A3237, U.S. application Ser. No. 10/727,289, filed Dec. 3, 2003, titled “Concentration and Focusing of Bio-agents and Micron-sized Particles Using Traveling Wave Grids”, and Attorney Docket Number A20031044, U.S. application Ser. No. ______, filed ______, titled “Continuous Flow Particle Concentrator”, are assigned to the same assignee of the present application. The entire disclosures of these copending applications are totally incorporated herein by reference in their entirety. 
     
    
     INCORPORATION BY REFERENCE  
       [0002]     The following U.S. patents are fully incorporated herein by reference: U.S. Pat. No. 4,289,270 to Warsinke (“Portable Concentrator”); U.S. Pat. No. 4,301,118 to Eddleman et al. (“Protein Concentrator”); U.S. Pat. No. 5,632,957 to Heller et al. (“Molecular Biological Diagnostic Systems Including Electrodes”); U.S. Pat. No. 6,272,296 to Gartstein (“Method and Apparatus Using Traveling Wave Potential Waveforms for Separation of Opposite Sign Charge Particles”); and U.S. Pat. No. 6,355,491 to Zhou et al. (“Individually Addressable Micro-electromagnetic Unit Array Chips”).  
       BACKGROUND  
       [0003]     This disclosure relates generally to the field of electrophoretic separation of bio-agents and particles, and more particularly, to systems and devices for focusing the bio-agents into regions of relatively high concentrations.  
         [0004]     Electrophoresis is a separation technique most often applied to the analysis of biological or other polymeric samples. It has frequent application to analysis of proteins and DNA fragment mixtures. The high resolution of electrophoresis has made it a key tool in the advancement of biotechnology. Variations of this methodology are used for DNA sequencing, isolating active biological factors associated with diseases such as cystic fibrosis, sickle-cell anemia, myelomas, and leukemia, and establishing immunological reactions between samples on the basis of individual compounds. Electrophoresis is an extremely effective analytical tool because it does not affect a molecule&#39;s structure, and it is highly sensitive to small differences in molecular charge and mass.  
         [0005]     Particles can be manipulated by subjecting them to traveling electric fields. Such traveling fields are produced by applying appropriate voltages to microelectrode arrays of suitable design. Traveling electric fields are generated by applying voltages of suitable frequency and phases to the electrodes.  
         [0006]     This technique of using traveling electric fields relates to an important method for separation and sorting of large particles and cells referred to as dielectrophoresis. Dielectrophoresis is defined as the movement of a polarizable particle in a non-uniform electric field. Essentially, the force arises from the interaction of the field non-uniformity with a field-induced charge redistribution in the separated particle.  
         [0007]     Particles are manipulated using non uniform electric fields generated by various configurations of electrodes and electrode arrays. As a general biotechnological tool, dielectrophoresis is extremely powerful. From a measurement of the rate of movement of a particle the dielectric properties of the particle can be determined. More significantly, particles can be manipulated and positioned at will without physical contact, leading to new methods for separation technology.  
         [0008]     A powerful extension of dielectrophoresis separation is traveling wave dielectrophoresis (TWD) in which variable electric fields are generated in a system of electrodes by applying time varying electric potential to consecutive electrodes. Such a method of Traveling Wave Field Migration was described by Parton et al. in U.S. Pat. No. 5,653,859, herein incorporated by reference. Although satisfactory, a need for improved strategies and methodologies remains. In addition, dielectrophoresis requires higher voltage (˜100 V), higher frequencies (˜10 MHZ), and finer electrode pitch (&lt;10 um).  
