FR3134894A1 - method for characterizing analytes comprising a temperature variation using an electronic nose of the interferometric type - Google Patents

Abstract

The invention relates to a method for characterizing analytes using an electronic nose of the interferometric type, comprising the following steps: exposing the functionalized surface 4 to the gaseous medium containing the analytes, which has an initial temperature at most equal to T1 , so that it presents an initial adsorbed state; generate an increase in the temperature of the functionalized surface 4 up to at least T2, so that it presents a final desorbed state; measure the optical signal transmitted by the interferometer 12;determine an extracted phase difference φ(k)(t), then an unfolded phase difference Φ(k)(t), and finally initial values Φ(k)i and final values Φ(k)f thus allowing to characterize the analytes. Figure: Fig. 5A

Description

method for characterizing analytes comprising a temperature variation using an electronic nose of the interferometric type

The field of the invention is that of the characterization of analytes present in a gaseous medium by an electronic nose of the interferometric type.

STATE OF PRIOR ART

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

Different characterization approaches exist, which are distinguished from each other in particular by the necessity or not of having to “mark” the analytes or the receptors beforehand with a revealing agent. Unlike, for example, detection by fluorescence which requires the use of such markers, detection using surface plasmon resonance imaging (SPRi for Surface Plasmon Resonance Imaging , in English), and that using an interferometric principle , for example of the Mach-Zehnder type (MZI, for Mach-Zehnder Interferometer , in English), are so-called label free techniques.

In an electronic nose with 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. As part of SPRi technology, for example, the intensity of optical signals coming from 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.

As such, the illustrates an example of an electronic nose 40 of the SPRi type similar to that described in the article by Brenet et al. titled 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 receivers, 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 of the analytes present in a gas sample. The measuring device further comprises a light source 43, an optical shaping device 44 formed here of a collimation 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 measuring device. The fluid 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 depends itself of the surface plasmons generated and the quantity of analytes located at each sensitive site.

There illustrates an example of interferometer 12 of an electronic nose 1 of interferometric type, as described in document EP3754326A1. This electronic nose 1 also includes 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 includes 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 receivers which define a sensitive site of the functionalized surface 4. The presence of The analytes adsorbed on the surface of the sensitive arm 14s modify the properties of the optical signal passing through it, and more precisely causes a modification of the phase of the optical signal, while 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.

A characterization process usually consists of acquiring and comparing values representative, for each sensitive site, of an initial physicochemical state of the sensitive site where the receptors are not linked to the analytes, and of a final physicochemical state where the receptors are linked with the analytes. The signature can then be formed from the difference between these initial and final values for each of the sensitive sites. A physicochemical state is therefore a state of a sensitive site or functionalized surface defined by the proportion of receptors linked to the analytes or even to other species capable of binding to the receptors. By proportion of receptors is meant the ratio of the number of bound receptors to the total number of receptors at the sensitive site. Thus, a physicochemical state can correspond to a so-called desorbed stationary state 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 so-called adsorbed physicochemical state corresponds to a stationary state where the receptors are linked 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, as part 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.

As such, the 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 su _(k) (t) corresponding to the temporal evolution of the variation Δ%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 %R reflectivity here is the ratio between the intensity of the optical measurement signal detected by the image sensor to the intensity of the optical excitation signal emitted by the light source. The variation in reflectivity Δ%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 su _(k) (t) all have the same constant initial value which is substantially zero.

Thus, a characterization process usually comprises at least two successive phases of exposure of the functionalized surface to different gas environments, namely a first so-called reference phase Ph1 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 to a third phase Ph3 called purging where the analytes are evacuated by the renewal of the gaseous environment. Thus, we determine the stationary values of the useful signals su _(k) (t) during the two phases Ph1 and Ph2, namely the first values su _(k)i (here substantially zero) representative of the initial physicochemical state desorbed from the sites sensitive, and the second su _{(k) f} values representative of the final physicochemical state adsorbed from 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.

However, as we see, the quality of the characterization depends in particular on the fact that the sensitive sites initially present an effectively desorbed physicochemical state on the one hand, and that the functionalized surface presents homogeneity between the physicochemical states of the sensitive sites on the other hand. go. We understand in fact that if one or the other of the sensitive sites presents an initial physicochemical state which is not really desorbed, that is to say whose quantity of available receptors is reduced compared to that of the sensitive sites neighbors, it will provide a response in terms of interaction with the analytes which is not comparable to those of other sensitive sites. This then leads to a signature that is no longer characteristic of the analytes.

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 which would not be desorbed can be easily identified by examining the measurement signals (reflectivity %R(t) during phase Ph1) acquired by the image sensor, in the extent that their values are directly representative of the physicochemical state of the sensitive site considered. More precisely, a sensitive site whose physicochemical state is not completely desorbed has a reflectivity value %R(t) higher than that of a sensitive site which would be completely desorbed.

