Method and system for accumulating micro-objects

Abstract

In this microobject collecting method, a plurality of microobjects dispersed in a sample are collected together. The microobject collecting method includes: a step of shining a plurality of laser beams, spaced apart from one another, onto a thin film (102) provided on a bottom surface of a collecting container (100) accommodating the sample; and a step of heating the sample by means of the plurality of laser beams to generate a plurality of microbubbles corresponding to the plurality of laser beams, and to generate heat convection in the sample. A gap between two adjacent laser beams among the plurality of laser beams is narrower than a distance in which it would be possible virtually to arrange, side-by-side, in a space between two microbubbles corresponding to the two laser beams, three of the larger microbubble among the two microbubbles.

Description

[Technical Field]

[0001] This disclosure relates to a method and system for accumulating micro-objects, and more specifically, to a technique for accumulating multiple micro-objects dispersed in a liquid. [Background technology]

[0002] Technologies have been proposed for accumulating multiple microscopic objects (such as fine particles, cells, and microorganisms) dispersed in a liquid. For example, the microscopic object accumulation device disclosed in International Publication No. 2018 / 159706 (Patent Document 1) comprises a light source and a container configured to hold a dispersion of multiple microscopic objects. The container has a bottom surface on which a photothermal conversion member is formed to convert light from the light source into heat, and an inner surface on which immersion wetting occurs when in contact with the dispersion. The photothermal conversion member generates thermal convection in the dispersion by heating the dispersion. The inner surface generates Marangoni convection at the gas-liquid interface, which is the interface between the dispersion and the gas surrounding the dispersion. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. 2018 / 159706 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] In accumulation systems that collect multiple microscopic objects dispersed in a liquid using light irradiation, there is a need to collect more microscopic objects in a shorter time, or in other words, to collect microscopic objects more efficiently.

[0005] This disclosure is made to solve the above-mentioned problems, and the purpose of this disclosure is to provide a technology that can efficiently accumulate multiple micro-objects dispersed in a liquid. [Means for solving the problem]

[0006] (1) A method for accumulating micro-objects according to a certain aspect of the present disclosure involves accumulating a plurality of micro-objects dispersed in a liquid. The method for accumulating micro-objects includes the steps of irradiating a photothermal conversion region provided on the bottom surface of a container containing a liquid with a plurality of light rays separated from each other, and heating the liquid with the plurality of light rays to generate a plurality of microbubbles corresponding to the plurality of light rays and to generate thermal convection in the liquid. The distance between two adjacent light rays among the plurality of light rays is narrower than the distance at which three larger microbubbles from the two microbubbles corresponding to the two light rays can be virtually placed side by side in the gap between the two microbubbles.

[0007] (2) The above-mentioned interval is narrower than the distance at which the above-mentioned large microbubbles can be virtually placed in the above-mentioned gap.

[0008] (3) The distance between the irradiation position of each of the multiple light rays onto the photothermal conversion region and the side wall of the container is longer than the diameter of the corresponding microbubble among the multiple microbubbles.

[0009] (4) The thermal conductivity of the side wall is greater than that of the liquid. (5) The irradiation area of ​​each of the two light rays onto the photothermal conversion region is greater than the contact area between the corresponding microbubble of the two microbubbles and the photothermal conversion region.

[0010] (6) The method for accumulating minute objects further includes, prior to the irradiation step, the step of placing the liquid in a container such that the gas-liquid interface between the liquid and the surrounding gas is flat.

[0011] (7) The micro-object integration system according to another aspect of the present disclosure integrates a plurality of micro-objects dispersed in a liquid. The micro-object integration system includes a holder configured to hold a liquid container having a bottom surface provided with a photothermal conversion region, a light source that emits a plurality of light rays, and an optical system that can irradiate the photothermal conversion region with the plurality of light rays while separating them from each other. By heating the liquid with the plurality of light rays, a plurality of microbubbles corresponding to the plurality of light rays are generated and thermal convection occurs in the liquid. The optical system is configured such that the distance between two adjacent light rays among the plurality of light rays is narrower than the distance at which three larger microbubbles among the two microbubbles can be virtually arranged side by side in the gap between the two microbubbles corresponding to the two light rays.

Advantages of the Invention

[0012] According to the present disclosure, a plurality of micro-objects dispersed in a liquid can be integrated with high efficiency.

Brief Description of the Drawings

[0013] [Figure 1] FIG. schematically shows an example of the overall configuration of the micro-object integration system according to Embodiment 1 of the present disclosure. [Figure 2] FIG. schematically shows the configuration of the integration container and the laser module. [Figure 3] FIG. is an image of the appearance of the integration container taken. [Figure 4] FIG. is a flowchart showing an example of the micro-object integration method in the present embodiment. [Figure 5] FIG. schematically shows another example of the overall configuration of the micro-object integration system according to Embodiment 1. [Figure 6] FIG. schematically shows another example of the configuration of the laser device. [Figure 7] FIG. is a flowchart showing another example of the micro-object integration method in the present embodiment. [Figure 8] FIG. is a diagram for explaining the micro-object integration mechanism. [Figure 9]This figure shows an example of the accumulation results of resin beads when irradiated with multiple laser beams. [Figure 10] This figure shows the simulation model used for the fluid simulation. [Figure 11] Figure 10 is a top view of the simulation model shown. [Figure 12] Figure 1 shows the fluid simulation results of thermal convection at each pitch. [Figure 13] Figure 2 shows the fluid simulation results of thermal convection at each pitch. [Figure 14] This figure shows the simulation results of the average flow velocity of thermal convection at each pitch. [Figure 15] This figure shows the measured number of resin beads at each pitch. [Figure 16] This diagram illustrates the gap between two microbubbles that occur at adjacent heat source locations in each pitch. [Figure 17] This figure shows the results of a fluid simulation of thermal convection around microbubbles. [Figure 18] This figure shows the simulation results and actual measurement results regarding the side wall temperature for each material of the storage container's side wall. [Figure 19] This figure shows the simulation results regarding the thermal convection velocity for each material of the side wall of the collection container. [Figure 20] This figure shows the measured number of resin beads. [Figure 21] This figure shows a simulation model for examining the effects of the shape and height of the gas-liquid interface. [Figure 22] This figure shows the results of a fluid simulation regarding the flow velocity of thermal convection. [Figure 23] This figure shows the results of a fluid simulation related to the flow rate of thermal convection. [Figure 24] This diagram compares the flow rate of thermal convection between a flat liquid surface and a curved liquid surface. [Figure 25] These are images of a flat liquid surface and a curved liquid surface. [Figure 26] This figure shows an example of measurement results for the number of resin beads accumulated and the accumulation efficiency on a flat liquid surface. [Figure 27] This figure shows an example of measurement results for the number of resin beads accumulated and the accumulation efficiency at a curved liquid surface. [Modes for carrying out the invention]

[0014] The embodiments of this disclosure will be described in detail below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and their descriptions will not be repeated.

