Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
  • G01N15/10—Investigating individual particles
  • G01N15/14—Optical investigation techniques, e.g. flow cytometry
  • G01N15/1434—Optical arrangements
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
  • G01N15/02—Investigating particle size or size distribution
  • G01N15/0205—Investigating particle size or size distribution by optical means
  • G01N15/0211—Investigating a scatter or diffraction pattern
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
  • G01N15/10—Investigating individual particles
  • G01N15/14—Optical investigation techniques, e.g. flow cytometry
  • G01N15/1429—Signal processing
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
  • G01N15/10—Investigating individual particles
  • G01N15/14—Optical investigation techniques, e.g. flow cytometry
  • G01N15/1456—Optical investigation techniques, e.g. flow cytometry without spatial resolution of the texture or inner structure of the particle, e.g. processing of pulse signals
  • G01N15/1459—Optical investigation techniques, e.g. flow cytometry without spatial resolution of the texture or inner structure of the particle, e.g. processing of pulse signals the analysis being performed on a sample stream
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
  • G01N15/01—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials specially adapted for biological cells, e.g. blood cells
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
  • G01N2015/0042—Investigating dispersion of solids
  • G01N2015/0046—Investigating dispersion of solids in gas, e.g. smoke
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
  • G01N15/10—Investigating individual particles
  • G01N2015/1006—Investigating individual particles for cytology
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N21/21—Polarisation-affecting properties
  • G01N2021/217—Measuring depolarisation or comparing polarised and depolarised parts of light

Definitions

• This invention pertains generally to aerosol analyzers and more specifically to optical analyzers for the real-time detection and classification of airborne biological and non-biological particles.
• LIF based biological particulate detection There are three primary limitations with LIF based biological particulate detection. First, is their ability to detect single vegetative or spore type organisms. Current fielded LIF based biological particle detectors are limited to detection of vegetative cell and spore aggregate particles or particles that contain numerous vegetative cells or spores per aerosol particle. For both biodefense and other applications the detection of single vegetative cells and spores is required and necessary to provide adequate protection or effective contamination control monitoring. For LIF based approaches, unless a laser source with considerable optical power is used an insufficient amount of light is emitted from fluorescence excitation to reliably and accurately classify a biological from a non-biological particle when the particle size is in the 0.5- 1.5 micron diameter in size. This is particularly true for longer excitation wavelengths such as the 350-450nm wavelength range but also applies, in most instances, for shorter wavelengths such as the 250-300nm wavelength range.
• LIF based particle detection approaches are useful for discrimination from inorganic particles and non-fluorescing man-made particles but face serious limitations for particles that have been doped with fluorophores, such as paper particles or clothing particles containing optical brighteners, and commonly encountered particles that have intrinsic fluorescence, such as human skin cell fragments and animal dander.
• fluorophores such as paper particles or clothing particles containing optical brighteners
• commonly encountered particles that have intrinsic fluorescence such as human skin cell fragments and animal dander.
• the use of LIF based multi -wavelength excitation approaches have some improved classification over single source approaches but the approaches are not cost effective for widespread application.
• Preferred embodiments of the present invention contemplate methods, apparatuses, and systems for detecting and classifying individual airborne biological and non-biological particles, in real time, based on polarized elastic scatter.
• Particle size and/or autofluorescene content may also be used along with polarized elastic scatter for further orthogonal classification.
• polarized elastic scattering With polarized elastic scattering, the degree of linear or circular depolarization produced from particle morphology, refractive index, internal asymmetric structures and molecular optical activity can be used for classifying individual airborne particles.
• circular intensity differential scattering (CIDS) and linear intensity differential scattering (LIDS) provide a means for discriminating individual particles.
• CIDS is based mainly on a particle's intrinsic molecular optical activity and internal asymmetric structures, such as from chiral macromolecular complexes and aggregates commonly found in biological particles.
• LIDS is based on a particle's shape or morphology, refractive index, intrinsic optical activity and internal asymmetric structures.
• the normalized depolarization of light scattered from a particle can be determined by the relationship:
• IH represents the scatter intensity for horizontally polarized light and is the same as the as the polarization state of the illumination beam and Iv represents the scatter intensity for vertically polarized light.
