Three-electrode microfluidic dielectric measurement system for microfluidic chip and preparation method thereof

Abstract

The present invention relates to a three-electrode microfluidic dielectric measurement system for a microfluidic chip and a preparation method thereof, and belongs to the field of electrical technology. The system comprises a microfluidic layer, an upper conductive glass and a lower conductive glass; the upper conductive glass and the lower conductive glass are respectively located on both sides of the microfluidic layer, and the conductive surfaces of the upper conductive glass and the lower conductive glass are bonded toward the microfluidic layer; the conductive surface of the upper conductive glass is etched to make the high-voltage electrode among the three electrodes; the conductive surface of the lower conductive glass is etched to make the low-voltage electrode and the shielding electrode among the three electrodes; the present invention realizes accurate measurement of the dielectric parameters of the microfluid in the microfluidic chip, and does not affect the microscopic observation of the fluid state in the microchannel.

Description

Technical Field

[0001] The invention belongs to the field of electrical technology and relates to a three-electrode microfluidic dielectric measurement system for a microfluidic chip and a preparation method thereof. Specifically, the invention adopts indium tin oxide transparent conductive glass and polydimethylsiloxane (PDMS) to make a microfluidic chip, and etches the upper conductive glass and the lower conductive glass of the microfluidic chip to make a transparent three-electrode system, thereby realizing accurate measurement of the dielectric parameters of a microfluid in the microfluidic chip without affecting a synchronous microscopic observation system of the microfluid. Background Art

[0002] Microfluidics technology uses microchannels with a width of tens to hundreds of microns to manipulate or process tiny volumes of fluids. It has the advantages of low sample consumption, fast reaction speed, and the ability to reflect the microscale behavior of fluids. When using microfluidic chips to study trace amounts of liquid dielectrics, it is usually necessary to simultaneously measure the dielectric-related parameters of the microfluidic while observing the microfluid under a microscope to reflect the changes that occur inside the microfluid or at the interface under different experimental conditions. The dielectric-related parameters of liquid dielectrics mainly include insulation resistance, impedance spectrum, dielectric spectrum, etc.

[0003] The existing microfluidic chips that can perform electrical measurements are usually planar electrode structures composed of two electrodes, that is, in the same test above or below the microchannel layer, positive electrodes and negative electrodes are made by metal deposition, which are used to apply measurement voltage excitation and collect response current. Unlike electrical measurements at a macro scale, on a microfluidic chip, the microfluid (test object) is surrounded by other solid materials of the microfluidic chip, and the space occupied by the microfluid is much smaller than the surrounding materials. Under the configuration of such planar electrodes, although the position of the electrodes can avoid the optical path of the microfluid without affecting the observation of the microfluid, the electric field distribution between the two electrodes is more divergent and not limited to the measurement object. In addition, due to processing technology limitations, both the positive and negative electrodes cannot directly contact the microfluid, and a thin layer of microfluidic chip material is usually separated between them. This results in that the dielectric data measured by such a two-electrode system is bound to be significantly affected by the surrounding structure of the microfluid and the dielectric properties of the material, resulting in a large measurement error.

[0004] At conventional macroscopic scales, the three-electrode method is usually used to measure the insulation resistance, dielectric spectrum, etc. of the medium. Currently, ASTMD 257-2014 and IEC-60093-1980 (the equivalent national standard is GB / T 1410-2006) regulate the three-electrode method. The measurement principle is to use high and low voltage electrodes to apply voltage to both ends of the test piece, measure the current flowing through the test piece, and calculate the dielectric parameters of the test piece. At the same time, a grounded shielding electrode in contact with the surface of the test piece is set outside the low voltage electrode as the third electrode to directly introduce the surface current of the test piece into the earth to eliminate the influence of surface current and edge effect on the measurement results.

[0005] Based on the above-mentioned macroscopic large-scale three-electrode concept, a micro three-electrode system on a chip can be designed to solve the dielectric measurement error problem of existing microfluidic chips. However, when measuring the dielectric parameters of the fluid inside the microchannel, a microscope is usually required to observe the condition of the fluid inside the microchannel. Although the three-electrode system has a high test accuracy, the spatial position of the upper and lower electrodes will cover most of the test samples. In this case, the metal electrodes used in the existing microfluidic chip will block the light path within the microfluidic range and in the observation direction of the microfluidic chip, which will lead to the inability to synchronously observe the microfluidic. This shows that the existing scheme has always been difficult to simultaneously achieve the two needs of accurately measuring the dielectric parameters of the microfluidic and conducting synchronous observation of the microfluidic.