[0015] <Definition of Terms> In this disclosure, "nanometer order" includes the range from 1 nm to 1000 nm (= 1 μm). "Micrometer order" includes the range from 1 μm to 1000 μm (= 1 mm). Therefore, the term "nanometer order to micrometer order" refers to the range from 1 nm to 1000 μm, but typically refers to the range from tens of nm to hundreds of μm, preferably from 100 nm to 100 μm, and more preferably from 1 μm to tens of μm.

[0016] In this disclosure, the term "micro-object" means an object having a size ranging from the nanometer order to the micrometer order. The shape of the micro-object is not particularly limited and may be spherical, ellipsoidal, rod-shaped, etc. If the micro-object is ellipsoidal, at least one of the lengths in the minor axis direction and the major axis direction of the ellipsoid may be in the range of the nanometer order to the micrometer order. If the micro-object is rod-shaped, at least one of the width and length of the rod may be in the range of the nanometer order to the micrometer order.

[0017] Examples of microscopic objects include metal nanoparticles, metal nanoparticle aggregates, metal nanoparticle aggregate structures, semiconductor nanoparticles, organic nanoparticles, resin beads, PM (Particulate Matter), and nanodiamonds. "Metal nanoparticles" are metal particles with a size on the order of nanometers. "Metal nanoparticle aggregates" are aggregates formed by the aggregation of multiple metal nanoparticles. "Metal nanoparticle aggregate structures" are structures in which, for example, multiple metal nanoparticles are fixed to the surface of a bead via interaction sites, with gaps between them, and are arranged at intervals smaller than the diameter of the metal nanoparticles. "Semiconductor nanoparticles" are semiconductor particles with a size on the order of nanometers. "Organic nanoparticles" are particles made of organic compounds with a size on the order of nanometers. "Resin beads" are particles made of resin with a size ranging from the order of nanometers to the order of micrometers. "PM" refers to particulate matter with a size on the order of micrometers. Examples of PM include PM2.5 and SPM (Suspended Particulate Matter).

[0018] The micro-objects may be substances of biological origin (biomaterials). More specifically, the micro-objects may include cells, microorganisms (bacteria, fungi, etc.), biomacromolecules (proteins, nucleic acids, lipids, polysaccharides, etc.), antigens (allergens, etc.), and viruses.

[0019] In this disclosure, "microbubble" means a bubble having a size (diameter) on the order of micrometers.

[0020] In the following explanation, the x and y directions represent the horizontal. The x and y directions are orthogonal to each other. The z direction represents the vertical. The direction of gravity is downward in the z direction. Upward in the z direction is abbreviated as "up," and downward in the z direction is abbreviated as "down."

[0021] [Embodiment 1] <System Configuration> Figure 1 is a schematic diagram showing an example of the overall configuration of a micro-object integration system according to Embodiment 1 of the present disclosure. The integration system 901 comprises a sample stage 1, a sample supply device 2, a light source stage 3, a laser module 4, a cooling device 5, an adjustment mechanism 6, a power supply 7, an imaging device 8, an illumination device 9, and a controller 10.

[0022] Sample stage 1 holds a collection container 100 containing a liquid sample. Sample stage 1 is, for example, an xyz-axis stage and is configured to be movable in the x, y, and z directions. Sample stage 1 corresponds to the "holder" in this disclosure.

[0023] The sample supply device 2 supplies the sample to the collection container 100 in response to a command from the controller 10. For example, a dispenser can be used as the sample supply device 2.

[0024] The light source stage 3 holds the laser module 4 and the cooling device 5. The light source stage 3 is, for example, an XYZ axis stage, configured to be movable in the x, y, and z directions. In this example, the light source stage 3 is located below the sample stage 1.

[0025] The laser module 4 is a laser light source, such as a semiconductor laser module, that emits multiple laser beams (indicated as L in the figure) in response to commands from the controller 10. In this example, the wavelength of the laser beams is in the near-infrared region, for example, 850 nm. The configuration of the laser module 4 is explained in more detail in Figure 2.

[0026] The cooling device 5 cools the laser module 4. The cooling device 5 is, for example, a Peltier element or a heat sink. By cooling the laser module 4, it is possible to prevent failure of the laser module 4 due to temperature rise and to suppress a decrease in laser output. Note that the cooling device 5 is not shown in Figure 2 and subsequent figures.

[0027] The adjustment mechanism 6 is configured to adjust the x, y, and z positions of the sample stage 1 in response to commands from the controller 10, as well as the x, y, and z positions of the light source stage 3. This allows the adjustment mechanism 6 to adjust the relative positional relationship between the integrated container 100 mounted on the sample stage 1 and the laser module 4 installed on the light source stage 3. However, the adjustment mechanism 6 may, for example, adjust the position of the integrated container 100 relative to the fixed laser module 4, or adjust the position of the laser module 4 relative to the fixed integrated container 100. In the example described below, when setting the light irradiation position, the horizontal position (x and y positions) of the sample stage 1 is adjusted, and the height (z position) of the light source stage 3 is adjusted. The light source stage 3 and the adjustment mechanism 6 correspond to the "optical system" in this disclosure.

[0028] Power supply 7 supplies current to drive the laser module 4 in response to commands from controller 10. Power supply 7 also supplies current to drive the cooling device 5 (such as a Peltier element or a heat sink fan).

[0029] The imaging device 8 responds to commands from the controller 10 to photograph the sample inside the integration container 100 and outputs the captured image to the controller 10. The imaging device 8 can be a video camera including a CCD (Charge Coupled Device) image sensor or a CMOS (Complementary Metal Oxide Semiconductor) image sensor.

[0030] The illumination device 9 emits illumination light (for example, white light, indicated by WL) to illuminate the sample on the accumulation container 100 in response to a command from the controller 10. For example, a white LED (Light Emitting Diode), a halogen lamp, etc., can be used as the illumination device 9. Note that the imaging device 8 and the illumination device 9 are merely devices for observing the sample and are not essential components for the accumulation of minute objects by the accumulation system 901.

[0031] The controller 10 is a microcomputer that includes, for example, a processor such as a CPU (Central Processing Unit), memory such as ROM (Read Only Memory) and RAM (Random Access Memory), and input / output ports (none of which are shown). The controller 10 controls each of the devices that make up the integrated system 901 (sample supply device 2, adjustment mechanism 6, power supply 7, imaging device 8, and lighting device 9).

[0032] Figure 2 is a schematic diagram showing the configuration of the integrated container 100 and the laser module 4. Figure 3 is an image of the external appearance of the integrated container 100. Referring to Figures 2 and 3, the integrated container 100 has, for example, a cylindrical shape with an open top and includes a substrate 101, a thin film 102, and side walls 103.

[0033] The substrate 101 is placed on the bottom surface of the integration container 100. The substrate 101 is made of a material that is transparent to the laser beam (near-infrared light) from the laser module 4 and transparent to the illumination light (white light) from the illumination device 9. Examples of such materials include glass, quartz, and silicone.

