Microfluidic chip surface hydrophilic and hydrophobic treatment method and microfluidic chip

Abstract

The application discloses a micro-fluidic chip surface hydrophilic-hydrophobic treatment method and a micro-fluidic chip, and relates to the technical field of micro-fluidic chips; the micro-fluidic chip surface hydrophilic-hydrophobic treatment method comprises the following steps: providing a first substrate and a second substrate, preparing a hydrophilic modification layer on the surface of the first substrate and the second substrate, then bonding the first substrate and the second substrate to form a fluid micro-channel of the micro-fluidic chip, and introducing modified gas or modified liquid into the fluid micro-channel to modify the hydrophilic modification layer on the inner wall of the fluid micro-channel into a hydrophobic modification layer. The micro-fluidic chip surface hydrophilic-hydrophobic treatment method has the advantages that the hydrophilic modification layer is prepared before the bonding of the substrates, the hydrophilic modification layer on the inner wall of the fluid micro-channel is modified to be hydrophobic by injecting modified gas or modified liquid after the bonding of the substrates, the uniformity of the hydrophobic modification layer on the inner wall of the fluid micro-channel is ensured, and the problems of the droplet generation flux and the droplet generation consistency of the micro-fluidic chip are effectively improved.

Description

Technical Field

[0001] This invention relates to the field of microfluidic chip technology, and in particular to a method for hydrophilic and hydrophobic treatment of the surface of a microfluidic chip and a microfluidic chip. Background Technology

[0002] Hydrogel single-cell reverse transcription is a technique that reverse transcribes RNA from a single cell into cDNA, and is commonly used for single-cell transcriptome analysis. This technique requires the use of microchannels and droplet generation devices in a microfluidic chip 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 surface contact angle and the intensity of modification are crucial for the fabrication of monodisperse microspheres or hydrogel spheres using microfluidic chips. PDMS, a widely used material in microfluidic chips, has a naturally hydrophobic surface, but it typically requires plasma treatment during bonding to ensure strong bonding. Plasma treatment enhances the hydrophilicity of the PDMS surface, and neither natural recovery nor thermal recovery can quantitatively control the recovery state of the PDMS surface, leading to uneven liquid surface contact angles on the inner walls of the formed fluid microchannels. Alternatively, methods such as vapor deposition or infusion of hydrophobic modification liquids can be used to coat the inner walls of the fluid microchannels with a hydrophobic modification layer. However, these methods struggle to guarantee uniform and stable modification within closed microchannels and may even cause channel blockage. Another approach uses a stepped emulsion structure with multiple channels in parallel to avoid the unstable hydrophobic modification step, but this significantly increases the production cost of monodisperse microspheres and, due to the relatively low droplet generation rate, can lead to inconsistent droplet formation or even failure to generate droplets. Summary of the Invention

[0004] This invention provides a method for hydrophilic and hydrophobic treatment 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 microfluidic chip surface hydrophilic / hydrophobic treatment method provided by the present invention includes the following steps:

[0006] S1, a first substrate and a second substrate are provided; at least one of the first substrate and the second substrate has a microchannel pattern on its surface;

[0007] S2, a hydrophilic modification layer is prepared on the surface of the first substrate and the second substrate;

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

[0009] S4, introduce modified gas or 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 silica nanoparticles, and step S2 specifically includes:

[0011] Silica 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 silica nanoparticles onto the surfaces of the first substrate and the second substrate by electrostatic adsorption specifically includes:

[0013] S21: Plasma cleaning: Oxygen plasma cleaning is performed on the first substrate and the second substrate;

[0014] S22: Adsorption and binding of silica nanoparticles: Immerse the first substrate and the second substrate in a nano silica modification solution for a preset time;

[0015] S23: Drying and curing: Clean the excess nano-silica modification liquid from the surfaces of the first substrate and the second substrate, and dry them in an oven.

[0016] Optionally, it also includes:

[0017] Repeat steps S22 and S23 multiple times.

[0018] Optionally, the nano-silica modified liquid is prepared by the following method:

[0019] Prepare an aqueous solution of nano-silica with a solid content of 0.5 wt%, and quickly adjust the pH of the aqueous solution of nano-silica to a preset value using concentrated sulfuric acid or hydrochloric acid.

