Resonant gas sensor
A method for detecting an analyte comprises providing a first carbon-based material comprising reactive chemistry additives, providing conductive electrodes connected to the first carbon-based material, exposing the first carbon-based material to an analyte, applying a plurality of alternating currents having a range of frequencies across the conductive electrodes, and measuring the complex impedance of the first carbon-based material using the plurality of alternating currents.
1. A method for detecting an analyte, comprising:
providing a first carbon-based material comprising reactive chemistry additives;
providing conductive electrodes connected to the first carbon-based material;
exposing the first carbon-based material to the analyte;
applying a plurality of alternating currents having a range of frequencies across the conductive electrodes; and
measuring a complex impedance of the first carbon-based material using the plurality of alternating currents;
wherein:
the providing the first carbon-based material comprises using a microwave plasma to produce carbon particles, and printing the carbon particles to form the first carbon-based material; and
the reactive chemistry additives are tuned to the analyte.
2. The method of claim 1 , wherein, the first carbon-based material comprises:
carbon aggregates comprising a plurality of carbon nanoparticles, each carbon nanoparticle comprising graphene;
the graphene in the plurality of carbon nanoparticles comprises up to 15 layers;
a percentage of carbon to other elements, except hydrogen, in the carbon aggregates is greater than 99%;
a median size of the carbon aggregates comprising the carbon nanoparticles is from 0.1 microns to 50 microns;
a surface area of the carbon aggregates is from 10 m 2 /g to 300 m 2 /g, when measured via a Brunauer-Emmett-Teller (BET) method with nitrogen as the adsorbate; and
the carbon aggregates, when compressed, have an electrical conductivity from 500 S/m to 20,000 S/m.
3. The method of claim 1 , wherein the plurality of alternating currents are applied across the conductive electrodes using a battery.
4. The method of claim 1 , wherein the plurality of alternating currents are applied in a first coarse sweep over a wider frequency range followed by one or more finer sweeps over narrower frequency ranges.
5. The method of claim 1 , further comprising:
comparing the measured complex impedance to a library of complex impedance spectra; and
identifying an analyte species when the measured complex impedance matches a complex impedance spectrum in the library.
6. A sensor for detecting an analyte, comprising:
a flexible substrate;
a resonant gas sensor circuit, comprising:
a transducer arranged on the flexible substrate;
a sensing material arranged on the flexible substrate and electrically coupled to the transducer, wherein the sensing material comprises a first particulate carbon and a reactive chemistry additive; and
a ground electrode electrically coupled to a first terminal of the transducer; and
a microprocessor arranged on the flexible substrate and electrically coupled to a second terminal of the transducer and to the ground electrode, the microprocessor comprising:
an alternating current (AC) source configured to supply a plurality of AC signals to the first terminal of the transducer, the plurality of AC signals comprising a range of frequencies; and
a detection circuit that measures a plurality of AC signals reflected from the first terminal of the transducer;
wherein the first particulate carbon in the sensing material comprises:
a plurality of carbon aggregates each comprising a plurality of carbon nanoparticles, each carbon nanoparticle comprising graphene;
the graphene in the plurality of carbon nanoparticles comprises up to 15 layers;
a percentage of carbon to other elements, except hydrogen, in the carbon aggregates is greater than 99%;
a median size of the carbon aggregates comprising the carbon nanoparticles is from 0.1 microns to 50 microns;
a surface area of the carbon aggregates is from 10 m 2 /g to 300 m 2 /g, when measured via a Brunauer-Emmett-Teller (BET) method with nitrogen as the adsorbate; and
the carbon aggregates, when compressed, have an electrical conductivity from 500 S/m to 20,000 S/m.
7. The sensor of claim 6 , wherein the reactive chemistry additive is a redox mediator that is covalently tethered, non-covalently tethered, or untethered to the first particulate carbon.
8. The sensor of claim 6 , wherein the flexible substrate comprises paper or a flexible polymer.
9. The sensor of claim 6 , wherein the transducer comprises a spiral antenna.
10. The sensor of claim 6 , wherein the transducer comprises particulate carbon.
11. The sensor of claim 6 , wherein the transducer comprises particulate carbon and the sensing material.
12. The sensor of claim 6 , wherein the sensing material is arranged adjacent to the transducer.
13. The sensor of claim 6 , wherein the sensing material further comprises a polymer binder and the sensing material is contained within the polymer binder.
14. The sensor of claim 6 , wherein the range of frequencies in the plurality of AC signals is from 500 MHz to 20 GHz.
15. The sensor of claim 6 , further comprising a capacitive element, wherein:
the capacitive element comprises electrodes, which are electrically coupled to the microprocessor and the transducer;
the capacitive element is wired with the transducer in a parallel or series arrangement;
the transducer comprises an inductance; and
the capacitive element and the transducer form a tank circuit.
16. The sensor of claim 15 , wherein the electrodes of the capacitive element are interdigitated.
17. The sensor of claim 15 , wherein the sensing material is arranged between the electrodes of the capacitive element.
18. The sensor of claim 6 , further comprising a battery arranged on the flexible substrate.
19. The sensor of claim 6 , further comprising an energy harvesting structure arranged on the flexible substrate.
20. The sensor of claim 6 , wherein the analyte is selected from the group consisting of acetone, ammonia, carbon monoxide, ethanol, hydrogen peroxide, nitro groups, oxygen, and water.