Flow velocity measuring method and microfluidic system

Abstract

The objective of the present invention is to provide a technique capable of accurately acquiring flow velocity information in a microchannel regardless of the shape of the microchannel.　To this end, one flow velocity measuring method according to the present invention includes: a first step for feeding a solution to a microfluidic device provided with a microchannel; a second step for emitting an optical signal into the microchannel and acquiring, as a time series, a light intensity distribution of the optical signal transmitted through the microchannel; and a third step for calculating a time-series change indicating a change between the light intensity distribution at a first time and the light intensity distribution at a second time, acquired in the second step, and calculating the flow velocity of the solution in the microchannel from the time-series change in the light intensity distribution.

Description

Flow velocity measurement method and microfluidic system

[0001] The present invention relates to a flow velocity measurement method and a microfluidic system.

[0002] Microfluidic devices, known as lab-on-a-chips, micro-TASs, microchemical chips, and the like, are known for their ability to manipulate minute volumes of fluid using microstructures including microchannels and microwells with capillary dimensions of approximately 1 μm to 1 mm. In recent years, such devices have attracted attention as instruments for downsizing chemical experiments or for easily and quickly performing sample analysis at sample generation sites, known as point-of-care testing (POCT). In particular, samples targeted for POCT analysis are primarily animal body fluids, such as blood, saliva, and urine. Generally, body fluids contain biologically derived particles, such as proteins and cells. By detecting these particles using optical or electrical sensors, it is possible to obtain biological information.

[0003] After a suspension containing particles is delivered to a microfluidic device, various pretreatment processes such as concentration, filtering, and mixing of the suspension are carried out before biological information is detected. These pretreatment processes enable more accurate analysis. Some of these pretreatment processes are carried out when the suspension passes through the microstructures in the microfluidic device. In such cases, proper pretreatment is achieved by ensuring that the suspension passes through the microfluidic device normally.

[0004] On the other hand, if particles, impurities, or air bubbles adhere to the microstructure, clogging can occur within the microfluidic device. In this case, fluid delivery is not performed properly, and detection and analysis can be performed without appropriate pretreatment, resulting in reduced accuracy. To prevent or predict such a decrease in analytical accuracy, it is necessary to obtain fluid delivery information, such as flow velocity, flow rate, and pressure, in real time within the microfluidic device.

[0005] Patent Document 1 proposes a flow velocity measurement method comprising: a first step of introducing a first liquid into a microchannel; a second step of introducing a second liquid containing a solute into the microchannel and causing it to flow as a laminar flow; a third step of measuring the refractive index of the liquid containing the first and second liquids introduced into the microchannel in a time series manner; a fourth step of generating, from the time series data of the refractive index, concentration boundary data indicating a change over time in the position of a concentration boundary at which the concentration of the solute in the liquid is half the concentration of the solute in the second liquid before contact between the first and second liquids; a fifth step of generating conversion data by converting the concentration boundary data based on the diffusion coefficient of the second liquid and the length of the microchannel in the thickness direction; and a sixth step of calculating the flow velocity of the liquid containing the first and second liquids in the microchannel based on the conversion data.

[0006] Japanese Patent Application Laid-Open No. 2018-9794

[0007] The flow velocity measurement method disclosed in Patent Document 1 requires laminar and uniform flow, and therefore limits the shape of the channel to a linear one. However, in microfluidic devices, when preprocessing samples, the flow is often made uneven or turbulent by making the microchannel shape more complex than a linear channel, such as a curved or serpentine channel, or by incorporating finer structures than a microchannel, such as micropillars, within the channel. However, the flow velocity measurement method disclosed in Patent Document 1 is not intended to be applied to microfluidic devices with microchannels of shapes other than linear. Therefore, the present invention aims to provide a technology that can accurately obtain flow velocity information within a microchannel regardless of the shape of the microchannel.

[0008] In order to solve the above-mentioned problems, one representative flow rate measurement method of the present invention includes: a first step of sending a solution to a microfluidic device having a microchannel; a second step of irradiating the microchannel with an optical signal and acquiring a time-series distribution of the light intensity of the optical signal that has passed through the microchannel; and a third step of calculating a time-series change indicating a change between the light intensity distribution at a first time and the light intensity distribution at a second time acquired in the second step, and calculating the flow rate of the solution in the microchannel from the time-series change in the light intensity distribution.

[0009] According to the present invention, it is possible to provide a technology that can accurately acquire flow velocity information in a microchannel regardless of the shape of the microchannel. Problems, configurations, and effects other than those described above will become clear from the description of the following embodiments of the invention.

[0010] FIG. 1 is a diagram schematically illustrating the configuration of a microfluidic device. FIG. 2 is a diagram schematically illustrating the structure of an optical filter. FIG. 3 is a diagram illustrating an example of a process for forming an optical filter. FIG. 4 is a diagram schematically illustrating the configuration of a microfluidic system. FIG. 5 is a diagram illustrating a case where an optical signal irradiated from a light source unit is transmitted through a microchannel. FIG. 6 is a diagram illustrating the time series of the light intensity of an optical signal detected by a light detection unit in the second transmission region of FIG. 5. FIG. 7 is a diagram illustrating the relationship between the optical properties of a substance and the properties required of an optical filter. FIG. 8 is a diagram illustrating the distribution of light intensity detected by a light detection unit. FIG. 9 is a diagram illustrating a case where the flow rate of a solution is calculated from the time series change in the light intensity distribution shown in FIG. 8. FIG. 10 is a diagram illustrating another case where the flow rate of a solution is calculated from the time series change in the light intensity distribution. FIG. 11 is a flowchart of flow rate measurement. FIG. 12 is a flowchart of a method for determining the occurrence of clogging in a microchannel. FIG. 13 is a flowchart of a modified example of the second embodiment. FIG. 14 is a flowchart of a method for determining the occurrence of clogging in a microchannel using light intensity. Fig. 15 is a diagram showing a schematic configuration of a microfluidic system. ｎ Fig. 17 is a flowchart of a modification of the third embodiment. Fig. 18 is a diagram schematically showing the configuration of a microfluidic system.

