Multi-channel dielectrophoresis microalgae screening device based on liquid metal bipolar electrode

Abstract

The invention provides a multichannel dielectrophoresis microalgae screening device based on a liquid metal bipolar electrode, and relates to the technical field of cell screening. The multichannel dielectrophoresis microalgae screening device based on the liquid metal bipolar electrode comprises a PDMS channel layer and a glass layer which are distributed up and down. According to the invention, cross-channel transmission of a three-dimensional electric field can be realized based on the charge-discharge effect of double electric layers on the surface of the liquid metal three-dimensional bipolar electrode, and cell screening channels have the same electric field intensity distribution and electric field frequency and have the same fluid flow velocity; by means of synchronous regulation and control of an electric field and a flow field, adjustment of the screening effect can be achieved, multiple screening channels are provided, the dielectrophoresis cell screening flux can be remarkably improved, the problem of complex ohmic connection is solved, the risk that cell screening is interfered due to complex ohmic connection is reduced during large-scale multi-channel integration, and the cell screening efficiency is improved. The cell screening flux and screening efficiency are effectively balanced, and meanwhile, the operation cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of cell screening, and specifically to a multi-channel dielectrophoresis microalgae screening device based on a liquid metal bipolar electrode. Background Art

[0002] Cell screening microfluidic chips based on dielectrophoresis effect have very important applications in the fields of early cancer diagnosis, environmental monitoring, food safety, etc. Currently, most of the electrodes of microfluidic chips for cell screening adopt the form of planar electrodes. The electrodes of such microfluidic chips are not only complex to process, but also the electric field intensity excited will significantly decay as the channel height increases, seriously limiting the efficiency of high-throughput dielectrophoresis cell screening. To overcome the influence of the electric field decay of planar electrodes on cell screening efficiency, liquid metal is used in the preparation of electrodes for dielectrophoresis cell screening microfluidic chips. This method can not only overcome the influence of electric field decay, but also simplify the processing steps of microfluidic chip electrodes and reduce the processing cost.

[0003] The planar electrodes of cell screening microfluidic chips based on dielectrophoresis effect usually need to be prepared by a series of precision micro-nano processing techniques such as photolithography, sputtering, evaporation plating, etc. This preparation process is not only complex in operation steps, but also long in production cycle. The electrodes processed by these methods cannot be recycled and reused, which not only increases the experimental cost, but also causes waste of resources. The electric field intensity excited by planar electrodes will rapidly decay in the height direction of the microfluidic channel. If the microalgae screening channel is relatively high, a large number of microalgae in the channel will be difficult to be accurately regulated by dielectrophoresis due to insufficient electric field intensity, significantly reducing the microalgae screening efficiency.

[0004] Current dielectrophoretic cell screening microfluidic chips based on liquid metal electrodes are all in single-channel form. When dealing with large-scale samples, the processing capacity of single-channel microfluidic chips is limited. When the screening throughput increases, the dielectrophoretic action time is limited, resulting in a significant decrease in the screening efficiency of microalgae as the throughput increases. If multiple chips are connected in parallel to increase the screening throughput, complex ohmic connections are inevitable. For example, at least 20 physical interfaces (one for each inlet / outlet) are required for 10 chips connected in parallel. A large number of physical interfaces not only increase the assembly difficulty and error, but also cannot ensure the same electric field distribution in all chip channels, making it difficult to synchronously regulate the electric fields in all channels. Ten chips require ten inlets, and it is difficult to ensure the same flow field distribution in all channels, resulting in different screening effects in each channel. Connecting 10 chips in parallel increases the risk of cell sample leakage. Once leakage occurs, it will not only cause sample loss, but also interfere with the electric field and fluid distribution in other channels, causing changes in the dielectrophoretic force and fluid force acting on the microalgae, and affecting the cell screening efficiency. If multiple chips are integrated in parallel to increase the microalgae screening throughput, complex ohmic connections will be generated, increasing the difficulty of controlling microalgae screening and the risk of reduced screening efficiency.

[0005] Therefore, it is necessary to study a new dielectrophoretic microalgae screening method. Summary of the Invention

[0006] Aiming at the deficiencies of the prior art, the present invention provides a multi-channel dielectrophoretic microalgae screening device based on liquid metal bipolar electrodes, which solves the problems of large screening difficulty and low efficiency in screening a large number of microalgae cell samples in the prior art.

[0007] To achieve the above objectives, the present invention is realized through the following technical solutions: A multi-channel dielectrophoretic microalgae screening device based on liquid metal bipolar electrodes includes a PDMS channel layer and a glass layer arranged vertically. The PDMS channel layer is bonded and fixed to the glass layer after being treated by a plasma cleaner. Liquid metal electrode channels are printed on the PDMS channel layer. The liquid metal electrode channels are composed of a first screening module and a second screening module located below the first screening module. The first screening module includes a liquid metal electrode first channel, a cell screening first channel, and a liquid metal electrode second channel arranged from top to bottom in sequence. The second screening module includes a liquid metal electrode second channel, a cell screening second channel, and a liquid metal electrode third channel arranged from top to bottom in sequence. Cell sample inlets, cell sample outlets, liquid metal first channel inlets, liquid metal first channel outlets, liquid metal second channel inlets, liquid metal second channel outlets, liquid metal third channel inlets, and liquid metal third channel outlets are formed on the PDMS channel layer by punching.

[0008] Preferably, nine sets of first-level secondary branches are provided between the first channel of the liquid metal electrode and the first channel of cell screening. Each set of the first-level secondary branches includes five first-level secondary branch channels. A plurality of first main branch channels are provided between the first channel of cell screening and the second channel of the liquid metal electrode. Nine sets of second-level secondary branches are provided between the second channel of the liquid metal electrode and the second channel of cell screening. Each set of the second-level secondary branches includes five second-level secondary branch channels. A plurality of second main branch channels are provided between the second channel of cell screening and the third channel of the liquid metal electrode.

[0009] Preferably, the cell sample inlet and the inlet of the second liquid metal channel are arranged side by side on the left side of the liquid metal electrode channel in sequence. The outlet of the second liquid metal channel and the cell sample outlet are arranged side by side on the right side of the liquid metal electrode channel in sequence. The inlet of the first liquid metal channel and the outlet of the first liquid metal channel are arranged side by side on the upper side of the liquid metal electrode channel in sequence. The inlet of the third liquid metal channel and the outlet of the third liquid metal channel are arranged side by side on the lower side of the liquid metal electrode channel in sequence. The inlet of the first liquid metal channel and the outlet of the first liquid metal channel are respectively communicated with the left and right ends of the first channel of the liquid metal electrode. The left ends of the first channel of cell screening and the second channel of cell screening are both communicated with the cell sample inlet. The right ends of the first channel of cell screening and the second channel of cell screening are both communicated with the cell sample outlet. The inlet of the second liquid metal channel and the outlet of the second liquid metal channel are respectively communicated with the left and right ends of the second channel of the liquid metal electrode. The inlet of the third liquid metal channel and the outlet of the third liquid metal channel are respectively communicated with the left and right ends of the third channel of the liquid metal electrode.

[0010] Preferably, the width of the cell sample inlet and the diameter of the cell sample outlet are both 2 mm; the widths of the first channel of cell screening and the second channel of cell screening are both 300 μm; the widths of the first channel of the liquid metal electrode, the second channel of the liquid metal electrode, and the third channel of the liquid metal electrode are all 200 μm.

[0011] Preferably, the widths of the first-level secondary branch channels, the first main branch channels, the second-level secondary branch channels, and the second main branch channels are all 30 μm; the length of the first-level secondary branch channels is 350 μm. The distance between two adjacent sets of the nine sets of first-level secondary branches is 250 μm. The distance between two adjacent ones of the five first-level secondary branch channels in each set of the first-level secondary branches is 110 μm.

