Electrophoresis microfluidic device for detecting soil nutrient ions and preparation method thereof

Abstract

The application discloses an electrophoresis microfluidic device for detecting soil nutrient ions and a preparation method thereof, which comprises a microfluidic chip and a 3D electrode assembly; the microfluidic chip comprises a chip with a microfluid channel and a microchip bottom film; the chip with the microfluid channel comprises three channels, namely, a sample inlet channel, a separation channel and an electrode channel; the 3D electrode assembly comprises an excitation electrode, a shielding electrode and a receiving electrode; the excitation electrode and the receiving electrode are respectively distributed on two sides of the end of the separation channel of the microchip and the bottom electrode at the same position of the microchip; the two side electrodes and the bottom electrode are connected through wires and connected to an excitation source; the shielding electrode comprises three parts of electrodes, namely, U-shaped electrodes distributed on two sides of the microfluid channel and a copper foil electrode crossing between the excitation electrode and the receiving electrode; the application has the advantages of simple structure, small volume of the liquid to be detected, and saving of reagents; the application can separate nutrient ions, has good separation degree, low detection limit and low excitation frequency.

Description

Technical Field

[0001] This invention relates to the field of soil testing technology, specifically to an electrophoretic microfluidic device and its preparation method for detecting soil nutrient ions. Background Technology

[0002] To increase crop yields, most agricultural workers focus on fertilization. Fertilization can effectively increase crop yields, but indiscriminate fertilization not only fails to increase yields but can also reduce them and even lead to decreased soil fertility, soil acidification, soil compaction, water pollution, and resource waste, ultimately impacting crop yields in the long term. Fertilizer input in agricultural production is high, but utilization rate is low. The excessive overall use of chemical fertilizers highlights four major problems in fertilizer application in my country: First, the average application rate per acre is too high; second, the uneven distribution of fertilization is prominent; third, the utilization rate of organic fertilizer resources is low; and fourth, the fertilization structure is unbalanced.

[0003] Agricultural workers typically rely on their experience to apply fertilizers, but soil nutrient content is influenced by many factors, making experience-based fertilization unreliable. Therefore, targeted fertilization based on the specific nutrients lacking in the soil can significantly increase crop yields. This requires precise monitoring of nutrient content in different soil areas to achieve localized fertilization, regulate plant nutrient composition, and ultimately increase crop yields and generate greater agricultural benefits.

[0004] Previously, the detection of nutrient components in these soils was mostly carried out in laboratories. The detection methods generally included atomic absorption spectrometry (AAS), inductively coupled plasma atomic emission spectrometry (ICP-AES), and ultraviolet spectroscopy. These detection methods all require a long pretreatment period, expensive experimental equipment, and operators with sufficient professional knowledge, making it difficult to complete the detection task conveniently and promptly.

[0005] To address this deficiency and achieve accurate monitoring of soil nutrients, microfluidic technology combined with capacitive coupling non-contact conductivity detection technology is an effective approach.

[0006] Microchip electrophoresis (ME) is a novel liquid-phase separation technology that uses microchannels within a microchip as separation channels and a high-voltage DC electric field as the driving force. It enables the rapid detection of nutrient ions in soil. Using microfluidic chips as an experimental platform greatly accelerates the detection speed, simplifies the detection process, reduces sample waste, and offers significant portability and low cost.

[0007] Traditional planar electrodes are typically deposited with thin metal films on the bottom or top of a microchip. This method requires specialized deposition equipment and skilled technicians, resulting in high manufacturing costs, limited mass production capabilities, and time-consuming processes. An inherent drawback of planar electrodes is that only one side is coupled to the solution, leading to poor or even undetectable detection results when soil nutrient ion content is low. Furthermore, the detection process requires excitation signals with frequencies up to several megahertz, placing higher demands on the detection circuitry and making them susceptible to electromagnetic interference, increasing noise.

[0008] Because the 3D electrode has a large coupling area with the solution, it can improve signal strength and reduce the detection limit to a certain extent. It also exhibits good spatial electric field uniformity, a large effective electrode surface area, high current capacity, and good robustness. It demonstrates good performance even when the soil nutrient ion content is low. This effectively reduces the required excitation signal frequency and the frequency requirements of the signal receiving circuit. Summary of the Invention

[0009] The present invention proposes an electrophoretic microfluidic device for soil nutrient ion detection, which can solve the problems of generally high detection limits of soil nutrient ions and excessively high excitation signal frequencies required in the detection process in the prior art.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] An electrophoretic microfluidic device for detecting soil nutrient ions includes a microfluidic chip and a 3D electrode assembly;

[0012] The microfluidic chip includes a chip with microfluidic channels and a thin film on the bottom of the microchip;

[0013] The chip with microfluidic channels includes three types of channels: a sample injection channel, a separation channel, and an electrode channel. The sample injection channel and the separation channel are cuboid in shape with the same height and width of 100 μm. The sample injection channel is 10 mm long, and the separation channel is 84 mm long. The two channels are located at a cross intersection at the midpoint of the sample injection channel and at a distance of 6 mm from the buffer tank of the separation channel, with an effective separation distance of 66 mm. Liquid storage tanks are provided at the beginning and end of the sample injection channel and the separation channel, respectively.