• two incident beams of orthogonal linear polarizations can be used for illumination of individual particles and scattered horizontally polarized light is used for measuring the degree of depolarization.
• the ratio of scattered intensity of horizontally polarized light collected during two spatially separated orthogonally linear polarized incident beams can be used to classify individual particles and is given by the relationship:
• IHH represents the scatter intensity for horizontally polarized light and horizontally polarized incident beam
• IHV represents the scatter intensity for
• the normalized depolarization of light scattered from a particle can be determined by the relationship:
• ⁇ +c represents circular depolarization when using right handed polarized light as the illumination source
• ⁇ -c represents circular depolarization when using left handed polarized light as the illumination source
• I_i_ represents the scatter intensity for perpendicularly polarized light
• In represents the scatter intensity for parallel polarized light.
• differential scattering of left and right circularly polarized light contributes to the circular dichroism of biological macromolecules.
• the diameter of the particle or macromolecular complex exceeds l/Xft 1 the excitation wavelength the differential scattering contribution to circular dichroism becomes important.
• differential scattering contributes to the circular dichroism.
• a chiral scattering particle will produce a differential scattering signal where both its sign and magnitude are directly related to the relative orientations and distances between its chiral scattering elements. This signal can be obtained in a quantitative manner and can be used for discrimination of biological from non-biological particles and for classifying one biological type particle from another.
• CIDS circular intensity differential scattering
• CIDS is not sensitive to size, shape or refractive index but is sensitive to the chirality of biological macromolecules which are present in all airborne bacteria, fungi, viruses and protein aggregate particles.
• LIDS detection differential scattering of vertically and horizontally polarized light is sensitive to the shape, refractive index and chiral content of particles, or more specifically, internal asymmetric structures and molecular optical activity.
• the linear intensity differential scattering (LIDS) at a scattering angle ⁇ can be determined by the relationship:
• LIDS is sensitive to size, shape and refractive index and is also sensitive to the chirality of biological macromolecules which are present in all airborne bacteria, fungi, viruses and protein aggregate particles.
• one preferred embodiment of the present invention includes a method for detecting and classifying a single particle comprising
• a single detector employing a horizontally polarized filter thereby captures polarized and depolarized scattering signals on single particles.
• the size of the particle can be determined by measuring the elastic scatter intensity with the horizontally polarized source. The degree of depolarization for a certain particle size range may then be compared to a library of signatures for various biological and non-biological type aerosols. With this method an orthogonal fluorescence detection channel can be added provided the selection of the source's excitation is one that can excite the desired endogenous fluorophores commonly encountered in biological particles.
• one preferred embodiment of the present invention includes a method for detecting and classifying a single particle comprising
• a polarizing beam splitter with two detectors captures parallel and perpendicularly polarized scattering signals on single particles.
• the size of the particle can be determined by summing the intensity of the two polarized scatter signals. The degree of depolarization for a certain particle size range may then be compared to a library of signatures for various biological and non-biological type aerosols.
• an orthogonal fluorescence detection channel can be added provided the selection of the source's excitation is one that can excite the desired endogenous fluorophores commonly encountered in biological particles.
• one preferred embodiment of the present invention includes a method for detecting and classifying a single particle comprising illuminating the particle with a circularly polarized light beam where its polarization is alternated from left to right (or right to left) handedness with two vertically spaced beams produced from a single source as the particle traverses the illumination region thereby capturing circular intensity differential scattering signals on single particles.
• the size of the particle can be determined by measuring the elastic scatter intensity.
• the intensity of left handed and right handed circular scatter signals is used to determine the CIDS value per aerosol event.
• the CIDS value may then be compared to a library of signatures for various biological and non-biological type aerosols.
• an orthogonal fluorescence detection channel can be added provided the selection of the source's excitation is one that can excite the desired endogenous fluorophores commonly encountered in biological particles.
• one preferred embodiment of the present invention includes a method for detecting and classifying a single particle comprising illuminating the particle with a linearly polarized light beam where its polarization is alternated from horizontal to vertical with two vertically spaced beams produced from a single source as the particle traverses the illumination region thereby capturing linear intensity differential scattering signals on single particles.
• the size of the particle can be determined by measuring the elastic scatter intensity.
• the intensity of vertically and horizontally polarized scatter signals is used to determine the LIDS value per aerosol event.
