Patent Publication Number: US-2023144260-A1

Title: Liquid supply method

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority from Japanese patent application JP 2021-180901 filed on Nov. 5, 2021, the entire content of which is hereby incorporated by reference into this application. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present disclosure relates to a liquid supply method. 
     2. Description of the Related Art 
     As a more accurate inspection method than a polymerase chain reaction (PCR), a method called dPCR (digital PCR) has attracted attention. The dPCR is a method for discriminating whether or not there is a DNA sequence to be detected for each microdroplet by fractionating a solution to be inspected into microdroplets, performing a PCR reaction, and then performing fluorescence observation of each microdroplet. Since a volume of the fractionated droplet is minute, even when there is one copy of the DNA sequence to be detected in the droplet, after DNA to be detected is amplified through the PCR reaction, the DNA sequence to be detected has a concentration that can be sufficiently observed in the droplet. Thus, even in a case where the solution to be inspected contains only an extremely small amount of DNA sequences to be detected, it is possible to discriminate whether or not there is the DNA sequence to be detected in the solution to be inspected. Usually, the volume of the fractionated microdroplet is sufficiently small, and only about one copy or zero copy of the DNA sequence to be inspected is contained in each microdroplet. Accordingly, it is possible to count the number of DNA sequences to be detected originally present in the solution to be inspected by observing each droplet after the PCR reaction and counting the number of droplets in which the DNA sequence to be detected is amplified. 
     JP 2015-512508 A discloses a method for fractionating a solution to be inspected in dPCR. That is, the solution to be inspected is fractionated and filled in each through-hole by supplying the solution to be inspected to a sample loader and sliding the sample loader on a front surface of a chip on which an array of through-holes is disposed. Thereafter, an upper surface and a lower surface of the chip are filled with oil, and thus, the solutions filled in the through-holes are prevented from evaporating or the solutions in the adjacent holes are prevented from coming into contact with each other. Subsequently, the PCR reaction is performed. 
     The PCR reaction is performed, for example, by installing an array chip (a substrate having arrayed spots) on a thermal cycler and setting a temperature of the thermal cycler such that two temperatures of, for example, 60° C. and 98° C. are repeated. An enzyme and a primer necessary for amplifying the DNA sequence to be detected by the PCR reaction, and a probe that is specifically bound to the DNA sequence to be detected are introduced into the solution to be inspected in advance, and a fluorescent substance is bound to the probe. After the PCR reaction, the DNA sequence to be detected is amplified, and the probe with the fluorescent substance is bound thereto. This fluorescent substance is engineered to be capable of emitting fluorescence only when the probe is bound to the DNA sequence (see, for example, Tatsuo Nakagawa, et al., Anal. Chem. 2020, 92, 17, 11705-11713). Accordingly, when fluorescence observation is performed by irradiating the array of through-holes with excitation light after the PCR reaction, fluorescence derived from the DNA sequence to be detected is observed in a case where there is the DNA sequence in the through-holes, and fluorescence is not observed otherwise. That is, it is possible to know whether or not there is the DNA sequence to be detected based on whether or not there is the through-hole that emits fluorescence. It is possible to know the number of copies of the DNA sequence to be detected originally present in the solution to be inspected by counting the number of through-holes that emits fluorescence. 
     Xu Gao, et al., Biomicrofluidics 14, 034109 (2020); https://doi.org/10.1063/5.0006374 describes another method for fractionating the solution to be inspected by using the array of through-holes. That is, the chip in which the array of through-holes is disposed is incorporated in a flow path. The solution to be inspected is supplied to the flow path by using a syringe pump, and subsequently air is supplied. Thus, the solution to be inspected is fractionated and filled into the through-holes. Thereafter, an upper surface and a lower surface of the chip are filled with oil, and thus, the solutions filled in the through-holes are prevented from evaporating or the solutions in the adjacent holes are prevented from coming into contact with each other. Subsequently, the PCR reaction is performed. The method of the PCR reaction and the method of the subsequent fluorescence observation may be the same as described above. 
     SUMMARY OF THE INVENTION 
     In JP 2015-512508 A, the solution to be inspected is fractionated and filled in the array of through-holes by sliding the sample loader on the front surface of the through-hole array chip. When the sample loader is slid onto the front surface of the through-hole array chip, an upper side of the chip is widely opened to the atmosphere. Thus, there is a high risk that foreign matters (particles), DNA, and the like floating in the atmosphere are mixed into the through-hole array. Due to a variation in an angle at which the loader comes into contact with the front surface of the array chip, a filling rate of the solution to be inspected into each through-hole changes, or partially there are through-holes that are not filled. Due to a variation in a position where the loader comes into contact with the chip front surface, partially there are through-holes that are not filled, or the solution to be inspected remains in a portion of a chip end other than the through-hole portion. Such a phenomenon leads to a decrease in inspection accuracy of the dPCR. 
     In JP 2015-512508 A, the solution filling into the through-hole using the loader is electrically performed by manufacturing a dedicated device. However, it takes a long time to complete the filling of the through-hole with the solution after mounting the chip on the device, and the through-hole cannot be filled with the solution unless electric power is used. 
     In Xu Gao, et al., Biomicrofluidics 14, 034109 (2020); https://doi.org/10.1063/5.0006374, the chip in which the array of through-holes is disposed is incorporated in the flow path. The solution to be inspected is supplied to the flow path by using the syringe pump, and subsequently the air is supplied. Thus, the solution to be inspected is fractionated and filled in the through-holes. In this method, since the array chip of the through-holes is incorporated in the flow path while the solution is being supplied, while each through-hole is being filled with the solution, and after each through-hole is filled with the solution, the upper side of the array chip is not widely opened to the atmosphere. Accordingly, as compared with the method in JP 2015-512508 A, there is a low risk that the foreign matters (particles), the DNA, and the like floating in the atmosphere are mixed into the through-hole array. The loader is not used unlike JP 2015-512508 A. Accordingly, as compared with the method in JP 2015-512508 A, the filling rate of the solution to be inspected into the through-hole becomes more uniform, and the solution to be inspected does not remain in the portion of the chip end other than the through-hole portion. However, the syringe pump is used for supplying the solution to the chip and supplying the air, and electric power is required for driving the syringe pump. Accordingly, even in this method, the solution cannot be filled into the through-hole without using electric power. 
     Therefore, the present disclosure provides a technology for filling a spot formed on a substrate with a solution to be inspected with good yield without using a loader, a syringe pump, and electric power. 
     In order to solve the above problems, the present disclosure provides a liquid supply method for supplying a solution to be inspected to a spot formed in a substrate. The method includes preparing a liquid supply pipe in which the solution to be inspected, air, and oil are disposed in this order, and installing the liquid supply pipe above the substrate at an angle such that the solution to be inspected is positioned on a lowermost side and the solution to be inspected, the air, and the oil flow onto a front surface of the substrate by gravity. A cross-sectional area of the liquid supply pipe is designed such that the air continues to be present between the solution to be inspected and the oil while the solution to be inspected, the air, and the oil are flowing through the liquid supply pipe, and after the solution to be inspected is supplied to the spot, the solution to be inspected present on the front surface of the substrate is replaced with the air, and then the liquid supply progresses such that the oil covers the front surface of the substrate. 
     Further features related to the present disclosure will become apparent from the description of the present specification and the accompanying drawings. The aspects of the present disclosure are achieved and realized by elements, combinations of various elements, the following detailed description, and aspects of the appended claims. The description of the present specification is merely a typical example, and does not limit the scope of claims or application examples of the present disclosure in any sense. 
     According to the technology of the present disclosure, it is possible to fill the spot formed on the substrate with the solution to be inspected with good yield without using the loader, the syringe pump, and the electric power. Other objects, configurations, and effects will be made apparent in the following descriptions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1 A  is a top view of an array chip according to a first embodiment; 
         FIG.  1 B  is a cross-sectional view taken along line A-A′ of  FIG.  1 A ; 
         FIG.  1 C  is a top view of a state where the array chip is incorporated in a flow cell; 
         FIG.  1 D  is a cross-sectional view taken along line B-B′ of  FIG.  1 C ; 
         FIG.  1 E  is a cross-sectional view taken along line C-C′ of  FIG.  1 C ; 
         FIG.  2 A  is a top view illustrating a first modified example of a structure of the flow cell; 
         FIG.  2 B  is a top view illustrating a second modified example of the structure of the flow cell; 
         FIG.  2 C  is a top view illustrating a third modified example of the structure of the flow cell; 
         FIG.  2 D  is a cross-sectional view taken along line D-D′ of  FIG.  2 C ; 
         FIG.  2 E  is a cross-sectional view taken along line E-E′ of  FIG.  2 C ; 
         FIG.  3 A  is a photograph in a case where the array chip is actually incorporated in the flow cell having the structure illustrated in  FIG.  2 A ; 
         FIG.  3 B  is a photograph in a case where the array chip is actually incorporated in the flow cell having the structure illustrated in  FIG.  1 C ; 
         FIG.  4 A  is a diagram illustrating an ideal procedure when a solution to be inspected is supplied to a through-hole array; 
         FIG.  4 B  is a diagram illustrating an ideal procedure when the solution to be inspected is supplied to the through-hole array; 
         FIG.  5 A  is a diagram for describing problems that occur when liquid supply is performed; 
         FIG.  5 B  is a diagram for describing the problems that occur when the liquid supply is performed; 
         FIG.  6 A  is a photograph of an upper surface of the flow cell before the solution to be inspected is supplied; 
         FIG.  6 B  is a photograph of a bottom surface of the flow cell before the solution to be inspected is supplied; 
         FIG.  6 C  is a photograph of the upper surface of the flow cell after the solution to be inspected is supplied and air is supplied; 
         FIG.  6 D  is a photograph of the bottom surface of the flow cell after the supply of the solution to be inspected and the air is supplied; 
         FIG.  7 A  is a diagram illustrating a liquid supply method to an array chip according to the first embodiment; 
         FIG.  7 B  is a diagram illustrating the liquid supply method to the array chip according to the first embodiment; 
         FIG.  8    is a top view of the flow cell in a state where a liquid supply pipe is connected; 
         FIG.  9 A  is a diagram for describing movement of a fluid in the liquid supply pipe in a case where an inner diameter of the liquid supply pipe is large; 
         FIG.  9 B  is a diagram for describing the movement of the fluid in the liquid supply pipe in a case where the inner diameter of the liquid supply pipe is small; 
         FIG.  10 A  is a diagram illustrating a force due to gravity applied to the solution and oil during liquid supply; 
         FIG.  10 B  is a diagram for describing a state of the solution to be inspected near a lower side of a through-hole; 
         FIG.  10 C  is a diagram for describing a state of the solution to be inspected near the lower side of the through-hole; 