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. However, the present invention is not limited to this embodiment. In addition, in the description of the drawings, the same parts are denoted by the same reference numerals. The position, size, shape, range, etc. of each component shown in the drawings may not represent the actual position, size, shape, range, etc., in order to facilitate understanding of the invention. Therefore, the present invention is not necessarily limited to the position, size, shape, range, etc. disclosed in the drawings.

[0012] In this disclosure, the term "surface" may refer not only to the surface of a plate-shaped member, but also to the interface of a layer contained in the plate-shaped member that is approximately parallel to the surface of the plate-shaped member. Furthermore, the terms "upper surface" and "lower surface" refer to the surface shown at the top or bottom of a drawing when a plate-shaped member or a layer contained in the plate-shaped member is illustrated. The "upper surface" and "lower surface" may also be referred to as the "first surface" and "second surface." Furthermore, "upper" refers to the vertically upward direction when a plate-shaped member or layer is placed horizontally. Furthermore, "upper" and its opposite, "lower," may also be referred to as the "positive z-axis direction" and the "negative z-axis direction," and the horizontal direction may also be referred to as the "x-axis direction" and the "y-axis direction." Furthermore, the distance in the z-axis direction is referred to as the "height," and the distance on the x-y plane defined by the x-axis and y-axis directions is referred to as the "width."

[0013] In this disclosure, the term "solution" refers to a substance that is used as a sample in a microfluidic system. Generally, a solution is a liquid state in which a solvent and a solute are uniformly mixed, but in this disclosure, it also includes cases in which the solute has precipitated and a solid and liquid are mixed. In addition, in this disclosure, the term "solution" also includes cases in which a mixture of a solid and a liquid is simply referred to as a solution.

[0014] [First embodiment] The configuration of a microfluidic system will be described with reference to Figures 1 to 4. First, a microfluidic device included in the microfluidic system will be described with reference to Figures 1 to 3, and then the configuration of the microfluidic system will be described with reference to Figure 4.

[0015] (Configuration of Microfluidic Device) Figure 1 is a diagram showing a schematic configuration of a microfluidic device. Figure 1(a) shows a perspective view of a microfluidic device 10, Figure 1(b) shows an AA' cross-sectional view of the microfluidic device 10, and Figure 1(c) shows a BB' cross-sectional view of the microfluidic device 10. The AA' cross-section is parallel to the y-axis direction, and the BB' cross-section is parallel to the x-axis direction.

[0016] As shown in Fig. 1(a), the microfluidic device 10 includes a substrate 11, a partition wall portion 12, and an upper surface portion 13, and has a structure in which the three members are stacked in the z-axis direction. A space is formed inside the partition wall portion 12, and a microchannel 30 through which a solution flows is formed in this space. The microchannel 30 has an inlet 32 ​​and an outlet 33. In a microfluidic system described below, a solution is introduced into the microchannel 30 from the inlet 32 ​​and discharged from the outlet 33 to the outside of the microfluidic device 10. Note that in Fig. 1(a), the upper surface portion 13 is shown as transparent in order to explain the structure of the microchannel 30, but the upper surface portion 13 does not necessarily have to be transparent.

[0017] In FIG. 1 , the microchannel 30 has a linear shape extending in the x-axis direction, but the present disclosure is not limited to this. The microchannel 30 may be a non-linear channel, such as a curved channel or a serpentine channel. The inlet 32 ​​and outlet 33 are provided for convenience of explanation, and the inlet and outlet may be interchanged. The number of inlets and outlets is not limited to one each, and multiple inlets and outlets may be provided. For example, multiple inlets may be provided, and when a blockage is detected in the microchannel, as described below, an inlet may be selected to avoid the blockage.

[0018] As shown in FIGS. 1B and 1C , in the microfluidic device 10, an optical filter 20 is disposed on the substrate 11, and a floor 14 is disposed on the optical filter 20. The optical filter 20 will be described later. In FIG. 1 , the microchannel 30 is a space formed between the floor 14, the partition 12, and the top surface 13, and the optical filter 20 is disposed over the entire surface of the microchannel 30. However, the present disclosure is not limited to the case where the optical filter 20 is disposed over the entire surface of the microchannel 30; the optical filter 20 may be formed in a portion of the microchannel 30. For example, the optical filter 20 may be disposed in a location in the microchannel 30 where clogging is a concern. As will be described later, an optical signal is irradiated onto the microfluidic device 10 from the positive direction of the z-axis, and the transmission of the optical signal through the microchannel 30 and the optical filter 20 is detected. The substrate 11 and the top surface 13 are configured to transmit optical signals so as not to block the optical signal irradiated from the light source 60.

[0019] Fig. 2 is a diagram schematically illustrating the structure of the optical filter 20. Fig. 2 is an enlarged view of a portion of the microchannel 30 of the microfluidic device 10 shown in Fig. 1, in which the floor 14 is depicted as transparent in order to explain the structure of the optical filter 20.

[0020] The optical filter 20 is composed of a plurality of light-transmitting regions and light-blocking regions. Specifically, the optical filter 20 has a light-blocking region 21, a first transmitting region 22, a second transmitting region 23, a third transmitting region 24, and a fourth transmitting region 25. The light-blocking region 21 blocks optical signals of all wavelengths used in the microfluidic system. In contrast, the first transmitting region 22, the second transmitting region 23, the third transmitting region 24, and the fourth transmitting region 25 each transmit optical signals of a specific wavelength range.

