Patent Description:
The present invention relates to the field of precaution and/or protection means for detecting and/or characterizing fluid-borne particles, for example, but not exclusively, airborne particles such as air pollution, air bio- and chemical contamination and/or airborne allergen, water-borne particle such as water pollution, water bio- and chemical contamination, etc. The growing concentration of different types of aerosols in the atmosphere, for example the increasing number airborne pollens, is becoming more and more an important public health issue. Moreover, new threats like bio-terrorism that employ airborne biological and chemical pathogens like anthrax or mustard gas as an arm of massive destruction have recently appeared. Reliable, operator-free and cost-effective detectors of fluid-borne particles, for example aerosol detectors, fast and with a high discrimination power, are thus highly desirable in the market. There is a need for detectors allowing real-time detection of particles present in a particular fluid environment, for example in the atmosphere, in a watercourse, in a drinking water distribution system, etc..

Species of aerosol particles, like pollens and spores, have a large impact on human health. Some of them are responsible for health problems like allergies affecting, according to statistical analysis, about <NUM>% of the European population.

The counting and identification of these particles is still done mostly manually under microscope. The size of airborne particles ranges from fractions of micrometer to some hundreds of micrometers, which brings additional difficulty in particle detection and identification.

Measurement devices and methods for the detection of airborne particles exist, that allow estimating the size of particles contained in an aerosol based on the measurement of light scattered by individual particles. These devices and methods use a source of light (laser, laser diode, LED, etc.) directed to a flow of air, and a photodetector collecting light scattered by individual airborne particles over a large angle, or, in some cases, multiple or array detectors (<NUM> or 2D) for collecting scattered light independently in different directions from the particle. The collected scattered light provides for a static representation of the airborne particle. The single-detector devices allow only very limited determination of single particle morphology, while the devices with multiple or array detectors usually allow a more precise determination of these parameters.

When particle chemistry is under investigation, the non-invasive methods like light scattering provide very few or no insight on particle composition. Some emerging invasive (destructive) methods like mass spectroscopy (MS), laser-induced breakdown spectroscopy (LIBS) or atomic emission spectroscopy (AES) provide a very good on-the-fly chemical analysis on molecular (for MS) and atomic (for LIBS and AES) levels. However, these methods, apart being invasive, suffer from several technical issues (limited particle size range, difficulty to operate in very polluted conditions, short continuous monitoring, cost, complex data output requiring expert knowledge, etc.) preventing from large deployment and cost reduction.

In the case of on-the-fly analysis of water embedded particles, morphology cares almost no information about its nature of the embedded particle, since it will mostly tend to be perfect sphere due to the water. Use of MS, LIBS and AES will be influenced or disturbed by the presence of water since all these methods are based on evaporation of the airborne particle by a strong laser emission or a flame. The most promising results can be obtained by non-invasive methods that can probe the chemical composition like laser induced fluorescence or Raman scattering.

<CIT> and <CIT> for example describe apparatuses and methods for characterizing particles using, among others, time-resolved fluorescence of the particles following their submitting to laser light. A drawback of these apparatuses and methods is that the information that can be obtained about the nature and characteristics of individual particles is limited. In most of the cases, it only allows distinction between particles with slow fluorescence decay in the order of dozens of nanoseconds, generally attributed to non-biological particles containing hydrocarbons, against particles with short fluorescence decay in the order of a few nanoseconds or less, generally considered biological. Given only fluorescence decay, one can still find quite many molecular compositions that would give a false response in this bio- and non-bio- classification. The following publications also form related prior art: <CIT>, <CIT>, <CIT>, <NPL>), and <NPL>.

In this regard, a primary object of the invention is to solve the above-mentioned problems and more particularly to provide a device and a method allowing an on-the-fly and instantaneous detection of presence and concentration of organic molecules in aerosols water droplets with estimation of concentration.

Another aim of the present invention is to provide a device and a method for the cost-effective detection and/or characterization of individual fluid-borne particles with a much better identification of the chemical composition of individual particles and consequently a lower false count rate.

These aims, and other advantages are achieved with a device and a method according to the corresponding independent claims.

