Abstract:
System and method of aerosolized agent detection. Multi-part collection tape is employed for capturing particles of interest for immediate analysis and optional forensic preservation and recording information related to capture and subsequent real-time analysis. Laser induced breakdown spectroscopic processing is employed and spectra attributable to known collection tape materials is subtracted to derive particle spectra for comparison to known hazardous agent spectra.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates generally to the capture and detection of aerosolized agents, such as, for example, chemical or biological biowarfare agents, and, more particularly to systems for and methods of continuous sampling and analysis of aerosol samples potentially containing such agents. 
   As the anthrax mailings of October of 2001 demonstrated, a number of vectors are available to the terrorist bent on social disruption. Biological warfare agents have long been a domestic terror concern and the use of the mails as a delivery method has many serious consequences. Not only are mail recipients at risk, but all those who handle or are in the vicinity of the mail piece during processing are at risk as well. In the extreme case, a few strategically posted items could bring a nation&#39;s postal administration, such as the United States Postal Service, to a complete halt. If mail delivery were to cease, even for a few days, the impact to trade, commerce, finance and general communication is incalculable. 
   Thus, it is desirable to capture and identify aerosolized particulate matter that may issue from sources requiring monitoring. Such sources could include mail pieces being sorted or otherwise processed, building ventilation systems, import and export cargo and military point detection systems. 
   Prior attempts to detect and identify pathogens in the mail use chemical or bio fluorescence methods. An example of a chemical method is Polymerase Chain Reaction (PCR). PCR is a DNA amplification technique that has been used successfully in laboratory environments in recent years. PCR is a powerful and useful technique but it does not generate results in real-time. The fastest PCR systems require a minimum of 30–60 minutes to process a sample and render a result. This time lag is problematic, as the mail piece containing the hazard will have traveled further down stream potentially affecting postal workers or postal customers. Other techniques using multi spectral ultra-violet (UV) fluorescence techniques may render a result quickly, but are prone to false alarms and are often non-specific relative to the threat. For example, non-threatening biological particulate in the right size range will typically cause a UV sensor system to indicate a false positive detection. Also, even if hazardous particles are correctly detected, UV based sensors will typically indicate the presence of the threat without specifically identifying the agent. 
   SUMMARY OF THE INVENTION 
   The present invention describes systems for and methods of capturing and rapidly identifying aerosolized particulate matter in fluid samples to be analyzed, such as, for example, hazardous agents issued from mail pieces during sorting and other processing steps. The invention is applicable to a range of uses outside of the mailing industry, including building ventilation systems, checking import and export cargo by customs officials and military point detection systems. The system provides this timely notification without the possible false alarms inherent in many of the systems described above. 
   The present invention provides a sample capture tape and an aerosolized agent detector employing the tape, the detector including a dispenser having a fluid sample input port and an exit port for providing a concentrated particle stream, an analyzer providing real-time detection of aerosolized agents, and a means for advancing a section of the tape from the vicinity of the dispenser exit port to the analyzer. The sample capture tape includes a data storage portion, and the tape is oriented and configured to receive the particle stream from the dispenser exit port and collect selected particles on one or more collecting portions. An encoder stores information relative to the fluid samples&#39; collection and analysis on the data storage portion. 
   The one or more sample collection portions of the capture tape further comprises an immediate analysis portion and an optional sample preservation portion. A wide variety of alternate approaches are available in capturing the desired particles. For example, the sample collection portions may be comprised of permeable filter, adhesive-coated or electrically charged materials, or may be comprised of a material with a surface incorporating microscopic features designed to capture particles impinged thereupon. Other capturing mechanisms will be readily apparent to artisans and are deemed to be within the scope of the present invention. 
   The particle stream exiting the dispenser preferably, though not exclusively, impinges nearly perpendicularly on the sample collection portions of the sample collection tape. In one preferred embodiment, the dispenser further comprises a virtual impactor for pre-concentrating the particle stream. As will be described in detail below, various configurations are allowed for in which the particle stream impinges from either side of the sample capture tape. 
   In certain embodiments, the means for advancing the sample capture tape comprises a reel-to-reel like system, wherein the sample capture tape is provided on a source reel and a take-up reel pulls the tape at the desired rate, or in indexed intervals, through the path of the particle stream. The collection process can, thus, continue in an uninterrupted fashion even as the sample capture tape is in the process of advancing. A sterile tape reel may additionally be employed to interleave a sterile enclosing layer between the sample collection tape layers on the take-up reel. 