[0034] The thin film 102 is placed on the substrate 101. The thin film 102 absorbs the laser beam from the laser module 4 and converts the light energy into thermal energy. The material of the thin film 102 is preferably a material with high photothermal conversion efficiency in the wavelength range of the laser beam (near-infrared region in this embodiment). In this example, a gold thin film is formed as the thin film 102. The gold thin film can be formed using known methods such as sputtering or electroless plating. The thickness (film thickness) of the thin film 102 is determined by design or experimentation considering the laser output and the absorption wavelength range and photothermal conversion efficiency of the material of the thin film 102, but is typically on the order of nanometers (e.g., 10 nm).

[0035] Free electrons on the surface of the thin film 102 form surface plasmons, which vibrate when exposed to laser light. This causes polarization. The energy of this polarization is converted into lattice vibration energy through Coulomb interaction between the free electrons and atomic nuclei. As a result, the thin film 102 generates heat. Hereafter, this effect will also be referred to as the "photothermal effect."

[0036] The material of the thin film 102 is not limited to gold, but may be a metal element other than gold that can produce a photothermal effect (for example, silver), or a metal nanoparticle aggregate structure (for example, a structure using gold nanoparticles or silver nanoparticles). The material of the thin film 102 may also be a non-metallic material that has a high light absorption rate in the wavelength range of laser light. Such materials include materials that are close to black bodies (for example, carbon nanotube black bodies).

[0037] The thin film 102 does not need to be formed over the entire surface of the substrate 101; it is sufficient if it is formed over at least a portion of the substrate 101. The region where the thin film 102 is formed corresponds to the "photothermal conversion region" as described in this disclosure.

[0038] In this example, the side wall 103 has a hollow cylindrical shape. The material of the side wall 103 is not particularly limited optically, but as will be described later, it is preferable to use a material that has good heat dissipation characteristics (high thermal conductivity). In this embodiment, the material of the side wall 103 is stainless steel (SUS: Steel Use Stainless).

[0039] The laser module 4 includes a substrate 41, a surface light-emitting element 42, a bonding member 43, an optical waveguide 44, and a lens 45.

[0040] The substrate 41 is a flat plate formed of an insulating material, such as a printed circuit board or a ceramic substrate. A surface light-emitting element 42 is mounted on the surface of the substrate 41. The substrate 41 supplies a drive current from the power supply 7 (see Figure 1) to the surface light-emitting element 42.

[0041] The surface light-emitting element 42 is, for example, an array-type vertical cavity surface-emitting laser (VCSEL). The surface light-emitting element 42 has multiple (nine in the example described later) light-emitting regions 421. The multiple light-emitting regions 421 are arranged in a two-dimensional array. All light-emitting regions 421 emit light simultaneously, and each of the multiple light-emitting regions 421 emits a laser beam (indicated by LB). Each laser beam is emitted in a direction perpendicular to the surface of the surface light-emitting element 42 (upward in the z direction).

[0042] The bonding member 43 is, for example, an adhesive, and bonds the optical waveguide 44 onto the surface light-emitting element 42. The bonding member 43 is made of a material that is transparent to light (near-infrared light) emitted from the surface light-emitting element 42.

[0043] The optical waveguide 44 focuses multiple laser beams emitted from the surface light-emitting element 42. The material of the optical waveguide 44 is transparent to the light emitted from the surface light-emitting element 42, for example, resin or glass. The optical waveguide 44 is A4 41 and The device includes a cladding 442. The core 441 has a cylindrical shape. The incident end of the core 441 is configured to cover the entire light-emitting region 421 so that all laser beams emitted from the surface light-emitting element 42 are incident on it. The cladding 442 has a hollow cylindrical shape. The cladding 442 is positioned to cover the sides of the core 441.

[0044] The lens 45 is a plano-convex lens having both a flat and a convex surface. The flat surface of the lens 45 is joined to the output end of the optical waveguide 44. The convex surface of the lens 45 protrudes in the direction of light emission from the laser output portion of the laser module 4.

[0045] The propagation path of the laser beam in the laser module 4 is described below. The optical waveguide 44 is a graded index (GI) optical fiber. Therefore, the refractive index of the core 441 of the optical waveguide 44 is highest at the radial center of the core 441 and decreases smoothly toward the radially outward direction. The laser beam propagating inside the core 441 has multiple modes with different propagation distances. Low-order modes travel through the core center, while higher-order modes travel away from the core center. Although the propagation distance of low-order modes is short, their propagation speed is relatively slow due to the high refractive index at the core center. Conversely, higher-order modes have a longer propagation distance but a relatively faster propagation speed. The refractive index distribution of the core 441 is designed so that the difference in propagation time between modes is sufficiently short.

[0046] Multiple laser beams propagating within the core 441, which has such a refractive index distribution, form nodes and antinodes. The positions of the nodes and antinodes may change depending on the wavelength of the laser beams. Regarding the direction of propagation of the laser beams, the length of the optical waveguide 44 is determined so that the exit end of the optical waveguide 44 is not located midway between the nodes and antinodes. In other words, the length of the optical waveguide 44 is determined so that the exit end of the optical waveguide 44 is located midway between the antinodes and nodes, or that the exit end of the optical waveguide 44 coincides with an antinode. As a result, the multiple laser beams propagating through the optical waveguide 44 are emitted from the exit end of the optical waveguide 44 with a tendency to converge. The emitted multiple laser beams are further focused by the lens 45 to form a single convergence point F. The multiple laser beams emitted upward from the laser module 4 are irradiated onto the integration container 100 on the sample stage 1.

[0047] Multiple laser beams emitted upward from the tip of the laser module 4 are separate near the lens 45, but above that they intersect to form a focal point F. Above the focal point F, the multiple laser beams separate again. As explained in Figure 1, the controller 10 can adjust the height of the light source stage 3 by controlling the adjustment mechanism 6. Therefore, when the height of the light source stage 3 is adjusted so that the focal point F is located on the bottom surface of the integration container 100, single irradiation of the integration container 100 is achieved (single irradiation method). On the other hand, when the height of the light source stage 3 is adjusted so that the focal point F is located below the bottom surface of the integration container 100, multi-point irradiation of the integration container 100 is achieved (multi-point irradiation method). In this way, the controller 10 can switch between the single irradiation method and the multi-point irradiation method.

[0048] When the multi-point irradiation method is selected, multiple laser spots are located on the bottom surface (thin film 102) of the integration container 100. The distance between the centers of these laser spots is called the "pitch." The pitch increases as the position of the bottom surface of the integration container 100 moves away from the focal point F. Therefore, the controller 10 can set the pitch to a desired value by controlling the adjustment mechanism 6.

[0049] <Integration Flow> Figure 4 is a flowchart showing an example of a method for accumulating minute objects in this embodiment. In this flowchart, each step from step S103 onward is basically implemented by software processing by the controller 10, but some or all of it may be implemented by hardware (electrical circuits) located within the controller 10. Hereinafter, steps will be abbreviated as S.

[0050] In S101, a sample in which minute objects are dispersed in a dispersion medium is prepared by the operator. The prepared sample is stored in the sample supply device 2.