[0014] The 3D electrode assembly includes an excitation electrode, a shielding electrode, and a receiving electrode;

[0015] The excitation electrode and the receiving electrode are respectively distributed on both sides of the end of the microchip separation channel and at the bottom of the microchip at the same position. The electrodes on both sides of the separation channel are inclined U-shaped, with the U-shaped electrode 50 μm away from the separation channel and 1 mm in length relative to the separation channel. The electrode width is the same as that of the microfluidic channel, 100 μm. The bottom electrode is L-shaped, with an effective length of 1 mm, an effective width of 0.5 mm, and a thickness of 0.2 mm. The electrodes on both sides and the bottom electrode are connected to the excitation source via wires. The receiving electrode has the same configuration, with the excitation electrode and the receiving electrode 1 mm apart. The three parts of the receiving electrode are connected to the detection end via wires.

[0016] The shielding electrode comprises three parts: a U-shaped electrode distributed on both sides of the microfluidic channel and a copper foil electrode spanning between the excitation electrode and the receiving electrode; the U-shaped electrode has a width of 200 μm and a length of 7 mm perpendicular to the separation channel direction, and a length of 0.5 mm relative to the separation channel.

[0017] Furthermore, the overall height of the microfluidic chip is 3mm, the width is 25mm, and the length is 90mm.

[0018] Furthermore, the storage tank has a diameter of 4mm and a height of 6mm.

[0019] Furthermore, the microfluidic chip also includes a microchip mounting bracket, which includes a bracket and a fixing plate. The bracket includes a plastic plate and a support frame. The plastic plate has a microchip alignment slot and eight fixing holes. The top and bottom four holes of the microchip are used for the support frame, and the other four holes are aligned in pairs.

[0020] Furthermore, the microchip is fixed to the plastic plate using screws, nuts, and a transparent acrylic sheet, the length of which is the same as the width of the plastic plate.

[0021] Furthermore, the microfluidic chip is made of PDMS material.

[0022] Furthermore, the support frame is made of nylon plastic.

[0023] Furthermore, the 3D electrode is made of gallium metal.

[0024] On the other hand, the present invention also discloses a method for preparing an electrophoretic microfluidic device for soil nutrient ion detection, including the following microfluidic chip preparation steps:

[0025] First, a master mold with channel patterns is manufactured using photolithography. Then, PDMS and curing agent are thoroughly mixed at a mass ratio of 10:1 and degassed. The mixture is then poured onto the master mold and cured at 60°C for 12 hours. After curing, the mixture is peeled off, drilled, and cleaned. Finally, it is plasma-treated together with the prepared PDMS film and bonded to form a chip with channels.

[0026] Furthermore, the 3D electrode fabrication steps are as follows:

[0027] Gallium with a purity of 99.9999% is placed in water at 70°C and heated in a water bath until it melts. Then, the gallium liquid is injected into the electrode channel using a syringe, and wires are connected to the electrode before the gallium liquid solidifies.

[0028] As can be seen from the above technical solution, the electrophoretic microfluidic device for soil nutrient ion detection of the present invention integrates a 3D electrode in the chip, which significantly increases the sensing area of ​​the microelectrode compared with traditional bottom microelectrodes. This solves the problem of generally high detection limits in soil nutrient ion detection by traditional microfluidic chips, enabling accurate acquisition of soil nutrient ion content and understanding of the distribution of various nutrient ions in the soil. The present invention includes a microfluidic chip and a 3D electrode, wherein the microfluidic chip is used for electrophoresis, and the 3D electrode is used for the detection end. The present invention first separates nutrient ions in the soil solution using the microfluidic chip, and then achieves trace detection of soil nutrient ions by combining the 3D electrode with capacitive coupling non-contact conductivity detection technology.

