Droplet fusion microfluidic method based on droplet fusion microfluidic device regulated by focused surface acoustic wave

Abstract

The application discloses a liquid droplet fusion microfluidic method based on a liquid droplet fusion microfluidic device regulated by focused surface acoustic waves, and the device comprises an interdigital transducer, two focusing arc electrodes arranged on the interdigital transducer, and a microfluid channel system bonded on the upper part of the interdigital transducer. The focusing arc electrodes are matched with the microfluid channel system, and the microfluid channel system is provided with a first collection outlet joint, a first dispersed phase inlet joint, a continuous phase inlet joint, a second dispersed phase inlet joint and a second collection outlet joint. The focusing surface acoustic waves generated by the interdigital transducer and the liquid droplet microfluid channel structure are used to flexibly realize the fusion control of liquid droplets with different sizes in the microfluid channel. The symmetrical structure is adopted to enhance the durability and repeatability of the microfluid device. The method is not only suitable for the fusion control between microdroplets, but also suitable for the fusion control between microbubbles and between microdroplets and microbubbles. The surface acoustic waves are non-contact and have good biological compatibility, and thus meet the needs of the liquid droplet fusion technology in the fields of biochemistry and medical treatment.

Description

Technical Field

[0001] This invention belongs to the field of microfluidics technology, and specifically relates to a droplet fusion microfluidic device and method based on focused surface acoustic wave control. Background Technology

[0002] Thanks to the continuous development of microfluidic chip technology, droplet microfluidics, as an important component of the microfluidics field, has developed rapidly from scratch. Droplet microfluidics aims to construct discrete microdroplets using incompatible multiphase fluids. The independent properties of these microdroplets ensure that biochemical reactions take place in a compartmentalized microfluidic environment; therefore, droplet microfluidics is also known as "digital microfluidics." It enables digitization and programmability, providing a platform for solving highly challenging research problems in biochemical and medical fields. Given the advantages of low reagent consumption, good uniformity, high specific surface area, and independent controllability, microdroplets have become an important experimental platform in biological, chemical, medical, and materials preparation applications.

[0003] After generation, microdroplets can serve as a closed biological environment simulation platform for research in areas such as PCR microreactions, single-cell protein analysis, single-cell gene analysis, single-cell culture, and chemical microreactions. Complex biochemical research often involves a series of intricate processes, including droplet sample encapsulation, mixing, reaction, and measurement. Precise droplet manipulation technologies, such as droplet sorting, splitting, fusion, capture, and release, will make these complex processes more convenient and simpler. Among these, droplet fusion is the most critical technology for droplet-based biochemical mixing and reactions.

[0004] To achieve precise fusion of microdroplets, researchers both domestically and internationally have proposed various microdroplet fusion methods. Currently, existing microdroplet fusion methods can be mainly classified into the following categories: 1) Relying on the design of the flow channel structure shape in the microfluidic chip, the fusion of adjacent droplets is achieved by changing the movement speed of adjacent droplets (see Xiize Niu, Shelly Gulati, Joshua B. Edel, et al. Pillar-induced droplet merging in microfluidic circuits[J]. Lab Chip, 2008, 8, 1837-1841. Sanghyun Lee, Hojin Kim, Dong-JoonWon, et al. Pillar-induced droplet merging in microfluidic circuits[J]. Microfluid Nanofluid, 2016, 20:1.). 2) With the aid of an external magnetic field, magnetic droplets were fused together by magnetic induction (see VB Varma1, A. Ray, ZM Wang, et al. Droplet Merging on a Lab-on-a-Chip Platform by Uniform Magnetic Fields[J]. ScientificReports, 2016, 6: 37671). 3) With the aid of an external electric field, an alternating current electric field was used to induce the fusion of adjacent droplets (see Adrian JT Teo, Say Hwa Tan, et al. On-Demand Droplet Merging with an ACElectric Field for Multiple-Volume Droplet Generation[J]. Anal. Chem, 2020, 92, 1147-1153).