[0021] Each transparent region is arranged such that its center is spaced a distance Δx in the x-axis direction and a distance Δy in the y-axis direction. Each transparent region is a square region having the same area in the xy plane, and the spacing between adjacent regions is a distance gx in the x-axis direction and a distance gy in the y-axis direction. The transparent regions can be identified using coordinates in the xy plane. For example, when i and j are positive integers, the first transparent region 22 can be identified as being located at coordinates (i-1, j-1), (i, j+2), (i+1, j+1), and (i+2, j). Similarly, the second transparent region 23 is located at coordinates (i-1, j), (i, j-1), (i+1, j+2), and (i+2, j+1). The third transparent region 24 is located at coordinates (i-1, j+1), (i, j), (i+1, j-1), and (i+2, J+2). Fourth transmission regions 25 are arranged at coordinates (i-1, j+2), (i, j+1), (i+1, j), and (i+2, j-1). Light-shielding regions 21 are located between the transmission regions and are formed over the entire microchannel 30 when viewed from the positive direction of the z-axis.

[0022] Although FIG. 2 shows a case where there are four types of transmissive regions, the present disclosure is not limited to this. The number of types of transmissive regions may be other than four. Furthermore, although the shape of the transmissive regions is square, they may also be other shapes. Furthermore, the spacing between the transmissive regions may be set as appropriate.

[0023] 3A and 3B are diagrams showing an example of a process for forming the optical filter 20. First, as shown in Fig. 3A, a light-shielding region 21 is formed on the substrate 11. The light-shielding region 21 is formed to have a grid-like pattern on the substrate 11, for example, by applying a resist having light-shielding properties (e.g., black resist) onto the substrate 11 and performing photolithography.

[0024] 3(b), a color resist 220 is applied to the entire surface of the substrate 11. The color resist 220 may be made of the same material as that of the first transmission region 22. Then, as shown in FIG. 3(c), exposure of a pattern in which the first transmission region 22 will be disposed is performed via a photomask 221.

[0025] Next, unnecessary portions of the color resist 220 are removed using a developer, and then a baking process is performed to harden the color resist 220. As a result, a state in which the first transmission region 22 is arranged on the substrate 11 can be obtained, as shown in FIG.

[0026] The application of the color resist shown in Fig. 3(b), the exposure shown in Fig. 3(c), and the development and baking process shown in Fig. 3(d) are performed on the color resist and patterns corresponding to the second transmissive region 23, the third transmissive region 24, and the fourth transmissive region 25. In this way, the transmissive regions of the optical filter 20 are formed on the substrate 11.

[0027] After forming the transmission region of the optical filter 20, the floor portion 14 and the partition portion 12 are also formed by applying a resist, exposing it to light, developing it, and baking it. The upper surface portion 13 is placed on the partition portion 12, and the microfluidic device 10 is formed. The steps for forming the optical filter 20 and the microfluidic device 10 have been described above. In this disclosure, a formation method utilizing photolithography has been described, assuming that the substrate 11 is glass. However, this disclosure is not limited to these formation methods, and other materials and molding techniques may also be applied.

[0028] 4 is a diagram showing a schematic configuration of a microfluidic system 100. The microfluidic system 100 includes a microfluidic device 10, a liquid delivery unit 40, a liquid waste unit 50, a light source unit 60, a light detection unit 70, an optical signal processing unit 80, and a control unit 90.

[0029] The liquid delivery unit 40 has a function of delivering a solution to the microfluidic device 10, and includes, for example, a centrifuge tube 41 that stores the solution, and a pump 42 that delivers the solution from the centrifuge tube 41 to the microfluidic device 10. The solution delivered from the liquid delivery unit 40 flows into the microfluidic device 10 through a connection tube 45 that is connected to the inlet 32 ​​of the microfluidic device 10.

[0030] The waste liquid section 50 collects the liquid that passes through the microchannel 30 of the microfluidic device 10 and is discharged from the microfluidic device 10. A connection tube 55 is connected to the discharge port 33 of the microfluidic device 10, and the solution flows from the microfluidic device 10 to the waste liquid section 50 via the connection tube 55.

[0031] The light source unit 60 irradiates the microfluidic device 10 with an optical signal OS. The optical signal OS that has passed through the microfluidic device 10 is detected by the optical detection unit 70. The optical signal processing unit 80 processes the optical signal detected by the optical detection unit 70. The control unit 90 controls the liquid delivery unit 40 based on the processing results of the optical signal processing unit 80.

[0032] The light source unit 60 can be one that emits light in the visible light range. Specifically, blue light from 450 nm to 500 nm, green light from 500 nm to 600 nm, and red light from 600 nm to 700 nm. It is also possible to emit light in the near-infrared range. The light detection unit 70 may also have a spectroscopic function.

[0033] (Flow Velocity Measurement) Measurement of flow velocity in a microfluidic system will be described with reference to FIGS. 5 to 10 . For ease of understanding, FIGS. 5 and 6 illustrate only the configuration particularly relevant to flow velocity measurement. Although the optical filter 20 has multiple transmission regions in the xy plane, FIG. 6 illustrates a configuration in which the transmission regions are arranged only in the x-axis direction for ease of understanding. Here, the microfluidic system 100 includes at least a microfluidic device 10, a light detection unit 70 that acquires light intensity, and a light source unit 60 that irradiates an optical signal. The microfluidic device 10 is positioned between the light detection unit 70 and the light source unit 60 such that the direction of irradiation of the optical signal irradiated from the light source unit 60 is perpendicular to the liquid flow direction LD of the microchannel 30. An optical filter 20 composed of multiple light transmission regions and light-blocking regions is positioned between the microchannel 30 and the light detection unit 70. A detailed description will be given below.

