Sensitive layer for a chemical acetone sensor, its method of preparation and method of acetone measurement

Abstract

A sensitive layer (1) for a chemical sensor (10) of acetone (100), the sensitive layer (1) being composed of a crystalline nanostructure (2) of a copper-substituted ferrite (FC) of generic chemical composition CuXFe(3-X)O(4 + δ) where (X) and (δ) denote constants, the sensitive layer (1) being obtained by: formation of an amorphous deposit of said copper-substituted ferrite (FC) by sputtering, and heat treatment of the amorphous deposit of said copper-substituted ferrite (FC) by stabilizing annealing. Abstract figure: Figure 1

Description

Title of the invention: Sensitive layer for a chemical acetone sensor, method for obtaining it and method for measuring acetone Technical field

[0001] The present invention relates to the field of chemical detection of gases, in particular acetone.

[0002] It is known to measure the concentration of a gas in a medium, such as acetone, using a metal oxide semiconductor sensor, also called a "MOX sensor" or "MOS sensor". Such a sensor comprises a sensitive layer configured to be heated on which the gas particles attach, this phenomenon being known to those skilled in the art under the term "adsorption". The adsorption of the gas particles causes a variation in the electrical resistance of the sensitive layer depending on the quantity of adsorbed particles, which makes it possible to determine the concentration of the gas in the medium.

[0003] As is known, acetone is a gas of interest in the assessment of air quality as well as a marker whose concentration in a patient's breath makes it possible to diagnose a risk of diabetes. To determine its concentration, it is known to use a sensitive layer in the form of a ferrite nanostructure substituted for copper with a generic chemical composition CuFe2O4. Such a sensitive layer can be obtained by various methods, which impacts the nanostructure of the sensitive layer and its physicochemical gas detection properties.

[0004] It is known from the document "X.Yang et al. Sensors & Actuators: B. Chemical 270 (2018) 538-544" to obtain such a sensitive layer by solvothermal synthesis, which consists of the chemical reaction of reagents dissolved in a solvent in a closed container under pressure heated to a temperature above the boiling point of the solvent. The document "Z.Sun et al. Sensors & Actuators: B 125 (2007) 144-148" describes a method of obtaining by chemical synthesis in the solid state at low temperature. The document "N.Rezlescu et al. Romanian Reports in Physics, vol.61, n°2, p.223-234, 2009" describes a method of obtaining by sol-gel auto-combustion (solution-gelation). The document "C.Zaho et al. Ceramics International 44 (2018) 2856-2863 » describes a process for obtaining nanotubes by electrospinning (called “electrospinning” in English).

[0005] The sensitive layers resulting from such production processes all have the disadvantage of being sensitive to humidity. In other words, for a given concentration of acetone in a medium, such sensitive layers provide different results depending on the humidity level of the medium.

[0006] To overcome this drawback, it is known to measure the humidity level and to correct the measurement of the sensitive layer from predetermined data. Such a correction is in practice imprecise and unreliable. Such sensors are thus reserved for measuring the concentration of acetone in environments having a substantially constant humidity level.

[0007] The invention thus aims to measure an acetone concentration precisely and reliably, in particular in an environment having a variable humidity level. PRESENTATION OF THE INVENTION

[0008] The invention relates to a sensitive layer for a chemical acetone sensor, the sensitive layer consisting of a crystallized nanostructure of a copper-substituted ferrite of generic chemical composition CuxFe(3_X)O(4+ô) where X and ô denote constants, the sensitive layer being obtained by: • Formation of an amorphous deposit of said ferrite substituted for copper by cathodic sputtering, and • Heat treatment of the amorphous deposit of said ferrite substituted for copper by stabilization annealing.

[0009] In the generic chemical composition of copper-substituted ferrite, the value of the constants X and δ represents the deviation from stoichiometry.

[0010] Such a method for obtaining a sensitive layer of ferrite substituted for copper successively by cathodic sputtering and by stabilization annealing advantageously makes it possible to give it a specific nanostructure making the layer insensitive to humidity. Such a property is unprecedented and had never been observed in the sensitive layers of ferrite substituted for copper of the state of the art obtained by other methods (by solvothermal route, by solid synthesis at low temperature, by sol-gel autocombustion, by electrospinning in particular). The insensitive nature of the sensitive layer to humidity results in a very low drift, not exceeding 1% in the experimental results. Such a property advantageously makes it possible to measure the concentration of acetone in a medium in a reliable and precise manner, independently of the humidity level of the medium.

