Patent Application
20210148877
Ammonia gas present in atmosphere at ppb-levels arises primarily from a variety of anthropogenic sources, such as combustion of fossil fuels, from use of fertilizes and metabolic activities. Since exposure to ammonia can cause health effects, there is a need for detection of ammonia in the environment. Ammonia is also produced in the human body and monitoring of ammonia in exhaled human breath can be correlated with several physiological conditions for disease diagnosis. The normal physiological range of breath ammonia is in the region of 50 to 2000 ppb. Each human breath contains over 1,000 trace volatile organic compounds, which makes breath a highly complex substance. Developing sensors for low level ammonia in the environment and human breath is a challenging problem because of the ppb sensitivity that is required and discrimination against other gases present at much higher concentrations.
Provided herein are p-n metal oxide semiconductor (MOS) heterostructure-based sensors and systems. The sensors and systems can be used for the detection and/or quantification of ammonia in a gas sample, such as a breath sample, an environmental sample, or a sample of combustion gas. In some cases, the sensors and systems described herein can be used for the detection and/or quantification of ammonia at concentrations of 5000 ppb or less (e.g., at concentrations of from 50 ppb to 2,000 ppb, at concentrations of from 50 ppb to 1,000 ppb, or at concentrations of from 50 ppb to 500 ppb). The sensors and systems can be used for the detection and/or quantification of ammonia in the presence of other gases, such as carbon monoxide and nitric oxide.
In some cases, the sensors and systems can be used to detect and/or quantify ammonia in the presence of one or more hydrocarbons, such as an aromatic hydrocarbon (e.g., toluene, o-xylene, or a combination thereof), an aliphatic hydrocarbon (e.g., hexane, pentane, isoprene, 3-methylpentane, or a combination thereof), a functional organic compound (e.g., acetone, acetonitrile, ethyl acetate, methyl vinyl ketone, ethanol, 2-methylfuran, hexanal, methacrolein, 1-propanol, 2-propanol, or a combination thereof), or a combination thereof. In certain embodiments, the sensors and systems can be used to detect and/or quantify ammonia at concentrations of 5000 ppb or less (e.g., at concentrations of from 50 ppb to 2,000 ppb, at concentrations of from 50 ppb to 1,000 ppb, or at concentrations of from 50 ppb to 500 ppb) in the presence of one or more hydrocarbons (e.g., one or more hydrocarbons at a concentration of from 50 ppb to 5 ppm), such as one or more aromatic hydrocarbons (e.g., toluene, o-xylene, or a combination thereof), one or more aliphatic hydrocarbons (e.g., hexane, pentane, isoprene, 3-methylpentane, or a combination thereof), one or more functional organic compounds (e.g., acetone, acetonitrile, ethyl acetate, methyl vinyl ketone, ethanol, 2-methylfuran, hexanal, methacrolein, 1-propanol, 2-propanol, or a combination thereof), or a combination thereof).
Devices for sensing ammonia in a gas sample can comprise a sensing element that comprises a first region comprising a p-type metal oxide semiconductor (MOS) material and a second region comprising an n-type MOS material. The first region is adjacent to and contacts the second region (e.g., at a diffuse p-n heterojunction formed at an interface between the first and second regions). The p-type MOS material can comprise NiO. In certain embodiments, the p-type MOS material can consist of NiO. The n-type MOS material can comprise In2O3. In certain embodiments, the n-type MOS material can consist of In2O3.
In other embodiments, the p-type MOS material can be chosen from Co3O4, Cr2O3, Mn3O4, or a combination thereof, and the n-type MOS material chosen from ZnO, WO3, SnO2, TiO2, Fe2O3, or a combination thereof. In other embodiments, the p-type MOS material does not include NiO and the n-type MOS material does not include In2O3.
The sensor device can further comprise one or more electrodes established and spaced apart within the first region and one or more electrodes established and spaced apart within the second region. In some embodiments, the sensor device can comprise a first electrode established within the first region, a second electrode established within the second region, and wiring interconnecting the first and second electrodes. A measured resistance along the wiring can be indicative of the presence of NH3 in a gas interfacing with the sensing element.
In some embodiments, the location of the first electrode relative to the first region and the location of the second electrode relative to the second region are selected such that the measured resistance is unaffected by the presence of a gas other than ammonia (e.g., an interfering gas such as CO, NO, a hydrocarbon, or a combination thereof) that is also present the gas sample interfacing with the sensing element.
In some cases, the location of the first electrode relative to the first region and the location of the second electrode relative to the second region are selected such that the measured resistance is unaffected by the presence of one or more hydrocarbons, such as one or more aromatic hydrocarbons (e.g., toluene, o-xylene, or a combination thereof), one or more aliphatic hydrocarbons (e.g., hexane, pentane, isoprene, 3-methylpentane, or a combination thereof), one or more functional organic compounds (e.g., acetone, acetonitrile, ethyl acetate, methyl vinyl ketone, ethanol, 2-methylfuran, hexanal, methacrolein, 1-propanol, 2-propanol, or a combination thereof), or a combination thereof. In certain embodiments, the location of the first electrode relative to the first region and the location of the second electrode relative to the second region are selected such that the measured resistance is unaffected by the presence of from 50 ppb to 5 ppm of one or more hydrocarbons, such as one or more aromatic hydrocarbons (e.g., toluene, o-xylene, or a combination thereof), one or more aliphatic hydrocarbons (e.g., hexane, pentane, isoprene, 3-methylpentane, or a combination thereof), one or more functional organic compounds (e.g., acetone, acetonitrile, ethyl acetate, methyl vinyl ketone, ethanol, 2-methylfuran, hexanal, methacrolein, 1-propanol, 2-propanol, or a combination thereof), or a combination thereof.
In some embodiments, the sensing element defines a length from a first side to an opposing second side, the first side being defined by an edge of the first region opposite the second region, the second side being defined by an edge of the second region opposite the first region, and the location of the first electrode relative to the first region and the location of the second electrode relative to the second region are selected such that the wiring encompasses a combined amount of the p-type MOS material and the n-type MOS material in the length direction that is pre-determined to generate a measured resistance indicative of the presence of NH3 in a gas sample interfacing with the sensing element. The pre-determined combined amount can be selected such that the measured resistance is unaffected by the presence of a gas other than ammonia (e.g., an interfering gas such as CO, NO, a hydrocarbon, or a combination thereof) that is also present the gas sample interfacing with the sensing element. In some cases, the pre-determined combined amount can be selected such that the measured resistance is unaffected by the presence of one or more hydrocarbons, such as one or more aromatic hydrocarbons (e.g., toluene, o-xylene, or a combination thereof), one or more aliphatic hydrocarbons (e.g., hexane, pentane, isoprene, 3-methylpentane, or a combination thereof), one or more functional organic compounds (e.g., acetone, acetonitrile, ethyl acetate, methyl vinyl ketone, ethanol, 2-methylfuran, hexanal, methacrolein, 1-propanol, 2-propanol, or a combination thereof), or a combination thereof. In certain embodiments, the pre-determined combined amount can be selected such that the measured resistance is unaffected by the presence of from 50 ppb to 5 ppm of one or more hydrocarbons, such as one or more aromatic hydrocarbons (e.g., toluene, o-xylene, or a combination thereof), one or more aliphatic hydrocarbons (e.g., hexane, pentane, isoprene, 3-methylpentane, or a combination thereof), one or more functional organic compounds (e.g., acetone, acetonitrile, ethyl acetate, methyl vinyl ketone, ethanol, 2-methylfuran, hexanal, methacrolein, 1-propanol, 2-propanol, or a combination thereof), or a combination thereof.