         FIG.  11    is a diagram for more accurately describing the force applied to the solution to be inspected on the upper side of the array chip; 
         FIG.  12    is a diagram for simplifying and describing the force applied to the solution to be inspected on the upper side of the array chip; 
         FIG.  13    is a diagram illustrating a modified example of the liquid supply pipe; 
         FIG.  14 A  is a diagram illustrating a liquid supply method to an array chip according to a second embodiment; 
         FIG.  14 B  is a diagram illustrating the liquid supply method to the array chip according to the second embodiment; 
         FIG.  15    is a diagram for describing a timing at which the solution to be inspected and the array chip come into contact with each other; 
         FIG.  16 A  is a diagram illustrating a liquid supply method to an array chip according to a modified example of the second embodiment; 
         FIG.  16 B  is a diagram illustrating a liquid supply method to an array chip according to a modified example of the second embodiment; 
         FIG.  17 A  is a diagram illustrating a liquid supply method to an array chip according to a third embodiment; 
         FIG.  17 B  is a diagram illustrating the liquid supply method to the array chip according to the third embodiment; 
         FIG.  17 C  is a diagram illustrating the liquid supply method to the array chip according to the third embodiment; 
         FIG.  17 D  is a diagram illustrating the liquid supply method to the array chip according to the third embodiment; 
         FIG.  18 A  is a diagram illustrating a liquid supply method to an array chip according to a fourth embodiment; 
         FIG.  18 B  is a diagram illustrating the liquid supply method to the array chip according to the fourth embodiment; 
         FIG.  19    is a diagram illustrating a structure of a liquid supply pipe according to a fifth embodiment; 
         FIG.  20 A  is a diagram illustrating a liquid supply method to an array chip according to a sixth embodiment; 
         FIG.  20 B  is a diagram illustrating the liquid supply method to the array chip according to the sixth embodiment; 
         FIG.  21    is a diagram illustrating a liquid supply method to an array chip according to a seventh embodiment; 
         FIG.  22    is a diagram for describing a PCR reaction and a method of fluorescence observation according to an eighth embodiment; 
         FIG.  23    is a schematic diagram illustrating an example of a result of fluorescence observation; 
         FIG.  24    is a diagram illustrating a flow cell in which an array chip is incorporated after a liquid supply method according to a ninth embodiment is performed; 
         FIG.  25 A  is a cross-sectional view of an array chip including an array of wells; 
         FIG.  25 B  is a cross-sectional view of an array chip having an array of hydrophilic spots; 
         FIG.  26    is a diagram illustrating a liquid supply method to an array chip according to a tenth embodiment; 
         FIG.  27    is a diagram illustrating the liquid supply method to the array chip according to the tenth embodiment; 
         FIG.  28 A  is a diagram illustrating a liquid supply method to an array chip according to an eleventh embodiment; 
         FIG.  28 B  is a diagram illustrating the liquid supply method to the array chip according to the eleventh embodiment; 
         FIG.  29 A  is a diagram illustrating a liquid supply method to an array chip according to Example 1; 
         FIG.  29 B  is a diagram illustrating the liquid supply method to the array chip according to Example 1; 
         FIG.  30 A  is a cross-sectional view of a flow cell in a state where a liquid supply pipe is connected; 
         FIG.  30 B  is a top view of a state of  FIG.  30 A ; 
         FIG.  31 A  is a photograph of a front surface of a flow cell after liquid supply in Example 1 is performed; and 
         FIG.  31 B  is a photograph of a back surface of the flow cell after liquid supply in Example 1 is performed. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In all the drawings for describing the embodiments of the present disclosure, components having the same function are denoted by the same reference signs, and redundant description thereof will be omitted as far as possible. The structures and materials described in the embodiments are examples for embodying the idea of the present disclosure, and are not intended to strictly specify materials, dimensions, detailed structures, and the like. In particular, the dimensions and scales of the drawings are not accurate due to a preference for visibility. 
     First Embodiment 
     Configuration Example of Array Chip 
       FIG.  1 A  is a top view of an array chip  100 . The array chip  100  has a through-hole array  110  in a central portion thereof in which through-holes  101  are arrayed. A material of the array chip  100  may be, for example, Si whose front surface is oxidized, or may be glass. A shape of an upper surface of the through-hole  101  is not limited to a quadrangle, and may be, for example, a circle, a hexagon, or another polygon. A density of the through-holes  101  can be, for example, about 170 holes/mm 2 . 
       FIG.  1 B  is a cross-sectional view taken along line A-A′ of  FIG.  1 A . A thickness of the array chip  100  can be, for example, 300 μm. 
     Configuration Example of Flow Cell 
       FIG.  1 C  is a top view of a state where the array chip  100  is incorporated in a flow cell  120 . The flow cell  120  includes a lower part  102 , a spacer  103 , an upper part  104 , an introduction port  105 , a discharge port  106 , an introduction port  107 , and a discharge port  108 . The introduction port  105  and the discharge port  106  are provided in the upper part  104 . The introduction port  107  and the discharge port  108  are provided in the lower part  102 . A material of the lower part  102  can be, for example, zinc, aluminum, glass, acrylic, polycarbonate, or other plastic materials. The upper part  104  is a transparent member. A material of the upper part  104  can be, for example, glass, acrylic, polycarbonate, or other plastic materials. The spacer  103  is provided between the array chip  100  and the upper part  104 , and defines a lemon-shaped space in top view. As described above, since the space defined by the spacer  103  has a rounded lemon shape, a fluid supplied to the space can efficiently permeate. 
       FIG.  1 D  is a cross-sectional view taken along line B-B′ of  FIG.  1 C . As illustrated in  FIG.  1 D , a lower surface of an end portion of the array chip  100  is supported by the lower part  102 . The array chip  100  and the lower part  102  are bonded to each other by using, for example, an adhesive. The array chip  100  can be incorporated into the flow cell  120  by disposing the spacer  103  on the array chip  100  and disposing the upper part  104  on the spacer  103 . A thickness of the spacer  103  determines a distance between the array chip  100  and the upper part  104 . The spacer  103  can be, for example, a double-sided tape having a thickness of about 100 μm. The introduction port  105  and the discharge port  106  are communicatively connected to a space on an upper side of the array chip  100 . A fluid (liquid or gas) can be supplied from the introduction port  105  to the upper side of the array chip  100  and can be discharged from the discharge port  106 . 
       FIG.  1 E  is a cross-sectional view taken along line C-C′ of  FIG.  1 C . The introduction port  107  and the discharge port  108  are communicatively connected to a space on a lower side of the array chip  100 . A fluid can be supplied from the introduction port  107  to the lower side of the array chip  100  and can be discharged from the discharge port  108 . A distance between the lower surface of the array chip  100  and the lower part  102  can be, for example, 300 μm. 
     Another Configuration Example of Flow Cell 
       FIG.  2 A  is a top view illustrating a first modified example of a structure of the flow cell  120 . In the example of  FIG.  2 A , the introduction port  105  and the discharge port  106  for introducing and discharging the fluid to and from the upper side of the array chip  100  are disposed at positions (on the same diagonal line) close to the introduction port  107  and the discharge port  108  for introducing and discharging the fluid to and from the lower side of the array chip  100 . 
       FIG.  2 B  is a top view illustrating a second modified example of the structure of the flow cell  120 . In the example of  FIG.  2 B , the introduction port  105  and the discharge port  106  for introducing and discharging the fluid to and from the upper side of the array chip  100  are not disposed on the diagonal line of the array chip  100 , and are disposed at positions shifted from corners of the array chip  100 . In the example of  FIG.  2 B , an opening of the spacer  103  (the space defined by the spacer  103 ) is not rounded but cut into a polygonal shape. 
       FIG.  2 C  is a top view illustrating a third modified example of the structure of the flow cell  120 . In the example of  FIG.  2 C , while one introduction port  111  for introducing the fluid is provided on the upper side of the array chip  100 , two discharge ports  112  and  113  for discharging the fluid on the upper side of the array chip  100  are provided. In  FIG.  2 C , a bulging shape  114  is provided in the middle of a flow path toward the discharge port  112 . 
       FIG.  2 D  is a cross-sectional view taken along line D-D′ of  FIG.  2 C . As illustrated in  FIG.  2 D , the introduction port  111  and the discharge port  112  are formed in the upper part  104 , and the introduction port  111  and the discharge port  112  are communicatively connected to the space on the upper side of the array chip  100 . 
       FIG.  2 E  is a cross-sectional view taken along line E-E′ of  FIG.  2 C . As illustrated in  FIG.  2 E , an introduction port  123  and a discharge port  124  are formed by openings provided in the upper part  104 , and the introduction port  123  and the discharge port  124  are communicatively connected to the space on the lower side of the array chip  100 . 
     The structure of the flow cell  120  is not limited to the structures illustrated in  FIGS.  1 C and  2 A to  2 E , and may be another structure. 
       FIG.  3 A  is a photograph in a case where the array chip is actually incorporated in the flow cell having the structure illustrated in  FIG.  2 A . A lemon-shaped space is defined at the central portion of the flow cell illustrated in  FIG.  3 A . This lemon-shaped space is sealed, and the fluid is supplied to this space. 
       FIG.  3 B  is a photograph in a case where the array chip is actually incorporated in the flow cell having the structure illustrated in  FIG.  1 C . Similarly to  FIG.  3 A , a lemon-shaped space is also defined in the central portion of the flow cell in  FIG.  3 B . 
     Ideal Liquid Supply Procedure 
       FIGS.  4 A and  4 B  are diagrams illustrating an ideal procedure when a solution to be inspected is fractionated into the through-hole array  110  of the array chip  100 . Hereinafter, in the description of the liquid supply procedure to the array chip  100 , a case where the flow cell  120  having the structure illustrated in  FIGS.  1 C to  1 E  is used will be described as a representative. 
     Step (i) of  FIG.  4 A  illustrates a state immediately before the supply of a solution  202  to be inspected. First, as illustrated in step (i) of  FIG.  4 A , an operator fills a distal end portion  201  of a pipette  200  with the solution  202  to be inspected, and connects the pipette to the introduction port  105 . Thereafter, the operator extrudes the solution  202  to be inspected by pressing a push button  204  by hand. Accordingly, as in step (ii), the solution  202  to be inspected is supplied to the upper side of the array chip  100  and into each through-hole  101 . A main body portion of the pipette  200  is representatively drawn only in step (i), and is omitted in step (ii) and subsequent steps. 
     Subsequently, as illustrated in step (iii), the operator fills the distal end portion  201  of the pipette  200  with air and connects the pipette to the introduction port  105 . Thereafter, the operator extrudes the air by pressing the push button  204 . Accordingly, as in step (iv) of  FIG.  4 B , the solution  202  to be inspected on the upper side of the array chip  100  is replaced with the air. The solution  202  to be inspected overflowing from the discharge port  106  due to the supply of the air is discarded. At this time, the solution  202  to be inspected remains in each through-hole  101  due to surface tension. 
     Subsequently, as illustrated in step (v), the operator fills the distal end portion  201  of the pipette  200  with oil  203  and connects the pipette to the introduction port  105 . Thereafter, the operator extrudes the oil  203  by pressing the push button  204 . Accordingly, the upper side of the array chip  100  is filled with the oil  203 . 
     Finally, as illustrated in step (vi), the operator fills the distal end portion  201  of the pipette  200  with the oil  203 , and connects the pipette to the introduction port  107 . Thereafter, the operator extrudes the oil  203  by pressing the push button  204 . Accordingly, the lower side of the array chip  100  is filled with the oil  203 . 
