Method and associated system for characterizing biological particles in aerosol form using laser-induced plasma spectroscopy

Abstract

The present invention relates to a method and associated system for characterizing biological particles in aerosol form (i.e., suspended in an ambient gas) using laser-induced plasma spectroscopy, comprising the steps of: a) collecting (Ea) the ambient gas containing the biological particles intended to be characterized; b) generating (Eb) a jet of said particles (JAB) in a vacuum chamber (CH); c) transmitting a laser beam (FL) in the form of pulses and focusing the laser beam in the vacuum chamber (CH) transversely to the propagation direction of the jet of particles (JP) so as to capture in a focusing volume (VF) the laser beam (FL) and at least one individual particle (N) of the jet. P ), wherein the plasma sends other particles that are specific to the interaction between the laser beam and individual particles of the jet; d) collecting the particles sent by the plasma (Ed); and e) performing spectroscopic analysis of said particles (Ee) to ultimately characterize the biological particles.

Description

[Technical Field]

[0001] The present invention relates to the field of characterization of biological particles in the form of aerosols in ambient gases. [Background technology]

[0002] The ambient gas may in particular be the ambient air inside or outside the building.

[0003] Today, detection of biological particles in the air is currently performed by drawing in ambient air and allowing the particles to accumulate in a (small) volume of liquid or gelatin filter. The presence of the desired biological particles is then checked by a method called the strip method or titrated microscopically.

[0004] Alternatively, an aerosol deposit may be obtained that is contained in the air, a deposit that may contain biological particles. The presence of the desired biological particles in the deposit is then established using a variety of techniques. There are many techniques that can be used, including X-ray fluorescence and microscopy, among others.

[0005] Thus, known techniques operate in two steps that are completely separate in time and space, the collection step and the detection step being carried out on completely different equipment. Summary of the Invention [Problem to be solved by the invention]

[0006] Therefore, existing techniques are time consuming and, moreover, are not usually performed in situ.

[0007] One object of the present invention is to propose a more efficient solution than existing solutions for characterizing biological particles present in the form of aerosols in ambient gases.

[0008] In particular, the present invention proposes a solution that can provide real-time and in-situ characterization of biological particles. [Means for solving the problem]

[0009] To this end, the present invention provides a method for characterizing biological particles in aerosol form, i.e. suspended in an ambient gas, by laser-induced plasma spectroscopy, comprising: a) sampling an ambient gas containing biological particles to be characterized; b) generating a jet of said particles in a chamber under vacuum; c) emitting a laser beam in the form of pulses and focusing said laser beam in the vacuum chamber transversely to the propagation direction of the particle jet to generate a plasma in the focusing volume by interaction between the laser beam and at most one individual particle of the jet, said plasma releasing other particles that are specific to the interaction between the laser beam and said individual particle of the jet; d) collecting the particles emitted from the plasma; e) performing a spectroscopic analysis of these particles to finally characterize said biological particles.

[0010] The method according to the invention may comprise at least one of the following features, either alone or in combination: Between step a) and step b) the following sub-steps: aa) introducing ambient gas into a chamber called the mixing chamber (CHM); ab) introducing into the mixing chamber in the form of an aerosol at least one type of receptor for a specific molecule of the biological particle to be characterized, said at least one type of receptor being marked in another way; ac) a substep of mixing in a mixing chamber an aerosol containing said at least one type of receptor marked with a molecule specific to the biological particle to be characterized with the sampled ambient gas containing said biological particle to be characterized is carried out. Before step ab), the aerosol containing said at least one type of receptor marked with a molecule specific for the biological particle whose characterization is sought is dried. After sub-step ac), the mixture formed is dried before step b) is carried out. If the marker is a magnetic material, after sub-step ac) and before carrying out step b), only particles comprising the magnetic material are selected by any suitable magnetic means. Said at least one type of receptor marked with a molecule specific for the biological particle sought to be characterized is obtained from a spray solution of said marked receptors. The solution is based on alcohol (eg, ethanol). Step ab) consists of introducing into a mixing chamber (CHM) in the form of an aerosol several different types of receptors for specific molecules of the biological particles that it is desired to characterize, each type of receptor being marked. Each type of receptor is marked differently.

