CN116618104A

CN116618104A - Graphene electrode digital microfluidic chip and preparation method thereof

Info

Publication number: CN116618104A
Application number: CN202310679880.9A
Authority: CN
Inventors: 张涛; 刘科; 何宇
Original assignee: Zhejiang University ZJU
Current assignee: Zhejiang University ZJU
Priority date: 2023-06-09
Filing date: 2023-06-09
Publication date: 2023-08-22

Abstract

The invention discloses a graphene electrode digital microfluidic chip, which comprises a substrate with a graphene electrode and an upper cover plate, wherein the substrate with the graphene electrode comprises a substrate with the graphene electrode, and the graphene electrode is generated by inducing the substrate through laser ablation and has one of the following structures: a) The device comprises a driving electrode array, a connecting wire and an interface electrode array, wherein the driving electrode array, the connecting wire and the interface electrode array are uniformly arranged on the upper surface of the substrate; b) The device comprises a driving electrode array and a penetrating electrode array, wherein the driving electrode array is uniformly arranged on the upper surface of a substrate, the penetrating electrode array vertically penetrates through the substrate, and a single driving electrode is vertically connected with a single penetrating electrode; c) Comprises a driving electrode array, a penetrating electrode array, a connecting wire and an interface electrode array. The graphene electrode digital microfluidic chip disclosed by the invention has the advantages of simple manufacturing process, high processing efficiency and short manufacturing period; a multi-layer electrode structure can be constructed, so that the density of an electrode array is greatly improved, and high flux is realized; and is environment-friendly.

Description

Graphene electrode digital microfluidic chip and preparation method thereof

Technical Field

The invention relates to the technical field of digital microfluidic chips, in particular to a graphene electrode digital microfluidic chip.

Background

Digital Microfluidics (DMF) is an emerging droplet manipulation technique in the field of microfluidics. The technology can realize the operations of droplet generation, movement, splitting, fusion and the like, and has the advantages of simple structure, flexible control and the like. Currently, digital microfluidic technology has been widely used in the fields of chemistry, biology, medicine, etc.

For most application scenarios of DMF, such as nucleic acid detection, protein detection, single cell analysis, etc., each chip should be "disposable" in order to avoid cross-contamination between samples. Meanwhile, practical applications such as Point-of-care (POCT) and the like also put high demands on the cost and the preparation period of the chip. In addition, when operations such as droplet splitting, fusion and sample mixing are performed on the chip, a plurality of electrodes are often required to be matched, so that the larger the density of the driving electrodes is, the stronger the capability of the chip for processing droplets is, and the operations such as multiplexing and parallel analysis are facilitated for the chip. However, the existing DMF chip technology still has many limitations in terms of cost, electrode density, manufacturing simplicity, environmental friendliness, and the like.

Conventional DMF chips mainly employ photolithography, etching, or sputtering techniques to process metal patterned electrodes on glass substrates. The chip has high cost, complex manufacturing process and low flux, and has strict requirements on processing environment and equipment, so the chip is only suitable for laboratory research and is not suitable for large-scale application. In addition, the driving electrodes, the connecting wires, the interface electrodes and the like of the chip are all positioned on the same plane due to the limitation of the process, so that the density and the number of the driving electrodes cannot be greatly improved.

Another more common class of DMF chips is based on printed circuit board (Printed circuit board, PCB) technology. The processing technology of the chip is mature, and simultaneously, more dense and more driving electrodes can be integrated through a multi-layer design. Although the cost of the chip is also reduced compared to that of the glass substrate, its final price is still dependent on the production scale, which is obviously not friendly for laboratory research and small-scale applications. In addition, as a typical electronic device, PCB-based DMF chips tend to generate a large amount of electronic waste when applied in a large scale (e.g., clinical testing). Therefore, how to recycle such electronic waste would also be one of the major challenges limiting the wide range of applications of such chips.

In order to solve the above problems of DMF chips, some studies have selected paper as a substrate of DMF chips. Such chips are formed by printing conductive ink on a substrate using ink jet printing or screen printing, etc., as a patterned electrode array. The cost of the paper-based DMF chip is lower, and the manufacturing process is simpler. However, during its processing, it is often necessary to additionally provide conductive ink, and there is also a high demand for paper as a substrate. In addition, the driving electrodes, the connecting wires, the interface electrodes and the like of the paper-based DMF chip are also located on the same plane, so that the density and the number of the driving electrodes cannot be greatly increased.

In summary, there is no DMF chip capable of simultaneously meeting the requirements of low cost, simple fabrication, high flux, high electrode density, environmental friendliness, and the like. Therefore, development of a novel DMF chip and a processing technology thereof are needed to solve the above problems comprehensively.

Disclosure of Invention

Aiming at the problems, the invention discloses a graphene electrode digital microfluidic chip which has the advantages of simple manufacturing process, high processing efficiency and short manufacturing period, and can greatly reduce the cost of the chip; the multi-layer electrode structure can be constructed through a special process, so that the density of the electrode array can be greatly improved, and high flux is realized; and the substrate raw material with the graphene electrode is selected from common polymer materials, does not relate to metal materials, does not generate electronic garbage, and is more environment-friendly.

The specific technical scheme is as follows:

a graphene electrode digital microfluidic chip comprises a substrate with a graphene electrode and an upper cover plate:

the substrate with the graphene electrode comprises a substrate with the graphene electrode from bottom to top, and a functional layer covered on the graphene electrode, wherein the functional layer is selected from an independent dielectric layer and a hydrophobic layer or is a composite hydrophobic dielectric layer;

the graphene electrode has one of the following structures:

a) The device comprises a driving electrode array, a connecting wire and an interface electrode array, wherein the driving electrode array, the connecting wire and the interface electrode array are uniformly arranged on the upper surface of the substrate, and the driving electrode array is connected with the interface electrode array through the connecting wire and then connected with an external control circuit through the interface electrode array;

b) The device comprises a driving electrode array and a penetrating electrode array, wherein the driving electrode array is uniformly arranged on the upper surface of a substrate, the penetrating electrode array vertically penetrates through the substrate, and a single driving electrode is vertically connected with a single penetrating electrode and is connected with an external control circuit through the penetrating electrode;

c) The device comprises a driving electrode array, a penetrating electrode array, a connecting wire and an interface electrode array, wherein the driving electrode array is uniformly arranged on the upper surface of a substrate, the penetrating electrode array vertically penetrates through the substrate, a single driving electrode is vertically connected with a single penetrating electrode, and then is connected with the interface electrode array and an external control circuit through the connecting wire;

The graphene electrode is induced to be generated by laser ablation of the substrate.

