Method for forming liquid flow and method for moving object using the liquid flow

Abstract

The present invention provides a method for moving a larger object non-contact and non-invasively. In the method for forming a liquid flow in a surface area of ​​the liquid, a laser (14) is irradiated on a specific surface area (18) of a liquid (10) containing dispersed particles in which the object is suspended, so that the temperature of the specific surface area of ​​the liquid is relatively higher than that of other surface areas around it, thereby forming a temperature gradient between the two surface areas of the liquid.

Description

Technical Field

[0001] The present invention relates to a method of forming a flow of liquid (ie, a liquid flow) using a laser, and a method of moving an object using the formed liquid flow. Background Art

[0002] Optical tweezers are known as a unit for manipulating particles using lasers. Optical tweezers are a well-known technology that uses the gravitational effect that occurs with the refraction near the focus of the laser to capture an object near the focus. For example, "'Optical tweezers' and 'High-intensity ultrashort pulse lasers' that have brought innovative optical technology" in Chemistry Vol. 73 No. 12 (published in December 2018) and the seventh issue of the Low Temperature Material Science Research Center Journal (published in November 2005) are described (see the following non-patent documents 1 and 2).

[0003] When the size of the particles is larger than the wavelength of light, Mie scattering occurs when light is irradiated to the particles dispersed in the liquid. At this time, when the light is focused by a lens, a force is exerted when the light enters the particles and then exits. In addition, due to the refraction and reflection of light on the surface of the particles, a force acts on the particles. As a result, the particles are pulled to the vicinity of the focal point.

[0004] In addition, when the size of the particles is sufficiently smaller than the wavelength of light, Rayleigh scattering occurs when light is irradiated on the particles dispersed in the liquid. At this time, the light as an electromagnetic wave generates an induced dipole in the particles, and the interaction between the induced dipole and the electromagnetic field causes an attractive force in the direction of the focal point. As a result, the particles can be pulled near the focal point.

[0005] In any case, the microparticles can be pulled to the vicinity of the focal point, that is, they can be held. If this phenomenon is utilized, the microparticles can be held, and in addition, the microparticles can be moved, for example, by changing the position of the focal point. Such operations using light not only avoid contact with the microparticles as the object, but can also be used as tweezers for non-invasively handling microparticles. Such optical tweezers can be used, for example, for the operation and movement of tiny objects such as proteins and DNA. Such optical tweezers can capture microparticles in a dispersion medium near the focal point of light. Therefore, by moving the focal point, tiny objects (usually 0.1μm to 50μm) with a size of less than tens of μm can be moved. However, it is desired to move larger objects, specifically millimeter-level objects. In addition, the capture and movement of objects using optical tweezers requires the use of a high-magnification convex lens, in which case it is usually necessary to set the distance from the lens to the object to less than 1mm, which greatly limits the freedom of operation.

[0006] Prior art literature

[0007] Non-patent literature

[0008] Non-patent document 1: Hiroshi Masuhara / Nobuaki Nakajima, "'Optical tweezers' and 'High-intensity ultrashort pulse lasers' have brought innovative optical technologies," Chemistry, Vol. 73, No. 12 (published in December 2018)

[0009] Non-patent document 2: Masahiro Nishiyama and Kenji Okamoto, "Optical Tweezers," Journal of the Center for Low Temperature Material Science, No. 7 (published in November 2005) Summary of the invention

[0010] Problems to be solved by the invention

[0011] When optical tweezers are used, each particle as an object can be manipulated in a non-contact and non-invasive manner. However, considering its practicality, it is desired to be able to manipulate larger objects (for example, larger than several hundred μm).

[0012] Solutions for solving problems

[0013] In order to solve the above-mentioned problem, the inventors and others have repeatedly conducted in-depth research, and as a result, they have found that the above-mentioned problem can be solved by the following method, that is, using a laser to irradiate a specific area on the surface of a liquid containing dispersed particles that efficiently absorbs the energy of the laser (hereinafter also referred to as the "specific surface area" of the liquid), and the particles dispersed in the specific surface area absorb the irradiated laser to make the specific surface area relatively high temperature relative to other surface areas around it, thereby forming a temperature gradient in the surface area of ​​the liquid, thereby forming a surface tension gradient and forming a flow of the liquid (i.e., liquid flow) in the surface area of ​​the liquid, and further, the flow is controlled by the irradiation direction and / or irradiation position of the laser.

