FR3115606A1 - Optical system for detecting at least one target compound present in an aerosol exhaled by a breath fluid - Google Patents

Abstract

The invention relates to an optical system for detecting at least one target compound present in an aerosol exhaled by a breath fluid, comprising: (a) a removable substrate comprising two opposite faces called the lower face and the upper face, the fluid of breath being exhaled on all or part of said substrate, (b) an emitter of optical radiation directed towards the upper face of said substrate, (c) a detector of all or part of the optical radiation emitted by the emitter, and in which all or part of the substrate is functionalized by a molecule having a specific chemical affinity to the target compound(s) so that the intensity of the detected optical radiation is substantially different in the presence or in the absence of the target compound(s) ) said target compound(s).

Description

Optical system for detecting at least one target compound present in an aerosol exhaled by a breath fluid

Technical area.

The subject of the invention is an optical system for detecting at least one target compound present in an aerosol exhaled by a breath fluid. It also relates to a method for carrying out a detection test for at least one target compound in a breath fluid by means of such a system.

State of the art.

The use of reliable tests to detect very quickly in humans whether they have used drugs or have a viral infection presents major challenges in terms of road safety and/or public health. This has recently been confirmed for the COVID-19 epidemic where the need for rapid tests to massively diagnose a population is proving to be a key factor in slowing down its evolution.

However, most of the tests on the market aimed at detecting and quantifying such compounds are essentially carried out by blood, nasopharyngeal or salivary samples. The first two types of samples have the disadvantage of being rather slow (several hours or even days for a diagnosis to be established) and require the presence of medical personnel to be carried out. This is the case of serological tests which measure the antibodies produced by the body during the immune response. This is also the case with PCR tests (abbreviation of the English term Polymerase Chain Reaction) which make it possible to directly detect a virus by amplifying its genetic material, as well as antigenic tests based on the recognition of viral antigens on the surface of proteins. of the virus. Saliva tests certainly have the advantage of being based on non-invasive samples, of having significantly lower response times (a few tens of minutes) and much lower costs than other tests, but they lack reliability. and specificity to detect a target compound.

The idea of indirect detection of metabolites in exhaled air has been considered by several research groups in order to be able to carry out tests in real time. The two main technical solutions proposed by research groups are based on mass spectrometry or on nanometric electro-chemical sensors (https://pubs.acs.org/doi/pdf/10.1021/acsnano.0c05657). In both cases, the idea is to simultaneously detect a plurality of volatile organic compounds whose nature and concentrations are specific to a given viral infection. In addition to the fact that these techniques must be coupled with elaborate algorithms to discriminate pathologies and increase the specificity of these tests, mass spectrometry remains an expensive technique that is difficult to miniaturize.

This is why the idea of direct detection of target compounds in exhaled air is particularly advantageous. Indeed, many compounds are found in the aerosols generated during exhalation, i.e. solid or liquid compounds suspended in the exhaled air. This is the case, for example, of solid compounds such as cannabinoids found in the breath of cannabis users, or of viruses trapped in micro-droplets. Researchers from the University of Nebraska recently published a study which shows that the SarS-Cov-2 coronavirus was found in microdroplets of less than 5µm exhaled in the ambient air by patients with COVID-9 (https ://doi.org/10.1038/s41598-020-69286-3).

Finally, several research teams have shown that there are synthetic antibodies with a very high affinity for certain viruses such as SarS-Cov-2 and capable of blocking the infection of lung cells by the virus (https: //doi.org/10.1101/2020.08.24.264077).

The present invention aims to solve all the drawbacks known in the state of the art by proposing an optical system capable of being integrated into a test device which can be both rapid, specific to the compounds targeted, reliable, compact, easy to use, based on non-invasive sampling, and inexpensive.

Presentation of the invention.

