Abstract:
A human-safe fluorescence particle that can be used for fluorescence detection instruments or act as a safe simulant for mimicking the fluorescence properties of microorganisms. The particle comprises a non-biological carrier and natural fluorophores encapsulated in the non-biological carrier. By doping biodegradable-polymer drug delivery microspheres with natural or synthetic fluorophores, the desired fluorescence can be attained or biological organisms can be simulated without the associated risks and logistical difficulties of live microorganisms.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 60/707,520 filed Aug. 10, 2005 and titled “Doped Spheres of Biodegradable Polymers as Fluorescence Simulants.” U.S. Provisional Patent Application No. 60/707,520 filed Aug. 10, 2005 and titled “Doped Spheres of Biodegradable Polymers as Fluorescence Simulants” is incorporated herein by this reference. 
     
    
       [0002]    The United States Government has rights in this invention pursuant to Contract No. W-7405-ENG-48 between the United States Department of Energy and the University of California for the operation of Lawrence Livermore National Laboratory. 
     
    
     BACKGROUND 
       [0003]    1. Field of Endeavor 
         [0004]    The present invention relates to particles and more particularly to a safe fluorescent particle. 
         [0005]    2. State of Technology 
         [0006]    The article “An examination of the urban dispersion curves derived from the St. Louis dispersion study” by Akula Venkatram in  Atmospheric Environment  39 (2005) 3813-3822, describes an aerosol study that was conducted over the period 1963-1965. The aerosol study was an investigation of large scale air dispersal to track particulate migration over vast areas, or for urban particle dispersion studies. Researchers performing these studies rely on air dispersion models and gas tracer tests to determine the movement and flow of aerosols in urban environments such as in cities—around and through occupied buildings—because “safe” particles were not available at the time. The St. Louis study consisted of a series of 26 daytime and 16 evening experiments in which fluorescent zinc cadmium sulfide particles were released near ground level at two different locations under a variety of meteorological conditions. During the first year of the experiments, the release was at ground level in a relatively open area in a park located west of the downtown area. In the second year, the tracer was released from the top of a three-story building surrounded by trees and similar buildings. The main downtown area, consisting of buildings with an average height of 40 m, was about 5 km away from both release locations. 
         [0007]    In an article titled, “U.S. Is Deploying a Monitor System for Germ Attacks,” by Judith Miller in The New York Times on Jan. 22, 2003, it was reported, “To help protect against the threat of bioterrorism, the Bush administration on Wednesday will start deploying a national system of environmental monitors that is intended to tell within 24 hours whether anthrax, smallpox and other deadly germs have been released into the air, senior administration officials said today. The system uses advanced data analysis that officials said had been quietly adapted since the September 11 attacks and tested over the past nine months. It will adapt many of the Environmental Protection Agency&#39;s 3,000 air quality monitoring stations throughout the country to register unusual quantities of a wide range of pathogens that cause diseases that incapacitate and kill . . . The new environmental surveillance system uses monitoring technology and methods developed in part by the Department of Energy&#39;s national laboratories. Samples of DNA are analyzed using polymerase chain reaction techniques, which examine the genetic signatures of the organisms in a sample, and make rapid and accurate evaluations of that organism . . . Officials who helped develop the system said that tests performed at Dugway Proving Ground in Utah and national laboratories showed that the system would almost certainly detect the deliberate release of several of the most dangerous pathogens. ‘Obviously, the larger the release, the greater the probability that the agent will be detected,’ an official said. ‘But given the coverage provided by the E.P.A. system, even a small release, depending on which way the wind was blowing and other meteorological conditions, is likely to be picked up.”’ 
         [0008]    In an article titled, “Biodetectors Evolving, Monitoring U. S. Cities,” by Sally Cole in the May 2003 issue of Homeland Security Solutions, it was reported, “The anthrax letter attacks of 2001, and subsequent deaths of five people, brought home the reality of bioterrorism to Americans and provided a wake-up call for the U.S. government about the need for a method to detect and mitigate the impact of any such future attacks. Long before the anthrax letter attacks, scientists at two of the U.S. Department of Energy&#39;s national laboratories, Lawrence Livermore National Laboratory (LLNL) and Los Alamos National Laboratory (LANL), were busy pioneering a “biodetector” akin to a smoke detector to rapidly detect the criminal use of biological agents. This technology is now expected to play a large role in the U.S. government&#39;s recently unveiled homeland security counter-terrorism initiative, Bio-Watch, which is designed to detect airborne bioterrorist attacks on major U.S. cities within hours. Announced back in January, Bio-Watch is a multi-faceted, multi-agency program that involves the U.S. Department of Energy, the Environmental Protection Agency (EPA), and the U.S. Department of Health and Human Services&#39; Centers for Disease Control and Prevention (CDC). Many of the EPA&#39;s 3,000 air-quality monitoring stations throughout the country are being adapted with biodetectors to register unusual quantities of a wide range of pathogens that cause diseases that incapacitate and kill, according to the EPA. The nationwide network of environmental monitors and biodetectors, which reportedly will eventually monitor more than 120 U.S. cities, is expected to detect and report a biological attack within 24 hours. Citing security reasons, the EPA declined to disclose further details about the program at this time . . . . The Autonomous Pathogen Detection System (APDS) is a file-cabinet-sized machine that sucks in air, runs tests, and reports the results itself. APDS integrates a flow cytometer and real-time PCR detector with sample collection, sample preparation, and fluidics to provide a compact, autonomously operating instrument capable of simultaneously detecting multiple pathogens and/or toxins. The system is designed for fixed locations, says Langlois, where it continuously monitors air samples and automatically reports the presence of specific biological agents. APDS is targeted for domestic applications in which the public is at high risk of exposure to covert releases of bioagents—subway systems, transportation terminals, large office complexes, and convention centers . . . . APDS provides the ability to measure up to 100 different agents and controls in a single sample,’ Langlois says. ‘It&#39;s being used in public buildings right now.’ The latest evolution of the biodetector, APDS-II, uses bead-capture immunoassays and a compact flow cytometer for the simultaneous identification of multiple biological simulants. Laboratory tests have demonstrated the fully autonomous operation of APDS-II for as long as 24 hours.” 
