Gas sensor for anesthetic gases and its use

1. A capacitively coupled field effect transistor gas sensor comprising:

a first, gas-sensitive, receptor layer with positive charge centers, wherein the first receptor layer is comprised of titanium nitride and titanium+ cations;

a second, gas-sensitive, receptor layer with positive charge centers, wherein the second receptor layer is comprised of copper phthalocyanine;

an insulation layer;

a substrate;

a drain;

a source;

a channel area located between the drain and the source;

a gate electrode; and

a sensor electrode, wherein the channel area is spatially in connection with the gate electrode and at least the drain, the source and the channel area are arranged within the substrate; wherein the gate electrode is connected electrically conductively to the sensor electrode and an air gap is present between the sensor electrode and the first receptor layer, and the sensor electrode and the first receptor layer are otherwise separated by the insulation layer; and wherein the sensor electrode and the first receptor layer are configured such that an analyte gas flows through the air gap, and the analyte gas is an anesthetic gas.

2. A gas sensor in accordance with claim 1 , wherein the anesthetic gas is selected from among one or more members of the group comprising desflurane, sevoflurane, isoflurane, enflurane and halothane.

3. A gas sensor in accordance with claim 1 , wherein the first receptor layer is configured as an electrically conductive layer and contains pure soft Lewis acids or mixtures of soft Lewis acids and wherein the second receptor layer is configured as an electrically conductive layer and contains pure soft Lewis acids or mixtures of soft Lewis acids.

4. A gas sensor in accordance with claim 3 , wherein the soft Lewis acids comprise Ti + , Ni 2+ , Pd 2+ , Pt 2+ , Cu + , Cu 2+ , Ag + , Au + , Zn 2+ , Cd 2+ , Hg 2+ , In 3+ , Ti 3+ , Ge 2+ , Sn 2+ or Pb 2+ or any combination of Ti + , Ni 2+ , Pd 2+ , Pt 2+ , Cu + , Cu 2+ , Ag + , Au + , Zn 2+ , Cd 2+ , Hg 2+ , In 3+ , Ti 3+ , Ge 2+ , Sn 2+ and Pb 2+ .

5. A capacitively coupled field effect transistor gas sensor according to claim 1 , wherein:

the first receptor layer is part of a first capacitively coupled field effect transistor sensor portion and the second receptor layer is part of a second capacitively coupled field effect transistor sensor portion;

the first capacitively coupled field effect transistor sensor portion comprises the insulation layer, the substrate, the drain, the source, the channel area located between the drain and the source, the gate electrode and the sensor electrode;

the second capacitively coupled field effect transistor sensor portion comprises a second insulation layer, a second substrate, a second drain, a second source, a second channel area located between the second drain and the second source a second gate electrode and a second sensor electrode; and

the air gap present between the sensor electrode and the first receptor layer is also present between the second sensor electrode and the second receptor layer as a shared air gap whereby the same gas stream flows through two different sensor portions or a second gap is present between the second sensor electrode and the second receptor layer and is arranged such that anesthetic gas flows through the plurality of gas sensor portions in parallel.

6. A capacitively coupled field effect transistor gas sensor according to claim 1 , wherein:

the first receptor layer is part of a first capacitively coupled field effect transistor sensor portion and the second receptor layer is part of a second capacitively coupled field effect transistor sensor portion; and

the air gap present between the sensor electrode and the first receptor layer is also present between the sensor electrode and the second receptor layer as a shared air gap whereby the same gas stream flows through two different sensor portions or a second gap is present between the sensor electrode and the second receptor layer and is arranged such that anesthetic gas flows through the plurality of gas sensor portions in parallel.

7. A closed-circuit ventilation system comprising:

a carrier gas source supplying a carrier gas;

an anesthetic gas source supplying for an anesthetic gas; and

a capacitively coupled field effect transistor sensor comprising a first, gas-sensitive, receptor layer with positive charge centers, wherein the first receptor layer is comprised of titanium nitride and titanium+ cations, a second, gas-sensitive, receptor layer with positive charge centers, wherein the second receptor layer is comprised of copper phthalocyanine, an insulation layer, a substrate, a drain, a source, a channel area located between the drain and the source, a gate electrode and a sensor electrode, wherein the channel area is spatially in connection with the gate electrode and at least the drain, the source and the channel area are arranged within the substrate; wherein the gate electrode is connected electrically conductively to the sensor electrode and an air gap is present between the sensor electrode and the first receptor layer, and the sensor electrode and the first receptor layer are otherwise separated by the insulation layer; and wherein the anesthetic gas, as an analyte gas, flows through the air gap.

8. A closed-circuit ventilation system in accordance with claim 7 , further comprising a closed ventilation circuit with a patient feed connection wherein the gas sensor is arranged within the closed ventilation circuit of the closed-circuit ventilation system of an anesthesia device to quantitatively determine a concentration of the anesthetic gas as the anesthetic gas is being fed to a patient.

9. A closed-circuit ventilation system in accordance with claim 8 , wherein the closed ventilation circuit comprises an outlet for the discharge the carrier gas and anesthetic gas and an anesthetic gas filter, wherein the anesthetic gas is sent at the outlet through the anesthetic gas filter and the gas sensor is arranged downstream of the anesthetic gas filter.

10. A closed-circuit ventilation system in accordance with claim 9 , further comprising a filter depletion indicator with an electronic detector, which indicates that the anesthetic gas filter is to be replaced when a defined threshold value is reached.

