Microfluidic chip based on temporary blocking and releasing of magnetic particles and application thereof

Abstract

This invention proposes a microfluidic chip based on transient liquid blocking and release using magnetic particles and its application. The chip includes a lower substrate and an upper substrate, which together form a microchannel. A transient liquid blocking structure is located at the end of the microchannel near the waste liquid area. This structure consists of a group of magnetic particles coated with a soluble or dispersible protective layer. In a dry state, the magnetic particles adhere to each other and are attached to the end of the microchannel, forming a capillary barrier to the liquid flow. The protective layer fully dissolves or disperses when the volume of liquid flowing through the magnetic particles exceeds a threshold. The magnetic particles can migrate under the influence of liquid flow or an external magnetic field to release the obstruction of the liquid flow. By pre-positioning dried magnetic particles at the end of the channel, a valve function can be formed, simplifying chip design and fabrication processes, reducing manufacturing costs, and making it suitable for mass production of disposable detection chips.

Description

Technical Field

[0001] This invention belongs to the field of microfluidic chip technology, and specifically relates to a microfluidic chip based on the transient liquid resistance and release of magnetic particles and its application. Background Technology

[0002] In microfluidic chips, especially those used for point-of-care testing (POCT), precise timing control of the reaction liquid (such as residence time, reaction, and post-reaction transfer at specific locations) is crucial for ensuring detection accuracy and reliability. For micro-volume reaction systems (e.g., 2-5 microliters), the liquid is highly susceptible to unintended flow due to gravity, capillary action, or the siphon effect created by chip tilting, leading to insufficient reaction time or premature entry of the liquid into the waste zone, resulting in detection failure.

[0003] In existing technologies, active microvalves (such as mechanical valves and pneumatic diaphragm valves) or magnetic granular plugs controlled by continuous magnetic fields are commonly used to achieve fluid flow control. However, mechanical valves or diaphragm valves are complex in structure, have high processing costs, and are not easy to mass-produce and integrate into disposable chips. In addition, traditional mechanical valves must include movable parts (such as diaphragms and valve cores) and cavities to accommodate the movement of these parts in order to open and close. When the valve is closed, the space occupied by these cavities and the surface of the parts, which cannot be replaced by the flowing liquid, will dilute the sample and affect the sensitivity of the detection. On the other hand, continuous magnetic control requires the detection instrument to continuously provide a magnetic field, which consumes a lot of energy, and the continuous magnetic field may generate thermal effects, affecting the sample response. These factors all restrict the commercialization of microfluidic chips, especially in low-cost, disposable scenarios.

[0004] Therefore, there is an urgent need for a microfluidic fluid control scheme that is simple in structure, requires no complex drive, has low manufacturing cost, and can achieve reliable liquid blocking and controllable release. Summary of the Invention

[0005] This invention aims to provide a microfluidic chip based on transient liquid blocking and release of magnetic particles and its application. By setting a group of magnetic particles coated with a soluble or dispersible protective layer at the end of the channel to form a transient liquid blocking structure, after static reaction, adding rinsing liquid into the microchannel dissolves or disperses the protective layer on the surface of the magnetic particle group and drives the magnetic particle group to migrate, thereby releasing the liquid blockage.

[0006] The technical solution of this invention is implemented as follows: a microfluidic chip based on transient liquid blocking and release of magnetic particles includes a lower substrate and an upper substrate. The lower substrate and the upper substrate enclose a microchannel. The two ends of the microchannel along the liquid flow direction are respectively connected to an injection area and a waste liquid area. A transient liquid blocking structure is provided at the end of the microchannel near the waste liquid area. The transient liquid blocking structure is composed of a group of magnetic particles with a soluble or dispersible protective layer on the surface. The magnetic particles are bonded to each other and attached to the end of the microchannel in a dry state, forming a capillary blockage of the liquid flow. The protective layer is fully dissolved or dispersed when the volume of liquid flowing through the magnetic particles exceeds a threshold. The magnetic particles can migrate under the flushing of the liquid flow or driven by an external magnetic field to release the blockage of the liquid flow.

[0007] In one embodiment of the present invention, the magnetic particle group consists of magnetic particles distributed on the microchannel in a dotted or locally packed manner.

