Methods and articles for identifying objects using encapsulated perfluorocarbon tracers

Abstract

A system and method for tagging, tracking, locating and identifying people and vehicles transporting people using Perfluorocarbon tracers. An on-going problem faced by military as well as law enforcement personnel is that of friendly fire incidents. To prevent possible friendly-fire incidents, troops would separate the two layers of the uniform patch, thereby releasing a controlled release of the Perfluorocarbon vapors. Other friendly troops, equipped with sensors tuned to the specific perfluorocarbon characteristics would thus be able to literally view a plume around the tagged person or object. The system may conversely be used to tag enemies. Formulations of mixed perfluorocarbons may be used to provide coding of emissions.

Claims

1. A tracer release device, comprising: a reservoir containing a volatile tracer having at least one CF.sub.2CF.sub.2 portion; a releasable barrier configured to prevent release of the volatile tracer prior to release of the barrier; an electronic controller configured to produce a variable signal to control a release rate of the volatile tracer after release of the barrier; a volatile tracer release control device, selected from the group consisting of a microelectromechanical device, a bubble jet device, and a piezoelectric device, configured to release the volatile tracer selectively dependent on the variable signal; and a battery, configured to provide power to the electronic controller and the volatile tracer release control device.

2. The tracer release device according to claim 1, wherein the reservoir comprises a non-volatile matrix saturated with the volatile tracer.

3. The tracer release device according to claim 1, wherein the volatile tracer is encapsulated, such that the matrix remains saturated with volatile tracer, with the encapsulated volatile tracer acting as a reservoir to replenish volatile tracer which is lost from a surface of the matrix, to provide a steady state release of volatile tracer dependent principally on a rate of loss of volatile tracer from the matrix.

4. The tracer release device according to claim 1, wherein the volatile tracer release control device comprises a physical volatile tracer-impermeable barrier to prevent loss of volatile tracer in at least one state of the variable signal.

5. The tracer release device according to claim 1, wherein the at least one volatile tracer having at least one CF.sub.2CF.sub.2 portion comprises a plurality of different perfluorinated tracer compositions, each having a unique characteristic.

6. The tracer release device according to claim 1, wherein the volatile tracer release control device is configured to actively control a rate of volatile tracer release over time.

7. The tracer release device according to claim 1, wherein the volatile tracer is stored within a polymer matrix comprising a polyphosphazene derivative.

8. The tracer release device according to claim 7, wherein the polyphosphazene derivative comprises a polymer of perfluorocarbon-functionalized phosphazene monomers.

9. The tracer release device according to claim 1, wherein the volatile tracer is encapsulated in a cyclodextrin shell.

10. The tracer release device according to claim 1, wherein the electronic controller is configured control the release rate in dependence on a remote control signal received from a remote source.

11. The tracer release device according to claim 1, wherein the volatile tracer is selected from one or more of the group consisting of: perfluorodimethylcyclobutane (PDCB), perfuoromethylcyclohexane (PMCH), perfluorodimethylcyclohexane (PDCH); hexafluorobenzene (HFB), octafluorotoluene (OFT), decafluorobiphenyl (DFBP), decafluoroxylene (DFX), octafluoronaphthalene (OFN), pentafluoropyridene (PFP), perfluorohexane (PFH), perfluoropentane (PFPT), perfluorooctane (PFO), decafluorocyclohexene (DFCH), octafluorocyclopentene (OFCP), pf-methylcyclopentane (PMCP), pf-1,2-dimethylcyclohexane (o-PDCH), pf-1,3-dimethylcyclohexane (m-PDCH), pf-1,4-dimethylcyclohexane (p-PDCH), pf-trimethylcyclohexanes (PTCH), perfluorodecalin (Octadecafluorodecahydonaphthalene, PFD, CAS 306-94-5), and perfluoro(methyl)decalin (PFMD, CAS 306-92-3).

12. A tracer release device, comprising: A reservoir comprising a volatile tracer embedded within a polymer matrix; A removable barrier configured to prevent release of the volatile tracer prior to removal of the barrier; A remote control configured to receive a wireless signal from a remote source; An electronic controller configured to produce a control signal to control a temporally variable release rate of the volatile tracer after release of the barrier in dependence on at least the wireless signal; and A volatile tracer release control device, selected from the group consisting of a microelectromechanical device, a bubble jet device, and a piezoelectric device, configured to release the volatile tracer selectively dependent on the control signal.

