Method for detecting particles present in a liquid

Abstract

The invention relates to a method for detecting particles of a first type, called first particles (P1), present in a liquid (L), said liquid also containing particles of a second type distinct from the first type, and called second particles (P2), said liquid (L) being placed in a fluidic chamber (10), said first particles (P1) each having a density distinct from that of the liquid (L) and from that of each of the second particles (P2), said fluidic chamber (10) having a closed volume occupied entirely by said liquid (L), said detection being implemented by capturing images of said fluidic chamber (10). Figure to be published with the abstract: Figure 1

Description

Title of the invention: Method for detecting particles present in a liquid Technical field of the invention

[0001] The present invention relates to a method for detecting particles present in a liquid. State of the art

[0002] In some applications, it is useful to detect the presence of certain particles in a liquid, in order to possibly classify and count them. This is the case, for example, to identify pollution problems, or to control the particle concentration in the liquid analyzed. The particles can be microplastic particles, air bubbles, metal particles, etc.

[0003] Patent EP3343201B1 describes a method for counting particles present in a fluid moving in a fluid chamber. The particles are carried along by the movement of the fluid. Detection is carried out by lensless imaging, using a light source and an image sensor. The image sensor is controlled to acquire several successive images of the fluid chamber. Processing means are used to calculate the trajectory of the particles and deduce therefrom the number of particles flowing through the fluid chamber.

[0004] The principle of this solution is based on a moving fluid and is not applicable to an inert fluid. In addition, treatment times can be long.

[0005] There is a need for a solution for detecting particles present in a liquid in order to possibly sort and / or count them, which is simple to implement and which does not require long processing times. Statement of the invention

[0006] This aim is achieved by a method for detecting particles of a first type, called first particles, present in a liquid, said liquid also containing particles of a second type distinct from the first type, and called second particles, said liquid being placed in a fluidic chamber, said first particles each having a density distinct from that of the liquid and from that of each of the second particles, said fluidic chamber having a closed volume occupied entirely by said liquid, said detection being implemented by capturing images of said fluidic chamber, said method consisting of: - Capturing at a first instant at least a first image of the fluidic chamber, said fluidic chamber being in a first position, - Capture at a second instant, subsequent to the first instant, at least one

[0007]

[0008]

[0009]

[0010]

[0011]

[0012]

[0013] second image of the fluidic chamber in a second position, said second position being a position inclined relative to a horizontal plane and adapted to trigger at least one movement of the first particles inside the liquid, - Process the captured images to determine the movement and / or speed of the first particles present in the liquid, - Discriminate the first particles from the second particles based on the movement and / or speed of said first particles in the liquid, said movement and / or speed of said first particles and said second particles in the liquid depending on their respective density relative to that of the liquid. According to a first particular embodiment, the first position is a position in which the fluidic chamber is oriented parallel to said horizontal plane. According to a second particular embodiment, the first position is a position inclined at a first angle of inclination relative to said horizontal plane and the second position is a position forming a second angle of inclination relative to the horizontal plane which is more pronounced than said first angle of inclination. According to a particularity of the second embodiment, the first position and the second position are identical. According to a particularity, the process comprises: - A step of determining the position of the first particles and the second particles at the first instant, and - A first step of estimating the position of the first particles and the second particles at the second instant and of determining, for each particle, a first zone of position estimated at the second instant. According to another feature, the process includes: - A verification step at the second instant of the position of the first particles and the second particles relative to their first estimated position zone, and - A step of determining the trajectory of each particle which was detected at the second instant in its first estimated position zone. According to another feature, the method comprises a second step of estimating the position of the undetected particles in their first estimated position zone and of determining a second estimated position zone for these particles. The invention also relates to a detection system, used to implement the detection method as defined above, the detection system comprising: - A fluidic chamber intended to be filled with the liquid containing the first particles and second particles, - A mechanical device operable to pivot the fluid chamber or the entire device to its second position, - An imaging device comprising at least one light source and an image sensor, said fluid chamber being placed between said light source and the image sensor, - Means of processing images acquired by the sensor.

[0014] According to one feature, the fluidic chamber is produced in a component having two parallel walls transparent to one or more wavelengths of the light emitted by the light source.