[0006] In addition, although the three electrodes in the present invention and the three electrodes in the field of electrochemistry have the same name, their concepts are completely different. Summary of the invention

[0007] In view of this, the purpose of the present invention is to provide a microfluidic chip made of indium tin oxide transparent conductive glass and polydimethylsiloxane (PDMS), and to etch a transparent three-electrode system on the upper conductive glass and the lower conductive glass of the microfluidic chip, so as to accurately measure the dielectric parameters of the microfluid in the microfluidic chip without affecting the synchronous microscopic observation of the microfluid state in the microchannel.

[0008] In order to achieve the above object, the present invention provides the following technical solutions:

[0009] A three-electrode microfluidic dielectric measurement system for a microfluidic chip, the system comprising a microfluidic channel layer, an upper conductive glass, and a lower conductive glass;

[0010] The upper conductive glass and the lower conductive glass are respectively located on both sides of the microchannel layer, and the conductive surfaces of the upper conductive glass and the lower conductive glass are both bonded toward the microchannel layer;

[0011] The conductive surface of the upper conductive glass is etched to form the high voltage electrode among the three electrodes;

[0012] The conductive surface of the lower conductive glass is used to etch the low-voltage electrode and the shielding electrode among the three electrodes;

[0013] The high voltage electrode, the low voltage electrode and the shielding electrode among the three electrodes are all in contact with the microfluidic channel.

[0014] Optionally, the upper conductive glass and the lower conductive glass are transparent indium tin oxide conductive glass.

[0015] Optionally, the upper conductive glass is provided with a mask of a high-voltage electrode pattern; and the lower conductive glass is provided with a mask of a low-voltage electrode pattern and a shielding electrode pattern.

[0016] A method for preparing a three-electrode microfluidic dielectric measurement system for a microfluidic chip, the method comprising the following steps:

[0017] S1 First, the microfluidic chip with a micro three-electrode system is divided into three layers. After each layer is prepared, it is bonded and packaged. The middle layer of the microfluidic chip is a microfluidic layer made of polydimethylsiloxane (PDMS). The upper and lower layers of the microfluidic layer are two conductive glass layers. The conductive surfaces of the two layers of conductive glass are bonded toward the microfluidic layer. The high-voltage electrode of the three electrodes is etched on the conductive surface of the upper conductive glass. The low-voltage electrode and the shielding electrode of the three electrodes are etched on the conductive surface of the lower conductive glass. The three electrodes are in contact with the microfluidic channel.

[0018] S2, according to the length and width of the microfluidic chip to be prepared, cut two pieces of glass of corresponding sizes from the conductive glass as the upper bottom surface and the lower bottom surface of the microfluidic chip;

[0019] S3 uses a physical wiping method to clean the upper and lower bottom surfaces scratched by S2, and uses acetone and alcohol cotton balls to wipe the conductive surfaces of the upper and lower bottom surfaces in turn; uses deionized water to rinse the conductive surface, and bakes it on a hot plate at 85°C to remove surface moisture and improve the surface adhesion to the photoresist;

[0020] S4: For the upper conductive glass, a mask of a high voltage electrode pattern is made; for the lower conductive glass, a mask of a low voltage electrode pattern and a shielding electrode pattern is made;

[0021] S5 uses a spin coating method to coat the conductive surface of the upper conductive glass and the conductive surface of the lower conductive glass with BP-212 positive photoresist respectively;

[0022] S6 places the upper conductive glass and the lower conductive glass treated with glue in S5 on UV exposure machines respectively, and uses the mask pattern prepared in S4 to perform contact exposure on the photoresist on the surface of the upper conductive glass and the lower conductive glass respectively, so that a chemical reaction occurs at the irradiated place of the photoresist, thereby changing the solubility of the photoresist in the developer;

[0023] S7: developing the exposed upper conductive glass and the lower conductive glass in a NaOH solution to remove the photoresist except for the microelectrode part, so as to expose the part to be etched;

[0024] S8: Place the upper conductive glass and the lower conductive glass on a hot plate at 85°C and bake for 30 minutes to remove the residual solvent and moisture after development, so that the film is completely cured and the adhesion between the film and the substrate is strengthened to prevent it from falling off during corrosion;

[0025] S9 uses HCl, HNO3 or HF solution to corrode the upper conductive glass and the lower conductive glass treated in S8, so that only the electrode pattern with the photoresist adhered is left on the conductive surface of the upper conductive glass and the lower conductive glass;