[0011] For this purpose, the invention also relates to a system for carrying out the method according to the invention, said system comprising: means for generating an aerosol of said at least one type of receptor marked with a molecule specific to the biological particle whose characterization is sought; A mixing chamber comprising: a first inlet for the gas to be sampled; a second inlet for the aerosol produced by said means for producing an aerosol of said at least one type of receptor marked with a molecule specific to the biological particle sought to be characterized; a mixing chamber including an outlet for mixing the aerosol containing the at least one type of receptor marked with a molecule specific to the biological particle sought to be characterized with the sampled ambient gas containing the biological particle to be characterized; 1. An apparatus for characterizing said particles by laser-induced plasma spectroscopy, comprising: a system for generating in a chamber a jet of said particles from gas coming from a mixing chamber, the system being associated with (connected to) a means for pumping the gas present in the chamber in order to create a vacuum in the chamber; a laser capable of emitting a laser beam in the form of pulses, the laser having associated thereto an optical device configured to focus the laser beam in a chamber transversely to the direction of propagation of a particle jet, the plasma being generated in a focal volume by interaction between the laser beam and particles of the jet, the plasma releasing other particles specific to the interaction between the laser beam and the particles of the jet; A system is proposed comprising an apparatus comprising at least one detection device including means for collecting particles emitted by the plasma and means for performing spectroscopic analysis of the particles.

[0012] The system according to the invention may include at least one of the following features, either alone or in combination: The mixing chamber comprises at least one dryer located either between the means for generating an aerosol of at least one type of marked receptor and the second inlet of the mixing chamber or at the level of the outlet of the mixing chamber. The mixing chamber is a Goldberg rotating drum. The means for collecting particles emitted by the plasma includes a plurality of N optical fibers (N is a natural number strictly greater than 1), one end of each optical fiber being arranged around and pointing towards the focal volume to ensure collection of particles emitted by the plasma. The optical fiber is attached to the spherical outer wall of the chamber. The means for performing spectroscopic analysis of particles emitted by the plasma comprises: a plurality of notch-type filters capable of ensuring filtering in different wavelength bands; Associated with each notch filter is a photodetector, for example of the electronic photomultiplier type.

[0013] Further features and advantages of the present invention will become apparent from the following detailed description when taken in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a schematic diagram of a method for characterizing biological particles according to the present invention. [Figure 2] 1 shows a cross-sectional view of an apparatus for characterizing biological particles in aerosols, operating by laser-induced plasma spectroscopy. [Figure 3] Schematically shows the region of interaction between the laser beam and the particle jet formed with particles coming from sampling the ambient gas containing biological particles in the device shown in FIG. 2. [Figure 4a] FIG. 3 is an external perspective view of a portion of the characterization device shown in FIG. 2, a portion of which shows means, in the form of a plurality of optical fibers, for collecting particles generated by interaction between the device's laser beam and aerosol particles. [Figure 4b] FIG. 4b is a view of the first cross-sectional plane of FIG. 4a. [Figure 4c] FIG. 4b is a view of the second cross-sectional plane of FIG. 4a. [Figure 5a] FIG. 4 is a schematic diagram of a detection device equipped with the optical fiber collection means shown in FIGS. 4a to 4c. [Figure 5b] 4a-4c are schematic diagrams of alternative detection devices with optical fiber collection means, also shown in FIGS. 4a-4c. [Figure 6] FIG. 3 is an enlarged cross-sectional view of a portion of the apparatus shown in FIG. 2. [Figure 7]3 is a general schematic diagram of a biological particle characterization system according to the present invention, including in particular the apparatus of FIG. 2; [Figure 8] 8 shows a mixing chamber used with the apparatus shown in FIG. 2 to form the system shown in FIG. 7. DETAILED DESCRIPTION OF THE INVENTION

[0015] In the following description, (O, X, Y, Z) defines an orthogonal reference frame.

[0016] The present invention particularly relates to a method for characterizing biological particles in aerosol form (i.e., suspended in an ambient gas) by laser-induced plasma spectroscopy, as shown diagrammatically in Figure 1. By biological particles, we mean particles that contain cells, intracellular components, microorganisms (e.g., bacteria, viruses), as well as non-biological macromolecules of biological origin (e.g., DNA, proteins, RNA). However, the method according to the present invention is particularly well suited for small biological particles, typically of the order of 100 nm, which is, for example, typically the size of viruses.

[0017] This method is a) sampling the ambient gas containing the biological particles sought to be characterized (Step Ea); b) generating a jet of particles JAB in a chamber CH under vacuum (step Eb); c) emitting a laser beam FL in the form of pulses and focusing the laser beam in the vacuum chamber CH transversely to the propagation direction of the particle jet JP so as to focus the laser beam FL and at most one individual particle N of the jet in the focusing volume VF; P generating a plasma by interaction between the laser beam and the individual particles of the jet, the plasma releasing other particles that are specific to the interaction between the laser beam and the individual particles of the jet (step Ec); d) collecting particles emitted by the plasma (step Ed); e) performing a spectroscopic analysis of these particles to finally characterize the biological particles (step Ee).