The method and device may find numerous applications in following fields such as drug manufacturing and quality control (measurement of drug dose concentration in sprays and aerosols); detection of organic impurities in water microdroplets (presence of Legionella bacteria in public bathrooms and hotel rooms), quality control for real-time viable particle detectors to be used in cleanrooms (as reference instrument to quantify detection thresholds and reaction time) and the like.

The above problems are solved by the present invention as defined in the appended claims.

Simultaneously, the mentioned laser source induces fluorescence and Raman emissions are resulted from the interaction of the laser light with molecules present in the particle. In this aspect, the intensity and wavelength of this laser beam as well as sensibility of all detectors are adjusted in a way to keep in optimal level all respective signal-to-noise ratios and simultaneously avoid saturation.

The laser light central wavelength is in a region from <NUM> to <NUM> to provide significant efficiency of photon absorption and thus high fluorescence emission. Moreover, Raman scattering efficiency is reversely proportional to the fourth power of the light wavelength, making the mentioned region the most convenient choice. The laser source wavelength spectrum width should be narrow enough to not interfere with Raman emission spectrum.

According to a preferred embodiment of the present invention, a second laser source is triggered only upon detection of light scattering by the scattered light detecting means.

Advantageously, the fluid source is a nozzle for producing a flow of water droplets with a flow path beyond the nozzle.

Preferably, the fluid source comprises a tube for producing a flow of water droplets with a flow path along the tube.

According to a preferred embodiment of the present invention, the measurement device further comprises a first lens set for collecting a first laser light scattered in the measurement volume by particles contained in the flow of fluid.

Advantageously, the first lens set is configured for focusing the scattered light in a line at a focal distance of the lens set, the line being transverse to a flow direction of the flow of fluid in the measurement volume.

Preferably, the first lens set is configured for focusing the scattered light in a line by focusing the scattered light in a direction parallel to the flow direction and for making the rays of scattered light parallel to each other in a plane perpendicular to the flow direction.

According to a preferred embodiment of the present invention, the scattered light detecting means is a multipixel light scattering detector.

Advantageously, the measurement device further comprises a second lens set for collecting the Raman signal emitted by the fluid molecule and fluorescence signal emitted by the particle upon excitation by the second laser beam.

According to a preferred embodiment of the present invention, the Raman and fluorescence detecting means is a photo-detector positioned for the detection of laser light collected by the second lens set.

Preferably, the photo-detector is a linear multipixel detector for capturing the laser light focused by the lens set, wherein the linear multipixel detector is positioned at a distance from the focal distance of the lens set and oriented with its longitudinal axis parallel to the line.

Advantageously, the first laser source is configured for emitting a continuous laser beam.

According to a preferred embodiment of the present invention, the first laser source is configured for emitting a laser beam having an emission spectrum up to tens of nm.

Advantageously, the first laser source is configured for emitting a laser beam having an output optical power range from few mW up to few W.

Preferably, the second laser source is configured for emitting a pulsed laser beam.

According to a preferred embodiment of the present invention, the second laser source is configured for emitting a laser beam having a wavelength of <NUM> to <NUM>.

Preferably, the second laser source is configured for emitting a laser beam having an optical peak power per pulse of more than a few kW.

Advantageously, the second laser source is configured for emitting a laser beam having an emission spectrum of less than few nm.

According to a preferred embodiment of the present invention, the measurement device further comprises a diffraction grating for wavelength separation.

According to a preferred embodiment of the present invention, the measurement method comprises a correction factor calculation step by taking ratios between measured and expected number of Stocks photons. Thus, the measurement is even more accurate.

Advantageously, the measurement method comprises an impurity mass concentration calculation step. In this manner, one can have a precise indication of the impurity quantity within a droplet.

Further particular advantages and features of the invention will become more apparent from the following non-limitative description of at least one embodiment of the invention which will refer to the accompanying drawings, wherein.

As mentioned earlier, the described method and device of the present invention are intended for on-the-fly and instantaneous detection of presence and concentration measurement of organic molecules or mixture of organic molecules, preferably in aerosols of water droplets.

Basically, the method and the device of the present invention uses simultaneously three basic physical effects:.