13. The tracer release device according to claim 12, further comprising a battery, configured to provide power to remote control, the electronic controller, and the volatile tracer release control device.

14. The tracer release device according to claim 13, wherein the battery is activated by exposure to air, wherein removal of the barrier simultaneously activates the battery and permits release of the volatile tracer.

15. The tracer release device according to claim 12, wherein the electronic controller is further configured to produce the control signal dependent on a desired release rate of the volatile tracer received through the wireless signal.

16. The tracer release device according to claim 12, wherein the volatile tracer contained within the polymer matrix is encapsulated, and the capsules disposed in the polymer matrix, wherein the capsules replenish volatile tracer released from the polymer matrix to provide a steady state release rate.

17. The tracer release device according to claim 12, wherein the volatile tracer is contained within a polyphosphazine derivative matrix.

18. The tracer release device according to claim 12, wherein the volatile tracer is selected from one or more of the group consisting of: perfluorodimethylcyclobutane (PDCB), perfuoromethylcyclohexane (PMCH), perfluorodimethylcyclohexane (PDCH); hexafluorobenzene (HFB), octafluorotoluene (OFT), decafluorobiphenyl (DFBP), decafluoroxylene (DFX), octafluoronaphthalene (OFN), pentafluoropyridene (PFP), perfluorohexane (PFH), perfluoropentane (PFPT), perfluorooctane (PFO), decafluorocyclohexene (DFCH), octafluorocyclopentene (OFCP), pf-methylcyclopentane (PMCP), pf-1,2-dimethylcyclohexane (o-PDCH), pf-1,3-dimethylcyclohexane (m-PDCH), pf-1,4-dimethylcyclohexane (p-PDCH), pf-trimethylcyclohexanes (PTCH), perfluorodecalin (Octadecafluorodecahydonaphthalene, PFD, CAS 306-94-5), and perfluoro(methyl)decalin (PFMD, CAS 306-92-3).

19. A release device, comprising: A reservoir, containing a volatile compound embedded within a polymer matrix; A wireless receiver, configured to receive at least a remote control signal from a remote transmitter; An electronic controller configured to receive the remote control signal from the wireless receiver, and to produce a control signal to control a release rate of the volatile compound over time in dependence on a release profile; A volatile compound release control device, comprising a mechanism selected from the group consisting of a microelectromechanical device, a bubble jet device, and a piezoelectric device, configured to release the volatile compound, selectively dependent on the control signal; and A power supply configured to power the wireless receiver, the electronic controller, and the volatile compound release control device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1A and 1B show representative cross sections of a tracer releasing apparatus having taggant capsules within a matrix, on a barrier layer, before and after release of the barrier.

DESCRIPTION OF THE INVENTION

(2) According to one embodiment of the invention, a method is provided for using Perfluorocarbon Tracers to Identify Personnel (Friend or Foe) on the Battlefield, e.g., traditional or urban. For example, an encapsulation formula of Perfluorocarbon tracers can be impregnated into one or both of the layers of separable patch, which prior to separation, has a minimal rate of PFT release, and after separation, has a steady rate of release sufficient to allow remote detection. The patch, for example, may be a tear-away Velcro patch adapted to be affixed to soldiers in a war zone. To prevent possible friendly-fire incidents, troops would separate the layers of the patch, thereby initiating a controlled release of the PFT vapors. Other friendly troops on the field of battle, equipped with sensors for the PFT emissions, which may operate passively by detecting absorption or fluorescent emission from normal light sources, or actively by stimulating optical emissions and/or measuring specific absorption. At night, for example, illuminators tuned to the fluorescent wavelength of the Perfluorocarbon gases and specially designed, wavelength-matched vision devices would thus be able to literally visible as a cloud that might surround or emanate directly from the friendly troops. Likewise, an automated system could be provided to automatically block fire against friendly troops, bypassing the user's discretion, and perhaps acting with faster response and accuracy.

(3) Alternately, a tag may be placed on personnel or objects, to assist in tracking them. For example, a patch, liquid, or powder, may be surreptitiously applied to an enemy vehicle, which could then be tracked to its destination. In this case, the tag may also be used to guide munitions, rather than inhibit them.

(4) In a normal scenario, multiple taggant compositions and combinations may be employed, for various purposes. Thus, even if an enemy were to gain control over a set of tags, it would have to know the encoding, which could change periodically, in order to effectively use them as a false defense or offensive tool.

