Microfluidic Devices Containing Microdroplets with Sol-Gel Matrices

Abstract

The present invention relates to a microfluidic device (1) comprising at least one capillary trap (12) and at least one microdroplet (15) having a sol-gel matrix, the microdroplet (15) being trapped within the capillary trap (12).

Description

[Technical field]

[0001] The present invention relates to a microfluidic device comprising a microdroplet having a sol-gel matrix trapped in a capillary trap of the device. The present invention also relates to a method for manufacturing such a device. Finally, the present invention relates to a method for detecting and / or trapping one or more analytes, as well as a method for evaluating the sol-gel matrix in such a microfluidic device. [Background technology]

[0002] The formation of microporous silica microdroplets by the sol-gel process using sol microdroplets formed in a microfluidic device is a routine procedure known from Chokkalingam V., Weidenhof B., Kramer M., Maier W., Herminghaus S., Seemann R. (2013). “Optimized droplet-based microfluidics scheme for sol-gel reactions Lab Chip 2013”. Gel formation and syneresis occurs outside the microfluidic device in a Teflon tube and then in a beaker.

[0003] International patent application WO2011 / 039475 discloses a microfluidic device comprising a trapping zone in which one or more microdroplets are trapped.

[0004] Patent applications FR2952436, FR3069534, FR3031592, WO2012 / 080665, FR3053602, and WO2005 / 100371 also disclose sol-gel materials that contain molecular sensors suitable for specific target analytes. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] WO2011 / 039475

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Non-licensed literature

[0006] [Non-licensed document 1] Chokkalingam V., Weidenhof B., Kramer M., Maier W., Herminghaus S., Seemann R. (2013). “Optimized droplet-based microfluidics scheme for sol-gel reactions Lab Chip 2013” [Non-licensed document 2] SL Anna, N. Bontoux and HA Stone, "Formation of dispersions using 'flow-focusing' in microchannels", Appl. Phys. Lett. 82, 364 (2003) [Non-licensed document 3] R. Seemann, M. Brinkmann, T. Pfohl and S. Herminghaus, in “Droplet-based microfluidics.,” Rep. Prog. Phys., volume 75, number. 1, page 016601, Jan. 2012 [Non-Patent Document 4] V. Chokkalingam, S. Herminghaus and R. Seemann in “Self-synchronizing pairwise production of monodisperse droplets by microfluidic step emulsification”, Appl. Phys. Lett., volume 93, number. 25, page 254101, 2008 [Non-Patent Document 5] GF Christopher and SL Anna in “Microfluidic methods for generating continuous droplet streams”, J. Phys. D. Appl. Phys., volume 40, number 19, pages R319-R336, Oct. 2007 [Non-Patent Document 6] R. Dangla, SC Kayi, and CN Baroud in “Droplet microfluidics driven by gradients of confinement.,”Proc. Natl. Acad. Sci. USA, volume 110, number 3, pages. 853-8, Jan. 2013 [Non-Patent Document 7] A. Funfak, R. Hartung, J. Cao, K. Martin, KH Wiesmuller, OS Wolfbeis and JM Kohler in “Highly resolved dose-response functions for drug-modulated bacteria cultivation obtained by fluorometric and photometric flow-through sensing in microsegmented flow”, Sensors Actuators, B Chem., volume 142, number 1, pages 66-72, 2009 [Non-Patent Document 8] E. Fradet, C. McDougall, P. Abbyad, R. Dangla, D. McGloin and CN Baroud in “Combining rails and anchors with laser forcing for selective manipulation within 2D droplet arrays.,” Lab Chip, volume 11, number 24, pages 4228-34, Dec. 2011 [Non-Patent Document 9] E. Fradet, P. Abbyad, MH Vos and CN Baroud in “Parallel measurements of reaction kinetics using ultralow-volumes.,” Lab Chip, volume 13, number 22, pages 4326-30, Oct. 2013 Summary of the Invention [Problem to be solved by the invention]

[0007] There is a need for microfluidic devices that can precisely control the formation of sol-gel matrices to perform analyses easily, rapidly, reproducibly, uniformly, reliably, and at low cost. [Means for solving the problem]

[0008] To this end, the present invention, according to a first aspect thereof, comprises: - at least one capillary trap; - at least one microdroplet comprising a sol-gel matrix, the microdroplet being trapped in the capillary trap; The present invention proposes a microfluidic device comprising:

[0009] The term "microfluidic device" refers to a set of interconnected microchannels and / or microchambers, some of which include at least a dimension of less than 1 millimeter measured in a straight line from one edge to the opposite edge.

[0010] The term "capillary trap" refers to a spatial zone of a microfluidic device that allows temporary or permanent fixation of one or more microdroplets circulating within the microfluidic device.

[0011] The term "microdroplet" refers to droplets or beads having a volume of 1 μL or less, even better still 50 nL or less, and even better still 40 nL or less.

[0012] The term "sol-gel matrix" means a matrix obtained by the sol-gel process, which in particular comprises, as precursors, a compound of formula M(OR) n Or R'-M(OR) n-1or sodium silicate, where M is a metal, transition metal or semimetal (metalloid), in particular silicon, R or R' is an alkyl group and n is the oxidation state of the metal. In the presence of water, hydrolysis of the alkoxy (OR) groups occurs, forming microparticles, generally less than 1 nanometer in size. These particles aggregate with each other to form agglomerates that remain in suspension without settling, forming the so-called sol. The increase in the agglomerates and their condensation increases the viscosity of the medium, forming the so-called gel. The gel can then continue to develop during a maturation stage, during which the polymer network present in the gel becomes dense. The gel then shrinks, during a process known as syneresis, to expel the solvent from the polymer network that has formed. The solvent then evaporates during a process known as drying, which results in a porous, glass-type solid material. The syneresis and drying steps can be simultaneous.

[0013] The sol-gel matrix of the microdroplet may be in gel or solid form after the syneresis and / or drying steps of the sol-gel process, the sol-gel matrix being in particular a porous solid, such as a xerogel. Preferably, the sol-gel matrix has a morphology depending on the progression of the sol-gel process in the microfluidic device before, during or after the syneresis step and before, during or after the drying step. Preferably, the sol-gel matrix of the or each microdroplet is in solid form, in particular a porous morphology, such as a xerogel, after the syneresis and drying steps in the microfluidic device.

[0014] Preferably, the microdroplets have a structure defined by a sol-gel matrix and therefore may have the properties of a gel or a solid, preferably a porous solid, such as a xerogel.

[0015] Such microfluidic devices make it possible to have microdroplets immobilized in capillary traps and therefore precisely control the ripening and / or syneresis and drying of the sol-gel matrix for small and easily controllable samples, allowing precise investigation of the sol-gel processes involved.

[0016] Furthermore, the microdroplets can be used to detect one or more analytes in the gas or liquid phase by pre-doping the microdroplets with one or more molecular sensors, allowing for direct and rapid detection that occupies a small volume and requires only minute amounts of sol-gel materials and molecular sensors.

[0017] Preferably, the microfluidic device comprises a plurality of spaced apart capillary traps and a plurality of microdroplets each comprising a sol-gel matrix, each trapped in one of the capillary traps. The number of capillary traps may be 10 or more, even better 100 or more, preferably 100-1000. Preferably, the capillary traps are spaced apart from each other. Preferably, the capillary traps are arranged in a matrix of the microfluidic device. Preferably, all the capillary traps are spaced apart the same fixed distance. By having a matrix of capillary traps, each receiving one or more microdroplets, it is possible to carry out studies or measurements with a large amount of data on a small volume. As a result, it is possible to carry out observations or statistical measurements to limit reproducibility and / or uniformity issues in a fast and easy manner for the user and on a small volume, and / or to carry out multiplexing of observations or measurements on various microdroplets. Such a device allows for fast, reproducible, uniform, reliable and low-cost observations or measurements.

[0018] Preferably, the microfluidic device comprises a channel having a capture chamber, the capture chamber comprising the capillary trap(s). Preferably, the capture chamber is bounded by four side walls, a top wall and a bottom wall, and the capillary trap(s) extend over the top wall and / or the bottom wall of the capture chamber.

[0019] Preferably, the microfluidic device comprises at least one fluid inlet channel and at least one fluid outlet channel in the microfluidic device, in particular in the capture chamber. The microfluidic device, in particular the capture chamber, is preferably closed to liquids except for the inlet and outlet channels. Preferably, the inlet channel starts from a first side of the capture chamber relative to the capillary trap(s) and the outlet channel extends from a second side of the capture chamber opposite the first side relative to the capillary trap(s). Such channels allow precise control of the circulation of fluids in the microfluidic device, in particular allowing the fluid to flow from the inlet channel to the outlet channel to contact the microdroplet(s) trapped in the capillary trap(s).

[0020] The capture chamber may include a step on a first or second side of the capture chamber having a height, measured between the upper and lower walls, greater than the height of the remainder of the capture chamber excluding the capillary trap(s). Such a step may create a liquid front on one side of the capillary trap(s) and in particular expose said traps to a gradient of gas arising from the liquid front due to vaporization of said liquid or one of the compounds contained therein.

[0021] The microfluidic device, in particular the capture chamber, may comprise at least one wall made of a porous material, in particular made of PDMS, that is at least partially gas permeable. Such a porous wall allows evaporation of the solvent during the syneresis step. The rate of the syneresis and / or drying steps can be controlled by the porosity of the porous material and / or by controlling the gas stream between the inlet and outlet channels.