More particularly, the method uses elastic light scattering for detecting water droplets, also called fluid particles, and fluorescence emission to estimate the quantity of impurities molecules, also called fluid-borne particles, present inside water droplet. On the other hand, the Raman scattering is used as a reference signal to correct eventual error due to fluid-borne particle position in a laser beam, nonhomogeneous laser beam intensity, or any other factors influencing light collection efficiency.

<FIG> with single laser shows a schematic view of an implementation of the device <NUM> according to a first embodiment of the present invention which is a measurement device <NUM> for the detection and/or measurement of fluid-borne particles in a fluid particle, and comprising a fluid source <NUM> for producing a flow of fluid <NUM> along a fluid flow path which can be a nozzle for producing a flow of water droplets with a flow path beyond the nozzle, or which can comprise a tube for producing a flow of water droplets with a flow path along said tube. More particularly, the measurement device <NUM> preferably comprises a single laser source <NUM>, preferably a continuous laser source, which is used for light elastic and Raman scattering and fluorescence excitation.

The first laser source <NUM> is positioned for emitting a, preferably continuous, laser beam <NUM> of laser light having a wavelength of <NUM> to <NUM>, preferably <NUM> to <NUM>, a narrow emission spectrum up to tens of nm and the output optical power ranges from hundreds mW up to tens of W in a measurement volume of the fluid flow path. A short, UV-region, central emission wavelength of this laser is necessary since it efficiently induces a fluorescence response from organic molecules. Moreover, shorter wavelengths are much more efficient for Raman scattering excitation (~ λ<NUM>) as well. The laser source <NUM> preferably also has a narrow emission spectrum, e.g. less than few nm.

It also comprises an elastically er scattered light detecting means <NUM>, which is preferably a multipixel light scattering detector, for detecting a presence of a fluid particle in the fluid flow path through detection and measurement of laser beam light elastically scattered on different angles by said fluid particle and a Raman and fluorescence detecting means <NUM> for detecting a Raman scattering signal emitted by the fluid particles and a fluorescence signal emitted by said fluid-borne particle upon excitation by said laser beam <NUM>.

Also, it further comprises a first lens set <NUM> for collecting a first laser light <NUM> scattered in the measurement volume by fluid particles contained in the flow of fluid <NUM> which is preferably configured for focusing the scattered light <NUM> in a line at a focal distance f2 of the lens set <NUM>, where the line is transverse to a flow direction of the flow of fluid in said measurement volume.

Also, the first lens set <NUM> is configured for focusing said scattered light in a line by focusing said scattered light in a direction parallel to said flow direction y and for making the rays of scattered light parallel to each other in a plane perpendicular to the flow direction.

Further, it comprises a second lens set <NUM> for collecting the Raman signal emitted by the fluid particle and fluorescence signal emitted by the fluid-borne particle upon excitation by the laser beam <NUM>. Preferably, the Raman and fluorescence detecting means <NUM> is a photo-detector positioned for the detection of laser light <NUM> collected by the second lens set <NUM>.

<FIG> shows a schematic view of an implementation of the device <NUM> according to a second embodiment of the present invention, based on method of the present invention where <NUM> is an injection nozzle, <NUM> is a multipixel light scattering detector, <NUM> is a collection lens for light scattering signal; <NUM> is a collection lens for Raman and fluorescence signals, <NUM> is a diffraction grating for wavelength separation, <NUM> is a multipixel Raman and fluorescence signal detector, <NUM> is a laser for light scattering, <NUM> is a laser for Raman and fluorescence excitation.

More particularly, the measurement device <NUM> of the present invention comprises a first laser source <NUM>, preferably a continuous laser source, which is used for light scattering and a second laser source <NUM>, preferably a pulsed laser source, for Raman and fluorescence excitation.

The first laser source <NUM> can have any central wavelength such as from <NUM> to <NUM>, for example, and a relatively broad emission spectrum, e.g. up to tens of nm, since it is only used for light scattering. The output optical power preferably ranges from a few mW up to hundreds of mW.

