Microfluidic device, system and method for manipulating a flowing fluid

Abstract

The invention relates to a microfluidic device (100) comprising at least one sheath fluid inlet channel (1, 2) and a sample fluid inlet channel (3), and a common channel (4) configured to guide the sample fluid (20), with hydrodynamic focusing, and the at least one sheath fluid (21, 22) in the direction of at least two outlet channels (11, 12, 13). According to the invention, the microfluidic device comprises heating means arranged to transmit over a short period of time an amount of heat localised in the at least one sheath fluid flow (21, 22) in the common channel (4) upstream of a junction between the at least two outlet channels (11, 12, 13), and the at least one sheath fluid having a thermal variation in viscosity suitable for diverting or extracting a portion (120, 130, 220) of the sample fluid selectively towards a given outlet channel.

Description

Microfluidic device, system and method for manipulating a flowing fluid Technical field

[0001] The present invention relates to the technical field of microfluidic devices and methods. More specifically, the present invention relates to a microfluidic manipulation device and method for rapidly controlling and diverting the flow direction of a fluid. The present invention finds applications in the precise and rapid manipulation of fluids or the extraction of very small volumes within a fluid. The invention particularly relates to the manipulation and sorting of individual nano-sized particles in a fluid. Prior art

[0002] In the above field, it is known to use flow cytometers to detect, count, identify cells or particles of micrometric dimensions suspended in a flowing fluid by passing them, one by one and at high speed, in the beam of one or more lasers and then to sort them by implementing sorting methods based on various techniques.

[0003] Advances in microscopy and biology have made it possible to focus on ever smaller objects, particularly nano-objects smaller than 100 nm.

[0004] Traditional flow cytometers only work well for objects larger than a micrometer. For objects smaller than 100 nm, cytometers are currently limited by their detection capacity. Furthermore, regarding the sorting of nano-objects, the fluid volumes typically used by known cell sorters and the size of the droplets used to encapsulate the objects to be sorted are not compatible with the sorting of nanometric objects.

[0005] There are different methods for sorting objects in a microfluidic chip. Some sorting methods rely on passive techniques. They can be based on inertial focusing methods or on the structure of the chip itself: this allows objects to be separated into subpopulations based on their physical characteristics (volume, mass, etc.). Other sorting methods, also Passive sorting methods are based on the microfabrication of micrometric pillars and allow on-chip chromatography, but are only applicable for micrometric objects or micrometric-length, polydisperse polymer chains. These passive sorting methods do not allow objects to be sorted one by one based on a specific signal, for example fluorescence.

[0006] Micromechanical techniques allow sorting of micrometer-sized objects at a relatively slow sorting rate. For example, the use of valves to separate cells, for example eukaryotic or prokaryotic cells, does not allow a sorting rate exceeding 1 Hz.

[0007] Other active sorting techniques rely on the application of an electric or magnetic field. For example, dielectrophoresis or the use of surface acoustic waves make it possible to achieve a sorting rate of around one kHz on preformed micrometric drops encapsulating individual objects.

[0008] To our knowledge, there is currently no method for actively sorting individual nanoobjects in a microfluidic chip capable of operating at a sorting rate greater than 1 kHz.

[0009] Devices are known for concentrating nanoparticles by centrifugation, precipitation or isolation. However, these techniques do not allow for individual sorting and / or sorting based on a specific signal of the nanoparticles, for example a fluorescence signal.

[0010] In some specific applications, there are also microfluidic devices suitable for sorting pre-encapsulated particles into drops in oil. These devices require a prior encapsulation step. The currently accessible droplet volume is not compatible with individual sorting of nanoparticles because this requires excessive dilution and therefore a sorting time that is prohibitive for biological and medical applications.

[0011] The publication by Haneoka et al. "Microfluidic active sorting of DNA molecules labeled with single quantum dots using flow switching by a hydrogel sol-gel transition", Sensors and Actuators B 159 pp. 314-320, 2011, describes a microfluidic device for sorting molecules in a fluid. On the other hand, document EP 3218107 discloses devices for sorting microparticles in a fluid stream. However, the switching frequency of these microfluidic devices is limited to a few hertz or a few hundred hertz.

[0012] US Patent 9,364,831 B2 discloses a microfluidic switch based on the absorption of an intense laser pulse to induce a gas bubble by cavitation. Such a microfluidic switch allows 10 μm diameter polystyrene beads to be moved laterally at a switching frequency of 10 kHz. However, cavitation is likely to affect the integrity of nano-objects or the viability of fragile biological cells in suspension.

[0013] One of the aims of the present disclosure is to propose an apparatus and method for manipulating and / or sorting in real time objects of micrometric to nanometric size, suspended in a flowing fluid, at a high switching frequency, of the order of at least one kilohertz, and with safety, that is to say without risk of harm to the integrity of nano-objects or the viability of fragile biological cells suspended in the fluid.

[0014] Another aim of the present disclosure is to propose, for certain applications, an apparatus and method for handling and / or sorting nanoobjects suspended in a fluid, with or without a prior encapsulation step and using a fluid compatible with the analysis of nano-objects. Statement of the invention

[0015] To this end, the invention relates to a microfluidic device comprising at least one sheath fluid inlet channel and one sample fluid inlet channel, at least two outlet channels and a common channel arranged between said inlet channels and said outlet channels, the common channel being fluidically connected to said inlet and outlet channels, the sample fluid inlet channel being able to inject a sample fluid into the common channel, the at least one sheath fluid inlet channel being able to inject at least one sheath fluid into the common channel so as to allow hydrodynamic focusing of the sample fluid in the common channel, the common channel being configured to conduct the focused sample fluid hydrodynamically and the at least one sheath fluid towards said at least two outlet channels.

[0016] According to the invention, the microfluidic device comprises heating means comprising an energy source and at least one transducer, the heating means being arranged to transmit over a short period a quantity of heat localized in said at least one flow of sheath fluid in the common channel upstream of a branch between said at least two outlet channels, the heating means being capable of locally heating said at least one flow of sheath fluid in the common channel and said at least one sheath fluid has a thermal variation in viscosity adapted to deflect or extract a portion of the sample fluid selectively towards a determined outlet channel among the at least two outlet channels.

[0017] According to a particular and advantageous aspect, the at least one sheath fluid inlet channel comprises a first inlet channel and a second inlet channel, the first inlet channel being capable of injecting a first sheath fluid and the second inlet channel being capable of injecting a second sheath fluid.

[0018] According to a first embodiment, the heating means comprise at least one photo-thermal transducer and the energy source comprises a laser source configured to generate a laser beam focused on said at least one photo-thermal transducer, said at least one photo-thermal transducer being capable of absorbing the laser beam and transmitting the heat induced by the laser beam to said at least one flow of sheath fluid by conduction.

[0019] For example, said at least one photothermal transducer comprises a layer of gold or indium.

[0020] According to a particular and advantageous aspect of the first embodiment, said at least one photo-thermal transducer comprises at least one first photo-thermal transducer and at least one second photo-thermal transducer, said at least one first photo-thermal transducer and, respectively, said at least one second photo-thermal transducer being capable of sequentially absorbing the laser beam, so as to modify the flow rate of the first sheath fluid and, respectively, of the second sheath fluid to extract said portion of the sample fluid.

[0021] Advantageously, said at least one first photothermal transducer comprises a plurality of photothermal transducers arranged on one side of the common channel and / or wherein said at least one second photothermal transducer comprises a plurality of photothermal transducers arranged on another side of the common channel relative to a longitudinal axis of the common channel.

[0022] Advantageously, the heating means comprise at least one third photo-thermal transducer arranged on one side of the first output channel and / or at least one fourth photo-thermal transducer arranged on one side of the second output channel.

[0023] According to a second embodiment, the heating means comprise a laser source configured to generate a focused laser beam in the hydrodynamic sheath inside the common channel and the sheath fluid is capable of absorbing the laser beam to transform it into heat.