[0012] Preferably, the length of each of the first main branch channels is 350 microns, and the distance between two adjacent groups among the multiple groups of the first main branch channels is 810 microns; the length of the second secondary branch channels is 200 microns, the distance between two adjacent groups among the nine groups of the second secondary branches is 250 microns, and the distance between two adjacent groups among the five second secondary branch channels in each group of the second secondary branches is 110 microns; the length of the second main branch channels is 350 microns, and the distance between two adjacent groups among the multiple groups of the second main branch channels is 810 microns.

[0013] Preferably, the working process of the multi-channel dielectrophoresis microalgae screening device based on the liquid metal bipolar electrode is as follows: An alternating current signal is applied to the liquid metal first channel inlet, the liquid metal electrode first channel, and the liquid metal first channel outlet, and the liquid metal third channel inlet, the liquid metal electrode third channel, and the liquid metal third channel outlet are grounded to generate a non-uniform electric field in the cell screening first channel and the cell screening second channel; under the action of the alternating current electric field, the liquid metal in the liquid metal electrode second channel is polarized, a large number of negative charges accumulate on the side of the liquid metal close to the cell screening first channel, and a large number of positive charges accumulate on the side close to the cell screening second channel; in order to maintain electrical neutrality, the positively charged ions in the cell screening first channel move directionally towards the liquid metal electrode second channel under the action of the electric field, and the negatively charged ions move directionally towards the liquid metal electrode first channel under the action of the electric field, causing a large number of negative charges to accumulate on the side of the liquid metal electrode second channel close to the cell screening first channel. The negatively charged ions in the cell screening second channel move directionally towards the liquid metal electrode second channel under the action of the electric field, and the positively charged ions move directionally towards the liquid metal electrode third channel under the action of the electric field, causing a large number of positive charges to accumulate on the side of the liquid metal electrode second channel close to the cell screening second channel, completing the charging process of the electric double layer. When the charging of the electric double layer is completed, under the action of the alternating current signal, the electric double layer starts to discharge; the polarity of the liquid metal in the liquid metal electrode second channel changes, that is, positive charges accumulate on the upper side and negative charges accumulate on the lower side inside the liquid metal electrode second channel; in order to maintain electrical neutrality, the cations and anions in the cell screening channels move in opposite directions and form an electric double layer on the surface of the liquid metal bipolar electrode, completing the reverse charging of the electric double layer; thus, the electric field is transmitted to different cell screening channels during the charging and discharging process of the electric double layer.

[0014] Preferably, the manufacturing process of the multi-channel dielectrophoresis microalgae screening device based on the liquid metal bipolar electrode is as follows:

[0015] S1. Machining of the channel mold:

[0016] Select a glass sheet with a length of 60 mm, a width of 40 mm, and a thickness of 1.1 mm as the base of the channel mold. First, wash the glass sheet with a cleaner, then rinse it with deionized water, and finally blow-dry the wet glass sheet with nitrogen to obtain a clean glass sheet;

[0017] Under the environment of yellow light, cut the dry film according to the size of the glass sheet. Then, rinse the cut dry film and the glass sheet with deionized water respectively. When both the dry film and the glass sheet are kept wet, paste the dry film on the glass sheet, and wrap the glass sheet with folded A4 paper and put it into a plastic-sealing machine to obtain a glass sheet with the first layer of dry film pasted on it;

[0018] Tear off the protective film of the dry film pasted on the glass sheet, cut a dry film with the same size as the glass sheet with the first layer of dry film pasted on it. Under the slow impact of deionized water, paste the new dry film on the surface of the first layer of dry film from which the protective film has been torn off, and wrap the glass sheet with folded A4 paper and put it into a plastic-sealing machine to obtain a glass sheet with two layers of dry film pasted on it;

[0019] After the glass sheet with the dry film pasted on it is exposed, place it in a sodium carbonate solution with a mass fraction of 2% for development. Subject the glass sheet with the completely developed dry film pasted on it to a hardening treatment, place it in an electrothermal constant-temperature forced-air drying oven at 50 °C for 3 - 6 minutes, and naturally cool it to room temperature. Cover the position of the microchannel structure with tape to prevent contamination;

[0020] Wrap the glass sheet after hardening with tin foil into a square open slot, paste the four sides and the bottom of the square open slot with tape, and place the glass sheet with the side pasted with the dry film facing up to obtain a channel mold;

[0021] S2. Processing of the PDMS channel:

[0022] Configuration of the PDMS channel material: On an electronic balance, mix PDMS and a curing agent in a ratio of 10:1, and fully stir the mixture with a glass rod for about 5 minutes to obtain the PDMS layer material;

[0023] Pouring of the channel: Pour the mixture of PDMS and the curing agent into the channel mold, place it in a vacuum autoclave, evacuate for 3 - 4 minutes to make the vacuum degree reach 0.1 MPa, close the air outlet of the vacuum autoclave, and at the same time close the vacuum pump. Let it stand for 30 minutes. After ensuring that there are no bubbles in the PDMS layer material in the channel mold, place it in an electrothermal constant-temperature forced-air drying oven at 80 °C and heat it for 2 hours for curing treatment;

[0024] Post-treatment of the PDMS channel: Use a blade to cut off the cured PDMS layer material outside the edge of the channel mold, and separate the PDMS cover sheet material and the channel mold with tweezers; Use a medical scalpel to cut off the uneven positions around the PDMS cover sheet, and then use a hole punch to punch holes in the liquid metal inlet end, liquid metal outlet end, microalgae solution inlet end, and microalgae solution outlet end of the PDMS layer channel. Use tape to stick the PDMS channel to prevent the channel from being contaminated and facilitate storage;

[0025] S3. Preparation of the chip:

[0026] Preparation of the glass slide substrate: Select a glass slide with a length of 60 mm, a width of 40 mm, and a thickness of 1.1 mm as the substrate of the chip. First, wash the glass slide with a cleaner, then rinse it with deionized water, and finally dry the wet glass slide with nitrogen to obtain a clean glass slide;

[0027] Bonding: Place the side of the glass slide substrate with the channel side of the PDMS layer facing up in the chamber of the plasma machine. Under the conditions of a chamber pressure of -100 kPa and a plasma generator power of 20 W, process for 32 s. Then place the exposed side of the glass slide substrate opposite to the channel side of the PDMS layer, and gently press the PDMS layer to make it contact the glass slide more tightly. Then wrap the chip with tin foil and place it in an electrothermal constant temperature blast drying oven at 60 °C for two hours of reinforcement. After taking it out, let it stand for 24 hours under the pressure of a heavy object;

[0028] Preparation of the liquid metal electrode: Place the bonded chip on a heating plate at 50 °C. Heat the liquid metal with a melting point of 30 °C to the liquid state by water bath, and then slowly inject it into the liquid metal channel with a syringe. During the injection process, to prevent the liquid metal from solidifying, continuously heat the injection port of the syringe with a hair dryer. The liquid metal fills the three electrode channels respectively and reaches the liquid metal outlet to form a liquid metal electrode pattern. Place the chip at room temperature and let it cool and solidify naturally for 24 hours to obtain a liquid metal multi-channel dielectrophoresis microfluidic chip based on the double-layer cross-channel charge-discharge effect;

[0029] S4. Installation of the wire:

