System for detecting airborne viruses

Abstract

SYSTEM FOR DETECTING AIRBOUND VIRUSES.A system for detecting airborne viruses, the system comprising at least one local detector, the local detector comprising: an aerosol collection module configured to collect particulate matter from an aerosol sample onto a collection tip, an analysis module configured to detect the amount of virus that is part of the particulate matter contained in the collected aerosol sample, and an output module configured to issue a warning signal if the total virus content exceeds a predetermined threshold.

Description

[Technical Field]

[0001] The present invention relates to a system and method for detecting airborne viruses. [Background technology]

[0002] Airborne viral epidemics, such as the SARS-CoV-2 epidemic, are known to originate from localized outbreaks. In most airborne viral diseases, infectivity precedes the symptomatic stage. During the so-called incubation period, the epidemic is not recognized, but viral concentrations in indoor environments may already be potentially very high. For SARS-CoV-2, the incubation period lasts on average several days. Over a timescale of several weeks, a localized outbreak can rapidly expand and spread to nearby epicenters, triggering a regional epidemic. When an epidemic is caused by an unidentified virus (whether the virus is new, e.g., as a result of zoonotic or viral mutation, or unexpected in that geographic region), the epidemic is usually not recognized until a sufficient number of clinical cases have been reported and health authorities notified. Clinical similarities to more common diseases may contribute to this delay. Furthermore, with current technology, epidemic recognition often involves pathogen isolation and genetic sequencing, which can take several weeks. Furthermore, it is worth noting that similar delays occurred in the discovery of viral variants such as the SARS-CoV-2 delta variant in December 2020 and the SARS-CoV-2 omicron variant in November 2021.

[0003] Furthermore, the primary route of infection is known to be airborne, especially in indoor environments where a small number of infected individuals in a room can produce viral particles in sufficient concentrations to infect other people, and they can also remain in the air indefinitely in the form of aerosols.

[0004] The international community is seeking systems that can efficiently counteract virus spread in both of these situations, even when an epidemic is not recognized. In the case of a local outbreak, an ideal virus sensor must be able to detect the presence of the virus within its incubation period in order to provide timely warning and thereby prevent viral transmission. In the case of a regional epidemic, typically caused by a new or unexpected virus, an ideal sensor must also be able to detect new, unexpected, and potentially harmful viruses on a timescale of less than a few weeks. This would allow for the containment of virus spread to the local level, mitigating its impact and preventing it from turning into a pandemic.

[0005] Currently, there are no means to uncover both unrecognized local outbreaks and regional epidemics in a useful timeframe. Current technology cannot measure airborne virus concentrations with a time response capable of dividing the incubation period while reliably signaling the presence of new, unidentified viruses on timescales of less than a few weeks. In this regard, state-of-the-art virus detection methods suffer from several drawbacks. In short, PCR-based methods take longer than the incubation period and can only detect known viruses. Immunoassay-based methods are faster than PCR, but are significantly less sensitive and can only detect known viruses. Finally, cell culture assay-based methods can detect unknown viruses, but they require several days and specialized laboratory equipment and personnel, making them impractical.

[0006] A system capable of fast response, airborne virus detection and timely monitoring of unidentified viruses is still lacking. Such a system can function as a comprehensive monitoring sensor, not only limiting epidemics caused by unidentified viruses on a regional scale but also enabling timely containment of local outbreaks. Summary of the Invention

[0007] The present invention aims to provide a system and method for detecting airborne viruses that overcomes the problems of the prior art. In particular, the present invention provides a system and method for detecting unknown airborne viruses or mutant strains of known airborne viruses, preferably mutant strains of known airborne viruses, with a fast response, and in some embodiments, with a near real-time response.

