Method for characterising analytes comprising varying the temperature using an interferometric electronic nose

Abstract

The invention relates to a method for characterising analytes using an interferometric electronic nose, the method comprising the following steps: o exposing the functionalised surface (4) to the gaseous medium containing the analytes, which functionalised surface has an initial temperature at most equal to T1 so that it has an adsorbed initial state; o increasing the temperature of the functionalised surface (4) to at least T2 so that it has a desorbed final state; o measuring the optical signal transmitted by the interferometer 12; o determining an extracted phase difference φ(k)(t) and subsequently an unwrapped phase difference Φ(k)(t), and finally initial Φ(k)i and final Φ(k) f values thus making it possible to characterise the analytes.

Description

METHOD FOR CHARACTERIZING ANALYTES COMPRISING A TEMPERATURE VARIATION BY MEANS OF AN INTERFEROMETRIC TYPE ELECTRONIC NOSE TECHNICAL FIELD

[0001] The field of the invention is that of the characterization of analytes present in a gaseous medium by an interferometric type electronic nose. STATE OF THE PRIOR ART

[0002] The ability to analyze and characterize analytes present in a gaseous environment or contained in a gaseous medium, such as for example odorous molecules or volatile organic compounds, is an increasingly important issue, particularly in the fields of health, the food industry, the perfume industry (fragrances), and even olfactory comfort in confined public or private places (automobile, hotels, shared places, etc.), etc. The characterization of such analytes present can be carried out by a characterization system called an "electronic nose".

[0003] Different characterization approaches exist, which are distinguished from each other in particular by the need or not to have to "mark" the analytes or receptors beforehand with a revealing agent. Unlike, for example, fluorescence detection which requires the use of such markers, detection using surface plasmon resonance imaging (SPRi) and that using an interferometric principle, for example of the Mach-Zehnder type (MZI), are so-called label-free techniques.

[0004] In an electronic nose using SPRi or MZI technology, the analytes present in a gaseous medium interact by adsorption / desorption with receptors located in one or more sensitive sites of a functionalized surface. This involves detecting in real time an optical signal associated with each of the sensitive sites, representative of the temporal variation of the local refractive index due to the adsorption / desorption interactions of the analytes with the receptors. In the context of SPRi technology, for example, the intensity of the optical signals coming from the different sensitive sites is measured in real time, these optical signals being a reflected part of an optical excitation signal emitted by a light source. The intensity of each optical signal detected by an optical sensor is directly correlated to the adsorption / desorption interactions of the analytes with the receptors.

[0005] In this respect, Figure 1A illustrates an example of an electronic nose 40 of the SPRi type similar to that described in the article by Brenet et al. entitled Highly-Selective Optoelectronic Noze Based On Surface Plasmon Resonance Imaging for Sensing Volatile Organic Compounds, Anal. Chem. 2018, 90, 16, 9879-9887. It comprises a functionalized surface 41 comprising the receptors, an SPR imaging measurement device, a processing unit 47, and a fluid management device (not shown). The functionalized surface 41 is located on one face of a prism 42, and is formed of a plurality of sensitive sites adapted to capture by adsorption analytes present in a gaseous sample. The measuring device further comprises a light source 43, an optical shaping device 44 formed here by a collimating lens and a polarizer, an optical imaging device 45 and a matrix photodetector 46 (image sensor).The processing unit 47 makes it possible to characterize the analytes from the measurement signals provided by the measurement device. The fluidic management device is designed to bring a gaseous sample containing the analytes into contact with the functionalized surface. In operation, the light source 43 emits the optical excitation signal towards the functionalized surface 41 at a working angle making it possible to generate surface plasmons there. The reflected part of the optical excitation signal, forming a measurement signal, is then detected by the image sensor 46. The intensity of the measurement signal depends on the local refractive index of the functionalized surface 41, which itself depends on the surface plasmons generated and the quantity of analytes located at each sensitive site.

[0006] Figure 1B illustrates an example of an interferometer 12 of an electronic nose 1 of the interferometric type, as described in document EP3754326A1. This electronic nose 1 also comprises a functionalized surface 4 where the receivers are located, a measuring device formed of a light source, a matrix of Mach-Zehnder interferometers 12 produced in an integrated photonic circuit, and photodetectors, and finally comprises a processing unit. Each interferometer 12 comprises two waveguides, one of which forms a reference arm 14r, and the other a sensitive arm 14s on the surface of which are located the receptors which define a sensitive site of the functionalized surface 4. The presence of analytes adsorbed on the surface of the sensitive arm 14s modifies the properties of the optical signal passing through it, and more precisely causes a modification of the phase of the optical signal, whereas the phase of the optical signal passing through the reference arm 14r is not modified.The phase difference between these optical signals leads to constructive or destructive interference which modulates the power of the output optical signal detected by the photodetector.

[0007] A characterization process usually consists of acquiring and comparing representative values, for each sensitive site, of an initial physicochemical state of the sensitive site where the receptors are not bound to the analytes, and of a final physicochemical state where the receptors are bound to the analytes. The signature can then be formed from the difference between these values initial and final for each of the sensitive sites. A physicochemical state is therefore a state of a sensitive site or of the functionalized surface defined by the proportion of receptors bound to the analytes or even to other species capable of binding to the receptors. By proportion of receptors, we mean the ratio of the number of bound receptors to the total number of receptors of the sensitive site. Thus, a physicochemical state can correspond to a stationary state called desorbed where the receptors are not bound to the analytes (or to any other chemical species), for example a majority of the receptors, or even almost all the receptors are not bound. Conversely, a physicochemical state called adsorbed corresponds to a stationary state where the receptors are bound to the analytes (or to any other chemical species), for example a majority of the receptors, or even almost all the receptors are bound.Thus, in the context of a characterization process, two values ​​are usually acquired, namely a first value linked to an initial desorbed physicochemical state, and a second value linked to a final adsorbed physicochemical state.

[0008] In this respect, Figure 1C illustrates an example of a signal (or sensorgram) obtained by an SPRi type electronic nose during such a characterization process. A sensorgram is a signal corresponding to the temporal evolution of a parameter representative of the adsorption / desorption interactions of analytes with the receptors of a sensitive site. These sensorgrams can be so-called useful signals on (k)(t) corresponding to the temporal evolution of the variation ^%R(k)(t) of the reflectivity associated with each of the sensitive sites (here referenced by the index k ranging from 1 to K). The reflectivity %R is here the ratio between the intensity of the optical measurement signal detected by the image sensor on the intensity of the optical excitation signal emitted by the light source. The variation of reflectivity ^%R is obtained by subtracting from the temporal evolution of the reflectivity %R(t) a reference value (baseline, in English) associated with a reference gas not containing analytes. Also, the useful signals on (k) (t) all have the same constant initial value which is approximately zero.

[0009] Thus, a characterization method usually comprises at least two successive phases of exposure of the functionalized surface to different gaseous environments, namely a first phase Ph1 called reference where the functionalized surface is exposed to a reference gas not containing the analytes, then a second phase Ph2 called characterization where it is exposed to a sample or a gaseous environment containing the analytes, and finally a third phase Ph3 called purge where the analytes are evacuated by the renewal of the gaseous environment. Thus, the stationary values ​​of the useful signals are determined on (k) (t) during both phases Ph1 and Ph2, namely the first values ​​su (k)i(here substantially zero) representative of the initial desorbed physicochemical state of the sensitive sites, and the second values ​​su(k)f representative of the final adsorbed physicochemical state of the sensitive sites. The signature S then corresponds to the set of values ​​{ su(k)f – su(k)i}1≤k≤K of the K sensitive sites.