[0029] Specifically, this invention features a simple structure and requires a small volume of test liquid, thus saving reagents. The microfluidic chip of this invention can separate nutrient ions with good separation accuracy. This invention has a low detection limit and a low excitation frequency for soil nutrient ions, enabling rapid and accurate detection. This invention can reduce the frequency of the excitation signal source, reduce electromagnetic interference, and lower the frequency requirements of the signal circuit. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the structure of an embodiment of the present invention;

[0031] Figure 2 This is a perspective view of the microchip structure in an embodiment of the present invention;

[0032] Figure 3 This is a top view of the 3D electrode in an embodiment of the present invention;

[0033] Figure 4 This is a schematic diagram of the 3D electrode in an embodiment of the present invention;

[0034] Among them, 1-3D electrode assembly, 2-microfluidic chip assembly, 3-microchip mounting bracket, 4-excitation source, 5-signal receiving module, 6-computer, 7-excitation electrode, 8-receiving electrode, 9-shielding electrode, 10-separation channel in microchip, 11-sample injection channel in microchip. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0036] like Figure 1 As shown, the electrophoretic microfluidic device for detecting soil nutrient ions described in this embodiment includes a microfluidic chip assembly 2 and a 3D electrode assembly 1.

[0037] The microfluidic chip assembly 2 includes a chip with microfluidic channels, a microchip bottom film, and a microchip mounting bracket 3. The 3D electrode assembly 1 includes an excitation electrode 7, a shielding electrode 9, and a receiving electrode 8.

[0038] The chip with microfluidic channels includes three types of channels: a sample injection channel, a separation channel, and an electrode channel. The sample injection channel 11 and the separation channel 10 are cuboid in shape, with the same height and width of 100 μm. The sample injection channel is 10 mm long, and the separation channel is 84 mm long. They intersect at the midpoint of the sample injection channel and 6 mm from the buffer solution reservoir of the separation channel, resulting in an effective separation distance (from the cross-section to the electrode) of 66 mm. Four reservoirs, each 4 mm in diameter and 6 mm high, are located at the beginning and end of the microchannels, each capable of holding approximately 40 μL of solution. The overall chip height is 3 mm, width is 25 mm, and length is 90 mm.

[0039] The microchip mounting bracket includes a bracket and a fixing plate. The bracket consists of a plastic plate and a support frame. The plastic plate has a microchip alignment slot and eight fixing holes. Four holes at the top and bottom of the microchip are used for the support frame, and the other four holes are aligned in pairs. The transparent acrylic plate is fixed with screws and nuts to secure the microchip. The width of the plastic plate is slightly wider than the width of the microchip, and the length of the acrylic plate is the same as the width of the plastic plate.

[0040] The 3D electrode assembly includes an excitation electrode, a shielding electrode, and a receiving electrode. The excitation and receiving electrodes consist of three parts: electrodes located on both sides of the end of the microchip separation channel and on the bottom of the microchip at the same position. The electrodes on both sides of the separation channel are inclined U-shaped, with a distance of 50 μm from the separation channel and a length of 1 mm relative to the separation channel. The electrode width is the same as the microfluidic channel, 100 μm. The bottom electrode is L-shaped, with an effective length of 1 mm, an effective width of 0.5 mm, and a thickness of 0.2 mm. The two side electrodes and the bottom electrode are connected to the excitation source 4 via wires. The receiving electrode has the same configuration, with the excitation and receiving electrodes 1 mm apart. The three parts of the receiving electrode are connected to the detection end via wires.

[0041] The shielding electrode comprises three parts: a U-shaped electrode distributed on both sides of the microfluidic channel, and a copper foil electrode spanning between the excitation electrode and the receiving electrode. The U-shaped electrode has a width of 200 μm and a length of 7 mm perpendicular to the separation channel direction, and a length of 0.5 mm relative to the separation channel.

[0042] The microfluidic chip manufacturing process is as follows: First, a master mold with channel patterns is manufactured by photolithography; then, PDMS and curing agent are thoroughly mixed at a mass ratio of 10:1 and degassed, and then poured onto the master mold and cured at 60°C for 12 hours. After curing, the chip is peeled off, punched, and cleaned. After plasma treatment with the prepared PDMS film, the chip with channels is formed.

[0043] The 3D electrode fabrication process involves immersing gallium (99.9999% purity) in a 70°C water bath and heating it until it melts. The molten gallium is then injected into the electrode channel using a syringe. Wires are then connected to the electrode before the molten gallium solidifies.

[0044] The microfluidic chip is made of PDMS material, the support frame is made of nylon plastic, and the 3D electrode is made of gallium metal.

[0045] In summary, this invention comprises a microfluidic chip and a 3D electrode. The microfluidic chip is used for electrophoresis, and the 3D electrode is used for detection. This invention first separates nutrient molecules in the soil solution using the microfluidic chip, and then uses the 3D electrode combined with capacitive coupling non-contact conductivity detection technology to achieve trace detection of soil nutrient molecules.

[0046] This invention features a simple structure and requires a small volume of test liquid, thus saving reagents. The microfluidic chip of this invention can separate nutrient ions with good separation accuracy. This invention has a low detection limit for soil nutrient ions, enabling rapid and accurate detection. This invention can reduce the frequency of the excitation signal source, decrease electromagnetic interference, and reduce the frequency requirements of the signal circuit.

