Hydrophilic and hydrophobic treatment method for surface of micro-fluidic chip and micro-fluidic chip

Abstract

The invention discloses a micro-fluidic chip surface hydrophilic and hydrophobic treatment method and a micro-fluidic chip, and relates to the technical field of micro-fluidic chips. The surface hydrophilic and hydrophobic treatment method for the micro-fluidic chip comprises the following steps: providing a first substrate and a second substrate, preparing hydrophilic modification layers on the surfaces of the first substrate and the second substrate, then bonding to form a fluid micro-channel of the micro-fluidic chip, introducing modified gas or modified liquid into the fluid micro-channel, and carrying out surface hydrophilic and hydrophobic treatment on the surface of the micro-fluidic chip. The hydrophilic modification layer on the inner wall of the fluid microchannel is modified into a hydrophobic modification layer. According to the micro-fluidic chip surface hydrophilic and hydrophobic treatment method provided by the invention, the hydrophilic modification layer is prepared before the substrate is bonded, and the modified gas or the modified liquid is injected after the substrate is bonded to carry out hydrophobic modification on the hydrophilic modification layer on the inner wall of the fluid micro-channel, so that the uniformity of the hydrophobic modification layer on the inner wall of the fluid micro-channel is ensured; the liquid drop generation flux and the liquid drop generation consistency of the micro-fluidic chip are effectively improved.

Description

Technical Field

[0001] The invention relates to the technical field of microfluidic chips, and in particular to a method for treating hydrophilicity and hydrophobicity on the surface of a microfluidic chip and the microfluidic chip. Background Art

[0002] Hydrogel single-cell reverse transcription is a technology that reverse transcribes the RNA of a single cell into cDNA, and is commonly used for single-cell transcriptome analysis; this technology requires the use of tiny channels and droplet generation devices in microfluidic chips to mix a solution containing single cells with a hydrogel precursor solution to form monodisperse microspheres or hydrogel spheres containing single cells.

[0003] The uniformity of the surface contact angle and the modification intensity are very important for the process of using microfluidic chips for monodisperse microspheres or hydrogel spheres; the PDMS material widely used in microfluidic chips has a natural hydrophobic surface, but it usually needs to be plasma treated in the bonding process to make it firmly bonded. The hydrophilicity of the PDMS surface after plasma treatment is enhanced, and natural recovery or thermal annealing cannot quantitatively control the state of surface recovery of the PDMS material, resulting in uneven liquid surface contact angles on the inner wall of the fluid microchannel formed after bonding; in-channel modification methods such as vapor deposition or injection of hydrophobic modification liquid can also be used to cover the inner wall of the fluid microchannel with a hydrophobic modification layer, but this method is difficult to ensure uniform and stable modification in a closed microchannel, and may even cause channel blockage; there is also a process that uses a step emulsification structure multi-channel parallel method to avoid the unstable hydrophobic modification step on the surface, but this method greatly increases the production cost of monodisperse microspheres, and due to the relatively low speed of droplet generation, it is easy to cause problems such as inconsistent droplet generation or even inability to generate droplets. Summary of the invention

[0004] The embodiment of the present invention provides a method for treating the hydrophilicity and hydrophobicity of the surface of a microfluidic chip and a microfluidic chip, aiming to improve the droplet generation flux and droplet generation consistency of the microfluidic chip.

[0005] The method for treating the surface of a microfluidic chip by hydrophilicity and hydrophobicity provided by the present invention comprises the following steps:

[0006] S1, providing a first substrate and a second substrate; a surface of at least one of the first substrate and the second substrate is provided with a microchannel pattern;

[0007] S2, preparing a hydrophilic modification layer on the surfaces of the first substrate and the second substrate;

[0008] S3, bonding the first substrate and the second substrate to form a fluid microchannel of the microfluidic chip;

[0009] S4, introducing a modified gas or a modified liquid into the fluid microchannel to modify the hydrophilic modification layer on the inner wall of the fluid microchannel into a hydrophobic modification layer.

[0010] Optionally, the hydrophilic modification layer is composed of silicon dioxide nanoparticles, and the step S2 specifically comprises:

[0011] The silicon dioxide nanoparticles are adsorbed and bonded to the surfaces of the first substrate and the second substrate by electrostatic adsorption.

[0012] Optionally, the step of adsorbing and bonding the silicon dioxide nanoparticles to the surfaces of the first substrate and the second substrate by electrostatic adsorption specifically includes:

[0013] S21: plasma cleaning: performing oxygen plasma cleaning on the first substrate and the second substrate;

[0014] S22: Adsorption and bonding of silica nanoparticles: placing the first substrate and the second substrate into a nano-silicon dioxide modification solution and soaking them for a preset period of time;

[0015] S23: Drying and curing: cleaning the excess nano-silicon dioxide modification liquid on the surfaces of the first substrate and the second substrate, and placing them in an oven for drying.