[0030] Wipe the surfaces of the inlet and outlet of the liquid metal channel of the microfluidic chip with absolute ethanol to remove possible impurities and oxides on the part where the liquid metal contacts the air. Use pliers to strip the insulating layer at the welding end of the wire to expose the internal metal part, clean it with ethanol and let it dry. Under a microscope, use tweezers to place the metal end of the wire on the surface of the liquid metal in the part that contacts the air, ensuring full contact between the wire and the liquid metal. Preheat the soldering iron to 200 °C, gently touch the part where the wire contacts the liquid metal with the soldering iron tip, and use the heat of the soldering iron tip to make the liquid metal and the wire fuse better. To avoid loss of liquid metal caused by splashing of liquid metal due to overheating, a small amount of liquid metal can be appropriately added during the fusion connection process of the liquid metal and the wire. After the wire and the liquid metal are fully fused, fix the wire on the chip with epoxy resin glue. After the glue is completely cured at room temperature, use a multimeter to test whether the welding part is firm and whether there is a short circuit. After the test is correct, connect the other end of the wire to the output end of the signal generator. After turning on the signal generator, if the liquid metal electrode is normally powered on, the wire is successfully installed;

[0031] S5. Installation of the delivery tube: Wipe the cell sample inlet and outlet of the microfluidic chip with an alcohol cotton sheet to remove air dust and oil stains at the inlet and outlet ends. Vertically cut the PTFE delivery tube with a scalpel to ensure a flat surface without burrs. Squeeze AB glue onto a clean glass slide according to the ratio, and stir it thoroughly with a toothpick for 30 seconds until the color is uniform and there are no bubbles. Use tweezers to hold the PTFE delivery tube and insert it into the cell sample inlet and outlet of the microfluidic chip. Dip the toothpick in the evenly mixed AB glue and fill the interface gap to form an annular sealing layer. Place the microfluidic chip with the installed PTFE delivery tube at room temperature and let it stand for 24 hours to obtain the finished screening device.

[0032] The present invention provides a multi-channel dielectrophoresis microalgae screening device based on a liquid metal bipolar electrode.

[0033] It has the following beneficial effects:

[0034] 1. Compared with the prior art, in this multi-channel dielectrophoresis microalgae screening device based on a liquid metal bipolar electrode, the three-dimensional liquid metal electrode makes the electric field intensity evenly distributed in the height direction, realizing precise control of the potential and the electric field. When facing a large-scale sample, based on the charge-discharge effect of the electric double layer on the surface of the three-dimensional liquid metal bipolar electrode, cross-channel transmission of the three-dimensional electric field can be achieved. The electric field intensity distribution and the electric field frequency are the same in all cell screening channels. By adjusting the voltage on the surface of the excitation electrode, the electric field in all cell screening channels can be regulated. The fluid flow rates in all cell screening channels are the same, and the flow rate in the screening channels can be regulated by adjusting the flow rate at the common inlet. Since the electric field and the flow field distributions are the same in each microalgae screening channel, the screening efficiency of cells is the same. By synchronously regulating the electric field and the flow field, the screening effect can be adjusted.

[0035] 2. Compared with the prior art, the multi-channel dielectrophoresis microalgae screening device based on a liquid metal bipolar electrode has multiple screening channels, which can not only significantly improve the throughput of dielectrophoresis cell screening, but also overcome the complex ohmic connection problem. When large-scale multi-channel integration is carried out, the risk of cell screening being interfered by complex ohmic connection is reduced, effectively balancing the cell screening throughput and screening efficiency, while reducing the operation cost. In addition, the number of screening channels can be increased according to the amount of the screening sample, and the electric field can be further expanded by using the liquid metal bipolar electrode to meet the requirements of high-throughput and high-efficiency screening. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic structural diagram of the present invention;

[0037] Figure 2 For the present invention Figure 1 A partial enlarged view at A in the present invention;

[0038] Figure 3 It is an exploded schematic view of the overall structure of the present invention;

[0039] Figure 4 It is a schematic diagram of the manufacturing method of the liquid metal electrode in the present invention;

[0040] Figure 5 It is a schematic diagram of the principle of injecting liquid metal in the present invention;

[0041] Figure 6 It is a schematic diagram of the principle of the present invention based on the double-layer cross-channel charge and discharge effect;

[0042] Figure 7 It is a multi-channel expansion schematic diagram of the present invention based on the double-layer cross-channel charge and discharge effect.

[0043] Among them, 1. PDMS channel layer; 2. Glass layer; 3. Liquid metal first channel inlet; 4. First cell screening channel; 5. First secondary branch channel; 6. First main branch channel; 7. Second secondary branch channel; 8. Second main branch channel; 9. Liquid metal electrode first channel; 10. Liquid metal first channel outlet; 11. Cell sample outlet; 12. Liquid metal second channel outlet; 13. Liquid metal third channel outlet; 14. Second cell screening channel; 15. Liquid metal electrode second channel; 16. Liquid metal electrode third channel; 17. Liquid metal third channel inlet; 18. Liquid metal second channel inlet; 19. Cell sample inlet. DETAILED DESCRIPTION OF THE INVENTION

[0044] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0045] Embodiment:

[0046] As Figures 1 to 7 shown, the embodiment of the present invention provides a multi-channel dielectrophoresis microalgae screening device based on a liquid metal bipolar electrode, including a PDMS channel layer 1 and a glass layer 2 which are distributed up and down. After the PDMS channel layer 1 is treated by a plasma cleaner, it is bonded and fixed to the glass layer 2.

[0047] In order to increase the screening throughput by increasing the number of cell screening channels through increasing the number of bipolar electrodes, liquid metal electrode channels are printed on the PDMS channel layer 1. The liquid metal electrode channels are composed of a first screening module and a second screening module located on the lower side of the first screening module. The first screening module includes a first liquid metal electrode channel 9, a first cell screening channel 4, and a second liquid metal electrode channel 15 arranged in sequence from top to bottom. The second screening module includes a second liquid metal electrode channel 15, a second cell screening channel 14, and a third liquid metal electrode channel 16 arranged in sequence from top to bottom. A cell sample inlet 19, a cell sample outlet 11, a first liquid metal channel inlet 3, a first liquid metal channel outlet 10, a second liquid metal channel inlet 18, a second liquid metal channel outlet 12, a third liquid metal channel inlet 17, and a third liquid metal channel outlet 13 are formed on the PDMS channel layer 1 by punching. The cell sample inlet 19 and the second liquid metal channel inlet 18 are arranged side by side on the left side of the liquid metal electrode channels. The second liquid metal channel outlet 12 and the cell sample outlet 11 are arranged side by side on the right side of the liquid metal electrode channels. The first liquid metal channel inlet 3 and the first liquid metal channel outlet 10 are arranged side by side on the upper side of the liquid metal electrode channels. The third liquid metal channel inlet 17 and the third liquid metal channel outlet 13 are arranged side by side on the lower side of the liquid metal electrode channels. The first liquid metal channel inlet 3 and the first liquid metal channel outlet 10 are respectively connected to the left and right ends of the first liquid metal electrode channel 9. The left ends of the first cell screening channel 4 and the second cell screening channel 14 are both connected to the cell sample inlet 19. The right ends of the first cell screening channel 4 and the second cell screening channel 14 are both connected to the cell sample outlet 11. The second liquid metal channel inlet 18 and the second liquid metal channel outlet 12 are respectively connected to the left and right ends of the second liquid metal electrode channel 15. The third liquid metal channel inlet 17 and the third liquid metal channel outlet 13 are respectively connected to the left and right ends of the third liquid metal electrode channel 16;

