Preparation method for electrostatic self-assembled film, and digital microfluidic chip

Abstract

The present invention relates to the field of the preparation of a self-assembled film, and in particular relates to a preparation method for an electrostatic self-assembled film, and a digital microfluidic chip for implementing the method. The preparation method for an electrostatic self-assembled film comprises the following steps: 1) preparation of a reagent, involving: respectively loading various film-forming liquid drops into corresponding liquid storage tank electrode units of a digital microfluidic chip, coating each of the film-forming liquid drops with silicone oil, loading deionized water into a cleaning liquid storage tank electrode unit, and pre-electrifying each of the liquid storage tank electrode units; and 2) preparation and accumulation of 1st to Nth molecular layer films (wherein N is an integer greater than or equal to 2), involving: preparing the molecular layer films layer by layer, and accumulating same layer by layer at hydrophilic points, thereby forming the electrostatic self-assembled film. By means of the method and the chip in the present invention, rapid preparation of an electrostatic self-assembled film can be achieved; fully-automatic operation and control can be achieved, and the consumption of manpower and reagents can be reduced; parallel synthesis of a variety of electrostatic self-assembled films can be performed at a high flux; and synthesis conditions for electrostatic self-assembled films can be screened.

Description

A preparation method of electrostatic self-assembled film and digital microfluidic chip Technical Field

[0001] The present invention relates to the field of preparation of self-assembled films, in particular to a method for preparing an electrostatic self-assembled film and a digital microfluidic chip for implementing the method. Background Art

[0002] Electrostatic self-assembly is a method of assembling film layers at a microscale using electrostatic interaction forces. Based on the principles of electrostatic attraction and repulsion, tiny charged particles or charged polymers spontaneously form ordered structures without external action. Electrostatic self-assembled films have a wide range of applications in many fields, including materials science (such as optical materials, electronic devices, sensors, nanocatalysts, etc.), nanotechnology (such as nanoelectronics, nanophotonics, nanomechanical systems, etc.), drug delivery systems, biosensors (such as self-assembly of biomolecules, antibodies or DNA probes on the sensor surface), tissue engineering (such as constructing three-dimensional biomaterial structures), optical devices (such as gratings, optical lenses), separation and filtration membranes (such as films used for bioseparation and water treatment). By precisely controlling film assembly conditions, material selection and surface modification, the desired functions and performance can be achieved to meet the needs of specific applications.

[0003] With the advancement of science and technology, the demand for ordered thin film materials with specific functions is increasing. Compared with thin film preparation methods such as chemical vapor deposition and molecular beam epitaxy, ultrathin films formed by self-assembly have advantages such as high order, good flatness, controllable film thickness and structure at the molecular level, and no restrictions on substrate shape. In self-assembled ultrathin film systems, methods such as adjusting film thickness, changing the materials used to assemble the film, introducing functional groups, or inducing the orientation of functional groups can be used to impart specific structures and functions to the self-assembled ultrathin films. This allows for the study of the relationship between structure and function, screening structures with specific functions as needed, and ultimately achieving the construction of functional devices from molecular assembly. Self-assembled ultrathin film technology not only has broad application prospects as a surface modification technique for achieving specific optical, electrical, magnetic, and nonlinear optical functions in thin films, but also has great potential for the fabrication of extremely microscale devices. Among self-assembled ultrathin film technologies, layer-by-layer electrostatic self-assembly, due to its simplicity and strong film stability, is an ideal choice for preparing high-quality multilayer films and molecular devices, and has broad application prospects in a wide range of fields.

[0004] The traditional method for preparing electrostatic self-assembled films is to pre-treat the substrate to make it charged, then immerse it in a polycation solution for a period of time to grow a polycation monolayer. When the surface is saturated with polycationic polymer chains, the substrate is rinsed in deionized water, and then immersed in an anionic polymer solution. The substrate is rinsed again before returning to the cationic polymer solution. This completes a bilayer growth cycle. This cycle is repeated, and the bilayer is grown layer by layer until the desired film thickness is reached. However, in practical applications, since the thickness of each bilayer of the electrostatic self-assembled film is at the nanometer level, it sometimes takes a very large number of cycles to meet the requirements for film thickness, which greatly limits actual device applications. Multiple cycles make the synthesis of the film extremely tedious, consuming a lot of time and repetitive manpower. Therefore, a preparation method that can be automated and reduces the time-consuming self-assembly process is of great significance for the development of electrostatic layer-by-layer self-assembly.