[0014] Therefore, in the first subject matter, the present invention provides a method for forming a liquid flow in the surface area of ​​a liquid, the method being characterized in that a laser is irradiated to a specific surface area of ​​a liquid containing dispersed particles, so that the temperature of the specific surface area of ​​the liquid is relatively higher than that of other surface areas around it, thereby forming a temperature gradient between the two surface areas of the liquid. In this way, when a temperature gradient is formed on the surface of the liquid, a surface tension gradient is formed correspondingly thereto, and as a result, the liquid flows from a relatively high temperature specific surface area to other surface areas around it at a relatively low temperature, that is, a liquid flow is formed. In other words, the surface tension gradient generated by the formation of the temperature gradient becomes a power source to form a liquid flow. It should be noted that, in general, surface tension has temperature dependence, and the higher the temperature, the smaller the surface tension (therefore, the surface tension of the specific surface area becomes relatively smaller). It should be noted that the "specific surface area" of the liquid is the area irradiated with laser, and the term "periphery" means that it is adjacent to the irradiated "specific surface area" and exists around the "specific surface area" (therefore, the laser is not irradiated).

[0015] In the present invention, in order to form the temperature gradient as described above in the surface area of ​​the liquid, it is necessary to heat the specific surface area to a relatively high temperature. Therefore, the surface area of ​​the liquid is formed in a manner that efficiently absorbs the energy of the laser irradiated to the specific surface area. Specifically, a liquid containing dispersed particles that efficiently absorbs the laser is used, and preferably the particles are substantially uniformly dispersed in the liquid.

[0016] It should be noted that in the method for forming a fluid flow of the present invention, in one embodiment, the liquid containing particles can be held in any suitable container as long as it is necessary to form a liquid flow in the surface area of ​​the contained liquid and to make the surface area of ​​the liquid adjacent to the gas. Such a container can be, for example, containers of various forms, various tubes, various forms of flow paths or channels, etc. The material constituting the container is preferably a material that can transmit laser light, such as transparent glass, plastic, etc. In a particularly preferred embodiment, the container is a so-called transparent glass container, a micro flow path, etc.

[0017] In a preferred embodiment, the container is a transparent glass container, a transparent plastic container, etc., and the liquid is maintained in a state adjacent to the gas in its flow path. In such a container, the gas phase adjacent to the surface area of ​​the liquid can be in an open state (i.e., it can be open) relative to the surrounding environment, or it can be in a closed state (i.e., it can also be closed). More specifically, the container may not have a part that functions as a cover (i.e., a cover part), or it may have a cover part. The cover part needs to be transmissive to the laser when irradiating a specific surface area with a laser through the cover.

[0018] In another preferred embodiment, the cover portion can also substantially seal the liquid in the container in a manner that the gas phase adjacent to the liquid does not substantially exist. For example, such a container can be various microchips, and in detail, can be a part of various containers that define a micro space portion such as a microchannel of a microchip, a micro mixer (a tiny portion with a mixing function), etc. More specifically, the container can be, for example, a micro space portion (e.g., a microchannel portion, a micro mixer portion, etc.) of a microchip such as a biochip (e.g., an antibody detection chip for immunoassay), a tissue chip (Organ on a Chip), an in vitro human model (BOC (Body on a Chip: human body on a chip)).

