Microfluidic processing method and device based on a thermal adhesive liquid

Abstract

The invention relates to a microfluidic processing device and method comprising the steps of: (a) injecting a sample liquid (20) into a common channel (4) of a microfluidic device; (b) injecting at least one protective liquid (21, 22) into the common channel (4), the at least one protective liquid comprising a thermotough liquid having a dynamic viscosity of less than 0.1 Pa.s at a defined injection temperature. According to the invention, the method comprises the step (c) of applying an energy source to at least one heating zone (31) upstream of a branch of the common channel (4) located between a first outlet channel (11) and a second outlet channel (12) for a limited duration of less than or equal to 10 ms, in order to locally heat said protective liquid (21, 22) having a dynamic viscosity of greater than or equal to 1.0 Pa.s to a high temperature Th and to extract a portion (120, 130, 220) of the sample liquid.

Description

Technical Field

[0001] This invention relates to the technical field of microfluidic processing devices and methods for rapidly controlling and changing the direction of liquid flow. The invention can be applied to precise, high-speed liquid processing or the extraction of extremely small volumes of substances from liquids. Particularly, this invention relates to the processing and sorting of individual nanoscale particles in liquids. Background Technology

[0002] In the aforementioned fields, it is known to use flow cytometry to detect, count, and identify micron-sized cells or particles suspended in flowing liquids. Specifically, this involves passing cells or particles one by one at high speed through one or more laser beams, followed by sorting the cells or particles using a sorting method based on various technologies.

[0003] Advances in microscopy and biology have enabled the detection of smaller objects, especially nano-objects smaller than 100 nm.

[0004] Conventional flow cytometers can only function properly for objects larger than micrometers. For nanoscale objects (e.g., smaller than 100 nm), the detection capabilities of current flow cytometers are limited. Furthermore, for sorting nanoscale objects, the liquid volume typically used in cell sorters, as well as the droplet size used to encapsulate the objects to be sorted, are incompatible with the sorting of nanoscale objects.

[0005] There are various methods for sorting objects in microfluidic chips. Some sorting methods are based on passive techniques. These methods can be based on inertial focusing methods or the chip's own structure: this allows objects to be separated into subgroups based on their physical properties (volume, mass, etc.). Other passive sorting methods are based on micron-scale columnar microfabrication, which can perform on-chip chromatography analysis, but are only suitable for micron-scale objects or micron-length polydisperse polymer chains. These passive sorting methods cannot sort objects one by one based on specific signals (such as fluorescence).

[0006] Micromechanical technology can sort objects with a size of micrometers at a relatively low sorting rate. Therefore, using valves to separate cells (such as eukaryotic or prokaryotic cells) cannot achieve a sorting rate exceeding 1 Hz.

[0007] Other active sorting techniques are based on the application of electric or magnetic fields. For example, applications of dielectrophoresis or surface acoustic waves can achieve sorting rates in the kHz range for prefabricated micrometer-sized droplets that encapsulate individual objects.

[0008] Microbial analysis of target nanoscale objects is particularly challenging because these objects are present within the sample liquid, which typically contains a large number of other objects from which the target nanoscale object must be separated. Therefore, to obtain only the target nanoscale object, an extremely small volume of sample liquid must be drawn each time an attempt is made to separate it from other objects. Furthermore, the same sample liquid may contain different types of nanoscale objects that need to be separated from each other. Additionally, to analyze these nanoscale objects, the concentration of specific types of nanoscale objects in the liquid needs to be increased. Given the extremely small size of nanoscale objects, a sufficient quantity needs to be extracted for subsequent analyses, such as proteomics analysis. It is currently estimated that approximately 10⁸ target nanoscale objects are required for proteomics analysis. To sort this number of nanoscale objects within a reasonable timeframe (e.g., on the order of 3 hours), a sorting rate of approximately 10⁴ nanoscale objects per second (i.e., 10 kHz) is required. Therefore, the sorting frequency is a key criterion for making nanoscale object sorting practical.

[0009] The purpose of this disclosure is to provide a microfluidic processing apparatus and method capable of sorting nanoscale objects in liquids at a high sorting frequency (e.g., above 1 kHz, preferably at least 10 kHz) without the risk of degradation of the nanoscale objects processed in this way.

[0010] One of the objectives of this disclosure is to provide a microfluidic processing apparatus and method with a faster time response, capable of extracting extremely small volumes of liquid samples ranging from a few to hundreds of femtoliters, or capable of sorting individual objects at a higher sorting frequency than in the prior art.

[0011] Another object of this disclosure is to provide a microfluidic processing apparatus and method for selectively extracting nanoscale objects from an initial sample liquid to obtain a new liquid sample, wherein the concentration of these nanoscale objects is higher than the concentration in the initial sample liquid and / or wherein the number of these nanoscale objects is sufficiently high, for example, higher than 10⁸.

[0012] Another object of this disclosure is to provide a microfluidic processing apparatus and method for rapidly obtaining sample liquids enriched with selected nanoscale objects. Summary of the Invention

[0013] To overcome the aforementioned deficiencies of the prior art, the present invention provides a microfluidic processing method comprising the following steps: (a) injecting a sample liquid into a common channel of a microfluidic device through an inlet channel; (b) injecting at least one protective liquid (or at least one stream) into the common channel through at least one other inlet channel at a determined injection temperature, so that the sample liquid undergoes hydrodynamic focusing in the common channel and flows towards a first outlet channel, the first outlet channel being located downstream of a branch between the first outlet channel and a second outlet channel, wherein the at least one protective liquid comprises a thermoviscous liquid, and the at least one protective liquid comprising a thermoviscous liquid has a dynamic viscosity of less than 0.1 Pa·s at the injection temperature.

[0014] According to the present invention, the method includes the following steps: (c) applying an energy source to a heating zone in a common channel upstream of a branch between a first outlet channel and a second outlet channel for a duration less than or equal to 10 ms, preferably less than 5 ms, 1 ms, 500 μs or even 1 μs, the heating zone being positioned in or in contact with at least one protective liquid comprising a thermoviscous liquid, so as to locally heat the at least one protective liquid to a high temperature Th in the heating zone of the common channel, the temperature difference between the injection temperature and the high temperature Th being less than or equal to 40°C, and at the high temperature Th, the dynamic viscosity of the at least one protective liquid comprising a thermoviscous liquid being greater than or equal to 1.0 Pa·s, thereby selectively diverting or extracting a portion of the sample liquid to the second outlet channel.

[0015] Advantageously, the at least one protective liquid, comprising a thermoviscous liquid, undergoes a thermoviscous change between the injection temperature and a high temperature after local heating in the heating zone. This thermoviscous change is adapted to selectively divert or extract a portion of the sample liquid to a designated outlet channel in at least two outlet channels.