[0020] Alternatively, the nano-silica modified liquid can also be prepared by the following method:

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

[0022] Alternatively, mix tetraethyl orthosilicate with 1.5 mL of ethanol and simultaneously add 3 mL of 25% ammonia. Stir the mixture at room temperature for 2 hours, then rapidly mix 2 mL of the stirred mixture with 18 mL of 1 M hydrochloric acid to obtain a nano-silica modified solution.

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

[0024] Step S4 specifically includes:

[0025] S41: The hexane-modified liquid is poured into the fluid microchannel, and decanyltrichlorosilane and silica nanoparticles self-assemble to form a superhydrophobic interface.

[0026] S42: After the reaction has been carried out for the preset time, place it in an oven to dry.

[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] Step S3 specifically includes:

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

[0030] Optionally, the first substrate and the second substrate are made of at least one of PMMA, PS, PP, and COC / COP.

[0031] Step S3 specifically includes:

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

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

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

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

[0036] This invention provides an embodiment of a hydrophilic modification layer that can be hydrophobically modified by a modified gas or liquid on the substrate surface before substrate bonding. This hydrophilic modification layer, due to its good hydrophilicity, enhances the surface energy of the substrate without reducing the bonding tightness or effectiveness. Furthermore, it facilitates the preparation of a uniform hydrophilic modification layer before substrate bonding, and the modification intensity and effect can be adjusted according to actual needs. After the substrate bonding forms a complete fluid microchannel, the hydrophobic modification of the hydrophilic modification layer can be quickly completed by injecting a modified gas or liquid into the fluid microchannel. This avoids the problem of uneven modification caused by traditional thermal reversion methods or in-channel modification methods, and eliminates the need for costly and slow multi-channel parallel methods using stepped emulsion structures. This effectively improves the droplet generation throughput and droplet generation consistency of microfluidic chips. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 This is a flowchart of an embodiment of the microfluidic chip surface hydrophilic-hydrophobic treatment method of the present invention;

[0039] Figure 2 This is a schematic diagram illustrating the principle of silica nanoparticle modification in one embodiment of the microfluidic chip surface hydrophilic-hydrophobic treatment method of the present invention;

[0040] Figure 3 This is a schematic diagram illustrating the principle of silicon dioxide nanoparticle surface modification cycle in one embodiment of the microfluidic chip surface hydrophilic-hydrophobic treatment method of the present invention. Detailed Implementation

[0041] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0042] The terms “first,” “second,” “third,” “fourth,” etc. (if present) in the specification and drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented, for example, in orders other than those illustrated or described herein. Furthermore, the terms “comprising” and “having,” and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0043] Explanation or description of the English terms used 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: Decanyltrichlorosilane; plasma: Plasma.

[0045] Traditional microfluidic chips can be classified into PDMS-glass chips, double-sided PDMS chips, and thermoplastic polymer chips, depending on the material used.

[0046] PDMS possesses a naturally hydrophobic surface with a water contact angle greater than 100°. Fabricating PDMS-glass chips requires high-energy physical treatments, such as oxygen plasma treatment, on the surfaces of both PDMS and glass materials. This increases surface hydrophilicity, activates functional and free groups on the material surfaces, and facilitates chemical cross-linking between the PDMS and glass materials, thus bonding the two materials. The plasma-activated PDMS surface is transient, recovering its hydrophobicity within hours or days. However, in reality, the water contact angle is not uniform after the PDMS surface hydrophobicity is restored. While PDMS can also be restored to hydrophobicity through heating and baking (thermal reversion), the temperature and time for thermal reversion are difficult to accurately estimate and judge, making it impossible to quantitatively control the restored state of the PDMS surface.

[0047] When fabricating microfluidic chips using double-sided PDMS material, the surface usually needs to be plasma treated to bond and form flow channels. After plasma treatment, the water contact angle of the PDMS material surface, which was originally greater than 100°, will be reduced to about 30°, making it difficult to form droplets. Similarly, the thermal reversibility method is not applicable to the fabrication of double-sided PDMS chips due to its strong uncertainty.

