Patent Publication Number: US-2021172904-A1

Title: Container including analyte sensing device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application is a continuation-in-part application and claims priority to U.S. patent application Ser. No. 16/887,293 entitled “RESONANT GAS SENSOR” filed on May 29, 2020, which claims priority to U.S. Provisional Patent Application No. 62/815,927 entitled “RESONANT GAS SENSOR” filed on Mar. 8, 2019 and is a continuation-in-part application of U.S. patent application Ser. No. 16/706,542 entitled “RESONANT GAS SENSOR” filed on Dec. 6, 2019, which is a continuation application of U.S. patent application Ser. No. 16/239,423 entitled “RESONANT GAS SENSOR” filed on Jan. 3, 2019, which claims priority to U.S. Provisional Patent Application No. 62/613,716 entitled “VOLATILES SENSOR” filed on Jan. 4, 2018. This patent application also claims priority to U.S. Provisional Patent Application No. 62/979,095 entitled “MULTIVARIATE IMPEDANCE SPECTROSCOPY SENSING” filed on Feb. 20, 2020, and to U.S. Provisional Patent Application No. 63/088,541 entitled “MULTIVARIATE CHEMICALLY-FUNCTIONALIZED CARBON-BASED RESONANT IMPEDANCE SPECTROSCOPY SENSOR ARRAYS” filed on Oct. 7, 2020, all of which are assigned to the assignee hereof. The disclosures of all prior applications are considered part of and are incorporated by reference in this patent application in their respective entireties. 
    
