A method and system for mixing substances inside a magnetically controlled liquid droplet

Abstract

This invention provides a method and system for mixing substances inside a magnetically controlled droplet. The method includes: adding a droplet containing the substance to be mixed onto a hydrophobic solid substrate infused with a magnetic fluid, causing the magnetic fluid to rapidly envelop the contacting droplet to form a magnetically responsive liquid shell; controlling the movement of the magnetically responsive liquid shell to drive the movement of the enveloped droplet, thereby accelerating the mixing of the substances inside the droplet. The system includes: a hydrophobic solid substrate and a magnetic fluid spread on the surface of the hydrophobic solid substrate. This invention, by causing the magnetically responsive shell enveloping the droplet to rotate around the droplet, generates shear flow at the two-phase interface, increasing the internal dynamics of the droplet and significantly accelerating the mixing process of the substances inside the droplet.

Description

Technical Field

[0001] This invention relates to a method and system for mixing substances inside a magnetically controlled droplet, belonging to the field of magnetically controlled droplet technology. Background Technology

[0002] High-precision, digital manipulation of microdroplets, including precise droplet generation, transport, and efficient droplet mixing control, forms the foundation for numerous applications such as drug delivery, energy harvesting, and microfluidics. The key and core of microdroplet manipulation technology lies in the driving force and braking materials of the droplets. Currently, various microdroplet manipulation technologies based on external stimuli such as electricity, light, heat, and sound have been successfully developed.

[0003] Electrowetting-based microdroplet control technology is multifunctional and flexible, forming the technological foundation for building digital microfluidics. Current digital microfluidics technologies, even the more mature electrowetting digital microfluidics (e.g., CN101679078B, CN103170384B, CN101679078B), require complex circuit designs and multiple dielectric layers. Furthermore, electrowetting technology places high demands on droplet size and the dielectric properties of the surface material, and the substrate is easily contaminated during droplet transport.

[0004] Pipeline-based liquid pump microfluidics often require the design of complex pipelines to assist in liquid mixing (e.g., US20160264924A1, CN101718795B), which can easily lead to pipeline blockage.

[0005] Other methods based on biomimetic structures, surface energy gradients, and external stimuli accelerate the droplet mixing process by driving the droplets to move. This makes the mixing efficiency highly dependent on the driving efficiency, resulting in slow mixing efficiency.

[0006] Various accelerated mixing modes based on sound waves, light, heat, or electric fields introduce external heat into droplets, which cannot meet the requirements for continuous droplet mixing control. Therefore, droplet manipulation based on light, heat, and acoustics is limited in response time and control flexibility, making these technologies difficult to use in highly integrated biochemical applications.

[0007] Magnetron technology offers a simpler and faster response mode. Currently, most of these control technologies rely on adding magnetic particles (such as magnetic beads) to droplets (e.g., CN113908897A, CN104345140B, CN105675900B), which can easily interfere with the internal substances of the droplets and limit the volume of the controllable droplets. Alternatively, some complex magnetically responsive hydrophobic substrates (CN110523451A) can be prepared to achieve mixing by deforming the substrate under a magnetic field, but the surface of the substrate is also easily contaminated.

[0008] Therefore, the various droplet manipulation methods currently in place still face challenges in terms of controllable droplet mixing.

[0009] Recent reports have described the use of magnetohydrodynamics as a control medium to achieve rapid transport of tiny droplets. However, in existing systems, the digital manipulation of tiny droplets, particularly the regulation of droplet hybrid dynamics and the control of biochemical reactions based on this, remains difficult to achieve, significantly limiting the application of these manipulation systems in fields such as chemical microreactors and biochemical detection. Summary of the Invention

[0010] To address the aforementioned technical problems, the present invention aims to provide a method and system for mixing substances inside a magnetically controlled droplet. The method and system of the present invention can regulate the dynamics of the mixing process inside a droplet.

[0011] To achieve the above objectives, a first aspect of the present invention provides a method for mixing substances inside a magnetically controlled liquid droplet, comprising the following steps:

[0012] (1) A droplet containing the substance to be mixed is added to a hydrophobic solid substrate infused with magnetic fluid, so that the magnetic fluid quickly encapsulates the contacting droplet to form a magnetically responsive liquid shell.

[0013] (2) Control the movement of the magnetically responsive liquid shell, causing the droplets it encloses to move along a specific trajectory, thereby accelerating the mixing of substances inside the droplets;

[0014] The motion of the magnetically responsive liquid shell includes at least rotational motion, and the motion of the droplet (i.e., the trajectory of the droplet) includes at least: rotational motion, linear motion, circular motion, oscillating motion, in-situ rotation, or a combination thereof.

[0015] It should be noted that, in the above-described droplet motion, generally speaking, for symmetrical systems (such as spheres), "rotational motion" and "in-situ rotation" have the same meaning. However, in the system of this invention, the magnetically responsive liquid shell is asymmetrical in most cases, and correspondingly, the droplet will also rotate in different directions. Therefore, the droplet motion of this invention can include both rotational motion and in-situ rotation.

[0016] In the above-described method for mixing substances inside a magnetron-controlled droplet, preferably, the rotation axis of the rotational motion is perpendicular to the surface of the hydrophobic solid substrate.

[0017] In the above-described method for mixing substances inside a magnetorheological droplet, preferably, the magnetically responsive liquid shell includes a wetting ridge formed between the droplet and the hydrophobic solid substrate by a magnetic fluid, and a thin layer of magnetic fluid wrapped around the surface of the droplet.

[0018] In the above-described method for mixing substances inside a magnetically controlled droplet, preferably, the movement of the droplet is influenced by the movement of the magnetically responsive liquid shell and exhibits a periodic reciprocating characteristic. It should be noted that when the droplet's movement includes linear movement on a hydrophobic solid substrate, as well as rotational, circular, oscillating, and / or in-situ rotation, the rotational, circular, oscillating, and / or in-situ rotation can occur before or after the linear movement.

[0019] In the above-described method for mixing substances inside a magnetically controlled droplet, preferably, the magnetically responsive liquid shell moves under the influence of an external magnetic field.

[0020] In the above-described method for mixing substances inside a magnetron-controlled droplet, preferably, the external magnetic field is positioned below the hydrophobic solid substrate.

[0021] According to a specific embodiment of the present invention, the present invention utilizes a magnetofluid to encapsulate a droplet. By applying a controllable magnetic field, the magnetofluid outside the droplet rotates, causing viscous shearing of the droplet. This allows for precise control of the dynamics of the mixing process inside the droplet, thereby achieving dynamic regulation of the mixing process.

[0022] In the above-described method for mixing substances inside a magnetically controlled droplet, preferably, the maximum magnetic field strength of the applied magnetic field at the location of the droplet is 50 mT. More preferably, the applied magnetic field can be generated by one or more of permanent magnets, electromagnets, and a magnet array composed of an array of iron needles and electromagnets. The iron needle array refers to an array composed of single iron needles.

[0023] It should be noted that in this invention, the magnetic field strength refers to the surface magnetic field strength. Due to the shielding effect of the hydrophobic solid substrate, the original magnetic field strength can be very large. This invention does not specifically limit it, but only limits the surface magnetic field strength, that is, the magnetic field strength at the location of the droplet.

