A micro-flow stirring device and stirring method based on optical fiber optical tweezers technology

Abstract

This invention discloses a microfluidic stirring device based on fiber optic tweezers technology, comprising a fiber laser, a fiber optic probe, and a microfluidic chip. The fiber laser is connected to the fiber optic probe. The microfluidic chip has a groove for mounting the fiber optic probe. The microfluidic chip has at least one microfluidic inlet for injecting liquid containing an active rotor, and at least one microfluidic inlet for injecting liquid containing a stirrer. The microfluidic chip has a microfluidic outlet. Microfluidic inlets one, two, and the microfluidic outlet intersect and converge. The fiber optic probe is located at the intersection and is immersed in the active rotor liquid and stirrer liquid environment within the microfluidic chip. This invention also discloses a stirring method based on the above-mentioned microfluidic stirring device based on fiber optic tweezers technology. This invention, employing the above-mentioned microfluidic stirring device and method based on fiber optic tweezers technology, has the advantages of simple device and high energy conversion efficiency.

Description

Technical Field

[0001] This invention relates to the field of microfluidic stirring technology, and in particular to a microfluidic stirring device and stirring method based on fiber optic tweezers technology. Background Technology

[0002] Macroscopic stirring often utilizes stir bar to uniformly mix different liquids. Magnetic stirring is the most common method, its basic principle being the repulsion of like poles and the attraction of unlike poles in a magnetic field. The magnetic field propels a magnetic stir bar placed in a container to rotate in a circular motion, thus achieving the purpose of stirring the liquid. The stir bar's size is on the millimeter scale. This limits the application of traditional millimeter-sized stir bar in microfluidics or droplet mixing. Nanoscale magnetic stir bar can be obtained using solution magnetic field self-assembly or electrospinning methods, but the fabrication process is complex and requires a high-quality experimental environment.

[0003] Research on micrometer-scale liquid stirring is currently limited. Micrometer-scale magnetic stirrers require specialized fabrication processes to create unique stirrers. Optical fibers are high-temperature and corrosion-resistant materials, exhibiting excellent adaptability to complex and harsh working environments. Fiber optic tweezers technology utilizes optical radiation pressure to capture and manipulate micro- and nano-sized particles. Traditional optical radiation pressure applies torque to particles by transferring angular momentum, causing them to rotate, but this method has very low energy conversion efficiency. The photothermal effect provides a more efficient way to convert light energy into mechanical energy. When the surface of an absorbing particle is unevenly heated by illumination, photophoresis is generated. Rough calculations show that photophoresis is at least five orders of magnitude greater than optical radiation pressure. The uniform rotation of the absorbing particle generates eddies within its orbit, which can be used to rotate the particle, thus achieving the function of a stirrer. Summary of the Invention

[0004] The purpose of this invention is to provide a microfluidic stirring device and method based on fiber optic tweezers technology. This invention utilizes fiber optic tweezers technology to accelerate microfluidic mixing within a microfluidic chip, addressing the problem of low energy conversion efficiency. The invention employs photophoresis to rotate an active rotor around an orbit, generating a vortex field in the liquid environment within the orbital range. The stirrer rotates within the vortex field under the influence of the viscous shear force, which acts as torque, thereby accelerating the microfluidic mixing speed in the microfluidic channel and achieving microfluidic stirring functionality based on fiber optic tweezers technology.

[0005] To achieve the above objectives, the present invention provides a microfluidic stirring device based on fiber optic tweezers technology, comprising a fiber laser, a fiber optic probe, and a microfluidic chip. The fiber laser is connected to the fiber optic probe. The microfluidic chip has a groove for mounting the fiber optic probe. The microfluidic chip has at least one microfluidic inlet 1 for injecting liquid containing an active rotor and at least one microfluidic inlet 2 for injecting liquid containing a stirrer. The microfluidic chip has a microfluidic outlet. The microfluidic inlet 1, microfluidic inlet 2, and microfluidic outlet intersect and converge. The fiber optic probe is located at the intersection and is immersed in the active rotor liquid and stirrer liquid environment within the microfluidic chip.

[0006] Preferably, the microfluidic inlet one, microfluidic inlet two, microfluidic outlet and the groove for mounting the fiber optic probe are arranged in a cross shape.

[0007] Preferably, the cross-section of the emitted light field of the fiber optic probe is circular, providing a rotational track for the active rotor.

[0008] Preferably, the active rotor is a sheet-like absorptive particle.

[0009] Preferably, the liquid is an incompressible, low Reynolds number fluid dominated by viscous forces.