    
     TECHNICAL FIELD 
     This disclosure relates generally to detecting analytes, and, more particularly, to increasing the accuracy of analyte sensing devices. 
     DESCRIPTION OF RELATED ART 
     Chemical sensors operate by generating a signal in response to the presence of a particular chemical. Conventional analyte sensors typically require relatively high power energy sources to detect relatively low concentrations of analytes (such as less than 1 part per-billion (ppb)), which has made widespread adoption of such sensors impractical. Further improvements of chemical and vapor sensors are desirable. 
     SUMMARY 
     This Summary is provided to introduce in a simplified form a selection of concepts that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to limit the scope of the claimed subject matter. 
     One innovative aspect of the subject matter described in this disclosure may be implemented as a sensing device for detecting analytes. The sensing device may include a substrate and a sensor array. The sensor array may be arranged on the substrate, and may include a plurality of carbon-based sensors. In some implementations, a first carbon-based sensor disposed between a first pair of electrodes may be configured to detect a presence of each analyte of a first group of analytes, and a second carbon-based sensor disposed between a second pair of electrodes may be configured to detect a presence of each analyte of a second group of analytes, where the second group of analytes is a subset of the first group of analytes. In some instances, the first group of analytes may include at least twice as many different analytes as the second group of analytes. In some implementations, the first carbon-based sensor may be configured to generate a first output signal in response to detecting the presence of one or more analytes of the first group of analytes, and the second carbon-based sensor may be configured to generate a second output signal in response to confirming the presence of the one or more analytes detected by the first carbon-based sensor. In one implementation, the first and second output signals may be currents based at least in part on an alternating current applied to the first and second carbon-based sensors. In some instances, a ratio of the current of the first output signal and the alternating current may be indicative of a concentration of at least one of the detected analytes, and a ratio of the current of the second output signal and the alternating current may be indicative of a concentration of at least one of the confirmed analytes. 
     In other implementations, the first and second output signals may be indicative of the impedances of the first and second carbon-based sensors, respectively. In some aspects, the first output signal may indicate a change in impedance of the first carbon-based sensor caused by exposure to one or more analytes of the first group of analytes, and the second output signal may indicate a change in impedance of the second carbon-based sensor caused by exposure to one or more analytes of the second group of analytes. In some other implementations, the first and second output signals may indicate frequency responses of the first and second carbon-based sensors, respectively. In some instances, the frequency response of the first carbon-based sensor may be indicative of the presence or absence of each analyte of the first group of analytes, and the frequency response of the second carbon-based sensor may be indicative of the presence or absence of each analyte of the second group of analytes. The frequency responses may be based on electrochemical impedance spectroscopy (EIS) sensing or resonant impedance spectroscopy (RIS) sensing. 
     In various implementations, the first carbon-based sensor may be functionalized with a first material configured to react with each analyte of the first group of analytes, and the second carbon-based sensor may be functionalized with a second material configured to react only with the analytes of the second group of analytes. In some instances, the first material may be cobalt-decorated carbon nano-onions (CNOs) configured to detect a presence of one or more of triacetone triperoxide (TATP), toluene, ammonia, or hydrogen sulfide (H 2 S), and the second material may be iron-decorated three-dimensional (3D) graphene-inclusive structures configured to confirm the presence of toluene. 
     The substrate may be paper, a flexible polymer, or other suitable material. In some implementations, the substrate and the sensor array may be integrated within a label configured to be removably printed onto a surface of a package or container. In some aspects, each of the carbon-based sensors may be printed on the substrate using a different carbon-based ink, and the pairs of electrodes may be printed on the substrate using an ohmic-based ink. In some instances, the first and second carbon-based sensors may be stacked on one another. In other instances, the first and second carbon-based sensor may be disposed next to one another. 
     In some implementations, each of the carbon-based sensors may include a plurality of different graphene allotropes. In some aspects, the different graphene allotropes of a respective carbon-based sensor may include one or more microporous pathways or mesoporous pathways. Each of the carbon-based sensors may include a polymer configured to bind the plurality of different graphene allotropes to one another. The polymer may include humectants configured reduce a susceptibility of a respective carbon-based sensor to humidity. 
     Another innovative aspect of the subject matter described in this disclosure may be implemented as a sensing device for detecting analytes within a package or container. In various implementations, the sensing device may include a substrate, one or more electrodes, and a sensor array. The sensor array may be disposed on the substrate, and may include a plurality of carbon-based sensors coupled to the one or more electrodes. In some implementations, the carbon-based sensors may be configured to react with unique groups of analytes in response to an electromagnetic signal received from an external device. In some instances, the carbon-based sensors may be configured to resonate at different frequencies in response to the electromagnetic signal. Each of the one or more electrodes may be configured to provide an output signal indicating whether a corresponding carbon-based sensor detected one or more analytes in a respective group of the unique groups of analytes. In some instances, each output signal may indicate an impedance or reactance of the corresponding carbon-based sensor. 
     In addition, or in the alternative, a first frequency response of the first carbon-based sensor to the electromagnetic signal may be indicative of the presence or absence of the analytes of the first group of analytes within the package or container, and a second frequency response of the second carbon-based sensor to the electromagnetic signal may be indicative of the presence or absence of the analytes of the second group of analytes within the package or container. In some instances, the first frequency response may be based at least in part on exposure of the first carbon-based sensor to the electromagnetic signal for a first period of time, and the second frequency response may be based at least in part on exposure of the second carbon-based sensor to the electromagnetic signal for a second period of time that is longer than the first period of time. In some instances, the second period of time is at least twice as long as the first period of time. The first and second frequency responses may be based on resonant impedance spectroscopy (RIS) sensing. 
     In various implementations, a first carbon-based sensor may be functionalized with a first material configured to detect the presence of each analyte of a first group of analytes, and a second carbon-based sensor may be functionalized with a second material configured to detect the presence of each analyte of a second group of analytes. The second group of analytes may be a subset of the first group of analytes, and the second material may be different than the first material. In some aspects, the first group of analytes may include at least twice as many different analytes as the second group of analytes. In some instances, the first material may be cobalt-decorated carbon nano-onions (CNOs) configured to detect the presence of one or more of triacetone triperoxide (TATP), toluene, ammonia, or hydrogen sulfide (H 2 S), and the second material may be iron-decorated three-dimensional (3D) graphene-inclusive structures configured to confirm the presence of toluene. In various implementations, a third carbon-based sensor may be functionalized with a third material configured to detect the presence of each analyte of a third group of analytes, where the third group of analytes may be another subset of the first group of analytes, and the third material may be different than the first and second materials. 
     In some implementations, at least two of the carbon-based sensors may be juxtaposed in a planar arrangement on the substrate. In other implementations, the carbon-based sensors may be stacked on top of one another in a vertical arrangement. For example, in one implementation, the carbon-based sensors may form a permittivity gradient. In some aspects, a single electrode may be configured to provide an output signal indicating whether the stacked carbon-based sensors detected one or more analytes. The single electrode may also be configured to provide the output signal to the external device. 
     The substrate may be paper, a flexible polymer, or other suitable material. In some implementations, the substrate and the sensor array may be integrated within a label that can be removably printed on a surface of the package or container. In some aspects, each of the carbon-based sensors may be printed on the substrate using a different carbon-based ink, and the one or more electrodes may be printed on the substrate using an ohmic-based ink. In some implementations, each of the carbon-based sensors may include a plurality of different graphene allotropes. In some aspects, the different graphene allotropes of a respective carbon-based sensor may include one or more microporous pathways or mesoporous pathways. Each of the carbon-based sensors may include a polymer configured to bind the plurality of different graphene allotropes to one another. The polymer may include humectants configured reduce a susceptibility of a respective carbon-based sensor to humidity. 
     Another innovative aspect of the subject matter described in this disclosure may be implemented as a sensing device for monitoring a battery pack. The sensing device may include a substrate and a plurality of carbon-based sensors disposed on the substrate. Each of the carbon-based sensors may be coupled between a corresponding pair of electrodes. In some implementations, the 3D graphene-based sensing materials of a first carbon-based sensor may be functionalized with a first material configured to detect a presence of each analyte of a first group of analytes, and the 3D graphene-based sensing materials of a second carbon-based sensor may be functionalized with a second material configured to detect a presence of each analyte of a second group of analytes. In some aspects, the second group of analytes is a subset of the first group of analytes, and the group of analytes may include at least twice as many different analytes as the second group of analytes. In some instances, the first and second carbon-based sensors may be stacked on top of one another. In other instances, the first and second carbon-based sensors may be disposed next to one another. In some implementations, the carbon-based sensors may be carbon-based inks printed on the substrate. In some instances, the first carbon-based sensor may be a first carbon-based ink, and the second carbon-based sensor may be a second carbon-based ink different than the first carbon-based ink. 