[0019] Hereinafter, the present invention will be further described by taking the case where a liquid is contained in an open glass container as described above as an example. In the present specification, a glass container refers to a glass container in which a flow path has a cross-section such as a rectangle, and the width and depth of the cross-section of the flow path have dimensions of several millimeters. More specifically, a container with a width of 8 mm and a depth of 13 mm can be exemplified. The length of the flow path is not particularly limited, and for example, it can be a length of millimeters, specifically a length of 30 mm to 200 mm. In another embodiment, for example, it can be a length of micrometers, specifically a length of 1 μm to 1000 μm. In the glass container, the liquid has a gas-liquid interface with a gas phase (such as air) as a surface. It should be noted that it can also be a glass container with other cross-sectional shapes, and the other cross-sectional shapes have an equivalent diameter equivalent to such a glass container. Of course, it can also be a thinner flow path with a cross-sectional size of micrometers.

[0020] In the second subject matter, the present invention provides a method for moving an object, characterized in that, in the method for forming a liquid flow of the first subject matter of the present invention, in a state where an object intended to be moved is suspended in a surface area of ​​a liquid, the surface area where the object is suspended, or a surface area located near the surface area is used as a "specific surface area of ​​the liquid", and a liquid flow is formed by laser irradiation, so that the suspended object is carried by the formed flow of the liquid to move. The suspended area refers to the surface area of ​​the liquid containing the suspended object, and the object may float on the surface area of ​​the liquid, and / or at least a part of it may also exist inside the surface area of ​​the liquid, and the term "suspended" is used as a meaning that includes both of these situations.

[0021] Effects of the Invention

[0022] In the method for forming a liquid flow of the present invention, microparticles are dispersed in a liquid, and the microparticles contained in a specific surface area of ​​the liquid absorb the energy of the irradiated laser and heat the liquid in the area, thereby forming a temperature gradient in the surface area of ​​the liquid, and thus forming a surface tension gradient corresponding to it, thereby forming a flow in the surface area of ​​the liquid. That is, in the present invention, the liquid in a specific surface area as a mass (or block) is heated by means of the dispersed particles, thereby forming a liquid flow as a mass from the area to the area close to it, that is, the liquid itself is moved.

[0023] Thus, moving the liquid as a mass means that a large force acts on the liquid. Therefore, in the object moving method of the present invention, when the object is suspended in a specific surface area of ​​the liquid or in a surface area of ​​the liquid near it (e.g., adjacent thereto), the object, in one embodiment, a relatively large object (e.g., an object having a size of several hundred μm to several mm), can be carried on the formed liquid flow and moved without directly contacting the object. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A scheme of irradiating a specific surface area of ​​a liquid with laser light in parallel with respect to the liquid surface is shown. Figure 1 (a) schematically shows a state where a transparent container made of a transparent material and containing water containing dispersed particles as liquid is observed from the side, Figure 1 (b) schematically shows a situation where the transparent container is observed from above the transparent container.

[0025] Figure 2 The invention shows a scheme of irradiating a specific surface area of ​​a liquid with a laser beam at an angle relative to the liquid surface so that the laser beam is totally reflected on the liquid surface. Figure 2 (a) schematically shows a state where a transparent container made of a transparent material and containing water containing dispersed particles as liquid is observed from the side, Figure 2 (b) schematically shows a situation where the transparent container is observed from above the transparent container.

[0026] Figure 3 A scheme for moving an object suspended on the surface of a liquid is shown. Figure 3 (a) schematically shows a state where a transparent container made of a transparent material and containing water containing dispersed particles as liquid is observed from the side, Figure 3 (b) schematically shows a situation where the transparent container is observed from above the transparent container.

[0027] Figure 4 This is a graph showing the measurement results of the absorption coefficient of the water containing gold nanoparticles used in Example 1 and the wavelength.

[0028] Figure 5 The transparent container in Example 3 is schematically shown as viewed from the side during the switching process. Figure 5 (a) schematically shows the case where the object is moved to the left. Figure 5 (b) schematically shows a situation where the object is moved to the right. DETAILED DESCRIPTION

[0029] Hereinafter, the present invention will be described in further detail by taking specific embodiments as examples with reference to the drawings, but the present invention is not limited to such embodiments.

