Microfluidic Devices

Abstract

To provide a thin micro flow channel device capable of stable measurement.SOLUTION: A micro flow channel device using a porous base material is provided. The micro flow channel device includes a flow channel region using the porous base material. A part of the flow channel region has a region A in which an ion selective component exists in a hole in the porous base material. In the region A, the ion selective component exists in the hole on one surface X side of the porous base material and a vacancy exists on the other surface Y side. On a surface on the surface X side of the region A, a working electrode is provided so as to be at least partially overlapped with the ion selective component. In a region B other than the region A in the flow channel region, a reference electrode is provided. The region A and the region B are formed on the same porous base material.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a microchannel device in which electrodes are formed using channels in a porous substrate. [Background technology]

[0002] In recent years, the development of microfluidic devices that utilize micro-sized fine channels to efficiently perform biochemical analysis (microvolumes, rapid, and simple) on a single chip has attracted attention in a wide range of fields. These fields include not only biochemical research but also medicine, drug discovery, healthcare, the environment, and food. Paper-based paper microanalysis chips offer many advantages over conventional devices, including light weight, low cost, no power supply required, and easy disposability. Therefore, they are expected to be used in medical activities in developing countries and remote areas with limited medical facilities, as well as at disaster sites, and as testing devices in airports and other locations where the spread of infectious diseases must be prevented at the border. Furthermore, because they are inexpensive and easy to use, they are attracting attention as healthcare devices that can manage and monitor one's own health status.

[0003] As an example of a paper microanalysis chip, Patent Document 1 uses two paper substrates with electrodes printed on their surfaces, sandwiches an ion-selective membrane between them, and dispenses a predetermined solution into each paper substrate, forming a structure equivalent to an ion-selective electrode and a reference electrode with an internal liquid. This structure enables the ion electrode method to be performed, and the ion concentration of a sample can be measured. Furthermore, Non-Patent Document 1 describes a method for forming an ion selective electrode and a reference electrode on a single paper substrate, and the ion concentration of a sample can be measured using the ion electrode method. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] US Patent Application Publication No. 2016 / 033438 [Non-patent literature]

[0005] [Non-Patent Document 1] Nipapan Ruecha, Orawon Chailapakul, Koji Suzuki and Daniel Chitterio “Fully Inkjet-Printed Paper-Based Potentiometric Ion-Sensing Devices” Analytical chemistry August 29, 2017 Published, 89, pp.10608-10616 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the method described in Patent Document 1, a layer of porous substrate is placed between the working electrode and the ion-selective membrane, and when a liquid that serves as an internal liquid is filled in, bubbles may form at the electrode interface, potentially causing instability in the measured values. Furthermore, since the ion-selective membrane is sandwiched between two sheets of paper substrate, the thickness of the analysis chip needs to be the thickness of two porous substrates in addition to the electrodes and ion-selective membrane. Furthermore, in the method described in Non-Patent Document 1, a sufficient amount of sample cannot penetrate into the area of ​​the paper substrate where the ion-selective membrane is formed, which results in an insufficient contact area between the sample and the ion-selective membrane, making the measurement unstable and potentially affecting measurement accuracy. The objective of one aspect of the present disclosure is to stabilize measurements by contacting the working electrode with the ion-selective membrane, to reduce size by forming all electrodes on a single porous substrate, and to stabilize measurements by ensuring a sufficient contact area between the ion-selective membrane and the sample without enlarging the electrode area. [Means for solving the problem]

[0007] According to one aspect of the present invention, there is provided a microchannel device using a porous substrate, comprising: The microchannel device has a channel region using a porous material, A part of the flow path region has a region A in which components having ion selectivity are present in pores in the porous substrate, and in the region A, the components having ion selectivity are present in pores on one surface X side of the porous substrate, and the other surface Y side forms a flow path in which pores are present; a working electrode is provided on the surface of the region A on the side of the surface X, a reference electrode is provided in a region B other than the region A of the flow channel region; There is provided a microchannel device in which the region A and the region B are formed on the same porous substrate. [Effects of the Invention]