     The first carbon-based sensor may be configured to generate a first output signal in response to detecting the presence of one or more analytes of the first group of analytes, and the second carbon-based sensor may be configured to generate a second output signal in response to confirming the presence of the one or more analytes detected by the first carbon-based sensor. In some implementations, the sensing device may include an input terminal to receive an alternating current, and the first and second output signals may be currents based at least in part on the alternating current. In some instances, a first difference between the alternating current and the first output signal may be indicative of the presence or absence of one or more analytes of the first group of analytes, and a second difference between the alternating current and the second output signal may be indicative of the presence or absence of one or more analytes of the second group of analytes. 
     In other implementations, the first output signal may indicate a change in impedance of the first carbon-based sensor caused by exposure to one or more analytes of the first group of analytes, and the second output signal may indicate a change in impedance of the second carbon-based sensor caused by exposure to one or more analytes of the second group of analytes. In some instances, a relatively small impedance change of a respective carbon-based sensor may indicate an absence of a corresponding group of analytes, and a relatively large impedance change of the respective carbon-based sensor may indicate a presence of the corresponding group of analytes. 
     In some other implementations, the sensing device may include an antenna configured to receive an electromagnetic signal from an external device, and the first and second output signals may be frequency responses of the 3D graphene-based sensing materials of the first and second carbon-based sensors, respectively, to the electromagnetic signal. For example, the frequency response of the 3D graphene-based sensing materials of the first carbon-based sensor may be indicative of the presence or absence of one or more analytes of the first group of analytes, and the frequency response of the 3D graphene-based sensing materials of the second carbon-based sensor may be indicative of the presence or absence of one or more analytes of the second group of analytes. In some aspects, the frequency responses may be based on resonant impedance spectroscopy (RIS) sensing. 
     In various implementations, at least one of the output signals may indicate an operating mode of the battery pack. In some implementations, the at least one output signal may indicate a normal mode based on an absence of the analytes of the first group of analytes, may indicate a maintenance mode based on the presence of one or more analytes of the first group of analytes not exceeding a threshold level, or may indicate an emergency mode based on the presence of one or more analytes of the first group of analytes exceeding a threshold level. In addition, or in the alternative, the first output signal may be indicative of a concentration level of one or more analytes of the first group of analytes, and the second output signal may be indicative of a concentration level of one or more analytes of the second group of analytes. 
     In some implementations, the analytes of the first and second groups of analytes may include one or more volatile organic compounds (VOCs). The one or more volatile organic compounds (VOCs) include any one or more of carbon dioxide (CO 2 ), carbon monoxide (CO), nitrogen dioxide (NO 2 ), one or more hydrocarbons including methane (CH 4 ), ethylene (C 2 H 4 ), ethane (C 2 H 6 ), or propane (C 3 H 8 ), one or more acids including hydrochloric acid (HCl) or hydrofluoric acid (HF), one or more fluorinated hydrocarbons including phosphorus oxyfluoride, hydrogen cyanide (HCN), one or more aromatics including benzene (C 6 H 6 ), toluene (C 7 H 8 ), ethanol (C 2 H 5 OH), hydrogen, carbonate based electrolytes including ethylene carbonate (C 3 H 4 O 3 ), dimethyl carbonate (C 3 H 6 O 3 ), propylene carbonate (C 4 H 3 O 3 ), or one or more reduced sulfur compounds including thiols having a form of R—SH. In some aspects, each of the 3D graphene-based sensing materials may be configured to adsorb the VOCs. In some aspects, each of the carbon-based sensors may include a plurality of different graphene allotropes. The plurality of different graphene allotropes of a respective carbon-based sensor may include one or more microporous pathways or mesoporous pathways. 
     Another innovative aspect of the subject matter described in this disclosure may be implemented as a container for storing one or more items. The container may include a surface defining a volume of the container and a label printed on the container. In various implementations, the label may include a substrate, a plurality of carbon-based sensors printed on the substrate, and one or more electrodes printed on the substrate. The carbon-based sensors may be collectively configured to detect a presence of one or more analytes within the container. In some implementations, each of the carbon-based sensors may be configured to react with a unique group of analytes in response to an electromagnetic signal received from an external device. The one or more electrodes may be coupled to at least some of the carbon-based sensors, and may be configured to provide one or more output signals indicating the presence or absence of the one or more analytes within the container. In some implementations, a first electrode coupled to the first carbon-based sensor may be configured to indicate the presence of one or more analytes of the first group of analytes, and a second electrode coupled to the second carbon-based sensor may be configured to confirm the presence of the analytes detected by the first carbon-based sensor. In some aspects, the carbon-based sensors may be configured to resonate at different frequencies in response to the electromagnetic signal. 
     In some implementations, a first carbon-based sensor may be functionalized with a first material configured to detect the presence of each analyte of a first group of analytes, and a second carbon-based sensor may be functionalized with a second material configured to detect the presence of each analyte of a second group of analytes, where the second group of analytes may be a subset of the first group of analytes. In some aspects, the first group of analytes may include at least twice as many different analytes as the second group of analytes. The second material may be different than the first material. For example, in one implementation, the first material may be cobalt-decorated carbon nano-onions (CNOs) configured to detect the presence of one or more of triacetone triperoxide (TATP), toluene, ammonia, or hydrogen sulfide (H 2 S), and the second material may be iron-decorated three-dimensional (3D) graphene-inclusive structures configured to confirm the presence of toluene. For another example, a third carbon-based sensor may be functionalized with a third material configured to detect the presence of each analyte of a third group of analytes, where the third group of analytes is another subset of the first group of analytes, and the third material is different than the first and second materials. 
     In some implementations, each output signal may indicate a frequency response of a corresponding carbon-based sensor to the electromagnetic signal. In some instances, a first frequency response of the first carbon-based sensor to the electromagnetic signal may be indicative of the presence or absence of the analytes of the first group of analytes within the container, and a second frequency response of the second carbon-based sensor to the electromagnetic signal may be indicative of the presence or absence of the analytes of the second group of analytes within the container. The first frequency response may be based at least in part on exposure of the first carbon-based sensor to the electromagnetic signal for a first period of time, and the second frequency response may be based at least in part on exposure of the second carbon-based sensor to the electromagnetic signal for a second period of time that is longer than the first period of time. In some aspects, the second period of time is at least twice as long as the first period of time. The first and second frequency responses may be based on resonant impedance spectroscopy (RIS) sensing. 
     In various implementations, an antenna may be printed on the substrate and configured to drive a current through the carbon-based sensors in response to the electromagnetic signal. In some aspects, each output signal may indicate an impedance or reactance of a corresponding carbon-based sensor to the current. The impedance or reactance of the carbon-based sensors may be indicative of the presence or absence of the one or more analytes within the container. For example, the impedance or reactance of the first carbon-based sensor may be indicative of the presence or absence of an analyte of the first group of analytes, and the impedance or reactance of the second carbon-based sensor may be indicative of the presence or absence of an analyte of the second group of analytes. In some instances, at least two of the carbon-based sensors are juxtaposed in a planar arrangement on the substrate. In other instances, the carbon-based sensors are stacked on top of one another. In some aspects, the carbon-based sensors may form a permittivity gradient. 
     In some implementations, each of the carbon-based sensing materials may include a plurality of different graphene allotropes. In some aspects, the different graphene allotropes of a respective carbon-based sensor may include one or more microporous pathways or mesoporous pathways. Each of the carbon-based sensors may include a polymer configured to bind the plurality of different graphene allotropes to one another. The polymer may include humectants configured reduce a susceptibility of a respective carbon-based sensor to humidity. 
     Details of one or more implementations of the subject matter described in this disclosure are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages will become apparent from the description, the drawings and the claims. Note that the relative dimensions of the following figures may not be drawn to scale. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an example sensing device configured to detect analytes, according to some implementations. 
         FIG. 2  is an illustration depicting the sensing device of  FIG. 1  coupled to a receptor, according to some implementations. 
         FIG. 3  is an illustration depicting the sensing device of  FIG. 1  configured to detect analytes in a battery pack, according to some implementations. 
         FIG. 4  is an illustration depicting the sensing device of  FIG. 1  configured to detect analytes in a battery pack, according to some implementations. 
         FIG. 5  is an illustration depicting reactions between one or more analytes and the sensing device of  FIG. 1 , according to some implementations. 
         FIG. 6  is a block diagram of an analyte detection system that includes the sensing device of  FIG. 1 , according to some implementations. 
         FIGS. 7A-7E  show sensor arrays configured to detect analytes, according to various implementations. 
         FIG. 8  shows a flow chart depicting an example operation for fabricating at least some of the sensing devices disclosed herein, according to some implementations. 
         FIG. 9  shows another sensor array, according to some implementations. 
         FIG. 10A  shows an example sensor configuration, according to some implementations. 
         FIG. 10B  shows an example sensor configuration, according to other implementations. 
         FIGS. 11A-11G  show illustrations of various structured carbon materials that can be used in the sensing devices disclosed herein, according to some implementations. 
         FIGS. 12A-12F  show example frequency responses of resonance impedance sensors to various analytes, according to some implementations. 
         FIG. 13A  shows the real (Z′) impedance component of an example frequency response of electrochemical impedance sensors, according to some implementations. 
         FIG. 13B  shows the imaginary (Z″) impedance component of an example frequency response of electrochemical impedance sensors, according to some implementations. 
         FIG. 14A  shows an example baseline frequency response and an example frequency response to hydrogen peroxide, according to some implementations. 
         FIG. 14B  shows example frequency responses to acetone and water, according to some implementations. 
         FIG. 14C  shows example frequency responses to ethanol and ammonia, according to some implementations. 
     
