METHOD AND SYSTEM FOR DETECTING PARTICLES IN A LIQUID

Description

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 certain applications, it is useful to detect the presence of specific particles in a liquid, potentially to classify and count them. This is the case, for example, to identify pollution problems or to monitor particle concentration in the analyzed liquid. These particles can include microplastics, air bubbles, metallic particles, and more.

[0003] Patent EP3343201B1 describes a method for counting particles present in a fluid moving within a fluidic chamber. The particles are carried along by the fluid's movement. Detection is performed by lensless imaging, using a light source and an image sensor. The image sensor is controlled to acquire several successive images of the fluidic chamber. Processing means are employed to calculate the particle trajectories and deduce the number of particles circulating through the fluidic chamber.

[0004] The principle behind this solution relies on a moving fluid and is not applicable to an inert fluid. Furthermore, treatment times can be lengthy.

[0005] FR 3 118 169 A1 discloses a method for characterizing moving particles in a sample from captured images of the sample.

[0006] There is a need for a solution to detect particles present in a liquid in order to possibly sort and / or count them, which is simple to implement and does not require long processing times. Description of the invention

[0007] This goal 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, 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 entirely occupied by said liquid, said detection being implemented by capturing images of said fluidic chamber, said method consisting of: Capture at a first instant at least one 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 second image of the fluidic chamber in a second position, said second position being an inclined position with respect to a horizontal plane and adapted to trigger at least one movement of the first particles inside the liquid, Process said captured images to determine the movement and / or velocity of the first particles present in the liquid, Discriminate the first particles from the second particles from the movement and / or velocity of said first particles in the liquid, said movement and / or velocity of said first particles and said second particles in the liquid depending on their respective density with respect to that of the liquid.

[0008] According to a first particular embodiment, the first position is a position in which the fluidic chamber is oriented parallel to said horizontal plane.

[0009] According to a second particular embodiment, the first position is an inclined position at a first angle of inclination with respect to said horizontal plane and the second position is a position forming a second angle of inclination with respect to the horizontal plane which is more pronounced than said first angle of inclination.

[0010] According to a peculiarity of the second realization, the first position and the second position are identical.

[0011] Depending on one particular feature, the process involves: 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 estimated position at the second instant.

[0012] Another distinctive feature of the process is: A step of verification at the second instant of the position of the first particles and the second particles with respect to their first estimated position zone, and a step of determination of the trajectory of each particle that was detected at the second instant in its first estimated position zone.

[0013] According to another particularity, the process includes a second step of estimating the position of undetected particles in their first estimated position zone and determining a second estimated position zone for these particles.

[0014] 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 the second particles, A mechanical device that can be actuated to rotate the fluidic chamber or the entire device to its second position, An imaging device comprising at least one light source and an image sensor, said fluidic chamber being placed between said light source and the image sensor, Means for processing the images acquired by the sensor.

[0015] According to one particular feature, the fluidic chamber is made in a component having two parallel walls transparent to one or more wavelengths of light emitted by the light source.

[0016] According to another characteristic, the light source includes one or more light-emitting diodes, or at least one laser diode. Brief description of the figures

[0017] Other features and advantages will appear in the detailed description that follows, in conjunction with the attached drawings, in which: There figure 1 represents, schematically, the system of the invention; The figure 2 represents the diagram of the steps in the detection process of the invention; The figures 3A to 3H illustrate the different stages of the process of detecting the invention; Detailed description of at least one embodiment

[0018] For the rest of the description, we define an orthonormal coordinate system X, Y, Z. The two directions X, Y represent a horizontal plane and the direction Z represents a vertical direction.

[0019] The invention relates to a method for detecting particles in a liquid L, implemented to discriminate the particles, in order to be able to count and / or sort them within the liquid L.

[0020] The particles to be detected can be of any type. Examples include microplastic particles, air bubbles, and metallic particles. They can also include dust, cells, microorganisms, or microbeads (commonly used in biological applications), or even microalgae. They can also be droplets insoluble in the liquid, such as oil droplets dispersed in an aqueous phase. The carrier medium is a liquid, such as water, oil, or a biological fluid.

[0021] One of the aims of the invention is in particular to be able to discriminate between particles of a first type, called first particles P1, in relation to particles of a second type, called second particles P2. The first particles P1 and the second particles P2 are differentiated from each other in particular by their density.

[0022] Furthermore, within the framework of the invention, it will be considered that the first particles P1 have a density distinct from that of the liquid L (for example higher than that of the liquid L).

[0023] Subsequently, two cases can be distinguished: A first case in which the second particles P2 each have a density distinct from that of the first particles P1 (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 P1 and also distinct from that of the liquid L (for example lower than that of the liquid L);

[0024] The process is implemented using a detection system that primarily 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 P1, P2 placed in the liquid; An imaging device; A mechanical device; Processing means; Fluidic device Figure 1

[0025] The fluidic chamber 10 can be made of 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 onto which a frame is placed to form the fluidic chamber. It can also be any type of container capable of holding a fluid and having at least one optically transparent face (in the case of a reflection imaging system) or two opposing transparent faces (in the case of a transmission imaging system).