[0005] Therefore, those skilled in the art are committed to developing a method for preparing an electrostatic self-assembled film with high synthesis efficiency and short time consumption, and a digital microfluidic chip that can implement the method. Technical issues

[0006] In view of the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is to provide a method for preparing an electrostatic self-assembled film with high synthesis efficiency and short time consumption, and a digital microfluidic chip capable of implementing the method. Solution

[0007] To achieve the above object, the present invention provides a method for preparing an electrostatic self-assembled film, comprising the following steps:

[0008] 1) Reagent Preparation: Various film-forming droplets are loaded into corresponding reservoir electrode units of the digital microfluidic chip, silicone oil is used to wrap each of the film-forming droplets, deionized water is loaded into the wash liquid reservoir electrode unit, and each of the reservoir electrode units is pre-energized;

[0009] 2) Preparation and accumulation of 1 to N molecular layer films, where N is an integer greater than or equal to 2: each molecular layer film is prepared layer by layer and accumulated layer by layer at the hydrophilic point to form an electrostatic self-assembled film. The preparation of each molecular layer film includes the following steps:

[0010] 21) Preparation of the first molecular layer membrane: dispense a first reagent droplet from the first liquid reservoir electrode unit and transport it to the hydrophilic site via the channel electrode. Allow it to stand for more than 5 seconds, allowing the charged species to adsorb to the hydrophilic site. Electrowetting forces are then used to pull the droplet away from the hydrophilic site and to the waste liquid collection electrode unit. Dispense a cleaning liquid droplet from the cleaning liquid reservoir electrode unit and transport it to the hydrophilic site via the channel electrode to wash away any residual reagent at the hydrophilic site, ensuring that only a monolayer with strong electrostatic attraction remains on the electrode.

[0011] 22) Preparation of an Nth molecular layer membrane: dispensing an Nth reagent droplet from an Nth reservoir electrode unit, transporting the droplet to a hydrophilic site via a channel electrode connected thereto, and allowing it to stand for more than 5 seconds. The Nth reagent droplet and the N-1th reagent droplet have opposite charges, thereby causing the oppositely charged polymers or particles in the Nth reagent droplet to be deposited on the surface of the N-1th molecular layer under the action of electrostatic force; using electrowetting force to move the droplet away from the hydrophilic site to a waste liquid collection electrode unit; after deposition is completed, transporting a cleaning droplet to the hydrophilic site via the channel electrode, and using the cleaning droplet to wash away residual reagent;

[0012] Preferably, the separated molecular layers are prepared using droplets of the same reagent, that is, using two film-forming materials with opposite charges to prepare the electrostatic self-assembled film.

[0013] Preferably, in step 2), the reagent droplets are dispensed from the target liquid reservoir electrode unit by sequentially switching the electrodes adjacent to the target liquid reservoir electrode unit on and off.

[0014] Preferably, the film-forming droplets can be selected from one or more of polycationic or anionic electrolytes, inorganic small particles, metal colloidal particles, and biological macromolecules.

[0015] Preferably, the polycationic or anionic electrolyte can be polyaniline, nitrogen-containing polyelectrolyte polyacrylonitrile, diazo resin, polydiallyldimethylammonium chloride, sodium polystyrene sulfonate, spirooxazine dye, polyvinyl alcohol, polyethylene sulfide, polypropylene, poly(allylamine hydrochloric acid); the inorganic small particles are charged II-VI semiconductor material nanoparticles synthesized from any one or more of SiO2, TiO2 or CdTe, CdS, and ZnS.

