Paper-based microfluidic chip, microfluidic detection system, liquid detection method and application

Abstract

This invention relates to the field of microfluidic detection technology, and discloses a paper-based microfluidic chip, a microfluidic detection system, a liquid detection method, and applications. The paper-based microfluidic chip includes a paper substrate with a detection cell. The detection cell has a first contact angle region and a second contact angle region, configured such that the contact angle of the liquid in the detection cell in the first contact angle region is greater than that in the second contact angle region. Based on the migration mechanism of color on the paper chip, this invention regulates the surface tension of the liquid to create a driving force pointing inwards towards the droplet. This causes the liquid to contract from the first contact angle region to the second contact angle region, which has a smaller contact angle, leading to the migration and enrichment of color in the second contact angle region. This improves the color and uniformity per unit area while maintaining the same concentration of the analyte, thereby increasing detection sensitivity and lowering the detection limit. Simultaneously, it increases the sampling range, improving sampling operability and detection repeatability.

Description

Technical Field

[0001] This invention relates to microfluidic detection technology, specifically to a paper-based microfluidic chip. Furthermore, it relates to a microfluidic detection system including the paper-based microfluidic chip and a liquid detection method utilizing the paper-based microfluidic chip. Moreover, this invention also relates to the application of the aforementioned paper-based microfluidic chip, microfluidic detection system, and liquid detection method. Background Technology

[0002] Microfluidic technology has broad application prospects in water quality testing, environmental monitoring, and food and medical fields due to its advantages such as rapid mass and heat transfer, high analytical efficiency, low reagent consumption, low analytical cost, environmental friendliness, and ease of integration, as well as its compatibility with small and portable testing and analysis instruments. While microfluidic technology provides a new direction for the development of testing and analysis instruments such as portable water quality analyzers, the additional fluid control requirements and the relatively large size of the testing equipment also present new challenges to achieving portability.

[0003] Paper-based microfluidic chips can effectively overcome this difficulty in fluid control. A paper-based microfluidic chip, or simply "paper chip," is a self-driven microfluidic analysis technology platform that relies on capillary forces. Compared to microfluidic chips based on other substrates, paper chips are characterized by low cost and high portability, showing great potential in water quality testing, environmental monitoring, and food and medical fields. With the continuous development and advancement of smartphone photography technology and software functions, images of the paper chip's detection cell can be captured by a mobile phone, allowing for colorimetric recognition and colorimetric analysis via built-in software. This eliminates the need for additional signal analysis equipment. The combination of paper chips and mobile phone image analysis can further promote the portability of detection equipment.

[0004] However, due to the limited reagent capacity, the inhomogeneity of paper materials, and the problems of insufficient color development, poor uniformity, and poor repeatability caused by capillary action (such as the coffee ring effect), paper chip detection suffers from low sensitivity and detection limit, as well as insufficient accuracy and repeatability. These issues have become common problems restricting the development of paper chip detection technology.

[0005] To improve the sensitivity and accuracy of paper-based microarray detection, researchers have made numerous efforts. For example, by designing bidirectional liquid inlet channels, reagents are pre-placed on both sides of the detection cell, and a dual-side injection method is adopted. This allows the reagents to enter the detection cell from both sides under the influence of the analyte liquid, reducing color diffusion towards the edge of the detection cell and thus improving color uniformity. Another example is utilizing the enrichment effect of the coffee ring effect, sampling color from the coffee rings formed after the colorimetric reaction, lowering the detection limit of the target analyte. Furthermore, existing technologies have proposed utilizing the adsorption of target analytes by noble metal nanoparticles and carbon quantum dots, loading these adsorbed substances onto the paper-based microarray for target enrichment, thereby improving detection sensitivity. However, these methods still have drawbacks: improving color uniformity can result in a more uniform color distribution, but it cannot improve detection sensitivity or lower the detection limit; quantification through coffee ring enrichment is problematic because the randomness and variability of coffee ring formation make it impossible to fix the sampling location, leading to significant color differences due to different sampling locations, which cannot guarantee the accuracy, repeatability, and operability of the detection. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of insufficient colorimetry, uneven colorimetric dispersion leading to unsatisfactory detection limits and sensitivity, and low detection accuracy and repeatability of existing colorimetric quantitative paper chips. This invention provides a paper-based microfluidic chip, a microfluidic detection system, and a liquid detection method. This paper-based microfluidic chip and liquid detection method have high detection accuracy and sensitivity, can effectively reduce the detection limit for liquids, and have good operability and repeatability.

[0007] To achieve the above objectives, the present invention provides a paper-based microfluidic chip, wherein the paper-based microfluidic chip includes a paper substrate, the paper substrate is provided with a detection pool, the detection pool has a first contact angle region and a second contact angle region, and is configured such that the contact angle of the liquid in the detection pool in the first contact angle region is greater than the contact angle in the second contact angle region.

[0008] A second aspect of the present invention provides a microfluidic detection system comprising the above-described paper-based microfluidic chip. The microfluidic detection system may include a control unit for regulating one or more of the following: ambient temperature, airflow velocity, humidity, and vacuum level in the area where the detection cell is located.