[0051] In S102, the controller 10 places the accumulation container 100 on the sample stage 1. This process can be achieved, for example, by a feeding mechanism (not shown) provided in the accumulation system 901.

[0052] In S103, the controller 10 controls the sample supply device 2 to supply an appropriate amount of sample to the accumulation container 100. The amount of sample supplied may be a small amount, for example, several tens of μL to several hundred μL, or it may be a larger amount (1 mL in the example described later). By using an accumulation container 100 provided with side walls 103 as in this embodiment, a larger amount of sample can be stored in the accumulation container 100 compared to when a flat substrate (not shown) is used.

[0053] In S104, the controller 10 controls the illumination device 9 to start irradiating the sample with illumination light (white light). The controller 10 also controls the imaging device 8 to start imaging the sample. Note that the process in S104 is for observing the sample and not for accumulating minute objects. Fluorescence observation of the sample may be performed during the process in S104.

[0054] In step S105, the controller 10 adjusts the horizontal position of the sample stage 1 by controlling the adjustment mechanism 6. This allows multiple laser beams from the laser module 4 to be directed to the target position within the sample. More specifically, the controller 10 can obtain the horizontal position of the sample by extracting the outline pattern of the sample from the image captured by the imaging device 8 using pattern recognition image processing technology. Then, the controller 10 adjusts the horizontal position of the light source stage 3 from its initial position as appropriate, thereby aligning the horizontal irradiation position of the multiple laser beams to the target position within the sample.

[0055] In S106, the controller 10 adjusts the height of the light source stage 3 by controlling the adjustment mechanism 6. This allows switching between single-point and multi-point irradiation modes, and adjusting the pitch in the multi-point irradiation mode. The vertical position of the focal point F, where all laser beams are focused, is known from the specifications of the laser module 4 (laser beam wavelength, and the shapes of the optical waveguide 44 and lens 45, etc.). Therefore, the controller 10 can switch between single-point and multi-point irradiation modes by appropriately adjusting the height of the light source stage 3 from its initial height. Furthermore, the controller 10 can set the pitch to a desired value by pre-storing the correspondence between the height of the light source stage 3 and the pitch in memory.

[0056] In S107, the controller 10 controls the power supply 7 to start irradiating the sample with multiple laser beams from the laser module 4. Subsequently, the controller 10 determines whether a specified time has elapsed since the laser beams were irradiated (S108). The specified time is, for example, several tens of seconds to several minutes, and is set by the operator according to the type of minute object, the type of dispersion medium, the volume of the dispersion medium, and the concentration of minute objects in the dispersion medium. The controller 10 continues irradiating with laser beams until the specified time has elapsed (NO in S108). With this light irradiation, minute objects accumulate according to the mechanism described later. Once the specified time has elapsed (YES in S108), the controller 10 controls the power supply 7 to stop irradiating the sample with multiple laser beams from the laser module 4 (S109). The controller 10 also controls the illumination device 9 to stop irradiating the sample with illumination light and controls the imaging device 8 to stop imaging the sample (S110). This completes the series of processes.

[0057] <Other laser configuration examples> Figures 1 to 4 illustrate an example configuration in which multiple laser beams are output from a single laser module 4, but a laser device including multiple laser modules may also be provided.

[0058] Figure 5 is a schematic diagram showing another example of the overall configuration of the micro-object integration system according to Embodiment 1. The integration system 902 differs from the integration system 901 (see Figure 1) in that it includes a laser device 46 instead of a laser module 4. The laser device 46 includes a plurality of laser modules 47. Figure 4 shows an example with nine laser modules 47, but the number of laser modules 47 is not particularly limited as long as it is two or more. Each laser module 47 includes a plurality of surface light-emitting elements 42.

[0059] Figure 6 is a schematic diagram illustrating another example of the configuration of the laser device. In this example, one laser beam is output from each laser module 47. In this case, various "pitches" (distance between laser spots) can be achieved on the bottom surface of the integration container 100 by changing the spacing between adjacent laser modules 47.

[0060] Figure 7 is a flowchart showing another example of the method for accumulating minute objects in this embodiment. The processes S201 to S203 are the same as the processes S101 to S103 in Figure 4, so the explanation will not be repeated.

[0061] In S204, the controller 10 selects the pitch according to the laser output, type of dispersion medium, etc., based on the simulation results and / or experimental results described later. For example, the integrated system 902 can be configured so that the laser devices 46 are interchangeable, and various interchangeable laser devices 46 can be prepared in advance. The spacing between adjacent laser modules 47 differs among the interchangeable laser devices 46. In other words, these laser devices 46 correspond to different pitches. A laser device 46 that realizes the pitch selected by the controller 10 (and of course, can also be selected by the operator) can be mounted on the integrated system 902.

[0062] In S205, the controller 10 controls the illumination device 9 to begin irradiating the sample with illumination light (white light). The controller 10 also controls the imaging device 8 to begin imaging the sample. Subsequently, the controller 10 adjusts the horizontal position of the sample stage 1 by controlling the adjustment mechanism 6 (S206). The controller 10 may also adjust the height of the light source stage 3 by controlling the adjustment mechanism 6. The processes in S207 to S210 are the same as the processes in S107 to S110 in Figure 4, respectively, so the explanation will not be repeated.

[0063] <Integration Mechanism> Figure 8 is a diagram illustrating the accumulation mechanism of micro-objects. This diagram is intended to provide a detailed explanation of the phenomena that occur during the execution of processes S107 and S108 in Figure 4, or during the execution of processes S207 and S208 in Figure 7. To avoid making the diagram too complex, the explanation here uses a configuration in which three laser beams are irradiated onto the sample as an example.

[0064] Referring to Figure 8(A), when light irradiation is started, multiple laser spots are locally heated by the photothermal effect of the thin film 102. As a result, as shown in Figure 8(B), the dispersion medium (e.g., ultrapure water) boils near each of the multiple laser spots, generating microbubbles (indicated as MB). Each microbubble grows over time.

[0065] Upon irradiation with laser light, regular thermal convection occurs steadily in the dispersion medium in addition to microbubbles. In Figure 8(C), the direction of thermal convection is indicated by arrows. Thermal convection is classified into buoyancy convection (indicated by BC) and Marangoni convection (indicated by MC).

[0066] The closer you are to the laser spot, the higher the temperature of the dispersion medium. In other words, light irradiation creates a temperature gradient in the dispersion medium. This temperature gradient causes buoyant convection. More specifically, the dispersion medium above the region where microbubbles are formed becomes relatively dilute due to heating and rises due to buoyancy. At the same time, the relatively cooler dispersion medium located horizontally to the microbubbles flows towards the microbubbles.

[0067] Furthermore, generally, the interfacial tension generated on the surface of a bubble depends on the molecular density at the bubble surface. The higher the molecular density, the lower the interfacial tension. In this embodiment, the molecular density is influenced not only by the density of the molecules constituting the dispersion medium but also by the density of the microparticles. Therefore, if a density gradient of microparticles exists at the gas-liquid interface between the microbubbles and the dispersion medium, the region with a higher density of microparticles (usually the lower region) is pulled towards the region with a lower density of microparticles (the upper region) so that the interfacial tension is balanced. This movement at the gas-liquid interface is transmitted into the liquid (bulk), generating Marangoni convection. Note that Marangoni convection depends on the density gradient but not on gravity.