The solution proposed by the invention is an optical system for detecting at least one target compound present in an aerosol exhaled by a breath fluid, comprising:
(a) a removable substrate comprising two opposite faces called the lower face and the upper face, the breath fluid being exhaled over all or part of the said substrate,
(b) an emitter of optical radiation directed towards the upper face of said substrate,
(c) a detector of all or part of the optical radiation emitted by the transmitter,

Said system is remarkable in that all or part of the substrate is functionalized by a molecule having a specific chemical affinity to the target compound(s) so that the intensity of the detected optical radiation is substantially different in the presence or in the absence of said target compound(s).

The system that is the subject of the present invention makes it possible to carry out a test for detecting the target compound in a breath fluid via a succession of steps consisting of:
(a) measure the intensity of the optical signal having interacted with the substrate functionalized by a molecule: this is the reference measurement,
(b) bringing all or part of the functionalized substrate into contact with the gas exhaled by the breath fluid so as to adsorb the target compound if it is present in the exhaled gas,
(c) measuring the intensity of the optical signal on all or part of the functionalized substrate having interacted with the breath fluid: this is the final measurement,
(d) comparing the two intensities measured during the reference measurement and the final measurement in order to evaluate whether the target compound is present or not.

The objective is therefore to trap the target compound by adsorbing it on the molecule used to functionalize the substrate, then to record on the detector the variation in the intensity of the optical signal over a range of wavelengths characteristic of the presence of the target compound on the substrate. This range of wavelengths can be the direct optical signature of the target compound, the variation in signal intensity being due to the absorption of said compound at these wavelengths. Alternatively, it may be the modification of the optical signature of the molecule in the presence of the target compound. This is the case, for example, if the molecule has an active fluorophore in the presence of the target compound and inactive in the opposite case. The change in structure or chemical nature of said molecule induced by the adsorbed target compound then leads to a change in fluorescence intensity.

The target wavelength range is preferentially narrow, i.e. with a width of less than 1 µm, so that the response is specific to the target compound. The narrower the band, the more specific the response. It can also be radiation located in the ultraviolet, the visible, or even in the near or medium infrared.

The substrate is the physical support of the molecule having an affinity for the target compound. The molecule is preferentially immobilized on one of the external faces or inside the substrate if it has cavities. This immobilization step, also called functionalization of the substrate, consists in depositing said molecules either in the liquid phase, or in the vapor or gas phase, and on one or more surfaces of the substrate. At the end of the functionalization process, the molecule is found on the surface of the substrate. The interactions between the substrate and said molecule can be strong in the case of the formation of covalent or ionic bonds, or weak in the case of hydrogen or Van der Waals bonds. It may be advantageous to prepare the surface to be functionalized by a chemical or physical treatment aimed at facilitating the immobilization of the target molecule on the substrate.

A more complex alternative to implement is to encapsulate inside the substrate, for example between two glass slides, a liquid matrix containing said molecules. This can be advantageous if the molecules are only stable in solution, and if the aforementioned processes degrade the structure of the molecule.

This substrate is removable, which means that it can be easily removed from the system during the detection test, for example between the reference measurement step and the final measurement step, or at the end of the test, by example to recycle said substrate.

Finally, the substrate can be either transparent or reflective at the wavelengths of interest. It can be rigid or flexible and have multiple geometric shapes. The respective positions of the emitter, the substrate and the detector depend on both the optical and geometric characteristics of said substrate.

Other advantageous characteristics of the invention will appear in the description. Each of these characteristics can be considered alone or in combination with the remarkable characteristics defined above. Each of these characteristics contributes, where appropriate, to the resolution of specific technical problems defined further on in the description and to which the remarkable characteristics defined above do not necessarily participate. The latter may be the subject, where appropriate, of one or more divisional patent applications.

Brief description of figures.