[0009] A third aspect of the present invention provides a liquid detection method, comprising: S1. introducing the liquid to be tested into the detection cell of the paper-based microfluidic chip; S2. allowing the paper-based microfluidic chip to stand for a predetermined time; and S3. performing colorimetric identification and / or colorimetric analysis on a predetermined area within the detection cell.

[0010] The fourth aspect of the present invention provides the application of the above-mentioned paper-based microfluidic chip, microfluidic detection system or liquid detection method in water quality detection, environmental detection, food and medical applications.

[0011] Through the above technical solution, the present invention, based on the migration mechanism of chromaticity on paper chips, sets up a first contact angle region and a second contact angle region with different contact angles in the detection cell, and regulates the surface tension of the liquid to give it a driving force pointing towards the interior of the droplet. As a result, the droplet contracts from the first contact angle region to the second contact angle region with a smaller contact angle, driving the chromaticity to migrate to and accumulate in the second contact angle region. Thus, under the premise of the same concentration of the target analyte, the chromaticity and uniformity per unit area are improved, the detection sensitivity is increased and the detection limit is reduced, while the sampling range is increased, improving the operability of sampling and the repeatability of detection. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of a paper-based microfluidic chip according to a preferred embodiment of the present invention;

[0013] Figure 2 This is a detection effect diagram of a paper-based microfluidic chip according to a preferred embodiment of the present invention;

[0014] Figure 3 This is a schematic diagram of the gradient distribution of different contact angle regions of the detection cell of a paper-based microfluidic chip according to a preferred embodiment of the present invention.

[0015] Figure 4 This is an exploded view of a paper-based microfluidic chip according to another preferred embodiment of the present invention;

[0016] Figure 5 It is a scatter plot showing the relationship between the color enrichment effect and the vent aperture.

[0017] Figure 6 This is a schematic diagram of a paper-based microfluidic chip according to another preferred embodiment of the present invention;

[0018] Figure 7 It is a display Figure 6 Detection results of paper-based microfluidic chips;

[0019] Figure 8 This is a comparison chart of the color enrichment effects of different paper-based microfluidic chips;

[0020] Figure 9 This is a schematic diagram of a paper-based microfluidic chip according to another preferred embodiment of the present invention;

[0021] Figure 10 This is a distribution diagram of the detection cells of a paper-based microfluidic chip according to another preferred embodiment of the present invention;

[0022] Figure 11 It is a scatter plot showing the relationship between colorimetric enrichment effect and detection time under different ambient temperatures;

[0023] Figure 12 This is an exploded view of a paper-based microfluidic chip according to Embodiment 1 of the present invention;

[0024] Figure 13 yes Figure 12 A schematic diagram of the color enrichment effect of a paper-based microfluidic chip;

[0025] Figure 14 This is a schematic diagram of the structure of a paper-based microfluidic chip according to Embodiment 2 of the present invention;

[0026] Figure 15 yes Figure 14 A schematic diagram of the color enrichment effect of a paper-based microfluidic chip;

[0027] Figure 16 and Figure 17 The figures are quantitative curves of the paper-based microfluidic chip of Embodiment 3 of the present invention.

[0028] Explanation of reference numerals in the attached figures

[0029] 1-Bottom layer; 2-Paper base layer; 21-Detection cell; 211-First contact angle region; 2111-First gradient region; 2112-Second gradient region; 212-Second contact angle region; 22-Sample loading area; 23-Diffusion channel; 24-Liquid storage tank; 25-Enrichment layer; 3-Cover layer; 31-Ventilation hole; 32-Sample loading hole; 4-Liquid. Detailed Implementation

[0030] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0031] In this invention, the endpoints of the disclosed ranges and any values ​​are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0032] Reference Figure 1As shown, the first aspect of the present invention provides a paper-based microfluidic chip, including a paper base layer 2. This paper base layer 2 can be made of paper / paper-like materials such as filter paper or cellulose membranes. As a microfluidic analysis technology platform for, for example, liquid detection, it has advantages over ordinary microfluidic chips, such as low cost, no need for external drive, good biocompatibility, and high portability. The paper-based microfluidic chip may have one or more layers of paper base layers 2, and the thickness of the paper base layer 2 is generally not particularly required. In the various embodiments shown in the accompanying drawings of the present invention, only the case of one layer of paper base layer 2 is schematically shown for the purpose of clearly illustrating the relevant structures (e.g., ...). Figure 4 and Figure 9 (As shown).

[0033] The paper-based microfluidic chip has a detection cell 21 formed on its paper substrate 2. The liquid to be detected (such as sewage, food, or pharmaceutical solutions) can be introduced into this detection cell 21 to detect / analyze information such as the composition and concentration of the liquid using methods such as colorimetric recognition and colorimetric analysis, as described later. In this invention, as... Figure 1 As shown, the detection pool 21 has a first contact angle region 211 and a second contact angle region 212, and the contact angle of the liquid to be tested that is introduced into the detection pool 21 is greater than the contact angle of the first contact angle region 211 than the contact angle of the second contact angle region 212.