[0008] To this end, the present invention provides a system according to claim 1, configured to detect airborne viruses. It is preferably configured for detecting unknown airborne viruses and variants of known airborne viruses. The system is preferably configured to detect airborne viruses rapidly, e.g., in near real time. This allows for real-time alerts to prevent the spread of localized outbreaks or to signal the presence of unknown epidemics in limited geographical areas. The system comprises at least one local detector, preferably multiple local detectors as further described below. The local detector comprises the following modules: An aerosol collection module configured to collect an aerosol sample from the air. The aerosol collection module samples the air surrounding the local detector. Preferably, the local detector is located indoors, so the air sample is an indoor air sample. The aerosol sample includes particulate matter, such as viruses and dust. The local detector must be able to distinguish virus particles from other particles. How the local detector does this is described further below. The aerosol collection module is further configured to collect particulate matter from the aerosol sample onto a collection tip. The collection tip is, for example, a surface on which particles can be collected dry. Alternatively, the collection tip is a liquid reservoir in which particulate matter is collected wet. Providing a wet reservoir rather than a dry collection surface has the advantage of being able to observe more parameters of the particulate matter, as described below. An analysis module configured to detect the amount of viruses that are part of particulate matter contained in the collected aerosol sample. The analysis module comprises an optical microscope. The optical microscope may be a label-free optical microscope. By providing a label-free optical microscope, it is not necessary to apply time-consuming staining procedures that slow the response of the local detector. The label-free optical microscope of the embodiment further has the advantage that it can detect unknown viruses and mutant strains of known viruses, since the detection method does not require genetic information of the virus, such as the virus's DNA sequence. The label-free optical microscope of the embodiment is configured to perform the following steps: Determining geometric and, optionally, dynamic parameters of particulate matter contained in the aerosol sample. Geometric parameters are, for example, the size and shape of the particles. Dynamic parameters are, for example, the diffusion coefficient of the particles. Dynamic parameters, especially the diffusion coefficient, are particularly advantageous when the collection tip is a liquid reservoir, as described above. Selecting candidate virus particles from the particulate matter based on the determined parameters. The selection takes into account, for example, typical geometric and / or dynamic parameters of viruses. At this stage, it is not necessary to know the type of virus being detected; we are only interested in determining whether the particle has characteristics indicative of a virus. Therefore, preferably, the local detector has a database with reference parameter values ​​indicative of a virus. Preferably, the reference parameter values ​​are indicative of a virus carried by humans. performing optical spectral measurements on the candidate virus particles; and comparing the obtained optical spectrum for each candidate virus particle with a set of predetermined reference optical spectra corresponding to viruses to determine whether the candidate virus particle is a virus. Again, at this stage, it is not necessary to know the type of virus being detected; one is only interested in determining whether the particle has characteristics indicative of being a virus. Thus, preferably, the local detector has a database with reference optical spectra indicative of a virus. Preferably, the reference optical spectra are indicative of a virus carried by humans. - Determining the number of viruses detected, i.e., the "total viral content" (TVC) in the aerosol sample based on the comparison step. An output module configured to issue a warning signal when the TVC exceeds a predetermined threshold.

[0009] Infected individuals in a room can release the virus through breathing, speaking, coughing, and sneezing. Furthermore, some individuals, known as superspreaders, are more likely to release the virus during exhalation. It is known from the literature that some exhaled viruses remain unstable and disperse into the air in the environment. When an infected individual approaches a local detector, for example, within the same room, their viruses are collected by the system in the same room or environment. Therefore, an increase in TVC can indicate the presence of an infected individual or a so-called "superspreader." This can then prompt further biological analysis of the collected virus samples (whether from aerosols or the people involved), such as viral sequencing to identify new variants.

[0010] According to one embodiment of the present invention, the system as described above is further configured to classify the detected viruses according to their virus family, such as Coronaviridae or Influenzaviridae. Preferably, for that purpose, the collection chip of the aerosol collection module comprises predetermined areas each functionalized with a virus receptor of one specific virus family. Preferably, the optical microscope is further configured to perform the following steps: Counting the number of detected viruses in each predetermined area, for example to determine the "family virus content" (FVC) in the aerosol sample.

[0011] This embodiment has the advantage of allowing the classification of detected viruses according to their virus family without requiring specific genetic information of the virus variants. It simply uses viral receptors with binding affinity to common virus families. Based on this family classification, the potential danger of different virus families can be taken into account before issuing a warning signal. For example, a higher FVC threshold can be set for less harmful virus families. According to one embodiment of the present invention, the output module is further configured to issue a warning signal when the FVC of a given virus family exceeds a predetermined threshold for the virus content of said virus family. Furthermore, the virus family information allows the most appropriate countermeasures to be taken (e.g., testing people using appropriate swab tests, suggesting isolation or self-monitoring, for example, by wearing protective masks, etc.).