[0022] Alternatively, the microfluidic device is made of one or more non-porous materials, in particular glass or a thermoplastic material, such as cyclic olefin polymer (COP), cyclic olefin copolymer (COC), polycarbonate or molded plastic. In this case, the syneresis and / or drying step may be performed by subjecting the microdroplets to a fluid stream between an inlet channel and an outlet channel. By controlling the velocity of the fluid stream, the syneresis and / or drying can be precisely controlled.

[0023] Preferably, the capillary trap(s) each form a cavity in the wall of the microfluidic device, in particular the capture chamber.

[0024] Preferably, the height of the cavity, which corresponds to the distance between the base of the cavity and the opposite wall of the microfluidic device, is at least twice the height of the microfluidic device at the edge of the capillary trap, which corresponds to the distance between the wall in which the cavity is formed at the edge of the capillary trap and the opposite wall.

[0025] Preferably, the smallest width of the cavity is at least twice the height of the microfluidic device at the edge of the capillary trap(s).

[0026] Preferably, the height of the microfluidic device at the edge of the capillary trap(s) is less than or equal to the smallest dimension of the or each trapped microdroplet containing the sol-gel matrix, in particular less than or equal to the smallest dimension of the or each trapped microdroplet after syneresis. In this way, the or each microdroplet cannot get out of the capillary trap without destroying the microfluidic device. This allows a permanent and precise positioning of the microdroplet and therefore easy observation of it at any time.

[0027] Such dimensions of the cavity also allow the formation of microdroplet(s) directly in the capillary trap(s) by breaking the sol or a liquid forming part of the sol, as will be described in more detail below in relation to methods for manufacturing a microfluidic device.

[0028] The at least one capillary trap may comprise a first trapping zone in which the microdroplet(s) comprising the sol-gel matrix are trapped, and at least one second trapping zone having a trapping force for a given microdroplet different from the trapping force of the first trapping zone for trapping a different microdroplet. Such capillary traps are described, inter alia, in International Patent Application WO2018 / 060471, which is incorporated herein by reference.

[0029] At least one capillary trap may have a single trapping zone configured to trap a single microdroplet comprising a sol-gel matrix, or a plurality of microdroplets, at least one of which comprises a sol-gel matrix.

[0030] Preferably, the sol-gel matrix(s) is obtained by a hydrolytic sol-gel process.

[0031] Preferably, the sol-gel matrix(s) is obtained from a precursor selected from alkoxides, in particular zirconium alkoxides, in particular zirconium butoxide (ZTBO), zirconium propoxide (ZTPO), alkoxides of titanium, niobium, vanadium, yttrium, cerium, aluminum or silicon, in particular tetramethoxysilane (TMOS), tetraethoxysilane (TEOS), tetrapropoxysilane (TPOS), tetrabutoxysilane (TBOS), trimethoxysilanes, in particular methyltrimethoxysilane (MTMOS), propyltrimethoxysilane (PTMOS) and ethyltrimethoxysilane (ETMOS), triethoxysilanes, in particular methyltriethoxysilane (MTEOS), ethyltriethoxysilane (ETEOS), propyltriethoxysilane (PTEOS) and aminopropyltriethoxysilane (APTES), and mixtures thereof.

[0032] The microdroplet(s) may comprise a solvent, in particular a solvent selected from water, methanol, ethanol, propanol, butanol, 2-methoxyethanol, acetone, DMSO, DMF, NMF, formamide, methyl ethyl ketone, chloroform, dichloromethane, acetic acid, and mixtures thereof, preferably a mixture of water and butanol.

[0033] The microdroplet(s) may contain other additives, in particular one or more catalysts, in particular one or more catalysts selected from acetic acid, nitric acid, sulfuric acid, hydrofluoric acid, and ammonium hydroxide, and / or one or more stabilizers, in particular one or more stabilizers selected from acetic acid, acetylacetone, glycol, methoxyethanol, glycol, and β-ketoesters.

[0034] The microdroplet(s) may be translucent, preferably transparent.

[0035] The device may contain a single microdroplet comprising a sol-gel matrix within the or each capillary trap.

[0036] Alternatively, the device may include a plurality of microdroplets containing the sol-gel matrix within the or each capillary trap. The microdroplets containing the sol-gel matrix may be arranged as a column within the capillary trap.

[0037] Preferably, the device comprises a plurality of microdroplets comprising a sol-gel matrix that are trapped within the capillary trap(s) of a microfluidic device.

[0038] The microdroplets may be substantially identical, and in particular may have substantially identical composition. In the case of a microfluidic device containing several capillary traps, this allows in particular to carry out statistical studies on a single microfluidic device. This limits problems of reproducibility and / or uniformity, as well as edge effects.

[0039] Alternatively, at least some of the microdroplets are different, in particular having different compositions or structures, which in the case of a microfluidic device comprising several capillary traps allows in particular multiplexing for small volumes on a single microfluidic device.

[0040] The microdroplets may all contain the same sol-gel material that constitutes the sol-gel matrix, which may allow investigations to be performed on specific sol-gel materials.

[0041] The microdroplets may contain a sol-gel matrix of the same composition, which may allow for statistical investigations into the structure of the sol-gel matrix or to easily form the microdroplets from the same initial solution under the same conditions.

[0042] As a variant, at least two microdroplets contain different sol-gel matrices, in particular matrices with different structures or compositions, which may allow investigating different sol-gel matrices in the same microfluidic device and may allow multiplexing of sol-gel matrices.

[0043] The microdroplet(s) comprising the sol-gel matrix may each comprise one or more molecular sensors. Each molecular sensor preferably comprises one or more identical detection units, each of which can react in the presence of a target analyte to induce an observable change and comprises one or more molecules. The molecular sensors are preferably incorporated in the sol-gel matrix to detect the presence of one or more specific target analytes in each of the corresponding capillary traps. Preferably, the molecular sensor(s) are dispersed in each microdroplet in the sol-gel matrix. Preferably, the or each molecular sensor is configured to have optical properties, in particular color, absorbance, reflectance, fluorescence or luminescence, which optical properties differ in the presence of the target analyte, in particular by reaction or binding with the target analyte. As a result, it is possible to use the microfluidic device to analyze the presence of one or more target analytes in a liquid or gaseous fluid by contacting it with a microdroplet in a microfluidic system. It is also possible to use the molecular sensor to capture the target analyte in the fluid to be tested, if a bond with the target analyte is formed. Achieving detection through a change in optical properties makes detection easy and straightforward, either visually or by simple optical devices.

[0044] The microdroplet(s) may contain at least two molecular sensors for detecting different target analytes.

[0045] At least one microdroplet may include at least two molecular sensors configured to detect the presence of different target analytes, the molecular sensors preferably having different optical properties in the presence of the corresponding target analytes. Preferably, the molecular sensors have reactions with the corresponding target analytes that are independent of each other. This allows simple detection of different analytes in parallel in the same microdroplet. For example, the color of each microdroplet allows the relative concentrations of the target analytes and the respective concentrations of the analytes to be determined.

[0046] Preferably, at least two microdroplets contain molecular sensors for detecting different target analytes. This allows for parallel detection of target analytes by different microdroplets, especially in the case of molecular sensors having similar responses to the presence of corresponding target analytes. Such a device is simple to use and allows for easy and immediate analysis of the presence or absence of different target analytes.

[0047] At least two microdroplets may contain molecular sensors with different concentrations of the same detection unit. Preferably, some microdroplets may contain paired molecular sensors with different concentrations of the same detection unit. The microdroplets may be arranged in multiple capillary traps or in the same capillary trap to form a concentration gradient of the detection unit between the inlet and outlet channels.

[0048] The molecular sensor(s) may comprise a detection unit selected from 4-amino-3-penten-2-one, p-dimethylaminobenzaldehyde, p-dimethylaminocinnamaldehyde, p-methoxybenzaldehyde, 4-methoxynaphthaldehyde, crotonic acid, p-diazobenzenesulfonic acid, 4-aminoantipyrine, carmine indigo, a quinone compound, a mixture of iodide and a compound selected from starch, amylose, amylopectin, xyloglucan, xylan, chitosan, glycogen, polyvinyl alcohol or a polyvinyl alcohol compound, cellulose or a cellulose compound, α-cyclodextrin, theobromine, or a block polymer of polypropylene oxide and polyethylene oxide, a mixture comprising phenol and sodium nitroprusside, and the compounds described in patent application WO2005 / 100371, which is incorporated herein by reference. The molecular sensor(s) may comprise one or more additives, in particular chosen from solvents, acids and bases, oxidizing and reducing agents for promoting a reaction with the target analyte, and / or one or more additional molecules which, alone or in combination with others, allow a more or less selective interaction with the target analyte and / or a particular chemical function, in particular the production of a particular color, a response by a color change to pH, or the production of a particular fluorescence.

[0049] Preferably, the molecular sensor(s) consist of the same detection unit(s) and optionally one or more additives. The molecular sensor(s) may each make it possible to detect a target analyte selected from volatile organic compounds, in particular those defined in the list of priority pollutants from ANSES (Agence Nationale de Securite Sanitaire de l'alimentation de l'environnement et du travail), in particular aldehydes, such as formaldehyde, acetaldehyde or hexaldehyde, carbon monoxide and / or carbon dioxide, dioxygen (O2), hydrogen, phenols and their derivatives, indole compounds, in particular indole, skatole or tryptophan, chloramines, nitrogen dioxide, ozone, halogenated compounds, in particular boron trifluoride, its derivatives, and boron trichloride, aromatic hydrocarbons, such as naphthalene, benzene and toluene, and non-aromatic hydrocarbons, such as pentane, hexane and heptane, acrolein, nitrogen dioxide, and ethylbenzene.