In some embodiments, the sensor device can further comprise a third electrode established within the first region, a fourth electrode established within the second region, and wiring interconnecting the third and fourth electrodes. A measured resistance along the wiring interconnecting the third and fourth electrodes in comparison with the measured resistance along the wiring interconnecting the first and second electrodes is indicative of a concentration of NH3 in a gas interfacing with the sensing element.
In some embodiments, the device can further comprise a platform assembly maintaining the first and second electrodes as part of an electrode lead array selectively contacting the sensing element. The platform assembly can be configured to selectively alter a location of contact of the first electrode within the first region and selectively alter a location of contact of the second electrode within the second region. The platform assembly can be configured to selectively alter a distance between the first electrode and the second electrode.
Also provided are sensor systems for sensing ammonia in a gas sample. The sensor system can comprise a sensor device that comprises a sensing element, a first electrode established within the first region, a second electrode established within the second region, and a database. The sensing element can comprise a first region comprising a p-type MOS material and a second region comprising an n-type MOS material. The first region is adjacent to and contacts the second region (e.g., at a diffuse p-n heterojunction formed at an interface between the first and second regions). The p-type MOS material can comprise NiO. In certain embodiments, the p-type MOS material can consist of NiO. The n-type MOS material can comprise In2O3. In certain embodiments, the n-type MOS material can consist of In2O3. In other embodiments, the p-type MOS material can be chosen from Co3O4, Cr2O3, Mn3O4, or a combination thereof, and the n-type MOS material chosen from ZnO, WO3, SnO2, TiO2, Fe2O3, or a combination thereof. In other embodiments, the p-type MOS material does not include NiO and the n-type MOS material does not include In2O3.
In certain embodiments, the system can be configured to estimate the concentration of NH3 in a biological sample, such as human breath. For example, the system can be configured to detect and/or quantify ammonia at concentrations of 5000 ppb or less (e.g., at concentrations of from 50 ppb to 2,000 ppb, at concentrations of from 50 ppb to 1,000 ppb, or at concentrations of from 50 ppb to 500 ppb) in a sample of human breath. In other embodiments, the system can be configured to estimate the concentration of NH3 a combustion gas. In other embodiments, the system can be configured to estimate the concentration of NH3 an environmental sample.
The database can correlate measured resistance along wiring between the first electrode and the second electrode with presence of NH3 in a gas sample interfacing with the sensing element. In some embodiments, the database can further correlate an estimate of a concentration of NH3 in the gas sample based upon the measured resistance. In certain embodiments, the database can comprise a calibration curve for NH3.
In some embodiments, the location of the first electrode relative to the first region and the location of the second electrode relative to the second region are selected such that the measured resistance is unaffected by the presence of a gas other than ammonia (e.g., an interfering gas such as CO, NO, a hydrocarbon, or a combination thereof) that is also present the gas sample interfacing with the sensing element. In some cases, the location of the first electrode relative to the first region and the location of the second electrode relative to the second region are selected such that the measured resistance is unaffected by the presence of one or more hydrocarbons, such as one or more aromatic hydrocarbons (e.g., toluene, o-xylene, or a combination thereof), one or more aliphatic hydrocarbons (e.g., hexane, pentane, isoprene, 3-methylpentane, or a combination thereof), one or more functional organic compounds (e.g., acetone, acetonitrile, ethyl acetate, methyl vinyl ketone, ethanol, 2-methylfuran, hexanal, methacrolein, 1-propanol, 2-propanol, or a combination thereof), or a combination thereof. In certain embodiments, the location of the first electrode relative to the first region and the location of the second electrode relative to the second region are selected such that the measured resistance is unaffected by the presence of from 50 ppb to 5 ppm of one or more hydrocarbons, such as one or more aromatic hydrocarbons (e.g., toluene, o-xylene, or a combination thereof), one or more aliphatic hydrocarbons (e.g., hexane, pentane, isoprene, 3-methylpentane, or a combination thereof), one or more functional organic compounds (e.g., acetone, acetonitrile, ethyl acetate, methyl vinyl ketone, ethanol, 2-methylfuran, hexanal, methacrolein, 1-propanol, 2-propanol, or a combination thereof), or a combination thereof.
In some embodiments, the sensing element defines a length from a first side to an opposing second side, the first side being defined by an edge of the first region opposite the second region, the second side being defined by an edge of the second region opposite the first region, and the location of the first electrode relative to the first region and the location of the second electrode relative to the second region are selected such that the wiring encompasses a combined amount of the p-type MOS material and the n-type MOS material in the length direction that is pre-determined to generate a measured resistance indicative of the presence of NH3 in a gas sample interfacing with the sensing element. The pre-determined combined amount can be selected such that the measured resistance is unaffected by the presence of a gas other than ammonia (e.g., an interfering gas such as CO, NO, a hydrocarbon, or a combination thereof) or a combination thereof, that is also present the gas sample interfacing with the sensing element. In some cases, the pre-determined combined amount can be selected such that the measured resistance is unaffected by the presence of one or more hydrocarbons, such as one or more aromatic hydrocarbons (e.g., toluene, o-xylene, or a combination thereof), one or more aliphatic hydrocarbons (e.g., hexane, pentane, isoprene, 3-methylpentane, or a combination thereof), one or more functional organic compounds (e.g., acetone, acetonitrile, ethyl acetate, methyl vinyl ketone, ethanol, 2-methylfuran, hexanal, methacrolein, 1-propanol, 2-propanol, or a combination thereof), or a combination thereof. In certain embodiments, the pre-determined combined amount can be selected such that the measured resistance is unaffected by the presence of from 50 ppb to 5 ppm of one or more hydrocarbons, such as one or more aromatic hydrocarbons (e.g., toluene, o-xylene, or a combination thereof), one or more aliphatic hydrocarbons (e.g., hexane, pentane, isoprene, 3-methylpentane, or a combination thereof), one or more functional organic compounds (e.g., acetone, acetonitrile, ethyl acetate, methyl vinyl ketone, ethanol, 2-methylfuran, hexanal, methacrolein, 1-propanol, 2-propanol, or a combination thereof), or a combination thereof.
In some embodiments, the sensor device can further comprise a third electrode established within the first region, a fourth electrode established within the second region, and wiring interconnecting the third and fourth electrodes. A measured resistance along the wiring interconnecting the third and fourth electrodes in comparison with the measured resistance along the wiring interconnecting the first and second electrodes is indicative of a concentration of NH3 in a gas interfacing with the sensing element.