[0030] In the method for forming a liquid flow of the present invention, in one embodiment, a laser is directly irradiated onto a specific intended surface area of ​​the liquid. In another embodiment, a laser is incident on the liquid in the container from the outside of the container (thus, indirectly) through the wall material of the container formed of a material that transmits laser light (a material that absorbs little laser light), and the specific surface area is irradiated with the laser light. This embodiment is suitable for a case where, for example, the liquid is contained in a transparent container formed of such a material, and the laser is incident on the inside of the transparent container from the outside of the transparent container through the wall material of the channel. Therefore, the wall material of the channel has the property of transmitting the laser light, that is, it is transparent to the laser light.

[0031] In the method of the present invention, the liquid containing particles is not particularly limited and can be any appropriate liquid that attempts to form the intended liquid flow. In one embodiment, the liquid can be water or an aqueous solution, for example, considering the viewpoints of stability, surface tension, etc. In addition, the gas phase adjacent to the surface area of ​​the liquid can be any appropriate gas, and in a preferred embodiment, the gas phase can be nitrogen, air, etc. For example, the liquid is added to a transparent container, and there is a surface area on the liquid side of the boundary surface (gas-liquid interface) of air and liquid. In another embodiment, instead of the gas-liquid interface, the formation method of the liquid flow of the present invention and the moving method of the object using the method can be applied in the liquid-liquid interface (for example, the interface between water and oil, common oil and fluorine-based oil, etc.) where the surface tension becomes large.

[0032] The particles contained in the liquid absorb at least a portion of the energy of the irradiated laser, preferably absorbing a larger proportion of the energy. The term "efficiently absorbing" means that the liquid containing the particles has a maximum absorption coefficient (Absorption Coefficient, such as molar absorption coefficient) at or near the wavelength of the irradiated light (preferably within the range of ±40nm of the wavelength of the light, more preferably within the range of ±25nm of the wavelength of the light, particularly preferably within the range of ±20nm of the wavelength of the light, for example, within the range of ±10nm of the wavelength of the light). Such a liquid, for example, preferably contains so-called nanoparticles, in particular metal nanoparticles (such as gold nanoparticles, silver nanoparticles, etc.). Such particles are all commercially available, and appropriate particles can be selected and dispersed in the intended liquid for use. In another embodiment, graphite particles and carbon nanotubes can be used as particles.

[0033] The size of the particles is not particularly limited, and the average particle size based on the length can be preferably 1nm to 100nm, more preferably 1nm to 60nm, and particularly preferably 5nm to 50nm particles, for example, 10nm to 15nm particles. Such an average particle size is usually preferred when a laser is used based on the present invention. For example, it is particularly preferred when a laser wavelength of 532nm is used. It should be noted that in the case of particles having a specific large size (for example, large particles with a diameter of about 5μm to 50μm), such particles (particles that do not cause adverse effects) are not expected to function as the particles of the present invention, so when calculating the average particle size, the presence of such particles can be ignored.

[0034] In the formation method of fluid flow of the present invention, as the preferred microparticle used by being dispersed in liquid, gold nanoparticles can be listed as a specific example. For example, in water, spherical gold nanoparticles (gold nanoparticle particle diameter is about 15nm) obtained by reducing chloroauric acid (HAuCl4) with citric acid can be used. The gold nanoparticles used in the embodiment described later are obtained by this method, with an average particle size of 15nm, but it is confirmed that the gold nanoparticles condense with each other due to time changes, and the large particles also contain particles with a particle diameter of about 30μm. In the case of such gold nanoparticles, the absorption maximum wavelength region (that is, the wavelength at which the absorption coefficient becomes the maximum) is 522±20nm, which efficiently absorbs the energy of the laser of wavelength 532nm.

[0035] The amount (i.e., content) of the particles contained in the liquid is not particularly limited, but is generally 0.5×10 －8 Mass%~10.0×10 －8 Mass %, preferably 0.7×10 －8 Mass%~6.0×10 －8The content of the particles is preferably selected in a manner close to the wavelength of the laser. These content ranges are also appropriate when using commonly commercially available particles, especially metal nanoparticles. It should be noted that if the content of the particles is too large, the particles may agglomerate and sometimes fail to absorb light energy as specified. In addition, if the content of the particles is too small, the absorption of light energy may be insufficient.