According to the preparation method disclosed by the invention, the electrode is manufactured by directly ablating the substrate by laser to induce graphene, so that the processing technology can be greatly simplified, the processing efficiency is improved, and the manufacturing period is shortened; and according to different application scenes, the graphene electrode has three selectable structures.

When the requirements on the electrode density or the electrode number in the application scene are not high, the graphene electrodes are arranged according to the scheme A), so that double-sided processing steps are omitted, and the manufacturing process is simplified;

when high-density or high-number electrodes are needed in an application scene, other equipment is not needed to be integrated below the driving electrode array, the graphene electrodes are arranged according to the scheme B), the density of the electrode array can be greatly improved through the arrangement of the double-layer electrode structure, high flux is realized, the processing steps of connecting wires and an interface electrode array are omitted, and the processing technology is simplified;

if other devices such as temperature control devices or electromagnets are required to be integrated below the driving electrode array, the graphene electrodes are arranged according to the scheme C), so that space is provided for the devices.

In the embodiments B) and C), preferably, the area of the single through electrode in the through electrode array is smaller than or equal to the area of the single driving electrode in the driving electrode array.

The upper cover plate comprises a hydrophobic layer, a selectively embedded conductive layer and an upper supporting layer which are sequentially arranged from bottom to top.

In the graphene electrode:

preferably: the square resistances of the single electrode or the single wire in the driving electrode array, the penetrating electrode array, the connecting wire and the interface electrode array are all selected from 5-300 omega;

experiments show that an ultrathin graphene electrode cannot be processed by adjusting parameters; when the height of the graphene electrode is too high, the phenomenon of uneven surface is easily generated at the interval between adjacent electrodes of the driving electrode array when the dielectric layer or the composite hydrophobic dielectric layer is processed, so that liquid drops cannot normally move.

Preferably: the heights h of the single electrode or the single wire in the driving electrode array, the connecting wire and the interface electrode array are all selected from 10-70 mu m; more preferably 15 to 35. Mu.m.

Experiments show that when the electrode spacing is too small, the risk of communication between adjacent electrodes is increased, which leads to the phenomena of breakdown or short circuit of the chip in the use process; when the electrode spacing is too large, the normal movement and splitting of the liquid drops are affected.

Preferably, the minimum distance d between adjacent electrodes in the driving electrode array is selected from 70-150 μm; further preferably 90 to 110. Mu.m.

Experiments show that when the width of the connecting conductive wire is too small, the resistance of the connecting conductive wire is greatly increased, and the risk of wire disconnection exists in the processing process; when the width of the connecting wire is too large, the wire may pull the liquid drop, influence the movement of the liquid drop, occupy a larger area, and be unfavorable for the surface wiring of the chip.

Preferably, the width w of the connecting wire is selected from 300 to 500 μm, more preferably 300 to 400 μm.

The area of the individual drive electrodes in the array of drive electrodes is determined by the volume of liquid to be treated on the chip.

The substrate is selected from a film, a thin plate, an adhesive tape or paper, and the material is selected from one or more of polyimide, phenolic resin, polysulfone, polyether sulfone and polyphenylene sulfone;

for the scheme A), preferably, the substrate is selected from polyimide adhesive tape to facilitate adhesion with the lower supporting layer, so as to avoid deformation of the substrate material in the processing process and ensure the processing precision; alternatively, the substrate is selected from polyimide sheets, which may provide good support strength by itself, thereby eliminating the need for an underlying support layer.

For the above aspects B) and C), it is preferable that the base material is selected from polyimide paper to facilitate double sided ablation of the base material to construct the through electrode array. Researches show that when the substrate material is a polyimide film, the processing position of the penetrating electrode array is easy to generate obvious deformation or damage, fracture and the like, thereby influencing the processing quality of the substrate.

When the substrate with the graphene electrode does not have supporting capacity, a lower supporting layer is arranged below the substrate; the invention has no special requirement on the lower supporting layer, and is generally a flat plate with good supporting strength, such as a glass sheet, a polymethyl methacrylate (PMMA) plate, a Polycarbonate (PC) plate and the like.

In the substrate with graphene electrode:

the dielectric layer is a thin layer with high dielectric constant, the thickness is selected from 10-120 mu m, and the relative dielectric constant is selected from 3-10;

the material of the dielectric layer is one or more selected from photoresist, parylene (parylene) and photo-curing dielectric layer materials;

the photocuring medium layer material is one or more of pentaerythritol tetra (3-mercaptopropionate), tris [2- (3-mercaptopropionic acid) ethyl ] isocyanurate, trimethylolpropane tris (3-mercaptopropionate), pentaerythritol tetra (2-mercaptoacetic acid), 1,3, 5-triallyl-1, 3, 5-triazine-2, 4,6 (1H, 3H, 5H) -trione, trimethylolpropane diallyl ether and the like;

the photo-curing medium layer material also comprises a photoinitiator which is selected from one or more of benzil compounds, alkyl benzene ketone compounds and acyl phosphorus oxides.