[0010] However, as can be seen, the quality of the characterization depends in particular on the fact that the sensitive sites initially present a physicochemical state that is actually desorbed on the one hand, and that the functionalized surface presents a homogeneity between the physicochemical states of the sensitive sites on the other hand. It is understood that if one or other of the sensitive sites presents an initial physicochemical state that is not actually desorbed, that is to say, the quantity of available receptors is reduced compared to that of the neighboring sensitive sites, it will provide a response in terms of interaction with the analytes that is not comparable to those of the other sensitive sites. This then leads to a signature that is no longer characteristic of the analytes.

[0011] In the case of an SPRi type measurement, it is easy to detect such a situation. Indeed, the initial physicochemical state of a sensitive site that would not be desorbed can be easily identified by examining the measurement signals (reflectivity %R(t) during phase Ph1) acquired by the image sensor, since their values ​​are directly representative of the physicochemical state of the sensitive site considered. More precisely, a sensitive site whose physicochemical state is not totally desorbed has a reflectivity value %R(t) higher than that of a sensitive site that would be totally desorbed.

[0012] On the other hand, in the case of an interferometric measurement, it is more difficult to identify a sensitive site whose initial physicochemical state would not be desorbed. Indeed, as indicated by Halir et al. in the article entitled Direct and Sensitive Phase Readout for Integrated Waveguide Sensors, Photonics Journal IEEE, vol. 5, no. 4, 2013, the power of the optical signal received by the photodetector is a sinusoidal function of the phase difference between the signals traveling through the two arms of the interferometer. Also, the temporal evolution of the phase difference determined from that of the detected optical power presents an indeterminacy modulo 2π which does not allow to know the initial effective physicochemical state of the sensitive site.

[0013] There is therefore a need to have an interferometric type electronic nose and a characterization method making it possible to reduce or even eliminate the risks of degradation in the quality of the characterization of the analytes. DISCLOSURE OF THE INVENTION

[0014] The invention aims to remedy at least in part the drawbacks of the prior art, and more particularly to propose a characterization method using an interferometric type electronic nose, making it possible to reduce or even eliminate the risks of degradation of the quality of the characterization of the analytes, in particular by ensuring that the or the sensitive sites of the functionalized surface present, during the process, a physicochemical state that is effectively desorbed and homogeneous.

[0015] For this purpose, an object of the invention is a method for characterizing analytes present in a gaseous medium, by means of an electronic nose. This comprises: - a functionalized surface containing at least one sensitive site having receptors with which the analytes are capable of interacting by adsorption / desorption, the sensitive site having a physicochemical state defined by a proportion of the receptors bound to the analytes; - a measuring device, comprising: at least one interferometer having two waveguides, one of which forms a sensitive arm on the surface of which the sensitive site is located and the other a reference arm, coupled to a light source; and at least one photodetector coupled to the interferometer; - a processing unit, connected to the photodetector; - a thermal module, adapted to generate a temperature variation of the functionalized surface.

[0016] The characterization method comprises the following steps: - a) exposing the functionalized surface to the gaseous medium containing the analytes, the functionalized surface having an initial temperature at most equal to a first predefined value T1, such that the functionalized surface has an initial physicochemical state called adsorbed where the proportion of receptors bound to the analytes is equal to a non-zero initial value pia; - b) generation by the thermal module of an increase in temperature of the functionalized surface up to at least a second predefined value T2, thus causing a change of state between the initial adsorbed physicochemical state and a final physicochemical state called desorbed where the proportion of receptors bound to the analytes is equal to a final value p fd less than p ia; - c) measurement by the photodetector of the optical signal transmitted by the interferometer, during the exposure and temperature increase generation steps; - d) determination by the processing unit: of a so-called extracted phase difference φ(k)(t) between the optical signals circulating in the waveguides, from the measured optical signal, the values ​​of which are included in a predefined width interval; then of a so-called unfolded phase difference Φ (k) (t), by unfolding the extracted phase difference φ (k) (t) by adding to it a positive or negative integer multiple of the interval width; then of initial values ​​Φ(k)i and final Φ(k)f of the unfolded phase difference Φ(k)(t), respectively representative of the initial adsorbed and final desorbed physicochemical states of the functionalized surface; - e) characterization of the analytes (2), from the initial values ​​Φ (k)i and final Φ (k)f .

[0017] Some preferred, but not limiting, aspects of this characterization method are as follows.

[0018] The temperature difference between the first value T1 and the second value T2 may be at least 5°C. The first value T1 may be at most 25°C, and the second value T2 may be at least 30°C. The first value T1 may be between 2°C and 25°C, and the second value T2 may be between 30°C and 60°C.

[0019] Steps a) to e) may be repeated successively, the functionalized surface then being successively exposed, at each new step a), either to the same gaseous medium in terms of type and concentration of analytes, or to different gaseous media in terms of type and / or concentration of analytes.

[0020] The invention also relates to an electronic nose suitable for characterizing analytes present in a gaseous medium, for implementing the characterization method according to any one of the preceding characteristics. The electronic nose comprises: - a functionalized surface containing at least one sensitive site having receptors with which the analytes are capable of interacting by adsorption / desorption, the sensitive site having a physicochemical state defined by a proportion of the receptors bound to the analytes; - a measuring device, comprising: at least one interferometer having two waveguides, one of which forms a sensitive arm on the surface of which the sensitive site is located and the other a reference arm, coupled to a light source; and at least one photodetector coupled to the interferometer;- a processing unit, connected to the photodetector, adapted to determine: a so-called extracted phase difference φ(k)(t) between the optical signals circulating in the waveguides, from an optical signal measured by the photodetector, the values ​​of which are included in a predefined width interval; then a so-called unfolded phase difference Φ(k)(t), by unfolding the extracted phase difference φ; (k) (t) by adding to it a positive or negative integer multiple of the interval width; then initial values ​​Φ (k)i and final Φ (k)fof the unfolded phase difference Φ(k)(t), respectively representative of initial adsorbed and final desorbed physicochemical states of the functionalized surface, then allowing the analytes to be characterized; - a thermal module adapted to generate a temperature variation of the functionalized surface, thus causing a transition of state between the initial adsorbed physicochemical state and the final desorbed physicochemical state, from: an initial temperature at most equal to a first predefined value T1 for which the functionalized surface has an initial adsorbed physicochemical state where a proportion of the receptors linked to the analytes is equal to an initial value p ia non-zero; at a final temperature at least equal to a second predefined T2 value for which the functionalized surface has a final desorbed physicochemical state where the proportion of receptors bound to the analytes is equal to a final pfd value lower than pia.

[0021] The thermal module may include a heater that extends opposite the arms of the interferometer.

[0022] The functionalized surface may be located on a first face of a support where the waveguides are located, the heater being arranged on a second face of the support opposite the first face, the support being made of a thermally conductive material.

[0023] The measuring device may comprise a plurality of interferometers, the heater extending opposite the arms of all said interferometers.

[0024] The thermal module can be adapted to increase the temperature of the functionalized surface to a final temperature between 30°C and 60°C.