   The analyzer, in preferred embodiments, is comprised of a laser-induced breakdown spectroscopic (LIBS) system adapted to differentiate between spectra elements attributable to portions of vaporized sample capture tape and spectra elements attributable to various potentially hazardous agent particles. 
   The present invention provides a method of continuous detection of aerosolized agents comprising the steps of: providing a source of sample capture tape comprised of at least a first collection portion and a data storage portion; collecting particles by impinging a particle-laden aerosol stream on the first collection portion; advancing the first collection portion from the particle stream to an analyzer; analyzing in real-time the particles collected on the first collection portion; and electronically encoding information on the data storage portion related to the sample collection and analysis. The method efficiency is enhanced by optionally pre-concentrating the fluid to be analyzed to form the particle-laden aerosol stream. The advancement of the sample capture tape allows the collection process to continue in an uninterrupted fashion, and synchronization between collection and analysis allows continuous detection. 
   The method may further include the step of collecting samples from the particle-laden stream on a second collection portion of the sample capture tape at a time nearly simultaneous with the sample collecting on the first portion, and preserving the samples collected on the second collection portion. The preservation may be effected by covering the particles collected on the second collection portion with a sterile tape, such as an interleaving reel-to-reel configuration as described in more detail below. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       FIG. 1  is diagrammatic view of a an aerosolized agent detecting system configured for use with mail processing equipment. 
       FIG. 2  is an isometric schematic diagram of an aerosolized agent detecting system employing an optional sterile tape. 
       FIG. 3A  is an isometric view of sample capture tape in roll form depicting multiple portions thereof. 
       FIGS. 3B–D  are diagrammatic views of various embodiments of materials usable as collection portions of the sample capture tape. 
       FIG. 4  is a flow diagram of the operational functions of an embodiment of the present invention. 
       FIG. 5  is an isometric schematic diagram of an alternate collection mechanism designed for continuous collection to eliminate the possibility that an event might be lost during the collection process. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Certain preferred embodiments of the present invention will now be described with reference to the figures identified above. 
   The present invention is now described more fully. For the purpose of illustration only, the present invention is described in embodiments configured for use in a mail testing system. As discussed above, the aerosol agent detection system and method are useful in a variety of testing and/or monitoring environments. Referring to  FIG. 1 , a mail testing system  10  is attached to a conventional piece of mail processing equipment,  12 . In order to transport and sort a mail piece, the processing equipment  12  typically pinches an envelope tightly between two flat transport belts (not shown) moving at high speed. An induction point into the mail processor is called a feeder  13 , and at this point an envelope is first pinched between the transport belts. As the envelope is pinched, air is forced from the envelope and with it any particulate matter contained therein. Aerosol collection sample tube  14 , which is under vacuum, captures air forced from the envelope. A virtual impactor  16  dispenses a pre-concentrated particle stream by separating smaller aerosolized particles from larger ones contained in the air delivered through collection tube  14 . 
   The smaller particles of interest are then impinged on a collection tape  18 , which captures a sufficient number of them to perform testing and, in certain preferred embodiments, sample preservation. After a predefined collection period, collection tape  18  is indexed to an adjacent location in order that a new sample of the air stream may be impinged upon a fresh portion of the collection tape. A Laser Induced Breakdown Spectroscopy (LIBS) method is used to analyze the particles collected on collection tape  18 . 
   The LIBS process requires that the particulate matter collected on the tape  18  be vaporized using a high-energy laser  20 . The electromagnetic spectrum radiated as a result of the vaporization of the collected particles and the portion of tape  18  upon which they are collected is captured by optics  22  and transmitted to a spectrometer  24 , such as the Ocean Optics LIBS2000+ Broad Band Spectrometer. Spectrometer  24  interprets the relative intensity of the radiation at all frequencies in the band of interest—typically 200–980 nm and generates a spectral curve. The spectral curve is then sent to control computer  26  for analysis. In order to protect personnel in the vicinity of system  10 , collected air is exhausted through a High Efficiency Particle Arresting (HEPA) filter  28  under the impetus of blower  29 . Control computer  26  compares the spectral curve to a library of spectral curves for known biohazards and typical hoax or naturally occurring powders. Control computer  26  may also subtract from the spectral curve spectral elements known to be attributable to the portion of vaporized tape  18 . 