[0024] Advantageously, the laser source is adapted to emit a laser pulse having an energy of between 10 nJ and 100 ps over a short duration of less than or equal to 50 ps.

[0025] According to a third embodiment, the heating means comprise at least one electro-thermal transducer capable of locally heating the hydrodynamic sheath.

[0026] Advantageously, the microfluidic device comprises a thermoelectric module capable of modifying the temperature either of the entire microfluidic device or of the sample fluid and / or of at least one sheath fluid upstream of the heating means.

[0027] Advantageously, the at least one sheath fluid has, at a temperature of 20°C, a viscosity of between 2 mPa.s and 30,000 mPa.s and a thermal variation in viscosity of between 0.2 mPa.s K 1 and 3,000 mPa.s K 1 .

[0028] For example, the at least one sheath fluid comprises propylene glycol, linseed oil, or a mixture containing water and glycerol, or a mixture of water and carbohydrates.

[0029] Advantageously, the at least two output channels comprise a first output channel and a second output channel arranged or configured symmetrically with respect to the common channel.

[0030] Alternatively, the first output channel and the second output channel are arranged or configured asymmetrically with respect to the common channel.

[0031] Advantageously, the at least one sheath fluid comprises particles, for example metallic, for example gold or indium, capable of absorbing the focused laser beam to transform it into heat.

[0032] The laser source operates in pulse-on-demand mode or operating at a repetition rate of less than or equal to 100 kHz.

[0033] The present disclosure also relates to a microfluidic system comprising a microfluidic device and comprising a detection module arranged upstream of the heating means, the detection module being configured to detect at least one signal representative of a nanoparticle in the sample fluid hydrodynamically focused in the common channel and feedback means on the heating means as a function of the detected signal.

[0034] The present disclosure also relates to a microfluidic manipulation method comprising the following steps: (a) injecting a sample fluid into a common channel of a microfluidic device; (b) injecting at least one sheathed fluid into the common channel to enable hydrodynamic focusing of the sample fluid in the common channel; (c) applying an energy source over a short period to at least one transducer capable of transmitting a quantity of heat localized in the at least one sheath fluid in the common channel upstream of a branch between said at least two outlet channels, the heating means being capable of locally heating said at least one sheath fluid flow in the common channel and the at least one sheath fluid having a thermal variation in viscosity adapted to divert or extract a portion of the sample fluid selectively to a determined output channel among the at least two output channels.

[0035] Advantageously, step c) comprises a time sequence of steps cl) and c2), a delay between step cl) and step c2) being adjusted so as to control the volume of the portion of the sample fluid extracted, wherein step cl) comprises applying the energy source for a short duration to a first transducer arranged on one side of the common channel so as to transmit to said at least one sheath fluid in the common channel a first quantity of localized heat and wherein step c2) comprises applying the energy source for another short duration to a second transducer arranged on another side of the common channel relative to a longitudinal axis of the common channel so as to transmit to said at least one sheath fluid in the common channel a second quantity of localized heat.

[0036] Of course, the various features, variants and embodiments of the invention may be combined with each other in various combinations to the extent that they are not incompatible or mutually exclusive. Brief description of the drawings

[0037] In addition, various other characteristics of the invention emerge from the appended description given with reference to the drawings which illustrate non-limiting embodiments of the invention and where:

[0038] Figure 1 is a top view of the central portion of a microfluidic chip according to one embodiment,

[0039] Figure 2 is a top view of a microfluidic chip according to one embodiment,

[0040] Figure 3 is a view along a section AA of the central part of the microfluidic chip shown in Figure 2,

[0041] Figure 4 is a schematic view of a microfluidic system according to one embodiment,

[0042] Figure 5 is a top view of a microfluidic chip according to an embodiment with 2 output channels, with injection of a sample fluid and symmetrical injection of the sheath fluid;

[0043] Figure 6 is a view along a BB section of the central portion of the microfluidic chip shown in Figure 5;

[0044] Figure 7 is a top view of a microfluidic chip according to a 3-output channel embodiment, with symmetrical injection of the sheath fluid;

[0045] Figure 8 is a top view of a microfluidic chip according to an embodiment with 2 output channels, with asymmetric injection of the sheath fluid;

[0046] Figure 9 is a top view of a microfluidic chip when applying a laser pulse to at least one heating zone according to an example;

[0047] Figure 10 is a top-view simulation of a microfluidic chip when applying an alternating sequence of laser pulses to two heating zones;

[0048] Figure 11 is a simulation of the flux rates transmitted in two output channels when applying an alternating sequence of laser pulses to two heating zones;

[0049] Figure 12 schematically represents a sequence for extracting a portion of sample fluid to a determined outlet;

[0050] Figure 13 is a sectional view of a microfluidic chip according to another embodiment, with rotational symmetry.

[0051] It should be noted that in these figures the structural and / or functional elements common to the different variants may have the same references. Detailed description

[0052] Generally, the present disclosure relates to a microfluidic device 100 also called a microfluidic chip.

[0053] In this document, fluid means a pure or mixed liquid, or a gel or emulsion.

[0054] Figures 1 to 8 represent a microfluidic device according to one embodiment of the invention. Figures 5 to 12 illustrate the operation of this microfluidic device. Device

[0055] The microfluidic device 100 comprises channels 1 and / or 2, 3, 4, 11, 12, which mechanically conduct a sample fluid 20 to be analyzed and / or at least one sheath fluid 21, 22 from different source inlets 5, 6, 7 to different outlets 8, 9. The microfluidic device 100 generally has a planar shape. According to a variant, the microfluidic device has a symmetry of revolution about a longitudinal axis. In this case, a single sheath fluid inlet channel can be used.

[0056] The microfluidic device 100 is for example manufactured from glass, ceramic or silicon. The microfluidic device can be manufactured monolithically or by assembling a support blade and a cover blade. The channels 1, 2, 3, 4, 11, 12 are formed for example by etching.

[0057] In an exemplary embodiment illustrated in Figures 3 and 6, the microfluidic device 100 is made up of the assembly of two parts: a support blade 15 on which the channels are formed and a blade 16 forming a cover. The support blade 15 is for example made of polydimethylsiloxane (PDMS). The blade 16 is preferably transparent to allow observation and detection of particles in the sample fluid. For example, slide 16 is a microscope slide to allow observation of the microfluidic device 100 under an optical microscope objective.

[0058] For example, as illustrated in FIG. 2, the microfluidic device 100 comprises a source inlet 5 of sample fluid 20 to be analyzed, a source inlet 6 for a first sheath fluid 21 and another source inlet 7 for a second sheath fluid 22. Alternatively, the first sheath fluid 21 and the second sheath fluid 22 are identical. Alternatively, the first sheath fluid 21 and the second sheath fluid 22 are stored in a single source reservoir. Alternatively, the sheath fluid is injected via a single sheath fluid inlet channel. The inlets source are generally connected by tubes to the reservoir of sample fluid and respectively sheath fluid(s). For example, the source inlets 5, 6, 7 are fluidically connected to syringes equipped with pumps for injecting the sample fluid and respectively the sheath fluid(s) into the microfluidic device 100.

[0059] The microfluidic device 100 comprises a common channel 4. The common channel 4 is connected to the different source inlets 5, 6, 7 by different inlet channels 1, 2 and 3. In particular, an inlet channel 1, respectively 2, connects the source inlet 6, respectively 7, of sheath fluid to the common channel 4. An inlet channel 3 fluidically connects the source inlet 5 of sample fluid to the common channel 4. In FIG. 1, the inlet channel 3 of the sample fluid 20 is arranged in the longitudinal axis 14 of the common channel 4 and the inlet channels 1, 2 of sheath fluid are arranged respectively on opposite lateral faces of the common channel 4. By convention, as illustrated in FIG. 3, the lower internal face 18, or lower face, is the internal surface of the common channel 4 on the side of the inlet 5. The upper internal face 19, or upper face, is the internal surface on the side opposite entrance 5.The internal lateral faces 17 or lateral faces denote the internal surfaces of the common channel 4 transverse to the lower face 18 and to the upper face 19. In the figures, an orthonormal Cartesian reference frame XYZ has been shown. The common channel 4 generally extends in the XY plane, the longitudinal axis 14 of the common channel being parallel to the X axis. The common channel 4 generally has a cylindrical shape with a generator parallel to the longitudinal axis 14. According to other variants (not shown), the device comprises other additional inlet channels.