         [0009]    U.S. Pat. No. 6,498,041 issued Dec. 24, 2002 to Mary Beth Tabacco and Laura C. Taylor for optical sensors for rapid, sensitive detection provides the following state of technology information: “The threat from biological weapons as tools of modern warfare and urban terrorism is increasing. Development of early detection, counter measures, and remediation technology is a high priority in many military, government and private laboratories around the world. Biological warfare (BW) agents of critical concern are bacterial spores, such as  Bacillus anthracis  (anthrax),  Clostridium tetani  (tetanus), and  Clostridium botulinum  (botulism).” 
         [0010]    United States Published Patent Application No. 2004/0125371 by Richard Chang et al published Jul. 1, 2004 for method and instrumentation for measuring fluorescence spectra of individual airborne particles sampled from ambient air provides the following state of technology information: “Detecting chemical composition of particles is desirable for a variety of applications, such as in detecting fugitive aerosol pollutants, differentiating between biological and non-biological aerosols (and classifying biological particles), or investigating aerosol drug-delivery systems. Light scattering particle counters are based on a single-particle detection approach, wherein particles entrained in air are rapidly drawn through an intense light beam, and light scattered by single particles is sensed and used to infer particle size. Recently, this approach has been expanded to measurement of the two-dimensional angular optical scattering of single aerosol particles and the intrinsic laser-induced fluorescence (LIF) of particles, both of which may be used for additional characterization. LIF can be used in addition to (or instead of) elastic scattering. These efforts concentrate on measurement of the undispersed fluorescence of particles, and consequently only have limited potential for providing information on particle composition. More capable techniques to measure the LIF spectra of single aerosol particles have been recently developed in order to obtain better aerosol classification. In these investigations the emphasis was on detecting biological aerosols using both cw and pulsed laser sources with wavelengths ranging from 263 nm to 488 nm.” 
       SUMMARY 
       [0011]    Features and advantages of the present invention will become apparent from the following description. Applicants are providing this description, which includes drawings and examples of specific embodiments, to give a broad representation of the invention. Various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this description and by practice of the invention. The scope of the invention is not intended to be limited to the particular forms disclosed and the invention covers all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the claims. 
         [0012]    The present invention provides a “safe” fluorescent particle for a variety of applications. The particle comprises a non-biological, biodegradable carrier and natural fluorophores encapsulated in the non-biological, biodegradable carrier. In some embodiments the particle is used as a simulant for mimicking the fluorescence properties of microorganisms. However, the particle need not mimic the fluorescent characteristics of a microorganism, rather it can be incorporated into one or more natural fluorophores as a means for fluorescence detection. Single or combinations of fluorophores are encapsulated to produce a desired fluorescent effect such as particles that fluoresce at 370 nm maxima. The particles can therefore be tuned to the excitation wavelength of a fluorescence detector. 
         [0013]    One application for these particles is their use in aerosol studies, such as large scale air dispersal to track particulate migration over vast areas, or for urban particle dispersion studies. Currently, researchers performing these studies rely on air dispersion models and gas tracer tests to determine the movement and flow of aerosols in urban environments such as in cities—around and through occupied buildings—because “safe” particles are not available. These particles would provide those safety benefits. Furthermore, these particles could be designed with the appropriate density and perhaps shape of a microorganism to mimic the aerodynamic movement of a microorganism. 
         [0014]    An example of aerosol study is described in the article, “An examination of the urban dispersion curves derived from the St. Louis dispersion study” by Akula Venkatram in  Atmospheric Environment  39 (2005) 3813-3822, which describes a study, “The St. Louis study was conducted over the period 1963-1965. The study consisted of a series of 26 daytime and 16 evening experiments in which fluorescent zinc cadmium sulfide particles were released near ground level at two different locations under a variety of meteorological conditions. During the first year of the experiments, the release was at ground level in a relatively open area in a park located west of the downtown area. In the second year, the tracer was released from the top of a three-story building surrounded by trees and similar buildings. The main downtown area, consisting of buildings with an average height of 40 m, was about 5 km away from both release locations.” The disclosure of the article, “An examination of the urban dispersion curves derived from the St. Louis dispersion study” by Akula Venkatram in  Atmospheric Environment  39 (2005) 3813-3822 is incorporated herein by this reference. 
         [0015]    Another example of aerosol study is described in the article, “Use of Salt Lake City URBAN 2000 Field Data to Evaluate the Urban Hazard Prediction Assessment Capability (HPAC) Dispersion Model” by Joseph C. Chang in  JOURNAL OF APPLIED METEOROLOGY  pages 485-501 (2005) which provides background about the study, “The potential impacts of the atmospheric release of chemical, biological, radiological, and nuclear (CBRN) or other hazardous materials are of increasing concern. Hazardous releases can occur due to accidents, such as the release of toxic industrial chemicals in Bhopal, India, in 1984 (e.g., Sharan et al. 1996) and the Chernobyl nuclear power plant disaster in the Ukraine in 1986 (e.g., Puhakka et al. 1990). They can also occur as an unintentional result of military actions, such as the U.S. destruction of rockets with chemical warheads at Khamisiyah, Iraq, after the 1991 Gulf War (Winkenwerder 2002). More recently, terrorist incidents in urban settings, such as the events on 11 Sep. 2001 in New York City, N.Y., and Washington, D.C., and military conflicts dramatically raise concerns for the possibility of mass casualties.” The disclosure of the article, “Use of Salt Lake City URBAN 2000 Field Data to Evaluate the Urban Hazard Prediction Assessment Capability (HPAC) Dispersion Model” by Joseph C. Chang in  JOURNAL OF APPLIED METEOROLOGY  pages 485-501 (2005) is incorporated herein by this reference. 