[0048] With the above structure, the number of liquid metal bipolar electrodes has a linear expansion relationship with the number of screening channels. The electric field intensity of each screening channel is independently transmitted through the charging and discharging of the electric double layer. When the flux is increased, the screening efficiency is not interfered by adjacent channels. All intermediate electrodes (the second channel 15 of the liquid metal electrode) passively transmit the electric field through the charging and discharging of the electric double layer without additional circuit connections, significantly reducing the device complexity. When adjusting the flow rate of the cell sample inlet 19, the flow field distribution of all screening channels changes synchronously, avoiding the flow rate difference problem caused by the split inlet and ensuring the consistency of screening conditions. When changing the voltage or frequency of the excitation electrode, the electric field distribution of all screening channels is adjusted synchronously without the need for channel-by-channel regulation, significantly simplifying the operation process. When simultaneously adjusting the inlet flow rate and the excitation voltage, the ratio of the fluid drag force and dielectrophoresis force on the microalgae cells changes synchronously, realizing the selective screening of cells with different sizes or electrical properties. The liquid metal electrode forms a continuous electric field distribution in the vertical direction, overcoming the electric field attenuation problem of the planar electrode and ensuring that the electric field intensity in the screening channel is uniform and stable;

[0049] To ensure the consistency of the electric field distribution in all screening channels, the diameter of the cell sample inlet 19 and the diameter of the cell sample outlet 11 are both 2 mm; the widths of the first cell screening channel 4 and the second cell screening channel 14 are both 300 μm; the widths of the first channel 9 of the liquid metal electrode, the second channel 15 of the liquid metal electrode, and the third channel 16 of the liquid metal electrode are all 200 μm;

[0050] When the electric field is transmitted through the charging and discharging of the electric double layer, the electrode spacing, branch density, and channel size of all screening channels are kept consistent, making the electric field distribution and screening effect of the first cell screening channel 4 and the second cell screening channel 14 exactly the same;

[0051] To achieve the electric field transmission between adjacent cell screening channels and improve the electric coupling efficiency, nine groups of first-level secondary branches are arranged between the first channel 9 of the liquid metal electrode and the first cell screening channel 4. Each group of first-level secondary branches includes five groups of first-level secondary branch channels 5. Multiple groups of first main branch channels 6 are arranged between the first cell screening channel 4 and the second channel 15 of the liquid metal electrode. Nine groups of second-level secondary branches are arranged between the second channel 15 of the liquid metal electrode and the second cell screening channel 14. Each group of second-level secondary branches includes five groups of second-level secondary branch channels 7. Multiple groups of second main branch channels 8 are arranged between the second cell screening channel 14 and the third channel 16 of the liquid metal electrode. The widths of the first-level secondary branch channels 5, the first main branch channels 6, the second-level secondary branch channels 7, and the second main branch channels 8 are all 30 μm; the length of the first-level secondary branch channels 5 is 350 μm. The distance between the left and right adjacent two groups among the nine groups of first-level secondary branches is 250 μm, and the distance between the adjacent two groups among the five groups of first-level secondary branch channels 5 in each group of first-level secondary branches is 110 μm;

[0052] Through the above structure, the charging and discharging effect of the solution in the branch channel and the electric double layer on the surface of the liquid metal electrode transmits the electric field to the adjacent cell screening channel, avoiding the electric field attenuation caused by traditional Ohmic connection. At the same time, the asymmetric branch distribution forms a difference in the ion migration path, ensuring the electric field transmission efficiency;

[0053] In order to excite a non-uniform electric field in the cell screening channel to enhance the dielectrophoretic force, the length of each of the first main branch channels 6 is 350 micrometers, and the distance between two adjacent groups among multiple groups of the first main branch channels 6 is 810 micrometers; the length of the second secondary branch channel 7 is 200 micrometers, the distance between two adjacent groups on the left and right among nine groups of the second secondary branches is 250 micrometers, and the distance between two adjacent groups among the five second secondary branch channels 7 in each group of the second secondary branches is 110 micrometers; the length of the second main branch channel 8 is 350 micrometers, and the distance between two adjacent groups among multiple groups of the second main branch channels 8 is 810 micrometers;

[0054] When an alternating current electric field acts on the first channel 9 of the liquid metal electrode, the asymmetric branch channel forms a gradient electric field distribution in the first cell screening channel 4 and the second cell screening channel 14 through the difference in the charging and discharging of the electric double layer, providing a directional dielectrophoretic force for the microalgae cells;

[0055] The working process of the screening device is as follows: An alternating current signal is applied to the inlet 3 of the first liquid metal channel, the first channel 9 of the liquid metal electrode, and the outlet 10 of the first liquid metal channel, and the inlet 17 of the third liquid metal channel, the third channel 16 of the liquid metal electrode, and the outlet 13 of the third liquid metal channel are grounded, generating a non-uniform electric field in the first cell screening channel 4 and the second cell screening channel 14; Under the action of the alternating electric field, the liquid metal in the second channel 15 of the liquid metal electrode is polarized, with a large number of negative charges accumulating on the side of the liquid metal close to the first cell screening channel 4, and a large number of positive charges accumulating on the side close to the second cell screening channel 14; To maintain electrical neutrality, the positively charged ions in the first cell screening channel 4 move directionally towards the second channel 15 of the liquid metal electrode under the action of the electric field, and the negatively charged ions move directionally towards the first channel 9 of the liquid metal electrode under the action of the electric field, causing a large number of negative charges to accumulate on the side of the second channel 15 of the liquid metal electrode close to the first cell screening channel 4. The negatively charged ions in the second cell screening channel 14 move directionally towards the second channel 15 of the liquid metal electrode under the action of the electric field, and the positively charged ions move directionally towards the third channel 16 of the liquid metal electrode under the action of the electric field, causing a large number of positive charges to accumulate on the side of the second channel 15 of the liquid metal electrode close to the second cell screening channel 14, completing the charging process of the double electric layer; When the charging of the double electric layer is completed, under the action of the alternating current signal, the double electric layer starts to discharge; The polarity of the liquid metal in the second channel 15 of the liquid metal electrode changes, that is, positive charges accumulate on the upper side and negative charges accumulate on the lower side inside the second channel 15 of the liquid metal electrode; To maintain electrical neutrality, the cations and anions in the cell screening channel move in opposite directions and form a double electric layer on the surface of the liquid metal bipolar electrode, completing the reverse charging of the double electric layer; Thus, the electric field is transmitted to different cell screening channels during the charge and discharge process of the double electric layer.

[0056] The manufacturing process of the screening device is as follows:

[0057] S1. Processing of the channel mold:

[0058] Select a glass sheet with a length of 60 mm, a width of 40 mm, and a thickness of 1.1 mm as the base of the channel mold. First, wash the glass sheet with a cleaner, then rinse it with deionized water, and finally dry the wet glass sheet with nitrogen to obtain a clean glass sheet;

[0059] Under the environment of yellow light, cut the dry film according to the size of the glass sheet, then rinse the cut dry film and the glass sheet with deionized water respectively. When both the dry film and the glass sheet are kept wet, paste the dry film on the glass sheet, and wrap the glass sheet with folded A4 paper and put it into a plastic sealing machine to obtain a glass sheet with the first layer of dry film adhered.