[0008] In one embodiment of the present invention, the equivalent water contact angle of the transient liquid-blocking structure is 20–50 degrees.

[0009] In one embodiment of the present invention, the protective layer is selected from proteins, polysaccharides, or hydrophilic polymers.

[0010] In one embodiment of the present invention, the magnetic particles have a particle size of 100-5000 nanometers.

[0011] In one embodiment of the present invention, the magnetic particle group can form a denser accumulation under the action of an external magnetic field to enhance its blocking ability.

[0012] On the other hand, the present invention also provides a fluid control method utilizing a microfluidic chip in any of the above-mentioned technical solutions, comprising at least the following steps: S1. A trace sample is introduced into the microchannel through the injection area; S2. The sample flows along the microchannel toward the waste liquid area and is intercepted by the transient liquid-blocking structure at the end of the microchannel. S3. When liquid needs to be released, flushing fluid is added into the microchannel to dissolve or disperse the protective layer on the surface of the magnetic particle group and drive the magnetic particle group to migrate, thereby removing the obstruction to the liquid and allowing the liquid to enter the waste liquid area.

[0013] In one embodiment of the invention, step S2 further includes applying an external magnetic field to the transient liquid-blocking structure to enhance its blocking stability.

[0014] In one embodiment of the present invention, step S3 further includes removing or moving the external magnetic field to drag the magnetic particle group into the waste liquid area by moving the external magnetic field.

[0015] In one embodiment of the present invention, the volume of the trace sample in step S1 is less than or equal to 10 microliters.

[0016] The microfluidic chip based on transient liquid resistance and release of magnetic particles obtained through the above technical solution and its application have the following beneficial effects: 1. Simple structure, low cost, suitable for disposable chips: This invention completely abandons the traditional micro mechanical valve, piezoelectric valve or complex membrane pneumatic valve structure. The "valve" function can be formed by pre-placing dried magnetic particles at the end of the channel. This structure does not require moving parts or precise alignment, which greatly simplifies chip design and processing technology, significantly reduces manufacturing costs, and is suitable for the mass production of disposable detection chips.

[0017] 2. Stable and reliable liquid blocking, active and controllable release: This invention creatively utilizes the capillary resistance effect (equivalent contact angle 20°–50°) generated by the accumulation of hydrophilic magnetic particles to achieve liquid blocking. Unlike the traditional approach that relies on hydrophobic surfaces, it has better liquid compatibility. Moreover, the release process is actively triggered by the liquid flux threshold. When sufficient flushing liquid flows through, the protective layer dissolves, causing the magnetic particle cluster structure to disintegrate. The particles migrate out of the flow channel cleanly and as a whole under the drive of magnetic field or fluid force, avoiding contamination or blockage caused by particle residue. This fundamentally solves the defect of uncontrollable release in traditional capillary valves.

[0018] 3. Significantly enhances the stability of the liquid-blocking structure and provides precise control over the reaction time: Applying a magnetic field during the retention stage can further enhance the aggregation between magnetic particles and their adsorption to the substrate through magnetic force, greatly improving the mechanical stability of the transient liquid-blocking structure. It can resist higher fluid pressure fluctuations (such as the impact generated by subsequent liquid addition), ensuring zero leakage within the preset incubation or reaction time. This provides a highly reliable time window for biochemical reactions and directly improves the repeatability and accuracy of detection. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the microfluidic chip based on transient liquid resistance and release of magnetic particles as described in this invention; Figure 2 This is a cross-sectional view of the microfluidic chip based on transient liquid resistance and release of magnetic particles as described in this invention. Figure 3 This is a schematic diagram illustrating the principle of the microfluidic chip described in this invention controlling the flow of a small amount of sample. Figure 4 This is a schematic diagram of another embodiment of the microfluidic chip of the present invention for controlling the flow of micro-samples; Figure 5This is a schematic diagram of another embodiment of the microfluidic chip described in this invention for controlling the flow of micro-samples.

[0020] In the figure, 1 is the upper substrate; 2 is the lower substrate; 3 is the microchannel; 4 is the sample injection area; 5 is the waste liquid area; and 6 is the transient liquid-blocking structure. Detailed Implementation

[0021] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0022] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art. Unless otherwise specified, the experimental reagents used in the following embodiments are conventional biochemical reagents; and the experimental methods described are conventional methods.