   If the control computer  26  detects a high likelihood of a biohazard event, a visual, audio and/or process control indication of the detection is provided. In the system depicted, event detection is indicated by turning a status light  30  on and invoking an E-Stop interface  32  for cessation of mail processing. If multiple systems are implemented in a single building, a central control system  34  may provide overall supervisory control and monitoring functions for all systems. In the embodiment depicted, central control system  34  is comprised of an Ethernet interface  35 , a control computer  36 , various peripherals including a printer  40 , uninterruptible power supply (UPS)  42 , an E-Stop switch  44 , and a reset switch  46 . A maintenance paging system  38  can also be integrated to alert site personnel if a bio detection event has occurred or if maintenance action is required. 
   A more detailed view of testing system  10  can be seen in  FIG. 2 . 
   A specifically designed collection tape  50  is arranged in a reel-to-reel configuration as shown with a source reel  86  and a take-up reel  78 . Collection tape  50 , as will be described in further detail below, is comprised of at least a first collection section  88  for particle collection for immediate analysis and a data encoding region  82 , but preferably further comprises a second collection section  90 . The two collection sections  88 , 90  of the particular configuration of system  10  depicted are used for particulate collection; one is designated the LIBS collection section  88  and is used for analysis of the particulate deposited thereon, and the other forensic section  90  for preserving part of the collected particle sample for forensic purposes. Encoding region  82  of tape  50  may be comprised of any number of mechanical and/or electrical encoding media, but is shown here as a magnetic strip for data storage along an edge of the tape. 
   Virtual impactor  16  receives an aerosolized particle stream  54 , separates unwanted particles  56  based on particle size, and dispenses an aerosolized stream laden with particles of interest  58 . The use of virtual impactor  16  raises the efficiency of testing system  10 , but it is not necessary to all embodiments of the present invention. Any dispenser capable of delivering a particle stream derived from a fluid sample is suitable for use. Referring again to  FIG. 2 , the particles of interest  58  are impinged on collection tape  50  while at Position A  59 . 
   After a predetermined collection period, the section of collection tape impinged upon is indexed to Position B  61 . A portion of the particles  58  at Position B is then vaporized using laser  20 . The resulting spectral emission is captured by the optics  22 , which focus the emitted light for transmission to the spectrometer  24  through a fiber optic link  74 . After the spectral characteristics are quantified by the spectrometer, spectral data is then sent to control computer  26  for analysis. Control computer  26  employs pattern-matching techniques to identify the particulate matter impinged and collected on collection tape  50 . 
   The invention also includes a means for advancing or indexing the tape relative to the impinging particle stream, laser  20  and optics  22 . Although a number of mechanisms could be employed, the advancing means is depicted as a reel-to-reel configuration. As the tape is indexed, it is stored on the take-up reel  78 . To prevent particles from being transferred between tape layers on take-up reel  78 , a sterile tape  80  is wound between the layers of collection tape. This creates a closed environment for effectively preserving any particles captured on the tape. After processing the spectral information, and as the tape is indexed, control computer  26  writes parametric information on the magnetic strip comprising the encoding region  82  in this embodiment, which is situated along the edge of the collection tape, using magnetic write head  84 . The magnetic write head  84  is illustrated as positioned between the impinging stream and the detection optics, but alternatively could be located further along the trajectory of the tape, or may even be comprised of multiple write heads. The type of data that may be encoded may include information related to the source of aerosolized particle stream  54 , time/date of collection, identity and/or location of equipment employed in capture and analysis, and the results of analysis, such as the spectral information captured, results of the pattern matching analysis, etc. 
   The collection tape  50 , as shown in  FIG. 3A  as supplied on a source reel  86 , is comprised of three distinct sections; the encoding region  82  (e.g., magnetic edge), the LIBS collection section  88 , and the forensic section  90 . The magnetic embodiment of encoding region  82  is designed to store digital information about when and where the LIBS analysis was done, and the results of the analysis. Any other storage media (e.g., optical, mechanical, etc.) suitable for quick recording of information can be suitably employed in the encoding region. The LIBS and forensic sections of the tape are specifically designed to capture the aerosolized particles impinged thereon. A number of design alternatives are suitable for use as the collection sections  88 , 90 .  FIG. 3B  illustrates an embodiment of a collection tape  100  comprised of a porous filter type material designed to trap particles as the air passes through the material. The tape  100  may have an adhesive coating designed to stick to the particles impinged on its surface.  FIG. 3C  illustrates an embodiment of a collection tape  102  having a surface engineered with microscopic hooks or protrusions that will tend to trap particles. As another alternative,  FIG. 3D  shows a collection tape  104  having a charged surface that attracts particles of interest that have passed through an electrostatic field imparting the opposite charge to them. As stated above, forensic section  90  allows material to be retained for confirmation testing using alternative methods and for legal evidence. 