[0010] A stirring method based on the above-mentioned microfluidic stirring device based on fiber optic tweezers technology includes the following steps:

[0011] S1. Prepare an optical fiber probe by grinding, tapering, or sticking a ball to one end of the optical fiber probe to create an outgoing light field with a circular cross-section.

[0012] S2. Connect the fiber optic probe to the fiber laser;

[0013] S3. Place the fiber optic probe into the groove of the microfluidic chip, and inject the liquid containing the active rotor through the microfluidic pump through the microfluidic inlet one, and inject the liquid containing the stir bar through the microfluidic inlet two.

[0014] S4. Turn on the fiber laser. The emitted light field of the fiber probe generates a thermal field in the liquid environment. The active rotor exchanges heat with the thermal field, causing the active rotor to be subjected to photophoretic force. The transverse component of the photophoretic force provides the centripetal force for the active rotor to rotate around the optical axis, causing the active rotor to rotate in a uniform circular motion in the thermal field. The rotation of the active rotor drives the liquid environment to generate a vortex field within the circular track range. The stir bar rotates under the action of viscous shear force. The rotation of the stir bar causes the fluid to be disturbed when flowing in the channel, and the contact area between the fluids increases, which accelerates the mixing speed of the microfluids in microfluidic inlet one and microfluidic inlet two. The mixed liquid flows out from the microfluidic outlet.

[0015] The advantages and positive effects of the microfluidic stirring device and stirring method based on fiber optic tweezers technology described in this invention are as follows:

[0016] 1. This invention utilizes an optical fiber tweezers system to rotate an absorptive active rotor and a vortex field to rotate a stirrer, which has the advantages of simple device, low cost and easy integration.

[0017] 2. This invention utilizes the photothermal effect to capture and rotate an absorptive active rotor, which has a higher energy conversion efficiency compared to the transfer of optical angular momentum and radiation pressure-induced rotation.

[0018] 3. The stir bar in this invention has a size on the micrometer scale, which expands the application of stir bars in the field of microfluidics.

[0019] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of an embodiment of a microfluidic stirring device and stirring method based on fiber optic tweezers technology according to the present invention;

[0021] Figure 2 This is a schematic diagram of the active rotor force structure of an embodiment of a microfluidic stirring device and stirring method based on fiber optic tweezers technology according to the present invention;

[0022] Figure 3 This is a schematic diagram of the fiber optic probe structure in Embodiment 1 of a microfluidic stirring device and stirring method based on fiber optic tweezers technology of the present invention.

[0023] Figure 4 This is a schematic diagram of the fiber probe and fiber laser tapered coupling structure in Embodiment 1 of a microfluidic stirring device and stirring method based on fiber optic tweezers technology of the present invention.

[0024] Figure 5 This is a schematic diagram of fiber optic probe grinding in Embodiment 2 of the microfluidic stirring device and stirring method based on fiber optic tweezers technology of the present invention.

[0025] Figure 6 This is a schematic diagram of the fiber optic probe structure in Embodiment 2 of the microfluidic stirring device and stirring method based on fiber optic tweezers technology of the present invention.

[0026] Figure Labels

[0027] 1. Fiber laser; 2. Fiber probe; 3. Microfluidic chip; 3-1. Microfluidic inlet one; 3-2. Microfluidic inlet two; 3-3. Microfluidic outlet; 4. Active rotor; 5. Stirrer; 6. Eddy current field; 7. Ring core fiber; 8. UV-curable adhesive; 9. Glass microspheres; 10. Graphite microsheets; 11. Yeast cells; 12. Single-mode fiber; 13. Oxyhydrogen flame; 14. Fiber optic sleeve; 15. Grinding disc; 16. Sandpaper. Detailed Implementation

[0028] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0029] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0030] Figure 1 This is a schematic diagram of an embodiment of a microfluidic stirring device and stirring method based on fiber optic tweezers technology according to the present invention. As shown in the figure, a microfluidic stirring device based on fiber optic tweezers technology includes a fiber laser 1, a fiber optic probe 2, and a microfluidic chip 3. The fiber laser 1 is connected to the fiber optic probe 2, and the microfluidic chip 3 has a groove for mounting the fiber optic probe 2. The emitted light field of the fiber optic probe 2 has a circular cross-section, providing a rotational track for the active rotor 4. The light field has a beam convergence point, and the axial component of the photophoretic force acting on the active rotor 4 provides a centripetal force for rotation around the optical axis.