[0005] However, among the above microdroplet fusion methods, the method relying solely on the flow channel structure requires strict flow channel design parameters to meet the needs of droplet fusion, and the applicable droplet size range is limited, resulting in poor flexibility; droplet fusion relying on magnetism is only applicable to magnetic droplets, limiting its scope of application; and while droplet fusion relying on electric fields is simple, the electrodes placed in the flow channel, while generating an electric field to act on the droplets, will inevitably cause damage to the biological sample, or even inactivate the sample, making it unsuitable for the needs of biomedical microfluidics. Summary of the Invention

[0006] To overcome the shortcomings of the aforementioned technical methods and promote the development of microdroplet fusion technology, the present invention aims to provide a microfluidic device and method for droplet fusion based on focused surface acoustic wave (SAW) modulation. By using focused SAW generated by a focused interdigital transducer and a droplet microchannel structure, flexible control of droplet fusion of different sizes can be achieved within the microchannel. The symmetrical structural design enhances the durability and repeatability of the microfluidic device. It is suitable not only for fusion manipulation between microdroplets but also for fusion manipulation between microbubbles and between microdroplets and microbubbles. Furthermore, SAW offers non-contact operation and good biocompatibility, meeting the needs of droplet fusion technology in fields including biomedicine.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A droplet fusion microfluidic device based on focused surface acoustic wave modulation includes an interdigital transducer with two focused arc-shaped electrodes. A microchannel system is bonded to the upper part of the interdigital transducer. The focused arc-shaped electrodes cooperate with the microchannel system. The microchannel system has a symmetrical structure and is equipped with a first collection outlet connector, a first dispersed phase inlet connector, a continuous phase inlet connector, a second dispersed phase inlet connector, and a second collection outlet connector. The first and second dispersed phase inlet connectors are symmetrically arranged with the continuous phase inlet connector as the center.

[0009] The aforementioned droplet fusion microfluidic device based on focused surface acoustic wave manipulation includes a microchannel system comprising a first dispersed phase channel, a continuous phase channel, and a second dispersed phase channel. The inlet end of the first dispersed phase channel is the first dispersed phase inlet, and the outlet end of the first dispersed phase channel is connected to the continuous phase channel. The first and second dispersed phase channels are symmetrical about the continuous phase channel as the central axis. The inlet end of the continuous phase channel is the continuous phase inlet, and the outlet end of the continuous phase channel is connected to the first and second transport channels. The end of the continuous phase channel is connected to the outlet ends of the first and second dispersed phase channels. The inlet end of the second dispersed phase channel is the second dispersed phase inlet, and the outlet end of the second dispersed phase channel is connected to the continuous phase channel at the end of the channel gap. The system is as follows: the inlet ends of the first and second conveying channels are connected to the continuous phase channel; the outlet ends of the first and second conveying channels converge at the inlet end of the converging channel; the inlet ends of the first and second merging channels are the outlet ends of the converging channel; the outlet end of the first merging channel is the first collection outlet; and the outlet end of the second merging channel is the second collection outlet; the first collection outlet connector is coaxially fitted and connected to the first collection outlet; the first dispersed phase inlet connector is coaxially fitted and connected to the first dispersed phase inlet; the continuous phase inlet connector is coaxially fitted and connected to the continuous phase inlet; the second dispersed phase inlet connector is coaxially fitted and connected to the second dispersed phase inlet; and the second collection outlet connector is coaxially fitted and connected to the second collection outlet.

[0010] The aforementioned droplet fusion microfluidic device based on focused surface acoustic modulation uses an interdigital transducer that is a focused interdigital transducer.

[0011] The aforementioned droplet fusion microfluidic device based on focused surface acoustic wave modulation, comprising a focused interdigital transducer, includes a piezoelectric substrate on which a first focused arc-shaped interdigital electrode and a second focused arc-shaped interdigital electrode are fabricated. Both the first and second focused arc-shaped interdigital electrodes include several pairs of arc-shaped interdigitates, which are staggered and share a common focusing center. The central angle of each arc-shaped interdigitate is 60°. Each of the first and second focused arc-shaped interdigital electrodes has two signal input terminals, one of which is a common terminal. The lower surface of the microfluidic channel system is bonded to the upper surface of the interdigital transducer. In the horizontal direction, the focusing center of the first focused arc-shaped interdigital electrode is located on the channel wall of the first fusion channel near the electrode, and the focusing center of the second focused arc-shaped interdigital electrode is located on the channel wall of the second fusion channel near the electrode. In the vertical direction, the first and second focused arc-shaped interdigital electrodes are symmetrically distributed on both sides of the converging channel.