On the other hand, in the case of an interferometric type 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 a modulo 2π indeterminacy which does not make it possible to know the initial effective physicochemical state of the sensitive site.

There is therefore a need to have an electronic nose of the interferometric type and a characterization process making it possible to reduce or even eliminate the risks of deterioration in the quality of the characterization of the analytes.

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 electronic nose of the interferometric type, 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 sensitive site(s) of the functionalized surface present, during the process, an effectively desorbed and homogeneous physicochemical state.

• une surface fonctionnalisée contenant au moins un site sensible ayant des récepteurs avec lesquels les analytes sont aptes à interagir par adsorption/désorption, le site sensible présentant un état physicochimique défini par une proportion des récepteurs liés aux analytes ;
• un dispositif de mesure, comportant : au moins un interféromètre présentant deux guides d’onde dont l’un forme un bras sensible à la surface duquel se situe le site sensible et l’autre un bras de référence, couplé à une source lumineuse ; et au moins un photodétecteur couplé à l’interféromètre ;
• une unité de traitement, connectée au photodétecteur ;
• un module thermique, adapté à générer une variation de température de la surface fonctionnalisée.

For this, an object of the invention is a method for characterizing analytes present in a gaseous medium, by means of an electronic nose. This includes:

• a functionalized surface containing at least one sensitive site having receptors with which the analytes are able to interact by adsorption/desorption, the sensitive site presenting a physicochemical state defined by a proportion of the receptors linked 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.

• a) exposition de la surface fonctionnalisée au milieu gazeux contenant les analytes, la surface fonctionnalisée présentant une température initiale au plus égale à une première valeur T₁prédéfinie, de sorte que la surface fonctionnalisée présente un état physicochimique initial dit adsorbé où la proportion des récepteurs liés aux analytes est égale à une valeur initiale p_ianon nulle ;
• b) génération par le module thermique d’une augmentation de température de la surface fonctionnalisée jusqu’à au moins une deuxième valeur T₂prédéfinie, provoquant ainsi un changement d’état entre l’état physicochimique initial adsorbé et un état physicochimique final dit désorbé où la proportion des récepteurs liés aux analytes est égale à une valeur finale p_fdinférieure à p_ia;
• c) mesure par le photodétecteur du signal optique transmis par l’interféromètre, au cours des étapes d’exposition et de génération de l’augmentation de température ;
• d) détermination par l’unité de traitement : d’une différence de phase dite extraite φ_(k)(t) entre les signaux optiques circulant dans les guides d’onde, à partir du signal optique mesuré, dont les valeurs sont comprises dans un intervalle de largeur prédéfini ; puis d’une différence de phase dite dépliée Φ_(k)(t), par dépliement de la différence de phase extraite φ_(k)(t) en lui ajoutant un multiple entier positif ou négatif de la largeur d’intervalle ; puis de valeurs initiale Φ_(k)iet finale Φ_(k)fde la différence de phase dépliée Φ_(k)(t), représentatives respectivement des états physicochimiques initial adsorbé et final désorbé de la surface fonctionnalisée ;
• e) caractérisation des analytes (2), à partir des valeurs initiale Φ_(k)iet finale Φ_(k)f.

The characterization process includes the following steps:

• a) exposure of 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 T ₁ , so that the functionalized surface presents an initial physicochemical state called adsorbed where the proportion of receptors linked to the analytes is equal to a non-zero initial value p _ia ;
• b) generation by the thermal module of an increase in temperature of the functionalized surface up to at least a second predefined value T ₂ , 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 stages of exposure and generation of the temperature increase;
• 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 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 Φ _(k)i and final Φ _(k)f values 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), based on the initial Φ _(k)i and final Φ _(k)f values.

Some preferred, but non-limiting, aspects of this characterization method are as follows.

The temperature difference between the first value T ₁ and the second value T ₂ can be at least equal to 5°C. The first value T ₁ can be at most equal to 25°C, and the second value T ₂ can be at least equal to 30°C. The first value T ₁ can be between 2°C and 25°C, and the second value T ₂ can be between 30°C and 60°C.

Steps a) to e) can 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 gaseous media different in terms of type and/or concentration of analytes.