[0015] According to another feature, the light source comprises one or more light-emitting diodes, or at least one laser diode. Brief description of the figures

[0016] Other characteristics and advantages will appear in the detailed description which follows, given with reference to the appended drawings in which: - [Fig.l] schematically represents the system of the invention; - [Fig.2] represents the diagram of the steps of the detection process of the invention; - Figures 3A to 3H illustrate the different stages of the detection method of the invention;

[0017] Detailed description of at least one embodiment

[0018] For the remainder of the description, we define an orthonormal reference frame X, Y, Z. The two directions X, Y materialize a horizontal plane and the direction Z materializes a vertical direction.

[0019] The invention relates to a method for detecting particles in a liquid L, implemented to discriminate the particles, with a view to being able to count and / or sort them inside the liquid L.

[0020] The particles to be detected can be of any type. They can be, for example, microplastic particles, air bubbles, metal particles. They can also be dust, cells, microorganisms or microbeads, usually used in biological applications, or even microalgae. They can also be droplets insoluble in the liquid, for example oil droplets dispersed in an aqueous phase. The carrier medium is a liquid, for example water, oil or a biological liquid.

[0021] One of the aims of the invention is in particular to be able to discriminate particles of a first type, called first particles PI, from particles of a second type, called second particles P2. The first particles PI and the second P2 particles differ from each other in particular by their density.

[0022] Furthermore, within the framework of the invention, it will be considered that the first particles PI have a density distinct from that of the liquid L (for example higher than that of the liquid L).

[0023] Subsequently, we can distinguish two cases: - A first case in which the second particles P2 each have a density distinct from that of the first particles PI (for example lower), but equivalent to that of the liquid L; - A second case in which the second particles P2 each have a density distinct from that of the first particles PI and also distinct from that of the liquid L (for example lower than that of the liquid L);

[0024] The method is implemented using a detection system which mainly comprises: - A fluidic device comprising a fluidic chamber 10, the fluidic chamber 10 delimiting an internal volume intended to be completely filled by the liquid L and the particles PI, P2 placed in the liquid; - An imaging device; - A mechanical device; - Means of treatment; Fluidic device

[0025] [Fig.l]

[0026] The fluidic chamber 10 can be made in a component 1 having two parallel walls 11, 12 transparent to the emission wavelengths of the light source 20 of the imaging device. The component 1 can be a fluidic card or a microscope slide on which a frame is placed intended to form the fluidic chamber. It can also be any type of container capable of receiving a fluid and having at least one optically transparent face (in the case of a reflection imaging system) or two transparent faces facing each other (in the case of a transmission imaging system).

[0027] The fluidic device may comprise a fluidic inlet 13 intended to be connected to the fluidic chamber 10 to inject the liquid L into the fluidic chamber and a fluidic outlet 14, also connected to the fluidic chamber 10, to evacuate the liquid L from the fluidic chamber. Valves may be placed on the fluidic inlet and the fluidic outlet, and a pump (not shown) may be controlled to control the injection of the liquid L into the fluidic chamber 10 via the fluidic inlet and the evacuation of the liquid L from the fluidic chamber 10 via the fluidic outlet. Imaging device

[0028] [Fig.l]

[0029] For reasons of simplicity, the imaging device is advantageously of the lensless type. In this case, it comprises a light source 20 composed of one or more light-emitting diodes. It can be associated with a diffuser and a "pinhole", or with an optical fiber. The light source 20 can also be a laser diode.

[0030] Of course, a conventional microscopy setup could also be considered, instead of the lensless imaging setup.

[0031] The fluidic chamber 10 is arranged between the light source 20 and an image sensor 21. The imaging device therefore operates in transmission.

[0032] The image sensor 21 used is capable of forming an image of the fluidic chamber 10. The fluidic chamber 10 is advantageously fixed relative to the image sensor 21, so as to limit disturbances. Thus, the particles P1, P2 set in motion in the fluidic chamber 10 are in motion relative to the image sensor 21.

[0033] The surface of the image sensor 21 is advantageously oriented parallel to the two walls 11, 12 of the fluidic chamber 10 so as to be able to acquire a uniform image of the entire fluidic chamber 10. It will be seen below that the image sensor 21 is for example mounted directly under the fluidic chamber component 1, on a support that can be pivoted. It therefore follows the movement of the component 1.

[0034] This may be, for example, a CCD or CMOS type image sensor.