[0018] In step c), the laser beam FL can in particular be focused perpendicular or approximately perpendicular to the direction of propagation of the particle jet JP.

[0019] To carry out the above method, an apparatus D can be used to characterize the particles by laser-induced plasma spectroscopy (LIBS), as shown in FIG.

[0020] The device D comprises a system SG for generating a particle jet JP from gas coming from a sampler E in a chamber CH associated with means MP for pumping the gas present in the chamber in order to create a vacuum in this chamber. Typically, the pressure in the chamber CH can be of the order of 1 mbar or less, for the characterization of biological particles.

[0021] The system SG may, for example, comprise an aerodynamic lens LA, a chamber CH' evacuated by pumping means MP', and advantageously a diverter ECO. At an inlet ENT', the aerodynamic lens LA is supplied with sampled and possibly diluted gas from a sampler E, which gas may contain particles in the form of an aerosol. Then, at the outlet SORT' of the aerodynamic lens LA, a jet J of particles in a carrier gas is released. G is generated in an expansion chamber CH', which is particularly under vacuum (typically for the characterization of biological particles, the pressure may be of the order of 10 mbar or less). A jet J of particles in a carrier gas is then generated. GP The particle jet JP passes through a diverter ECO, which removes most of the carrier gas, leaving only the particle jet JP after the diverter, i.e., in the chamber CH. On the other hand, with the use of an aerodynamic lens, the particle jet JP is typically 10 -3 A vacuum defined by a pressure of 1 mbar to 1 mbar can be created in the chamber CH. This ensures optimal operation.

[0022] Instead of the aerodynamic lens LA, a nozzle can be provided (not shown). The nozzle has the same purpose of ensuring optimal operation, typically 10 -3 A vacuum defined by a pressure of 1 mbar to 1 mbar can be created within the chamber CH.

[0023] The device D also comprises a laser L capable of emitting a laser beam FL in the form of pulses.

[0024] Associated with this laser L is an optical device DO arranged to focus the beam FL in the chamber CH transversely to the propagation direction DP of the particle jet JP, which in the illustrated case is perpendicular to the propagation direction DP of the particle jet JP.

[0025] This allows the laser beam FL and the particles N in the particle jet JP to P A plasma can be generated in the focal volume VF by the interaction between the laser beam FL and the particles in the jet, which then emits other particles specific to the interaction between the laser beam FL and the particles in the jet. These other particles can be ions, electrons, or photons.

[0026] Laser beam FL and jet JP particles N P The fact that it operates in a vacuum in the chamber CH, where the interaction between the particles and the target takes place, allows for easy individual detection of very small biological particles, typically less than a few hundred nanometers in size (especially those with sizes below 200 nm, 150 nm, or even 100 nm). It should be remembered that viruses are usually around 100 nm in size.

[0027] In particular, reference may be made to FIG.

[0028] For biological particle applications, 1 cm within the particle jet 3 10 per 3 ~10 7A particle density of 100 μm is typical. The particle density in the particle jet depends on the particle density in the surrounding gas. It also depends on the nature and size of the particles. For example, for a biological particle (e.g., a virus particle) on the order of 100 nm in diameter attached to a receptor marked with 50 nm metal nanoparticles, a well-collimated particle jet with a diameter D on the order of 100 μm is obtained, which allows for a particle density of 100 μm within the jet. 6 ~10 7 particles / cm 3 Densities of biological particles on the order of 10 ...

[0029] The focal volume is typically 10 4 μm 3 can be of the order of .

[0030] The laser L may be, for example, a fiber laser.

[0031] The repetition frequency is typically between 1 kHz and 1 MHz. A minimum repetition frequency is important to characterize a large number of sampled aerosol particles in a reasonable time. If the concentration of particles in the gas sampled by the sampler is relatively low, a much higher repetition rate, on the order of 1 MHz, may be important to increase the probability of encountering a particle within the focal volume VF with each shot or laser pulse.

[0032] The minimum intensity implemented at the level of the focal volume is typically 10 GW / cm 2 This corresponds roughly to the intensity required to generate a plasma in the focal volume VF. To achieve this, the intrinsic properties of the laser L can obviously be used, but alternatively or in addition, the properties of the optical device DO can also be used.

[0033] The optical device DO may in particular be in the form of an optical lens or simply a microscope objective.

[0034] A fiber laser L operating at 1065 nm with a pulse energy of about 0.2 mJ, typically associated with a 10x magnification microscope objective DO, provides 10 GW / cm within the focal volume VF. 2 This allows the device to provide a minimum strength of 1000 psi.