[0060] At the other end of the common channel 4 there is a junction, for example of the Y junction type comprising at least a first outlet channel 11 and a second outlet channel 12. The outlets 8 and respectively 9 are connected to the common channel 4 of the microfluidic device via the first outlet channel 11 and, respectively, the second outlet channel 12. In the example illustrated in FIG. 1, the first outlet channel 11 and the second outlet channel 12 are of the same dimensions and are arranged symmetrically with respect to the longitudinal axis 14 of the common channel 4. Alternatively, the first outlet channel 11 and the second outlet channel 12 are of the same dimensions and are arranged symmetrically with respect to the longitudinal axis 14 of the common channel 4. different dimensions and / or are arranged asymmetrically with respect to the longitudinal axis 14 of the common channel 4. For example, the first outlet channel 11 has a cross-section 20% smaller than the cross-section of the second outlet channel 12 so that the first outlet channel 11 has a fluid resistance greater than that of the second outlet channel 12. This structural asymmetry makes it possible to direct the sample fluid 20 towards the second outlet channel 12 in steady state.

[0061] According to yet another variant illustrated in Figure 7, the microfluidic device 100 comprises a third outlet channel 13. In this example, the third outlet channel 13 is arranged in the longitudinal axis 14 of the common channel 4. This configuration makes it possible to sort particles according to two sorting criteria. According to other variants (not shown), the device comprises more than three outlet channels to allow sorting based on several criteria.

[0062] According to yet another variant illustrated in FIG. 13, the microfluidic device 100 has, in its central part, a symmetry of revolution around the longitudinal axis 14. In this configuration, the microfluidic device 100 comprises a single inlet channel 1 for sheath fluid. The inlet channel 3 of the sample fluid 20 is arranged in the longitudinal axis 14. The inlet channel is connected to a frustoconical part arranged concentrically around the inlet channel 3. The inlet channel 1 makes it possible to inject the single sheath fluid 21 concentrically around the sample fluid 20. This configuration allows a focusing of the sample fluid 20 inside a cylindrical sheath of sheath fluid 21 in the common channel 4. In the example of FIG. 13, the first outlet channel 11 is arranged in the longitudinal axis 14. The second outlet channel 12 is connected to a frustoconical part arranged concentrically around the first outlet channel 11.The transducers 31, 32 are arranged in the common channel 4, for example on a side wall. Thus, the sample fluid 20 which is not diverted by the heating means is collected via the first outlet channel 11. On the contrary, when the heating means divert the sample fluid 20, it is collected by the second outlet channel 12. In the example illustrated in FIG. 13, the inlet channel 3 of the sample fluid 20, the common channel 4, the first outlet channel 11 and the. frustoconical parts connected to the sheath fluid inlet channel 1 and to the second outlet channel 12 are of revolution around the longitudinal axis 14. Alternatively, it is possible to combine inlet channels with symmetry of revolution with a common channel and outlet channels of planar geometry. According to another variant, it is possible to combine inlet channels and a common channel of planar geometry with outlet channels with symmetry of revolution.

[0063] Advantageously, the microfluidic device 100 comprises a detection unit 50. The detection unit 50 is for example based on a system for detecting a fluorescence signal emitted by particles marked by a fluorescent marker and passing through the common channel 4.

[0064] According to the present disclosure, the microfluidic device 100 further comprises at least one energy source (optical or electrical) and at least one transducer 31, 32 located in a heating zone located in the common channel 4, upstream of the output channels 11, 12. In the case where a detection unit 50 is present, the transducer(s) 31, 32 are located downstream of the detection unit 50. The transducer 31, 32 transforms the energy received from the energy source into a quantity of heat. The transducer is thus a very localized heat source that can be switched quickly. The transducer 31, 32 transmits the quantity of heat to the sheath fluid so that the temperature of the sheath fluid increases locally.

[0065] The sheath fluid is chosen to have a viscosity with a suitable temperature dependence, depending on the amount of heat received, to modify the fluid flow in the microfluidic chip, while avoiding bubble generation by cavitation or boiling.

[0066] In this document, viscosity means the dynamic viscosity of a fluid, when the fluid consists of a single homogeneous component. In the case of a fluid composed of an inhomogeneous mixture, viscosity means the real or effective viscosity of the fluid considered.

[0067] The energy source and transducer are configured to induce a local temperature increase in the heating zone where the sheath fluid forms a hydrodynamic sheath, so as to locally modify the flow velocity field in norm and direction, and consequently modify the flow rate of the sheath fluid. However, the intensity of the energy supplied is lower than the threshold for bubble generation by cavitation in the sheath fluid. In addition, the temperature of the sheath fluid remains lower than the threshold for bubble generation by boiling in the sheath fluid. In other words, the sheath fluid remains in the same physical state, before and after receiving the quantity of heat suitable for modifying the flow velocity of the fluid.

[0068] As described in detail below, this arrangement allows a portion of the sample fluid to be diverted selectively to a determined outlet channel among at least two outlet channels up to a very high rate. Depending on the signal detected upstream of the heating zone, these localized heating means applied over a short period of time allow a very small volume of sample fluid to be extracted to individually sort a detected particle to one or other of the different outlet channels. The volume of sample fluid extracted is for example between 0.1 and 500 femtoliters (fl), for example from 0.1 to 10 fl or from 10 fl to 100 fl, or from 100 fl to 500 fl.

[0069] We will describe several embodiments, depending on the energy source, the type of heat transducer and the sheath fluid used.

[0070] In a first embodiment, the energy source comprises a laser source and the transducer comprises a solid element capable of absorbing the radiation from the laser source and transmitting the heat to the sheath fluid in a zone of the hydrodynamic sheath. By convention we call this type of transducer a photo-thermal transducer.

[0071] In a second embodiment, the energy source comprises a laser source and the transducer is constituted by the sheath fluid which is capable of directly absorbing the radiation from the laser source in a zone of the hydrodynamic sheath. The transducer is then of the photo-thermal type.

[0072] In a third embodiment, the energy source comprises an electric current source and the transducer comprises a dissipative element resistive or inductive capable of locally heating the sheath fluid inside the common channel 4 in an area of ​​the hydrodynamic sheath. By convention we call this type of transducer, electro-thermal transducer

[0073] In all embodiments, the sheath fluid 21, 22 is chosen to have a variable viscosity as a function of an increase in temperature, so as to modify the flow rate of the sheath fluid flow, in norm and / or in orientation. Advantageously, the sheath fluid 21, 22 has a large variation in viscosity as a function of temperature. Generally, the viscosity of the sheath fluid decreases as the temperature increases. For example, the sheath fluid has, at a temperature of 20°C, a viscosity of between 2 mPa.s and 30,000 mPa.s, for example between 10 and 1000 mPa.s and a thermal variation in viscosity of between 0.2 mPa.s K 1 and 3000 mPa. s K 1, preferably between 1 and 100 mPa.s K -1for example at least 1 mPa.s per degree Kelvin in absolute value. Advantageously, the sheath fluid 21, 22 has a viscosity of between 10 and 1000 mPa.s at an ambient temperature of 20°C to allow flow in the microfluidic device. By way of non-limiting example, the sheath fluid 21, 22 is used as a liquid based on a mixture of water and glycerol (1,2,3-propanetriol of chemical formula HOH2C-CHOH-CH2OH) or a mixture of water and simple or complex carbohydrates (for example a syrup or agar-agar), or propylene glycol (propane-1,2-diol, of chemical formula CH3-CHOH-CH2OH) or linseed oil. Glycerol has a viscosity that varies greatly with temperature: its viscosity decreases 5000 times more than that of water when heated by 1°C. On the other hand, pure glycerol has a very high viscosity, which requires pressure differences that are difficult to implement in practice in a microfluidic system.Advantageously, a sheath fluid is selected having both a dynamic viscosity of less than 500 mPa.s and a temperature dependence of its viscosity greater than 2 mPa.s per degree Celsius. For example, a sheath fluid consisting of 10% water and 90% glycerol by mass concentration is used. In another example, a mixture consisting of 25% water and 75% glycerol by mass concentration is used.