[0034] (Detection of Light Intensity) FIG. 5 is a diagram illustrating a case where an optical signal OS irradiated from a light source unit 60 passes through a microchannel 30. In the microchannel 30 of the microfluidic device 10, a solution flows in a liquid transfer direction (hereinafter also referred to as the "liquid transfer direction LD") indicated by an arrow LD pointing in the positive x-axis direction. The microfluidic device 10 is disposed between the light source unit 60 and the light detection unit 70, and the optical signal OS irradiated from the light source unit 60 travels in the negative z-axis direction, which is perpendicular to the liquid transfer direction LD, and enters the microchannel 30. Note that the liquid transfer direction LD indicates the macroscopic direction of liquid transfer in the microfluidic device 10; microscopically, solution molecules may move in various directions.

[0035] The optical filter 20 is disposed between the microchannel 30 and the photodetector 70. The optical signal OS passes through the first transmission region 22 and the third transmission region 24 of the optical filter 20 to reach the photodetector 70. On the other hand, the substance 31 contained in the solution prevents the optical signal OS from passing through, and the optical signal does not reach the second transmission region 23. The light-shielding region 21 also functions to prevent the optical signal OS from passing through.

[0036] Fig. 6 is a diagram showing the light intensity of the optical signal detected by the optical detection unit 70 in a time series in the second transmission region 23 of Fig. 5. The optical detection unit 70 acquires the distribution of the light intensity of the optical signal transmitted through the microchannel 30 in a time series, and acquires the light intensity of the optical signal OS at time intervals Δt as shown on the horizontal axis.

[0037] Here, one or more of the optical filter 20's multiple light transmission regions can transmit light in a specific wavelength region, allowing the light detection unit 70 to detect the light intensity for each wavelength region. A specific example will be described below. Assume that the light source unit 60 emits light including wavelengths λ1, λ2, and λ3 as the optical signal OS, and the second transmission region 23 blocks only light in the wavelength region including wavelengths λ1 and λ3, while transmitting light in the wavelength region including wavelength λ2. Furthermore, assume that the substance 31 blocks light in the wavelength region including wavelength λ1, and transmits light in the wavelength region including wavelengths λ2 and λ3.

[0038] The intensity S0 refers to a base intensity, which is the reference light intensity for the optical signal OS. For example, the light intensity detected when the light source unit 60 irradiates the optical signal OS before a solution is flowed through the microfluidic device 10 can be used as the base intensity. Alternatively, the light intensity detected when only a solvent is flowed through the microfluidic device 10 instead of a sample solution can be used as the base intensity. The light intensity ST is a threshold light intensity for determining the transmission of the optical signal OS. If a light intensity lower than the light intensity ST is detected, it is determined that the optical signal OS is blocked. For example, the threshold ST may be set to 50% of the base intensity S0. The threshold ST can be set based on the properties of the solvent or substance, etc.

[0039] The optical signal OS can include optical signals of multiple wavelengths, and Figure 6(a) shows the case where the optical intensity of an optical signal of wavelength λ1 is detected, Figure 6(b) shows the case where the optical intensity of an optical signal of wavelength λ2 is detected, and Figure 6(c) shows the case where the optical intensity of an optical signal of wavelength λ3 is detected.

[0040] As shown in FIG. 6A, the light intensity of wavelength λ1 increases at time t１ At time t ２ and t ３ At time t, a value between the base intensity S0 and the threshold value ST is detected. １ Since the light intensity detected at time t １ , it is determined that the substance 31 is present above the second transmission region 23 and has been blocking the optical signal OS.

[0041] 6(b) and 6(c), in both cases, a light intensity greater than the threshold value ST is detected, and therefore, at time t １ From t ３ 6(b) , it is not possible to detect that substance 31 was present above second transmission region 23. Second transmission region 23 blocks only light in the wavelength range including wavelength λ3 and transmits light in the wavelength range including wavelength λ2. For this reason, the light intensity for wavelength λ2 shown in FIG. 6(b) is detected as a greater value than the light intensity for wavelength λ3 shown in FIG. 6(c) .

[0042] In this way, the presence of the substance 31 can be determined based on the wavelength region of the optical signal OS irradiated from the light source unit 60, the characteristics of the substance 31 contained in the solution, and the characteristics of the transmission region of the optical filter 20. FIG. 7 illustrates the relationship between the optical characteristics of the substance 31 and the characteristics required of the optical filter 20. As a first case, as described above, the substance 31 may transmit light in a certain wavelength region and absorb light in wavelength regions other than the transmitted wavelength region. In this case, the light detection unit 70 is required to detect light in the wavelength region transmitted by the substance 31. The first characteristic required of the transmission region of the optical filter 20 is to block light in a certain wavelength region transmitted by the substance 31. Alternatively, the second characteristic may be to transmit only light in the wavelength region absorbed by the substance 31. These two characteristics may be imparted to a single transmission region, or the optical filter 20 may have the first characteristic imparted to one transmission region and the second characteristic imparted to another transmission region. By imparting these two characteristics to the transmission region within the optical filter 20 in either manner, different light intensities can be detected when the substance 31 is present and when it is not, making it possible to determine the position of the substance 31.