In some embodiments, the sensor system can further comprise a controller maintaining the database and electronically associated with the wiring. The controller can comprise a memory on which is stored: the database; instructions for receiving a plurality of measured resistance values generated by the sensor device in the presence of the gas sample; and instructions for estimating a concentration of NH3 in the gas sample based upon the plurality of measured resistances. In some embodiments, a first one of the plurality of measured resistances can correspond to a first distance between corresponding electrodes in the first and second regions, respectively, and a second one of the plurality of measured resistances can correspond to a second distance between corresponding electrodes in the first and second regions, respectively, the first distance being different from the second distance. The controller can further comprise a memory on which is stored instructions for performing appropriate resistance measurements to detect and/or quantify NH3 in the gas sample. The controller can further comprise a memory on which is stored instructions for eliminating (e.g., subtracting or otherwise correcting for) the influence of a gas other than ammonia (e.g., an interfering gas such as CO, NO, a hydrocarbon, or a combination thereof) or a combination thereof, that is also present the gas sample interfacing with the sensing element. This can include, for example, calibration curve(s) for possible interferents (e.g., CO, NO, and/or one or more hydrocarbons) in the gas sample.
Optionally, in the case of systems configured to estimate the concentration of NH3 in a biological sample such as human breath, the controller can comprise a memory on which is stored instructions for assigning a score for disease progression in a patient based on the estimated concentration of NH3 in the gas sample associated with a biological sample from the patient (e.g., a breath sample from the patient). For example, the controller can comprise a memory on which is stored instructions for assigning a score for the progression of a liver disease in the patient, a kidney disease in the patient, an H. pylori infection in the patient, or halitosis in the patient. The score can be a numerical score assessing diseases progression or severity. Alternatively, the score can be a binary indicator of disease (e.g., a ‘positive’ or ‘negative’ indicator signifying the presence of an infection, such as an H. pylori infection). Optionally, in the case of systems configured to estimate the concentration of NH3 in a biological sample such as human breath, the controller can comprise a memory on which is stored instructions for selecting one or more treatment instructions (e.g., one or more treatment options) based on the estimated concentration of NH3 in the gas sample associated with a biological sample from the patient (e.g., a breath sample from the patient). The controller can comprise a memory on which is stored instructions for outputting these results to a person administering the test (e.g., the patient and/or a clinician). In this way, the sensors can be used as point-of-care diagnostic systems to assess the incidence and/or progression of a liver disease in a patient, a kidney disease in a patient, an H. pylori infection in a patient, and/or or halitosis in a patient.
Also provided are method of sensing ammonia using p-n MOS heterostructure-based sensors and systems. Methods can comprise providing a p-n MOS heterostructure-based sensor system; contacting the sensor element of the sensor system with the gas sample; measuring resistance along wiring between the first electrode and the second electrode, and detecting ammonia in the gas sample based upon the measured resistance. The sensor system can comprise a sensor device that comprises a sensing element, a first electrode established within the first region, a second electrode established within the second region, and a database. The sensing element can comprise a first region comprising a p-type MOS material and a second region comprising an n-type MOS material. The first region is adjacent to and contacts the second region (e.g., at a diffuse p-n heterojunction formed at an interface between the first and second regions). The p-type MOS material can comprise any suitable p-type MOS. In some cases, the p-type MOS material can comprise NiO, CuO, Co3O4, Cr2O3, Mn3O4, or a combination thereof. In some embodiments, the p-type MOS material can be chosen from NiO, Co3O4, Cr2O3, Mn3O4, or a combination thereof. In some embodiments, the p-type MOS material can be chosen from Co3O4, Cr2O3, Mn3O4, or a combination thereof. In some embodiments, the p-type MOS material can be chosen from NiO, CuO, or a combination thereof. In some embodiments, the p-type MOS material can comprise NiO. In certain embodiments, the p-type MOS material can consist of NiO. In other embodiments, the p-type material does not include NiO. The n-type MOS material can comprise any suitable n-type MOS. In some cases, the n-type MOS material can comprise In2O3, SnO2, ZnO2, TiO2, WO3, ZnO, Fe2O3, or a combination thereof. In some cases, the n-type MOS material can comprise In2O3, ZnO, WO3, SnO2, TiO2, Fe2O3, or a combination thereof. In some cases, the n-type MOS material can comprise ZnO, WO3, SnO2, TiO2, Fe2O3, or a combination thereof. In some cases, the n-type MOS material can comprise In2O3, SnO2, ZnO2, TiO2, WO3, or a combination thereof. In some embodiments, the n-type MOS material can comprise In2O3. In certain embodiments, the n-type MOS material can consist of In2O3. In other embodiments, the n-type material does not include In2O3. In one embodiment, the p-type MOS material does not include NiO and the n-type MOS material does not include In2O3.
The database can correlate measured resistance along wiring between the first electrode and the second electrode with presence of NH3 in a gas sample interfacing with the sensing element. In some embodiments, the database can further correlate an estimate of a concentration of NH3 in the gas sample based upon the measured resistance. In certain embodiments, the database can comprise a calibration curve.
In some embodiments, the location of the first electrode relative to the first region and the location of the second electrode relative to the second region are selected such that the measured resistance is unaffected by the presence of a gas other than ammonia (e.g., an interfering gas such as CO, NO, a hydrocarbon, or a combination thereof) that is also present the gas sample interfacing with the sensing element.
In some embodiments, the sensing element defines a length from a first side to an opposing second side, the first side being defined by an edge of the first region opposite the second region, the second side being defined by an edge of the second region opposite the first region, and the location of the first electrode relative to the first region and the location of the second electrode relative to the second region are selected such that the wiring encompasses a combined amount of the p-type MOS material and the n-type MOS material in the length direction that is pre-determined to generate a measured resistance indicative of the presence of NH3 in a gas sample interfacing with the sensing element. The pre-determined combined amount can be selected such that the measured resistance is unaffected by the presence of a gas other than ammonia (e.g., an interfering gas such as CO, NO, a hydrocarbon, or a combination thereof) that is also present the gas sample interfacing with the sensing element.
In some embodiments, the sensor device can further comprise a third electrode established within the first region, a fourth electrode established within the second region, and wiring interconnecting the third and fourth electrodes. A measured resistance along the wiring interconnecting the third and fourth electrodes in comparison with the measured resistance along the wiring interconnecting the first and second electrodes is indicative of a concentration of NH3 in a gas interfacing with the sensing element.
In some embodiments, the sensor system can further comprise a controller maintaining the database and electronically associated with the wiring. The controller can comprise a memory on which is stored: the database; instructions for receiving a plurality of measured resistance values generated by the sensor device in the presence of the gas sample; and instructions for estimating a concentration of NH3 in the gas sample based upon the plurality of measured resistances. In some embodiments, a first one of the plurality of measured resistances can correspond to a first distance between corresponding electrodes in the first and second regions, respectively, and a second one of the plurality of measured resistances can correspond to a second distance between corresponding electrodes in the first and second regions, respectively, the first distance being different from the second distance.
Contacting the sensor element with the gas sample can comprise exposing the sensor element to the gas sample for a period of time effective to induce a change in the measured resistance along wiring between the first electrode and the second electrode. In some embodiments, contacting the sensor element with the gas sample comprises exposing the sensor element to the gas sample for a period of time effective to induce an change in resistance in the same direction in both the p-type MOS material and the n-type MOS material. In certain embodiments, contacting the sensor element with the gas sample comprises exposing the sensor element to the gas sample for a period of time effective to induce a decrease in the resistance of the p-type MOS material and a decrease in the resistance of the n-type MOS material. For example, contacting the sensor element with the gas sample can comprise exposing the sensor element to the gas sample for from 30 seconds to five minutes (e.g., for from 1 to 3 minutes).