[0008] According to one aspect of the present disclosure, it is possible to provide a microchannel device that is small and has high measurement stability. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a top view of the microchannel device M1 after the formation of channel walls 11 in Example 1. [Figure 2] FIG. 2 is a schematic diagram of the microfluidic device M1 after forming various electrodes in Example 1. [Figure 3] FIG. 1 is a schematic explanatory diagram of the permeation of a specimen in the microfluidic device M1 of Example 1. [Figure 4] FIG. 10 is a schematic diagram of a microchannel device M2 after forming a channel wall 12 in Example 2. [Figure 5] FIG. 10 is a schematic diagram of a microfluidic device M2 after forming various electrodes in Example 2. [Figure 6] FIG. 1 is a schematic diagram of a conventional configuration example in which the periphery of a working electrode is covered with an ion selective membrane. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings. Note that the following embodiments are merely examples, and the present invention is not limited to the contents of the embodiments. Furthermore, in the following drawings, components that are not necessary for explaining the embodiments are omitted from the drawings.

[0011] The microchannel device according to the present invention is a microchannel device using a porous substrate, and has a channel region surrounded by a channel wall. Examples of porous substrates include paper such as filter paper, plain paper, fine paper, watercolor paper, Kent paper, and synthetic paper that exhibit appropriate porosity and hydrophilicity, but are not limited to paper and may also include synthetic resin porous films, fabrics, and textile products. The flow path region has a working electrode placement area (region A) and a reference electrode placement area (region B). It may also have an area connecting the working electrode placement area (region A) and the reference electrode placement area (region B), and may further have a dispensing area. The material of the flow path wall may be a hydrophobic resin, but is not limited to a hydrophobic resin.

[0012] The flow path walls can be formed by electrophotographically printing a hydrophobic resin as toner and then heating the resin to melt and penetrate it. The resin can be a thermoplastic resin. The thermoplastic resin is not particularly limited, and for example, the following known resins can be used: polyester resin, vinyl resin, acrylic resin, styrene-acrylic resin, polyethylene, polypropylene, polyolefin, ethylene-vinyl acetate copolymer resin, ethylene-acrylic acid copolymer resin, etc. Among the above resins, polyester resin or styrene-acrylic resin is preferred, and styrene-acrylic resin is more preferred. The method for forming the flow path walls is not limited to the method of heating the resin to melt and penetrate it, but may also be a method of penetrating wax using a wax printer or a method of penetrating resin by screen printing.

[0013] <Working electrode arrangement section> The microfluidic device has a working electrode arrangement area (area A) in which a component having ion selectivity is present in the pores of the porous substrate in a part of the flow channel area. In the working electrode arrangement area (area A), a component having ion selectivity is present in the pores on one surface X side of the porous substrate, and an ion-selective membrane is formed. The other surface Y side of the porous substrate forms a flow channel in which pores are present. A working electrode is provided on the surface of the ion selective membrane formed in the working electrode placement portion (region A) on the surface X side.

[0014] The working electrode is preferably in contact with the ion selective membrane over the entire surface facing the surface X of the porous substrate in region A. This configuration can prevent the liquid that has permeated the flow path from coming into direct contact with the working electrode without passing through the ion selective membrane, allowing only ions selected by the ion selective membrane to come into contact with the working electrode and preventing other ions from coming into contact with the working electrode.

[0015] The working electrode placement portion (region A) has, on the surface of plane X, a portion (13 in FIG. 5(c)) that becomes a flow path using a porous material and a portion (12 in FIG. 5(c)) that does not function as a flow path because the porous material is filled in, It is preferable that a portion having ion selectivity (ion selective membrane 22 in FIG. 5(c)) exists across the portion that functions as a flow path (13 in FIG. 5(c)) and the portion that does not function as a flow path (12 in FIG. 5(c)). This is to ensure that only ions selected by the ion selective membrane 22 come into contact with the working electrode 31, and that other ions do not come into contact with the working electrode 31.

[0016] <Reference electrode placement area> A reference electrode is provided in an area B other than the area A of the flow channel area, that is, in a reference electrode placement area other than the working electrode placement area.