[0012] The aforementioned droplet fusion microfluidic device based on focused surface acoustic modulation includes a focused interdigital transducer comprising 10 pairs of interdigitals with a finger width of 20 micrometers.

[0013] The aforementioned droplet fusion microfluidic device based on focused acoustic surface modulation uses a piezoelectric substrate 703 made of single-sided polished 128°Y lithium niobate.

[0014] The aforementioned droplet fusion microfluidic device based on focused acoustic surface modulation uses a three-layer structure for the first and second focused arc-shaped interdigital electrodes: a 40-nanometer bottom layer of chromium, a 200-nanometer middle layer of gold, and a 50-nanometer top layer of silicon dioxide.

[0015] The aforementioned droplet fusion microfluidic device based on focused acoustic surface modulation has a flow channel height of 90 micrometers in its microchannel system, and the first dispersed phase inlet, continuous phase inlet, second dispersed phase inlet, first collection outlet, and second collection outlet are all through holes.

[0016] The aforementioned droplet fusion microfluidic device based on focused acoustic surface modulation uses polydimethylsiloxane as the material for its microchannel system.

[0017] The above-mentioned droplet fusion microfluidic method based on focused surface acoustic wave manipulation includes the following steps:

[0018] 1) First, fix the droplet fusion microfluidic device controlled by focused surface acoustic wave on the stage of the microscope. Observe through the objective lens to ensure that the outlet end of the first dispersed phase channel and the connection point of the continuous phase channel are connected, and the outlet end of the second dispersed phase channel and the connection point of the continuous phase channel are within the field of view of the microscope and are not tilted.

[0019] 2) Seal the second collection outlet connector with an iron needle. Connect the first dispersed phase inlet connector, the continuous phase inlet connector, and the second dispersed phase inlet connector to the first dispersed phase solution storage bottle, the continuous phase solution storage bottle, and the second dispersed phase solution storage bottle on the nitrogen pressure injection pump through PEEK tubes, respectively. Collect droplets through the first collection outlet connector.

[0020] 3) Turn on the nitrogen pressure injection pump, set the corresponding flow rates for the first dispersed phase inlet connector, the continuous phase inlet connector, and the second dispersed phase inlet connector, and stably generate microdroplets at the connection between the outlet end of the first dispersed phase flow channel and the continuous phase flow channel, and at the connection between the outlet end of the second dispersed phase flow channel and the continuous phase flow channel.

[0021] 4) Move the stage and observe through the objective lens to ensure that the first fusion channel and the first focusing arc-shaped interdigitated electrode are properly positioned within the microscope's field of view and without tilting. Observe that two different droplets are generated at the connection point between the outlet end of the first dispersed phase channel and the continuous phase channel, and at the connection point between the outlet end of the second dispersed phase channel and the continuous phase channel. After passing through the first transport channel and the second transport channel, the two different droplets are arranged in an orderly interval at the converging channel and enter the first fusion channel in an orderly manner.

[0022] 5) Connect the positive and negative poles of the output signal of the signal generator after amplification by the power amplifier to the two poles of the first focusing arc-shaped interdigital electrode, and adjust the output signal of the signal generator to be a continuous sinusoidal output;

[0023] 6) Press the “Output” button on the signal generator. The first focusing arc-shaped interdigitated electrode generates a focused surface acoustic wave. The focused surface acoustic wave acts on the first fusion channel to form a focused acoustic pressure field. The droplets arranged in an orderly interval in the first fusion channel merge under the capture effect of the focused surface acoustic wave, which is like a beam of light, forming a larger droplet. The droplet breaks through the constraint of the surface acoustic wave and flows out with the fluid to the first collection outlet, and is finally collected at the first collection outlet connector.

[0024] 7) Similarly, when the first collection outlet connector is blocked with an iron needle, droplet fusion can also be achieved by using the second focusing arc-shaped interdigital electrode and the second fusion channel. The steps are the same as (1-6), and the droplets are finally collected at the second collection outlet connector.