         [0016]    The evaluation of different biofluorescence detectors as tools to detect biological attack is currently difficult and balkanized due to the lack of a single, common standard with which to compare the different instruments. Biological organisms present substantial drawbacks in that they are difficult to transport and aerosolize without damaging them, exposure to them may present a health risk, and they have a tendency to agglomerate which makes their aerosolization difficult to perform reliably. Furthermore, they have a short shelf life, they are not conveniently disposable, their use requires extensive training, any equipment exposed to them requires bleach or other bactericides/sporicides for cleaning, they are difficult to manufacture, and many aspects of their growth and handling affect their final state. Therefore, biological organisms are not optimal evaluation, calibration, and training standards for biofluorescence instruments. They are, however, fluorescent in the precise manner of a microorganism (obviously), which is ultimately necessary for a test agent or surrogate. 
         [0017]    The present invention provides a simulant for mimicking the fluorescence properties of microorganisms. The simulant comprises a non-biological carrier and natural fluorophores encapsulated in the non-biological carrier. By doping biodegradable-polymer drug delivery microspheres with natural or synthetic fluorophores, the fluorescence of biological organisms can be simulated without the associated risks and logistical difficulties associated with handling live microorganisms. The particles can be “tuned” to exhibit the fluorescence characteristics of any microorganism by changing the fluorophore ratios. Because the particles are both inert and biodegradable, and because the natural fluorophores are not harmful to humans, there would be no risks to human exposure in the course of training, evaluating or tuning, and calibrating conventional fluorescence bioaerosol particle sensors. 
         [0018]    The invention is susceptible to modifications and alternative forms. Specific embodiments are shown by way of example. It is to be understood that the invention is not limited to the particular forms disclosed. The invention covers all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0019]    The accompanying drawings, which are incorporated into and constitute a part of the specification, illustrate specific embodiments of the invention and, together with the general description of the invention given above, and the detailed description of the specific embodiments, serve to explain the principles of the invention. 
           [0020]      FIG. 1  illustrates one embodiment of a system constructed in accordance with the present invention. 
           [0021]      FIG. 2  illustrates another embodiment of a system constructed in accordance with the present invention. 
           [0022]      FIG. 3  illustrates yet another embodiment of a system constructed in accordance with the present invention. 
           [0023]      FIG. 4  is an illustration showing that the naturally occurring fluorophores are chosen to match the spectral characteristics of the microorganism that is to be detected. 
           [0024]      FIG. 5  illustrates one embodiment of a system for producing simulants to mimic the fluorescence properties of microorganisms. 
           [0025]      FIG. 6  illustrates another embodiment of a system for producing simulants to mimic the fluorescence properties of microorganisms. 
           [0026]      FIG. 7  illustrates another embodiment of a system constructed in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0027]    Referring to the drawings, to the following detailed description, and to incorporated materials, detailed information about the invention is provided including the description of specific embodiments. The detailed description serves to explain the principles of the invention. The invention is susceptible to modifications and alternative forms. The invention is not limited to the particular forms disclosed. The invention covers all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the claims. 
         [0028]    The January/February 2002 issue of Science &amp; Technology Review, in an article titled “Rapid Field Detection of Biological Agents,” describes two systems to rapidly detect and identify biological agents, including pathogens such as anthrax and plague. The systems are the Handheld Advanced Nucleic Acid Analyzer (HANAA) and the Autonomous Pathogen Detection System (APDS). About the size of a brick, the HANAA biodetection system can be held in one hand and weighs less than a kilogram. The system was designed for emergency response groups, such as firefighters and police, who are often first on the scene at sites where bioterrorism may have occurred. Each handheld system can test four samples at once—either the same test on four different samples or four different tests on the same sample. HANAA can provide results in less than 30 minutes, compared with the hours to days that regular laboratory tests typically take. To detect the DNA in a sample, a synthesized DNA probe tagged with a fluorescent dye is introduced into the sample before it is inserted into the heater chamber. Each probe is designed to attach to a specific organism, such as anthrax or plague. Thus, the operator must have an idea of what substances might be involved. “The system doesn&#39;t test for all unknowns,” says Langlois. “A responder has to decide what kinds of pathogens to test for ahead of time and set up the system accordingly.” If that organism is present in the sample, the probe attaches to its DNA, which is then amplified during the PCR process, releasing the fluorescent tag. HANAA measures the sample&#39;s fluorescence and the presence (or absence) of the targeted organism. Whereas HANAA can be hand-carried to sites at which an attack is suspected to have happened, the APDS is stationed in one place for continuous monitoring and is designed to work much like a smoke detector, but for pathogens. When fully developed, the APDS could be placed in a large area such as an airport, a stadium, or a conference hall. The system will sample the air around the clock and sound an alarm if pathogens are detected. The disclosure of the article titled “Rapid Field Detection of Biological Agents,” in the January/February 2002 issue of Science &amp; Technology Review is incorporated herein by this reference. 