     As in the above steps (i) to (vi), a structure in which the solution  202  to be inspected is fractionated into the through-holes  101 , and the upper side and the lower side of the solution  202  to be inspected in each through-hole  101  are covered with the oil  203  is formed. Thereafter, the flow cell  120  in which the array chip  100  is incorporated is installed in a thermal cycler, and a PCR reaction is performed. After completion of the PCR reaction, fluorescence observation of the array chip  100  from the upper surface side is performed, and thus, it can be seen whether or not a DNA sequence to be detected is present in the solution  202  to be inspected. Detailed methods of the PCR and the fluorescence observation are as described in [Description of the Related Art]. Since the upper side and the lower side of the solution  202  to be inspected present in the through-hole array  110  are covered with the oil  203 , the solution  202  to be inspected present in the adjacent through-holes  101  is basically not mixed during the PCR reaction. 
     According to the method of  FIGS.  4 A and  4 B , the upper side of the array chip  100  is not largely opened to the atmosphere, including during and before and after liquid supply. Accordingly, as compared with the method using the loader as in JP 2015-512508 A, there is a low risk that the foreign matters (particles), the DNA, and the like floating in the atmosphere are mixed into the through-hole array  110  during liquid supply and before and after liquid supply. Since the loader is not used, the filling rate of the solution to be inspected into each through-hole does not change or there are no through-holes partially that are not filled due to a variation in an angle or a position at which the loader comes into contact with the front surface of the array chip. Accordingly, a yield of the inspection of the dPCR is improved, and high inspection accuracy can be secured. Since the pipette  200  is manually operated, a device using electric power is not required to fill the through-hole array  110  with the solution  202  to be inspected. Thus, as compared with JP 2015-512508 A and Xu Gao, et al., Biomicrofluidics 14, 034109 (2020); https://doi.org/10.1063/5.0006374 using the syringe pump, the solution to be inspected can be fractionated into each through-hole in an energy-saving and simple manner. 
     Problems in Liquid Supply 
       FIGS.  5 A and  5 B  are diagrams for describing problems that occur when the method illustrated in  FIGS.  4 A and  4 B  is executed. The main body portion of the pipette  200  is representatively drawn only in step (i) of  FIG.  5 A , and is omitted in step (ii) and subsequent steps. According to the method of  FIGS.  4 A and  4 B , the pipette  200  is manually operated during liquid supply and air supply to extrude the solution and the air. Thus, there are variations in speed and force during extrusion. In a case where the extrusion speed is too fast or the extrusion force is too strong, a strong pressure is applied to the solution in the flow cell. When this force is too strong, the solution  202  to be inspected that remains in the through-hole  101  due to the surface tension cannot continue to remain due to the surface tension, and leaks out below the through-hole  101 . In step (ii), solutions  210  and  211  leaking out below the through-holes  101  are illustrated. The solutions  202  to be inspected filled in the different through-holes  101  are connected by the solutions  210  and  211 . This is a problem in the dPCR measurement. This is because even though there is originally the DNA sequence to be detected only in a certain through-hole  101 , in a case where the solution  202  in the through-hole  101  is connected to the solution  202  in a plurality of another through-holes  101 , there are the amplified DNA sequences to be detected in all the through-holes  101  (that is, the through-holes  101  in which the solutions are connected) after the PCR reaction. By doing this, in the fluorescence observation after the PCR, fluorescence suggesting the presence of the DNA sequence to be detected is observed from all of these through-holes  101 . In the dPCR, usually, the number of DNA sequences to be detected in an aqueous solution to be inspected is counted by counting the number of through-holes in which fluorescence is observed. However, as described above, when the solutions in the through-holes are connected to each other and the DNA sequence to be detected to be proliferated in one through-hole spreads over the plurality of through-holes, the accuracy of counting (accuracy of counting the number of DNA sequences to be detected originally present in the aqueous solution to be inspected) decreases. 
     As illustrated in step (iii), the solution may leak out below the through-holes  101  also when the air is supplied. In a case where the extrusion speed and the extrusion force of the air by the pipette  200  vary, and the extrusion speed is too fast or the extrusion force is too strong, a strong pressure is applied to the solution  202  in the flow cell  120 . As a result, the solution cannot remain in the through-hole  101  due to the surface tension and leaks out below the through-holes  101 . In step (iii), solutions  212  and  213  leaking out below the through-holes  101  are illustrated. 
     As illustrated in step (v) of  FIG.  5 B , the liquid may leak out below the through-holes  101  also during the injection of the oil  203 . Similarly, in a case where the extrusion speed and extrusion force of the oil  203  by the pipette  200  vary, and the extrusion speed is too fast or the extrusion force is too strong, a strong pressure is applied to the oil  203  in the flow cell  120 . As a result, the solution  202  present in the through-hole  101  cannot remain in the through-hole  101  due to the surface tension, and leaks out together with the oil  203  below the through-hole  101 . In step (v), solutions  214  and  215  leaking out together with the solution  202  and the oil  203  are illustrated. As illustrated in step (vi), when the solution  202  or the oil  203  leaks out, the solutions  202  in the adjacent through-holes  101  are connected with the leaked solutions, or the through-holes  101  filled with the oil  203  are present. As a result, the yield of the inspection decreases. 
       FIG.  6 A  is a photograph of an upper surface of the flow cell before the solution is supplied.  FIG.  6 B  is a photograph of a back surface of the flow cell before the solution is supplied.  FIG.  6 C  is a photograph of the upper surface of the flow cell after steps (i) to (iv) illustrated in  FIGS.  4 A and  4 B  are performed.  FIG.  6 D  is a photograph of the back surface of the flow cell after steps (i) to (iv) illustrated in  FIGS.  4 A and  4 B  are performed. As illustrated in  FIGS.  6 C and  6 D , it can be confirmed that the solution to be inspected introduced from the front surface side of the array chip  100  leaks out to the back surface through the through-holes and the liquids in the different through-holes are connected to each other. This is because since the pipette is manually operated, the extrusion force and the extrusion speed during the liquid supply and the air supply vary, and as a result, the extrusion force is too strong or the extrusion speed is too fast, and the solution in the through-hole is extruded below the through-hole. 
     In Xu Gao, et al., Biomicrofluidics 14, 034109 (2020); https://doi.org/10.1063/5.0006374, the solution to be inspected and the air are supplied to the flow path (flow cell) at a constant low speed by using the syringe pump instead of the manual operation using the pipette. Accordingly, the solution in the through-hole is not extruded below the through-hole, and the through-hole is filled with the solution to be inspected. However, electric power is required to drive the syringe pump. Since the size of the syringe pump is considerably larger than the size of the flow cell, a large work space is required for supplying the liquid to the flow cell. Accordingly, a method for filling the through-hole array with the solution in an energy-saving and simple manner without using electric power is desired. 
     Liquid Supply Procedure According to First Embodiment 
       FIGS.  7 A and  7 B  are diagrams illustrating a liquid supply method to the array chip  100  according to the first embodiment. In the present embodiment, a method of supplying the solution  202  to be inspected, the air, and the oil  203  to the flow cell  120  by using a liquid supply pipe will be described. 
     First, as illustrated in step (1) of  FIG.  7 A , the operator prepares a liquid supply pipe  300  filled with the solution  202  to be inspected, air  301  separating the solution  202  to be inspected and the oil  203 , and the oil  203  in advance. The liquid supply pipe  300  may have flexibility or may have rigidity. Next, the operator connects the liquid supply pipe  300  to the introduction port  105  such that the solution  202  to be inspected is positioned on the side (lowermost) closest to the array chip  100 . The flow cell  120  in which the array chip  100  is incorporated is installed substantially horizontally. An angle between the flow cell  120  and the liquid supply pipe  300  is defined as θ (0°≤θ≤90°). That is, the angle θ is an approximate angle of the liquid supply pipe  300  with respect to a horizontal plane. After setting to the state illustrated in step (1), almost no operation is required up to step (5) in  FIG.  7 B . 
     In step (2) of  FIG.  7 A , the solution  202  to be inspected is filled on the upper side of the array chip  100  and the through-holes  101  in the array chip  100  by gravity applied to the solution  202  to be inspected and the oil  203 . Thereafter, in step (3) of  FIG.  7 A , the air  301  in the liquid supply pipe  300  is extruded to the flow cell by the gravity applied to the oil  203 , and the air  301  extrudes (replaces) the solution  202  to be inspected present on the upper side of the array chip  100 . At this time, the operator discards the solution overflowing from the discharge port  106 . In step (4) of  FIG.  7 B , the solution  202  to be inspected that was present on the upper side of the array chip  100  is completely replaced with the air  301 . Thereafter, in step (5) of  FIG.  7 B , the oil  203  enters the flow cell by the gravity applied to the oil  203 , and the upper side of the array chip  100  is filled with the oil  203 . Thereafter, in step (6) of  FIG.  7 B , the operator connects a liquid supply pipe  350 , filled with the oil  203  in advance, to the introduction port  107  at an angle θ′. Accordingly, the oil  203  enters the flow cell by the gravity applied to the oil  203 , and the lower side of the array chip  100  is filled with the oil  203 . The angle θ′ may be the same as or different from the angle θ. As described above, in the liquid supply in steps (1) to (6) illustrated in  FIGS.  7 A and  7 B , a power source of the fluid is gravity, and the electric power is not used. Such liquid supply by the gravity can be realized by the presence of two air holes of the introduction port  105  and the discharge port  106  on the upper side of the array chip  100  and the presence of two air holes of the introduction port  107  and the discharge port  108  on the lower side of the array chip  100 . In other words, when the liquid is supplied from one air hole, the other air hole is released to the atmosphere, thereby the liquid supply by the gravity is achieved. 
       FIG.  8    is a top view of the flow cell  120  in a state where the liquid supply pipes  300  and  350  are connected. In step (6) of  FIG.  7 B , although a scene where the liquid supply pipe  300  is pulled out from the introduction port  105  and then the liquid supply pipe  350  is connected to the introduction port  107  is illustrated, the liquid supply pipe  350  may be connected to the introduction port  107  while the liquid supply pipe  300  is connected to the introduction port  105 . 
     About Role of Air Layer 
     In the liquid supply method of the present embodiment, the layer of the air  301  is important. From step (3) to step (4), the solution  202  to be inspected present on the upper side of the array chip  100  once disappears and is replaced with the air. Accordingly, the front surface (upper surface) of the array chip  100  other than the inside of the through-hole  101  is dried, and the solution  202  to be inspected disappears from the front surface of the array chip  100 . Therefore, even though the PCR reaction is performed after the front surface and the back surface of the array chip  100  are filled with the oil  203 , the solutions  202  to be inspected in the adjacent through-holes  101  are not mixed during the PCR. 