Preferably, the thickness of the dielectric layer is greater than the height h of the driving electrode array; experiments show that when the thickness of the dielectric layer is too large, the driving force exerted by the liquid drops is smaller; when the thickness of the dielectric layer is too small, breakdown phenomenon is easy to occur, meanwhile, the graphene electrode part is possibly exposed, and electrolysis occurs after the liquid drop is electrified.

Preferably, the thickness of the dielectric layer is 70-90 μm to ensure good droplet driving performance of the chip.

In the invention, the hydrophobic layer in the substrate with the graphene electrode is denoted as a lower hydrophobic layer, and the hydrophobic layer in the upper cover plate is denoted as an upper hydrophobic layer.

The upper and lower hydrophobic layers are thin layers with hydrophobicity, and the water contact angles of the upper and lower hydrophobic layers are both larger than 105 degrees; the components of the two can be the same or different, but the components are one or more selected from Teflon, hydrophobic light curing agent, hydrophobic modifying agent and fluorine-containing silane coupling agent.

The hydrophobic photo-curing agent is selected from photo-curing aids with good hydrophobic properties, such as fluorine-containing photo-curing aids, or photo-curing materials with good hydrophobic properties, such as one or more of 1H, 2H-perfluorodecyl acrylate, 2- (perfluorooctyl) ethyl methacrylate, 1H, 2H-perfluorodecyl mercaptan, allyl 1H, 1H-perfluorooctyl ether, polysiloxane acrylate oligomer, perfluoropolyether acrylate oligomer, polysiloxane methacrylate oligomer, perfluoropolyether methacrylate oligomer, mercapto polysiloxane oligomer, mercapto perfluoropolyether oligomer, alkenyl polysiloxane oligomer, alkenyl perfluoropolyether oligomer, epoxy polysiloxane oligomer, epoxy perfluoropolyether oligomer.

Experiments have found that when the lower hydrophobic layer is too thick, it may result in difficulties in droplet movement; when the upper cover plate contains a conductive layer, if the thickness of the upper hydrophobic layer is too thick, droplets may not be split or generated normally, i.e., the conductive layer may not exert an effect.

Preferably, the thickness of both the upper and lower hydrophobic layers is not more than 30 μm.

Preferably:

the medium layer and the lower hydrophobic layer are combined into a composite hydrophobic medium layer so as to simplify the chip processing technology;

the raw materials for preparing the composite hydrophobic medium layer are prepared by mixing the raw materials for preparing the medium layer and the raw materials for preparing the hydrophobic layer;

the thickness of the composite hydrophobic medium layer is 10-120 mu m, the relative dielectric constant is 3-10, and the water contact angle is more than 105 degrees;

the thickness of the composite hydrophobic medium layer is larger than the height h of the driving electrode array.

Further preferred is:

the composite hydrophobic medium layer is a light-cured composite hydrophobic medium layer and is prepared by mixing a light-cured medium layer material and a hydrophobic light-cured reagent.

In the invention, the upper cover plate further comprises a conductive layer which is selectively embedded;

the material of the conductive layer is one or more selected from conductive oxide (such as ITO, etc.), conductive metal (such as Ag, etc.), conductive polymer (such as PEDOT, etc.), and graphene;

The sheet resistance of the conductive layer is selected from 1 to 300 omega, and the thickness is selected from 30 to 700nm.

Preferably, the material of the conductive layer is selected from conductive polymers; when the conductive polymer is selected as the conductive layer, the full polymer digital micro-fluidic chip can be formed, namely, all parts of the chip are processed by the polymer, so that the environmental friendliness of the chip is further improved, and the cost of the chip is reduced.

Preferably:

the conductive polymer is selected from poly (3, 4-ethylenedioxythiophene)/polystyrene sulfonate (PEDOT/PSS) to ensure good conductivity and light transmittance, and is easy to process; the research shows that when the thickness of the conductive layer is too small, the resistance of the conductive layer is greatly increased, which is unfavorable for the normal splitting and fusion of the liquid drops; when the thickness of the conductive layer is too large, the transparency thereof will be deteriorated, which affects the observation and detection in practical application, and therefore, the thickness of the conductive layer is preferably selected from 100 to 400nm.

A protective layer can be selectively embedded between the conductive layer and the upper hydrophobic layer, and the protective layer is a high polymer compound thin layer with insulating property; the thickness of the protective layer is 0.1-50 mu m.

The invention also discloses a preparation method of the graphene electrode digital microfluidic chip, which comprises the following steps: substrate processing with graphene electrodes, upper cover plate processing and chip assembly/sealing, wherein the substrate processing with graphene electrodes is processed according to one of the following methods:

Scheme a) fixing a base material on a laser platform and then focusing; generating graphene by laser ablation of a substrate, and processing a driving electrode array, a connecting wire and an interface electrode array on the upper surface of the substrate;

scheme B) fixing the substrate material on the laser platform and then focusing; generating graphene by laser ablation of a substrate, and processing a driving electrode array on the upper surface of the substrate; turning over the substrate material and performing alignment patterning, and then processing the through electrode array on the lower surface by a similar method;

scheme C) fixing the substrate material on a laser platform, and then focusing; generating graphene by laser ablation of a substrate, and processing a driving electrode array on the upper surface of the substrate; turning over the substrate material, performing alignment patterns, and then penetrating the electrode array by laser processing; finally, the laser is used for processing the connecting wire and the interface electrode array on the surface.

The laser used for laser ablation is preferably a carbon dioxide laser, and the laser wavelength is 10.6 mu m;

preferably, the laser power of the laser is selected from 2-5W; the scanning speed of the laser is selected from 200-400 mm/s.

Research shows that when the laser power is too small, graphene is not beneficial to stably form on a substrate material; when the laser power is too high, there may be a communication condition between adjacent driving electrodes.

Further preferably, the laser power of the laser is selected from 3 to 3.6W.

Researches show that when the scanning speed is too slow, the condition of communication between adjacent electrodes is easy to occur; when the scanning speed is too high, there is a risk that the integrity of the formed graphene pattern is poor.

