JP7540564B1 - Flow velocity measurement method and microfluidic system - Google Patents

Abstract

[Problem] The present invention aims to provide a technology that can accurately obtain flow rate information in a microchannel regardless of the shape of the microchannel. [Solution] One of the flow rate measurement methods of the present invention includes a first step of sending a solution to a microfluidic device equipped with a microchannel, a second step of irradiating the microchannel with an optical signal and obtaining 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 that indicates a change between the light intensity distribution at a first time and the light intensity distribution at a second time obtained 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. [Selected Figure] Figure 1

Description

The present invention relates to a flow rate measurement method and a microfluidic system.

Conventionally, microfluidic devices called Lab-on-a-Chip, microTAS, microchemical chips, etc., have been known, which can manipulate minute volumes of fluids using microstructures including microchannels and microwells with capillary dimensions of approximately 1 μm to 1 mm. In recent years, such devices have been attracting attention as devices for downsizing chemical experiments, or devices for easily and quickly performing sample analysis at the site of sample generation, so-called point-of-care testing (POCT). In particular, in POCT, the samples that are the subject of sample analysis are mainly animal body fluids, such as blood, saliva, and urine. Generally, body fluids contain biological particles such as proteins and cells, and by detecting these particles with optical sensors or electrical sensors, it is possible to obtain biological information.

After a suspension containing fine particles, which is a specimen, is sent to a microfluidic device, various pretreatment processes such as concentrating, filtering, and mixing the suspension are carried out in the microfluidic device until biological information is detected. Such 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, appropriate pretreatment is achieved by the suspension passing normally through the microfluidic device.

However, if fine particles, impurities, or air bubbles adhere to the microstructure, clogging may occur inside the microfluidic device. In this case, liquid delivery may not be performed properly, and detection and analysis may be performed without proper pretreatment, resulting in a decrease in accuracy. To prevent such a decrease in analysis accuracy or to predict the occurrence of a decrease in analysis accuracy, it is necessary to obtain liquid delivery information, such as flow velocity, flow rate, and pressure, in real time within the microfluidic device.

Patent Document 1 presents a flow velocity measurement method that includes 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 flowing it in 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 concentration boundary data indicating a change in time at the position of a concentration boundary where the concentration of the solute in the liquid is half the concentration of the solute in the second liquid before the first liquid and the second liquid come into contact from the time series data of the refractive index, 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.

JP 2018-9794 A

In the flow velocity measurement method of Patent Document 1, the flow must be laminar and uniform, so the shape of the flow channel is limited to a linear type. However, in microfluidic devices, when pre-treating a sample, the flow is often made non-uniform or turbulent by making the shape of the microchannel more complicated than a linear channel, such as a curved or meandering type, or by providing a finer structure than a microchannel, such as a micropillar, in the channel. However, the flow velocity measurement method presented in Patent Document 1 is not intended to be applied to microfluidic devices having microchannels with shapes other than linear.
Therefore, an object 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 solve the above problem, 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 transmitted 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.

According to the present invention, it is possible to provide a technique capable of accurately acquiring flow velocity information in a microchannel regardless of the shape of the microchannel.
Problems, configurations and effects other than those described above will become apparent from the following description of the preferred embodiment of the invention.

FIG. 1 is a diagram showing a schematic configuration of a microfluidic device. FIG. 2 is a diagram showing a schematic structure of an optical filter. FIG. 3 is a diagram showing an example of a process for forming an optical filter. FIG. 4 is a diagram showing a schematic configuration of a microfluidic system. FIG. 5 is a diagram showing a case where an optical signal irradiated from a light source unit passes through a micro flow channel. FIG. 6 is a diagram showing the light intensity of the optical signal detected by the optical detection unit in the second transmission region of FIG. 5 in a time series manner. FIG. 7 is a diagram showing the relationship between the optical properties of a substance and the properties required for an optical filter. FIG. 8 is a diagram showing the distribution of light intensity detected by the light detection unit. FIG. 9 is a diagram showing a case where the flow velocity of the solution is calculated from the time series change in the distribution of the light intensity shown in FIG. FIG. 10 is a diagram showing another case in which the flow velocity of a solution is calculated from the time series change in the distribution of light intensity. FIG. 11 is a flow chart of the flow velocity 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 flow chart 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. FIG. 16 is a diagram showing the relationship between S0 and _Sn . FIG. 17 is a flowchart of a modified example of the third embodiment. FIG. 18 is a diagram showing a schematic configuration of a microfluidic system.