• the LIDS value may then be compared to a library of signatures for various biological and non-biological type aerosols.
• an orthogonal fluorescence detection channel can be added provided the selection of the source's excitation is one that can excite the desired endogenous fluorophores commonly encountered in biological particles.
• FIG. 1 is a schematic representation illustrating an optical detector including a linear depolarization detection configuration having a dual vertically and horizontally polarized beam source and a single detector with horizontally polarized filter.
• FIG. 1A is an enlarged schematic representation illustrating a preferred optical viewing region having two illumination points or areas.
• FIG. 2 is a schematic representation illustrating an optical detector including a linear depolarization detection configuration having a single horizontally polarized beam source and two detectors with one having a horizontally polarized filter and the other a vertically polarized filter.
• FIG. 3 is a schematic representation illustrating an optical detector including a linear depolarization detection configuration having a dual vertically and horizontally polarized beam source and a single detector with horizontally polarized filter and an orthogonal fluorescence detection channel.
• FIG. 4 is a schematic representation illustrating an optical detector including a linear depolarization detection configuration having a vertically and horizontally polarized beam source, a polarizing beam splitter and two detectors for detecting parallel and perpendicularly polarized scatter.
• FIG. 5 is a schematic representation illustrating an optical detector including a circular depolarization detection configuration having a dual left handed and right handed circularly polarized beam source, a polarizing beam splitter and two detectors for detecting parallel and perpendicularly polarized scatter.
• FIG. 6 is a schematic representation illustrating an optical detector including a circular intensity differential scattering detection configuration having a dual left handed and right handed circularly polarized beam source and a single detector.
• FIG. 7 is a schematic representation illustrating an optical detector including a linear intensity differential scattering detection configuration having a dual vertically and horizontally polarized beam source and a single detector.
• FIG. 8 is a schematic representation illustrating an optical detector including a linear depolarization detection configuration having a single horizontally polarized beam source and a single detector having a vertically polarized filter and an orthogonal fluorescence detection channel.
• FIG. 9 illustrates the detection event for a single particle for the optical analyzer depicted in Figure 1.
• FIGS. 10 and 11 illustrate the linear depolarization response where the degree of depolarization is determined by dividing the scatter intensity collected from a horizontally polarized filtered signal and a horizontally polarized excitation source by the scatter intensity collected from a horizontally polarized filtered signal and a vertically polarized excitation source.
• FIG. 12 illustrates additional linear depolarization responses using the same ratio measurement as in FIGS. 10 and 11 and the use of depolarization ratio distributions to classify particles of interest from commonly encountered particles from different environments.
• Three different environments are provided as examples: an indoor building, a subway platform and an urban background.
• FIG. 13 illustrates additional linear depolarization responses using the same ratio measurement as in FIGS. 10 and 11 and 3D scatter analysis approach.
• the preferred forms of the present invention relate to enhanced methods, apparatuses and systems for the detection and classification of biological and non-biological particulates in a realtime manner.
• the various detection schemes exploit one physical phenomena which involves the interaction of light with a single aerosol particle (i.e., polarized elastic scattering).
• a second physical phenomena which involves the interaction of light with a single aerosol particle may be used (i.e., fluorescence).
• fluorescence i.e., fluorescence
• the particle's size is preferably determined substantially simultaneously.
• the preferred forms of the present invention are capable of detecting and classifying single airborne particles having an aerodynamic diameter of 10 microns or less (e.g., 0.5 to 1.5 microns).
• FIGS. 1-4 and 8 provide block diagrams outlining various embodiments of preferred optical detectors where linear depolarization measurements can be performed on individual particles using one or more excitation sources.
• FIG. 5 provides a block diagram outlining an embodiment of a preferred optical detector where circular depolarization measurements can be performed on individual particles using one or more excitation sources.
• FIG. 6 provides a block diagram outlining an embodiment of a preferred optical detector where circular intensity differential scattering or CIDS measurements can be performed on individual particles using one or more excitation sources.
• FIG. 7 provides a block diagram outlining an embodiment of a preferred optical detector where linear intensity differential scattering or LIDS measurements can be performed on individual particles using one or more excitation sources.
• the excitation source can be an edge emitting laser diode, vertical cavity surface emitting laser diode, light emitting diode or other laser source.