The second laser source <NUM> preferably presents UV or deep-UV wavelengths such as from <NUM> up to <NUM>, for example, and a high optical peak power per pulse, preferably more than few kW. The second laser source <NUM> preferably presents a short wavelength which is necessary since it efficiently induces a fluorescence response from organic molecules. Moreover, shorter wavelengths are much more efficient for Raman scattering excitation (~ λ<NUM>) as well. The second laser source <NUM> preferably also has a narrow emission spectrum, e.g. less than few nm.

The measurement device <NUM> of the present invention also preferably comprises a detector for detecting the presence of an individual fluid particle in the beam of the first laser source <NUM> and measures the light scattered at different angles. At the same moment, when a fluid particle is detected, the second laser source <NUM> shots with a single pulse, or multiple pulses, on the fluid particle, which induces Raman scattering on water molecules and fluorescence emission organic impurities if there are present in the droplet.

The following paragraphs will now more precisely describe the measurement method carried out by the above-described device. In addition to the control of the laser sources of the device, the measurement method of the present invention comprises a light scattering measurement step, a Raman scattering detection step and a fluorescence measurement step.

The light scattering measurement preferably consists in a Mie light scattering. Mie light scattering is a commonly used and very powerful tool for precise measurement of particles. The light scattering measurement of the method preferably uses a multipixel detector D1 to measure scattered light, preferably in the range of angles of <NUM> deg to <NUM> deg (side scattering) with respect to the laser direction, with unpolarized, or circularly polarized laser source S1 with resolution of <NUM> deg/pixel, then the expected scattering patterns will look like on the graph shown in <FIG>, which shows an example of expected light scattering pattern from spherical fluid particles of <NUM>, <NUM>, and <NUM> diameters, refractive index of water is <NUM>.

In addition, this step preferably uses advanced pattern recognition algorithms such as gradient boosting trees or support vector machine, where one can extract very precise size estimation (+/- <NUM>).

Such measurement allows instantaneous and precise estimation of equivalent optical diameter. Considering that water droplets always have perfect spherical shape due to the surface tension, this measurement provides direct droplet size and volume estimation. Using standard water density <NUM>/m<NUM> and molecular mass around <NUM>×<NUM>-<NUM> kg/molecule, one can also estimate the droplet mass and approximate number of H<NUM>O molecules thanks to the following equation: <MAT>.

Where r is the measured fluid particle radius and ρw is the water mass density.

The second step of the method is a Raman scattering detection. In this step, the second laser source S2 is a pulsed laser which emits laser pulses which hit the droplet to induce Raman scattering. The number of Stocks photons (photons resulted from Raman scattering) detected on the detector D2 can be estimated according following equation: <MAT>.

Where σR is the Raman scattering cross section, typically <NUM>-<NUM> for resonant scattering and <NUM>-<NUM> for non-resonant scattering, m is the number of atoms in molecule, Nmol is the number of H<NUM>O molecules, E. is the laser (S2) pulse energy, A is the cross section of the laser (S2), h is the Plank constant, v is the frequency of electromagnetic field of the laser (S2)and σD is the detection efficiency of the optical system (L2 + G1 + D2).

To give a rough estimation of number of expected photons from a water droplet of <NUM> in diameter, one does the following assumptions:
The main contribution into Raman spectrum of water comes from valent band at <NUM>-<NUM>. A typical spectrum presented in <FIG>, which is a typical Raman emission spectrum of distilled water.

Preferably, the measurement is done with nitrogen laser source with, for example, an emission wavelength of <NUM>, in such a case most of the Stocks photons resulted from Raman scattering by a <NUM> water droplet will have wavelength around <NUM>, which is easily resolved by a diffraction grating G1 from the excitation wavelength of the laser.

As an example, this Raman emission is resonant so <MAT> laser pulse energy is taken <NUM>µJ, laser cross section is <NUM> * <NUM>-<NUM>m<NUM> (corresponds to a focused beam of <NUM> in diameter), detection efficiency is taken as <NUM> %. The result is around <NUM> Stocks photons detected around <NUM> wavelength, which is a very significant number for modern detectors like vacuum tube photomultipliers and silicon photomultipliers (matrixes of avalanche photodiodes).

It is important to mention at this point that distilled water does not exhibit any fluorescence emission while excited in a wavelength range of <NUM> - <NUM> since water molecules do not have any π- or σ- electron orbitals that could absorb such photons.