In some embodiments, methods can further comprise heating the sensor element to a temperature of from 250° C. to 450° C. In some embodiments, detecting ammonia in the gas sample based upon the measured resistance comprises estimating a concentration of NH3 in the gas sample based upon the measured resistance.
In some embodiments, the concentration of NH3 in the gas sample can be 5,000 ppb or less (e.g., from 50 ppb to 2,000 ppb, from 50 ppb to 1,000 ppb, or from 50 ppb to 500 ppb). In some embodiments, the gas sample can comprise a biological sample, such as a human breath sample. In some embodiments, the gas sample can comprise a sample of a combustion gas, such as a sample of a combustion gas from a diesel engine. In some embodiments, the gas sample can comprise an environmental sample. In some embodiments, the gas sample can comprise a sample from an industrial process.
Also provided are sensor systems and methods for diagnosing an H. pylori infection in a patient. The sensor systems can comprise a sensor device that comprises a sensing element, a first electrode established within the first region, a second electrode established within the second region, and a database. The sensing element can comprise a first region comprising a p-type MOS material and a second region comprising an n-type MOS material. The first region is adjacent to and contacts the second region (e.g., at a diffuse p-n heterojunction formed at an interface between the first and second regions). The p-type MOS material can comprise NiO. In certain embodiments, the p-type MOS material can consist of NiO. The n-type MOS material can comprise In2O3. In certain embodiments, the n-type MOS material can consist of In2O3. In other embodiments, the p-type MOS material can be chosen from Co3O4, Cr2O3, Mn3O4, or a combination thereof, and the n-type MOS material chosen from ZnO, WO3, SnO2, TiO2, Fe2O3, or a combination thereof. In other embodiments, the p-type MOS material does not include NiO and the n-type MOS material does not include In2O3.
In certain embodiments, the systems can be configured to estimate the concentration of NH3 in a breath sample collected for a patient. For example, the system can be configured to detect and/or quantify ammonia at concentrations of 5000 ppb or less (e.g., at concentrations of from 50 ppb to 2,000 ppb, at concentrations of from 50 ppb to 1,000 ppb, or at concentrations of from 50 ppb to 500 ppb) in the breath sample. The system can further include a mouthpiece configured to receive a breath sample exhaled from a patient, and deliver the sample to the sensor device.
The database can correlate measured resistance along wiring between the first electrode and the second electrode with presence of NH3 in a gas sample interfacing with the sensing element. In some embodiments, the database can further correlate an estimate of a concentration of NH3 in the gas sample based upon the measured resistance. In certain embodiments, the database can comprise a calibration curve for NH3.
In some embodiments, the location of the first electrode relative to the first region and the location of the second electrode relative to the second region are selected such that the measured resistance is unaffected by the presence of a gas other than ammonia (e.g., an interfering gas such as CO, NO, a hydrocarbon, or a combination thereof) that is also present the breath sample interfacing with the sensing element. In some cases, the location of the first electrode relative to the first region and the location of the second electrode relative to the second region are selected such that the measured resistance is unaffected by the presence of one or more hydrocarbons, such as one or more aromatic hydrocarbons (e.g., toluene, o-xylene, or a combination thereof), one or more aliphatic hydrocarbons (e.g., hexane, pentane, isoprene, 3-methylpentane, or a combination thereof), one or more functional organic compounds (e.g., acetone, acetonitrile, ethyl acetate, methyl vinyl ketone, ethanol, 2-methylfuran, hexanal, methacrolein, 1-propanol, 2-propanol, or a combination thereof), or a combination thereof. In certain embodiments, the location of the first electrode relative to the first region and the location of the second electrode relative to the second region are selected such that the measured resistance is unaffected by the presence of from 50 ppb to 5 ppm of one or more hydrocarbons, such as one or more aromatic hydrocarbons (e.g., toluene, o-xylene, or a combination thereof), one or more aliphatic hydrocarbons (e.g., hexane, pentane, isoprene, 3-methylpentane, or a combination thereof), one or more functional organic compounds (e.g., acetone, acetonitrile, ethyl acetate, methyl vinyl ketone, ethanol, 2-methylfuran, hexanal, methacrolein, 1-propanol, 2-propanol, or a combination thereof), or a combination thereof.
In some embodiments, the sensing element defines a length from a first side to an opposing second side, the first side being defined by an edge of the first region opposite the second region, the second side being defined by an edge of the second region opposite the first region, and the location of the first electrode relative to the first region and the location of the second electrode relative to the second region are selected such that the wiring encompasses a combined amount of the p-type MOS material and the n-type MOS material in the length direction that is pre-determined to generate a measured resistance indicative of the presence of NH3 in the breath sample interfacing with the sensing element. The pre-determined combined amount can be selected such that the measured resistance is unaffected by the presence of a gas other than ammonia (e.g., an interfering gas such as CO, NO, a hydrocarbon, or a combination thereof) or a combination thereof, that is also present the gas sample interfacing with the sensing element. In some cases, the pre-determined combined amount can be selected such that the measured resistance is unaffected by the presence of one or more hydrocarbons, such as one or more aromatic hydrocarbons (e.g., toluene, o-xylene, or a combination thereof), one or more aliphatic hydrocarbons (e.g., hexane, pentane, isoprene, 3-methylpentane, or a combination thereof), one or more functional organic compounds (e.g., acetone, acetonitrile, ethyl acetate, methyl vinyl ketone, ethanol, 2-methylfuran, hexanal, methacrolein, 1-propanol, 2-propanol, or a combination thereof), or a combination thereof. In certain embodiments, the pre-determined combined amount can be selected such that the measured resistance is unaffected by the presence of from 50 ppb to 5 ppm of one or more hydrocarbons, such as one or more aromatic hydrocarbons (e.g., toluene, o-xylene, or a combination thereof), one or more aliphatic hydrocarbons (e.g., hexane, pentane, isoprene, 3-methylpentane, or a combination thereof), one or more functional organic compounds (e.g., acetone, acetonitrile, ethyl acetate, methyl vinyl ketone, ethanol, 2-methylfuran, hexanal, methacrolein, 1-propanol, 2-propanol, or a combination thereof), or a combination thereof.
In some embodiments, the sensor device can further comprise a third electrode established within the first region, a fourth electrode established within the second region, and wiring interconnecting the third and fourth electrodes. A measured resistance along the wiring interconnecting the third and fourth electrodes in comparison with the measured resistance along the wiring interconnecting the first and second electrodes is indicative of a concentration of NH3 in the breath sample interfacing with the sensing element.
In some embodiments, the sensor systems can further comprise a controller maintaining the database and electronically associated with the wiring. The controller can comprise a memory on which is stored: the database; instructions for receiving a plurality of measured resistance values generated by the sensor device in the presence of the breath sample; and instructions for estimating a concentration of NH3 in the breath sample based upon the plurality of measured resistances. In some embodiments, a first one of the plurality of measured resistances can correspond to a first distance between corresponding electrodes in the first and second regions, respectively, and a second one of the plurality of measured resistances can correspond to a second distance between corresponding electrodes in the first and second regions, respectively, the first distance being different from the second distance. The controller can further comprise a memory on which is stored instructions for performing appropriate resistance measurements to detect and/or quantify NH3 in the breath sample.