[0034] Therefore, when the liquid to be tested enters the detection cell 21, the different contact angle regions within the detection cell 21 can regulate the surface tension of the liquid, giving it a driving force pointing inwards towards the droplet. This causes the liquid to contract from the first contact angle region 211 towards the second contact angle region 212, which has a smaller contact angle, leading to the migration and enrichment of color in the second contact angle region. By setting different contact angle regions, the paper-based microfluidic chip of the present invention can improve the color and uniformity per unit area while maintaining the same concentration of the target analyte, thereby increasing detection sensitivity and lowering the detection limit. Simultaneously, it increases the sampling range, improving sampling operability and detection repeatability.

[0035] It should be understood that the contact angle of the liquid to be tested in different areas of the detection cell 21 mainly refers to the contact angle of these areas with water or hydrophilic liquids. Therefore, although the paper-based microfluidic chip of the present invention does not contain the liquid to be tested, the same liquid to be tested has different wettability in different contact angle areas of its detection cell 21, thus having different contact angles. For example, the water contact angle of the first contact angle region 211 can be set to be greater than 90°, making it difficult for water or hydrophilic liquids to wet this region; while the water contact angle of the second contact angle region 212 can be set to be less than 30°. Thus, when the liquid to be tested is introduced into the detection pool 21, the relatively large contact angle of the first contact angle region 211 causes the liquid to be tested in the detection pool 21 to generate a driving force pointing towards the second contact angle region 212 during the evaporation process, causing the droplets to shrink towards the second contact angle region 212. As the water in the liquid to be tested evaporates, this shrinkage process can drive the color to migrate towards the second contact angle region 212, thereby converging in the second contact angle region 212 in the detection pool 21 to form a spot with high color intensity, which is convenient for colorimetric identification and colorimetric analysis using portable detection devices (such as smartphones with built-in software). Figure 2 The diagram illustrates the detection effect of a paper-based microfluidic chip according to the present invention. The first contact angle region 211 surrounds the second contact angle region 212 and has a water contact angle of 91°. The second contact angle region 212 is circular and has a diameter of 2 mm. It can be seen that the different contact angle regions result in better color enrichment within the detection cell, improving detection sensitivity and lowering the detection limit. Simultaneously, it increases the sampling range, improves sampling operability and detection repeatability, and facilitates colorimetric identification and colorimetric analysis.

[0036] In this invention, the first contact angle region 211 and the second contact angle region 212 can be formed in the detection pool 21 in a variety of different ways. For example, a hydrophobic material can be laid, deposited, or impregnated in the portion of the detection pool 21 near the outer peripheral edge to form the first contact angle region 211, and / or a hydrophilic material can be laid, deposited, or impregnated in the central portion of the detection pool 21 to form the second contact angle region 212. Specifically, a polytetrafluoroethylene film can be laid on the portion near the outer periphery of the detection pool 21, or a hydrophobic material such as a silanizing agent or fluorine-containing material can be deposited or impregnated on the surface of this portion. This allows a first contact angle region 211 with a large contact angle to be obtained by isolating the test solution from the paper substrate or by water-modifying the paper substrate. The central portion of the detection pool 21 can be left untreated, and a hydrophilic second contact angle region 212 can be formed by the filter paper or cellulose filter membrane of the paper substrate itself. Alternatively, the surface of this portion can be plasma-treated or coated with bovine serum albumin (BSA) solution to reduce the contact angle through surface modification, thus forming a second contact angle region 212 with a smaller contact angle.

[0037] In the detection cell 21 of the paper-based microfluidic chip of the present invention, the first contact angle region 211 can be set to a water contact angle greater than 60°, preferably greater than 90°, and more preferably greater than 120°; the second contact angle region 212 can be set to a water contact angle less than 30°, or even close to 0°. Thus, the solution in the detection cell 21 will converge towards the second contact angle region 212 during the evaporation process, causing color to accumulate in the second contact angle region 212 and form spots. This effectively detects low concentrations of the liquid to be detected, improving detection sensitivity and lowering the detection limit.

[0038] As described above, the present invention enriches color in specific areas by providing regions with different contact angles within the detection pool 21. This allows for selection of the detection sampling point as needed, the sampling point depending on the position of the second contact angle region 212 within the detection pool 21. In the illustrated preferred embodiment, the detection pool 21 is formed as a circle with a diameter of 2mm-8mm, and the second contact angle region 212 is located at the center of the detection pool 21. This allows the liquid to be detected entering the detection pool 21 to uniformly converge towards the center from all directions, improving detection accuracy and precision. In an alternative embodiment, the second contact angle region 212 may also be located at other positions within the detection pool 21, such as other intermediate portions offset from the center, with the first contact angle region 211 surrounding the second contact angle region 212. Alternatively, the detection pool 21 may be formed as a regular polygon with a circumscribed circle diameter of 2mm-8mm, and the second contact angle region 212 may be arranged at the center of this regular polygon.