• une surface fonctionnalisée contenant au moins un site sensible ayant des récepteurs avec lesquels les analytes sont aptes à interagir par adsorption/désorption, le site sensible présentant un état physicochimique défini par une proportion des récepteurs liés aux analytes ;
• un dispositif de mesure, comportant : au moins un interféromètre présentant deux guides d’onde dont l’un forme un bras sensible à la surface duquel se situe le site sensible et l’autre un bras de référence, couplé à une source lumineuse ; et au moins un photodétecteur couplé à l’interféromètre ;
• une unité de traitement, connectée au photodétecteur, adaptée à déterminer : une différence de phase dite extraite φ_(k)(t) entre les signaux optiques circulant dans les guides d’onde, à partir d’un signal optique mesuré par le photodétecteur, dont les valeurs sont comprises dans un intervalle de largeur prédéfini ; puis une différence de phase dite dépliée Φ_(k)(t), par dépliement de la différence de phase extraite φ_(k)(t) en lui ajoutant un multiple entier positif ou négatif de la largeur d’intervalle ; puis des valeurs initiale Φ_(k)iet finale Φ_(k)fde la différence de phase dépliée Φ_(k)(t), représentatives respectivement d’états physicochimiques initial adsorbé et final désorbé de la surface fonctionnalisée, permettant ensuite de caractériser les analytes ;
• un module thermique adapté à générer une variation de température de la surface fonctionnalisée, provoquant ainsi un passage d’état entre l’état physicochimique initial adsorbé et l’état physicochimique final désorbé, à partir : d’une température initiale au plus égale à une première valeur T₁prédéfinie pour laquelle la surface fonctionnalisée présente un état physicochimique initial adsorbé où une proportion des récepteurs liés aux analytes est égale à une valeur initiale p_ianon nulle ; à une température finale au moins égale à une deuxième valeur T₂prédéfinie pour laquelle la surface fonctionnalisée présente un état physicochimique final désorbé où la proportion des récepteurs liés aux analytes est égale à une valeur finale p_fdinférieure à p_ia.

The invention also relates to an electronic nose adapted to characterize analytes present in a gaseous medium, for implementing the characterization method according to any of the preceding characteristics. The electronic nose includes:

• a functionalized surface containing at least one sensitive site having receptors with which the analytes are able to interact by adsorption/desorption, the sensitive site presenting a physicochemical state defined by a proportion of the receptors linked 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, whose values 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 Φ _(k)i and final Φ _(k)f values of the unfolded phase difference Φ _(k) (t), respectively representative of initial adsorbed and final desorbed physicochemical states of the functionalized surface, then making it possible to characterize analytes;
• a thermal module adapted to generate a temperature variation of the functionalized surface, thus causing a change 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 T ₁ for which the functionalized surface has an initial adsorbed physicochemical state where a proportion of the receptors linked to the analytes is equal to a non-zero initial value p _ia ; at a final temperature at least equal to a second predefined value T ₂ for which the functionalized surface has a final desorbed physicochemical state where the proportion of receptors linked to the analytes is equal to a final value p _fd less than p _ia .

The thermal module may include a heater which extends opposite the arms of the interferometer.

The functionalized surface can 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.

The measuring device may include a plurality of interferometers, the heater extending opposite the arms of all said interferometers.

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

The thermal module may include an electrical source adapted to apply to a heater a stepped electrical signal causing the temperature increase.

The thermal module may be adapted to cause the temperature to increase from the initial temperature to the final temperature in a period of not more than 5 seconds.

The interferometer can be a Mach-Zehnder interferometer or a resonant ring interferometer.

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. on which ones :
there , 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;
there , 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;
there , already described, illustrates examples of sensorgrams su _(k) (t) determined by an electronic nose of the SPR imaging type during a determination process;
there is a schematic and partial view of an electronic nose of the interferometric type according to one embodiment;
there is a schematic view, from above, of the electronic nose measuring device of the , comprising the light source, a matrix of interferometers and photodetectors;
there is a schematic top view of the sensitive arm and the reference arm of an interferometer of the ;
there illustrates temporal 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 the , highlighting the phase unfolding;
there 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 the , during a characterization process;
there , there and the illustrate temporal evolutions of the extracted phase difference φ _(k) (t) and the unfolded phase difference Φ _(k) (t) relating to a nose interferometer in the case of a usual characterization method ( ), and in the case where the initial physicochemical state of the sensitive site is effectively desorbed ( ), and finally in the case where the initial physicochemical state is not desorbed ( ) ;
there is a schematic and partial view of an electronic nose of the interferometric type according to one embodiment of the invention;
there is a schematic view, from above, of the thermal module of the electronic nose of the ;
there is a schematic top view of the thermal module and the interferometers of the electronic nose of the ;
there illustrates an example of evolution of the interactions between the analytes and the receptors of the functionalized surface, during a characterization process according to one embodiment of the invention, where the desorption is carried out by increasing the temperature variation of the functionalized surface;
There illustrates an increase in the temperature of the functionalized surface during a characterization process according to one embodiment of the invention;
there illustrates temporal evolutions of the extracted phase difference φ _(k) (t) and the unfolded phase difference Φ _(k) (t) during the process of characterizing the and 6B;
there illustrates an example of variation in the temperature of the functionalized surface, during a succession of phases of characterization of gaseous media;
there illustrates an example of temporal evolutions of the unfolded phase difference Φ _(k) (t) during the succession of phases of characterization of the , in the case where the functionalized surface is exposed to the same gaseous medium (identical type and concentration of analytes);
there illustrates another example of temporal evolutions of the unfolded phase difference Φ _(k) (t) during the succession of phases of characterization of the , in the case where the functionalized surface is exposed to gaseous media different in terms of type and/or concentration of analytes.
DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