[0048] Besides thermal reversibility, PDMS-glass chips and double-sided PDMS chips can also employ in-channel modification methods to coat the inner walls of the channels with hydrophobic modification layers, such as chemical vapor deposition of fluorosilane agents and cyclohexane vapor deposition of phenelzine under vacuum conditions. However, vapor deposition modification methods are difficult to guarantee uniform and stable inner wall modification in closed microchannels. For closed channels with a depth or width of less than 40 μm, gas is difficult to penetrate deep into the channel even in a vacuum environment. Furthermore, the fluorinated material surface 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 channels through a syringe pump, but it is necessary to ensure that excess modification liquid is continuously dried by air; otherwise, the modification liquid residue in the microchannels will cause blockage of the chip microchannels.

[0049] Thermoplastic polymer chips often use injection molding with thermoplastic polymer substrates such as PMMA, PS, PP, and COC / COP to achieve mass production and cost control. However, after the polymer materials are bonded, it is often difficult to guarantee the consistency of the surface modification effect within the channels during mass production, as well as the effective control of modification process points. Therefore, in-channel modification methods cannot be used. The hydrophobic modification effect of the material surface can only be effectively controlled before material bonding. Fluorination is usually used to hydrophobically modify the polymer material surface, but fluorination reduces the adhesion and bonding strength of the material surface, making it difficult to bond the hydrophobically treated material firmly. For example, after bonding and sealing microfluidic chips by methods such as thermal bonding, ultrasonic sealing, UV curing adhesive, and double-sided adhesive, liquid leakage is prone to occur when a certain pressure is applied. The only solution is to locally remove the hydrophobic surface modification layer at the bonding and sealing area, such as laser removal using carbon dioxide lasers or excimer lasers, or local cleaning using hydrogen plasma. However, this increases the complexity and instability of the microfluidic chip manufacturing process.

[0050] In addition, a multi-channel parallel method with a stepped emulsification structure can be used to eliminate the unstable hydrophobic modification step on the surface of the microfluidic chip material. In this method, while each droplet generation channel generates stable and uniform droplets at a relatively low speed, multiple channels need to be connected in parallel to ensure the efficiency of droplet generation, which significantly increases the production cost of monodisperse microspheres. Moreover, this method also encounters some problems when generating some monomer-polymerized microspheres or hydrogel spheres. For example, after the aqueous phase of polyacrylamide monomer is prepared, it will undergo a certain degree of polymerization during the droplet generation process. This causes the relevant physical properties of the aqueous phase of the monomer to gradually change with the increase of droplet generation time, thus affecting the consistency of the generated droplets. At the same time, the viscosity of the aqueous phase will also change during the polymerization process. Under extreme conditions, such as excessive aqueous phase flow rate or low surface tension of the aqueous phase, the droplet generation chip may not be able to generate droplets.

[0051] In summary, ensuring the droplet generation throughput and consistency of microfluidic chips has been a long-standing problem in microfluidic chip fabrication, hindering research and production based on microfluidic chips.

[0052] This invention proposes a method for hydrophilic and hydrophobic treatment of the surface of a microfluidic chip and a microfluidic chip, aiming to solve the above-mentioned problems.

[0053] See Figure 1 In one embodiment, the microfluidic chip surface hydrophilic / hydrophobic treatment method proposed in this invention includes the following steps:

[0054] S1, a first substrate and a second substrate are provided; at least one of the first substrate and the second substrate has a microchannel pattern on its surface.

[0055] Specifically, microfluidic chips typically have different structures and fabrication processes depending on the materials used.

[0056] In the first case, one of the first substrate and the second substrate of the traditional PDMS-glass chip is made of PDMS material, and the other is a glass substrate or glass cover. Microchannel patterns are prepared on the surface of one of the first substrate and the second substrate (usually PDMS). The two substrates are bonded together to form a microfluidic chip with internal fluid microchannels.