• one or more of the sources can be configured to produce dual circularly or linearly polarized beams separated in space (e.g., vertically separated) using birefringent optics for illumination of single particles with two or more wavelengths and two polarization states for each wavelength at a time exciting the particle.
• laser line generating optics may be used to generate a laser line thickness of from about 5 to about 300 micron, and a depth of field and laser line width that is at least two times (2x) the diameter of the inlet (aerosol orifice).
• a circular inlet may become restrictive and a rectangular inlet may be preferred.
• a laser line generating approach is preferred with the depth of field and laser line width adjusted to illuminate, at a minimum, the entire rectangular nozzle area.
• the above laser line generating approaches are to ensure complete illumination of the air sampling region with the purpose of near 100% percent illumination of the aerosol particles sampled.
• the laser line thickness is desired to be small as permissible with the optical design to ensure the highest possible aerosol count rate without illuminating more than one aerosol particle, in the size range of interest, so as to minimize particle coincidence.
• the configurations described in the present invention can be operated without an aerosol inlet nozzle.
• the laser line illumination geometry and collection optics are used to interrogate a predefined region of the sampling volume providing a means for individual particle detection with low pressure drop and low audible noise through the use of axial fans as the vacuum source.
• FIG. 1 is a schematic representation illustrating an optical detector including a linear depolarization detection configuration having a dual vertically and horizontally polarized beam source and a single detector with a horizontally polarized filter.
• Aerosol from the air surrounding the optical detector is drawn into the sensor cell 140 through an aerosol nozzle as shown in FIG. 1A or inlet port with no nozzle by a vacuum source (not shown) and is introduced into an optical viewing region 145. Any suitable vacuum source may be used.
• the aerosol nozzle preferably is circular for flow rates below 20 liters per minute and can incorporate sheath flow in applications containing aerosol concentrations that would accelerate the fouling rate of the collection optics. For flow rates above 20 liters per minute, and a nozzle preferably is employed.
• the nozzle is preferably rectangular with the long side of the nozzle inlet following the light beam path and the short side orthogonal to the light beam.
• the excitation source 100 is preferably a continuous source or modulated at 20 MHz or greater frequency and can be an edge emitting laser diode, vertical cavity surface emitting laser diode, light emitting diode or some other laser.
• the wavelength of excitation source 100 can be in the range of 200-1500nm.
• Light emitted from source 100 is collimated using an aspheric lens 110. Depending on the source spatial filtering between the source 100 and the aspheric lens 110, or after lens 110 but before the aerosol cell 140 may be necessary. Collimated light is then introduced to beam shaping optics 125.
• the beam shaping optics 125 can be a single lens or group of lens designed to create a sheet of light at the aerosol nozzle region that is preferably from about 5 to about 300 micron in thickness and a depth of field and beam width that is preferably two times (2x) larger than the diameter of the inlet.
• the beam shaping optics 125 can be a spherical lens and a cylinder lens designed to generate the above geometry. In another embodiment, only a cylinder lens is used for the beam shaping optics 125.
• the beam shaping optics 125 are comprised of top hat beam shaping optics which distributes the energy of a Guassian beam to a top hat profile.
• the beam shaping optics 125 can be a single Powell lens or a spherical lens coupled with a Powell lens.
• the beam shaping optics 125 can be comprised of the same components as listed above for circular nozzles but optical designs are preferably pursued that fulfill the depth of field requirements since the depth of field will be longer than the laser line width in these instances.
• the depth of field length in these instances can be greater than ten times (10X) the laser line width.
• a linear polarizer 120 with an extinction ratio preferably ranging from 100: 1 to 10 7 : 1. Certain sources such as edge emitting laser diodes and vertical cavity surface emitting laser diodes possess an inherent polarization ratio around 100: 1 and depending on the accuracy requirements of the polarization measurement for a particular application the linear polarizer 120 can be omitted.
• the collimated light is then introduced to a quarter wave retarder 130 to circularly polarize the beam before introduction to a birefringent crystal 135.
• birefringent crystals that can be used include yttrium vandate, barium borate, calcite and rutile.
• the introduction of the circularly polarized light to the birefringent crystal 135 produces vertically and horizontally polarized beams of equal intensity and separated in space (e.g., vertically separate) by a certain distance depending on the length of the crystal. In various configurations a separation of 250 micron to 1000 micron is preferred.