[0025] The thermal module may comprise an electrical source adapted to apply to a heater a stepped electrical signal causing the temperature to increase.

[0026] The thermal module can be adapted to cause the temperature to increase from the initial temperature to the final temperature in a period of at most 5 seconds.

[0027] The interferometer can be a Mach-Zehnder interferometer or a resonant ring interferometer. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Other aspects, aims, advantages and characteristics of the invention will appear better on reading the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and made with reference to the appended drawings in which: Figure 1A, already described, is a schematic and partial view of an electronic nose of the SPR imaging type according to an example of the prior art; Figure 1B, already described, is a schematic and partial view of an interferometer of an electronic nose of the interferometric type according to an example of the prior art; Figure 1C, already described, illustrates examples of sensorgrams su(k)(t) determined by an electronic nose of the SPR imaging type during a determination method; Figure 2A is a schematic and partial view of an electronic nose of the interferometric type according to one embodiment; Figure 2B is a schematic top view of the electronic nose measuring device of Fig. 2A, comprising the light source, an interferometer matrix and photodetectors; Figure 2C is a schematic top view of the sensitive arm and the reference arm of an interferometer of Fig. 2B; Figure 3A illustrates time evolutions of the extracted phase difference φ(k)(t) and the unfolded phase difference Φ (k) (t) associated with the optical signals traveling through the arms of an interferometer of Fig. 2B, highlighting the phase unfolding; Figure 3B illustrates a flowchart of steps for determining the extracted phase difference φ(k)(t) and the unfolded phase difference Φ(k)(t), associated with an interferometer of Fig. 2B, during a characterization process; Figures 4A to 4C illustrate time evolutions of the extracted phase difference φ (k) (t) and the unfolded phase difference Φ (k)(t) relating to an interferometer of a nose in the case of a usual characterization method (fig.4A), and in the case where the initial physicochemical state of the sensitive site is effectively desorbed (fig.4B), and finally in the case where the initial physicochemical state is not desorbed (fig.4C); figure 5A is a schematic and partial view of an electronic nose of the interferometric type according to an embodiment of the invention; figure 5B is a schematic view, from above, of the thermal module of the electronic nose of fig.5A; figure 5C is a schematic view, from above, of the thermal module and the interferometers of the electronic nose of fig.5A; Figure 6A illustrates an example of evolution of the interactions between the analytes and the receptors of the functionalized surface, during a characterization method according to an embodiment of the invention, where the desorption is carried out by increasing the temperature variation of the functionalized surface; Figure 6B illustrates an increase in the temperature of the functionalized surface during a characterization method according to an embodiment of the invention; Figure 6C illustrates temporal evolutions of the extracted phase difference φ(k)(t) and of the unfolded phase difference Φ(k)(t) during the characterization method of Figs. 6A and 6B; Figure 7A illustrates an example of variation of the temperature of the functionalized surface, during a succession of characterization phases of gaseous media; Figure 7B illustrates an example of temporal evolutions of the unfolded phase difference Φ. (k)(t) during the succession of characterization phases of fig.7A, in the case where the surface functionalized surface is exposed to the same gaseous medium (identical type and concentration of analytes); Figure 7C illustrates another example of temporal evolutions of the unfolded phase difference Φ(k)(t) during the succession of characterization phases of Fig. 7A, in the case where the functionalized surface is exposed to different gaseous media in terms of type and / or concentration of analytes. DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

[0029] In the figures and in the remainder of the description, the same references represent identical or similar elements. In addition, the different elements are not shown to scale so as to enhance the clarity of the figures. Furthermore, the different embodiments and variants are not mutually exclusive and may be combined with each other. Unless otherwise indicated, the terms "substantially", "approximately", "of the order of" mean to within 10%, and preferably to within 5%. Furthermore, the terms "between ... and ..." and equivalents mean that the limits are included, unless otherwise indicated.

[0030] The invention relates generally to the characterization of analytes present in a gaseous sample or in a gaseous medium to be analyzed. The characterization is carried out by means of an interferometric type electronic nose, which comprises at least: a functionalized surface comprising at least one sensitive site where receptors are located; a measuring device comprising a light source, at least one interferometer comprising two waveguides which form a sensitive arm and a reference arm, at least one photodetector; and a processing unit. It also comprises a thermal module adapted to generate an increase in the temperature of the functionalized surface, thus causing a change in state of the sensitive site(s), namely the passage from an initial physicochemical state called adsorbed E ia where receptors are bound to the analytes, in a final physicochemical state called desorbed E fdwhere at least part of these receptors is no longer bound to the analytes. The characterization of the analytes is then carried out from initial values ​​Φ(k)i and final Φ(k)f of the unfolded phase difference Φ(k)(t) associated respectively with the initial adsorbed state Eia and the final desorbed state Efd.

[0031] In the initial adsorbed physicochemical state Eia, the sensitive site has a certain proportion of its receptors that are bound to the analytes, equal to an initial value p ia non-zero, or even, equivalently, a certain quantity of receptors bound to the analytes. The proportion p of receptors bound to the analytes is the ratio of the quantity of receptors then bound to the analytes to the total quantity of receptors of the sensitive site. The initial proportion pia can be equal to 20%, 30%, 50%, 80%, or even approximately 100%, of the total quantity of receptors of the site sensitive. Moreover, in the final desorbed physicochemical state Efd , the sensitive site has a proportion of receptors bound to the analytes equal to a final value p fd , or even a quantity of receptors bound to the analytes. This final proportion pfd is lower than the initial value pia since there has been desorption of the analytes. It can be equal to 80%, 50%, 30%, 20% of the initial value pia, or even be equal to approximately 0% of pia, which corresponds to the fact that none of the receptors of the sensitive site are bound to the analytes. The initial states E ia and final E fd are preferably stationary states (but may not be). By stationary state, we mean that the relative variation of the measurement signal from the photodetector, between two successive measurement times, is less than a predefined threshold value, for example equal to 10% or even 5%.

[0032] The electronic nose according to the invention thus makes it possible to improve the quality of the characterization, insofar as the initial values ​​Φ (k)i and final Φ (k)f are associated with initial and final states which are effectively adsorbed and desorbed states, even though the extracted phase difference φ(k)(t) still has an indeterminacy modulo 2π. It also allows the use of a simplified fluidic device for fluidic management, or can even operate without any fluidic device. Thus, it is no longer necessary to use a fluidic device dedicated to the purge phase ensuring the desorption of the analytes.

[0033] Generally speaking, characterization means obtaining information representative of the interactions of the analytes contained in the gaseous medium with the receptors of the sensitive site(s) of the functionalized surface of the electronic nose. The interactions in question here are events of adsorption and / or desorption of the analytes with the receptors. This information thus forms an interaction pattern, in other words a “signature” of the analytes, this pattern being able to be represented for example in the form of a histogram or a radar diagram. More precisely, in the case where the electronic nose comprises K distinct sensitive sites, the interaction pattern is formed by the K representative scalar or vector information, these being derived from the measurement signal associated with the sensitive site considered associated with an initial state here adsorbed and a final state here desorbed.