[0039] Based on the migration mechanism of chromaticity within the detection cell 21, the size and degree of chromaticity enrichment of the resulting spots largely depend on the size of the second contact angle region 212. That is, when the second contact angle region 212 is smaller, the degree of chromaticity enrichment is higher, resulting in smaller spots, which is more advantageous for detecting lower concentration solutions. Therefore, the size of the second contact angle region 212 can be determined according to the size of the detection cell 21, ensuring that the area of ​​the second contact angle region 212 within the detection cell 21 does not exceed 50%, preferably not exceeding 30%. For a typical detection cell (a circle with a diameter of 2mm-8mm or a regular polygon with a circumscribed circle diameter of 2mm-8mm), the second contact angle region 212 can be set as a circular region with a diameter of 0.5mm-5mm (preferably 1mm-3mm) or a regular polygonal region with a circumscribed circle diameter of 0.5mm-5mm (preferably 1mm-3mm).

[0040] Combination Figure 1 and Figure 3As shown, to enhance the color enrichment and uniform distribution effect, the paper-based microfluidic chip of the present invention can also be provided with multiple levels of contact angle regions within the detection cell 21, such that the contact angle gradually increases from the center of the detection cell 21 to the periphery, forming multiple contact angle regions with a gradient distribution. Specifically, the first contact angle region 211 may include a first gradient region 2111 near the outer edge of the detection cell 21 and a second gradient region 2112 near the second contact angle region 212. The contact angle of the second gradient region 2112 is smaller than that of the first gradient region 2111. Thus, during the liquid evaporation process, the driving force along the direction from the edge of the detection cell 21 towards the second contact angle region 212 gradually decreases, which can gradually reduce the acceleration of the liquid moving towards the second contact angle region 212, which is beneficial to the uniform distribution of color in the second contact angle region 212. Figure 3 A schematic diagram of the gradient distribution in different contact angle regions of the detection cell is shown. It is understood that the first contact angle region 211, which includes two gradient regions, is merely exemplary, and the paper-based microfluidic chip of the present invention can have more gradient regions set in the detection cell 21.

[0041] In the paper-based microfluidic chip of the present invention, the detection cell 21 can be configured to be open to the outside, allowing volatile components in the liquid to be detected to evaporate directly through the upper opening of the detection cell 21 until the color is enriched in the second contact angle region 212. Furthermore, the present invention can control the migration direction and speed of color by controlling the confined evaporation of the liquid to be detected, further improving the color enrichment effect within the detection cell, which will be described in detail below.

[0042] Reference Figure 4As shown, a paper-based microfluidic chip according to another preferred embodiment of the present invention includes a paper base layer 2 with a detection cell (not shown) and a cover layer 3 and a bottom layer 1 respectively disposed on the upper and lower sides of the paper base layer 2. The bottom layer 1 can cover the lower side (first side) of the paper base layer 2 by means of adhesion or the like, and the cover layer 3 can also cover the upper side (second side) of the paper base layer 2 by means of adhesion or the like. The cover layer 3 and the bottom layer 1 can be formed as non-water-permeable and air-permeable portions, either entirely or only covering the portion of the detection cell. For example, the cover layer 3 and the bottom layer 1 can be made entirely of a non-water-permeable and air-permeable material, or only the portion covering the detection cell can be made of a non-water-permeable and air-permeable material. Specifically, the non-water-permeable and air-permeable material can be polyvinyl chloride, polyethylene, polypropylene, polystyrene, silicone, polytetrafluoroethylene, etc. Alternatively, the cover layer 3 and the bottom layer 1 made of a water-permeable material can be treated to be hydrophobic, such as by coating filter paper with wax and heating it to impregnate the filter paper, or by immersing the filter paper in a plastic solution dissolved in an organic solvent and drying it. The bottom layer 1 and the cover layer 3 may or may not be in contact with each other. Their areas and shapes do not need to be the same, nor do they need to be larger than the paper base layer 2, but both must completely cover the detection pool. In addition, the bottom layer 1 and the cover layer 3 can be made of transparent or opaque materials, preferably transparent materials.

[0043] The capping layer 3, covering the detection pool, has vent holes 31, allowing the liquid 4 within the detection pool to evaporate within a confined area. Thus, the vent holes 31 guide the liquid 4 within the detection pool to converge towards the vent holes 31 during evaporation, thereby enriching the color at that location. Specifically, the capping layer 3 covers the edge of the detection pool, preventing the liquid 4 from evaporating from the edge. Simultaneously, the vent holes 31 on the capping layer 3 connect the detection pool to the external space, ensuring that the liquid within the detection pool can only evaporate outwards through these vent holes 31. Therefore, during evaporation, the moisture near the vent holes 31 evaporates faster, and moisture from the edge replenishes the area near the vent holes 31, carrying color to that location and forming color-enriched spots.

[0044] In this case, the position of the vent 31 relative to the detection cell can be set such that the position of the vent 31 corresponds to the position of the aforementioned second contact angle region 212 in the detection cell (on the same vertical line), which can effectively enhance the enrichment of color in the detection cell, thereby reducing the detection limit and improving the detection sensitivity.