[0012] According to one embodiment of the present invention, the aerosol collection module comprises a "condensation growth tube" (CGT). During the collection stage of aerosol particles, which takes place within the aerosol collection module, it is important that the collection process maintains the integrity of the virus particles. A promising approach to maintaining said integrity is by using the well-established CGT technique, which allows gentle sampling by growing water droplets around each collected particle. According to one embodiment of the present invention, a size-selective cyclone can be further implemented on top of the CGT. The size-selective cyclone selects particles with a size smaller than a limit. This allows for the separation of larger particles that may interfere with the measurement.

[0013] According to one embodiment of the present invention, the analysis module performs analysis directly on the collection chip. This ensures that there is less loss of particles in the sample compared to an analysis module that requires the sample to be transferred from the collection chip to the analysis module. Therefore, this embodiment allows the use of substantially all of the sample for analysis, which results in better virus detection. This embodiment increases the overall virus detection sensitivity.

[0014] According to one embodiment of the present invention, the analysis module performs steps for selecting candidate virus particles and / or determining the TVC using artificial intelligence (AI). This allows for fully automated detection, fast response, and correlation between different local detectors to continuously learn how to distinguish between viruses and non-viruses. Preferably, an encoder / decoder algorithm relying on semantic segmentation performs automated particle detection from acquired microscopic images. These detections are then fed into an algorithm that preferably detects regions of higher intensity for these particles to extract each particle's geometric and, optionally, dynamic parameters, as well as their optical spectrum. Using these parameters, the algorithm performs automated spectral analysis, e.g., using PCA or regression models, and calculates the TVC index. Furthermore, if virus family classification is required, a second AI algorithm automatically counts viruses bound to their receptors based on the image classification and calculates the FVC index.

[0015] According to one embodiment of the present invention, the geometrical properties of the particulate matter include the shape and / or size of the particles. According to one embodiment of the present invention, the dynamical properties of the particulate matter include the diffusion coefficient of the particles.

[0016] According to one embodiment of the present invention, the analysis module performs a step of selecting candidate virus particles by selecting particles with geometric and, optionally, dynamic parameters consistent with those of viruses. A typical size range for viruses is 50-200 nm. In practice, these sizes cannot be measured optically due to the diffraction limit of light. Particles with sizes below approximately 200-300 nm appear to have the same size under a microscope. Simply selecting particles with sizes below this limit allows the particles to be considered candidate virus particles. Alternatively, other, more complex techniques, such as Patterson (2008) "Optical Signatures of Small Nanoparticles in a Conventional Microscope," which utilizes caustic signals, can be used. Generally, according to this embodiment, a particle is considered a candidate virus particle if its size can be attributed to a particle in the range of 50-200 nm (i.e., the typical size range for viruses; this range can be adjusted to include larger viruses).

[0017] According to one embodiment of the present invention, the analysis module performs the comparison step based on reference optical spectra obtained by simulation, such as Mie scattering simulation, or experiment, or alternatively, based on unsupervised learning of the reference optical spectra, preferably using principal component analysis (PCA).

[0018] According to one embodiment of the present invention, the analysis module normalizes the measured spectrum of a candidate virus particle to a normalized spectrum measured from a standard particle located elsewhere on the same chip. This operation overcomes the problem of being unable to directly measure the absolute spectrum of a particle due to inherent system inhomogeneities, such as light source instability, the presence of optical aberrations, and misalignment of different system components, e.g., misalignment of the chip relative to the optical path. Therefore, a normalized spectrum must be obtained for each measurement of a particle spectrum. Normalizing the particle spectrum with the normalized spectrum eliminates these inhomogeneities and thus enables sequential comparison between the normalized measured spectrum and a predetermined reference optical spectrum that has already undergone the same normalization process. The standard particles used to generate the normalized spectrum may be preferentially spherical polystyrene beads with a very uniform size and shape, such as NIST-traceable size-standard monodisperse polystyrene spheres. These particles are highly stable and reproducible, making them ideal standard reference materials for obtaining normalized optical spectra.