     On the other hand, in a case where there is no layer of the air  301  between the solution  202  to be inspected and the oil  203 , there is no step of evaporating the solution  202  to be inspected from the front surface of the array chip  100  and drying the front surface of the array chip  100 . Thus, the oil  203  is supplied to the upper side and the lower side of the array chip  100  while the solution  202  to be inspected remains on the front surface of the array chip  100  (that is, the solutions in the adjacent through-holes  101  remain connected on the front surface of the array chip  100  between the through-holes  101 ). Since the upper and lower surfaces of the array chip  100  are covered with the oil  203  after the supply of the oil  203 , the solution  202  to be inspected cannot be evaporated or moved, and the solutions in the adjacent through-holes remain connected during the PCR reaction. This is a problem in the dPCR measurement. This is because even though there is originally the DNA sequence to be detected only in a certain through-hole, in a case where the solution in the through-hole is connected to the solution in the plurality of another through-holes, there are amplified DNA sequences to be detected in all the through-holes (that is, the through-holes in which the solutions are connected) after the PCR reaction. By doing this, in the fluorescence observation after the PCR, fluorescence suggesting the presence of the DNA sequence to be detected is observed from all of these through-holes. In the dPCR, usually, the number of DNA sequences to be detected in an aqueous solution to be inspected is counted by counting the number of through-holes in which fluorescence is observed. However, as described above, when the solutions in the plurality of through-holes are connected to each other and the DNA sequence to be detected to be proliferated in one through-hole spreads over the plurality of through-holes, the accuracy of counting (accuracy of counting the number of DNA sequences to be detected originally present in the aqueous solution to be inspected) decreases. About Conditions for Inner Diameter of Liquid Supply Pipe 
     The liquid is supplied to satisfy conditions to be described below, and thus, the liquid can be ideally supplied as in steps (1) to (6) illustrated in  FIGS.  7 A and  7 B . One of the conditions is that an inner diameter of the liquid supply pipe  300  is smaller than 2.5 mm. 
       FIG.  9 A  is a diagram for describing the movement of the fluid in the liquid supply pipe  300  in a case where the inner diameter of the liquid supply pipe  300  is large. Here, the liquid supply pipe  300  is inclined by the angle θ with respect to the horizontal plane. In a case where the inner diameter of the liquid supply pipe  300  is large, even though there is the layer of the air  301  between the solution  202  to be inspected and the oil  203  at the beginning (at a certain time t=t0), the oil  203  cannot maintain an original shape in the liquid supply pipe  300 , and enters a collapsing state drawn at t=t1 after a lapse of a certain period of time. This is because the oil  203  has a low surface tension, a small contact angle with respect to the liquid supply pipe  300 , and a weak adhesive force with a wall surface of the liquid supply pipe  300 . Since the oil  203  has a weak frictional force with an inner wall of the liquid supply pipe  300 , a speed at which the oil falls downward is high. As a result, the oil enters a state drawn at t=t2, that is, a state where the solution  202  to be inspected and the oil  203  stick to each other and there is no layer of the air therebetween. The solution  202  to be inspected is usually an aqueous solution, and has a stronger surface tension, a larger contact angle with respect to the liquid supply pipe  300 , a larger adhesive force with the wall surface of the liquid supply pipe  300 , and a stronger frictional force with the inner wall of the liquid supply pipe  300 , compared with the oil  203  in many cases. Thus, even though the shape of the oil  203  collapses as in the diagram of t=t1, a situation in which the shape of the solution  202  to be inspected does not collapse may occur. 
       FIG.  9 B  is a diagram for describing the movement of the fluid in the liquid supply pipe  300  in a case where the inner diameter of the liquid supply pipe  300  is small. In a case where the inner diameter of the liquid supply pipe  300  is sufficiently small, the shape of the oil  203  does not collapse after a lapse of a certain period of time. This is because, in a case where the inner diameter of the liquid supply pipe  300  is sufficiently small, the oil  203  is energetically more stable when the oil is present in a form in which the shape does not collapse as drawn in t=t1 of  FIG.  9 B  than when the oil is present in the collapsing form as drawn in t=t1 of  FIG.  9 A . Accordingly, in a case where the inner diameter of the liquid supply pipe  300  is sufficiently small, the solution  202  to be inspected and the oil  203  advance downward in the liquid supply pipe  300  by gravity, but at this time, the layer of the air  301  is constantly present between the solution  202  to be inspected and the oil  203 . 
     The present inventors have conducted studies on a large number of oils and a large number of liquid supply pipes at various angles θ of 0 degrees or more and 90 degrees or less and resultantly have found that in a case where the inner diameter of the liquid supply pipe  300  is equal to or larger than 2.5 mm, the shape of the oil  203  collapses and the oil  203  and the solution  202  to be inspected stick to each other as illustrated in  FIG.  9 A . It has been found that in a case where the inner diameter of the liquid supply pipe  300  is smaller than 2.5 mm, the oil  203  and the solution  202  to be inspected may advance downward while the air between the oil  203  and the solution  202  to be inspected is held as illustrated in  FIG.  9 B . In particular, in a case where the inner diameter of the liquid supply pipe  300  is equal to or smaller than 1.5 mm, it has been found that the oil  203  and the solution  202  to be inspected advance downward while the air between the oil  203  and the solution  202  to be inspected is reliably held as illustrated in  FIG.  9 B . 
     Here, examples of the oil  203  include mineral oil, paraffin, silicone oil, Fluorinert, other fluorine-containing oils, and oils partially containing these oils as components. The oil  203  may contain one of these oils alone, or may contain two or more oils. Examples of a material of the liquid supply pipe  300  include fluorocarbon resin, silicone, PDMS, acrylic, rubber, elastomer, polyester, olefin, polyamide, urethane, polyurethane, polypropylene, vinyl chloride, polycarbonate, other plastic materials, and materials containing a portion of these materials as components. The material of the liquid supply pipe  300  may include one of these materials alone, or may include a plurality of materials. 
     As described above, from the studies of the present inventors, it has been found that when the inner diameter of the liquid supply pipe  300  is at least smaller than 2.5 mm, particularly equal to or smaller than 1.5 mm, the liquid can be supplied while the air between the oil and the solution to be inspected is maintained. The liquid supply pipe  300  may not have a perfect cylindrical shape. In this case, a cross-sectional area of a hollow portion of the liquid supply pipe  300  is set to be smaller than 2.5×2.5×n/4 mm 2 , particularly equal to or smaller than 1.5×1.5×n/4 mm 2 , it is possible to supply the liquid while the air between the oil and the solution to be inspected is maintained. 
     About Conditions for Pressure in Flow Path 
     Hereinafter, conditions for a pressure in the flow path for ideal liquid supply as in steps (1) to (6) illustrated in  FIGS.  7 A and  7 B  will be described. 
       FIG.  10 A  is a diagram illustrating a force due to the gravity applied to the solution and the oil during the liquid supply. The solution to be inspected is divided into a portion  401 , a portion  402 , and the other portion  403  by dotted lines. A pressure applied to the portion  403  on the upper side of the array chip  100  in the solution to be inspected is determined by forces applied to the portion  403  by the portion  402 , the portion  401 , and the oil  203 . In the case of  FIG.  10 A , there are a force m aq2 .g due to gravity applied to the portion  402 , a force m aq1 .g sin θ due to gravity applied to the portion  401 , and a force m oil g sin θ due to gravity applied to the oil  203 . Here, g is a gravitational acceleration, m aq1 . is a mass of the portion  401  of the solution to be inspected, m aq2 . is a mass of the portion  402  of the solution to be inspected, and m oil  is a mass of the oil  203 . Accordingly, the pressure on the portion  403  of the solution to be inspected becomes (m oil g sin θ+m aq1 .g sin θ)/S 1 +m aq2 .g/S 2 . Here, S 1  is a cross-sectional area of the liquid supply pipe  300 , and S 2  is a cross-sectional area of the portion  402  (that is, an area of a cross section of the introduction port  105  parallel to the front surface of the array chip  100 ). 
       FIGS.  10 B and  10 C  are diagrams for describing a state of the solution  202  to be inspected near the lower side of the through-hole  101 . Usually, the solution  202  near the lower side of the through-hole  101  remains due to the surface tension without falling down as illustrated in  FIG.  10 B . However, when a certain pressure or more is applied to the solution  202 , a state where the solution  202  remains without falling down due to the surface tension cannot be maintained, and the solution  202  leaks out downward or in a left-right direction as illustrated in  FIG.  10 C . A threshold pressure at which the solution  202  leaks out is referred to as a “bursting pressure P B ”. That is, when a pressure equal to or higher than the bursting pressure P B  is applied to the solution  202 , the solution  202  leaks out downward or in the left-right direction as illustrated in  FIG.  10 C . The bursting pressure P B  is determined by P B =LGsin θ B /A. Here, L is a circumferential length of a cross section of the through-hole, A is across-sectional area of the through-hole, σ is surface tension of the solution to be inspected, and θ B  is a contact angle of the solution  202  to be inspected with respect to the array chip  100 . All of L, σ, θ B , and A are measurable parameters. As illustrated in  FIG.  10 C , when the solution to be inspected leaks out downward or in the left-right direction, the solutions  202  to be inspected inside the adjacent through-holes are connected to each other. By doing this, the inspection accuracy of the dPCR decreases as described above. 
     Accordingly, when (m oil g sin θ+m aq1 .g sin θ)/S 1 +m aq2 .g/S 2 &lt;P B  (hereinafter, this inequality is referred to as “Condition 1”) is satisfied, the solution  202  to be inspected can be supplied without leaking out to the lower side and the left and right of the through-hole  101 . That is, the pressure applied to the solution  202  to be inspected on the upper side of the array chip  100  may not exceed the bursting pressure P B  during the flow of  FIGS.  7 A and  7 B . Preventing the pressure applied to the solution  202  to be inspected on the upper side of the array chip  100  from exceeding the bursting pressure P B  is possible by performing the adjustment of the amounts (masses) of the solution  202  to be inspected and the oil  203  to be filled in the liquid supply pipe  300  and the adjustment of the angle θ of the liquid supply pipe  300 . Simply, the amount of the solution  202  to be inspected, the amount of the oil  203 , and the angle θ of the liquid supply pipe  300  may be adjusted to satisfy Condition 1. Within the range satisfying Condition 1, the larger the angle θ, the faster the liquid supply speed. Thus, the liquid can be efficiently supplied. 
       FIG.  11    is a diagram for more accurately describing the force applied to the solution  202  to be inspected on the upper side of the array chip  100 . As illustrated in  FIG.  11   , a frictional force F m_oil  between the oil  203  and an inner wall surface of the liquid supply pipe  300 , a frictional force F m_aq.1  between the solution  202  and the inner wall surface of the liquid supply pipe  300 , and a frictional force F m_aq.2  between the solution  202  and an inner wall surface of the introduction port  105  (an inner wall surface of the opening of the upper part  104 ) can also be considered. In this case, the expression of Condition 1 is transformed into (m oil g sin θ−F m_oil +m aq1 .g sin θ−F m_aq.1 )/S 1 +(m aq2 .g−F m_aq.2 )/S 2 &lt;P B  (hereinafter, this inequality is referred to as “Condition 2”). In consideration of the frictional force, the amounts of the solution  202  to be inspected and the oil  203  to be supplied to the liquid supply pipe  300  estimated under Condition 2 are larger than an allowable amount when the amounts are estimated under Condition 1. That is, as long as the inequality of Condition 1 is satisfied, Condition 2 is constantly satisfied, so only Condition 1 may be considered in a case where a simple estimation is desired. 