[0016] Optionally, it also includes:

[0017] Step S22 and step S23 are repeated multiple times.

[0018] Optionally, the nano-silicon dioxide modification solution is prepared by the following method:

[0019] A nano-silicon dioxide aqueous solution with a solid content of 0.5 wt % is prepared, and concentrated sulfuric acid or hydrochloric acid is used to quickly adjust the pH of the nano-silicon dioxide aqueous solution to a preset value.

[0020] Optionally, the nano-silicon dioxide modification solution can also be prepared by the following method:

[0021] TEOS was added dropwise into 50 mL of 1 mM NaOH solution, and the mixture was stirred for 24 h. The pH of the mixed solution was quickly adjusted to a preset value with hydrochloric acid to obtain a nano-silica modified solution.

[0022] Alternatively, ethyl orthosilicate was mixed with 1.5 mL of ethanol, and 3 mL of 25% ammonia water was added at the same time, the mixed solution was stirred at room temperature for 2 h, and then 2 mL of the stirred mixed solution was quickly mixed with 18 mL of 1 M hydrochloric acid to obtain a nano-silica modified solution.

[0023] Optionally, the modified liquid is a n-hexane modified liquid prepared by n-hexane and trichlorodecylsilane, wherein the volume fraction of trichlorodecylsilane is 0.5%;

[0024] The step S4 specifically includes:

[0025] S41: pouring the n-hexane modification solution into the fluid microchannel, and allowing trichlorosilane and silica nanoparticles to self-assemble to form a super-hydrophobic interface;

[0026] S42: After the preset reaction time, place in an oven for drying.

[0027] Optionally, one of the first substrate and the second substrate is made of PDMS, and the other is made of glass or PDMS;

[0028] The step S3 specifically includes:

[0029] The first substrate and the second substrate are bonded by plasma sealing.

[0030] Optionally, the material of the first substrate and the second substrate is at least one of PMMA, PS, PP, and COC / COP;

[0031] The step S3 specifically includes:

[0032] The first substrate and the second substrate are bonded by at least one of thermal bonding, ultrasonic sealing, laser welding, UV light curing adhesive sealing, and double-sided adhesive sealing.

[0033] The microfluidic chip provided by the present invention has a fluid microchannel, and the inner wall of the fluid microchannel is covered with a hydrophobic modification layer;

[0034] The preparation process of the microfluidic chip includes the above-mentioned method for treating the surface of the microfluidic chip with hydrophilicity and hydrophobicity.

[0035] It can be seen from the above technical solutions that the present invention has the following beneficial effects:

[0036] The embodiment of the present invention prepares a hydrophilic modification layer on the surface of the substrate that can be hydrophobically modified by a modification gas or a modification liquid before the substrates are bonded. The hydrophilic modification layer has good hydrophilicity, which improves the surface energy of the substrate and does not cause a decrease in the bonding tightness and bonding effect of the substrates. Moreover, a uniform hydrophilic modification layer can be easily prepared before the substrates are bonded, and the modification strength and effect of the hydrophilic modification layer can be adjusted according to actual needs. After the substrates are bonded to form a complete fluid microchannel, only the modification gas or modification liquid needs to be injected into the fluid microchannel to quickly complete the hydrophobic modification of the hydrophilic modification layer, thereby avoiding the problem of uneven modification caused by traditional thermal annealing methods or in-channel modification methods, and there is no need to adopt a high-cost and low-speed step emulsification structure multi-channel parallel method, thereby effectively improving the droplet generation flux and droplet generation consistency of the microfluidic chip. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0038] Figure 1 This is a flowchart of an embodiment of a method for treating hydrophilicity and hydrophobicity on the surface of a microfluidic chip according to the present invention;

[0039] Figure 2 This is a schematic diagram of the principle of modification of silicon dioxide nanoparticles in one embodiment of the method for hydrophilicity and hydrophobicity treatment of the surface of a microfluidic chip of the present invention;

[0040] Figure 3 This is a schematic diagram of the surface modification cycle principle of silicon dioxide nanoparticles in one embodiment of the method for hydrophilicity and hydrophobicity treatment on the surface of a microfluidic chip of the present invention. DETAILED DESCRIPTION

[0041] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] The terms "first", "second", "third", "fourth", etc. (if any) in the specification and drawings of the present application are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein, for example. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0043] Relevant explanations or descriptions of the English terms involved in the embodiments of this application:

[0044] PDMS: polydimethylsiloxane; PMMA: polymethyl methacrylate; PS: polystyrene; PP: polypropylene; COC / COP: cyclic olefin copolymer / cyclic olefin polymer; TEOS: tetraethoxysilane; SiNPs: silica nanoparticles; DTS: deoxytrichlorosilane; plasma: plasma.