         [0029]    The October 2004 issue of Science &amp; Technology Review, in an article titled “Detecting Bioaerosols When Time is of the Essence,” states that Livermore researchers received seed funding from the Laboratory Directed Research and Development Program to develop an instrument that counters bioterrorism by providing a rapid early warning system for pathogens, such as anthrax. That instrument, the Autonomous Pathogen Detection System (APDS), is now ready for deployment to better protect the public from a bioaerosol attack, and the development team has been honored with a 2004 R&amp;D 100 Award. In September 2003, APDS passed a series of pathogen exposure tests at a high-containment laboratory at the Dugway Proving Ground in Utah. In these trials, the system clearly demonstrated that it could detect real pathogens and confirm the identifications with a fully automated second assay method. APDS units were also deployed at the Albuquerque Airport in New Mexico and at a Washington, D.C., Metro station, where they provided continuous monitoring for up to seven days, unattended. The system can be adapted for situations where environmental or clinical pathogens require monitoring. For example, APDS could test for mold or fungal spores in buildings or for the airborne spread of contagious materials in hospitals. It also could identify disease outbreaks in livestock transport centers or feedlots. The disclosure of the article titled “Detecting Bioaerosols When Time is of the Essence,” in the October 2004 issue of Science &amp; Technology Review is incorporated herein by this reference. 
         [0030]    The evaluation of different biofluorescence detectors as tools to detect biological attack is currently difficult and balkanized due to the lack of a single, common standard with which to compare the different instruments. Biological organisms present substantial drawbacks in that they are difficult to transport and aerosolize without damaging them, exposure to them presents a health risk, and they have a tendency to agglomerate which makes their aerosolization difficult to perform reliably. Furthermore, they have a short shelf life, they are not conveniently disposable, their use requires extensive training, any equipment exposed to them requires bleach or other bactericides/sporicides for cleaning, they are difficult to manufacture, and many aspects of their growth and handling affect their final state. Therefore, biological organisms are not optimal evaluation, calibration, and training standards for biofluorescence instruments. They are, however, fluorescent in the precise manner of a microorganism (obviously), which is ultimately necessary for a test agent or surrogate. 
         [0031]    Referring now to the drawings and in particular to  FIG. 1 , one embodiment of a system constructed in accordance with the present invention is illustrated. The system is designated generally by the reference numeral  100 . The system  100  provides encapsulation of natural fluorophores in non-toxic, abiotic materials as a simulant to mimic the fluorescence properties of microorganisms. 
         [0032]    As illustrated in  FIG. 1 , naturally occurring fluorophores  101  are combined with a non-biological carrier  102  to produce a simulant  103  that mimics the fluorescence properties of microorganisms. The system  100  provides the simulant  103  that is used for field aerosol studies, mock biowarfare training, training for rapid assessment of bioweapons labs, calibrating fluorescence-based detection equipment, and other uses. 
         [0033]    The naturally occurring fluorophores  101  are chosen to match the spectral characteristics of the microorganism that is to be detected. The naturally occurring fluorophores  101  include different fluorophores with different spectral characteristics. As illustrated in  FIG. 1  the fluorophores  101  comprise fluorophores  101 A,  101 B,  101 C,  101 D, etc. The make up of the fluorophores  101  are chosen so that the ratio of the fluorophores  101 A,  101 B,  101 C,  101 D, etc. matches the spectral characteristics of a preselected microorganism. By altering the fluorophore ratios, the spectral characteristics of any microorganism can be matched. The simulant  103  that is produced includes the fluorophores  101 A,  101 B,  101 C,  101 D, etc. that have a ratio of fluorescence that matches the spectral characteristics of a microorganism that has been preselected for testing. The simulant  103  provides a microsphere that can be “tuned” to exhibit the fluorescence characteristics of threat agents. 
         [0034]    The non-biological carrier  102  is made of non-toxic materials. In one embodiment the non-biological carrier  102  is made of abiotic materials. In another embodiment the non-biological carrier  102  is made of a biodegradable polymer. The non-biological carrier  102  illustrated in  FIG. 1  is made of a biodegradable polymer that is approved by the U.S. Food and Drug Administration (US-FDA) for in vivo research. The biodegradable polymer used as the non-biological carrier  102  is a polymer of lactic and/or glycolic acids such as poly(lactide-co-glycolide) (PLGA). The non-biological carrier  102  has advantages because it is US-FDA approved, is safe for humans, is used for drug delivery, is directed to localized regions in the body by injection, is digested/destroyed by the natural immune response, and has sustained-release properties. 
         [0035]    The simulant  103  is a biodegradable polymer microsphere. Biodegradable polymer microspheres are currently used in the pharmaceutical field for in vivo drug delivery. Some of the advantages of using microspheres in therapeutics are: (1) they are safe for humans, (2) they can target localized regions by injection or functionalization, (3) they may be used for sustained release delivery of chemo and hormone therapeutic regimens, and (4) they are digested by macrophages and dendritic cells. 
         [0036]    The simulant  103  is a biodegradable polymer microsphere that can be “tuned” to exhibit the fluorescence characteristics of threat agents. Most of the fluorescence in biological organisms comes from natural fluorophores such as the aromatic amino acids; tryptophan, phenylalanine, and tyrosine; NADH, picolinic acid, and flavins. These microspheres combine the fluorescence characteristics of the microorganisms, the handling characteristics of the polystyrene latex microspheres, and the safety characteristics of the biodegradable polymer microspheres. If these natural fluorophores are doped into biodegradable polymer microspheres in the correct ratios, then those spheres will act as fluorescent analogs to microorganisms. Furthermore, by varying the concentrations of the various fluorophores, different agents can be simulated. If inhaled or ingested, the natural fluorophore-doped biodegradable polymer particles would be digested by the human macrophages and so are not detrimental to human health. The doped biodegradable polymers have the combined advantages of the fluorescence characteristics of the microorganisms, the handling characteristics of the polystyrene latex microspheres and the safety characteristics of the biodegradable polymer microspheres. 