[0017] [Example 1] <Substrate / Flow path> The base material of the microfluidic device M1 will be described with reference to Figure 1. Figure 1 is a simplified top view of the microfluidic device M1 before the various electrodes are formed. In this example, paper was used as the porous substrate S1. The material was cellulose, with a thickness of 100 μm and a porosity of 50%. The minute gaps between the cellulose fibers allow capillary action, and the substrate also has good hydrophilicity, functioning as a flow path through which liquid can smoothly penetrate. A hydrophobic resin was impregnated into a portion of this porous substrate S1 to form a flow path wall 11 with a height H1 = 10 mm and a width L1 = 22 mm. The flow path wall 11 was formed by electrophotographically printing a hydrophobic resin as toner using the method described in JP 2021-37612 A, and then heating the resin to melt and penetrate it.

[0018] Additionally, the inner region of the flow channel wall 11 includes a region that is not permeated with the hydrophobic resin that forms the flow channel wall, and this region forms a flow channel using the porous nature of the porous substrate S1. The flow channel comprises a working electrode placement section S1b, a reference electrode placement section S1c, and a dispensing section S1d, as well as a 2 mm-wide flow channel connecting the dispensing section S1d to the working electrode placement section S1b and a 2 mm-wide flow channel connecting the dispensing section S1d to the reference electrode placement section S1c. A working electrode is placed in the working electrode placement section S1b, and a reference electrode is placed in the reference electrode placement section S1c. The dispensing section S1d is located between the working electrode placement section S1b and the reference electrode placement section S1c. The working electrode placement section S1b and the reference electrode placement section S1c are 6 mm squares, and the dispensing section S1d is a circle with a diameter of 3 mm. Note that while the size and shape of the flow channel in Example 1 are as described above, the size and shape of the flow channel are not limited to these. Hereinafter, the formation of various components of the microchannel device M1 will be described with reference to FIG. FIG. 2(a) is a top view of the microfluidic device M1 after various electrodes and the like have been formed, and FIG. 2(b) shows a cross section of the dashed line portion D1.

[0019] <Ion-selective membrane> The ion-selective membrane 21, which selectively reacts with Na ions and is used to measure the Na ion concentration, was prepared by mixing the materials listed in Table 1 below, stirring until completely dissolved, and applying the mixture to the working electrode placement section S1b. Note that the material types and ratios are not limited to those listed above, and any material may be used as long as it has ion selectivity. It is possible to select an ionophore appropriate for the ion type to be measured, and to select materials and ratios suitable for the configuration.

[0020] [Table 1]

[0021] The ion-selective membrane 21 was uniformly applied to the working electrode placement area S1b using a Biospot reagent spotting device manufactured by Microjet Co., Ltd. The diameter of the discharge pipe was 200 μm, the droplet size was 4 nL / drop, and the discharge frequency was 4 Hz. The film thickness was adjusted by applying five coats at 300 μm intervals. The stage used to secure the porous substrate S1 during application of the ion-selective membrane 21 was a heated stage set to 90°C. A solution with a solute concentration of 10% by mass kept the solution viscosity relatively low, facilitating stable dispensing. Meanwhile, heating the stage allowed the solvent in the solution applied to the porous substrate S1 to evaporate smoothly, allowing it to harden before penetrating the thickness of the porous substrate S1 and filling the flow channels. Therefore, even if the ion-selective membrane 21 was applied to the X-side surface shown in Figure 2(b), a flow channel remained on the Y-side surface, which is the reverse side of the X-side surface. This allowed the sample dispensed into the dispensing unit S1d to penetrate the entire working electrode placement area S1b. Heating the stage is not essential, and the flow path on the Y side surface can be left by reducing the droplet size, expanding the pitch between printed dots, reducing the printing speed, etc.

[0022] Furthermore, in this example, the ion selective membrane 21 was applied by an inkjet method that ejects minute droplets, but the method is not limited to this and may be performed by, for example, a dispenser or screen printing. Since a dispenser or screen printing can apply a solution with a higher viscosity than the inkjet method, increasing the viscosity by increasing the solute concentration or the like can make it more difficult for the material that forms the ion selective membrane 21 to penetrate in the thickness direction of the porous substrate S1.