         [0009]     A microfluidic device for electrophoretic separation of biomolecules such as DNA and protein was described by Dunphy et al. in “Rapid Separation and Manipulation of DNA by a Ratcheting Electrophoresis Microchip (REM),” Proceedings of IMECE2002, Nov. 17-22, 2002, New Orleans, La., No. IMECE2002-33564, herein incorporated by reference. The device utilizes thousands of electrodes along the length of a microchannel. An electrical potential is applied across the electrodes and selectively varied to separate molecules within the microchannel into two groups using a ratcheting mechanism. This mechanism does not employ traveling waves. Although directed to the separation of biomolecules, this strategy is based upon micro device technology and is not readily compatible with conventional laboratory equipment. Accordingly, a need exists for a device and technique for utilizing electrostatic traveling waves for selectively concentrating bio-agents and particles, and particularly, for subsequent analysis.  
         [0010]     Detection of miniscule amounts of bio-agents, such as toxins, viruses, spores, etc., is important in the bio-sciences, particularly with respect to public health matters and the protection of emergency and military personnel. However, these bioagents are often life-threatening at miniscule concentrators and undetectable without concentration. Laboratory procedures may provide up to two orders of magnitude of concentration (e.g. ultra filtration) for biomolecules, but filtration is a lengthy process and requires a high-pressure source not readily available in the field. Therefore, there is a need for a compact, portable device to extract charged bio-agents (e.g. toxins, viruses, weaponized bacteria or their spores, or oocytes of harmful parasites, etc.) that are suspended in a liquid, concentrate them in a high viscosity medium and focus them into a detector.  
       BRIEF SUMMARY  
       [0011]     The disclosed embodiments provide examples of improved solutions to the problems noted in the above Background discussion and the art cited therein. There is shown in these examples an improved portable apparatus for extracting and concentrating bioagents within a fluid medium. The apparatus includes a container with sample solution inlet port and traveling wave grids patterned on surfaces of the container. The traveling wave grids cause bioagents to migrate to a specified surface within the container and then to an extraction port. The traveling wave grids include a substrate, across which extend a collection of closely spaced and parallel electrically conductive electrodes, and a collection of buses providing electrical communication with the collection of conductive electrodes. A voltage controller provides a multiphase electrical signal to the collection of buses and electrodes of the traveling wave grids. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     The foregoing and other features of the embodiments described herein will be apparent and easily understood from a further reading of the specification, claims and by reference to the accompanying drawings in which:  
         [0013]      FIG. 1  is a perspective illustration of one embodiment of the portable particle concentrator;  
         [0014]      FIG. 2  is a schematic illustration of the portable particle concentrator according to the embodiment of  FIG. 1 ;  
         [0015]      FIG. 3  is a representative four phase traveling wave voltage pattern employed in the traveling wave grids;  
         [0016]      FIG. 4  is a schematic illustration of biomolecule transport from one electrode to another;  
         [0017]      FIG. 5  is a schematic illustration of an example configuration of traveling wave grids;  
         [0018]      FIG. 6  is a perspective illustration of another embodiment of the portable particle concentrator;  
         [0019]      FIG. 7  is a schematic illustration of the portable particle concentrator according to the embodiment of  FIG. 6 ;  
         [0020]      FIG. 8  is a perspective illustration of yet another embodiment of the portable particle concentrator;  
         [0021]      FIG. 9  is a schematic illustration of the portable particle concentrator according to the embodiment of  FIG. 8 ; and  
         [0022]      FIG. 10  is an electrical diagram illustrating the operation of one embodiment of a controller that produces traveling wave bias voltages. 
     
    
     DETAILED DESCRIPTION  
       [0023]     The portable particle concentrator uses electrostatic fields and traveling wave grids to concentrate charged biomolecules, such as spores, viruses, toxins, etc., in the liquid phase. The portable particle concentrator includes an inlet for a sample solution introduction, a set of electrical grids on the inner sides and bottom of the device, a port for concentrated sample retrieval, and an interface with portable power sources and controller for extended operation. In the liquid phase, with water as the medium, the majority of biomolecules carry charges. By biasing the voltage on the two sides, charged biomolecules are directed toward the two walls and concentrated. Two-dimensional traveling waves on the walls are concurrently swept across both surfaces and the bottom plate to focus these charged particles to single points, where they may be retrieved with a syringe. Focusing occurs simultaneously with operation of the biased field until the molecules on the surfaces are moved to the retrieval port. A charge control agent may be added to the sample solution to alter the pH to provide charge to those biomolecules having isoelectric points at the pH of the sample that would otherwise be neutral. The portable concentrator may be utilized as an additional process step for water already concentrated by another process, such as tangential flow filtration, to further concentrate and reduce the sample size.  