• the optical viewing region 145 includes two spatially separated illumination points or areas, one for each beam as see in FIG. 1 A. Particles are illuminated, one at a time, in each of the two spatially separated illumination areas of region 145 by the corresponding beam with an aerosol migration time 100 nanoseconds to 10 microseconds depending on the nozzle dimensions and whether a nozzle is used, sample flow rate, and laser line thickness. Light exiting this region in the forward direction is collected using a light trap 150.
• the illumination area illuminated by the horizontally polarized beam is positioned below the illumination area illuminated by the vertically polarized beam as seen in FIG. 1 A.
• collection optic 170 is preferably used to collect elastically scattered light.
• various types of collection optics and angular collection ranges can be used.
• the collection optic 170 can be omitted in some instances.
• an aspheric collector lens, parabolic collectors, or cylinder lens can be used.
• the angular collection range can be controlled by the size of the aspheric or cylinder lens or the geometry of the parabolic collectors. Those skilled in the art are aware of numerous approaches using aspheric lens or parabolic collectors as the collection optic 170. Which collection optic 170 to use depends on the sensitivity of the photo-detector 210 employed and application. For applications where the aerosol concentration sampled is considered high, it is preferred to use a collection optic 170 that is easy to clean and would possess a low fouling rate from sampled aerosol. In this case collection optic 170 may be omitted or an aspheric lens can be used instead of parabolic collectors as the collection optic 170.
• the light detector 210 can be a silicon photodiode, gallium arsenide photodiode, avalanche photodiode, silicon photomultiplier, photomultiplier tube or arrays of these types of detectors.
• the type of detector will vary depending on the collection optic 170 used, the amount of scattered light excepted per aerosol event, the dynamic range of the detector, and the detector's cut-off frequency or response time.
• the signal produced from light detector 210 is then introduced to an amplifier circuit 220 whereby a 100 nanosecond to 10 microsecond current pulse is first converted to an analog voltage and then to a digital signal using an analog-to-digital converter 230.
• the signal from 230 is then introduced to the signal processor 240 for analysis.
• the signal processor 240 can be a microcontroller, digital signal processor, field programmable gate array or a microcomputer, as would be readily understood by one skilled in the field of signal processing.
• the first illumination region is preferably illuminated by the horizontally polarized beam with a laser line thickness of 5-300 micron.
• the second illumination region is preferably illuminated by the vertically polarized beam of equal thickness (i.e., a laser line thickness of 5-300 micron) and laser intensity separated by a preferred distance of approximately 250-1000 micron.
• a laser line thickness of 5-300 micron i.e., a laser line thickness of 5-300 micron
• the amplifier circuits 220 for each channel can be configured to perform analog signal processing functions.
• the analog input bandwidth for the amplifier circuits 220 for each channel can be configured to capture the fastest expected current pulses.
• the pulse time is primarily a function of the aerosol particle's migration time through the optical viewing region 145 and is expected to be in the range of 100 nanoseconds to 10 microseconds.
• Additional analog signal processing functions include the triggering of a pulse detector circuit when an analog voltage level from the detection channels exceeds a preprogrammed level, integration and holding of light detector pulse for each detection event, production of a pulse height level for each detection channel, the use of one or more amplifier stages for each detection channel to capture the entire signal range for particles ranging in size from submicron in aerodynamic diameter to 25 micron or larger, and the production of an analog to digital conversion signal for each of the two detection events.
• the signal processor 240 is preferably configured to receive digital signals from the two detections events that occurred as the single particle traversed the horizontally and vertically polarized beams.
• the first detection event is preferably used to size the particle and pulse height analysis is performed on each of the aerosol events occurring in the first and second illumination points or areas in the optical viewing region 145.
• the amplitudes of each detection per aerosol event is used for the depolarization measurement. The degree of depolarization for each aerosol event can be calculated by performing one of the calculations below:
• the linear depolarization value is then preferably binned with the particle size for each aerosol event.
• particle size and linear depolarization value data for each aerosol particle preferably a comparison can be made to a library of aerosol types from the previous
• polarized elastic scatter plots can be generated as a function of particle size permitting the detection and classification of biological and non- biological particles.