(5) Likewise, the detector may be provided which requires authentication, such as biometric, token, security code, or the like, which would impede unauthorized use. This technique is especially useful where the PFTs themselves are dynamically encoded, and therefore without certain secret knowledge, the output of the detector would be difficult to interpret at any given time. For example, according to one embodiment, the PFTs release a time coded coded plume, which may alternately indicate friend, foe, or other identification. Likewise, release of dummy PFTs may be employed, to obscure particularly encoded releases, and thus requiring a sophisticated detector.

(6) It is noted that a sophisticated adversary might seek to develop measures to track a reading device, and thus a passive (relying on ambient illumination) or remotely operable illuminator is preferred in such circumstances. Likewise, it is preferred that the reader incorporate at least one sophisticated and difficult to obtain critical technology, to impede unauthorized recreation.

(7) It is also useful to provide an interrogator detection system, in the event that unauthorized devices are or become available, so that the badge wearers can take immediate action to avoid personal or other risk, when an unauthorized interrogator is detected. For example, authorized interrogators may produce a cryptographically encoded emission, the authenticity of which is determinable by an authentication device. Even in the event that an authentic device is diverted, the encoding may be device-specific, permitting individual detection and countermeasures to be employed, without requiring all authorized devices to be modified. For example, if an interrogator includes a laser illuminator, the laser itself, or an associated signal, may be individually modulated corresponding to an encoded signal. In the event of an unencoded, unauthorized, or deauthorized encoding in an illuminator suitable for detecting PFTs, users can immediately detect this illuminator when targeted by it, and take countermeasures, such as targeting the illuminator for destruction, and removing the PFT emitting devices from their person or vehicles. The detectors may also be protected by code or biometrics, to prevent their unauthorized use.

(8) It is noted that since there are a number of usable compounds which are perfluorocarbons, or are closely related to perfluorocarbons, a large number of recipes are available. Therefore, it is preferred that the reader or interrogator permit individual detection of the various usable compounds, as well as distinguishing the components of a mixture and/or quantitatively determine ratios thereof. Typically, this detection will employ a laser illuminator to determine a specific spectrographic and/or fluorescence optical response of each PFT employed.

(9) The reader or interrogator will typically employ a narrow bandwidth directional illumination source. The specific absorption wavelengths for perfluorocarbons and related compounds are in the UV range. Thus, a suitable illuminator would be a filtered broadband lamp, UV LED, LED (or other source) excited photon capture UV fluorescent emitter, a laser, or other emission source. Typically, a high efficiency design is preferred, since a low efficiency illuminator would emit heat and have high power demands, limiting portability and duration of battery life. Thus, a preferred design employs an LED excited emitter, or electroluminescent design, to provide a significant battery life and a low level of undesired emissions.

(10) The detector is typically a spectrophotometric-type detector, capable of distinguishing specific PFT signatures from interfering emissions or absorptions. It is also preferably battery operated and small. The detector may also be provided as a broadband sensitive detector with one or more specific filters.

(11) The PFT emitting device itself is, for example, a flat sheet-like patch, for example 1-25 square inches, composed of two sheets which are impermeable to perfluorocarbon vapors. These may be, for example, metallized or aluminized Mylar Biaxially-oriented polyethylene terephthalate (boPET) polyester film, or other suitable material. A base sheet preferably has a removable attachment means, such as Velcro, snaps, magnets, or other suitable method for removable attachment, e.g., to a uniform or object. Between the sheets is a controlled release perfluorocarbon material. For example, a polyphosphazine matrix, wax, or other material impregnanted with PFT's, or microencapsulated PFT's in a matrix, is provided, which selectively adheres to the base sheet. The controlled release perfluorocarbon material is covered during storage with a cover sheet which is removable, and which easily releases from the controlled release perfluorocarbon material. For example, an adhesive or heat-generated seal is formed around the periphery junction of the two sheets, which is frangible when subjected to a peeling force.

(12) While a relatively homogeneous material (i.e., homogeneous matrix or embedded microcapsule matrix) is preferred, a macroscopic barrier or atomizer may also be used to control release of PFT. In the later case, a pump, MEMS device, piezoelectric device, bubble jet, or other electrically operated device may be operated to release PFT. Such a device could have an electronic control, capable of arbitrary release profile generation, and remote activation/deactivation. Likewise, the device could employ separate control over a plurality of tracers, each with a separate release profile. Thus, an authorized device could have a predefined but secret temporal release profile (for example defined by a cryptographic function), allowing authentication of PFT releasing devices. The device could further have RF-ID attributes and/or a wireless receiver for remote controllability. Advantageously, an electronic embodiment employs a zinc air battery, activated by unsealing, and thus storage stable and activated along with the release of PFTs. Indeed, a film battery technology may permit formation of the battery together with the film forming the barrier to contain the PFT prior to intended release. Typically, a seal is provided for storage, since even low levels of unintended leakage over time will deplete the device and potentially pollute the atmosphere, making specific detection more difficult.