[0023] This invention relates to the field of microfluidic chip technology, specifically to a microfluidic chip based on transient liquid blocking and release of magnetic particles and its application. It involves forming a transient liquid blocking structure by setting a group of magnetic particles with a protective coating at the end of the channel. During the reaction settling stage, an external magnetic field is applied to the magnetic particles to enhance the liquid blocking strength. After the reaction is complete, the magnetic force is released, and the protective coating is dissolved by a rinsing solution, causing the magnetic particles to disperse or the magnetic beads to be dragged away from the channel by the magnetic field. The liquid automatically flows into the waste liquid area under the action of siphon or capillary force, ultimately completing the detection process.

[0024] The present invention will be further explained and described below with reference to the embodiments and accompanying drawings. It should be understood that the present invention is not limited to the specific embodiments described.

[0025] like Figure 1 , Figure 2 As shown, this invention proposes a microfluidic chip based on transient liquid blocking and release of magnetic particles, including a lower substrate 1 and an upper substrate 2. The lower substrate 1 and the upper substrate 2 enclose a microchannel 3. The two ends of the microchannel 3 along the liquid flow direction are respectively connected to a sample injection area 4 and a waste liquid area 5. A transient liquid blocking structure 6 is provided at the end of the microchannel 3 near the waste liquid area 5. The transient liquid blocking structure 6 is composed of a group of magnetic particles with a soluble or dispersible protective layer on the surface. The magnetic particles are bonded to each other and attached to the end of the microchannel 3 in a dry state, forming a capillary blockage of the liquid flow. The protective layer is fully dissolved or dispersed when the volume of liquid flowing through the magnetic particles exceeds a threshold. The magnetic particles can migrate under the flushing of the liquid flow or driven by an external magnetic field to release the blockage of the liquid flow.

[0026] In a dry state, the magnetic particles form a stable liquid-blocking region through capillary forces and adsorption forces between the particles and between the particles and the substrate. This structure can reliably retain the reaction liquid under the conventional driving force of the microfluidic chip by relying on its capillary resistance effect.

[0027] When release is required, it can be actively triggered in two ways: first, by adding sufficient buffer solution to make the liquid flux flowing through the structure reach the release threshold, so that the protective layer is fully dissolved, the particles are dispersed and migrate under the flushing of the liquid flow; second, by actively pulling the particle group under the influence of an external magnetic field, the entire particle group is driven to migrate.

[0028] The principle of using the microfluidic chip of this invention to control the flow of micro-samples is as follows: Figure 3 As shown: A. Add a small amount of biological sample (less than 10 μL) through the 4-way microchannel in the sample introduction area; B. The sample flows along the microchannel 3 toward the waste liquid area 5 and is intercepted at the end of the microchannel 3 by the transient liquid-blocking structure 6. C. When liquid needs to be released, add rinsing solution from the injection area; D. The rinsing fluid dissolves or disperses the protective layer on the surface of the magnetic particle group and drives the magnetic particle group to migrate, thereby removing the obstruction to the liquid and allowing the liquid to enter the waste liquid area.

[0029] The magnetic particle group consists of magnetic particles distributed on the microchannel in a dotted or locally packed form.

[0030] This invention utilizes the capillary pressure generated by the accumulation of magnetic particles to block liquid. This pressure exhibits an overwhelming advantage when the liquid volume is small and the driving pressure is extremely low, enabling stable blocking without the need for continuous external energy.

[0031] As a further improvement of the present invention, the equivalent water contact angle of the transient liquid-blocking structure 6 is 20–50 degrees.

[0032] The equivalent water contact angle refers to the static contact angle formed by deionized water on the surface of the dry magnetic particle stack structure, measured by the pendant drop method or the seated drop method.