[0043] A second case may occur when the substance 31 absorbs light in a certain wavelength range but emits light in another wavelength range. In this case, the light detection unit 70 is required to detect light of a transmitted wavelength within a wavelength range that includes the wavelength of the emitted light in the other wavelength range. The first characteristic required of the transmission region included in the optical filter 20 is to block the wavelength range of the emitted light. The second characteristic is to block light in the wavelength range that is transmitted through the substance 31. The third characteristic is to transmit only light in the wavelength range absorbed by the substance 31. By imparting these three characteristics to the transmission region of the optical filter 20, it is possible to detect different light intensities depending on whether the substance 31 is present or not, thereby making it possible to determine the position of the substance 31. As in the first case described above, the three characteristics may be combined in one region or may be shared by separate regions.

[0044] A third case is when the substance 31 absorbs all wavelengths of light emitted from the light source unit 60. In this case, if the substance 31 is present, the light detection unit 70 will not be able to detect any wavelengths of light. Here, there is no requirement for a blocking wavelength range as a characteristic required for the transmission region of the optical filter 20. In other words, the blocking wavelength range in the transmission region can be set arbitrarily. For example, it is possible to adopt a transmission region that transmits light in all wavelength ranges.

[0045] As described above, by allowing one or more of the transmission regions to transmit light in a specific wavelength range, it is possible to measure the flow rate even for substances that absorb light in a specific wavelength range. Examples of the substance 31 include biological substances such as plankton (approximately 1 mm), cells (approximately 20 μm), bacteria (several μm to 10 μm), viruses (on the order of 100 nm), and proteins (on the order of 10 nm). Non-biological substances include microplastics, metal particles, and other organic substances. The present disclosure is not limited to these and can be applied to solutions containing various particles. For example, it is possible to measure the flow rate by including indicator particles different from the solute in the solution and detecting changes in light intensity due to the indicator particles.

[0046] (Light Intensity Distribution) FIG. 8 is a diagram showing the distribution of light intensity detected by the light detection unit 70. FIG. 8(a) is for time t=t0, FIG. 8(b) is for time t=t0+Δt, and FIG. 8(c) is for time t=t0+2Δt. In FIG. 8, the liquid delivery direction LD is the positive direction of the x-axis. Note that t0 indicates a predetermined time, and Δt indicates a predetermined time interval. FIG. 8 shows how the distribution of light intensity that has passed through the microchannel 30 changes over time. This will be explained in detail below.

[0047] Because the light intensity is detected as data distributed two-dimensionally in accordance with the arrangement of the transmission and light-blocking regions of optical filter 20, rectangular regions are shown in Fig. 8 according to the arrangement of the transmission regions. When k and m are positive integers, coordinates (m, k) and coordinates (m, k+1) in Fig. 8(a) indicate locations where the light intensity is smaller than threshold ST, and therefore indicate locations where it is determined that substance 31 is present. Note that, for ease of understanding, the rectangular regions shown in Fig. 8 are shown in an arrangement (four arranged in the x-axis direction and six arranged in the y-axis direction) that differs from the arrangement of the transmission regions in optical filter 20 in Fig. 2 (four arranged in the x-axis direction and four arranged in the y-axis direction).

[0048] In Fig. 8(b), coordinates (m+1, k) and (m+1, k+1) indicate the locations where the light intensity becomes smaller than the threshold value ST, and in Fig. 8(c), coordinates (m+2, k) and (m+2, k+1) indicate the locations where the light intensity becomes smaller than the threshold value ST. Note that the direction of movement of the light intensity in Fig. 8(a) to Fig. 8(c) coincides with the liquid flow direction LD, so it is determined that the changes in light intensity in Fig. 8(a) to Fig. 8(c) are caused by the movement of the same substance.

[0049] FIG. 9 is a diagram illustrating a case where the flow rate of a solution is calculated from the time-series change in the light intensity distribution shown in FIG. 8 . The time-series change refers to the change in data acquired at equal time intervals. Arrow A1 extends from coordinates (m, k) and (m, k+1) in FIG. 8( a) to coordinates (m+2, k) and (m+2, k+1) in FIG. 8( c). For example, the magnitude and direction of arrow A1 can be used to represent the flow rate of the solution at coordinates (m, k) and (m, k+1).

[0050] FIG. 10 shows another example of calculating the flow rate of a solution from the time-series change in the distribution of light intensity. While FIGS. 8 and 9 show the case of a single substance 31, FIG. 10 shows the case of a region containing three substances. Arrow A2 is shown narrower than arrow A1. This is because arrow A1 indicates the flow rate at coordinates (m, k) and (m, k+1), while arrow A2 indicates the flow rate at coordinates (m+1, k+3). Comparing the two, it can be inferred that the amount of solution flowing through the region of the microchannel corresponding to the coordinates (m+1, k+3) is different from that of the coordinates (m, k) and (m, k+1).

[0051] Furthermore, arrow A3 indicates the flow velocity at coordinates (m+4, k-2). Arrows A1 and A2 point in the positive x-axis direction, which is the same direction as the liquid feed direction LD, but arrow A3 points in a direction away from the positive x-axis direction. Furthermore, arrow A3 is smaller in size than arrows A1 and A2. Therefore, it is inferred that there is a sign of a clog that will hinder the flow of solution in the microchannel corresponding to the position of coordinates (m+4, k-2).

[0052] In this way, when changes in light intensity are detected at multiple points in the light intensity distribution, the flow velocity in the microchannel is acquired as data distributed two-dimensionally. Note that although the flow velocity distribution is expressed as arrows pointing to the liquid flow channel, the manner of expression is not limited to this. For example, the flow velocity distribution can also be expressed in the form of a heat map, a contour map, or the like.

[0053] (Flowchart of Flow Rate Measurement) A method of flow rate measurement will be described with reference to FIG. 11 . FIG. 11 is a flowchart of flow rate measurement. The flow rate measurement method includes a first step (step S10) of feeding a solution into a microfluidic device 10 including a microchannel 30, a second step (step S11) of irradiating the microchannel 30 with an optical signal and acquiring a time-series distribution of the light intensity of the optical signal transmitted through the microchannel 30, and a third step (step S12) of calculating a time-series change indicating a change between the light intensity distribution at a first time and the light intensity distribution at a second time acquired in the second step, and calculating the flow rate of the solution in the microchannel 30 from the time-series change in the light intensity distribution. A specific description will be given below.