[0024] In the above-described method for mixing substances inside a magnetronically controlled droplet, preferably, the external magnetic field is controlled by a rotary motor or its array.

[0025] In the above-described method for mixing substances inside a magnetized droplet, preferably, the applied magnetic field includes a rotating magnetic field, which is generated by a permanent magnet, a coil electromagnet, or an array thereof. More preferably, the rotating magnetic field is generated by applying rotation to the center of the magnetic field generated by the permanent magnet, the coil electromagnet, or an array thereof using a rotating motor.

[0026] In the above-described method for mixing substances inside a magnetically controlled droplet, preferably, the rotation radius of the rotating magnetic field is 0.1 times to 3 times the droplet radius.

[0027] In the above-described method for mixing substances inside a magnetron-controlled droplet, preferably, the rotation axis of the rotating magnetic field is perpendicular to the surface of the hydrophobic solid substrate. The rotation axis of the rotating magnetic field may or may not overlap with the center of the droplet.

[0028] According to a specific embodiment of the present invention, when the rotating magnetic field is generated by a coil electromagnet array, it can be used to realize the individual or continuous manipulation of multiple droplets. Utilizing the spatial symmetry of the magnetic field, multiple droplets can move simultaneously toward the same magnetic field center and merge at that center, enabling the sequential manipulation of a large-area droplet array.

[0029] In the above-described method for mixing substances inside a magnetronically controlled droplet, preferably, the movement of the droplet includes linear motion as well as rotational motion, circular motion, oscillating motion, and / or in-situ rotation. The linear motion, rotational motion, circular motion, oscillating motion, and / or in-situ rotation of the droplet on the hydrophobic solid substrate are achieved through the following methods:

[0030] (a) When one or more coil electromagnets far from the droplet are energized, a magnetic field is generated, which drives the magnetically responsive liquid shell to move the droplet enclosed in it linearly toward the center of the magnetic field on the hydrophobic solid substrate.

[0031] (b) A rotating magnetic field is generated by applying rotation to the center of the magnetic field produced by a permanent magnet, a coil electromagnet or an array thereof by a rotating motor, thereby controlling the magnetically responsive liquid shell to rotate, rotate, oscillate and / or rotate in place of the droplets enclosed therein.

[0032] This magnetically responsive liquid shell can guide droplets to perform linear reciprocating motion on a hydrophobic solid substrate under the influence of a magnetic field, thereby achieving droplet manipulation. This invention does not impose a special limitation on the order of steps (a) and (b) above; step (a) can be performed first, or step (b) can be performed first.

[0033] According to a specific embodiment of the present invention, the linear motion, rotational motion, circular motion, oscillating motion, and / or in-situ rotation of the droplets on the hydrophobic solid substrate can be used to achieve simultaneous mixing and acceleration of multiple droplets.

[0034] Compared to traditional methods of driving droplet motion with magnetic beads, the method of this invention does not require the addition of magnetic beads or other magnetically responsive materials inside the droplet, effectively avoiding potential contamination and interference with the mixing and biochemical reactions of substances within the droplet. Furthermore, the method of this invention does not require a (electro)magnet to move with the droplet, and the energized electromagnet coil does not need to fill the path of the droplet's movement, greatly simplifying the system design.

[0035] According to a specific embodiment of the present invention, preferably, the above method further includes: the magnetically responsive liquid shell responds to different magnetic field strengths (0-50 mT) and opens or closes in situ on the surface of the droplet, for regulating the exchange between the droplet and external substances, and / or controlling the continuous merging and mixing of multiple droplets. More preferably, the magnetically responsive liquid shell is closed under a weak magnetic field strength, and the magnetically responsive liquid shell is opened by strong interaction under a strong magnetic field strength; wherein, the magnetic field strength is the magnetic field strength at the location of the droplet, the weak magnetic field strength is 0-1 mT, and the strong magnetic field strength is >1 mT.

[0036] In some specific embodiments of the present invention, when the magnetically responsive liquid shell is in a closed state ensured by continuous movement, it can seal the droplet, effectively slow down the evaporation of the droplet, and shield the droplet from material exchange with the external environment.

[0037] In the above-described method for mixing substances inside a magnetically controlled droplet, preferably, in step (2), the magnetically responsive liquid shell rotates at a speed of 1Hz-100Hz under the guidance of an external magnetic field. It should be noted that in this invention, 1Hz = 1 rps (revolutions per second, i.e., the number of rotations per second). In some specific embodiments of this invention, a controllable rotational speed difference (0-100Hz) can be generated between the magnetically responsive liquid shell and the droplet, accelerating the fluid shearing inside the droplet and enabling rapid and efficient mixing of substances inside the tiny droplet.

[0038] In the above-described method for mixing substances inside a magnetically controlled droplet, the rotation axis of the rotating magnetic field may not overlap with the center of the droplet; that is, the magnetically responsive liquid shell may rotate with an arbitrary radius, and the droplet will respond accordingly. Preferably, in step (2), the rotation radius of the magnetically responsive liquid shell is between 0.1 times and 3 times the radius of the droplet.

[0039] In the above-described method for mixing substances inside a magnetron droplet, preferably, the water contact angle of the hydrophobic solid substrate is 90-180°, more preferably 150-180°.

[0040] In the above-described method for mixing substances inside a magnetron droplet, preferably, the surface roughness of the hydrophobic solid substrate is 0.1-1000 nm, more preferably 0.1-200 nm.

[0041] In the above-described method for mixing substances inside a magnetron droplet, preferably, the hydrophobic solid substrate comprises a porous aluminum plate having hydrophobic or superhydrophobic properties.

[0042] In some specific embodiments of the present invention, the porous aluminum plate with hydrophobic or superhydrophobic properties can be obtained by the following steps: immersing the porous aluminum plate in hot water at 80-95°C for 20-60 minutes to roughen its surface, and then modifying it with silane and / or siloxane for hydrophobicity to obtain the porous aluminum plate with hydrophobic or superhydrophobic properties. The specific steps for hydrophobic modification of the aluminum plate with silane and / or siloxane can be performed according to conventional procedures in the art, such as immersing the surface-roughened porous aluminum plate in a silane and / or siloxane solution for a period of time. Afterwards, conventional drying steps can be performed to obtain the porous aluminum plate with hydrophobic or superhydrophobic properties. The silane and / or siloxane used can be conventional in the art, such as, but not limited to, dimethylsilane, perfluorodecyltriethoxysilane, hexadecyltrimethoxysilane, etc.

[0043] In some specific embodiments of the present invention, the porous aluminum plate may be prepared based on materials such as aluminum sheet, polymethyl methacrylate (PMMA), polydimethylsiloxane (PDMS) and glass. The specific preparation process can be carried out in accordance with conventional methods in the art, and the present invention does not specifically limit it.

[0044] In the above-described method for mixing substances inside a magnetronically controlled droplet, preferably, the magnetic fluid comprises an oil-phase magnetic fluid loaded with magnetic nanoparticles. More preferably, the magnetic fluid includes, but is not limited to, one or a combination of several of the following: silicone oil-based magnetic fluid, kerosene-based magnetic fluid, engine oil-based magnetic fluid, polyphenylene ether-based magnetic fluid, and fluorine-based magnetic fluid.

[0045] In the above-described method for mixing substances inside a magnetronically controlled droplet, preferably, the oil phase in the oil phase magnetorheological fluid comprises dimethyl silicone oil and / or perfluoropolyether.

