Chemistry: analytical and immunological testing – Phosphorus containing – Organic
Reexamination Certificate
2000-06-09
2004-08-31
Warden, Jill (Department: 1743)
Chemistry: analytical and immunological testing
Phosphorus containing
Organic
C436S151000, C422S090000, C422S082010, C422S082020
Reexamination Certificate
active
06783989
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to conductive polymer compositions which are used to detect the presence of toxic substances in the environment. The conductive polymers of this invention are intrinsically conductive polymers which are conductive without the necessity of doping. These conductive polymers can be used in sensors and incorporated in dosimeters to selectively detect the presence of extremely toxic substances in the environment, such as chemical warfare agents.
Accurate selective detection and quantification of toxic substances is generally achievable at relatively high cost. Paper tape sensors coated with a compound which changes color when exposed to a toxic substance can be relatively inexpensive. However, the tape coating layer may respond to a number of discrete substances, making selectivity difficult. Since many substances are present in the environment in trace amounts, the potential for interference or false readings with such devices is significant.
Another category of relatively inexpensive chemical sensors is solid state devices, such as metal oxide films, which display a conductivity change in the presence of certain toxic chemical species, but usually at elevated temperatures. Although adequate for the gross detection of certain chemicals, these metal oxide sensors typically respond to a variety of substances, leading to problems with accuracy and selectivity. In addition, since the devices operate at elevated temperatures, they require a power source for heating and are subject to degradation.
The sensing techniques which have the required sensitivity and selectivity are typically extremely sophisticated, expensive scientific instruments which need to be operated by a skilled technician. For example, mass spectrometers are very sensitive and can achieve the desired selectivity, unless two or more species present in the sample give rise to ions with the same mass to charge ratio. Spectroscopic techniques in principle can achieve the desired selectivity and sensitivity provided that the chemicals do not overlap in terms of their spectroscopic features. However, such instruments typically cost tens of thousands of dollars.
Recent developments in chemical detection involve electronic “noses.” These devices are described as being capable of detecting the presence of vapors including methanol, acetone, benzene, and toluene. Such devices are described in U.S. Pat. Nos. 5,698,089; 5,571,401; 5,788,833; and 5,891,398. The devices of these patents relate to chemical sensors, arrays of sensors, and sensor manufacturing techniques. The sensor contains a resistor element which is composed of a nonconductive organic polymer and a conductive material. When the analyte contacts the resistor element, the resistance changes (presumably due to a swelling of the substrate), and this change in resistivity is measured by an electronic signal measuring device. The conductive material can be a conductive polymer, such as doped polyaniline or polypyrrole, and these materials can be incorporated in a portable hand-held electronic device with an LCD read out. The devices described in these patents appear to operate at or near the percolation threshold of the polymer such that the resistivity of the polymer is changed due to the absorption of volatile organic compounds by the polymer matrix.
The use of conductive polymers for fabricating chemical sensors is a relatively recent technological advance. U.S. Pat. Nos. 5,145,645 and 5,310,507 relate to dosimeters for the selective detection of chemical species. The dosimeters include a doped conductive polyaniline which detects the presence of a specific chemical substance by an irreversible change in resistance of the polyaniline. The resistance is measured and displayed in an electronic device connected to the sensor. The individual chemical is identified by correlating the initial polymer resistance with the altered resistance, and comparing this difference with a calibration curve of known chemical entities. Typical chemical entities which may be detected using this approach include hydrazine and ammonia.
Polyaniline is a conductive polymer which has been extensively investigated, both in terms of its properties and potential uses. U.S. Pat. No. 5,624,605 relates to high molecular weight, plasticized, conductive polyaniline compositions. The conductivity of these compositions is provided by adding a functionalized protonic acid to the polyaniline. U.S. Pat. No. 5,378,402 relates to polymeric dopants for enhancing the conductivity of polymers, such as polypyrrole and polyaniline. Sulphonated polystyrene is an example of a negatively charged polymer which is suitable as a dopant. U.S. Pat. No. 5,227,092 is directed to electrically conductive polyaniline block copolymers which are doped using para-toluenesufonic acid as a sulfonated dopant.
U.S. Pat. No. 5,519,147 relates to polythiophene derivatives which contain crown ether moieties covalently bound to the 3 position of adjacent thiophene units. The modified polythiophenes can be used to measure the presence of chemical species, such as metal ions and organic molecules, in a reversible manner. The modified polythiophenes can be used to prepare sensors by coating the polymer onto an insulating substrate, and measuring the difference in conductivity of the polymer in the presence and absence of the species to be detected.
Recent incidents of terrorism around the world have underscored the need for devices for detection of chemical warfare agents (“CW agents”) for use by both military and civilian personnel. Despite this need, the sensitive and chemically specific detection of CW agents remains a significant challenge. This is due, in part, to the extreme toxicity of CW agents: the median lethal dose for the nerve agent VX is 7 &mgr;g per kg of body weight for a normal adult, requiring sensitivity levels in the range of parts per billion. Furthermore, to provide maximum effectiveness, CW agent sensors should preferably be used in a badge format that can be worn by each individual to ascertain exposure. This portability requirement places additional constraints on sensor design: the device should be low-cost, have a small form-factor (credit card size), and use very little power (e.g., battery-operated). In addition, it would be useful for a sensor system to have characteristics which are applicable to both military and commercial product markets. Satisfying these demanding requirements necessitates a novel approach to the measurement of low concentrations of CW agents.
It will be readily appreciated that a need exists for a compact dosimeter for the rapid and accurate detection of extremely toxic substances in the environment.
SUMMARY OF THE INVENTION
The present invention features a device and method for detecting the presence of toxic substances in the environment. The device of this invention can incorporate an array of individual sensing elements or sensors which are configured and designed to detect one or more specific toxic substances in the environment. The individual sensors are prepared from conductive polymers which are inherently conductive without the use of a dopant. The conductive polymers are included in a polymeric composition, which also includes at least one additive which reacts with a toxic substance to be detected. The reaction results in a change in a detectable characteristic of the polymeric composition which can be measured and displayed by the detector. Preferably, the change in the detectable characteristic is a change in conductivity of the composition.
Accordingly, in one aspect, inherently conductive polymers are provided for use in sensors for detecting toxic substances in the environment. The inherently or intrinsically conductive polymers do not require the use of dopants to achieve acceptable and measurable levels of conductivity, and, in fact, the use of a doping agent may render the polymers less effective. Polymers which are preferred in this invention include the substituted polythiophenes, such as regioregular poly (3-hexylt
Cole Monique
Physical Sciences Inc.
Warden Jill
LandOfFree
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