Further preferably, the scanning speed of the laser is selected from 300-350 mm/s.

The upper hydrophobic layer can be used for processing various channel structures, or a channel structure layer with the channel structure is embedded on the upper hydrophobic layer; the channel structures include, but are not limited to, fluidic channels, micropillars, microwells, chambers, etc.;

and the upper cover plate and the substrate with the graphene electrode are sealed to form the integrated flow channel digital micro-fluidic chip.

The graphene electrode digital microfluidic chip disclosed by the invention can perform all basic control functions of droplet generation, movement, splitting and fusion, and has an ideal driving effect.

Compared with the prior art, the invention has the following beneficial effects:

the invention discloses a graphene electrode digital microfluidic chip, which is provided with a graphene electrode substrate formed by processing by using a laser-induced graphene technology. The introduction of the electrode substrate with the graphene avoids the complicated process with high cost, long time consumption or larger requirements on the operation environment such as photoetching, etching, sputtering or deposition in the preparation of the chip, and the preparation of the electrode array can be completed in the conventional environment by only using the polyimide and other organic materials which are easy to obtain and the common laser. Therefore, the graphene electrode substrate greatly reduces the cost of the chip, simplifies the manufacturing process of the chip, and has the economic cost and the time cost far lower than those of the current typical glass or PCB substrate DMF chip. Compared with partial paper-based DMF chips, the graphene electrode digital microfluidic chip disclosed by the invention can finish processing without providing additional conductive ink, so that the graphene electrode digital microfluidic chip is more economical and convenient. Because no metal material, glass fiber reinforced thermosetting resin (FR-4) and other materials are introduced into the chip, and complex processes such as photoetching are not involved, compared with the traditional DMF chip, the graphene electrode digital microfluidic chip disclosed by the invention is better in environmental friendliness and is more beneficial to large-scale application.

The invention also discloses a processing method of the graphene electrode digital microfluidic chip. Through the optimization of the laser parameters and the graphene electrode parameters, the advantage technology of laser induced graphene is successfully applied to the processing of the digital microfluidic chip. When the graphene electrode substrate is processed, the driving electrode array, the connecting wire and the interface electrode array are located on the same plane to form a coplanar electrode structure, and the penetrating electrode array can be introduced by a double-sided ablation method, so that the driving electrode array, the connecting wire and the interface electrode array are located on two sides of the substrate material to form a vertically excited double-plane electrode structure. Through the constructed biplane electrode structure, the processing method enables the graphene electrode digital microfluidic chip to integrate a higher-density and higher-quantity driving electrodes, meets the requirement of high flux, and has the capability of processing more complex liquid drop driving tasks.

In addition, the graphene electrode digital microfluidic chip disclosed by the invention can also preferably combine the dielectric layer and the lower hydrophobic layer into a composite hydrophobic dielectric layer. The traditional DMF chip is usually provided with a dielectric layer and a hydrophobic layer which are mutually independent, the materials of the two parts are different, and the manufacturing process is also different. Therefore, in the traditional DMF chip manufacturing process, the dielectric layer and the hydrophobic layer are required to be processed respectively in two steps, and the process is complicated. The composite hydrophobic medium layer disclosed by the invention ensures the dielectric property of the medium layer and the hydrophobic property of the hydrophobic layer by mixing the medium layer material and the hydrophobic layer material, so that the structure can be directly processed in one step, and the manufacturing process of the DMF chip is further optimized.

The graphene electrode digital microfluidic chip disclosed by the invention can also adopt conductive polymers (such as PEDOT and the like) as conductive layer materials to form the full-polymer digital microfluidic chip. All the structures of the all-polymer digital microfluidic chip are formed by processing organic polymers, so that the cost of the chip can be further reduced, and the environmental friendliness of the chip is improved.

In conclusion, the graphene electrode digital microfluidic chip and the processing method thereof disclosed by the invention have the advantages of low cost, simple and convenient manufacturing process, high flux, environmental friendliness and the like, and can be comprehensively applied to various fields of biomedical research, clinical diagnosis, field detection and the like.

Drawings

Fig. 1 is a schematic structural diagram of a graphene electrode digital microfluidic chip disclosed by the invention;

fig. 2 is a schematic structural diagram of a substrate with graphene electrodes disclosed in the scheme a) of the present invention;

fig. 3 is a schematic structural diagram of a substrate with graphene electrodes disclosed in the scheme B) of the present invention;

fig. 4 is a schematic structural diagram of a substrate with graphene electrodes disclosed in the scheme C) of the present invention;

fig. 5 is a graph of the graphene electrode pattern used in example 1, wherein a is a CAD drawing used in processing, and B is a schematic dimensional diagram of the windmill-shaped electrode in the CAD drawing;

Fig. 6 is a schematic structural diagram of a graphene electrode digital microfluidic chip prepared in example 2, (a) is a schematic structural diagram of the graphene electrode digital microfluidic chip, (B) is a substrate physical diagram with a graphene electrode pattern, and (C) is a partial enlarged diagram of a driving electrode array in (B);

fig. 7 is a graph of the manipulation effect of the graphene electrode digital microfluidic chip prepared in example 2 on droplets, including droplet generation (a), movement (B), splitting (C), and fusion (D).