[0046] In some specific embodiments of the present invention, the magnetic nanoparticles include one or a combination of several of ferromagnetic nanoparticles, antiferromagnetic nanoparticles, ferrimagnetic nanoparticles, synthetic magnetic nanoparticles, paramagnetic nanoparticles, and superparamagnetic nanoparticles. Preferably, the magnetic nanoparticles include magnetite nanoparticles; more preferably, the magnetite nanoparticles have a particle size of 5-300 nm.

[0047] In some specific embodiments of the present invention, magnetic nanoparticles are uniformly dispersed in an oil phase; the mass / volume percentage of the magnetic nanoparticles therein is 1%-52%, based on the volume of the oil phase in the magnetic fluid being 100%.

[0048] In some specific embodiments of the present invention, the magnetic fluid comprises a silicone oil-based magnetic fluid in which the oil phase is dimethyl silicone oil and the nanoparticles of iron oxide are loaded. Preferably, the silicone oil-based magnetic fluid can be prepared by the following steps: adding iron oxide nanoparticles to dimethyl silicone oil and ultrasonically dispersing them to obtain the silicone oil-based magnetic fluid. More preferably, the iron oxide nanoparticles comprise siloxane-functionalized iron oxide nanoparticles. The siloxane-functionalized iron oxide nanoparticles can be prepared by conventional methods in the art. For example, they can be prepared by mixing iron oxide nanoparticles with a functionalized monomer and reacting them at a suitable temperature for a suitable time. Preferably, the siloxane-functionalized iron oxide nanoparticles are prepared using monocarboxyl-terminated polysiloxane (PDMS-COOH) as the functionalized monomer.

[0049] In other specific embodiments of the present invention, the magnetic fluid comprises a perfluoropolyether-based magnetic fluid in which the oil phase is perfluoropolyether and the magnetic fluid is loaded with iron(III) oxide nanoparticles. Preferably, the perfluoropolyether-based magnetic fluid can be prepared by the following steps: adding iron(III) oxide nanoparticles to perfluoropolyether and ultrasonically dispersing them to obtain the perfluoropolyether-based magnetic fluid. More preferably, the iron(III) oxide nanoparticles comprise fluorinated iron(III) oxide nanoparticles. The fluorinated iron(III) oxide nanoparticles can be prepared by conventional methods in the art. For example, they can be prepared by mixing iron(III) oxide nanoparticles with a functionalized monomer and reacting them at a suitable temperature for a suitable time. Preferably, the fluorinated iron(III) oxide nanoparticles are prepared using a monocarboxyl-terminated perfluoropolyether as the functionalized monomer.

[0050] In the above-described method for mixing substances inside a magnetronically controlled droplet, preferably, when the droplet is an aqueous phase droplet, an oil-phase magnetic fluid loaded with magnetic nanoparticles and containing dimethyl silicone oil as the oil phase is selected as the magnetic fluid; when the droplet is an oil-phase droplet, an oil-phase magnetic fluid loaded with magnetic nanoparticles and containing perfluoropolyether as the oil phase is selected as the magnetic fluid. According to specific embodiments of the present invention, a suitable magnetic fluid can be selected based on the type of droplet; preferably, a silicone oil-based magnetic fluid is used for aqueous phase droplets, and a perfluoropolyether-based magnetic fluid is used for oil phase droplets.

[0051] In the above-described method for mixing substances inside a magnetronically controlled droplet, preferably, the viscosity of the magnetorheological fluid is 0.01-600 cst, more preferably 0.1-100 cst.

[0052] In the above-described method for mixing substances inside a magnetron-controlled droplet, preferably, the contact angle of the magnetorheological fluid on the hydrophobic solid substrate is 0-50°, more preferably 0-30°.

[0053] In the above-described method for mixing substances inside a magnetron droplet, preferably, the hydrophobic solid substrate infused with magnetic fluid is obtained by the following steps: an appropriate amount of the magnetic fluid (preferably the above-described silicone oil-based magnetic fluid or perfluoropolyether-based magnetic fluid) is dropped onto the surface of the hydrophobic solid substrate, and the magnetic fluid spreads spontaneously under the action of surface capillary force to obtain the hydrophobic solid substrate infused with magnetic fluid.

[0054] In the above-described method for mixing substances inside a magnetically controlled droplet, preferably, the droplet is selected from one or more of water, ethylene glycol, glycerol, silicone oil, dimethyl sulfoxide, petroleum ether, toluene, ethanol, ethyl acetate, plant essential oil, and ionic liquid, or from one or more of nanoparticle solution, cell culture medium, bacterial culture medium, protein solution, and inorganic salt solution.

[0055] According to specific embodiments of the present invention, the substances to be mixed in the droplets containing the substances to be mixed can include substances to be mixed or reacted in various fields such as material driving, material mixing, chemical reaction, biological detection, and chemical processes. The present invention does not specifically limit these substances. The present invention adds droplets containing the substances to be mixed onto a hydrophobic solid substrate infused with magnetic fluid. The magnetic fluid rapidly and perfectly encapsulates the contacting droplets, forming a magnetically responsive liquid shell. The rotational motion of the magnetic field is controlled to control the rotational motion of the magnetically responsive liquid shell, causing the droplets it encapsulates to rotate. This creates a controllable velocity difference between the magnetically responsive liquid shell and the droplets, accelerating the fluid shearing inside the droplets. This achieves rapid and efficient mixing of substances within the tiny droplets and allows for precise control of the dynamics of the mixing process, enabling dynamic regulation of the mixing process.

[0056] A second aspect of the present invention provides a system for mixing substances inside a magnetically controlled droplet, which is used to achieve the above-mentioned method for mixing substances inside a magnetically controlled droplet. The system includes: a hydrophobic solid substrate and a magnetic fluid spread on the surface of the hydrophobic solid substrate; in use, the magnetic fluid rapidly envelops the contacting droplet to form a magnetically responsive liquid shell, and the magnetically responsive liquid shell moves, causing the droplet it envelops to move along a specific trajectory, thereby accelerating the mixing of substances inside the droplet; wherein, the movement of the magnetically responsive liquid shell includes at least rotational movement, and the movement of the droplet includes at least: rotational movement, linear movement, circular movement, oscillating movement, in-situ rotation, or a combination thereof.

[0057] In the above-described system for mixing substances inside a magnetron-controlled droplet, preferably, the rotation axis of the rotational motion is perpendicular to the surface of the hydrophobic solid substrate.

[0058] In the above-described system of mixing substances inside a magneto-controlled droplet, preferably, the magnetically responsive liquid shell includes a wetting ridge formed between the droplet and the hydrophobic solid substrate by a magnetofluid, and a thin layer of magnetofluid wrapped around the surface of the droplet.

[0059] According to a specific embodiment of the present invention, preferably, the above system further includes: a magnet or a magnet array. More preferably, the magnet or magnet array includes a permanent magnet, an electromagnet, or a magnet array composed of an array of iron needles and an electromagnet. More preferably, the magnet or magnet array is a coil electromagnet or an array thereof.

[0060] In the above-described system for mixing substances inside a magnetized droplet, preferably, the magnet or magnet array is disposed below the hydrophobic solid substrate.