[0026] S10 removes the photoresist on the surface of the electrode pattern to obtain an upper conductive glass and a lower conductive glass each containing only the electrode pattern;

[0027] S11: uniformly mixing the main agent and curing agent required for preparing PDMS in a mass ratio of 10:1 in a glass container, stirring the mixture sufficiently, and performing vacuum exhaust treatment;

[0028] S12 cuts and manufactures a silicon wafer mold of the same size as the microfluidic layer, cleans the mold surface with anhydrous ethanol and dries it; uses DUPONOLWAQ 5% isopropanol solution as a release agent and sprays it on the mold surface; uses a spinner to spin-coat PDMS on the surface of the silicon wafer mold; after spin coating, puts it in a vacuum drying oven at 100°C for curing and demolding to prepare a PDMS film; and controls the spin coating process parameters to prepare PDMS films of different thicknesses and hardnesses;

[0029] S13 uses an ultraviolet laser cutting machine to cut a desired microchannel structure on the PDMS film prepared in S12;

[0030] S14: placing the upper conductive glass, the lower conductive glass and the PDMS film together in a plasma cleaning machine, and opening the plasma cleaning machine for cleaning for 3 minutes; after the cleaning is completed, taking them out and preparing for bonding;

[0031] S15 places the upper conductive glass and the microfluidic layer under a microscope, adjusts the focal length and viewing distance of the microscope, aligns the central axis of the upper electrode and the microfluidic channel, and then slowly bonds the microfluidic layer to the upper conductive glass to complete the bonding; similarly, bonds the lower conductive glass to the microfluidic layer;

[0032] S16 presses the bonded microfluidic chip to ensure that it is fastened together, thereby packaging the microfluidic chip into one piece.

[0033] Optionally, the spin coating process parameters include spin coating speed, spin coating acceleration, spin coating time, vacuum drying temperature and vacuum drying time.

[0034] Optionally, after S16, the step further includes: placing the entire microfluidic chip in a constant temperature oven, setting the temperature to 85° C., and baking for 15 minutes to accelerate the packaging of the microfluidic chip.

[0035] The beneficial effects of the present invention are as follows: it solves the problem of large measurement error in the two-electrode design adopted by the existing microfluidic chip when measuring the dielectric parameters of the microfluid, and the problem of blocking the light path when the three-electrode system is made by the existing microfluidic metal electrode deposition method. A solution is proposed for making a microfluidic chip by using indium tin oxide transparent conductive glass and polydimethylsiloxane (PDMS), and etching the upper conductive glass and the lower conductive glass of the microfluidic chip to make a transparent three-electrode system, thereby achieving accurate measurement of the dielectric parameters of the microfluidic in the microfluidic chip without affecting the microscopic observation of the fluid state in the microchannel.

[0036] The method proposed in the present invention can infer the individual dielectric variables of each medium in the multi-medium composite insulation based on the overall dielectric response, which can make up for the problem that the existing dielectric response technology can only obtain the overall dielectric response in application but cannot know the individual dielectric characteristics of each part.

[0037] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0039] Figure 1 It is a schematic diagram of the structure of the present invention. DETAILED DESCRIPTION

[0040] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0041] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0042] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0043] The present invention comprises the following steps:

[0044] S1 First, the microfluidic chip with a micro three-electrode system is divided into three layers. After each layer is prepared, it is bonded and packaged. The middle layer of the microfluidic chip is a microfluidic layer made of PDMS. The upper and lower layers of the microfluidic layer are two conductive glass layers (hereinafter referred to as "upper conductive glass and lower conductive glass", respectively). The conductive surfaces of the two layers of conductive glass are bonded toward the microfluidic layer. The high-voltage electrode of the three electrodes is etched on the conductive surface of the upper conductive glass. The low-voltage electrode and the shielding electrode of the three electrodes are etched on the conductive surface of the lower conductive glass. The three electrodes are in direct contact with the microfluidic channel. The overall structure is as follows: Figure 1 shown.