[0068] Microscopic particles are transported towards microbubbles by thermal convection (buoyant convection and / or Marangoni convection) and trapped by the microbubbles. More specifically, a "stagnation region" is created around the microbubble where the velocity of thermal convection is nearly zero. As a result of the microscopic particles transported by thermal convection being trapped in the stagnation region, the microscopic particles accumulate near the laser spot (see Figure 8(D)). In this way, the microbubbles function as "stoppers" that block the microscopic particles, becoming accumulation sites for them. The process of concentrating and accumulating microscopic particles dispersed in a sample near the laser spot according to the above mechanism can also be called "photoconcentration."

[0069] Irradiation with multiple laser beams (multi-point irradiation) generates rapid convection towards the gaps between adjacent microbubbles. Due to the influence of this convection, many minute objects accumulate in the stagnant regions that form between adjacent microbubbles. Therefore, when conditions such as laser output are the same for single irradiation and multi-point irradiation, multi-point irradiation tends to result in a greater accumulation of minute objects.

[0070] Figure 9 shows an example of the accumulation results of resin beads when irradiated with multiple laser beams. In this example, multi-point irradiation was performed using 9-point and 17-point irradiation, and single irradiation was also performed for comparison. The horizontal axis represents the number of resin beads introduced into the sample (introduced number). The upper vertical axis represents the total number of resin beads accumulated in all laser spots (accumulated number). The lower vertical axis represents the accumulation efficiency. Accumulation efficiency is the number of accumulated beads relative to the number introduced. For example, if the number of accumulated beads is 500 for an introduced number of 10,000, the accumulation efficiency is calculated as 500 / 10,000 × 100 = 5%.

[0071] It was confirmed that by performing multi-point irradiation, the number of accumulated resin beads (accumulation count) increased compared to single irradiation, and the accumulation efficiency of the resin beads also improved. Specifically, with an input of 10,000 beads, the accumulation count of 183 in 9-point irradiation was 15.2 times that of 12 in single irradiation. From this, it can be seen that the accumulation count per microbubble in 9-point irradiation was 1.69 times that of single irradiation. Also, with the same input of 10,000 beads, the accumulation count of 333 in 17-point irradiation was 27.8 times that of 12 in single irradiation. From this, it can be seen that the accumulation count per microbubble in 17-point irradiation was 1.63 times that of single irradiation.

[0072] <The effect of pitch> The inventors investigated the effect of the spacing (pitch) between laser spots at the bottom surface of the accumulation container 100 on the accumulation efficiency of minute objects. First, we will describe the fluid simulation of thermal convection when the pitch is set to various values.

[0073] Figure 10 shows the simulation model used for the fluid simulation. Figure 11 is a top view of the simulation model shown in Figure 10. In this example, nine heat sources were arranged in a 3x3 grid on the bottom surface of the accumulation container 100. Each of the nine heat sources corresponds to a laser spot. The position of the central heat source among the nine heat sources was aligned with the center of the circular bottom surface of the accumulation container 100. The inner and outer diameters of the cylindrical side walls 103 were set to 14 mm and 18 mm, respectively. The volume of the sample contained in the accumulation container 100 was set to 1 mL.

[0074] Figures 12 and 13 show the results of fluid simulations of thermal convection at various pitches. In these simulations, the pitch (distance between the centers of the heat sources) was set to eight different values: 0.57 mm, 0.58 mm, 0.6 mm, 0.8 mm, 1 mm, 2 mm, 3 mm, and 4 mm. The microbubble size was set to a diameter of 500 μm (= 0.5 mm). Note that Figures 12 and 13 only show vertical cross-sections containing three heat sources arranged in a single line.

[0075] In each pitch, thermal convection rose from the three microbubbles (particularly the central microbubble) towards the gas-liquid interface. The thermal convection then flowed horizontally outward along the gas-liquid interface. Finally, the thermal convection descended along the side wall 103 and returned to the three microbubbles. Within the accumulation container 100, the sample circulates due to the thermal convection flowing in this direction.

[0076] When the pitch is extremely narrow, specifically when the pitch is 1 mm or less, it can be observed that the thermal convection from the central microbubble and the thermal convection from the microbubbles at both ends are inseparable. Furthermore, when the pitch is 2 mm, although the inseparability is weaker compared to when the pitch is 1 mm or less, it can be observed that the thermal convection from the central microbubble and the thermal convection from the microbubbles at both ends merge in a narrow area. Thus, when the pitch is 2 mm or less, a synergistic effect is created in which the thermal convection from the three microbubbles merge or reinforces each other, resulting in a faster thermal convection velocity compared to single irradiation.

[0077] In contrast, when the pitch was wide, specifically 3 mm or more, the synergistic effect of thermal convection was weaker compared to when the pitch was 2 mm or less. In addition, the existence of regions where thermal convection stagnated in the gaps between adjacent microbubbles was clearly observed. In these regions, the thermal convection flowed in a swirling manner, and the flow velocity of the thermal convection was also slow.

[0078] Figure 14 shows the simulation results of the average thermal convection velocity at each pitch. The horizontal axis represents the pitch, and the vertical axis represents the average thermal convection velocity. The average velocity is calculated by determining the local velocity for each region across the entire sample area and then finding the average value. A tendency was observed for the average velocity to be higher as the pitch narrowed.

[0079] Next, we will describe the results of actually accumulating resin beads as an example of the "micro-objects" related to this disclosure. In this example, polystyrene resin beads were used.

[0080] Figure 15 shows the measured number of resin beads accumulated at each pitch. The horizontal axis represents the pitch, and the vertical axis represents the number of resin beads accumulated per microbubble. For comparison, the number of resin beads accumulated in microbubbles during a single irradiation is shown by a dashed line.

[0081] If the pitch is 3mm or more, 1mm stomach The number of resin beads accumulated per chlorobubble was less than the number of resin beads accumulated during single irradiation. On the other hand, when the pitch was 2 mm or less, 1 mm stomach The number of resin beads accumulated per chlorobubble was greater than the number of resin beads accumulated during single irradiation. In particular, when the pitch was 1 mm, 1 mm stomach The highest number of resin beads accumulated per chlorobubble was observed. These measured results are in good agreement with the fluid simulation results explained in Figures 12 and 13. Therefore, it can be inferred that an accumulation rate equivalent to or greater than that of a 1 mm pitch can be achieved even when the pitch is less than 1 mm.

[0082] Thus, in this embodiment, when the microbubble size is 0.5 mm in diameter, it is desirable to set the pitch to 2 mm or less, and more desirable to set the pitch to 1 mm or less. Here, at least within the range of small sample volumes, the "scaling law" holds true, where the same phenomenon occurs even when the scale is enlarged or reduced. Therefore, below, by using the microbubble size as a reference, the condition that it is desirable to set the pitch to 2 mm or less or 1 mm or less is generalized.