[0031] The microfluidic chip 3 has at least one microfluidic inlet 3-1 for injecting liquid containing the active rotor 4, and at least one microfluidic inlet 3-2 for injecting liquid containing the stirrer 5. The microparticle chip has a microfluidic outlet 3-3. The microfluidic inlets 3-1, 3-2, and 3-3 intersect and converge. The microfluidic inlets 3-1, 3-2, and 3-3, along with the groove for mounting the fiber optic probe 2, are arranged in a cross shape. The fiber optic probe 2 is located at the intersection and is immersed in the liquid environment of the active rotor 4 and the stirrer 5 within the microfluidic chip 3. The liquid is an incompressible, low Reynolds number fluid dominated by viscous forces, exhibiting high energy conversion efficiency between the liquid and the light field, and capable of generating a thermal field. Glycerin can be selected as the liquid.

[0032] The active rotor 4 consists of sheet-like absorptive particles. The length and width of the active rotor 4 are much greater than its thickness, enabling heat exchange with the liquid environment. Furthermore, the thermal adaptability coefficients differ between the illuminated and unilluminated portions. The stirrer 5 has a large contact area with the microfluidic liquid environment and exhibits high rotational efficiency within the vortex field 6.

[0033] The stirring method of the microfluidic stirring device based on the above-mentioned fiber optic tweezers technology includes the following steps:

[0034] S1. Prepare fiber optic probe 2 by grinding, tapering or sticking a ball to prepare an outgoing light field with a circular cross-section at one end of fiber optic probe 2.

[0035] S2. Connect the fiber probe 2 to the fiber laser 1;

[0036] S3. Place the fiber optic probe 2 into the groove of the microfluidic chip 3, and inject the liquid containing the active rotor 4 through the microfluidic inlet 3-1 and the liquid containing the stir bar 5 through the microfluidic inlet 3-2.

[0037] S4. Turn on the fiber laser 1. The emitted light field of the fiber probe 2 generates a thermal field in the liquid environment. The active rotor 4 exchanges heat with the thermal field and is attracted to the vicinity of the beam convergence point. The active rotor 4 is subjected to photophoretic force. The transverse component of the photophoretic force provides the centripetal force for the active rotor 4 to rotate around the optical axis, causing the active rotor 4 to rotate in a uniform circular motion in the thermal field. The rotation of the active rotor 4 drives the liquid environment to generate a vortex field 6 within the circular track range. The stir bar 5 is subjected to viscous shear force and rotates. The rotation of the stir bar 5 causes the fluid to be disturbed when flowing in the channel, and the contact area between the fluids increases, which accelerates the mixing speed of the microfluids in microfluidic inlet 1 3-1 and microfluidic inlet 2 3-2. The mixed liquid flows out from the microfluidic outlet 3-3.

[0038] Figure 2This is a schematic diagram of the force structure of the active rotor in an embodiment of a microfluidic stirring device and stirring method based on fiber optic tweezers technology according to the present invention. As shown in the figure, the intersecting rays represent light beams, and the active rotor 4 is located on the sidewall of the light beam. The direction of light beam propagation is defined as the z-axis, and the direction perpendicular to the light beam upwards is defined as the x-axis. The directions parallel to and perpendicular to the upper surface of the active rotor 4 are defined as the ε-axis and η-axis, respectively. Since the length and width of the active rotor 4 are much larger than its thickness, the photophoretic force it experiences in the thermal field is F. ε and F η These two forces are decomposed into F along the z and x axes. εz F εx F ηz F ηx Among them, F εz and F ηz Equal in size but opposite in direction, the forces on the driving rotor 4 are balanced along the z-axis; F εx and F ηx The directions are consistent and always point to the z-axis, providing the centripetal force for the active rotor 4 to rotate around the z-axis. Since the magnitude of the centripetal force is constant, the active rotor 4 makes uniform circular motion around the z-axis, and the circle of the cross-section of the light field is the circular track of the active rotor 4.

[0039] The forces acting on the fluid flowing within the channel are primarily viscous forces, with the viscous forces playing a dominant role and the fluid exhibiting a laminar flow state. The rotation of the active rotor 4 generates a vortex field 6 within the circular orbit of the liquid environment, with the flow direction of the vortex field 6 aligned with the rotation direction of the active rotor 4. The stirrer 5, situated within the vortex field 6, is subjected to viscous shear forces, which act as torque to rotate the stirrer 5. The rotation of the stirrer 5 causes disturbance in the fluid flow within the channel, expanding the contact area between fluid particles and accelerating the liquid mixing speed, thus achieving microfluidic stirring based on fiber optic tweezers technology. The rotational speed of the stirrer 5 is directly related to the optical power of the laser.

[0040] Example 1

[0041] A microfluidic stirring method based on graphite microplates 10 using optical tweezers with a sticky ball-shaped annular core fiber 7. The active rotor 4 is a graphite microplate 10, the liquid is pure glycerol, and the stir bar 5 is a yeast cell 11.