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 represented to scale so as to favor the clarity of the figures. Furthermore, the different embodiments and variants are not exclusive of each other and can be combined with each other. Unless otherwise indicated, the terms “substantially”, “approximately”, “of the order of” mean to the nearest 10%, and preferably to the nearest 5%. Furthermore, the terms “between… and…” and equivalents mean that the limits are included, unless otherwise stated.

The invention generally relates to the characterization of analytes present in a gaseous sample or in a gaseous medium to be analyzed. The characterization is carried out using an electronic nose of the interferometric type, 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 includes a thermal module adapted to generate an increase in the temperature of the functionalized surface, thus causing a change of state of the sensitive site(s), namely the transition from an initial physicochemical state called adsorbed E _ia where receptors are linked to the analytes, to a final physicochemical state called desorbed E _fd where at least part of these receptors is no longer linked to the analytes. The characterization of the analytes is then carried out from initial Φ _(k)i and final Φ _(k)f values of the unfolded phase difference Φ _(k) (t) associated respectively with the initial adsorbed state E _ia and with the final desorbed state E _fd .

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

The electronic nose according to the invention thus makes it possible to improve the quality of the characterization, to the extent that the initial Φ _(k)i and final Φ _(k)f values are associated with initial and final states which are effectively states adsorbed and desorbed, even though the extracted phase difference φ _(k) (t) always presents 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 purging phase ensuring the desorption of the analytes.

Generally speaking, by characterization we mean 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 adsorption and/or desorption events of the analytes with the receptors. This information thus forms an interaction pattern, in other words a “signature” of the analytes, this pattern can 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 scalar or vector representative information, this coming from the measurement signal associated with the sensitive site considered associated with a state initial here adsorbed and to a final state here desorbed.

Analytes are elements intended to be characterized by the electronic nose, and are present in a gaseous medium. They can be, by way of illustration, volatile organic or inorganic molecules, water molecules, among others. Furthermore, the receptors ( ligands , in English) are elements fixed 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 different sensitive sites preferably have different physicochemical properties, which impact their ability to interact with analytes. These may be, for example, amino acids, peptides, nucleotides, polypeptides, proteins, organic polymers, oligo- or polysaccharides, among others. The analytes and the 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.

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, to from the intensity or 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.

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

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 sensitive arms 14s of the interferometers 12, and include receptors 3 capable of interacting with the analytes 2 to be characterized. They can be distinct from each other in the sense that they include 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 different interaction information from one sensitive site to another. The sensitive sites form different zones of the functionalized surface 4. The electronic nose 1 can also include several identical sensitive sites in terms of physicochemical affinity, with the aim for example of detecting a possible measurement drift and/or allowing the identification of a defective sensitive site.

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 has a main opening 22, located here above and perpendicular to the functionalized surface 4. L 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.

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 source (VCSEL), a type III-V/Si hybrid laser source, 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 divider, which divides the optical signal and directs it towards the K interferometers 12 arranged here in parallel to each other.

Each interferometer 12 here is of the Mach-Zehnder type, but it could be of the resonant ring type. As illustrated by the and 2C, an interferometer 12 comprises an input divider 13, two distinct 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.

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 forms the reference arm 14r. The waveguide of the sensitive arm 14s (material with a high refractive index) is located at a depth of the functionalized surface 4, therefore of the receivers 3, such that the optical signal (guided mode) propagating there presents an effective index which depends on the quantity of analytes 2 bound to receptors 3 of the sensitive site.

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 mode index corresponds, in some way, to the refractive index of the waveguide ‘seen’ by the optical mode. It is usually between the core index and the waveguide cladding index. We therefore understand that the quantity of analytes 2 adsorbed in the sensitive site modify the properties of the optical mode and/or the waveguide, in particular the phase of the guided mode.

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 traveling through it, and more precisely causes a modification of the phase of the guided mode, while the phase of the guided mode traveling 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.

Each interferometer 12 is coupled to at least one photodetector 16. This measures the value of the intensity or power of the optical output 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 optical output signals then being phase shifted by 2π/3 and detected by photodetectors 16. powers of these three optical output signals are denoted here P ₁ , P ₂ and P ₃ , and the in-phase component denoted I (like In-phase , in English) is calculated as: I = 2×P ₂ - P ₁ – P ₃ , as well as the Q component in phase quadrature with respect to the I component: Q = √3×(P ₁ -P ₃ ). The extracted phase difference φ is then calculated such that φ=arctan(Q/I). Its values are therefore well understood in 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 optical output signals are phase shifted by π/2. We can also use a 2x1 coupler, 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.