[0035] The imaging device is said to be lensless because it does not have an optical system. image formation, in particular magnification optics between the image sensor 21 and the fluidic chamber 10.

[0036] The advantage of this type of lensless device is that it can perform wide-field imaging on microscopic objects, and therefore be able to observe / detect a large number of objects, unlike a conventional microscope where the field is much smaller.

[0037] Also, the image acquired by the image sensor 21 comprises interference patterns (or diffraction patterns), each interference pattern being generated by a particle present in the liquid L contained in the fluidic chamber 10.

[0038] In an alternative embodiment, it is possible to propose a light source 20 capable of emitting at several distinct wavelengths, in order to obtain additional information on the samples.

[0039] It can also be combined with other detection systems or other modalities to obtain more precision on the objects observed in the case of complex samples having several families of particles of densities various. Mechanical device

[0040] [Fig.l]

[0041] One of the particularities of the invention is to be able to incline the fluidic chamber 10 relative to the horizontal plane X, Y, so that its two opposite walls 11, 12 each form a non-zero angle A with said horizontal plane X, Y.

[0042] For this, the system of the invention may comprise a mechanical device used to tilt the fluidic chamber 10, at the chosen angle A.

[0043] This mechanical device may comprise separate wedges, each wedge allowing an inclination at a determined angle. In a non-limiting manner, the mechanical device may also comprise a support 30 mounted on a hinge 31 and a jack mechanism 32 or equivalent, fixed to said support 30 and controlled to lift said support 30 and pivot it around the axis of the hinge 31 to the desired inclination. The control of the jack may be carried out by the processing means UC or by any other means.

[0044] It should be noted that it is also possible to tilt the fluid chamber 10, accompanied by the image sensor 21.

[0045] In a non-limiting manner, the fluidic chamber 10 will be inclined at an angle A sufficient to observe a significant displacement of the particles (by significant displacement, it is meant that the distance traveled by the particle corresponds to several times the size of the particle), without all the particles disappearing from one image to the next captured by the image sensor 21. The choice of this angle A will depend in particular on the density ratios between the liquid L and the particles, as well as the viscosity of the liquid L used. Means of processing

[0046] [Fig.l]

[0047] The processing means UC are configured to process the images acquired by the image sensor 21. The processing means UC comprise a microprocessor and storage means. The microprocessor is configured to execute a sequence comprising the instructions necessary to carry out the image processing operations and the particle trajectory calculations in order to be able to discriminate them (see below). It can also be programmed to control the mechanical device in order to control the inclination of the fluidic chamber 10. Principle implemented

[0048] It has been observed that when a particle more or less dense than this liquid is placed in a liquid L, it will tend to move (in one direction or the other, depending on its density and that of the liquid) along the axis of inclination of the fluidic chamber. 10.

[0049] Indeed, by applying the principle of dynamics to particles during low-speed movement in a viscous fluid, assumed to be homogeneous and isotropic in the absence of fluid movement (friction assumed to be constant), we can obtain the equations governing the acceleration and speed of a particle projected along the axis of the inclination of the fluidic chamber:

[0050] = 4.g.sin(a)V.(p / ra^^ 100511 jMO =§sin(«) ■

[0052] With: - v: the coefficient of friction between the particle and the surrounding fluid. - V; the volume of the particle - : the intensity of gravity - a: the angle of inclination of the device (which corresponds to the angle A defined above) - m: the mass of the particle - P: the density

[0053] It thus appears that, depending on whether a particle is more or less dense than the surrounding fluid, its displacement will be in one direction or the other, the projection of the acceleration on the axis of inclination being of the same sign as ( n _n 1. \ ^fluid particle /

[0054] In other words, by tilting the fluidic chamber 10 relative to the horizontal by a non-zero angle A, if the first particles PI and the second particles P2 have distinct densities between them, with the density of the first particles PI greater than that of the liquid L and the density of the second particles P2 less than that of the liquid L, the first particles PI, which are denser, will tend to move in the natural direction which follows the inclination of the fluidic chamber 10, along a direction parallel to the axis of inclination of the chamber, and the second particles, which are less dense, will tend to move in the direction opposite to that which follows the inclination of the fluidic chamber 10, along a direction parallel to the axis of inclination of the fluidic chamber 10.