[0016] This method is configured to avoid generating one or more bubbles, avoid heating the sample liquid, and avoid heating the entire cross-section of the protective liquid. Notably, the brief, localized heating of the protective liquid does not cause fluid blockage in the common channel or any outlet branches; it only creates a limited spatial disturbance to the fluid and its distribution within the common channel over time. This disturbance induces dynamic changes in the fluid downstream of the heated zone without interrupting the flow, which, unlike existing techniques, makes it possible to achieve a rapid and localized diversion effect on the sample liquid.

[0017] Because the branch between the two outlet channels is pointed, the viscosity disturbance of the protective fluid causes the sample liquid to deflect towards the first outlet channel. Once heating is interrupted, the viscous heating zone is carried away by the fluid, and the temperature quickly returns to the injection temperature.

[0018] Advantageously, the temperature difference between the injection temperature and the high temperature is less than or equal to 40°C, 30°C, 20°C, or even 10°C.

[0019] This method enables the transfer or extraction of extremely small portions of a sample liquid, ranging in volume from 1 to 900 fettoliters, for example, on the order of approximately 10 to 100 fettoliters. This method may be able to process and sort single cells or nanoscale particles suspended in a sample liquid. Furthermore, this method is capable of sorting at a much higher rate compared to existing methods.

[0020] According to a particular and advantageous aspect, thermoviscous protective fluids include thermosensitive polymers.

[0021] Advantageously, the protective fluid comprises 1% to 30% of the thermosensitive polymer by weight.

[0022] In one example, the thermosensitive polymer includes at least one thermosensitive polyoxyethylene linear chain, at least one end of which is connected to an organic group via a urethane bond or ester bond to extend the chain length.

[0023] In another example, the thermosensitive polymer comprises, on the one hand, a water-soluble unit and on the other hand, a unit selected from polyurethanes containing poly(ethylene oxide-b-propylene oxide-b-ethylene oxide)(POE-b-POP-b-POE) groups, wherein the mass concentration of the unit in the aqueous solution is less than or equal to 10%.

[0024] According to the first embodiment, the method further includes the following steps after step (c): (d) For a limited duration, another energy source is applied to a second heating zone in a common channel located upstream of the branch between the first and second outlet channels, for a duration less than or equal to 10 ms; the second heating zone is positioned in or in contact with at least one protective liquid comprising a thermoviscous liquid to locally heat the at least one protective liquid in the second heating zone of the common channel to a high temperature Th, thereby restoring the flow of the sample liquid to the first outlet channel.

[0025] Advantageously, the duration of the interval between step d) and step c) is less than or equal to 500 μs.

[0026] According to a particular and advantageous aspect, the energy source for step c) includes a laser that emits a first laser pulse with a wavelength between 100 nm and 10 μm.

[0027] According to another specific aspect, another energy source in step d) includes a laser that emits a second laser pulse with a wavelength between 100 nm and 10 μm.

[0028] Advantageously, the protective liquid, including the thermoviscous liquid, is capable of absorbing the first laser pulse and / or the second laser pulse.

[0029] For example, the protective fluid includes components suspended or dissolved therein that are capable of absorbing the first laser pulse and / or the second laser pulse.

[0030] According to another specific and advantageous aspect, the heating zone or the second heating zone each includes a photothermal transducer.

[0031] According to another specific and advantageous aspect, the first heating zone or the second heating zone each includes an electrothermal transducer, and the energy source for step c) or step d) includes various types of electrical energy.

[0032] Preferably, the high temperature Th is less than or equal to 60°C, 50°C, 40°C, 35°C, or 30°C.

[0033] At least one protective fluid exhibits a dynamic viscosity that increases with increasing temperature within a defined temperature range greater than or equal to the injection temperature.

[0034] The temperature range is determined to extend approximately 10 degrees above the injection temperature, or 15, 20, 25, or even 30, 35, or 40 degrees.

[0035] According to a specific aspect, within a defined temperature range, the maximum value of the thermodynamic viscosity change is greater than or equal to 3 Pa·sK. -1 (or equivalent to 3 Pa·sC) -1 (where C represents temperature in degrees Celsius), or 5 Pa·sK. -1 Even 7Pa.sK -1 .

[0036] Advantageously, the sample liquid does not include hot viscous liquids.

[0037] The present invention also relates to a microfluidic device comprising: a sample liquid inlet channel, at least one other protective liquid inlet channel, a first outlet channel, a second outlet channel, and a common channel disposed between the inlet channel and the outlet channel, the common channel being in fluid communication with the inlet channel and the outlet channel; a branch that separates the first outlet channel and the second outlet channel downstream; the sample liquid inlet channel containing sample liquid injected into the common channel, the at least one other protective liquid inlet channel containing at least one protective liquid injected into the common channel at a defined injection temperature, the at least one protective liquid comprising a thermoviscous liquid; the at least one protective liquid comprising a thermoviscous liquid having a dynamic viscosity of less than 0.1 Pa·s at the injection temperature, thereby allowing the sample liquid to be hydrodynamically focused in the common channel, the microfluidic device being configured to guide the sample liquid in the common channel after being hydrodynamically focused by at least one protective liquid at the injection temperature to the first outlet channel.

[0038] According to the present invention, a microfluidic device includes a heating element comprising an energy source and at least one heating zone located in a common channel upstream of a branch between a first outlet channel and a second outlet channel. The at least one heating zone is positioned in or in contact with at least one protective liquid comprising a thermoviscous liquid. The heating element is configured to apply the energy source in the at least one heating zone for a defined duration of less than or equal to 10 ms, thereby locally heating the at least one protective liquid in the common channel to a high temperature Th in the at least one heating zone, wherein the temperature difference between the injection temperature and the high temperature is less than or equal to 40°C, and preferably less than or equal to 30°C, 20°C, or even 10°C, and the dynamic viscosity of the at least one protective liquid comprising a thermoviscous liquid at the high temperature Th is greater than or equal to 1.0 Pa·s, thereby selectively diverting or extracting a portion of the sample liquid to the second outlet channel.

[0039] According to a particular and advantageous aspect, the energy source includes a pulsed laser capable of generating pulses with pulse energies between 10 nJ and 10,000 nJ, for example, on the order of approximately 100 nJ.

[0040] Of course, different features, variations and embodiments of the present invention can be combined with each other in various ways, as long as they do not contradict or exclude each other. Attached Figure Description

[0041] Furthermore, various other features of the invention will become apparent from the following description with reference to the accompanying drawings, which illustrate non-limiting embodiments of the invention, wherein: Figure 1 This is a schematic diagram of the microfluidic device and method according to the present disclosure; Figure 2 The example shows the solid line curve of viscosity versus temperature and the dashed line curve of viscosity versus temperature for a sheath flow fluid based on a thermoviscous liquid. Figure 3 A first embodiment of a method based on the application of two energy pulses is shown, which cause a continuous increase in temperature of the sheath fluid; the application of the first pulse is shown here. Figure 4 The first embodiment is shown, immediately after the second pulse is applied; Figure 5 The first embodiment is shown, along with the extraction of a portion of the sample liquid into an outlet channel; Figure 6 The first embodiment is shown, along with the extraction of a portion of the sample liquid into an outlet channel; Figure 7 A second embodiment of the method based on applying a single pulse is shown, during which; Figure 8 The second embodiment is shown, illustrating the extraction of a portion of the sample liquid into the output channel after the pulse ends. Detailed Implementation

[0042] In this document, hot viscous liquids refer to liquids whose viscosity increases significantly and reversibly with temperature.

