Microfluidic system for regulating ferrofluid motion by micro-magnetic column array and processing method thereof

Abstract

The application discloses a kind of micro-magnetic column array regulation and control ferromagnetic fluid movement microfluidic system and processing method, through the synergistic effect of micro-magnetic column array and Halbach magnet array, on the one hand, using the micro-magnetic column array with special arrangement structure, the distribution of space flow field is changed, on the other hand, using the high local magnetic field gradient generated by micro-magnetic column array, the movement of ferromagnetic fluid is accurately regulated, under the joint action of the two, the precise regulation and control of high-throughput and high-efficiency mixing of different solutions in cross-shaped microfluidic channel is realized, the mixing efficiency between different solutions is improved, the mixing time is also shortened, and the high-efficiency mixing of different solutions is flexibly regulated in real time, time and economic cost are saved, have strong use value, at the same time, the microfluidic system with passive mixing and active mixing is first proposed, also has very strong academic significance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of microfluidics, and particularly relates to a microfluidic system for regulating ferrofluid movement by means of a micro magnetic column array and a processing method. BACKGROUND

[0002] Microfluidic systems have obvious advantages in accelerating chemical analysis and reaction, reducing reagent consumption, improving mass transfer efficiency, and reducing cost and harm, and are widely used in electronic, biological, chemical, medical, and environmental fields. In recent years, in the field of biomedicine, researchers often use microfluidic systems to integrate sample collection, dilution, mixing, reaction, dilution, sorting, and detection processes on the same microchip to simplify experimental procedures while maintaining high detection efficiency. Strengthening the mixing of samples and markers is an important step in achieving high-precision sample detection, but in traditional microfluidic systems, the low Reynolds number of microfluidic channels leads to a long mixing time between samples and markers. Therefore, how to improve the mixing efficiency between different solutions while shortening the mixing time is a key concern.

[0003] Currently, methods commonly used to enhance the mixing of different samples can be divided into active mixing and passive mixing. Active mixing often relies on the action of external fields (such as electric fields, magnetic fields, thermal fields, ultrasonic fields, microwave fields, etc.) to achieve precise control of the mixing of different samples, but this method often requires the use of complex field generating devices and consumes a large amount of external energy, which is not conducive to the realization of portable medical diagnosis functions. Passive mixing relies on the design of microfluidic channel structure to increase the contact area between different fluids by changing the flow direction of the fluid, thereby achieving efficient mixing of samples. However, the mixing efficiency of passive mixing is greatly dependent on the distribution of the flow field in the microchannel, and when the microchannel structure is fixed, the spatial flow field distribution is difficult to change, making it impossible to achieve real-time flexible control of sample mixing. Therefore, how to improve the mixing efficiency between different samples while achieving real-time flexible control of sample mixing is a key concern.

[0004] A stable colloid formed by superparamagnetic nanoparticles with a diameter of 5-15 nm stably dispersed in a carrier liquid by means of a surfactant is called ferrofluid. Due to its magnetic, fluidic, and good biocompatibility, it can not only promote the mixing of different samples under the action of an external magnetic field, but also has obvious advantages in flexible control of sample mixing efficiency. In addition, the non-contact nature of magnetic field control, the independence of temperature and pH, the precise controllability, and the simplicity of the magnetic field generating device also lay a solid foundation for its application in medical detection.

[0005] However, the current research on the magnetic field control of ferromagnetic fluid movement to enhance the mixing between different samples is mostly limited to low flux and low Reynolds number. When the loading flux of the sample is increased, the mass exchange between the fluids is greatly weakened, which greatly reduces the mixing efficiency of the sample. SUMMARY

[0006] The present application provides a micro-magnetic column array regulated ferromagnetic fluid movement microfluidic system and processing method to overcome the problem of long time and low mixing efficiency when mixing different samples. The present application realizes real-time regulation of high-efficiency mixing of different solutions.