[0083] Figure 16 is a diagram illustrating the void (space) between two microbubbles that occur at adjacent heat source locations in each pitch.

[0084] When the pitch is 1 mm, a 0.5 mm gap is created between two adjacent microbubbles (the microbubbles that actually occur). The size of this gap is equal to the size (diameter) of the microbubble. In other words, one microbubble can be virtually placed in this gap. Similarly, when the pitch is 1.5 mm, a 1 mm gap is created between two adjacent microbubbles. Two microbubbles can be virtually placed in this gap. When the pitch is 2 mm, a 1.5 mm gap is created between two adjacent microbubbles. Three microbubbles can be virtually placed in this gap.

[0085] For simplicity, this example assumes that all microbubbles are the same size, but in reality, there can be some variation in the size of the microbubbles that actually occur. The size of each virtually placed microbubble can be determined by using the size (diameter) of the larger of the two microbubbles that actually occur. If the size of the smaller microbubble were used, it cannot be ruled out that the gaps between adjacent microbubbles would become excessively narrow, potentially hindering thermal convection.

[0086] The condition of setting the pitch to 2 mm or less can be rephrased as "the pitch is narrower than the distance at which three of the larger microbubbles corresponding to two light rays can be virtually placed side by side in the gap between those two microbubbles." Similarly, the condition of setting the pitch to 1 mm or less can be rephrased as "the pitch is narrower than the distance at which the larger of the two microbubbles corresponding to two light rays can be virtually placed in the gap between those two microbubbles."

[0087] <Distance between microbubbles and the side wall> Figure 17 shows the results of a fluid simulation of thermal convection around microbubbles. From Figure 17, it can be seen that particularly strong thermal convection occurs within a range of 1 mm from the heat source (laser spot). Therefore, from the viewpoint of effectively utilizing thermal convection, it is desirable to position the side wall 103 of the accumulation container 100 outside the above range. In other words, it is desirable to design the size and / or shape of the accumulation container 100 or set the position of the laser spot so that the side wall 103 is located at a distance greater than the distance at which two virtual microbubbles can be placed from the laser spot. This makes it less likely for the strong thermal convection inside the above range to be obstructed, making it possible to accumulate minute objects with high efficiency.

[0088] <Heat dissipation characteristics> Generally, the dimensionless Marangoni number Ma is used as an indicator of the strength of Marangoni convection. The Marangoni number Ma for Marangoni convection caused by a temperature difference is written as shown in the following equations (1) and (2). σ represents the interfacial tension of the free liquid surface of the fluid layer (sample). θ represents the temperature of the fluid layer. Δθ represents the temperature difference between the upper and lower surfaces of the fluid layer. d represents the depth of the fluid layer. μ is the viscosity coefficient of the fluid. x is the thermal diffusivity coefficient of the fluid.

[0089]

number

[0090] From equations (1) and (2), it can be understood that the Marangoni number Ma is proportional to the temperature difference Δθ between the top and bottom of the sample. Therefore, in order to increase the Marangoni number Ma (i.e., to enhance Marangoni convection), the temperature difference Δθ should be increased. The bottom surface of the sample is heated by the photothermal effect of the thin film 102. Therefore, in order to increase the temperature difference Δθ, the temperature of the top surface of the sample should be lowered as much as possible. Thus, it is conceivable to promote heat dissipation from the side walls 103 of the accumulation container 100 into the atmosphere.

[0091] In this embodiment, a comparison was made between using a metal with excellent heat dissipation properties and using a resin with inferior heat dissipation properties as the material for the side wall 103 of the storage container 100. Specifically, stainless steel (SUS) was used as the metal and acrylic as the resin. The thermal conductivity of acrylic is in the range of 0.3 [W / m·K], while the thermal conductivity of SUS is 16.3 [W / m·K]. The thermal conductivity of water is 0.582 [W / m·K] (10℃).

[0092] Figure 18 shows the simulation results and measured results for the temperature of the side walls 103 of the storage container 100 for each material. The horizontal axis represents elapsed time. The vertical axis represents the temperature of the side walls 103 of the storage container 100. Figure 18 shows the simulation results (see thick solid line) and measured results (see thin solid line) when the material of the side walls 103 of the storage container 100 is SUS, as well as the simulation results (see thick dashed line) and measured results (see thin dashed line) when the material of the side walls 103 is acrylic.

[0093] Simulations showed that when the material of the side wall 103 of the accumulation container 100 is SUS (stainless steel), the temperature rise of the side wall 103 is suppressed compared to when the material is acrylic. This simulation result was in good agreement with the measured result. The suppression of the temperature rise of the side wall 103 means that heat dissipation from the sample to the atmosphere through the side wall 103 is promoted. Therefore, by using SUS as the material of the side wall 103, the temperature difference Δθ between the top and bottom of the sample can be increased, thereby enhancing Marangoni convection.

[0094] Furthermore, if the size of the laser spot (the irradiation area of ​​the laser beam) in the thin film 102 is made excessively small, the energy of the laser beam passing through the thin film 102 increases without generating a photothermal effect, which may prevent efficient heating of the bottom surface of the sample. Therefore, it is desirable to make the size of the laser spot larger than the contact area between the microbubbles and the thin film 102. By heating a wide area of ​​the bottom surface of the sample, the bottom surface of the sample can be heated efficiently. As a result, it becomes possible to increase the temperature difference Δθ between the top and bottom of the sample, thereby enhancing Marangoni convection.

[0095] Figure 19 shows the simulation results regarding the thermal convection velocity for each material of the side wall 103 of the collection container 100. The horizontal axis represents elapsed time. The vertical axis represents the maximum thermal convection velocity within a predetermined time range. Fluid simulations also confirmed that Marangoni convection is enhanced by using SUS as the material for the side wall 103.

[0096] Figure 20 shows the measured results of the number of resin beads accumulated. The vertical axis represents the resin bead accumulation rate. The accumulation rate is the ratio of the number of resin beads accumulated near the microbubbles to the total number of resin beads contained in the sample. As shown in Figure 20, it was confirmed that when the material of the side wall 103 of the accumulation container 100 is SUS, the resin bead accumulation rate improves by approximately 1.4 times compared to when the material of the side wall 103 is acrylic.

[0097] As described above, in Embodiment 1, the pitch between laser spots is set so that it is shorter than the distance at which three microbubbles can be virtually placed in the gap between two microbubbles that actually occur. By setting the pitch so narrowly, a synergistic effect is created in the thermal convection generated around the two microbubbles, and the thermal convection is enhanced. As a result, the flow velocity of thermal convection can be increased compared to the case of single irradiation. Therefore, according to Embodiment 1, multiple minute objects dispersed in a liquid can be accumulated with high efficiency.

[0098] [Embodiment 2] <Influence of the shape of the gas-liquid interface> In Embodiment 2, the results of investigating the influence of the shape and height of the gas-liquid interface on thermal convection will be described. The overall configuration of the micro-object accumulation system and the configuration of the accumulation container 100 are the same as those described in Figures 1 to 3. In Embodiment 2, the pitch between laser spots is set in the same way as in Embodiment 1.