Other advantages and characteristics of the invention will appear better on reading the description of a preferred embodiment which will follow, with reference to the appended drawings, produced by way of indicative and non-limiting examples and in which:
schematizes a substrate according to the invention.
illustrates the conformation of a substrate in the form of a tube.
schematizes a detection system according to a first embodiment of the invention.
schematizes a detection system according to a second embodiment of the invention.
schematizes an alternative embodiment of the detection system according to the second embodiment.
diagrams another alternative embodiment of the detection system according to the second embodiment.
schematizes a detection system according to a third embodiment of the invention.
diagrams a variant embodiment of the detection system according to the third embodiment.
diagrams another alternative embodiment of the detection system according to the third embodiment.

Description of embodiments.

The target compound is advantageously a virus, that is to say one or more nucleic acid(s) enclosed in a protein capsid, of size between 10 nm and 300 nm. All of the proteins that make up the virus are made up of a large number of amino acids linked together by a covalent chemical bond called a peptide bond. The vibration of the amide groups of the peptide bond produces an absorption of infrared radiation in 3 spectral bands, including 2 intense absorption bands between 5.9 µm and 6.7 µm and a broad band between 7.1 µm and 8.3 µm. This absorption is a signature of the proteins, which is why it is advantageous to detect the variation in intensity of the radiation (in the presence or in the absence of virus) on one of these two wavelength ranges.

The transmitter can emit in the infrared over a wide spectrum by Joule effect, typically between 2 µm and 15 µm. The emitter can for example consist of a black body of the MEMS type. In this case, the optical system can integrate, on the optical path located between the emitter and the detector, a narrow band-pass optical filter (not shown) centered between 6.0 μm and 8.2 μm, and preferably centered at 6.1 µm or 6.5 µm. The detector itself can be a pyroelectric detector, a micro-bolometer or a thermopile or even a photodetector.

Alternatively, the transmitter can be designed so that it transmits over a narrow band of wavelengths. These may include photonic emitters such as quantum cascade lasers, LEDs or even nanostructured MEMS micro-sources which preferentially emit at the optical resonance wavelength of the nanostructures. The interest is then to avoid energy losses related to the emission of the part of the spectrum not useful for detection, while avoiding the integration of an optical filter in the system.

In addition, the substrate is functionalized with a molecule having a chemical affinity specific to the virus that one wishes to detect. This molecule may be a synthetic protein endowed with one or more recognition sites specific to said virus, so that said virus can be adsorbed on the functionalized substrate. The chemical recognition mechanism involved is then similar to that used in the body for antibody-antigen recognition. The desorption of the target compound, necessary to recycle the substrates after a virological test has taken place, can be done by heating the substrate to temperatures above 50°C, or by using acidic or basic solutions. In both cases, the mechanism consists in breaking the bonds between the target compound and the molecule serving to functionalize the substrate.

According to a variant embodiment, the system can also embed a device for heating the substrate in order to be able to desorb the target compound without damaging the chemical structure of the molecules. This makes it possible to recycle the functionalized substrate or to avoid an accumulation of humidity that could interfere with the optical measurement.

Alternatively, the substrate may contain within it a heating resistor placed so that the functionalized part of the substrate can be heated. It may be, for example, a resistive metallic filament which heats up by the Joule effect. This variant obviously increases the cost of the substrate and therefore only has economic interest if it is desired to recycle the functionalized substrate.

The optical system that is the subject of the invention can be integrated into an apparatus for detecting target compound(s) in an aerosol exhaled by a breath fluid. The user must then exhale air on all or part of the functionalized substrate, typically for 3 seconds to 30 seconds and at a distance of 1 cm to 15 cm from said substrate. This operation can be done via a duct (not shown) allowing the aerosol exhaled by the user to be guided from his mouth towards the functionalized surface of the substrate. The system can integrate an exhalation flow measurement, via a pressure sensor for example, to calculate the volume of exhaled air and indicate to the operator that the test is complete. If the volume is insufficient to guarantee the reliability of the test, then he may be asked to perform an expiration operation again.

It can be a medical test device to detect viral pathology in breath fluid.

Another possible application concerns the detection of drugs in a breath fluid, for example with target compounds of the cannabinoid family. In this specific case, the affinity molecules can then be synthetic mimics of the CB1 and CB2 receptors on which the cannabinoids bind in the body.