[0050] Preferably, the microfluidic device comprises a number of spaced apart capillary traps each containing a microdroplet comprising a sol-gel matrix, in particular a sol-gel matrix made of a material that is solid after syneresis, and one or more molecular sensors within each sol-gel matrix. If the sol-gel matrix is ​​a solid matrix obtained after syneresis, the microfluidic device in its given form is particularly stable. It may therefore be prepared and then stored before its use, for example in a laboratory, or it may be used directly thereafter, in particular in the field.

[0051] The microdroplet or several microdroplets may contain observable, in particular fluorescent, microbeads within the sol-gel matrix, which may allow the assessment of the gel time during the formation of the sol-gel matrix.

[0052] The device may include a system for controlling the temperature of the microfluidic device so that it can be cooled or heated, in particular to control the formation of a sol-gel matrix by a sol-gel process.

[0053] Preferably, the device comprises a system for the circulation of a fluid within the microfluidic device, in particular from an inlet channel to an outlet channel, in particular a pump, a syringe pump or a pressure differential.

[0054] According to a second aspect of the invention, the subject of the invention is also a method for manufacturing a microfluidic device, in particular a microfluidic device as described above, comprising the steps of trapping at least one microdroplet comprising a sol in a capillary trap of the microfluidic device and using said sol to form a sol-gel matrix in the trapped microdroplet by a sol-gel process.

[0055] Such a method allows the formation of microdroplets containing a sol-gel matrix directly in a capillary trap that is precisely located within a microfluidic device. The formation of the sol-gel matrix within the capillary trap allows for precise and reproducible control of its formation. Furthermore, the small volumes involved facilitate uniformity and speed of formation.

[0056] Additionally, by trapping a microdroplet within a capillary trap, its location in the microfluidic device can be precisely known, facilitating its analysis or use to detect a target analyte, especially if it contains one or more molecular sensors.

[0057] Preferably, the method comprises trapping a plurality of microdroplets comprising a sol in one or more capillary traps of a microfluidic device, in particular in a trapping chamber, and using the sol to form a sol-gel matrix in each microdroplet by a sol-gel process.

[0058] Preferably, the method comprises the steps of trapping at least one microdroplet, in particular a single microdroplet, comprising a sol in each capillary trap of a microfluidic chip comprising a number of spaced apart capillary traps, and using the sol to form a sol-gel matrix in each microdroplet by a sol-gel process. The trapping of one or more microdroplets in several capillary traps allows the formation of a matrix of spatially positioned microdroplets in the microfluidic device, allowing statistical analysis and / or multiplexing depending on the composition of the microdroplets.

[0059] Alternatively, the method may include trapping a plurality of microdroplets comprising a sol-gel matrix in capillary traps of a microfluidic device, the device comprising one or more capillary traps capable of trapping a plurality of microdroplets, and forming a sol-gel matrix in each microdroplet using said sol by a sol-gel process, where the capillary traps may be arranged, for example, in a column and contain the microdroplets comprising the sol.

[0060] Preferably, the method comprises the step of adding one or more molecular sensors and / or microbeads observable in the microdroplet(s) before or after the formation of the sol-gel matrix, preferably before the syneresis step, each molecular sensor allowing the detection of at least one target analyte. The molecular sensor(s) may be as described above in connection with the microfluidic device.

[0061] The step of adding one or more observable molecular sensors and / or microbeads may be performed into the microdroplet(s) containing the sol after the capture of the microdroplet(s) containing the sol. The method may include the steps of adding additional microdroplets containing observable molecular sensors and / or microbeads in the microfluidic device, capturing one or more additional microdroplets in the or each capillary trap, and merging the additional microdroplet(s) and the microdroplet containing the sol or sol-gel matrix. In this case, each capillary trap preferably captures only one microdroplet containing the sol at the time of capture. The step of adding one or more microdroplets may be performed according to the method described in patent application FR3056927, using a capillary trap comprising different capture zones with different capture forces.

[0062] Alternatively, the step of adding observable molecular sensors and / or microbeads to the sol may be carried out prior to trapping the microdroplets, in particular during a step prior to forming the microdroplets, or directly to the sol prior to forming the microdroplets.

[0063] Trapping one or more microdroplets in the capillary trap(s), each microdroplet comprising a sol, comprising: (i) trapping a first microdroplet comprising a portion of the sol in the or each capillary trap; (ii) sequentially adding n times (n being an integer between 1 and 10) to the microfluidic device one or more complementary microdroplets containing another portion of the sol, in particular water, to trap it (them) in the or each capillary trap and coalescence of the first microdroplet and the complementary microdroplet (s) in each capillary trap to obtain a sol, the coalescence taking place after each or after all sequential additions; (iii) optionally adding additional microdroplets, optionally including one or more observable molecular sensors and / or microbeads, to the microfluidic device, capturing said additional microdroplets in capillary trap(s), and coalescing the additional microdroplets and the microdroplets in the or each capillary trap; wherein step (iii) is carried out before or after step (ii).

[0064] The step of combining the additional microdroplets may be performed simultaneously with the step of combining the complementary microdroplets. The additional microdroplets may be the same or different.

[0065] Preferably, the step of trapping one or more microdroplets each comprising a sol in the capillary trap(s) comprises: (i) trapping a first microdroplet comprising a portion of the sol in the or each capillary trap; (ii) optionally adding to the microfluidic device additional microdroplets comprising one or more molecular sensors and / or microbeads, trapping said additional microdroplets in capillary trap(s), and combining the additional microdroplets and the first microdroplets in the or each capillary trap to form a first doped microdroplet; (iii) adding to the microfluidic device one or more complementary microdroplets containing the remaining part of the sol, in particular water, and trapping it / them in the or each capillary trap; (iv) combining the first doped or undoped microdroplet and the complementary microdroplet(s) in each capillary trap to obtain a sol; may include:

[0066] Preferably, the step of trapping the sol-containing microdroplet(s) occurs in a carrier fluid surrounding the or each microdroplet.

[0067] The method may comprise a preliminary step of forming the microdroplet(s) comprising the sol or a first microdroplet(s) comprising a part of the sol, prior to the step of trapping in the capillary trap. The microdroplets may be formed in an auxiliary microdroplet formation system, in particular in another microfluidic device, or may be formed directly in the microfluidic device upstream of the capillary trap, in particular at the inlet of the trapping chamber. The microdroplets are preferably formed and mixed in a carrier fluid immiscible with the sol and are entrained in circulation by the carrier fluid in the microfluidic device and trapped in the capillary trap(s). Formation of the microdroplets prior to trapping makes it possible, in appropriate cases, to trap multiple microdroplets by the capillary trap and / or to trap a panel of microdroplets that are not all identical in terms of composition.

[0068] Alternatively, the step of capturing the microdroplet(s) comprising the sol or the first microdroplet(s) comprising a portion of the sol may comprise: - filling a microfluidic device with a first solution comprising a sol or a portion of the sol, and optionally one or more molecular sensors and / or one or more microbeads in the sol; - injecting a second solution of a carrier fluid immiscible with the sol upstream of the capillary trap(s) and pushing the first solution towards an outlet of the microfluidic device downstream of the capillary trap(s), the microfluidic device being configured to enable formation of micro-droplets of the first solution in the or each capillary trap during injection of the second solution into the microfluidic device. With this trapping process, the microdroplets are formed directly in the capillary trap and trapped there as soon as they are formed. This eliminates the constraints associated with handling the microdroplets before trapping them and forming them before trapping them. It also allows the microdroplets to be formed all at the same time, which reduces the risk of gel formation in the microdroplet(s) outside the capillary trap. In this trapping process, only one microdroplet is formed in each capillary trap, and all formed microdroplets have the same composition since they are formed from the same first solution.

[0069] At least two microdroplets trapped in one or two different capillary traps, preferably in two different traps, may be different, in particular may contain different sols, in particular sols differing in the nature and / or concentration of at least one compound of the sol, or may contain molecular sensors that differ, in particular in terms of the concentration of detection units or the nature of the detection units. This difference may be - capturing a microdroplet containing a different sol or a first microdroplet containing a part of a sol, and / or - the capture of additional microdroplets, which differ in particular in terms of a different concentration of one or more molecular sensors, or different molecular sensors, or different amounts of microbeads, and / or - trapping a different number of the same or different additional microdroplets in the capillary trap; and / or - forming a first microdroplet in a capillary trap, the first microdroplet containing a portion of the sol in the same capillary trap, and adding a complementary microdroplet of a different composition or amount to the capillary trap containing the first microdroplet. can be obtained by:

[0070] Having different micro-droplets in different capillary traps allows multiplexing of the microfluidic device, so that it is possible to investigate the evolution of different sols or detect different target analytes with the same microfluidic device.

[0071] At least two microdroplets trapped in one or two different capillary traps, preferably in two different traps, may contain the same sol, so that it is possible to statistically study the evolution of the sol, in particular its gel time or its diameter, on the same microfluidic chip.

[0072] The microfluidic device may include several capillary traps each trapping a microdroplet containing a sol, the microdroplets being derived from a panel of microdroplets having groups of microdroplets in which the microdroplets are identical, the groups of microdroplets containing different sols from each other.