[0035] After leaving the focal volume VF, i.e. after interacting with the particles of the particle jet JP, the laser beam FL is advantageously recollimated by a so-called recollimation optical device DOR, for example in the form of a set of lenses. The recollimated laser beam FL can then be sent to means (not shown in the accompanying figures) that can measure the power of the laser beam FL, so that it can be verified after the fact that the power theoretically injected by the laser L was actually provided by this laser L.

[0036] The device D also comprises at least one detection device DD comprising means MC for collecting particles emitted by the plasma and means MAS for spectroscopic analysis of these particles.

[0037] The means MC for collecting the particles emitted by the plasma can be of various designs.

[0038] However, within the scope of the present invention, the collection means may be a plurality of N optical fibers FO1, FO2, FO3, ..., FO N-1 ,FO N (N is a natural number strictly greater than 1), and each optical fiber FO1, FO2, FO3, ..., FO N-1 ,FO N One end E1, E2, E3, ..., E N-1 , E N are positioned for this purpose around the focal volume VF and point towards it.

[0039] This possibility is illustrated in different cross-sectional views of device D in Figures 4(a) to 4(c).

[0040] The advantage of providing a large number of optical fibers is that it doubles the number of particles collected, especially compared to using a single optical fiber to collect particles emitted by the plasma, thereby increasing the sensitivity of the detection device DD. It can be seen that the greater the number of optical fibers, the greater the sensitivity.

[0041] Advantageously, the exterior wall P EXT It is also possible to provide a chamber CH in which the optical fibers FO are spherical. In this case, the optical fibers FO attached to the walls of the chamber CH can be arranged on this sphere so as to best cover the maximum solid angle of 4π steradians around the focal volume VF where the plasma is generated. This configuration allows for an increased sensitivity of the detection device DD compared to other configurations for a given number N of collection optical fibers. Each of the optical fibers FO1, FO2, FO3, ..., FO N-1 ,FO N The end of the optical fiber optics 10 can be advantageously positioned at a distance of a few millimeters from the center of the focal volume VF, the most suitable adjustment value of which depends inter alia on the core diameter of the optical fiber used.

[0042] As a non-limiting example, one possible implementation is shown below: N=158 optical fibers are arranged around the spherical outer wall P of the chamber CH. EXT The core diameter of each optical fiber is 1 mm. With this arrangement, theoretically, the ends E1, E2, E3, ..., E N-1 , E N When the collection means is positioned 4-6 mm from the center of the focal volume VF, it is possible to collect 44% of all particles emitted by the plasma. The amount of particles emitted by the plasma that can be collected is theoretically 317 times greater than that collected by a collection means comprising a single optical fiber with a core diameter of 600 microns and whose collection end is positioned 4 mm from the center of the focal volume VF.

[0043] Of course, collection could alternatively be performed using a single optical fiber, but this would reduce the sensitivity of detection.

[0044] For the spectroscopic analysis means MAS, MAS', various options are available.

[0045] Thus, according to a first option shown in Fig. 5(a), one can envisage spectroscopic analysis means MAS comprising at least one notch filter FCB capable of ensuring filtering in a given wavelength band and at least one photodetector PDT (for example of the electronic photomultiplier type). In particular, one can use the PMT H12775 proposed by the company Hamamatsu (https: / / www.hamamatsu.com / eu / en / product / type / H12775 / index.html).

[0046] The notch filter therefore selects a particular spectral region, and the intensity of light (photons are among the particles emitted by the plasma) within this spectral region is determined by the photodetector PDT.

[0047] For example, considering four spectral bands A, B, C, and D, the strength of the signal in each of the considered bands (i.e., I I (I=A, B, C or D)) is obtained. For this purpose, it is necessary to provide several notch filters FCB ensuring selection in distinct bands, and an equal number of photodetectors PDT (in particular of the electronic photomultiplier type) as there are filters FCB.

[0048] Also, the overall strength of the signal I G (i.e., the intensity acquired over a long integration time for all of bands A, B, C, and D) can also be measured.

[0049] Alternatively, for each of the considered spectral bands A, B, C, and D, the number of events N EI (I=A, B, C, or D) can be counted.

[0050] These different data, N EI , I I , and I G are related to different physical quantities of the particles in the particle jet being analyzed.

[0051] Therefore, event N EI The number of particles in the sampled ambient gas can be related to the number of particles in the detected particle jet. In this way, the number of particles in the sampled ambient gas, i.e., the number concentration (i.e., volume) of particles in the sampled gas, can be determined.