So, if the water droplet does not contain any organic or other complex impurities, the only signal observed will be Raman scattering while excited with UV light.

The third measurement step is therefore a fluorescence measurement. Fluorescence emission is preferably estimated from the following equation: <MAT>.

Where σA is the Photon absorption cross section, typically <NUM>-<NUM> for endogenous fluorophores, Nmol is the number of fluorophore molecules (organic impurities), Q is the quantum efficiency of radioactive deexcitation of fluorophore, typically <NUM> %, E is the laser (S2) pulse energy, A is the cross section of the laser (S2, h is the Plank constant, and ν is the frequency of electromagnetic field of the laser (S2), σD is the detection efficiency of the optical system (L2 + G1 + D2).

Compared with Raman scattering, the fluorescence efficiency is much higher if measured under the same conditions. For example, if a water droplet contains only <NUM><NUM> fluorophore molecules, it would already emit around <NUM>*<NUM><NUM> fluorescence photons spread over large rage of wavelengths (at the room temperature).

The last step of the method consists in a measurement of the concentration of the organic impurities in the droplet.

As mentioned before, the described method is intended for instantaneous measurement of organic impurities in water droplets. The whole process can therefore be split over following steps of producing a flow of fluid particles <NUM> along a fluid flow path, the flow of fluid potentially containing fluid-borne particles to be detected; emitting a first beam <NUM> of laser light in a measurement volume of the fluid flow path; collecting the laser light <NUM> scattered in the measurement volume by fluid particles contained in the flow of fluid and focusing the scattered light in a line; detecting the scattered laser light <NUM> with a scattered light detecting means <NUM> and acquiring a of light scattering pattern; emitting a second beam <NUM> of laser light in a measurement volume of the fluid flow path; collecting the laser light <NUM> scattered in the measurement volume by fluid particles contained in the flow of fluid and focusing the scattered light in a line; detecting the scattered laser light <NUM> with a Raman and fluorescence detecting means (<NUM>) and acquiring Raman signal intensities and fluorescence signal intensities; calculating the measured number of fluid-borne particles.

The measured number of impurities molecules is preferably given by the following equation: <MAT>.

Where <MAT> is the expected number of Stocks photons coming from Raman scattering, , <MAT> is the number of Stocks photons coming from Raman scattering, detected by the device, <MAT> is the number of fluorescence photons detected by the device.

By inserting this equation with the first one above, the expression becomes: <MAT>.

By simplifying this equation and applying the constants for H<NUM>O, the expression takes the following form: <MAT>.

When the molecular mass of impurity is known, then the mass concentration can be estimated as well with the following equation: <MAT>.

It can be noted that the result depends only on the number of measured photons from fluorescence emission and Raman scattering and measured optical size in third power. It does not depend on the second laser energy or detection efficiency of the system. If one groups all the constants in this equation the expression becomes: <MAT>.

Claim 1:
Measurement device (<NUM>) for the detection and/or measurement of fluid-borne particles in a fluid particle, the measurement device comprising:
a fluid source (<NUM>) for producing a flow of fluid particles (<NUM>) along a fluid flow path,
a laser source (<NUM>) positioned for emitting a laser beam (<NUM>) of laser light in a measurement volume of the fluid flow path and adapted to emit a laser light having a wavelength of <NUM> to <NUM>;
an elastically scattered light detecting means (<NUM>) for detecting a presence of a fluid particle in the fluid flow path through detection and measurement of laser beam light elastically scattered on different angles by said fluid particle, and
a Raman and fluorescence detecting means (<NUM>) for detecting a Raman scattering signal emitted by the fluid particle and a fluorescence signal emitted by a fluid-borne particle upon excitation by said laser beam (<NUM>, <NUM>) when emitting a laser light having a wavelength of <NUM> to <NUM>, characterized in that
the device is adapted to use the Raman scattering signal for correcting eventual errors taken in the group comprising fluid particle position in a laser beam, nonhomogeneous laser beam intensity, or any other factors influencing light collection efficiency, and the fluorescence emission is for determining the quantity of fluid-borne particles present inside a fluid particle.