[0060] Tear off the protective film of the dry film pasted on the glass slide, cut a piece of dry film with the same size as the glass slide with the first layer of dry film pasted on it. Under the slow impact of deionized water, paste the new dry film on the surface of the first layer of dry film from which the protective film has been torn off. Wrap the glass slide with folded A4 paper and put it into a laminator to obtain a glass slide with two layers of dry film pasted on it;

[0061] After the glass slide with the dry film pasted on it is exposed, place it in a sodium carbonate solution with a mass fraction of 2% for development. Subject the glass slide with the completely developed dry film to hardening treatment, place it in an electrothermal constant temperature blast drying oven at 50 °C for 3 - 6 minutes, and let it cool naturally to room temperature. Cover the position of the microchannel structure with tape to prevent contamination;

[0062] Wrap the glass slide after hardening treatment with tin foil to form a square open groove, paste the four sides and the bottom of the square open groove with tape, and place the glass slide with the side pasted with the dry film facing up to obtain a channel mold;

[0063] S2. Processing of the PDMS channel:

[0064] Configuration of the PDMS channel material: On an electronic balance, mix PDMS and the curing agent in a ratio of 10:1, and fully stir the mixture with a glass rod for about 5 minutes to obtain the PDMS layer material;

[0065] Pouring of the channel: Pour the mixture of PDMS and the curing agent into the channel mold, place it in a vacuum autoclave, evacuate for 3 - 4 minutes to make the vacuum degree reach 0.1 MPa, close the air outlet of the vacuum autoclave, and at the same time close the vacuum pump. Let it stand for 30 minutes. After ensuring that there are no bubbles in the PDMS layer material in the channel mold, place it in an electrothermal constant temperature blast drying oven at 80 °C and heat it for 2 hours for curing treatment;

[0066] Post - processing of the PDMS channel: Use a blade to cut off the cured PDMS layer material outside the edge of the channel mold, and separate the PDMS cover sheet material and the channel mold with tweezers; Use a medical scalpel to cut off the uneven positions around the PDMS cover sheet, and then use a puncher to punch holes at the liquid metal inlet end, liquid metal outlet end, microalgae solution inlet end, and microalgae solution outlet end of the PDMS layer channel. Use tape to stick the PDMS channel to prevent the channel from being contaminated and facilitate storage;

[0067] S3. Fabrication of the chip:

[0068] Preparation of the glass slide substrate: Select a glass slide with a length of 60 mm, a width of 40 mm, and a thickness of 1.1 mm as the substrate of the chip. First, wash the glass slide with a cleaner, then rinse it with deionized water, and finally blow dry the wet glass slide with nitrogen to obtain a clean glass slide;

[0069] Bonding: Place the side of the glass substrate and the side of the PDMS layer with channels facing upward in the chamber of the plasma machine. Process for 32 s under the conditions of a chamber pressure of -100 kPa and a plasma generator power of 20 W. Then place the exposed side of the glass substrate opposite to the side of the PDMS layer with channels, and gently press the PDMS layer to make it contact the glass more tightly. Then wrap the chip with tin foil and place it in an electrothermal constant temperature forced air drying oven at 60 °C for two hours of reinforcement. After taking it out, let it stand under the pressure of a heavy object for 24 hours;

[0070] Preparation of liquid metal electrodes: Place the bonded chip on a hot plate at 50 °C. Heat the liquid metal with a melting point of 30 °C to the liquid state through a water bath, suck it up with a syringe and slowly inject it into the liquid metal channel. During the injection process, to prevent the liquid metal from solidifying, continuously heat the injection port of the syringe with a hair dryer. The liquid metal fills the three electrode channels respectively and reaches the liquid metal outlet to form a liquid metal electrode pattern. Place the chip at room temperature and let it cool and solidify naturally for 24 hours to obtain a liquid metal multi-channel dielectrophoresis microfluidic chip based on the double-layer cross-channel charge-discharge effect;

[0071] S4. Installation of wires:

[0072] Wipe the surfaces of the liquid metal channel inlet and the liquid metal channel outlet of the microfluidic chip with absolute ethanol to remove possible impurities and oxides on the part where the liquid metal contacts the air. Use pliers to strip the insulating layer of the welded end of the wire, expose the internal metal part, clean it with ethanol and let it dry. Under a microscope, use tweezers to place the metal end of the wire on the liquid metal surface in the part that contacts the air, ensuring full contact between the wire and the liquid metal. Preheat the soldering iron to 200 °C, gently touch the part where the wire contacts the liquid metal with the soldering iron tip, and use the heat of the soldering iron tip to make the liquid metal and the wire fuse better. To avoid excessive heating causing the liquid metal to splash and resulting in liquid metal loss, a small amount of liquid metal can be appropriately added during the fusion connection process of the liquid metal and the wire. After the wire and the liquid metal are fully fused, fix the wire on the chip with epoxy resin glue. After the glue is completely cured at room temperature, use a multimeter to test whether the welding part is firm and whether there is a short circuit, etc. After the test is correct, connect the other end of the wire to the output end of the signal generator. After turning on the signal generator, if the liquid metal electrode is normally powered on, the wire is successfully installed;

[0073] S5. Installation of the delivery tube: Wipe the cell sample inlets and outlets of the microfluidic chip with an alcohol cotton swab to remove air dust and oil stains at the inlets and outlets. Vertically cut the PTFE delivery tube with a scalpel to ensure a flat surface without burrs. Squeeze AB glue in proportion onto a clean glass slide and stir it thoroughly with a toothpick for 30 seconds until the color is uniform and no bubbles are generated. Use tweezers to hold the PTFE delivery tube and insert it into the cell sample inlets and outlets of the microfluidic chip. Dip the toothpick into the well-mixed AB glue and fill the interface gap to form an annular sealing layer. Place the microfluidic chip with the installed PTFE delivery tube at room temperature and let it stand for 24 hours to obtain the finished screening device.

[0074] Working principle: In the present invention, an alternating current signal is applied to the upper liquid metal excitation electrode in the microfluidic chip, and the lower liquid metal excitation electrode is grounded, as shown in formulas (1a) and (1b):

[0075]

[0076] In formula (1a), is the potential of the alternating current signal, A0 is the amplitude of the alternating current signal, f is the electric field frequency, t is the time, is the electric field phase. Since the microalgae screening solution has a uniform conductivity, the potential of the microalgae screening channel is calculated by the Laplace equation as follows:

[0077]

[0078] In formula (2), is the Laplace operator. By analyzing the dynamic behavior of the electric field during the charging and discharging process of the double electric layer and the electric field distribution in the screening channel, it can provide theoretical support for the optimal design of the micro-nano fluidic device structure and the improvement of the dielectrophoresis particle manipulation accuracy.

[0079] In order to transmit the applied alternating current signal across the channel through the liquid metal bipolar electrode and achieve the simultaneous regulation of the insulating barrier channel, the present invention realizes the cross-channel transmission of the electric field based on the double electric layer charging and discharging effect. The calculation formula for the current density in the double electric layer cross-channel region is as follows:

[0080]

[0081] In formula (3), J j is the current density in the double electric layer cross-channel, reflecting the spatial distribution of the current in this channel, σ j represents the conductivity of the electrolyte solution in the cross-channel, is the gradient of the potential φ in the cross-channel, describing the rate of change of the potential in this channel in space, with the direction pointing to the direction where the potential changes fastest. E is the electric field strength, describing the strength and direction of the force exerted by the electric field on the charge. By deriving the relationship between the current density and the potential and the electric field strength through formula (3), the electric field distribution in the double-layer cross-channel region of this microfluidic chip can be regulated.

[0082] The calculation formula for the migration rate of charged particles in the double layer across the channel based on the charge-discharge effect of the double layer across the channel in the present invention is as follows:

[0083]

[0084] In formula (4), μj is the migration rate of the j-th charged particle, which is used to reflect the ease of movement of the charged particle in the electric field. Dj is the diffusion coefficient of the j-th charged particle, kB is the Boltzmann constant, q is the charge carried by a single particle, T is the thermodynamic temperature, F is the Faraday constant, representing the charge carried by each mole of electrons, and R is the gas constant. Through formula (11), the migration rate of particles in the microfluidic chip of the present invention can be calculated, and the movement law of particles in the channel under dielectrophoresis can be analyzed.