[0073] Alternatively, the microfluidic device may comprise several capillary traps each trapping a microdroplet containing a sol, the microdroplets being derived from a panel of identical microdroplets.

[0074] Preferably, the volume percentage of alcohol in the sol is less than or equal to 80%. Preferably, the volume percentage of alcohol in the sol is greater than or equal to 20%.

[0075] Preferably, the physical properties of the microdroplet(s), of the carrier fluid and of the walls of the microfluidic device, the viscosity of the microfluid(s) and the carrier fluid, as well as the functioning mode of the device, in particular the flow rates of the microdroplet(s) and the carrier fluid in the microfluidic device, are selected such that the microdroplet(s) comprising the sol are separated from the walls of the microfluidic device, in particular by a layer of carrier fluid. Preferably, the carrier fluid completely envelops the or each microdroplet. Preferably, the carrier fluid wets the walls of the microfluidic device better than the sol of the or each microdroplet.

[0076] Preferably, the gel time of the sol is greater than or equal to 5 minutes, and even better still greater than or equal to 10 minutes.

[0077] The method may include circulating a fluid between the inlet and outlet channels during the trapping of the sol-containing microdroplet(s) and / or the formation of the sol-gel matrix. By such circulation of the fluid, the contents of the trapped microdroplet(s) may be displaced so as to homogenize the contents of said microdroplet(s). This is particularly useful when the sol microdroplets are formed by adding one or more complementary and / or additional microdroplets and / or during the formation of the sol-gel matrix. This may also allow the movement of microbeads in the sol so that the formation of the gel can be assessed.

[0078] The method may comprise controlling the temperature of the microfluidic device during the trapping of the microdroplets, in particular decreasing the temperature of the microfluidic device, and increasing the temperature of the microfluidic device during the formation of the sol-gel matrix. Preferably, the temperature of the microfluidic device during trapping is between 0 and 30°C, even better between 5 and 15°C. Preferably, the temperature of the microfluidic device during the formation of the sol-gel matrix is ​​between 20 and 80°C, even better between 20 and 60°C, even better between 30 and 50°C. By controlling the temperature of the device during the process, it is possible to precisely control the formation of the sol-gel matrix and to have a reproducible device. By decreasing the temperature during trapping, it is possible to increase the gel time and to avoid the formation of the sol-gel matrix outside the capillary trap, which may block the microfluidic device. By increasing the temperature during the formation of the sol-gel matrix, it is possible to control the syneresis and / or drying steps, in particular by accelerating the formation of the gel.

[0079] Preferably, the method comprises the additional step of drying the microfluidic matrix by evaporating the solvent contained in the microdroplets. The drying step may comprise evaporation of the solvent through a gas permeable surface of the microfluidic device and / or circulation of fluids in the microfluidic device between at least one inlet channel upstream of the capillary trap and at least one outlet channel downstream of the capillary trap. The method may comprise controlling the drying rate by controlling the flow rate of the fluids in the microfluidic device and / or by selection of the pore size.

[0080] The method may include a step of displacing the fluid surrounding the microdroplets after the drying step. In the case of a liquid, this may be done by evaporation of this liquid through the inlets and outlets of the microchannel or through a permeable surface. Displacement may also be forced by injection of another liquid or gas through the microchannel. In this case, the flow of liquid or gas replaces the original liquid.

[0081] The method may include visualizing the syneresis and drying in real time using a device for observing the sol-gel matrix in the or each capillary trap, in particular using an optical device for forming an image of each microdroplet.

[0082] According to a third aspect, the subject of the present invention is also a method for detecting and / or capturing one or more analytes in a fluid to be tested using a microfluidic device as described above, or a microfluidic device manufactured using the method as described above, in which the microdroplet(s) trapped in the capillary trap(s) each comprise one or more molecular sensors in a sol-gel matrix configured to detect and / or capture one or more target analytes, the method comprising the steps of exposing the microdroplet(s) trapped in the microfluidic device to the fluid to be tested and detecting and / or capturing the target analyte(s) in the fluid to be tested.

[0083] Precise positioning of the microdroplets within the microfluidic device allows for direct visualization of the presence of the target analyte(s) in the fluid being tested. Capture of the target analyte may allow for its extraction from the fluid being tested to reduce the concentration of the target analyte in the fluid exiting the microfluidic device, and / or for capture of the target analytes in the fluid to allow for their recovery and, optionally, their subsequent use.

[0084] By integrating microdroplets within a microfluidic device and immobilizing them there, they can be easily exposed to the fluid to be tested, allowing for detection and / or capture of target analytes without the need to handle the microdroplets or modify the device, which also facilitates the analysis of the microdroplets.

[0085] When the device comprises several molecular sensors, it allows the parallel detection and / or capture of several target analytes in the fluid being treated.

[0086] Moreover, in contrast to electronic devices for detecting one or more target analytes, such devices do not require any specific calibration.

[0087] Preferably, the molecular sensor(s) is as described above in relation to the microfluidic device.

[0088] Preferably, the fluid to be tested is a liquid or a gas.

[0089] Preferably, the method comprises circulating a fluid in a microfluidic device from an inlet channel of the microfluidic device upstream of the capillary trap(s) to an outlet channel of the microfluidic device downstream of the capillary trap(s) using a microfluidic system, in particular a pump, a syringe pump or a pressure differential.

[0090] Preferably, the presence of the target analyte(s) is detected by a change in an optical property of the or each molecular sensor, in particular the colour, absorbance, reflectance, fluorescence or luminescence of the or each molecular sensor.

[0091] Preferably, the fluid is a gas, in particular ambient air, and the step of exposing the microdroplet(s) is performed by circulation of the gas between the inlet and outlet channels of the microfluidic device, in particular the capture chamber. The forced circulation of the gas can be obtained using a mass flow rate regulator, a pump, a syringe pump, a pressure difference, or an equivalent system. To detect an analyte, the user simply injects the gas present in the environment in which the detection is to be performed into the microfluidic device to check for the presence or absence and / or the concentration of the target analyte and / or capture it.

[0092] If the fluid is a gas, in particular ambient air, the exposure of the microdroplet(s) may be through a gas-permeable wall of the microfluidic device, in particular the capture chamber. Thus, to check the presence or absence and / or concentration of a target analyte and / or to capture the target analyte, the microfluidic device may be placed in an environment in which detection is to take place.

[0093] The method may include introducing liquid into the microfluidic device until a liquid front is formed adjacent to the microdroplet(s), particularly along a step in the microfluidic device, where the microdroplet(s) is not in contact with the liquid but is in contact with gas formed by evaporation of the liquid in the microfluidic device from the liquid front.

[0094] Alternatively, the method includes introducing a liquid into the microfluidic device and its circulation between the inlet and outlet channels, and detecting the presence or absence of the target analyte directly in the liquid.

[0095] Preferably, the method comprises a step of determining the concentration of at least one target analyte in the fluid to be tested, to which the or each microdroplet of the microfluidic device is exposed, in particular by the intensity of a measured optical property, in particular by color, fluorescence or luminescence intensity, where the concentration can be precisely determined by reference to a pre-established calibration curve.

[0096] The method may in particular comprise detecting a concentration gradient of one or more target analytes in the fluid to be tested by visualization of different detection intensities that vary depending on the position of the microdroplets on the microfluidic device.

[0097] According to a fourth aspect, the subject of the present invention is also a method for evaluating a sol-gel matrix in a microfluidic device as described above or in a microfluidic device manufactured using the method as described above, in which the microdroplet(s) trapped in a capillary trap comprise said sol-gel matrix.

[0098] The method may include a step of observing in real time the formation of the matrix or the syneresis of the sol-gel matrix, in particular the diameter of the microdroplets during the steps of gel formation, syneresis and drying.

[0099] The method may comprise the step of evaluating the gel time of the sol in the microdroplet during the formation of said sol-gel matrix in the microdroplet, in particular to derive therefrom the gel time of the macroscopic volume of sol-gel material.The method may comprise the steps of applying a fluid stream, in particular an oil, in the microfluidic device to cause movement of the fluid in the or each microdroplet, and observing the movement of observable microbeads, in particular fluorescent microbeads, in the microdroplet, the gel time being determined by observing the fixation of the microbeads in the gel.

[0100] The method may include controlling the temperature of the, or each, microdroplet.