[0054] In step S10 (first process), a solution is delivered to the microfluidic device 10. The control unit 90 controls the pump 42 to deliver the solution from the liquid delivery unit 40 to the microfluidic device 10.

[0055] Subsequently, in step S11 (second process), the optical signal processing unit 80 acquires, in time series, the distribution of the light intensity of the optical signal transmitted through the microchannel 30. The optical signal processing unit 80 acquires the light intensity detected by the light detection unit 70 as time-series information. The light intensity is acquired as data distributed two-dimensionally in accordance with the arrangement of the transmission regions in the optical filter 20.

[0056] Subsequently, in step S12 (third process), the control unit 90 calculates the flow velocity of the solution in the microchannel 30 from the time-series change in the distribution of light intensity. The control unit 90 calculates the velocity of the substance movement and adopts the velocity of the substance movement as the velocity of the solution.

[0057] (Actions and Effects) As described above, the present disclosure enables accurate acquisition of flow velocity information within a microchannel. Furthermore, because each transmission region of the optical filter 20 transmits an optical signal according to the wavelength of the optical signal, the characteristics of the optical filter 20 may be affected by factors such as the angle of incidence of the optical signal. In contrast, the present disclosure provides a configuration in which the optical filter 20 is disposed within the microfluidic device 10 and is in close proximity to the microchannel. This prevents deviations in the angle of incidence of the optical signal between the optical filter 20 and the microchannel, enabling appropriate evaluation of the optical signal detected by the optical filter 20. Furthermore, while there is a possibility that light intensity may decrease due to absorption by the object when an optical signal passes through the object, the present disclosure provides an integrated configuration of the optical filter 20 and the microchannel device 10, thereby minimizing the decrease in light intensity. Furthermore, the integration of the optical filter 20 and the microchannel device 10 allows for a more compact configuration of the microfluidic system 100. Following the process of forming the optical filter 20 shown in FIG. 3 , the floor portion 14, the partition portion 12, and the top surface portion 13 are formed using photolithography, thereby obtaining the microchannel device 10. Because common lithography equipment can be used, the manufacturing cost of the microchannel device 10 can be reduced. Furthermore, since the location where the optical filter 20 is set within the microchannel is not limited, it is possible to measure the flow velocity regardless of the shape of the microchannel. Furthermore, the flow velocity can be measured according to the arrangement of the transmission regions within the optical filter, making it possible to measure the detailed flow velocity distribution within the microchannel. Measuring the local flow velocity within the channel using an optical filter enables measurements that are independent of the shape of the microchannel or the uniformity of the solution flow.

[0058] In addition, although the above explanation is based on the assumption that the substance is approximately the same size as the transparent region, it is possible to measure flow velocity according to the size of the substance by changing the size and shape of the patterning of the transparent region and the light-shielding region. Furthermore, if the light detection unit is given the function of acquiring the shape of the light signal intensity, it is also possible to calculate the size of the substance contained in the solvent from the Q value of the signal shape.

[0059] [Modification of First Embodiment] Note that a step of acquiring liquid transfer direction information, which is information indicating the direction in which the solution moves relative to the microchannel 30, may be included between steps S10 and S11. For example, the control unit 90 determines that the solution has started to flow from the inlet 32 ​​to the outlet 33 of the microchannel 30, triggered by the actuation of the pump 42, and acquires information indicating the direction in which the solution has flowed as liquid transfer direction information. Alternatively, a flow rate sensor or a liquid pressure sensor may be provided for the microchannel 30, and the liquid transfer direction may be determined from the amount of liquid transferred and the amount of waste liquid. If the location of the pump 42 and the locations of the inlet 32 ​​and outlet 33 are already determined and the liquid transfer direction in the microfluidic system 100 is already determined, there is no need to acquire the liquid transfer direction information, since the liquid transfer direction information is already known. However, for example, if the microchannel has multiple paths and the liquid transfer direction changes at predetermined intervals, the control unit 90 acquires the liquid transfer direction information and calculates the flow rate of the solution in the microchannel from the liquid transfer direction information and the time-series change in the distribution of light intensity. For example, the control unit 90 determines the position of the substance by comparing the light intensity with a threshold value ST using the optical signal processing unit 80, and if the deviation between the direction of change in the position of the substance and the liquid transfer direction falls within a predetermined range, the control unit 90 treats the movement of the substance as the flow rate of the solution.

[0060] [Second Embodiment] The second embodiment differs from the first embodiment in that a flow velocity measurement method is applied to determine the occurrence of clogging in a microchannel. In the following description, the same or equivalent components as those in the first embodiment described above are denoted by the same reference numerals, and their description will be simplified or omitted.

[0061] Fig. 12 is a flowchart of a method for determining whether clogging has occurred in a microchannel. The method of Fig. 12 is performed in the same system as the microfluidic system 100 of the first embodiment. Steps S20 to S22 of Fig. 12 are similar to steps S10 to S12 of the first embodiment shown in Fig. 11, and therefore will not be described here.