[0074] The sample fluid 20 and the sheath fluid(s) 21, 22 may be miscible or immiscible with each other. The sample fluid 20 is composed, for example, of water or a phosphate buffer saline (PBS) solution in which there are micro-objects or nano-objects to be categorized and manipulated.

[0075] According to a particular aspect, the microfluidic device further comprises at least one thermoelectric module capable of modifying the temperature either of the entire microfluidic device or of the sample fluid and / or the sheath fluid upstream of the heating zone(s), for example at the level of the inlet channels 1, 2 and / or 3 or even of the common channel 4. Such a thermoelectric module makes it possible, for example, to maintain the sample fluid at a temperature compatible with specific biological samples. According to a particular aspect, the thermoelectric module makes it possible to adapt the temperature of the sheath fluid(s) so as to be at an optimal operating temperature of the device. For example, the thermoelectric module comprises a Peltier effect module.The temperature of the sheath fluid can thus be lowered, upstream of the heating zone, by several degrees or even ten or twenty degrees, so that the sheath fluid has a higher coefficient of thermal variation of dynamic viscosity in absolute value for the same quantity of heat supplied by the energy source, to the extent that the sample contained in the sample fluid (or core or analysis fluid) can tolerate such a lowering of temperature.

[0076] According to an example of the first embodiment, illustrated in Figures 5 and 6, the heating means comprise a first photothermal transducer 31 in a first heating zone and a second photothermal transducer 32 in a second heating zone. Advantageously, the first photothermal transducer 31 and the second photothermal transducer 32 are formed on an inner surface of the common channel 4 so as to be in contact with the sheath fluid during operation of the microfluidic device. For example, the first photothermal transducer 31 and the second photothermal transducer 32 are arranged on the upper inner surface 19. The first photothermal transducer 31 and the second photothermal transducer 32 are separate and at a distance from each other of the order of the width W of the channel. common channel 4, for example about 15 micrometers (pm). Alternatively, the first photothermal transducer 31 and the second photothermal transducer 32 are arranged on two opposite lateral surfaces 17 of the common channel. According to another variant, the first photothermal transducer 31 and the second photothermal transducer 32 are arranged on the lower face 18 of the common channel 8.

[0077] In this first embodiment, the photothermal transducers are not electrically connected to a source of electric current, but are passive elements. According to the example of the first embodiment illustrated in FIG. 5, the first photothermal transducer 31 and the second photothermal transducer 32 each comprise, for example, a metal surface, for example made of gold or indium. This metal surface is formed, for example, by deposition of a thin metal layer. More precisely, the first photothermal transducer 31 and the second photothermal transducer 32 respectively have a surface adapted to receive a laser beam 41, respectively 42. The thickness of the metal surface is generally of the order of magnitude of the skin depth at the wavelength of the laser used, for example between 10 nm and 500 nm.The material of the photothermal transducers 31 and 32 respectively and the wavelength of the laser source are adapted to allow absorption of the laser radiation 41 and 42 respectively from the laser source. In an exemplary embodiment, the first photothermal transducer 31 and the second photothermal transducer 32 are located inside the microfluidic device. In this case, the wall of the microfluidic device 100 is transparent to the laser radiation 41 and 42 respectively so that it is absorbed by the first photothermal transducer 31 and / or the second photothermal transducer 32 respectively to be transformed into heat. In this way, the first photothermal transducer 31 makes it possible to locally heat by conduction the first sheath fluid 21 in a first heating zone of the hydrodynamic sheath upstream of the branch of the outlet channels 11 and 12.Similarly, the second photothermal transducer 32 makes it possible to locally heat by conduction the second sheath fluid 22 in a second heating zone of the hydrodynamic sheath upstream of. the branching of the outlet channels 11 and 12. The amount of heat deposited remains localized in the sheath fluid and is evacuated by the flow of the sheath fluid, so that the heat deposited does not reach the hydrodynamically focused sample fluid. In the case where the laser beam passes through the sheath fluid before reaching the transducer 31, 32, the wavelength of the laser beam is chosen so that the sheath fluid is transparent to the laser beam.

[0078] According to a variant of the first embodiment, the first photothermal transducer 31 and the second photothermal transducer 32 each comprise a rod passing through the wall of the microfluidic device. In this case, the laser beam 41, 42 is configured to be focused on the first transducer 31 and / or respectively the second transducer 32 outside the microfluidic device. By conduction, the rods make it possible to transmit the absorbed heat22 into a first, respectively second, heating zone of the hydrodynamic sheath upstream of the branch of the outlet channels 11 and 12.

[0079] In the first embodiment, the first photothermal transducer 31 and the second photothermal transducer 32 have a shape adapted to the geometry of the device, for example a square, disc, or oblong shape. Alternatively, the first transducer 31 and the second transducer 32 are in the shape of a rod or needle with an axis Z. According to the example of the first embodiment illustrated in FIG. 1, the first photothermal transducer 31, and respectively the second photothermal transducer 32 are located at a distance P upstream of the junction with the first output channel 11, and respectively the second output channel 12. In an exemplary embodiment, the first photothermal transducer 31 and the second photothermal transducer 32 have a disc shape with a diameter of between 1 and 15 μm.

[0080] According to a variant of the first embodiment, illustrated in Figure 9, the microfluidic device comprises a plurality of first photothermal transducers 31 arranged on an internal face of the common channel 4 upstream of the Y junction and / or a plurality of second photothermal transducers 32 arranged on the other opposite lateral face 17 upstream of the Y junction. According to yet another variant, the first photothermal transducer 31 extends along one side of the common channel 4 and the second photo-thermal transducer 32 extends along the opposite side of the common channel 4.

[0081] Optionally, the microfluidic device further comprises at least one third photothermal transducer 33, respectively at least one fourth photothermal transducer 34, arranged on an internal face of the first outlet channel 11, and respectively of the second outlet channel 12, i.e. downstream of the Y junction. Alternatively, the third photothermal transducer 33 extends along one side of the first outlet channel and / or the fourth photothermal transducer 34 extends along one side of the second outlet channel 12. The extended shape of the transducer makes it possible to modulate the amplitude of deflection of the sample fluid. This amplitude modulation of the deflection of the fluid is used, for example in the case of multi-criteria sorting to direct a volume of sample fluid between more than two outlet channels.

[0082] According to the second embodiment, the energy source comprises a laser source similar to that described in connection with the first embodiment. However, instead of being directed towards a solid transducer fixed relative to the microfluidic device, the laser beam is directed directly onto the fluid of the hydrodynamic sheath in the common channel. Indeed, in this second embodiment, the transducer 31, 32 is constituted by a portion of the sheath fluid which is illuminated by the laser beam and which is capable of directly absorbing the radiation from the laser source. The wavelength of the laser source is chosen so that it is absorbed by the sheath fluid 21 and / or 22. For example, the sheath fluid contains absorbent particles, for example gold particles in order to absorb laser radiation with a wavelength between 500nm and 700nm, or graphite particles.This second embodiment makes it easier to scan the laser beam over a heating zone of suitable size and dimensions depending on the application, for example for multi-criteria sorting towards several output channels.