[0045] Therefore, the vent 31 can be configured to have the same shape and size as the second contact angle region 212, but its area and aperture are smaller than those of the second contact angle region 212. For example, the vent 31 can be a regular polygon or a circle, with a diameter or circumscribed circle diameter of 0.5mm-5mm, preferably 1mm-3mm. The vent 31 can be positioned above the center of the detection pool to ensure uniform color concentration during the liquid evaporation process within the detection pool.

[0046] In addition, the pore size of the vent 31 has a significant impact on the color enrichment effect, such as Figure 5 As shown, within a certain range (before the color reaches saturation), the smaller the aperture of the vent, the higher the color of the resulting spot. For example, when the vent aperture is 3 mm, the enriched color (distance) is only about 120; while when the vent aperture is 1.5 mm, the enriched color (distance) can reach over 200. Therefore, to achieve better color enrichment, the diameter or circumscribed circle diameter of the vent 31 can be set to 1 mm-3 mm, but this may require a longer enrichment time. To address this, liquid evaporation can be accelerated by controlling the ambient temperature, humidity, and vacuum level of the detection cell area, which will be explained later.

[0047] Figure 6 An improved embodiment of the paper-based microfluidic chip of the present invention is shown, which provides a chip structure with a gain effect. Specifically, the paper-based microfluidic chip has a liquid reservoir 24 arranged around the detection cell 21 on the paper base layer 2. When the liquid in the detection cell 21 cannot fully migrate to the vicinity of the vent hole 31 due to the excessively fast evaporation rate, colorless liquid can be added to the liquid reservoir 24 to replenish the liquid that needs to be evaporated in the detection cell 21, thereby continuing to drive the color to migrate to the vicinity of the vent hole 31. As a channel for replenishing the liquid, one or more openable and closable liquid replenishment holes can be formed on the portion of the cover layer 3 covering the liquid reservoir 204. The liquid replenishment holes can be opened when liquid replenishment is needed and closed after liquid replenishment is completed. In actual detection, the colorless liquid added to the liquid reservoir 24 can be water or a mixture of different solvents, but the added liquid needs to be able to dissolve / carry the color and not interact with other parts of the chip. The detection effect of the paper-based microfluidic chip with added liquid reservoir 24 is as follows: Figure 7 As shown; Figure 8 A comparison of the color enrichment effect of paper-based microfluidic chips with and without the liquid reservoir 24 is shown. It can be seen that by adding supplementary liquid to the liquid reservoir 24, the enrichment degree of color near the vent can be significantly improved. Under the same conditions, the chip without the liquid reservoir (chip 2) enriches the color from 48.2 to 190.3, while the chip with the liquid reservoir (chip 1) enriches the color from 49.4 to 257.4.

[0048] In some embodiments of the present invention, the liquid to be tested can be directly added to the detection pool 21 from above, for example, the aforementioned vent 31 can be used as a sample addition port. In other embodiments, a sample addition area 22 can be provided at other locations on the paper base layer 2 that are separated from the detection pool 21, and the sample addition area 22 and the detection pool 21 can be connected by a diffusion channel 23. Correspondingly, a sample addition port 32 can be provided on the cover layer 3 at the position corresponding to the sample addition area 22, such as... Figure 9 As shown. Thus, the liquid to be tested can be injected into the sample application area 22 through the sample application port 32, and under self-driving action, enter the detection cell 21 through the diffusion channel 23, where it will then undergo subsequent color enrichment and detection processes. In some embodiments of the present invention, such as... Figure 10 As shown, the detection cells 21 can be configured in multiple ways, and the number can be determined according to the number of samples to be detected and / or the number of parameters to be detected. Preferably, each detection cell 21 is equidistant from the sample application area 22, meaning that the lengths of each diffusion channel 23 are equal. Seven detection cells 21 are arranged around the central sample application area 22, so that when multiple samples need to be detected in parallel or repeated tests are required, detection can be completed in a single chip test, improving detection throughput and further reducing errors between parallel tests.

[0049] To facilitate detection, a colorimetric reagent can be pre-placed in the detection pool 21 or the aforementioned diffusion channel 23. This colorimetric reagent can make the liquid in the detection pool 21 exhibit a clearly visible color through methods such as chemical reactions, so as to perform colorimetric identification and colorimetric analysis.

[0050] A second aspect of the present invention provides a microfluidic detection system including the above-described paper-based microfluidic chip, wherein the microfluidic detection system may have related equipment used in conjunction with the above-described paper-based microfluidic chip, such as a chip carrier, a camera, etc.

[0051] Specifically, for paper-based microfluidic chips with vents, the microfluidic detection system can be configured with one or more control units for regulating one or more of the following environmental factors: ambient temperature, airflow velocity, humidity, and vacuum level in the area where the detection cell 21 is located. By adjusting these environmental factors, the evaporation rate of the liquid in the detection cell 21 can be controlled to improve the color enrichment effect. For example, a heating plate can be provided to heat the ambient temperature of the area where the detection cell 21 is located, maintaining the ambient temperature of the area where the detection cell 21 is located within a predetermined temperature range of 35°C to 45°C. Figure 11 The graphs show the relationship between chromaticity distance and detection time at ambient temperatures of 25℃, 35℃, and 45℃. It can be seen that the chromaticity enrichment rate at 35℃ and 45℃ is significantly higher than that at 25℃, while the final enrichment levels are essentially the same. Therefore, by setting appropriate control units, detection efficiency can be effectively improved.