[0033] When the equivalent water contact angle of the transient liquid-blocking structure 6 is within the hydrophilic range of 20° to 50°, its liquid-blocking effect and release reliability achieve the best balance. Within this range, although the liquid wets the particle surface, the high-density packing of the dry magnetic particles forms a network of extremely small capillary pores between the particles. When the liquid front arrives, the strong capillary negative pressure (capillary resistance) generated by these pores is sufficient to counteract the pressure driving the liquid flow (such as capillary force, negative pressure, etc.), thereby achieving stable retention. This hydrophilic surface also ensures that the subsequent rehydration liquid can quickly and uniformly penetrate the entire structure, allowing the protective layer to completely dissolve and creating conditions for the smooth migration of the magnetic particle group. If the contact angle is less than 20°, the surface is too hydrophilic, which may cause the liquid to penetrate into the deeper layers of the structure prematurely, weakening the strength of capillary resistance; if it is greater than 50°, it tends to be hydrophobic, which may be detrimental to the uniform rehydration and dispersion of the protective layer, affecting the thoroughness of release.

[0034] As a further improvement of the present invention, the protective layer is selected from proteins, polysaccharides, or hydrophilic polymers, preferably albumin, gelatin, polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), or combinations thereof. The protective layer maintains the adhesion between magnetic particles and to the substrate in a dry or semi-dry state, while rapidly dissolving or swelling and dispersing in an aqueous environment (with rinsing solution added), thereby ensuring the stability of the magnetic particles during the liquid-blocking stage and their effective rehydration during the release stage.

[0035] As a further improvement of the present invention, the particle size of the magnetic particles is 100-5000 nanometers, preferably 200-2000 nanometers, and more preferably 500-1000 nanometers.

[0036] The particle size range of magnetic particles is one of the key parameters for achieving stable liquid blocking and controlled release. When the particle size is less than 100 nm, the magnetic responsiveness of the particles may be insufficient, and the liquid blocking structure is prone to instability due to Brownian motion. When the particle size is greater than 5000 nm, the particles are prone to premature settling before drying due to gravity, and the resulting aggregate structure may be too loose, easily clogging microchannels during migration. However, when the particle size is in the range of 200 nm to 2000 nm, the particles can form a dense and stable transient liquid blocking structure, while possessing good magnetic responsiveness and rehydration dispersibility. In particular, when the particle size is in the range of 500 nm to 1000 nm, rapid and overall migration can be achieved under the magnetic field provided by conventional permanent magnets, resulting in the most reliable and thorough release.

[0037] As a further improvement of the present invention, the magnetic particle group can form a dense accumulation under the action of an external magnetic field to enhance its blocking ability. By using a magnetic field to assist the adsorption of magnetic particles 5, pressure fluctuations caused by temperature changes, vibrations, evaporation, etc., can be resisted, ensuring that the reaction takes place in an absolutely stable liquid flow environment and effectively preventing the liquid from prematurely entering the waste liquid area during the reaction process.

[0038] The principle of controlling the flow of micro-samples using the microfluidic chip of this invention with the assistance of an external magnetic field is as follows: Figure 4 As shown: A. Add a small amount of biological sample (less than 10 μL) through the 4-way microchannel in the sample introduction area; B. An external magnetic field is applied to the transient liquid-blocking structure 6, and the sample flows along the microchannel 3 toward the waste liquid area 5 to the end of the microchannel 3, where it is intercepted by the transient liquid-blocking structure 6. C. When liquid needs to be released, add rinsing solution from the injection area and remove the magnetic field; D. The rinsing fluid dissolves or disperses the protective layer on the surface of the magnetic particle group and drives the magnetic particle group to migrate, thereby removing the obstruction to the liquid and allowing the liquid to enter the waste liquid area.

[0039] Another implementation principle of controlling the flow of micro-samples using the microfluidic chip of the present invention with the assistance of an external magnetic field is as follows: Figure 5 As shown: A. Add less than 10 microliters of biological sample to the microchannel through the sample introduction area; B. An external magnetic field is applied to the transient liquid-blocking structure 6, and the sample flows along the microchannel 3 toward the waste liquid area 5 to the end of the microchannel 3, where it is intercepted by the transient liquid-blocking structure 6. C. When liquid needs to be released, add rinsing solution from the sample injection area and move the magnetic field to drag the magnetic particle group towards the waste liquid area 5; D. Magnetic particles are dragged into waste liquid zone 5 by the magnetic field, and the liquid in the microchannel flows into waste liquid zone 5 under the driving action of capillary force and the pressure of the rinsing liquid. Example