[0025] Compared with the prior art, the present invention has the following beneficial technical effects:

[0026] (1) The present invention can arrange different droplets in an orderly manner, thereby achieving flexible and precise droplet fusion.

[0027] (2) The present invention can achieve effective fusion between microdroplets of the same size and different sizes, between microbubbles, and between microdroplets and microbubbles, and has wide applicability.

[0028] (3) The present invention adopts a comprehensive design of flow channel spacing structure, which can effectively solve the problem of frequency instability caused by mutual interference when different droplets are generated.

[0029] (4) The present invention adopts a symmetrical flow channel structure and a dual-focusing arc-shaped interdigital transducer structure. The whole structure is also symmetrical. Each focused arc-shaped interdigital electrode can realize the droplet fusion function. Even if one focused arc-shaped interdigital electrode or fusion flow channel is damaged, the other half can still be used, which enhances the durability and repeatability of microfluidic devices.

[0030] (5) Surface acoustic waves are non-contact and have good biocompatibility, which can meet the needs of droplet fusion technology in fields including biomedicine. Attached Figure Description

[0031] Figure 1 This is an isometric side view of the droplet fusion microfluidic device for focusing on surface acoustic wave modulation according to the present invention.

[0032] Figure 2 The middle image is an isometric side view of the microfluidic system 100.

[0033] Figure 3 This is a rear view of the microfluidic system 100.

[0034] Figure 4 This is an isometric side view of the focused interdigital transducer 700.

[0035] Figure 5 This is a schematic diagram of the droplet fusion principle of a microfluidic device for droplet fusion controlled by focused surface acoustic waves.

[0036] Figure 6 These are experimental images of droplet fusion before (left) and after (right) focusing of surface acoustic waves. Implementation

[0037] Refer to the instruction manual appendix Figure 1-6 The present invention will be described in detail.

[0038] A droplet fusion microfluidic device based on focused acoustic surface modulation, such as Figure 1 As shown, the system includes an interdigital transducer 700 with two focusing arc-shaped electrodes. A microfluidic system 100 is bonded to the upper part of the interdigital transducer. The focusing arc-shaped electrodes cooperate with the microfluidic system 100. The microfluidic system 100 is equipped with a first collection outlet connector 200, a first dispersed phase inlet connector 300, a continuous phase inlet connector 400, a second dispersed phase inlet connector 500, and a second collection outlet connector 600. The microfluidic system has a symmetrical structure, with the first dispersed phase inlet connector 300 and the second dispersed phase inlet connector 500 symmetrically arranged around the continuous phase inlet connector 400.

[0039] The droplet fusion microfluidic device based on focused acoustic surface modulation, the specific structure of the microchannel system 100 is as follows: Figure 2 , Figure 3 and Figure 5As shown, the microfluidic system 100 includes a first dispersed phase channel 102, a continuous phase channel 104, and a second dispersed phase channel 106. The inlet end of the first dispersed phase channel 102 is a first dispersed phase inlet 101, and the outlet end of the first dispersed phase channel 102 is connected to the continuous phase channel 104. The first dispersed phase channel 102 and the second dispersed phase channel 106 are symmetrically arranged about the continuous phase channel 104 as the central axis. The inlet end of the continuous phase channel 104 is a continuous phase inlet. The outlet end of the continuous phase flow channel 104 is connected to the first conveying flow channel 107 and the second conveying flow channel 113. The end of the continuous phase flow channel 104 is connected to the outlet end of the first dispersed phase flow channel 102 and the outlet end of the second dispersed phase flow channel 106. The inlet end of the second dispersed phase flow channel 106 is the second dispersed phase inlet 105. The outlet end of the second dispersed phase flow channel 106 is connected to the continuous phase flow channel 104 at the end of the flow channel interval 114. The first conveying flow channel... The inlet end of the first conveying channel 107 and the inlet end of the second conveying channel 113 are connected to the continuous phase channel 104. The outlet ends of the first conveying channel 107 and the second conveying channel 113 converge and connect at the inlet end of the converging channel 112. The inlet ends of the first merging channel 110 and the second merging channel 109 are the outlet ends of the converging channel 112. The outlet end of the first merging channel 110 is the first collection outlet 111, and the outlet end of the second merging channel 109 is the second collection outlet 108. The first collection outlet connector 200 is coaxially fitted and connected to the first collection outlet 111. The first dispersed phase inlet connector 300 is coaxially fitted and connected to the first dispersed phase inlet 101. The continuous phase inlet connector 400 is coaxially fitted and connected to the continuous phase inlet 103. The second dispersed phase inlet connector 500 is coaxially fitted and connected to the second dispersed phase inlet 105. The second collection outlet connector 600 is coaxially fitted and connected to the second collection outlet 108.

