A method for surface processing of DMF chips with stepped wetting properties

Abstract

This invention relates to a method for processing the surface of a DMF chip with stepped wetting properties, comprising: step S1, providing a substrate having an electrode pattern; step S2, bonding a hydrophobic film to the substrate having the electrode pattern; and step S3, forming a hydrophobic coating on a local area of ​​the surface of the hydrophobic film, wherein the hydrophobicity of the hydrophobic coating is different from that of the hydrophobic film. This invention can solve the problems of the inability to achieve coexistence of gas and oil phases in current digital microfluidic chips, the strict sealing of the oil phase medium, and the spontaneous movement of its droplets, thereby reducing the manufacturing difficulty of digital microfluidic chips.

Description

Technical Field

[0001] This invention relates to the field of digital microfluidics technology, and more specifically to a method for processing the surface of a DMF chip with stepped wetting characteristics. Background Technology

[0002] Digital microfluidics (DMF) based on dielectric electrowetting (EWOD) has seen widespread development in recent years. It manipulates liquids and processes discrete droplets by applying an electric potential. Through control of the electrodes, basic droplet operations such as droplet generation, movement, splitting, and merging can be achieved. DMF chips are widely used in biochemical detection fields, effectively reducing manual labor and reagent consumption, and significantly improving automation levels.

[0003] Currently, most DMF chips employ a parallel-plate design consisting of upper and lower plates. In this design, the upper plate, connected to the ground electrode, is made of a transparent material, such as indium tin oxide (ITO) glass, and is in most cases coated with a hydrophobic material like Teflon. The lower plate comprises a substrate, a dielectric layer, and a hydrophobic layer. Currently, the most common method for fabricating the lower plate is to deposit metal on a glass substrate, create electrode patterns using photolithography, then form a dielectric layer through spin coating with SU-8, thermal growth by depositing terephthalene-c or SiO2, and finally spin-coating a hydrophobic material as the hydrophobic layer.

[0004] In most biochemical experiments on DMF chips, droplets are always manipulated in an oil medium such as silicone oil, rather than in a DMF air medium. Using an oil medium can reduce interfacial tension and droplet driving voltage, prevent evaporation, and reduce bioadsorption. However, an oil phase medium also reduces the droplet's velocity during movement, making it more susceptible to shear stress and breakage. Currently, there are no reports of simultaneous gas and oil phases within a single DMF chip. Therefore, creating an oil phase environment within the chip requires filling the entire internal space and strict chip sealing to prevent oil leakage, increasing the manufacturing cost of the DMF chip. Furthermore, in current DMF chip applications, to consider chip lifespan, the high-voltage signal is disconnected after the droplet reaches its designated position. Without dielectric confinement, the droplet will spontaneously move due to uneven surface tension, deviating from its original position or even detaching from the electrode area, resulting in dead volume. Some studies have used microstructures to restrict droplet movement, but the fabrication of microstructures increases the number of processing steps and complexity, hindering cost reduction. Summary of the Invention

[0005] To address the problems in the prior art, this invention provides a DMF chip surface processing method with stepped wetting characteristics, which can solve the problems of the inability of gas and oil phases to coexist in current digital microfluidic chips, the strict sealing of the oil phase medium, and the spontaneous movement of its droplets, thereby reducing the process difficulty of digital microfluidic chips and enhancing their practical value.

[0006] The present invention provides a method for surface processing of DMF chips with stepped wetting characteristics, comprising: step S1, providing a substrate having an electrode pattern on the substrate; step S2, bonding a hydrophobic film to the substrate having the electrode pattern; and step S3, forming a hydrophobic coating in a local area on the surface of the hydrophobic film, wherein the hydrophobicity of the hydrophobic coating is different from that of the hydrophobic film.

[0007] Furthermore, the hydrophobic membrane is a PTFE membrane or an ETFE membrane.

[0008] Furthermore, the hydrophobic film is bonded to the substrate by an adhesive.

[0009] Furthermore, the hydrophobic coating is formed by brushing, coating, or spraying.

[0010] Preferably, the hydrophobic coating is made of Teflon material.

[0011] The DMF chip surface processing method with stepped wetting characteristics of the present invention has the following beneficial effects:

[0012] 1) The processing method of the present invention is simple and does not require additional cleanroom processes, complex precision instruments and professional personnel. Chip fabrication can be completed under ordinary laboratory conditions.

[0013] 2) The processing method based on the present invention can effectively confine the oil phase medium to a local area, so that the oil phase and gas phase coexist in the DMF chip, thus expanding the application scenarios of DMF;

[0014] 3) DMF chips processed based on the method of the present invention can prevent leakage without strict chip sealing after filling with dielectric oil, thus reducing the processing difficulty;

[0015] 4) The processing method of the present invention can limit the droplets in the electrode area inside the chip, effectively avoiding the occurrence of dead volume in the experiment. Attached Figure Description

[0016] Figure 1 This is a structural diagram of a DMF chip processed according to the DMF chip surface processing method with stepped wetting characteristics of the present invention.

[0017] Figure 2(a) shows images of silicone oil on the hydrophobic film and hydrophobic coating; Figure 2(b) shows a partial oil phase image.

[0018] Figures 3(a) to 3(b) Figure 3(c) shows the contact angle difference between the hydrophobic film and the hydrophobic coating; Figure 3(d) shows the liquid on the energized storage electrode; Figure 3(d) shows the liquid on the de-energized storage electrode. Detailed Implementation

[0019] The preferred embodiments of the present invention are given below with reference to the accompanying drawings and described in detail.