[0040] Preparation of hydrophilic magnetic particles coated with protein layers (taking the preparation of carboxylated magnetic beads coupled with goat anti-rabbit IgG as an example) 1. Prepare buffer solution 1.1 Activation buffer: 0.1M MES, pH 5.0; 1.2 Coupling buffer: 0.1M MES, pH 5.0; 1.3 Activators: EDC (10 mg / ml) and Sulfo-NHS (10 mg / ml) were prepared using activation buffer and used immediately. 1.4 Blocking solution: 0.01M PBS (NaCl 8g / L, KCl 0.2g / L, Na2HPO4·12H2O 3.63g / L, KH2PO4 0.24g / L), 1% BSA, 0.25% ethanolamine, Procline 3001mL / L, pH 7.4; 1.5 Cleaning solution: Tris 6.6g / L, BSA 0.5g / L, Tween-20 0.5mL / L, Procline 300 0.5mL / L, BND-10 0.5mL / L, pH 7.4; 1.6 Preservation buffer: Tris 6.6 g / L, BSA 0.5 g / L, Tween-20 0.5 mL / L, Procline 300 0.5 mL / L, BND-10 0.5 mL / L, pH 7.4; 2. Coupling process (labeling 10mg of 500nm diameter magnetic beads) 2.1 Take out the required raw materials and reagents and allow them to equilibrate to room temperature; 2.2 Calculate the amount of magnetic beads, activator, and antibody used for labeling (NHS / magnetic beads: 25 μg / mg, EDC / magnetic beads: 40 μg / mg, antibody / magnetic beads labeling ratio: 15 μg / mg). 2.3 Mix the magnetic beads thoroughly, place them on a magnetic rack for magnetic separation, and discard the supernatant; add 1 mL of activation buffer, place them on a vortex mixer and mix for 5 s, then magnetically separate to remove the supernatant. Repeat this process twice more. 2.4 Weigh appropriate amounts of EDC and NHS that have been equilibrated to room temperature and dissolve them in an appropriate amount of activation buffer to make their concentrations 10 mg / mL. Add 1 mL of activation buffer to the magnetic beads that have been cleaned in step 2.3, resuspend them, add 25 μL of NHS, mix on a vortex mixer for 5 s, add 40 μL of EDC, mix on a vortex mixer for 5 s, and then activate the reaction in a vertical mixer at 25 °C for 0.5 h. 2.5 After activation, perform magnetic separation on a magnetic rack and discard the supernatant; add 1 mL of coupling buffer, mix on a vortex mixer for 5 s, perform magnetic separation, and discard the supernatant; 2.6 After washing, add 1 mL of coupling buffer to resuspend, place on a vortex mixer to mix for 5 s, then add 0.15 mg of antibody to the magnetic beads, and place in a vertical mixer at 37 °C for 3 h of coupling reaction; 2.7 After the coupling reaction is completed, magnetic separation is performed on a magnetic rack, the supernatant is removed, 1 mL of blocking solution is added, and the mixture is placed on a vortex mixer for 5 seconds. The mixture is then sealed overnight (16-20 h) in a vertical mixer at 37°C. 2.8 After sealing, perform magnetic separation on a magnetic rack, remove the supernatant, add 1 mL of washing solution, mix on a vortex mixer for 5 s, perform magnetic separation, remove the supernatant, and repeat 2 times. 2.9 After washing, add 1 mL of storage buffer to preserve the product at a concentration of 10 mg / mL and store at 2-8℃.

[0041] The prepared magnetic beads were verified using the following examples: Example 1: Verification of the liquid-blocking capability of the transient liquid-blocking structure Magnetic beads coated with good goat anti-rabbit IgG were diluted 10-fold with 1xPBS to obtain a magnetic bead suspension with a concentration of 1 mg / mL. Using a precision pipette, 1.5 µL of the magnetic bead suspension was applied to the end of the microfluidic chip channel (located between the sample application area and the waste liquid area) and allowed to air dry to form a transient liquid-blocking structure with local accumulation. No magnetic beads were added to the control group.

[0042] After bonding the lower and upper substrates together to form a microfluidic chip, 2, 5, 10, and 15 μL of human serum were added to the sample wells, respectively, and the flow behavior was observed.

[0043] Experimental Results: The magnetic bead stacking structure formed during drying effectively retains liquid. When the sample volume is ≤10µL, the liquid is completely blocked within the channel, with the liquid-solid interface being most stable at a volume of 5µL. In the control group (blank channel without magnetic beads), all volumes of sample rapidly flowed into the waste liquid area.