[0040] The droplet fusion microfluidic device based on focused surface acoustic wave modulation, wherein the interdigital transducer is a focused interdigital transducer. Figure 4As shown, the focused interdigital transducer 700 includes a piezoelectric substrate 703. A first focused arc-shaped interdigital electrode 701 and a second focused arc-shaped interdigital electrode 702 are fabricated on the piezoelectric substrate 703. Both the first and second focused arc-shaped interdigital electrodes include several pairs of arc-shaped interdigitates, which are arranged in an alternating pattern and have a common focusing center. The central angle of each arc-shaped interdigitate is 60°. The first focusing arc-shaped interdigital electrode 701 and the second focusing arc-shaped interdigital electrode 702 each have two signal input terminals, one of which is a common terminal; the lower surface of the microfluidic system 100 with a flow channel is bonded to the upper surface of the focusing interdigital transducer 700 with interdigital electrodes; in the horizontal direction, the focusing center of the first focusing arc-shaped interdigital electrode 701 is located on the flow channel wall of the first fusion flow channel 110 near the electrode side, and the focusing center of the second focusing arc-shaped interdigital electrode 702 is located on the flow channel wall of the second fusion flow channel 109 near the electrode side; in the vertical direction, the first focusing arc-shaped interdigital electrode 701 and the second focusing arc-shaped interdigital electrode 702 are symmetrically distributed on both sides of the converging flow channel 112.

[0041] The focused interdigital transducer 700 of the present invention includes 10 pairs of interdigitals with a finger width of 20 micrometers; the piezoelectric substrate 703 is made of single-sided polished 128°Y lithium niobate; the first focused arc-shaped interdigital electrode 701 and the second focused arc-shaped interdigital electrode 702 adopt a three-layer structure of 40 nanometer bottom chromium, 200 nanometer middle gold, and 50 nanometer top silicon dioxide.

[0042] The droplet fusion microfluidic device based on focused acoustic surface modulation has a flow channel height of 90 micrometers in the microchannel system 100. The first dispersed phase inlet 101, the continuous phase inlet 103, the second dispersed phase inlet 105, the first collection outlet 108, and the second collection outlet 111 are all through holes. The material of the microchannel system 100 is polydimethylsiloxane.

[0043] The symmetrical flow channel structure and the dual-focusing arc-shaped interdigital transducer structure of the present invention are also symmetrical overall. Each focusing arc-shaped interdigital electrode can realize the droplet fusion function. Even if one focusing arc-shaped interdigital electrode or fusion flow channel is damaged, the other half can still be used, which enhances the durability and repeatability of microfluidic devices.

[0044] A droplet fusion microfluidic method based on focused acoustic surface modulation includes the following steps:

[0045] 1) First, fix the droplet fusion microfluidic device controlled by focused surface acoustic wave on the stage of the microscope. Observe through the objective lens to ensure that the outlet end of the first dispersed phase channel 102 and the connection point of the continuous phase channel 104 are connected, and the outlet end of the second dispersed phase channel 106 and the connection point of the continuous phase channel 104 are within the field of view of the microscope and are not tilted.

[0046] 2) Seal the second collection outlet connector 600 with an iron needle. Connect the first dispersed phase inlet connector 300, the continuous phase inlet connector 400, and the second dispersed phase inlet connector 500 to the first dispersed phase solution storage bottle, the continuous phase solution storage bottle, and the second dispersed phase solution storage bottle on the nitrogen pressure injection pump through PEEK tubes, respectively. Collect droplets through the first collection outlet connector 200 using a Teflon hose.

[0047] 3) Turn on the nitrogen pressure injection pump, set the corresponding flow rates for the first dispersed phase inlet connector 300, the continuous phase inlet connector 400, and the second dispersed phase inlet connector 500, and stably generate microdroplets at the connection between the outlet end of the first dispersed phase channel 102 and the continuous phase channel 104, and at the connection between the outlet end of the second dispersed phase channel 106 and the continuous phase channel 104.