[0020] like Figure 1 As shown, the DMF chip surface processing method with stepped wetting characteristics of the present invention includes the following steps:

[0021] Step S1: Provide a substrate 1 having an electrode pattern 2.

[0022] Step S2 involves bonding the hydrophobic film 3 to the substrate 1 having the electrode pattern 2. The hydrophobic film 3 can serve as the dielectric and hydrophobic layer of the DMF chip, and it is a thin film made of PTFE, ETFE, or other hydrophobic materials. In this embodiment, the hydrophobic film 3 is bonded to the substrate 1 with an adhesive to avoid air bubbles and bending wrinkles.

[0023] Step S3: A hydrophobic coating 4 is formed in a localized area on the surface of the hydrophobic film 3. The hydrophobicity of the hydrophobic coating 4 differs from that of the hydrophobic film 3, thus allowing multiple materials with different wetting degrees to coexist on the surface of the DMF chip. The hydrophobic coating 4 is formed by coating, spraying, or other methods.

[0024] In this embodiment, the hydrophobic film 3 is a PTFE film with both hydrophobic and oleophilic properties, and the hydrophobic coating 4 is a Teflon material with oleophobic properties and stronger hydrophobicity than the PTFE film. Specifically, a Teflon pattern is created on a localized area of ​​the PTFE film surface by brushing, thus achieving a combination of multiple hydrophobic materials. It should be understood that the hydrophobic film 3 and hydrophobic coating 4 of this invention can also be combinations of other hydrophobic materials, as long as different hydrophobic materials are used.

[0025] The wetting properties of liquids on PTFE films and Teflon coatings differ. This invention achieves localized modification by coating the PTFE film surface with Teflon, creating oleophilic and oleophobic regions. This confines the silicone oil to localized areas, avoiding additional sealing steps and allowing the DMF chip to remain in a semi-open state. Furthermore, based on the concept of a virtual fence due to the different hydrophobicities of the PTFE film and the Teflon coating, the Teflon coating forms a virtual fence around the electrode, restricting liquid in the electrode area and preventing its autonomous movement.

[0026] To further understand, the characteristics of the DMF chip processed using the method of the present invention will be described in detail below.

[0027] like Figures 2(a) to 2(b)As shown, a Teflon pattern is locally brushed onto the surface of the PTFE film (black circle). The pattern is a hollow rectangular frame, forming a local rectangular oleophilic region. The oil-phase medium is confined within the rectangular frame, thereby creating a medium environment where the oil and gas phases coexist within the chip. In existing technologies, the oil-phase environment is typically filled with silicone oil throughout the chip, including both electrode and non-electrode areas. When a small amount of silicone oil is injected, it spontaneously moves due to interfacial tension. This invention reduces the amount of silicone oil by allowing the oil-phase environment to be created only in the desired areas through localized oil phase. Furthermore, the localized oil phase integrates the gas phase medium and the oil phase medium environment into a single chip, allowing droplets to move between different media. Moreover, the oil-gas phase coexistence medium environment can manipulate droplets in the gas phase and serve as a reagent reaction or incubation zone in the oil phase to prevent reagent evaporation, which is beneficial for further biochemical applications on DMF chips.

[0028] like Figures 3(a) to 3(b) As shown, due to the different wetting properties of the two materials, the contact angle of the droplets in the Teflon region is higher than 120°, while the contact angle of the droplets in the PTFE film region is lower than 105°. At the coating interface, the surface tension generated by the different contact angles causes the droplets to be hindered when moving from the PTFE film to the Teflon coating, thus stopping at the boundary. Compared with the Teflon coating, the droplets tend to stay on the untreated PTFE film, while a virtual fence is formed at the boundary to prevent the droplets from moving to the non-electrode area. When the storage electrode is energized, it can be seen that the liquid can maintain the shape of the electrode in Figure 3(c). After the electrode is de-energized, as shown in Figure 3(d), the storage electrode without the virtual fence (right) becomes circular due to surface tension, and part of the liquid separates from the electrode area, while the liquid in the storage electrode with the virtual fence (indicated by the arrow) (left) remains in the electrode area, fully demonstrating the effectiveness of the virtual fence.

[0029] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the invention. Various variations can be made to the above embodiments of the present invention. That is, all simple and equivalent changes and modifications made based on the claims and description of this invention fall within the protection scope of the claims of this patent. All aspects not described in detail in this invention are conventional technical content.

Claims

1. A method for processing the surface of a DMF chip with stepped wetting characteristics, characterized in that, include: Step S1: Provide a substrate having an electrode pattern. Step S2: Adhere the hydrophobic film to the substrate with the electrode pattern; Step S3: A hydrophobic coating is formed in a local area on the surface of the hydrophobic film, wherein the hydrophobicity of the hydrophobic coating is different from that of the hydrophobic film.

2. The method for processing the surface of a DMF chip with stepped wetting characteristics according to claim 1, characterized in that, The hydrophobic membrane is made of PTFE or ETFE.

3. The method for processing the surface of a DMF chip with stepped wetting characteristics according to claim 1, characterized in that, The hydrophobic film is bonded to the substrate by an adhesive.

4. The method for processing the surface of a DMF chip with stepped wetting characteristics according to claim 1, characterized in that, The hydrophobic coating is formed by brushing, coating, or spraying.

5. The method for processing the surface of a DMF chip with stepped wetting characteristics according to claim 1, characterized in that, The hydrophobic coating is made of Teflon material.

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