    
    
     Like reference numbers and designations in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     The following description is directed to some example implementations for the purposes of describing innovative aspects of this disclosure. However, a person having ordinary skill in the art will readily recognize that the teachings herein can be applied in a multitude of different ways. The described implementations can be implemented in any environment to detect the presence of a plurality of different analytes within or near any device, battery pack, package, container, structure, or system that may be susceptible to analytes. Moreover, implementations of the subject matter disclosed herein can be used to detect the presence of any harmful or dangerous chemical, gas, or vapor. As such, the disclosed implementations are not to be limited by the examples provided herein, but rather encompass all implementations contemplated by the attached claims. Additionally, well-known elements of the disclosure will not be described in detail or will be omitted so as not to obscure the relevant details of the disclosure. 
     Batteries typically include a plurality of electrochemical cells that can be used to power a wide variety of devices including, for example, mobile phones, laptops, and electric vehicles (EVs), factories, and buildings. When batteries are exposed to harsh environmental conditions or become damaged, toxic chemicals and vapors within the electrochemical cells may leak from the battery&#39;s casing and pose serious health and safety risks. When released from a battery, these toxic chemicals and vapors can cause respiratory problems, allergic reactions, and may even explode. The chemicals typically used in the cells of Lithium-ion batteries may be particularly dangerous due to their high reactivities and susceptibility to explosion when inadvertently released from the battery casing. As such, there is a need to quickly and accurately determine whether a particular battery or battery pack is leaking such toxic chemicals or vapors. Moreover, when the presence of one or more analytes (or other toxic chemicals or vapors) is detected, it may be desirable to determine the concentration of such analytes. It may also be desirable to predict battery failure and/or to determine the operational integrity of such batteries. 
     Various aspects of the subject matter disclosed herein relate to detecting a presence of one or more analytes in an environment. In accordance with various implementations of the subject matter disclosed herein, a sensing device may include a plurality of carbon-based sensors configured to the presence of a variety of different analytes. In some implementations, at least some of the carbon-based sensors may include different types of three-dimensional (3D) graphene-based sensing materials configured to react with different analytes or different groups of analytes. In some aspects, the sensing materials of different sensors may be functionalized with different materials, for example, to increase the sensitivity of each sensor to one or more corresponding analytes. 
     In some implementations, changes in the impedances of the sensors may be used to determine a presence of one or more analytes in a vicinity of the sensing device. In other implementations, changes in current flow through the sensors may be used to determine the presence of the one or more analytes in the vicinity of the sensing device. In some other implementations, frequency responses of the sensors may be used to determine the presence of the one or more analytes in the vicinity of the sensing device. In some aspects, the frequency responses of the sensors may be compared with one or more reference frequency responses corresponding to the one or more analytes to identify which analytes are present in the environment. In this way, the sensor systems disclosed herein can accurately detect the presence of a variety of different analytes in a given environment. 
     In one implementation, a first sensor may be configured to detect the presence of a relatively large number of different analytes, and one or more second sensors may be configured to confirm the presence of one or more analytes detected by the first sensor. Specifically, the first sensor may be configured to react with each analyte of a first group of analytes, and the one or more second sensors may be configured to react with corresponding second groups of analytes that are unique subsets of the first group of analytes. In some instances, the first sensor may be exposed to the surrounding environment for a relatively short period of time to provide an initial coarse indication of whether the analytes of the first group of analytes are present, and each of the second sensors may be exposed to the surrounding environment for a relatively long period of time to provide a fine indication of whether any of the analytes of the corresponding second group of analytes are present. For example, while the first sensor may be able to detect a greater number of analytes than any of the second sensors, configuring each of the second sensors to detect only one or two different analytes may increase the sensitivity of the second sensors to their respective “target” analytes, thereby increasing the accuracy with which the sensing device is able to detect the presence of various analytes. As such, when indications provided by the second sensors are used to confirm indications provided by the first sensor, the number of false positive indications decreases, which in turn increases overall accuracy of the sensing device. 
     Particular implementations of the subject matter described in this disclosure can be implemented to realize one or more of the following potential advantages. In some implementations, the sensing devices disclosed herein can not only detect the presence of a variety of analytes and other harmful chemicals and gases, but can also reduce the occurrence of false positives. Specifically, by using a first sensor to quickly detect a presence of one or more analytes of a group of analytes and using one or more second sensors to confirm the presence of analytes detected by the first sensor, aspects of the present disclosure can reduce the number of false positives indicated by the sensing device. This is in contrast to conventional analyte sensors that may not only be insensitive to differences between different analytes of a group of analytes and/or that do not employ a multi-tiered analyte detection system. 
       FIG. 1  shows an example sensing device  100  configured to detect analytes, according to some implementations. The sensing device  100  may include an array  110  of carbon-based sensors  120  disposed on a substrate  130 . In some aspects, each of the carbon-based sensors  120  may include a carbon-based sensing material  125  disposed between a corresponding pair of electrodes  121 - 122 , for example, as depicted in  FIG. 1 . In other aspects, the carbon-based sensors  120  may be coupled to only one electrode. The carbon-based sensors  120 , as well as their respective carbon-based sensing materials  125 , may be formed from any suitable materials that react to, or that can be configured to react to, a variety of different analytes. Reactions between the carbon-based sensors  120  and various analytes may be used to detect a presence of a particular analyte or a particular group of analytes. For example, the reactions may cause changes in current flow through one or more carbon-based sensors  120 , may cause changes in the impedances or reactance of one or more carbon-based sensors  120 , may produce unique or different frequency responses in one or more carbon-based sensors  120 , or any combination thereof. 
     In the example of  FIG. 1 , a plurality of different analytes  151 - 155  are in the presence of the sensing device  100 . Although only five analytes  151 - 155  are shown in  FIG. 1 , the sensing device  100  can detect a greater number of different analytes. In some aspects, the analytes  151 - 155  can include any vapor phase and/or fluidic composition including one or more volatile organic compounds (VOCs) such as (but not limited to) carbon dioxide (CO 2 ), carbon monoxide (CO), nitrogen dioxide (NO 2 ), one or more hydrocarbons including methane (CH 4 ), ethylene (C 2 H 4 ), ethane (C 2 H 6 ), or propane (C 3 H 8 ), one or more acids including hydrochloric acid (HCl) or hydrofluoric acid (HF), one or more fluorinated hydrocarbons including phosphorus oxyfluoride, hydrogen cyanide (HCN), one or more aromatics including benzene (C 6 H 6 ), toluene (C 7 H 8 ), ethanol (C 2 H 5 OH), hydrogen, or one or more reduced sulfur compounds including thiols having a form of R—SH. 
     In some implementations, the carbon-based sensors  120  may include carbon particulates or 3D graphene structures that react with (or that can be configured to react with) analytes associated with batteries, for example, to determine whether a particular battery is leaking analytes that may be harmful or dangerous. In other implementations, the carbon-based sensors  120  may include carbon particulates or 3D graphene structures that react with (or that can be configured to react with) a group of analytes deemed to be harmful or dangerous, either individually or in combination with each other. For example, the carbon-based sensors  120  may be configured to produce detectable reactions when exposed to acetone and hydrogen peroxide to detect a presence of acetone peroxide (which is highly explosive). For another example, one or more of the carbon-based sensors  120  may be configured to detect a presence of triacetone triperoxide (TATP) or tri-cyclic acetone peroxide (TCAP), which are trimers for acetone peroxide. 
     In some implementations, each of the sensors  120  may be configured to react with a unique group of analytes. In some aspects, the sensors  120  may be functionalized with different materials configured to detect different analytes or different groups of analytes. In one implementation, a first sensor of the sensor array  110  may be functionalized with a first material configured to detect a presence of a first group of analytes, and one or more second sensors of the sensor array  110  may be functionalized with second materials configured to detect a presence of one or more corresponding second groups of analytes, where the second materials are different than each other and are different than the first material, and the second groups of analytes are unique subsets of the first group of analytes. For example, the first sensor may be configured to detect each of the five analytes  151 - 155 , while each of the second sensors may be configured to detect only one of the five analytes  151 - 155 . The first sensor may sense the environment for a relatively short period of time to provide a coarse detection of any of the analytes  151 - 155 , and each of the second sensors may sense the environment for a relatively long period of time to confirm the presence of a respective one of the five analytes  151 - 155 . In this way, the one or more second sensors  120  may be used to verify the detection of various analytes by the first sensor  120 , thereby reducing or even eliminating false positives. 
     In other implementations, the sensors  120  may be configured to react with overlapping groups of analytes. In some other implementations, the sensors  120  may be configured to react with the same or similar groups of analytes. 
     The substrate  130  may be any suitable material. In some instances, the substrate may be paper or a flexible polymer. In other instances, the substrate  130  may be a rigid or semi-rigid material such as, for example, a printed circuit board. 
       FIG. 2  is an illustration  200  depicting the sensing device  100  of  FIG. 1  coupled to a receptor  180 , according to some implementations. The receptor  180  can be any suitable device, component, or mechanism capable or collecting, guiding, or steering analytes  151 - 155  present in a surrounding environment towards the sensing device  100 . As shown, the receptor  180  includes an inlet  182  and a plurality of outlets  184 . The inlet  182  may be configured to receive or attract the analytes  151 - 155  into the receptor  180 , and the outlets  184  may be configured to steer the analytes  151 - 155  towards one or more exposed surfaces of the sensing device  100 . In some implementations, each of the outlets  184  of the receptor  180  may be aligned with a corresponding sensor  120 , for example, so that analytes  151 - 155  entering the receptor  180  can be released and exposed to each of the sensors  120  of the array  110 . In this way, the receptor  180  may concentrate the analytes  151 - 155  on or near corresponding sensing materials  125  of the array  110 , thereby increasing the likelihood of detection by the sensing device  100 . For example, in instances for which the sensing device  100  is printed on a surface of a shipping package, a portion of the shipping package (e.g., a foldable flap) may be used as the receptor  180 . 
       FIG. 3  is an illustration  300  depicting the sensing device  100  of  FIG. 1  configured to detect a presence of analytes within or near a battery pack  310 , according to some implementations. The battery pack  310  is shown to include a plurality of battery cells  320  arranged as a planar array on a substrate  312 . One or more sensing devices  100  may be positioned near or coupled to a corresponding number of the battery cells  320  of the battery pack  310 . In some implementations, a subset of the battery cells  320  may be associated with the sensing devices  100  such that the number of sensing devices  100  is less than the number of battery cells  320 , for example, as depicted in the example of  FIG. 3 . In other implementations, each of the battery cells  320  may be associated with or coupled to a corresponding sensing device  100 . In some instances, the sensors  120  of a respective sensing device  100  may be stacked on top of one another (such as in a vertical arrangement). In other instances, the sensors  120  of the respective sensing device  100  may be disposed next to one another (such as in a planar arrangement). 
     The sensing devices  100  may be configured to detect a presence of analytes  340  leaked from one or more of the battery cells  320  of the battery pack  310  in a manner similar to that described above with reference to  FIG. 1 . Specifically, each of the sensors  120  may be coupled between a corresponding pair of electrodes  121 - 122  and may include a plurality of 3D graphene-based sensing materials  125  configured to detect a presence of certain analytes (such as the analytes  151 - 155  of  FIG. 1 ). In some implementations, the sensing materials  125  within different sensors  120  may be configured to detect the presence of different analytes or different groups of analytes. For example, in some instances, the sensing materials  125  of a first sensor  120   1  may be functionalized with a first material configured to detect a presence of each analyte of a first group of analytes, and the sensing materials  125  of a second sensor  1202  may be functionalized with a second material configured to detect a presence of each analyte of a second group of analytes, where the second group of analytes is a subset of the first group of analytes. In other implementations, the sensing materials  125  within different sensors  120  may be configured to detect the presence of the same analytes or the same group of analytes. 