[0048] 4) Move the stage and observe through the objective lens to ensure that the first fusion channel 110 and the first focusing arc-shaped interdigitated electrode 701 are properly positioned within the microscope field of view and without tilting. Observe that two different droplets are generated at the connection between the outlet end of the first dispersed phase channel 102 and the continuous phase channel 104, and at the connection between the outlet end of the second dispersed phase channel 106 and the continuous phase channel 104. After passing through the first transport channel 107 and the second transport channel 113, the two different droplets are arranged in an orderly interval at the converging channel 112 and enter the first fusion channel 110 in an orderly manner.

[0049] 5) Connect the positive and negative poles of the output signal of the signal generator after amplification by the power amplifier to the two poles of the first focusing arc-shaped interdigital electrode 701, and adjust the output signal of the signal generator to be a continuous sinusoidal output;

[0050] 6) Press the “Output” button of the signal generator. The first focusing arc-shaped interdigital electrode 701 generates a focused surface acoustic wave. The focused surface acoustic wave acts on the first fusion channel 110 to form a focused acoustic pressure field. The droplets arranged in an orderly interval in the first fusion channel 110 merge under the capture effect of the focused surface acoustic wave, which is like a beam of light, and form a larger droplet. The droplet breaks through the constraint of the surface acoustic wave and flows out with the fluid to the first collection outlet 111. Finally, it is collected at the first collection outlet connector 200.

[0051] 7) Similarly, when the first collection outlet connector 200 is blocked with an iron needle, droplet fusion can also be achieved by using the second focusing arc-shaped interdigital electrode 702 and the second fusion channel 109. The steps are the same as (1-6), and the droplets are finally collected at the second collection outlet connector 600.

[0052] Reference Figure 1 , Figure 2 , Figure 3, Figure 4 , Figure 5 and Figure 5 The fusion process of microdroplets in a microfluidic device for droplet fusion controlled by focused surface acoustic waves is as follows: the second collection outlet connector 600 is blocked and sealed with an iron needle; the first dispersed phase solution passes through the first dispersed phase inlet connector 300 and the first dispersed phase inlet 101, filling the first dispersed phase channel 102; the continuous phase solution passes through the continuous phase inlet connector 400 and the continuous phase inlet 103, filling the continuous phase channel 104, the first transport channel 107, the second transport channel 113, the converging channel 112, and the first fusion channel 11. 0. The second fusion channel 109, through the second dispersed phase inlet connector 500 and the second dispersed phase inlet 105, fills the second dispersed phase channel 106. The input pressure of the first dispersed phase solution, the second dispersed phase solution, and the continuous phase solution is adjusted by a nitrogen pressure injection pump to fill each channel, thereby adjusting the flow rates of the first dispersed phase solution, the second dispersed phase solution, and the continuous phase solution to the appropriate flow rates. This achieves the dissolution of the first and second dispersed phase solutions by the continuous phase solution. The liquid shearing process stably and continuously generates microdroplets A and B at the connection point between the outlet end of the first dispersed phase channel 102 and the continuous phase channel 104, and at the connection point between the outlet end of the second dispersed phase channel 106 and the continuous phase channel 104, respectively. Microdroplets A and B are transported with the continuous phase through the first transport channel 107 and the second transport channel 113 to the converging channel 112, where they are arranged in an orderly, spaced pattern before flowing into the first fusion channel 110. Then, the "output" button on the signal generator is pressed. The first focusing arc-shaped interdigitated electrode 701 generates a focused surface acoustic wave (SAW). This SAW acts on the first fusion channel 110 to form a focused acoustic pressure field. When the input voltage peak-to-peak value and input frequency are adjusted to an appropriate level, the spaced microdroplets A and B are captured and merged by the beam-like focused SAW acoustic radiation force, forming a larger droplet. Driven by fluid force, the larger droplet breaks free from the SAW's constraints and flows with the fluid towards the first collection outlet 111, where it is finally collected at the first collection outlet connector 200. The droplet fusion experiment process is as follows: Figure 6 As shown.