[0052] The control unit can be configured to regulate environmental factors other than ambient temperature. For example, it may include a ventilation device that can release pressurized gas or displace the air above the detection pool 21 to accelerate the airflow around the vent 31 or reduce the humidity near the vent 31. Alternatively, the control unit may include a vacuum drying oven, in which the paper-based microfluidic chip is placed for a predetermined time during the detection process to accelerate color enrichment.

[0053] A third aspect of the present invention provides a liquid detection method based on the above-described paper-based microfluidic chip, comprising the following steps: S1. introducing the liquid to be tested into the detection cell 21 of the paper-based microfluidic chip; S2. allowing the paper-based microfluidic chip to stand for a predetermined time; and S3. performing colorimetric identification and / or colorimetric analysis on a predetermined area within the detection cell 21. The predetermined area is a color-rich region within the detection cell 21.

[0054] As mentioned above, in order to accelerate the liquid evaporation rate and improve the color enrichment effect, one or more of the ambient temperature, humidity and vacuum degree of the area where the detection cell 21 is located can be controlled in step S2 above. For example, the ambient temperature of the area where the detection cell 21 is located can be controlled to be maintained within a predetermined temperature range of 25℃-60℃.

[0055] A fourth aspect of the present invention provides applications of the aforementioned paper-based microfluidic chip, microfluidic detection system, or liquid detection method in water quality testing, environmental monitoring, and food and medical applications. For example, the aforementioned paper-based microfluidic chip, microfluidic detection system, and liquid detection method can be used to detect the content of nickel, chromium, phosphate, etc. in water, or to determine various indicators in biomedicine and to determine the compliance of various substances in food.

[0056] The paper-based microfluidic chip, microfluidic detection system, and liquid detection method of this invention can improve quantitative accuracy and lower the detection limit. Compared with the prior art, this invention: 1) enhances the color intensity of the detection cell during colorimetric quantification, deepening the color intensity that was originally only weak or even invisible, thereby lowering the detection limit of the analyte; 2) by controlling the color intensity, the color intensity on the paper chip is improved while the uniformity of distribution is increased, thereby increasing the sampling point, improving operability, and thus improving the accuracy and repeatability of detection; 3) it is achieved through a simple method of three-dimensional structural design supplemented by material surface modification, without the need for additional complex equipment, ensuring the portability of paper chip detection; 4) it is applicable to most paper chips based on colorimetric quantification, and has high feasibility and universality.

[0057] The present invention will be described in detail below through embodiments, wherein the contact angle is measured by an OCA200 fully automatic single fiber contact angle measuring instrument.

[0058] Example 1

[0059] Figure 12 The paper-based microfluidic chip shown in this embodiment includes a bottom layer 1, a paper base layer 2, and an enrichment layer 25. The paper base layer 2 has six detection cells 21 arranged in a ring array and a blank control detection cell located in the middle; the enrichment layer 25 is an enrichment carrier attached to each detection cell 21, which is located in the middle of the detection cell 21 (including but not limited to the center). The detection cells 21 are made of a material with a large contact angle (such as filter paper modified with fluorinated silane reagents or plastic sheets with a large contact angle), and the enrichment carrier is made of a material with a smaller contact angle (such as filter paper, cellulose filter membrane, or other materials treated with plasma or surface modified). The enrichment carrier is smaller than the detection cells 21 and forms a second contact angle region with a smaller contact angle, which is generally preferably circular or regular polygonal with a circumscribed circle diameter of 1mm-3mm; the other parts within the detection cells 21 form a first contact angle region with a larger contact angle. The enrichment carrier, detection cells, and bottom layer are adhered to each other by adhesive or other means.

[0060] The reacted colored solutions (e.g., a 0.1% dye solution, or a mixture of analyte solutions of different concentrations and specific reagents) were added dropwise to the detection cells arranged in a ring array. The central detection cell served as a blank control. The color enrichment effect was as follows: Figure 13 As shown in the table below. After colorimetric enrichment under specific conditions (e.g., 35℃, 10 min), the detection cell was photographed under natural light, and the RGB values ​​of the photographs were analyzed to calculate the colorimetric distance D. The colorimetric values ​​after enrichment with a 0.1% red dye solution are shown in the table below:

[0061]

[0062] Example 2

[0063] This embodiment uses a three-layer paper chip as the base chip for color enhancement and an aqueous solution with added dye as the sample. This is to illustrate that the present invention can enhance the color of all color-based solutions and to show that the color enrichment phenomenon occurs in any small area that is open to the atmosphere, without needing to be coaxial with the sample well.