[0011] The nanostructure conferred by the process also makes it possible to measure very low concentrations of acetone, the minimum detection threshold not being reached for a concentration of 100ppb.

[0012] According to one aspect of the invention, said copper-substituted ferrite has a ratio of the element copper to the element iron of between 0.54 and 0.67, preferably of between 0.55 and 0.60, preferentially of between 0.57 and 0.58. The copper-substituted ferrite is thus superstoichiometric in copper.

[0013] According to one aspect of the invention, the stabilization annealing is carried out by heating the amorphous deposit of said copper-substituted ferrite to a temperature above 400°C, preferably above 450°C, preferably above 500°C. Preferably, the temperature is below 600°C. According to a preferred aspect, cooling to room temperature is carried out after heating during the stabilization annealing. Such a heat treatment advantageously makes it possible to obtain a specific crystalline microstructure making it possible to obtain the properties of insensitivity to humidity.

[0014] According to one aspect of the invention, the stabilization annealing is carried out by heating the amorphous deposit of said copper-substituted ferrite for at least 10 hours, preferably at least 12 hours and preferentially at least 14 hours. Preferably, the heating time is less than 20 hours. Such a heat treatment advantageously makes it possible to obtain a specific crystalline microstructure making it possible to obtain the properties of insensitivity to humidity.

[0015] According to a preferred aspect of the invention, cathode sputtering consists of projecting a plurality of particles of iron, copper and oxygen onto a substrate at a deposition pressure of between 0.2 Pa and 3 Pa, so as to form the amorphous deposit of said ferrite substituted for copper. Such deposition conditions advantageously make it possible, in synergy with annealing, to obtain a specific microstructure making it possible to obtain the properties of insensitivity to humidity.

[0016] According to a preferred aspect, the sensitive layer has a humidity drift of less than 10%, preferably less than 5%, preferentially less than 1%. Such a drift is calculated as the ratio between, on the one hand, the difference between the minimum value and the maximum value of the electrical resistance of the sensitive layer measured for the same given concentration of acetone at different humidity levels, and on the other hand, said maximum measured value. The experimental results from which the drift is determined are described and illustrated in Figures 6 to 8 of the invention. Such a property had never been observed in the prior art and is directly linked to the crystallized nanostructure of the sensitive layer conferred by its particular method of obtaining.

[0017] According to one aspect of the invention, the sensitive layer is configured to react chemically with acetone present in a medium at a concentration greater than 300 ppb, preferably greater than 200 ppb, preferentially greater than 100 ppb. Preferably, the sensitive layer is configured to react chemically with acetone present in a medium at a concentration greater than 3000 ppb. As illustrated in the experimental results of [Fig. 5], the minimum detection threshold of the sensitive layer is not reached for a concentration of 100 ppb, which advantageously makes it possible to measure very low concentrations of acetone. Such a property is directly linked to the crystallized nanostructure of the sensitive layer. conferred by its particular process of obtaining.

[0018] The invention also relates to an assembly of a sensitive layer as described above and a substrate on which the sensitive layer is fixed, in which, preferably, the amorphous deposit of said copper-substituted ferrite is formed on the substrate by cathodic sputtering.

[0019] The invention also relates to a chemical acetone sensor comprising a sensitive layer as described above, at least one heating element of the sensitive layer, at least one element for measuring a resistance of the sensitive layer and at least one element for calculating a measurement of the concentration of acetone from the measured resistance and a predetermined conversion function of the chemical sensor.

[0020] The invention also relates to a method for obtaining a sensitive layer as described above, consisting of: • Form an amorphous deposit of said ferrite substituted for copper by cathodic sputtering, and • Heat treat the amorphous deposit of said ferrite substituted for copper by stabilization annealing.

[0021] The invention also relates to a method for measuring acetone in a medium using a chemical sensor as described above, said measuring method consisting of: • Heat the sensitive layer to a predetermined temperature above 200°C, • Supply the sensitive layer with a polarization current, • Measure a resistance of the sensitive layer in the medium, and • Determine a measurement of acetone concentration from the measured resistance and a predetermined conversion function of the chemical sensor.

