Patent Application
20140273184
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The field of the present invention is air sampling devices and testing. It includes electrokinetic methods for propulsion of charged particles. The present invention relates to the collection of and sampling of assayable agents in a dielectric medium. This includes, but is not limited to, sampling air for agents whose presence or absence is determinable by bio-specific assays.
Prior art for air sampling and testing has been extensively summarized in U.S. Pat. No. 8,038,944. Further prior art devices for numerous applications are listed in Table 1, below.
The table summarizes key features of devices so far as can be obtained from the respective companies web sites. Important features are volume flow and sample volume. The ratio between these, defined as the concentration ratio, determines the ultimate detection limits. All of the devices depend on a pump, and the pump usually has to work against back-pressure created by forcing through a small pore size filter, or through fine jets to create an impact on a surface for collection. The requirement for a pump has the disadvantage of high power consumption and generation of noise. Thus, there is a need for devices with a high concentration ratio, low power requirement and ability to run unobtrusively in any location. Some use electret filters with permanent electrostatic charge pairs which attract charged particles, but these also do not use electrical potentials applied to electrodes to direct the flow. They also do not impart charge to uncharged material.
Several of the devices in Table 1 have battery operation and a degree of portability, but are still relative large, cumbersome and power-hungry.
There exist numerous commercially available systems for air purification based on filtration or electrostatic precipitation. For a general description see the Environmental Protection Agency article “Guide to Air Cleaners in the Home”, U.S. EPA/OAR/ORIA/lndoor Environments Division (MC-6609J) EPA 402-F-08-004, May 2008. The company 3M commercializes an electret-based air filtration medium under the Filtrete™. Numerous commercial examples of systems exist using either High Efficiency Particulate Air (HEPA) filters or electrostatic precipitation filters. Such systems are widely used for removal of particulate matter or allergens from air, including as part of domestic heating, ventilation and air conditioning (HVAC) systems. HEPA filters have the advantage of removal of particles down to the micron size range, whereas electrostatic precipitation methods have the advantage of entailing high volume flow with little or no pressure differential. See by Bourgeois, U.S. Pat. No. 3,191,362 as a detailed example for the technical specification of an electrostatic precipitation system. While efficiently removing agents from the air, such air purification systems do not lend themselves to collection of samples for analysis.
Electrokinetic devices are useful for providing low power consumption and silent air purification devices. The original electrokinetic principle was enunciated by Brown in U.S. Pat. No. 2,949,550. This was further improved by Lee in U.S. Pat. No. 4,789,801 for improving airflow and minimizing ozone generation. Further improvements for the commercially available system are described in by Taylor and Lee, U.S. Pat. No. 6,958,134; Reeves et al, U.S. Pat. No. 7,056,370; Botvinnik, U.S. Pat. No. 7,077,890; Lau et al, U.S. Pat. No. 7,097,695; Taylor et al, U.S. Pat. No. 7,311,762. In the foregoing descriptions of devices using electrokinetic propulsion, a common element is a high voltage electrode consisting of wires or sharp points. A very steep voltage gradient is generated orthogonally to the wire because of the very small cross-sectional area of the wire, and similarly in the neighborhood of a sharp point. The high voltage gradient causes the creation of plasma consisting of charged particles. Similarly, St. Elmo's fire is a weather phenomenon in which luminous plasma is created by a coronal discharge from a sharp or pointed object in a strong electric field in the atmosphere, and was observed historically on ships masts or rigging. In the cleaning devices, kinetic energy is imparted to the charged particles by the high voltage gradient. The resulting net air flow is created by exchange of kinetic energy between charged and uncharged particles, and the net air flow is directed by the juxtaposition of planar electrodes which are at zero or opposite sign voltage to that of the wire electrode. Charged particles are electrostatically precipitated on to the planar electrodes, which may periodically be removed for cleaning. A variety of electrokinetic-based air cleaning systems are now commercialized, for example by Envion (Van Nuys, Calif.), Heaven Fresh (Waukesha Wis.) and Sharper Image (Tokyo, Japan). Table 2 lists the air flow performance of some of these devices so that comparison can be made with the collection devices of Table 1
This body of work is directed toward air purification, not sample collection. Prior art on the use of the Sharper image Quadra for air sampling for allergen detection was reviewed in U.S. Pat. No. 8,038,944. In U.S. Pat. No. 8,038,944 was described methodology for electrokinetically driving charged particles created by a high voltage plasma, on to a capture electrodes, and the use of non-conducting materials to intercept the charged particles in such a way that the sample could easily be transferred into a bio-specific assay. However, it has been noted that use of a nonconductive material may result in reduction in air flow. Further, the information in Table 1 shows that air flow is at a premium for maximizing the amount of material that can be collected, and that the ICD is in the lower end of the range of the flow values of the devices listed. Thus, there is a need to increase the flow rate, preferably without use of moving parts.