The systems can further include a controller that comprises a memory on which is stored instructions for assigning a score for the progression of an H. pylori infection in the patient. The score can be a numerical score assessing the progression or severity of an H. pylori infection in the patient. Alternatively, the score can be a binary indicator of H. pylori infection (e.g., a ‘positive’ or ‘negative’ indicator signifying the presence of an H. pylori infection). In one embodiment, the instructions for assigning a score for the progression of an H. pylori infection can include instructions to provide a ‘positive’ indicator signifying the presence of an H. pylori infection in a patient when the estimated concentration of N3 in the breath sample is from 50 ppb to 400 ppb, and to provide a ‘negative’ indicator signifying the absence of an H. pylori infection in a patient when the estimated concentration of NH3 in the breath sample is from 500 ppb to 600 ppb.
The systems can further include a controller that comprises a memory on which is stored instructions for performing appropriate resistance measurements to detect and/or quantify NH3 in the control breath sample, instructions for receiving a plurality of measured resistance values generated by the sensor device in the presence of the control breath sample; and instructions for estimating a concentration of NH3 in the control breath sample based upon the plurality of measured resistances. The systems can further include a controller that comprises a memory on which is stored instructions for subtracting the estimated concentration of NH3 in the control breath sample from the estimated concentration of NH3 in the breath sample. This can be used to determine the net change in the concentration of NH3 in a patient's breath sample upon administration of urea.
In some cases systems can further include a controller that comprises a memory on which is stored instructions for assigning a score for the progression of an H. pylori infection in the patient based on the net change in the concentration of NH3 in a patient's breath sample upon administration of urea. The score can be a numerical score assessing the progression or severity of an H. pylori infection in the patient. Alternatively, the score can be a binary indicator of H. pylori infection (e.g., a ‘positive’ or ‘negative’ indicator signifying the presence of an H. pylori infection). In one embodiment, the instructions for assigning a score for the progression of an H. pylori infection can include instructions to provide a ‘positive’ indicator signifying the presence of an H. pylori infection in a patient when the net change in the concentration of NH3 in a patient's breath sample upon administration of urea is from 50 ppb to 400 ppb, and to provide a ‘negative’ indicator signifying the absence of an H. pylori infection in a patient when the net change in the concentration of NH3 in a patient's breath sample upon administration of urea is from 500 ppb to 600 ppb.
Optionally, the controller can further comprise a memory on which is stored instructions for selecting one or more treatment instructions (e.g., one or more treatment options) based on the estimated concentration of NH3 in the breath sample and/or the net change in the concentration of NH3 in a patient's breath sample upon administration of urea. The controller can comprise a memory on which is stored instructions for outputting these results to a person utilizing the system to diagnose an H. pylori infection in a patient (e.g., the patient and/or a clinician). In this way, the systems can be used as point-of-care diagnostic systems to assess the incidence and/or progression of an H. pylori infection in a patient.
Methods for diagnosing an H. pylori infection in a patient can comprise administering urea (e.g., non-labeled urea) to a patient, collecting a breath sample from the patient, and measuring the concentration of NH3 in the breath sample using the sensors and systems described herein. In one example, the concentration of NH3 in the breath sample can be measured using a system described herein that is specifically configured to assess the incidence and/or progression of an H. pylori infection in a patient. Methods can further include collecting a control breath sample from the patient prior to administration of urea (e.g., non-labeled urea) to the patient, and measuring the concentration of NH3 in the control breath sample using the sensors and systems described herein. In these cases, the methods can involve subtracting the estimated concentration of NH3 in the control breath sample from the estimated concentration of NH3 in the breath sample to determine the net change in the concentration of NH3 in a patient's breath sample upon administration of urea. The net change in the concentration of NH3 in a patient's breath sample upon administration of urea can be used to assess the incidence and/or progression of an H. pylori infection in a patient.
Provided herein are sensor devices and corresponding sensor systems that employ a p-n semiconducting oxide heterojunction. The devices and systems described herein can be used to detect and/or quantify the amount of NH3 in a gas sample. In some cases, the devices and systems described herein can be used to detect and/or quantify the amount of NH3 in a gas sample in the presence of other gases such as CO, NO, or a combination thereof. The sensors described herein comprise p-type and n-type materials arranged adjacent one another, forming the sensing element of the sensor device. In this regard, techniques for obtaining data from the so-constructed sensor device can assist in distinguishing NH3 from a mixture of gases, and allow for the detection and/or quantification of NH3 in the presence of one or more interfering gases, such as CO, NO, or a combination thereof.
In some cases, the sensors and systems can be used to detect and/or quantify ammonia in the presence of one or more hydrocarbons, such as an aromatic hydrocarbon (e.g., toluene, o-xylene, or a combination thereof), an aliphatic hydrocarbon (e.g., hexane, pentane, isoprene, 3-methylpentane, or a combination thereof), a functional organic compound (e.g., acetone, acetonitrile, ethyl acetate, methyl vinyl ketone, ethanol, 2-methylfuran, hexanal, methacrolein, 1-propanol, 2-propanol, or a combination thereof), or a combination thereof. In certain embodiments, the sensors and systems can be used to detect and/or quantify ammonia at concentrations of 5000 ppb or less (e.g., at concentrations of from 50 ppb to 2,000 ppb, at concentrations of from 50 ppb to 1,000 ppb, or at concentrations of from 50 ppb to 500 ppb) in the presence of one or more hydrocarbons, such as an aromatic hydrocarbon (e.g., toluene, o-xylene, or a combination thereof), an aliphatic hydrocarbon (e.g., hexane, pentane, isoprene, 3-methylpentane, or a combination thereof), a functional organic compound (e.g., acetone, acetonitrile, ethyl acetate, methyl vinyl ketone, ethanol, 2-methylfuran, hexanal, methacrolein, 1-propanol, 2-propanol, or a combination thereof), or a combination thereof).
An example sensor device (10) is schematically illustrated in
The sensor device (10) can be provided as part of a sensor system (18) as described herein. The sensor system (18) can include components conventionally employed with MOS-type gas sensor systems, such as a housing (not shown) for directing a gas or other substance of interest across the sensing element 11, electronics for establishing and measuring conductivity at the desired connections (e.g., RP, RN, RPN), and a controller 19 (e.g., a computer or other logic device) for receiving and/or interpreting the measured conductivity signals. In some embodiments, a measurement device (e.g., a multimeter) can be provided apart from the controller 19 that measures resistance at the selected connection(s), and signals the measured resistance value(s) to the controller 19 for interpretation as described below. The sensor system 18 can, in some embodiments, be provided as a single unit, such as a hand-held device providing an inlet port through which a gas sample is introduced. Regardless, the controller 19 can further programmed to determine the presence and amount (e.g., in ppm or ppb) of one or more analytes (e.g., ammonia) of interest based upon the measured conductivity signals. In certain embodiments, the controller 19 can be programmed to operate the sensor device 10 and analyze data generated thereby to detect the presence of, and estimate the concentration of, ammonia in various sample types, including human breath samples and combustion gas samples. In other embodiments, some or all of the measured resistance interpretation can be performed manually, such that the controller 19 can be optional.