[0062] Steps S23 and S24 are performed in real time after the start of liquid transfer in step S20 and each time the flow rate is calculated in step S22. In step S23 (fourth step), when t0 is a predetermined time, the flow rate v at a predetermined position in the microchannel at time t0+Δt·n (n is a positive integer) is calculated. ｎ and the flow velocity v at time t0 + Δt (n-1) ｎ－１ In other words, at a given position coordinate (i, j), at a certain time t ｎ (For example, t ｎ = t0 + Δ n) is the flow velocity at v ｎ (i, j), and t ｎ－１ , t ｎ , t ｎ＋１ , ..., when the flow velocity is calculated in time series, ｎ in v ｎ (i, j) and v ｎ－１ (i, j) are compared. Specifically, referring to FIG. 9, in a rectangular region (k, m), the flow velocity v ｎ is the velocity calculated from the change in light intensity between time t0 and time t0+2Δt, and the flow velocity v ｎ－１ is the velocity calculated from the change in light intensity between time t0-Δt and time t0+Δt, ｎ (m, k) and v ｎ－１ (m, k) and judge whether the flow velocity is increasing or decreasing. The same judgment is made for a plurality of coordinates.

[0063] Subsequently, in step S24 (fifth process), it is determined from the increase or decrease in the flow rate that a blockage has occurred at a predetermined position in the microchannel 30. Specifically, in step S23, the control unit 90 ｎ (i, j) is v ｎ－１ If it is determined that the difference is greater than (i, j) (Yes in step S23), it is determined that a blockage has occurred in the microchannel 30 corresponding to the position of the coordinates (i, j) (step S24). To deal with the occurrence of the blockage, the control unit 90 controls, for example, the pump 42 to stop the liquid delivery from the liquid delivery unit 40.

[0064] In step S23, v ｎ(i, j) is v ｎ－１ If it is determined that the value is equal to or less than (i, j) (No in step S23), the process returns to step S22, and the flow velocity is calculated.

[0065] [Modification of Second Embodiment] Fig. 13 is a flowchart of a modification of the second embodiment. Steps S200 to S240 in Fig. 13 are the same as steps S20 to S24 of the second embodiment in Fig. 12, and therefore description thereof will be omitted.

[0066] After determining in step S240 that a blockage has occurred in the microchannel 30, the control unit 90 increases the amount of liquid being sent in step S200 (step S250). For example, the control unit 90 controls the pump 42 to increase the discharge rate.

[0067] Subsequently, in step S260, the control unit 90 performs the process at time t ｐ (p is an integer greater than n) ｐ (i, j) is calculated. Step S260 includes the same processes as steps S210 and S220.

[0068] Next, the control unit 90 ｐ (i, j) and v ｎ (i, j) (step S270). ｐ (i, j) is v ｎ If it is determined that the value is greater than (i, j) (Yes in step S270), it is determined that clogging has occurred in the microchannel 30 corresponding to the position of the coordinates (i, j) (step S280).

[0069] In step S270, v ｐ (i, j) is v ｎ If it is determined that the value is equal to or less than (i, j) (No in step S270), the process returns to step S220, and the flow velocity is calculated.

[0070] (Functions and Effects) As described above, by measuring the flow velocity distribution in real time and determining whether the flow velocity increases or decreases, it is possible to detect blockages in the microchannel. Furthermore, in a modified example of the second embodiment, a process is added in which the amount of liquid sent is changed and then a change in the flow velocity is confirmed. This makes it possible to more reliably determine whether a blockage has occurred.

[0071] [Third Embodiment] The third embodiment differs from the second embodiment in that light intensity is used to determine the occurrence of clogging. In the following description, the same or equivalent components as those in the first and second embodiments are denoted by the same reference numerals, and their description will be simplified or omitted.

[0072] Fig. 14 is a flowchart of a method for determining the occurrence of clogging in a microchannel using light intensity. Fig. 15 is a diagram schematically showing the configuration of a microfluidic system. Microfluidic system 100a differs from microfluidic system 100 in Fig. 4 in that it has a centrifuge tube 43 and a pump 44 in the liquid delivery section 40. While centrifuge tube 41 stores a solution, centrifuge tube 43 stores only a solvent.

[0073] In step S30, the control unit 90 transfers a solvent that does not contain a solute. For example, the control unit 90 can transfer the solvent from the centrifuge tube 43 that contains only the solvent.

[0074] Subsequently, in step S31, the control unit 90 causes the light source unit 60 to emit light and irradiate the microchannel 30 with an optical signal.

[0075] Here, the light intensity at the coordinates (i, j) of a predetermined position is represented as S(i, j). In step S32, the light signal emitted from the light source unit 60 is transmitted only through the solvent, so the control unit 90 can obtain the base intensity S0(i, j).

[0076] Subsequently, in step S33, the control unit 90 sends a solvent containing a solute, i.e., a solution as a specimen. For example, the control unit 90 switches the solution sending unit 40 to the centrifuge tube 41 containing the solution, and starts sending the solution.

[0077] Next, in step S34, the control unit 90 acquires the light intensity S(i, j) at regular time intervals. For example, the control unit 90 can acquire the light intensity every Δt.

[0078] Here, at a certain time t ｎ = t0 + Δt n, and time t ｎ The light intensity at S ｎ In step S35, the control unit 90 ｎ If (i, j) is obtained, S0(i, j) and S ｎ The absolute value of the difference between (i, j) is calculated, and it is determined whether the absolute value is greater than 0. Here, FIG. 16 shows the relationship between S0 and S ｎ 1 is a diagram showing the relationship between the base strength S0 and time t ｎ Light intensity S at ｎ If there is a difference between the two, a change in light intensity is detected as shown in FIG.

[0079] If a change in light intensity is detected (Yes in step S35), in step S36, the control unit 90 determines that a clog has occurred in the microchannel 30. To deal with the occurrence of the clog, the control unit 90 controls, for example, the pump 42 to stop the liquid delivery from the liquid delivery unit 40.

[0080] If no change in light intensity is detected in step S35 (No in step S35), the process returns to step S34, and light intensity is acquired.