[0023] <Working electrode> Ag was used as the material for the working electrode 31. A paste in which Ag is dispersed in a hydrophobic solvent can be applied to the ion selective membrane 21, which also has hydrophobicity, without being repelled, and a good electrode can be formed. However, the material is not limited to this, and any material can be used as long as it can be stably formed on the ion selective membrane 21 and functions as a working electrode. The working electrode 31 was applied by coating the ion selective membrane 21 on the porous substrate S1 and then printing using a screen printer DP-320 manufactured by Newlong Co., Ltd. The printing conditions were #200, and drying was performed at a temperature of 80°C for 10 minutes. The printed shape consisted of a 4 mm square that fit within the ion selective membrane 21 (6 mm square) and a 1 mm wide and 5 mm long rectangle that extended from one side of the 4 mm square to the outside of the flow path wall 11. The working electrode 31 could be connected to a measuring device that measures the electrode potential in the area outside the flow path wall 11. By printing the working electrode 31 directly on the ion selective membrane 21, a solid contact type ion selective electrode is formed, which prevents air bubbles from adhering to the electrode interface and allows stable measurement.

[0024] <Reference electrode> Ag / AgCl was used as the material for the reference electrode 32. By using Ag / AgCl, an equilibrium reaction according to the following formula (1) occurs in the aqueous solution, so that the Cl around the reference electrode 32 - A stable potential can be obtained when the concentration is stable.

[0025]

number

[0026] The reference electrode 32 was applied to the reference electrode placement area S1c using a screen printer DP-320 manufactured by Newlong Co., Ltd. The printing conditions were #200, and drying was carried out at a temperature of 80°C for 10 minutes. The reference electrode 32 has a shape consisting of a 6 mm square connected to a 1 mm wide and 3 mm long rectangle that extends from one side of the 6 mm square to the outside of the flow channel wall 11, and can be connected to a measuring device that measures the electrode potential in the area outside the flow channel wall 11.

[0027] <Electrolyte layer> The role of the electrolyte layer 41 is to dissolve in the water content of the sample when the sample permeates the reference electrode placement area S1c, saturating Cl- and thereby stabilizing the potential of the reference electrode 32. KCl was used as the material for this purpose. KCl was selected because it is easily soluble in water, and the diffusion rates of K ions and Cl ions are approximately equal, making it unlikely to generate a liquid junction potential. Naturally, the material for the electrolyte layer 41 is not limited to this, and any material that can stabilize the potential of the reference electrode 32 may be used, for example, NaCl.

[0028] The electrolyte layer 41 was applied using a Biospot reagent spotting device manufactured by Microjet Co., Ltd. The solution was prepared by dissolving KCl in pure water to a concentration of 16 wt %. The droplet size was 6 nL / droplet, the discharge frequency was 10 Hz, and the KCl amount was adjusted by printing over the entire reference electrode placement area S1c at a pitch of 300 μm both vertically and horizontally. The amount of KCl was adjusted by applying three coats. The amount of KCl can be adjusted to saturate the KCl relative to the amount of sample permeating the reference electrode placement area S1c, thereby stabilizing the potential of the reference electrode 32. Therefore, the amount of KCl applied is not limited to this amount, as long as there is enough KCl to create saturated KCl.

[0029] <Sample penetration> The permeation of a specimen in the microfluidic device M1 will be described with reference to FIG. FIG. 3(a) is a top view of a microfluidic device M1 in which various electrodes are configured, and FIG. 3(b) shows a cross section of a dashed line portion D2. When using the microfluidic device M1, the sample is dispensed into the dispensing section S1d. The dispensed sample then follows the flow path by capillary action and permeates in the directions of arrows A1 and A2. At this time, as shown in FIG. 3(b), the ion selective membrane 21 does not fill the thickness of the porous substrate S1, allowing the sample to permeate into the working electrode placement section S1b. Furthermore, the reference electrode 32 fills the thickness of the paper, and the sample that has permeated up to the reference electrode 32 continues to permeate into the reference electrode placement section S1c while dissolving the electrolyte layer 41 applied to the surface of the reference electrode 32, resulting in Cl. - is retained around the reference electrode 32 in a saturated concentration state. As a result, as described above, the reference electrode 32 stably exhibits a potential at the saturated state of KCl regardless of the analyte, while the working electrode 31 exhibits a potential at which the ion selective membrane 21 exhibits a Nernst response in response to the Na ion concentration of the analyte. Therefore, by measuring the potential difference between the reference electrode 32 and the working electrode 31 of the microfluidic device M1 and using the following equation (2), the Na ion concentration of the analyte can be detected by the ion electrode method.