[0101] The invention can be better understood on reading the following description of a non-limiting embodiment of the invention in connection with the attached drawings, in which: [Brief description of the drawings]

[0102] [Figure 1] FIG. 1 is a schematic diagram illustrating an example of a microfluidic device according to the present invention. [Diagram 2] FIG. 2 is a cross-sectional view of the device of FIG. 1 taken along line II-II. [Diagram 3] FIG. 1 is a perspective view of a variant of the microfluidic device according to the present invention. [Figure 4] FIG. 4 is a schematic diagram of the microfluidic device of FIG. 3 along line IV. [Diagram 5] FIG. 5 is a schematic diagram of a cross section along VV of the microfluidic device of FIGS. 3 and 4. [Figure 6A] 1A-1D are diagrams illustrating different steps of a method for manufacturing a device according to the invention. [Figure 6B] FIG. 6B illustrates another step of the method of FIG. 6A. [Figure 6C] FIG. 6C illustrates another step of the method of FIGS. 6A and 6B. [Figure 7] FIG. 6 shows a detail of a device obtained by the method shown in FIGS. 6A-6C after syneresis and drying of the sol-gel matrix. [Figure 8] FIG. 4 shows a variant of the device according to the invention. [Figure 9] FIG. 9 is a cross-sectional view of the device of FIG. 8 along line IX-IX. [Figure 10] FIG. 5 represents a fluorescence measurement of detail X of the device of FIG. 4 made according to Example 3. [Figure 11] 13 is a graph showing the fluorescence intensity of the microdroplets of the device of Example 3 as a function of time for various groups of microdroplets. [Figure 12] 13A-13D are images of microdroplets of a device made according to Example 4 at different times during the formation of the gel. [Figure 13]1 is a graph depicting the gel time measured as a function of temperature using the device of Example 4. [Figure 14] 13 is a graph showing the calculated gel time difference between microfluidic and macroscopic devices as a function of temperature using the device of Example 4. [Figure 15] 13 shows images of microdroplets of a device made according to Example 4 before and after syneresis. [Figure 16] 1 is a graph showing the measured microdroplet diameter as a function of time using the device of Example 4. [Figure 17] 1 is a graph depicting the gel time measured as a function of temperature using the device of Example 5. [Figure 18] 13 is a graph showing the calculated gel time difference between microfluidic and macroscopic devices as a function of temperature using the device of Example 5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0103] FIG. 1 shows diagrammatically a first embodiment of a microfluidic device 1 according to the invention.

[0104] In the example shown in Figure 1, the device comprises a microchannel 2 containing a capillary trap 12 in which a microdroplet 15 containing a sol-gel matrix is ​​trapped. The microchannel 2 has a rectangular cross-section and is bounded by a top wall 4, a bottom wall 6 and two side walls 8, as shown in Figure 2.

[0105] In the example shown in Figures 1 and 2, the microdroplets 15 are microbeads containing a sol-gel matrix in solid form after the syneresis step of the sol-gel process, i.e. the microbeads do not contain any solvent, said solvent has evaporated and the sol-gel matrix has shrunk. The microdroplets then have the smallest possible size and are non-deformable.

[0106] The capillary trap 12 is formed by a cavity in the lower wall 6, in which the microdroplets are captured (trapped). In the example shown in FIG. 2, the cavity is a cavity in the lower wall 6, but it could also be a cavity in the upper wall 4, and the microdroplets would be trapped in the same way. As will be seen below, the microdroplets are trapped in the capillary trap 12 in liquid form, the matrix being in particular in sol form. A liquid microdroplet that has entered the microchannel 2 and been crushed has a large external surface area. This microdroplet therefore naturally seeks to reduce its external surface area, which causes it to move towards the capillary trap 12, which has a greater height, when it comes in the vicinity of the capillary trap. The capillary trap 12 makes it possible to fix one or more microdroplets, which makes it possible to examine them, for example using a microscope, and / or to monitor the progress of a reaction in the trap over a long period of time.

[0107] 2, the height H of the microchannel 2 defined by the distance between the upper wall 4 and the lower wall 6 of the edge of the capillary trap 12 is less than the minimum dimension d of the microdroplet 15 after the syneresis step of the sol-gel process. Thus, the microdroplet 15 is securely trapped within the capillary trap 12.

[0108] Preferably, the height h of the capillary trap 12 defined between the base of the capillary trap 12 and the opposite wall of the microchannel 2 is at least twice the height H of the microchannel 2 at the edge of the capillary trap 12. Preferably, the width l of the capillary trap 12 is at least twice the height H of the microchannel 2 at the edge of the capillary trap 12. These dimensions allow efficient trapping of the microdroplets prior to the gel formation, syneresis and drying steps of the sol-gel process to obtain a sol-gel matrix.

[0109] The height H of the microchannel 2 at the edge of the capillary trap 12 is preferably between 15 μm and 200 μm, even better between 50 μm and 150 μm, for example substantially equal to 100 μm.

[0110] The height h of the capillary trap 12 is preferably between 30 μm and 800 μm, and even better still between 450 μm and 600 μm, for example substantially equal to 520 μm.

[0111] In the example shown in Figure 1, the capillary trap 12 has a hexagonal cross section. However, the invention is not limited to capillary traps of such a shape. The trap may, for example, have a circular or polygonal cross section, or may include a primary capture zone and one or more secondary capture zones, as described in patent application WO2018 / 060471, which is incorporated herein by reference.

[0112] The sol-gel matrix is ​​preferentially obtained by a hydrolytic sol-gel process.

[0113] The sol-gel matrix is ​​obtained from a precursor selected from alkoxides, in particular zirconium alkoxides, in particular zirconium butoxide (ZTBO), zirconium propoxide (ZTPO), alkoxides of titanium, niobium, vanadium, yttrium, cerium, aluminum or silicon, in particular tetramethoxysilane (TMOS), tetraethoxysilane (TEOS), tetrapropoxysilane (TPOS), tetrabutoxysilane (TBOS), trimethoxysilanes, in particular methyltrimethoxysilane (MTMOS), propyltrimethoxysilane (PTMOS) and ethyltrimethoxysilane (ETMOS), triethoxysilanes, in particular methyltriethoxysilane (MTEOS), ethyltriethoxysilane (ETEOS), propyltriethoxysilane (PTEOS) and aminopropyltriethoxysilane (APTES), and mixtures thereof.

[0114] The microdroplet(s) may comprise a solvent, in particular a solvent selected from water, methanol, ethanol, propanol, butanol, 2-methoxyethanol, acetone, DMSO, DMF, NMF, formamide, methyl ethyl ketone, chloroform, dichloromethane, acetic acid, and mixtures thereof, preferably a mixture of water and butanol.

[0115] The microdroplet(s) may contain other additives, particularly catalysts such as acetic acid, nitric acid, sulfuric acid, hydrofluoric acid, and ammonium hydroxide, or stabilizers such as acetic acid, acetylacetone, glycol, methoxyethanol, glycol, and β-ketoesters.

[0116] 3 and 5 show diagrammatically a second embodiment of a microfluidic device 1 according to the invention.

[0117] In the example shown in Figures 3 to 5, the device 1 comprises a capture chamber 20 comprising a number of capillary traps 12 arranged as a number of rows of traps 12 that are slightly offset from one another. The capture chamber 20 is connected upstream of the capillary traps 12 to an inlet microchannel 30 to which fluid is supplied via two fluid supply microchannels 32, and downstream to an outlet microchannel 34. The capture chamber 20 has a rectangular cross section and is bounded by an upper wall 24 and a lower wall 26, which can be seen in particular in Figure 5, and four side walls 28, which can be seen in particular in Figures 3 and 4.

[0118] The number of capillary traps is preferably between 10 and 5000, in particular between 100 and 500, for example equal to 231.

[0119] As can be seen in Figure 3, the microfluidic device 1 may be formed in a plate of suitable material, for example PDMS (polydimethylsiloxane), by using common flexible lithography techniques as known in the art. The microchannels 30 and capture chambers 20 may be formed in the surface of the plate onto which, for example, a microscope slide is bonded.

[0120] The capture chamber 20 also comprises a step 40 downstream of the capillary trap 12, which at its edge has a height m that is greater than the height of the capture chamber. Such a step 40 allows the insertion of liquid via the outlet channel 34 to form a liquid front downstream of the capillary trap 12 in the capture chamber 20, the liquid front being defined by the shape of the step. In particular, the liquid is maintained by interfacial tension in a zone of maximum height. Preferably, the step has a height m between 80 μm and 250 μm, preferably between 100 μm and 150 μm. Preferably, the step has a height m at the edge of the step 40 that is substantially equal to 105% to 200%, preferably between 110% to 130%, in particular substantially equal to 115% of the height of the capture chamber 20.

[0121] Each capillary trap 12 is preferably as described above and is capable of trapping a microdroplet 15 containing a sol-gel matrix.

[0122] Preferably, the volume percentage of alcohol in the sol is between 80% and 20%.

[0123] The capillary traps can capture microdroplets by a process illustrated in connection with Figures 6A-6C, described below as "breaking of the drops in capillary traps", for example as described in patent application FR3056927, the contents of which are incorporated herein by reference.

[0124] During a first step, shown in FIG. 6A, a first solution 42 containing a sol is introduced into the capture chamber 20 via one of the feed microchannels 32 so as to fill it.

[0125] During a second step shown in Fig. 6B, a second solution 44, comprising a solvent that is immiscible with the first solution, in particular an oil, is introduced into the trapping chamber 20 via one of the supply microchannels 32. The second solution washes the first solution out of the trapping chamber and forms microdroplets of the first solution directly in the capillary traps 12 by breaking the first solution (i.e. breaking the solution apart) in each capillary trap, as seen in Fig. 6C.

[0126] Preferably, the wetting properties are such that the carrier fluid wets the solid walls and thus forms a film around the microdroplet(s) containing the sol, in which case the microdroplets formed in the capillary trap are substantially the same.

[0127] As a variant (not shown), the trapping of the microdroplets 15 occurs by formation of a microdroplet containing the sol upstream of the capillary trap 12 and by trapping of an already formed microdroplet 15. The formation of the microdroplets can occur directly in the mobile phase between the inlet channel 30 and the outlet channel 34 of the microfluidic device.