         [0037]    The system  100  combines the advantages of natural fluorophores, common to both humans and microorganisms, with the safety benefits of a biodegradable polymer. The system  100  has advantages because it has properties conducive to field operations/tests including (1) it is easily used by untrained personnel, (2) it is stable in most environments, (3) it has long shelf-life, (4) it is stable at pH&gt;3, and (5) it may have increased hydrophobicity=stability in wetter conditions. Degradation studies indicate: 
         [0038]    Lyophilized lactide and/or glycolide microspheres (50:50 polymer ratio) stable for&gt;3 months when stored at 4° C. or frozen, stable during testing and calibration procedures at elevated temperatures (&gt;37° C. for 6 days), have the precision of an analytical reagent, labeled (fluorescent tag) to differentiate between test simulants and threat agents, and surface properties can be altered by functionalization/derivatization, hydrophobicity, surface charge, surface proteins/antigens for special applications. 
         [0039]    The system  100  enables the mimicking of the fluorescence signatures of threat agents and the development of a field-deployable simulant  103 . The system  100  provides simulant  103  that can be used for field aerosol studies, mock biowarfare training, training for rapid assessment of bioweapons labs, calibrating fluorescence-based detection equipment, and other uses. The system  100  can also be use in other applications, for example the system  100  can be used to provide a simulant for air dispersion studies (large scale); for urban aerosol studies (small scale); for tagging, tracking, and locating; and for subsurface colloidal transport studies/radionuclide migration studies. The system  100  can be used to simulate the fluorescent properties of microorganisms. Size can be adjusted to simulate different degrees of agglomeration. The system  100  can be used as challenge-test standards for determining sensitivity and specificity of fluorescent detection technologies. The system  100  can be used for large-scale air current deployments or tests for determining the movement and distribution of particles in urban environments. The system  100  can be labeled to distinguish between “test” microspheres and background microorganisms/organic particles. The system  100  can be used as a calibration standard for bio-fluorescence detectors. The system  100  can be used to train personnel to operate bio-fluorescence detectors. Surface properties, such as hydrophobicity and surface charge, can be tuned/altered for various applications. 
         [0040]    Referring now to  FIG. 2 , another embodiment of a system constructed in accordance with the present invention is illustrated. The system is designated generally by the reference numeral  200 . The system  200  provides encapsulation of natural fluorophores  201  in non-toxic, abiotic materials  202  to provide simulants  203  that mimic the fluorescence properties of microorganisms. 
         [0041]    The simulants  203  are biodegradable polymer microspheres. The biodegradable polymer microsphere simulants  203  can be “tuned” to exhibit the fluorescence characteristics of threat agents. Most of the fluorescence in biological organisms comes from natural fluorophores such as the aromatic amino acids; tryptophan, phenylalanine, and tyrosine; NADH, picolinic acid, and flavins. These microspheres combine the fluorescence characteristics of the microorganisms, the handling characteristics of the polystyrene latex microspheres, and the safety characteristics of the biodegradable polymer microspheres. If these natural fluorophores are doped into biodegradable polymer microspheres in the correct ratios, then those spheres will act as fluorescent analogs to microorganisms. By varying the concentrations of the various fluorophores, different agents can be simulated. 
         [0042]    As illustrated in  FIG. 2 , naturally occurring fluorophores  201  are combined with non-biological carriers  202  to produce simulants  203  that mimic the fluorescence properties of microorganisms. The system  200  provides simulants  203  that are useful for field aerosol studies, mock biowarfare training, training for rapid assessment of bioweapons labs, calibrating fluorescence-based detection equipment, and other uses. 
         [0043]    The naturally occurring fluorophores  201  include different fluorophores with different spectral characteristics. As illustrated in  FIG. 2  the fluorophores  201  comprise fluorophores  201 A,  201 B,  201 C,  201 D, etc. The make up of the fluorophores  201  are chosen so that the ratio of the fluorophores  201 A,  201 B,  201 C,  201 D, etc. matches the spectral characteristics of a preselected microorganism. By altering the fluorophore ratios, the spectral characteristics of any microorganism can be matched. The simulants  203  that are produced include the fluorophores  201 A,  201 B,  201 C,  201 D, etc. that have a ratio of fluorescence that matches the spectral characteristics of a microorganism that has been preselected for testing. The simulants  203  are microspheres that can be “tuned” to exhibit the fluorescence characteristics of threat agents. 
         [0044]    The non-biological carrier  202  is made of non-toxic materials. In one embodiment the non-biological carrier  202  is made of abiotic materials. In another embodiment the non-biological carrier  202  is made of a biodegradable polymer. The non-biological carrier  202  illustrated in  FIG. 2  is made of a biodegradable polymer that is approved by the U.S. Food and Drug Administration (US-FDA) for in vivo research. The biodegradable polymer used as the non-biological carrier  202  is a polymer of lactic and/or glycolic acids such as poly(lactide-co-glycolide) (PLGA). The non-biological carrier  202  has advantages because it is US-FDA approved, is safe for humans, is used for drug delivery, is directed to localized regions in the body by injection, is digested/destroyed by the natural immune response, and has sustained-release properties. 