[0052] Furthermore, I I is proportional to the number of atoms of a given chemical element present in each analyzed particle, i.e., the proportion of the corresponding chemical element in each analyzed particle. Therefore, by comparing the intensities measured in the different spectral bands A, B, C, and D, it is clear that the proportion of each of the various chemical elements (four, if there are intensities in the four spectral bands mentioned above) present in each analyzed particle can be obtained.

[0053] Also, the overall strength I G is proportional to the number of atoms present in the individual particle being analyzed. In this way, the mass concentration of particles in the gas sampled by sampler E can be determined.

[0054] It is therefore possible to obtain a certain amount of information about the biological particles present in the sampled gas in the form of aerosols.

[0055] From a practical point of view, this can be done after calibration of the type of biological particle to be detected, which must first be performed in the laboratory so that the assembly of these data can be determined in the field.

[0056] Furthermore, it should be noted that the response time of electronic photomultiplier-type photodetectors is very short, typically on the order of a few nanoseconds. Therefore, this type of detection is particularly suitable for the use of pulsed lasers with high repetition rates, as is the case in the present invention. No special precautions need to be taken to avoid the response / integration time of the photodetector PDT being longer than one laser cycle (cycle = time between two pulses of the laser).

[0057] According to a second option, shown in FIG. 5(b), one can envisage spectroscopic analysis means MAS' comprising an optical spectrograph SO equipped with an intensifier charge-coupled device ICCD type camera.

[0058] This second option allows for complete spectral analysis over a very wide wavelength range.

[0059] It is also possible, after laboratory calibration, to quantify the chemical elements present in the individual particles of the particle jet being analyzed.

[0060] This option ultimately allows access to the same information obtained in the first option: mass concentration, number concentration and size of the aerosol particles.

[0061] In fact, the intensity I G can be obtained by selecting a mode called "accumulation" on the camera ICCD.

[0062] On the other hand, I I and N IETo acquire a signal (I = A, B, C, or D in the example above), a specific operating mode of the camera ICCD must be used to compensate for the camera's slow acquisition speed. The response time of this type of camera is on the order of 100 milliseconds, which is not necessarily compatible with the use of pulsed lasers operating at high repetition rates. Furthermore, the integration time of the camera ICCD must be kept shorter than the time between two laser pulses, taking into account the delay between the laser pulse and the start of acquisition by the camera ICCD, the gate width (i.e., the time it takes the camera ICCD to integrate the signal), and the readout time of the camera ICCD (i.e., the time it takes the electronics associated with the camera to read the information contained in the camera ICCD's pixels).

[0063] To perform all these measurements, it must be ensured that the laser-induced plasma spectroscopy particle characterization device D analyzes only one individual particle in the focal volume VF at a time. From a statistical point of view, it can be shown that the focal volume VF of device D represents an individual particle from the particle jet only if the particle is detected at most once in 10 laser shots (see Figure 3). In the case of the detection of biological particles (e.g., viruses or bacteria), this condition is practically met in practice due to the concentration levels expected for such particles. Indeed, virus concentrations in the air are usually very low (e.g., 100 viruses / cm). 3 However, such concentrations are often sufficient to infect humans.

[0064] Finally, it should be noted that it may be interesting to collect particles for ex situ analysis and to confirm or complete by various techniques the results obtained in real time with the device D according to the invention.

[0065] For this reason, it is useful to provide a substrate holder MET in which the device D can contain a substrate (the deposits of which can then be used to generate, for example, X-ray fluorescence) and grids on either side of it (to perform transmission electron microscopy), as can be seen in particular in Figure 6. The substrate holder is advantageously mounted so that it can rotate around its main axis so that the grids can be exposed to the particle jet for a relatively short time. In fact, with the aim of performing transmission electron microscopy, the actual agglomeration state of the particles in the jet can be investigated (this could not be taken into account if a layer of particles were deposited on these grids, as would be performed on a substrate).

[0066] As previously mentioned, the measurement technique used can provide a certain amount of information about the biological particle sought to be detected.

[0067] However, the above measurement techniques do not necessarily allow for the unequivocal detection of all types of biological particles. For example, by using different spectral bands A, B, C, and D corresponding to carbon, hydrogen, nitrogen, and oxygen, respectively, and measuring the intensity of each spectral band, the respective proportions of each of these four chemical elements can actually define entirely different biological particles. In some cases, very specific spectral bands can be added to detect very specific chemical elements found only in the biological particle of interest, but this does not allow for unequivocal identification of all biological particles.

[0068] It is therefore the intention of the present invention to provide such a possibility for any biological particle.