   Referring again to  FIG. 2 , regardless of how the particles are captured, the LIBS collection section  88  is reserved for LIBS processing, which requires the particles in the section  88  be vaporized by the high-energy laser  20 . The resulting spectra are captured for analysis. Control computer  26  performs the analysis, subtracting the known spectral characteristics of the collection tape from the spectral information captured. This is done to isolate the signal of the particulate from that of the tape substrate. 
   A flow chart illustrating a preferred method of using system  10  is shown in  FIG. 4 . The first step is the particulate collection process  106 . The length of time required for the collection is a programmable parameter, which will depend on several factors related to the application of the invention, including the background particulate loading, the expected duration of a bio-release event, and the expected biohazard particulate concentration of the event in terms of agent containing particles per liter of air (ACPLA). For a postal application, the expected release will have high ACPLA count over a very short duration. The dwell time for the postal application is therefore short, on the order of 1 to 10 minutes. For open-air environment point detection applications, where much lower ACPLA is expected, the dwell time may be 30–90 minutes or more. 
   In step  108 , after collecting particulate for the specified dwell time, the tape is indexed. When the tape is indexed, a fresh section of the tape is moved into position for particulate collection. Also, as the tape is indexed, the portion of the tape most recently exposed to the aerosolized particle stream for the programmed dwell time is moved into position for LIBS analysis. In step  110 , LIBS processing requires that a portion of the collection tape be exposed to a high-energy laser, for example the ULTRA CFR Nd:YAG laser from Big Sky Laser Technologies. When the laser is activated, the high-temperature of the laser focused on the LIBS portion of the collection tape creates plasma. As the plasma cools, the excited atoms in the plasma emit light at wavelengths characteristic of the elements contained in the particulate sample on the tape, as well as the elemental constituents of the tape itself. Since the tape is a known quantity previously characterized using the LIBS process, the spectral elements of the tape can be algorithmically subtracted, in step  112 , from the captured plasma spectrum. 
   In step  114 , the resulting differential spectrum is then used for the signal processing and pattern matching process. The pattern matching process first resolves the captured differential spectrum into a set of characteristic features. These features are then compared to a library of feature sets for known biohazards previously characterized using the LIBS process and a similar apparatus. Several established methods exist for the pattern-matching algorithm including neural network and least sum of squares techniques. The output of the pattern matching process is a set of probabilities for each of the library substances the captured spectrum is tested against. In step  116 , the probabilities are compared to one or more predefined thresholds for a determination whether a hazardous agent has been detected. 
   If any of the probabilities exceed the one or more predefined thresholds, an alarm condition exists. If an alarm condition exists, an alarm protocol is initiated in step  120 . The protocol will be defined by the user of the technology, but will typically include shutting down any associated equipment, activating appropriate audio/visual alarms and initiating events such as paging key personnel and notifying the appropriate first responder agency. The method of communication can be via e-mail, telephone messages, pager messages, or a combination, based on the user&#39;s preference. All information relative to the bio-detection event is recorded on the encoding region  82  of the collection tape  50 . If, after processing the differential spectrum, an alarm condition does not exist, the results of the spectrum analysis are still encoded on the encoding region of the tape, and the process begins again as determined by the programmed collection interval. 
   In another embodiment of the invention, the collection process occurs in a continuous fashion, without any interruptions that might be introduced in indexer-based configurations. Referring to  FIG. 5 , a continuous collection device  126  is comprised of a rotating pulley  128  on a hollow shaft  130 . A particle-containing air stream  132  enters through the hollow shaft  130 . For a half of the rotation of pulley  128 , air stream  132  follows path  134  through outlet port  144  to impinging point  138 . For the other 180 degrees of rotation, port  144  is effectively closed as a result of its adjacency to sealing surface  142 . During this interval, port  146 , which is 180 degrees out of phase with port  144 , is simultaneously open and air stream  132  will follow path  148  to impinge upon a different portion of collection tape  50 . This mechanism allows sample collection to be performed in a continuous fashion, eliminating the possibility of missing a very short duration release as the tape is indexed. Collected particulate  150  are then processed as described in proceeding paragraphs. Depending on the design of the ports incorporated into the pulley  128 , air stream  132  can be either draw through the collection tape if the tape is made from a porous material mesh, such as depicted in  FIG. 3B , or it can be impinged against collection tapes comprised of solid materials with particle-arresting surface features, such as shown in  FIGS. 3C and 3D . 
   Although the invention has been described with respect to various embodiments, it should be realized this invention is also capable of a wide variety of further and other embodiments within the spirit and scope of the appended claims.