         [0045]    The system  200  combines the advantages of natural fluorophores, common to both humans and microorganisms, with the safety benefits of a biodegradable polymer. The system  200  has advantages because it has properties conducive to field operations/tests including (1) it is easily used by untrained personnel, (2) it is stable in most environments, (3) it has long shelf-life, (4) it is stable at pH&gt;3, and (5) it can be designed to have increased hydrophobicity=stability in wetter conditions. Degradation studies indicate: 
         [0046]    Lyophilized PLGA microspheres (50:50 polymer ratio) are stable for&gt;3 months when stored at 4° C. or frozen, and stable during testing and calibration procedures at elevated temperatures (&gt;37° C. for 6 days). Furthermore, they can be used with the precision of an analytical reagent, labeled (fluorescent tag) to differentiate between test simulants and threat agents, their surface properties can be altered by functionalization/derivatization to alter surface charge or attach surface proteins/antigens for special applications. 
         [0047]    The system  200  enables the mimicking of the fluorescence signatures of threat agents and the development of field-deployable simulants  203 . The system  200  provides simulants  203  that can be used for field aerosol studies, mock biowarfare training, training for rapid assessment of bioweapons labs, calibrating fluorescence-based detection equipment, and other uses. The system  200  can also be use in other applications, for example the system  200  can be used for to provide simulants for air dispersion studies (large scale); for urban aerosol studies (small scale); for tagging, tracking, and locating; and for subsurface colloidal transport studies/radionuclide migration studies. The system  200  can be used to simulate the fluorescent properties of microorganisms. Size can be adjusted to simulate different degrees of agglomeration. The system  200  can be used as challenge-test standards for determining sensitivity and specificity of fluorescent detection technologies. The system  200  can be used for large-scale air current deployments or tests for determining the movement and distribution of particles in urban environments. The system  200  can be labeled to distinguish between “test” microspheres and background microorganisms/organic particles. The system  200  can be used as a calibration standard for bio-fluorescence detectors. The system  200  can be used to train personnel to operate bio-fluorescence detectors. Surface properties, such as hydrophobicity and surface charge, can be tuned/altered for various applications. 
         [0048]    Referring now to  FIG. 3 , yet another embodiment of a system constructed in accordance with the present invention is illustrated. The system is designated generally by the reference numeral  300 . The system  300  provides encapsulation of natural fluorophores  301  in non-toxic, abiotic materials  302  to provide simulants  303  and  304  that mimic the fluorescence properties of microorganisms. 
         [0049]    As illustrated in  FIG. 3 , naturally occurring fluorophores  301  are combined with non-biological carriers  302  to produce simulants  303  and  304  that mimic the fluorescence properties of microorganisms. The system  300  provides simulants  303  and  304  that are useful for field aerosol studies, mock biowarfare training, training for rapid assessment of bioweapons labs, calibrating fluorescence-based detection equipment, and other uses. 
         [0050]    The naturally occurring fluorophores  301  include different fluorophores with different spectral characteristics. As illustrated in  FIG. 3  the fluorophores  301  comprise fluorophores  301 A,  301 B,  301 C,  301 D, etc. The make up of the fluorophores  301  are chosen so that the ratio of the fluorophores  301 A,  301 B,  301 C,  301 D, etc. matches the spectral characteristics of a preselected microorganism. By altering the fluorophore ratios, the spectral characteristics of any microorganism can be matched. The simulants  303  and  304  that are produced include the fluorophores  301 A,  301 B,  301 C,  301 D, etc. that have a ratio of fluorescence that matches the spectral characteristics of a microorganism that has been preselected for testing. The simulants  303  and  304  are microspheres that can be “tuned” to exhibit the fluorescence characteristics of threat agents. 
         [0051]    The non-biological carrier  302  is made of non-toxic materials. In one embodiment the non-biological carrier  302  is made of abiotic materials. In another embodiment the non-biological carrier  302  is made of a biodegradable polymer. The non-biological carrier  302  illustrated in  FIG. 3  is made from a biodegradable polymer that is approved by the U.S. Food and Drug Administration (US-FDA) for in vivo research. The biodegradable polymer used as the non-biological carrier  302  is a polymer of lactic and/or glycolic acids such as poly(lactide-co-glycolide) (PLGA). The non-biological carrier  302  has advantages because it is US-FDA approved, is safe for humans, is used for drug delivery, is directed to localized regions in the body by injection, is digested/destroyed by the natural immune response, and has sustained-release properties. 
         [0052]    The simulants  303  and  304  are biodegradable polymer microspheres. The biodegradable polymer microsphere simulants  303  and  304  can be “tuned” to exhibit the fluorescence characteristics of threat agents. Most of the fluorescence in biological organisms comes from natural fluorophores such as the aromatic amino acids; tryptophan, phenylalanine, and tyrosine; NADH, picolinic acid, and flavins. These microspheres combine the fluorescence characteristics of the microorganisms, the handling characteristics of the polystyrene latex microspheres, and the safety characteristics of the biodegradable polymer microspheres. If these natural fluorophores are doped into biodegradable polymer microspheres in the correct ratios, then those spheres will act as fluorescent analogs to microorganisms. By varying the concentrations of the various fluorophores, different agents can be simulated. 
         [0053]    The system  300  combines the advantages of natural fluorophores, common to both humans and microorganisms, with the safety benefits of a biodegradable polymer. The system  300  has advantages because it has properties conducive to field operations/tests including (1) is easily used by untrained personnel, (2) it is stable in most environments, (3) it has long shelf-life, (4) it is stable at pH&gt;3, and (5) it can be designed to have increased hydrophobicity=stability in wetter conditions. Degradation studies indicate that: 
         [0054]    Lyophilized PLGA microspheres (50:50 polymer ratio) are stable for&gt;3 months when stored at 4° C. or frozen, and stable during testing and calibration procedures at elevated temperatures (&gt;37° C. for 6 days). Furthermore, they can be used with the precision of an analytical reagent, can be labeled (fluorescent tag) to differentiate between test simulants and threat agents, their surface properties can be altered by functionalization/derivatization to alter surface charge or attach surface proteins/antigens for special applications. 