[0043] Figure 1 A microfluidic device 100 according to an exemplary embodiment of the present disclosure is shown. The microfluidic device 100 is generally a planar device commonly referred to as a microfluidic chip. Figure 1 The plane represents an orthogonal standard XY coordinate system.

[0044] The microfluidic device 100 includes inlet channels 1, 2, and 3, a common channel 4, and at least two outlet channels 11 and 12. Inlet channels 1 and 2 are each in communication with a source fluid of a protective liquid, which may be stored, for example, in a common container or two separate containers. Inlet channel 3 is in communication with a source fluid of the sample liquid 20 to be analyzed, which may be stored, for example, in another container. A connector (e.g., a Y-connector) is provided at the other end of the common channel 4, which includes at least a first outlet channel 11 and a second outlet channel 12, arranged approximately symmetrically with respect to the longitudinal axis 14 of the common channel 4. Here, the longitudinal axis 14 is parallel to the X-axis of the XY coordinate system. A branch (here, a pointed branch) separates the first outlet channel 11 from the second outlet channel 12. The acute angle formed by the tip of the branch is typically between 5 and 40 degrees. In another variation, the microfluidic device includes three outlet channels: a first outlet channel located on the longitudinal axis 14 of the common channel, a second outlet channel located on one side of the common channel, and a third outlet channel located on the other side of the common channel. In another variation, the microfluidic device includes more than three outlet channels. In these variations, each pair of adjacent outlet channels is separated by a branch.

[0045] In known methods, the microfluidic device 100 is made of, for example, glass, ceramic, or silicon, or a polymer (such as polydimethylsiloxane (PDMS)). The microfluidic device can be manufactured integrally or by assembling a support block and a strip forming a cap. The support is made of, for example, PDMS. Channels 1, 2, 3, 4, 11, and 12 can be molded, for example, during the manufacturing of the support. For example, the support has dimensions of 5 mm thickness and side lengths of 20 to 40 mm. The strip forming the cap is preferably transparent to allow observation and detection of particles in the sample liquid. For example, the strip is a microscope slide to allow observation of the microfluidic device 100 under an optical microscope lens. For example, an extremely thin glass strip with a thickness of 0.15 mm can be used.

[0046] W represents the width of common passage 4, H represents the depth of common passage 4, and L represents the length of common passage 4. For example, in Figure 1 In the microfluidic device shown, the width W of the common channel is 25 μm, the depth H of the common channel is 7 μm, and the length L is approximately 100 μm. The distance G between the starting end of the outlet channels 11 and 12 and the end of the branch of the Y-shaped connector is between 10 μm and 30 μm.

[0047] In one variant, the microfluidic device is rotationally symmetrical about its longitudinal axis. In this case, a single protective fluid inlet channel can be used.

[0048] Sample liquid 20 is composed, for example, of water or phosphate-buffered saline (PBS), in which micron or nano-sized objects to be sorted and processed are suspended. Sample liquid 20 may contain particles to be sorted, extracted, and / or concentrated.

[0049] The sample liquid 20 and the protective liquids (one or more) 21, 22 may or may not be miscible with each other. Typically, the first protective liquid 21 and the second protective liquid 22 are identical. Advantageously, in this case, the first protective liquid 21 and the second protective liquid 22 are stored in a single source container. An electric injector (commonly referred to as an "injection pump") or a pressure generator-based system can be used to inject the sample liquid 20 and the protective liquids (one or more) 21, 22 into the microfluidic device 100, respectively. The electric injector controls the flow rate of the injector, while the pressure generator-based system controls the injection pressure.

[0050] Simultaneously, the first protective liquid 21 is injected through inlet channel 1, the second protective liquid 22 is injected through inlet channel 2, and the sample liquid 20 is injected through inlet channel 3. The first protective liquid 21 and / or the second protective liquid 22 are injected into the common channel 4 at a determined injection temperature. For example, the injection temperature is equal to the ambient temperature, which may be 18°C, 19°C, 20°C, 22°C, or 25°C.

[0051] Inlet channel 3, along with inlet channels 1 and 2, directs the sample liquid 20 and protective fluids (one or more) 21 and 22 to a common channel 4, where the sample liquid 20 undergoes hydrodynamic focusing. Based on the ratio between the flow rate of the sample liquid and the total flow rate of the protective fluid, the sample liquid 20 achieves a reduced width D relative to the width W through hydrodynamic focusing in the common channel 4. For example, this can result in a flow of sample liquid 20 with a reduced width D between 2 μm and 7 μm. At the outlet of the common channel, when sorting is not in progress, the flow of sample liquid 20 continues to one or the other of outlet channels 11 and 12.

[0052] The microfluidic device 100 includes a detection unit 50 disposed in a common channel 4. The detection unit 50 is based, for example, on a system for detecting one or more fluorescent signals emitted by particles passing through the common channel 4, the particles being detected being labeled with one or more fluorescent markers. The particles labeled with fluorescent markers are, for example, particles included in a sample liquid, to be sorted, or extracted. For example, fluorescence is measured at one or more wavelengths, and sorting is initiated when a fluorescence signal including a predetermined combination of these wavelengths is detected. The detection unit 50 may also be based on particle size measurement by scattering one or more incident laser beams onto the particles, or by combining several optical or electrical methods to perform particle size measurement.

[0053] The microfluidic device 100 includes at least a first heating zone 31 located in the common channel 4, downstream of the detection unit 50. For example, Figure 1 Two heating zones 31 and 32 are shown, which are disposed in the common channel 4 and located upstream of the outlet channels 11 and 12. The first heating zone 31 is located on the same side of the microfluidic device 100 as the inlet channel 1 and the first outlet channel 11. The second heating zone 32 is located on the same side of the microfluidic device 100 as the inlet channel 2 and the second outlet channel 12. Laser beams 41 and 42, respectively focused on the first heating zone 31 and the second heating zone 32, can locally heat the protective liquid 21 and the protective liquid 22, respectively. Figure 1 In the plane, each heating zone 31, 32 extends within a finite area, for example, in the shape of a disk, square, or rectangle. Specifically, each heating zone 31, 32 is laterally restricted along the Y-axis of the XY coordinate system such that its width is less than the width of the first protective liquid 21 and the second protective liquid 22, respectively. Advantageously, the width of each heating zone 31, 32 is less than or equal to 35%, 25%, 20%, or 10% of the width W. In the example above, the width W is 25 μm, and the width of each heating zone 31, 32 is approximately 6 μm.

[0054] The first heating zone 31 and the second heating zone 32 are located at distances D1 and D2 from the detection unit 50, respectively. The first heating zone 31 and the second heating zone 32 are located at distances P1 and P2 from the ends of the branches of the Y-shaped connector separating the first outlet channel 11 and the second outlet channel 12, respectively. For example, distances D1 (and D2) are between 1 μm and 10 μm, and distances P1 (and P2) are between 0 μm and 20 μm.