[0069] For this purpose, the method according to the invention comprises, between step a) and step b), the following sub-steps: aa) introducing ambient gas into a chamber CHM, called the mixing chamber; ab) introducing into the mixing chamber in the form of an aerosol at least one type of receptor for a specific molecule of the biological particle to be characterized, said at least one type of receptor being marked in another way; and ac) mixing in a mixing chamber an aerosol comprising said at least one type of receptor marked with a molecule specific to the biological particle sought to be characterized with the sampled ambient gas comprising said biological particle to be characterized.

[0070] A system S suitable for carrying out steps aa), ab) and ac) is shown in Figure 7, in place relative to the device D for characterizing said particles by laser-induced plasma spectroscopy shown in the previous figures. Also, a more detailed view of the mixing chamber CHM and the various elements making it possible to supply the various chemical components thereto is shown in Figure 8.

[0071] The system S comprises means M for generating an aerosol of said at least one type of receptor marked with molecules specific for the biological particle whose characterization is sought.

[0072] System S is a first inlet E1 for the gas to be sampled; a second inlet E2 for the aerosol generated by said means M for generating an aerosol of said at least one type of receptor marked with a molecule specific to the biological particle whose characterization is sought; It also comprises a mixing chamber CHM including an outlet OUT for mixing the aerosol containing said at least one type of receptor marked with a molecule specific to the biological particle to be characterized with the sampled ambient gas containing said biological particle to be characterized.

[0073] The importance of the mixing chamber CHM can be better understood from FIG.

[0074] In this Figure 8, to the left of the inlet E1, we can see the ambient gas containing two types of particles, referred to as the biological particles PB to be characterized and all other particles AP. All of these particles then enter the mixing chamber CHM through the inlet E1. Before the inlet E2 of the mixing chamber, a solution SOL of marked receptors is sprayed by the sprayer PUL in the form of droplets G (aerosol) containing the marked receptors. The marked receptors RM are dried by passing through the (optional) dryer SECH1. The marked receptors RM then enter the mixing chamber through the inlet E2. Within the mixing chamber, the marked receptors then bind to specific molecules of the biological particles to be characterized, forming marked biological particles PBM. The purpose of the mixing chamber, of course, is to obtain a maximum number of marked biological particles. However, as can be seen in Figure 8, at the level of the mixing chamber outlet OUT, there are marked receptors RM that were unable to bind to the biological particles PB as well as the other particles AP present in the ambient gas sampled at the inlet E1 of the mixing chamber CHM.

[0075] The mixing chamber CHM may comprise at least one dryer SECH1, SECH2.

[0076] A dryer SECH1 can be arranged between the means M for generating an aerosol of said at least one type of receptor and the second inlet DE of the mixing chamber CHM. This allows the aerosol containing said at least one type of marked receptor to be dried before carrying out step ab). This drying step can be important if the specific molecules in question of the desired biological particles and / or their receptors can be bound in the drying medium. Drying is necessary for use of the device D arranged after the mixing chamber CHM.

[0077] Alternatively, the dryer SECH2 can be placed at the level of the outlet OUT of the mixing chamber CHM, and therefore the dryer SECH1 is not present. This allows the mixture formed to be dried after substep ac) before step b) is performed. This drying step can be envisaged if the specific molecule in question and / or its receptor of the desired biological particle can only be bound in an aqueous medium. Drying is only carried out at the outlet of the mixing chamber after binding has been carried out.

[0078] Of course, even if the dryer SECH1 is installed, the dryer SECH2 can also be operated.

[0079] In one particular embodiment, the mixing chamber CHM can be a Goldberg rotating drum, which allows for increased stability of the aerosol over time (thus preventing aerosol deposition on the walls to a large extent).

[0080] Advantageously, the receptor can be marked with a magnetic material (e.g., cobalt-containing nanoparticles). In this case, after step a) and before step b) is performed, only particles containing this magnetic material can be selected by any suitable magnetic means, for example, placed at the outlet OUT of the mixing chamber CHM. In other words, only particles containing magnetic material can enter the device D for characterization by laser-induced plasma spectroscopy, while the rest remain in the mixing chamber CHM. Thus, according to the scheme of FIG. 8, it can be ensured that the other particles AP sampled from the ambient gas do not enter the device D for characterizing the particles by laser-induced plasma spectroscopy.

[0081] As shown in FIG. 8, generating a marked receptor aerosol MR from a solution SOL is just one option.

[0082] However, if this option is used, the solution SOL can be water-based (aqueous solution). However, if the nature of the receptor allows, the solution SOL can also be alcohol-based (e.g., ethanol). This facilitates drying, as alcohol is more volatile than water. Finally, this also allows for the optional dryers SECH1 and / or SECH2 to be dispensed within the system S.