[0019] According to one embodiment of the present invention, the collection tip is a collection surface on which particles are collected dry as described above. Alternatively, the collection tip is a liquid collection vessel into which particles are received as described above. In the latter alternative, dynamic parameters such as the diffusion coefficient of the particles are preferably taken into account by the analysis module. According to one embodiment of the present invention, the collection tip includes hydrophilic and hydrophobic regions, which allow for the transport and concentration of aerosol particles at specific locations on the collection tip for easier detection and characterization.

[0020] According to a first embodiment of the present invention, the optical microscope in the analysis module is a "hyperspectral enhanced dark field" (HSEDF) microscope. The HSEDF microscope preferably operates in transmission mode. According to one embodiment of the present invention, the analysis module performs a step of collecting optical spectral measurements of candidate virus particles by obtaining an optical spectrum that is a scatter spectrum. Preferably, obtaining the scatter spectrum is included in the above-mentioned hyperspectral enhanced dark field technique, which measures a scatter spectrum for each pixel (and therefore each particle).

[0021] According to a second embodiment of the present invention, the optical microscope in the analysis module is a "hyperspectral bright-field" (HSBF) microscope. Preferably, the HSBF microscope operates in reflection mode. According to one embodiment of the present invention, the analysis module performs an optical spectral measurement on candidate virus particles by obtaining an optical spectrum, which is a reflection spectrum. Preferably, the collection tip of the aerosol collection module includes a nanometer cavity, preferably created by a focused ion beam. When particles fill the nanometer cavity, the optical signal coming from the cavity, e.g., the aforementioned reflection spectrum, changes according to the principles of wave optics. Preferably, the nanometer cavity has a size and shape comparable to that of a virus. Preferably, the nanometer cavity has a diameter of, for example, 100 nm to 1 μm, thereby allowing typical viruses to enter the nanometer cavity while excluding larger particles. Preferably, hydrophilic regions are arranged corresponding to the nanometer cavity, not only inside it but also in the surrounding area. This area is favorable for droplets containing (virus) particles to reach the collection tip. When the droplets dry, they release particles into the nanometer cavity, where they can be detected.

[0022] According to one embodiment of the present invention, a region, i.e., a geographical area, is monitored by a plurality of local detectors. Preferably, the local detectors are interconnected in a regional network. Preferably, the system is configured to correlate TVCs and FVCs from different local detectors. In this way, it may be possible, for example, to track the dynamic evolution of an epidemic in a geographical area.

[0023] According to one embodiment of the present invention, the TVC of each local detector in the regional network is accumulated in a "Regional TVC" (RTVC), and the system is configured to issue an alert signal when the RTVC exceeds a predetermined threshold. According to one embodiment of the present invention, the FVC of each virus family of each local detector in the regional network is accumulated in a "Regional FVC" (RFVC) for each virus family, and the system is configured to issue an alert signal when the RFVC of a given virus family exceeds a predetermined threshold for the regional viral content of said virus family.

[0024] It is a further object of the present invention to provide a method for detecting airborne viruses, preferably unknown airborne viruses or mutants of known airborne viruses, more preferably mutants of known airborne viruses, preferably in real time, which method comprises the use of the system described above.

[0025] As described above, the system is preferably configured to detect airborne viruses rapidly, e.g., in near real time. This system can be viewed as an artificial lung with an inflow similar to our respiratory system. The reference "warning" amount can be an infectious amount, which is known in the literature to be approximately several hundred to several thousand virions (i.e., infectious viruses). Meanwhile, the present system and related detection methods can, in principle, detect single virus particles. However, for statistical robustness and reliable AI computation, a good target number of collected virus particles can be considered to be approximately 100 to 1,000, i.e., less than the infectious amount (or, in any case, the same order of magnitude). Thus, the present system can, in principle, detect the presence of airborne viruses before the inhaled amount becomes infectious. Consider a situation in which a person enters a room where the air is already concentrated with viruses. Upon entering, our sensor begins "breathing." It can issue a warning signal before the amount of virus inhaled by the person becomes infectious. In any case, the system is always on and can constantly monitor the presence of viruses in the environment. To provide some figures, we can refer to Lednicky et al.'s "Viable SARS-CoV-2 in the Air of a Hospital Room with COVID-19 Patients" (2020), which measured approximately 16 / 94 virus particles / L in a hospital room with two COVID-19 patients, with approximately 6 / 74 viable virus particles / L. These viruses are uniformly dispersed in the air, are very small and therefore highly mobile, and can remain suspended in the air for very long periods of time (several hours). For example, by using aerosol sampling technology with a sampling rate of 1.5 L / min, it is possible, in principle, to collect the target particle count in approximately 2–20 minutes. AI analysis then processes the image almost instantly and reports the number of particles that may be virus. Therefore, it can be said that this system can issue an alert within a useful time frame to prevent further infection.This time is much faster than the gold standard method of PCR, and is more advantageous than immunogenicity assay or cell culture assay.In one embodiment, the system and related detection method can be considered in real time based on the concept of the amount of infection and the possibility of stopping the virus replication (or transmission) cycle.When considering the possibility of detecting the presence of any virus in the environment, it can be considered in near real time according to the concentration of virus particles in the environment. [Brief explanation of the drawings]