[0057] In the second case, microfluidic chips used for research and development typically employ double-sided PDMS material, meaning that both the first and second substrates are PDMS materials with microchannel patterns. The microchannel patterns on the two substrates are arranged correspondingly so that a complete fluid microchannel is formed after the first and second substrates are bonded together. The first and second substrates can be prepared by mixing a prepolymer and a curing agent and casting it into a mold.

[0058] In the third case, microfluidic chips used for mass production and cost control are often injection molded from thermoplastic polymers such as PMMA, PS, PP, and COC / COP. 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 the first substrate and the second substrate can form a complete fluid microchannel after bonding.

[0059] S2, a hydrophilic modification layer is prepared on the surface 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 and second substrates, i.e., to reduce the water contact angle of the surfaces. The material of the hydrophilic modification layer can be silica nanoparticles, which enhance the hydrophilicity of the substrate surface by increasing the roughness. Alternatively, the hydrophilic modification layer can be made of other metal or non-metal compound nanoparticles with stable chemical properties, such as titanium dioxide nanoparticles or barium sulfate nanoparticles, to increase the roughness of the substrate surface and thus enhance the hydrophilicity of the substrate surface.

[0061] S3, the first substrate and the second substrate are bonded together to form the fluid microchannel of the microfluidic chip.

[0062] Specifically, the appropriate bonding process is selected based on the material of the microfluidic chip.

[0063] In the first scenario mentioned above, the microfluidic chip is a traditional PDMS-glass chip, and the first and second substrates are bonded by plasma sealing. After plasma treatment, the surface functions and free radicals of the PDMS material and the glass material are activated, which causes the PDMS material and the glass material to undergo chemical cross-linking, thereby bonding the two materials.

[0064] In the second case, both the first substrate and the second substrate are made of PDMS material. The first substrate and the second substrate are bonded by plasma sealing, and chemical cross-linking occurs between the first substrate and the second substrate, thereby bonding the first substrate and the second substrate together.

[0065] In the third case, the first substrate and the second substrate are made of thermoplastic polymers, specifically at least one of PMMA, PS, PP, and COC / COP; the first substrate and the second substrate are bonded by at least one of the following methods: thermal bonding, ultrasonic sealing, laser welding, UV curing adhesive sealing, and double-sided adhesive sealing.

[0066] S4. Introduce a modified gas or 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, after the first substrate and the second substrate are bonded together, a complete fluid microchannel is formed. Since the surfaces of the first substrate and the second substrate used for bonding 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 liquid into the fluid microchannel. For example, in one embodiment, when silica nanoparticles are selected as the material of the hydrophilic modification layer, a gaseous or liquid hydrophobic silane can be introduced into the fluid microchannel to form a silica nanoparticle-hydrophobic silane superhydrophobic interface through molecular self-assembly. In other embodiments, the hydrophilic modification layer can be selected from 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 fluorinated alkyl modifiers to form a hydrophobic fluoropolymer layer on the surface. Similarly, barium sulfate nanoparticles can also be hydrophobically modified with hydrophobic silanes, similar to silica nanoparticles.

[0069] This invention provides an embodiment of a hydrophilic modification layer that can be hydrophobically modified by a modified gas or liquid on the substrate surface before substrate bonding. This hydrophilic modification layer, due to its good hydrophilicity, enhances the surface energy of the substrate without causing a decrease in the bonding tightness or bonding effect. More importantly, it facilitates the preparation of a uniform hydrophilic modification layer before substrate bonding, and the modification intensity and effect of the hydrophilic modification layer can be adjusted according to actual needs. After the substrate bonding forms a complete fluid microchannel, the hydrophobic modification of the hydrophilic modification layer can be quickly completed by injecting a modified gas or liquid into the fluid microchannel. This avoids the problem of uneven hydrophobic modification caused by traditional thermal reversion methods or in-channel modification methods, ensuring the droplet generation throughput and droplet generation consistency of the microfluidic chip.