The processing unit 5 allows the implementation of the processing operations described below as part of the characterization process. It may include 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 includes 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 process. The memory is also suitable for storing 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 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 .

There illustrates an example of temporal evolutions of the so-called extracted phase difference φ _(k) (t) and of the so-called unfolded phase difference Φ _(k) (t) associated with an interferometer 12 of the electronic nose 1 of the . There 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).

As indicated previously, the power of the optical output signal varies periodically, and more precisely sinusoidally, as a function of the phase difference between the optical signals traveling through the sensitive arm 14s and the reference arm 14r of the interferometer 12 As phase extraction methods generally use an inverse trigonometric function such as an arc-tangent, the extracted phase difference φ _(k) (t) then has values modulo 2π.

In reference to the , 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 difference in extracted phase φ _(k) (t) increases by 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 with a value of -2π to go back down 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].

In reference to the , the determination of the unfolded phase difference Φ _(k) (t) is carried out for each successive measurement instant t _i going from t ₀ to t _N . During step 10, the temporal evolution of the intensity I _(k) (t _i ) or the power P _(k) (t _i ) of the optical output signal measured by the photodetector 16 over a duration is acquired. detection T. 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) (t _i ) of the so-called extracted phase difference φ _(k) between the optical signals circulating in the arms.

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], denoted m( t _i )×2π, where m(t _i ) is a positive or negative integer. The latter is an increment which varies by one unit +1 or -1 at each discontinuity of the extracted phase difference φ _(k) (t _i ). This operation of correcting the extracted phase difference φ _(k) (t) is usually called phase unfolding or phase unwrapping . It makes it possible to obtain an unfolded 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.

The detection method therefore comprises an unfolding phase 30, formed by a step 31 of calculating an instantaneous variation δφ _(k) (t _i ) = φ _(k) (t _i ) – φ _(k) (t _{i -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, the value of this instantaneous variation δφ _(k) (t _i ) is compared to a predefined threshold value S1, for example approximately π, to add or not a positive or negative unit to the increment m(t _i-1 ). Finally, during a step 33, the unfolded phase difference Φ _(k) (t _i ) is determined by adding to the extracted phase difference φ _(k) (t _i ) the multiple of 2π, i.e. m(t _i )×2π.

Then, within the framework of a conventional characterization process such as that described with reference to the , 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) (t _i ), respectively during the first phase Ph1 reference where the sensitive sites present an initial desorbed physicochemical state and during the second Ph2 phase of characterization where the sensitive sites present a final adsorbed physicochemical state.

However, as indicated above, the signature obtained may not be representative of the analytes 2 when the initial physicochemical state of one or other of the sensitive sites is not really desorbed, thus making the functionalized surface 4 heterogeneous in physicochemical state terms. 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 the , to identify the situation where the signature is characteristic of analytes 2 or not.

Thus, the illustrates an example of temporal evolution of the extracted phase differences φ and unfolded Φ in the case of a characterization process comprising a first reference phase Ph1 followed by a second characterization phase Ph2. There illustrates a similar situation, where the effective phase difference between the two guided signals has not varied before the first phase Ph1. And the illustrates another similar situation, where, contrary to the , the effective phase difference between the two guided signals varied before the first phase Ph1. Here, a single sensitive site (a single interferometer) is considered.

In reference to the , 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 optical signal received, and the processing unit 5 determines the difference in extracted phase φ(t). To the extent that 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 desorbed type. The unfolded phase difference Φ(t) has a constant value Φ _i .

Then, during the second Ph2 phase of characterization, 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 difference in optical path 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 stationary physicochemical state final adsorbed type. The processing unit 5 then determines the unfolded phase difference Φ(t) from the evolution of the extracted phase difference φ(t), as described previously with reference to the flowchart of the . The signature S is then equal here to the difference ΔΦ = Φ _f - Φ _i between the final value Φ _f and the initial value Φ _i of the unfolded phase difference Φ(t).

In reference to the , we now assume that, prior to the first reference phase Ph1 (phase denoted Ph0), the functionalized surface 4 has not been exposed to analytes 2 or to parasitic species capable of binding to receptors 3. We represent in dotted line the effective unfolded phase difference Φ _eff (t). It has an initial value Φ _eff,i equal to the initial value Φ _i . Then, the effective unfolded phase difference Φ _eff (t) evolves by having the same values as the unfolded phase difference Φ(t). Also, the signature S is equal to the deviation ΔΦ which is identical to ΔΦ _eff .

Let us now suppose, with reference to the , 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 can consist of a storage time of the electronic nose 1 where the functionalized surface 4 would not have been protected. In the figure, we also represent in dotted lines the different effective phases extracted φ _eff (t) and unfolded Φ _eff (t).