• FIG. 9 illustrates the detection event for a single particle for the linear depolarization configuration described above.
• the single particle traverses two beams, first a horizontally polarized beam then a vertically polarized beam. As the particle traverses each beam, the particle emits polarized elastically scattered light producing two signals per aerosol particle event.
• FIG. 9 shows data for a single aerosol event and a single detector. The data represents the linear depolarization response for a 3 micron aerodynamic diameter Bacillus globigii spore aggregate. The particle was produced using an ECBC inkjet aerosol generator. The degree of depolarization can be calculated by performing one of the calculations above.
• 10 and 11 illustrate the linear depolarization response where the degree of depolarization is determined by dividing the scatter intensity collected from a horizontally polarized filtered signal and a horizontally polarized excitation source by the scatter intensity collected from a horizontally polarized filtered signal and a vertically polarized excitation source.
• This data shows 6 particle size channels with the following channel ranges: 0.5-0.7 micron, 0.7-1 micron, 1-2 micron, 2-5 micron, 5-7 micron, and >7 micron.
• Ten polarization ratio increments are used for each particle size range giving a total of 60 channels with the signal processor having programmable depolarization ratio increments. Aerosol particle events are detected and then binned into one of the 60 channels depending on their size and degree of linear depolarization.
• FIG. 12 illustrates additional linear depolarization responses using the same ratio measurement as in FIGS. 10 and 11 and the use of depolarization ratio distributions to classify particles of interest from commonly encountered particles from different environments.
• Three different environments are provided as examples: an indoor building, a subway platform and an urban background.
• the 3D scatter plots represent 3 depolarization ratios for a given particle size range.
• Each sphere in the 3D scatter plot represents 10 liters of air sample and was collected using a sensor with a 100 liter per minute sampling rate or 6 seconds of aerosol data.
• Four biological class types are also applied in the 3D scatter plot.
• the coordinates for the 3 axes are obtained by selecting three depolarization increments at a defined particle size range. Particle counts for each of the 3 selected depolarization increments for a 10 liter sampling rate are divided by the sum of the total particle counts for each of the 3 depolarization increments at a defined particle size range. The ratio for each depolarization increment is then used as one of the three coordinates for the 3D scatter plot.
• spore simulant dry disseminated Bacillus globigii spore
• ovalbumin toxin simulant
• Erwinia herbicola vegetable simulant
• MS2 virus viral simulant
• the four biological threat class types are labeled a through d, representing dry spore, dry toxin, viral and vegetative classes respectively.
• FIG. 12 provides 3D scatter plots for 2 particle size ranges, 1-2 micron and 2-5 micron, for each background environment. Air samples representing the background environments are labeled e through g representing indoor building, a subway platform, and an urban background respectively.
• the linear depolarization approach applied in this embodiment provides a very useful method for discriminating all four disseminated biological threat types from relevant operational environments. The approach provides a rapid near realtime early warning capability against biological threats and the ability to classify biological threat types providing end users with additional options for applying countermeasures that reduce the aerosol spread in a facility or subway system and a more rapid application of prophylactics.
• FIG. 13 illustrates additional linear depolarization responses using the same ratio measurement as in FIGS. 10 and 11 and 3D scatter analysis approach.
• This data illustrates a wet disseminated or nebulized Bacillus globigii spore sample in which nearly the entire sample aerosolized is comprised of individual spores.
• the graph labeled h provides the particle size distribution of the sample aerosolized.
• the aerosol distribution was measured using a TSI 3321 Aerodynamic Particle Sizer and shows an aerodynamic median diameter of 0.819 micron with a geometric standard deviation of 1.20, or, a monodisperse population.
• the four biological threat class types are labeled a through d, representing dry spore, dry toxin, viral and vegetative classes respectively.
• the nebulized Bacillus spore sample is labeled i in the scatter plot.
• This example illustrates the effectiveness of the depolarization approach to detect and classify single Bacillus spores which is very difficult for currently available LIF based biological aerosol detectors.
• FIG. 2 is a schematic representation illustrating a preferred optical detector including a linear depolarization detection configuration having a single horizontally polarized beam source and two detectors with one having a horizontally polarized filter and the other a vertically polarized filter.