[0070] Furthermore, for PDMS, the most widely used material in microfluidic chips, its high adsorption capacity for biomolecules means that if the generated droplets contain biomolecules such as antibodies, the surface contact angle of PDMS will gradually decrease with the adsorption of biomolecules, making it difficult for the droplets to form stably. The hydrophilic-hydrophobic modification layer provided in this embodiment can also serve as a barrier protective layer for the inner wall of the PDMS fluid microchannel, effectively preventing the adsorption of biomolecules by the PDMS material. For microfluidic chips made of thermoplastic polymers, it is not necessary to remove the hydrophobic modification layer in the bonding area before substrate bonding, simplifying the process and improving the standardization of production.

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

[0072] Silica nanoparticles are adsorbed and bonded to the surfaces of the first and second substrates by electrostatic adsorption.

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

[0074] It is understandable that when the silica nanoparticles used are negatively charged, the substrate is processed to be positively charged; when the silica nanoparticles used are positively charged, the substrate is processed to be negatively charged, so that the silica nanoparticles are electrostatically adsorbed onto the substrate surface.

[0075] In this embodiment, the substrate can obtain the 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 bond the silica nanoparticles to the substrate surface, an acid solution can usually be used to allow the silica nanoparticles to stably bond with the substrate through the silanol groups on the surface, which has 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 particle aggregation and ensures that the silicon nanoparticles are evenly spread on the substrate, thus exhibiting good modification uniformity.

[0078] In some embodiments, the step of adsorbing and bonding silica nanoparticles onto the surfaces of the first and second substrates by electrostatic adsorption specifically includes:

[0079] S21: Plasma cleaning: Oxygen plasma cleaning is performed on the first substrate and the second substrate.

[0080] Oxygen plasma interacts with the surface of the substrate, generating an electric charge on the substrate surface. The amount of charge on the substrate surface can be controlled by adjusting plasma parameters such as gas flow rate, discharge power, and processing time. The substrate surface treated with plasma exhibits good charge stability.

[0081] S22: Adsorption and bonding of silica nanoparticles: Immerse the first substrate and the second substrate in the nano silica modification solution for a preset time.

[0082] S23: Drying and curing: Clean the excess nano-silica modification liquid from the surfaces of the first and second substrates, and place them in an oven to dry.

[0083] The preset soaking time can be set by considering various factors such as the density of the hydrophilic modification layer, the concentration of nanoparticles, the temperature, and the plasma treatment time, and is not limited here.

[0084] In some embodiments, uniform adsorption can be achieved by repeating steps S22 and S23 multiple times; 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 liquid so that the residual solvent can be completely evaporated.

[0085] Based on the embodiments of the above-described microfluidic chip surface hydrophilic-hydrophobic treatment method, the present invention also provides the following specific embodiments.

[0086] Example 1

[0087] See Figure 2 and Figure 3 , Figure 2 This is a schematic diagram illustrating the principle of silica nanoparticle modification. Figure 3 This is a schematic diagram illustrating the cyclic principle of surface modification of silica nanoparticles. This embodiment includes the following steps:

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

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

[0090] Substrate covered with hydrophilic modification layer: The plasma-treated substrate is immersed in the prepared nano silica modification solution for 10 minutes, the excess modification solution on the substrate surface is cleaned with pure water, and then dried in a 90° oven for 15 minutes.

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

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

[0093] Hydrophobic modification: Prepare a hexane-modified solution consisting of a mixture of n-hexane and decanyltrichlorosilane, wherein the volume fraction of decanyltrichlorosilane is 0.5%;

[0094] The sealed microfluidic chip is immersed in n-hexane modification solution, or the n-hexane modification solution is poured into the fluid microchannel of the microfluidic chip. After waiting for 5 minutes, the immersed microfluidic chip is placed in a 120° oven until completely dry to obtain the target microfluidic chip.

[0095] In this embodiment, decanyltrichlorosilane (DTS) and silica nanoparticles on the inner wall of the fluid microchannel self-assemble to form a SiNPs-DTS superhydrophobic interface with a water contact angle greater than 150°, exhibiting excellent hydrophobic properties.

[0096] Example 2

[0097] The steps in this embodiment are the same as in Embodiment 1, except that the difference lies in the step of preparing the nano-silica modification liquid.