[0007] To achieve the above object, the present application adopts the following technical scheme:

[0008] A micro-magnetic column array regulated ferromagnetic fluid movement microfluidic system, comprising a cross-shaped microfluidic channel, a micro-magnetic column array, a microfluidic channel outlet and an external bias magnetic field, wherein the cross-shaped microfluidic channel is connected to the microfluidic channel outlet, the micro-magnetic column array is arranged inside the cross-shaped microfluidic channel, and the external bias magnetic field is arranged outside the cross-shaped microfluidic channel.

[0009] Further, the cross-shaped microfluidic channel comprises a ferromagnetic fluid channel, a linear mixed liquid channel and a microfluidic straight channel, wherein the linear mixed liquid channel comprises a first mixed liquid channel and a second mixed liquid channel located on the same straight line, the outlet end of the first mixed liquid channel is connected to the outlet end of the second mixed liquid channel, the ferromagnetic fluid channel is perpendicular to the linear mixed liquid channel, the flow rate of the ferromagnetic fluid in the ferromagnetic fluid channel is 0.5 times the flow rate of the mixed liquid in the linear mixed liquid channel, and the microfluidic channel outlet is arranged at the free end of the microfluidic straight channel.

[0010] Further, the micro-magnetic column array is arranged through the microfluidic straight channel, and the bottom end of the micro-magnetic column array is at the same horizontal plane as the bottom side of the microfluidic straight channel, and the top end of the micro-magnetic column array is at the same horizontal plane as the top side of the microfluidic straight channel.

[0011] Further, the inside of the microfluidic straight channel is provided with a plurality of micro-magnetic column arrays, each micro-magnetic column array is composed of a plurality of micro-magnetic columns, the micro-magnetic column is a cylindrical shape, the radius of each micro-magnetic column is 30 μm, and the height is 60 μm.

[0012] Further, the micro-magnetic column array comprises 13 micro-magnetic columns, 12 of which are arranged in a regular octagonal structure, the center-to-center distance of the adjacent two micro-magnetic columns in the regular octagonal structure along the x-axis and y-axis directions is 90 μm, and one micro-magnetic column is arranged at the center of the regular octagonal structure.

[0013] Further, the micro-magnetic column is obtained by mixing, bubble-removing and curing of PDMS and NdFeB magnetic powder in a mass ratio of 1:1.

[0014] Further, the magnetization direction of the micro-magnetic column is along the height direction of the micro-magnetic column.

[0015] Further, the external bias magnetic field is generated by two concentric Halbach magnet arrays, each of which is composed of NdFeB N50 cuboid permanent magnets with the same size and magnetization strength arranged at different rotation angles; the outer circle radius r1 of the outer ring of the two concentric Halbach magnet arrays is 142 mm, the inner circle radius r2 of the outer ring is 85 mm, the outer circle radius of the inner ring is the same as the inner circle radius of the outer ring, and the inner circle radius r3 of the inner ring is 50 mm.

[0016] Further, each of the Halbach magnet arrays on the rings can rotate at any angle, and the adjustment range of the external bias magnetic field is 0-100 mT.

[0017] A processing method of a micro-magnetic column array regulated microfluidic system for controlling ferromagnetic fluid movement, comprising the following steps:

[0018] Step one: using micro-nano lithography technology and deep silicon etching technology, a mold with a cross-shaped microfluidic channel and a micro-magnetic column structure is made on a silicon substrate;

[0019] Step two: after mixing PDMS and NdFeB magnetic powder in a mass ratio of 1:1, the mixture is injected into the micro-magnetic column structure of the mold using a dropper, and after the bubble-removing and curing steps, a cross-shaped microfluidic channel and a micro-magnetic column array are obtained;

[0020] Step three: using oxygen plasma bonding technology, the cross-shaped microfluidic channel and the micro-magnetic column array are packaged together, and a micro-magnetic column array regulated microfluidic system for controlling ferromagnetic fluid movement is obtained.