• Aerosol is drawn into the sensor cell 140 through an aerosol nozzle as shown in FIG. 1A or inlet port with no nozzle by a vacuum source (not shown) and is introduced into an optical viewing region 145 in a similar manner as described for FIG. 1.
• the illumination scheme and detection scheme are different for this configuration from that utilized in FIG. 1.
• the excitation source 100 is preferably a continuous source or modulated at 20 MHz or greater frequency and can be an edge emitting laser diode, vertical cavity surface emitting laser diode, light emitting diode or some other laser.
• the wavelength of excitation source 100 can be in the range of 200-1500nm.
• Light emitted from source 100 is collimated using an aspheric lens 110. Depending on the source, spatial filtering between the source 100 and the aspheric lens 110, or after lens 110 but before the aerosol cell 140 may be necessary. Collimated light is then introduced to beam shaping optics 125, as described in FIG. 1, followed by a horizontally polarized filter 120. In the embodiment illustrated in FIG.
• the horizontally polarized scatter signal is used to size the particle and pulse height analysis is performed on the scatter amplitudes from vertically and horizontally polarized light.
• the amplitudes from each detection event for the two detectors is used for the depolarization measurement.
• the degree of depolarization for each aerosol event can be calculated by performing one of the calculations below:
• the linear depolarization value is then binned with the particle size for each aerosol event.
• a comparison is preferably made to a library of aerosol types from the previous measurements of known aerosols that include bacterial spores, vegetative cells, viruses, viral aggregates, protein toxin aggregates, fungal particles, pollen particles, man-made biological particles and non-biological aerosols such as salt particles, water droplets, dust particles, organic carbon particles and other relevant non- biological particles depending on the application.
• polarized elastic scatter plots can be generated as a function of particle size permitting the detection and classification of biological and non-biological particles.
• FIG. 3 is a schematic representation illustrating a preferred optical detector including a linear depolarization detection configuration having a dual vertically and horizontally polarized beam source and a single detector with a horizontally polarized filter and an orthogonal fluorescence detection channel.
• the configuration is the same as that described for the embodiment illustrated in FIG. 1 except for the additional fluorescence detection channel 208 and the corresponding collection optics 170, light detector 210, amplifier 220 and analog to digital converter 230.
• the excitation wavelengths need to be within the absorption bands of the endogenous fluorophores of interest such as 250-300nm and 350-450nm. These excitation wavelength ranges correspond to the absorption bands to one or more endogenous fluorophores commonly encountered in biological particles, which include, but are not limited to aromatic amino acids, NADH, flavins, chlorophylls, and sideophores.
• endogenous fluorophores commonly encountered in biological particles, which include, but are not limited to aromatic amino acids, NADH, flavins, chlorophylls, and sideophores.
• similar detection electronics and detectors as that described in the above embodiments can be used with an additional fluorescence filter 208 for passing a band of light that is matched with the emission wavelengths of the desired endogenous fluorophores.
• both the linear depolarization value obtained for each particles and the presence or absence of fluorescence and the fluorescence intensity can be used for classification of biological particles from non- biological particles and to classify biological types from one another.
• FIG. 4 is a schematic representation illustrating a preferred optical detector including a linear depolarization detection configuration having a vertically and horizontally polarized beam source, a polarizing beam splitter and two detectors for detecting parallel and perpendicularly polarized scatter.
• a polarizing beam splitter 195 is used for separating the two polarizations so that measurement of the scatter intensity of both vertically and horizontally polarized light can be performed.
• An optional focusing lens 200 can be used to focus the scattered light onto a light detector 210. The same signal processing steps as outlined in the embodiment illustrated in FIG. 2 can be applied.
• FIG. 5 is a schematic representation illustrating a preferred optical detector including a circular depolarization detection configuration having a dual left handed and right handed circularly polarized beam source, a polarizing beam splitter and two detectors for detecting parallel and perpendicularly polarized scatter.
• the dual polarized beam as that described in the embodiment illustrated in FIG. 1 is used except an additional quarter wave retarder 130 is employed after the birefringent crystal 135 to create dual right handed and left handed circularly polarized beams.
• Signal processing for this embodiment involves measuring the polarized scatter intensity of parallel and perpendicularly polarized light for each illumination event per aerosol particle and then calculating the left handed and right handed circular depolarization ratios for each particle.
• the circular depolarization values are then binned with the particle size for each aerosol event.