[0026] [Figure 1] FIG. 1 is a schematic diagram of a local detector according to an embodiment of the present invention, in which the collection tip is a collection surface for collecting particles in a dry manner. [Figure 2a-2b] 2A and 2B show side and top views, respectively, of a collection tip used in the local detector of FIG. 1, the collection tip adapted for use with an HSEDF microscope. [Figure 3a-3b] 1A and 1B show side and top views, respectively, of a collection chip suitable for use with a local detector similar to that shown in Figure 1, with the HSEDF microscope replaced by an HSBF microscope and the collection chip adapted for use with the HSBF microscope. [Figure 4] FIG. 1 is a schematic diagram of a local detector according to one embodiment of the present invention, in which the collection tip is a liquid collection reservoir for collecting particles. [Figure 5a-5b] 5A and 5B show side and top views, respectively, of the collection chip used in the local detector shown in FIG. 4, the collection chip adapted for use with an HSEDF microscope. [Figure 6a-6b] Shown are scanning electron microscope (SEM) images of collected particulate matter spiked with virus-like particles (VLPs), and optical spectral measurements of candidate virus particles containing VLPs, respectively. DETAILED DESCRIPTION OF THE INVENTION

[0027] BRIEF DESCRIPTION OF THE DRAWINGS 1 and 4 show an embodiment of a system for near real-time detection of unknown airborne viruses according to the present invention. The system allows for real-time warning to prevent the spread of a local outbreak or to signal the presence of an unknown epidemic in a limited geographic area. The system comprises at least one local detector 1. The local detector 1 comprises the following modules: an aerosol collection module 2, an analysis module 7, and an output module 12.

[0028] The aerosol collection module 2 is configured to collect an aerosol sample from air 3. The aerosol sample includes particulate matter such as viruses and dust. The aerosol collection module 2 is further configured to collect the particulate matter from the aerosol sample onto a collection tip 4. The collection tip is, for example, a surface 5 on which particles can be collected in a dry manner, as shown in FIG. 1. Alternatively, the collection tip 4 is a liquid reservoir 6 in which particulate matter is collected in a wet manner, as shown in FIG. 4. The aerosol collection module 2 includes a "condensation growth tube" (CGT) 23 for collecting the particles.