- The substrate 1 comprises two faces 1a, 1b which are opposite and called lower face 1a and upper face 1b. In the first two embodiments according to the invention, the upper face 1b of said substrate is reflective. All or part of the optical radiation emitted is then reflected on the upper face 1b of the substrate to be directed towards the detector. Typically, the substrate can be covered with one or more thin layers 2 of metal, preferably chosen from the following group: copper, silver, gold, cobalt, nickel, palladium, aluminum, chromium, zinc. These layers 2 have a thickness of between 100 nm and a few tens of μm, and can be deposited by bonding, by electrochemical deposition, by electrolytic deposition, by printing, by screen printing, heating, or by any other thin layer deposition process. The substrate can be rigid or flexible, transparent or not, for example made of glass or plastic.

- In a first embodiment, the substrate 1 whose upper face 1b is reflective is a thin film with a total thickness of less than 250 μm so that it is flexible. The substrate is advantageously made of a material chosen from the following group: polyimide, polyepoxide, polyester, epoxy resin reinforced with glass fibers, aluminum. This substrate 1 can be shaped so as to form a tube 3. This tube 3 may be cylindrical in shape (the 2 ends of the tube 3a, 3b being circular openings of the same dimensions) or truncated conical (the 2 ends of the tube being circular openings of different sizes), without these shapes being limiting. The layer of metal 2 forming the upper face 1b is then found inside the tube 3. It is this upper face 1b which is functionalized by a molecule having a specific chemical affinity for the target compound. The functionalization of the reflective surface can consist for example of a metal-ligand bond or of a covalent bond.

- The emitter 5 and the detector 4 are located at each of the two ends 3a, 3b of said tube, the purpose of which is to guide the radiation emitted towards the detector 4 by multiple reflections on the metal layer 2. The advantage of such a configuration is to cause the radiation emitted to interact several times with the functionalized substrate, and thus to increase the sensitivity of the system. The transmitter 5 advantageously includes an optical reflector 6 designed to concentrate and direct most of the optical radiation emitted onto the tube 3 (in order to limit the losses in emissivity and to optimize the number of optical reflections) while avoiding as far as possible that the detector does not receive direct radiation from the unreflected emitter. Substrate 1 forming tube 3 may be pierced with one or more orifices (not shown) located close to ends 3a, 3b, said orifices being in fluid communication with the duct. This configuration makes it possible to exhale the breath fluid directly on the upper face 1b situated inside the tube 3 which is prepositioned in the optical system. This has the advantage of not modifying the respective positions of the substrate 1, the emitter 5 and the detector 4 between the reference measurement and the final measurement.

- In a second embodiment, the substrate 1 whose upper face 1b is reflective is advantageously plane, the emitter 5 and the detector 4 being located on the same side of the plane in which said substrate 1 is inscribed, namely on the side of said upper face 1b. The substrate 1 can be flexible or rigid. It is advantageous in this configuration to use an optical reflector 6 on the emitter 5 in order to control the zone of interaction of the optical radiation emitted with the substrate, as well as a collector 7 on the detector in order to direct the maximum radiation optics reflected on the face 1b of the substrate towards the detector 4. The reflector 6 and the collector 7 have perfectly reflective walls in order to maximize the specular reflections of the optical radiation on these two waveguides. It is also possible for the reflector 6 and the collector 7 to form only one and the same part (not shown). A person skilled in the art who knows the laws of geometric optics would know how to design the shapes of the reflector 6 and of the collector 7, as well as the distances and angles between the emitter 5, the detector 4 and the substrate 1 to maximize the intensity of the optical signal collected at the detector 4, and thus increase the sensitivity of the optical system.