[0098] Preparation of nano-silica modification solution: A certain amount of tetraethyl orthosilicate (TEOS) was added dropwise to 50 mL of 1 mM NaOH solution and stirred continuously for 24 h. The pH of the mixed solution was quickly adjusted to 2 with hydrochloric acid.

[0099] This embodiment uses a nano-silica modification solution with small-diameter particles.

[0100] Example 3

[0101] The steps in this embodiment are the same as in Embodiment 1, except that the difference lies in the step of preparing the nano-silica modification liquid.

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

[0103] This embodiment uses a nano-silica modification solution with large-diameter microparticles.

[0104] Example 4

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

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

[0107] Substrate covered with hydrophilic modification layer: The plasma-treated substrate is immersed in the prepared SiNPs Ludox™-50 nano silica modification solution for 10 minutes, the excess modification solution on the substrate surface is cleaned with pure water, and then dried in a 90° oven for 15 minutes.

[0108] After drying, the substrate was immersed in the prepared SiNPs Ludox LS-35 nano silica modification solution for 10 minutes. The excess modification solution on the surface of the substrate was cleaned off with pure water and then dried in a 90° oven for 15 minutes.

[0109] After alternating immersion in two different nano-silica modification solutions and drying in an oven 3-5 times, uniform adsorption was achieved, completing the hydrophilic modification. Finally, the substrate was placed in a 120°C oven and baked for 1 hour.

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

[0111] Hydrophobic modification: Prepare a hexane-modified solution consisting of a mixture of n-hexane and decanyltrichlorosilane, wherein the volume fraction of decanyltrichlorosilane is 0.5%;

[0112] The sealed microfluidic chip is immersed in n-hexane modification solution, or the n-hexane modification solution is poured into the fluid microchannel of the microfluidic chip. After waiting for 5 minutes, the immersed microfluidic chip is placed in a 120° oven until completely dry to obtain the target microfluidic chip.

[0113] The hydrophilic-hydrophobic modification layer prepared in this embodiment includes two sizes of silica nanoparticles, which have a larger roughness than the previous embodiments. The modified microfluidic chip substrate and fluid microchannel have a smaller water contact angle.

[0114] The microfluidic chips prepared through the above specific embodiments of the silica nanoparticle modification layer do not suffer any damage from ultrasonic cleaning, ultrasonic sealing, laser welding, high-temperature and high-pressure thermal bonding processes, provided that they are not immersed in a solution with a pH greater than 7 for a long period of time.

[0115] As can be seen from the above embodiments, the microfluidic chip surface hydrophilic-hydrophobic treatment method proposed in this invention prepares a uniform hydrophilic modification layer before substrate bonding, and then rapidly completes the hydrophobic modification of the hydrophilic modification layer by injecting modified gas / liquid into the fluid microchannel after substrate bonding. As shown in the preferred embodiment based on silica nanoparticles, the modified layer prepared by this method has good uniformity, which can solve the long-standing problem of uneven hydrophobic modification in PDMS-based microfluidic chips. The modification effect of the modification layer can be controlled by adjusting its density, and it can also act as a barrier. The barrier layer avoids the problem of reduced contact angle caused by the adsorption of biomolecules by PDMS material; for microfluidic chips made of thermoplastic polymer materials, this method eliminates the need to remove the modification layer in the bonding area, simplifying the process and improving the standardization of production; therefore, the hydrophilic-hydrophobic treatment method for microfluidic chip surfaces proposed in this invention improves the droplet generation flux and droplet generation consistency of microfluidic chips by enhancing the hydrophobic uniformity of the inner wall of the microfluidic channel, which is of great significance for promoting the research and production of microfluidic chips and the development of related industries such as biology and medicine.

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

[0117] The hydrophobic modification layer of the fluid microchannel of the microfluidic chip is prepared by the hydrophilic-hydrophobic treatment method on the surface of the microfluidic chip provided in the foregoing embodiments. Therefore, the microfluidic chip proposed in this invention has all the beneficial effects of the foregoing embodiments, which will not be elaborated here.

[0118] Depending on their specific functions, microfluidic chips include microfluidic droplet chips, microreactor chips, cell culture chips, and separation and analysis chips.