[0016] The present invention also provides a digital microfluidic chip for preparing an electrostatic self-assembled film, comprising an upper electrode plate and a lower electrode plate; the upper electrode plate and a first hydrophobic layer; the lower electrode plate comprises a control electrode, a dielectric layer and a second hydrophobic layer; at least one hydrophilic point is etched on the first hydrophobic layer of the upper electrode plate.

[0017] Preferably, the control electrode comprises at least two liquid reservoir electrode units, each of the liquid reservoir electrode units is connected to a channel electrode, and the intersection of each channel electrode is a membrane preparation area, and the membrane preparation area is opposite to the hydrophilic point.

[0018] Preferably, the liquid reservoir electrode unit comprises at least a first liquid reservoir electrode unit and a second liquid reservoir electrode unit for carrying oppositely charged film-forming liquid droplets, and a cleaning liquid reservoir electrode unit.

[0019] Preferably, the control electrode includes a waste liquid collecting electrode unit, and the waste liquid collecting electrode unit is connected to the membrane preparation area via a channel electrode.

[0020] Preferably, a plurality of hydrophilic points are provided on the upper electrode plate to form a hydrophilic point array.

[0021] This invention combines a digital microfluidic chip with the preparation of electrostatic self-assembled membranes. Hydrophilic spots are created on the chip's top plate, and membrane-forming droplets are sequentially transported to these spots. Under the action of electrostatic force, adjacent polycationic electrolyte layers and polyanionic electrolyte layers (or colloidal nanoparticles, etc.) are alternately deposited, and a self-assembled membrane with a specific thickness, number of layers, and composition is automatically grown layer by layer at the hydrophilic spots. Beneficial effects

[0022] 1) Extremely Fast Electrostatic Self-Assembled Monolayer Preparation: This invention proposes a method for preparing electrostatic self-assembled monolayers based on a digital microfluidic chip. Due to the small droplet volume, rapid mass transfer, and rapid molecular layer deposition in digital microfluidics, the preparation of electrostatic self-assembled monolayers using this method significantly shortens the time compared to traditional self-assembled film preparation methods, significantly improving the synthesis efficiency of electrostatic self-assembled monolayers. In experiments conducted, the synthesis time for a single bilayer self-assembled using a digital microfluidic chip was reduced to 2 minutes, a time saving of 81%.

[0023] 2) Fully automatic control reduces manpower and reagent consumption: The digital microfluidic chip, through peripheral control circuits and control software, can transport film-forming droplets to hydrophilic points for deposition according to a pre-set path. The entire process requires no human operation, enabling fully automatic preparation of electrostatic self-assembled membranes. At the same time, the droplet volume is very small, reducing reagent consumption.

[0024] 3) High-throughput parallel synthesis of multiple electrostatic self-assembled membranes: Hydrophilic spots can be made into large-scale arrays. For example, on a digital microfluidic chip with 1000×1000 drive units, a 100×100 hydrophilic spot array can be made, which can be used for high-throughput parallel synthesis of electrostatic self-assembled membranes with different numbers of layers, different components and different arrangement orders.

[0025] 4) Screening of electrostatic self-assembled membrane synthesis conditions: The synthesis of electrostatic self-assembled membranes is influenced by conditions such as pH, temperature, salt concentration, solution concentration, deposition time, and substrate surface properties. Droplets with varying salt concentrations, solution concentrations, and pH values ​​can be prepared on the digital microfluidic chip. Furthermore, the chip can integrate a micro-heating system and create different chemically modified layers at the hydrophilic sites of the upper plate, enabling screening of different electrostatic self-assembled membrane formation conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a schematic structural diagram of a digital microfluidic chip according to Example 1 of the present invention;

[0027] Figure 2 is a schematic diagram of the control electrode structure of a digital microfluidic chip according to Example 1 of the present invention;

[0028] Figure 3(a) and Figure 3(b) are the surface morphology micrographs of 10-layer and 20-layer PDDA / PSS electrostatic self-assembled films, respectively;

[0029] Figure 4 is a conventional method and Example 1 different number of layers of PDDA / PSS electrostatic self-assembled film synthesis time comparison chart;