[0022] The invention further relates to a method for evaluating the air quality of a given medium consisting of implementing the measurement method as described previously by placing the sensitive layer in the given medium and comparing the measurement of acetone concentration with a predetermined maximum pollution threshold.

[0023] The invention further relates to a method for measuring a risk of diabetes in a subject consisting of implementing the measurement method as described above by placing the sensitive layer in contact with the subject's breath and comparing the measured concentration measurement to a predetermined diabetes risk threshold. PRESENTATION OF FIGURES

[0024] The invention will be better understood on reading the description which follows, given by way of example, and referring to the following figures, given by way of non-limiting examples: mitatives, in which identical references are given to similar objects.

[0025] [Fig.l] is a schematic representation of a chemical acetone sensor comprising a sensitive layer according to one embodiment of the invention.

[0026] [Fig. 2] is a schematic representation of a method for obtaining a sensitive layer according to one embodiment of the invention.

[0027] [Fig. 3] is a schematic representation of the formation of an amorphous deposit of copper-substituted ferrite by sputtering according to the manufacturing method of [Fig. 2].

[0028] [Fig.4] is a schematic representation of a method for measuring acetone according to one embodiment of the invention.

[0029] [Fig.5] is a schematic representation of experimental results of measurements of the resistance of the sensitive layer for different concentrations of acetone at constant humidity.

[0030] [Fig.6], [Fig.7] and [Fig.8] are schematic representations of experimental results of measurements of the resistance of the sensitive layer for different humidity levels at constant acetone concentration.

[0031] It should be noted that the figures set out the invention in detail for implementing the invention, said figures can of course be used to better define the invention where appropriate. DETAILED DESCRIPTION OF THE INVENTION

[0032] With reference to [Fig.l], the invention relates to a sensitive layer 1 for a chemical acetone sensor 10 which is made up of a crystallized nanostructure 2 of a ferrite substituted for copper of generic chemical composition CuxFe(3_x)O(4+ô) where X and ô denote constants, the sensitive layer being capable of being obtained by the following production method ([Fig.2]): • form an amorphous deposit 3 of said ferrite substituted for copper by cathodic sputtering A ([Fig.3]), and • heat treat the amorphous deposit 3 of said ferrite substituted for copper by a stabilization annealing B.

[0033] The constant X corresponds to the quantity of copper atoms, and (3-X) to the quantity of iron atoms. The constant ô represents the deviation from oxygen stoichiometry.

[0034] Preferably, the copper-substituted ferrite is over-stoichiometric in copper and has a ratio of the element copper to the element iron of between 0.54 and 0.67, preferably of between 0.55 and 0.60, preferably of between 0.57 and 0.58. For a ratio of 0.54, the copper content X verifies: X / (3-X) = 0.54 or X = 1.05. For a ratio of 0.67, the copper content X verifies: X / (3-X) = 0.67 or X = 1.20. The value of the copper content X is preferably between 1.05 and 1.20.

[0035] The sensitive layer 1 according to the invention has, thanks to its production process, a particular crystallized nanostructure giving it the unprecedented property of being insensitive to humidity, as shown by the experimental results of Figures 6, 7 and 8 described below. Such a property has never been observed in the sensitive layers made of copper-substituted ferrite of the prior art which are obtained by different processes. In addition, the sensitive layer 1 according to the invention is advantageously sensitive to very low concentrations of acetone, in particular of the order of 100ppb, as shown by the experimental results of [Fig. 5] described below. The sensitive layer 1 according to the invention thus makes it possible to measure the acetone concentration precisely and reliably, in particular in an environment with a variable humidity level.It should be noted that the English acronym "ppb" means "parts per billion" and that 100ppb corresponds to 0.1ppm, the acronym "ppm" meaning "parts per million".

[0036] With reference to [Fig.l], the sensitive layer 1 is configured to be mounted in a chemical sensor 10, typically of the metal oxide semiconductor type, known as a “MOX sensor” or “MOS sensor”. The chemical sensor 10 comprises a substrate 4, on which the sensitive layer 1 extends, and a heating element 5, configured to heat the sensitive layer 1 to a predetermined operating temperature Tref. The sensitive layer 1 is also electrically powered by a bias current i.