- According to a first variant embodiment, the upper face 1b can also be subdivided into at least two zones 1b' and 1b''. The two zones 1b' and 1b'' are functionalized by a molecule having a specific chemical affinity to the target compound. The surface density of said molecule on the two zones 1b' and 1b'' are substantially identical so that the reference optical signal level of these two zones is the same. Only zone 1b' receives the exhaled air fluid, reference zone 1b'' being protected for example during the test by a film which is removed at the end of the test. After the expiration phase, substrate 1 is positioned so that the radiation emitted by emitter 5 only interacts with zone 1b'' before being collected by detector 4 (not shown). This first measurement step makes it possible to carry out the reference measurement. Thanks to a translation of the substrate 1 along the X axis, it is possible in a second measurement step to make the radiation emitted interact only with the zone 1b' so as to carry out the final measurement. In this configuration, the positions of the emitter 5 and of the detector 4 are fixed and only the substrate 1 moves in the optical system.

- According to a second embodiment, the constituent material of the substrate 1 is transparent, and the emitter 5 and the detector 4 are located on the side of the lower face 1a of the substrate, that is to say opposite of the face 1b containing the reflective layer 2. In this variant, it is the lower face 1a which is functionalized. The advantage of such a configuration is that a ray emitted by the emitter 5 crosses twice the interface formed by the functionalized surface 1a, before and after reflection on the layer 2. Thus, the variation in intensity of the optical signal in the presence of the target compound is increased, which makes it possible to increase the detection sensitivity of the optical system.

Figures 3 - In a third embodiment, the substrate 10 must be transparent ( ). The emitter 5 and the detector 4 are located on either side of the plane in which the substrate 1 is inscribed, namely on the side of the lower face 1a for the emitter 5 and on the side of the upper face 1b for the detector 4. All or part of the optical radiation emitted is then transmitted through the substrate 10 to be directed towards the detector 4. The material of the substrate 10 is chosen so that the transmission of said material at the wavelengths of interest is maximum . It can be for example a glass or a transparent plastic. Only one of the two faces 1a or 1b, or both faces 1a and 1b can be functionalized. The advantage of functionalizing several surfaces rather than one lies in the fact that the variation in intensity of the optical signal in the presence of the target compound is increased. This can be generalized to a stack of several substrates 10', 10'', 10''' on top of each other, the radiation emitted by the emitter 5 then passing through a plurality of functionalized surfaces before being collected at the detector 4 ( ), which increases the detection sensitivity of the system. Another alternative is to use a substrate 10 structured by microgrooves 8 parallel to each other ( ). It is also advantageous, in the different configurations of FIGS. 3A, 3B and 3C, to use an optical reflector 6 on the emitter 5 in order to control the zone of interaction of the optical radiation emitted with the substrate, as well as a collector 7 on the detector in order to direct the maximum optical radiation towards the detector 4.

Said collectors 6 and 7 can be replaced respectively by diverging and converging lenses that a person skilled in the art would be able to place to obtain a comparable effect.

The arrangement of the various elements and/or means and/or steps of the invention, in the embodiments described above, should not be understood as requiring such an arrangement in all implementations. Other variants may be provided. Further, one or more features disclosed only in one embodiment may be combined with one or more other features disclosed only in another embodiment. Likewise, one or more features disclosed only in one embodiment can be generalized to the other embodiments, even if this or these features are described only in combination with other features.
:

Claims (10)