Fig. 8 is a diagram of a graphene electrode digital microfluidic chip prepared in example 3, (a) is a top view of a substrate physical image, and (B) is a bottom view of the substrate physical image;

fig. 9 is a diagram of a graphene electrode digital microfluidic chip prepared in example 4, (a) is a top view of a substrate physical image, and (B) is a bottom view of the substrate physical image;

fig. 10 is a microscope image of the distance between two adjacent driving electrodes in the substrate surface physical diagram of the graphene electrode digital microfluidic chip prepared in comparative example 1;

fig. 11 is a microscope image of the distance between two adjacent driving electrodes in the substrate surface physical diagram of the graphene electrode digital microfluidic chip prepared in comparative example 2;

fig. 12 is an image of a graphene electrode digital microfluidic chip prepared in comparative example 2, in which the adjacent electrodes are broken down due to the resistance (i.e., communication) between the adjacent driving electrodes when the liquid droplets are handled, and the liquid droplets cannot move normally;

FIG. 13 is a graph showing the relationship between the width of a connecting wire and the resistance value (wherein the length of the connecting wire is 1 cm) when the width of the connecting wire is 180-600 μm;

fig. 14 is an image of the graphene electrode digital microfluidic chip prepared in comparative example 5, in which the droplets cannot normally move due to the traction of the droplets by the connection wires when the droplets are manipulated;

FIG. 15 is a graph showing the processing effect of graphene induced by double-sided ablation in comparative example 6;

in the figure:

1-a substrate with a graphene electrode, 11-a lower supporting layer, 12-a substrate with a graphene electrode, 13-a dielectric layer, 14-a lower hydrophobic layer and 15-a composite hydrophobic dielectric layer;

2-upper cover plate, 21-upper supporting layer, 22-conducting layer, 23-upper hydrophobic layer;

3-graphene electrode, 31-driving electrode array, 32-connecting wire, 33-interface electrode array, 34-penetrating electrode array, 311-windmill-shaped electrode and 312-reservoir electrode.

Detailed Description

For further understanding of the present invention, the present invention will be described in detail with reference to the drawings and examples, but the present invention is not limited to these examples, and the present invention is not limited to the essential improvements and modifications made by those skilled in the art under the core teaching ideas of the present invention, and still falls within the scope of the present invention.

Fig. 1 is a schematic structural diagram of a graphene electrode digital microfluidic chip disclosed by the invention, which comprises a substrate 1 with a graphene electrode and an upper cover plate 2;

the substrate 1 with the graphene electrode comprises a lower supporting layer 11, a substrate 12 with the graphene electrode, a dielectric layer 13 and a lower hydrophobic layer 14 from bottom to top in sequence; the graphene electrode 3 is provided on the substrate 12 with the graphene electrode.

The upper cover plate 2 is sequentially provided with an upper supporting layer 21, a conductive layer 22 and an upper hydrophobic layer 23 from top to bottom.

Aiming at different application scenes, the substrate 1 with the graphene electrode disclosed by the invention has three different structures, which are respectively shown in figures 2 to 4.

Fig. 2 is a schematic diagram of a substrate with a graphene electrode disclosed in scheme a), (a) is a schematic diagram of a side view thereof, and (B) is a schematic diagram of an upper view, in which the graphene electrode 3 includes a driving electrode array 31, a connecting wire 32, and an interface electrode array 33, and all the three are located on an upper surface of a substrate to form a coplanar electrode structure; the driving electrode array 31 is connected to the interface electrode array 33 through the connection wire 32, and is connected to an external control circuit through the interface electrode array 33.

Fig. 3 is a schematic diagram of a substrate with a graphene electrode disclosed in scheme B), (a) is a schematic diagram of a side view thereof, (B) is a schematic diagram of an upper view, and (C) is a schematic diagram of a lower view, in which the graphene electrode 3 includes a driving electrode array 31 and a penetrating electrode array 34, the driving electrode array 31 is located on an upper surface of a substrate, the penetrating electrode array 34 vertically penetrates the substrate, and a single driving electrode is vertically connected with a single penetrating electrode; the driving electrode array 31 is connected to an external control circuit through the penetrating electrode array 34. At this time, the driving electrode array 31 and the penetrating electrode array 34 are located on both sides of the base material, forming a vertically excited biplane electrode structure.

Fig. 4 is a schematic diagram of a substrate with a graphene electrode disclosed in scheme C), (a) is a schematic diagram of a side view thereof, (B) is a schematic diagram of an upper view, and (C) is a schematic diagram of a lower view, in which the graphene electrode 3 includes a driving electrode array 31, a connection wire 32, an interface electrode array 33, and a penetrating electrode array 34, the driving electrode array 31 is located on an upper surface of the substrate, the connection wire 32 and the interface electrode array 33 are located on a lower surface of the substrate, the penetrating electrode array 34 vertically penetrates the substrate, and a single driving electrode is vertically connected with a single penetrating electrode; the driving electrode array 31 is communicated with the penetrating electrode array 34, and is connected with an external control circuit through the connecting lead 32 and the interface electrode array 33. At this time, the driving electrode array 31, the connection wire 32 and the interface electrode array 33 are located on both sides of the base material, forming a vertically excited biplane electrode structure.

The constructed biplane electrode structure enables the graphene electrode digital microfluidic chip to integrate a higher-density and higher-number driving electrodes, meets the requirement of high flux, and has the capability of processing more complex liquid drop driving tasks.

Example 1: coplanar graphene electrode digital microfluidic chip processing (processing scheme A)

A) Processing a substrate: a clean glass plate was used as the lower support layer, with dimensions 62.3mm by 62.3mm. The polyimide adhesive tape is cut into the same size as the lower support layer and is flatly attached to the lower support layer. It is placed in a carbon dioxide laser and then focused. The pattern shown in fig. 5 (a) is introduced in software, wherein the pitch of adjacent drive electrodes in the drive electrode array 31 is d=110 μm, and the width of the connection wire 32 is w=350 μm. The windmill electrode 311 has dimensions of l=2 mm, a=0.9 mm, b=0.3 mm, the reservoir electrode 312 has dimensions of 4mm×3.3mm, and the individual interface electrodes in the interface electrode array 33 have dimensions of 1.5mm×1.5mm. The laser power was set at 3.3W and the scanning speed was 350mm/s. And (3) forming a graphene electrode array by using a laser to ablate the substrate, wherein the thicknesses of the processed driving electrode array, the processed interface electrode array and the processed connecting wires are the same, and h=35 mu m. And (3) washing the surface of the graphene electrode array by using absolute ethyl alcohol, and blowing out the graphene electrode array by using air to serve as a substrate for standby.