[0026] The fluidic device may include a fluidic inlet 13 for connection 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, for removing 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 inject the liquid L into the fluidic chamber 10 via the fluidic inlet and to remove the liquid L from the fluidic chamber 10 via the fluidic outlet. Imaging device Figure 1

[0027] For simplicity, the imaging device is advantageously of the lensless type. In this case, it comprises a light source 20 consisting of one or more light-emitting diodes. It can be combined with a diffuser and a pinhole, or with an optical fiber. The light source 20 can also be a laser diode.

[0028] Of course, a conventional microscopy setup could also be considered, instead of the lensless imaging setup.

[0029] The fluidic chamber 10 is positioned between the light source 20 and an image sensor 21. The imaging device therefore operates in transmission.

[0030] 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 within the fluidic chamber 10 are in motion relative to the image sensor 21.

[0031] 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 acquire a uniform image of the entire fluidic chamber 10. As will be seen below, the image sensor 21 is, for example, mounted directly under the fluidic chamber component 1, on a pivotable support. It therefore follows the movement of component 1.

[0032] This could be, for example, a CCD or CMOS type image sensor.

[0033] The imaging device is said to be lensless because it does not have an optical image formation system, in particular no magnification optics between the image sensor 21 and the fluidic chamber 10.

[0034] The advantage of this type of lensless device is that it can perform wide-field imaging on microscopic objects, and therefore can observe / detect a large number of objects, unlike a conventional microscope where the field is much smaller.

[0035] Also, the image acquired by the image sensor 21 includes interference patterns (or diffraction patterns), each interference pattern being generated by a particle present in the liquid L contained in the fluidic chamber 10.

[0036] In one 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.

[0037] It can also be combined with other detection systems or other modalities to obtain greater accuracy on the objects observed in the case of complex samples possessing several families of particles of various densities. Mechanical device Figure 1

[0038] One of the features of the invention is the ability to tilt 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.

[0039] For this purpose, the system of the invention may include a mechanical device used to tilt the fluidic chamber 10, to the chosen angle A.

[0040] This mechanical device may include separate wedges, each wedge allowing inclination to a predetermined angle. Without limitation, the mechanical device may also include 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 rotate it around the axis of the hinge 31 to the desired inclination. The jack may be controlled by the processing means UC or by any other means.

[0041] It should be noted that it is also possible to tilt the fluidic chamber 10, along with the image sensor 21.

[0042] Without limitation, the fluidic chamber 10 will be inclined at an angle A sufficient to observe a significant displacement of the particles (by significant displacement, we mean 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 other 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 on the viscosity of the liquid L used. Methods of treatment Figure 1

[0043] The processing unit (PU) is configured to process images acquired by the image sensor 21. The PU comprises a microprocessor and storage means. The microprocessor is configured to execute a sequence containing the instructions necessary to perform image processing operations and calculate particle trajectories in order to discriminate between them (see below). It can also be programmed to control the mechanical device for adjusting the tilt of the fluidic chamber 10. Principle implemented

[0044] It has been observed that when a particle more or less dense than that 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.

[0045] 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 velocity of a particle projected along the axis of inclination of the fluidic chamber: v t = 1 ν . g . sin α . V . ρ particule − ρ fluide e ν m t − 1 d dt v t = Vg m sin α ⋅ ρ particule − ρ fluide . e ν m t With : v: the coefficient of friction between the particle and the surrounding fluid. V : the volume of the particle g : the intensity of gravity α : the angle of inclination of the device (which corresponds to angle A defined above) m: the mass of the particle ρ : densities

[0046] It thus appears that, depending on whether a particle is more or less dense than the surrounding fluid, its movement will be in one direction or the other, the projection of the acceleration onto the axis of inclination being of the same sign as ( ρ particle - ρ fluid ).

[0047] In other words, by inclining the fluidic chamber 10 with respect to the horizontal by a non-zero angle A, if the first particles P1 and the second particles P2 have distinct densities, with the density of the first particles P1 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 P1, being denser, will tend to move in the natural direction that follows the inclination of the fluidic chamber 10, following a direction parallel to the axis of inclination of the chamber, and the second particles, being less dense, will tend to move in the opposite direction to that which follows the inclination of the fluidic chamber 10, following a direction parallel to the axis of inclination of the fluidic chamber 10.

[0048] It should be noted that if the first particles P1 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 Figure 2 Figures 3A to 3H

[0049] The process consists of discriminating the particles P1, P2 present in the liquid L placed in the fluidic chamber 10. In this description, it is assumed that the first particles P1 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.

[0050] It comprises the following steps, described below: E1 - Figure 3AThe 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.

[0051] Two variants are then possible.

[0052] First variant: E2 - Figure 3B The processing means UC command the image sensor 21 for a first acquisition at a first instant T0, with the fluidic chamber 10 in a horizontal position. The first and second particles in a first position at T0 are referenced P1_TO and P2_T0. E3 - Figure 3CThe UC processing means control the mechanical device to tilt the chamber to the desired angle A, which is non-zero with respect to the horizontal plane, for example at an angle of 30°. This tilting 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.