[0045] Traditional microfluidic chips can be divided into PDMS-glass chips, double-sided PDMS chips and thermoplastic polymer chips according to different materials.

[0046] PDMS has a naturally hydrophobic surface with a water contact angle greater than 100°; the production of PDMS-glass chips requires high-energy physical treatment of the surfaces of PDMS and glass materials, such as oxygen plasma treatment, to increase the surface hydrophilicity, activate the functional groups and free groups on the surface of the materials, and chemically cross-link the PDMS and glass materials, thereby bonding the two materials. The surface of the PDMS material after plasma activation is transient and will recover its hydrophobicity within a few hours or days; but in fact, after the hydrophobicity of the PDMS material surface is restored, the water contact angle is uneven; PDMS can also be restored to hydrophobicity by heating and baking (thermal annealing), but the temperature and time of thermal annealing are difficult to accurately estimate and judge, and it is impossible to quantitatively control the state of PDMS material surface restoration.

[0047] When using double-sided PDMS materials to make microfluidic chips, the surface usually needs to be plasma treated before bonding to form a flow channel cavity. After plasma treatment, the water contact angle on the surface of the PDMS material, which was originally greater than 100°, will be reduced to about 30°, making it difficult to generate droplets. Similarly, the thermal annealing method is not applicable to the production of double-sided PDMS chips due to its strong uncertainty.

[0048] In addition to thermal annealing, PDMS-glass chips and double-sided PDMS chips can also use in-channel modification methods to cover the inner wall of the channel with a hydrophobic modification layer, such as chemical vapor deposition of fluorosilane agents, parylene CVD vapor deposition, and other vapor deposition modification methods under vacuum conditions; however, the vapor deposition modification method is difficult to ensure uniform and stable inner wall modification in closed microchannels. For closed channels with a depth or width of less than 40 μm, it is difficult for gases to enter the deep channels even in a vacuum environment, and the surface of the fluorinated material requires nitrogen storage to avoid the influence of water vapor and oxygen in the air on the hydrophobic properties of the material surface; various hydrophobic modification liquids can also be used and injected into the chip channel through a syringe pump, but it is necessary to ensure that the excess modification liquid is blown dry by continuous air, otherwise the modification liquid remaining in the microchannel will cause blockage of the chip microchannel.

[0049] Thermoplastic polymer chips are often made of thermoplastic polymer substrates such as PMMA, PS, PP, COC / COP, etc., which are injection molded to achieve mass production and cost control. However, after the polymer materials are bonded, it is usually difficult to ensure the consistency of the surface modification effect in the channel during mass production and the effective control of the modification process points. Therefore, the method of in-channel modification cannot be used. The hydrophobic modification effect on the surface of the material can only be effectively controlled before the material is bonded. Fluorination treatment is usually used to hydrophobically modify the surface of polymer materials, but fluorination treatment will reduce the adhesion and adhesion of the material surface, making it difficult to bond the hydrophobic treated material firmly. For example, after the microfluidic chip is bonded and sealed by thermal bonding, ultrasonic sealing, UV light curing glue, double-sided adhesive, etc., liquid leakage is likely to occur when a certain pressure is applied. The only way to deal with it is to partially remove the hydrophobic surface modification layer at the bonding and sealing, such as laser removal by carbon dioxide laser, excimer laser, etc. or local cleaning using hydrogen plasma, which will increase the complexity and instability of the microfluidic chip production process.

[0050] In addition, a step emulsification structure with multiple channels in parallel can be used to avoid the unstable hydrophobic modification step on the surface of the microfluidic chip material. In this method, each droplet generation channel generates stable and uniform droplets at a relatively low speed, and multiple channels need to be connected in parallel to ensure the efficiency of droplet generation, which greatly increases the production cost of monodisperse microspheres. Moreover, this method will also encounter some problems when generating some monomer-polymerized microspheres or hydrogel spheres. For example, after the polyacrylamide monomer water phase is configured, a certain degree of polymerization will occur during the entire droplet generation process, causing the relevant physical properties of the monomer water phase to gradually change during the droplet generation process as the droplet generation time increases, thereby affecting the consistency of the generated droplets. At the same time, the viscosity of the water phase will also change during the polymerization of the water phase. Under extreme conditions, such as excessive water phase flow or low water phase surface tension, general droplet generation chips may not be able to generate droplets.