[0034] Analytes are elements intended to be characterized by the electronic nose, and are present in a gaseous medium. They can be, for example, volatile organic or inorganic molecules, water molecules, among others. Furthermore, receptors (ligands, in English) are elements attached to sensitive sites and which have a capacity to interact with the analytes, although the chemical and / or physical affinities between the analytes and the receptors are not necessarily known. The receptors of the different sensitive sites preferably have different physicochemical properties, which impact their capacity to interact with the analytes. These can be, for example, amino acids, peptides, nucleotides, polypeptides, proteins, organic polymers, oligo- or polysaccharides, among others. The analytes and receptors are chosen so that the analytes can be desorbed upon an increase in temperature of the functionalized surface controlled by a thermal module of the electronic nose.

[0035] Figures 2A to 2C are schematic and partial views of a conventional electronic nose 1 of the interferometric type. It comprises a functionalized surface 4, a measuring device 10 comprising at least one interferometer 12 coupled to a light source 11 and to at least one photodetector, and a processing unit 5. The processing unit 5 is adapted to determine, from the intensity or the power of the optical signal received by the photodetector, the so-called extracted phase difference φ(k)(t) then the so-called unfolded phase difference Φ(k)(t), and then to characterize the analytes 2. In this example, the electronic nose 1 comprises several interferometers 12, referenced by the index k ranging from 1 to K>1. These are Mach-Zehnder interferometers, but they can also be resonant ring interferometers.

[0036] The interferometers 12 are here produced in a photonic chip containing an integrated photonic circuit, produced for example from silicon. The light source 11 and the photodetectors 16 can be located on or in the photonic chip, or can be remote and coupled to it by optical couplers (diffraction gratings, etc.). Similarly, the processing unit 5 can be located in or on the photonic chip, or be remote.

[0037] The electronic nose 1 comprises a functionalized surface 4 comprising at least one sensitive site, and here a plurality K of sensitive sites. The sensitive sites are surfaces located at the level of the sensitive arms 14s of the interferometers 12, and comprise receptors 3 capable of interacting with the analytes 2 to be characterized. They may be distinct from one another in the sense that they comprise receptors 3 that are different from one sensitive site to another in terms of physicochemical affinity with respect to the analytes 2 to be characterized, and are therefore intended to provide interaction information that is different from one sensitive site to another. The sensitive sites form different zones of the functionalized surface 4. The electronic nose 1 may further comprise several identical sensitive sites in terms of physicochemical affinity, for the purpose, for example, of detecting a possible measurement drift and / or enabling the identification of a defective sensitive site.

[0038] In this example, the electronic nose 1 comprises a housing 21 which delimits a measuring chamber 20 with the functionalized surface 4. The housing 21 comprises a main opening 22, located here above and perpendicular to the functionalized surface 4. The main opening 22 can be closed, in particular to protect the functionalized surface 4 during the storage phases of the electronic nose 1. Of course, this housing 21 remains optional and can therefore be absent.

[0039] The light source 11 is preferably a source of a continuous and monochromatic signal, coherent or not, of predefined wavelength for example located in the near infrared. It can be a vertical cavity surface emitting laser (VCSEL) source, a hybrid laser source of type III-V / Si, or any other type of laser source. It can also be a light-emitting diode. The light source 11 is optically coupled to an input waveguide produced here in the photonic chip. The input waveguide is coupled to an optical splitter, which splits the optical signal and directs it towards the K interferometers 12 arranged here in parallel to each other.

[0040] Each interferometer 12 is here of the Mach-Zehnder type, but it could be of the resonant ring type. As illustrated in Figs. 2B and 2C, an interferometer 12 comprises an input divider 13, two separate waveguides called arms 14s, 14r, coupled to the input divider 13, and an output coupler 15 combining the optical signals circulating in the two arms. The recombined optical signal then circulates in the output waveguide to the corresponding photodetector 16.

[0041] The interferometers 12 each comprise a sensitive arm 14s on the surface of which receptors 3 are arranged to form a sensitive site, the other arm not comprising receptors 3 and forming the reference arm 14r. The waveguide of the sensitive arm 14s (high refractive index material) is located at a depth from the functionalized surface 4, therefore from the receptors 3, such that the optical signal (guided mode) propagating there has an effective index which depends on the quantity of analytes 2 bound to the receptors 3 of the sensitive site.

[0042] Recall that the effective index of a guided mode is defined as the product of the propagation constant β and λ / 2π, λ being the wavelength of the optical signal. The propagation constant β depends on the wavelength λ and the mode of the optical signal, as well as the properties of the waveguide (refractive indices and geometry). The effective index of the mode corresponds, in a certain way, to the refractive index of the waveguide 'seen' by the optical mode. It is usually between the index of the core and the index of the cladding of the waveguide. It is therefore understood that the quantity of analytes 2 adsorbed in the sensitive site modifies the properties of the optical mode and / or the waveguide, in particular the phase of the guided mode.

[0043] It therefore follows that the presence of analytes 2 adsorbed on the sensitive site of the sensitive arm 14s modifies the properties of the guided mode passing through it, and more precisely causes a modification of the phase of the guided mode, whereas the phase of the guided mode passing through the reference arm 14r is not substantially modified. The phase difference between the signals received by the output coupler 15 results in a modification of the intensity of the optical signal recombined and detected by the photodetector 16, due to constructive or destructive interference between the optical signals circulating in the two arms 14s, 14r.

[0044] Each interferometer 12 is coupled to at least one photodetector 16. The latter measures the value of the intensity or the power of the output optical signal, at each measurement instant, and transmits this information to the processing unit 5. According to one approach (not shown), each interferometer 12 is coupled to a 2x3 multimode coupler (MMI, for Multi Mode Interference, in English), the output optical signals then being phase shifted by 2π / 3 and detected by photodetectors 16. The powers of these three output optical signals are noted here P1, P2 and P3, and the in-phase component noted I (as In-phase, in English) is calculated such that: I = 2×P2- P1 – P3, as well as the Q component in phase quadrature with respect to the I component: Q = √3×(P1-P3). The extracted phase difference φ is then calculated such that φ=arctan(Q / I).Its values ​​are therefore well within an interval such as [-π ; +π], while the effective phase difference Φ(t) can take any value. Other approaches are possible, for example using a 2x4 multimode coupler where the four output optical signals are phase shifted by π / 2. Alternatively, a 2x1 coupler can be used, where the intensity can be correlated with the phase unambiguously over an interval [0 ; π], with 0 corresponding to the maximum intensity and π to the minimum intensity.

[0045] The processing unit 5 allows the implementation of the processing operations described below within the framework of the characterization method. It may comprise at least one microprocessor and at least one memory. It is connected to the measuring device 10, and more precisely to the photodetectors 16. It comprises a programmable processor capable of executing instructions recorded on an information recording medium. It further comprises at least one memory containing the instructions necessary for implementing the characterization method. The memory is also adapted to store the information calculated at each measurement instant. The processing unit 5 is adapted to determine the extracted phase difference φ(k)(t) from the optical signal received by the photodetector(s) 16, to deduce therefrom the unfolded phase difference Φ(k)(t) as well as the initial values ​​Φ(k)i (associated with the initial adsorbed physicochemical state E ia ) and final Φ(k)f (associated with the final desorbed physicochemical state E fd ), then to determine the signature S = { Φ (k)f – Φ (k)i} 1≤k≤K .

[0046] Figure 3A illustrates an example of time evolutions of the so-called extracted phase difference φ(k)(t) and the so-called unfolded phase difference Φ(k)(t) associated with an interferometer 12 of the electronic nose 1 of Fig. 2A. Figure 3B is a flowchart of an example of phase unfolding steps, to obtain the unfolded phase difference Φ (k) (t) from the so-called extracted phase difference φ(k)(t).