(13) During storage, the sheets thus prevent release of PFT, while when the cover sheet is removed, the PFT is continually or controllably released over an extended period. It is preferred that, in a passive device, the release be at a relatively constant rate. Various known methods for temporally controlling release rates, such as employed in conjunction with pharmaceuticals, may also be employed. See, e.g., Temporal Control of Drug Delivery, Hrushesky, Langer, & Theeuwes, Eds., NY Acad. Sci 618 (1991), expressly incorporated herein by reference, and especially, Langer, Robert & Kost, Joseph, Real Time Response Polymeric Delivery Systems, pp. 330-334.

(14) Preferably, the PFT is not a single material, but at least two different materials, which are combined such that they are both released in detectable quantities. This combination permits coding of the patches, and makes counterfeiting more difficult. It likewise facilitates detection, since the composite spectral signature will have more features available for analysis. It is noted that, in the case of a combination release, it is possible to employ a different composition entirely, for example one that is not a PFT. Preferably, the detection system for the plural compositions will include substantial common elements, although this is not required.

(15) Another aspect of the invention provides a method of using tracers to identify friendly vehicles, e.g., on the battlefield. For example, an encapsulated formulation, either in the form of a patch, or aerosolized by an aerosolizing apparatus, can used in conjunction with a vehicle, for example, tanks, HUMVEES, personnel carriers, Jeeps, etc. The vehicle will this emit a distinguishable plume, which can be remotely detected by its characteristic fluorescent pattern, can be used to identify various friendly vehicles. The detector can be used as part of a manual weapons targeting system, or as part of an automated trigger inhibition or fusing system.

(16) On the other hand, such a plume may also be used to target or track vehicles (e.g., enemy or suspect) or other objects, especially where it is not the vehicle, but its future contents, which are of interest, since tagging the vehicle will generally require intimate contact.

(17) A further aspect of the invention provides a method and composition for tracking, detecting and/or identifying suspected terrorists or criminals by ingestion, or for tracking potential kidnap or abduction risks. It has been determined that following exposure to perfluorocarbon materials that a human subject will emit a detectable chemical signal of perfluorocarbon for a period of up to one month, or longer depending upon individual metabolism and exposure dosage. The perfluorocarbons are emitted through bodily pores, excreted bodily fluids, and/or exhalation.

(18) It is thus known that perfluorocarbons can be retained in the human body for extended periods of time. This is particularly obvious in the presence of technologies such as the DSITMS which provides very low detection levels in real-time. In the course of preparing for the demonstrations described below, it was noted that perfluorocarbon could be detected from one of the researchers at the Oak Ridge National Laboratory (breath, skin, urine) for three days after limited contact with a wax crayon formulation. Perfluorocarbons are nonmetabolizable, however, they do induce hepatic metabolizing enzymes. PFD given to rats was shown to induce cytochrome P-450 in a manner similar to phenobarbital. As with Phenobarbital induction, the activities of cytrochrome P-450 IIA1 and IIA2 (a.k.a. cytochrome P450.sub.b and cytochrome P450.sub.e) were increased approximately two-fold following PFD treatment. Likewise, the activities of benzphetamine-N-demethylase and aldrin-epoxidase were increased. The activities of cytochrome P-450 IA1 and IA1 (induced by 3-methylcholanthrene-type inducers) and cytochrome P450 IV (induced by fatty acids and perfluoronated fatty acids) were unaffected. Although the perfluorocarbons are sequestered in the fat and later transferred to the liver, over time they are eliminated from the body via the lungs by exhalation. See, Final Report for CRADA Number ORNL99-0562, under funding from Tracer Detection Technology Corp. under contract of the National Institute of Justice, Jul. 26, 2000.