[0083] Advantageously, step ab) can consist of introducing into the mixing chamber CHM, in the form of an aerosol, several different types of receptors for molecules specific for different types of biological particles to be characterized, each type of receptor being marked. It is thus possible to have a first type of receptor capable of binding to a first type of biological molecule (e.g. SARS-CoV 1) and a second type of receptor capable of binding to a second type of biological molecule (e.g. SARS-CoV 2).

[0084] Also, different markings can be provided for each type of receptor to improve characterization. Thus, using this example, the marking for the receptor of the specific molecule SARS-CoV 1 can be silver nanoparticles, and the marking for the receptor of the specific molecule SARS-CoV 2 can be gold nanoparticles.

[0085] The receptor / specific molecule pair can be diverse: in particular, it can be an antibody / antigen, an avidin / biotin, a lectin / polysaccharide, or a DNA-PNA (deoxyribonucleic acid-peptide nucleic acid) pair.

[0086] As mentioned above, marking allows for unique characterization of any type of biological particle (e.g., SARS-CoV 2 bound to a receptor marked with gold nanoparticles can be uniquely characterized).

[0087] There are cases where no particles are actually detected by the laser shot at the level of the focal volume VF. In practice, this is the most frequent case, since it concerns at least 9 out of 10 laser shots.

[0088] Also, in some cases, non-biological particles AP present in the sampled gas may be detected, which is not relevant to the scope of the present invention.

[0089] However, if biological particles are present within the focal volume VF, they can be detected by performing detection of the characteristic wavelengths of one of the chemical elements, for example, carbon (247.86 nm), hydrogen, nitrogen (746-776 nm), or oxygen (77.2-77.5 nm). However, because these chemical elements are present in all organic matter, analyzing the respective composition of each of these chemical elements with spectral band detection often does not provide unambiguous information. This is why detection of rarer chemical elements, such as phosphorus (identifiable at 178 nm, 214 nm, or 254 nm), present in SARS-CoV 2, can be added.

[0090] However, this does not allow unambiguous detection in all cases.

[0091] The presence of a marking therefore improves the problem, since if properly chosen (e.g., gold nanoparticles), it provides an easily distinguishable signal LIBS at a wavelength that is otherwise strong (268 nm or 275 nm in the case of gold nanoparticles). However, as shown in the description of Figure 8, marked receptors RM that are not bound to the biological particles PB sought to be detected (despite the presence of the mixing chamber) can enter the device D operating by LIBS.

[0092] Therefore, to ensure unambiguous detection of a biological particle, it is necessary to simultaneously detect the characteristic signal of the marking and the characteristic signal of the biological particle in question. Taking SARS-CoV 2 as an example, its presence can be assured beyond doubt by detecting the peak in the signal intensity detected by both the wavelength characteristic of the chemical element phosphorus and the wavelength characteristic of gold nanoparticles. It should be noted that, by elaboration, gold nanoparticles mark receptors (e.g., antibodies) for specific molecules (e.g., antigens) of SARS-CoV 2.

[0093] Finally, it should be noted that insofar as the present invention allows for the unambiguous detection of biological particles, it is also possible to count the number of detections of these biological particles per unit time. Then, due to previous laboratory calibration (counting the number of detections of a given biological particle per unit time is carried out for a known concentration of said biological particle), during use, this count value can be related to the numerical concentration (number per unit volume) of the biological particle in question (e.g., virus), and thus, in the case of SARS-CoV 2, its concentration and, consequently, the probability of a person being infected can be determined.

Claims

1. 1. A method for characterizing biological particles of 200 nm or less in size suspended in an ambient gas as an aerosol by laser-induced plasma spectroscopy, comprising: a) sampling an ambient gas containing the biological particles sought to be characterized; b) generating a jet of said biological particles (JAB) in a chamber (CH) under vacuum; c) emitting a laser beam (FL) in the form of pulses with a repetition frequency of 1 kHz to 1 MHz and focusing said laser beam in said vacuum chamber (CH) transversely to the propagation direction of a particle jet (JP) so that in a focusing volume (VF) the laser beam (FL) and at most one individual particle (N) of said jet are focused; Ｐ generating a plasma by interaction between the laser beam and the individual particles of the jet, the plasma releasing other particles that are specific to the interaction between the laser beam and the individual particles of the jet; d) collecting the particles emitted from the plasma; e) performing spectroscopic analysis of said particles to finally characterize said biological particles.