[0081] [Modification of Third Embodiment] Fig. 17 is a flowchart of a modification of the third embodiment. Steps S300 to S350 in Fig. 17 are the same as steps S30 to S35 of the third embodiment in Fig. 14, and therefore description thereof will be omitted.

[0082] After determining in step S360 that a blockage has occurred in the microchannel 30, the control unit 90 increases the flow rate of the liquid being transferred in step S43 (step S370). For example, the control unit 90 controls the pump 42 to increase the discharge rate.

[0083] Subsequently, the control unit 90 performs the step S370 at the time t ｐ (p is an integer greater than n), and S0(i, j) and S ｎ The absolute value of the difference between (i, j) (hereinafter referred to as "time t ｎ ) and S0(i, j) and S ｐ The absolute value of the difference between (i, j) (hereinafter referred to as "time t ｐ (hereinafter referred to as the "absolute value of t") is compared with (step S380). ｎ The absolute value of ｐ If the absolute value of the time t is smaller than or equal to the absolute value of the time t (No in step S380), the control unit 90 determines that a blockage has occurred in the microchannel 30 (step S390). ｎ The absolute value of ｐ If the absolute value of the light intensity is greater than the absolute value of (Yes in step S380), the control unit 90 returns to step S340 and acquires the light intensity.

[0084] (Actions and Effects) In the third embodiment and its modified examples, it is possible to determine whether a blockage has occurred in a microchannel based on a change in light intensity. Compared to the second embodiment, the process of calculating the flow velocity can be omitted, which reduces the processing load on the control unit. Furthermore, in the modified example of the third embodiment, a process is added in which the flow velocity is changed and then a change in the absolute value of the difference in light intensity is confirmed. This makes it possible to more reliably determine whether a blockage has occurred.

[0085] [Fourth Embodiment] The fourth embodiment differs from the first embodiment in that a pump and a centrifuge tube are provided in the waste liquid section. In the following description, the same or equivalent components as those in the first embodiment are denoted by the same reference numerals, and their description will be simplified or omitted.

[0086] 18 is a diagram schematically illustrating the configuration of a microfluidic system. In the microfluidic system 100b, the waste liquid section 50 has a centrifuge tube 51 and a pump 52. When transferring a liquid, the control unit 90 controls the pump 52 to flow a solution from the centrifuge tube 41 of the liquid transfer unit 40 to the microfluidic device 10. The solution that has flowed through the microchannel 30 is stored in the centrifuge tube 51 of the waste liquid section 50.

[0087] (Actions and Effects) Even if the configurations of the liquid delivery section and the liquid waste section are changed, it is possible to measure the flow rate of the microchannel. Furthermore, the configuration of the fourth embodiment can be applied to the first to third embodiments. Even if the microfluidic device 10 is provided with multiple branched microchannels, requiring multiple liquid delivery sections and liquid waste sections, it is possible to measure the flow rate by controlling each of the liquid delivery section and the liquid waste section.

[0088] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the gist of the present invention.

[0089] REFERENCE SIGNS LIST 10 Microfluidic device, 11 Substrate, 12 Partition wall portion, 13 Upper surface portion, 14 Floor portion, 20 Optical filter, 21 Light-shielding region, 22 First transmission region, 23 Second transmission region, 24 Third transmission region, 25 Fourth transmission region, 30 Microchannel, 31 Substance, 32 Inlet, 33 Outlet, 40 Liquid delivery portion, 41 Centrifuge tube, 42 Pump, 43 Centrifuge tube, 44 Pump, 45 Connecting tube, 50 Waste liquid portion, 51 Centrifuge tube, 52 Pump, 55 Connecting tube, 60 Light source portion, 70 Light detection portion, 80 Optical signal processing portion, 90 Control portion, 100, 100a, 100b Microfluidic system, 220 Color resist, 221 Photomask

Claims

1. A flow velocity measurement method comprising: a first step of sending a solution to a microfluidic device having a microchannel; a second step of irradiating an optical signal into the microchannel and acquiring a time-series distribution of the light intensity of the optical signal that has transmitted through the microchannel; and a third step of calculating a time-series change in the light intensity distribution at a first time and a light intensity distribution at a second time acquired in the second step, and calculating the flow velocity of the solution in the microchannel from the time-series change in the light intensity distribution.

2. In the flow velocity measurement method according to claim 1, the light intensity in the second step is acquired at a predetermined time interval Δt, and when t0 is the predetermined time, a flow velocity v at a predetermined position in the microchannel at time t0+Δt・n (n is a positive integer) is calculated. ｎ and the flow velocity v at time t0+Δt・(n−1) ｎ－１ and a fourth step of comparing the measured flow rate and determining whether the flow rate has increased or decreased.

3. A flow velocity measuring method as claimed in claim 2, further comprising a fifth step of determining whether a blockage has occurred at said predetermined position of said microchannel based on an increase or decrease in said flow velocity.

4. A microfluidic system in which the flow velocity measurement method of claim 1 is performed, the microfluidic system including at least the microfluidic device, a light detection unit which acquires the light intensity in the second step, and a light source unit which irradiates the light signal in the second step, the microfluidic device being disposed between the light detection unit and the light source unit such that the direction of irradiation of the light signal irradiated from the light source unit is perpendicular to the liquid flow direction of the microchannel, and an optical filter constituted by a plurality of light-transmitting regions and light-shielding regions is disposed between the microchannel and the light detection unit.

5. A microfluidic system as claimed in claim 4, wherein said optical filter allows one or more of said plurality of light transmitting regions to transmit light of a particular wavelength region.

6. A microfluidic system according to claim 4 or 5, wherein the optical filter is disposed within the microfluidic device.

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