(19) By incorporating encapsulated Perfluorocarbon tracers into food stuffs or other supplies or provisions anticipated to be delivered to, being transported to the hideouts of, or ingested by mammals of interest, the location, even if hidden, can be remotely detected. In this embodiment, preferably a pure form of PFT, or an encapsulation formulation thereof, in which the PFT can be mixed with food, other ingestible items or other supplies which are ultimately ingested, will emit a plume of the vapor taggant that can be detected through various means of sensing. Alternately, the PFT is released or volatilized during cooking, and thus the location of a hideout may be determined by searching for an associated plume from this release. Therefore, the PFT may be absorbed in, or placed in conjunction with, a food which requires cooking, such as rice.

(20) The present invention further encompasses a method of using PFTs to track, detect and identify suspected terrorists or criminals, or hideouts of terrorists or criminals, by marking vehicles suspected of traveling to terrorist or criminal hideouts or other objects which are carried to these locations.

(21) Effective inspection of large containers and trucks for controlled substances and narcotics is essential for the success of drug interdiction efforts. A significant fraction of drugs are smuggled through this avenue. Without prior knowledge provided through intelligence activities, the chances for drug detection are very slim. A successful drug interdiction program therefore requires efficient, rapid and cost-effective inspection techniques for large objects. The current technique used to thoroughly inspect containers is manual, highly labor intensive and can hardly be expanded to meet the challenge of abating the flow of illicit drugs from one country to another. Hence, an efficient way to meet the goal of an effective counter-drug effort is to provide a rapid, automatic, non-intrusive inspection system to inspect shipments and cargo containers without removing all of the contents for manual inspection. Thus, if a shipment can be tagged near its point of origin, it may be tracked using PFTs to distribution, permitting an entire chain to be tracked, without seizing the contraband at an intermediate stage.

(22) In order for PFT tagging to function effectively, the release should be of sufficient concentration as to enable unambiguous identification, and also should be sufficiently long-lasting as to fulfill various usage parameters. Thus, in order to provide a sustained release of PFTs, a matrix is provided which provides a desired release profile. One type of matrix is a paraffin wax matrix or one based on large molecule inclusion complexes, however, such matrices may be difficult to control.

(23) Polyphosphazenes are a class of polymers with backbones consisting of alternating phosphorus and nitrogen atoms. A repeating unit in polyphosphazenes is shown below, where the side groups G can be organic, inorganic or organometallic, and need not be the same. Interest in these polymers relies on the fact that, compared to various other biodegradable polymer materials, polyphosphazenes are easier to manipulate with different side groups. In addition, their physical and chemical properties are greatly affected by the nature of the side groups. Therefore, polymers with a wide range of properties can be obtained by appropriately choosing side chain groups. The possibility of obtaining polyorganophosphazene with different tunable properties makes those polymers potentially useful in many fields, ranging from pharmaceutical, industrial to agricultural applications. See, Shan Cheng, Stimuli-Responsive Polyphosphazenes as Controlled Drug Delivery Matrix Materials (2001), dspace.library.drexel.edu/retrieve/963/end.pdf.

(24) ##STR00001##

(25) Two different fundamental routes to synthesize substituted polyphosphazenes are generally used. A first method one starts from substitution reactions of the chlorine atoms on hexachlorocyclotriphosphazene to prepare phosphazene cyclic trimers with different side groups. By ring-opening polymerization of these small cyclic trimers, polyphosphazenes with different substituents can be obtained.

(26) Many new materials have been prepared through this direct synthesis. However, the steric hindrance effect greatly limits the variety and the amount of the substituent on polymer chains. To solve this problem Allcock and his co-workers developed a synthesis route which involves the preparation of poly(dichlorophosphazene) and a sequential substitution reaction of chlorine atoms. In the first step, poly(dichlorophosphazene) as highly reactive macromolecular intermediate, can be prepared by several different methods. The most effective route to high molecular weight poly(dichlorophosphazene) is via the ring-opening polymerization of the cyclic trimer, hexachlorocyclotriphosphazene at 250 C. in the molten phase or in solution. This reaction gives a polymer with a broad molecular weight distribution, but with an Mw near 2,000,000, which corresponds to approximately 15,000 repeating units per chain. More recently, a room-temperature, living cationic condensation polymerization of Me3SiNPCl3 method has also been developed. This reaction yields narrow molecular weight distribution polymers, with excellent control of the molecular weight and access to block copolymers.

(27) The second step in the synthesis involves the replacement of the chlorine atoms by reactions with different organic or organometallic groups. Typically, an average of 30,000 chlorine atoms per molecule could be replaced at this stage as the result of high reactivity of the PCl bond. Based on this macromolecular substitution reaction, several hundred different polyorganophosphazenes have been synthesized. Most of the current industrial important polyphosphazenes are made by this method.