[0051] In short, how to ensure the droplet generation flux and droplet generation consistency of microfluidic chips is a problem that has plagued the microfluidic chip preparation process for a long time, and it has posed a certain obstacle to the research and production based on microfluidic chips.

[0052] The present invention provides a microfluidic chip surface hydrophilicity and hydrophobicity treatment method and a microfluidic chip, aiming to solve the above problems.

[0053] See also Figure 1 In one embodiment, the method for treating the surface of a microfluidic chip with hydrophilicity and hydrophobicity provided by the present invention comprises the following steps:

[0054] S1, providing a first substrate and a second substrate; a surface of at least one of the first substrate and the second substrate is provided with a microchannel pattern.

[0055] Specifically, microfluidic chips usually have different structures and preparation processes depending on the material.

[0056] In the first case, one of the first substrate and the second substrate of the traditional PDMS-glass chip is a PDMS material, and the other is a glass substrate or a glass cover plate. A microchannel pattern is prepared on the surface of one of the first substrate and the second substrate (usually PDMS), and the two substrates are bonded to form a microfluidic chip with fluid microchannels inside.

[0057] In the second case, microfluidic chips used for research and development purposes usually use double-sided PDMS materials, that is, the first substrate and the second substrate are both PDMS materials prepared with microchannel patterns, and the microchannel patterns on the two substrates are arranged correspondingly so that the first substrate and the second substrate can form a complete fluid microchannel after bonding; the first substrate and the second substrate can be prepared by a method of mixing a prepolymer and a curing agent and pouring them into a mold.

[0058] In the third case, microfluidic chips used for mass production and cost control are often obtained by injection molding of thermoplastic polymers such as PMMA, PS, PP, COC / COP, etc. The first substrate and the second substrate are injection-molded thermoplastic polymers, and the surfaces of the first substrate and the second substrate have corresponding microchannel patterns so that a complete fluid microchannel is formed after the first substrate and the second substrate are bonded.

[0059] S2, preparing a hydrophilic modification layer on the surfaces of the first substrate and the second substrate.

[0060] Specifically, the hydrophilic modification layer is used to enhance the hydrophilicity of the surfaces of the first substrate and the second substrate, that is, to reduce the water contact angle of the surface; the material of the hydrophilic modification layer can be selected from silicon dioxide nanoparticles to enhance the hydrophilicity of the substrate surface by increasing the roughness; the hydrophilic modification layer can also be selected from titanium dioxide nanoparticles, barium sulfate nanoparticles and other metal or non-metal compound nanoparticles with stable chemical properties to increase the roughness of the substrate surface, thereby enhancing the hydrophilicity of the substrate surface.

[0061] S3, bonding the first substrate and the second substrate to form a fluid microchannel of the microfluidic chip.

[0062] Specifically, a suitable bonding process is selected according to the material of the microfluidic chip.

[0063] In the first case mentioned above, the microfluidic chip is a traditional PDMS-glass chip, and the first substrate and the second substrate are bonded by plasma sealing; after the surfaces of the PDMS material and the glass material are treated with plasma, the functions and free radicals on the surfaces of the materials are activated, so that the PDMS material and the glass material are chemically cross-linked, thereby bonding the two materials.

[0064] In the second case, the first substrate and the second substrate are both made of PDMS, and the first substrate and the second substrate are bonded by plasma sealing, and the first substrate and the second substrate are chemically cross-linked, thereby bonding the first substrate and the second substrate.

[0065] In the third case, the material of the first substrate and the second substrate is a thermoplastic polymer, specifically at least one of PMMA, PS, PP, COC / COP; the first substrate and the second substrate are bonded by at least one of thermal bonding, ultrasonic sealing, laser welding, UV light curing glue sealing, and double-sided tape sealing.

[0066] S4, introducing a modified gas or a modified liquid into the fluid microchannel to modify the hydrophilic modification layer on the inner wall of the fluid microchannel into a hydrophobic modification layer.

[0067] Specifically, a complete fluid microchannel is formed after the first substrate and the second substrate are bonded. Since the bonding surfaces of the first substrate and the second substrate are covered with a hydrophilic modification layer, the inner wall of the fluid microchannel formed after bonding is covered with the hydrophilic modification layer.