[0099] Figure 21 shows a simulation model for examining the effects of the shape and height of the gas-liquid interface. As shown in Figure 21, the cases of a flat and curved gas-liquid interface were examined. When the sample is an aqueous liquid, a flat liquid surface (liquid surface meaning the gas-liquid interface) can be formed by using a hydrophobic material (e.g., hydrophobic silicone, hydrophobic acrylic) for the sidewall 103, while a curved liquid surface can be formed by using a hydrophilic material (e.g., hydrophilic silicone, hydrophilic acrylic) for the sidewall 103. Conversely, when the sample is an organic solvent, a flat liquid surface can be formed by using a hydrophilic material for the sidewall 103, and a curved liquid surface can be formed by using a hydrophobic material for the sidewall 103.

[0100] In this example, it is assumed that the curved liquid surface is described by the catenary curve shown in equation (3) below. r represents the distance from the center of the cylindrical collection container 100. h represents the height of the liquid surface relative to the bottom of the collection container 100. a, b, and c are parameters that define the catenary curve.

[0101]

number

[0102] Using equation (3), the volume V of the sample contained in the collection container 100 is calculated as shown in equation (4) below.

[0103]

number

[0104] Solving equation (4) for c yields equation (5). Substituting a=0 into equation (5) gives a flat liquid surface, while setting a≠0 gives a curved liquid surface.

[0105]

number

[0106] The inner radius R of the accumulation container 100 was set to 7 mm, and the outer radius to 9 mm. For a flat liquid surface, a=0 and b=3. For a curved liquid surface, a=0.25 and b=3. The radius of the microbubbles was set to 400 μm. The thickness of the thin film 102 was set to 0.15 mm. The absorptivity of the thin film 102 for a 20 mW laser beam was set to 0.03. The hydrodynamic properties of the surface of the accumulation container 100 were given parameters corresponding to those of glass.

[0107] The sample volume V was set to three values: 0.3 mL, 0.5 mL, and 1 mL. The height c of the flat liquid surface at the center of the accumulation container 100 was measured. flat The values ​​were 1.95 mm (when V=0.3 mL), 3.25 mm (when V=0.5 mL), and 6.50 mm (when V=1.0 mL). Height c of the curved liquid surface at the center of the accumulation container 100 cate The values ​​were 1.49 mm (when V=0.3 mL), 2.79 mm (when V=0.5 mL), and 6.04 mm (when V=1.0 mL).

[0108] Figure 22 shows the results of a fluid simulation regarding the flow velocity of thermal convection. Figure 22 shows the flow velocity field (vector field of flow velocity) of thermal convection. Furthermore, to explain the relationship with Figure 23, which will be discussed later, the distance r at which the absolute value of the horizontal flow rate is maximized and the flow rate in the height direction (up and down direction) of the sample is minimized is shown by a dashed line.

[0109] As shown in Figure 22, it was found that thermal convection flows along the gas-liquid interface connecting the center of the sample (r=0) and the inner wall surface of the collection container 100 (r=7mm) in both flat and curved liquid surfaces. When comparing conditions with equal sample volume, the surface area of ​​the flat liquid surface is smaller than that of the curved liquid surface. Therefore, when convection is generated by applying a laser beam of the same output, the distance the transported liquid travels is smaller and the energy loss due to friction is smaller in the flat liquid surface compared to the curved liquid surface. Consequently, it is thought that the flow rate per unit time of thermal convection is larger. In addition, the larger volume near the center of the liquid surface in the flat liquid surface compared to the curved liquid surface may also have influenced the increase in flow rate.

[0110] Next, the simulation results regarding the flow rate per unit time of thermal convection will be described. Hereinafter, the flow rate per unit time of thermal convection [unit: mm 3 / s] will simply be referred to as the flow rate of thermal convection.

[0111] In the present embodiment, the flow rate Q of thermal convection pos , Q neg can be defined as in the following formulas (6) and (7). u(r, z) is the flow velocity of thermal convection at the coordinates (r, z).

[0112]

Equation

[0113] The flow rate Q pos The function pos used in the definition of is such that when the argument x is positive (more specifically, 0 or more), it returns the argument x as it is, and when the argument x is negative, it returns 0 (see the following formula (8)). The flow rate Q neg The function neg used in the definition of is such that when the argument x is negative (more specifically, 0 or less), it returns the argument x as it is, and when the argument x is positive, it returns 0 (see the following formula (9)).

[0114]

Equation

[0115] Formulas (6) and (7) represent that by integrating the flow velocity u(r) of thermal convection in the z direction (height direction), the flow rate of thermal convection at each distance r is calculated. The outward flow rate (the direction in which r increases) is represented by a positive value, and the inward flow rate (the direction in which r decreases) is represented by a negative value.

[0116] Figure 23 is a diagram showing the fluid simulation results regarding the flow rate of thermal convection. The horizontal axis represents the distance r [unit: mm]. The vertical axis represents the flow rate Q pos or -Q neg [unit: mm 3 / s] represents the absolute value of the outward or inward flow rate along the r-axis. -Q neg The negative sign indicates that the absolute value is evaluated to determine the flow rate Q. pos This was added to facilitate comparison.

[0117] When comparing samples with the same volume, Figure 23 shows that the thermal convection flow rate is higher at a flat liquid surface than at a curved liquid surface. Furthermore, the thermal convection flow rate Q... pos ,-Q neg It was found that the distance r at which the velocity is maximized coincides well with the distance r at which the flow velocity in the vertical direction is minimized (see Figure 22).

[0118] Note that the sample was treated as an incompressible fluid here, therefore Q pos =-Q neg It was expected that this would happen, but the actual simulation results showed Q pos to-Q neg A slight difference occurred between the two. This difference is considered to be a numerical error. Also, the flow rate Q pos The oscillation is likely due to the unstable output value near the gas-liquid interface.

[0119] Figure 24 is a diagram for comparing the flow rate of thermal convection between a flat liquid surface and a curved liquid surface. The horizontal axis represents the distance r [unit: mm] from the center of the collection container 100. The vertical axis represents the absolute value of the thermal convection flow rate |Q neg Regarding |, the difference between the value at a flat liquid surface and the value at a curved liquid surface [unit: mm] 3 This represents [ / s].

[0120] When the sample volume V was largest (V=1 mL), the difference value at a distance close to the microbubbles (a distance close to the center of the sample, for example, a distance within the range of r=1 to 3 mm) was almost 0. This is thought to be because, when the sample volume V is largest, the distance between the gas-liquid interface and the microbubbles is large, so the influence of the shape of the gas-liquid interface on thermal convection (especially Marangoni convection) is relatively small.