[0045] S2, according to the length and width of the microfluidic chip to be prepared, two pieces of glass of corresponding sizes are cut from commercially produced indium tin oxide transparent conductive glass as the upper and lower bottom surfaces of the microfluidic chip;

[0046] S3 uses a physical wiping method to clean the conductive surface of the microfluidic chip scratched by S2, using acetone and alcohol cotton balls to wipe the conductive surface in turn; rinse the conductive surface with deionized water, and bake it on a hot plate at 85°C to remove surface moisture, so as to improve the cleanliness of the surface and enhance the adhesion of the surface to the photoresist;

[0047] S4 For upper conductive glass, follow Figure 1 Make a mask according to the "high voltage electrode pattern" in the figure. For the lower conductive glass, Figure 1 The "low voltage electrode pattern" and "shielding electrode pattern" are used to make masks;

[0048] S5 uses a spin coating method to coat a layer of BP-212 positive photoresist on the conductive surface of the upper conductive glass and the conductive surface of the lower conductive glass respectively;

[0049] S6 places the upper conductive glass and the lower conductive glass treated with glue in S5 on UV exposure machines respectively, and uses the mask pattern prepared in S4 to perform contact exposure on the photoresist on the surface of the upper conductive glass and the lower conductive glass respectively, so that a chemical reaction occurs at the irradiated part of the photoresist, thereby changing the solubility of the photoresist in the developer;

[0050] S7: developing the exposed upper conductive glass and the lower conductive glass in a NaOH solution to remove the photoresist except for the microelectrode part, so as to expose the part to be etched;

[0051] S8: Place the upper conductive glass and the lower conductive glass on a hot plate at 85°C and bake for 30 minutes to remove the residual solvent and moisture after development, so that the film is completely cured and the adhesion between the film and the substrate is strengthened to prevent it from falling off during corrosion;

[0052] S9: The upper conductive glass and the lower conductive glass processed in step S8 are corroded by using HCl / HNO3 / HF solution, so that only the electrode pattern with the photoresist adhered is left on the conductive surface of the upper conductive glass and the lower conductive glass;

[0053] S10 removes the photoresist on the surface of the electrode pattern to obtain an upper conductive glass and a lower conductive glass respectively containing only the electrode pattern;

[0054] S11: uniformly mixing the main agent and curing agent required for preparing PDMS in a mass ratio of 10:1 in a glass container, stirring the mixture sufficiently, and performing vacuum exhaust treatment;

[0055] S12 cuts and produces a silicon wafer mold of the same size as the microfluidic layer, cleans the mold surface with anhydrous ethanol and dries it; uses DUPONOLWAQ 5% isopropanol solution as a release agent and sprays it on the mold surface. Use a spinner to spin-coat PDMS on the surface of the silicon wafer mold; after spin coating, put it in a vacuum drying oven at 100°C for curing and demolding to prepare a PDMS film; by controlling the spin coating process parameters (spin coating speed, spin coating acceleration, spin coating time, vacuum drying temperature, vacuum drying time), PDMS films of different thicknesses and hardnesses can be prepared;

[0056] S13 uses an ultraviolet laser cutting machine to cut a desired microchannel structure on the PDMS film prepared in S12;

[0057] S14: placing the upper conductive glass, the lower conductive glass and the PDMS film together in a plasma cleaning machine, and opening the plasma cleaning machine for cleaning for 3 minutes; after the cleaning is completed, taking them out and preparing for bonding;

[0058] S15 places the upper conductive glass and the microfluidic layer under a microscope, and adjusts the focus and viewing distance of the microscope, aligns the central axis of the upper electrode and the microfluidic channel, and then slowly fits the microfluidic layer to the upper conductive glass to complete the bonding; then, the lower conductive glass is bonded to the first two parts in a similar manner;

[0059] S16 gently presses the bonded microfluidic chip to ensure that it is completely and tightly fastened. Then the microfluidic chip is placed in a constant temperature oven, the temperature is set to 85°C, and baked for 15 minutes to accelerate the packaging of the microfluidic chip into one.

[0060] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A three-electrode microfluidic dielectric measurement system for a microfluidic chip, characterized in that: The system includes a microfluidic layer, an upper conductive glass, and a lower conductive glass; The upper conductive glass and the lower conductive glass are respectively located on both sides of the microchannel layer, and the conductive surfaces of the upper conductive glass and the lower conductive glass are both bonded toward the microchannel layer; The conductive surface of the upper conductive glass is etched to form the high voltage electrode among the three electrodes; The conductive surface of the lower conductive glass is used to etch the low-voltage electrode and the shielding electrode among the three electrodes; The high voltage electrode, the low voltage electrode and the shielding electrode among the three electrodes are all in contact with the microfluidic channel; The upper conductive glass and the lower conductive glass are transparent indium tin oxide conductive glass; The upper conductive glass is provided with a mask of a high-voltage electrode pattern; the lower conductive glass is provided with a mask of a low-voltage electrode pattern and a shielding electrode pattern.