[0068] The hydrophilic modification layer is modified by introducing a modified gas or a modified liquid into the fluid microchannel; for example, in one embodiment, when the material of the hydrophilic modification layer is selected from silica nanoparticles, a gaseous or liquid hydrophobic silane can be introduced into the fluid microchannel to form a silica nanoparticle-hydrophobic silane super-hydrophobic interface through molecular self-assembly; in other embodiments, the hydrophilic modification layer can be made of other metal or non-metal compound nanoparticles with stable chemical properties, such as titanium dioxide nanoparticles, which can react with the active groups on the surface of titanium dioxide through a fluorinated alkyl modifier, etc., to form a hydrophobic fluorine-containing polymer layer on the surface; for example, barium sulfate nanoparticles, similar to silica nanoparticles, can also be hydrophobically modified by hydrophobic silane.

[0069] The embodiment of the present invention prepares a hydrophilic modification layer on the surface of the substrate that can be hydrophobically modified by a modification gas or a modification liquid before the substrates are bonded. The hydrophilic modification layer has good hydrophilicity, which improves the surface energy of the substrate and does not cause a decrease in the bonding tightness and bonding effect of the substrates. More importantly, a uniform hydrophilic modification layer can be easily prepared before the substrates are bonded, and the modification strength and effect of the hydrophilic modification layer can be adjusted according to actual needs. After the substrates are bonded to form a complete fluid microchannel, the hydrophobic modification of the hydrophilic modification layer can be quickly completed by injecting a modification gas or a modification liquid into the fluid microchannel, thereby avoiding the problem of uneven hydrophobic modification caused by traditional thermal annealing methods or in-channel modification methods, and ensuring the droplet generation flux and droplet generation consistency of the microfluidic chip.

[0070] In addition, for the PDMS material, which is the most widely used in microfluidic chips, since the PDMS material has a high adsorption capacity for biological molecules, if the generated droplets contain biological molecules such as antibodies, the surface contact angle of the PDMS will gradually decrease with the adsorption of the biological molecules, making it difficult to stably generate droplets. The hydrophilic and hydrophobic modified layer provided in the embodiment of the present invention can also be used as a barrier protective layer for the inner wall of the PDMS fluid microchannel, effectively preventing the PDMS material from adsorbing biological molecules. For microfluidic chips made of thermoplastic polymer materials, it is not necessary to remove the hydrophobic modification layer in the bonding area before bonding the substrate, which simplifies the process flow and improves the degree of production standardization.

[0071] Based on the above embodiments, in a preferred embodiment of the present invention, the hydrophilic modification layer is composed of silicon dioxide nanoparticles, and step S2 specifically includes:

[0072] The silicon dioxide nanoparticles are adsorbed and combined onto the surfaces of the first substrate and the second substrate by electrostatic adsorption.

[0073] In this embodiment, the finished product of silica nanoparticles is usually a dispersion product. There are a large number of silanol groups on the surface of the silica nanoparticles, which have natural hydrophilicity. These silanol groups will ionize under different environmental conditions. In an aqueous solution in an alkaline environment, the silica nanoparticles carry more negative charges. The silica nanoparticles can also adsorb cations and thus carry positive charges to a certain extent.

[0074] It is understood that when the silicon dioxide nanoparticles used are negatively charged, the substrate is processed to be positively charged; when the silicon dioxide nanoparticles used are positively charged, the substrate is processed to be negatively charged, so that the silicon dioxide nanoparticles are electrostatically adsorbed on the surface of the substrate.

[0075] In this embodiment, the substrate can obtain corresponding electrical properties through surface treatment methods such as plasma treatment, electron beam irradiation, electrostatic adsorption of electrolytes, and chemical grafting.

[0076] In this embodiment, in order to stably bind the silica nanoparticles to the substrate surface, an acid solution can usually be used to stably bind the silica nanoparticles to the substrate via the silanol groups on the surface, thereby achieving a long-term modification effect.

[0077] In this embodiment, since the silicon nanoparticles carry the same charge, electrostatic repulsion is generated between the particles, which helps to prevent the particles from agglomerating and ensures that the silicon nanoparticles are evenly spread on the substrate, thus having good modification uniformity.

[0078] In some embodiments, the step of adsorbing and bonding the silicon dioxide nanoparticles to the surfaces of the first substrate and the second substrate by electrostatic adsorption specifically includes:

[0079] S21: Plasma cleaning: performing oxygen plasma cleaning on the first substrate and the second substrate.

[0080] Oxygen plasma interacts with the surface of the substrate, causing charges to be generated on the substrate surface. The amount of charge on the substrate surface can be controlled by adjusting plasma parameters such as gas flow, discharge power, and processing time. The substrate surface after plasma treatment has good charge stability.