[0083] According to the third embodiment, the energy source comprises an electric current source and the transducers 31, 32 are of the electro-thermal type. For example, each electro-thermal transducer comprises a resistor heating element or an inductive dissipative element. Such electrothermal transducers are connected to an electric current source which is configured to sequentially power each electrothermal transducer. The electrothermal transducer 31, respectively 32, is in contact with the hydrodynamic sheath of the first, respectively second, sheath fluid in the common channel 4 to allow heat exchange. The electrothermal transducers 31, 32, are electrically insulated from the sheath fluid(s). An electrothermal transducer can have various shapes. The different variants of shape and number of transducers described in connection with FIG. 9 also apply to this embodiment.

[0084] Figure 4 represents a microfluidic system 200 adapted to control the operation of the microfluidic chip 100. The microfluidic system 200 comprises a system of micro-pumps or syringe pumps for injecting the inlet fluids 20, 21, 22 into the inlets 5, 6, 7.

[0085] The microfluidic system 200 also comprises an energy source 40. In the first and second embodiments, the energy source 40 is a laser source suitable for generating laser pulses. For example, the laser source 40 may be a modulated continuous laser beam, with pulse durations of, for example, between 1 ps and 10 ms. Alternatively, the laser source 40 is a pulsed laser generating ultrashort pulses, for example picoseconds or femtoseconds. In the third embodiment, the energy source 40 is a power supply, suitable for delivering or not delivering an electric current. The energy source 40 makes it possible to supply a determined quantity of energy to the transducers 31, 32 which transform this energy into a local heat source. In the first embodiment, the transducers 31, 32 are solid photothermal transducers, in the form of a pellet or a metal rod for example.In the second embodiment, the transducers 31, respectively 32 are photothermal transducers each consisting of a portion of the sheath fluid which is illuminated by the laser beam 41, respectively 42. In the third embodiment, the transducers 31, 32 are solid electrothermal transducers.

[0086] In the first and second embodiments, the laser source 40 is configured to generate a first laser beam 41 towards a first transducer 31 in a first heating zone and respectively a second laser beam 42 towards a second transducer 32 in a second heating zone. Advantageously, the first laser beam 41 is focused on the first transducer 31, respectively the second laser beam 42 is focused on the second transducer 32. For example, the first laser beam 41 is focused on an area with dimensions between 1 and 20 μm, for example a square with a side of 3 μm.

[0087] In the third embodiment, the source 40 of electric current is connected to the electro-thermal transducers (for example heating resistors). The microfluidic system 200 comprises a switching system configured to apply one or more electrical pulses selectively to the first transducer 31 and / or the second transducer 32. In this case, the duration of an electrical pulse capable of heating the transducer is generally between 1 s and 1 ms.

[0088] Optionally, the microfluidic system 200 comprises a detection unit 50. The detection unit 50 is for example based on a system for detecting a fluorescence signal emitted by particles marked by a fluorescent marker in the hydrodynamically focused sample fluid and passing through the common channel 4. The detection unit 50 is positioned upstream of the transducers 31, 32 and the heating zones. Thus, a signal representative of a particle is detected in a zone of the sample fluid 20 which is not likely to be disturbed by a rise in temperature of the heating zone. This detection signal is transmitted to a controller 10 which controls the energy source 40, for example the laser source. A signal of the presence of a particle is detected before applying at least one laser or electrical pulse to heat the sheath fluid downstream of the detection device.The distance between the detection unit 50 and the transducers 31, 32 is generally between 2 pm and 2 mm, for example between 20 and 500 pm, for example 50 pm. Considering the flow speed of the fluids, the time between the detection of a particle and the heating to deflect the sample fluid is. generally between 1ps and 100ms, for example between 5ps and 10ms, for example of the order of 1 ms. Process

[0089] We will now describe the operation of the microfluidic device 100 first in a steady state of fluid flow, then in a pulsed heating state. For clarity of the presentation, we consider a planar (quasi-2D) microfluidic device comprising two sheath fluids. However, given the laminar nature of microfluidic flows, the method also applies in the case of a single sheath fluid forming a sheath of revolution around the sample fluid.

[0090] The sample fluid 20 is injected into the center of the common channel 4 via the inlet channel 3. Simultaneously, the first sheath fluid 21 and the second sheath fluid 22 are injected laterally on each side of the sample fluid 20. In this way, by adjusting the respective flow rates of the sample fluid 20, the first sheath fluid 21 and the second sheath fluid 22, the microfluidic device makes it possible to form a hydrodynamic sheath in at least two dimensions on either side of the sample fluid 20 in the common channel 4. The sample fluid 20 is hydrodynamically focused in the common channel 4. W denotes the width, H the height and L the length of the common channel 4. Depending on the ratio between the flow rate of the sample fluid and the flow rate of the sheath fluid, the sample fluid 20 has a width D reduced compared to the width W by hydrodynamic focusing.

[0091] For example, in a microfluidic device as illustrated in Figures 2-3, the sample fluid 20 is injected with a flow rate of 20 pL.h 1 and the first and second sheath fluids 21, 22 have an identical flow rate of 50 pL.h ~ 1 . The width W of the common channel is 25 pm, the depth H of the common channel is 7 pm and the length L is approximately 74 pm. The width D of each inlet channel is 11 pm. The distance P between the heating zone 31, 32 and the start of the outlet channel 31, 32 is between 5 and 30 pm. The distance G between the start of the outlet channel 31, 32 and the tip of the junction Y is between 10 and 30 pm. The sample fluid 20 thus forms a fluid vein of width D between 2 and 7 micrometers.

[0092] According to an example illustrated in Figure 5, the microfluidic device comprises two sheath fluid inlet channels 1 and 2 arranged symmetrically with respect to the longitudinal axis 14 and two outlet channels 11 and 12, arranged symmetrically with respect to the longitudinal axis 14. The same sheath fluid, for example a mixture composed of 25% water and 75% glycerol, is injected symmetrically via the first inlet channel 1 and the second inlet channel 2 with the same flow rate, for example 100 pL.h ~ 1 . The sample fluid 20 comprises a PBS-based carrier liquid and dispersed nanoparticles or nano-objects. In this case, the hydrodynamically focused sample fluid 20 is located in the center of the common channel 4, equidistant from the two side faces 17.

[0093] Once focused, the sample fluid 20 is directed towards a branch with at least two branches depending on the type of device (figures 5, 7, 8).

[0094] We first consider a permanent or equilibrium operating regime of the microfluidic device, i.e. in the presence of a flow rate of the sheath fluid and the sample fluid and in the absence of application of a laser source or an electrical power supply to the opto- or electro-thermal transducers 31, 32, 33, 34.

[0095] In the exemplary embodiment illustrated in Figure 5, in steady state, the sample fluid 20 separates into two fluid streams 120 and 220 at the Y junction. The sample stream 120 and the first sheath fluid 21 flow in the first outlet channel 11 while the sample stream 220 and the second sheath fluid 22 flow in the second outlet channel 12. Each fluid stream 120, 220 has approximately half the flow rate of the sample fluid 20 in the common channel 4.

[0096] In the three-outlet channel embodiment illustrated in FIG. 7, in steady state, the sample fluid 20 flows in the third outlet channel 13, in the longitudinal axis 14 of the common channel 4 while the first sheath fluid 21 flows mainly in the first outlet channel 11 and the second sheath fluid 22 flows mainly in the second outlet channel 12.

[0097] Alternatively, when the arrangement of the inlet channels 1 and 2 is asymmetrical and / or when the flow rate of the first sheath fluid 21 is different from the flow rate of the second sheath fluid 22 (see FIG. 8), in steady state, the sample fluid 20 and the second sheath fluid 22 flow in the second outlet channel 12 while the first sheath fluid 21 flows mainly in the first outlet channel 11.

[0098] In connection with Figures 9 and 10, we now consider an on-demand switching regime of the microfluidic device, i.e. in the presence of a flow rate of the sheath fluid and the sample fluid and by applying a sequence of at least one pulse from an energy source, laser or power supply, to at least one transducer 31, 32 in a heating zone.