2. A method for preparing a three-electrode microfluidic dielectric measurement system for a microfluidic chip, characterized in that: The method comprises the following steps: S1 First, the microfluidic chip with a micro three-electrode system is divided into three layers. After each layer is prepared, it is bonded and packaged. The middle layer of the microfluidic chip is a microfluidic layer made of polydimethylsiloxane (PDMS). The upper and lower layers of the microfluidic layer are two conductive glass layers. The conductive surfaces of the two layers of conductive glass are bonded toward the microfluidic layer. The high-voltage electrode of the three electrodes is etched on the conductive surface of the upper conductive glass. The low-voltage electrode and the shielding electrode of the three electrodes are etched on the conductive surface of the lower conductive glass. The three electrodes are in contact with the microfluidic channel. S2, according to the length and width of the microfluidic chip to be prepared, cut two pieces of glass of corresponding sizes from the conductive glass as the upper bottom surface and the lower bottom surface of the microfluidic chip; S3 uses a physical wiping method to clean the upper and lower bottom surfaces scratched by S2, and uses acetone and alcohol cotton balls to wipe the conductive surfaces of the upper and lower bottom surfaces in turn; uses deionized water to rinse the conductive surface, and bakes it on a hot plate at 85°C to remove surface moisture and improve the surface adhesion to the photoresist; S4: For the upper conductive glass, a mask of a high voltage electrode pattern is made; for the lower conductive glass, a mask of a low voltage electrode pattern and a shielding electrode pattern is made; S5 uses a spin coating method to coat the conductive surface of the upper conductive glass and the conductive surface of the lower conductive glass with BP-212 positive photoresist respectively; S6 places the upper conductive glass and the lower conductive glass treated with glue in S5 on UV exposure machines respectively, and uses the mask pattern prepared in S4 to perform contact exposure on the photoresist on the surface of the upper conductive glass and the lower conductive glass respectively, so that a chemical reaction occurs at the irradiated place of the photoresist, thereby changing the solubility of the photoresist in the developer; S7: developing the exposed upper conductive glass and the lower conductive glass in a NaOH solution to remove the photoresist except for the microelectrode part, so as to expose the part to be etched; S8: Place the upper conductive glass and the lower conductive glass on a hot plate at 85°C and bake for 30 minutes to remove the residual solvent and moisture after development, so that the film is completely cured and the adhesion between the film and the substrate is strengthened to prevent it from falling off during corrosion; S9 uses HCl, HNO3 or HF solution to corrode the upper conductive glass and the lower conductive glass treated in S8, so that only the electrode pattern with the photoresist adhered is left on the conductive surface of the upper conductive glass and the lower conductive glass; S10 removes the photoresist on the surface of the electrode pattern to obtain an upper conductive glass and a lower conductive glass each containing only the electrode pattern; S11: uniformly mixing the main agent and curing agent required for preparing PDMS in a mass ratio of 10:1 in a glass container, stirring the mixture sufficiently, and performing vacuum exhaust treatment; S12 cuts and manufactures a silicon wafer mold of the same size as the microfluidic layer, cleans the mold surface with anhydrous ethanol and dries it; uses DUPONOLWAQ 5% isopropanol solution as a release agent and sprays it on the mold surface; uses a spinner to spin-coat PDMS on the surface of the silicon wafer mold; after spin coating, puts it in a vacuum drying oven at 100°C for curing and demolding to prepare a PDMS film; and controls the spin coating process parameters to prepare PDMS films of different thicknesses and hardnesses; S13 uses an ultraviolet laser cutting machine to cut a desired microchannel structure on the PDMS film prepared in S12; S14: placing the upper conductive glass, the lower conductive glass and the PDMS film together in a plasma cleaning machine, and opening the plasma cleaning machine for cleaning for 3 minutes; after the cleaning is completed, taking them out and preparing for bonding; S15 places the upper conductive glass and the microfluidic layer under a microscope, adjusts the focal length and viewing distance of the microscope, aligns the central axis of the upper electrode and the microfluidic channel, and then slowly bonds the microfluidic layer to the upper conductive glass to complete the bonding; similarly, bonds the lower conductive glass to the microfluidic layer; S16 presses the bonded microfluidic chip to ensure that it is fastened together, thereby packaging the microfluidic chip into one piece; The spin coating process parameters include spin coating speed, spin coating acceleration, spin coating time, vacuum drying temperature and vacuum drying time; After S16, the method further includes: placing the entire microfluidic chip in a constant temperature oven, setting the temperature to 85° C., and baking for 15 minutes to accelerate the packaging of the microfluidic chip.

Images