     In various implementations, each of the sensors  120  within a respective sensing device  100  may be configured to provide an output signal in response to detecting the presence of one or more analytes. In some implementations, the output signal may be a current generated in response to an alternating current provided to the respective sensor  120 . In some instances, a difference between the alternating current and the output signal may be indicative of the presence or absence of the one or more analytes of the first group of analytes. In other implementations, the output signal may indicate a change in impedance of the corresponding sensor  120  caused by exposure to the one or more analytes. In some instances, a relatively small impedance change of the sensor  120  may indicate an absence of the one or more analytes, and a relatively large impedance change of the sensor  120  may indicate a presence of the one or more analytes. 
     In some other implementations, one or more of the sensing devices  100  may include an antenna (not shown for simplicity) configured to receive an electromagnetic signal from an external device, and the output signals may be frequency responses of the sensing materials  125  to the electromagnetic signal. For example, the frequency response of the sensing materials  125  of the first sensor  120   1  may be indicative of the presence or absence of the first group of analytes, and the frequency response of the sensing materials  125  of the second sensor  1202  may be indicative of the presence or absence of the second group of analytes. In some aspects, the frequency responses may be based on resonant impedance spectroscopy (RIS) sensing. 
     In various implementations, the output signals generated by each sensing device  100  may indicate an operating mode of a corresponding battery cell  320  of the battery pack  310 . In some implementations, the output signals may indicate a normal mode for the corresponding battery cell  320  based on an absence of analytes, may indicate a maintenance mode for the corresponding battery cell  320  based on the presence of analytes not exceeding a threshold level, or may indicate an emergency mode for the corresponding battery cell  320  based on the presence of analytes exceeding the threshold level. The output signals may also indicate a concentration level of each analyte detected by the sensing device  100 . 
       FIG. 4  is an illustration  400  depicting the sensing device  100  of  FIG. 1  configured to detect analytes in a shipping package  410 , according to some implementations. The shipping package  410  is shown to include a surface  412  defining a volume within which one or more items (not shown for simplicity) can be contained. The defined volume of the shipping package  410  also includes a plurality of analytes  414  which can be, for example, one or more of the analytes  151 - 155  of  FIG. 1 . As shown, the sensing device  100  may be a label  430  that is printed onto the surface  412  of the shipping package  410 . In various implementations, the label  430  may include a substrate  432 , a plurality of carbon-based sensors  434  printed on the substrate, and one or more electrodes  436  printed on the substrate. The sensors  434 , which may be examples of the carbon-based sensors  120  of  FIG. 1 , may be collectively configured to detect a presence of the analytes  414  within the shipping package  410 . 
     In some implementations, each of the sensors  434  may be configured to react with a unique group of analytes in response to an electromagnetic signal  442  received from an external device  440 . For example, a first sensor  434   1  may be configured to detect the presence of a first group of analytes, and a second sensor  434   2  may be configured to detect the presence of a second group of analytes that is a first subset of the first group of analytes. In one implementation, a third sensor  434   3  may be configured to detect the presence of a third group of analytes that is a second subset of the first group of analytes. As discussed, the first sensor  434   1  may be functionalized with a first material configured to react with the first group of analytes, the second sensor  434   2  may be functionalized with a second material configured to react with the second group of analytes, and the third sensor  434   3  may be functionalized with a third material configured to react with the third group of analytes. In this way, the second sensor  434   2  may be used to confirm detection of the first subset of analytes by the first sensor  434   1 , and the third sensor  434   3  may be used to confirm detection of the second subset of analytes by the first sensor  434   1 . In other implementations, one or more groups of sensors  434  may be configured to react with overlapping groups of analytes in response to the electromagnetic signal  442 . 
     The electrodes  436 , which may be examples of the electrodes  121 - 122  of  FIG. 1 , may be coupled to the sensors  434 . In some implementations, each sensor  434  may be coupled between a corresponding pair of electrodes  436 . The first electrode  436  of each electrode pair may be configured to receive the electromagnetic signal  442 , and the second electrode  436  of each electrode pair may be configured to provide an output signal indicating whether the corresponding sensor  434  detected the presence of analytes. 
     In some implementations, each output signal may indicate a frequency response of a corresponding sensor  434  to the electromagnetic signal  442 . For example, the frequency response of the first sensor  434   1  may indicate the presence (or absence) of the first group of analytes within the shipping package  410 , the frequency response of the second sensor  434   2  may confirm the presence (or absence) of the second group of analytes, and the frequency response of the third sensor  434   3  may confirm the presence (or absence) of the third group of analytes. In some instances, the first sensor  434   1  may be exposed to the electromagnetic signal  442  for a relatively short period of time to provide a coarse indication of whether the analytes of the first group of analytes are present, and the second and third sensors  434   2  and  434   3  may be exposed to the electromagnetic signal  442  for a relatively long period of time to confirm indications of the presence of the second and third respective groups of analytes by the first sensor  434   1 . In this way, the sensors  434   1 - 434   3  can collectively reduce the number of false positives indicated by the sensing device  100 . 
     In at least some implementations, an antenna (not shown for simplicity) may be printed on the substrate  432  and configured to drive an alternating current through the sensors  434  in response to the electromagnetic signal  442 . Because the sensors  434  may be functionalized with different materials that can have different electrical and/or chemical characteristics, the resulting sensor output currents may indicate the presence (or absence) of different analytes. For example, in some instances, each output signal may indicate an impedance or reactance of a corresponding sensor  434  to the alternating current. The impedance or reactance of each sensor  434  can be measured and compared with a reference impedance or reactance to determine whether one or more analytes associated with the sensor  434  are present in the shipping package  410 . In some instances, the reference impedances or reactance may be determined by driving the alternating current through the sensors  434  in the absence of all analytes, and measuring the impedances or reactance of the output signals from the sensors  434 . 
     In some aspects, the sensors  434  may be juxtaposed in a planar arrangement on the substrate  432 . In other instances, the sensors  434  may be stacked on top of one another in a vertical arrangement. In some implementations, the sensors  434  may form a permittivity gradient. 
     As discussed, the analyte sensing devices disclosed herein can be integrated into a product or package, such as on a cardboard box, or food package. The analyte sensing devices disclosed herein can be placed adjacent to a product or package and can detect analytes on or within the product or package. For example, the analyte sensing device can be integrated into or placed adjacent to a scale that is used to weigh shipping containers, and the analyte sensing device can be used to detect analytes on or within any shipping package being weighed by the scale. As another example, the analyte sensing device can be integrated into or placed adjacent to a component of a vehicle that is used to transport shipping containers, such as within a mail truck, and the analyte sensing device can be used to detect analytes on or within any shipping package being transported by the vehicle. As still further examples, the analyte sensing device can be integrated into a conveyor belt or mounted onto a portion of a mechanical conveyance device. Additionally, or alternatively, the analyte sensing device can be integrated into handling equipment, such as a robot arm, or handling apparel, such as gloves, etc., and the analyte sensing device can be used to detect analytes on or within any shipping package being conveyed or handled. 
     In one implementation, a fan or a suction device, such as a vacuum pump, may be used to direct environmental gasses (which may include one or more analytes) towards the analyte sensing device and/or into an enclosure containing the analyte sensing device. For example, the analyte sensing device can be placed into an enclosure, and a fan or vacuum pump can draw the surrounding environmental gasses into the enclosure such that any analytes present in the environmental gasses are exposed to the analyte sensing device. In another example, the analyte sensing device may be placed adjacent to a set of objects, such as shipping packages, mousepads, or other products, and can monitor for the presence of one or more analytes. 
       FIG. 5  is an illustration  500  depicting example reactions between one or more analytes and the sensor  120  of  FIG. 1 , according to some implementations. As discussed, the sensor  120  may include 3D graphene-based sensing materials  125  disposed on the substrate  130 , and the sensing materials  125  may be functionalized with a material  126  configured to detect the presence of analytes  151 - 152 . In some implementations, the sensing materials  125  may include a plurality of different graphene allotropes having one or more microporous pathways or mesoporous pathways. Although not shown for simplicity, a polymer may bind the plurality of different graphene allotropes to one another. In some instances, the polymer may include humectants configured reduce the susceptibility of the carbon-based sensors to humidity. 
     As shown, analytes  151 - 152  may take a variety of paths to penetrate and react with the sensing material  125 . Specifically, inset  510  depicts the analytes  151 - 152  being adsorbed by the functionalized material  126  and/or various exposed surfaces of the sensing material  125 . Inset  520  depicts a carbon particulate  522  from which the sensing material  125  may be formed. In some instances, a reactive chemistry additive (such as a salt dissolved in a carrier solvent) may be deposited on and within exposed surfaces, pores and/or pathways of the particulate carbon  522 . In some instances, the reactive chemistry additives may be incorporated into the particulate carbon  522  to increase the sensitivity of the sensor  120  to one or more specific analytes. 
       FIG. 6  is a block diagram of an analyte detection system  600 , according to some implementations. The analyte detection system  600  is shown to include an input circuit  610 , a sensor array  620 , a measurement circuit  630 , and a controller  640 . The input circuit  610  is coupled to the controller  640  and the sensor array  620 , and may provide an interface through which currents, voltages, and electromagnetic signals can be applied to the sensor array  620 . The sensor array  620 , which may be one example of the sensor array  110  of  FIG. 1 , is shown to include eight carbon-based sensors  120   1 - 120   8  coupled between respective pairs of electrodes  121   1  and  122   1  through  121   8  and  122   8 . In some instances, each of the first electrodes  121   1 - 121   8  may be coupled to a corresponding terminal of the input circuit  610 , and each of the second electrodes  122   1 - 122   8  may be coupled to a corresponding terminal of the measurement circuit  630 . In other instances, each terminal of the input circuit  610  may be coupled to a corresponding group of the sensors  120   1 - 120   8 . 
     The controller  640  may generate an excitation signal or field from which current levels, voltage levels, impedances, and/or frequency responses of the carbon-based sensors  120   1 - 120   n  can be measured or determined by the measurement circuit  630 . For example, in some implementations, the controller  640  may be a current source configured to drive either a direct current or an alternating current through each of the sensors  120   1 - 120   8 . In other implementations, the controller  640  may be a voltage source that can apply various voltages across the sensors  120   1 - 120   8  via corresponding pairs of electrodes  121  and  122 . In some instances, the controller  640  can adjust the sensitivity of a respective sensor  120  to a particular analyte by changing the voltage applied across the respective sensor  120 . For example, the controller  640  can increase the sensitivity of the respective sensor  120  by decreasing the applied voltage, and can decrease the sensitivity of the respective sensor  120  by increasing the applied voltage. In some other implementations, an antenna (not shown for simplicity) coupled to the sensor array  620  can receive one or more electromagnetic signals from an external device. In some aspects, the first electrodes  121   1 - 121   8  may be configured to receive the electromagnetic signals. 
     As discussed, the sensors  120   1 - 120   8  may include respective sensing materials  125   1 - 125   8  that can be functionalized with different materials configured to react with and/or detect different analytes or different groups of analytes. In some implementations, the sensors  120   1 - 120   8  may include cobalt in particulate form, and the sensing materials  125   1 - 125   8  may include carbon nano-onions (CNOs). Specifically, active sites on exposed surfaces of the CNOs may, in some aspects, be functionalized (such as through surface modification) with solid-phase cobalt (Co (S) ) (such as Co particles) and/or cobalt oxide (Co 2 O 3 ), which reacts with available carbon on exposed surfaces of the CNOs. For example, the chemical reactions associated with using cobalt oxide to detect the presence of hydrogen peroxide (H 2 O 2 ) may be expressed as: 
     