[0061] In the aforementioned system for mixing substances within a magnetically controlled droplet, preferably, the magnet or magnet array generates a magnetic field, and the magnetically responsive liquid shell moves under the influence of the magnetic field. More preferably, the magnetic field includes a rotating magnetic field, which is generated by a permanent magnet, a coil electromagnet, or an array thereof. Even more preferably, the rotating magnetic field is generated by applying rotation to the center of the magnetic field generated by the permanent magnet, the coil electromagnet, or an array thereof using a rotary motor.

[0062] In the above-described system of mixing substances inside a magnetized droplet, preferably, the maximum magnetic field strength is 50 mT.

[0063] In the above-described system for mixing substances inside a magnetron-controlled droplet, preferably, the rotation axis of the rotating magnetic field is perpendicular to the surface of the hydrophobic solid substrate.

[0064] In the above-described system for mixing substances inside a magnetized droplet, preferably, the rotation radius of the rotating magnetic field is 0.1 times to 3 times the droplet radius.

[0065] In the above-described system for mixing substances inside a magnetized droplet, preferably, the magnetically responsive liquid shell rotates at a speed of 1Hz-100Hz.

[0066] In the above-described system for mixing substances inside a magnetron-controlled droplet, preferably, the water contact angle of the hydrophobic solid substrate is 90-180°, more preferably 150-180°.

[0067] In the above-described system for mixing substances inside a magnetron-controlled droplet, preferably, the surface roughness of the hydrophobic solid substrate is 0.1-1000 nm, more preferably 0.1-200 nm.

[0068] In the above-described system for mixing substances inside a magnetron-controlled droplet, preferably, the hydrophobic solid substrate comprises a porous aluminum plate with hydrophobic or superhydrophobic properties.

[0069] In the aforementioned system for mixing substances within a magnetron-controlled droplet, preferably, the magnetic fluid comprises an oil-phase magnetic fluid loaded with magnetic nanoparticles. More preferably, the magnetic fluid includes, but is not limited to, one or a combination of several of the following: silicone oil-based magnetic fluid, kerosene-based magnetic fluid, engine oil-based magnetic fluid, polyphenylene ether-based magnetic fluid, and fluorine-based magnetic fluid.

[0070] In the above-described system of mixing substances inside a magnetronically controlled droplet, preferably, the oil phase in the oil phase magnetorheological fluid is dimethyl silicone oil and / or perfluoropolyether.

[0071] In some specific embodiments of the present invention, the magnetic nanoparticles include one or a combination of several of ferromagnetic nanoparticles, antiferromagnetic nanoparticles, ferrimagnetic nanoparticles, synthetic magnetic nanoparticles, paramagnetic nanoparticles, and superparamagnetic nanoparticles. More preferably, the magnetic nanoparticles include magnetite nanoparticles; even more preferably, the magnetite nanoparticles have a particle size of 5-300 nm; and particularly preferably, the magnetic nanoparticles include functionalized magnetite nanoparticles.

[0072] In the above-described system of mixing substances inside a magnetron-controlled droplet, preferably, the magnetic nanoparticles are uniformly dispersed in the oil phase; and the mass / volume percentage of the magnetic nanoparticles therein is 1%-52%, based on the volume of the oil phase in the magnetofluid being 100%.

[0073] In some specific embodiments of the present invention, the magnetic fluid comprises a silicone oil-based magnetic fluid in which the oil phase is dimethyl silicone oil and the nanoparticles of iron oxide are loaded. Preferably, the silicone oil-based magnetic fluid can be prepared by the following steps: adding iron oxide nanoparticles to dimethyl silicone oil and ultrasonically dispersing them to obtain the silicone oil-based magnetic fluid. More preferably, the iron oxide nanoparticles comprise siloxane-functionalized iron oxide nanoparticles. The siloxane-functionalized iron oxide nanoparticles can be prepared by conventional methods in the art. For example, they can be prepared by mixing iron oxide nanoparticles with a functionalized monomer and reacting them at a suitable temperature for a suitable time. Preferably, the siloxane-functionalized iron oxide nanoparticles are prepared using monocarboxyl-terminated polysiloxane (PDMS-COOH) as the functionalized monomer.

[0074] In other specific embodiments of the present invention, the magnetic fluid comprises a perfluoropolyether-based magnetic fluid in which the oil phase is perfluoropolyether and the magnetic fluid is loaded with iron(III) oxide nanoparticles. Preferably, the perfluoropolyether-based magnetic fluid can be prepared by the following steps: adding iron(III) oxide nanoparticles to perfluoropolyether and ultrasonically dispersing them to obtain the perfluoropolyether-based magnetic fluid. More preferably, the iron(III) oxide nanoparticles comprise fluorinated iron(III) oxide nanoparticles. The fluorinated iron(III) oxide nanoparticles can be prepared by conventional methods in the art. For example, they can be prepared by mixing iron(III) oxide nanoparticles with a functionalized monomer and reacting them at a suitable temperature for a suitable time. Preferably, the fluorinated iron(III) oxide nanoparticles are prepared using a monocarboxyl-terminated perfluoropolyether as the functionalized monomer.

[0075] In the aforementioned system for mixing substances within a magnetron-controlled droplet, preferably, when the droplet is an aqueous phase droplet, an oil-phase magnetic fluid loaded with magnetic nanoparticles and containing dimethyl silicone oil as the oil phase is selected as the magnetic fluid; when the droplet is an oil-phase droplet, an oil-phase magnetic fluid loaded with magnetic nanoparticles and containing perfluoropolyether as the oil phase is selected as the magnetic fluid. According to specific embodiments of the present invention, a suitable magnetic fluid can be selected based on the type of droplet; preferably, a silicone oil-based magnetic fluid is used for aqueous phase droplets, and a perfluoropolyether-based magnetic fluid is used for oil phase droplets.

[0076] In the above-described system for mixing substances inside a magnetron-controlled droplet, preferably, the viscosity of the magnetorheological fluid is 0.01-600 cst, more preferably 0.1-100 cst.

[0077] In the above-described system for mixing substances inside a magnetron-controlled droplet, preferably, the contact angle of the magnetorheological fluid on the hydrophobic solid substrate is 0-50°, more preferably 0-30°.

[0078] In the above-described system of mixing substances inside a magnetron droplet, preferably, the magnetic fluid is spread on the surface of the hydrophobic solid substrate by: adding an appropriate amount of magnetic fluid (preferably the above-described silicone oil-based magnetic fluid or perfluoropolyether-based magnetic fluid) to the surface of the hydrophobic solid substrate, whereby the magnetic fluid spontaneously spreads on the surface of the hydrophobic solid substrate under the action of surface capillary force.

[0079] In the above-described system of mixing substances inside a magnetically controlled droplet, preferably, the droplet is selected from one or more of water, ethylene glycol, glycerol, silicone oil, dimethyl sulfoxide, petroleum ether, toluene, ethanol, ethyl acetate, plant essential oil, and ionic liquid, or from one or more of nanoparticle solution, cell culture medium, bacterial culture medium, protein solution, and inorganic salt solution.