[0047] As previously indicated, the power of the output optical signal varies periodically, and more precisely sinusoidally, depending on the phase difference between the optical signals traveling through the sensitive arm 14s and the reference arm 14r of the interferometer 12. Since phase extraction methods generally use an inverse trigonometric function such as an arctangent, the extracted phase difference φ (k) (t) then presents values ​​modulo 2π.

[0048] Referring to Figure 3A, as the analytes 2 bind to the receptors 3 of a sensitive arm 14s (here of index k), the phase difference increases between the optical signals traveling through the two arms of the interferometer 12. Also, the extracted phase difference φ (k)(t) increases, presenting discontinuities of the order of 2π each time it reaches one of the limits of the interval [-π; +π] of width 2π. Thus, it increases until it reaches +π, then presents a discontinuity of a value of -2π to fall back to the value of -π, and then resumes its growth. The unfolded phase difference Φ(k)(t), which is representative of the effective phase difference between the optical signals traveling through the arms of the interferometer, increases continuously without being constrained to remain in the interval [-π; +π].

[0049] With reference to Figure 3B, the determination of the unfolded phase difference Φ(k)(t) is carried out for each successive measurement instant ti ranging from t0 to tN. During step 10, the temporal evolution of the intensity I(k)(ti) or of the power P(k)(ti) of the output optical signal measured by the photodetector 16 over a detection duration T is acquired. Then, during step 20, the processing unit 5 determines (extracts) the phase information contained in the measured signal, and more precisely here the temporal evolution φ(k)(ti) of the so-called extracted phase difference φ(k) between the optical signals circulating in the arms.

[0050] It is then appropriate to correct the temporal evolution of the extracted phase difference φ(k) by adding a positive or negative integer multiple of the width 2π of the interval [-π ;+π], noted m(t i )×2π, where m(t i) is a positive or negative integer. The latter is an increment that varies by one unit +1 or -1 at each discontinuity of the extracted phase difference φ(k)(ti). This operation of correcting the extracted phase difference φ(k)(t) is usually called phase unwrapping. It allows to obtain an unwrapped phase difference Φ (k) whose values ​​are no longer included in the interval in question, and which is then effectively representative of the effective phase difference.

[0051] The detection method therefore comprises an unfolding phase 30, formed by a step 31 of calculating an instantaneous variation δφ(k) (ti) = φ(k)(ti) – φ(k)(ti-1) of the extracted phase difference φ(k) between two successive measurement instants, then a step 32 of determining the increment m(t i ). During this step, we compare the value of this instantaneous variation δφ (k) (ti ) to a predefined threshold value S1, for example at approximately π, to add or not a positive or negative unit to the increment m(ti-1). Finally, during a step 33, the unfolded phase difference Φ(k)(ti) is determined by adding to the extracted phase difference φ(k)(ti) the multiple of 2π, i.e. m(ti)×2π.

[0052] Then, in the context of a conventional characterization method such as that described with reference to Fig. 1C, the signature characterizing the analytes 2 can then be determined from the initial Φ(k)i and final Φ(k)f values ​​of the unfolded phase difference Φ(k)(ti), respectively during the first reference phase Ph1 where the sensitive sites have an initial desorbed physicochemical state and during the second characterization phase Ph2 where the sensitive sites have a final adsorbed physicochemical state.

[0053] However, as indicated above, the obtained signature may not be representative of the analytes 2 when the initial physicochemical state of one or other of the sensitive sites is not actually desorbed, thus making the functionalized surface 4 heterogeneous in terms of physicochemical state. As such, Figures 4A to 4C illustrate the fact that it may not be possible, with a conventional interferometric electronic nose 1 of the type of that of Fig. 2A, to identify the situation where the signature is characteristic of the analytes 2 or not.

[0054] Thus, Fig.4A illustrates an example of the temporal evolution of the extracted φ and unfolded Φ phase differences in the case of a characterization process comprising a first reference phase Ph1 followed by a second characterization phase Ph2. Fig.4B illustrates a similar situation, where the effective phase difference between the two guided signals has not varied before the first phase Ph1. And Fig.4C illustrates another similar situation, where, unlike Fig.4B, the effective phase difference between the two guided signals has varied before the first phase Ph1. Here, only one sensitive site (one interferometer) is considered.

[0055] With reference to Fig. 4A, during the first reference phase Ph1, the functionalized surface 4 is exposed to a reference gas not containing the analytes 2. The photodetector 16 acquires the power of the received optical signal, and the processing unit 5 determines the extracted phase difference φ(t). Since there are no analytes 2 which bind to the receptors 3, the extracted phase difference φ(k)(t) has a constant initial value included in the interval [-π; +π], representative of an initial stationary physicochemical state of the desorbed type. The unfolded phase difference Φ(t) has a constant value Φi.

[0056] Then, during the second characterization phase Ph2, the functionalized surface 4 is exposed to a gaseous medium containing the analytes 2. The latter bind by adsorption to the receptors 3, which increases the optical path difference between the two arms of the interferometer 12 and therefore the phase difference between the two guided optical signals. The extracted phase difference φ(t) then increases until reaching the upper threshold +π, presents a discontinuity of -2π, then increases, and so on until reaching a final stationary value representative of a final stationary physicochemical state of the adsorbed type. The unit processing unit 5 then determines the unfolded phase difference Φ(t) from the evolution of the extracted phase difference φ(t), as previously described with reference to the flowchart in Fig. 3B. The signature S is then equal here to the difference ΔΦ = Φf - Φi between the final value Φf and the initial value Φi of the unfolded phase difference Φ(t).

[0057] With reference to Fig. 4B, we now assume that, prior to the first reference phase Ph1 (phase noted Ph0), the functionalized surface 4 has not been exposed to analytes 2 or to parasitic species likely to bind to the receptors 3. The effective unfolded phase difference Φeff(t) is represented in dotted lines. It has an initial value Φeff,i equal to the initial value Φi. Then, the effective unfolded phase difference Φeff(t) evolves by having the same values ​​as the unfolded phase difference Φ(t). Also, the signature S is equal to the gap ΔΦ which is identical to ΔΦ eff.

[0058] Let us now suppose, with reference to Fig. 4C, that, during this preliminary phase Ph0, the functionalized surface 4 was exposed to analytes 2 or to parasitic species which bind by adsorption to the receptors 3. This preliminary phase Ph0 may consist of a storage time of the electronic nose 1 where the functionalized surface 4 would not have been protected. In the figure, the different effective extracted phases φ are also represented in dotted lines. eff (t) and unfolded Φ eff (t).

[0059] In the pre-phase Ph0, initially, the extracted phase difference φeff(t) remains constant, then increases as species bind to the receptors 3, while remaining within the interval [-π; +π], thus showing several discontinuities of -2π. The unfolded phase difference Φ eff (t) therefore increases continuously (without discontinuities) until reaching a final value Φeff,f0 stationary. Remember that these interactions take place before the characterization process and are therefore not known to the user (processing unit 5 is not active).