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

In this disclosure, the term "surface" may refer not only to the surface of a plate-like member, but also to the interface of a layer contained in the plate-like member that is approximately parallel to the surface of the plate-like 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-like member or a layer contained in the plate-like member is illustrated. The "upper surface" and "lower surface" may also be referred to as the "first surface" and the "second surface".
Additionally, "upper" refers to the vertically upward direction when a plate-like member or layer is placed horizontally. Furthermore, "upper" and its opposite, "lower", are sometimes referred to as the "positive z-axis direction" and the "negative z-axis direction", and the horizontal direction is sometimes 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 xy plane defined by the x-axis and y-axis directions is referred to as the "width".

In this disclosure, the term "solution" refers to a specimen in a microfluidic system. Generally, a solution is a liquid state in which a solvent and a solute are mixed uniformly, 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, it also includes cases in which a solution simply refers to a mixture of a solid and a liquid.

[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.

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

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

1, the microchannel 30 has a shape of a straight channel extending in the x-axis direction, but the present disclosure is not limited to this. The microchannel 30 can be applied to cases other than straight channels, such as cases including a curved channel or a meandering channel. The inlet 32 and outlet 33 are set for convenience of explanation, and the inlet and outlet may be set interchangeably. 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 can be selected to avoid the location where the blockage has occurred.

1(b) and 1(c), in the microfluidic device 10, an optical filter 20 is disposed on the substrate 11, and a floor portion 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, and the optical filter 20 may be formed in a part of the microchannel 30. For example, the optical filter 20 can be disposed in a portion of the microchannel 30 where clogging is a concern. As described later, an optical signal is irradiated onto the microfluidic device 10 from the positive direction of the z-axis, and the state in which the optical signal passes through the microchannel 30 and the optical filter 20 is detected. The substrate 11 and the top surface 13 are made of materials that transmit optical signals so as not to block the optical signal irradiated from the light source unit 60.

Figure 2 is a schematic diagram showing the structure of the optical filter 20. Figure 2 is an enlarged view of a portion of the microchannel 30 of the microfluidic device 10 shown in Figure 1, with the floor 14 shown as transparent in order to explain the structure of the optical filter 20.

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

Each transparent region is arranged such that the center of each transparent region is spaced Δx apart in the x-axis direction and Δy apart in the y-axis direction. Each transparent region is a square region having the same area in the xy plane, and the distance between adjacent regions is gx apart in the x-axis direction and gy apart in the y-axis direction. The transparent regions can be specified using coordinates in the xy plane. For example, when i and j are positive integers, the first transparent region 22 can be specified 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). The fourth transmission regions 25 are located at coordinates (i-1, j+2), (i, j+1), (i+1, j), and (i+2, j-1). The light-shielding regions 21 are located between the transmission regions, and are formed over the entire microchannel 30 when viewed from the positive z-axis direction.

Note that while FIG. 2 shows a case where there are four types of transmissive regions, the present disclosure is not limited to this. The types of transmissive regions may be other than four. In addition, although the shape of the transmissive regions is a square, they may also be other shapes. In addition, the spacing at which the transmissive regions are arranged may also be set as appropriate.

(Optical filter forming process)
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 lattice 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.

Next, as shown in FIG. 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 the material that constitutes the first transmissive region 22. Next, as shown in FIG. 3(c), exposure is performed via a photomask 221 to a pattern in which the first transmissive region 22 will be disposed.

Next, unnecessary portions of the color resist 220 are removed using a developing solution, and then a baking process is performed to harden the color resist 220. This results in the first transmissive region 22 being disposed on the substrate 11, as shown in FIG. 3(d).

The color resist application 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, respectively. This forms the transmissive regions of the optical filter 20 on the substrate 11.

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, developing, and baking the resist. The upper surface portion 13 is disposed on the partition portion 12, and the microfluidic device 10 is formed.
The steps of forming the optical filter 20 and the microfluidic device 10 have been described above. In this disclosure, the formation method utilizing photolithography has been described on the assumption that the substrate 11 is made of glass. However, this disclosure is not limited to these formation methods, and other materials and molding techniques may also be applied.