[0080] This invention provides a method and system for magneto-controlled mixing of substances within a droplet. This method and system are additive-free and non-interfering droplet manipulation techniques. The invention utilizes a magnetofluid pre-wetting hydrophobic solid substrate, thus preventing direct contact between the droplet and the substrate during droplet movement, avoiding contamination and wear. Furthermore, by applying a rotating magnetic field, the magnetofluid response shell enveloping the droplet rotates around it, generating shear flow at the two-phase interface, increasing the droplet's internal dynamics and significantly accelerating the mixing process. Most importantly, the mixing process can be controllably adjusted by changing the angular velocity of the rotating magnetic field.

[0081] Droplet mixing plays a crucial role in biochemical reactions and synthesis. Controllable droplet mixing expands the application range of droplets as individual microreactors. The technical solution of this invention enables chemical synthesis reactions in small-volume, low-cost droplets within an open system, facilitating high-throughput screening of reaction conditions. Accelerating the internal dynamics of the droplet increases the probability of molecular collisions, which can be used to accelerate reaction detection in the field of molecular diagnostics.

[0082] Based on its controllability, this invention provides a novel, programmable, simple, substrate-resistant, and fast-responding magnetically controlled droplet method and system. This invention does not interfere with the droplet or introduce heat. Most importantly, the process of accelerating the mixing of substances within the droplet using the rotating magnetic field occurs in situ, which is beneficial for subsequent application to various in-situ detection techniques for interpreting biochemical reaction results.

[0083] From an application perspective, this invention represents a low-cost, simple, and sustainable green manipulation technology with promising applications in the development of novel digital microfluidics. Droplet manipulation is performed on an open surface, eliminating the need for channel design and fabrication. Furthermore, current digital microfluidics technologies, even the more mature electrowetting digital microfluidics, require complex circuit designs and the placement of multiple dielectric layers. In contrast, the magnetically responsive substrate of this invention (i.e., a hydrophobic solid substrate infused with magnetic fluid) is simple to fabricate and, thanks to its anti-fouling properties, enables repeatable and reconfigurable droplet manipulation, significantly reducing usage costs.

[0084] Specifically, the technical solution of this invention can be designed as a microfluidic chip for detecting nitrate ions, maintaining excellent detection stability compared to traditional detection technologies. Furthermore, the novel droplet mixing method of this invention can easily achieve rapid mixing of high-viscosity liquids, which can be used for protein crystallization and the synthesis of functional materials. In addition, the technical solution of this invention can be used for screening material synthesis conditions. The droplet-based bioreactor has the significant advantage of low sample loss, and the in-situ reaction facilitates direct visualization of results using optical detection instruments. It has good commercial development potential as a product for screening production conditions in pharmaceutical and chemical companies. Moreover, in this invention, the droplet technology controlled by wetting ridges is expected to be combined with existing advanced diagnostic technologies, such as Raman-enhanced spectroscopy and colorimetric reagents, to achieve rapid on-site disease screening. A mature chip can also become a backup biochemical analysis and testing device for every household, possessing significant market development potential in the biomedical field.

[0085] In summary, the technical solution of this invention is green and simple, addresses the major needs of various industries, and has broad application prospects in many fields such as biomedical research, drug synthesis and screening, environmental monitoring and protection, health quarantine, forensic identification, and detection and diagnosis of biological samples. Attached Figure Description

[0086] Figure 1 This is a schematic diagram of the mechanically controlled rotating magnetic field in the system for mixing substances inside the magnetized droplets in Example 1.

[0087] Figure 2 This is a schematic diagram and illustration of Example 1, showing the magnetic response liquid shell rotating under the condition that the surface magnetic field strength is <1mT, and causing the droplets it encloses to rotate in situ.

[0088] Figure 3 An optical image of the process by which the magnetically responsive liquid shell in Example 1 rotates, causing the droplets it encloses to rotate in situ.

[0089] Figure 4 This is a comparison diagram of the mixing of the internal substances of the droplet by controlling the rotation of the magnetically responsive liquid shell in Example 1, and the natural mixing of the internal substances of the droplet without a magnetic field.

[0090] Figure 5 An optical image of the process in Example 1 where the magnetically responsive liquid shell rotates, causing the droplets it encloses to move in a circular motion.

[0091] Figure 6 This is a scanning electron microscope image of the surface of the porous aluminum plate in Example 1.

[0092] Figure 7This is an optical diagram of the water droplet contact angle on the surface of the porous aluminum plate with superhydrophobic properties in Example 1.

[0093] Figure 8 The image shows the spontaneous spreading optical pattern of the silicone oil-based magnetic fluid in Example 1 on a porous aluminum plate with superhydrophobic properties.

[0094] Figure 9 The diagram shows the state of the magnetically responsive liquid shell in Example 2 under conditions of no magnetic field, weak rotating magnetic field strength, and strong rotating magnetic field strength.

[0095] Figure 10 This is a schematic diagram and illustration of Example 3, showing how a magnetically responsive liquid shell guides a droplet to linear motion under the influence of a magnetic field.

[0096] Figure 11 The optical diagrams show how different magnetofluids in Example 4 guide water droplets and silicone oil droplets to move along paths 'M' and 'N' in a programmable manner within a two-dimensional plane.

[0097] Figure 12 This is an optical diagram of manipulating multiple droplets using a coil electromagnet array in Example 5. Detailed Implementation

[0098] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0099] Example 1

[0100] This embodiment provides a system for mixing substances inside a magnetically controlled droplet. The system includes: a hydrophobic solid substrate, a magnetic fluid spread on the surface of the hydrophobic solid substrate, and a coil electromagnet disposed below the hydrophobic solid substrate. In use, the magnetic fluid rapidly envelops the contacting droplet to form a magnetically responsive liquid shell. The magnetically responsive liquid shell rotates, causing the droplet it envelops to rotate in situ, thereby accelerating the mixing of substances inside the droplet.

[0101] This embodiment also provides a method for mixing substances inside a magnetized droplet, which includes the following steps:

[0102] (1) A droplet containing the substance to be mixed is added to a hydrophobic solid substrate infused with magnetic fluid, so that the magnetic fluid quickly encapsulates the contacting droplet to form a magnetically responsive liquid shell.

[0103] (2) Control the magnetically responsive liquid shell to rotate under the action of the rotating magnetic field, which drives the droplets it encloses to rotate in situ, thereby accelerating the mixing of substances inside the droplets.

[0104] The magnetically responsive liquid shell includes a wetting ridge formed between the droplet and the hydrophobic solid substrate by a magnetic fluid, and a thin layer of magnetic fluid wrapped around the surface of the droplet.

[0105] In this embodiment, the droplet is a water droplet.

[0106] In this embodiment, a rotating magnetic field is generated by a coil electromagnet. This rotating magnetic field is generated by mechanically rotating a single coil electromagnet, thereby applying a small offset rotation to the center of the magnetic field. Specifically, as... Figure 1 As shown, the rotating magnetic field is generated by rotating a coil electromagnet fixed to a rotating motor, and the rotating motor is connected to a speed controller to control the angular velocity of rotation. The axis of rotation of the rotating magnetic field is perpendicular to the surface of the hydrophobic solid substrate. The maximum magnetic field strength at the location of the droplet is 50 mT.

[0107] Figure 2 This diagram illustrates how a magnetically responsive liquid shell rotates and causes the enclosed droplet to rotate in situ under a surface magnetic field strength of <1 mT (i.e., a weak magnetic field). Figure 2 It can be seen that under a weak magnetic field, the asymmetric magnetically responsive liquid shell rotates around the droplet in response to the rotating magnetic field. In this embodiment, by controlling the angular velocity of the coil electromagnet, the magnetically responsive liquid shell can be controlled to rotate at a speed of 0.1Hz-100Hz. Furthermore, the radius of rotation is one time the radius of the droplet.