[0029] The analysis module 7 is configured to detect the amount of viruses that are part of the particulate matter contained in the collected aerosol sample. In the dry collection embodiment shown in FIG. 1, the collection surface 5 is transferred from the collection module 2 to the analysis module 7. In other embodiments not shown in this figure, the collection chip is not transferred and is analyzed directly on the collection module by the analysis module, thereby creating a more integrated system. In the wet collection embodiment shown in FIG. 4, the liquid reservoir 6 is fixed to the analysis module and is in fluid communication with the aerosol collection module 2 by an inlet tube 8. The liquid and the sample contained therein are drawn from the aerosol collection module 2 through the inlet tube 8 toward the liquid reservoir 6 by a pump 9 connected to the liquid reservoir 6 by an outlet tube 10. The analysis module includes an optical microscope 11. The optical microscope shown in FIGS. 1 and 4 is a "hyperspectral enhanced dark field" (HSEDF) microscope. A collection chip 4 used in such a microscope is shown in FIGS. 2 and 5. The collection chip 6 shown in FIG. 3 is suitable for use with a "hyperspectral bright field" (HSBF) microscope, not shown in FIGS. 1 or 4. Such HSEDF microscopes are well known in the state of the art and comprise an illumination source 13 emitting light 17 towards the sample, a microscope objective 14 receiving the light 18 after interaction with the sample, an optical filter 15 receiving light 19 from the objective, and a camera 16 receiving light 20 that has passed through the optical filter 15 and has been optically filtered by the optical filter 15 for optical spectrum measurement. The optical microscope is configured to perform the following steps: Determining geometric and, optionally, dynamic parameters of particulate matter contained in the aerosol sample. Geometric parameters are, for example, the size and shape of the particles. Dynamic parameters are, for example, the diffusion coefficient of the particles. Dynamic parameters, in particular the diffusion coefficient, are particularly relevant when the collection tip 4 is a liquid reservoir 6, as described above. Selecting candidate virus particles from the particulate matter based on the determined parameters. The selection takes into account, for example, typical geometric and / or dynamic parameters of viruses. At this stage, it is not necessary to know the type of virus being detected; we are only interested in determining whether the particle has characteristics indicative of being a virus. Therefore, the local detector 1 has a database (e.g., associated with the camera 16) with reference parameter values ​​indicative of a virus. Performing an optical spectral measurement on the candidate virus particles, preferably via an optical filter 15. Light 19 entering the optical filter 15 is shown to contain a mix of frequencies. Light 20 exiting the optical filter 15 and entering the camera 16 is shown as distinct frequency bands (dark light representing light of smaller wavelengths than bright light), indicating that the light has been optically filtered to perform the optical spectral measurement. Comparing the resulting optical spectrum for each candidate virus particle with a set of predetermined reference optical spectra corresponding to viruses to determine whether the candidate virus particle is a virus. Again, at this stage, it is not necessary to know what type of virus is being detected; we are only interested in determining whether the particle has characteristics indicative of it being a virus. - Determining the number of viruses detected, i.e., the "total viral content" (TVC) in the aerosol sample based on the comparison step.

[0030] The analysis module 7 performs the above steps of selecting candidate virus particles and / or determining the TVC by means of artificial intelligence.

[0031] The output module 12 is configured to issue a warning signal when the TVC exceeds a predetermined threshold. It is known that infected individuals can release viruses through breathing, speaking, coughing, and sneezing. Furthermore, some individuals, known as super-spreaders, are more likely to release viruses during exhalation. It is known in the literature that some exhaled viruses remain unstable and disperse into the air in the environment. When an infected individual approaches a local detector, for example, within the same room as the local detector, those viruses are collected by the system within the same room or environment. Therefore, an elevated TVC can indicate the presence of an infected individual or a so-called "super-spreader."

[0032] The local detector 1 as described above is further configured to classify the detected viruses according to a virus family, such as the coronavirus family or the influenza virus family. To this end, the collection chip 4 of the aerosol collection module 2 includes predetermined regions 21a, 21b, and 21c, each functionalized with a virus receptor for one specific virus family. This is shown in Figures 2, 3, and 5. In Figures 2 and 3, each virus family has two circular regions with dedicated receptors. In Figure 3, each virus family has three circular regions with dedicated receptors. However, the number of regions is not important to the present invention. In Figure 3, the circular regions are located within wells 22. The optical microscope 11 is configured to perform the following steps: Counting the number of detected viruses in each predetermined area, for example to determine the "family virus content" (FVC) in the aerosol sample.

[0033] The SEM image in Figure 6a shows particulate matter (PM) collected on the collection chip by the aerosol collection module for 10 minutes in an environment containing VLPs. The particles are well separated and distributed across the entire surface. VLPs are perfectly circular and characterized by a typical size (100 nm in this case). Other PM particles are also present in the air sample, including particles much larger than VLPs, particles smaller than VLPs, and particles similar in size to VLPs but with different shapes and compositions (and therefore different refractive indices). The different particle sizes allow for the identification of candidate virus particles, including VLPs and other PM with similar sizes. A typical scattering spectrum measured by HSEDF is shown in the graph in Figure 6b (larger particles are not shown because they have very different spectra, with scattering intensities greater than one order of magnitude). Smaller particles exhibit much lower scattering intensities. PM of similar size have different spectral shapes (e.g., higher scattering intensity in the NIR region). This allows the system to distinguish viruses, in this case VLPs, from other candidate virus particles.