       
         
           
             
               
                 
                   
                     
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     In addition, or the alternative, cobalt-based functionalization may be used to detect TATP according to the following chemical reaction: 
       TATP+H + →3(CH 3 ) 2 CO+3H 2 O 2   (Eq. 4)
 
     In other implementations, the presence of TATP may be detected based on the following steps or operations:
         adsorption of TATP (50 ppb) onto exposed carbon surfaces (300-700 m 2 /g), which are acidic in nature by adding acid (such as HCl at an approximate 0.1 m concentration level). Example acid treatment levels include 10 mg carbon (C) corresponding to 100 mg HCl at 0.1 m diluted in a suitable carrier solvent. Over time, the adsorbed HCl evaporates and protonates hydroxyl and/or carboxylic groups on exposed carbon surfaces to leave such surfaces in a relatively acidic state;   hydrolysis of TATP into acetone and peroxide;   performance of peroxide oxidation shown by Eq. (1)-(3) above; and   the generation of free electrons and associated observable changes in one or more electrical or chemical characteristics of the sensing device.       

     In some implementations, Cobalt decorated CNOs may provide the most selective and sensitive response to triacetone triperoxide (TATP) relative to other types of 3D graphene-based sensing materials. Applicant notes that since hydrogen peroxide has a chemical structure somewhat similar to triacetone triperoxide (TATP) or tri-cyclic acetone peroxide (TCAP), sensing devices configured to detect a presence of hydrogen peroxide can also be used to detect a presence of TATP. 
     The exact chemical reactivity and/or interactions between an analyte and exposed carbon surfaces of the materials  125   1 - 125   8  may depend on the type of analyte and the structure or organization of the corresponding materials  125   1 - 125   8 . For example, certain analytes, such as hydrogen peroxide (H 2 O 2 ) and TATP, may be detected by one or more oxidation-reduction (“redox”) type chemical reactions with metals decorated onto exposed carbon surface of the sensing materials  125   1 - 125   8 . In some implementations, some of the sensing materials  125   1 - 125   8  may be prepared or created to include free amines, which may react with electronic deficient nitroaromatic analytes, such as TNT and DNT. 
     The measurement circuit  630  may measure the output signals provided by the sensors  120   1 - 120   8  to determine whether certain analytes are present in the surrounding environment. For example, when the sensor array  120  is pinged with an electromagnetic signal (e.g., received from an external device such as the device  440  of  FIG. 4 ), the measurement circuit can measure the frequency responses of the sensors  120   1 - 120   8 , and compare the measured frequency responses with one or more reference frequency responses. If the measured frequency response of a sensor  120  matches a particular reference frequency response, then the measurement circuit  630  may indicate a presence of analytes associated with the particular reference frequency response. Conversely, if the measured frequency response of the sensor  120  does not match any of the reference frequency responses, then the measurement circuit  630  may indicate an absence of analytes associated with the particular reference frequency response. 
     For another example, application of an alternating current to the sensor array  120  may cause one or more electrical and/or chemical characteristics of the sensors  120   1 - 120   8  to change (e.g., to increase or decrease). The measurement circuit  630  can detect the resultant changes in the electrical and/or chemical characteristics of the sensors  120   1 - 120   8 , and can determine whether certain analytes are present based on the changes. In some implementations, the measurement circuit  630  can measure the output currents of sensors  120   1 - 120   8  caused by the alternating current, and can compare the measured output currents with one or more reference currents to determine whether certain analytes are present. Specifically, if the measured output current of a sensor  120  matches a particular reference current, then the measurement circuit  630  may indicate the presence of analytes associated with the particular reference current. Conversely, if the measured output current of the sensor  120  does not match any of the reference currents, then the measurement circuit  630  may indicate an absence of analytes associated with the particular reference current. 
     In other implementations, the measurement circuit  630  can measure the impedances or reactance of the sensors  120   1 - 120   8  to the alternating current, and can compare the measured impedances or reactance with one or more reference impedances or reactance to determine whether certain analytes are present. Specifically, if the measured impedance or reactance of a sensor  120  matches a reference impedances or reactance, then the measurement circuit  630  may indicate the presence of analytes associated with the reference impedances or reactance. Conversely, if the measured impedance or reactance of the sensor  120  does not match any of the reference impedances or reactance, then the measurement circuit  630  may indicate an absence of analytes associated with the reference impedances or reactance. 
       FIG. 7A  shows another sensor array  700 A, according to some implementations. 
     As shown, the sensor array  700 A includes a plurality of sensors  701 - 704  disposed in a planar arrangement, with each of the sensors  701 - 704  including a different carbon-based sensing material. In some aspects, the sensors  701 - 704  may be examples of the sensors  120  of  FIGS. 1-3  and  FIGS. 5-6 . In other aspects, the sensors  701 - 704  may be examples of the sensors  434  of  FIG. 4 . Although the example  700 A of  FIG. 7A  shows four sensors  701 - 704  arranged in a 2-row by 2-column array, in other implementations, the other numbers of sensors can be disposed in other suitable arrangements. 
     The sensors  701 - 704  may include routing channels between individual deposits of the carbon-based sensing materials. These routing channels may provide routes through which electrons can flow through the sensors  701 - 704 . The resulting currents through the sensors  701 - 704  can be measured through ohmic contact with the respective electrode pairs E 1 -E 4 . For example, a measurement M 1  of the first sensor  701  can be taken via electrode pair E 1 , a measurement M 2  of the second sensor  702  can be taken via electrode pair E 2 , a measurement M 3  of the third sensor  703  can be taken via electrode pair E 3 , and a measurement M 4  of the fourth carbon-based sensor  704  can be taken via electrode pair E 4 . 
     In various implementations, each of the sensors  701 - 704  can be configured to react with and/or to detect a corresponding analyte or group of analytes. For example, the first sensor  701  can be configured to react with or detect a first group of analytes in a coarse-grained manner, and the second sensor  702  can be configured to react with or detect a subset of the first group of analytes in a fine-grained manner. In some instances, the sensors  701 - 704  can be printed onto a substrate using different carbon-based inks. Ohmic contact points can be used to capture the measurements M 1 -M 4 , either concurrently or sequentially. 
       FIG. 7B  shows another sensor array  700 B, according to some implementations. The sensor array  700 B includes a plurality of carbon-based sensors  701 - 704  stacked on top of one another in a vertical or stacked arrangement. In some aspects, the sensors  701 - 704  may be examples of the sensors  120  of  FIGS. 1-3  and  FIGS. 5-6 . In other aspects, the sensors  701 - 704  may be examples of the sensors  434  of  FIG. 4 . The sensors  701 - 704  (and their respective sensing materials) can be sequentially deposited upon one another to form the stacked array. In some instances, separators (not shown for simplicity) can be provided between the sensors  701 - 704 . As discussed, the sensors  701 - 704  may be functionalized with different materials and/or may include different types of carbon-based sensing materials that can be printed in successive layers onto a substrate or label. 
     As the demand for low-cost analyte sensors continues to increase, it is increasingly important to reduce or even eliminate the need for electronic components in analyte sensors. For example, the high cost of electronic components typically found in conventional analyte sensors render their widespread deployment in shipping containers, packages, and envelopes impractical. As such, some implementations of the subject matter disclosed herein may provide a cost-effective solution to the long-standing problem of monitoring large numbers of shipping containers, packages, and envelopes for the presence of harmful chemicals and gases such as, for example, the various analytes described herein. 
       FIG. 7C  is an illustration  700 C depicting an ink-jet or bubble-jet print head  720  printing various sensing devices disclosed herein onto the surface of a shipping container, package, or envelope, according to some implementations. Specifically, the illustration  700 C depicts a process by which multiple layers of different carbon-based sensing materials  711 - 714  can be printed onto a substrate  710 . As shown, the print head  720  can print a first layer  711  of carbon-based sensing materials onto the substrate  710  using a first carbon-based ink  721 , can print a second layer  712  of carbon-based sensing materials onto the substrate  710  using a second carbon-based ink  722 , can print a third layer  713  of carbon-based sensing materials onto the substrate  710  using a third carbon-based ink  723 , and can print a fourth layer  714  of carbon-based sensing materials onto the substrate  710  using a fourth carbon-based ink  724 . In some instances, the carbon-based inks  721 - 724  may be different from one another, for example, such that the resulting sensing material layers  711 - 714  are configured to react with and/or detect different analytes or different group of analytes. The print head  720  can also print electrodes E 1 -E 4  for the different sensing material layers  711 - 714 , respectively, using an ohmic-based ink  725 . Ohmic contacts can be printed onto the substrate  710  and/or portions of the sensing material layers  711 - 714  using multiple passes of the multi-jet print head  720 . In some implementations, the sensing device may include vias through which the resulting electrodes E 1 -E 4  can be accessed. In other implementations, other suitable mechanisms can be used to provide ohmic contacts for the electrodes E 1 -E 4 . 
       FIG. 7D  is an illustration  700 D depicting the print head  720  printing various sensing devices disclosed herein onto the surface of a shipping container, package, or envelope, according to other implementations. Specifically, the illustration  700 D depicts a process by which multiple layers of different carbon-based sensing materials  711 - 714  can be printed onto a substrate  710  in a pyramid arrangement. The illustration  700 D also depicts ohmic contacts  705  printed on the sensing material layers  711 - 714  using an ohmic-based ink  725 . In some aspects, the different sizes and different exposed surface areas of the sensing material layers  711 - 714  may cause the respective sensors to have different electrical and/or chemical characteristics, which in turn may configured the respective sensors to react with and/or detect different types of analytes. 
     Further details pertaining to various carbon-based sensing materials, tunings, and calibration techniques that can be used to form carbon-based sensors disclosed herein are summarized below in Table 1. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Components 
                 Tuning 
                 Sensitivity 
                 Calibration 
               
               
                   
               
             
            
               
                 Different carbon 
                 Select carbon 
                 Surface area of 
                 Response of the 
               
               
                 types and/or 
                 functionalization 
                 carbon-based 
                 selected carbon 
               
               
                 different carbon 
                 materials to detect 
                 sensor 
                 functionalization 
               
               
                 decorations 
                 selected analytes 
                   
                 materials to the 
               
               
                   
                   
                   
                 selected analytes 
               
               
                 Physical 
                 Select size and/or 
                 Surface area of 
                 Sensitivity is based on 
               
               
                 dimensions of the 
                 aspect ratio of 
                 carbon-based 
                 physical dimensions 
               
               
                 sensing material 
                 exposed portion of 
                 sensor 
                 and characteristics of 
               
               
                   
                 sensor 
                   
                 carbon-based sensor 
               
               
                 Adjacency or 
                 Select distance 
                 Select distance 
                 Calibrate based on test 
               
               
                 proximity to other 
                 between sensors to 
                 between sensors 
                 sample over a range 
               
               
                 carbon-based 
                 reduce overlapping 
                 to reduce 
                 conditions 
               
               
                 sensing materials 
                 response signals 
                 overlapping 
                   
               
               
                   
                   
                 response signals 
                   
               
               
                 Different 
                 Tune permittivity 
                 Select distance 
                 Calibrate based on test 
               
               
                 permittivity of the 
                 based on sensor 
                 between sensors 
                 sample over a range 
               
               
                 different materials 
                 material/function- 
                 to reduce 
                 conditions 
               
               
                   
                 alization 
                 overlapping 
                   
               
               
                   
                   
                 response signals 
               
               
                   
               
            
           
         
       
     