[0044] Example 2: Magnetic Bead Release Experiment The chip prepared according to the method in Example 1, which had successfully retained 5 µL of serum sample, was selected. 20, 30, 40, and 50 µL of PBS buffer were added to the chip through the dilution inlet at the other end for flushing, and structural changes and the restoration of fluid flow were observed.

[0045] Experimental Results: After the addition of PBS, the liquid-blocking structure gradually disintegrated. When the added volume was ≥30µL, the magnetic microspheres were completely flushed out and migrated to the waste liquid area within 3–4 minutes, the channel was restored to unobstructed flow, and no visible particles remained. When the added volume was 20µL, the release was incomplete, and some magnetic beads remained in the channel. These results indicate that a minimum liquid flux threshold needs to be reached to achieve reliable and complete release; under the experimental conditions, this threshold corresponds to a PBS flushing volume of 30µL.

[0046] Example 3: Comparison of liquid-blocking and release effects of different hydrophilic / hydrophobic magnetic beads To verify the effect of the equivalent water contact angle of the transient liquid-blocking structure on the release performance, the following comparative experiment was conducted: Three types of magnetic particles with different surface properties were selected: A. Polystyrene (PS) magnetic beads (equivalent water contact angle of approximately 85°–105°); B. Magnetic beads with carboxyl groups modified on the surface (equivalent water contact angle of approximately 45°–70°); C. Magnetic beads with antibodies conjugated on the surface (equivalent water contact angle of approximately 15°–35°).

[0047] The three types of magnetic beads were prepared into suspensions of 1 mg / mL using PBS buffer, and transient liquid-blocking structures were prepared at the end of the channels of each microfluidic chip according to the method described in Example 1.

[0048] Experimental procedure: Add 5 μL of serum sample to each chip well and let stand for 2 minutes; then add 30 μL of PBS buffer to the diluent well and observe the behavior of the liquid and particles over 4 minutes.

[0049] Experimental results: Liquid barrier capability: The transient liquid barrier structure composed of the three types of magnetic beads can successfully block 5μL serum sample from entering the waste liquid area.

[0050] Release effect: Group A (PS magnetic beads): The liquid-blocking structure remains unchanged after the addition of PBS and cannot be flushed into the waste liquid area. The liquid-blocking state cannot be relieved.

[0051] Group B (carboxyl magnetic beads): The liquid-blocking structure partially disintegrates, and most of the magnetic beads can be flushed into the waste liquid area, but there are obvious particle residues in the channel.

[0052] Group C (antibody-conjugated magnetic beads): The liquid-blocking structure is rapidly and completely disintegrated, and the magnetic beads can be completely and cleanly flushed into the waste liquid area, restoring the channel to unobstructed flow without any residue.

[0053] Experimental conclusion: The above comparison shows that the surface hydrophilicity of magnetic particles (manifested as the equivalent water contact angle) is the key factor determining whether they can achieve complete release after completing their liquid-blocking function. When the equivalent water contact angle is within the hydrophilic range of 20° to 50° (as in group C), the optimal balance between liquid-blocking stability and complete release can be achieved. Excessively hydrophobic surfaces (as in group A, >85°) lead to irreversible blockage; insufficient surface hydrophilicity (as in group B, >50°) results in incomplete release.

[0054] Example 4: Active control of transient liquid resistance and release process by external magnetic field To verify the enhancing and controllable release effect of the external magnetic field on the transient liquid-blocking structure, the following experiment was conducted: Take the prepared antibody-conjugated magnetic microspheres (concentration 1 mg / mL) and prepare a transient liquid-blocking structure at the end of the microfluidic chip channel according to the method in Example 1.

[0055] Experimental group: 5 μL of human serum sample was added to the chip sample well. At the same time as the sample was added, a stable magnetic field generated by a small square permanent magnet (5 mm × 5 mm) was applied to the outside of the chip, corresponding to the position of the transient liquid-resistant structure at the end of the channel.

[0056] Subsequently, 30 μL of PBS buffer was added to the diluent well. The liquid was observed to be firmly retained in the channel and did not enter the waste liquid area.