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

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 φ _eff,f0 then increases while remaining within 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 ) to a final value Φ _f . The processing unit 5 then determines the signature S as being equal to ΔΦ = Φ _f - Φ _i .

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 greater than the value Φ _i determined by the processing unit 5. In other words, the processing unit 5 considers that the initial physicochemical state of the sensitive site is a desorbed state, when this is in fact not the case. It follows that the processing unit 5 will determine a signature S as being equal to ΔΦ, whereas the effective signature should be ΔΦ _eff . This error when determining the signature comes from the indetermination 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 phase Ph1 reference. It therefore does not seem possible, in the case of such a characterization process using an electronic nose 1 of the interferometric type, to identify and rule out erroneous signature values of sensitive sites.

Figures 5A to 5C are schematic and partial views of an electronic nose 1 of the interferometric type according to one embodiment of the invention, for the implementation of a characterization method making it possible to obtain a signature effectively characteristic of the analytes 2. In fact, we avoid taking into account a physicochemical state that would not be completely desorbed.

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 the at 2C. But, it also comprises a thermal module 30 adapted to generate an increase in temperature of the functionalized surface 4, thus causing the transition of the physicochemical state of the functionalized surface 4 and therefore of the sensitive sites: from an initial adsorbed physicochemical state E _ia where the proportion (or quantity) of receptors 3 bound to analytes 2 is equal to an initial value p _ia not zero, to a final desorbed physicochemical state E _id where the proportion (or quantity) of receptors 3 bound to analytes is equal to a final value p _fd less than p _ia . The initial adsorbed states E _ia and final desorbed states E _fd are here stationary states (but they may not be).

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 d 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 the analytes 2 is caused by increasing the temperature to pass to the final desorbed state E _fd .

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. The heater 31 extends here facing 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 increase in temperature by the Joule effect.

The measuring support 23 and the lower support 24 are made of a thermally conductive material. The heater 31 is arranged facing the functionalized surface 4, at the level of the rear face of the lower support 24. Alternatively, it can be located between the lower support 24 and the measuring support 23, in which case the lower support 24 n It does not need to be made of a thermally conductive material.

As illustrated by , the heater 31 is made in the form of at least one track of an electrically conductive and resistive material, for example metallic. Preferably, the heater 31 extends facing all the arms of the interferometers 12, therefore facing the sensitive arms 14s like 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.

The electrical source 32 is adapted to apply an electrical signal, for example in step, to the heater 31. A stepped electrical signal corresponds to an electrical signal whose intensity passes from a first initial value to a second final value in a short duration, 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 level of the functionalized surface 4 and therefore of the sensitive sites, so that their temperature passes from an initial value less than or equal to a first threshold value T ₁ to a final value greater than or equal to a second threshold value T ₂ . The difference between the T ₁ and T ₂ values can be at least equal to 5°C, and can be of the order of approximately 20°C to cause effective desorption of the analytes from a significant proportion of the receptors. The value T ₁ can be between 2°C and 25°C, for example equal to 20°C, and the value T ₂ can be between 30°C and 60°C, for example equal to 50°C. It can 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 by continues or even in successive increments, among others.

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

As indicated previously, the characterization process provides for 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 T ₁ ; followed by a desorption phase Ph2 where a desorption of the analytes 2 is caused by means of an increase in the temperature to at least the second value T ₂ .

In reference to the , during the adsorption phase Ph1, the sensitive site is exposed to a gaseous medium containing the analytes 2. The latter can be brought to contacts 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 in which there is a balance 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 we consider that the receptors 3 are linked to the analytes 2. The sensitive site then presents the initial physicochemical state of adsorption Eia where the proportion (or quantity) of receptors 3 linked to analytes 2 is equal to the non-zero initial value pia.

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 the analyte A to the receptor L to form a analyte/receptor compound LA (for ligand-analyte , in English), and by a desorption constant k _b (in s ^-1 ) corresponding to the dissociation of the compound LA. The ratio k _d /k _a forms the equilibrium dissociation constant k _D (in mol) which gives the value of the concentration c _A of the analytes A making it possible to saturate 50% of the L receptors.

The steady state is reached when the concentration c _LA (t) of compounds LA is stationary dc _LA /dt=0, that is to say when the product of the constant k _a with the concentrations of the analytes c _A (t) and receptors c _L (t) (number of adsorption events) is equal to the product of the constant k _d with the concentration c _LA (t) of compounds LA (number of desorption events), in other words when l The following evolution equation is verified dc _LA /dt = k _a ×c _A ×c _L – k _d ×c _LA = 0. The maximum stationary value of the measurement signal is proportional to the concentration c _A (t) of the analytes A. Saturation of the L receptors of the sensitive site, that is to say the fact that all the receptors are bound to analytes, can be reached when the concentration c _A of analytes A is sufficient, which is assumed be the case here.