[0108] Figure 3 An optical diagram illustrating the in-situ rotation of a magnetically responsive liquid shell that causes the encapsulated droplet to rotate. Figure 3 As can be seen, in this embodiment, by adding droplets containing the substances to be mixed onto a hydrophobic solid substrate infused with magnetic fluid, the magnetic fluid rapidly and perfectly encapsulates the contacting droplets, forming a magnetically responsive liquid shell. The rotational motion of the magnetic field is controlled to make the magnetically responsive liquid shell rotate, causing the droplets it encapsulates to rotate in situ. This creates a controllable velocity difference between the magnetically responsive liquid shell and the droplets, thereby generating viscous shear force on the droplets. This accelerates the fluid shearing inside the droplets, and thus allows for precise control of the dynamics of the mixing process inside the droplets, achieving dynamic regulation of the mixing process.

[0109] Figure 4 This image shows a comparison between controlling the rotation of the magnetically responsive liquid shell to mix the substances inside the droplet in this embodiment, and the natural mixing of substances inside the droplet without a magnetic field. Figure 4 In the droplet, the substances to be mixed are Congo red and fruit green. Figure 4 In this process, the magnetically responsive liquid shell is controlled to rotate at a speed of 1 Hz, and the radius of rotation is one time the radius of the droplet. Figure 4 As can be seen, in this embodiment, controlling the rotation of the magnetically responsive liquid shell causes the droplets it encloses to rotate in situ, which can generate viscous shear force on the droplets. This can accelerate the mixing of substances inside the droplets and achieve rapid and efficient mixing of substances inside the tiny droplets.

[0110] The method in this embodiment further includes the following steps: controlling the magnetically responsive liquid shell to rotate under the action of a rotating magnetic field, causing the droplets it encloses to move in a circular motion, thereby accelerating the mixing of substances inside the droplets.

[0111] Figure 5 An optical diagram illustrating the process of a magnetically responsive liquid shell rotating and causing the encapsulated droplets to undergo circular motion. Figure 5 As can be seen, this embodiment sets the rotation radius of the magnetically responsive liquid shell to twice the droplet radius, thereby driving the droplet it encloses to perform circular motion. The viscous friction between the magnetically responsive liquid shell and the droplet, as well as between the droplet and the substrate, accelerates the fluid shearing inside the droplet. This allows for precise control of the dynamics of the mixing process inside the droplet, achieving dynamic control of the mixing process.

[0112] In this embodiment, the hydrophobic solid substrate is a porous aluminum plate with superhydrophobic properties, which is obtained through the following steps: The porous aluminum plate is immersed in hot water at 80-95°C for 30 minutes to roughen its surface, and then hydrophobically modified with perfluorodecyltriethoxysilane to obtain a porous aluminum plate with superhydrophobic properties. The specific steps for hydrophobically modifying the porous aluminum plate with perfluorodecyltriethoxysilane can be performed according to conventional procedures in the art, such as immersing the surface-roughened porous aluminum plate in a perfluorodecyltriethoxysilane solution for a period of time. Conventional drying steps can then be performed to obtain the porous aluminum plate with superhydrophobic properties.

[0113] The scanning electron microscope image of the porous aluminum plate surface used in this embodiment is shown below. Figure 6 As shown. By Figure 6 The microstructure of the porous aluminum plate surface used in this embodiment can be seen. The optical diagram of the water droplet contact angle on the surface of the porous aluminum plate with superhydrophobic properties in this embodiment is shown below. Figure 7 As shown. By Figure 7 As can be seen, the surface contact angle of the porous aluminum plate modified with fluorosilane is approximately 161°, exhibiting superhydrophobic properties. The surface roughness of the superhydrophobic porous aluminum plate in this embodiment is 100 nm.

[0114] In this embodiment, the magnetic fluid is a silicone oil-based magnetic fluid with dimethyl silicone oil as the oil phase and siloxane-functionalized iron oxide nanoparticles loaded on it. This silicone oil-based magnetic fluid is prepared by the following steps: adding siloxane-functionalized iron oxide nanoparticles to dimethyl silicone oil and ultrasonically dispersing them to ensure uniform dispersion of the siloxane-functionalized iron oxide nanoparticles in the dimethyl silicone oil, thus obtaining the silicone oil-based magnetic fluid. The particle size of the iron oxide nanoparticles is 5-100 nm. The siloxane-functionalized iron oxide nanoparticles are prepared by the following steps: reacting monocarboxyl-terminated polysiloxane with iron oxide particles at 80°C for 12 h. The mass / volume ratio of the siloxane-functionalized iron oxide nanoparticles to dimethyl silicone oil is 12%. The viscosity of this silicone oil-based magnetic fluid is 10 cSt.

[0115] In this embodiment, the magnetic fluid is spread on the surface of the hydrophobic solid substrate in the following manner: an appropriate amount of silicone oil-based magnetic fluid is dropped onto the surface of the hydrophobic solid substrate, and the silicone oil-based magnetic fluid spontaneously spreads on the surface of the hydrophobic solid substrate under the action of surface capillary force, thereby obtaining a hydrophobic solid substrate infused with magnetic fluid. Figure 8 This is an optical image of the spontaneous spreading of the silicone oil-based magnetorheological fluid on a porous aluminum plate with superhydrophobic properties, as described in this embodiment. Figure 8 It can be seen that the silicone oil-based magnetic fluid spreads rapidly on the surface of a porous aluminum plate with superhydrophobic properties under the action of capillary force. In this embodiment, the contact angle of the magnetic fluid on the hydrophobic solid substrate is 3°.

[0116] Example 2

[0117] This embodiment provides a method for mixing substances inside a magnetically controlled droplet. The method employs the magnetically controlled droplet mixing system described in Embodiment 1 and includes the following steps:

[0118] (1) A droplet containing the substance to be mixed is added to a hydrophobic solid substrate infused with magnetic fluid, so that the magnetic fluid quickly encapsulates the contacting droplet to form a magnetically responsive liquid shell.

[0119] (2) Control the magnetically responsive liquid shell to rotate under the action of the rotating magnetic field, which drives the droplets it encloses to rotate in situ, thereby accelerating the mixing of substances inside the droplets;

[0120] (3) The magnetically responsive liquid shell responds to different rotating magnetic field intensities, thereby opening or closing in situ on the surface of the droplet, which is used to regulate the exchange between the droplet and external substances, and / or to control the continuous merging and mixing of multiple droplets.

[0121] Figure 9 This is a state diagram of a magnetically responsive liquid shell under conditions of no magnetic field, a weak rotating magnetic field strength (0–1 mT), and a strong rotating magnetic field strength (>1 mT). Figure 9It can be seen that under no magnetic field conditions, the droplet is enveloped by the magnetohydrodynamic fluid, forming a magnetically responsive liquid shell; under a weak rotating magnetic field strength, the magnetically responsive liquid shell is in a closed state; under a strong rotating magnetic field strength, the magnetically responsive liquid shell is opened by strong interaction.