       FIG.  12    is a diagram for simplifying and describing the force applied to the solution  202  to be inspected on the upper side of the array chip  100 . As illustrated in  FIG.  12   , in a starting state, that is, in a state where the solution  202  to be inspected and the oil  203  are only in the liquid supply pipe  300 , when (m oil g sin θ+m aq .g sin θ)/S 1 &lt;P B  (hereinafter, this inequality is referred to as “Condition 3”. m aq . is a mass of the solution  202  to be inspected) is satisfied, the solution  202  to be inspected can be supplied without leaking out to the lower side, the left and right of the through-hole  101  during the liquid supply. 
     More simply, since the bursting pressure P B  satisfies P B =LGsin θ B /A&lt;Lσ/A, when (m oil g sin θ+m aq .g sin θ)/S 1 &lt;Lσ/A is satisfied in the starting state illustrated in  FIG.  12   , the solution  202  to be inspected can be supplied without leaking out to the lower side and the left and right of the through-hole  101 . 
     Here, details of the amount of the air  301  will be described. Basically, in the present disclosure, it is sufficient that even a small amount of air  301  is held between the solution  202  to be inspected and the oil  203 . However, more preferably, it is desirable that an amount of air  301  sufficient to realize the state of  FIG.  7 B ( 4 ) is present between the solution  202  to be inspected and the oil  203 . 
     The state of  FIG.  7 B ( 4 ) is a state where the solution  202  to be inspected disappears from the upper side of the array chip  100  in the flow cell  120 , the oil  203  does not yet come into contact with the array chip  100 , and the air present on the upper side of the array chip  100  is connected to external air through the discharge port  106 . In a state where the air present on the upper side of the array chip  100  is connected to the external air through the discharge port  106 , the evaporation and drying of the excess solution  202  to be inspected remaining on the front surface of the array chip  100  are promoted. Thus, it is possible to greatly reduce a risk that the solutions  202  to be inspected inside the adjacent through-holes  101  are connected via the front surface of the array chip  100 . As described above, the reduction of this risk leads to improvement of the inspection accuracy of the dPCR. As is clear from  FIG.  7 B , in order to create the state of  FIG.  7 B ( 4 ) described above, the amount of the air  301  needs to be larger than a total volume of a space through which the air and the liquid can flow (a total volume from the introduction port  105  to the discharge port  106 ) in a region of the flow cell  120  positioned on the upper side of the array chip  100 . 
     Next, details of the amount of the oil  203  will be described. Of course, the amount of the oil  203  needs to be equal to or larger than the amount necessary to completely cover the front surface of the array chip  100 . It is desirable that the mass of the oil  203  is larger than the mass of the solution  202  to be inspected filled in the liquid supply pipe  300 . In a case where the mass of the oil  203  is smaller than the mass of the solution  202  to be inspected filled in the liquid supply pipe  300 , in  FIGS.  7 A ( 3 ) to  7 B( 4 ), the solution  202  to be inspected is not completely extruded from the discharge port  106 , and there is a possibility that the solution  202  to be inspected remains in the flow cell  120  and the flow stops on the way. On the other hand, in a case where the mass of the oil  203  is sufficiently larger than the mass of the solution  202  to be inspected filled in the liquid supply pipe  300 , there is no such concern. 
     The supply of the oil  203  by the liquid supply pipe  350  to the back surface of the array chip  100  illustrated in  FIG.  7 B ( 6 ) will be described. There is no problem even though the mass and the angle θ′ of the oil  203  in the liquid supply pipe  350  are not necessarily adjusted such that the pressure applied to the oil present on the lower side of the array chip  100  does not exceed the bursting pressure P B . This is because since the upper surface of the array chip  100  is already filled with the oil  203 , the solution  202  to be inspected in the through-hole  101  is hardly spilled upward from below by the pressure. 
     Nevertheless, it is safe design to adjust the mass and the angle θ′ of the oil  203  in the liquid supply pipe  350  such that the pressure applied to the oil  203  present on the lower side of the array chip  100  does not exceed the bursting pressure P B . 
     Modified Example of First Embodiment 
       FIG.  13    is a diagram illustrating a modified example of the liquid supply pipe. As illustrated in  FIG.  13   , the liquid supply pipe  310  is not straight, and the thickness varies depending on the location. Even in such a case, it is possible to supply the liquid only by gravity as described above and to favorably fill the through-holes  101  with the solution  202  to be inspected. In this case, first, the inner diameter of the thickest portion of the liquid supply pipe  310  may be smaller than 2.5 mm (particularly, 1.5 mm or less). In a case where the cross-section of the liquid supply pipe  310  is not circular, the cross-sectional area of the hollow portion of the liquid supply pipe  310  may be smaller than 2.5×2.5×n/4 mm 2 , and particularly 1.5×1.5×n/4 mm 2  or less. Accordingly, the liquid is supplied while the layer of the air  301  between the oil  203  and the solution  202  to be inspected is maintained. In addition, it is sufficient that the pressure applied to the solution (portion  403 ) to be inspected positioned on the upper surface of the array chip  100  at the time of the liquid supply does not exceed the bursting pressure P B  from beginning to end. If so, the solution to be inspected can be supplied without leaking out to the lower side and the left and right of the through-holes. Since the liquid supply pipe  310  is not straight and the thickness varies depending on the location, the pressure applied to the portion  403  cannot be written in a simplified formula as in the first embodiment. However, it is possible to calculate the pressure applied to the portion  403  by dividing the liquid supply pipe  310  into minute regions, calculating the force acting in the parallel direction of the liquid supply pipe  310  in the gravity force applied to the solution  202  to be inspected or the gravity force applied to the oil  203  in each portion, and integrating them. The mass of the solution to be inspected, the mass of the oil, the degree of bending of the liquid supply pipe  310 , and the angle of the liquid supply pipe  310  may be adjusted so that the pressure calculated in this manner does not exceed the bursting pressure P B . 
     Conclusion of First Embodiment 
     As described above, the liquid supply method of the first embodiment is a liquid supply method for supplying the solution  202  to be inspected to the through-holes  101  (spots) formed in an array in the array chip  100  (substrate), and includes preparing the liquid supply pipe  300  in which the solution  202  to be inspected, the air  301 , and the oil  203  are disposed in this order, and installing the liquid supply pipe  300  above the array chip  100  at the angle θ at which the solution  202  to be inspected is positioned at the lowest position and the solution  202  to be inspected, the air  301 , and the oil  203  flow onto the front surface of the array chip  100  by gravity. The cross-sectional area of the liquid supply pipe  300  is designed such that the air  301  continues to be present between the solution  202  to be inspected and the oil  203  while the solution  202  to be inspected, the air  301 , and the oil  203  are flowing through the liquid supply pipe  300 . After the solution  202  to be inspected is supplied to the through-holes  101 , the solution  202  to be inspected present on the front surface of the array chip  100  is replaced with the air  301 , and then the liquid supply advances such that the oil  203  covers the front surface of the array chip  100 . 
     According to the liquid supply method of the present embodiment, a driving force required for the liquid supply is gravity and does not require electric power. Since the loader is not used, the filling rate of the solution  202  to be inspected into each through-hole  101  does not change or there are no through-holes  101  partially that are not filled due to the variation in the angle or the position at which the loader comes into contact with the front surface of the array chip  100 . That is, the filling rate of the solution  202  to be inspected into the through-holes  101  becomes uniform. Accordingly, the solution  202  to be inspected can be filled in the through-holes  101  with a good yield. 
     Since the array chip  100  is housed in the flow cell  120 , the upper side of the array chip  100  is not largely opened to the atmosphere, including during and before and after the liquid supply. Accordingly, there is a low risk that the foreign matters (particles), the DNA, and the like floating in the atmosphere are mixed into the through-hole array  110  during and before and after liquid supply. 
     Second Embodiment 
     In a second embodiment, a method for supplying a solution to the array chip  100  including a step of filling the liquid supply pipe  300  with the solution  202  to be inspected, the air  301 , and the oil  203  will be described. 
       FIGS.  14 A and  14 B  are diagrams illustrating a liquid supply method to the array chip  100  according to the second embodiment. First, the operator aspirates the solution  202  to be inspected from a container (not illustrated) containing the solution  202  to be inspected to the distal end portion  201  of the pipette  200 . Thereafter, in step (1) of  FIG.  14 A , the operator connects the pipette  200  to the liquid supply pipe  300 , and manually pressing the push button  204  to fill the liquid supply pipe  300  with the solution  202  to be inspected. A connecting portion  500  between the liquid supply pipe  300  and the introduction port  105  is movable, and the angle θ of the liquid supply pipe  300  with respect to the flow cell  120  (the angle of the liquid supply pipe  300  with respect to the horizontal plane) can be adjusted. The amount of the solution  202  to be inspected to be filled in the liquid supply pipe  300  is set to A μL. A liquid amount adjustment scale  250  of the pipette  200  may be set to A μL in advance. 
     In step (2) of  FIG.  14 A , the operator fills the liquid supply pipe  300  with the solution  202  to be inspected, and then removes the pipette  200  from the liquid supply pipe  300 . In this state, the solution  202  to be inspected is stopped in the liquid supply pipe  300 . 
     In step (3) of  FIG.  14 A , the operator connects the distal end portion  201  of the pipette  200  to the liquid supply pipe  300  again, and manually presses the push button  204  to send air. The amount of air to be injected is B μL. The liquid amount adjustment scale  250  of the pipette  200  may be set to B μL in advance. 
     In step (4) of  FIG.  14 A , the operator removes the pipette  200  from the liquid supply pipe  300 . 
     Thereafter, the operator aspirates the oil  203  from a container (not illustrated) containing the oil  203  to the distal end portion  201  of the pipette  200 . In step (5) of  FIG.  14 B , the operator connects the distal end portion  201  of the pipette  200  to the liquid supply pipe  300  again, and manually presses the push button  204  to send the oil  203 . The amount of air to be injected is set to C μL. The liquid amount adjustment scale  250  of the pipette  200  may be set to C μL in advance. 
     In step (6) of  FIG.  14 B , the operator removes the pipette  200  from the liquid supply pipe  300 . 
     In step (7) of  FIG.  14 B , the operator increases the angle of the liquid supply pipe  300  from θ 1  to θ 2 . By holding the liquid supply pipe in this state, in step (8) of  FIG.  14 B , the solution  202  to be inspected flows out to the front surface of the array chip  100  in the flow cell  120  and is filled in the through-holes in the array chip  100 . Thereafter, the excess solution  202  to be inspected on the front surface of the array chip  100  is replaced with the air, and then the air on the front surface of the array chip  100  is replaced with the oil  203 . The mass of the solution  202  to be inspected and the mass of the oil  203  are adjusted such that the pressure applied to the solution to be inspected on the front surface of the array chip  100  does not exceed the bursting pressure P B  in liquid supply in a state where the angle of the liquid supply pipe is θ 2 . 