[0037] As illustrated in [Fig.l], the substrate 4 is an electrically insulating support, made for example of silicon oxide, aluminum oxide or zirconium oxide, preferably of silicon oxide. The sensitive layer 1 is preferably formed directly on the substrate 4. The heating element 5 is preferably mounted in contact with the substrate 4 to heat the sensitive layer 1 by conduction, and is preferably in the form of heating resistors. The operating temperature Tref is preferably between 350°C and 550°C, preferably between 450°C and 500°C. The density of the polarization current i is preferably between 0.045 A / cm2 and 90 A / cm2, and is provided for example by an electric generator.

[0038] As illustrated in [Fig.l], when heated to the operating temperature Tref and supplied with the bias current i, the sensitive layer 1 is configured to react chemically at least with the acetone 100, known as “propanone”, present in a medium 110. The acetone molecules 100 become fixed on the sensitive layer 1 by adsorption, which causes a variation in the electrical resistance R of the sensitive layer 1 due to the oxidation of the acetone 100.

[0039] Still with reference to [Fig.l], the chemical sensor 10 comprises a measuring element 6 for measuring the variation in electrical resistance R which depends on the quantity of acetone molecules 100 adsorbed. The measuring element 6 is for example in the form of an ohmmeter connected to the sensitive layer 1 by electrodes, preferably made of platinum or tantalum. The chemical sensor 10 also comprises a calculating element 7, such as a calculator, which, from the resistance measurement R and a predetermined conversion function f specific to the sensor 10, is configured to determine the concentration Cmes of acetone 100 in the medium 110. The operation of a MOX sensor 10 is known per se to those skilled in the art and will not be described further.

[0040] Figures 2 and 3 illustrate a method for obtaining the sensitive layer 1 according to the invention. In a first step, an amorphous deposit 3 of ferrite substituted for copper is formed by cathodic sputtering A, known by the English term "sputtering". In a second step, the amorphous deposit 3 of ferrite substituted for copper is heat treated by stabilization annealing B to form the sensitive layer 1 according to the invention.

[0041] As illustrated in [Fig. 3], the cathode sputtering A is implemented in a closed enclosure 11 in a rarefied atmosphere comprising at least one neutral gas 120, namely one that does not react chemically with the ferrite substituted for copper, among the rare gases (neon, argon, krypton, xenon), preferably argon. A radiofrequency generator 9 is electrically connected to the target which is placed in the closed enclosure 11 and makes it possible to generate a polarization field which partially ionizes the neutral gas 120 by electromagnetic excitation so as to form a plasma. A magnetic field can be added (process called magnetron deposition). The generator 9 preferably applies electromagnetic pulses with a local power density of between 2 W / cm2 and 8 W / cm2 at the level of the sputtered surface. The frequency of the imposed electromagnetic field is 13.56 MHz.

[0042] As illustrated in [Fig. 3], the closed enclosure 11 also comprises a cathode 8 made of copper-substituted ferrite, known as the "target", as well as the substrate 4. Alternatively, the cathode 8 is a mixture of copper and iron in the desired proportions for the copper-substituted ferrite and the plasma is enriched with oxygen. Alternatively, two cathodes 8 are used, one made of iron and the other of copper, the plasma being enriched with oxygen. The cathode(s) 8 are placed in the electromagnetic field generated by the radiofrequency generator 9. The substrate 4 is placed at a predetermined distance d from the cathode 8, preferably between 4 cm and 10 cm.

[0043] As illustrated in [Fig.3], when implementing cathode sputtering A, the plasma energy exerted on the cathode 8 (namely the energy transferred by each neutral gas ion 120 striking the cathode 8) makes it possible to tear off the atoms of the material of the cathode 8 one by one and to project them onto the substrate 4, preferably at a deposition pressure of between 0.2 Pa and 3 Pa, depending on the predetermined distance d. The principle of cathode sputtering A is known per se to those skilled in the art and is not described further.

[0044] At the end of the cathode sputtering A, an amorphous deposit 3 of ferrite substituted for copper 3 is formed on the substrate 4. The deposit 3 is in the form of a solid thin layer having a thickness of less than 100 nm forming a nanostructure. The amorphous state of the deposit 3, as opposed to a crystallized state, is characterized by a disordered arrangement of the atoms in space.