[0047] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An electrophoresis microfluidic device for soil nutrient ion detection, comprising a microfluidic chip, characterized in that, Also including 3D electrode assembly; The microfluidic chip includes a chip with microfluidic channels and a microchip bottom film; The chip with microfluidic channels includes three channels, a sample injection channel, a separation channel and an electrode channel; the sample injection channel and the separation channel are cuboids with the same height of 100 um and width of 100 um, the sample injection channel has a length of 10 mm, the separation channel has a length of 84 mm, and the two are at a cross position at the midpoint of the sample injection channel and 6 mm away from the buffer tank of the separation channel, and the effective separation distance is 66 mm; reservoirs are arranged at the beginning and end of the sample injection channel and the separation channel, respectively; The 3D electrode assembly includes an excitation electrode, a shielding electrode and a receiving electrode; The excitation electrode and the receiving electrode are respectively distributed on both sides of the end of the microchip separation channel and on the bottom electrode of the microchip at the same position, wherein the electrodes on both sides of the separation channel are inclined U-shaped, the U-shaped electrode is 50 um away from the separation channel, and the length relative to the separation channel is 1 mm, and the electrode width is the same as the microfluidic channel, which is 100 um; the bottom electrode is L-shaped, the effective length is 1 mm, the effective width is 0.5 mm, and the thickness is 0.2 mm; the two side electrodes are connected to the excitation source through wires; the receiving electrode has the same configuration, the excitation electrode and the receiving electrode are 1 mm apart, and the three parts of the receiving electrode are connected by wires and connected to the detection end; The shielding electrode includes three electrodes, U-shaped electrodes distributed on both sides of the microfluidic channel and a copper foil electrode across between the excitation electrode and the receiving electrode; the width of the U-shaped electrode is 200 um and the length perpendicular to the direction of the separation channel is 7 mm, and the length relative to the separation channel is 0.5 mm; The 3D electrode adopts metal gallium material; The preparation steps of the microfluidic chip are as follows: First, a master mold with channel pattern is manufactured by photolithography process; then PDMS and curing agent are mixed thoroughly with mass ratio of 10:1 and degassed, and then poured into the master mold, and cured at 60 o C, 12 hours. After curing, stripping, punching, cleaning, and plasma treatment with the prepared PDMS film, the chip with channels is formed. The preparation steps of the 3D electrode are as follows: Put the gallium with a purity of 99.9999% into water at 70℃ for water bath heating until it melts, then inject the gallium liquid into the electrode channel through a syringe, and connect the wires into the electrode before the gallium liquid solidifies.

2. The electrophoresis microfluidic device for soil nutrient ion detection according to claim 1, characterized in that: The overall height of the microfluidic chip is 3 mm, the width is 25 mm, and the length is 90 mm.

3. The electrophoresis microfluidic device for soil nutrient ion detection according to claim 2, characterized in that: The reservoir has a diameter of 4 mm and a height of 6 mm.

4. The electrophoresis microfluidic device for soil nutrient ion detection according to claim 1, characterized in that: The microfluidic chip further includes a microchip mounting support, the microchip mounting support includes a support and a fixing plate, the support includes a plastic plate and a support frame, the plastic plate is provided with a microchip alignment slot and eight fixing holes, the top and bottom four holes of the microchip are used for the support frame, and the other four holes are aligned in pairs.

5. The electrophoresis microfluidic device for soil nutrient ion detection according to claim 4, characterized in that: The microchip is fixed on the plastic plate by screws, nuts and transparent acrylic plates, and the length of the acrylic plate is the same as the width of the plastic plate.

6. The electrophoresis microfluidic device for soil nutrient ion detection according to claim 1, characterized in that, The microfluidic chip adopts PDMS material.

7. The electrophoresis microfluidic device for soil nutrient ion detection according to claim 1, wherein, The support frame adopts nylon plastic material.

8. A method for fabricating an electrophoresis microfluidic device for soil nutrient ion detection, characterized in that, The preparation steps of the microfluidic chip are as follows: First, a master mold with channel pattern is manufactured by photolithography process; then PDMS and curing agent are mixed thoroughly with mass ratio of 10:1 and degassed, and then poured into the master mold, and cured at 60 o C, 12 hours. After curing, stripping, punching, cleaning, and plasma treatment with the prepared PDMS film, the chip with channels is formed. The preparation steps of the 3D electrode are as follows: Put the gallium with a purity of 99.9999% into water at 70℃ for water bath heating until it melts, then inject the gallium liquid into the electrode channel through a syringe, and connect the wires into the electrode before the gallium liquid solidifies.

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