     In the present embodiment, when the liquid supply pipe  300  is filled with the solution  202  to be inspected, the air, and the oil  203 , the angle θ of the liquid supply pipe  300  is θ 1 . The angle θ 1  is an angle at which the solution  202  to be inspected and the oil  203  do not spontaneously advance toward the flow cell  120  and the array chip  100  after the solution  202  to be inspected and the oil  203  are loaded in the liquid supply pipe  300  and the pipette  200  is removed. That is, at the angle θ 1 , the frictional force generated between the solution  202  to be inspected and the oil  203  and the liquid supply pipe  300  is balanced with the force derived from gravity applied to the solution  202  to be inspected and the gravity applied to the oil  203 , and the solution  202  to be inspected and the oil  203  cannot flow in the liquid supply pipe  300  and are stopped. On the other hand, when the solution  202  to be inspected, the air, and the oil  203  are supplied from the liquid supply pipe  300  to the flow cell  120  and the array chip  100 , the angle θ of the liquid supply pipe  300  is θ 2 . At this angle θ 2 , since the force derived from gravity applied to the solution  202  to be inspected and the gravity applied to the oil  203  is larger than the frictional force generated between the solution  202  to be inspected and the oil  203  and the liquid supply pipe  300 , the solution  202  to be inspected and the oil  203  can flow in the liquid supply pipe  300 . 
     A range of the angle θ 1  at which the solution  202  to be inspected and the oil  203  are stopped in the liquid supply pipe  300  and a range of the angle θ 2  at which the solution  202  to be inspected and the oil  203  can flow in the liquid supply pipe  300  change depending on the material or the inner diameter of the liquid supply pipe  300 , the composition of the solution  202  to be inspected, and the type of the oil  203 . However, it is needless to say that the ranges of the angles θ 1  and θ 2  can be easily obtained experimentally by using the liquid supply pipe  300  to be used, the solution  202  to be inspected, and the oil  203 . 
       FIG.  15    is a diagram for describing a contact timing between the solution  202  to be inspected and the array chip  100 . As described above, it is important that the solution  202  to be inspected does not come into contact with the array chip  100  until the solution  202  to be inspected, the air, and the oil  203  are completely filled in the liquid supply pipe  300 . The reason will be described below. In a case where the oil  203  is supplied to the liquid supply pipe  300  after the solution  202  to be inspected reaches the front surface of the array chip  100 , and when the extrusion force is too strong or the extrusion speed is too fast due to the variation in the extrusion force or the extrusion speed when the oil  203  is supplied to the liquid supply pipe  300 , the pressure applied to the solution  202  to be inspected exceeds the bursting pressure P B . As a result, as illustrated in  FIG.  15   , the solution  202  to be inspected may leak out to the back surface of the array chip  100  through the through-holes  101 . By doing this, the solutions to be inspected inside different through-holes  101  are connected to each other, and the inspection accuracy of the dPCR decreases. Accordingly, it is important that the solution  202  to be inspected does not come into contact with the array chip  100  until the liquid supply pipe  300  is completely filled with the solution  202  to be inspected, the air, and the oil  203 . 
     Modified Example of Second Embodiment 
       FIGS.  16 A and  16 B  are diagrams illustrating a liquid supply method to the array chip  100  according to a modified example of the second embodiment. In a method adopted in the present modified example, the solution  202  to be inspected, the air, and the oil  203  are filled into the liquid supply pipe  300  in a state where the liquid supply pipe  300  is removed from the flow cell  120 , and then it is attached to the flow cell  120  to supply the liquid. The other points are performed as described in the second embodiment. Steps (1) to (6) illustrated in  FIGS.  16 A and  16 B  are different from steps (1) to (6) illustrated in  FIGS.  14 A and  14 B  only in that the liquid supply pipe  300  is not connected to the flow cell  120 . In step (7) of  FIG.  16 B , the operator connects the liquid supply pipe  300  to the flow cell  120 . The distal end portion of the liquid supply pipe  300  is formed of a flexible material, and can be tightly inserted into the introduction port  105 . Thereafter, step (8) is the same as the step in the second embodiment. 
     Conclusion of Second Embodiment 
     As described above, the liquid supply method of the second embodiment includes filling the liquid supply pipe  300  with the solution  202  to be inspected, the air  301 , and the oil  203  in a state where the angle of the liquid supply pipe  300  with respect to the array chip  100  is θ 1  (first angle), and supplying the liquid in a state where the angle of the liquid supply pipe  300  is θ 2  (second angle) larger than θ 1  after completion of the filling. The other points are the same as the points of the first embodiment. The angle θ 1  is an angle at which the solution  202  to be inspected is stopped in the liquid supply pipe  300  at a stage where only the solution  202  to be inspected is filled in the liquid supply pipe  300 . As described above, similarly to the first embodiment, in the second embodiment, the driving force required for supplying the liquid is also gravity, and electric power is also not required. It is possible to fill the through-holes  101  with the solution  202  to be inspected with a good yield. 
     Third Embodiment 
     In the second embodiment, it has been described that an inclination angle of the liquid supply pipe  300  is changed between when the liquid supply pipe  300  is filled with the solution  202 , the air, and the oil  203  and when the solution  202  is supplied to the flow cell  120 . Therefore, in a third embodiment, a technology for executing the method described in the second embodiment without changing the inclination angle of the liquid supply pipe  300  is proposed. 
       FIGS.  17 A to  17 D  are diagrams illustrating a liquid supply method to the array chip  100  according to the third embodiment. Since the overall flow of the liquid supply method of the present embodiment is similar to the flow of the second embodiment, differences will be mainly described below. 
     As illustrated in  FIGS.  17 A to  17 D , in the present embodiment, the angle of the liquid supply pipe  300  is constantly θ 3 . The angle θ 3  is an angle at which the solution  202  to be inspected does not spontaneously advance toward the flow cell  120  and the array chip  100  after only the solution  202  to be inspected is loaded in the liquid supply pipe  300  and the pipette  200  is removed. That is, at the angle θ 3 , the frictional force generated between the solution  202  to be inspected and the liquid supply pipe  300  is balanced with the gravity-derived force applied to the solution  202  to be inspected, and the solution  202  to be inspected is stopped without being able to flow in the liquid supply pipe  300 . On the other hand, the angle θ 3  is an angle at which the oil  203  spontaneously advances toward the flow cell  120  and the array chip  100  after only the oil  203  is loaded in the liquid supply pipe  300  and the pipette  200  is removed. That is, at the angle θ 3 , the gravity-derived force applied to the oil  203  is larger than the frictional force generated between the oil  203  and the liquid supply pipe  300 , and the oil  203  can flow to the flow cell  120  and the array chip  100  in the liquid supply pipe  300 . The angle θ 3  is an angle at which the oil  203  and the solution  202  to be inspected spontaneously advance toward the flow cell  120  and the array chip  100  in a case where the solution  202  to be inspected is injected into the liquid supply pipe  300  and then the oil  203  is supplied onto the solution to be inspected (to a position higher than a position of the solution  202  to be inspected in the liquid supply pipe  300  from the ground). That is, at the angle θ 3 , the solution  202  to be inspected can flow to the flow cell  120  and the array chip  100  by the gravity-derived force applied to the oil  203 . Whether or not such an angle θ 3  exists depends on the material and the inner diameter of the liquid supply pipe  300 , the composition of the solution  202  to be inspected, and the type of the oil  203 . In a case where such an angle θ 3  exists, the range of the angle θ 3  changes depending on the material or the inner diameter of the liquid supply pipe, the composition of the solution  202  to be inspected, and the type of the oil  203 . However, it is needless to say that whether the angle θ 3  exists and the range of the angle θ 3  in a case where the angle θ 3  exists can be easily obtained experimentally by using the liquid supply pipe  300  to be used, the solution  202  to be inspected, and the oil  203 . 
     In  FIG.  17 A ( 1 ), the operator fills the liquid supply pipe with the solution  202  to be inspected, and then removes the pipette  200  from the liquid supply pipe  300 . Thus, a state illustrated in  FIG.  17 A ( 2 ) is obtained. At this time, as described above, a gravity-derived force m aq .g sin θ 3  applied to the solution  202  to be inspected and a frictional force F m_aq  acting between the solution  202  to be inspected and the inner wall of the liquid supply pipe  300  are balanced. Accordingly, the solution  202  to be inspected is stopped without flowing down toward the flow cell  120  and the array chip  100 . 
     In  FIG.  17 B ( 3 ), the air is supplied to the liquid supply pipe  300  and the pipette  200  is removed from the liquid supply pipe  300 . Thus, a state illustrated in  FIG.  17 B ( 4 ) is obtained. At this time, as described above, the gravity-derived force m aq .g sin θ applied to the solution  202  to be inspected and the frictional force F m_aq  acting between the solution  202  to be inspected and the inner wall of the liquid supply pipe  300  are balanced. Accordingly, the solution  202  to be inspected is stopped without flowing down toward the flow cell and the array chip  100 . 
     Thereafter, in  FIG.  17 C ( 5 ), the distal end portion  201  of the pipette  200  is connected to the liquid supply pipe again, and the oil  203  is supplied. Thereafter, the pipette  200  is removed from the liquid supply pipe  300 , and thus, a state as illustrated in  FIG.  17 C ( 6 ) is obtained. At this time, as described above, since m oil g sin θ 3 &gt;F m_oil  (F m_oil  is a frictional force acting between the oil and the inner wall of the liquid supply pipe) and m oil g sin θ 3 −F m_oil +m aq .g sin θ 3 −F m_aq &gt;0, the solution  202  to be inspected, the air, and the oil  203  flow out toward the flow cell  120  and the array chip  100 , and a state as illustrated in  FIG.  17 D ( 7 ) is obtained. In the liquid supply of the present embodiment, the mass of the solution  202  to be inspected and the mass of the oil  203  are also adjusted such that the pressure applied to the solution  202  to be inspected on the front surface of the array chip  100  does not exceed the bursting pressure P B . 
     Conclusion of Third Embodiment 
     According to the present embodiment, since the solution  202  can be fractionated into the through-holes  101  without changing the inclination angle of the liquid supply pipe  300 , it can be said that the method is a simpler liquid supply method. 
     Fourth Embodiment 
     In the second and third embodiments, it has been described that the angle of the liquid supply pipe  300  during the liquid supply to the flow cell  120  is constant at the angle θ 2  (second embodiment) or the angle θ 3  (third embodiment). Therefore, in a fourth embodiment, a method for changing the angle of the liquid supply pipe  300  during the liquid supply to the flow cell  120  is proposed. 