[0057] After maintaining the magnetic field for 1 minute, the permanent magnet was removed from the chip. After the magnetic field was removed, the liquid trapped in the microchannel (including the sample and PBS) along with the magnetic microspheres quickly and smoothly flowed into the waste liquid area, and the channel was restored to its original patency.

[0058] Control group: Except for not applying an external magnetic field, the operation was exactly the same as the experimental group. The results showed that after adding 30 μL of PBS, the liquid was not effectively retained in the channel, but flowed directly into the waste liquid area.

[0059] Experimental Results and Conclusions: This experiment demonstrates that applying an external magnetic field significantly enhances the stability of the transient liquid-blocking structure, enabling it to withstand greater fluid pressure (such as the pressure generated by subsequent flushing fluid), thereby achieving active extension and control of the reaction time. Conversely, removing the external magnetic field can serve as an independent, active trigger signal, enabling controllable liquid release. This proves that in addition to "liquid flux threshold" triggering release, this invention also possesses a flexible control dimension of "magnetic signal" triggering release.

[0060] The above technical solutions only embody the preferred technical solutions of the present invention. Any modifications that may be made by those skilled in the art to certain parts thereof embody the principles of the present invention and fall within the protection scope of the present invention.

[0061] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0062] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0063] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "setting" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

Claims

1. A microfluidic chip based on transient liquid blocking and release of magnetic particles, comprising a lower substrate (1) and an upper substrate (2), wherein the lower substrate (1) and the upper substrate (2) enclose a microchannel (3), and the two ends of the microchannel (3) along the liquid flow direction are respectively connected to a sample injection area (4) and a waste liquid area (5), characterized in that, The end of the microchannel (3) close to the waste liquid zone (5) is provided with a transient liquid blocking structure (6), which is composed of a group of magnetic particles coated with a soluble or dispersible protective layer on the surface, the group of magnetic particles are bonded to each other and attached to the end of the microchannel (3) in a dry state, forming a capillary barrier to the liquid flow, the protective layer is fully dissolved or dispersed when the liquid volume flowing through the group of magnetic particles exceeds a threshold value, and the group of magnetic particles can migrate under the action of liquid flow or external magnetic field to remove the barrier to the liquid flow. 2.The microfluidic chip based on magnetic particle transient liquid blocking and releasing according to claim 1, wherein, The group of magnetic particles are magnetic particles distributed on the microchannel in the form of dots or local accumulation. 3.The microfluidic chip based on magnetic particle transient liquid blocking and releasing of claim 1, wherein, The equivalent water contact angle of the transient liquid blocking structure (6) is 20-50 degrees. 4.The microfluidic chip based on magnetic particle transient liquid blocking and releasing of claim 1, wherein, The protective layer is selected from proteins, polysaccharides or hydrophilic polymers.

5. The microfluidic chip based on magnetic particle transient liquid blocking and releasing according to claim 2, wherein, The particle size of the magnetic particles is 100-5000 nanometers. 6.The microfluidic chip based on magnetic particle transient liquid blocking and releasing of claim 1, wherein, The group of magnetic particles can form a dense accumulation under the action of an external magnetic field to enhance its blocking ability.

7. A method of fluid control based on the microfluidic chip according to any one of claims 1 to 6, characterized in that, Comprising at least the following steps: S1. Introducing a micro sample into the microchannel (3) through the sample introduction zone (4); S2. The sample flows along the microchannel (3) to the end of the microchannel (3) in the direction of the waste liquid zone (5) and is intercepted by the transient liquid blocking structure (6); S3. When it is necessary to release the liquid, add a flushing liquid into the microchannel, so that the protective layer on the surface of the group of magnetic particles is dissolved or dispersed, and the group of magnetic particles is driven to migrate, thereby removing the liquid retention, and the liquid enters the waste liquid zone.

8. The fluid control method of claim 7, wherein, The S2 step further comprises applying an external magnetic field to the transient liquid blocking structure (6) to enhance its blocking stability.

9. The fluid control method of claim 8, wherein, The S3 step further comprises removing or moving the external magnetic field, and dragging the group of magnetic particles into the waste liquid zone (5) by moving the external magnetic field.

10. The fluid control method of claim 7, wherein, The volume of the micro sample in the S1 step is less than or equal to 10 microliters.

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