[0036] The laser is not particularly limited, but it is preferred to use a laser that emits dispersed particles and absorbs light of a wavelength of light energy efficiently. In other words, as a liquid containing dispersed particles that absorbs light energy efficiently, it is preferred to use a liquid that has a large absorption coefficient at or near the wavelength of light emitted by the laser used, preferably a maximum absorption coefficient. Therefore, the absorption coefficient depends on the particles used (therefore, the type, size, and content of the particles) and the type of liquid used, so it is preferred to select an appropriate combination of a large absorption coefficient and the wavelength of the laser.

[0037] It should be noted that the maximum absorption coefficient of a liquid can be obtained as follows: a sample of a dispersion of the intended liquid containing the intended type and content of particles is prepared, and the sample is added to a cell of an absorption coefficient measuring device to measure the absorption coefficient distribution. Based on the result, a laser that emits light at a wavelength showing the maximum absorption coefficient or a wavelength near that showing the maximum absorption coefficient is applied. In this way, when selecting the type and amount of liquid and particles to be used, the wavelength of the laser that is preferably used can be determined. Specifically, at the wavelength of the laser used (e.g., 500nm to 560nm), the liquid containing particles preferably shows a 1×10 8 M －1 cm －1 More preferably, it shows an absorption coefficient of 9.5×10 8 M －1 cm －1 ~14×10 8 M －1 cm －1 The absorption coefficient is 12×10 8 M －1 cm －1 ~14×10 8 M －1 cm －1 The absorption coefficient of .

[0038] For example, when a laser emitting green light (wavelength: 532 nm) is used, gold nanoparticles (average particle size: about 15 nm can be calculated from the wavelength at which the absorption coefficient reaches a peak) showing a maximum absorption coefficient at 522 nm can be made to emit light at 2.2×10 －8 The content of % by mass is dispersed in water to prepare a solution, and the solution is used as a liquid. Water containing the gold nanoparticles has a wavelength of, for example, 13.8×10 8 M －1 cm －1 Absorption coefficient (refer to Figure 4 Absorption coefficient distribution shown).

[0039] The output of the laser can be appropriately selected in consideration of the type and content of the liquid and particles used. For example, a laser with an output range of 400 mW to 1000 mW and a beam diameter of 3 mm can be used.

[0040] The term "surface region" refers to the region on the liquid side of the gas-liquid interface of the liquid containing particles, which is actually affected by the gradient of surface tension generated by laser irradiation. The surface region is affected depending on the conditions such as the liquid, particles, and laser used, but generally refers to the liquid region present in the region preferably at a depth of 1500 μm, more preferably at a depth of 1000 μm from the gas-liquid interface.

[0041] In a preferred embodiment, laser light is irradiated to the wall material of the channel at the end face of a transparent container, directly below the liquid surface (specifically, a position within a depth of 3 mm from the liquid surface) in a manner such that the optical axis is parallel to the liquid surface. In this case, the laser light passes through the wall material at the end face of the container and penetrates directly below the liquid surface, and a specific surface area of ​​the liquid close to the end face becomes the highest temperature, and the surface tension of the area becomes the lowest. As a result, a flow is generated in the surface area of ​​the liquid in a direction away from the end face, and the liquid moves.

[0042] In a particularly preferred embodiment, the irradiation is performed in such a way that the upper edge of the beam diameter area reaches a position millimeter-level (for example, 1mm to 1.5mm) deeper than the liquid surface, so that the upper edge of the laser beam diameter area (beam diameter is about 3mm) does not directly illuminate the liquid surface.

[0043] Referring to the scheme shown Figure 1 . Figure 1 (a) schematically shows a state where a container 12 made of a transparent material and containing water containing dispersed particles as a liquid 10 is viewed from the side. Figure 1(b) schematically shows a situation where the transparent container 12 is observed from above the transparent container 12. The transparent container 12 is in the form of an elongated open channel with a rectangular cross section, for example, and has an end face 16 at one end. In the transparent container 12, water containing dispersed particles is adjacent to air, and the liquid side of the gas-liquid interface 22 corresponds to the surface area of ​​the liquid. The laser 14 is incident on the liquid from the end face 16 through its wall material just below the gas-liquid interface in the end face 16, for example, below the liquid surface (for example, a position 3 mm from the liquid surface), as shown in the figure, in a manner in which the optical axis becomes parallel to the liquid surface.