[0081] S22: Adsorption and bonding of silica nanoparticles: placing the first substrate and the second substrate into the nano-silica modification liquid and soaking them for a preset time.

[0082] S23: Drying and curing: Clean the excess nano-silicon dioxide modification liquid on the surfaces of the first substrate and the second substrate, and place them in an oven for drying.

[0083] The preset duration of immersion can be set based on multiple factors such as the required tightness of the hydrophilic modification layer, nanoparticle concentration, temperature, plasma treatment time, etc., and is not limited here.

[0084] In some embodiments, the above steps S22 and S23 can be repeated multiple times to achieve uniform adsorption; in the final drying and curing step, the temperature of the oven should be greater than the boiling point of the solvent of the nano-silica modification solution to completely evaporate the residual solvent.

[0085] Based on the above-mentioned embodiment of the method for treating the surface of a microfluidic chip with hydrophilicity and hydrophobicity, the present invention further provides the following specific embodiments.

[0086] Example 1

[0087] See also Figure 2 and Figure 3 , Figure 2 Schematic diagram of the modification principle of silica nanoparticles. Figure 3 The schematic diagram of the surface modification cycle of silicon dioxide nanoparticles is shown in FIG. 1 . This embodiment includes the following steps:

[0088] Prepare nano-silica modification solution: Use the finished product of nano-silica particles, such as SiNPs Ludox TM-50 nano-silica aqueous solution, dilute the SiNPs solid content to 0.5 wt% in water, and use concentrated sulfuric acid or hydrochloric acid to quickly adjust the pH of the diluted solution to 2.

[0089] Substrate plasma treatment: The substrate was cleaned with oxygen plasma. The power of the oxygen plasma was 75W, the treatment time was 300s, and the gas flow rate was 100sccm.

[0090] Substrate covered with hydrophilic modification layer: Soak the plasma-treated substrate in the prepared nano-silicon dioxide modification liquid for 10 minutes, clean the excess modification liquid on the surface of the substrate with pure water, and dry it in a 90° oven for 15 minutes.

[0091] Repeat this operation 3-5 times to achieve uniform adsorption and complete hydrophilic modification. Finally, place the substrate in a 120° oven and bake for 1 h.

[0092] Substrate bonding: sealing the hydrophilically modified substrate.

[0093] Perform hydrophobic modification: prepare a n-hexane modification solution made of a mixture of n-hexane and trichlorodecylsilane, wherein the volume fraction of trichlorodecylsilane is 0.5%;

[0094] The sealed microfluidic chip was immersed in the n-hexane modification solution, or the n-hexane modification solution was perfused into the fluid microchannel of the microfluidic chip, and the immersed microfluidic chip was placed in a 120° oven until it was completely dried to obtain the target microfluidic chip.

[0095] In this embodiment, deoxytrichlorosilane (DTS) self-assembles with silica nanoparticles on the inner wall of the fluid microchannel to form a SiNPs-DTS super hydrophobic interface with a maximum water contact angle greater than 150°, which has excellent hydrophobic properties.

[0096] Example 2

[0097] The steps of this embodiment refer to those of Embodiment 1, and the difference from Embodiment 1 lies in the step of preparing the nano-silicon dioxide modification solution.

[0098] Prepare nano-silica modification solution: add a certain amount of tetraethyl orthosilicate (TEOS) dropwise into 50 mL of 1 mM NaOH solution, continue stirring for 24 h, and quickly adjust the pH of the mixed solution to 2 with hydrochloric acid.

[0099] This embodiment configures a nano-silicon dioxide modification solution with small diameter particles.

[0100] Example 3

[0101] The steps of this embodiment refer to those of Embodiment 1, and the difference from Embodiment 1 lies in the step of preparing the nano-silicon dioxide modification solution.

[0102] Prepare nano-silica modification solution: mix a certain amount of tetraethyl orthosilicate (TEOS) with 1.5 mL of ethanol, and add 3 mL of 25% ammonia water at the same time, stir the mixed solution at room temperature for 2 h, and then quickly mix 2 mL of the stirred mixed solution with 18 mL of 1 M hydrochloric acid.

[0103] This embodiment is configured with a nano-silicon dioxide modification solution of large-diameter particles.

[0104] Example 4

[0105] Prepare nano-silica modification solution: Select two nano-silica aqueous solutions with different particle diameters, SiNPs Ludox TM-50 and SiNPs Ludox LS-35, dilute the solid content of the two SiNPs to 0.5 wt% in water, and use concentrated sulfuric acid or hydrochloric acid to quickly adjust the pH of the diluted solution to 2.