[0128] Many processes have already been proposed for forming such first microdroplets in a mobile phase, for example the following processes can be mentioned as examples: a) the "flow-focusing" process, as described, for example, in S. L. Anna, N. Bontoux and H. A. Stone, "Formation of dispersions using 'flow-focusing' in microchannels", Appl. Phys. Lett. 82, 364 (2003), the contents of which are incorporated herein by reference; b) the "stepwise emulsification" process, as described, for example, by R. Seemann, M. Brinkmann, T. Pfohl and S. Herminghaus, in "Droplet-based microfluidics.," Rep. Prog. Phys., volume 75, number. 1, page 016601, Jan. 2012, the contents of which are incorporated herein by reference; c) processes combining the "flow focusing" and "step emulsification" processes, as described, for example, in V. Chokkalingam, S. Herminghaus and R. Seemann in "Self-synchronizing pairwise production of monodisperse droplets by microfluidic step emulsification", Appl. Phys. Lett., volume 93, number. 25, page 254101, 2008, the contents of which are incorporated herein by reference; d) the "T-branch" process, as described, for example, by GF Christopher and SL Anna in "Microfluidic methods for generating continuous droplet streams", J. Phys. D. Appl. Phys., volume 40, number 19, pages R319-R336, Oct. 2007, the contents of which are incorporated herein by reference; e) the "confined gradient" process, as described, for example, in R. Dangla, S. C. Kayi, and C. N. Baroud in "Droplet microfluidics driven by gradients of confinement.," Proc. Natl. Acad. Sci. USA, volume 110, number 3, pages. 853-8, Jan. 2013, the contents of which are incorporated herein by reference; or f) The "microsegmented flow" process, as described, for example, in A. Funfak, R. Hartung, J. Cao, K. Martin, KH Wiesmuller, OS Wolfbeis and JM Kohler in "Highly resolved dose-response functions for drug-modulated bacteria cultivation obtained by fluorometric and photometric flow-through sensing in microsegmented flow", Sensors Actuators, B Chem., volume 142, number 1, pages 66-72, 2009, the contents of which are incorporated herein by reference (wherein two solutions in different proportions are mixed at the level of function outside the microfluidic system to form microliter droplets separated by an immiscible phase, followed by a process of splitting these droplets into microdroplets, for example by injection into a microfluidic system containing a gradient).

[0129] These processes can in particular form multiple microdroplets of substantially equal size, the size of the resulting microdroplets being controllable by varying the microdroplet formation parameters, in particular the flow rates of the fluids within the device and / or the geometry of the device.

[0130] The microdroplets 15 may be generated in the same microfluidic system as the present process, or in a different device. In the latter case, the microdroplets 15 may be stored in one or more external containers before being injected into the microfluidic system. These microdroplets 15 may all be identical, or some of them may have different compositions, concentrations, and / or sizes.

[0131] After the formation of these microdroplets 15, they may be transported to the capillary trap 12 by entrainment with a stream of fluid and / or by means of a relief in the form of a gradient or rails. In both cases, the addition of rails allows the filling of the capillary trap 12 to be selectively optimized, for example by combining with the use of an infrared laser as described in E. Fradet, C. McDougall, P. Abbyad, R. Dangla, D. McGloin and CN Baroud in “Combining rails and anchors with laser forcing for selective manipulation within 2D droplet arrays.,” Lab Chip, volume 11, number 24, pages 4228-34, Dec. 2011.

[0132] If microdroplet generation is performed outside the microfluidic device, transport from the reservoir to the microfluidic device 1 may be performed, for example, directly via tubing connecting the generation system and the capture system, or by aspiration and injection with a syringe.

[0133] The microdroplets 15 trapped in the capillary trap contain a sol that forms a sol-gel matrix by a sol-gel process. In the above process, the sol-gel process starts as soon as the sol is formed and before the microdroplets 15 are trapped. Therefore, the gel time is preferably shorter than the time required from preparation of the sol to trapping the microdroplets 15, so as to avoid the formation of a sol-gel matrix outside the capillary trap 12, which would block the problematic microdroplet(s) outside the capillary trap.

[0134] As a variant, the microdroplets 15 containing the sol trapped in the capillary traps 12 can be formed in several steps by the coalescence of several microdroplets in each capillary trap 12. The microdroplets enabling the formation of the microdroplets containing the sol can be added in one or more steps. It is possible to increase the possibilities by making the sol in the microdroplets in several steps by the addition of complementary microdroplets. It is possible to have a first microdroplet all identical in the capillary traps and to add complementary microdroplets of different composition and / or different amounts to it in different capillary traps. This also allows the formation of a sol-gel matrix only in the capillary traps 12, the sol-gel process not taking place as long as the sol is incomplete. For example, a microdroplet of a first solution containing a part of the sol can be trapped in the capillary traps 12 by one of the methods previously described, then a complementary microdroplet containing another part of the sol, for example water, can be added and trapped in each capillary trap 12 to form the microdroplets 15 containing the sol by coalescence.

[0135] The coalescence may or may not be selective.

[0136] To fuse all of the contacting microdroplets in the capture chamber 20, the device may be perfused with a surfactant-free fluid. The surfactant concentration in the fluid of the microfluidic system may be reduced, thereby shifting the equilibrium of surfactant adsorption at the interface towards desorption. The microdroplets lose their stabilizing effect and spontaneously fuse with the contacting microdroplets.

[0137] Alternatively, the microfluidic device is perfused with a fluid containing a destabilizing agent, for example 1H,1H,2H,2H-perfluorooctan-1-ol in fluoro oil in the case of aqueous microdroplets.

[0138] As another alternative, all of the contacting microdroplets within the capture chamber 20 are fused by applying an external physical stimulus, such as a mechanical wave, a pressure wave, a temperature change, or an electric field.

[0139] Microdroplets may be selectively fused using an infrared laser as described in E. Fradet, P. Abbyad, MH Vos and CN Baroud in “Parallel measurements of reaction kinetics using ultralow-volumes.,” Lab Chip, volume 13, number 22, pages 4326-30, Oct. 2013, or an electrode 37 located at the interface of the microdroplets between the capture zones may be activated as shown in FIG. 51, or a mechanical wave may be focused at one or more points.

[0140] The present invention is not limited to the coalescence examples described above: any method for destabilizing the interface between two contacting microdroplets can be used to fuse the microdroplets.

[0141] Measurements of the state of the resulting microdroplets can then be made and / or real-time observations of said microdroplets can be made, which allows, for example, investigation of the sol-gel process.

[0142] The trapping process described above allows trapping identical and / or different microdroplets 15 in the capillary trap, in particular microdroplets having different sol compositions or different concentrations of sol compounds.

[0143] During this sol-gel process, each sol-gel matrix undergoes a step of expulsion of the solvent, i.e. syneresis, and shrinkage of the sol-gel matrix due to evaporation of the solvent, also called drying of the matrix, to form microbeads containing the sol-gel matrix as shown in Figure 7. In the aforementioned microfluidic device, the microdroplets 15 are encapsulated in the microfluidic device. In this case, the solvent can evaporate through the walls of the device if said walls are gas permeable, in particular through walls made of PDMS, or by circulation of gas within the microfluidic device between the inlet channel 30 and the outlet channel 34. Evaporation of the solvent during the syneresis step can be controlled by controlling the pore size of the porous walls and / or by controlling the flow rate of the gas within the microfluidic device.

[0144] Preferably, the microfluidic device 1 comprises a system (not shown) for controlling the temperature in the trapping chamber 20, allowing in particular to control the formation of the sol-gel matrix. The control system makes it possible to reduce the temperature of the microfluidic device 1 in particular during trapping of the microdroplets 15 in order to slow down the formation of the gel and prevent said gel from forming before the trapping of the microdroplets 15, and / or to increase the temperature of the microfluidic device during the formation of the sol-gel matrix in order to accelerate its formation. Preferably, the temperature of the microfluidic device during trapping is between 0 and 30°C, even better between 5 and 15°C, and the temperature of the microfluidic device during the formation of the sol-gel matrix is ​​between 20 and 80°C, even better between 20 and 60°C, even better between 30 and 50°C.

[0145] In the above mentioned examples, the microdroplet 15 may also include one or more molecular sensors integrated in the sol-gel matrix, which have optical properties, in particular color or fluorescence, that change upon contact with a particular target analyte. The change in optical properties may occur upon reaction or binding with the target analyte, allowing rapid detection of the presence or absence of the corresponding target analyte(s) in the fluid in contact with the microdroplet by simple observation of the microdroplet 15 in the capillary trap 12. If the molecular sensor(s) form a bond with the corresponding target analyte, it is also possible to collect the analyte by recovering the microdroplet in the capillary trap(s).

[0146] The molecular sensor(s) may include detection molecules selected from 4-amino-3-penten-2-one, p-dimethylaminobenzaldehyde, p-dimethylaminocinnamaldehyde, p-methoxybenzaldehyde, 4-methoxynaphthaldehyde, crotonic acid, p-diazobenzenesulfonic acid, 4-aminoantipyrine, carmine indigo, quinone compounds, mixtures of iodide and compounds selected from starch, amylose, amylopectin, xyloglucan, xylan, chitosan, glycogen, polyvinyl alcohol or polyvinyl alcohol compounds, cellulose or cellulose compounds, α-cyclodextrin, theobromine and block polymers of polypropylene oxide and polyethylene oxide, sensors containing phenol and sodium nitroprusside, and compounds described in patent application WO2005 / 100371, which is incorporated herein by reference. Additives such as solvents, oxidizing agents, reducing agents, acids, or bases may be added to promote reaction with the target analyte. This list is not exhaustive and any molecule that allows, alone or in combination with others, a more or less selective interaction or chemical function with the target analyte may be added to the molecular sensor, in particular polymers, complexing agents, colored pH indicators, dyes, fluorophores, phthalocyanines and porphyrins.