[0042] S1. Take a 1m long ring-core optical fiber 7 and attach a glass microsphere 9 to one end with UV-curable adhesive 8 to focus the light and generate a thermal field that can make the graphite microsheet 10 rotate. Figure 3This is a schematic diagram of the fiber optic probe structure in Embodiment 1 of a microfluidic stirring device and stirring method based on fiber optic tweezers technology according to the present invention. As shown in the figure, the specific operation steps for fabricating the fiber optic probe 2 are as follows: First, use Miller pliers to peel off about 3 cm of the coating layer from one end of the fiber to expose the cladding. After cleaning the fiber end with alcohol, cut off a small section with a fiber optic cleaver to make the fiber end face flat. Place the fiber with the flat end face vertically. Under a microscope, dip the flat end face of the fiber into UV-curable adhesive 8. Due to surface tension, the adhesive droplets converge into a hemispherical shape on the fiber end face. Then, attach a glass microsphere 9 with a diameter of about 100 μm. The center of the microsphere is roughly on the central axis of the fiber. Irradiate the UV-curable adhesive 8 with a UV lamp for about 30 seconds to make the microsphere adhere to the fiber end face, thereby fabricating the ring-core fiber optic probe 2. The emitted light field of the fiber optic probe 2 is funnel-shaped.

[0043] S2. Cut the unprocessed end of the fiber probe 2 made in step S1 flat and connect it to the pigtail of the fiber laser 1 using a tapered coupling method. Figure 4 This is a schematic diagram of the fiber probe and fiber laser tapered coupling structure in Embodiment 1 of a microfluidic stirring device and stirring method based on fiber optic tweezers technology of the present invention. As shown in the figure, the single-mode fiber 12 and the ring-core fiber 7 of the laser pigtail are first fused together using a fiber optic fusion splicer; the fused single-mode fiber 12 and the ring-core fiber 7 are then placed on the two slots of the fiber tapering machine and clamped, and the solder joint is heated and the fiber is stretched using an oxyhydrogen flame 13. The fiber gradually becomes thinner, and a tapered region appears. Heating is stopped when the stretching length L is approximately 22 mm; finally, the fiber is wrapped with heat shrink tubing to cover the tapered region.

[0044] S3. Place the fiber optic probe 2 into the groove on the left side of the cross-shaped microfluidic chip 3. Use a microfluidic pump to pass pure glycerol (mixed with red ink) mixed with graphite microplates 10 into the microfluidic inlet 3-1 at the upper port of the microfluidic chip 3. Pass pure glycerol (mixed with blue ink) mixed with yeast cells 11 into the microfluidic inlet 3-2 at the right port of the microfluidic chip 3.

[0045] S4. The fiber laser 1 is turned on. The graphite microplate 10 near the glass microsphere 9 of the fiber probe 2 is attracted and rotates around the z-axis under the action of the transverse component of photophoresis force as the centripetal force. The rotational motion of the graphite microplate 10 generates a vortex field at the center of the path. The yeast cell 11 is subjected to the viscous shear force of the vortex field as torque and rotates within the vortex field 6. The yeast cell 11 acts as a stirrer 5 to thoroughly mix the red and blue glycerol. The mixed purple glycerol flows out from the microfluidic outlet 3-3 at the lower port of the chip, realizing the microfluidic stirring function based on the spherical ring-core fiber 7 optical tweezers. The greater the incident laser power, the greater the rotational speed of the active rotor 4 of the graphite microplate 10, thereby increasing the rotational speed of the yeast cell 11.

[0046] Example 2

[0047] A microfluidic stirring method for graphite microplates based on frustum-shaped annular core optical fiber 7 optical tweezers 10.

[0048] S1. Fabricate a frustum-shaped fiber probe 2 based on a frustum-shaped ring-core fiber 7. Perform fiber end-face pretreatment on a 1m long ring-core fiber 7 according to the method in step S1 of Example 1. After cleaning one end of the ring-core fiber 7 with alcohol, place the ring-core fiber 7 into the fiber sleeve 14 of the polishing device, ensuring that 2cm of the fiber protrudes from the edge of the sleeve. Figure 5 As shown. First, place a drop of clean water in the center of the grinding disc 15. Use the water droplet to adhere the sandpaper 16 to the grinding disc 15, removing any air and ensuring stable contact between the optical fiber and the sandpaper 16 without significant fluctuations. Adjust the pitch angle and height of the optical fiber sleeve 14, and use 6000-grit sandpaper 16 to grind the ring-core optical fiber 7 at an angle θ (the angle between the central axis of the optical fiber and the grinding disc 15, approximately 17.5°) for about 40 minutes. Stop grinding when the end face diameter of the ring-core optical fiber 7 is approximately 50 μm. Replace with 10000-grit fine sandpaper 16 and repeat grinding for 2 hours until the ring-core optical fiber 7 is polished to a smooth surface. This completes the fabrication of a frustum-shaped fiber optic tweezers probe, with the structure shown below. Figure 6 As shown.