       FIGS.  18 A and  18 B  are diagrams illustrating a liquid supply method to the array chip  100  according to the fourth embodiment. As illustrated in  FIG.  18 A , in an initial stage when liquid supply is started, the angle of the liquid supply pipe  300  is θ 4 . As illustrated in  FIG.  18 B , when the liquid supply is about to end, the angle of the liquid supply pipe  300  is adjusted to be an angle θ 5  (θ 5 &gt;θ 4 ). The angle of the liquid supply pipe  300  may gradually change during the liquid supply, or may change only once. In a case where the angle of the liquid supply pipe  300  is constant, the supply speeds of the solution  202  to be inspected and the oil  203  to the array chip  100  decrease as the amounts of the solution  202  to be inspected and the oil  203  in the liquid supply pipe  300  decrease. However, the inclination angle of the liquid supply pipe  300  is increased as the liquid supply progresses, thereby the force acting in a parallel direction of the liquid supply pipe  300  within the gravity applied to the solution  202  to be inspected and the oil  203  in the liquid supply pipe  300  can be increased. As a result, it is possible to supply the solution  202  to be inspected and the oil  203  without reducing the supply speed. Accordingly, the inspection efficiency of the dPCR increases. In the present embodiment, the mass of the solution  202  to be inspected and the mass of the oil  203  are also adjusted such that the pressure applied to the solution  202  to be inspected on the front surface of the array chip  100  does not exceed the bursting pressure P B . 
     Conclusion of Fourth Embodiment 
     According to the present embodiment, since the inclination angle of the liquid supply pipe  300  is increased during the liquid supply to the array chip  100 , it is possible to suppress a decrease in the liquid supply speed, and it is possible to efficiently supply the liquid. 
     Fifth Embodiment 
       FIG.  19    is a diagram illustrating a structure of a liquid supply pipe according to a fifth embodiment. As illustrated in  FIG.  19   , since the liquid supply pipe  300  has a zigzag structure or a spiral structure, it is possible to save a space occupied by the liquid supply pipe  300 . 
     Sixth Embodiment 
     In the first to fifth embodiments, the technology of supplying the liquid by using a liquid supply pipe having a tubular shape from one end to the other end has been described. In a sixth embodiment, a liquid supply method using a liquid supply pipe having another shape is proposed. 
       FIGS.  20 A and  20 B  are diagrams illustrating a liquid supply method to the array chip  100  according to the sixth embodiment. In the present embodiment, a liquid supply pipe  600  having a funnel shape at one end and a tubular shape at the other end is used. The liquid supply pipe  600  is attached to the introduction port  105 . First, as illustrated in  FIG.  20 A ( 1 ), the operator supplies the solution  202  to be inspected to a funnel-shaped portion of the liquid supply pipe  600 . Accordingly, the solution  202  to be inspected fills the front surface of the array chip  100  and the through-holes  101 . The solution  202  to be inspected overflowing from the discharge port  106  is discarded. 
     As illustrated in  FIG.  20 A ( 2 ), when the supply of the solution  202  to be inspected is completed, a height of a liquid level of the introduction port  105  and a height of a liquid level of the discharge port  106  become the same. 
     Subsequently, as illustrated in  FIG.  20 A ( 3 ), the operator supplies the oil  203  to the funnel-shaped portion of the liquid supply pipe  600 . At this time, in a case where an inner diameter or a cross-sectional area of a portion  610  surrounded by a broken line in a flow path between the liquid supply pipe  600  and the flow cell is sufficiently small (in a case where the inner diameter is smaller than 2.5 mm or the cross-sectional area is smaller than 2.5×2.5×π/4 mm 2 ), the oil  203  and the solution  202  to be inspected are supplied while the layer of the air  301  is maintained between the oil  203  and the solution  202  to be inspected. Accordingly, the liquid is supplied as illustrated in  FIG.  20 B ( 4 ). The solution  202  and the oil  203  overflowing from the discharge port  106  are discarded. When the filling of the front surface of the array chip  100  with the oil  203  is completed, a state illustrated in  FIG.  20 B ( 5 ) is obtained. 
     Thereafter, as illustrated in  FIG.  20 B ( 6 ), the operator connects the liquid supply pipe  600  to the introduction port  107  and supplies the oil  203  to the funnel-shaped portion to fill the back surface of the array chip  100  with the oil  203 . 
     In the present embodiment, the mass of the solution  202  to be inspected and the mass of the oil  203  supplied to the funnel-shaped portion of the liquid supply pipe  600  are also adjusted so that the pressure applied to the solution  202  to be inspected on the front surface of the array chip  100  does not exceed the bursting pressure P B . 
     Conclusion of Sixth Embodiment 
     According to the present embodiment, since one end portion of the liquid supply pipe  600  has the funnel shape, the solution  202  and the oil  203  can be easily supplied into the liquid supply pipe  600  as compared with a case where the one end portion has a tubular shape. In particular, it is not necessary to aspirate the solution  202  into the pipette from the container containing the solution  202  or to aspirate the oil  203  into the pipette from the container containing the oil  203 , and the solution  202  and the oil  203  may be merely poured into the funnel-shaped portion directly from these containers. 
     Seventh Embodiment 
     In the first to sixth embodiments, it has been described that the liquid supply pipe is inclined with respect to the horizontal plane (flow cell). On the other hand, in a seventh embodiment, the flow cell is inclined with respect to the horizontal plane and the liquid is supplied. 
       FIG.  21    is a diagram illustrating a liquid supply method to the array chip  100  according to the seventh embodiment. As illustrated in  FIG.  21   , the flow cell is inclined with respect to the horizontal plane by an angle θ 7 . The flow cell is inclined in this manner, and thus, the speed at which the solution  202  to be inspected and the oil  203  are supplied into the flow cell can be increased. Accordingly, the inspection efficiency of the dPCR increases. 
     Eighth Embodiment 
     In an eighth embodiment, a method of PCR reaction and fluorescence observation after the solution to be inspected and the oil are supplied to the flow cell will be described. 
       FIG.  22    is a diagram for describing the method of PCR reaction and fluorescence observation according to the eighth embodiment. As illustrated in  FIG.  22   ( 1 ), the liquid supply pipes  300  and  350  are connected to the flow cell after the solution to be inspected and oil are supplied. Subsequently, as illustrated in  FIG.  22   ( 2 ), the operator removes the liquid supply pipes  300  and  350  from the flow cell  120 . Thereafter, as illustrated in  FIG.  22   ( 3 ), the operator installs the flow cell  120  in a thermal cycler  810 . The thermal cycler  810  includes an upper lid  800 , a lower pedestal  801 , and a spacer  802 . Temperatures of the upper lid  800  and the lower pedestal  801  can be controlled. The temperatures of the upper lid  800  and the lower pedestal  801  are controlled such that, for example, two temperatures of 60° C. and 98° C. are repeated, the PCR reaction can be caused. After the PCR reaction is completed, as illustrated in  FIG.  22   ( 4 ), the operator performs the fluorescence observation of the array chip  100 . Specifically, excitation light is emitted from a light source  803  toward the flow cell  120 , and the through-hole array is observed with a CMOS camera  804 . 
       FIG.  23    is a schematic diagram illustrating an example of a result of the fluorescence observation of the flow cell  120 . As illustrated in  FIG.  23   , fluorescence  820  is observed from the through-holes  101  in which there are the DNA sequences to be detected. 
     Ninth Embodiment 
     In the first to eighth embodiments, a target to be detected is DNA. However, the technology of the present disclosure is also useful other than detecting the DNA by the dPCR. As an example, in a ninth embodiment, a method for inspecting whether there is an influenza virus in the solution to be inspected will be described. 
     As a premise knowledge, it is first described that influenza has an enzyme in a protruding shape like a mushroom called neuraminidase on a front surface thereof and there is a fluorogenic substrate (for example, 2′-(4-Methylumbelliferyl)-α-D-N-acetylneuraminic acid (MUNANA)) that emits fluorescence when the fluorogenic substrate is decomposed by the neuraminidase of the influenza virus. 
     A procedure of the present embodiment will be described below. First, the operator mixes the fluorogenic substrate that emits fluorescence when the fluorogenic substrate is decomposed by the neuraminidase of the influenza virus in the solution  202  to be inspected. The other points are the same as the liquid supply procedure described in the first embodiment, and thus, the description thereof is omitted. 
       FIG.  24    is a diagram illustrating the flow cell  120  in which the array chip  100  is incorporated after the liquid supply method according to the ninth embodiment is performed. As illustrated in  FIG.  24   , there are through-holes  101  in which there are the influenza viruses  1000  and through-holes  101  in which there is no influenza virus  1000 . There is a fluorogenic substrate  1001  in each through-hole  101 . Since the fluorogenic substrate  1001  emits fluorescence when the fluorogenic substrate is decomposed by the neuraminidase of the influenza virus  1000 , fluorescence is observed from the through-holes  101  in which there are the influenza viruses  1000  among the through-holes  101 . Accordingly, when the through-hole array is observed with a camera from the upper surface and fluorescence is observed from any of the through-holes  101 , it can be determined that there is the influenza virus in the solution to be inspected. If the number of through-holes is sufficiently larger than the number of influenza viruses to be inspected and the size of the through-holes is also small, only about 0 or 1 influenza virus enters each through-hole. When the through-hole array is designed in this manner, it is also possible to count the influenza virus in the solution to be inspected by counting the number of through-holes emitting fluorescence. 
     In the present embodiment, it has been described that influenza is detected, substances other than influenza can be detected by a similar method. In short, a component that specifically exhibits fluorescence for the presence of a substance to be detected may be introduced into the solution to be inspected. In other words, the component in the solution to be inspected may be adjusted so as to be specifically fluorescent for the presence of the substance to be detected. 
     Conclusion of Ninth Embodiment 
     In the present embodiment, according to the liquid supply method of the present disclosure, any substance to be detected can also be detected. In the present embodiment, it is possible to favorably fractionate the solution to be inspected into the through-holes without using electric power. That is, detection accuracy of the substance to be inspected does not decrease by connecting the solutions in the adjacent through-holes. 
     Tenth Embodiment 
     In the first to ninth embodiments, the liquid supply method to the array chip  100  having the through-hole array has been described. However, the method of the present disclosure is also useful for array chips other than the array chip  100  having the through-hole array. In a tenth embodiment, a technology of supplying a liquid to an array chip having an array of spots to which the solution to be inspected is supplied will be described. 
       FIG.  25 A  is a cross-sectional view of an array chip  900  having an array of wells  901 . The well  901  is a recess not penetrating the array chip  900 . In such an array chip  900 , a portion to be the well  901  can be formed by patterning a silicon (Si) substrate by using, for example, a lithography technology and a dry etching technology. In  FIG.  25 A , an inner diameter of the wells  901  is constant, but may not be constant. Although not illustrated, a shape of an upper surface of the well  901  can be a circle, an ellipse, a triangle, a quadrangle, another polygon, or the like. 
       FIG.  25 B  is a cross-sectional view of an array chip  910  having an array of hydrophilic spots  911 . A portion other than the hydrophilic spot  911  of the array chip  910  is hydrophobic. A material of the array chip  910  is, for example, silicon (Si), and a material of the hydrophilic spot  911  is, for example, silicon oxide (SiO). Such an array chip  910  can form a hydrophilic spot of SiO by, for example, depositing a SiO film on a Si substrate and then patterning the SiO film into a shape of the spots  911  by using a lithography technology and a dry etching technology. 