In addition, the size range of particles collected by the devices listed in Table 1 is limited to more than about 0.5 micron, possibly 0.2 micron. All fall off in efficiency of collection as the particle size decreases.
There is thus a need for a device that can sample large volumes of air, but to concentrate into a very small volume for analysis, and to work silently with low energy consumption
The present invention encompasses the use of an electrode or electrodes to create a potential well that will draw charged particles out of a flowing dielectric fluid stream and focus them on to the collection means of an assay device. Improvements result from the use of pulsed voltages applied to electrodes that create potential differences varying in time so that transport of ionized particles from one electrode set to the next is enhanced. The voltage changes serve to sample from an initially large aperture with attendant high volume flow, increase the flow velocity, as well as to efficiently capture the particles and enhance sensitivity by means of the focusing effect on the collection means. If not already electrically charged, charge is imparted to the agent to be analyzed by means of a high voltage wire electrode arrangement and consequent plasma generation; the agent is focused on to the collection means of the assay device by the potential well; and finally electrostatically precipitated thereon.
In one aspect of the invention, a device for collection of a sample from a dielectric fluid medium for assay comprises an enclosure. Flow means direct fluid flow of the dielectric fluid medium in the enclosure. One or more wire electrodes in the enclosure subject dielectric fluid medium flowing in the enclosure to an ionizing plasma. Supporting means operatively associated with the enclosure support the bio-specific assay device. One or more capture electrodes are positioned proximate the supporting means to create a voltage potential well whereby charged particles thus generated within the dielectric fluid medium, or pre-existing in said dielectric fluid medium, are propelled into the supported bio-specific assay device thereby electroprecipitating the charged particles on to a sample collection region of the bio-specific assay device.
In a further aspect of the invention, voltage pulses between successive electrodes are synchronized such that the maximum in one set coincides with a minimum in the preceding set, so that any tendency to be attracted to the preceding set is neutralized by the potential attraction to the following set. Specifications for creating pulses are described in the prior art, as in the Ionic Breeze patent estate. A secondary circuit senses the sum of the voltages between successive sets of electrodes. This secondary set voltage feeds into the pulse generating circuit of the second pulse generator, and regulates the phase of the pulses such that the secondary voltage is zero. This ensures that the pulses between the successive electrodes are 180° out of phase.
In a still further aspect of the invention, successive sets of electrodes are of progressively smaller dimensions resulting in a progressive focusing effect and progressive enhancement of the flow velocity. A further aspect of the current invention is the ability to transmit a voltage across a non-conducting material if the high voltage is supplied as pulses, rather than constant DC. This gives greater freedom in the design of simpler means for covering a removable capture electrode with a non-conductive material which will not interfere with the transmission of the pulsed voltage.
Other objects, features, and advantages of the invention will become apparent from a review of the entire specification, including the appended claims and drawings.