(Configuration of Microfluidic System)
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 section 40, a waste liquid section 50, a light source section 60, a light detection section 70, an optical signal processing section 80, and a control section 90.

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 to the microfluidic device 10 through a connection tube 45 that is connected to the inlet 32 of the microfluidic device 10.

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. The 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.

The light source unit 60 irradiates the optical signal OS to the microfluidic device 10. 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 performs signal processing of 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.

The light source unit 60 can be one that irradiates 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 irradiate light in the near-infrared range. The light detection unit 70 may also have a spectroscopic function.

(Measurement of flow rate)
Measurement of flow velocity in a microfluidic system will be described with reference to Figures 5 to 10. In Figures 5 and 6, for ease of understanding, configurations that are particularly relevant to measurement of flow velocity are extracted and shown. In addition, although the optical filter 20 has a plurality of transmission regions in the xy plane, in order to facilitate understanding, Figure 6 shows a case in which the transmission regions are arranged only in the x-axis direction. Here, the microfluidic system 100 includes at least the 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 disposed between the light detection unit 70 and the light source unit 60 such that the direction of irradiation of the optical signal emitted from the light source unit 60 is perpendicular to the liquid sending direction LD of the microchannel 30. An optical filter 20 composed of a plurality of light transmitting regions and light blocking regions is disposed between the microchannel 30 and the light detection unit 70. This will be described in detail below.

(Light Intensity Detection)
5 is a diagram showing 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 sending direction (hereinafter also referred to as a "liquid sending direction LD") indicated by an arrow LD pointing in the positive direction of the x-axis. 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 direction of the z-axis, which is perpendicular to the liquid sending direction LD, and enters the microchannel 30. Note that the liquid sending direction LD indicates a macroscopic liquid sending direction in the microfluidic device 10, and the molecules of the solution may move in various directions microscopically.

The optical filter 20 is disposed between the microchannel 30 and the light detection unit 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 light detection unit 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 prevents the optical signal OS from passing through.

Figure 6 is a diagram showing the light intensity of the optical signal detected by the optical detection unit 70 in the second transmission region 23 of Figure 5 in a time series. 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.

Here, in the optical filter 20, one or more of the light transmission regions can transmit light of a specific wavelength region, so that the light detection unit 70 can detect the light intensity for each wavelength region. Specific examples will be described below.
It is assumed that the light source unit 60 irradiates light including wavelengths λ1, λ2, and λ3 as the optical signal OS, the second transmission region 23 blocks only light in the wavelength region including wavelengths λ1 and λ3, and transmits light in the wavelength region including wavelength λ2, and the material 31 blocks light in the wavelength region including wavelength λ1, and transmits light in the wavelength regions including wavelengths λ2 and λ3.

The intensity S0 means a base intensity, which is a reference light intensity for the optical signal OS. For example, the light intensity detected when the optical signal OS is irradiated from the light source unit 60 before a solution is flowed through the microfluidic device 10 can be used as the base intensity. It is also possible to use the light intensity detected when only a solvent is flowed through the microfluidic device 10 instead of a sample solution as the base intensity. The light intensity ST is a threshold value of the light intensity for determining the transmission of the optical signal OS. When 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 value ST may be set to 50% of the base intensity S0. The threshold value ST can be set according to the properties of the solvent or substance.

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

6A, for the light intensity of wavelength λ1, a light intensity S1 below threshold ST is detected at time _t1 , and values between base intensity S0 and threshold ST are detected at times _t2 and _t3 . Because the light intensity detected at time _t1 is smaller than threshold ST, it is determined that substance 31 was present above second transmission region 23 at time _t1 and was blocking optical signal OS.

6(b) and 6(c), in both cases, a light intensity greater than the threshold ST is detected, and therefore it is not possible to detect that the substance 31 was present above the second transmission region 23 between times _t1 and _t3 . The second transmission region 23 blocks only light in a wavelength range including the wavelength λ3 and transmits light in a wavelength range including the wavelength λ2. For this reason, the light intensity in the case of the wavelength λ2 shown in FIG. 6(b) is detected as being greater than the light intensity in the case of the wavelength λ3 shown in FIG. 6(c).