[0021] Compared with the prior art, the present application has the following beneficial technical effects:

[0022] The present application discloses a micro-magnetic column array regulated microfluidic system for controlling ferromagnetic fluid movement, which realizes the improvement of the mixing efficiency between different solutions, the shortening of the mixing time, the real-time and flexible regulation of the high-efficiency mixing of different solutions, and the specific advantages are as follows:

[0023] The system of the present application utilizes, on one hand, the micro-magnetic column array with special arrangement structure to change the distribution of space flow field, and on the other hand, the space high local magnetic field gradient generated by the micro-magnetic column array and the special flow field distribution caused by the distribution can greatly improve the mass exchange between different solutions, promote the high-throughput rapid mixing, and accurately control the movement of ferromagnetic fluid, and under the joint action of the two, the real-time control of the high-efficiency mixing of different solutions in a wide Reynolds number range can be realized.

[0024] Further, the radius of the cylindrical micro-magnetic column is 30 μm, and the height is 60 μm, and the high local magnetic field gradient can be generated,

[0025] Further, the micro-magnetic column array is arranged in an octagonal structure, which can greatly improve the action range on the ferromagnetic fluid, and the micro-magnetic column placed in the center of the octagonal structure of the micro-magnetic column array can be used for adjusting the distribution of the space magnetic field, changing the movement trajectory of the ferromagnetic fluid, and increasing the contact area between different fluids.

[0026] Further, the micro-magnetic column array of the present application is obtained by mixing, bubble removal and curing operation of PDMS and NdFeB magnetic powder according to the mass ratio of 1:1, instead of traditional electroplating technology, which greatly saves the manufacturing cost.

[0027] Further, under the action of the pulse magnetizing device, the cylindrical micro-magnetic column can be permanently magnetized, showing the characteristics of a permanent magnet.

[0028] Further, the Halbach magnet array is used to generate an external bias magnetic field with adjustable amplitude and direction in real time.

[0029] The processing method of the present application adopts the combination of micro-nano lithography technology and deep silicon etching technology to process the micro-fluid channel and the micro-magnetic column, without complex metal corrosion process, so that the micro-magnetic column array with a height of 60 μm can be obtained, greatly simplifying the difficulty of processing technology and improving the precision of processing structure. BRIEF DESCRIPTION OF DRAWINGS

[0030] The drawings attached to the specification provide further understanding of the present application, and form a part of the present application. The illustrative embodiments of the present application and their descriptions serve to explain the present application, and do not constitute an improper limitation of the present application.

[0031] Figure 1 The structure diagram of the micro-fluidic system for regulating the movement of ferromagnetic fluid by the micro-magnetic column array proposed in the present application, 1 is a first liquid to be mixed channel, 2 is a ferromagnetic fluid channel, 3 is a second liquid to be mixed channel, 4 is a micro-magnetic column array, 5 is a micro-fluid straight channel, 6 is a micro-fluid channel outlet, and 7 is an external bias magnetic field.

[0032] Figure 2This is a schematic diagram of the Halbach magnet array with two concentric rings proposed in this invention. Detailed Implementation

[0033] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0034] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0035] Example 1

[0036] This invention provides a microfluidic system for controlling the motion of ferrofluids using a micromagnetic column array, such as... Figure 1 As shown, the system includes a first mixing channel 1, a ferrofluid channel 2, a second mixing channel 3, a micromagnetic column array 4, a microfluidic straight channel 5, a microfluidic channel outlet 6, and an external bias magnetic field 7. The first mixing channel 1 and the second mixing channel 3 form a straight mixing channel, while the ferrofluid channel 2, the straight mixing channel, and the microfluidic straight channel 5 form a cross-shaped microfluidic channel. Ferrofluid is injected into the ferrofluid channel 2, and the solution to be mixed is injected into the straight mixing channel. The mixed sample is collected at the microfluidic channel outlet 6.

[0037] The applied bias magnetic field 7 is generated by an array of two concentric circular rings of Halbach magnets, such as... Figure 2As shown, the Halbach magnet array on each annular ring is composed of NdFeB N50 cuboid permanent magnets with the same size and magnetization strength arranged at different rotation angles. The Halbach magnet array on each annular ring can be rotated by any angle, so as to flexibly change the size and direction of the spatial bias magnetic field. By adjusting the rotation angle of each Halbach magnet array, the magnetic field in the range of 0-100 mT can be arbitrarily adjusted. The outer circle radius r1 of the outer ring in the two concentric annular rings of the Halbach magnet array is 142 mm, the inner circle radius r2 of the outer ring is 85 mm, the outer circle radius of the inner ring is the same as the inner circle radius of the outer ring, the inner circle radius r3 of the inner ring is 50 mm, and the cross-shaped microfluidic channel can be placed inside.