This application describes an electrokinetic device used for air sampling and testing. It uses electrokinetic methods for propulsion of charged particles. The device is used for collection of and sampling of assayable agents in a dielectric medium. This includes, but is not limited to, sampling air for agents whose presence or absence is determinable by bio-specific assays. The field includes sampling of air for biological agents, direction to, and deposition on, a collection means for an assay device. The agent-specific assays may include immunoassays, nucleic acid hybridization assays, or any other assays entailing ligand—antiligand interactions. Assays may include, but are not limited to, detection means which are colorometric, fluorescent, turbidimetric, electrochemical or voltammetric. Agents assayed include,
Acinetobacter
Absidia
Actinomyces
Acremonium
Alkaligenes
Alternaria
Bacillus
Aspergillus
Bordetella
Aureobasidium
Cardiobacterium
Blastomyces
Chlamydia
Botrytis
Clostridium
Candida
Corynebacteria
Chaetomium
Coxiella
Cladosporium
Enterobacter
Coccidioides
Enterococcus
Cryptococcus
Francisella
Emericella
Haemophilus
Epicoccum
Klebsiella
Eurotium
Legionella
Exophiala
Micromonospora
Fusarium
Micropolyspora
Geomyces
Moraxella
Helminthosporium
Mycobacterium
Histoplasma
Mycoplasma
Mucor
Neisseria
Oidiodendron
Nocardia
Paecilomyces
Pseudomonas
Paracoccidioides
Saccharomonospora
Penicillium
Serratia
Phialaphora
Staphylococcus
Phoma
Streptococcus
Pneumocystis
Thermoactinomyces
Rhizomucor
Thermomonospora
Rhizopus
Yersinia
Rhodoturula
Scopulariopsis
Sporothrix
Stachybotris
Trichoderma
Ulocladium
Wallemia
but are not limited to, bio-warfare agents, pathogens, allergens, toxins or pollutants. Possible pathogens are listed in Table 3. Allergens may include those derived from domestic animals, household pets, mites, insects such as cockroaches. Toxins include such as ricin, botulinus toxin, or bacterial endotoxin. Further dielectric media may include sampling of dielectric fluid medium such as oil for the food industry, or petrochemical and industrial oil.
The device is used to practice methods for accelerating charged particles in electric fields. The device utilizes electric fields which have frequency matched to the velocity of the charged particle, and acceleration takes place by increasing the frequency between successive electrode pairs. Further acceleration takes place by using the field to confine the particles to ever-decreasing volumes by successive reduction of the size of the electrodes. Increase in flow will also take place by the Venturi effect, which will have the effect of sucking in larger volumes of air via the interstices between the electrodes. One advantage of the high velocity of the particles is that they will stick more effectively on the final capture material.
From the underlying physics, the methodology of the current invention is indefinitely scalable, and so can be constructed to analyze very large volumes of fluid. Further, the scaled-up version can be used to create a very simple wind-tunnel. This is both easier to construct than a conventional wind tunnel, having no moving parts, and there will also not be any necessity to compensate for the rotation of the air mass due to the rotation of a fan.
A further aspect of the present invention is the use of the fact that the force on particles in an electric field is proportional to the field gradient and the particle charge. The effect is thus relatively independent of mass. Prior art sampler methods depend on particle mass for their effect. The present invention thus has the capability of sampling in the region referred to as Aerobiome Incognito in
The included figures show in detail specific electrode arrangements which illustrate various embodiments of the invention. In its simplest form, the design consists of a wire electrode, a pair of plate electrodes and a capture electrode. The advantages of this geometry may be enhanced by the synchrony and amplitudes of the voltages applied between a wire electrode and the plate electrodes, and the plate electrodes and the capture electrode.
Each of
The device 200 in its most basic form may operate similar to the devices described and illustrated in our U.S. Pat. No. 8,038,944, the specification of which is hereby incorporated by reference herein. As described with respect to the embodiments therein, a constant DC voltage was applied to the various electrodes. As described herein, a pulsed voltage is used for propulsion of charged particles. The principles described herein can be applied the devices in the '944 patent, as will be apparent.
A similar housing 205 may be used for alternative designs in
The functionality of the control circuit of
It can be seen that a wave of peak voltage may be caused to travel through the system of electrodes, thus creating a synchrotron effect. The timing and magnitudes of the successive sets of voltages may be optimized to maximize the ionic flow without undue experimentation.
In order to transport the sampled material for subjecting the sample to a bio-specific assay it is desirable to include a removable transport element.
The sleeve 700 leaves little or no exposed surface of the capture electrode 203 in order to maximize the capture of analyte. The dimensions are in mm, and the material is cut from silk habotai, from the Dharma Trading Company, Petaluma, Calif. The dotted line 701 is a fold line and the dashed lines 702 are seam-lines. After the sleeve 700 is stitched, it is inverted so that no cut edges are on the outside. The stitching is such that there is a sufficient gap for the electrode 203 to be inserted. After enveloping with the non-conductive sleeve 700, the electrode 203 is remounted in the housing 205 and secured in place with a plastic latch.
In accordance with the teachings of the invention, the capture electrode 203 creates a potential well that will act as a trap for charged particles of interest in a flowing fluid stream and to synchronize voltage patterns to maximize the flow performance of charged particles generated. The device 200 has the capability to interpose a non-conductive material between physical contact surfaces, and to maintain voltage transmission from the use of the pulsed voltage.