[0055] According to one variation, the two heating zones 31 and 32 are located in a common channel 4, and on the same side of the microfluidic device 100 as the inlet channel 1 and the first outlet channel 11. In this case, the first heating zone 31 is located upstream of the second heating zone 32.

[0056] The microfluidic device 100 is typically planar. However, in another exemplary embodiment, the inlet channel 3, common channel 4, first outlet channel 11, and portions connected to the protective liquid inlet channel 1 and second outlet channel 12 of the sample liquid 20 are rotatable about a longitudinal axis 14. Alternatively, the rotationally symmetric inlet channel can be combined with the planar geometry of the common and outlet channels. In this variation, the microfluidic device 100 includes a single protective liquid inlet channel, or two or more protective liquid inlet channels. According to another variation, the inlet channel and the planar geometry of the common channel can be combined with the rotationally symmetric outlet channel.

[0057] According to this disclosure, a protective liquid with specific viscosity-varying characteristics that change with temperature is used. More specifically, at least one protective liquid 21 and / or 22, including hot-viscosity liquids, is used.

[0058] The viscosity of hot-viscosity fluids increases significantly and reversibly with temperature. The initial viscosity of a hot-viscosity liquid at its injection temperature (e.g., ambient temperature) is preferably close to that of water, and its viscosity increases with increasing temperature. Conversely, when the temperature of a hot-viscosity liquid decreases and returns to ambient temperature, its viscosity decreases, returning to its initial value.

[0059] Protective liquids 21 and 22 include, for example, mixtures based on water and thermosensitive polymers, or thermosensitive polymer-based thermoreversible hydrogels. Thermosensitive polymers are, for example, composed of thermosensitive hydrophobic segments of polypropylene oxide (PPO) and hydrophilic segments of polyethylene oxide (POE). Such thermosensitive polymers are used in cosmetics.

[0060] In one example, the thermosensitive polymer includes at least one thermosensitive polyoxyethylene linear chain, at least one end of which is connected to an organic group via a urethane bond or ester bond to extend the chain length, as described in Polymerexpert's patent document FR2840907, and the product is suitable for the cosmetics field.

[0061] In another example, the thermosensitive polymer comprises, on the one hand, a water-soluble unit and on the other hand, a unit selected from polyurethanes containing poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) (POE-b-POP-b-POE) groups, wherein the mass concentration of the unit in the aqueous solution is less than or equal to 10%, as described in Polymerexpert's patent document FR2940761. This thermosensitive polymer is suitable for preparing formulations for treating and / or preventing snoring and capable of being administered via nasal or oral spray.

[0062] The hot viscous liquid is prepared, for example, by dissolving a heat-sensitive polymer in an aqueous solution (e.g., water), and one or more additives that can adjust the viscosity characteristics of the hot viscous liquid may optionally be added to the aqueous solution.

[0063] For example, a protective solution comprising 5% by weight of a thermosensitive polymer diluted in pure water can be used. Advantageously, the protective solution includes about 2% by weight of a substance with high absorption for laser wavelengths, such as ink, dye, or pigment, to absorb the laser beam. Preferably, a food-grade, biocompatible black ink is used. Alternatively, carbon nanoparticles (e.g., nanoparticles with a size of about 90 nm) are suspended in the protective solution.

[0064] These types of thermoviscous liquids are characterized by: low viscosity at ambient temperature, less than or equal to 100 mPa·s, even less than or equal to 40 mPa·s, for example, between 10 mPa·s and 30 mPa·s (and even less than 10 mPa·s in some physicochemical configurations); and viscosity increasing over a specific temperature range above or equal to ambient temperature, reaching a maximum of 1.0 Pa·s, several Pa·s, or even tens of Pa·s at approximately 37°C ± 10°C. This results in a viscosity change with temperature, with the maximum viscosity change reaching 1 Pa·s / K or several Pa·s / K, for example, 5 Pa·s / K or 10 Pa·s / K, within a narrow temperature range above ambient temperature.

[0065] The minimum viscosity value, maximum viscosity value, change in thermal viscosity value, and the temperature corresponding to the maximum viscosity value depend on the selected hot viscous liquid, its mass concentration in water, and optional additives (one or more) incorporated into the protective liquid.

[0066] Within a defined temperature range starting from the injection temperature of the microfluidic chip, the dynamic viscosity of the thermoviscous liquid increases with increasing temperature. The injection temperature is between 5°C and 30°C, preferably between 15°C and 25°C, and more preferably between 18°C ​​and 22°C. Advantageously, the injection temperature is equal to the ambient temperature, which is 18°C, 19°C, 20°C, 21°C, 22°C, 23°C, 24°C, or 25°C.

[0067] For example, thermosensitive protective solutions 21 and 22 are used, comprising a thermosensitive polymer from PolymerExpert, trade name EG230 (CAS No. 93665-35-1). EG230 is a branched polyurethane containing POE-b-POP-b-POE units, and its INCI (International Cosmetic Ingredient Nomenclature) designation is methoxy PEG-13 PEG-502 / PPG-57 SMDI copolymer. The weight percentage of the thermosensitive polymer in the protective solution is between 0.5% and 10%, preferably between 1% and 7.5%, for example, 5%, 6%, or 7.5%, and the thermosensitive polymer is diluted in pure water.

[0068] Figure 2 The graph shows the viscosity V (solid line) as a function of temperature for a protective solution based on the thermosensitive polymer EG230 diluted in water at a concentration of 7.5%, between 12°C and 50°C, along with the viscosity change. V / The curve T (dashed line) represents the change in viscosity with temperature. It can be observed that, unlike conventional protective fluids, the viscosity V of the protective fluid, including this thermoviscous liquid, continuously increases with increasing temperature from 12°C to approximately 45°C. Furthermore, the viscosity value is very low below 22°C, approximately 0.02 Pa·s. Finally, in this example, the maximum viscosity value is very high: this maximum value reaches approximately 35 Pa·s at a temperature of 46°C. When the temperature is above 46°C, the viscosity continues to decrease, but still remains at a relatively high value; for example, the viscosity is approximately 28 Pa·s at 50°C.

[0069] It can be observed that the protective liquid, including thermoviscous liquids based on thermosensitive polymers, exhibits a positive slope in its viscosity change, particularly pronounced in the low-temperature range of approximately 25°C to 40°C. This slope is approximately 0.3 Pa·s / K near 30°C, approximately 1.0 Pa·s / K near 33°C, approximately 2.0 Pa·s / K near 36°C, and approximately 4.0 Pa·s / K near 40°C. In other words, the maximum slope of the viscosity change curve in this example is 4.0 Pa·s / K. Above 46°C, the slope of the viscosity change for the protective liquids, including thermoviscous liquids, becomes negative.