In reference to the , during this first adsorption phase Ph1, the thermal module 30 maintains the temperature of the functionalized surface 4 at a temperature less than or equal to a first threshold value T ₁ 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 stationary adsorbed state E _ia . 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, less than or equal to the adsorption value T ₁ predefined which can be equal to 25°C.

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

In reference to the , 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 Ph1 phase, 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) presents an initial constant value. The processing unit 5 then determines the unfolded phase difference Φ(t), which then presents the initial constant value Φ _i . Note that the processing unit 5 can alternatively determine the unfolded phase difference Φ(t) from the start of the first phase Ph1. It would then present a value Φ _eff,i which is greater than the value Φ _i .

Then, during the second phase of desorption Ph2, due to the increase in temperature which causes the rapid desorption of the 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 the processing unit 5 had determined the unfolded phase difference Φ(t) from the start of the first phase Ph1, it would then have the value Φ _eff,f which is greater than the value Φ _f .

The processing unit 5 can then determine the signature S which is equal to the difference (in absolute value) between the final value Φ _f and the initial value Φ _i : S = ΔΦ = | Φ _{f -} Φ _i | which is also equal to ΔΦ _eff = | Φ _{eff,f -} Φ _eff,i |. The differences acquired for each of the sensitive sites can be normalized so that they are between 0 and 1.

It emerges that, within the framework of the characterization process according to the invention, the signature is determined while the sensitive site has an initial adsorbed state E _ia and a final desorbed state E _fd , and not, as in the art anterior, from an initial desorbed state (or even partially desorbed) and a final adsorbed state. Furthermore, in the context of the invention, the gaseous medium to which the functionalized surface is exposed does not vary significantly or little between the adsorption phase Ph1 and the desorption phase Ph2, only the state of the functionalized surface changes between the initial adsorbed state E _ia and the final desorbed state E _fd 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). We thus limit or even eliminate 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 indetermination modulo 2π of the extracted phase difference φ(t ).

Furthermore, in the context of the invention, the transition from the initial adsorbed state E _ia to the final desorbed state E _fd is caused by the increase in temperature of the functionalized surface 4, and not by fluid management. controlled, which makes it possible in particular to simplify the structural configuration of the electronic nose 1. The quality of characterization of the analytes 2 is also improved, to the extent that desorption by thermal effect can be more effective than desorption by fluidic effect and can be effective for each sensitive site, so that the functionalized surface 4 presents a final state that is effectively desorbed and substantially homogeneous.

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 periods of time, for example of the order of a few seconds to minutes, or over long periods of time, for example of the order of a few hours to days.

There illustrates an example of variation in the temperature of the functionalized surface, during a succession of phases of characterization of gaseous media, denoted here A, B, C (the electronic nose can thus carry out a large number of successive phases of characterization A , B, C, D, E…).

Thus, each characterization phase A, B, C, etc. includes the adsorption phase Ph1 where the temperature remains at most equal to the value T ₁ and where the functionalized surface is exposed to a gaseous medium containing the analytes; followed by the Ph2 desorption phase where the temperature is increased to at least the T ₂ value to cause the desorption of the analytes with respect to the receptors.

There illustrates an example of temporal evolutions of the unfolded phase difference Φ _(k) (t) during the succession of characterization phases A, B, C… of the , 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.

The effective unfolded phase difference Φ _eff (t) varies between a stationary value here Φ _eff,i representative of the initial adsorbed state E _ia , and a stationary value here Φ _eff,f representative of the final desorbed state E _fd . Consequently, the unfolded phase difference Φ(t) varies between a stationary value Φ _i representative of the initial adsorbed state E _ia , and a stationary value Φ _f representative of the final desorbed state E _fd . To the extent that the gaseous medium is the same in terms of analytes from one characterization phase to another, the difference between Φ _i and Φ _f here remains the same for each of the characterization phases A, B, C, etc. . Note that, at time t ₀ , the value Φ _eff (t ₀ ) can 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.

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

Here, the effective unfolded phase difference Φ _eff (t) varies between a stationary value Φ _eff,i representative of the initial adsorbed state E _ia which is here different from a characterization phase A, B, C… to l 'other, to the extent that the proportion p _ia of receptors bound to the analytes may be different. On the other hand, during the final desorbed state E _fd , we consider that the analytes are all desorbed, so that the value Φ _eff,f is substantially zero for each of the characterization phases A, B, C, etc..

Consequently, the unfolded phase difference Φ(t) varies between the stationary values Φ _i (initial adsorbed state E _ia ) and Φ _f (final desorbed state E _fd ), with a gap Φ _f – Φ _i which differs here from one characterization phase A, B, C… to the other, to the extent that the functionalized surface is successively exposed to gaseous media different from each other in terms of analytes.