[0053] Second variant: E20 - 3D Figure The processing means UC control the mechanical device to tilt the fluidic chamber 10 to the desired non-zero angle A relative to the horizontal plane X, Y, for example, to an angle A of 30°. This tilting of the fluidic chamber 10 causes a displacement of the particles P1, P2, according to their density relative to that of the liquid L. E30 - Figure 3EThe processing means UC command the image sensor 21 for a first acquisition at a first instant 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 P1_T0 and P2_T0.

[0054] Then the process is identical for both variants: E4 - Figure 3F The UC processing means are configured to estimate the position that each particle should have at a second instant T1. The UC processing means thus determine a zone Z1 of estimated position, in which each particle should be located following a displacement in the direction that follows the inclination of the fluidic chamber 10. E5 - Figure 3G : The UC processing means command the image sensor 21 for a second acquisition at the second instant T1.

[0055] The UC processing means identify the particles that are indeed located within their estimated position zone Z1. In the example above, the first, denser particles P1 are each located within their estimated position zone Z1, while the second, less dense particles P2 are not within their estimated position zone Z1. This is because the first P1 particles move in the direction that follows the inclination of the fluidic chamber 10, while the second P2 particles, being less dense than the liquid L, move in the opposite direction to the inclination of the fluidic chamber 10.

[0056] The UC processing means determine the trajectory of the first P1 particles and can easily identify them for sorting and counting.

[0057] The first and second particles in position T1 are referenced P1_T1 and P2_T1.

[0058] E6 - Figure 3H: The UC treatment means 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.

[0059] From the image acquired at the second instant T1, the UC processing means determine if the second particles P2 are located in the second zone Z2 of estimated position.

[0060] The UC processing means identify the particles that 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.

[0061] The UC processing means determine the trajectory of the second particles and can easily identify them for sorting and counting.

[0062] 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 subject to a new position prediction step or not be considered because they are likely immobile relative to the sensor.

[0063] In a case where the second particles P2 would have a density equivalent to that of the liquid L, the UC processing means can discriminate them from the first particles P1, even if they do not migrate in the liquid L to their estimated position zone.

[0064] It should be noted that if several particles are found in the same area of ​​estimated position, the processing means are configured for example to choose the one that minimizes a distance, either purely spatial in the absence of a particle descriptor, or by taking into account the different descriptive variables chosen.

[0065] The process can of course be continued after time T1, in order to reconstruct the trajectory of each particle present in the liquid L.

[0066] It should be noted that when calculating the estimated position zone for each particle, the processing methods take into account the velocity at which the particle is expected to move through the fluid, for example, by making an assumption about the density of the target particle and / or by observing its behavior during preliminary tests. Since the particle displacement, linked to the application of an inclination angle to the fluidic chamber, is deterministic, it is possible to define an average displacement to be used as a reference.

[0067] 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 and to be counted.

[0068] It should also be noted that if the first particles P1 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 particle position range could be adjusted by making an assumption about the density of each particle type and / or by conducting preliminary tests.

[0069] We thus have a simple solution for discriminating particles within a liquid, using a simple mechanical device to tilt the fluidic chamber 10 and a lensless imaging device.

Claims

1. Method of detection of 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 achieved by capturing images of said fluidic chamber (10), the method consisting in: - capturing at a first time at least a first image of the fluidic chamber (10), said fluidic chamber (10) being in a first position, - capturing at a second time, subsequent to the first time, at least a second image of the fluidic chamber (10) in a second position, said second position being a position that is inclined with respect to a horizontal plane and that is configured to initiate at least one movement of the first particles (P1) inside the liquid, - processing said captured images to determine the movement and / or speed of the first particles (P1) present in the liquid (L), - discriminating between the first particles (P1) and second particles (P2) on the basis of the movement and / or speed of said first particles (P1) in the liquid, said movement and / or speed of said first particles (P1) and said second particles (P2) in the liquid depending on their respective density with respect 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 that is inclined at a first angle of inclination with respect to said horizontal plane and in that the second position is a position making a second angle of inclination to the horizontal plane that 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 (P1) and of the second particles (P2) at the first time (T0), and - a first step of estimating the position of the first particles (P1) and of the second particles (P2) at the second time (T1) and of determining, for each particle, a first estimated position zone (Z1) at the second time (T1).

6. Method according to Claim 5, characterized in that it comprises: - a step of verifying at the second time (T1) the position of the first particles (P1) and of the second particles (P2) with respect to their first estimated position zone (Z1), and - a step of determining the path of each particle detected at the second time (T1) in its first estimated position zone (Z1).

7. Method according to Claim 5 or 6, characterized in that it comprises a second step of estimating the position of the particles not detected in their first estimated position zone (Z1) and of determining a second estimated position zone (Z2) for these particles.

8. Detection system employed to implement the detection method such 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 second particles, - a mechanical device that is able to be actuated to make the fluidic chamber (10) or the entire device pivot 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 formed in a component (1) having two parallel walls (11, 12) that are 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.