[0099] For the sake of clarity, a microfluidic device with two symmetrical output channels is considered according to the first embodiment. Those skilled in the art will easily adapt the method to other embodiments. As illustrated in FIG. 9, a first laser beam 41 is applied to the first transducer 31. The first laser beam 41 is configured to be absorbed by the first transducer 31. For this purpose, the first laser beam 41 is focused on the first transducer 31 and has a wavelength capable of being absorbed by the first transducer 31. For example, a laser is used which generates, on demand, pulses at a wavelength between 500 nm and 800 nm, for example 660 nm, focused with a beam size of the order of 2 μm. A laser pulse or a series of laser pulses is applied to heat the first transducer 31.The laser beam passes through the microfluidic device 100 before being absorbed by the first transducer 31. It is emphasized here that in this example, the first laser beam 41 does not pass through the first sheath fluid 21 and is not absorbed directly by the sheath fluid. On the contrary, the energy of the laser beam is focused and absorbed by the first transducer 31. Under this illumination, the first transducer 31 heats up and locally heats by contact the first sheath fluid 21 in a first heating zone. It is observed that the heating zone remains localized in the sheath fluid. For example, for a laser illumination of 70 nJ, the local temperature rise is 100°C for 30 ps over an area of ​​3. pm in diameter. This local heating of the first sheath fluid 21 modifies the viscosity of the first sheath fluid 21, which modifies the flow of the first sheath fluid 21 and consequently that of the sample fluid 20. In an example where the first sheath fluid 21 consists of a mixture of 25% water and 75% glycerol, the viscosity of the first sheath fluid 21 varies locally because the local temperature rise is 100°C. This local variation in viscosity locally modifies the direction and flow rate of the first sheath fluid 21. As illustrated in FIG. 9, this local heating makes it possible to divert the sample fluid 120 so that it flows only in the first outlet channel 11, instead of being distributed between the two outlet channels as in the steady state.However, local and brief heating around the first transducer 31 in a first heating zone is limited to a small volume of the first sheath fluid 21, which is evacuated by the flow of the sheath fluid and does not modify the temperature of the sample fluid 20 or of the second sheath fluid 22. Fragile particles located in the sample fluid that one wishes to detect and sort are therefore not affected by this local and brief heating despite the proximity of the local heating source.

[0100] Sequentially, the first laser beam 41 is interrupted and a second laser beam 42 is applied to the second transducer 32. The second laser beam 42 is configured to be absorbed by the second transducer 32. The same laser source 50 can alternately generate the first laser beam 41 and the second laser beam 42. Alternatively, a laser source is used to generate the first laser beam 41 and, sequentially, another laser source to generate the second laser beam 42. The second laser beam 42 is focused on the second transducer 32 and has a wavelength capable of being absorbed by the second transducer 32. A single laser pulse or a series of laser pulses 42 is applied to heat the second transducer 32. In an example of the first embodiment, the second laser beam 42 passes through the microfluidic device 100 before being absorbed by the second transducer 32.Here too, the second laser beam 42 does not pass through the second sheath fluid 22 and is not absorbed directly by the sheath fluid. On the contrary, the energy of the second. pulsed laser beam 42 is focused and absorbed by the second transducer 32. Under this illumination, the second transducer 32 heats up and locally heats by contact the second sheath fluid 22 in a second heating zone. This local and brief heating of the second sheath fluid 22 modifies the viscosity of the second sheath fluid 22, which modifies the flow of the second sheath fluid 22 and consequently of the sample fluid 20. This local heating makes it possible to switch the orientation of the sample fluid 20 so that it then flows into the second outlet channel 12. The microfluidic device thus makes it possible to switch the sample fluid 20 on demand from the first outlet channel 11 to the second outlet channel 12 and vice versa.

[0101] By heating either the first transducer 31 or the second transducer 32, the microfluidic device 100 allows the output channel of the sample fluid to be controlled, as illustrated in FIG. 11.

[0102] By alternating sequential application of laser pulses to the transducers 31 and 32, the microfluidic device 100 makes it possible to extract a portion 120 of the sample fluid selectively towards the first outlet channel 11 and / or to extract another portion 220 of the sample fluid selectively towards the second outlet channel 12. The microfluidic device 100 of the present disclosure makes it possible to manipulate very small objects, for example nano-objects or fragile biological cells, without altering their integrity or viability. In addition, the microfluidic device 100 of the present disclosure makes it possible to achieve a switching or extraction frequency of at least 10 kHz, i.e. several orders of magnitude higher than the maximum frequency achieved by most prior microfluidic devices, in particular for the manipulation of nanoparticles.

[0103] Advantageously, the microfluidic system uses a particle detection signal from the detection unit 50 to trigger the heating of the first transducer 31 or the second transducer 32. Depending on whether or not the desired particles are detected, it is thus possible to extract a portion of the sample fluid to one or other of the output channels to carry out sorting according to the detected signal.

[0104] In the embodiment with three output channels, a detection signal is advantageously used which is capable of distinguishing two distinct categories of particles so as to direct a first category of particles corresponding to a first detection signal towards the first output channel 11, and to direct a second category of particles corresponding to a second detection signal towards the second output channel 12. In the absence of a detection signal, the sample fluid is directed, as in steady state, towards the third output channel 13, which corresponds to a discharge outlet. The particles of the first category are then collected via the outlet 8 while the particles of the second category are then collected via the outlet 9.

[0105] The device of the present disclosure has the advantage of making it possible to divide the sample fluid stream 20 into portions 120, 130, 220 without necessarily requiring prior encapsulation. Isolated sections of sample fluid flowing inside the sheath fluid are thus extracted. The isolated volume is generally less than a picoliter. In certain applications, the encapsulation step can be omitted for a substantial time saving.

[0106] The present disclosure uses a flow model in a shallow common channel approximation to model the operation of the microfluidic device. The flow axis in the common channel is parallel to the X axis of the orthonormal reference frame. The sample fluid 20 is for example made of water. The sheath fluids 21, 22 are made of the same mixture of water and glycerol. The viscosity of the sample fluid 20 and the sheath fluids 21, 22 is calculated from the publication Cheng N. -S. (Formula for viscosity of a glycerol-water mixture, Ind. Eng. Chem. Res., 47:3285-3288, 2008) to which the publication Volker and Kâhler (Density model for aqueous glycerol solutions, Experiments in Fluids, 75, 2018) made corrections to the volume model. We apply a flow rate of 20 pL.h 1 to the sample fluid 20 and an identical one of 50 pL.h 1to the first sheath fluid 21 and to the second sheath fluid 22. A no-slip condition is imposed on all the internal walls and the two branches of the Y junction form the two outlet channels 11, 12. Modeling based on a phase field method highlights the interface between the sample fluid and the sheath fluid. The The position of the interface is monitored by solving a transport equation. In addition, minimizing the mixing energy allows determining the interface movements. This model is based on the following system of equations.

[0107] [Math. 1]

[0112] Equation Mathl represents the conservation of momentum, equation Math2 the conservation of mass, equation Math3 the conservation of energy and equations Math4 and Math5 the phase field transport. The subscript j=l represents the sample fluid and the subscript j=2 represents the sheath fluid, pj represents the density of each fluid phase, Uj = (u XJ , u XJ ) represents the velocity field, pj the pressure, r|j the dynamic viscosity and e z the depth of the channels of the microfluidic chip; C PJ represents the heat capacity, Tj represents the temperature field, kj the conduction coefficient and Qj the source term, <kj est a phase field variable and j is an auxiliary phase field variable. The parameter λ = 3SG / 8 is the free energy density of the mixture and G is the interfacial tension between phases 1 (sample fluid) and 2 (sheath fluid).

[0113] Results of this modeling are illustrated in Figures 8 and 10. The interface between the sample fluid and the sheath fluid is shown in black line in Figures 8 to 10.