[0070] In another example, a protective solution comprising a thermosensitive polymer diluted in pure water was used. The protective solution has extremely low viscosity (less than or equal to 0.04 mPa·s) at temperatures below or equal to 20°C, and its viscosity increases significantly between 20°C and 40°C with a positive slope exceeding 10 Pa·s / K. At 35°C, the viscosity of the protective solution is approximately 5000 mPa·s. At 40°C, the viscosity is approximately 18000 mPa·s. Above 40°C, the viscosity of the protective solution decreases with increasing temperature.

[0071] It can be observed that, relative to an ambient temperature of approximately 20°C, even a small increase in temperature on the order of 10°C, 15°C, 20°C, or 30°C is sufficient to significantly increase the viscosity of the thermoviscosity-based protective fluid.

[0072] Furthermore, this protective fluid is thermally reversible. Therefore, the viscosity change is reversible. Based on the 7.5% thermosensitive polymer EG230, the viscosity of the thermoviscous protective fluid can be reduced from about 20 Pa·s (at 40°C) to less than or equal to 0.04 mPa·s (at 20°C) when the temperature is reduced from 40°C to 20°C.

[0073] According to this disclosure, the sample liquid typically consists of nanoscale cells or particles suspended in a generally aqueous liquid. The sample liquid comprises a medium adapted to the delivered particles, which may be pure water, phosphate-buffered saline (PBS), or a nutrient culture medium for the biological particles. Between 0°C and 100°C, particularly within a defined temperature range starting from the injection temperature (preferably ambient temperature), the dynamic viscosity of the sample liquid decreases slightly with temperature. The sample liquid 20 does not include hot-viscosity liquids. In fact, adding hot-viscosity liquids to this sample liquid may compromise the integrity of the particles to be separated.

[0074] The microfluidic device utilizes the properties of at least one thermoviscous protective liquid 21 and / or 22 to regulate the fluidity of the sample liquid 20, so as to sort or extract a portion of the sample liquid to a designated outlet channel.

[0075] Now we will refer to Figure 1 and Figures 3 to 8 Explain the operation of this microfluidic device.

[0076] Sample liquid 20 is injected into the microfluidic chip 100 through inlet channel 3. Protective liquids 21 and 22 are injected into the microfluidic chip through inlet channels 1 and 2, respectively. In the illustrated example, the common channel 4 of the microfluidic chip 100 has a depth of 7 μm and a width of 25 μm measured perpendicular to the longitudinal flow direction of the liquid. Here, protective liquids 21 and 22 are the same liquid. According to this disclosure, the injection temperature of the protective liquid is approximately equal to the ambient temperature, for example, 20°C. The flow rate of sample liquid 20 is, for example, 5 μl / h. In the illustrated example, the flow rates of the two protective liquids 21 and 22 are adjusted to slightly different values ​​(e.g., 80 μl / h and 81 μl / h, respectively) to guide sample liquid 20 to the first outlet channel 11 without heating in the heating zone. In this configuration, the first outlet channel 11 is a so-called waste liquid outlet, and the second outlet arm 12 is used to collect sorted particles.

[0077] At ambient temperature, the low viscosity of the thermoviscous protective fluid enables the generation of fluids with high linear velocities (tens of cm / s) even with small channel sizes in microfluidic chips. Furthermore, the highly significant reversible viscosity change with temperature allows for rapid switching by first slightly increasing and then decreasing the temperature within the protective fluid.

[0078] In one exemplary embodiment, the energy source used is a laser that emits a laser beam of a defined wavelength, and the protective liquids 21 and 22 are capable of absorbing the laser beam and converting it into heat. More specifically, the laser beam 41 is guided and focused onto the first heating region 31, and the beam size within the focused region is between approximately 1 μm and 10 μm. Alternatively, another laser beam 42 is guided and focused onto the second heating region 32, such as... Figure 4 As shown.

[0079] For example, protective liquids 21 and 22 are composed of thermoviscous liquids based on a thermosensitive polymer dissolved in water and an absorbent material for that laser wavelength. The absorbent material is suspended or dissolved in the protective liquid. The absorbent material may include, for example, ink or even carbon nanoparticles, capable of absorbing the laser beam focused within the protective liquid in the heating zones 31 and 32, thereby converting it into heat. Alternatively, the wavelength of the laser beam corresponds to the absorption spectrum of the carrier liquid of the protective liquid, for example, to the absorption spectrum of water. Figure 1 In the middle, the diameter of heating zones 31 and 32 is approximately 5 μm.

[0080] In another embodiment, each heating zone 31, 32 includes a photothermal transducer configured to contact a protective liquid, and each photothermal transducer is capable of absorbing a laser beam focused in the heating zone 31, 32. Each photothermal transducer includes a metal surface with a deposition thickness between 10 nm and 500 nm and an area of ​​1 μm. 2 Up to 100 μm 2 A thin metal layer (e.g., gold or indium) is formed between them. Each photothermal transducer is able to absorb the laser beam focused within the heating zones 31, 32 and convert it locally into heat.

[0081] According to another exemplary embodiment, each heating zone 31, 32 includes an electrothermal transducer, such as a heating resistor or an inductive energy-dissipating element. Each electrothermal transducer is connected to a power source. The electrothermal transducers are in contact with the first protective liquid 21 and the second protective liquid 22 in the common channel 4, respectively, to achieve localized heat exchange.

[0082] Figure 1 An example is shown where laser beams 41 and 42 directly heat the first protective liquid 21 and the second protective liquid 22 in the first heating zone 31 and the second heating zone 32, respectively. Protective liquids 1 and 2 consist of a thermoviscous liquid and an absorbent material specific to the laser wavelength, the absorbent material being suspended or dissolved in the protective liquid. The thermoviscous liquid consists of water and a thermosensitive polymer (here, EG230 at a mass concentration of 7.5% in water). Sample liquid 20 consists of water containing the target particles.

[0083] The heating zones are located in or in contact with the protective liquid, and preferably at a non-zero distance from the sample liquid. For example, the distance between the first heating zones 31 and 32 and the sample liquid 20 is on the order of approximately 4 μm. In this way, the temperature rise is explicitly confined within the protective liquid, which includes a thermoviscous liquid. This arrangement spatially confines the temperature rise within the protective liquid and outside the sample liquid, thereby preventing the sample liquid from experiencing a temperature rise and thus preventing damage or modification of particles in the sample liquid. Furthermore, the temperature rise is spatially confined to a portion of the cross-section of the protective liquid, thereby preventing blockage of the common channel 4 or one of the outlet channels 11 and 12 when the viscosity of the protective liquid increases.

[0084] exist Figures 3 to 6 In the first exemplary embodiment shown at different times, after the detection unit 50 detects the target particles in the sample liquid, a sequence of two consecutive laser pulses 41 and 42 is triggered. Each laser pulse has a defined duration or a short duration, between 1 μs and 500 μs, for example, about 50 μs here. The laser power is about 5 mW. The pulse energy is between 10 nJ and 10000 nJ, for example, 250 nJ here. The first laser pulse 41 is focused on the first heating zone 31 for a duration of 50 μs. Figure 3 Subsequently, after a time interval between 0 and 50 μs, the second laser pulse 42 is focused on the second heating region 32 for a duration of 50 μs. Figure 4 It can be concluded that the protective fluid absorbed the full power of the laser pulse.