[0030] Figure 5 is a graph showing the thickness of the PDDA / PSS electrostatic self-assembled film corresponding to different bilayers in Example 1;

[0031] Figure 6 is a schematic structural diagram of the digital microfluidic chip in Example 2;

[0032] FIG7 is a schematic structural diagram of the digital microfluidic chip of Example 3. Best Mode for Carrying Out the Invention

[0033] During implementation, the hydrophilic spot arrays on a digital microfluidic chip can be used for the simultaneous synthesis of multiple electrostatic self-assembled membranes. For example, a digital microfluidic platform controlled by a 1000×1000 thin-film transistor switch array can produce an array of 100,000 hydrophilic spots, capable of storing over 600 types of film-forming material droplets. Each droplet can be randomly arranged and simultaneously deposited at the hydrophilic spots on a large scale, resulting in the production of multiple electrostatic self-assembled membranes with varying sequences, compositions, and number of layers.

[0034] The present invention's method for preparing electrostatic self-assembled films based on a digital microfluidic chip can be used to screen various synthesis conditions for electrostatic self-assembled films. For example, the synthesis of electrostatic self-assembled films is influenced by the following factors: 1. Temperature. High temperatures can accelerate the film assembly rate, but may also lead to unstable membrane structures. Appropriate temperatures can yield desired membrane properties. 2. pH. Different film-forming materials have different charge states under different pH conditions, and this charge state influences the strength and direction of electrostatic interactions. By adjusting the solution pH, the assembly rate and structure can be controlled. 3. Salt concentration. At high salt concentrations, ions compete for interactions with surface molecules, reducing the stability of the self-assembled film. Therefore, when preparing electrostatic self-assembled films, controlling the salt concentration is generally necessary to achieve the desired membrane structure and properties. 4. Solution concentration and deposition time. Higher solution concentrations and longer deposition times generally result in thicker films. 5. Substrate surface properties. Different surface properties can guide the adsorption and arrangement of self-assembled molecules, thereby influencing the structure and properties of the film. On the digital microfluidic chip, the droplets undergo a large amount of mixing and splitting, and can have different concentrations of membrane solutions, salt solutions or different pH values, and then deposited at hydrophilic points, which can screen out the optimal conditions for electrostatic self-assembled films. Modes for Carrying Out the Invention

[0035] The present invention will be described in detail below through specific examples. Example 1

[0036] As shown in FIG3 , a method for preparing an electrostatic self-assembled film comprises the following steps:

[0037] 1) Reagent Preparation. Each film-forming droplet was loaded into the corresponding reservoir electrode unit of the digital microfluidic chip. Silicone oil was used to encapsulate each film-forming droplet. Deionized water was loaded into the wash reservoir electrode unit. Each reservoir electrode unit was pre-energized.

[0038] 2) Preparation and accumulation of the 1st to Nth molecular layer membranes, where N is an integer greater than or equal to 2: Each molecular layer membrane is prepared layer by layer and accumulated layer by layer at the hydrophilic point to form an electrostatic self-assembled membrane. An electrostatic self-assembled membrane is composed of a plurality of molecular layers accumulated layer by layer. Specifically, it can be a bilayer (an electrostatic self-assembled membrane formed by alternating deposition of two oppositely charged film-forming material molecular layers) or a layer by layer accumulation of three or more different film-forming materials to achieve arbitrary adjustment of the components within the membrane. The preparation of each molecular layer membrane includes the following steps:

[0039] 21) Preparation of the first monolayer: Dispensing a first reagent droplet from the first reservoir electrode unit. Specifically, the reagent droplet can be dispensed from the target reservoir electrode unit by sequentially turning the electrodes adjacent to the target reservoir electrode unit on and off via peripheral electronic control circuitry and control software. In this step, the target reservoir electrode unit, i.e., the first reservoir electrode unit, dispenses the reagent droplet, which is then transported to the hydrophilic site via the channel electrode. The droplet drive device and method can utilize the technologies described in patents such as ZL201711171133.5 and ZL202122866108.7, or other related technologies. These technologies are all prior art and are not described here.