[0045] With reference to [Fig. 2], the amorphous deposit 3 then undergoes a stabilization annealing B, namely a post-synthesis heat treatment making it possible to develop in the deposit 3 a crystalline network so as to form a compacted sensitive layer 1. The stabilization annealing B is implemented by placing the deposit in the amorphous state 3 in a closed enclosure, such as a furnace, which is heated to a high temperature, namely above 400°C. Preferably, the heating temperature is between 450°C and 600°C, preferably between 500°C and 550°C. The heating time is preferably greater than 12 hours, preferably greater than 14 hours and less than 16 hours. The sensitive layer 1 is then cooled in the open air.

[0046] At the end of the stabilization annealing B, the sensitive layer 1 is formed. The sensitive layer 1 is in the form of a solid thin layer having a thickness of less than 100 nm forming a nanostructure. The sensitive layer 1 has a crystallized state, namely in which the atoms are arranged in an orderly and compact manner. The combination of a synthesis by cathode sputtering A and a stabilization annealing B together make it possible to obtain a specific crystallized structure at the nanometric scale which gives the sensitive layer 1 particular properties, which are detailed in the experimental measurement results of Figures 5 to 8 presented subsequently.

[0047] [Fig. 4] represents a method for measuring the concentration of acetone 100 in a medium 110 which is implemented using the chemical sensor of [Fig. 1] and which consists of: • Heat El the sensitive layer 1 to a predetermined temperature Tref greater than 200°C, • Supply E2 to the sensitive layer 1 with a polarization current i, • Measure E3 a resistance R of the sensitive layer 1 in the medium 110, and • Determine E4 a concentration measurement Cmes of acetone 100 from the measured resistance R and a predetermined conversion function f of the chemical sensor 10.

[0048] The heating step E1 is implemented by the heating element 5 at an operating temperature Tref preferably between 350°C and 550°C, preferably between 450°C and 500°C. The power supply step E2 is preferably implemented by the electrical generator and the density of the polarization current i is preferably between 0.045 A / cm2 and 90 A / cm2. Once the heating steps E1 and supply E2 have been implemented, the chemical sensor 10 is operational and makes it possible to measure E3 the variation in resistance R induced by the adsorption of the acetone 100 present in the medium 110 on the sensitive layer 1. The measurement step E3 is implemented by the measuring element 6 and is transmitted to the calculation element 7. During the determination step E4, the measured concentration Cmes is determined from the measured resistance R and the predetermined conversion function f specific to the sensor 10.

[0049] According to a preferred aspect, the method is implemented by placing the sensitive layer 1 of the sensor 10 in a medium whose air quality is to be evaluated. The measured concentration Cmes is then compared to a maximum pollution threshold.

[0050] According to another preferred aspect, the method is implemented by placing the sensitive layer 1 of the sensor 10 in the breath expelled by a subject. The measured concentration Cmes is then compared to a risk threshold for developing diabetes. Such a measurement is advantageously non-invasive.

[0051] The experimental results of [Fig. 5] illustrate the resistance R measured by the chemical sensor 10 for different Creel concentrations of acetone 100 in a medium 110 having a humidity level H equal to 50%. The concentration of acetone 110 in the medium 110, namely a closed volume of small volume, is controlled. In the context of the experiment, the medium 110 is at the initial instant t=0 devoid of acetone and the value of the resistance R measured corresponds to the baseline of the chemical sensor 10. At successive spaced time intervals (dotted in [Fig. 5]), a known decreasing Creel concentration of acetone 100 is injected into the medium 110 and the resistance R is measured. Between two time intervals, the injection of acetone 100 is stopped and the medium 110 contains only 50% humid air. The time scale illustrated in [Fig.5] is expressed in hours.

[0052] As illustrated in [Fig. 5], the measured resistance R increases when the acetone concentration Creel decreases in the medium 110. In addition, the minimum detection threshold is not reached for the value Creel = 100ppb, the chemical sensor 10 thus being suitable for measuring very low concentrations of acetone 100. The saturation threshold is furthermore not reached for the value Creel = 2500ppb, the chemical sensor 10 thus being suitable for measuring a wide range of acetone concentrations 100 between 100ppb and 2500ppb.

[0053] The experimental results in [Fig.6] illustrate the resistance R measured by the chemical sensor 10 for a predetermined Creel concentration of acetone 100 of 2500ppb in a medium 110 with a decreasing humidity level H. In the experiment, the medium 110 is at the initial time t=0 devoid of acetone and the value of the resistance R measured corresponds to the baseline of the chemical sensor 10. At successive spaced time intervals (dotted in [Fig.5]), acetone 100 is injected to reach a Creel concentration = 2500ppb in the medium 110. Between two time intervals, the acetone 100 is stopped. At the same time, for each time interval, the humidity level H of the medium decreases by 10%. The time scale illustrated in [Fig.6] is expressed in hours.