[0085] Figures 3 to 6 The dual laser pulse sequence is clearly shown. Figure 3 In the process, a first laser pulse 41, located in the first heating zone 31 on the first side of the microfluidic device 100, initiates the diversion of the sample liquid towards the second outlet channel 12. Figure 4 Once the steering is initiated, a second laser pulse 42 within the second heating zone 32 on the second side of the microfluidic device 100 reverses the motion. However, since the sample liquid has already propagated between the two laser pulses, a small portion of the sample liquid continues to flow towards the second outlet channel 12. Figure 5 During the process, although the two laser pulses 41 and 42 have been turned off, the effect of the localized increase in viscosity of the protective liquid continues to propagate: it can be observed that the extracted portion 130 forms in the second outlet channel 12, while the remaining fluid of the sample liquid 20 returns to the first outlet channel 11 or the waste liquid arm. Figure 6 In the process, the extraction portion 130 has been separated from the sample liquid 20, and the sample liquid 20 resumes flow in the first outlet channel 11 (waste liquid arm).

[0086] Figures 3 to 8The local temperature changes of the protective fluids 21 and 22 during and immediately after each laser pulse are also shown. The corresponding color of the protective fluid according to temperature changes is schematically illustrated. When the protective fluid is at ambient temperature, i.e., at a low viscosity (below 0.1 Pa·s), the color of the protective fluid is lighter. The color of the protective fluid becomes particularly darker locally as the temperature increases. In other words, the higher the local viscosity of the protective fluid, the darker its color becomes. Figures 3 to 8 The darker the color in the middle.

[0087] exist Figures 3 to 8 In the process, upstream of heating zones 31 and 32, the sample liquid 20 and protective liquids 21 and 22 are both at the injection temperature, for example, an ambient temperature of approximately 20°C. Here, the injection temperature is the temperature at which the protective liquids 21 and 22 have extremely low viscosity. At 20°C, the protective liquids 21 and 22, including the thermoviscous liquids, have a low viscosity of approximately 20 mPa·s. After each laser pulse 41 and 42 is absorbed, the local temperature of the protective liquid 21 in the first heating zone 31 and the protective liquid 22 in the second heating zone 32 rises until it reaches a high temperature Th of approximately 40°C. Within the heating zone of the protective liquid, the temperature rises during the pulse duration, reaches its maximum value at the end of the pulse, and then decreases at almost the same rate. By limiting the energy supply in terms of both duration and power, the maximum heating temperature of the protective liquid can be limited, which is referred to herein as the high temperature Th. This high temperature Th is much lower than the boiling temperature of the protective liquid to avoid bubble formation. The high temperature Th can be less than, equal to, or even greater than the temperature at which the protective liquid reaches its maximum viscosity value. Advantageously, the high-temperature Th is lower than the temperature at which the protective fluid reaches its maximum viscosity, thus limiting the heating of the protective fluid. Furthermore, the high-temperature Th of the protective fluid is adjusted so that its dynamic viscosity at this high-temperature Th is much greater than its viscosity at the injection temperature. For example, at the high-temperature Th, the dynamic viscosity of the protective fluid is greater than or equal to 1.0 Pa·s. This localized, instantaneous heating of the protective fluid serves the following purpose: during the laser pulse, it causes the viscosity of the thermoviscous liquid in the heated zone to become extremely high, thereby deflecting the current streamlines by altering the flow state.

[0088] In fact, at 40°C, the viscosity of a hot viscous liquid is greater than 10 Pa·s. This will induce the flow of sample liquid 20 to deflect around the viscosity-enhancing region, specifically, to redirect the sample liquid flow. Stopping heating will cause the protective liquid to cool almost instantaneously and reduce its viscosity.

[0089] Confining the space for viscosity increase to a cross-section smaller than the target protective fluid's cross-section avoids the formation of blockages that would impede the protective fluid's flow. Instead, this spatial restriction on viscosity increase within the protective fluid maintains its flow to the outlet channel, which, after the heating laser pulse stops, promotes rapid cooling. In this way, because the overall flow is uninterrupted, the heated area of ​​the protective fluid can be carried downstream even before it has fully cooled. This further accelerates the recovery of initial conditions and facilitates high-frequency operation. In contrast, in the prior art, the heated area is located in one of the outlet arms and extends across the entire width of the outlet arm, creating a blockage within the arm where fluid flow is interrupted and the temperature remains high. This operation means a slower recovery of initial conditions, which can only be completed after the heated area has fully cooled.

[0090] According to this disclosure, the continuous flow of the protective liquid enables the initial flow direction to be quickly restored after the heating sequence ends. However, after the protective liquid is locally heated, the circulation of the sample liquid 20 changes, causing a very small portion of the sample liquid to flow towards the second outlet channel 12, which serves as the collection path (see [link]). Figures 3 to 6 Nevertheless, the thickening zone does not impede liquid flow because, due to the laser focusing effect, the thickening zone is spatially confined and does not extend to cover the entire width of the protective liquid. Specifically, the liquid flow within the two outlet channels 11 and 12 is uninterrupted. Furthermore, the heating duration is very short, causing the temperature and viscosity of the thickening zone to drop very rapidly after heating is stopped.

[0091] exist Figure 6 It can be observed that the portion 111 of the protective liquid, after being heated, shifts in position relative to the first heating zone 31 to which laser pulse 41 was applied. Furthermore, the highest temperature of this portion 111 of the protective liquid 21 is approximately 35°C, which is below the high temperature of 40°C. In fact, Figure 4 This occurred 50 μs after the laser pulse 41 was turned off. The temperature shift and rapid cooling in this portion 111 of the protective liquid 21 can be explained by thermal diffusion and the continuous flow of the protective liquid toward the outlet channel 11.

[0092] Similarly, Figures 4 to 6 The cooling process of portion 112 of the protective liquid 21, heated by the second laser pulse 42, is shown. Figure 4 In the process, the portion 112 of the protective liquid that has undergone heating is located in the second heating zone 32, at a temperature of approximately 40°C. Figure 5 In the middle, the heated portion 112 of the protective liquid shifts towards the second outlet channel 12, with a temperature of approximately 35°C. Figure 6In the middle, the heated portion 112 of the protective liquid has left the second heating zone 32 and is now located in the second outlet channel 12 at a temperature of approximately 30°C. Figure 2 This temperature corresponds to the viscosity at approximately the recovery injection temperature.

[0093] In addition, Figures 3 to 6 It can be clearly observed that the sample liquid hardly experiences a temperature rise, especially near the heating zones 31 and 32. Maintaining the sample liquid at the injection temperature ensures the integrity of the particles or cells being analyzed.