[0060] In a second step, the characterization process is carried out, with a first reference phase Ph1 where the functionalized surface 4 is exposed to the reference gas, then with the second characterization phase Ph2 where the functionalized surface 4 is exposed to the analytes 2. The processing unit 5 then determines the extracted phase difference φ(t) which presents an evolution always contained in the interval [-π; +π], then determines the unfolded phase difference Φ(t). The phase difference φ(t) is initially equal to the value φeff,f0 then increases while remaining included in the interval [-π; +π], therefore presenting discontinuities of -2π. The unfolded phase difference Φ(t) then varies from an initial value Φ i (equal to φ eff,f0) up to a final value Φf. The processing unit 5 then determines the signature S as being equal to ΔΦ = Φf - Φi.

[0061] However, it appears that the effective unfolded phase difference Φ eff (t) has a value Φ efff0 during the first reference phase Ph1 which is much higher than the value Φ i determined by processing unit 5. In other words, processing unit 5 considers that the initial physicochemical state of the sensitive site is a desorbed state, whereas this is in fact not the case. It follows that processing unit 5 will determine a signature S as being equal to ΔΦ, whereas the actual signature should be ΔΦ eff. This error in determining the signature comes from the indeterminacy modulo 2π of the extracted phase difference φ(t), which leads to a loss of information on the effective physicochemical state of the sensitive site during the first reference phase Ph1. It therefore does not appear possible, in the case of such a characterization process implementing an interferometric type electronic nose 1, to identify and discard the erroneous signature values ​​of the sensitive sites.

[0062] Figures 5A to 5C are schematic and partial views of an electronic nose 1 of the interferometric type according to an embodiment of the invention, for the implementation of a characterization method making it possible to obtain a signature that is actually characteristic of the analytes 2. This avoids taking into account a physicochemical state that would not be totally desorbed.

[0063] The electronic nose 1 according to the invention comprises a functionalized surface 4, a measuring device 10, and a processing unit 5 identical or similar to those of the electronic nose 1 according to fig. 2A to 2C. But, it further comprises a thermal module 30 adapted to generate an increase in temperature of the functionalized surface 4, thus causing the passage of the physicochemical state of the functionalized surface 4 and therefore of the sensitive sites: from an initial adsorbed physicochemical state Eia where the proportion (or quantity) of receptors 3 bound to the analytes 2 is equal to a non-zero initial value pia, to a final desorbed physicochemical state Eid where the proportion (or quantity) of receptors 3 bound to the analytes is equal to a final value pfd less than p ia . The initial adsorbed states E ia and final desorbed E fd are stationary states here (but they may not be).

[0064] Also, the characterization method according to the invention comprises two successive phases during which the differences in extracted phase φ(k)(t) and unfolded phase Φ(k)(t) are determined, namely a first phase Ph1 called adsorption where the functionalized surface 4 is exposed to the analytes 2 until its physicochemical state reaches the initial adsorbed state E ia , then a second phase Ph2 called desorption where the desorption of analytes 2 is caused by increasing the temperature to move to the final desorbed state Efd.

[0065] The thermal module 30 comprises in this example an electrical source 32 connected to a resistive track 31 (heater) made of an electrically conductive material. heater 31 extends here opposite the functionalized surface 4, and more precisely the sensitive arms 14s of the interferometers 12. It is connected to the electrical source 32 to receive an electrical signal causing the temperature to increase by the Joule effect.

[0066] The measuring support 23 and the lower support 24 are made of a thermally conductive material. The heater 31 is arranged opposite the functionalized surface 4, at the rear face of the lower support 24. Alternatively, it may be located between the lower support 24 and the measuring support 23, in which case the lower support 24 does not need to be made of a thermally conductive material.

[0067] As illustrated in Fig. 5B, the heater 31 is produced in the form of at least one track of an electrically conductive and resistive material, for example metallic. Preferably, the heater 31 extends opposite all the arms of the interferometers 12, therefore opposite the sensitive arms 14s as well as the reference arms 14r. Thus, the heater 31 is adapted to modify the temperature T of the functionalized surface 4 in a spatially homogeneous manner.

[0068] The electrical source 32 is adapted to apply to the heater 31 an electrical signal, for example in steps. A stepped electrical signal corresponds to an electrical signal whose intensity changes from a first initial value to a second final value in a short time, here less than or equal to a few seconds, preferably in at most 5 seconds. This electrical signal is here adapted to cause by Joule effect a positive variation in temperature at the functionalized surface 4 and therefore the sensitive sites, so that their temperature changes from an initial value less than or equal to a first threshold value T1 to a final value greater than or equal to a second threshold value T2. The difference between the values ​​T1 and T2 may be at least equal to 5°C, and may be of the order of approximately 20°C to cause effective desorption of the analytes from a significant proportion of the receptors.The value T1 may be between 2°C and 25°C, for example equal to 20°C, and the value T2 may be between 30°C and 60°C, for example equal to 50°C. It may have an electrical power of a few tens of watts, for example 0.5 to 2W. Preferably, the temperature during the second phase is less than or equal to 60. o C, so as not to degrade the physicochemical properties of the receptors 3. However, the electrical signal may not be in step, and increase for example continuously or even in successive increments, among others.

[0069] Figures 6A to 6C illustrate steps of a characterization method according to one embodiment, using the electronic nose 1 illustrated in Fig. 5A. Fig. 6A illustrates an evolution of the interactions between the analytes 2 and the receptors 3 of the functionalized surface 4, during a characterization method according to the invention implementing an increase in the temperature to move from the absorption phase Ph1 to the desorption phase Ph2. Fig.6B illustrates an increase in the temperature of the functionalized surface 4; and Fig.6C illustrates time evolutions of the extracted phase difference φ(k)(t) and the unfolded phase difference Φ(k)(t) during the characterization process.

[0070] As indicated previously, the characterization method provides an adsorption phase Ph1 during which the functionalized surface 4 is exposed to the analytes 2, the initial temperature being less than or equal to the first value T1; followed by a desorption phase Ph2 where desorption of the analytes 2 is caused by means of an increase in temperature up to at least the second value T2.

[0071] With reference to Fig. 6A, during the adsorption phase Ph1, the sensitive site is exposed to a gaseous medium containing the analytes 2. The latter can be brought into contact with the receptors 3 in a controlled manner (for example by forced advection) or not (for example by diffusion or natural advection). The interactions ultimately present a stationary regime here in which there is an equilibrium between the number of adsorption events and the number of desorption events. In other words, each desorption event is immediately followed by an adsorption event, so that the receptors 3 are considered to be bound to the analytes 2. The sensitive site then presents the initial physicochemical state of adsorption Eia where the proportion (or quantity) of the receptors 3 bound to the analytes 2 is equal to the initial non-zero value pia.

[0072] Let us note in this regard that the interaction between an analyte A and a receptor L is a reversible phenomenon characterized by an adsorption constant k a (in mol -1 .s -1 ) of analyte A to receptor L to form an analyte / receptor compound LA (for ligand-analyte, in English), and by a desorption constant kb (in s -1 ) corresponding to the dissociation of the LA compound. The kd / ka ratio forms the equilibrium dissociation constant kD (in mol) which gives the value of the concentration cA of the A analytes allowing 50% of the L receptors to be saturated.

[0073] The steady state is reached when the concentration c LA (t) in compounds LA is stationary dc LA / dt=0, that is, when the product of the constant k awith the concentrations of analytes cA(t) and receptors cL(t) (number of adsorption events) is equal to the product of the constant kd with the concentration cLA(t) of LA compounds (number of desorption events), in other words when the following evolution equation is verified dcLA / dt = ka×cA×cL – k d ×c LA = 0. The maximum stationary value of the measurement signal is proportional to the concentration c A (t) of A analytes. Saturation of the L receptors of the sensitive site, i.e., the fact that all receptors are bound to analytes, can be achieved when the concentration cA of A analytes is sufficient, which is assumed to be the case here.