B) Processing a dielectric layer: a thiol-ene mixture solution containing 74% pentaerythritol tetrakis (3-mercaptopropionate), 25% triallyl isocyanurate, and 1% 2-hydroxy-2-methyl-1-phenyl-1-propanone was prepared in mass fractions. The solution is placed on a drive electrode array of a substrate. Another clean glass plate was pressed over the solution to a liquid thickness of about 80 μm, followed by ultraviolet irradiation (365 nm,2.5 mW/cm) ² ) Curing for about 3 s. And removing the upper glass plate, and processing to form the dielectric layer.

C) Processing a lower hydrophobic layer: a solution of 1wt% Teflon (dissolved in FC-40 fluoride solution) was spin coated onto the dielectric layer surface at about 3000rpm for 30 seconds. Then the mixture is placed on a hot plate at 85 ℃ for about 15min to evaporate to dryness, and a lower hydrophobic layer is formed by processing, wherein the thickness of the lower hydrophobic layer is about 200nm.

And after the steps A), B) and C), forming the substrate with the graphene electrode.

D) Processing an upper cover plate: a piece of clean Indium Tin Oxide (ITO) glass was taken, 1wt% Teflon solution was added dropwise and spin-coated on the ITO conductive glass surface at about 3000rpm for 30s. Then the mixture is placed on a hot plate at 85 ℃ for about 15min to evaporate to dryness, and an upper hydrophobic layer is formed by processing, wherein the thickness of the upper hydrophobic layer is about 200nm.

And assembling the substrate with the graphene electrode with the upper cover plate to form the complete graphene electrode digital microfluidic chip. The external control circuit is connected to the chip through the interface electrode array 33, thereby applying a voltage to the driving electrode array 31.

Example 2: full polymer coplanar graphene electrode digital microfluidic chip processing and droplet driving method with composite hydrophobic medium layer

A) Processing a substrate: processing was performed using a graphene electrode pattern similar to that in example 1, the preparation process was substantially the same as in example 1, except that:

The lower support layer is replaced by a PMMA plate with the same size;

the distance d=90 μm between the driving electrodes in the graphene electrode pattern, and the wire width w=300 μm;

b) Processing a composite hydrophobic medium layer: a composite hydrophobic medium layer mixture solution containing 70% pentaerythritol tetrakis (3-mercaptopropionate), 24% triallyl isocyanurate, 5% silicofluoridated urethane acrylate, and 1% 2-hydroxy-2-methyl-1-phenyl-1-propanone was prepared in mass fractions. The solution is placed on a drive electrode array of a substrate. Another clean glass plate was pressed over the solution to a liquid thickness of about 80 μm, followed by ultraviolet irradiation (365 nm,2.5 mW/cm) ² ) Curing for about 3 s. The upper glass plate is removed and processed to form the composite hydrophobic medium layer 15.

After the two steps of A) and B), a substrate with a graphene electrode is formed.

C) Processing an upper cover plate: a clean PMMA plate was used as the upper support layer 21, and the dimensions thereof were 75mm by 25mm. The composition contains 95% poly (3, 4-ethylenedioxythiophene) -poly (styrenesulfonic acid) by mass fractionAnd 5% dimethyl sulfoxide in PEDOT mixture. The solution was spin-coated on the surface of the upper support layer at 500rpm for 30 seconds with a film thickness of about 100nm. And then heating on a hot plate at 85 ℃ for about 15min, and evaporating to dryness to obtain the conductive layer 22 for standby. Then dripping the compound hydrophobic medium layer mixture solution prepared in the step B) on the surface of the conductive layer, pressing another clean glass plate on the solution to make the thickness of the solution be about 30 μm, and then irradiating with ultraviolet light (365 nm,2.5 mW/cm) ² ) Curing for about 3 s. The upper glass plate is removed and processed to form the upper hydrophobic layer 23.

And assembling the substrate with the graphene electrode with the upper cover plate to form a complete graphene electrode digital microfluidic chip, wherein a side view structural schematic diagram of the graphene electrode digital microfluidic chip prepared by the embodiment is shown in fig. 6 (A). Fig. 6 (B) is a schematic view of a substrate with graphene electrodes prepared in this embodiment, and (C) is a partial enlarged view of the driving electrode array 31 in (B), in this embodiment, an external control circuit is connected to the chip through the interface electrode array 33, so as to apply a voltage to the driving electrode array 31.

Application test:

the graphene electrode digital microfluidic chip prepared by the embodiment is used for controlling liquid drops, the control effect is shown in fig. 7, and the amplitude and frequency of the voltage applied to the graphene electrode are 190VAC and 1kHz. The control test comprises generation (A), movement (B), splitting (C) and fusion (D) of liquid drops, and experimental results show that the graphene electrode digital microfluidic chip has all basic control functions of liquid drop generation, movement, splitting and fusion, and has an ideal driving effect.

Example 3: double-plane graphene electrode digital microfluidic chip processing with through electrode array (processing scheme B)

A) Processing a substrate: a clean glass plate was taken, polyimide paper was cut to 62.3mm by 62.3mm size, and was flatly attached to the glass plate. It is placed in a carbon dioxide laser and then focused. In the software, a pattern of the driving electrode array 31 was introduced, and the driving electrode array 31 was composed of a plurality of driving electrodes each having a size of 3mm×3mm, and a pitch d=100 μm between adjacent driving electrodes. Setting the laser power to be 3.0W, the scanning speed to be 380mm/s, and forming a driving electrode array by using laser to ablate the substrate, wherein the thickness h=20 μm of the processed driving electrode array. . And then blown clean with air. And taking the polyimide paper off the glass plate, turning over the substrate material, and flatly and closely attaching the polyimide paper on the glass plate again. It is placed in the carbon dioxide laser described above and then the pattern is aligned and refocused. The pattern of the penetrating electrode array 34 is introduced into the software, the penetrating electrode array 34 is composed of a plurality of penetrating electrodes, each penetrating electrode is cylindrical, the diameter of the bottom surface is 2.0mm, the penetrating electrode penetrates through the base material, and each penetrating electrode is vertically connected with each driving electrode in the driving electrode array processed before. The through electrode array is then machined on the lower surface using the same method and parameters as the drive electrode array.