[0049] S2. The tail end of the ring core fiber 7 is connected to the laser pigtail using the same tapered coupling method as in Example 1.

[0050] S3. Same as step S3 in Example 1, place the frustum-shaped fiber optic probe 2 into the microfluidic chip 3; inject glycerol mixed with graphite microplates 10 and yeast cells 11 into the microfluidic chip 3 through a syringe pump into the microfluidic inlet 3-1 and microfluidic inlet 3-2, respectively.

[0051] S4. Turn on the fiber laser 1. The graphite microplate 10 near the beam convergence point rotates around the z-axis. The yeast cells 11 within the circumferential orbit are rotated by the viscous shear force in the eddy current field 6. The mixed purple glycerol flows out from the microfluidic outlet 3-3 at the lower port of the chip, realizing the microfluidic stirring function based on the frustum-shaped annular core fiber 7 optical tweezers.

[0052] Therefore, the present invention employs the aforementioned microfluidic stirring device and stirring method based on fiber optic tweezers technology. Based on fiber optic tweezers technology, a stirrer is used to accelerate microfluidic mixing in a microfluidic chip. Photophoretic force is used to achieve the rotation of the active rotor around the track, which drives the liquid environment within the track range to generate a vortex field. The stirrer is rotated in the vortex field under the action of the viscous shear force of the vortex field as torque, thereby accelerating the microfluidic mixing speed in the microfluidic channel and realizing the microfluidic stirring function based on fiber optic tweezers technology.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A microfluidic stirring device based on fiber-optic tweezer technology, characterized by: The device includes a fiber laser, a fiber probe, and a microfluidic chip. The fiber laser is connected to the fiber probe. The microfluidic chip has a groove for mounting the fiber probe. The microfluidic chip has at least one microfluidic inlet 1 for injecting liquid containing an active rotor and at least one microfluidic inlet 2 for injecting liquid containing a stirrer. The microfluidic chip has a microfluidic outlet. Microfluidic inlet 1, microfluidic inlet 2, and microfluidic outlet intersect and converge. The fiber probe is located at the intersection and is immersed in the active rotor liquid and stirrer liquid environment within the microfluidic chip.

2. The microfluidic stirring device based on fiber-optic tweezers technology according to claim 1, characterized in that: The microfluidic inlet 1, microfluidic inlet 2, microfluidic outlet, and the groove for installing the fiber optic probe are arranged in a cross shape.

3. The microfluidic stirring device based on fiber-optic tweezers technology according to claim 1, wherein: The emitted light field of the fiber optic probe has a circular cross-section, providing a rotational track for the active rotor.

4. The microfluidic stirring device based on fiber-optic tweezers technology according to claim 1, wherein: The active rotor is composed of sheet-like absorptive particles.

5. The microfluidic stirring device based on fiber-optic tweezers technology according to claim 1, wherein: The liquid is an incompressible, low Reynolds number fluid dominated by viscous forces.

6. A stirring method based on a microfluidic stirring device using fiber optic tweezers technology as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Prepare an optical fiber probe by grinding, tapering, or sticking a ball to one end of the optical fiber probe to create an outgoing light field with a circular cross-section. S2. Connect the fiber optic probe to the fiber laser; S3. Place the fiber optic probe into the groove of the microfluidic chip, and inject the liquid containing the active rotor through the microfluidic pump through the microfluidic inlet one, and inject the liquid containing the stir bar through the microfluidic inlet two. S4. Turn on the fiber laser. The emitted light field of the fiber probe generates a thermal field in the liquid environment. The active rotor exchanges heat with the thermal field, causing the active rotor to be subjected to photophoretic force. The transverse component of the photophoretic force provides the centripetal force for the active rotor to rotate around the optical axis, causing the active rotor to rotate in a uniform circular motion in the thermal field. The rotation of the active rotor drives the liquid environment to generate a vortex field within the circular track range. The stir bar rotates under the action of viscous shear force. The rotation of the stir bar causes the fluid to be disturbed when flowing in the channel, and the contact area between the fluids increases, which accelerates the mixing speed of the microfluids in microfluidic inlet one and microfluidic inlet two. The mixed liquid flows out from the microfluidic outlet.

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