[0122] Example 3

[0123] This embodiment provides a method for mixing substances inside a magnetically controlled droplet. The method employs the magnetically controlled droplet mixing system described in Embodiment 1 and includes the following steps:

[0124] (1) A droplet containing the substance to be mixed is added to a hydrophobic solid substrate infused with magnetic fluid, so that the magnetic fluid quickly encapsulates the contacting droplet to form a magnetically responsive liquid shell.

[0125] (2) Control the movement of the magnetically responsive liquid shell to drive the movement of the droplets enclosed by it; the movement of the magnetically responsive liquid shell includes rotational movement, and the movement of the droplets includes in-situ rotation and linear movement on the hydrophobic solid substrate.

[0126] In this embodiment, the linear motion of the droplet on the hydrophobic solid substrate is achieved by energizing a single coil electromagnet located away from the droplet to generate a magnetic field, which drives the magnetically responsive liquid shell to move the droplet enclosed within it linearly towards the center of the magnetic field on the hydrophobic solid substrate. Figure 10 A schematic diagram and illustration showing how a magnetically responsive liquid shell guides a droplet into linear motion under the influence of a magnetic field. (From...) Figure 10 It can be seen that when a strong magnetic field is present, the magnetically responsive liquid shell is magnetized, which drives the droplet to move.

[0127] Example 4

[0128] This embodiment provides a system for mixing substances inside a magnetically controlled droplet. This system is essentially the same as the system for mixing substances inside a magnetically controlled droplet in Embodiment 1, except that the magnetic fluid is a perfluoropolyether-based magnetic fluid with a perfluoropolyether oil phase and fluorine-functionalized iron(III) oxide nanoparticles loaded onto it.

[0129] This perfluoropolyether-based magnetic fluid was prepared through the following steps: fluorinated iron oxide (Fe3O4) nanoparticles were added to perfluoropolyether and ultrasonically dispersed to ensure uniform dispersion of the nanoparticles. The particle size of the iron oxide nanoparticles was 5-100 nm. The fluorinated iron oxide nanoparticles were prepared by reacting monocarboxyl-terminated perfluoropolyether with iron oxide particles at 90°C for 12 hours. The mass / volume ratio of the fluorinated iron oxide nanoparticles to the perfluoropolyether was 12%. The viscosity of this perfluoropolyether-based magnetic fluid was 100 cSt.

[0130] In this embodiment, the contact angle of the perfluoropolyether-based magnetic fluid on the hydrophobic solid substrate is 3°.

[0131] When the droplet is an aqueous phase droplet, the silicone oil-based magnetic fluid of Example 1 is selected; when the droplet is an oil phase droplet, the perfluoropolyether-based magnetic fluid of this example is selected.

[0132] In this embodiment, the water droplets are coated with the silicone oil-based magnetic fluid of Example 1, and the silicone oil droplets are coated with the perfluoropolyether-based magnetic fluid of this embodiment. The magnetically responsive liquid shell is controlled to rotate under the influence of a rotating magnetic field using the method described in Example 3. This causes the droplets it encapsulates to rotate in situ, accelerating the mixing of the substances inside the droplets. Furthermore, the magnetically responsive liquid shell guides the droplets to linear motion under the influence of the magnetic field. The results are as follows: Figure 11 As shown. Figure 11 Optical diagrams illustrating how different magnetic fluids (left: silicone oil-based magnetic fluid; right: perfluoropolyether-based magnetic fluid) guide water droplets (left) and silicone oil droplets (right) along programmable 'M' and 'N' paths in a two-dimensional plane, respectively. Figure 11 It can be seen that various types of droplets can be moved by changing the magnetofluid, and programmable droplet manipulation in a two-dimensional plane can be achieved.

[0133] Example 5

[0134] This embodiment provides a system for mixing substances inside a magnetically controlled droplet. The system includes: a hydrophobic solid substrate, a magnetic fluid spread on the surface of the hydrophobic solid substrate, and a coil-type electromagnet array disposed below the hydrophobic solid substrate. In use, the magnetic fluid rapidly envelops the contacting droplet to form a magnetically responsive liquid shell. The magnetically responsive liquid shell rotates, causing the enveloped droplet to rotate in situ, accelerating the mixing of substances inside the droplet. The magnetic fluid and hydrophobic solid substrate are the same as in Embodiment 1, and the droplet is a water droplet.

[0135] This embodiment also provides a method for mixing substances inside a magnetized droplet, which includes the following steps:

[0136] (1) Multiple droplets containing the substance to be mixed are added to a hydrophobic solid substrate infused with magnetic fluid, so that the magnetic fluid can quickly encapsulate the droplets to form a magnetically responsive liquid shell.

[0137] (2) Control the magnetically responsive liquid shell to rotate under the action of the rotating magnetic field, which drives the droplets it encloses to rotate in situ and accelerates the mixing of substances inside the droplets.

[0138] The magnetically responsive liquid shell includes a wetting ridge formed between the droplet and the hydrophobic solid substrate by a magnetic fluid, and a thin layer of magnetic fluid wrapped around the surface of the droplet.

[0139] In this embodiment, the rotating magnetic field is generated by rotating the center of the magnetic field generated by the coil electromagnet array using a rotary motor. The axis of rotation of this rotating magnetic field is perpendicular to the surface of the hydrophobic solid substrate. The maximum magnetic field strength at the location of the droplet is 30 mT. By controlling the rotary motor, the magnetically responsive liquid shell can be controlled to rotate at a speed of 1 Hz to 100 Hz. Furthermore, the radius of rotation is twice the radius of the droplet.

[0140] In this embodiment, the rotating magnetic field is an array of rotating magnetic fields, with a rotational offset applied to each magnetic field center simultaneously or individually, thereby enabling individual or continuous manipulation of multiple droplets. Utilizing the spatial symmetry of the magnetic field, multiple droplets can move simultaneously toward the same magnetic field center and merge at that center, enabling sequential manipulation of large-area droplet arrays. Figure 12 In this embodiment, a coil electromagnet array is used to manipulate multiple droplets. Figure 12 The image shows an optical diagram of a droplet array. The method in this embodiment can be used to mix multiple droplets. Figure 12 The white circled area represents a water droplet encased in a magnetically responsive liquid shell, formed by... Figure 12 It can be seen that by building an electromagnet array, it is possible to manipulate and mix multiple droplets, which may then be used for high-throughput microdroplet analysis.

Claims

1. A method for mixing substances inside a magnetron-controlled droplet, comprising the following steps: (1) Droplets containing the substance to be mixed are added to a hydrophobic solid substrate infused with magnetic fluid, so that the magnetic fluid quickly encapsulates the contacting droplets to form a magnetically responsive liquid shell. (2) Control the movement of the magnetically responsive liquid shell to drive the droplets enclosed by it to move along a specific trajectory, thereby accelerating the mixing of substances inside the droplets. The magnetically responsive liquid shell moves under the action of an external magnetic field, which includes a rotating magnetic field. The motion of the magnetically responsive liquid shell is rotational, and the motion of the droplet is rotational. The rotational motion of the droplets on the hydrophobic solid substrate is achieved in the following way: A rotating magnetic field is generated by applying rotation to a permanent magnet, a coil electromagnet, or an array of coil electromagnets through a rotating motor, thereby controlling the magnetically responsive liquid shell to rotate and causing the droplets enclosed within it to rotate. (3) The magnetically responsive liquid shell responds to different magnetic field strengths, thereby opening or closing in situ on the surface of the droplet, for regulating the exchange between the droplet and external substances, and / or controlling the continuous merging and mixing of multiple droplets; the magnetically responsive liquid shell is closed under weak magnetic field strength, and the magnetically responsive liquid shell is opened by strong interaction under strong magnetic field strength; wherein, the magnetic field strength is the magnetic field strength at the location of the droplet, the weak magnetic field strength is 0~1 mT, and the strong magnetic field strength is >1 mT.