     As discussed, different materials may resonate at different frequencies, and many materials may resonate at different frequencies depending on whether one or more certain analytes are present. In some implementations, the permittivity of carbon-based sensing materials described herein can be modified by exposing the materials to ultraviolet (UV) radiation. 
       FIG. 7E  is an illustration  700 E depicting UV radiation emitted towards the sensor  701 . As shown, a UV beam source  753  may be used to shower the sensor  701  with UV radiation. The power and wavelength of the UV radiation can be controlled by a power control unit  751  and a wavelength control unit  752 , respectively. In some implementations, adjusting the power level and/or wavelength of UV radiation can change the permittivity of each of the sensing material layers  711 - 714 . That is, after bombarded with the UV radiation, each of the sensing material layers  711 - 714  may resonate at a different frequency. In some aspects, the different permittivity of the sensing material layers  711 - 714  may collectively a permittivity gradient  725 . The permittivity gradient  725  may correspond to a stair shaped gradient  761 , a linearly shaped gradient  762 , or a curvilinearly shaped gradient  763 . 
       FIG. 8  shows a flow chart  800  depicting an example operation for fabricating at least some of the sensing devices disclosed herein, according to some implementations. In various implementations, the permittivity of a carbon-based sensing material can be altered to cause a particular resonance signature in the carbon-based sensing material when exposed to certain analytes. In some cases, different portions of the carbon-based sensing material may be configured to have different permittivity values specifically selected to cause particular resonance frequencies and/or or resonance signatures. In particular, it is sometimes desired that a first portion of the carbon-containing material with a first permittivity that is tuned to resonate with a particular resonance signature when the first portion of the carbon-containing material has imbibed a first analyte of interest, whereas a second portion of the carbon-containing material has a second permittivity that is tuned to resonate with a particular resonance signature when the second portion of the carbon-containing material has imbibed a second analyte of interest. 
     Formation of different portions of the carbon-containing material having different permittivity values can be accomplished using a combination of masking and UV treatments. At block  802 , a carbon-containing material is deposited onto a substrate or electrode  811 . At block  804 , a UV-opaque mask is deposited or printed on top the carbon-containing material. At block  806 , the carbon-containing material is activated, for example, via bombardment by UV photons. This results in a first portion  812   1  of the carbon-containing material having a first permittivity, and a second portion  812   2  of the carbon-containing material having a second permittivity different than the first permittivity. At block  808 , the mask can be washed away, ablated, or otherwise removed. Two or more of the resulting analyte-sensing devices can be used as a multi-element, multi-analyte sensor and/or as a high-sensitivity analyte sensor. In addition, or in the alternative, the resulting analyte-sensing devices can be exposed to an additional bombardment of UV photons at block  810 , for example, to further alter portions of the carbon-containing material previously beneath the UV-opaque mask. 
     Some example alternative implementations are summarized below in Table 2: 
     
       
         
           
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 Manufacturing Process Aspect(s) 
                 Result(s) 
               
               
                   
               
             
            
               
                 Add a hardener or binder to the carbon- 
                 UV treatment causes curing and hardening to 
               
               
                 containing materials 
                 a controllable degree (such as to be more 
               
               
                   
                 rigids or more flexible) 
               
               
                 Use the UV photon to ablate some of the 
                 Form patterns in the carbon-containing 
               
               
                 carbon-containing material 
                 material that absorb an analyte into the 
               
               
                   
                 carbon-containing material and/or that 
               
               
                   
                 increase coupling between the carbon- 
               
               
                   
                 containing material and the electrode. 
               
               
                 Deposit a slurry of carbon-containing 
                 Low cost, high-volume manufacture of 
               
               
                 materials over a sheet of conductive, semi- 
                 analyte-sensing devices. 
               
               
                 conductive, or non-conductive material. 
                   
               
               
                 Add metallic and/or semiconducting and/or 
                 Facilitates permeation of certain analytes into 
               
               
                 dielectric, and/or polymeric materials to the 
                 the matrix and/or tunes the matrix to be 
               
               
                 carbon-containing materials (such as to the 
                 sensitive to particular analytes. 
               
               
                 slurry) to form an open-pore matrix. 
                   
               
               
                 Add metallic and/or semiconducting and/or 
                 Tunes the matrix to be sensitive to particular 
               
               
                 dielectric, and/or polymeric materials to the 
                 analytes and/or facilitates permeation of 
               
               
                 carbon-containing materials (such as to the 
                 certain analytes into the matrix. 
               
               
                 slurry) to form an open-pore matrix. 
                   
               
               
                 Maintain low temperatures during processing. 
                 Avoid loss of conductivity that may occur at 
               
               
                   
                 higher temperatures (such as when polymers 
               
               
                   
                 unwantedly coat metallics). 
               
               
                   
               
            
           
         
       
     
       FIG. 9  shows another sensor array  900 , according to some implementations. The sensor array  900  includes a plurality of layers  911 - 914  of individually-functionalized carbon-containing materials. As shown, the layers  911 - 914  are successively disposed to form a stack of layers, with the first layer  911  disposed on the substrate  910 . Each layer is formed of a corresponding individually-functionalized carbon-containing matrix (such as carbon matrix1, carbon matrix2, carbon matrix3, carbon matrix4), wherein each individually-functionalized carbon-containing matrix includes a respective additive A-D). The combinations of carbon-containing matrices and additive may be selected based on the particular combination&#39;s sensitivity to a particular analyte of interest. 
     In forming the analyte sensor array, the different layers can be deposited using any known technique. Furthermore, each of the different layers can be configured to be of a particular thickness. Strictly as one example, and as shown, a first deposited layer can have a first thickness  924  in a first range (such as 10 nm-100 nm, whereas another deposited layer can have a thickness in a different range (such as 500 nm-1,000 nm), and so on. The particular thickness of a particular layer can be selected based upon any combination of:
         characteristics of the additive for that particular layer, and/or   characteristics of the analyte of interest, and/or   innate binary-tertiary interactions by and between the constituents of the layer.       

     In some implementations, the open pore structure of carbon-based sensing materials disclosed herein may allow certain analytes to more easily penetrate the materials and/or to more easily interact with carbon matrices within the materials. As such, these open pores may increase the sensitivity of sensors disclosed herein to analytes than conventional analyte detection systems. 
       FIG. 10A  shows an example sensor configuration  1000 A, according to some implementations. The sensor configuration  1000 A includes mappings between sensors of an analyte detection system and various analytes, according to some implementations. For example, the 3D graphene-based sensing materials of the carbon-based sensors  120  of  FIG. 1  may be or include the carbon recipes shown in the sensor configuration  1000 A. That is, in a configuration in which the sensor array  120  includes 8 carbon-based sensors  120 , each sensor may have a corresponding carbon recipe as shown by the example sensor configuration  1000 A. For example, a first sensor may be cobalt oxide (Co 2 O 3 ) decorated CNO and produce a percentage change in current (% ΔI) over initial current (I 0 ) and/or percentage increase in measured impedance of 9.26244%, and so on. In this way, the carbon recipes of the sensor configuration  1000 A may be used to configure the carbon-based sensors to detect and identify different analytes (such as TATP, DNT, H 2 S, and so on), even at relatively low concentration levels, based on their respective chemical fingerprints. As such, the sensing devices disclosed herein may be able to detect relatively low concentrations of analytes and/or other chemical threat agents, even in the presence of common interferents. 
       FIG. 10B  shows another example sensor configuration  1000 B, according to some implementations. The sensor configuration  1000 B may be similar to the sensor configuration  1000 A of  FIG. 10A , for example, such that: 
     Sensor No. 1: Carbon #29, corresponding to carbon nano-onion (CNO) oxides produced in a thermal reactor; cobalt(II) acetate (C 4 H 6 CoO 4 ), the cobalt salt of acetic acid (often found as tetrahydrate Co(CH 3 CO 2 ) 2 . 4H 2 O, abbreviated Co(OAc) 2 .4H 2 O, is flowed into the thermal reactor at a ratio of approximately 59.60 wt % corresponding to 40.40 wt % carbon (referring to carbon in CNO form), resulting in the functionalization of active sites on the CNO oxides with cobalt, showing cobalt-decorated CNOs at 15,000× and 100,000× levels, respectively; suitable gas mixtures used to produce Carbon #29 and/or the cobalt-decorated CNOs may include the following steps:
         Ar purge 0.75 standard cubic feet per minute (scfm) for 30 min;   Ar purge changed to 0.25 scfm for run;   temperature increase: 25° C. to 300° C. 20 mins; and   temperature increase: 300°-500° C. 15 mins.       

     Sensor No. 2: corresponding to TG JM (thermal graphene jet milled; thermal reactor carbon unfunctionalized) as shown in  FIG. 11A . 
     Sensor No. 3: Carbon #19, corresponding to “DXR” (as characterized by  FIGS. 5A and/or 5B ) type or configuration carbons produced in a microwave reactor (such as a reactor coupled to a microwave source such that microwave energy propagates through the reactor exciting carbon-containing gases and/or plasmas inside the reactor); silver acetate (CH 3 CO 2 Ag), a white, crystalline solid particulate substance suspended in carrier gas to create silver acetate vapor, is flowed into the microwave reactor at a ratio of approximately 58.18 wt % corresponding to 41.82 wt % carbon (referring to carbon in DXR form), resulting in the functionalization of active sites on the DXR configuration carbons with silver as substantially shown in  FIG. 11D  (in undecorated form) and/or in  FIG. 11G  (showing actual decoration with cobalt instead of silver). Example gas mixtures used to produce Carbon #19 and/or the silver-decorated DXR carbons substantially shown in  FIGS. 11D and 11G  may include the following steps:
         flow of carrier gas over DXR carbon structures at a volume ratio of 6.7% H 2  per 93.3% Ar for approximately 1 minute and 8 seconds       

     Sensor No. 4: CNO (carbon nano-onion; thermal reactor carbon unfunctionalized) as shown in  FIG. 11B . 
     Sensor No. 5: Carbon #16, corresponding to “DXR” (as characterized by  FIGS. 5A and/or 5B ) type or configuration carbons produced in a microwave reactor; iron(II) acetate, a white solid particulate substance suspended in carrier gas to create iron acetate vapor, is flowed into the microwave reactor at a ratio of approximately 65.17 wt % corresponding to 34.83 wt % carbon (referring to carbon in DXR form), resulting in the functionalization of active sites on the DXR configuration carbons with silver as substantially shown in  FIG. 11D  (in undecorated form) and/or in  FIG. 11G  (showing actual decoration with cobalt instead of iron). Example gas mixtures used to produce Carbon #16 and/or the iron-decorated DXR carbons substantially shown in  FIGS. 11D and 11G  may include the following steps:
         flow of carrier gas over DXR carbon structures at a volume ratio of 6.7% H 2  per 93.3% Ar for approximately 1 minute and 13 seconds.       