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 Ph2 desorption phase during which the thermal desorption of the analytes is caused (preferably total), thus making it possible to remove possible errors linked to the indetermination modulo 2π of the extracted phase difference φ(t).

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

Claims (13)

Method for characterizing analytes (2) present in a gaseous medium, using an electronic nose (1) comprising:

• 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 presenting a physicochemical state defined by a proportion of the receptors (3) related to analytes (2);
• 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 an arm of reference (14r), coupled to a light source (11); and at least one photodetector (16) coupled to the interferometer (12);
• a processing unit (5), connected to the photodetector (16);
• a thermal module (30), adapted to generate a temperature variation of the functionalized surface (4);
• the process comprising the following steps:
• a) 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 T ₁ , so that the functionalized surface (4) presents an initial physicochemical state called adsorbed where the proportion of receptors linked to the analytes is equal to a non-zero initial value p _ia ;
• b) generation by the thermal module (30) of an increase in temperature of the functionalized surface (4) up to at least a second predefined value T ₂ , thus causing a change of state between the initial adsorbed physicochemical state and a final physicochemical state called desorbed where the proportion of receptors linked to the analytes is equal to a final value p _fd less than p _ia ;
• c) measurement by the photodetector (16) of the optical signal transmitted by the interferometer (12), during the stages of exposure and generation of the temperature increase;
• d) determination by the processing unit (5):
  • 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
  • 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 Φ _(k)i and final Φ _(k)f values of the unfolded phase difference Φ _(k) (t), respectively representative of the initial adsorbed and final desorbed physicochemical states of the functionalized surface (4);
• e) characterization of the analytes (2), based on the initial Φ _(k)i and final Φ _(k)f values.

Characterization method according to claim 1, in which the temperature difference between the first value T ₁ and the second value T ₂ is at least equal to 5°C. Characterization method according to claim 1 or 2, in which the first value T ₁ is at most equal to 25°C, and the second value T ₂ is at least equal to 30°C. Characterization method according to any one of claims 1 to 3, in which the first value T ₁ is between 2°C and 25°C, and the second value T ₂ is between 30°C and 60°C. Characterization method according to any one of claims 1 to 4, in which steps a) to e) are repeated successively, the functionalized surface (4) then being successively exposed, at each new step a), i.e. at 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. Electronic nose (1) adapted to characterize analytes (2) present in a gaseous medium, for the implementation of the characterization method according to any one of the preceding claims, comprising:

• 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 presenting a physicochemical state defined by a proportion of the receptors (3) related to analytes (2);
• 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 an arm of reference (14r), coupled to a light source (11); and at least one photodetector (16) coupled to the interferometer (12);
• a processing unit (5), connected to the photodetector (16), 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 (16), the values of which are included in a width interval predefined; 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 Φ _(k)i and final Φ _(k)f values of the unfolded phase difference Φ _(k) (t), respectively representative of initial adsorbed and final desorbed physicochemical states of the functionalized surface (4), then allowing to characterize the analytes (2);
• a thermal module (30) adapted to generate a temperature variation of the functionalized surface (4), thus causing a state transition between the initial adsorbed physicochemical state and the final desorbed physicochemical state, from:
  • an initial temperature at most equal to a first predefined value T ₁ for which the functionalized surface (4) has an initial adsorbed physicochemical state where a proportion of the receptors linked to the analytes is equal to a non-zero initial value p _ia ;
  • at a final temperature at least equal to a second predefined value T ₂ for which the functionalized surface (4) has a final desorbed physicochemical state where the proportion of receptors linked to the analytes is equal to a final value p _fd less than p _ia .

Electronic nose (1) according to claim 6, in which the thermal module (30) comprises a heater (31) which extends opposite the arms of the interferometer (12). Electronic nose (1) according to claim 7, in which the functionalized surface (4) is located on a first face of a support (23, 24) where the waveguides (14s, 14r), the heater ( 31) being arranged on a second face of the support (23, 24) opposite the first face, the support (23, 24) being made of a thermally conductive material. Electronic nose (1) according to claim 7 or 8, in which the measuring device (10) comprises a plurality of interferometers (12), the heater (31) extending opposite the arms (14s, 14r) of all said interferometers (12). Electronic nose (1) according to any one of claims 6 to 9, in which 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 . Electronic nose (1) according to any one of claims 1 to 10, in which the thermal module (30) comprises an electrical source (32) adapted to apply to a heater (31) an electrical signal in steps causing the increase in temperature. 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 increase from the initial temperature to the final temperature in a duration of at most 5 seconds . Electronic nose (1) according to any one of claims 1 to 12, in which the interferometer (12) is a Mach-Zehnder interferometer or a resonant ring interferometer.