[0064] The structure of a paper chip is as follows Figure 14As shown, transparent, non-breathable films are applied to the upper and lower sides of a paper substrate prepared by cutting. The upper film (cover layer) has ventilation holes at the corresponding detection cells. Sample application holes are located at the same distance from each detection cell. A dye solution is injected through the sample application holes, distributing along hydrophilic diffusion channels and reaching each detection cell 1-7. The paper chip is placed naturally (ambient temperature 26℃, humidity 70%). After a period of time (10 min–60 min), chromaticity is enriched in the ventilation hole areas of the detection cells. Over time, the chromaticity of the enriched areas becomes increasingly distinct from that of other areas. RGB values ​​of the chromaticity in different detection cells and multiple areas within the same detection cell are read, and the results are shown in the table below. Figure 15 As shown:

[0065]

[0066]

[0067] As can be seen from the table above, the R, G, and B values ​​are similar between different detection pools and between different regions of the same detection pool. Furthermore, the standard deviation of the R, G, and B values ​​between different detection pools and between different regions of the same detection pool is less than 3%, indicating that the color enhancement and liquid detection method proposed in this invention has good uniformity and repeatability.

[0068] Example 3

[0069] This example illustrates how the chromatic enrichment structure reduces the limit of nickel detection in water.

[0070] The paper-based microfluidic chip used in this embodiment has a bottom layer of transparent, non-permeable membrane. The paper base layer is a hydrophobically modified filter paper (the sample application area, diffusion channel, and detection cell remain hydrophilic, while the remaining areas are modified to be hydrophobic; the detection cell is pre-filled with a compound reagent with dimethylglyoxime as the main component, which can undergo a specific colorimetric reaction with nickel). The top layer is a transparent, non-permeable membrane with a sample application port communicating with the sample application area and a vent communicating with the detection cell. The detection cell has a diameter of 4 mm, and the vent has a pore size of 2 mm.

[0071] During testing, a nickel-containing aqueous sample is injected through the sample loading port. The sample flows along the diffusion channel to the detection cell and reacts with the compound reagent to generate a pink substance. After the chip is left to stand for a period of time, water vapor evaporates along the vent holes on the cover layer. The colorimetric components diffuse and accumulate in the color-rich area under the influence of evaporation, gradually deepening the color. After the reaction is complete, the color-rich area of ​​the paper chip is photographed, and the colorimetric information of this area is extracted using MATLAB for quantitative calculation.

[0072] according to Figure 16 and Figure 17It can be seen that the detection limit of ordinary paper chips for nickel in water is relatively high; after color enrichment, the detection limit of nickel in water is reduced to 0.1 mg / L, showing a significant reduction in the detection limit. Standard curve fitting was performed on nickel solutions within the linear range, revealing a very significant improvement in the linearity of the fitted lines.

[0073] Example 4

[0074] This embodiment illustrates the reduction in the detection limit of chromium in water resulting from a color enrichment structure.

[0075] The paper-based microfluidic chip used in this embodiment has a bottom layer of transparent, non-permeable membrane, an intermediate layer of hydrophobically modified filter paper (the sample application area, diffusion channel, and detection cell remain hydrophilic, while the remaining areas are modified to be hydrophobic; the detection cell is pre-filled with a compound reagent mainly composed of diphenylcarbazide, which can undergo a specific colorimetric reaction with chromium), and a top layer of transparent, non-permeable membrane with a sample application port communicating with the sample application area and a vent port communicating with the detection cell. The detection cell has a diameter of 4 mm, and the vent port has a diameter of 2.5 mm.

[0076] During testing, a chromium-containing aqueous sample is injected into the sample application area. The sample flows along the diffusion channel to the detection cell and reacts with the compound reagent to generate a pink substance. After the chip is left for a period of time, water vapor evaporates along the vent holes on the cover layer. Driven by evaporation, the colorimetric components diffuse and accumulate in the color-rich area, and the color gradually deepens.

[0077] The results showed that before color enrichment, the detection limit for chromium on ordinary paper chips was 0.05 mg / L; after enhanced color development based on the paper chips of this embodiment, the detection limit decreased to 0.03 mg / L.

[0078] Example 5

[0079] This example illustrates how the color enrichment structure reduces the detection limit of nitrite in water.

[0080] The paper-based microfluidic chip used in this embodiment has a bottom layer of transparent, non-permeable membrane. The paper base layer is hydrophobically modified filter paper (the sample application area, diffusion channel, and detection cell remain hydrophilic, while the remaining areas are modified to be hydrophobic; the detection cell is pre-filled with Gliese reagent, which can undergo a specific colorimetric reaction with nitrite). The top layer is a transparent, non-permeable membrane with a sample application port communicating with the sample application area and a vent hole communicating with the detection cell. The detection cell has a diameter of 5 mm, and the vent hole has a diameter of 2 mm.

[0081] During testing, a chromium-containing aqueous sample is added from the sample application area. The sample flows along the diffusion channel to the detection cell and reacts with the compound reagent to generate a pink substance. After the chip is left for a period of time, water vapor evaporates along the vent holes on the cover layer. The color-developing components diffuse and accumulate in the color-rich area under the influence of evaporation, and the color gradually deepens.