[0030] E-E0=2.303×(RT / nF)×log(f×c)...Equation (2) E: electrode potential of the working electrode, E0: electrode potential of the reference electrode R: Gas constant (8.314JK -1 mol -1 ), T: measurement temperature expressed in absolute temperature n: valence of the ion to be measured, F: Faraday constant (9.649 × 10 -4 C mol -1 ) f: activity coefficient, c: molar concentration of ion

[0031] As described above, by applying the ion-selective membrane 21 so that it does not completely fill the porous substrate S1 in the thickness direction, and then applying the working electrode 31 on top of it, the contact area between the ion-selective membrane 21 and the sample can be increased without increasing the area or perimeter of the ion-selective membrane 21, resulting in stable measurements. For comparison, FIG. 6 shows a conventional configuration example in which the working electrode 31 is formed and then covered with the ion-selective membrane 21. In the configuration of FIG. 6, the ion-selective membrane 21 fills the entire thickness direction of the porous substrate S1, so the sample dispensed into S1d only penetrates up to the portion indicated by arrow A3. The sample and the ion-selective membrane 21 only come into contact at the interface of S1e, resulting in a small contact area. Therefore, the configuration of this embodiment allows for a larger contact area between the ion-selective membrane 21 and the sample compared to the conventional configuration. In addition, the contact between the ion-selective membrane 21 and the working electrode 31 is solid-state contact, with no internal liquid between them, so that stable measurement can be performed without bubbles adhering to the surface of the base electrode. Furthermore, because the ion-selective membrane 21 and the working electrode 31 are constructed on a single porous substrate, it is possible to make the device thinner than when the ion-selective membrane is formed on a first porous substrate and the working electrode is formed on a second porous substrate placed on the ion-selective membrane.

[0032] [Example 2] Regarding the microchannel device M2 of this embodiment, only the differences from the microchannel device M1 of the first embodiment will be described, the same members will be given the same reference numerals, and the description of similar parts will be omitted.

[0033] <Flow path> The flow channels of the microchannel device M2 will be described with reference to FIG. FIG. 4(a) is a simplified top view of the microfluidic device M2 before the formation of various electrodes, and FIG. 4(b) shows a cross section of the dashed line portion D3. In addition to the same channel walls 11 as in the microchannel device M1, the microchannel device M2 also has channel walls 12 formed in the working electrode placement section S1b. The channel walls 12 have a 500 μm square checkerboard pattern. As in Example 1, a hydrophobic resin is printed by electrophotography, and printing can be easily performed by changing the image pattern. Furthermore, by reducing the printing density of the hydrophobic resin compared to the channel walls 11, it is possible to adjust the pattern so that the resin does not fill the entire thickness of the porous substrate S1. Note that the "500 μm square checkerboard pattern" refers to a state in which square areas with 500 μm sides where a channel wall is formed are alternately arranged with square areas with 500 μm sides where a channel wall is not formed, as shown in FIG. 4(a).

[0034] In this example, the printing density of the flow path wall 12 was 20% of the printing density of the flow path wall 11. As a result, a portion of the X-side surface of the working electrode placement portion S1b was covered with resin, leaving a flow path through which the sample permeates on the Y-side surface behind it. Furthermore, in the portion of the X-side surface where the flow path wall 12 is formed, the pores of the porous substrate S1 are filled with hydrophobic resin, preventing capillary action and preventing liquid from permeating. On the other hand, in the portion of the X-side surface where no hydrophobic resin is present (i.e., where no flow path wall 12 is formed), the pores of the porous substrate S1 remain, functioning as a flow path through which the liquid permeates. The amount of liquid permeating into the porous substrate S1 from the X-side surface can be controlled by changing the ratio (hereinafter also referred to as the area ratio) of the area of ​​the flow path wall 12 (the sum of the areas of the flow path walls 12) to the area of ​​the working electrode placement portion S1b. 4(a), the flow path walls are checkered and the area ratio is 50%, but the size, shape, and area ratio of each flow path wall 12 are not limited to this and can be selected appropriately according to various configurations. Furthermore, the size and shape of each flow path wall may differ depending on the position of the flow path wall (for example, the distance from the dispensing unit S1d). The formation of the ion selective membrane 22 will be described below with reference to FIG. FIG. 5(a) is a top view of the microchannel device M2 after various electrodes and the like have been formed, FIG. 5(b) shows a cross section of the dashed line portion D4, and FIG. 5(c) shows an enlarged view of a portion of FIG. 5(b).