In this way, it is possible to determine the presence of the substance 31 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. Here, FIG. 7 is a diagram showing the relationship between the optical characteristics of the substance 31 and the characteristics required for the optical filter 20. In the first case, as described above, the substance 31 may transmit light in a certain wavelength region and absorb light in a wavelength region 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. Here, the first characteristic required for the transmission region of the optical filter 20 is to block light in a certain wavelength region transmitted by the substance 31. Also, 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 one transmission region, or the optical filter 20 may be one in which the first characteristic is imparted to one transmission region and the second characteristic is imparted to the other transmission region. By imparting these two characteristics to the transmission region in the optical filter 20 in either manner, it is possible to detect different light intensities when the substance 31 is present and when it is not, making it possible to determine the position of the substance 31.

In the second case, the substance 31 may absorb light in a certain wavelength range, but emit light in another wavelength range. In this case, the light detection unit 70 is required to detect the light of the transmitted wavelength among the wavelength range including the wavelength of the emitted light in the other wavelength range. Here, the first characteristic required for 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 the light of the wavelength range that has passed through the substance 31. The third characteristic is to transmit only the light of 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 when the substance 31 is present and when it is not present, and it is 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 each may be shared by different regions.

In addition, as a third case, the substance 31 may absorb all wavelengths of light irradiated from the light source unit 60. In this case, if the substance 31 is present, the light detection unit 70 cannot detect any wavelengths of light. Here, there is no requirement for the wavelength range to be blocked as a characteristic required for the transmission region of the optical filter 20. In other words, the wavelength range to be blocked in the transmission region can be set arbitrarily. For example, it is possible to adopt a transmission region that transmits light of all wavelength ranges.

As described above, by having one or more of the transmission regions transmit light of a specific wavelength range, it becomes possible to measure the flow rate even for a substance that absorbs light of 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 (order of 100 nm), and proteins (order of 10 nm). Non-living 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 also possible to include indicator particles different from the solute in the solution and measure the flow rate by detecting the change in light intensity caused by the indicator particles.

(Light Intensity Distribution)
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 sending 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 the light intensity that has passed through the microchannel 30 changes over time. A specific description will be given below.

Since the light intensity is detected as data distributed two-dimensionally according to the arrangement of the transmission and light-shielding regions of the optical filter 20, rectangular regions according to the arrangement of the transmission regions are shown in FIG. 8. When k and m are positive integers, the coordinates (m, k) and (m, k+1) in FIG. 8(a) indicate the locations where the light intensity is smaller than the threshold ST, and therefore indicate the locations where it is determined that the substance 31 was 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) different from the arrangement of the transmission regions in the optical filter 20 in FIG. 2 (four arranged in the x-axis direction and four arranged in the y-axis direction).

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, while 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 since the direction of movement of the light intensity in FIG. 8(a) to FIG. 8(c) coincides with the liquid delivery direction LD, the changes in light intensity in FIG. 8(a) to FIG. 8(c) are determined to have been caused by the movement of the same substance.

Figure 9 is a diagram showing the case where the flow velocity of the solution is calculated from the time series change in the light intensity distribution shown in Figure 8. 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 Figure 8(a) to coordinates (m+2, k) and (m+2, k+1) in Figure 8(c). For example, the magnitude and direction of arrow A1 can be used as the flow velocity of the solution at coordinates (m, k) and (m, k+1).

Figure 10 shows another case where the flow rate of the solution is calculated from the time series change in the distribution of light intensity. While Figures 8 and 9 show the case where there is one substance 31, Figure 10 shows the case where three substances are included in the region. Arrow A2 is shown narrower than arrow A1. This is because arrow A1 shows the flow rate at coordinates (m, k) and coordinates (m, k+1), while arrow A2 shows 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 is different in the microchannel corresponding to the position of coordinates (m+1, k+3) compared to coordinates (m, k) and coordinates (m, k+1).

Also, arrow A3 indicates the flow velocity at coordinate (m+4, k-2). Arrows A1 and A2 point in the positive x-axis direction, which is the same direction as the liquid delivery direction LD, but arrow A3 points away from the positive x-axis direction. Also, arrow A3 is smaller in size than arrows A1 and A2. Therefore, it is presumed that there is a sign of a blockage that will impede the flow of solution in the microchannel corresponding to the position of coordinate (m+4, k-2,).