11. A closed-circuit ventilation system in accordance with claim 9 , wherein the closed ventilation circuit further comprises a nonreturn valve wherein the gas sensor is arranged between the anesthetic gas filter and the nonreturn valve.

12. A closed-circuit ventilation system in accordance with claim 7 , wherein:

the first receptor layer is part of a first capacitively coupled field effect transistor sensor portion and the second receptor layer is part of a second capacitively coupled field effect transistor sensor portion;

the first capacitively coupled field effect transistor sensor portion comprises the insulation layer, the substrate, the drain, the source, the channel area located between the drain and the source, the gate electrode and the sensor electrode;

the second capacitively coupled field effect transistor sensor portion comprises a second insulation layer, a second substrate, a second drain, a second source, a second channel area located between the second drain and the second source, a second gate electrode and a second sensor electrode;

the air gap present between the sensor electrode and the first receptor layer is also present between the second sensor electrode and the second receptor layer as a shared air gap whereby the same gas stream flows through two different sensor portions or a second gap is present between the second sensor electrode and the second receptor layer and is arranged such that anesthetic gas flows through the plurality of gas sensor portions in parallel.

13. A closed-circuit ventilation system in accordance with claim 7 , wherein the gas sensor further comprises a heating element or is surrounded by a heating element to heat the first receptor layer or to heat the first receptor layer and the sensor electrode prior to a measurement or to heat the first receptor layer or to heat the first receptor layer and the sensor electrode for regeneration between two measurements.

14. A closed-circuit ventilation system in accordance with claim 13 , wherein the heating element heats first the receptor layer or heats the first receptor layer and the sensor electrode for a time Δt H of 10 sec to 10 minutes to a temperature T of 60° C. to 120° C.

15. A closed-circuit ventilation system in accordance with claim 7 , wherein the first receptor layer is configured as an electrically conductive layer and contains pure soft Lewis acids or mixtures of soft Lewis acids and wherein the second receptor layer is configured as an electrically conductive layer and contains pure soft Lewis acids or mixtures of soft Lewis acids.

16. A closed-circuit ventilation system in accordance with claim 15 , wherein the soft Lewis acids comprise Ti + , Ni 2+ , Pd 2+ , Pt 2+ , Cu + , Cu 2+ , Ag + , Au + , Zn 2+ , Cd 2+ , Hg 2+ , In 3+ , Ti 3+ , Ge 2+ , Sn 2+ or Pb 2+ or any combination of Ti + , Ni 2+ , Pd 2+ , Pt 2+ , Cu + , Cu 2+ , Ag + , Au + , Zn 2+ , Cd 2+ , Hg 2+ , In 3+ , Ti 3+ , Ge 2+ , Sn 2+ and Pb 2+ .

17. A closed-circuit ventilation system in accordance with claim 7 , wherein:

the first receptor layer is part of a first capacitively coupled field effect transistor sensor portion and the second receptor layer is part of a second capacitively coupled field effect transistor sensor portion; and

the air gap present between the sensor electrode and the first receptor layer is also present between the sensor electrode and the second receptor layer as a shared air gap whereby the same gas stream flows through two different sensor portions or a second gap is present between the sensor electrode and the second receptor layer and is arranged such that anesthetic gas flows through the plurality of gas sensor portions in parallel.

18. A method for a quantitative determination of at least one anesthetic gas, the method comprising the steps of:

providing a ventilation system comprising a carrier gas source supplying a carrier gas, an anesthetic gas source supplying an anesthetic gas and a capacitively coupled field effect transistor sensor comprising a first, gas-sensitive, receptor layer with positive charge centers, wherein the first receptor layer is comprised of titanium nitride and titanium+ cations, a second, gas-sensitive, receptor layer with positive charge centers, wherein the second receptor layer is comprised of copper phthalocyanine, an insulation layer, a substrate, a drain, a source, a channel area located between the drain and the source, a gate electrode and a sensor electrode, wherein the channel area is spatially in connection with the gate electrode and at least the drain, the source and the channel area are arranged within the substrate; wherein the gate electrode is connected electrically conductively to the sensor electrode and an air gap is present between the sensor electrode and the first receptor layer, and the sensor electrode and the first receptor layer are otherwise separated by the insulation layer;

providing a flow of an analyte gas, comprising the anesthetic gas, through the air gap; and

determining quantitatively the anesthetic gas.

19. A method according to claim 18 , wherein the anesthetic gas is desflurane, sevoflurane, isoflurane, enflurane or halothane or any combination of desflurane, sevoflurane, isoflurane, enflurane and halothane.

20. A method according to claim 18 , wherein:

the first receptor layer is part of a first capacitively coupled field effect transistor sensor portion and the second receptor layer is part of a second capacitively coupled field effect transistor sensor portion;

the first capacitively coupled field effect transistor sensor portion comprises the insulation layer, the substrate, the drain, the source, the channel area located between the drain and the source, the gate electrode and the sensor electrode;

the second capacitively coupled field effect transistor sensor portion comprises a second insulation layer, a second substrate, a second drain, a second source, a second channel area located between the second drain and the second source a second gate electrode and a second sensor electrode; and

the air gap present between the sensor electrode and the first receptor layer is also present between the second sensor electrode and the second receptor layer as a shared air gap, whereby the same gas stream flows through two different sensor portions, or a second gap is present between the second sensor electrode and the second receptor layer and is arranged such that anesthetic gas flows through the plurality of gas sensor portions in parallel.