Electrodes are separated from the removable electrode assembly of the exemplary device as in the description for
Table 3 shows that, while some reduction in flow results from enclosing the electrode in a silk envelope, there is no reduction due to the interposition of the silk between the electrode contacts. The reduction in flow is a result of the capacitance of the silk envelope on the electric field gradient generated by a pulsed DC field with a frequency of about 50 KHz. In any design there will be a compromise between features that result in ease of use and the actual performance. The reduced flow from about 100 L/min to about 60 L/min still permits the sampling of a large volume of air in a air in a limited time. Thus, in a typical run of 30 minutes, about 2,000 L of air will be sampled.
It is possible to design innumerable devices within the scope of this invention, and the configuration shown in the illustrations of this document are intended to be exemplary only. Creation of a potential well provides a universal and efficient trap for charged particles and provides for seamless transfer on to a measuring or detection device. The sensitivity of the measurement of the detection or detection device is considerably enhanced by the ability to sample large volumes of fluid and to concentrate the charged particles on to a small area of a detection device. The utility of sampling and testing devices is determined by the ability to measure and detect analytes at a very low concentration. Assuming the assay method can only handle a fixed volume, the sampling efficiency is then determined by the volume flow of fluid divided by the final sampled volume. Thus, both high volume flow rate and low final sample volume are advantageous. Because the properties, disposition and dimensions of non-conducting materials do not excessively affect the voltage field distribution, there are unlimited possibilities for the design and fabrication of devices for practical applications, using, for example any of a wide range of plastic or polymeric non-conducting materials.
In consideration of the fabrication of user-friendly devices, it may be necessary or desired to interpose a layer of non-conductive capture element between an electric contact and a corresponding removable electrode. While such material would effectively insulate at the interface between the contacts in the case of a DC high voltage, in the case of a pulsed or alternating voltage, the non-conductive material would act like a capacitance and permit the transmission of the voltage across the interface.
In the devices described in the foregoing, the area of the capture electrode is small compared with other electrodes in the system, thus providing a large voltage gradient. In the examples, typical ratios of areas of capture electrodes are 20:1. Depending on the construction of the specific device, this ratio may vary in the range 5:1 to 1000:1 or even greater, limited only by the performance requirements of the specific system. The capture electrode is usually in the form of a plate, but may also take the form of a metal grid or mesh. The capture electrode may be of any suitable geometry, rectangular, square, circular, or elliptical, depending on the specific design requirements. The only constraint is that the geometry of the capture electrode may not be such as to create a potential gradient so steep as to initiate plasma generation, and generate charged particles that will be launched out of the potential well.
In the case of a multiplicity of wire electrodes for generating plasma, these are usually arrayed as parallel wires, but may also be arranged as a rectangular grid, depending on the requirements or constraints of a specific design. The wire electrodes advantageously do not exceed 1.0 mm in diameter and in one embodiment may have a diameter of approximately 0.1 mm. However, the geometry of the wires may be varied and they may also take the form of spikes with pointed tips. In this case, the pointed tip may give rise to a local potential gradient high enough to give rise to the formation of charged plasma.
The voltages applied must be sufficiently large to create the conditions for the functioning of the invention, but voltages can be varied to optimize the performance. The voltage values may be positive or negative at either the wire electrodes or the capture electrodes. For functioning, only relative voltages are important, so that any electrode may also be set at ground or low voltage, for example, for safety reasons.
For reduction to practice, the devices of the current invention can be fabricated from simple modifications of existing devices. Thus, all the specifications for details of hardware, electronic control, aesthetic considerations, dimensions, portability, power supply from ac mains or battery, are all described in detail in the prior art references given in this document, and so need no further elaboration here.
Application of the synchrotron principles elaborated herein can also be used for cleaning as well as sampling. The designs are scalable, so that extremely large volumes of air could be sampled for testing in public places where there is a risk of bioterrorism, as well as to air cleaning applications for HVAC systems and entire buildings. There would be great advantages to a whole building HVAC system with no moving parts.
Further applications to capture of entities to be assayed in dielectric media other than air can be created using the same principles as enunciated throughout this document. The dielectric fluid medium may further include non-conductive liquids, such as oils. Oils may be sampled for the presence of contaminants, contaminating organisms or bio-degrading organisms.