         [0055]    The system  300  enables the mimicking of the fluorescence signatures of threat agents and the development of field-deployable simulants  303  and  304 . The system  300  provides simulants  303  and  304  that can be used for field aerosol studies, mock biowarfare training, training for rapid assessment of bioweapons labs, calibrating fluorescence-based detection equipment, and other uses. The system  300  can also be use in other applications, for example the system  300  can be used for to provide simulants for air dispersion studies (large scale); for urban aerosol studies (small scale); for tagging, tracking, and locating; and for subsurface colloidal transport studies/radionuclide migration studies. The system  300  can be used to simulate the fluorescent properties of microorganisms. Size can be adjusted to simulate different degrees of agglomeration. The system  300  can be used as challenge-test standards for determining sensitivity and specificity of fluorescent detection technologies. The system  300  can be used for large-scale air current deployments or tests for determining the movement and distribution of particles in urban environments. The system  300  can be labeled to distinguish between “test” microspheres and background microorganisms/organic particles. The system  300  can be used as a calibration standard for bio-fluorescence detectors. The system  300  can be used to train personnel to operate bio-fluorescence detectors. Surface properties, such as hydrophobicity and surface charge, can be tuned/altered for various applications. 
         [0056]    Referring now to  FIG. 4 , an illustration shows that the naturally occurring fluorophores of the simulant are chosen to match the spectral characteristics of the microorganism that is to be detected. The illustration is designated generally by the reference numeral  400 . 
         [0057]    A display  403  represents spectral characteristics of naturally occurring fluorophores in the simulant  401  and the spectral characteristics of the microorganism of interest  405 . The spectral characteristics of the simulant  401  are represented by the display  403  as illustrated by the arrow  402 . The spectral characteristics the microorganism of interest  405  is represented by the display  403  as illustrated by the arrow  404 . 
         [0058]    The simulant  401  includes different fluorophores with different spectral characteristics. The make up of the fluorophores of the simulant  401  are chosen so that the ratio of the fluorophores matches the spectral characteristics of the preselected microorganism  405 . The fluorescence spectrum of simulant  401  matches spectrum of the target microorganism  405 . In the illustration  400  the preselected microorganism  405  is  B. anthracis  spore. The simulant  401  and  B. anthracis  spore  405  exhibit the same spectra. 
         [0059]    Most of the fluorescence in biological organisms comes from natural fluorophores such as the aromatic amino acids, tryptophan, tyrosine and phenylalanine, and NADH, dipicolinic acid and flavins. These microspheres combine the fluorescence characteristics of the microorganisms, the handling characteristics of the polystyrene latex microspheres, and the safety characteristics of the biodegradable polymer microspheres. If these natural fluorophores are doped into biodegradable polymer microspheres in the correct ratios, then those spheres will act as fluorescent analogs to microorganisms. Furthermore, by varying the concentrations of the various fluorophores, different agents can be simulated. The simulant  401  is a biodegradable polymer microsphere that can be “tuned” to exhibit the fluorescence characteristics of threat agents. 
         [0060]    By altering the fluorophore ratios of the simulant  401 , the spectral characteristics of any microorganism can be matched. The simulant  401  includes a mixture of fluorophores that match the spectral characteristics of the microorganism  405  that has been preselected for testing. The simulant  401  provides a microsphere that can be “tuned” to exhibit the fluorescence characteristics of threat agents. 
         [0061]    The present invention enables the mimicking of the fluorescence signatures of threat agents and the development of a field-deployable simulant  401 . The simulant  401  can be used for field aerosol studies, mock biowarfare training, training for rapid assessment of bioweapons labs, calibrating fluorescence-based detection equipment, and other uses. The simulant  401  can also be use in other applications, for example the simulant  401  can be used to provide a fluorescence simulant for air dispersion studies (large scale); for urban aerosol studies (small scale); for tagging, tracking, and locating; and for subsurface colloidal transport studies/radionuclide migration studies. The simulant  401  can be used to simulate the fluorescent properties of microorganisms. Size can be adjusted to simulate different degrees of agglomeration. The simulant  401  can be used as challenge-test standards for determining sensitivity and specificity of fluorescent detection technologies. The simulant  401  can be used for large-scale air current deployments or tests for determining the movement and distribution of particles in urban environments. The simulant  401  can be labeled to distinguish between “test” microspheres and background microorganisms/organic particles. The simulant  401  can be used as a calibration standard for bio-fluorescence detectors. The simulant  401  can be used to train personnel in identifying bio-threat agents with fluorescence detection technologies. Surface properties, such as hydrophobicity and surface charge, can be tuned/altered for various applications. 
         [0062]    Referring now to the drawings and in particular to  FIG. 5 , one embodiment of a system for producing simulants to mimic the fluorescence properties of microorganisms constructed in accordance with the present invention is illustrated. The system is designated generally by the reference numeral  500 . The system  500  is an oil-in-water emulsion system. The system  500  provides a system for producing natural fluorophores in non-toxic, abiotic materials that can be used as a simulants to mimic the fluorescence properties of microorganisms. 
         [0063]    As illustrated in  FIG. 5 , biodegradable polymers  501  in solvent  502  are introduced into a container  503  as illustrated by the arrow  504 . Also natural fluorophores  505  in water  506  are introduced into the container  503  as illustrated by the arrow  507 . The biodegradable polymers  501  in solvent  502  and natural fluorophores  505  in water  506  are mixed in container  503  by mixing system  508  to produce polydisperse microspheres  509  as illustrated by the arrow  510 . 