[0053] The technical means disclosed in the present invention are not limited to those disclosed in the above embodiments, but also include technical solutions composed of any combination of the above technical features. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered within the scope of protection of the present invention.

Claims

1. A droplet fusion microfluidic method based on a droplet fusion microfluidic device regulated by focused surface acoustic wave, the microfluidic device comprising an interdigital transducer (700), characterized in that, Two focused arc-shaped electrodes are provided on the interdigital transducer (700). A microfluidic system (100) is bonded to the upper part of the interdigital transducer. The focused arc-shaped electrodes cooperate with the microfluidic system (100). The microfluidic system has a symmetrical structure. The microfluidic system (100) is equipped with a first collection outlet connector (200), a first dispersed phase inlet connector (300), a continuous phase inlet connector (400), a second dispersed phase inlet connector (500), and a second collection outlet connector (600). The first dispersed phase inlet connector (300) and the second dispersed phase inlet connector (500) are symmetrically arranged with the continuous phase inlet connector (400) as the center. The microfluidic system (100) includes a first dispersed phase channel. (102), continuous phase flow channel (104), and second dispersed phase flow channel (106), wherein the first dispersed phase flow channel (102) and the second dispersed phase flow channel (106) are symmetrical structures with the continuous phase flow channel (104) as the central axis. The inlet end of the first dispersed phase flow channel (102) is the first dispersed phase inlet (101), and the outlet end of the first dispersed phase flow channel (102) is connected to the continuous phase flow channel (104). The inlet end of the continuous phase flow channel (104) is the continuous phase inlet (103), and the outlet end of the continuous phase flow channel (104) is connected to the first conveying flow channel (107) and the second conveying flow channel (113). The end of the continuous phase flow channel (104) is connected to the first dispersed phase flow channel (102). The outlet end of the first conveying channel (107) and the outlet end of the second dispersed phase channel (106) are connected and connected; the inlet end of the second dispersed phase channel (106) is the second dispersed phase inlet (105), and the outlet end of the second dispersed phase channel (106) is connected and connected to the continuous phase channel (104) at the end of the channel interval (114); the inlet end of the first conveying channel (107) and the inlet end of the second conveying channel (113) are connected and connected to the continuous phase channel (104), and the outlet end of the first conveying channel (107) and the outlet end of the second conveying channel (113) are connected and connected at the inlet end of the converging channel (112); the inlet end of the first merging channel (110) and the inlet end of the second merging channel (109) are the outlet of the converging channel (112). The outlet end of the first fusion channel (110) is the first collection outlet (111), and the outlet end of the second fusion channel (109) is the second collection outlet (108); the first collection outlet connector (200) is coaxially fitted with and connected to the first collection outlet (111); the first dispersed phase inlet connector (300) is coaxially fitted with and connected to the first dispersed phase inlet (101); the continuous phase inlet connector (400) is coaxially fitted with and connected to the continuous phase inlet (103); the second dispersed phase inlet connector (500) is coaxially fitted with and connected to the second dispersed phase inlet (105); and the second collection outlet connector (600) is coaxially fitted with and connected to the second collection outlet (108). The droplet fusion microfluidic method based on the focused surface acoustic wave-controlled droplet fusion microfluidic device includes the following steps: 1) First, fix the droplet fusion microfluidic device controlled by focused surface acoustic wave on the stage of the microscope. Observe through the objective lens to ensure that the outlet end of the first dispersed phase channel (102) and the connection point of the continuous phase channel (104) are connected, and the outlet end of the second dispersed phase channel (106) and the connection point of the continuous phase channel (104) are within the field of view of the microscope and are not tilted. 2) The second collection outlet connector (600) is plugged and sealed with an iron needle. The first dispersed phase inlet connector (300), the continuous phase inlet connector (400), and the second dispersed phase inlet connector (500) are connected to the first dispersed phase solution storage bottle, the continuous phase solution storage bottle, and the second dispersed phase solution storage bottle on the nitrogen pressure injection pump through PEEK tubes, respectively. The first collection outlet connector (200) collects droplets through a Teflon hose. 3) Turn on the nitrogen pressure injection pump, set the corresponding flow rates for the first dispersed phase inlet connector (300), the continuous phase inlet connector (400), and the second dispersed phase inlet connector (500), and stably generate microdroplets at the connection between the outlet end of the first dispersed phase channel (102) and the continuous phase channel (104), and at the connection between the outlet end of the second dispersed phase channel (106) and the continuous phase channel (104). 4) Move the stage and observe through the objective lens to ensure that the first fusion channel (110) and the first focusing arc-shaped interdigitated electrode (701) are properly positioned within the microscope field of view and without tilting. Observe that two different droplets are generated at the connection between the outlet end of the first dispersed phase channel (102) and the continuous phase channel (104), and at the connection between the outlet end of the second dispersed phase channel (106) and the continuous phase channel (104). After passing through the first transport channel (107) and the second transport channel (113), the two different droplets are arranged in an orderly interval at the converging channel (112) and enter the first fusion channel (110) in an orderly manner. 5) Connect the positive and negative poles of the output signal of the signal generator after amplification by the power amplifier to the poles of the first focusing arc-shaped interdigital electrode (701) respectively, and adjust the output signal of the signal generator to be a continuous sinusoidal output; 6) Press the "output" button of the signal generator. The first focusing arc-shaped interdigital electrode (701) generates a focused surface acoustic wave. The focused surface acoustic wave acts on the first fusion channel (110) to form a focused acoustic pressure field. The droplets arranged in an orderly interval in the first fusion channel (110) merge under the capture effect of the focused surface acoustic wave, which is like a beam of light, forming a larger droplet. The droplet breaks through the constraint of the surface acoustic wave and flows out with the fluid to the first collection outlet (111). Finally, it is collected at the first collection outlet connector (200). 7) Similarly, when the first collection outlet connector (200) is blocked with an iron needle, and the droplet is fused using the second focusing arc-shaped interdigital electrode (702) and the second fusion channel (109), the steps are the same as (1-6), and the droplet is finally collected at the second collection outlet connector (600).