         [0024]      FIG. 1  shows a perspective view of an example embodiment of the portable particle concentrator. This embodiment is in the form of a parallelepiped having sides  110  and  120 , which have a height H and a length L. For the purposes of describing an approximately liter-sized concentrator which would be hand portable, the sides may be twenty centimeters in both height and length. An input port  140 , located on a top plate  170 , permits sample introduction and outlet ports  130  for concentrated sample retrieval are provided at the lower corners of each of sides  110  and  120 . While for the purposes of this discussion input port  140  is located in the center of the top plate, it will be appreciated that it may be placed at any location on the top plate or at the top corner of either of the end plates  180 . Additionally, the inlet port may take any form convenient for the introduction and decanting of processed water, such as a circular configuration. The inlet port cover mechanism may take any of many forms known in the art.  
         [0025]     Two dimensional traveling wave grids  150  are patterned on the inside of side plates  110  and  120  and on bottom plate  170 . For the purposes of the description of this embodiment, the traveling wave grids may have a grid width of 10 μm and a pitch of 40 μm, although those skilled in the art will appreciate that other configurations would be possible, all of which are contemplated by the scope of the specification and claims herein. The pitch may be optimized to a particular particle size range and effective fringing field height. The traveling wave grid includes a substrate, a collection of closely spaced and parallel electrically conductive electrodes extending across the substrate, and a collection of buses providing electrical communication with the collection of electrodes. The surface of the traveling wave grid may include a thin (for example 20 μm) coating of polymer or gel to entrain the bioagents and mitigate back diffusion. The traveling wave grids may be fabricated on 4-inch wafers, with four such wafers tiled for each collection side.  
         [0026]     The portable particle concentrator also includes connection for a controller  190  and for portable battery  160 . After a water sample is introduced through sample inlet  140 , the inlet is closed and traveling waves and bias voltages are applied to the two side plates  110  and  120 , with up to +/−50V relative to the ground on each side. Biomolecules with isoelectric points (pI) higher than the pH of the sample solution carry positive charges and experience the pull from the negative plate located on side  120 . Similarly, biomolecules with lower pI have negative charges and are pulled toward the positive plate located on side  110 . While these charged particles are pulled to the side plates of the device, traveling waves are applied simultaneously to move these molecules in direction d 1  toward bottom plate  180 , where another traveling wave grid  150  moves the molecules in direction d 2  toward the corners of the device. Concurrent operation of the traveling wave grids reduces bioagent accumulation on the grids while focusing them onto retrieval ports  130 . Operation of the traveling wave grids is further described in U.S. patent application Ser. No. 10/727,289, “Concentration and Focusing of Bio-agents and Micron-sized Particles Using Traveling Wave Grids”, incorporated by reference hereinabove.  
         [0027]     Turning now to  FIG. 2 , there is shown a schematic cross-sectional view of one example embodiment of the particle concentrator. In this embodiment, liquid sample is introduced at inlet port  210 . Two dimensional traveling wave grids are patterned on the inside of side plates  240  and  242  and on bottom plate  230 . For the purposes of the description of this embodiment, the traveling wave grids may have a grid width of 10 μm and a pitch of 40 μm, although those skilled in the art will appreciate that other configurations would be possible, all of which are contemplated by the scope of the specification and claims herein. For example, a 100 um pitch with 50 um electrode width and 200 um pitch with 100 um electrode width both work well for particle sizes up to 20 um. Optimal dimension selection may be made through simulation. The traveling wave grid includes a substrate, a collection of closely spaced and parallel electrically conductive electrodes extending across the substrate, and a collection of buses providing electrical communication with the collection of electrodes. The surface of the traveling wave grid may include a thin (for example 20 μm) coating of polymer or gel to entrain the bioagents and mitigate back diffusion. The traveling wave grids may be fabricated on 4-inch wafers, with four such wafers tiled for each collection side.  