[0121] On the other hand, when the sample volume V was smaller (V = 0.3 mL, 0.5 mL), the difference value at a distance close to the microbubble was larger compared to when the sample volume V was largest (V = 1 mL). In other words, the absolute value of the flow rate at a flat liquid surface |Q neg | is the absolute value of the flow rate at a curved liquid surface |Q neg It was significantly larger compared to |. The reason for this is explained as follows: When considering a cylindrical micro-region in the range from distance r to r+dr, at distances close to the microbubble, the volume of the micro-region with a flat liquid surface is larger than the volume of the micro-region with a curved liquid surface. And the larger the volume of the micro-region, the greater the flow rate through that micro-region. Therefore, it is thought that by making the shape of the gas-liquid interface flat, it is possible to increase the flow rate of thermal convection compared to when the gas-liquid interface is curved.

[0122] As described above, in Embodiment 2, as in Embodiment 1, the pitch between laser spots is set to be shorter than the distance at which three microbubbles can be virtually placed in the gap between two microbubbles that actually occur. This allows for highly efficient accumulation of multiple microscopic objects dispersed in the liquid. Furthermore, in Embodiment 2, the sample volume is adjusted so that the gas-liquid interface is flat, and the wettability of the side wall 103 of the accumulation container 100 is set. When the gas-liquid interface is flat, the streamlines of thermal convection are shorter compared to when the gas-liquid interface is curved, thus increasing the flow rate of thermal convection flowing along the gas-liquid interface. Also, when the gas-liquid interface is flat, the volume of the microscopic region within the same distance from the center of the sample (from r to r+dr) is larger compared to when the gas-liquid interface is curved, thus increasing the flow rate of thermal convection at distance r. Therefore, according to Embodiment 2, multiple microscopic objects dispersed in the liquid can be accumulated with even higher efficiency.

[0123] Figures 25 to 27 describe the results of actually accumulating resin beads. Figure 25 shows images of a flat liquid surface and a curved liquid surface. Both images were obtained for a sample volume V = 1 mL. The flat liquid surface was formed by a hydrophobic silicone side wall 103, and the curved liquid surface was formed by a hydrophilic acrylic side wall 103. In both cases, the inner diameter of the accumulation container 100 was 14 mm. A circular arrangement of white LEDs was used as the illumination device 9. It can be seen that in the curved liquid surface, the light from the white LEDs is reflected on the liquid surface because the curved liquid surface acts as a concave lens, whereas no such light was captured in the flat liquid surface.

[0124] Figure 26 shows an example of measurement results for the number of resin beads accumulated and the accumulation efficiency on a flat liquid surface. The sample volume V was set to two values: 0.5 mL and 1 mL. The horizontal axis represents the particle concentration (concentration of resin beads introduced into the sample) [unit: beads / mL]. The upper vertical axis represents the total number of resin beads accumulated in all laser spots. The lower vertical axis represents the accumulation efficiency. The same applies to Figure 27.

[0125] On a flat liquid surface, when the sample volume V was small (V=0.5mL), the number of resin beads accumulated increased, and the accumulation efficiency also improved, compared to when the sample volume V was large (V=1mL). This trend was particularly pronounced when the particle concentration was high (10,000 particles / mL).

[0126] Figure 27 shows an example of measurement results for the number of resin beads accumulated and the accumulation efficiency on a curved liquid surface. Unlike a flat liquid surface, on a curved liquid surface, when the sample volume V was small, the number of resin beads accumulated decreased compared to when the sample volume V was large. On the other hand, similar to a flat liquid surface, on a curved liquid surface, when the sample volume V was small, the accumulation efficiency of resin beads increased compared to when the sample volume V was large.

[0127] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure is indicated by the claims rather than by the description of the embodiments above, and all modifications within the meaning and scope of the claims are intended to be included. [Explanation of Symbols]

[0128] 1 Sample stage, 2 Sample supply device, 3 Light source stage, 4 Laser module, 41 Substrate, 42 Surface light-emitting element, 421 Light-emitting region, 43 Bonding member, 44 Optical waveguide, 441 Core, 442 Cladding, 45 Lens, 46 Laser device, 47 Laser module, 5 Cooling device, 6 Adjustment mechanism, 7 Power supply, 8 Imaging equipment, 9 Illumination device, 10 Controller, 100 Integration container, 101 Substrate, 102 Thin film, 103 Side wall, 901, 902 Integration system.

Claims

1. A method for accumulating multiple micro-objects dispersed in an aqueous liquid, The steps include: placing the liquid in a container having hydrophobic side walls so that the gas-liquid interface between the liquid and the surrounding gas is flat; The steps include irradiating a photothermal conversion region provided on the bottom surface of the container with multiple light rays separated from each other, The step includes heating the liquid with the plurality of light rays to generate a plurality of microbubbles corresponding to the plurality of light rays and to generate thermal convection in the liquid, A method for accumulating minute objects, wherein the distance between two adjacent rays among the plurality of rays is narrower than the distance at which three larger microbubbles from the two microbubbles corresponding to the two rays can be virtually placed side by side in the gap between the two microbubbles.

2. The method for accumulating minute objects according to claim 1, wherein the interval is narrower than the distance at which the large microbubbles can be virtually placed in the gap.

3. The method for accumulating microscopic objects according to claim 1 or 2, wherein the distance between the irradiation position of each of the plurality of light rays onto the photothermal conversion region and the side wall of the container is longer than the diameter of the corresponding microbubble among the plurality of microbubbles.

4. The method for accumulating minute objects according to claim 1 or 2, wherein the thermal conductivity of the side wall of the container is greater than the thermal conductivity of the liquid.

5. The method for accumulating minute objects according to claim 1 or 2, wherein the irradiation area of ​​each of the two light rays onto the photothermal conversion region is greater than the contact area between the corresponding microbubble of the two microbubbles and the photothermal conversion region.

6. A method for accumulating multiple microscopic objects dispersed in a liquid, The process involves irradiating a photothermal conversion area located on the bottom surface of a container with multiple light rays separated from each other, The step includes heating the liquid with the plurality of light rays to generate a plurality of microbubbles corresponding to the plurality of light rays and to generate thermal convection in the liquid, The distance between two adjacent rays among the plurality of rays is narrower than the distance at which three of the larger of the two microbubbles can be virtually placed side by side in the gap between the two microbubbles corresponding to the two rays. A method for accumulating microscopic objects, wherein the distance between the irradiation position of each of the plurality of light rays onto the photothermal conversion region and the side wall of the container is longer than the diameter of the corresponding microbubble among the plurality of microbubbles.

7. A micro-object accumulation system for accumulating a plurality of micro-objects dispersed in an aqueous liquid, A liquid container having a bottom surface provided with a photothermal conversion region and hydrophobic side walls such that the gas-liquid interface between the liquid and the surrounding gas is flat, A light source that emits multiple rays, The system includes an optical system capable of irradiating the photothermal conversion region with the plurality of light rays separated from each other, By heating the liquid with the plurality of light rays, a plurality of microbubbles are generated at the irradiation positions of the plurality of light rays, and thermal convection occurs in the liquid. The optical system is configured such that the distance between two adjacent rays among the plurality of rays is narrower than the distance at which three of the larger microbubbles generated by the two rays can be virtually placed side by side in the gap between the two microbubbles.

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