[0040] After standing for more than 5 seconds, the charged substances are adsorbed to the hydrophilic sites under the electrostatic effect of the membrane itself. The electrowetting force pulls the droplets away from the hydrophilic sites to the waste liquid collection electrode unit. Specifically, the waste liquid can be transferred to the waste liquid collection electrode unit by energizing the target electrode (here, the waste liquid collection electrode unit). Cleaning droplets are then distributed from the cleaning liquid reservoir electrode unit and transported to the hydrophilic sites through the channel electrode to wash away the residual reagent at the hydrophilic sites. Similarly, the cleaned waste liquid is transferred to the waste liquid collection electrode unit, and only the monolayer with strong electrostatic attraction remains on the electrode plate.

[0041] 22) Preparation of the Nth monolayer membrane: Dispense an Nth reagent droplet from the Nth reservoir electrode unit and transport the droplet to a hydrophilic site via a connected channel electrode. Allow the droplet to rest for at least 5 seconds. The Nth reagent droplet and the N-1th reagent droplet have opposite charges, causing the oppositely charged polymers or particles in the Nth reagent droplet to deposit onto the surface of the N-1th molecular layer under the action of electrostatic force. Electrowetting forces are used to move the droplet away from the hydrophilic site to the waste liquid collection electrode unit. After deposition is complete, a cleaning droplet is transported to the hydrophilic site via the channel electrode, where it is used to rinse away any residual reagent. Waste liquid is then transferred to the waste liquid collection electrode unit via the channel electrode.

[0042] The accumulation of molecular layers on the hydrophilic points eventually reaches a predetermined number of layers, completing the preparation of the electrostatic self-assembled film.

[0043] Because the area of ​​the hydrophilic points is small, the electrostatic self-assembled film synthesized by the digital microfluidic chip has high uniformity, and as the number of single-layer membranes increases, the flatness and density of the membrane layer will gradually increase.

[0044] The film-forming droplets in the present invention can be selected from one or more of polycationic or anionic electrolytes, inorganic small particles, metal colloidal particles, and biomacromolecules. The polycationic or anionic electrolytes can be polyaniline (PANI), nitrogen-containing polyelectrolyte polyacrylonitrile (PN-CAN), diazo resin (NDR), polydiallyldimethylammonium chloride (PDDA), polystyrene sulfonic acid (PSS), spiroxazine dyes, polyvinyl alcohol (PVA), polyvinyl sulfate (PVS), polypropylene (PP), poly(allylamine hydrochloride) (PAH), etc. The inorganic small particles can be charged Group II-VI semiconductor material nanoparticles synthesized from any one or more of SiO2, TiO2, CdTe, CdS, and ZnS.

[0045] The present invention uses electrowetting force to transport film-forming material droplets to hydrophilic sites, and automatically grows a composite film of specific thickness, number of layers and composition layer by layer on the hydrophilic sites of a digital microfluidic chip through electrostatic interaction.

[0046] The present invention also provides a digital microfluidic chip for preparing the above-mentioned electrostatic self-assembled film, as shown in Figure 1, comprising an upper plate 1 and a lower plate 2, the upper plate 1 comprising a ground electrode 11 and a first hydrophobic layer 12; the lower plate 2 comprising a control electrode 21, a dielectric layer 22 and a second hydrophobic layer 23; at least one hydrophilic point 13 is etched on the first hydrophobic layer 12 of the upper plate 1, and the etching can be performed by laser ablation or dry etching.

[0047] In the present invention, the upper plate is a ground electrode coated with a hydrophobic material. Wherein, the ground electrode can be a conductive material such as gold, silver, chromium, copper, aluminum, ITO, and the deposition method can be magnetron sputtering, electron beam thermal evaporation, etc. The hydrophobic material can be perfluoro (1-butyl vinyl ether) polymer CYTOP, polytetrafluoroethylene PTFE, fluorinated ethylene propylene copolymer FEP, ethylene-chlorotrifluoroethylene copolymer ECTE, polyfluoroethylene ETFE, perfluoroalkyl compound PFA, Teflon Teflon, polyolefin, polyamide, polyacrylonitrile, molten paraffin, polydimethylsiloxane PDMS, alkoxysilane hybrid material, fluorinated polyethylene, etc. The production of the hydrophilic pattern of the hydrophobic layer adopts general local stripping technology (such as dry etching, laser ablation, etc.), and the shape can be circular, square, half-moon, etc.