[0074] With reference to Fig. 6B, during this first adsorption phase Ph1, the thermal module 30 maintains the temperature of the functionalized surface 4 at a temperature lower than or equal to a first threshold value T1 for which the analytes 2 remain adsorbed to the receptors 3. Also, the physicochemical state of the sensitive site gradually passes from a desorbed (or partially desorbed) state to a here stationary adsorbed state Eia. The electrical signal applied by the electrical source 32 to the heater 31 can here remain zero, so that the temperature generated at the sensitive sites has for example the ambient temperature of approximately 20°C, lower than or equal to the predefined adsorption value T1 which can be equal to 25°C.

[0075] Then, the second desorption phase Ph2 is carried out. For this, the electrical source 32 applies an electrical signal to the heater 31, here a stepped signal, so as to cause an increase in temperature to at least the second threshold value T2, leading to the desorption of the analytes 2 with respect to the receptors 3. The proportion (or quantity) of receptors bound to the analytes then passes from the initial value pia which is not zero, to the final value pfd which is less than pia. The value pfd can be equal to or close to 0%. The electrical signal has a positive step so that it passes from the value, for example, zero to a constant non-zero value in a very short time, for example in 1s or less. The temperature T(t) thus passes quickly from the initial value which is less than or equal to T1, to a final value which is greater than or equal to T2 in a very short time, for example in less than 10s or in less than 5s.The physicochemical state of the sensitive site rapidly changes from the initial adsorbed state Eia to the final desorbed state E. fd .

[0076] With reference to Fig. 6C, during the first adsorption phase Ph1 and the second desorption phase Ph2, the processing unit 5 receives the optical signal received by the photodetector, and determines the extracted phase difference φ(t). As the analytes 2 bind to the receptors 3 during the phase Ph1, the extracted phase difference φ(t) gradually increases while remaining in the interval [-π; +π], and thus presents discontinuities of -2π. When the steady state is established, the extracted phase difference φ(t) has an initial constant value. The processing unit 5 then determines the unfolded phase difference Φ(t), which then has the initial constant value Φi. Note that the processing unit 5 can alternatively determine the unfolded phase difference Φ(t) from the beginning of the first phase Ph1. It would then present a value Φ eff,i which is greater than the value Φ i .

[0077] Then, during the second desorption phase Ph2, due to the increase in temperature which causes the rapid desorption of analytes 2, the extracted phase difference φ(t) decreases rapidly while remaining in the interval [-π; +π], and thus presents discontinuities of +2π. When the steady state is established, the extracted phase difference φ(t) presents a final constant value. The processing unit 5 then determines the unfolded phase difference Φ(t) which then presents the final value Φ f . If processing unit 5 had determined the unfolded phase difference Φ(t) from the beginning of the first phase Ph1, it would then have the value Φ eff,f which is greater than the value Φf.

[0078] The processing unit 5 can then determine the signature S which is equal to the difference (in absolute value) between the final value Φf and the initial value Φi: S = ΔΦ = | Φf - Φi | which is also equal to ΔΦ eff = | Φeff,f - Φ eff,i |. The deviations acquired for each of the sensitive sites can be normalized so that they are between 0 and 1.

[0079] It emerges that, in the context of the characterization method according to the invention, the signature is determined while the sensitive site has an initial adsorbed state Eia and a final desorbed state Efd, and not, as in the prior art, from an initial desorbed (or even partially desorbed) state and a final adsorbed state. In addition, in the context of the invention, the gaseous medium to which the functionalized surface is exposed does not vary significantly or only slightly between the adsorption phase Ph1 and the desorption phase Ph2, only the state of the functionalized surface changes between the initial adsorbed state Eia and the final desorbed state Efd due to the increase in temperature, whereas in the prior art, the gaseous medium changes (absence of the analytes to measure the baseline, then presence of the analytes, and finally evacuation of the analytes).This limits or even eliminates the error when determining the signature which comes from the loss of information on the real initial state of the sensitive site(s) linked to the indeterminacy modulo 2π of the extracted phase difference φ(t).

[0080] Furthermore, within the framework of the invention, the transition from the initial adsorbed state Eia to the final desorbed state E fd is caused by the increase in temperature of the functionalized surface 4, and not by controlled fluidic management, which in particular makes it possible to simplify the structural configuration of the electronic nose 1. The quality of characterization of the analytes 2 is also improved, insofar as desorption by thermal effect can be more efficient than desorption by fluidic effect and can be effective for each sensitive site, so that the functionalized surface 4 has a final state that is effectively desorbed and substantially homogeneous.

[0081] Figures 7A, 7B and 7C illustrate the situation where several successive characterization phases are carried out by the electronic nose, in the case where the functionalized surface is exposed to the same gaseous medium (same type and same concentration of analytes) and in the case where the functionalized surface is successively exposed to different gaseous media in terms of type and / or concentration of analytes. The different successive characterization phases can take place over short times, for example of the order of a few seconds to minutes, as well as over long periods of time, for example of the order of several hours to days.

[0082] Fig. 7A illustrates an example of variation in the temperature of the functionalized surface, during a succession of characterization phases of gaseous media, noted here A, B, C (the electronic nose can thus carry out a large number of successive characterization phases A, B, C, D, E, etc.).

[0083] Thus, each characterization phase A, B, C… includes the adsorption phase Ph1 where the temperature remains at most equal to the value T1 and where the functionalized surface is exposed to a gaseous medium containing the analytes; followed by the desorption phase Ph2 where the temperature is increased to at least the value T2 to cause the desorption of the analytes with respect to the receptors.

[0084] Fig.7B illustrates an example of temporal evolutions of the unfolded phase difference Φ(k)(t) during the succession of characterization phases A, B, C… of Fig.7A, in the case where the functionalized surface is exposed to the same gaseous medium in terms of analytes (same type and same concentration). The concentration of the analytes remains constant in the gaseous medium from one characterization phase A, B, C… to the next.

[0085] The effective unfolded phase difference Φ eff (t) varies between a value here stationary Φ eff,irepresentative of the initial adsorbed state Eia, and a stationary value here Φeff,f representative of the final desorbed state Efd. Consequently, the unfolded phase difference Φ(t) varies between a stationary value Φi representative of the initial adsorbed state Eia, and a stationary value Φf representative of the final desorbed state E fd . As the gaseous medium is the same in terms of analytes from one characterization phase to another, the difference between Φ i and Φ f remains the same here for each of the characterization phases A, B, C…. It is noted that, at time t0, the value Φeff(t0) may be non-zero, or even arbitrary, due to a possible initial 'pollution' of the functionalized surface. In any case, the method according to the invention makes it possible to carry out a quality characterization of the analytes from one phase A, B, C to the other.

[0086] Fig. 7C illustrates another example of temporal evolutions of the unfolded phase difference Φ(k)(t) during the succession of characterization phases A, B, C… of Fig. 7A, in the case where the functionalized surface is exposed to different gaseous media in terms of analytes. Thus, the analytes can be the same but the concentration varies over time, or they can be different analytes from one characterization phase A, B, C… to another.