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

[0120] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A method for hydrophilic / hydrophobic treatment of a microfluidic chip surface, characterized in that, Includes the following steps: S1, a first substrate and a second substrate are provided; at least one of the first substrate and the second substrate has a microchannel pattern on its surface; S2, a hydrophilic modification layer is prepared on the surface of the first substrate and the second substrate; the hydrophilic modification layer is composed of silica nanoparticles, and the silica nanoparticles are adsorbed and bound to the surface of the first substrate and the second substrate by electrostatic adsorption, specifically including the following steps: S21, plasma cleaning: oxygen plasma cleaning is performed on the first substrate and the second substrate; S22, adsorption and binding of silica nanoparticles: the first substrate and the second substrate are immersed in a nano silica modification solution for a preset time; S23, drying and curing: excess nano silica modification solution is cleaned from the surface of the first substrate and the second substrate, and they are placed in an oven to dry; S3, the first substrate and the second substrate are bonded together to form a fluid microchannel of the microfluidic chip; S4, a modified gas or liquid containing hydrophobic silane is introduced into the fluid microchannel, and the hydrophilic modification layer on the inner wall of the fluid microchannel and the hydrophobic silane form a silica nanoparticle-hydrophobic silane superhydrophobic interface through molecular self-assembly.

2. The method for treating the surface of a microfluidic chip with hydrophilicity and hydrophobicity according to claim 1, characterized in that, Specifically, it also includes: Repeat steps S22 and S23 multiple times.

3. The method for treating the surface of a microfluidic chip with hydrophilicity and hydrophobicity according to claim 1, characterized in that, The nano-silica modified liquid was prepared by the following method: Prepare an aqueous solution of nano-silica with a solid content of 0.5 wt%, and quickly adjust the pH of the aqueous solution of nano-silica to a preset value using concentrated sulfuric acid or hydrochloric acid.

4. The method for treating the surface of a microfluidic chip with hydrophilicity and hydrophobicity according to claim 1, characterized in that, The nano-silica modified liquid was prepared by the following method: Tetraethyl orthosilicate was added dropwise to 50 mL of 1 mM NaOH solution and stirred continuously for 24 h. The pH of the mixed solution was quickly adjusted to the preset value with hydrochloric acid to obtain the nano-silica modified solution. Alternatively, mix tetraethyl orthosilicate with 1.5 mL of ethanol and simultaneously add 3 mL of 25% ammonia. Stir the mixture at room temperature for 2 hours, then rapidly mix 2 mL of the stirred mixture with 18 mL of 1 M hydrochloric acid to obtain a nano-silica modified solution.

5. The method for treating the surface of a microfluidic chip with hydrophilicity and hydrophobicity according to claim 1, characterized in that, The modified liquid is a hexane-modified liquid prepared from n-hexane and decanyltrichlorosilane, wherein the volume fraction of decanyltrichlorosilane is 0.5%. Step S4 specifically includes: S41: The hexane-modified liquid is poured into the fluid microchannel, and decanyltrichlorosilane and silica nanoparticles self-assemble to form a superhydrophobic interface. S42: After the reaction has been carried out for the preset time, place it in an oven to dry.

6. The method for hydrophilic / hydrophobic treatment of microfluidic chip surface according to any one of claims 1-5, 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. Step S3 specifically includes: The first substrate and the second substrate are bonded by plasma sealing.

7. The method for treating the surface of a microfluidic chip with hydrophilicity and hydrophobicity according to any one of claims 1-5, characterized in that, The first substrate and the second substrate are made of at least one of PMMA, PS, PP, and COC / COP. Step S3 specifically includes: The first substrate and the second substrate are bonded by at least one of the following methods: thermal bonding, ultrasonic sealing, laser welding, UV curing adhesive sealing, and double-sided adhesive sealing.

8. A microfluidic chip, characterized in that, It has fluid microchannels, the inner walls of which are covered with a hydrophobic modification layer; The hydrophobic modification layer of the fluid microchannel is prepared by the hydrophilic-hydrophobic treatment method on the surface of the microfluidic chip as described in any one of claims 1-7.

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