[0147] The molecular sensor(s) each make it possible to detect a target analyte chosen from volatile organic compounds, in particular those defined in the list of priority pollutants by ANSES (Agence Nationale de Securite Sanitaire de l'alimentation de l'environnement et du travail), in particular aldehydes, such as formaldehyde, acetaldehyde, and hexaldehyde, carbon monoxide or carbon dioxide, dioxygen (O2), hydrogen, phenols and their derivatives, indole compounds, in particular indole, skatole, or tryptophan, chloramines, nitrogen dioxide, ozone, halogenated compounds, in particular boron trifluoride, its derivatives, and boron trichloride, aromatic hydrocarbons, such as naphthalene, benzene, and toluene, and non-aromatic hydrocarbons, such as pentane, hexane, and heptane, acrolein, nitrogen dioxide, and ethylbenzene.

[0148] The concentration of the detection molecules constituting the molecular sensor in the sol microdroplets can be adapted to have the highest possible concentration while maintaining solubility in the microdroplets and in the final form specific for the analysis, in particular in gels or solid materials. The optimal concentration varies depending on the molecules constituting the molecular sensor and the sol-gel formulation. For example, in a sol formulation containing zirconium butoxide, acetylacetate, butanol, TEOS and water in the molar proportions (1:1:16:1:22), respectively, the concentration of 4-amino-3-penten-2-one for detecting formaldehyde in the sol precursor of the microdroplets 15 is preferably between 0.05 and 0.4 M in the sol, even better between 0.2 and 0.3 M.

[0149] The microdroplets 15 may all contain the same molecular sensors in the same concentration, or they may contain different molecular sensors or different concentrations of molecular sensors.

[0150] Alternatively, the microdroplets 15 may each contain several molecular sensors exhibiting a different response to the target analyte, for example a different color.

[0151] The molecular sensor(s) may be placed directly in the sol during the formation of the sol prior to entrapment, or may be placed directly in the first solution that includes a portion of the sol.

[0152] Alternatively, the molecular sensor(s) can be placed in the form of additional microdroplets in the capillary trap 12 and then merged with the microdroplet containing part of the sol or containing the sol prior to formation of a gel or the gel in the process of formation. The additional microdroplets may be the same or different, in particular may contain one or more different molecular sensors and / or different concentrations of molecular sensors, and / or the number of additional microdroplets trapped in each capillary trap may be the same or different.

[0153] As described in patent application FR3056927, which is incorporated herein by reference, the addition of complementary or additional microdroplets can be controlled by the morphology of the microdroplets and the method for adding the complementary or additional microdroplets.

[0154] It can therefore be clearly seen that by the various processes described above in combination with the morphology of the microfluidic device 1, in particular the capillary trap 12, and with the composition and morphology of the microdroplets, it is possible to obtain a variety of devices for performing research or statistical measurements and / or multiplexing.

[0155] The concentration at which an analyte must be detected is generally a concentration that is subject to precise specifications, in particular those related to a particular industrial process or according to regulations. The composition of the microdroplets and the formation of the sol-gel matrix vary depending on the concentration that must be detected according to specifications and / or regulations. For example, the current regulation for formaldehyde in France is 100 μg / m 3 The microdroplets 15 containing the sol-gel matrix formed in the example preferably have a concentration of 10 to 500 μg / m 3 This allows the detection of formaldehyde at concentrations of 0.01 to 0.1%.

[0156] The device may also make it possible to determine the concentration of an analyte in the fluid to be tested, or the concentration gradient of an analyte in the fluid to be tested, by visualizing the detection intensity of each microdroplet 15 comprising a sol-gel matrix, in particular depending on its position on the microfluidic device.

[0157] During the step of detecting the target analyte, the fluid to be tested is preferably introduced into the device via the inlet channel 30, in particular by means of a fluid circulation system (not shown), and circulated within the device to contact the microdroplets 15.

[0158] Alternatively, if the fluid to be tested is gaseous, the fluid is brought into contact with the microdroplet 15 by diffusion through the porous walls of the microfluidic device, in particular made of PDMS, and the device therefore only needs to be placed in an environment containing the gas to be tested.

[0159] As a further variant, the fluid to be tested is placed in the device in liquid form to form a delimited liquid front by step 40 as described above, and the microdroplets 15 are then brought into contact with vapour coming from the liquid diffusing within the microfluidic device.

[0160] 8 and 9 show diagrammatically a third embodiment of a microfluidic device 1 according to the invention, which differs from the previous one in that the device comprises a capillary trap 12 trapping a number of microdroplets 15 comprising a sol-gel matrix. In this device, the microdroplets 12 are preferably formed before trapping. In the example shown, the capillary trap 12 is formed from a cavity in the top wall 4, and the microdroplets 15 comprising a sol-gel matrix form a column of microdroplets in the capillary trap 12. Preferably, in such a device comprising several microdroplets per capillary trap 12, the microdroplets 15 comprise a surfactant to prevent droplet coalescence.

[0161] In this embodiment, microdroplets 15 containing the sol are formed before being trapped in the capillary trap 12 . EXAMPLES

[0162] A first mixture is prepared at room temperature (20° C.) using equal proportions of zirconium butoxide and acetylacetate in butanol as solvent to obtain a zirconium butoxide solution. In a preferential embodiment, the respective molar proportions are (1:1:16). The mixture is left to stand overnight, then TEOS and water are added to it to obtain a final respective molar proportion of (1:1:16:1:22), followed by vigorous stirring. The resulting sol solution is quickly introduced at 20° C. into a microfluidic device according to the second embodiment described above, pre-filled with fluoro oil. The sol solution is dispensed into the capillary trap by the disruption method described above. The microsystem is then heated, for example to 40° C., to accelerate the formation of gel in the microdroplets 15, syneresis, and evaporation of the solvent through the PDMS walls of the microfluidic device.

[0163] Thereby, a microfluidic device according to FIG. 7 is obtained. EXAMPLES

[0164] A microfluidic device is prepared as in Example 1, except that 4-amino-3-penten-2-one is dissolved in the zirconium butoxide solution before adding TEOS and water. 4-amino-3-penten-2-one is the detection unit for detecting formaldehyde. It goes from colorless to dark yellow in the presence of the latter and emits yellow fluorescence.

[0165] The microdroplets 15 are indeed formed. EXAMPLES

[0166] The microfluidic device, prepared as in Example 2, is then exposed to gaseous formaldehyde by positioning the front of the liquid formaldehyde solution 60 according to the method described above. The fluorescence of the microdroplets 15 is observed over time. A photograph of a part of the device close to the liquid front 60 at a given time point is shown in FIG. 10. In this figure, it can be seen that the fluorescence of the microdroplets 15 close to the liquid front is stronger than that of the microdroplets 15 further away. The microdroplets 15 in the device are divided into three groups according to their distance from the liquid front, and a statistical measurement of the fluorescence according to the groups is performed as a function of time in FIG. 11, with group A being closest to the liquid front 60 and group C being the furthest from the liquid front 60. The microdroplets 15 of group A, represented by curve A, show the strongest fluorescence, and the microdroplets 15 of group C, represented by curve C, show the weakest fluorescence. The fluorescence monitoring of the microdroplets 15 demonstrates the reaction between gaseous formaldehyde and 4-amino-3-penten-2-one in the microdroplets. The gradual increase in intensity over time as a function of distance from the front demonstrates the possibility of measuring the concentration of gaseous formaldehyde in a fluid. Thus, the microdroplets 15 detect the presence of formaldehyde and respond correctly as a function of its concentration. Moreover, they are able to record small local fluctuations. The reorganization of the microdroplets as a row clearly shows that this microsystem makes it possible to measure concentrations statistically with a single microsystem. EXAMPLES

[0167] Fluorescent microbeads 50 were added to the sol of the microfluidic device prepared according to Example 1 and then injected into the microfluidic system. The sol microdroplet 15 confined in the capillary trap 12 is subjected to a flow of oil, which causes the movement of the microbeads within the sol. As can be seen in FIG. 12, where the fluorescent microbeads 50 are observed within the microdroplet 15 at different time points, the movement of the beads stops when the gel hardens, allowing the determination of the gel time, which corresponds to the time from the formation of the sol to the hardening of the gel. This observation is carried out at different temperatures as shown in FIG. 13, which shows the statistically measured gel time t in the microfluidic device as a function of temperature T. G The temperature in the microfluidic device is controlled by a Peltier effect module on which the microfluidic device is placed, and an estimation of the gel time is performed for several microdroplets, specifically 20 microdroplets, thereby obtaining a statistical measurement.

[0168] The gel times measured in microfluidic devices are much shorter than those conventionally measured in tubes. Figure 14 shows curves representing the mathematical relationships that allow the transition from one to the other for the sol-gel matrices investigated.