         [0028]     The portable particle concentrator also includes connections (not shown) for portable battery power. After a water sample is introduced through sample inlet  210 , the inlet is closed and power is supplied to the two side plates  240  and  242 , with up to +/−50V relative to the ground on each side. Biomolecules  252  with isoelectric points (pI) higher than the pH of the sample solution carry positive charges and experience the pull from the negative plate located on side  242 . Similarly, biomolecules  250  with lower pI have negative charges and are pulled toward the positive plate located on side  240 . While these charged particles are pulled to the side plates of the device, traveling waves are applied simultaneously to move these molecules in direction d, toward bottom plate  230 , where another traveling wave grid moves the molecules toward the collection ports  220  and  222  of the device. Concurrent operation of the traveling wave grids reduces bioagent accumulation on the grids while focusing them onto retrieval ports  220  and  222 .  
         [0029]      FIG. 3  is a representative four phase voltage pattern or waveform used in the example embodiment systems and traveling wave grids of the particle concentrator. For the purposes herein, the four phase voltage waveform has a 90 degree separation between phases. Each waveform occurring in each phase is a square wave pulse, with each pulse sequentially applied to an adjacent electrode. Thus, a first pulse in phase N 1  is applied to a first electrode for a desired time period, such as T/ 4 . Upon completion of that first pulse, such as at time T/ 4 , a second pulse in phase N 2  is applied to a second electrode, which may be immediately adjacent to the first electrode. Upon completion of that second pulse, such as at time T/ 2 , a third pulse in phase N 3  is applied to a third electrode, which may be adjacent to the second electrode. Upon completion of that third pulse, such as at time 3T/ 4 , a fourth pulse in phase N 4  is applied to a fourth electrode, which may be adjacent to the third electrode. This sequential and ordered array of voltage pulsing results in bio-agents or particles dispersed in the liquid to “hop” from the vicinity of one electrode to another.  
         [0030]     The synchronous mode of propagation is depicted in  FIG. 4  and may be described as a “hopping” mode where the bio-agent or particles hop from electrode to electrode in the direction of the pulse train. The transit time to migrate across the dielectric space is then given by: 
 
 t   transit   =s/μE, 
 
 where pitch is given by p=w+s, and w and s are the electrode width and dielectric space, respectively. Electric field and mobility are given by E and μ, respectively. The period for one cycle through the four phases is 4*t transit , so that the maximum sweep frequency is: 
 
 f&lt;μE/ 4 s. 
 
 For sustained transport, the bio-agent or particle has to have sufficient speed (μE) and time (t transit ) to traverse the distance of the dielectric space, s. This equation implies that for sustained transport, there is a critical frequency for bio-agents or particles of a certain mobility. Therefore, by starting with the highest operational frequency, one can progressively scan downwards in frequency until the bio-agent or particle of the right mobility starts to move. This means that for certain bio-agents, the fastest (and lowest molecular weight) bio-agents, i.e. biomolecules, may be separated out from the sample one at a time. 