       FIG.  26    is a diagram illustrating a liquid supply method to the array chip  900  according to the tenth embodiment. First, as illustrated in  FIG.  26   ( 1 ), the operator connects the liquid supply pipe  300  in which the solution  202  to be inspected, the air  301 , and the oil  203  are disposed to the introduction port  105  of the flow cell  120 . Thereafter, as illustrated in  FIG.  26   ( 2 ), the solution  202  to be inspected flows into the front surface of the array chip  900  and the wells  901 , and subsequently, the air  301  replaces the solution  202  to be inspected on the front surface of the array chip  900 . At this time, the solution  202  to be inspected present in the well  901  is not replaced. Thereafter, as illustrated in  FIG.  26   ( 3 ), the oil  203  flows into the front surface of the array chip  900  and covers the front surface of the array chip  900 . When the layer of the air  301  passes through the front surface of the array chip  900  before the front surface of the array chip  900  is covered with the oil  203 , the excess solution  202  to be inspected remaining on the front surface of the array chip  900  is evaporated and disappears from the front surface of the array chip  900 . Accordingly, the solutions  202  to be inspected in the adjacent wells  901  are not connected to each other. In this manner, a spot array of the solution  202  to be inspected can be formed in the array of the wells  901 . 
       FIG.  27    is a diagram illustrating a liquid supply method to the array chip  910  according to the tenth embodiment. First, as illustrated in  FIG.  27   ( 1 ), the operator connects the liquid supply pipe  300  in which the solution  202  to be inspected, the air  301 , and the oil  203  are disposed to the introduction port  105  of the flow cell  120 . Thereafter, as illustrated in  FIG.  27   ( 2 ), the solution  202  to be inspected flows into the front surface of the array chip  910  and the hydrophilic spot  911 , and subsequently, the air  301  replaces the solution  202  to be inspected on the front surface of the array chip. At this time, the solution  202  to be inspected present on the hydrophilic spot  911  is not replaced. Thereafter, as illustrated in  FIG.  27   ( 3 ), the oil  203  flows into the front surface of the array chip  910  and covers the front surface of the array chip  910  and the spot  911 . When the layer of the air  301  passes through the front surface of the array chip  910  before the front surface of the array chip  910  is covered with the oil  203 , the excess solution  202  to be inspected remaining on the front surface of the array chip  910  other than the hydrophilic spot  911  is evaporated and disappears from the front surface of the array chip  910 . Accordingly, the solutions  202  to be inspected present in the adjacent hydrophilic spots  911  are prevented from being connected to each other. In this manner, the spot array of the solutions  202  to be inspected can be formed in the array of the hydrophilic spots  911 . 
     Eleventh Embodiment 
     In an eleventh embodiment, a liquid supply method using a flow cell having a liquid pool structure in a part of a flow path will be described. 
       FIGS.  28 A and  28 B  are diagrams illustrating a liquid supply method to the array chip  100  according to the eleventh embodiment. As illustrated in  FIG.  28 A ( 1 ), a flow cell  2120  has a lower part  2102  and an upper part  2104 . The lower part  2102  has a liquid pool structure  2000  on a downstream side of the array chip  100  in the flow path. The lower part  2102  has the introduction port  107  and the discharge port  108 . The upper part  2104  has the introduction port  105  and the discharge port  106 . 
     As illustrated in  FIG.  28 A ( 1 ), the operator prepares the liquid supply pipe  300  filled with the solution  202  to be inspected, the air  301  separating the solution  202  to be inspected and the oil  203 , and the oil  203  in advance. Next, the operator connects the liquid supply pipe  300  to the introduction port  105  such that the solution  202  to be inspected is positioned on the side (lowermost) closest to the array chip  100 . An angle between the flow cell  2120  and the liquid supply pipe  300  is defined as θ. After setting to the state illustrated in step (1), almost no operation is required up to step (5) in  FIG.  28 B . 
     In step (2) of  FIG.  28 A , the solution  202  to be inspected is filled on the upper side of the array chip  100  and the through-holes  101  in the array chip  100  by the gravity applied to the solution  202  to be inspected and the oil  203 . Thereafter, as illustrated in  FIG.  28 A ( 3 ), the air  301  in the liquid supply pipe  300  is extruded to the flow cell by the gravity applied to the oil  203 , and the air  301  extrudes (replaces) the solution  202  to be inspected present on the upper side of the array chip  100 . The extruded solution  202  to be inspected is accumulated in the liquid pool structure  2000 . As illustrated in  FIG.  28 B ( 4 ), the solution  202  to be inspected on the upper side of the array chip  100  is completely replaced with the air  301 . Thereafter, as illustrated in  FIG.  28 B ( 5 ), the oil  203  enters the flow cell by the gravity applied to the oil  203 , and the upper side of the array chip  100  is filled with the oil. The oil also flows into the liquid pool structure  2000 , and finally, as illustrated in  FIG.  28 B ( 6 ), the liquid pool structure is filled with the solution  202  to be inspected and the oil  203 . Thereafter, as illustrated in  FIG.  28 B ( 6 ), the operator connects the liquid supply pipe  350  filled with the oil  203  in advance to the introduction port  107  at an angle θ′. Accordingly, the oil  203  enters the flow cell  2120  by the gravity applied to the oil  203 , and the lower side of the array chip  100  is filled with the oil  203 . The angle θ′ may be the same as or different from the angle θ. 
     Conclusion of Eleventh Embodiment 
     In the present embodiment, since the flow cell  2120  has the liquid pool structure  2000 , the solution  202  to be inspected extruded by the air  301  does not come out of the discharge port  106 . Accordingly, it is possible to save time and effort required in the first to tenth embodiments to discard the solution to be inspected discharged from the discharge port  106 . Accordingly, the liquid supply to the array chip  100  can be more easily performed. Since the solution  202  to be inspected does not come out from the discharge port  106 , it is possible to reduce a risk that a component in the solution  202  to be inspected contaminates a component of another solution to be inspected in a laboratory. 
     Modified Examples 
     The present disclosure is not limited to the above-described embodiments, and includes various modified examples. The aforementioned embodiments are described in detail in order to facilitate easy understanding of the present disclosure, and are not limited to necessarily include all the described components. A part of a certain embodiment can be replaced with a configuration of another embodiment. The configuration of another embodiment can be added to the configuration of a certain embodiment. A part of the configuration of another embodiment can be added to, deleted from, or replaced with a part of the configuration of each embodiment. 
     EXAMPLES 
     Hereinafter, examples of the technology of the present disclosure will be described. The scope of the technology of the present disclosure is not limited to the contents described in the examples. 
     Example 1 
     In Example 1, a target to be inspected was DNA, and the liquid supply method of the second embodiment was actually tested. A silicone tube (inner diameter of 1 mm) was prepared as the liquid supply pipe. As the solution to be inspected, a solution containing water, a primer for amplifying the DNA to be detected, a probe that specifically binds to the DNA to be detected and emits fluoresces, an enzyme required for the PCR reaction, dNTPs, and the like (QuantStudio (registered trademark)  3 D Digital PCR Master Mix v2 manufactured by Thermo Fisher Scientific Inc.) was prepared. A QuantStudio (registered trademark)  3 D Digital PCR Immersion fluid manufactured by Thermo Fisher Scientific Inc. was prepared as the oil. 
       FIGS.  29 A and  29 B  are diagrams illustrating a liquid supply method to the array chip  100  according to Example 1. First, the operator attached a nozzle  700  to a distal end of the liquid supply pipe  300 . As illustrated in  FIG.  29 A ( 1 ), the solution  202  to be inspected was manually injected by using the pipette. The injection amount of the solution  202  to be inspected was set to about 30 μL. Thereafter, as illustrated in  FIG.  29 A ( 2 ), the pipette was removed from the liquid supply pipe  300 . Subsequently, as illustrated in  FIG.  29 A ( 3 ), the distal end of the pipette was connected to the liquid supply pipe  300 , and air was injected. The amount of air was about 150 μL to 300 μL. Thereafter, as illustrated in  FIG.  29 A ( 4 ), the pipette was removed from the liquid supply pipe  300 . Thereafter, as illustrated in  FIG.  29 B ( 5 ), a distal end of the pipette was connected to the liquid supply pipe  300 , and oil was injected. The amount of oil was about 50 μL. Thereafter, as illustrated in  FIG.  29 B ( 6 ), the pipette was removed from the liquid supply pipe  300 . Subsequently, as illustrated in  FIG.  29 B ( 7 ), the liquid supply pipe was stretched. In the operation so far, a portion of the liquid supply pipe  300  other than the vicinity where the distal end portion of the pipette is inserted was installed on a substantially horizontal surface. Thus, the inserted solution to be inspected or oil did not leak out from a nozzle of the nozzle  700 . 
       FIG.  30 A  is a cross-sectional view of the flow cell in a state where the liquid supply pipe  300  is connected. As illustrated in  FIG.  30 A , the nozzle  700  of the liquid supply pipe  300  was fitted into the introduction port  105  of the flow cell. The angle of the liquid supply pipe  300  was about 45 degrees. A thickness of the upper part  104  of the flow cell was about 1 mm. A thickness of the spacer  103  between the upper part of the flow cell and the array chip  100  was about 50 μm. The cross section of the introduction port  105  and the discharge port  106  of the flow cell parallel to the front surface of the array chip  100  was circular shape, and the diameter thereof was about 1 mm. The through-hole array  110  of the array chip  100  was present in a region of about 1 cm×1 cm. The cross section of the through-hole  101  parallel to the front surface of the array chip  100  was circular, and the diameter of the circle was about 60 μm. A shortest distance between the adjacent through-holes  101  was about 15 μm. A thickness of the array chip  100  was about 300 μm. A distance between the lower surface of the array chip  100  and the lower part  102  of the flow cell was about 300 μm. 
       FIG.  30 B  is a top view of the state of  FIG.  30 A . After setting to the state illustrated in  FIG.  30 A , the solution to be inspected, the air, and the oil were automatically supplied, and finally, the solution to be inspected was filled in the through-hole, and the front surface of the array chip  100  was filled with the oil. 
       FIG.  31 A  is a photograph of the front surface of the flow cell after the liquid supply in Example 1 is performed. As illustrated in  FIG.  31 A , it can be seen that the liquid could be supplied to the flow cell without any problem. 
       FIG.  31 B  is a photograph of the back surface of the flow cell after the liquid supply in Example 1 is performed. From the photograph of  FIG.  31 B , there was no scene where the liquid leaks to the back surface of the array chip  100 . In particular, when  FIG.  31 B  is compared with the photograph ( FIG.  6 D ) where the liquid leaked to the back surface of the array chip  100 , it is obvious that the liquid did not leak to the back surface of the array chip  100  in Example 1. That is, in Example 1, due to the use of the method of the present disclosure, it could be demonstrated that the solution to be inspected can be confined in the through-holes and the front surface of the array chip  100  can be covered with the oil without leakage of the solution to be inspected to the back surface side of the array chip  100  through the through-holes or connection between the solutions in the adjacent through-holes. Thereafter, although not illustrated, the back surface side of the array chip  100  could also be covered with the oil by connecting the liquid supply pipe  350  to the introduction port  107  to the back surface side of the array chip  100  and pouring the oil from the liquid supply pipe. Thereafter, the PCR reaction is performed, and then excitation light is applied from the upper surface of the array chip  100  to perform fluorescence observation. In a case where the DNA sequence to be detected is present in the through-hole, fluorescence derived therefrom is observed.