[0094] Applying two consecutive laser pulses, staggered in time, induces a shearing effect in the flow of sample liquid 20, thereby extracting a small portion 130 of the sample liquid in the direction of the second outlet channel 12. In effect, the first laser pulse 41 creates a first viscosity-enhancing zone before entering the first outlet channel 11. The sample liquid 20 is thus diverted to the second outlet channel 12. The first pulse initially diverts the fluid from the first outlet channel 11 (waste arm) to the second outlet channel 12 (sample arm), increasing the flow rate in the second outlet channel. Shortly thereafter or immediately following, the second laser pulse 42 counteracts the initial deflection, redirecting the sample liquid back to the first outlet channel 11 while leaving only a very small portion 130 of the sample liquid in the second outlet channel 12 (sample arm). In effect, the fluid flowing towards the first outlet channel 11 is subsequently restored by a significant decrease in viscosity in the first protective fluid 21, which, during the duration of the second pulse, induces the fluid to resume its flow towards the first outlet channel 11. The sequence of two consecutive laser pulses divides the sample liquid into small volumes or portions of 130, directing these portions towards the second outlet channel 12 (collection arm). Simultaneously, it restores the main flow of the sample liquid to the first outlet channel 11 or the waste arm. Therefore, this device and method can extract sample liquid volumes ranging from a few fetoliters to several hundred fetoliters in a very short time, as the extraction process does not require interruption of the entire fluid flow in each arm. With constant energy, increasing the laser pulse power to shorten the pulse duration can further shorten the extraction time for a portion of the sample fluid, thereby further reducing the extraction volume.

[0095] The two consecutive laser pulse sequences worked well because the local temperature change was extremely low, approximately 20°C, which gave the microfluidic processing method low inertia and extremely fast dynamic response characteristics. In the example above, Figure 3 and Figure 6 A period of 150 μs elapsed. It's also important to note that the sudden increase in viscosity within the highly fluid liquid acts as a deflector, which is quite different from what might happen when the viscosity decreases. Therefore, this device and method offer superior efficiency compared to existing microfluidic processing devices and methods based on localized viscosity reduction.

[0096] The dual-pulse method can be similarly applied to heating zones 31 and 32, each including an electrothermal transducer, by applying an electrical pulse instead of a laser pulse. The duration of the electrical pulse can be in the millisecond range, less than or equal to 10 ms, 1 ms, or 100 μs to 10 μs.

[0097] exist Figure 1 In the example, the two heating zones 31 and 32 are symmetrically arranged with respect to the longitudinal axis 14 of the common channel 4, and are at the same distance from the tip of the Y-shaped connector, P1=P2=approximately 5μm.

[0098] According to one variation, heating zones 31 and 32 are staggered relative to each other along the longitudinal axis 14 of the common channel 4. For example, the first heating zone 31 is closer to the Y-joint than the second heating zone 32. A first laser pulse 41 is applied to the first heating zone 31 for 50 μs, followed by a second laser pulse 42 applied to the second heating zone 32 after a 50 μs interval, for a duration of 50 μs. For example, the first heating zone 31 is positioned just before entering the first outlet channel 11. Along the longitudinal axis 14, the second heating zone 32 is located upstream of the first heating zone 31. For example, the distance P1 from the end of the Y-joint is 2 μm for the first heating zone 31, and the distance P2 from the end of the Y-joint is 7 μm for the second heating zone 32. The function of the first laser pulse 41 is to locally and temporarily increase the viscosity of a portion 111 of the protective liquid 21 at the inlet of the first outlet channel 11, causing the sample liquid flow to redirect to the second outlet channel 12. After 50 μs, the second laser pulse 42 locally and temporarily increases the viscosity of another part 112 of the protective liquid 22 in the common channel, so that the entire flow of the sample liquid is restored to the waste channel 11.

[0099] according to Figure 7 and Figure 8 The second embodiment shown employs a single laser pulse focused on a single heating zone 31. In this embodiment, the protective liquid 21 comprises a thermoviscous liquid. On the other hand, the protective liquid 22 does not necessarily comprise a thermoviscous liquid. However, using the same protective liquid 22 as the thermoviscous liquid-based protective liquid 21 still has advantages.

[0100] The laser's operating parameters (power, energy per pulse, pulse duration, wavelength, etc.) are equivalent to the parameters described for the first pulse in the first embodiment.

[0101] Figure 7 and Figure 8 The flow of the sample liquid and the temperature of the protective liquid are shown (the temperature rise is represented by the intensity of the black color in the protective liquid 21).

[0102] Figure 7A simulated image of the microfluidic device is shown 50 μs after a laser pulse 41 lasting 50 μs is applied to the heating zone 31. The laser pulse 41 serves to locally raise the temperature to a high temperature of approximately 40°C, thereby increasing the viscosity of the protective liquid 21. The laser pulse 41 forms a thickening zone upstream of the branch between the two outlet channels, locally and briefly interfering with the flow of the protective liquid 21 and the sample liquid 20. Specifically, the thickening zone reduces the flow rate of the protective liquid 21 to the first outlet channel 11 and diverts the flow of the sample liquid to the second outlet channel 12. It is also possible to... Figure 7 It was observed that the temperature rise caused by the laser pulse remained confined to a region with a diameter of approximately 10 μm within the protective liquid 21. The temperature within the heating zone of the protective liquid 21 reached approximately 40°C. On the other hand, the sample liquid experienced almost no temperature rise, especially around the heating zone 31.

[0103] Turning off the single laser pulse 41 allows a small amount of sample liquid to be cut out, and this portion of the sample liquid is guided to the collection arm ( Figure 8 ,correspond Figure 7 (Approximately 100 μs thereafter). Figure 8 It was observed that the sample liquid was discontinuous in the first outlet channel 11. The interruption of fluid flow within the first outlet channel 11 corresponds to the portion 130 of the sample liquid being extracted moving towards the second outlet channel 12. Therefore, the sample liquid flows continuously. Figure 8 It can also be observed that the temperature of the protective liquid 21 has actually returned to ambient temperature. Furthermore, the portion 130 of the sample liquid drawn into the second outlet channel 12 does not experience any temperature rise, which would damage the sample liquid and / or the sorted particles. Similarly, the sample liquid 20 upstream of the heating zone 31 also does not experience any temperature rise.

[0104] In the second embodiment, fluid recovery after the heating laser pulse is passive, and the recovery speed is slower than that in the two-pulse configuration. The second embodiment is simpler because it implements only a single laser pulse within a single heating zone, but it is slower and less accurate than the first embodiment. In fact, in the first embodiment using two pulses, the second pulse is used to force the initial fluid recovery. Therefore, the first embodiment is faster and more accurate because the second pulse can trim the sample flow flowing into the collection arm. In the second embodiment, this trimming is gradual as the fluid recovers.

[0105] In all embodiments, the short distance between the detection unit 50 and the heating zones (one or more) 31, 32 allows for the application of a laser beam within a very short time after the target particle is detected, thereby shortening the switching time for directing the detected particle to the collection channel for extraction. In other words, this configuration increases the frequency of switching, sorting, or extracting particles.

[0106] This disclosure advantageously enables the sampling of individual particles from a concentrated liquid.