 
         [0031]     Referring to  FIG. 5 , a traveling wave grid system  500  is illustrated. The system  500  comprises a first traveling wave grid  520  including a substrate  522  and a plurality of electrodes  532 ,  534 ,  536 , and  538 ;  532   a ,  534   a ,  536   a , and  538   a ; and  532   b ,  534   b ,  536   b , and  538   b.  The system  500  also comprises a second traveling wave grid  540  including a substrate  542  and a plurality of electrodes  552 ,  554 ,  556 , and  558 ; and  552   a ,  554   a ,  556   a , and  558   a . The grids  520  and  540  are arranged at angles with respect to each other, within the ranges of 10° to 170°, 80° to 100°, or at 90°. In this configuration all charged particles that are within the reach of the electric field generated from grid  520  are moved to the wall of grid  540 . That is, particles suspended above the grid  520  are transported toward the grid  540 , which in  FIG. 5 , is towards the left side of the grid  520 . The grid  540  moves the particles along the corner or region of intersection of the grids  540  and  520 , and concentrates the particles either in one region that is determined by the pulse sequence of the waveform or at one of the ends of grid  540 , such as where a detector is placed. If diffusion of the particles is sufficiently suppressed (e.g. by using a high-viscosity transport medium), the particles will remain confined in a small area near the corner of the grids, and the second grid  540  can concentrate them into a single small region, i.e. typically less than 1 cm 3  or 1 mL.  
         [0032]     Referring further to  FIG. 5 , in one embodiment, grid  520  concentrates the particles in line(s) parallel to its electrodes. The extent and manner of concentration depends on the pulse sequence and transport medium properties. Grid  540  concentrates the particles further into one or more individual regions of relatively high particle concentration. Because the effectiveness of a traveling wave grid decreases the further the particles are located from its electrodes, a biasing grid can provide a bias voltage to keep the particles in a thin layer just above the active grid and can also maintain a bias voltage to keep the particles from escaping from this layer while they are undergoing transport.  
         [0033]     Turning now to  FIGS. 6 and 7 , a perspective diagram of another embodiment of the portable particle concentrator is illustrated. This embodiment is in the form of a cylinder having side  640  with a height H and top and bottom plates  680  and  650 , respectively, both having a diameter D. For an approximately liter-sized concentrator, the sides may be approximately 2.2 inches in height with the diameter of top and bottom plates  680  and  650  being approximately 6 inches. Alternatively, a 2 inch diameter and 1 inch height would provide a total volume of approximately 50 mL, and other height and length specifications could also be utilized, as will be appreciated by one skilled in the art. Inlet port  620 , located on side wall  640  permit sample introduction. Retrieval ports  610 , located in both top and bottom plates  680  and  650 , provide for concentrated sample retrieval from either side of the device. Covering or latching mechanisms for inlet port  620  and sample retrieval ports  610  may utilize any of numerous forms known in the art, such as flaps, an iris structure, etc.  
         [0034]     Two dimensional traveling wave grids  630  are patterned on the inside of plates  680  and  650  and can be seen in  FIG. 7  as grids  730 . For the purposes of the description of this embodiment, the traveling wave grids may have a grid pitch of 40 μm, although those skilled in the art will appreciate that other configurations would be possible, all of which are contemplated by the scope of the specification and claims herein. Each of the traveling wave grids includes a substrate, a collection of closely spaced and concentric electrically conductive electrodes extending across the substrate, and a collection of buses providing electrical communication with the collection of electrodes. The surface of the traveling wave grids may include a thin (for example 20 μm) coating of polymer or gel to entrain the bioagents and mitigate back diffusion. The traveling wave grids may be fabricated on wafers of varying dimensions.  
         [0035]     The portable particle concentrator also includes connection  670  for portable battery pack  660  and controller  690 . After a water sample is introduced through a selected sample inlet  620 , a biased electric field is applied to force charged biomolecules toward the opposing plate, to which power is supplied. For example, when a sample is introduced through inlet port  620  in side wall  640 , then the electric field causes the charged biomolecules to migrate toward bottom plate  650 , to which power is supplied, with up to +/−50V relative to the ground. Traveling waves are applied to concentrate these molecules toward the center and sample retrieval port  610  in bottom plate  650 . The bias and traveling wave voltages are applied by the controller  690 . As a result the traveling wave voltages are superimposed on top of the bias voltages. Alternatively, the biased field direction may be inverted to concentrate particles of opposite charges.  