The p-type material region 12 includes a p-type MOS material that conducts with positive holes being the majority charge carrier. Generally, in the presence of an oxidizing gas, the p-type MOS materials exhibit an increase in conductivity (or decrease in resistivity). An opposite effect is generally exhibited by the p-type MOS material in the presence of a reducing gas. However, in the case of NiO, a transient decrease in resistance upon exposure of low levels of NH3 can be observed. This effect can be exploited to amplify the response of the sensors described herein towards ammonia. The p-type MOS material can comprise NiO. In certain embodiments, the p-type MOS material can comprise at least 75% wt NiO (e.g., at least 80% wt NiO, at least 85% wt NiO, at least 90% wt NiO, at least 95% wt NiO, at least 96% wt NiO, at least 97% wt NiO, at least 98% wt NiO, or at least 99% wt NiO), based on the total weight of the p-type MOS material. In certain embodiments, the p-type MOS material can consist of NiO.
The n-type material region (14) includes an n-type MOS material in which the majority charge carriers are electrons. Generally, upon interaction with an oxidizing gas, the n-type MOS material exhibits a decrease in conductivity (or increase in resistivity). An opposite effect is exhibited by the n-type MOS material in the presence of a reducing gas. The n-type MOS material can comprise In2O3. In certain embodiments, the n-type MOS material can comprise at least 75% wt In2O3 (e.g., at least 80% wt In2O3, at least 85% wt In2O3, at least 90% wt In2O3, at least 95% wt In2O3, at least 96% wt In2O3, at least 97% wt In2O3, at least 98% wt In2O3, or at least 99% wt In2O3), based on the total weight of the n-type MOS material. In certain embodiments, the n-type MOS material can consist of In2O3.
In other embodiments, the p-type MOS material can be chosen from NiO, Co3O4, Cr2O3, Mn3O4, or a combination thereof, and the n-type MOS material chosen from In2O3, ZnO, WO3, SnO2, TiO2, Fe2O3, or a combination thereof. In certain embodiments, the p-type MOS material can be chosen from CO3O4, Cr2O3, Mn3O4, or a combination thereof; and the n-type MOS material chosen from ZnO, WO3, SnO2, TiO2, Fe2O3, or a combination thereof. In certain embodiments, the p-type MOS material does not include NiO. In certain embodiments, the n-type MOS material does not include In2O3. In one embodiment, the p-type MOS material does not include NiO and the n-type MOS material does not include In2O3.
The measured conductivities at the p-type region RP, at the n-type region RN, and across the p-n junction RPN can be evaluated to determine the presence and amount of a particular gas, such as ammonia, as different changes in conductivity are expected in each of these regions upon exposure to a gas such as NH3. The signal analysis can assume various forms, and can include obtaining a multiplicity of p-n junction measurements at differing nodes within the p-type region and the n-type region. For example,
With the above in mind, it should be noted that the null response data can be used as a “fingerprint” signature that is unique to a specific analyte. Thus, in a blind study, sensors and systems can elucidate the identity of analytes using this “fingerprint” signature technique. For example, the controller 19 (
With these principles in mind, an example ammonia sensor incorporating NiO as the p-type material and In2O3 as the n-type material is schematically illustrated in
The measured resistance at each of the channels 64-68 differs in the presence of NH3, NO, or CO, and varies as a function of the NH3, NO, or CO concentrations. By way of example,
In the case of NH3 (see
With the above explanations in mind, sensor devices (and corresponding sensor systems) can be used to effectively sense the presence and concentration of NH3, including discriminating against the presence of CO and/or NO and/or hydrocarbons, as described above.
As described below, non-limiting examples of NH3 sensor devices in accordance with certain embodiments of the present disclosure were constructed and subjected to testing to confirm viability in sensing NH3, including sensing NH3 in human breath.
The detection of low levels of ammonia is relevant for environmental, combustion and health-related applications. Resistive semiconducting metal oxide sensing platforms can be used for ammonia and other gas detection. Two important aspects of gas sensing are enhancing sensitivity and selectivity. A sensor platform with n-type In2O3 and p-type NiO placed side-by-side with a shared 30 μm interface was investigated. The substrate on which these metal oxides are placed allows for measuring the resistance change across In2O3, NiO or any combination of both oxides. With low concentrations of NH3 (<100 ppb), the change in resistance with NiO was anomalous at 300° C., the resistance decreased and then gradually increased over tens of minutes before decreasing again to reach the baseline. In situ diffuse reflectance infrared spectroscopy exhibited a band at 1267 cm−1, which was assigned to O2− and the change in intensity of this band with time mirrored the transient change in resistance with 1 ppm NH3 at 300° C., indicating that NH3 chemisorption was correlated with the O2− species. Taking advantage of the transient resistance decrease of NiO with NH3, and combining the In2O3 and NiO allowed selectivity enhancement towards NH3 at concentrations as low as 100 ppb. Interference to CO, NOx and humidity were studied. By selecting a suitable combination of both oxides, the response to CO at <10 ppm could be negated. Similarly, with NO at <10 ppb, there was minimal sensor response. The sensor was used to analyze NH3 mixed into human breath at 10-1000 ppb concentrations.
Water had to be completely removed from the breath via a moisture trap, since water interfered with the NH3 chemisorption chemistry. Potential applications of this sensor platform in breath analysis are discussed
Herein, ammonia sensors with ppb sensitivity, with possible application in breath analysis, were investigated.
Introduction
Methods for measurement of ammonia (NH3) are relevant to environmental, combustion and health related industries. Ammonia in the atmosphere arises primarily from anthropogenic sources, including agriculture (nitrogen fixation, ammonification) and emissions from chemical industry involved in development of refrigeration and fertilizers. Ammonia is a lachrymatory gas, and breathing ammonia at high concentrations (˜1000 ppm) can induce laryngospasms, and cause bronchiectasis. Thus, there is a need for environmental ammonia monitors. The transportation industry is also interested in measuring ammonia from exhaust emissions, air quality control in passenger compartment and in a new generation of lean-burn combustion engines, where the exhaust gas after-treatment includes reaction of nitrogen oxides with ammonia. Ammonia is also produced in the human body, and monitoring ammonia in exhaled human breath has potential applications in healthcare settings (e.g., for disease diagnosis). As an example, breath ammonia measurement can be used to probe several diseases including malfunctioning of liver and kidney, H. pylori infection, and halitosis. The concentration ranges over which ammonia detection is relevant for these applications range from 0.1 ppm (health) to hundreds of ppm (environmental).
Different measurement principles have been applied for the detection of ammonia, including optical spectroscopy, electrochemistry and wet-chemistry methods. A particularly challenging application is the detection of ammonia in human breath. Tunable diode laser absorption spectroscopy has been used to detect ammonia in breath, with detection limit of 1 ppm. A quantum cascade laser diode was able to measure ammonia as low as 4 ppb. Other strategies include use of quartz crystal microbalance and liquid-film conductive sensor. Sensors based on conducting polymer junctions can detect ppb ammonia in human breath, and a p-n heterojunction polyaniline-TiO2 sensor is reported to have ppt sensitivity. Mass spectrometry also can measure ammonia down to ppb levels. Instruments for measuring ammonia are often bulky, and there is a drive for obtaining miniaturized sensors.