[0087] Here, the effective unfolded phase difference Φ eff (t) varies between a value here stationary Φeff,i representative of the initial adsorbed state Eia which is here different from one characterization phase A, B, C… to another, insofar as the proportion pia of the receptors bound to the analytes can be different. On the other hand, during the final desorbed state Efd, it is considered that the analytes are all desorbed, so that the value Φ eff,fis substantially zero for each of the characterization phases A, B, C….

[0088] Consequently, the unfolded phase difference Φ(t) varies between the stationary values ​​Φi (initial adsorbed state Eia) and Φf (final desorbed state Efd), with a gap Φf – Φi which differs here from one characterization phase A, B, C… to another, to the extent that the functionalized surface is successively exposed to gaseous media which are different from each other in terms of analytes.

[0089] Thus, it is possible to use the electronic nose to carry out successive characterizations of the gaseous medium, whether it is the same from one characterization phase to another or whether it is different. This is due in particular to the fact that each characterization phase includes a second desorption phase Ph2 during which the thermal desorption of the analytes is caused (preferably total) thus making it possible to remove any errors linked to the indeterminacy modulo 2π of the extracted phase difference φ(t).

[0090] Particular embodiments have just been described. Different variants and modifications will appear to those skilled in the art.

Claims

CLAIMS 1. A method for characterizing analytes (2) present in a gaseous medium, using an electronic nose (1) comprising: o a functionalized surface (4) containing at least one sensitive site having receptors (3) with which the analytes (2) are capable of interacting by adsorption / desorption, the sensitive site having a physicochemical state defined by a proportion of the receptors (3) bound to the analytes (2); o a measuring device (10), comprising: at least one interferometer (12) having two waveguides, one of which forms a sensitive arm (14s) on the surface of which the sensitive site is located and the other a reference arm (14r), coupled to a light source (11); and at least one photodetector (16) coupled to the interferometer (12); o a processing unit (5), connected to the photodetector (16); o a thermal module (30), adapted to generate a temperature variation of the functionalized surface (4);o the process comprising the following steps: oa) exposure of the functionalized surface (4) to the gaseous medium containing the analytes (2), the functionalized surface (4) having an initial temperature at most equal to a first predefined value T1, so that the functionalized surface (4) has an initial physicochemical state called adsorbed where the proportion of receptors bound to the analytes is equal to an initial value p; ia non-zero; ob) generation by the thermal module (30) of a temperature increase of the functionalized surface (4) up to at least a second predefined value T2, thus causing a change of state between the initial adsorbed physicochemical state and a final desorbed physicochemical state where the proportion of receptors bound to the analytes is equal to a final value p fd less than p ia; oc) measurement by the photodetector (16) of the optical signal transmitted by the interferometer (12), during the exposure and temperature rise generation stages; od) determination by the processing unit (5): ^ of a so-called extracted phase difference φ (k) (t) between the optical signals circulating in the waveguides, from the measured optical signal, whose values ​​are within a predefined width interval; then ^ of a so-called unfolded phase difference Φ (k) (t), by unfolding the extracted phase difference φ(k)(t) by adding to it a positive or negative integer multiple of the interval width; then ^ of initial values ​​Φ(k)i and final Φ(k)f of the unfolded phase difference Φ(k)(t), respectively representing the initial adsorbed and final desorbed physicochemical states of the functionalized surface (4); oe) characterization of the analytes (2), from the initial values ​​Φ (k)i and final Φ(k)f2. A characterization method according to claim 1, wherein the temperature difference between the first value T1 and the second value T2 is at least 5°C.

3. A characterization method according to claim 1 or 2, wherein the first value T1 is at most 25°C, and the second value T2 is at least 30°C.

4. A characterization method according to any one of claims 1 to 3, wherein the first value T1 is between 2°C and 25°C, and the second value T2 is between 30°C and 60°C.

5. A characterization method according to any one of claims 1 to 4, wherein steps a) to e) are repeated successively, the functionalized surface (4) being successively exposed, at each new step a), to the same gaseous medium in terms of the type and concentration of analytes,or to different gaseous media in terms of the type and / or concentration of analytes.

6. Electronic nose (1) adapted to characterize analytes (2) present in a gaseous medium, for carrying out the characterization process according to any one of the preceding claims, comprising: o a functionalized surface (4) containing at least one sensitive site having receptors (3) with which the analytes (2) are capable of interacting by adsorption / desorption, the sensitive site having a physicochemical state defined by a proportion of the receptors (3) bound to the analytes (2); o a measurement device (10), comprising: at least one interferometer (12) having two waveguides, one of which forms a sensitive arm (14s) on the surface of which the sensitive site is located and the other a reference arm (14r), coupled to a light source (11); and at least one photodetector (16) coupled to the interferometer (12); o a processing unit (5),connected to the photodetector (16), adapted to determine: ^ an extracted phase difference φ(k)(t) between the optical signals circulating in the waveguides, from an optical signal measured by the photodetector (16), whose values ​​are within a predefined width interval; then ^ an unfolded phase difference Φ(k)(t), by unfolding the extracted phase difference φ(k)(t) by adding to it a positive or negative integer multiple of the interval width; then, ^ initial values ​​Φ(k)i and final values ​​Φ(k)f of the unfolded phase difference Φ(k)(t), representing respectively the initial adsorbed and final desorbed physicochemical states of the functionalized surface (4), allowing the analytes (2) to be characterized subsequently; o a thermal module (30) adapted to generate a temperature variation of the functionalized surface (4), thus causing a transition of state between the initial adsorbed physicochemical state and the final desorbed physicochemical state,starting from: ^ an initial temperature at most equal to a first predefined value T1 for which the functionalized surface (4) has an initial physicochemical state of adsorption where a proportion of the receptors bound to the analytes is equal to a non-zero initial value pia; ^ a final temperature at least equal to a second predefined value T2 for which the functionalized surface (4) has a final physicochemical state of desorption where the proportion of the receptors bound to the analytes is equal to a final value pfd less than pia.

7. Electronic nose (1) according to claim 6, wherein the thermal module (30) comprises a heater (31) which extends opposite the arms of the interferometer (12).

8. Electronic nose (1) according to claim 7, wherein the functionalized surface (4) is located on a first face of a support (23, 24) on which the waveguides (14s, 14r) are located, the heater (31) being disposed on a second face of the support (23,24) opposite the first face, the support (23, 24) being made of a thermally conductive material.

9. Electronic nose (1) according to claim 7 or 8, wherein the measuring device (10) comprises a plurality of interferometers (12), the heater (31) extending opposite the arms (14s, 14r) of all said interferometers (12).

10. Electronic nose (1) according to any one of claims 6 to 9, wherein the thermal module (30) is adapted to increase the temperature of the functionalized surface (4) to a final temperature between 30°C and 60°C.

11. Electronic nose (1) according to any one of claims 1 to 10, wherein the thermal module (30) comprises an electrical source (32) adapted to apply a step electrical signal to a heater (31) causing the temperature increase.

12. Electronic nose (1) according to any one of claims 1 to 11,in which the thermal module (30) is adapted to cause the temperature to rise from the initial temperature to the final temperature in a period of at most 5 seconds.

13. Electronic nose (1) according to any one of claims 1 to 12, wherein the interferometer (12) is a Mach-Zehnder interferometer or a resonant ring interferometer.

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