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 obtained 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, contour map, or the like.

(Flow chart for flow velocity measurement)
A method of measuring the flow rate will be described with reference to Fig. 11. Fig. 11 is a flow chart of measuring the flow rate. The method of measuring the flow rate includes a first step (step S10) of feeding a solution to a microfluidic device 10 having 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 the first time and the light intensity distribution at the second time acquired in the second step, and calculating the flow rate of the solution in the microchannel 30 from the time-series change of the light intensity distribution. The method will be described in detail below.

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

Next, in step S11 (second process), the optical signal processing unit 80 acquires the distribution of the light intensity of the optical signal transmitted through the microchannel 30 in a time series. 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.

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

(Action and Effects)
As described above, according to the present disclosure, it is possible to accurately obtain flow velocity information in a microchannel. In addition, since 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 the angle of incidence of the optical signal, etc. In contrast, in the present disclosure, the optical filter 20 is disposed in the microfluidic device 10 and is configured to be close to the microchannel, so that it is possible to suppress the occurrence of a deviation in the angle of incidence of the optical signal between the optical filter 20 and the microchannel, and it is possible to appropriately evaluate the optical signal detected by the optical filter 20. In addition, generally, when an optical signal passes through an object, the light may be absorbed by the passing object, resulting in a decrease in light intensity, but in the present disclosure, since the optical filter 20 and the microchannel device 10 are integrated, it is possible to suppress a decrease in light intensity.
Furthermore, by integrating the optical filter 20 and the microchannel device 10, the configuration of the microfluidic system 100 is made smaller. Following the process of forming the optical filter 20 shown in Fig. 3, the floor portion 14, the partition portion 12, and the upper surface portion 13 are formed by utilizing photolithography to obtain the microchannel device 10. Since a common lithography facility can be utilized, the manufacturing cost of the microchannel device 10 can be reduced.
Furthermore, since there is no restriction on the location where the optical filter 20 is set in the microchannel, it is possible to measure the flow rate without being influenced by the shape of the microchannel. Furthermore, the flow rate can be measured according to the arrangement of the transmission regions in the optical filter, making it possible to measure a detailed flow rate distribution in the microchannel. By measuring the local flow rate in the channel using an optical filter, it becomes possible to perform measurements that are not dependent on the shape of the microchannel or the uniformity of the solution flow.

In addition, the above explanation is based on the assumption that the substance is approximately the same size as the transparent region, but by changing the size and shape of the patterning of the transparent and light-shielding regions, it is possible to measure the flow rate according to the size of the substance. Furthermore, if the light detection section 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.

[Modification of the first embodiment]
Note that between step S10 and step S11, a step of acquiring liquid sending direction information, which is information indicating the direction in which the solution moves with respect to the microchannel 30, may be included. For example, the control unit 90 determines that the solution has started to flow in the direction from the inlet 32 to the outlet 33 of the microchannel 30, triggered by driving the pump 42, and acquires information indicating the direction in which the solution has flowed as liquid sending direction information. It is also possible to provide a flow rate sensor or a liquid pressure sensor for the microchannel 30 and determine the liquid sending direction of the solution from the amount of liquid sent and the amount of waste liquid. If the arrangement position of the pump 42 and the arrangement positions of the inlet 32 and the outlet 33 are determined and the liquid sending direction in the microfluidic system 100 is fixed, the liquid sending direction information is already known, and therefore it is not necessary to acquire the liquid sending direction information. However, for example, if the microchannel has multiple paths and the liquid sending direction is changed at a predetermined period, the control unit 90 acquires the liquid sending direction information and calculates the flow velocity of the solution in the microchannel from the liquid sending 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 direction of liquid delivery falls within a specified range, it treats the movement of the substance as the flow rate of the solution.

[Second embodiment]
The second embodiment differs from the first embodiment in that a method for measuring flow velocity 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 the description thereof will be simplified or omitted.