Solid state electrochemical sensors have been developed for monitoring ammonia. This technology is attractive since high sensitivity, selectivity, and fast response time are possible. In addition, these devices have advantages of low power consumption, light-weight, low maintenance cost, harsh environment tolerance and portability. There are numerous papers on resistive semiconducting metal oxide sensors for ammonia. The working principle of these devices is associated with the adsorption of gas molecules on the oxide's surface inducing charge transfer, which result in changes in resistance of the oxide. Semiconducting metal oxides such as n-type WO3, SnO2, In2O3, ZnO, TiO2, MoO3 as well as p-type Cr2O3, NiO, CuO, have been studied as sensing materials to detect NH3. To promote sensitivity and selectivity, noble metals like Pt, Pd, Au, and Ag have been introduced to metal oxides. Of these, MoO3-based sensors have been developed for measuring ammonia in human breath.
However, developing an electrochemical sensor platform that can measure low concentrations of ammonia in the environment, in optimizing combustion processes and in human breath is still a challenge. There is the need for ppb sensitivity, discrimination against other gases present at much higher concentrations, and in the case of combustion, the ability to tolerate harsh environments, and be insensitive to other exhaust gases.
Mixtures of p- and n-semiconducting oxides can improve sensor performance. Examples include anatase/rutile for CO detection, ZnO/NiO for NH3 detection, In2O3/NiO for ethanol detection, and CuO/SnO2 for H2S detection. These designs are mixtures of p- and n-powders, or the p-type material grown on n-type powders and vice versa. In addition, isotype heterojunctions, prepared by mixing powders, such as WO3 and ZnO have also shown selective gas sensing.
Provided herein is a sensor device that includes an adjacent alignment of p-type NiO and n-type In2O3 deposited on a gold microspring array. This semiconductor hetero-junction structure can be used for the detection of ammonia at ppb levels, while discriminating against nitric oxide at ppb levels, and carbon monoxide at significantly higher ppm concentrations. The potential application of detection of ammonia in human breath samples is also demonstrated, suggesting the application of this sensor platform in a future breath monitoring device.
Chemicals and Materials
Indium (II) oxide (99.99%, metals basis, ˜325 mesh powder), nickel (II) oxide (99.998%, metals basis), alpha-terpineol (96%), gold wires (0.127 mm dia, 99.99%) were purchase from Alfa Aesar (Ward Hill, USA). The plastic substrates with gold microspring arrays were obtained from FormFactor, Inc. (USA). The interdigitated electrodes were obtained from Case Western Reserve University. All test gases including nitrogen, oxygen, ammonia and carbon monoxide were supplied by Praxair (Danbury, USA).
Sensor Fabrication
The procedures of sensor fabrication is shown in
Characterization
The phase and crystallinity of the metal oxides were analyzed by a Bruker D8 Advance X-ray diffractometer. The surface morphology of the sensor was investigated by a Quanta 200 scanning electron microscope. The chemical state of the metal oxides was examined by a Kratos X-ray photoelectron spectrometer with a mono Al source. The current-voltage measurement was performed on a CHI760D electrochemical workstation. The gas-solid interactions were studied by a PerkinElmer Spectrum 400 FTIR spectrometer coupled with a diffuse reflectance accessory. The Raman mapping of the interface was performed on a Renishaw—Smiths Raman Microprobe.
Gas Sensing Measurements
All gas sensing experiments were performed within a quartz tube placed inside a tube furnace (Lindberg/Blue) at 300° C., with a PC-controlled gas delivery system with calibrated mass flow controllers (Sierra Instruments INC.). The test gas mixtures containing different concentrations of NH3 at constant oxygen content of 20 vol % were prepared by diluting NH3 with O2 and N2. The total flow rate was maintained at 200 cm3/min. The resistance of the sensor was recorded by an Agilent 34972A LXI data acquisition/switch unit or a HP34970A at a scan rate of 0.1 Hz.
Human Breath Sensing Measurements
A system that simulates human breath with trace ammonia gas was developed. The system comprises a Mylar bag containing exhaled human breath samples and an ammonia gas cylinder. The trace ammonia gas at physiologically relevant concentrations was determined by controlling the flow rates of breath samples from the Mylar bags and ammonia supply, respectively. The total flow rate was maintained at 200 cm3/min. Three setups were designed. A first setup used a 37° C. water vapor bath to keep a constant humidity in the mixture of NH3 and breath sample. The second setup used a dry ice/acetonitrile bath maintained at −20 to −25° C. to completely remove humidity in the mixture of breath+NH3 and also an ice bath to reduce humidity. In both these setups, the breath sample was used as the background and NH3 was spiked into the sample at increasing concentrations. In the third setup, air was used as the background, and the breath sample was measured, and then increasing amounts of NH3 was added in, all gases passing through a moisture trap at −20 to −25° C.
Results
Characterization
The two semiconducting oxides of interest in this study—NiO and In2O3—were obtained from commercial sources. Detailed characterization is presented in
NiO: The X-ray diffraction (XRD) pattern (
In2O3: XRD pattern of In2O3 shown in
Sensor Characteristics
Design:
Microstructure:
Electrical Characteristics
Infrared Spectroscopy
Infrared spectroscopy of the NiO surface was examined upon NH3 exposure at 300° C.
Sensing Characteristics
Carbon monoxide: All sensing experiments were done with 2 min pulses of the analyte gas.
Nitric Oxide:
Ammonia: With NH3 (1 ppm, 0.5 ppm, 0.1 ppm) on for a 2 min pulse, as shown in
Mixture of gases: These experiments were then repeated with both NH3 and CO in the gas stream with the 2 min pulses of gas.
Human Breath Samples
Three sets of experiments were carried out with human breath samples, and are schematically represented in
Using breath as background: Breath samples were collected in Mylar bags. These samples were independently mixed via mass flow controllers with 10, 50, 100, 500, 1000 ppb of NH3 and these samples were analyzed using the combined NiO—In2O3 sensor (CH3). In these experiments, the background signal was that of the breath alone, followed by introducing NH3 in the gas mixture. The first experiment involved equilibrating the breath with water vapor at 37° C. with a measured relative humidity of 93% (
Using air as background: In another set of experiments, air was used as the background (
Discussion
In order to demonstrate the practical application of the sensor described in this paper, human breath sample was utilized as a proof-of-principle sample. The detection of NH3 in human breath at ˜ppb levels could be helpful for diagnosis of various diseases. Typical levels for CO and NO in human breath are at ppm and ppb levels, respectively. The outcome of this study is a sensor that can detect NH3 at low concentrations (<1000 ppb) with selectivity against CO at ppm and NO at ppb levels.
The sensor design employs a mixture of p- and n-type semiconducting oxide, but physically separated with a common interface (
The two oxides examined here are n-type In2O3 and p-type NiO. The conduction model for both n-type and p-type metal oxide gas sensors has been reviewed. In both n- and p-type oxides, oxygen ionosorption plays a key role in the sensing paradigm. In the case of n-type, such chemisorption leads to a decrease of majority carrier electrons at the surface of grains, whereas in p-type oxides, the oxygen ionosorption leads to a surface accumulation of holes. In n-type oxides, conduction is through the bulk of the oxide, whereas in p-type, conduction is along the surface. Under certain conditions, resistance changes from n- to p-type and vice versa has been observed. This effect is observed on Fe2O3, MoO3, In2O3, SnO2, TeO2 and TiO2, and several explanations have been proposed, including formation of a surface inversion layer driven via surface adsorption, different types of surface reactions, influence of polymorphs and morphology, as well as the effect of ionic dopants/impurities.
