Chemistry: analytical and immunological testing – Tracers or tags
Reexamination Certificate
2000-03-06
2003-03-04
Snay, Jeffrey (Department: 1743)
Chemistry: analytical and immunological testing
Tracers or tags
C252S408100, C422S051000, C422S119000, C250S458100
Reexamination Certificate
active
06528318
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an arrangement which exploits scatter-controlled emissions for chemical sensor or taggant arrangements and more specifically to an arrangement which permits an increase in the security of scatter-controlled emissions, and/or which permits a small change in a chemical environment to be detected.
2. Description of the Related Art
Various attempts have been made to develop taggant arrangements. One example of this can be found in U.S. Pat. No. 5,763,891 issued to Yoshinaga, et al. on Jun. 9, 1998. This arrangement is such that an identification mark is formed using a plurality of recording materials having fluorescent characteristics in wavelength regions that almost overlap each other but which are such that the maximum absorbing characteristics of each occurs at different wavelengths. Thus, in order to detect the presence of the unique combination of fluorescing material, it is necessary to sequentially irradiate a target containing these materials with two different light sources, or at least a source, which is capable of sequentially emitting radiation at two different distinct frequencies.
A further problem which is encountered with this arrangement is that the two fluorescing agents that are contained in an ink or the like type of carrier, are arranged to be sensitive to radiation in a near infrared region, and to have absorption spectrums wherein the maximum wavelengths do not overlap each other. This greatly inhibits the use of such materials outdoors or in environments wherein, merely by way of example, heat from hot machinery or objects lying in the hot sun, and/or the sun itself, are apt to produce so much background IR noise as to render such a taggant useful only in special controlled environments.
On the other hand, an example of a sensing arrangement, which utilizes fluorescing materials, is found in U.S. Pat. No. 5,498,549 issued to Nagel et al. on Mar. 12, 1996. This arrangement is direct to sensing the concentration, for example, partial pressure, of a component or analyte of interest, such as oxygen, in a medium, for example, an aqueous-based medium, such as blood. The aim of this arrangement is to provide accurate, reliable and reproducible concentration determinations, and to enable such determinations in spite of signal transmission problems, such as, bent optical fibers, and other operational difficulties which may affect the quality of the signals being transmitted.
Nevertheless, these arrangements are individually limited in their scope of application and the underlying technology cannot be applied to both sensor and taggant arrangements.
SUMMARY OF THE INVENTION
The invention centers on the novel emissive properties of high optical gain materials in a high scattering environment. High optical gain materials emit intense and spectrally narrow light that is dependent on the chemical environment in which high gain materials are contained. When two high-gain materials are placed in the same environment, the properties of each emitter will depend on the chemical composition of the surrounding medium. The invention enables the switching or transferring of energy from one emitter to the other when the chemical environment is changed in a specific manner. Thus, a shift in the spectral emissions can be detected, caused and/or predicted.
While this concept can be applied to a wide variety of different technologies, identifying taggants and sensors are two exemplary forms of application. In the case of a taggant, various possibilities are presented. Merely by way of example, it is possible to impregnate a polymer with at least two optically high gain materials which, for the sake of explanation, shall be referred to as emitters, and to form a thread, fiber, particle, film surface or the like with the thus modified polymer. By engineering the polymer to be selectively porous to one or both liquids or gases (or both), it is possible to place an article in a testing device and to irradiate it to the degree that one of the emitters will be excited to a stimulated level and emit photonic energy at a first expected wavelength. By applying a spray (merely by way of example) containing a predetermined analyte or mediating material, the wavelength will, in the case of a genuinely tagged fiber, shift to a second known wavelength. If this shift is ascertained, then the article being examined can be deemed to have been positively identified.
In the same manner a gas “sniffer” type sensor (for example) can be created in a manner wherein, if the shift from one wavelength to the other is detected, then the presence of a predetermined gas can be ascertained, and a warning, if it is necessary, issued. It should, of course, be appreciated that many and varied variants are possible without deviating from the concept upon which the present invention is based.
More specifically, scatter controlled emission is an optical scattering process that produces stimulated emission from random media with high-gain. The high-gain media for scatter controlled emissions in an embodiment of the invention resides in a mixture of laser dye molecules and sub-micron scatters dispersed in either a liquid or a solid host material. The emission characteristics of this media fall into two categories, weak broadband features under low intensity illumination (which produces spontaneous emission) and intense, narrow band laser-like emission which occurs when the optical excitation source is above a threshold intensity level (which produces stimulated emissions).
In accordance with the present invention, the stimulated emissions from the random media have a markedly higher chemical sensitivity as compared to spontaneous emissions. By way of example, stimulated emission from a methanol solution containing two laser dyes (4-dicyanmethyline-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM) and Carbazine 720), in the presence of 10
10
/cm
3
concentration of titanium dioxide particles (sizes ranging from a few micrometers to less than one micrometer), was able to detect parts per million benzylamine (relative to the dye concentration) in the scattering medium.
Another advantage of this invention is the ability to generate small and efficient light sources, which can serve as replacements for more complex and expensive conventional laser systems. This is due to the composition of the random media, which contain both the active laser material and the feedback mechanism (scatterers). A suitable pump source for excitation is however, required.
A first aspect of the invention resides in a photonically excitable arrangement comprising: a first material which is capable of absorbing and emitting photonic energy and which, when sufficiently excited by photonic energy from an external source, emits stimulated radiation in a first narrow wavelength band; a second material which is capable of absorbing and emitting photonic energy; and a mediating material which causes the photonic emission of the first material to be transferred to the second material which is excited to emit stimulated radiation in a second narrow wavelength band at least partially in place of the emission from the first material in the first narrow wavelength band. This arrangement further comprises a host material in which the first and second materials are dispersed, and scattering particles dispersed amongst the first and second materials for scattering emissions from the first material to the second material.
In this arrangement the mediating material is selected to modify the first material and to change at least one of its characteristics to the degree that the photonic radiation which is emitted from the first material under stimulated conditions, is changed to a form wherein it is absorbed by the second material. A laser can be used as the source.
The scattering particles can be selected from, but not limited to, the group consisting essentially of: silicon carbide, diamond, alumina, barium titanate, zinc oxide and titanium dioxide. The first material
Benson Richard C.
Miragliotta Joseph A.
Osiander Robert
Cooch Francis A.
Snay Jeffrey
The Johns Hopkins University
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