[0114] According to one mode of operation, one or more series of laser pulses 41 are applied only to the first transducer 31 to deflect the sample fluid selectively towards the first output channel 11. The series of laser pulses 41 are interrupted, then one or more other series of laser pulses 42 are applied only to the second transducer 32 to deflect the sample fluid selectively towards the second output channel 12.

[0115] According to another mode of operation, a single laser pulse 41 is applied for a short duration to the first transducer 31 to extract a portion 120 of the sample fluid and direct it towards the first outlet channel 11.

[0116] According to another example (figure 10), a sequence is applied comprising a first laser pulse 41 on the first transducer 31 and a second laser pulse 42 on the second transducer 32 to extract a portion 130 of the sample fluid towards the first outlet channel 11. For example, laser pulses each having a duration of 50 ps are applied, with a cycle duration of 100 ps (i.e. a duty cycle of 50%) and a repetition frequency of 10 4 Hz. Each laser pulse used to heat the sheath fluid on one side or the other has a total energy of 70 nJ. The distance P from the heating zone 31, respectively 32, to the beginning of the outlet channel 11, respectively 12, is 5 pm.

[0117] In such a two-pulse sequence, it has been found that adjusting the delay between the first laser pulse 41 and the second laser pulse 42, in an otherwise identical sequence, advantageously makes it possible to adjust the volume of the portion 130 of the extracted sample fluid. This method makes it easy to individually size the volume of each portion 130 of the extracted sample fluid.

[0118] Figure 11 shows a simulation of the sample fluid flow rate flowing in the first outlet channel 11 and respectively in the second outlet channel 12 as a function of time by applying a series of laser pulses 41, 42 alternating between the two heating zones 31, 32 at a frequency of 10 4Hz with the parameters indicated above. An oscillation of the sample fluid flow rate is observed in each outlet channel which corresponds to a deflection of the fluid jet with an amplitude of approximately ± 3 pm at the branch of the Y junction. A switching of the sample fluid between the two outlet channels is observed at the frequency of 10 4 Hz.

[0119] The oscillation frequency of the jet can reach several kHz, for example 2kHz, 4 kHz, or 10 kHz

[0120] A simulation of the sample fluid flow rate flowing in the first outlet channel 11 as a function of time was also carried out by applying a series of laser pulses 41 with the same parameters as above for a distance P between the heating zone 31 and the Y junction having different values, for example 10 pm and 25 pm respectively. A time shift is observed between the two flow rate curves. It is deduced from this that the position of the heating zone critically determines the switching of the sample fluid to the first outlet channel 11 or to the second outlet channel 12. This parameter P was not a priori identified as being critical for determining the outlet channel to which the portion 130 of fluid is extracted.

[0121] The simulation shows that the deflection of the sample fluid changes when the distance P varies, all other conditions remaining the same. For example, for a distance P equal to 5pm, it is observed in the above simulation that the sample fluid is deflected towards the outlet channel which is on the same side as the heating zone, with respect to the longitudinal axis 14. For a distance P equal to 10pm, it is observed by a simulation based on the above model that the sample fluid is deflected towards the outlet channel which is on the same side as the heating zone, with respect to the longitudinal axis 14. For a distance P equal to 25pm, it is observed by simulation that the sample fluid is deflected towards the outlet channel which is on the opposite side of the heating zone, with respect to the longitudinal axis 14.

[0122] Without being bound by a theory, the local heating of the sheath fluid in the part of the common channel where the sample fluid is hydrodynamically focused, just upstream of the junction of the outlet channels, creates a pinching or twisting effect of the sample fluid, which allows it to be oriented towards one or the other outlet channel. Depending on the distance P between the heating zone, the twisting of the sample fluid allows it to be diverted towards one outlet channel or the other outlet channel. In addition, this twisting effect allows the sample fluid to be sectioned into isolated sections selectively oriented towards one or the other outlet channel. Following the detection of a particle, it is thus possible to isolate a portion of the sample fluid containing this particle and to divert this portion of sample fluid containing the detected particle towards a specific outlet channel, where it will be analyzed.Particularly advantageously, the method of the present disclosure makes it possible to extract a volume of sample fluid containing one and only one detected particle and to divert this droplet towards a predetermined outlet channel (see figure 10). The microfluidic device and method of the present disclosure make it possible to guarantee high purity of the extracted fluid and of the nano-objects thus isolated.

[0123] The microfluidic device of the present disclosure does not heat the sheath fluid upstream of the inlet into the common channel or upstream of the detection system. On the contrary, the microfluidic device of the present disclosure heats the sheath fluid in the common channel, downstream of the detection system and upstream of the outlet channels. Since the heating is very localized in the sheath fluid, the sample fluid remains at a constant temperature. The proximity between the detection unit 50, the heating zones 31, 32 and the outlet channels 11, 12 makes it possible to very quickly switch the sample fluid from one outlet channel to another outlet channel while avoiding routing errors. A switching frequency of 2 kHz, 4 kHz, or 10 kHz can be achieved, which is several orders of magnitude above the microfluidic devices of the prior art.

[0124] The time sequence illustrated in Figure 11 is an example to illustrate a sequence consisting of heating alternations on a first transducer 31 and on a second transducer 32, with a repetition frequency. This model makes it possible to evaluate the operation of the device and to determine the maximum frequency at which it can operate. In practice, the sequences are generally not predetermined, but adapted in real time depending on the particles detected or not in the sample fluid.

[0125] An example of operation consists of extracting a portion of the fluid containing a detected particle via the detection module 50. In this case, an isolated heating switching sequence is applied between the first transducer 31 and the second transducer 32, as illustrated in FIG. 12. In FIG. 12, the power density applied by the laser beam 41 to the first photothermal transducer 31 and respectively by the laser beam 41 to the second transducer 32 as a function of time is shown on the two lower curves. In this example, it can be seen that the laser pulses are not applied simultaneously to the two photothermal transducers, but successively. The duration of each laser pulse is here of the order of 50 ps.In the two upper curves of Figure 12, the flow rate of the sample stream 120 extracted in the first outlet channel 11 and, respectively, the flow rate of the sample stream 220 extracted in the second outlet channel 12 are shown as a function of time. Before the application of the pulses, in steady state, the sample fluid stream flows in the second outlet channel 12. Immediately after the application of the two pulses, a very small volume of the sample stream 120 is extracted in the first outlet channel 11 for a short duration of the order of 100 ps. The steady state is then returned to.

[0126] Another example of operation consists of successively extracting two portions of the fluid, each containing a particle detected successively via the detection module 50. In this case, two successive heating switching sequences are applied between the first transducer 31 and the second transducer 32.

[0127] These different examples are therefore based on the application of a temporal and spatial sequence of localized heating pulses, to enable the extraction of a section, i.e. a small volume, adapted to the sample fluid to be analyzed.

[0128] In the case where a high concentration of objects (micro- or nano-objects) is suspended in the sample fluid 20, the present disclosure makes it possible to extract a volume (a section) as small as possible containing only one object per section. This separation into small volumes allows the objects to be counted one by one. The minimum volume that can be extracted is between 50 femtoliters and 1 picoliter depending on the flow rate of the sample fluid and the delay between the laser pulses on the first transducer 31 and the second transducer 32.

[0129] However, too small an extracted volume can be a source of error if the detected object is not included in this small volume of fluid. Adjusting the temporal and spatial sequence can make it possible to adjust the extracted volume to optimize sorting differently depending on the applications. For example, to extract a determined fraction towards an outlet channel, a first pulse is successively applied to the first transducer 31, a second pulse to the second transducer and a final pulse again to the first transducer 31. Such a sequence makes it possible to avoid smears due to small residues of sample fluid, resulting from a simple sequence with the first two pulses, and which can be directed in an uncontrolled manner towards one or the other outlet. Other more complex sequences allow multi-criteria sorting.