[0048] The bottom plate is the control electrode, covered with a dielectric layer and a hydrophobic layer. The electrode material can be gold, silver, chromium, copper, aluminum, or ITO. The dielectric material can be parylene, alumina, silicon nitride, polyamide, polyethylene, polytetrafluoroethylene, or a composite film thereof. The hydrophobic material can be the same as the top plate.

[0049] As shown in FIG2 , the control electrode 21 includes at least two reservoir electrode units 3 . Each reservoir electrode unit 3 is connected to a channel electrode 4 . The intersection of each channel electrode 4 is a membrane preparation area 41 . The membrane preparation area 41 is opposite to the hydrophilic point 13 .

[0050] The reservoir electrode unit 3 includes at least two, first and second, reservoir electrode units 31 and 32, for carrying oppositely charged film-forming droplets, and a cleaning liquid reservoir electrode unit 33. Of course, third and fourth reservoir electrode units may also be provided as needed. The control electrode 21 includes a waste liquid collection electrode unit 34, which is connected to the membrane preparation area 41 via a channel electrode 4.

[0051] The above example illustrates a single synthesis site for an electrostatic self-assembled membrane on a digital microfluidic chip. In other embodiments, multiple hydrophilic sites 13 may be provided on the upper plate 1 to form an array of hydrophilic sites. This allows for simultaneous synthesis of multiple electrostatic self-assembled membranes of the same type, significantly improving membrane synthesis efficiency and enabling high-throughput, automated synthesis of electrostatic self-assembled membranes.

[0052] Typically, because each hydrophilic site is very small (less than 1mm x 1mm), hundreds or even thousands of hydrophilic sites can be integrated into a given upper plate area. Each hydrophilic site in the array can quickly and uniformly synthesize a droplet of electrostatic self-assembled film. In large-scale arrays, each hydrophilic site can produce the same type of electrostatic self-assembled film, enabling the preparation of a certain amount of electrostatic self-assembled film.

[0053] In large-scale hydrophilic point arrays, different types of electrostatic self-assembled composite films can also be prepared to achieve high-throughput thin film synthesis; or for the same film-forming material, different synthesis conditions can be used, such as changing different pH values, concentrations, deposition times, external electric fields and other factors to achieve the screening of the optimal conditions for electrostatic self-assembled thin film synthesis.

[0054] Specifically, in this embodiment, the digital microfluidic chip and the electrostatic self-assembled film preparation method were used to prepare a bilayer electrostatic self-assembled film using PDDA and PSS as the film-forming materials. Specifically, the interleaved molecular layers were formed using the same reagent droplets. Specifically, during operation, the electrostatic self-assembled film preparation method was used to form a bilayer of PDDA and PSS droplets in a cross-layered manner until the desired number of layers was reached.

[0055] As shown in Figures 3(a) and 3(b), Figures 3(a) and 3(b) correspond to the surface morphologies of self-assembled films with 10 and 20 monolayers, respectively. In this embodiment, a monolayer refers to a bilayer, i.e., a film synthesized from a layer of PDDA and PSS. By comparing Figures 3(a) and 3(b), it is found that the 10-layer (PDDA / PSS) electrostatic self-assembled film has a relatively rough surface structure. As the number of bilayers increases, the surface of the 20-layer (PDDA / PSS) electrostatic self-assembled film is relatively flat and smooth. The electrostatic self-assembled films synthesized on the digital microfluidic chip have high uniformity, and as the number of layers increases, the flatness and density of the film layer gradually increase. A larger number of bilayers will make the rough and defective surface morphology of the base film become relatively smooth and dense.