[0038] The micro-magnetic column array 4 is composed of 13 cylindrical micro-magnetic columns, which are obtained by mixing, bubble removal and curing operations of NdFeB magnetic powder and PDMS in a mass ratio of 1:1, instead of traditional electroplating technology, which greatly saves the manufacturing cost. The flow rate of the ferromagnetic fluid channel 2 is 0.5 times that of the linear mixed liquid channel. The radius of the cylindrical micro-magnetic column is 30 μm, and the height is 60 μm, which can generate a high-local magnetic field gradient. Under the action of the pulse magnetizing device, the cylindrical micro-magnetic column can be permanently magnetized, showing the characteristics of a permanent magnet, and the magnetization direction of the cylindrical micro-magnetic column is along the height direction of the magnetic column. The 12 cylindrical micro-magnetic columns in the micro-magnetic column array 4 are arranged in a regular octagonal structure, and the center distance of the adjacent two cylindrical micro-magnetic columns along the x-axis and y-axis directions is 90 μm, which can greatly improve the action range on the ferromagnetic fluid. Placing a micro-magnetic column in the center of the regular octagonal structure can adjust the distribution of the spatial magnetic field, change the motion trajectory of the ferromagnetic fluid, and increase the contact area between different fluids.

[0039] The microfluidic system provided by the application has passive mixing and active mixing functions. The special arrangement of the micro-magnetic column array 4 generates a high-local magnetic field gradient and a special spatial flow field with a special distribution structure. When the ferromagnetic fluid and the solution to be mixed are injected into the channel, the magnetism of the ferromagnetic fluid and the flow characteristics of the special spatial flow field greatly improve the mass exchange between different solutions, thereby promoting high-throughput and rapid mixing. The synergistic effect of the micro-magnetic column array 4 and the Halbach magnet array realizes precise regulation and control of high-throughput and high-efficiency mixing of different solutions in the cross-shaped microfluidic channel in a wide Reynolds number range.

[0040] Example 2

[0041] The application provides a processing method of a micro-magnetic column array regulated micro-fluid system for ferromagnetic fluid movement. The micro-nano lithography technology is used to process the mixer, including the processing of the micro-fluid channel unit and the micro-magnetic column and the packaging of the two. Based on the micro-nano lithography technology and the deep silicon etching technology, a mold with a cross-shaped micro-fluid channel and a micro-magnetic column structure is made on a silicon substrate, then a mixed liquid with a mass ratio of 1:1 of PDMS and NdFeB magnetic powder is injected into the micro-magnetic column structure of the mold by using a dropper, after the bubble removal and curing steps, a cross-shaped micro-fluid channel and a micro-magnetic column array 4 are obtained, finally, the cross-shaped micro-fluid channel and the micro-magnetic column array 4 are packaged together by means of the oxygen plasma bonding technology, and the micro-magnetic column array regulated micro-fluid system for ferromagnetic fluid movement is obtained. When the flux of the solution at the channel inlet changes from several muL / h to hundreds of mL / h, the magnetic mixing efficiency can be kept high.

[0042] It is to be understood by those skilled in the art that the application can be implemented by other embodiments without departing from the spirit or essential characteristics thereof. Therefore, the above disclosed embodiments are merely exemplary in all aspects and are not the only ones. All changes within the scope of the application or within the equivalent scope of the application are intended to be included in the application.