[0106] Substrate plasma treatment: The substrate was cleaned with oxygen plasma. The power of the oxygen plasma was 75W, the treatment time was 300s, and the gas flow rate was 100sccm.

[0107] Substrate covered with hydrophilic modification layer: Place the plasma-treated substrate into the prepared SiNPs Ludox TM-50 nano-silicon dioxide modification liquid and soak for 10 minutes. Use pure water to clean the excess modification liquid on the surface of the substrate and place it in a 90° oven to dry for 15 minutes.

[0108] The dried substrate was placed in the prepared SiNPs Ludox LS-35 nano-silica modification solution and soaked for 10 minutes. The excess modification solution on the surface of the substrate was cleaned with pure water and placed in a 90° oven to dry for 15 minutes.

[0109] After alternately soaking in two nano-silica modification solutions and drying in an oven for 3-5 times, uniform adsorption is achieved and hydrophilic modification is completed. Finally, the substrate is placed in a 120° oven and baked for 1 hour.

[0110] Substrate bonding: sealing the hydrophilically modified substrate.

[0111] Perform hydrophobic modification: prepare a n-hexane modification solution made of a mixture of n-hexane and trichlorodecylsilane, wherein the volume fraction of trichlorodecylsilane is 0.5%;

[0112] The sealed microfluidic chip was immersed in the n-hexane modification solution, or the n-hexane modification solution was perfused into the fluid microchannel of the microfluidic chip, and the immersed microfluidic chip was placed in a 120° oven until it was completely dried to obtain the target microfluidic chip.

[0113] The hydrophilic and hydrophobic modification layer prepared in this embodiment includes silicon dioxide nanoparticles of two particle sizes and has a greater roughness than the previous embodiments. The modified microfluidic chip substrate and fluid microchannel have a smaller water contact angle.

[0114] The microfluidic chip prepared by the above specific embodiment of the silica nanoparticle modification layer has no damaging effect on the silica nanoparticle modification layer by processes such as ultrasonic cleaning, ultrasonic sealing, laser welding, high temperature and high pressure thermal bonding, etc., provided that it is not immersed in a solution with a pH greater than 7 for a long time.

[0115] It can be seen from the above embodiments that the method for treating the hydrophilicity and hydrophobicity of the surface of a microfluidic chip proposed in the present invention prepares a uniform hydrophilic modification layer before substrate bonding, and injects a modified gas / liquid into the fluid microchannel after substrate bonding to quickly complete the hydrophobic modification of the hydrophilic modification layer; it can be seen from the preferred embodiment based on silica nanoparticles that the modified modification layer prepared by the method has good uniformity, which can solve the problem of uneven hydrophobic modification that has long existed in microfluidic chips with PDMS as the substrate, and the modification effect of the modified layer can be controlled by adjusting the compactness of the modified layer, which can also be used as a barrier The barrier layer avoids the problem of reduced contact angle caused by the adsorption of biological molecules by the PDMS material; for microfluidic chips made of thermoplastic polymer materials, the method does not need to remove the modification layer in the bonding area, which simplifies the process flow and improves the degree of production standardization; therefore, the method for hydrophilic and hydrophobic treatment of the surface of a microfluidic chip proposed in the present invention improves the droplet generation flux and droplet generation consistency of the microfluidic chip by improving the hydrophobic uniformity of the inner wall of the microfluidic channel, which is of great significance to promoting the research and production of microfluidic chips, as well as the development of related industries such as biology and medicine.

[0116] The present invention also provides a microfluidic chip. The microfluidic chip has a fluid microchannel, and the inner wall of the fluid microchannel is covered with a hydrophobic modification layer.

[0117] The hydrophobic modification layer of the fluid microchannel of the microfluidic chip is prepared by the microfluidic chip surface hydrophilicity and hydrophobicity treatment method provided by the aforementioned embodiment. Therefore, the microfluidic chip proposed by the present invention has all the beneficial effects of the aforementioned embodiments, which will not be described in detail here.

[0118] Among them, according to different specific functions, microfluidic chips include microfluidic droplet chips, microreactor chips, cell culture chips, separation and analysis chips, etc.

[0119] In one embodiment, the microfluidic chip provided by the present invention is a microfluidic droplet chip, the inner wall of which has a uniform hydrophobic modification layer on the fluid microchannel. The microfluidic droplet chip is used for hydrogel single-cell reverse transcription, can stably generate droplets of uniform size, and has a high droplet generation efficiency.