[0130] The use of several heating zones 31 or 32 in the common channel, possibly supplemented by the use of auxiliary heating zones 33, 34 at the input of the output channels allows further adjustments of the time sequence of heating pulses both spatially and temporally.

[0131] According to a variant, the microfluidic device comprises a plurality of heating zones 31, respectively 32, arranged on one side of the common channel 4 following one another in the direction of the flow of the fluids, in other words in the direction of the longitudinal axis 14. This configuration makes it possible to apply a determined sequence of laser pulses to the successive heating zones 31 and / or respectively 32, following the flow of the fluid. This makes it possible to obtain a greater and adjustable deviation of the sample fluid towards more than two outlet channels and allows multi-criteria sorting.

[0132] Optionally, the microfluidic device comprises one or a plurality of heating zones 33, respectively 34, arranged on one side of the first, respectively second, outlet channel 11, respectively 12. This configuration allows to apply a determined sequence of laser pulses to the plurality of heating zones 33 and / or respectively 34 which makes it possible, for example, to optimize a multi-criteria sorting

[0133] The microfluidic device, system and method of the present disclosure makes it possible to sort objects in a fluid, in particular micro-objects or even nano-objects with dimensions less than 10 nm.

[0134] The present disclosure finds applications in biology (sorting of nanometric-sized objects), in physics (granulometry) or in chemistry (purification of nanometric probes).

[0135] Of course, various other modifications may be made to the invention within the scope of the appended claims.

Claims

Claims: A microfluidic device (100) comprising at least one sheath fluid inlet channel (1, 2) and one sample fluid inlet channel (3), at least two outlet channels (11, 12, 13), and a common channel (4) disposed between said inlet channels (1, 2, 3) and said outlet channels (11, 12, 13), the common channel (4) being fluidically connected to said inlet and outlet channels (1, 2, 3, 11, 12, 13), the sample fluid inlet channel (3) being capable of injecting a sample fluid (20) into the common channel (4), and at least one sheath fluid inlet channel (1, 2) being capable of injecting at least one sheath fluid (21, 22) into the common channel (4) so ​​as to allow hydrodynamic focusing of the sample fluid (20) into the common channel. (4), the common channel (4) being configured to conduct the hydrodynamically focused sample fluid (20) and at least one sheath fluid (21, 22) towards said at least two outlet channels (11, 12, 13),characterized in that the microfluidic device comprises heating means including an energy source (40) and at least one transducer, the heating means being arranged to transmit over a short period a quantity of heat localized in said at least one sheath fluid flow (21, 22) in the common channel (4) upstream of a branch between said at least two outlet channels (11, 12, 13), the heating means being capable of locally heating said at least one sheath fluid flow (21, 22) in the common channel (4) and in that said at least one sheath fluid has a thermal viscosity variation adapted to deflect or extract a portion (120, 130, 220) of the sample fluid selectively towards a determined outlet channel among the at least two outlet channels (11, 12, 13). Microfluidic device (100) according to claim 1 in which the at least one inlet channel (1,2) Sheath fluid comprises a first inlet channel (1) and a second inlet channel (2), the first inlet channel (1) being capable of injecting a first sheath fluid (21) and the second inlet channel (2) being capable of injecting a second sheath fluid (22). Microfluidic device (100) according to claim 1 or 2 in which the heating means comprise at least one photothermal transducer (31, 32) and the energy source comprises a laser source configured to generate a laser beam (41, 42) focused on said at least one photothermal transducer (31, 32), said at least one, A photothermal transducer (31, 32) capable of absorbing the laser beam (41, 42) and transmitting the heat induced by the laser beam (41, 42) to at least one sheath fluid flow (21, 22) by conduction. A microfluidic device (100) according to claims 2 and 3, wherein said at least one photothermal transducer (31, 32) comprises at least a first photothermal transducer (31) and at least a second photothermal transducer (32), said at least one first photothermal transducer (31) and, respectively, said at least one second photothermal transducer (32) being capable of sequentially absorbing the laser beam (41, 42), so as to modify the flow rate of the first sheath fluid (21) and, respectively, of the second sheath fluid (22) to extract said portion (130) of the sample fluid.A microfluidic device (100) according to claim 4, wherein said at least one first photothermal transducer (31) comprises a plurality of photothermal transducers arranged on one side of the common channel (4) and / or wherein said at least one second photothermal transducer (32) comprises a plurality of photothermal transducers arranged on another side of the common channel (4) with respect to a longitudinal axis (14) of the common channel. A microfluidic device (100) according to any one of claims 3 to 5, wherein the heating means comprise at least one third photothermal transducer (33) arranged on one side of the first outlet channel and / or at least one fourth photothermal transducer (34) arranged on one side of the second outlet channel (12).A microfluidic device (100) according to any one of claims 1 to 6, wherein the heating means comprise a laser source configured to generate a focused laser beam in the hydrodynamic sheath inside the common channel (4), and wherein the sheath fluid is capable of absorbing the laser beam and converting it into heat. A microfluidic device (100) according to any one of claims 3 to 7, wherein the laser source is adapted to emit a laser pulse (41, 42) having an energy between 10 nJ and 10PJ over a short duration of 50 ps or less. A microfluidic device (100) according to any one of claims 1 to 8, wherein the heating means comprise at least one electro-thermal transducer (31, 32) capable of locally heating the hydrodynamic sheath. A microfluidic device (100) according to any one of claims 1 to 9, further comprising a thermoelectric module capable of modifying the temperature of either the entire microfluidic device (100) or the sample fluid (20) and / or at least one sheath fluid (21, 22) upstream of the heating means. A microfluidic device (100) according to any one of claims 1 to 10, wherein at least one sheath fluid (21, 22) has, at a temperature of 20°C, a viscosity between 2 mPa·s and 30,000 mPa·s and a thermal viscosity variation between 0.2 mPa·s and K. 1 and 3000 mPa·s K 1A microfluidic device (100) according to claim 11, wherein at least one sheath fluid (21, 22) comprises propylene glycol, linseed oil, or a mixture containing water and glycerol, or a mixture of water and carbohydrates. A microfluidic system (200) comprising a microfluidic device (100) according to any one of claims 1 to 12 and comprising a detection module (50) disposed upstream of the heating means, the detection module (50) being configured to detect at least one signal representative of a nanoparticle in the sample fluid (20) hydrodynamically focused in the common channel (4), and feedback means on the heating means based on the detected signal.A microfluidic manipulation method comprising the following steps: (a) injecting a sample fluid (20) into a common channel (4) of a microfluidic device; (b) injecting at least one sheath fluid (21, 22) into the common channel (4) to enable hydrodynamic focusing of the sample fluid (20) into the common channel (4); (c) applying an energy source for a short time to at least one transducer (31, 32) capable of transmitting a quantity of heat localized into the at least one sheath fluid (21, 22) in the common channel (4) upstream of a branch between said at least two outlet channels (11, 12, 13), the heating means being capable of locally heating said at least one sheath fluid flow (21, 22) in the common channel (4) and the at least one sheath fluid (21, 22) exhibiting a thermal variation in viscosity. adapted to divert or extract a portion (120, 130, 220) of the sample fluid selectively to a specified outlet channel among at least two outlet channels (11, 12, 13).A microfluidic manipulation method according to claim 14, wherein step c) comprises a time sequence of steps c1) and c2), a delay between step c1) and step c2) being adjusted to control the volume of the portion (130) of the extracted sample fluid, wherein step c1) comprises applying the energy source for a short time to a first transducer (31) disposed on one side of the common channel (4) so ​​as to transmit to said at least one sheath fluid (21) in the common channel (4) a first quantity of localized heat, and wherein step c2) comprises applying the energy source for another short time to a second transducer (32) disposed on another side of the common channel (4) with respect to a longitudinal axis (14) of the common channel so as to transmit to said at least one sheath fluid in the common channel (4) a second quantity of localized heat.

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