Claims

1. A microfluidic system for regulating the motion of ferrofluids using an array of micromagnetic pillars, characterized in that, The cross-shaped microfluidic channel, the micro-magnetic column array (4), the microfluidic channel outlet (6) and the external bias magnetic field (7) are included, wherein the cross-shaped microfluidic channel is connected with the microfluidic channel outlet (6), the micro-magnetic column array (4) is arranged inside the cross-shaped microfluidic channel, and the external bias magnetic field (7) is arranged outside the cross-shaped microfluidic channel. The cross-shaped microfluidic channel includes a ferromagnetic fluid channel (2), a linear mixed liquid channel and a microfluidic straight channel (5), wherein the linear mixed liquid channel includes a first mixed liquid channel (1) and a second mixed liquid channel (3) located on the same straight line, the outlet end of the first mixed liquid channel (1) is connected with the outlet end of the second mixed liquid channel (3), the ferromagnetic fluid channel (2) is perpendicular to the linear mixed liquid channel, the flow rate of the ferromagnetic fluid in the ferromagnetic fluid channel (2) is 0.5 times the flow rate of the mixed liquid in the linear mixed liquid channel, and the microfluidic channel outlet (6) is arranged at the free end of the microfluidic straight channel (5). The micro-magnetic column array (4) includes 13 micro-magnetic columns, 12 of which are arranged in a regular octagonal structure, the center-to-center distance of adjacent two micro-magnetic columns in the regular octagonal structure along the x-axis and y-axis directions is 90 μm, and one micro-magnetic column is arranged at the center of the regular octagonal structure. The external bias magnetic field (7) is generated by two concentric circular Halbach magnet arrays, each circular Halbach magnet array is composed of NdFeB N50 cuboid permanent magnets with the same size and magnetization strength arranged at different rotation angles.

2. The microfluidic system for manipulating ferrofluid motion by micro magnetic column array according to claim 1, wherein, The micro-magnetic column array (4) penetrates through the microfluidic straight channel (5), and the bottom end of the micro-magnetic column array (4) is at the same horizontal plane as the bottom side of the microfluidic straight channel (5), and the top end of the micro-magnetic column array (4) is at the same horizontal plane as the top side of the microfluidic straight channel (5).

3. The microfluidic system of claim 2, wherein the micro-magnetic column array is configured to control the motion of the ferrofluid by applying a magnetic field to the ferrofluid. The micro-magnetic column array (4) is arranged in the microfluidic straight channel (5), and each micro-magnetic column is a cylinder with a radius of 30 μm and a height of 60 μm.

4. The microfluidic system of claim 3, wherein the micro-magnetic column array is configured to control the motion of the ferrofluid by applying a magnetic field to the ferrofluid. The micro-magnetic column is obtained by mixing, degassing and curing PDMS and NdFeB magnetic powder in a mass ratio of 1:

1.

5. The microfluidic system of claim 3, wherein the micro-magnetic column array is configured to control the motion of the ferrofluid by applying a magnetic field to the ferrofluid. The magnetization direction of the micro-magnetic column is along the height direction of the micro-magnetic column.

6. The microfluidic system of claim 1, wherein the micro-magnetic column array is configured to regulate the movement of the ferrofluid. The outer radius r1 of the outer ring of the two concentric circular Halbach magnet arrays is 142 mm, the inner radius r2 of the outer ring is 85 mm, the outer radius of the inner ring is the same as the inner radius of the outer ring, and the inner radius r3 of the inner ring is 50 mm.

7. The microfluidic system of claim 6, wherein the micro-magnetic column array is configured to regulate the movement of the ferrofluid. Each circular Halbach magnet array can rotate at any angle, and the adjustment range of the external bias magnetic field (7) is 0-100 mT.

8. A method for fabricating a microfluidic system of claim 1-7 for controlling the motion of ferrofluids by micro-magnetic column array, characterized in that, The method comprises the following steps: Step 1: using micro-nano lithography technology and deep silicon etching technology to manufacture a mold with a cross-shaped microfluidic channel and a micro-magnetic column structure on a silicon substrate; Step 2: mixing PDMS and NdFeB magnetic powder in a mass ratio of 1:1, then using a dropper to inject the mixture into the micro-magnetic column structure of the mold, and after the steps of degassing and curing, a cross-shaped microfluidic channel and a micro-magnetic column array (4) are obtained. Step three: cross microfluidic channel and micro magnetic column array (4) are packaged together by using oxygen plasma bonding technology, namely micro magnetic column array regulated ferromagnetic fluid movement microfluidic system is obtained.

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