[0082] The results showed that before color enrichment, the detection limit for chromium on ordinary paper chips was 0.1 mg / L. After enhanced color development based on the paper chips of this embodiment, the detection limit decreased to 0.05 mg / L.

[0083] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various specific technical features in any suitable manner. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately. However, these simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A paper-based microfluidic chip for colorimetric detection, wherein, The paper-based microfluidic chip includes a paper base layer (2), a bottom layer (1) disposed on a first side of the paper base layer (2), and a capping layer (3) disposed on a second side of the paper base layer (2) opposite to the first side. The paper base layer (2) is provided with a detection pool (21) and a reservoir (24) arranged around the detection pool (21) for replenishing liquid to the detection pool (21). The bottom layer (1) and the capping layer (3) have non-water-permeable and air-permeable portions covering the detection pool (21), and the portion of the capping layer (3) covering the detection pool (21) forms a vent hole (31). The detection pool (21) has a first contact angle region (21). 1) and the second contact angle region (212), and configured such that the contact angle of the liquid in the detection pool (21) in the first contact angle region (211) is greater than the contact angle in the second contact angle region (212), so that the color will migrate and accumulate from the first contact angle region (211) to the second contact angle region (212) during the liquid evaporation process, wherein the position of the vent (31) on the cover layer (3) corresponds to the position of the second contact angle region (212) in the detection pool (21), and the portion of the cover layer (3) covering the liquid storage pool (24) is formed with one or more openable and closable liquid replenishment holes.

2. The paper-based microfluidic chip according to claim 1, wherein, The detection pool (21) is provided with a first contact angle region (211) formed by laying, depositing or wetting a hydrophobic material and a second contact angle region (212) formed by laying, depositing or wetting a hydrophilic material.

3. The paper-based microfluidic chip according to claim 1, wherein, The second contact angle region (212) is located in the middle part of the detection pool (21), and the first contact angle region (211) surrounds the second contact angle region (212).

4. The paper-based microfluidic chip according to claim 3, wherein, The detection pool (21) is formed as a circle with a diameter of 2mm-8mm or a regular polygon with a circumscribed circle diameter of 2mm-8mm. The second contact angle region (212) is located at the center of the detection pool (21), and / or the second contact angle region (212) is a circular region with a diameter of 0.5mm-5mm or a regular polygonal region with a circumscribed circle diameter of 0.5mm-5mm.

5. The paper-based microfluidic chip according to claim 3, wherein, The first contact angle region (211) is configured such that the contact angle of the liquid in the detection pool (21) increases from the second contact angle region (212) toward the edge of the detection pool (21).

6. The paper-based microfluidic chip according to claim 1, wherein, The water contact angle of the first contact angle region (211) is greater than 60°.

7. The paper-based microfluidic chip according to claim 6, wherein, The water contact angle of the first contact angle region (211) is greater than 90°.

8. The paper-based microfluidic chip according to claim 1, wherein, The vent (31) is a regular polygon or a circle, and its area and diameter are both smaller than the second contact angle region (212).

9. The paper-based microfluidic chip according to claim 8, wherein, The diameter or circumscribed circle diameter of the vent hole (31) is 0.5mm-5mm.

10. The paper-based microfluidic chip according to claim 9, wherein, The diameter or circumscribed circle diameter of the vent hole (31) is 1mm-3mm.

11. The paper-based microfluidic chip according to claim 1, wherein, The paper base layer (2) is also provided with a sample feeding area (22) and a diffusion channel (23) connecting the sample feeding area (22) and the detection pool (21). Furthermore, a sample feeding hole (32) is provided on the cover layer (3) at the position corresponding to the sample feeding area (22).

12. The paper-based microfluidic chip according to claim 11, wherein, The detection pool (21) and / or the diffusion channel (23) are pre-filled with colorimetric reagents.

13. A microfluidic detection system, wherein, Includes the paper-based microfluidic chip according to any one of claims 1 to 12.

14. The microfluidic detection system according to claim 13, wherein, It also includes a control unit for regulating one or more of the ambient temperature, air flow rate, humidity and vacuum level in the area where the detection pool (21) is located.

15. A method for detecting a liquid, wherein, include: S1. Pass the liquid to be tested into the detection cell (21) of the paper-based microfluidic chip according to any one of claims 1 to 12; S2. Allow the paper-based microfluidic chip to stand for a predetermined time; S3. Perform colorimetric identification and / or colorimetric analysis on the predetermined area within the detection pool (21).

16. The liquid detection method according to claim 15, wherein, In step S2, the ambient temperature of the area where the detection pool (21) is located is between 25°C and 60°C.

17. The liquid detection method according to claim 15, wherein, In step S2, the control unit is used to control one or more of the ambient temperature, humidity and vacuum level in the area where the detection pool (21) is located.

18. The application of a paper-based microfluidic chip according to any one of claims 1 to 12, a microfluidic detection system according to claim 13 or 14, or a liquid detection method according to any one of claims 15 to 17 in environmental monitoring, food and medical applications.

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