Claims

1. 1. A system for detecting airborne viruses, the system comprising at least one local detector, the local detector comprising: an aerosol collection module configured to collect an aerosol sample from air, the aerosol sample comprising particulate matter such as viruses and dust, the aerosol collection module further configured to collect the particulate matter from the aerosol sample onto a collection tip; an analysis module configured to detect the amount of the virus that is part of the particulate matter contained in the collected aerosol sample, - determining the geometric and optionally dynamic parameters of particulate matter contained in said aerosol sample; - selecting candidate virus particles from said particulate matter based on said determined parameters; - performing optical spectral measurements on the candidate virus particles; - comparing, for each candidate virus particle, the obtained optical spectrum with a set of predetermined reference optical spectra corresponding to viruses to determine whether the candidate virus particle is a virus; and - determining the number of viruses detected, i.e. the "total viral content" (TVC) in the aerosol sample based on said comparison step; an analysis module comprising an optical microscope configured to perform an output module configured to issue a warning signal when said TVC exceeds a predetermined threshold; A system comprising:

2. further configured to classify the detected virus according to a virus family, such as Coronaviridae or Influenzaviridae; the collection chip of the aerosol collection module includes predetermined regions each functionalized with a viral receptor of one specific virus family; The optical microscope is - counting the number of detected viruses in each defined area, for example to determine the "family virus content" (FVC) in the aerosol sample; The system of claim 1 , further configured to:

3. The system of any one of claims 1 to 2, wherein the analysis module performs the analysis directly on the collection chip.

4. the analysis module performs normalization of the measured spectrum with a normalized spectrum measured from a standard particle placed at a separate location on the same collection chip; The normalized spectrum is compared to the reference spectrum that has already undergone the same normalization process; The system of any one of claims 1 to 3, wherein the standard particles used to generate the normalized spectrum are preferentially highly uniform, monodisperse spherical polystyrene beads.

5. The system of any one of claims 1 to 4, wherein the collection tip is a collection surface on which the particles are collected dry.

6. The system of any one of claims 1 to 4, wherein the collection tip is a liquid collection container in which the particles are received.

7. The system according to any one of claims 1 to 6, wherein the optical microscope in the analysis module is a "hyperspectral enhanced dark field" (HSEDF) microscope, preferably operating in transmission mode.

8. 8. The system of claim 7, wherein the analysis module performs the step of collecting optical spectral measurements of the candidate virus particles by obtaining an optical spectrum that is a scatter spectrum.

9. The system according to any one of claims 1 to 6, wherein the optical microscope in the analysis module is a "hyperspectral bright field" (HSBF) microscope, preferably operating in reflectance mode.

10. 10. The system of claim 9, wherein the analysis module performs the step of performing an optical spectral measurement on the candidate virus particle by obtaining an optical spectrum that is a reflectance spectrum.

11. The system according to any one of claims 9 to 10, wherein the collection tip of the aerosol collection module comprises a nanometric cavity, preferably created by a focused ion beam.

12. A system according to any one of claims 1 to 11, wherein an area is monitored by a number of local detectors, preferably interconnected in an area network.

13. The system of claim 12, wherein the TVC of each local detector in the regional network is accumulated in a "Regional TVC" (RTVC), and the system is configured to issue a warning signal when the RTVC exceeds a predetermined threshold.

14. 14. The system of claim 13 in combination with claim 2, wherein the FVCs for each virus family for each local detector in the regional network are compiled into a "regional FVC" (RFVC) for each virus family, and the system is configured to issue an alert signal when the RFVC for a given virus family exceeds a predetermined threshold for the regional viral content of that virus family.

15. The system of any one of claims 1 to 14, wherein the optical microscope is a label-free optical microscope.

16. 16. The system of claim 1, wherein the step of determining geometric and optionally dynamic parameters of particulate matter contained in the aerosol sample and selecting candidate virus particles from the particulate matter based on the determined parameters is carried out by selecting particles from the particulate matter having a size of less than 300 nm, preferably less than 200 nm, more preferably in the range of 50 nm to 200 nm.

17. A method for detecting unknown airborne viruses or mutant strains of known airborne viruses, preferably for detecting mutant strains of known airborne viruses, comprising the use of the system according to any one of claims 1 to 17.

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