2. Between step a) and step b) the following sub-steps are performed: aa) introducing said ambient gas into a chamber called the mixing chamber (CHM); ab) introducing, as an aerosol, into the mixing chamber at least one type of receptor for a specific molecule of the biological particle to be characterized, said at least one type of receptor being marked in another way; 2. The method of claim 1, further comprising the steps of: a) mixing in the mixing chamber an aerosol containing the at least one type of receptor marked with a molecule specific to the biological particle sought to be characterized with the sampled ambient gas containing the biological particle to be characterized.

3. 3. The method according to claim 2, wherein, before step ab), the aerosol containing the at least one type of receptor marked with a molecule specific for the biological particle whose characterization is sought is dried.

4. 3. The method of claim 2, wherein after substep ac) and before performing step b), the mixture formed by said mixing is dried.

5. 5. The method according to claim 2, wherein the marker is a magnetic material, and after sub-step ac) and before carrying out step b), only particles comprising said magnetic material are selected by any suitable magnetic means.

6. 6. The method according to claim 2, wherein the aerosol comprising the at least one type of receptor marked with a molecule specific for the biological particle whose characterization is sought is obtained from an nebulized solution of marked receptors (SOL).

7. 7. The method of claim 6, wherein the spray solution (SOL) is ethanol-based.

8. 8. The method according to any one of claims 2 to 7, wherein step ab) consists of introducing into the mixing chamber (CHM) as an aerosol several different types of receptors for specific molecules of the biological particles sought to be characterized, each type of receptor being marked in a different way.

9. 9. The method of claim 8, wherein each type of receptor is marked differently.

10. A system (D) for carrying out the method according to any one of claims 2 to 9, said system (S) comprising: means (M) for generating said aerosol of said at least one type of receptor marked with a molecule specific for the biological particle whose characterization is sought; A mixing chamber (CHM), comprising: a first inlet (E1) for the gas to be sampled; a second inlet (E2) for the aerosol generated by the means (M) for generating an aerosol of said at least one type of receptor marked with a molecule specific to said biological particle whose characterization is sought; said mixing chamber (CHM) comprising an outlet (OUT) for mixing said aerosol containing said at least one type of receptor marked with a molecule specific to the biological particles sought to be characterized with said sampled ambient gas containing said biological particles to be characterized; An apparatus (D) for characterizing said biological particles by laser-induced plasma spectroscopy, comprising: a system (SG) for generating in a chamber (CH) a jet (JP) of said biological particles from gas coming from said mixing chamber (CHM), said jet (JP) being associated with means (MP) for pumping the gas present in said chamber in order to create a vacuum in said chamber; a laser (L) capable of emitting said laser beam (FL) in the form of pulses having a repetition frequency of 1 kHz to 1 MHz, said laser (L) being associated with an optical device (DO) configured to focus said laser beam in said chamber (CH) transversely to the direction of propagation of the particle jet (JP), and to allow the laser beam (FL) and the particles (N) of said jet to be focused; Ｐ said laser (L), which generates said plasma in a focal volume (VF) by interaction between said laser beam and said particles of said jet, said plasma releasing other particles specific to the interaction between said laser beam and said particles of said jet; at least one detection device (DD, DD') comprising means (MC) for collecting the particles emitted by the plasma and means (MAS, MAS') for spectroscopic analysis of the particles; The device (D) comprises: A system (S) comprising:

11. 11. The system (S) according to claim 10, wherein the mixing chamber (CHM) comprises at least one dryer (SECH1, SECH2) located either between the means (M) for generating the aerosol of the at least one type of marked receptor and the second inlet (DE) of the mixing chamber (CHM) or at the level of the outlet (OUT) of the mixing chamber (CHM).

12. The means (MC) for collecting the particles emitted by the plasma are made up of a plurality of N optical fibers (FO １ , F.O. ２ , F.O. ３ , ..., FO Ｎ－１ , F.O. Ｎ ) (N is a natural number strictly greater than 1), each optical fiber (FO １ , F.O. ２ , F.O. ３ , ..., FO Ｎ－１ , F.O. Ｎ 12. The system (S) according to claim 10 or 11, wherein one end (E1, E2, E3, ..., EN) of each of the plasma generating elements (P1, P2, P3, ..., P4) is arranged around and points towards the focal volume (VF) to ensure collection of the particles emitted by the plasma.

13. The optical fiber (FO) is inserted into the spherical outer wall (P) of the chamber (CH). ＥＸＴ 13. The system (S) according to claim 12, wherein the system (S) is mounted on a

14. The means (MAS, MAS') for spectroscopic analysis of the particles emitted by the plasma, a plurality of notch-type filters (FCBs) capable of ensuring filtering in different wavelength bands; A system (S) according to any one of claims 10 to 13, comprising a photodetector (PDT) associated with each notch filter.

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