[0085] The calculation formula for the diffusion coefficient of charged particles in the double layer across the channel based on the charge-discharge effect of the double layer across the channel in the present invention is as follows:

[0086]

[0087] In formula (5), Dj represents the diffusion coefficient of the j-th particle, which is used to measure the speed of particle diffusion in the medium. kB is the Boltzmann constant, T is the thermodynamic temperature, η is the dynamic viscosity of the medium. The greater the viscosity, the greater the resistance to particle movement, a j is the radius of the j-th particle, q is the charge carried by a single particle, R is the gas constant, and F is the Faraday constant. By calculating formula (5), we can analyze the random motion characteristics of charged ions in the fluid, and improve the accuracy and efficiency of cell screening by balancing the relationship between dielectrophoretic directional manipulation and particle diffusion interference.

[0088] The calculation formula for the current conduction efficiency during the charge and discharge of the double layer in the present invention is as follows:

[0089] λ j =z j Fμ j (6)

[0090] In formula (6), λ j$\Lambda_j$ is the molar conductivity of the $j$-th charged particle, which is used to measure the ability of charged ions with a unit amount of substance to conduct current in a solution. $z_j$ is the charge number of the $j$-th charged particle, $F$ is the Faraday constant, and $\mu_j$ is the mobility of the $j$-th charged particle.

[0091] The calculation formula for the conductivity of the solution in the electric double layer region in the microfluidic chip of the present invention is as follows:

[0092]

[0093] In formula (7), $\sigma$ is the conductivity of the solution, $\sum$ j is the summation symbol, $\lambda$ j is the molar conductivity of the $j$-th charged particle, and $c_j$ is the amount-of-substance concentration of the $j$-th charged particle.

[0094] Figure 6 is a schematic diagram of the principle of the cross-channel charge and discharge effect of the electric double layer in the present invention. Figure 6 As shown in Fig. a, it is a schematic diagram of the movement of charged particles in the particle channel when the AC signals shown in formulas (1a) and (1b) are initially applied to the liquid metal electrodes at the upper and lower ends of the microfluidic chip of the present invention. For example, the upper liquid metal electrode channel is positively charged, and the lower liquid metal electrode channel is grounded. The charged ions in the electrolyte solution of the particle channel are subjected to the electric field force excited by the liquid metal electrodes at the upper and lower ends and start to move directionally. A current is generated in the electrolyte solution of the particle channel due to the directional movement of the charged ions. Figure 6 As shown in Fig. b, it is a schematic diagram of the movement of charged ions in the particle channel when the charging of the electric double layer is completed in the present invention. Due to the directional movement of the charged ions, different polar charged ions are adsorbed on the upper and lower sides of the outside of the middle liquid metal electrode, and charges with polarities opposite to those of the external charged particles are aggregated on both sides of the inside, so that the middle liquid metal can cooperate with the adjacent liquid metal electrode channels to excite an electric field although no AC signal is applied. Figure 6 As shown in Fig. c, it is a schematic diagram of the movement of charged ions in the particle channel when the electric double layer discharges in the present invention. At this time, the polarities of the liquid metal electrodes at the upper and lower ends of the microfluidic chip are opposite to those during the charging of the electric double layer channel. The charged particles at the upper and lower ends inside the middle liquid metal electrode are subjected to the electric field force in the opposite direction to that during charging and start to move in the opposite direction to that during charging. At the same time, the differently polar charged ions in the electrolyte solution of the microalgae screening channel move in the opposite direction to that during charging. At this time, a current is generated in the electrolyte solution of the microalgae screening channel due to the directional movement of the charged ions.

[0095] Figure 7 is a multi-channel expansion schematic diagram of the cross-channel charge and discharge effect of the electric double layer in the present invention. Figure 7As shown in a, the microfluidic chip of the present invention for realizing the cross-channel transfer of electric fields based on three-dimensional bipolar electrodes of liquid metal includes three liquid metal electrode channels and two particle channels. By combining the principle of exciting a three-dimensional electric field by liquid metal electrodes with the cross-channel transfer effect of electric fields realized by liquid metal bipolar electrodes, only by applying an alternating current signal to the upper and lower liquid metal electrodes, the simultaneous regulation of the insulating barrier channels can be achieved, avoiding the interference of complex ohmic connections in the external circuit on the cell screening efficiency. Figure 7 b and Figure 7 As shown in c, the microfluidic chips of the present invention for realizing the cross-channel transfer of electric fields based on liquid metal bipolar electrodes include those with five liquid metal electrode channels, four particle channels, and those with seven liquid metal electrode channels and six particle channels. By only applying an alternating current signal to the upper and lower liquid metal bipolar electrodes, the bipolar electrodes can transfer the electric field across the particle channels to the second liquid metal bipolar electrode from top to bottom. The second liquid metal bipolar electrode receiving the transferred electric field can excite an electric field and transfer the electric field across the particle channels to the third liquid metal bipolar electrode. Due to the transfer of the electric field by the liquid metal bipolar electrodes, the electric field distribution in each cell screening channel is the same. By changing the electric signal on the exciting electrode, the electric field distribution in all screening channels can be synchronously adjusted. This method can be used for the fabrication of large-scale multi-channel integrated microfluidic chips, avoiding complex ohmic connections and achieving high-throughput and high-efficiency screening of cells.

[0096] A method for realizing the present invention's cross-channel charge and discharge effect based on the electric double layer is as follows:

[0097] First, apply the AC signals shown in formulas (1a) and (1b) to the first channel 9 of the liquid metal electrode and the third channel 16 of the liquid metal electrode respectively. At this time, the charged ions in the electrolyte solution in the first cell screening channel 4 and the second cell screening channel 14 move directionally under the action of the electric field force. For example, when the first channel 9 of the liquid metal electrode is at a positive potential and the third channel 16 of the liquid metal electrode is grounded, the positively charged ions in the first cell screening channel 4 move directionally to the upper side of the second channel 15 of the liquid metal electrode, and the negatively charged ions in the first cell screening channel 4 move directionally to the lower side of the first channel 9 of the liquid metal electrode. The directional movement of charges generates a current from top to bottom in the first cell screening channel 4. The negatively charged ions in the second cell screening channel 14 move directionally to the lower side of the second channel 15 of the liquid metal electrode, and the positively charged ions in the second cell screening channel 14 move directionally to the upper side of the third channel 16 of the liquid metal electrode. The directional movement of charges generates a current from top to bottom in the second cell screening channel 14. Since the positive ions in the first cell screening channel 4 accumulate on the upper side and the negative ions in the second cell screening channel 14 accumulate on the lower side in the second channel 15 of the liquid metal electrode without the applied AC signal, a large amount of negative charges and positive charges accumulate on both sides near the first cell screening channel 4 and the second cell screening channel 14 inside it respectively, making the second channel 15 of the liquid metal electrode have the characteristic of forming an electric field. The present invention can achieve that by only applying AC signals to the electrodes on the upper and lower sides of the microfluidic chip, based on the cross-channel charge-discharge effect of the double electric layer, charges can be directionally moved and accumulated on the liquid metal electrode in the middle without the applied AC signal, so that opposite-polarity charges accumulate on both sides inside the liquid metal electrode, showing the energized characteristic. This not only reduces the complex connection of the external circuit, but also enables the middle part of the electrode to generate an electric field gradient and a non-uniform electric field force like the electrode with the applied AC signal, reducing the electric field interference between adjacent electrode channels and improving the microalgae screening throughput. The number of channels of the middle liquid metal electrode in the present invention can be infinitely expanded, and the number of microalgae screening channels and liquid metal bipolar electrodes can be increased according to the needs of microalgae cell screening, while significantly improving the microalgae screening throughput and ensuring the screening efficiency of each channel.