[0056] At the same time, the applicant has made statistics on the synthesis time. Since the droplet volume of the digital microfluidic chip is small and the mass transfer speed is very fast, the synthesis time of the electrostatic self-assembled membrane is greatly reduced. Taking the PDDA / PSS electrostatic self-assembled membrane as an example, compared with the traditional layer-by-layer electrostatic self-assembly process, the self-assembly process time on the digital microfluidic platform of the present invention is greatly reduced. Figure 4 shows the synthesis time of the traditional electrostatic self-assembly process and the time required to synthesize different numbers of PDDA / PSS bilayer electrostatic self-assembled membranes using the electrostatic self-assembled membrane of the present invention. It can be found in Figure 4 that on the digital droplet microfluidic platform, that is, using the present invention, the average time required for the automated self-assembly of a single bilayer membrane is only 2 minutes, which is 18.87% of the time required for the traditional process, saving 81.13% of the time.

[0057] The applicant also tested the PDDA / PSS bilayer electrostatic self-assembled film. The test results are shown in Figure 5. When the number of bilayer films is 10, the thickness of the self-assembled film is 20 nm. When the number of bilayer films is 15, the thickness of the self-assembled film is 31 nm. Continuing to increase the number of layers to 20, the thickness of the self-assembled film is 43 nm. As can be seen from the figure, the thickness shows a basically linear increase with the increase in the number of layers, indicating that the electrostatic self-assembled film prepared using the method and chip of the present invention has a good assembly effect and a stable film formation process. Therefore, after thousands of cycles of alternating deposition, bilayer films with thousands or tens of thousands of layers can be synthesized, that is, the synthesis of electrostatic self-assembled micron-level or even millimeter-level thick films can be achieved. Example 2

[0058] As shown in Figure 6, the preparation method of the electrostatic self-assembled film and the digital microfluidic chip used in Example 2 are basically the same as those in Example 1, except that Example 2 uses three different film-forming materials A, B, and C. The film-forming materials A, B, and C have two opposite charges. The specific film-forming materials A, B, and C can be selected from the above-mentioned film-forming materials. The only difference from Example 1 is that there are three film-forming materials, and it is sufficient to ensure that the two adjacent molecular layers have opposite charges. At the same time, there are at least three liquid reservoir electrode units to load the three different reagent droplets A, B, and C. As shown in Figure 6, the three different film-forming droplets all move towards the hydrophilic point, i.e., the electrostatic self-assembled film preparation area, under the action of the electrowetting force, and eventually accumulate layer by layer to form a film. Example 3

[0059] As shown in Figure 7, the difference between Example 3 and Example 1 is that a hydrophilic point array structure is prepared on the upper plate of the digital microfluidic chip. Each hydrophilic point can self-assemble into a thin film, and the array hydrophilic point can realize the parallel synthesis of multiple thin films. The size of the hydrophilic point is between 10 microns and 1 mm. On a digital microfluidic chip controlled by a 100×100 to 1000×1000 array thin film transistor, 1000-100,000 hydrophilic points can be made, so 1000-100,000 of the same electrostatic self-assembled films can be synthesized simultaneously, which will greatly improve the synthesis efficiency of the film layer and realize the high-throughput automated synthesis of electrostatic self-assembled films. Industrial Applicability

[0060] The above descriptions are merely preferred embodiments of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention shall fall within the scope of the claims of the present invention.