[0169] It is also possible to observe the syneresis over time, as shown in FIG. 15, which represents three microdroplets 15 at t=0 and t=65 hours after syneresis. The size of the microdroplets 16 can then be statistically measured over time, as shown in FIG. 15. The curve is obtained by taking a series of images at different times of 10 microdroplets in 10 different traps and measuring the size of the microdroplets in each image. The size of the microdroplets 15 goes from about 380 μm to 175 μm, which is a shrinkage of more than 50%. This allows optimizing the sol-gel process, especially for the preparation of microfluidic devices for the detection of analytes. EXAMPLES

[0170] The curves in Figures 17 and 18 are obtained with the same procedure as in Example 4, but with different sols and over a wider temperature range. A first mixture is prepared with (TMOS) and water in methanol as solvent at room temperature (20°C) to obtain a tetramethylorthosilicate (TMOS) solution. The molar ratios of TMOS, methanol and water are (1:2:4), respectively. The mixture is heated at 70°C for 10 minutes, and then water is added to it to obtain a final respective molar ratio of (1:2:9), followed by vigorous stirring. The sol of the prepared microfluidic device is added with fluorescent microbeads 50 and then injected into a microfluidic system pre-filled with fluoro oil. The sol solution is distributed into the capillary trap by the disruption method described above. The microsystem is then heated to a given temperature T.

[0171] The gel time is determined by observing the movement of the beads at different temperatures as shown in Figure 17, which shows the statistically measured gel time t in the microfluidic device as a function of temperature T. G The sol defined in this example can be used in microfluidic devices up to 70° C.

[0172] FIG. 18 shows curves representing the mathematical relationships that can be transferred from a microfluidic device according to the invention to conventional tubing for the sol-gel matrices investigated.

[0173] Thus, it is possible to predict the gel time of a sol-gel process on a macroscopic scale by investigating microdroplets using the same sol-gel process, as can be clearly seen in Examples 4 and 5. This allows very fast measurement of different gel times in the microfluidic device according to the invention without the need to perform macroscopic experiments, resulting in time savings, automation of measurements and less reagent consumption. [Explanation of symbols]

[0174] 1. Microfluidic Device 2. Microchannel 4 Upper wall 6 Lower wall 8 side wall 12 Capillary Trap 15 Microdroplets 20 Capture Chamber 24 Upper Wall 26 Lower Wall 28 Side wall 30 Inlet microchannel, inlet channel 32 Fluid supply microchannel, supply microchannel 34 Outlet microchannel, outlet channel 40 Steps 42 First Solution 44 Second Solution

Claims

1. at least one capillary trap (12), at least one microdroplet (15) containing a sol-gel matrix, the microdroplet (15) being trapped in a capillary trap (12); A microfluidic device (1).

2. 10. The device of claim 1, comprising a plurality of spaced apart capillary traps (12) and a plurality of microdroplets (15) each including a sol-gel matrix, each microdroplet (15) being trapped in one of the capillary traps (12).

3. The device according to claim 2, wherein the number of capillary traps (12) is 10 or more.

4. 4. The device according to any one of claims 1 to 3, wherein the capillary trap(s) (12) each form a cavity in a wall (4, 6) of the microfluidic device (1).

5. 5. The device according to claim 4, wherein a height H of the edge of the capillary trap(s) (12), corresponding to the distance between a wall (4, 6) in which a cavity is formed and an opposite wall (4, 6) at the edge of the capillary trap (12), is less than or equal to a smallest dimension of the or each trapped microdroplet (15) comprising a sol-gel matrix.

6. A device according to any one of claims 1 to 5, wherein the sol-gel matrix of the or each microdroplet (15) is in gel or solid form after syneresis and / or drying steps of the sol-gel process.

7. A device according to any one of claims 1 to 6, wherein the device (1) comprises in the or each capillary trap (12) only one microdroplet (15) comprising a sol-gel matrix.

8. 7. A device according to any preceding claim, comprising a plurality of microdroplets comprising a sol-gel matrix within the or each capillary trap.

9. The device according to any one of claims 1 to 8, wherein the device (1) comprises a plurality of microdroplets (15) all comprising substantially the same sol-gel matrix.

10. 10. The device of any one of claims 1 to 9, wherein the microdroplet(s) (15) each comprise one or more molecular sensors within a sol-gel matrix, each molecular sensor being configured to detect the presence of a target analyte.

11. 11. A device according to claim 10, wherein the or each molecular sensor is configured to have optical properties which differ in the presence of a target analyte.

12. 12. The device according to claim 10 or 11, wherein the microdroplet(s) (15) comprise at least two different molecular sensors for detecting different target analytes.

13. 13. The device of any one of claims 10 to 12, wherein at least one microdroplet (15) comprises at least two different molecular sensors within a sol-gel matrix, the molecular sensors being configured to detect the presence of different target analytes.

14. 13. The device according to any one of claims 10 to 12, wherein at least two microdroplets (15) contain different molecular sensors for detecting different target analytes.

15. 14. The device according to any one of claims 10 to 13, wherein at least two microdroplets (15) contain different concentrations of at least one molecular sensor.

16. A method for manufacturing a microfluidic device (1), comprising trapping at least one microdroplet (15) comprising a sol in a capillary trap (12) of the microfluidic device, and using the sol to form a sol-gel matrix in the microdroplet (15) by a sol-gel process.

17. 17. The method of claim 16, comprising trapping a plurality of microdroplets (15) containing a sol in one or more capillary traps (12) of a microfluidic device (1) and using the sol to form a sol-gel matrix in each microdroplet (15) by a sol-gel process.

18. 18. The method of claim 16 or 17, comprising the step of adding one or more molecular sensors to the microdroplet(s) before or after formation of the sol-gel matrix, each molecular sensor allowing the detection of at least one target analyte.

19. trapping one or more microdroplets (15) each containing a sol in a capillary trap (12); (i) trapping a first microdroplet comprising a portion of the sol in the or each capillary trap; (ii) sequentially adding n times (n being an integer) to the microfluidic device one or more complementary microdroplets containing different portions of the sol, trapping it (them) in the or each capillary trap (12), and merging the first microdroplet and the complementary microdroplet(s) in each capillary trap (12) to obtain a microdroplet (15) containing the sol, wherein merging occurs after each or after all sequential additions; 19. The method of any one of claims 16 to 18, comprising:

20. 20. The method according to any one of claims 16 to 19, comprising a preliminary step of forming microdroplet(s) (15) comprising the sol or first microdroplet(s) comprising a part of the sol prior to the step of trapping in the capillary trap.

21. The step of capturing the microdroplet(s) (15) containing the sol or the first microdroplet(s) containing a portion of the sol comprises: - filling the microfluidic device (1) with a first solution (42) containing a sol or a sol portion; - injecting a second solution (44) upstream of the capillary trap(s) (12) and pushing the first solution towards an outlet of the microfluidic device (1) downstream of the capillary trap(s), the microfluidic device (1) being configured to allow the formation of micro-droplets of the first solution (42) in the or each capillary trap (12) during the injection of the second solution into the microfluidic device (1); 20. The method of any one of claims 16 to 19, comprising:

22. 22. The method according to any one of claims 16 to 21, wherein the gel time of the sol is 5 minutes or more.

23. 23. The method according to any one of claims 16 to 22, comprising the step of controlling the temperature of the microfluidic device (1) during the process of the method.

24. 24. The method according to any one of claims 16 to 23, comprising a syneresis and drying step, said syneresis and drying step being carried out by evaporation of a solvent contained in the sol-gel matrix through a gas-permeable surface of the microfluidic device (1) or by circulation of fluids in the microfluidic device (1) between at least one inlet channel (30) upstream of the capillary trap and at least one outlet channel (34) downstream of the capillary trap (12).

25. 25. A method for detecting and / or capturing one or more analytes in a fluid to be tested using a microfluidic device (1) according to any one of claims 1 to 15 or manufactured by the method according to any one of claims 16 to 24, wherein microdroplets (15) trapped in the capillary traps (15) each comprise one or more molecular sensors in a sol-gel matrix configured to detect and / or capture one or more target analytes, the method comprising the steps of exposing the microdroplets (15) trapped in the microfluidic device to the fluid to be tested and detecting and / or capturing the target analyte(s) in the fluid to be tested.

26. 26. The method of claim 25, wherein the fluid is a gas and the step of exposing the microdroplets (10, 100, 1000) is performed by circulating the gas in the microfluidic device (12) through a gas-permeable wall of the microfluidic device (1) or using a microfluidic system from an inlet channel (30) of the microfluidic device upstream of the capillary trap (10, 100, 1000) to an outlet channel (34) of the microfluidic device downstream of the capillary trap (10, 100, 1000)

27. 26. The method of claim 25, comprising the step of introducing a liquid into the microfluidic device (1) until a liquid front is formed in the vicinity of the microdroplet(s) (15), wherein the microdroplet(s) (15) are not in contact with the liquid and the microdroplet(s) (15) are exposed to gas formed by evaporation of the liquid in the microfluidic device (1) from the liquid front.

28. 28. The method according to any one of claims 25 to 27, comprising a step of determining the concentration of at least one target analyte in a fluid to be tested, to which the or each microdroplet (15) of the microfluidic device is exposed.

29. A method for evaluating a sol-gel matrix in a microfluidic device (1) according to any one of claims 1 to 15 or produced by the method according to any one of claims 16 to 24, comprising: a microdroplet(s) (15) trapped in a capillary trap (12) comprising said sol-gel matrix; A method for evaluating a sol-gel matrix in said microfluidic device (1), comprising the step of observing the formation of the matrix or the syneresis of the sol-gel matrix over time.

30. The method of claim 29, comprising evaluating the gel time of the sol during the formation of the sol-gel matrix in the microdroplet (15).

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