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

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, a flow rate _vn at time t0+Δt·n (n is a positive integer) is compared with a flow rate _vn-1 at time t0+Δt·(n-1) at a predetermined position in the microchannel to determine an increase or decrease in the flow rate. In other words, when the flow rate at a certain time _tn (e.g., _tn =t0+Δn) at the coordinates (i,j) of a predetermined position is _vn (i,j), and the flow rate is calculated in time series such as _tn-1 , _tn , _tn+1 , ..., _vn (i,j) at a certain time _tn is compared with _vn-1 (i,j). 9, in a rectangular region (k, m), if the flow velocity _vn is the velocity calculated from the change in light intensity between time t0 and time t0+2Δt, and the flow velocity _vn-1 is the velocity calculated from the change in light intensity between time t0-Δt and time t0+Δt, _vn (m, k) is compared with _vn-1 (m, k) to determine whether the flow velocity has increased or decreased. Similar determinations are made for multiple coordinates.

Next, in step S24 (fifth step), 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, when the control unit 90 determines in step S23 that v _n (i, j) is greater than v _n-1 (i, j) (Yes in step S23), it determines that a blockage has occurred in the microchannel 30 corresponding to the position of coordinates (i, j) (step S24). In order 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.

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

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

After it is determined 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.

Subsequently, in step S260, the control unit 90 calculates a flow velocity v _p (i, j) at a time t _p (p is an integer greater than n) after performing step S250. Step S260 includes the same processes as steps S210 and S220.

Next, the control unit 90 compares _vp (i,j) with _vn (i,j) (step S270). If the control unit 90 determines that _vp (i,j) is greater than _vn (i,j) (Yes in step S270), it determines that a blockage has occurred in the microchannel 30 corresponding to the position of the coordinates (i,j) (step S280).

If it is determined in step S270 that v _p (i, j) is equal to or less than v _n (i, j) (No in step S270), the process returns to step S220, and the flow velocity is calculated.

(Action and Effects)
As described above, by measuring the flow velocity distribution in real time and determining an increase or decrease in the flow velocity, it is possible to detect clogging in the microchannel.
In addition, in the modified example of the second embodiment, a step is added in which the amount of liquid sent is changed and then it is confirmed that the flow rate changes, which makes it possible to more reliably determine whether clogging has occurred.

[Third embodiment]
The third embodiment differs from the second embodiment in that the occurrence of clogging is judged using light intensity. 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 the description thereof will be simplified or omitted.

Figure 14 is a flow chart of a method for determining the occurrence of clogging in a microchannel using light intensity. Also, Figure 15 is a diagram showing a schematic configuration of a microfluidic system. Microfluidic system 100a differs from microfluidic system 100 in Figure 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.

In step S30, the control unit 90 delivers a solvent that does not contain a solute. For example, the control unit 90 can deliver the solvent from a centrifuge tube 43 that contains only the solvent.

Next, 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.

Here, the light intensity at the coordinates (i, j) of a given position is denoted as S(i, j). In step S32, the light signal irradiated from the light source unit 60 passes only through the solvent, so the control unit 90 can obtain the base intensity S0(i, j).

Next, in step S33, the control unit 90 delivers a solvent containing a solute, i.e., a solution as a specimen. For example, the control unit 90 switches the liquid delivery unit 40 to a centrifuge tube 41 containing a solution, and delivers the liquid.

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.

Here, a certain time _tn = t0 + Δt·n, and the light intensity at time _tn is expressed as _Sn (i,j). In step S35, when _Sn (i,j) is acquired, the control unit 90 calculates the absolute value of the difference between S0(i,j) and _Sn (i,j) and judges whether the absolute value is greater than 0. Here, Fig. 16 is a diagram showing the relationship between S0 and _Sn . When there is a difference between the base intensity S0 and the light intensity _Sn at time _tn , a change in light intensity as shown in Fig. 16 is detected.

If a change in light intensity is detected (Yes in step S35), in step S36, the control unit 90 determines that a blockage has occurred in the microchannel 30 (step S36). 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.

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

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

After it is determined in step S360 that a blockage has occurred in the microchannel 30, the control unit 90 increases the flow rate of the liquid being delivered in step S43 (step S370). For example, the control unit 90 controls the pump 42 to increase the discharge rate.