Claims

1. A method for preparing an electrostatic self-assembled film, characterized in that: The following steps are involved: 1) Reagent preparation: various film-forming droplets are loaded in the corresponding liquid reservoir electrode units of the digital microfluidic chip, silicone oil is used to wrap each of the film-forming droplets, deionized water is loaded in the cleaning liquid reservoir electrode unit, and each of the liquid reservoir electrode units is pre-energized; 2) Preparation and accumulation of the 1st to Nth molecular layer films, wherein N ≥ 2 and is an integer: each molecular layer film is prepared layer by layer and accumulated layer by layer at the hydrophilic point to form an electrostatic self-assembled film, and the preparation of each molecular layer film includes the following steps: 21) Preparation of the first molecular layer membrane, dispensing a first reagent droplet from the first liquid reservoir electrode unit, and transporting it to the hydrophilic point through the channel electrode, standing for more than 5 seconds, the charged substance is adsorbed to the hydrophilic site, and the droplet is moved away from the hydrophilic position by the electrowetting force to the waste liquid collection electrode unit; dispensing a cleaning liquid droplet from the cleaning liquid reservoir electrode unit, transporting it to the hydrophilic point through the channel electrode, washing away the residual reagent at the hydrophilic point, and ensuring that only a single layer with strong electrostatic attraction remains on the electrode plate; 22) Preparation of the Nth molecular layer membrane, dispensing the Nth reagent droplet from the Nth liquid reservoir electrode unit, transporting the droplet to the hydrophilic site through the channel electrode connected thereto, and standing for more than 5 seconds, the Nth reagent droplet and the N-1th reagent droplet have opposite charges, so that the oppositely charged polymers or particles in the Nth reagent droplet are deposited on the surface of the N-1th molecular layer under the action of electrostatic force; using electrowetting force to move the droplet away from the hydrophilic position to the waste liquid collection electrode unit; after the deposition is completed, transporting cleaning droplets to the hydrophilic point through the channel electrode, and washing away the residual reagent with the cleaning droplets.

2. The method for preparing an electrostatic self-assembled film according to claim 1, wherein: In step 2), the separated molecular layers are treated with droplets of the same reagent.

3. The method for preparing an electrostatic self-assembled film according to claim 1, wherein: In the step 2), the reagent droplets are dispensed from the target liquid reservoir electrode unit by sequentially turning on and off the electrodes adjacent to the target liquid reservoir electrode unit.

4. The method for preparing an electrostatic self-assembled film according to claim 1, wherein: The film-forming droplets may be selected from one or more of polycationic or anionic electrolytes, inorganic small particles, metal colloidal particles, and biological macromolecules.

5. The method for preparing an electrostatic self-assembled film according to claim 4, wherein: The polycationic or anionic electrolyte can be polyaniline, nitrogen-containing polyelectrolyte polyacrylonitrile, diazo resin, polydiallyldimethylammonium chloride, sodium polystyrene sulfonate, spirooxazine dye, polyvinyl alcohol, polyvinyl sulfate, polypropylene, poly(allylamine·hydrochloric acid); the inorganic small particles are charged II-VI group semiconductor material nanoparticles synthesized from any one or more of SiO2, TiO2 or CdTe, CdS, and ZnS.

6. A digital microfluidic chip for preparing an electrostatic self-assembled film, characterized in that: The invention comprises an upper electrode plate (1) and a lower electrode plate (2); the upper electrode plate (1) comprises a grounding electrode (11) and a first hydrophobic layer (12); the lower electrode plate (2) comprises a control electrode (21), a dielectric layer (22) and a second hydrophobic layer (23); and at least one hydrophilic point (13) is etched on the first hydrophobic layer (12) of the upper electrode plate (1).

7. The digital microfluidic chip according to claim 6, characterized in that: The control electrode (21) comprises at least two liquid reservoir electrode units (3), each of which is connected to a channel electrode (4), and the intersection of each channel electrode (4) is a membrane preparation area (41), and the membrane preparation area (41) is opposite to the hydrophilic point (13).

8. The digital microfluidic chip according to claim 7, characterized in that: The liquid reservoir electrode unit (3) comprises at least a first liquid reservoir electrode unit (31) and a second liquid reservoir electrode unit (32) for carrying oppositely charged film-forming liquid droplets, and a cleaning liquid reservoir electrode unit (33).

9. The digital microfluidic chip according to claim 7, characterized in that: The control electrode (21) comprises a waste liquid collecting electrode unit (34), and the waste liquid collecting electrode unit (34) is connected to the membrane preparation area (41) via a channel electrode (4).

10. The digital microfluidic chip according to claim 6, characterized in that: The upper electrode plate (1) is provided with a plurality of hydrophilic points (13) to form a hydrophilic point array.

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