B) Processing a composite hydrophobic medium layer:

exactly as in step B) of example 2.

C) Processing an upper cover plate: a clean glass slide was taken as the upper support layer. A PEDOT mixture solution containing 94% poly (3, 4-ethylenedioxythiophene) -poly (styrenesulfonic acid) and 6%D-sorbitol was prepared in mass fractions. Spin-coating the solution on the surface of the upper support layer at 1000rpm for 30s with a film thickness of about 75nm, and heating on a hot plate at 85deg.C for about 15min to evaporate to dryness to obtain the conductive layer. Then the solution of the compound hydrophobic medium layer mixture prepared in the step B) in the example 2 is dripped on the surface of the conductive layer, another clean glass plate is pressed and covered on the solution to ensure that the thickness of the liquid is about 30 mu m, and then ultraviolet irradiation (365 nm, 2.5W/cm) ² ) Curing for about 3 s. And removing the upper glass plate, and processing to form an upper hydrophobic layer to form an upper cover plate.

And assembling the substrate with the graphene electrode with the upper cover plate to form the complete graphene electrode digital microfluidic chip. In fig. 8, (a) is a top view and (B) is a bottom view of a substrate physical diagram of a biplane graphene electrode digital microfluidic chip with a penetrating electrode array prepared in this embodiment, and when a droplet is driven, the penetrating electrode array on the bottom surface of the substrate is closely attached to a corresponding external control circuit interface array, so that a voltage is directly applied to the driving electrode array through the penetrating electrode.

The application test conditions are the same as those in the embodiment 2, and the result shows that the graphene electrode digital microfluidic chip prepared by the embodiment also has all basic control functions of droplet generation, movement, splitting and fusion, and the driving effect is ideal.

Example 4: double-sided graphene electrode digital microfluidic chip processing (processing scheme C) with penetrating electrode array, conducting wire and interface electrode array

A) Processing a substrate: substantially the same as in step A) in example 3, except that the diameter of the bottom surface of the through electrode was replaced with 1.0mm. After the preparation of the through electrodes was completed, the pattern alignment was performed again, and the patterns of the connection wires 32 and the interface electrode array 33 were introduced in software, wherein the width w=300 μm of the connection wires, the size of the individual interface electrodes was 1.5mm×1.5mm, the laser power was set to 2.7W, and the scanning speed was 350mm/s. The connection wires 32 and the interface electrode array 33 are formed by laser ablation of the substrate, and the thicknesses of the processed interface electrode array and connection wires are the same, and h=15 μm.

B) Processing a dielectric layer: a thiol-ene mixture solution containing 42% pentaerythritol tetrakis (3-mercaptopropionate), 57% triallyl isocyanurate, and 1% 2-hydroxy-2-methyl-1-phenyl-1-propanone was prepared in mass fractions. The solution is placed on a drive electrode array of a substrate. Another clean glass plate was pressed over the solution to a liquid thickness of about 80 μm, followed by ultraviolet irradiation (365 nm,2.5 mW/cm) ² ) Curing for about 3 s. And removing the upper glass plate, and processing to form the dielectric layer.

C) Processing a hydrophobic layer: a hydrophobic light modification solution containing 79% absolute ethanol, 20%1H, 2H-perfluorodecanethiol and 1% 2-hydroxy-2-methyl-1-phenyl-1-propanone was prepared in mass fraction. The solution was uniformly spread on the surface of the dielectric layer, followed by ultraviolet irradiation (365 nm,2.5mW/cm ² ) About 30s, so that the 1H, 2H-perfluorodecanethiol molecules are co-located with the surface of the dielectric layerValence links, forming a hydrophobic layer.

D) Processing an upper cover plate: a piece of clean Indium Tin Oxide (ITO) glass is taken, the thiol-ene mixture solution prepared in the step B) is spin-coated on the conductive surface of the ITO glass, the rotating speed is about 3000rpm, the time is 30s, the thickness of the liquid film is about 10 mu m, and then ultraviolet irradiation (365 nm, 2.5W/cm) ² ) And curing for about 3 seconds to form a protective layer. And then processing the upper hydrophobic layer on the surface of the protective layer according to the same steps in the step C) to form the upper cover plate.

And assembling the substrate with the graphene electrode with the upper cover plate to form the complete graphene electrode digital microfluidic chip. In fig. 9, (a) is a top view and (B) is a bottom view of a substrate physical diagram of a biplane graphene electrode digital microfluidic chip with a through electrode array prepared in this embodiment, and an external control circuit is connected to the chip through an interface electrode array when driving a droplet, so as to apply a voltage to the driving electrode array.

Comparative example 1

The preparation process was essentially the same as in example 1, except that:

the drive electrode spacing d=30μm in the graphene electrode pattern.

Fig. 10 is a microscope image of the distance between two adjacent driving electrodes in the substrate surface physical image of the graphene electrode digital microfluidic chip prepared in this comparative example. As can be seen from an examination of this figure, two adjacent drive electrodes communicate over a wide range (as in the figure at the circles). The edge shape of the graphene grown by the conventional laser-induced graphene technology has certain irregularity, so that the spatial resolution of the technology per se has certain limitation. Because the designed distance between adjacent driving electrodes is too small, the driving electrode arrays which are not communicated with each other cannot be processed under the precision by the laser-induced graphene technology, and therefore, the method cannot be applied to digital microfluidic chips.

Comparative example 2

The preparation process was essentially the same as in example 1, except that:

the drive electrode spacing d=60 μm in the graphene electrode pattern.