2. The microfluidic method of claim 1, wherein, The interdigital transducer is a focused interdigital transducer.

3. The microfluidic method of claim 2, wherein, A focused interdigital transducer (700) includes a piezoelectric substrate (703). A first focused arc-shaped interdigital electrode (701) and a second focused arc-shaped interdigital electrode (702) are fabricated on the piezoelectric substrate (703). Both the first and second focused arc-shaped interdigital electrodes include several pairs of arc-shaped interdigitals, which are arranged in an alternating pattern and have a common focusing center. The central angle of each arc-shaped interdigital electrode is 60°. The first focusing arc-shaped interdigital electrode (701) and the second focusing arc-shaped interdigital electrode (702) each have two signal input terminals, one of which is a common terminal; the lower surface of the microfluidic system (100) is bonded to the upper surface of the interdigital electrode of the focusing interdigital transducer (700); in the horizontal direction, the focusing center of the first focusing arc-shaped interdigital electrode (701) is located on the channel wall of the first fusion channel (110) near the electrode, and the focusing center of the second focusing arc-shaped interdigital electrode (702) is located on the channel wall of the second fusion channel (109) near the electrode; in the vertical direction, the first focusing arc-shaped interdigital electrode (701) and the second focusing arc-shaped interdigital electrode (702) are symmetrically distributed on both sides of the converging channel (112).

4. The microfluidic method of claim 3, wherein, The focused interdigital transducer (700) includes 10 pairs of interdigitals with a finger width of 20 micrometers.

5. The microfluidic method of claim 3, wherein, The piezoelectric substrate (703) is made of single-sided polished 128°Y lithium niobate.

6. The microfluidic method of claim 3, wherein, The first focused arc-shaped interdigital electrode (701) and the second focused arc-shaped interdigital electrode (702) adopt a three-layer structure with a 40-nanometer bottom layer of chromium, a 200-nanometer middle layer of gold, and a 50-nanometer top layer of silicon dioxide.

7. The microfluidic method of claim 1, wherein, The flow channel height of the microfluidic system (100) is 90 micrometers, and the first dispersed phase inlet (101), continuous phase inlet (103), second dispersed phase inlet (105), first collection outlet (111), and second collection outlet (108) are all through holes.

8. The microfluidic method of claim 1, wherein, The microfluidic system (100) is made of polydimethylsiloxane.

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