[0055] It should be noted that if the first particles PI and the second particles P2 are both denser or less dense than the surrounding liquid L, they will move in the same direction but at different relative speeds. Detection method

[0056] [Fig.2]

[0057] Figures 3A to 3H

[0058] The method consists of discriminating the particles PI, P2 present in the liquid L placed in the fluidic chamber 10. In this description, it is considered that the first particles PI have a higher density than that of the liquid L in which they are placed and that the second particles P2 have a lower density than that of the liquid L in which they are placed.

[0059] It involves the following steps, described below:

[0060] El - [Fig.3A]: The fluidic chamber 10 is filled, via the fluidic inlet 13, with the liquid L containing the particles (first particles and second particles), until its volume is entirely occupied by the liquid L.

[0061] Two variants are then possible.

[0062] First variant:

[0063] E2 - [Fig.3B]: The processing means UC control the image sensor 21 for a first acquisition at a first instant T0, the fluidic chamber 10 being in a horizontal position. The first particles and the second particles in a first position at T0 are referenced Pl_T0 and P2_T0.

[0064] E3 - [Fig.3C]: The processing means UC control the mechanical device to tilt the chamber at the desired angle A, non-zero relative to the horizontal plane, for example at an angle of 30°. This inclination of the fluidic chamber 10 is intended to cause a displacement of the particles, according to their density relative to that of the liquid L.

[0065] Second variant:

[0066] E20 - [Fig.3D]: The UC processing means control the mechanical device to tilt the fluidic chamber 10 at the desired angle A, non-zero relative to the horizontal plane X, Y, for example at an angle A of 30°. This tilting of the fluidic chamber 10 causes a displacement of the particles PI, P2, according to their density relative to that of the liquid L.

[0067] E30 - [Fig.3E]: The processing means UC control the image sensor 21 for a first acquisition at a first time T0, the fluidic chamber 10 being in an inclined position. The first particles and the second particles in a first position at T0 are referenced Pl_T0 and P2_T0.

[0068] Then the process is identical for the two variants:

[0069] E4 - [Fig.3F]: The processing means UC are configured to estimate the position that each particle should have at a second instant TL. The processing means UC thus determine a zone ZI of estimated position, in which each particle should be located following a movement in the direction which follows the inclination of the fluidic chamber 10.

[0070] E5 - [Fig.3G]: The processing means UC control the image sensor 21 for a second acquisition at the second instant TL

[0071] The UC processing means identify the particles which are well within their estimated position zone ZI. In the example above, the first "denser" particles PI are each in their estimated position zone ZI, while the second "less dense" particles P2 are not in the estimated position zone ZI. We can see that the first particles PI then move in the direction that follows the inclination of the fluidic chamber 10, while the second particles P2, less dense than the liquid L, move in the opposite direction to that which follows the inclination of the fluidic chamber 10.

[0072] The UC processing means determine the trajectory of the first PI particles and can easily identify them for sorting and counting.

[0073] The first particles and the second particles in position T1 are referenced P1_T1 and P2_TL

[0074] E6 - [Fig.3H]: The processing means UC determine a second zone Z2 of estimated position at time T1 for the second particles P2, considering that these second particles are less dense than the liquid L. The second zone Z2 of estimated position will be a zone in which each second particle P2 will tend to rise.

[0075] From the image acquired at the second instant T1, the processing means UC determine whether the second particles P2 are located in the second zone Z2 of estimated position.

[0076] The processing means UC identify the particles which are indeed located in the second zone Z2 of estimated position. In the example above, the second "less dense" particles are each indeed located in the second zone Z2 of estimated position.

[0077] The UC processing means determine the trajectory of the second particles and can easily identify them for sorting and counting.

[0078] The particles still isolated (unidentified) after these two processing steps (E5 and E6) will either be particles whose density varies greatly compared to the other two types of particles, and may then be the subject of a new position prediction step or not be considered because they are probably immobile relative to the sensor.

[0079] In a case where the second particles P2 would be of density equivalent to that of the liquid L, the processing means UC can discriminate them with respect to the first particles PI, even if they do not migrate in the liquid L to their estimated position zone.

[0080] It should be noted that if several particles are located in the same estimated position zone, the processing means are for example configured to choose the one which minimizes a distance, either purely spatial in the absence of a particle descriptor, or by taking into account the different descriptive variables chosen.