(28) As a relatively new biodegradable polymer, polyphosphazene as drug delivery material has been widely studied. Compared with other drug delivery matrix materials, polyphosphazene shows particular advantages because it has an inorganic backbone that is biocompatible over time and that degrades to harmless small molecule products: ammonia, phosphate, and water. The system can be tailored to respond to different physiological environmental conditions by appropriate choice of substituted side chains. Many results show that the delivery systems designed with this material can accommodate a large variety of drugs including small drugs and macromolecules. Release study has been explored with both hydrophobic and hydrophilic polyphosphazene. The former ones are usually studied for polymer matrix erosion and diffusion release systems, while the latter ones are used to prepare hydrogel matrices after being crosslinked.

(29) With respect to perfluorocarbons, it is well known that they have a high self-affinity, and thus a fluorinated alkyl or perfluorinated substituent will be compatible with the PFT, thus leading to a high loading capacity and slowed release. Likewise, PFTs are incompatible with polar substituents, leading to lower loading capacity and higher release rates. As is known, the properties of a matrix may be tailored by balancing the proportions of the various substituents.

(30) An alternate method for controlling release rate of PFTs is to provide a mechanical barrier, such as a perforated sheet, which allows volatilization dependent on the perforated area. In this case, the release rate is decoupled from the PFT holding capacity, though the mechanical structure is somewhat more complex and the composite structure will be more sensitive to mechanical treatment during use.

(31) Indeed, both a matrix and a barrier technique may be combined, for example as shown in FIGS. 1A and 1B. FIG. 1 shows a representative cross section of a perfluorocarbon tracer having taggant microcapsules within a matrix, on a carrier layer, before and after release of a cover layer. The taggant capsules provide a relatively high bulk storage capacity, while the matrix provides release profile control. Typically, the matrix will be saturated with taggant, with the capsules providing a replenishing source. The release rate will be dependent on the surface area and an air-matrix release coefficient for the taggant, which in turn will be dependent on the vapor pressure of the taggant and the affinity of the matrix for the taggant.

(32) The present invention therefore provides a system and method for identifying and tracking persons and objects, comprising use of a controlled taggant release device which has a very low rate of release prior to activation, and has an extended duration consistent rate of release after activation, which may be conveniently applied to persons or objects.

(33) The present invention also provides a system for detection of taggant release device, comprising remote optical detection system which employs an illuminator emitting an optical wavelength for exciting a fluorescent emission from a taggant, and an imaging detector for sensing and/or imaging the excited fluorescence. This detector is preferably battery operated, portable by a human. The device may operate independently, but is preferably integrated with a fusing or triggering mechanism for munitions. The device is further preferably configured as part of an identify friend or foe (IFF) system, which may be manually or automatically operable. In one embodiment, the detector or imager is mounted on an unmanned vehicle, such as an unmanned aerial vehicle (UAV).

(34) It is therefore an object of the invention to provide a method of using volatile perfluorocarbons to identify personnel, comprising the steps of applying a selectively activatable controlled release perfluorocarbon to a person. Preferably, the controlled release mechanism employs a substituted polyphosphazene matrix. The PFT is preferably one or more perfluorocarbons selected from the group of PMCH, PMCP, o-PDCH, m-PDCH, p-PDCH and PTCH. The controlled release is preferably initiated by removal of a barrier, such as a confining film. Preferably, the controlled release continues after initiation for 4-48 hours, and thereafter occurs at only a low level. Longer duration formulations may also be provided. The PFT matrix may be provided as an aerosol, paint or powder. The PFT is preferably released from a substituted polyphosphazene matrix, formulated to control a capacity and release profile of the PFT from the matrix.

(35) The volatile perfluorocarbons may also be used to identify land vehicles. Thus, according to another embodiment, it is an object of the invention to provide a method of using perfluorocarbon tracers to identify vehicles, comprising of the steps of applying a formulation of perfluorocarbon tracers in a paint or aerosol spray to a vehicle, and detecting the vehicle remotely based on perfluorocarbon emissions.

(36) According to a further embodiment of the invention, a PFT is provided as a part of a food or liquid product, for human ingestion. Preferably, the PFT is provided in a PFT-polyphosphazene matrix, in such form as it will not release until heated or otherwise changed chemically. The PFT can be detected by urinalysis, breath testing, of other body fluid testing. Vapor emissions may be used to detect the location of a tagged individual.

(37) The numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.