[0120] The embodiments described above are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for treating the surface of a microfluidic chip by hydrophilicity and hydrophobicity, characterized in that: The following steps are involved: S1, providing a first substrate and a second substrate; a surface of at least one of the first substrate and the second substrate is provided with a microchannel pattern; S2, preparing a hydrophilic modification layer on the surfaces of the first substrate and the second substrate; S3, bonding the first substrate and the second substrate to form a fluid microchannel of the microfluidic chip; S4, introducing a modified gas or a modified liquid into the fluid microchannel to modify the hydrophilic modification layer on the inner wall of the fluid microchannel into a hydrophobic modification layer.

2. The method for treating the surface of a microfluidic chip with hydrophilicity and hydrophobicity according to claim 1, characterized in that: The hydrophilic modification layer is composed of silicon dioxide nanoparticles, and the step S2 specifically comprises: The silicon dioxide nanoparticles are adsorbed and bonded to the surfaces of the first substrate and the second substrate by electrostatic adsorption.

3. The method for treating the surface of a microfluidic chip with hydrophilicity and hydrophobicity according to claim 2, characterized in that: The step of adsorbing and bonding the silicon dioxide nanoparticles to the surfaces of the first substrate and the second substrate by electrostatic adsorption specifically comprises: S21: plasma cleaning: performing oxygen plasma cleaning on the first substrate and the second substrate; S22: Adsorption and bonding of silica nanoparticles: placing the first substrate and the second substrate into a nano-silicon dioxide modification solution and soaking them for a preset period of time; S23: Drying and curing: cleaning the excess nano-silicon dioxide modification liquid on the surfaces of the first substrate and the second substrate, and placing them in an oven for drying.

4. The method for treating the surface of a microfluidic chip with hydrophilicity and hydrophobicity according to claim 3, characterized in that: Specifically include: Step S22 and step S23 are repeated multiple times.

5. The method for treating the surface of a microfluidic chip with hydrophilicity and hydrophobicity according to claim 3, characterized in that: The nano-silicon dioxide modification solution is prepared by the following method: A nano-silicon dioxide aqueous solution with a solid content of 0.5 wt % is prepared, and concentrated sulfuric acid or hydrochloric acid is used to quickly adjust the pH of the nano-silicon dioxide aqueous solution to a preset value.

6. The method for treating the surface of a microfluidic chip with hydrophilicity and hydrophobicity according to claim 3, characterized in that: The nano-silicon dioxide modification solution is prepared by the following method: Add ethyl orthosilicate dropwise into 50 mL of 1 mM NaOH solution, continue stirring for 24 h, and quickly adjust the pH of the mixed solution to a preset value with hydrochloric acid to obtain a nano-silica modified solution; Alternatively, ethyl orthosilicate was mixed with 1.5 mL of ethanol, and 3 mL of 25% ammonia water was added at the same time, the mixed solution was stirred at room temperature for 2 h, and then 2 mL of the stirred mixed solution was quickly mixed with 18 mL of 1 M hydrochloric acid to obtain a nano-silica modified solution.

7. The method for treating the surface of a microfluidic chip with hydrophilicity and hydrophobicity according to claim 2, characterized in that: The modified liquid is a n-hexane modified liquid prepared from n-hexane and trichlorosilane, wherein the volume fraction of trichlorosilane is 0.5%; The step S4 specifically includes: S41: pouring the n-hexane modification solution into the fluid microchannel, and allowing trichlorosilane and silica nanoparticles to self-assemble to form a super-hydrophobic interface; S42: After the preset reaction time, place in an oven for drying.

8. The method for treating the surface of a microfluidic chip with hydrophilicity and hydrophobicity according to any one of claims 1 to 7, characterized in that: One of the first substrate and the second substrate is made of PDMS, and the other is made of glass or PDMS; The step S3 specifically includes: The first substrate and the second substrate are bonded by plasma sealing.

9. The method for treating the surface of a microfluidic chip with hydrophilicity and hydrophobicity according to any one of claims 1 to 7, characterized in that: The material of the first substrate and the second substrate is at least one of PMMA, PS, PP, and COC / COP; The step S3 specifically includes: The first substrate and the second substrate are bonded by at least one of thermal bonding, ultrasonic sealing, laser welding, UV light curing adhesive sealing, and double-sided adhesive sealing.

10. A microfluidic chip, characterized in that: A fluid microchannel is provided, wherein the inner wall of the fluid microchannel is covered with a hydrophobic modification layer; The hydrophobic modification layer of the fluid microchannel is prepared by the hydrophilic and hydrophobic treatment method for the surface of a microfluidic chip according to any one of claims 1 to 9.

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