[0081] The method can of course be continued after time T1, with a view to reconstructing the trajectory of each particle present in the liquid L.

[0082] It should be noted that when calculating the estimated position area for each particle, the processing means take into account the speed at which the particle should be made to move in the fluid, for example by making an assumption about the density of the targeted particle and / or by observing their behavior during preliminary tests. Since the displacement of the particles, linked to the application of an angle of inclination to the fluidic chamber, is deterministic, it is possible to define an average displacement to be taken as a reference.

[0083] If the particle is indeed in its estimated position zone at time T1, the processing means will be able to conclude that it is indeed the targeted particle to be counted.

[0084] It should also be noted that if the first particles PI and the second particles P2 are both denser or less dense than the surrounding liquid L, they will move in the same direction but at different speeds. The estimated position area of ​​the particle could be adapted by making an assumption about the density of each type of particle and / or by carrying out preliminary tests.

[0085] This provides a simple solution for discriminating particles within a liquid, using a simple mechanical device for tilting the fluidic chamber 10 and a lensless imaging device.

Claims

Claims

1. Method for detecting particles of a first type, called first particles (PI), present in a liquid (L), said liquid also containing particles of a second type distinct from the first type, and called second particles (P2), said liquid (L) being placed in a fluid chamber (10), said first particles (PI) each having a density distinct from that of the liquid (L) and from that of each of the second particles (P2), said fluid chamber (10) having a closed volume occupied entirely by said liquid (L), said detection being implemented by capturing images of said fluid chamber (10), characterized in that it consists of: - Capturing at a first instant at least a first image of the fluid chamber (10), said fluid chamber (10) being in a first position, - Capturing at a second instant, subsequent to the first instant,at least one second image of the fluidic chamber (10) in a second position, said second position being a position inclined relative to a horizontal plane and adapted to trigger at least one movement of the first particles (PI) inside the liquid, - Processing said captured images to determine the movement and / or the speed of the first particles (PI) present in the liquid (L), - Discriminating the first particles (PI) from the second particles (P2) from the movement and / or the speed of said first particles (PI) in the liquid, said movement and / or the speed of said first particles (PI) and said second particles (P2) in the liquid depending on their respective density relative to that of the liquid.,

2. Method according to claim 1, characterized in that the first position is a position in which the fluidic chamber (10) is oriented parallel to said horizontal plane.

3. Method according to claim 1, characterized in that the first position is a position inclined at a first angle of inclination relative to said horizontal plane and in that the second position is a position forming a second angle of inclination relative to the horizontal plane which is more pronounced than said first angle of inclination.

4. Method according to claim 3, characterized in that the first position and the second position are identical.

5. Method according to one of claims 1 to 4, characterized in that it comprises: - A step of determining the position of the first particles (PI) and the second particles (P2) at the first instant (TO), and - A first step of estimating the position of the first particles (PI) and the second particles (P2) at the second instant (Tl) and of determining, for each particle, a first zone (Zl) of estimated position at the second instant (Tl).

6. Method according to claim 5, characterized in that it comprises: - A step of verifying at the second instant (Tl) the position of the first particles (PI) and of the second particles (P2) relative to their first zone (Zl) of estimated position, and - A step of determining the trajectory of each particle which has been detected at the second instant (Tl) in its first zone (Zl) of estimated position.

7. Method according to claim 5 or 6, characterized in that it comprises a second step of estimating the position of the undetected particles in their first zone (Z1) of estimated position and of determining a second zone (Z2) of estimated position for these particles.

8. Detection system, used to implement the detection method as defined in one of claims 1 to 7, characterized in that it comprises: - A fluidic chamber (10) intended to be filled with the liquid containing the first particles and the second particles, - A mechanical device operable to pivot the fluidic chamber (10) or the entire device to its second position, - An imaging device comprising at least one light source (20) and an image sensor (21), said fluidic chamber (10) being placed between said light source (20) and the image sensor (21), - Means for processing the images acquired by the sensor.

9. System according to claim 8, characterized in that the fluidic chamber (10) is produced in a component (1) having two parallel walls (11, 12) transparent to one or more wavelengths of the light emitted by the light source (20).

10. System according to claim 8 or 9, characterized in that the light source comprises one or more light-emitting diodes, or a laser diode.

Images