[0098] In order to generate a non-uniform electric field required for dielectrophoresis in the microalgae screening channel, the present invention adopts an asymmetric setting for each group of branch channels on both sides of the liquid metal electrode channel. For example, five secondary branch channels 5 in a group are arranged at the connection part between the lower part of the first channel 9 of the liquid metal electrode and the upper part of the first cell screening channel 4, while a main branch channel 6 in a group is arranged at the connection part between the upper part of the second channel 15 of the liquid metal electrode and the lower part of the first cell screening channel 4. The main branch channel 6 on the lower side of the first cell screening channel 4 is aligned with the central position of the secondary branch channel 5 at the middle position on the upper side.

[0099] Under the action of a non-uniform electric field in the screening channel, the dielectrophoretic force on the cells is calculated as follows:

[0100]

[0101]

[0102] In Equation (8a), a is the radius of the particle, is the Clausius-Mossotti factor, and E rms is the root mean square of the alternating electric field. The direction of the dielectrophoretic force acting on the particle is related to the real part of the complex Clausius-Mossotti factor which is determined by the difference in polarizability between the particle and the separation solution. For high polarizability particles (Clausius-Mossotti factor greater than zero), they are subjected to a positive dielectrophoretic force and move towards the region with a stronger electric field intensity; while for low polarizability particles (Clausius-Mossotti factor less than zero), they are guided by a negative dielectrophoretic force and move towards the region with a weaker electric field intensity. In the same electric field, different particles are subjected to different dielectrophoretic force directions. Under the continuous action of the dielectrophoretic force, different movement trajectories are generated, resulting in separation.

[0103] In Equations (8b-d), and represent the complex permittivities of the electrolyte solution and the particle respectively, ε p and ε m represent the permittivities of the particle and the electrolyte solution respectively, σ p and σ m represent the conductivities of the particle and the electrolyte solution respectively, j is the imaginary unit, ω is the angular frequency of the alternating signal, and ε0 is the permittivity of free space.

[0104] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made therein without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A multi-channel dielectrophoresis microalgae screening device based on a liquid metal bipolar electrode, characterized in that: It includes a PDMS channel layer (1) and a glass layer (2) distributed vertically. After being processed by a plasma cleaner, the PDMS channel layer (1) is bonded and fixed to the glass layer (2). A liquid metal electrode channel is printed on the PDMS channel layer (1). The liquid metal electrode channel consists of a first screening module and a second screening module located below the first screening module. The first screening module includes a first liquid metal electrode channel (9), a first cell screening channel (4), and a second liquid metal electrode channel (15) distributed in sequence from top to bottom. The second screening module includes a second liquid metal electrode channel (15), a second cell screening channel (14), and a third liquid metal electrode channel (16) distributed in sequence from top to bottom. A cell sample inlet (19), a cell sample outlet (11), a first liquid metal channel inlet (3), a first liquid metal channel outlet (10), a second liquid metal channel inlet (18), a second liquid metal channel outlet (12), a third liquid metal channel inlet (17), and a third liquid metal channel outlet (13) are formed on the PDMS channel layer (1) by punching.

2. The multi-channel dielectrophoresis microalgae screening device based on a liquid metal bipolar electrode according to claim 1, wherein: Nine groups of first secondary branches are provided between the first liquid metal electrode channel (9) and the first cell screening channel (4). Each group of the first secondary branches includes five groups of first secondary branch channels (5). Multiple groups of first main branch channels (6) are provided between the first cell screening channel (4) and the second liquid metal electrode channel (15). Nine groups of second secondary branches are provided between the second liquid metal electrode channel (15) and the second cell screening channel (14). Each group of the second secondary branches includes five groups of second secondary branch channels (7). Multiple groups of second main branch channels (8) are provided between the second cell screening channel (14) and the third liquid metal electrode channel (16).

3. The multi-channel dielectrophoresis microalgae screening device based on a liquid metal bipolar electrode according to claim 2, wherein: The cell sample inlet (19) and the liquid metal second channel inlet (18) are arranged in a left-right distribution in sequence on the left side of the liquid metal electrode channel. The liquid metal second channel outlet (12) and the cell sample outlet (11) are arranged in a left-right distribution in sequence on the right side of the liquid metal electrode channel. The liquid metal first channel inlet (3) and the liquid metal first channel outlet (10) are arranged in a left-right distribution in sequence on the upper side of the liquid metal electrode channel. The liquid metal third channel inlet (17) and the liquid metal third channel outlet (13) are arranged in a left-right distribution in sequence on the lower side of the liquid metal electrode channel. The liquid metal first channel inlet (3) and the liquid metal first channel outlet (10) are respectively connected to the left and right ends of the liquid metal electrode first channel (9). The left end of the first cell screening channel (4) and the left end of the second cell screening channel (14) are both connected to the cell sample inlet (19). The right end of the first cell screening channel (4) and the right end of the second cell screening channel (14) are both connected to the cell sample outlet (11). The liquid metal second channel inlet (18) and the liquid metal second channel outlet (12) are respectively connected to the left and right ends of the liquid metal electrode second channel (15). The liquid metal third channel inlet (17) and the liquid metal third channel outlet (13) are respectively connected to the left and right ends of the liquid metal electrode third channel (16).

4. The multi-channel dielectrophoresis microalgae screening device based on a liquid metal bipolar electrode according to claim 3, wherein: The diameters of the cell sample inlet (19) and the cell sample outlet (11) are both 2 mm. The widths of the first cell screening channel (4) and the second cell screening channel (14) are both 300 μm. The widths of the liquid metal electrode first channel (9), the liquid metal electrode second channel (15), and the liquid metal electrode third channel (16) are all 200 μm.

5. The multi-channel dielectrophoresis microalgae screening device based on a liquid metal bipolar electrode according to claim 4, wherein: The widths of the first secondary branch channel (5), the first main branch channel (6), the second secondary branch channel (7), and the second main branch channel (8) are all 30 μm. The length of the first secondary branch channel (5) is 350 μm. The distance between two adjacent groups of the nine groups of the first secondary branches is 250 μm. The distance between two adjacent ones of the five first secondary branch channels (5) in each group of the first secondary branches is 110 μm.

6. The multi-channel dielectrophoretic microalgae screening device based on a liquid metal bipolar electrode according to claim 5, characterized in that: The lengths of the first main branch channels (6) are all 350 μm. The distance between two adjacent groups of the multiple groups of the first main branch channels (6) is 810 μm. The length of the second secondary branch channel (7) is 200 μm. The distance between two adjacent groups of the nine groups of the second secondary branches is 250 μm. The distance between two adjacent ones of the five second secondary branch channels (7) in each group of the second secondary branches is 110 μm. The length of the second main branch channel (8) is 350 μm. The distance between two adjacent groups of the multiple groups of the second main branch channels (8) is 810 μm.

7. The multi-channel dielectrophoretic microalgae screening device based on a liquid metal bipolar electrode according to claim 6, characterized in that: The working process of the multi-channel dielectrophoresis microalgae screening device based on a liquid metal bipolar electrode is as follows: An alternating current signal is applied to the liquid metal first channel inlet (3), the liquid metal electrode first channel (9), and the liquid metal first channel outlet (10), and the liquid metal third channel inlet (17), the liquid metal electrode third channel (16), and the liquid metal third channel outlet (13) are grounded, generating a non-uniform electric field in the cell screening first channel (4) and the cell screening second channel (14). Under the action of the alternating current electric field, the liquid metal in the liquid metal electrode second channel (15) is polarized. A large number of negative charges accumulate on the side of the liquid metal close to the cell screening first channel (4), and a large number of positive charges accumulate on the side close to the cell screening second channel (14). To maintain electrical neutrality, the positively charged ions in the cell screening first channel (4) move directionally towards the liquid metal electrode second channel (15) under the action of the electric field, and the negatively charged ions move directionally towards the liquid metal electrode first channel (9) under the action of the electric field, causing a large number of negative charges to accumulate on the side of the liquid metal electrode second channel (15) close to the cell screening first channel (4). The negatively charged ions in the cell screening second channel (14) move directionally towards the liquid metal electrode second channel (15) under the action of the electric field, and the positively charged ions move directionally towards the liquid metal electrode third channel (16) under the action of the electric field, causing a large number of positive charges to accumulate on the side of the liquid metal electrode second channel (15) close to the cell screening second channel (14), completing the charging process of the electric double layer. When the charging of the electric double layer is completed, under the action of the alternating current signal, the electric double layer starts to discharge. The polarity of the liquid metal in the liquid metal electrode second channel (15) changes, that is, positive charges accumulate on the upper side and negative charges accumulate on the lower side inside the liquid metal electrode second channel (15). To maintain electrical neutrality, the cations and anions in the cell screening channels move in opposite directions and form an electric double layer on the surface of the liquid metal bipolar electrode, completing the reverse charging of the electric double layer. Thus, the electric field is transmitted to different cell screening channels during the charge and discharge process of the electric double layer.