         [0064]    The polydisperse microspheres  509  contain the naturally occurring fluorophores  505 . This provides a simulant that mimics the fluorescence properties of microorganisms. The polydisperse microspheres simulant  509  can be used for field aerosol studies, mock biowarfare training, training for rapid assessment of bioweapons labs, calibrating fluorescence-based detection equipment, and other uses. 
         [0065]    The naturally occurring fluorophores  505  are chosen to match the spectral characteristics of the microorganism that is to be detected. The naturally occurring fluorophores  505  include different fluorophores with different spectral characteristics. The make up of the fluorophores  505  are chosen so that the ratio of the fluorophores match the spectral characteristics of a preselected microorganism. By altering the fluorophore ratios, the spectral characteristics of any microorganism can be matched. 
         [0066]    The oil-in-water emulsion system  500  utilizes a simple water-in-oil emulsion. Fluorophores  505  are dissolved in water  506 . Polymer  501  is dissolved in solvent  502 . The next step is to disperse aqueous phase in polymer solution with ultrasonic probe  508 . Particle size distribution is dependent on the degree of ultrasonication. The solvent is subsequently evaporated or spray-dried and the microspheres are washed and dried under vacuum. 
         [0067]    Referring now to the drawings and in particular to  FIG. 6 , another embodiment of a system for producing simulants to mimic the fluorescence properties of microorganisms constructed in accordance with the present invention is illustrated. The system is designated generally by the reference numeral  600 . The system  600  is a pulsed/jetted system. The system  600  provides a system for producing natural fluorophores in non-toxic, abiotic materials that can be used as a simulants to mimic the fluorescence properties of microorganisms. 
         [0068]    As illustrated in  FIG. 6 , biodegradable polymers  601  in a solvent  602  are contained in container  603 . Natural fluorophores  604  are introduced into the container  603  as illustrated by the arrow  605 . The biodegradable polymers  601  and natural fluorophores  604  mix in container  603 . Monodisperse microspheres  607  of a desired size can be produced directly from the fluorophore/polymer dispersion by using a vibrating orifice aerosol generator, ink jet aerosol generator, or other particle generator  606  with subsequent drying to remove the solvent. A VOAG, ink jet particle generator, or other particle generator  606  is used to produce the monodisperse microspheres  607 . 
         [0069]    The monodisperse microspheres  607  contain the naturally occurring fluorophores  604 . This provides simulants that mimic the fluorescence properties of microorganisms. The monodisperse microspheres simulants  607  can be used for field aerosol studies, mock biowarfare training, training for rapid assessment of bioweapons labs, calibrating fluorescence-based detection equipment, and other uses. 
         [0070]    The naturally occurring fluorophores  604  are chosen to match the spectral characteristics of the microorganism that is to be detected. The naturally occurring fluorophores  604  include different fluorophores with different spectral characteristics. The make up of the fluorophores  604  are chosen so that the ratio of the fluorophores match the spectral characteristics of a preselected microorganism. By altering the fluorophore ratios, the spectral characteristics of any microorganism can be matched. 
         [0071]      FIG. 7  illustrates the encapsulation of natural fluorophores in non-toxic, abiotic materials as a safe test particle. This system is designated generally by the reference number  700 . 
         [0072]    The naturally occurring fluorophores  701  include different fluorophores with different spectral characteristics. As illustrated in  FIG. 7  the fluorophores  701  comprise fluorophores  701 A,  701 B, etc. 
         [0073]    The non-biological carrier  702  is made of non-toxic materials. In one embodiment the non-biological carrier  702  is made of abiotic materials. In another embodiment the non-biological carrier  702  is made of a biodegradable polymer. The non-biological carrier  702  illustrated in  FIG. 7  is made of a biodegradable polymer that is approved by the U.S. Food and Drug Administration (US-FDA) for in vivo research. The biodegradable polymer used as the non-biological carrier  702  is a polymer of lactic and/or glycolic acids such as poly(lactide-co-glycolide) (PLGA). The non-biological carrier  702  has advantages because it is US-FDA approved, is safe for humans, is used for drug delivery, is directed to localized regions in the body by injection, is digested/destroyed by the natural immune response, and has sustained-release properties. 
         [0074]    The particle  703  that is produced includes the fluorophores in different concentrations or ratios for a desired effect. The simulant  703  provides a microsphere that can be “tuned” to exhibit the desired fluorescence characteristics. 
         [0075]    The simulant  703  is a safe biodegradable polymer microsphere that can be “tuned” to exhibit the desired fluorescence effect. Most of the fluorescence in biological organisms comes from natural fluorophores such as the aromatic amino acids; tryptophan, phenylalanine, and tyrosine; NADH, picolinic acid, and flavins. These microspheres combine natural fluorophores with the safety characteristics of the biodegradable polymer. By varying the concentrations and ratios of the natural fluorophores, different fluorescent effects can be expressed. If inhaled or ingested, the natural fluorophore-doped biodegradable polymer particles would be digested by the human macrophages and so are not detrimental to human health. The doped biodegradable polymers have the combined advantages of using natural fluorophores, the safety characteristics of the biodegradable polymer, and the handling characteristics of the polystyrene latex microspheres. 
         [0076]    The simulant  703  can be used in many applications, for example the simulant  703  can be used to provide a fluorescence simulant for fluorescence detection instruments used in air dispersion studies (large scale), urban aerosol studies (small scale), tagging, tracking, and locating, and for subsurface colloidal transport studies/radionuclide migration studies. 
         [0077]    While the invention may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the following appended claims.