[0054] As illustrated in [Fig.6], the resistance R measured in air is substantially identical regardless of the humidity level H of the medium 110, namely between 29 1000 Ohm and 30 3000 hm, which corresponds to a drift d = (30 300 - 29 100) / 30 300 = 3.96%, less than 4%. In addition, the response is substantially identical and equal to 2 + 0.1 regardless of the humidity level H of the medium 110.

[0055] Figures 7 and 8 illustrate the same experiment as [Fig.6] with a concentration respectively Creel=500ppb and Creel=100ppb. Similarly, the measured resistance R is substantially identical regardless of the humidity level H of the medium 110, namely that the measured drift is less than 1%. The chemical sensor 10 is advantageously insensitive to humidity, which makes it possible to carry out measurements in environments 110 with a variable humidity level.

Claims

Claims

1. Sensitive layer (1) for a chemical sensor (10) of acetone (100), the sensitive layer (1) consisting of a crystallized nanostructure (2) of a copper-substituted ferrite (FC) of generic chemical composition CuxFe(3_x)O(4+ô) where (X) and (ô) denote constants, the sensitive layer (1) being obtained by: • formation of an amorphous deposit (3) of said copper-substituted ferrite (FC) by cathodic sputtering (A), and • heat treatment of the amorphous deposit (3) of said copper-substituted ferrite (FC) by stabilization annealing (B).

2. The sensitive layer (1) according to claim 1, wherein said copper-substituted ferrite (FC) has an atomic ratio of the element copper to the element iron of between 0.54 and 0.67, preferably between 0.55 and 0.60, preferentially between 0.57 and 0.

58.

3. Sensitive layer (1) according to one of claims 1 and 2, wherein the stabilization annealing (B) is carried out by heating the amorphous deposit (3) of said copper-substituted ferrite (FC) to a temperature (T) greater than 400°C, preferably greater than 450°C, preferentially greater than 500°C.

4. Sensitive layer (1) according to one of claims 1 to 3, wherein the stabilization annealing (B) is carried out by heating the amorphous deposit (3) of said copper-substituted ferrite (FC) for at least 10 hours, preferably at least 12 hours, preferentially at least 14 hours.

5. Sensitive layer (1) according to one of claims 1 to 4, comprising a humidity drift of less than 10%, preferably less than 5%, preferably less than 1%.

6. Sensitive layer (1) according to one of claims 1 to 5, configured to react chemically with acetone (100) present in a medium (110) at a concentration (Creel) greater than 300ppb, preferably greater than 200ppb, preferentially greater than 100ppb.

7. An assembly of a sensitive layer (1) according to one of claims 1 to 6 and a substrate (4) on which the sensitive layer (1) is fixed, in which, preferably, the amorphous deposit (3) of said copper-substituted ferrite (FC) is formed on the substrate (4) by ca- theodic (A).

8. Chemical sensor (10) for acetone (100), comprising a sensitive layer (1) according to one of claims 1 to 6, at least one heating element (5) of the sensitive layer (1), at least one measuring element (6) of a resistance (R) of the sensitive layer (1) and at least one calculating element (7) of a concentration measurement (Cmes) of the acetone (100) from the measured resistance (R) and a predetermined conversion function (f) of the chemical sensor (10).

9. Method for obtaining a sensitive layer (1) according to one of claims 1 to 6 consisting of: • Forming an amorphous deposit (3) of said copper-substituted ferrite (FC) by cathodic sputtering (A), and • Heat treating the amorphous deposit (3) of said copper-substituted ferrite (FC) by stabilization annealing (B).

10. Method for measuring (E) acetone (100) in a medium (110) from a chemical sensor (10) according to claim 8, said measuring method (E) consisting of: • Heating (El) the sensitive layer (1) to a predetermined temperature (Tref) greater than 200°C, • Supplying (E2) the sensitive layer (1) with a polarization current (i), • Measuring (E3) a resistance (R) of the sensitive layer (1) in the medium (110), and • Determining (E4) a concentration measurement (Cmes) of the acetone (100) from the measured resistance (R) and a predetermined conversion function (f) of the chemical sensor (10).

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