[0107] Furthermore, heating the hot viscous liquid in the common channel before it enters the outlet channel enables excellent performance in terms of sorting rate and small sample volume. Due to the low viscosity at the injection temperature, this method achieves high flow rates. Flow rates can actually reach tens of centimeters per second, which is very high for microfluidic devices with tiny geometries. The instantaneous increase in local viscosity in the protective fluid is achieved under low temperature rise conditions (temperature rise during switching is less than 40°C, preferably less than 30°C, or 20°C, or even less than 10°C), thus avoiding damage to the sample liquid from heating. Because of the small temperature range of viscosity change, this method achieves extremely high switching rates, allowing for rapid temperature rise and fall without dissipating large amounts of energy, while also limiting the thermal inertia of the device and the method.

[0108] Lasers require relatively low optical power (on the order of a few milliwatts) to perform the switching.

[0109] The apparatus and method disclosed herein can extract extremely small volumes of samples (on the order of tens of fetoliters) while maintaining the high liquid flow rates required for analyzing large volumes.

[0110] By employing a thermoviscous protective fluid and setting a heating zone upstream of the branches between the outlet channels, rapid switching can be achieved without interrupting the sample liquid flow.

Claims

1. A microfluidic processing method, comprising the following steps: (a) The sample liquid (20) is injected into the common channel (4) of the microfluidic device (1) via the inlet channel (3); (b) Injecting at least one protective liquid (21, 22) at a predetermined injection temperature into the common channel (4) via at least one other inlet channel (1, 2) to cause the sample liquid (20) to be hydrodynamically focused within the common channel (4) and to cause the sample liquid (20) to flow toward a first outlet channel (11), the common channel (4) being located downstream of a branch of the first outlet channel (11) and the second outlet channel (12), the at least one protective liquid comprising a thermoviscous liquid, wherein the at least one protective liquid (21, 22) comprising the thermoviscous liquid has a dynamic viscosity of less than 0.1 Pa·s at the injection temperature; characterized in that the method comprises the following steps: (c) For a finite duration of less than or equal to 10 ms, an energy source is applied to a heating zone (31) located upstream of the branch of the first outlet channel (11) and the second outlet channel (12) in the common channel (4), the heating zone (31) being located in or in contact with the at least one protective liquid (21, 22) comprising the thermoviscous liquid, to locally heat the at least one protective liquid (21, 22) to a high temperature Th in the heating zone (31) of the common channel (4), the temperature difference between the injection temperature and the high temperature being less than or equal to 40°C, and the dynamic viscosity of the at least one protective liquid comprising the thermoviscous liquid at the high temperature Th being greater than or equal to 1.0 Pa·s, to selectively divert or extract a portion (120, 130, 220) of the sample liquid to the second outlet channel (12).

2. The method according to claim 1, further comprising the following steps after step (c): (d) For a finite duration of less than or equal to 10 ms, another energy source is applied in a second heating zone (32), wherein the second heating zone (32) is located in the common channel (4) upstream of the branch between the first outlet channel (11) and the second outlet channel (12), the second heating zone (32) being defined as being in or in contact with the at least one protective liquid (21, 22) of the thermoviscous liquid, to locally heat the at least one protective liquid (21, 22) to the high temperature Th in the second heating zone (32) of the common channel (4) to restore the flow of the sample liquid to the first outlet channel (11).

3. The method according to claim 2, wherein the duration of the interval between step d) and step c) is less than or equal to 500 μs.

4. The method according to any one of claims 1 to 3, wherein, The energy source in step c) includes a laser that emits a first laser pulse with a wavelength between 100 nm and 10 μm.

5. The method according to claim 2, wherein, The other energy source in step d) includes a laser that emits a second laser pulse with a wavelength between 100 nm and 10 μm.

6. The method according to any one of claims 4 to 5, wherein, The protective liquid, comprising the thermoviscous liquid, is adapted to absorb the first laser pulse and / or the second laser pulse.

7. The method according to claim 4 or claim 5, wherein, The heating zone (31) or the second heating zone (32) includes a photothermal transducer.

8. The method according to any one of claims 1 to 3, wherein, The heating zone (31) or the second heating zone (32) includes an electrothermal transducer, and wherein the energy source of step c) or step d) includes electrical energy.

9. The method according to any one of claims 1 to 8, wherein, Within a defined temperature range extending from the injection temperature to approximately 10, 15, 20, 25, or even 30, 35, or 40 degrees above the injection temperature, the maximum value of the thermodynamic viscosity change of the protective liquid, including the thermoviscous liquid, is greater than or equal to 3 Pa·sK. -1 .

10. The method according to any one of claims 1 to 9, wherein the sample liquid (20) is free of hot viscous liquid.

11. A microfluidic device (100) comprising a sample liquid inlet channel (3), at least one other protective liquid inlet channel (1, 2), a first outlet channel (11), a second outlet channel (12), a common channel (4), and a branch, wherein the common channel (4) is disposed between the inlet channel (1, 2, 3) and the outlet channel (11, 12), the common channel (4) being in fluid communication with the inlet channel and the outlet channel (1, 2, 3, 11, 12), and the branch separating the first outlet channel (11) and the second outlet channel (12) downstream, the sample liquid inlet channel (3) containing sample liquid (20) injected into the common channel (4), the at least one other inlet channel (1, 2) containing at least one protective liquid (21, 22) injected into the common channel (4) at a defined injection temperature, the at least one protective liquid comprising a thermoviscous liquid, wherein the at least one protective liquid (21, 22) comprising the thermoviscous liquid has a dynamic viscosity of less than 0.1 at the injection temperature. Pa.s., to allow the sample liquid (20) to undergo hydrodynamic focusing in the common channel (4), the microfluidic device is configured such that the hydrodynamically focused sample liquid (20) in the common channel (4) is directed to the first outlet channel (11) by the at least one protective liquid (21, 22) at the injection temperature. Its features are: The microfluidic device includes a heating element comprising an energy source (40) and at least one heating zone (31), the at least one heating zone being located upstream of the branches of the first outlet channel (11) and the second outlet channel (12) in the common channel (4), the at least one heating zone (31) being positioned within or in contact with the at least one protective liquid (21, 22) comprising the thermoviscous liquid, the heating element being configured to apply the energy source in the at least one heating zone (31) for a finite duration of less than or equal to 10 ms to locally heat the at least one protective liquid (21, 22) in the common channel (4) to a high temperature Th in the at least one heating zone (31) of the common channel (4), the temperature difference between the injection temperature and the high temperature Th being less than or equal to 40°C, and characterized in that the dynamic viscosity of the at least one protective liquid comprising the thermoviscous liquid at the high temperature Th is greater than or equal to 1.0 Pa·s, to allow a portion of the sample liquid (120, 130, 220) are selectively transferred or extracted to the second exit channel (12).

12. The microfluidic device according to claim 11, wherein the energy source comprises a pulsed laser capable of generating pulses with single-pulse energy between 10 nJ and 10000 nJ.

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