2. The method for mixing substances inside a magnetized droplet according to claim 1, wherein, The rotational motion of the droplet is either circular motion or in-situ rotation.

3. The method for mixing substances inside a magnetized droplet according to claim 1, wherein, The magnetically responsive liquid shell includes a wetting ridge formed between the droplet and the hydrophobic solid substrate by a magnetic fluid, and a thin layer of magnetic fluid wrapped around the surface of the droplet.

4. The method for mixing substances inside a magnetized droplet according to claim 1, wherein, The external magnetic field is positioned below the hydrophobic solid substrate.

5. The method for mixing substances inside a magnetized droplet according to claim 1, wherein, The maximum magnetic field strength of the applied magnetic field at the location of the droplet is 50 mT.

6. The method for mixing substances inside a magnetized droplet according to claim 1, wherein, The radius of rotation of the rotating magnetic field is between 0.1 times and 3 times the radius of the droplet.

7. The method for mixing substances inside a magnetron-controlled droplet according to claim 1, wherein, In step (2), the magnetically responsive liquid shell rotates at a speed of 0.1Hz-100Hz under the guidance of an external magnetic field.

8. The method for mixing substances inside a magnetron-controlled droplet according to claim 1, wherein, The water contact angle of the hydrophobic solid substrate is 90-180°.

9. The method for mixing substances inside a magnetron-controlled droplet according to claim 8, wherein, The water contact angle of the hydrophobic solid substrate is 150-180°.

10. The method for mixing substances inside a magnetized droplet according to claim 1, wherein, The surface roughness of the hydrophobic solid substrate is 0.1-1000 nm.

11. The method for mixing substances inside a magnetized droplet according to claim 10, wherein, The surface roughness of the hydrophobic solid substrate is 0.1-200 nm.

12. The method for mixing substances inside a magnetized droplet according to claim 1, wherein, The hydrophobic solid substrate includes a porous aluminum plate with hydrophobic or superhydrophobic properties.

13. The method for mixing substances inside a magnetized droplet according to claim 1, wherein, The magnetic fluid includes an oil-phase magnetic fluid loaded with magnetic nanoparticles.

14. The method for mixing substances inside a magnetron-controlled droplet according to claim 13, wherein, The magnetic fluid includes one or a combination of several of the following: silicone oil-based magnetic fluid, kerosene-based magnetic fluid, machine oil-based magnetic fluid, polyphenylene ether-based magnetic fluid, and fluorine-based magnetic fluid.

15. The method for mixing substances inside a magnetized droplet according to claim 13, wherein, The oil phase in the oil-phase magnetofluid includes dimethyl silicone oil and / or perfluoropolyether.

16. The method for mixing substances inside a magnetron-controlled droplet according to claim 13, wherein, The magnetic nanoparticles include one or a combination of several of ferromagnetic nanoparticles, antiferromagnetic nanoparticles, and subferromagnetic nanoparticles.

17. The method for mixing substances inside a magnetized droplet according to claim 13, wherein, The magnetic nanoparticles include synthetic magnetic nanoparticles.

18. The method for mixing substances inside a magnetron-controlled droplet according to claim 13, wherein, The magnetic nanoparticles include paramagnetic nanoparticles or superparamagnetic nanoparticles.

19. The method for mixing substances inside a magnetron-controlled droplet according to claim 13, wherein, The magnetic nanoparticles include iron oxide nanoparticles; the particle size of the iron oxide nanoparticles is 5-300 nm.

20. The method for mixing substances inside a magnetized droplet according to claim 13, wherein, The magnetic nanoparticles are uniformly dispersed in the oil phase; with the volume of the oil phase in the magnetic fluid being 100%, the mass / volume percentage of the magnetic nanoparticles therein is 1%-52%.

21. The method for mixing substances inside a magnetron-controlled droplet according to claim 13, wherein, The magnetic fluid includes a silicone oil-based magnetic fluid in which the oil phase is dimethyl silicone oil and the magnetic fluid is loaded with iron oxide nanoparticles, wherein the iron oxide nanoparticles include siloxane-functionalized iron oxide nanoparticles; or, the magnetic fluid includes a perfluoropolyether-based magnetic fluid in which the oil phase is perfluoropolyether and the magnetic fluid is loaded with iron oxide nanoparticles, wherein the iron oxide nanoparticles include fluorine-functionalized iron oxide nanoparticles.

22. The method for mixing substances inside a magnetron-controlled droplet according to claim 15, wherein, When the droplet is an aqueous phase droplet, an oil-phase magnetic fluid loaded with magnetic nanoparticles and containing dimethyl silicone oil as the oil phase is selected as the magnetic fluid; when the droplet is an oil-phase droplet, an oil-phase magnetic fluid loaded with magnetic nanoparticles and containing perfluoropolyether as the oil phase is selected as the magnetic fluid.

23. The method for mixing substances inside a magnetized droplet according to claim 1, wherein, The viscosity of the magnetic fluid is 0.01-600 cSt.

24. The method for mixing substances inside a magnetron-controlled droplet according to claim 23, wherein, The viscosity of the magnetic fluid is 0.1-100 cSt.

25. The method for mixing substances inside a magnetized droplet according to claim 1, wherein, The contact angle of the magnetorheological fluid on the hydrophobic solid substrate is 0-50°.

26. The method for mixing substances inside a magnetron-controlled droplet according to claim 25, wherein, The contact angle of the magnetorheological fluid on the hydrophobic solid substrate is 0-30°.

27. The method for mixing substances inside a magnetized droplet according to claim 1, wherein, The droplets are selected from one or more of water, ethylene glycol, glycerol, silicone oil, dimethyl sulfoxide, petroleum ether, toluene, ethanol, ethyl acetate, plant essential oil, and ionic liquid, or from one or more of nanoparticle solutions, cell culture media, bacterial culture media, protein solutions, and inorganic salt solutions.

28. A system for mixing substances inside a magnetically controlled droplet, used to achieve the method for mixing substances inside a magnetically controlled droplet according to any one of claims 1-27, the system comprising: A hydrophobic solid substrate, and a magnetic fluid spread on the surface of the hydrophobic solid substrate; In use, the magnetorheological fluid rapidly envelops the contacting droplets to form a magnetically responsive liquid shell. The movement of the magnetically responsive liquid shell causes the droplets it envelops to move along a specific trajectory, accelerating the mixing of the substances inside the droplets. The motion of the magnetically responsive liquid shell is rotational, and the motion of the droplet is rotational. The system further includes: a magnet or a magnet array; the magnet or magnet array includes permanent magnets, or coil electromagnets or coil electromagnet arrays; the magnet or magnet array generates a magnetic field, and the magnetically responsive liquid shell moves under the action of the magnetic field; the magnetic field includes a rotating magnetic field.

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