Optical system for detecting at least one target compound present in an aerosol exhaled by a breath fluid, comprising:
(a) a removable substrate (1) comprising two opposite faces called lower face (1a) and upper face (1b), the breath fluid being exhaled over all or part of said substrate,
(b) an emitter (5) of optical radiation directed towards the upper face (1b) of said substrate,
(c) a detector (4) of all or part of the optical radiation emitted by the transmitter (5),
and in which all or part of the substrate (1) is functionalized by a molecule having a specific chemical affinity to the target compound(s) so that the intensity of the optical radiation detected is substantially different in the presence or in the absence of said target compound(s). System according to claim 1, in which the target compound is a virus, the molecule functionalizing the substrate (1) being a synthetic protein endowed with one or more recognition sites specific to said virus, so that said virus can be adsorbed on said functionalized substrate. System according to claim 1, in which the target compounds are from the cannabinoid family, the molecules functionalizing the substrate (1) being synthetic mimics of the CB1 and CB2 receptors on which the cannabinoids bind in the organism. System according to one of the preceding claims, in which the upper face (1b) of the substrate (1) is reflective and functionalized by the molecule having a specific chemical affinity for the target compound(s), all or part optical radiation emitted being reflected on said upper face to be directed towards the detector (4). System according to claim 4, comprising one of the following characteristics:
- the substrate (1) is in the form of a tube having two ends (3a, 3b), the emitter (5) and the detector (4) being located at each of the two said ends, or
- the substrate (1) is flat, the emitter (5) and the detector (4) being located on the side of the functionalized upper face (1b) of said substrate. System according to one of Claims 1 to 3, in which:
- the constituent material of the substrate (1) is transparent,
- the upper face (1b) contains a reflective layer (2),
- the emitter (5) and the detector (4) are located on the side of the lower face (1a) of the substrate (1), that is to say opposite the upper face (1b) containing the reflective layer (2),
- the lower face (1a) is functionalized by the molecule having a specific chemical affinity to the target compound(s), so that a ray emitted by the emitter (5) crosses the diopter formed twice by the lower face (1a) functionalized, before and after reflection on the reflective layer (2). System according to one of Claims 1 to 3, in which:
- the constituent material of the substrate (10) is transparent,
- the emitter (5) and the detector (4) are located on either side of the plane in which the substrate (10) is inscribed, namely on the side of the lower face (1a) for the emitter (5 ) and on the side of the upper face (1b) for the detector (4),
- the lower face (1a) and/or the upper face (1b) of the substrate (10) are functionalized by the molecule having a specific chemical affinity for the target compound(s). A method for carrying out a test for the detection of at least one target compound in a breath fluid by means of a system according to claim 1, comprising the steps of:
(a) measure the intensity of the optical signal having interacted with the substrate (1) functionalized by a molecule: this is the reference measurement,
(b) bringing all or part of the functionalized substrate into contact with the gas exhaled by the breath fluid so as to adsorb the target compound if it is present in the exhaled gas,
(c) measuring the intensity of the optical signal on all or part of the functionalized substrate (1) having interacted with the breath fluid: this is the final measurement,
(d) comparing the two intensities measured during the reference measurement and the final measurement in order to evaluate whether the target compound is present or not. A method according to claim 8, comprising the steps of:
- subdividing the upper face (1b) of the substrate (1) into at least a first zone (1b') and a second zone (1b''),
- functionalizing the two zones (1b', 1b'') with a molecule having a specific chemical affinity for the target compound, the surface density of said molecule on the two said zones being substantially identical so that the reference optical signal level of these two areas are the same,
- in a first test phase, only the first zone (1b') receives the exhaled air fluid, the second zone (1b'') being protected by a film which is removed at the end of the test,
- after the test phase, position the substrate (1) so that the radiation emitted by the emitter (5) only interacts with the second zone (1b'') before being collected by the detector (4 ), this first measurement step making it possible to carry out the reference measurement,
- in a second final measurement step, translating the substrate (1) along an axis (X), so that the radiation emitted only interacts with the first zone (1b'). Method according to one of Claims 8 or 9, comprising at least one of the following steps:
- carrying out the detection test on a target compound which is a virus consisting of proteins, which proteins are formed of amino acids linked together by a peptide bond, the vibration of the amide groups of said peptide bond producing an absorption of infrared radiation in three spectral bands, including two intense absorption bands between 5.9 µm and 6.7 µm and a broad band between 7.1 µm and 8.3 µm,
- using an emitter (5) which emits in the infrared on a Joule effect spectrum between 2 µm and 15 µm,
- integrating, on the optical path located between the emitter (5) and the detector (4), a narrow band-pass optical filter centered between 6.0 μm and 8.2 μm, and preferably centered at 6.1 μm or 6 .5 µm.