Next, the control unit 90 acquires the light intensity at time _tp (p is an integer greater than n) after performing step S370, and compares the absolute value of the difference between S0(i,j) and _Sn (i,j) calculated in step S350 (hereinafter referred to as "absolute value at time _tn ") with the absolute value of the difference between S0(i,j) and _Sp (i,j) (hereinafter referred to as "absolute value at time _tp ") (step S380). If the absolute value of time _tn is equal to or less than the absolute value of time _tp (No in step S380), the control unit 90 determines that a blockage has occurred in the microchannel 30 (step S390). On the other hand, if the absolute value of time _tn is greater than the absolute value of time _tp (Yes in step S380), the control unit 90 returns to step S340 and acquires the light intensity.

(Action and Effects)
In the third embodiment and its modified example, it is possible to determine whether or not a blockage has occurred in the microchannel based on a change in light intensity. Compared to the second embodiment, the process of calculating the flow velocity can be omitted, so that the processing load on the control unit can be reduced.
In addition, in the modified example of the third embodiment, a step is added in which the flow rate is changed and then it is confirmed that the absolute value of the difference in light intensity changes, which makes it possible to more reliably determine whether clogging has occurred.

[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 described above are denoted by the same reference numerals, and the description thereof will be simplified or omitted.

Figure 18 is a diagram showing a schematic 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 liquid, the control unit 90 controls the pump 52 to flow the 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.

(Action and Effects)
Even if the configurations of the liquid sending section and the liquid waste section are changed, it is possible to measure the flow rate of the microchannel. Also, the configuration of the fourth embodiment can be applied to the first to third embodiments. Even if a plurality of branched microchannels are provided in the microfluidic device 10 and a plurality of liquid sending sections and liquid waste sections are required, it is possible to measure the flow rate by controlling each of the liquid sending section and the liquid waste section.

Although the embodiment of the present invention has been described above, the present invention is not limited to the above-mentioned embodiment, and various modifications are possible without departing from the gist of the present invention.

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

Claims (6)

1. A microfluidic system comprising:
The microfluidic system includes a microfluidic device including at least a microchannel and an optical filter , a light detection unit that acquires light intensity , and a light source unit that irradiates the microchannel with an optical signal;
the microfluidic device is disposed between the light detection unit and the light source unit such that an irradiation direction of the optical signal emitted from the light source unit is perpendicular to a liquid sending direction of the microchannel;
The optical filter is disposed in the microfluidic device between the microchannel and the light detection unit, and is composed of a plurality of light-transmitting regions and a light-shielding region.
Microfluidic systems. 2. The microfluidic system of claim 1 , wherein the optical filter is configured such that one or more of the plurality of light-transmitting regions can transmit light in a specific wavelength range.
Microfluidic systems. A first step of delivering a solution to a microfluidic device including a microchannel and an optical filter;
a second step of irradiating the microchannel with an optical signal and acquiring a time-series distribution of the optical intensity of the optical signal transmitted through the microchannel;
a third step of calculating a time series change indicating a change between the distribution of the light intensity at a first time and the distribution of the light intensity at a second time acquired in the second step, and calculating a flow velocity of the solution in the microchannel from the time series change of the distribution of the light intensity,
The method for measuring flow velocity, wherein the optical filter is disposed within the microfluidic device. 4. The flow velocity measuring method according to claim 3,
The light intensity in the second step is acquired at predetermined time intervals Δt;
a fourth step of comparing a flow velocity vn at a time t0+Δt・n (n is a positive integer) with a flow velocity vn-1 at a time t0+Δt・(n-1) at a predetermined position in the microchannel, where t0 is a predetermined time, to determine whether the flow velocity has increased or decreased. 5. The flow velocity measuring method according to claim 4, further comprising a fifth step of determining whether a blockage has occurred at the predetermined position of the microchannel based on an increase or decrease in the flow velocity. 4. The flow velocity measuring method according to claim 3,
In the second step, the light intensity is acquired by a light detection unit;
In the second step, the optical signal is irradiated from a light source unit,
the microfluidic device is disposed between the light detection unit and the light source unit such that an irradiation direction of the optical signal emitted from the light source unit is perpendicular to a liquid sending direction of the microchannel;
The optical filter is disposed between the microchannel and the light detection unit, and is composed of a plurality of light transmitting regions and a light blocking region.
Flow velocity measurement method.

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