[0035] <Ion-selective membrane> The ion selective membrane 22 is made of the same material as the ion selective membrane 21; only the substrate on which the material forming the ion selective membrane is applied is different. The ion selective membrane 22 was applied onto the flow path wall 12 in the same manner as in Example 1. Since the ion selective membrane 22 penetrates into the porous substrate S1 only from the resin-free portions of the flow path wall 12, the amount of ion selective membrane that penetrates into the porous substrate S1 is reduced compared to Example 1, allowing the ion selective membrane 22 to be formed while leaving a flow path in the thickness direction of the paper. This increases the rate at which the sample penetrates into the working electrode placement portion S1b after dispensing the sample into the dispensing portion S1d, enabling more rapid measurement.

[0036] In addition, the working electrode 31, the reference electrode 32, and the electrolyte layer 41 are formed in the same manner as in Example 1 to obtain the microchannel device M2 shown in Fig. 5. After dispensing the sample into the dispensing section S1d, the potential difference between the reference electrode 32 and the working electrode 31 is measured, thereby measuring the Na ion concentration of the sample. As explained above, by forming a flow path wall in advance in a part of the flow path within the region where the ion selective membrane is formed, it is possible to control the penetration of the ion selective membrane into the thickness direction of the porous substrate after it has been applied to that region, and by leaving a wider flow path, it is possible to perform rapid measurements. However, if the area ratio of the flow path wall 12 is too large, the contact area between the ion selective membrane 22 and the sample will be small, so it should be appropriately selected depending on the size of the working electrode placement portion S1b, the thickness of the porous substrate, and other factors such as the desired measurement accuracy and speed. The area ratio of the flow path wall 12 is not limited to the conditions in this embodiment. [Explanation of symbols]

[0037] M1: Microfluidic device S1…Porous base material S1b…Working electrode placement area (area A) S1c...Reference electrode placement area (area B) S1d...Dispensing section 11...Channel wall 12...Channel wall 21, 22...Ion selective membrane 31...Working electrode 32…reference electrode 41…Electrolyte layer

Claims

1. A microchannel device using a porous substrate, The microchannel device has a channel region using a porous material, A part of the flow path region has a region A in which a component having ion selectivity is present in the pores in the porous substrate, and in the region A, the component having ion selectivity is present in the pores on one surface X side of the porous substrate, and the other surface Y side forms a flow path in which pores are present, a working electrode is provided on the surface of the region A on the side of the surface X so as to overlap at least a portion of the working electrode with the component having ion selectivity; a reference electrode is provided in a region B other than the region A of the flow channel region; A microchannel device, characterized in that the region A and the region B are formed on the same porous substrate.

2. The microchannel device according to claim 1 , wherein the working electrode is in contact with the component having ion selectivity over the entire surface of the porous substrate in the region A that faces the surface X.

3. The region A has, on the surface of the face X, a portion that becomes a flow path using a porous material and a portion that does not function as a flow path because the porous material is filled, 3. The microchannel device according to claim 1, wherein a component having ion selectivity exists across the portion that functions as the channel and the portion that does not function as the channel.

4. 4. The microchannel device according to claim 3, wherein the portion that does not function as a channel due to the porous portion being filled is a portion that does not function as a channel due to the porous portion being filled with a hydrophobic resin.

5. 3. The microchannel device according to claim 1, wherein the region A and the region B are connected by a channel.

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