8. The multi-channel dielectrophoretic microalgae screening device based on a liquid metal bipolar electrode according to claim 7, characterized in that: The manufacturing process of the multi-channel dielectrophoresis microalgae screening device based on a liquid metal bipolar electrode is as follows: S1. Processing of the channel mold: Select a glass sheet with a length of 60 mm, a width of 40 mm, and a thickness of 1.1 mm as the substrate of the channel mold. First, wash the glass sheet with a cleaner, then rinse it with deionized water, and finally dry the wet glass sheet with nitrogen to obtain a clean glass sheet. Under a yellow light environment, cut the dry film according to the size of the glass sheet. Then, rinse the cut dry film and the glass sheet with deionized water respectively. When both the dry film and the glass sheet are wet, paste the dry film on the glass sheet, and wrap the glass sheet with folded A4 paper and put it into a laminator to obtain a glass sheet with the first layer of dry film adhered to it. Tear off the protective film of the dry film pasted on the glass slide, cut a piece of dry film with the same size as the glass slide with the first layer of dry film adhered, and under the slow impact of deionized water, paste the new dry film on the surface of the first layer of dry film from which the protective film has been torn off. Wrap the glass slide with folded A4 paper and put it into a laminator to obtain a glass slide with two layers of dry film adhered; After the glass slide with the dry film adhered is subjected to exposure treatment, place it in a sodium carbonate solution with a mass fraction of 2% for development. Subject the glass slide with the completely developed dry film to hardening treatment, place it in an electrothermal constant temperature blast drying oven at 50 °C for 3 - 6 minutes, and naturally cool it to room temperature. Cover the position of the microchannel structure with tape to prevent contamination; Wrap the glass slide after hardening treatment with tinfoil into a square open groove, paste the four sides and the bottom of the square open groove with tape, and place the glass slide with the side where the dry film is adhered facing upwards to obtain a channel mold; S2. Processing of the PDMS channel: Configuration of the PDMS channel material: On an electronic balance, mix PDMS and the curing agent in a ratio of 10:1, and fully stir the mixture with a glass rod for about 5 minutes to obtain the PDMS layer material; Pouring of the channel: Pour the mixture of PDMS and the curing agent into the channel mold, place it in a vacuum autoclave, evacuate for 3 - 4 minutes to make the vacuum degree reach 0.1 MPa, close the air outlet of the vacuum autoclave, and at the same time close the vacuum pump. Let it stand for 30 minutes. After ensuring that there are no bubbles in the PDMS layer material in the channel mold, place it in an electrothermal constant temperature blast drying oven at 80 °C and heat it for 2 hours for curing treatment; Post - treatment of the PDMS channel: Use a blade to cut off the cured PDMS layer material outside the edge of the channel mold, and separate the PDMS cover sheet material and the channel mold with tweezers; Use a medical scalpel to cut off the uneven positions around the PDMS cover sheet, and then use a punch to punch holes at the liquid metal inlet end, liquid metal outlet end, microalgae solution inlet end, and microalgae solution outlet end of the PDMS layer channel. Use tape to stick the PDMS channel to prevent the channel from being contaminated and facilitate storage; S3. Fabrication of the chip: Preparation of the glass slide substrate: Select a glass slide with a length of 60 mm, a width of 40 mm, and a thickness of 1.1 mm as the substrate of the chip. First, wash the glass slide with a cleaner, then rinse it with deionized water, and finally blow dry the wet glass slide with nitrogen to obtain a clean glass slide; Bonding: Place one side of the glass slide substrate and the side of the PDMS layer with the channel facing upwards in the chamber of a plasma machine. Under the conditions of a chamber pressure of - 100 kPa and a plasma generator power of 20 W, process for 32 s. Then place the exposed side of the glass slide substrate opposite to the side of the PDMS layer with the channel, gently press the PDMS layer to make it contact the glass slide more closely. Then wrap the chip with tinfoil and place it in an electrothermal constant temperature blast drying oven at 60 °C to reinforce for two hours. After taking it out, let it stand under the pressure of a heavy object for 24 hours; Preparation of liquid metal electrodes: Place the bonded chip on a heating plate at 50 °C. Heat the liquid metal with a melting point of 30 °C to the liquid state through a water bath, suck it up with a syringe, and slowly inject it into the liquid metal channel. During the injection process, to prevent the liquid metal from solidifying, continuously heat the injection port of the syringe with a hair dryer. The liquid metal fills the three electrode channels respectively and reaches the liquid metal outlet to form a liquid metal electrode pattern. Place the chip at room temperature and let it cool and solidify naturally for 24 hours to obtain a liquid metal multi-channel dielectrophoresis microfluidic chip based on the double-layer cross-channel charge and discharge effect; S4. Installation of wires: Wipe the surfaces of the liquid metal channel inlet and the liquid metal channel outlet of the microfluidic chip with absolute ethanol to remove possible impurities and oxides on the part where the liquid metal contacts the air. Use pliers to strip the insulating layer of the welding end of the wire, expose the internal metal part, clean it with ethanol and let it dry. Under a microscope, use tweezers to place the metal end of the wire on the liquid metal surface of the part in contact with the air to ensure full contact between the wire and the liquid metal. Preheat the soldering iron to 200 °C, gently touch the part where the wire contacts the liquid metal with the soldering iron tip, and use the heat of the soldering iron tip to make the liquid metal and the wire fuse better. To avoid loss of liquid metal caused by splashing of liquid metal due to overheating, a small amount of liquid metal can be appropriately added during the fusion connection process of the liquid metal and the wire. After the wire and the liquid metal are fully fused, fix the wire on the chip with epoxy resin glue. After the glue is completely cured at room temperature, use a multimeter to test whether the welding part is firm and whether there is a short circuit. After the test is correct, connect the other end of the wire to the output end of the signal generator. After turning on the signal generator, if the liquid metal electrode is normally powered on, the wire is successfully installed; S5. Installation of the delivery tube: Wipe the cell sample inlet and outlet of the microfluidic chip with an alcohol cotton sheet to remove air dust and oil stains at the inlet and outlet ends. Vertically cut the PTFE delivery tube with a scalpel to ensure that the surface is flat and free of burrs. Squeeze AB glue in proportion onto a clean glass slide, stir it thoroughly with a toothpick for 30 seconds until the color is uniform and there are no bubbles. Use tweezers to hold the PTFE delivery tube and insert it into the cell sample inlet and outlet of the microfluidic chip. Dip the toothpick in the evenly mixed AB glue and fill the interface gap to form an annular sealing layer. Place the microfluidic chip with the PTFE delivery tube installed at room temperature and let it stand for 24 hours to obtain the finished screening device.

Images