• Particle size and circular depolarization value data for each aerosol particle is then compared to a library of aerosol types from the previous measurements of known aerosols that include bacterial spores, vegetative cells, viruses, viral aggregates, protein toxin aggregates, fungal particles, pollen particles, man-made biological particles and non-biological aerosols such as salt particles, water droplets, dust particles, organic carbon particles and other relevant non- biological particles depending on the application.
• polarized elastic scatter plots can be generated as a function of particle size permitting the detection and classification of biological and non-biological particles.
• FIG. 6 is a schematic representation illustrating a preferred optical detector including a circular intensity differential scattering detection (CIDS) configuration having a dual left handed and right handed circularly polarized beam source and a single detector.
• the excitation source for this embodiment is similar to the embodiment illustrated in FIG. 5.
• a single detector scheme similar to that illustrated in FIG. 1 is used capturing polarized elastic scatter signals and scatter intensities are measured using both left handed and right handed circular polarized excitation per aerosol particle. No filter is used on the detection channel so unfiltered scatter signals are collected for each illumination event.
• the circular intensity differential scattering (CUDS) value for each aerosol event can be determined using the following equation:
• Where II is the light scattered intensity when the incident beam is left circularly polarized and IR is the light scattered intensity when the incident beam is right circularly polarized.
• the current pulses produced from the detection events are used for measuring the CUDS value for each particle.
• the CUDS value is then binned with the particle size for each aerosol event.
• a comparison can be made to a library of aerosol types from the previous measurements of known aerosols that include bacterial spores, vegetative cells, viruses, viral aggregates, protein toxin aggregates, fungal particles, pollen particles, man-made biological particles and non-biological aerosols such as salt particles, water droplets, dust particles, organic carbon particles and other relevant non-biological particles depending on the application.
• polarized elastic scatter plots can be generated as a function of particle size permitting the detection and classification of biological and non-biological particles.
• FIG. 7 is a schematic representation illustrating a preferred optical detector including a linear intensity differential scattering detection (LIDS) configuration having a dual vertically and horizontally polarized beam source and a single detector.
• the LIDS configuration is identical to the CIDS configuration except no quarter wave retarder 130 is used.
• the linear intensity differential scattering (LIDS) value for each aerosol event can be determined using the following equation:
• IH is the light scattering intensity when the incident beam is horizontally polarized and Iv is the light scattered when the incident beam is vertically polarized.
• the current pulses produced from the detection events are used for measuring the LIDS value for each particle.
• the LIDS value is then binned with the particle size for each aerosol event.
• particle size and LIDS value data for each aerosol particle a comparison can be made to a library of aerosol types from the previous measurements of known aerosols that include bacterial spores, vegetative cells, viruses, viral aggregates, protein toxin aggregates, fungal particles, pollen particles, man-made biological particles and non-biological aerosols such as salt particles, water droplets, dust particles, organic carbon particles and other relevant non-biological particles depending on the application.
• polarized elastic scatter plots can be generated as a function of particle size permitting the detection and classification of biological and non-biological particles.
• FIG. 8 is a schematic representation illustrating a preferred optical detector including a linear depolarization detection configuration having a single horizontally polarized beam source and a single detector having a vertically polarized filter 207 and an orthogonal fluorescence detection channel 208.
• a single horizontally polarized beam source is used to illuminate single particles in the sample stream passing through the optical viewing region 145.
• only depolarized scatter events are detected with the degree of depolarization being a function of particle size and morphology.
• particle auto-fluorescence is also measured for each depolarized scatter event.
• the excitation wavelengths need to be within the absorption bands of the endogenous fluorophores of interest such as 250- 300nm and 350-450nm. These excitation wavelength ranges correspond to the absorption bands to one or more endogenous fluorophores commonly encountered in biological particles, which include, but are not limited to aromatic amino acids, NADH, flavins, chlorophylls, and sideophores.
• similar detection electronics and detectors as that described in the above embodiments can be used with an additional fluorescence filter 208 for passing a band of light that is matched with the emission wavelengths of the desired endogenous fluorophores.
• both depolarized elastic scatter intensity obtained for each particle and the presence or absence of fluorescence and the fluorescence intensity can be used for classification of biological particles from non-biological particles and to classify biological types from one another.

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