         [0036]     In another embodiment, top and bottom plates  680  and  650  are oppositely charged, to enable the separation and retrieval of oppositely-charged particles. In this embodiment, biomolecules with isoelectric points (pI) higher than the pH of the sample solution carry positive charges and experience the pull from the negative plate  680 . Similarly, biomolecules with lower pI have negative charges and are pulled toward the positive plate  650 . While these charged particles are pulled to the top or bottom plates of the device, traveling waves are applied simultaneously to move these molecules toward the center of each plate. Operation of the traveling wave grids is further described in U.S. patent application Ser. No. 10/727,289, “Concentration and Focusing of Bio-agents and Micron-sized Particles Using Traveling Wave Grids”, incorporated by reference hereinabove.  
         [0037]     Referring now to  FIG. 8 , a schematic diagram of another embodiment of the portable particle concentrator is illustrated. In this embodiment, traveling wave grids  820  and  825  are located in the inner surface of cylinder wall  810  and run parallel to the length L of the device up to collection slot  850 . Collection slot  850  includes traveling wave grid  840 , which runs perpendicular to the length of the particle concentrator. Side plates  870  have a diameter D, that can be closed after the container is filled. The inner cylindrical (fluid) core will have a diameter of D 1  and includes a center electrode  830 . The traveling waves and bias voltages are produced by a controller  890 .  
         [0038]     As can be seen in  FIG. 9 , traveling wave grids  965  will transport molecules counterclockwise in direction  930  to the collection trench and traveling wave grids  960  have an opposite direction and will transport molecules clockwise in direction  940  until both meet at the collection trench  910 . Traveling wave grid  970  in the collection trench will further transport molecules along the length of the device toward the back wall. For a portable concentrator, the cylindrical core D 1  diameter may be approximately 2 inches and the length of the concentrator can be 6 inches, which will yield a fluid volume of approximately 300 mL when filled. In one embodiment, this device may be operated after the fluid core is filled and the side plates are closed. In this mode, the center electrode will have a biased voltage relative to the traveling wave grids on the inner surface of the shell so that oppositely charged molecules will be attracted to the traveling wave grids. Simultaneously, a traveling wave is applied so that molecules will be swept toward the collection trench. At the collection trench, molecules will experience a traveling wave electric field perpendicular to the length of the device so they are further transported to the collection slit at the end plate where they can be retrieved (e.g. with a syringe). However, if higher process volume is desired, the device can be connected to a larger reservoir and slowly the sample water can be flowed through the cylinder core. In such an embodiment, an opening on the top plate will allow proper tubing to be connected and a small peristaltic pump can be used to pump sample water from reservoir to the device. There will be a similarly-sized opening in the bottom plate with properly connected tubing that can drain the processed water out. Flow rate can be adjusted through the pump depending on the process time and volume of the sample water.  
         [0039]     Turning now to  FIG. 10  an electrical diagram illustrates the operation of one embodiment of a controller that produces traveling wave bias voltages. The controller uses the power of battery to produce positive and negative bias voltages  1060  and to produce the traveling wave pulses  1020  on traveling wave grids  1030  and  1032 . For the purposes of clarity, only four positive pulses provided to four electrodes on a first traveling wave grid  1032  and four negative pulses provided to another traveling wave grid  1030  are shown. However, it will be appreciated that a traveling wave grid may have numerous electrodes, with each electrode being driven by a separate traveling wave pulse. The traveling wave pulses may be applied sequentially or simultaneously, depending on the configuration of the portable particle concentrator and the desired concentration results.  
         [0040]     While the present discussion has been illustrated and described with reference to specific embodiments, further modification and improvements will occur to those skilled in the art. For example, any of the embodiments described herein could be utilized to operate the traveling wave grid as a high pass filter to collect only those particles with mobilities above a threshold value. Additionally, the bio-agents to be collected may be pre-selected through customization of traveling wave grid parameters, such as pulse sequence or frequency. It is to be understood, therefore, that this disclosure is not limited to the particular forms illustrated and that it is intended in the appended claims to embrace all alternatives, modifications, and variations which do not depart from the spirit and scope of the embodiments described herein.