     Sensor No. 6: Carbon #1, corresponding to “Anvel” (as characterized by  FIG. 7C ) type or configuration carbons produced in a microwave reactor; platinum(II) bis(acetylacetonate), a coordination compound with the formula Pt(O 2 C 5 H 7 ) 2 , abbreviated Pt 2 , is flowed as a particulate dispersed in carrier gas to create platinum(II) bis(acetylacetonate) vapor, is flowed into the microwave reactor at a ratio of approximately 76.62 wt % corresponding to 23.38 wt % carbon (referring to carbon in Anvel form), resulting in the functionalization of active sites on the Anvel configuration carbons with platinum as substantially shown in  FIG. 11C  (in undecorated form); suitable gas mixtures used to produce Carbon #1 and/or the undecorated Anvel carbons substantially shown in  FIG. 11C  may include the following steps:
         flow of carrier gas over Anvel carbon structures at a volume ratio of 6.7% H 2  per 93.3% Ar for approximately 15 minutes       

     Sensor No. 7: Carbon #6, corresponding to “Anvel” (as characterized by  FIG. 7C ) type or configuration carbons produced in a microwave reactor; palladium(II) acetate, a chemical compound of palladium described by the formula [Pd(O 2 CCH 3 ) 2 ] n , abbreviated [Pd(OAc) 2 ] n , is flowed as a particulate dispersed in carrier gas to create palladium(II) acetate vapor, is flowed into the microwave reactor at a ratio of approximately 65.17 wt % corresponding to 34.83 wt % carbon (referring to carbon in Anvel form), resulting in the functionalization of active sites on the Anvel configuration carbons with platinum as substantially shown in  FIG. 11C  (in undecorated form). Example gas mixtures used to produce Carbon #6 and/or the palladium-decorated Anvel carbons substantially shown in  FIG. 11C  may include the following steps:
         flow of carrier gas over Anvel carbon structures at a volume ratio of 6.7% H 2  per 93.3% Ar for approximately 15 minutes.       

     Sensor No. 8: 1,3-diaminonaphthalene complexed to TG-JM, such as that shown in  FIG. 11A , to produce an organically modified carbon. 
       FIGS. 11A-11G  show illustrations of various structured carbon materials that can be used in the sensing devices disclosed herein, according to some implementations. For example,  FIG. 11A  shows a micrograph  1100 A of thermogravimetric (TG) carbons, according to various implementations.  FIG. 11B  shows a micrograph  1100 B of undecorated CNOs, according to various implementations.  FIG. 11C  shows a micrograph  1100 C of Anvel carbons, according to various implementations.  FIG. 11D  shows a micrograph  1100 D of DXR carbons, according to various implementations.  FIG. 11E  shows a micrograph  1100 E of cobalt decorated CNOs at a magnification level of 15,000×, according to various implementations.  FIG. 11F  shows a micrograph  1100 F of cobalt decorated CNOs at a magnification level of 100,000×, according to various implementations.  FIG. 11G  shows a micrograph  1100 G of a cobalt decorated DXR carbons, according to various implementations. 
     In contrast to a conventional 2D graphene material, the 3D graphene sensing materials disclosed by the present implementations may be designed to have a convoluted 3D structure to prevent graphene restacking, avoiding several drawbacks of using 2D graphene as a sensing material. This process also increases the areal density of the materials, yielding higher analyte adsorption sites per unit area, thereby improving chemical sensitivity, as made possible by a corresponding library of carbon allotropes used to customize the sensor arrays disclosed herein to chemically fingerprint leaked analytes for multiple applications. 
     The structured carbon materials shown in  FIGS. 11A-11G  may be produced using flow-through type microwave plasma reactors configured to create pristine 3D graphene particles continuously from a hydrocarbon gas at near atmospheric pressures. Operationally, as the hydrocarbon flows through a relatively hot zone of a plasma reactor, free carbon radicals may be formed that flow further down the length of the reactor into the growth zone where 3D carbon particulates (based on multiple 2D graphenes joined together) are formed and collected as fine powders. The density and composition of the free-radical carbon-inclusive gaseous species may be tuned by gas chemistry and microwave (MW) power levels. By controlling the reactor process parameters, these reactors may produce carbons with a wide, yet tunable, range of morphologies, crystalline order, and sizes (and distributions). For example, possible sizes and distributions may range from flakes (few 100 nm to μm wide and few nm thin) to spherical particles (10 s of nm in diameter) to graphene clusters (10 s of μm). The 3D nature of the materials prevents agglomeration effectively allowing for the materials to be disseminated as un-agglomerated particles. As a result, highly responsive and selective sensing materials can be produced. Graphene, an atomically thin two dimensional (2D) material, has many advantageous properties for sensing, including outstanding chemical and mechanical strength, high carrier mobility, high electrical conductivity, high surface area, and gate-tunable carrier density. 
     To improve the chemical selectivity, the 3D graphenes of the presently disclosed graphenes may be functionalized with various reactive materials in such a manner that the binding of target molecules and the carbon may be optimized. This functionalization step along with the ability to measure the complex impedance of the exposed sensor may be critical for efficient and selective detection of analytes. For example, different metal nanoparticles or metal oxide nanoparticles may be decorated on the surface of 3D graphenes to selectively detect hydrogen peroxide (a TATP degradation product) as peroxides are known to react with different metals. Further, nanoparticle decorated graphene structures may act synergistically to offer desirable and advantageous properties for sensing applications. 
       FIGS. 12A-12F  show example frequency responses of resonance impedance sensors to various analytes, according to some implementations. Specifically,  FIG. 12A  shows an example frequency response  1200 A of sensors  120  to alongside a baseline or reference frequency response. Specifically,  FIG. 12A  shows an example frequency response  1200 A of sensors  120  to acetone alongside a baseline or reference frequency response.  FIG. 12B  shows an example frequency response  1200 B of sensors  120  to acetonitrile alongside a baseline or reference frequency response.  FIG. 12C  shows an example frequency response  1200 C of sensors  120  to Ethanol alongside a baseline or reference frequency response.  FIG. 12D  shows an example frequency response  1200 A of sensors  120  to isopropanol alongside a baseline or reference frequency response.  FIG. 12E  shows an example frequency response  1200 E of sensors  120  to water alongside a baseline or reference frequency response.  FIG. 12F  shows an example frequency response  1200 F of sensors  120  to xylenes alongside a baseline or reference frequency response. 
       FIG. 13A  is a graph  1300 A depicting the real (Z′) impedance component of example frequency responses of sensors  120  to Acetone, Ethanol (EtOH), water, and hydrogen peroxide (H 2 O 2 ) alongside a baseline or reference frequency response, according to some implementations.  FIG. 13B  is a graph  1300 B depicting the imaginary (Z″) impedance component of example frequency responses of sensors  120  to Acetone, Ethanol (EtOH), water, and hydrogen peroxide (H 2 O 2 ) alongside a baseline or reference frequency response, according to some implementations. 
       FIG. 14A  shows an example frequency response of sensors  120  to hydrogen peroxide alongside a baseline or reference frequency response, according to some implementations.  FIG. 14B  shows example frequency responses of sensors  120  to acetone and water, according to some implementations.  FIG. 14C  shows example frequency responses to ethanol and ammonia, according to some implementations. 
     As used herein, a phrase referring to “at least one of” or “one or more of” a list of items refers to any combination of those items, including single members. For example, “at least one of: a, b, or c” is intended to cover the possibilities of: a only, b only, c only, a combination of a and b, a combination of a and c, a combination of b and c, and a combination of a and b and c. 
     The various illustrative components, logic, logical blocks, modules, circuits, operations, and algorithm processes described in connection with the implementations disclosed herein may be implemented as electronic hardware, firmware, software, or combinations of hardware, firmware, or software, including the structures disclosed in this specification and the structural equivalents thereof. The interchangeability of hardware, firmware and software has been described generally, in terms of functionality, and illustrated in the various illustrative components, blocks, modules, circuits and processes described above. Whether such functionality is implemented in hardware, firmware or software depends upon the application and design constraints imposed on the overall system. 
     Various modifications to the implementations described in this disclosure may be readily apparent to persons having ordinary skill in the art, and the generic principles defined herein may be applied to other implementations without departing from the spirit or scope of this disclosure. Thus, the claims are not intended to be limited to the implementations shown herein, but are to be accorded the widest scope consistent with this disclosure, the principles and the novel features disclosed herein. 
     Additionally, various features that are described in this specification in the context of separate implementations also can be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation also can be implemented in multiple implementations separately or in any suitable subcombination. As such, although features may be described above in combination with one another, and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination. 
     Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. Further, the drawings may schematically depict one more example processes in the form of a flowchart or flow diagram. However, other operations that are not depicted can be incorporated in the example processes that are schematically illustrated. For example, one or more additional operations can be performed before, after, simultaneously, or between any of the illustrated operations. In some circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products.