Resistance changes in NiO and In2O3 upon exposure to CO and NO were observed (
Under conditions in which NH3 can react with chemisorbed oxygen, it usually behaves as a reducing gas, with proposed reactions such as:
2NH3+3O−→N2+3H2O+3e (1)
2NH3+5O−→2NO+3H2O+5e (2)
These reactions are more favorable at higher temperature. The resistance changes upon interaction of NH3 with metal oxides can be anomalous. For n-type oxides, such as In2O3 and WO3, at lower temperatures (<300° C.), there is a resistance decrease. However at higher temperatures, initial resistance decrease is followed by a resistance increase. For n-type semiconductors, NO, the product of NH3 oxidation upon chemisorption will lead to an increase in resistance. This competition between NH3 oxidation and NO chemisorption is used to explain the anomalous sensing behavior. For avoiding the anomalous sensing behavior due to NOx, low temperature operation or the use of catalysts have been suggested. Other explanations for anomalous behavior, as in hexagonal-WO3 have been ascribed to the formation of an inversion layer.
Our data on In2O3 at 300° C. indicates that NH3 is behaving as a reducing gas (
The in situ IR spectra shown in
Several previous studies have noted a band in the 1200-1300 cm−1 region upon oxygen chemisorption on metal oxides. On Fe2O3, bands between 1250-1350 cm−1 have been assigned to perturbed O2− species, and in particular, the band at 1270 cm−1 is prominent and stable up to 300° C. There are few infrared studies of oxygen adsorption on NiO, bands at 1070 and 1140 cm−1 were observed at 77K and assigned to O2−. On Fe2O3, bands in the 900-1100 cm−1 were assigned to O22− species. Formation of O on NiO has been proposed, though no distinct infrared bands were identified. Peroxo species (O22−) have been proposed upon oxygen adsorption on NiO. On CuCl and CuBr, a band around 1270 cm−1 has been assigned to O2 coordinated with Cu+, and intensity of this infrared band also decreased upon exposure to NH3. Based on these studies, the band at 1267 cm−1 (
The reactivity of NH3 on metal oxide surfaces is enhanced in the presence of oxygen. On Mg (0001) surface, NH3 was reactive with the surface only in the presence of oxygen. Chemisorbed oxygen on Ni (110) and Ni (100) is reactive with NH3 with H abstraction and formation of NHx species. Surface spectroscopic studies have shown the high reactivity of NH3 with adsorbed oxygen on Ni (111).
It has been proposed that the O2− is in equilibrium with O−:
O2−⇄+O− (3)
NH3 chemisorption at lower temperatures can lead to NH2 and OH− via reaction with the O−:
Mx+ . . . NH3+O−→Mx+ . . . NH2+OH− (4)
Ammonia adsorption on alumina surface (acid/base sites) can lead to NH2 and OH formation for about 10% of all the NH3 molecules that are absorbed. Bands due to NH2 were reported at 3386 and 3355 cm−1. Dissociative chemisorption of NH3 to NH2 and OH driven by oxygen functionality is noted on epoxide groups in reduced graphene oxide, with vibrational bands assigned as 3208, 3270 cm−1 (NH2) and 3400 cm−1 (OH). With the 1 ppm NH3 on NiO, bands due to NH2 were observed, but with 100 ppm NH3 on NiO at 300° C., and subsequent cooling to room temperature, a band appears at 3220 cm−1 in the presence of O2, but not in the presence of only N2 (these spectra are shown in
Based on these observations, the anomalous behavior of 1 ppm NH3 observed in
The transient decrease in resistance upon exposure of low levels of NH3 on NiO was exploited to amplify the sensor signal. This was done by exposing the NiO to only 2 min of NH3, thus giving time for the chemisorption effects to occur (reactions 3 and 4,
Since the need for detecting NH3 in human breath is of the order of hundreds of ppb, breath samples were investigated as possible samples for use with this sensor. The high humidity in breath posed a significant interference (
By removing the humidity, the sensor can detect NH3 that is mixed into the breath. We have done the breath+NH3 experiments in two ways. The breath is used as the background sample, and any increase in NH3 in breath can be measured (
This example demonstrates using p-type of NiO and n-type In2O3 placed side-by-side on a substrate with common interface as a sensor platform. The adjacent placement of the oxides allows for ease of variation of the amount of oxide to be included for making the resistance measurements in the presence of analyte gas. With this strategy, the change in resistance with 3-10 ppm CO was almost nil, since In2O3 and NiO give opposite responses to CO. Ammonia is also a reducing gas, but at low concentrations of NH3 (<1 ppm) at 300° C., the response with In2O3 was a decrease in resistance, but with NiO, the resistance change was anomalous. For the first 8 min of a 10 min exposure to NH3, there was a resistance decrease followed by a gradual resistance increase over the next 20 min, followed by a 10 min decrease to baseline resistance. With the help of in situ infrared spectroscopy, this behavior was correlated with NH3 chemisorption and involvement of O2− species. Advantage was taken of the transient decrease with NH3 on NiO to design a sensor that shows a resistance decrease for both NiO and In2O3 by controlling the gas pulses to a duration of 2 min. With this strategy, combining the two oxides enhanced the signal of NH3, allowing ready detection at 100 ppb concentration. These sensors were used to detect NH3 that was mixed with human breath. As long as the humidity is completely removed from the breath sample, 10-1000 ppb of added ammonia could be detected. Water interference arises from competing reactions with O2− and the transient decrease in resistance with NH3 on NiO is no longer observed, thus removing the amplification. A potential application of such a sensor would be in H. pylori diagnosis.
The devices, systems, and methods of the appended claims are not limited in scope by the specific devices, systems, and methods described herein, which are intended as illustrations of a few aspects of the claims. Any devices, systems, and methods that are functionally equivalent are intended to fall within the scope of the claims. Various modifications of the devices, systems, and methods in addition to those shown and described herein are intended to fall within the scope of the appended claims. Further, while only certain representative devices, systems, and method steps disclosed herein are specifically described, other combinations of the devices, systems, and method steps also are intended to fall within the scope of the appended claims, even if not specifically recited. Thus, a combination of steps, elements, components, or constituents may be explicitly mentioned herein or less, however, other combinations of steps, elements, components, and constituents are included, even though not explicitly stated.
The term “comprising” and variations thereof as used herein is used synonymously with the term “including” and variations thereof and are open, non-limiting terms. Although the terms “comprising” and “including” have been used herein to describe various embodiments, the terms “consisting essentially of” and “consisting of” can be used in place of “comprising” and “including” to provide for more specific embodiments of the invention and are also disclosed. Other than where noted, all numbers expressing geometries, dimensions, and so forth used in the specification and claims are to be understood at the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, to be construed in light of the number of significant digits and ordinary rounding approaches.
Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of skill in the art to which the disclosed invention belongs. Publications cited herein and the materials for which they are cited are specifically incorporated by reference.
This application claims the benefit of U.S. Provisional Patent Application Ser. No. 62/262,067 filed Dec. 2, 2015, the disclosure of which is expressly incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62262067 | Dec 2015 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 15781460 | Jun 2018 | US |
| Child | 17142079 | US |