Fig. 11 is a microscope image of the distance between two adjacent driving electrodes in the substrate surface physical image of the graphene electrode digital microfluidic chip prepared in this comparative example. By observing the graph, no obvious connection of the driving electrodes appears in the graph. Further testing showed that after a conventional cleaning step, the resistance between two adjacent drive electrodes was measured by a multimeter to be about 200kΩ, indicating that connectivity still exists.

Further experiments have found that when a resistance exists between two adjacent driving electrodes, after the electrodes are opened, an electric spark appears between the electrodes and the adjacent electrodes, and the electrodes break down (as shown in fig. 12). The droplet cannot normally move to the designated electrode.

Comparative example 3

The preparation process was essentially the same as in example 1, except that:

the width w=100 μm of the connection wire is set in the graphene electrode pattern.

Research shows that the precision of the laser-induced graphene technology is limited, and the connecting wires with the width cannot be processed, so that the interface electrode array cannot be communicated with the driving electrode array. And thus cannot be applied to digital microfluidic chips.

Comparative example 4

The preparation process was essentially the same as in example 1, except that:

the graphene electrode pattern is provided with a connecting wire width w=180 μm. The resistance of the connecting wire with a length of 1cm is about 50.3kΩ.

The study showed that the connection wire width versus resistance is shown in FIG. 13 (where the connection wire lengths were 1cm during the test). It can be seen that the resistance value of the connecting wire at a wire width of 180 μm is much larger than that at a wire width of 300 μm (3.7 kΩ) for each 1cm connecting wire. The resistance of the lead is larger, and the subsequent control effect on the liquid drop is affected.

Example 5

The preparation process was essentially the same as in example 1, except that:

the graphene electrode pattern is provided with a connecting wire width w=400 μm.

Comparative example 5

The preparation process was essentially the same as in example 1, except that:

the graphene electrode pattern is provided with a connecting wire width w=600 μm.

Fig. 14 is an image of the droplet driving effect of the graphene electrode digital microfluidic chip finally prepared in this comparative example in an operating state. By observing the graph, the connecting wires have larger traction force on the liquid drops, and the deformation of the liquid drops is obvious, so that the connecting wires cannot contact the next driving electrode. The droplets cannot be driven normally, and thus cannot be applied to a digital microfluidic chip.

Comparative example 6

The preparation process was essentially the same as in example 3, except that:

the substrate was replaced with a polyimide film of equal size and thickness of 50 μm.

Fig. 15 shows a processing state of the graphene electrode. As can be seen from an examination of this figure, breakage and chipping occurred throughout the electrode array process. Therefore, the polyimide film material cannot be applied to chip processing of either scheme B or scheme C.

Claims

1. The utility model provides a digital micro-fluidic chip of graphite alkene electrode, includes base plate and upper cover plate that has the graphite alkene electrode, its characterized in that:

the graphene electrode has one of the following structures:

2. The graphene electrode digital microfluidic chip according to claim 1, wherein the upper cover plate comprises a hydrophobic layer, a selectively embedded conductive layer, and an upper support layer, which are sequentially arranged from bottom to top.

3. The graphene electrode digital microfluidic chip according to claim 1, wherein in the graphene electrode:

the square resistances of the single electrode or the single wire in the driving electrode array, the penetrating electrode array, the connecting wire and the interface electrode array are all selected from 5-300 omega;

the heights h of the single electrode or the single wire in the driving electrode array, the connecting wire and the interface electrode array are all selected from 10-70 mu m;

the minimum distance d between adjacent driving electrodes in the driving electrode array is selected from 70-150 mu m;

The width w of the connecting wire is selected from 300-500 mu m.

4. The graphene electrode digital microfluidic chip according to claim 1, wherein:

the substrate with the graphene electrode is further provided with a lower supporting layer at the lowest part.

5. The graphene electrode digital microfluidic chip according to claim 1, wherein:

the thickness of the dielectric layer is larger than the height h of the driving electrode array;

the hydrophobic layer in the substrate with the graphene electrode is a thin layer with hydrophobicity;

the water contact angle of the hydrophobic thin layer is larger than 105 degrees, and the component is one or more selected from Teflon, a hydrophobic photo-curing agent, a hydrophobic modifying agent and a fluorine-containing silane coupling agent.

6. The graphene electrode digital microfluidic chip according to claim 1, wherein: the thickness of the composite hydrophobic medium layer is 10-120 mu m, the relative dielectric constant is 3-10, and the water contact angle is more than 105 degrees;

7. The graphene electrode digital microfluidic chip according to claim 2, wherein:

the hydrophobic layer in the upper cover plate is a thin layer with hydrophobicity;

the water contact angle of the hydrophobic thin layer is larger than 105 degrees, and the component is one or more selected from Teflon, a hydrophobic photo-curing agent, a hydrophobic modifying agent and a fluorine-containing silane coupling agent;

the sheet resistance of the conductive layer is selected from 1-300 omega, and the thickness is selected from 30-700 nm;

the conductive layer can be made of conductive polymer to form the full polymer digital micro-fluidic chip.

8. A method of manufacturing a graphene electrode digital microfluidic chip according to any one of claims 1 to 7, comprising processing a substrate with a graphene electrode, processing an upper cover plate, and chip assembling/sealing, wherein the substrate with a graphene electrode is processed according to one of the following methods:

9. The method for preparing the graphene electrode digital microfluidic chip according to claim 8, which is characterized in that:

the laser power adopted by the laser ablation is selected from 2-5W, and the scanning speed adopted by the laser ablation is selected from 200-400 mm/s.

10. The graphene electrode digital microfluidic chip according to claim 1, wherein:

the upper hydrophobic layer can be used for processing various channel structures, or a channel structure layer with the channel structure is embedded on the upper hydrophobic layer;

The channel structures include, but are not limited to, fluidic channels, micropillars, microwells, chambers;