[0044] When the laser is incident in this way, the particles existing in the surface area 18 adjacent to the end face 16 (corresponding to the specific surface area) absorb the light energy efficiently and are locally heated, forming a temperature gradient between the heated area 18 and the (relatively low temperature) non-heated area around it. As a result, a surface tension gradient is generated corresponding to it, and a liquid flow to the right is formed in the surface area (see arrow 20). As shown in the figure, the shape of the gas-liquid interface is an elongated rectangle, so Figure 1 As can be seen from (b), a relatively low temperature region in the surface region of the liquid exists substantially on the right side of the heating region 18, so the liquid flow formed in the surface region of the liquid flows substantially to the right (in the direction of arrow 20).

[0045] In other preferred embodiments, the laser is incident on the wall material of the end face of the transparent container in such a manner that the light passes through the liquid and advances obliquely toward the gas-liquid interface, that is, in such a manner that the optical axis is inclined relative to the liquid surface (that is, in a cross manner). In this case, the laser is irradiated in such a manner that the incident angle of the light at the gas-liquid interface (that is, the angle formed by the optical axis and the perpendicular line of the gas-liquid interface) is greater than the critical angle. In this way, the light passing through the liquid is totally reflected at the gas-liquid interface, and the irradiated light energy is not emitted to the outside of the liquid, that is, not emitted into the gas phase, but reflected at the reflection point, but advances in the liquid and contributes to the local heating of the surface area near the reflection point of the liquid (equivalent to a specific surface area). That is, the temperature of the specific surface area of ​​the liquid near such a reflection point becomes relatively high temperature relative to the surface area surrounding it. As a result, a liquid flow from the reflection point toward the surroundings is formed in the surface area of ​​the liquid.

[0046] Referring to the scheme shown Figure 2 .and Figure 1 Likewise, Figure 2 (a) schematically shows a transparent container 12 containing a liquid 10 containing particles observed from the side, Figure 2(b) schematically shows the situation of observing the transparent container from above the transparent container. The laser 14 is incident into the liquid through the wall material of the end face 16 of the transparent container just below the gas-liquid interface 22 of the liquid, for example, at a position below the interface (a position about 2 mm from the liquid surface), and then moves toward the reflection point 24. The incident angle θ of the light is preferably greater than the critical angle (48.6° when the liquid is water and the gas is air), more preferably greater than 80°, for example, about 84°.

[0047] In this case, all the light incident on the reflection point 24 is reflected, and the particles existing in the surface area 26 (corresponding to the specific surface area) near the reflection point 24 absorb the reflected light energy due to the reflected light and are locally heated. That is, the surface area 26 can absorb the energy of both the incident light and the reflected light. A temperature gradient is formed between the heated area 26 and the (relatively low temperature) surrounding non-heated area, and as a result, a surface tension gradient is generated to form a leftward liquid flow (see arrow 28) and a rightward liquid flow (see arrow 30).

[0048] In the illustrated scheme, the shape of the gas-liquid interface is Figure 1 The case is also a long and narrow rectangle, so Figure 2 As shown in (b), relatively low temperature areas exist on both sides of the heated area 26 (left and right sides in the illustrated scheme) in the surface area of ​​the liquid, so the liquid flows from the heated area to both sides as shown by arrows 28 and 30. It should be noted that, in fact, the laser light is refracted when passing through the wall material, but for simplicity, the refraction is omitted in the illustration.

[0049] As reference Figure 1 and Figure 2 As already explained, the laser can be incident through the wall material of the container containing the liquid to indirectly irradiate a specific surface area of ​​the liquid. In another embodiment, the liquid is contained in a container in an open channel form, and the laser is directly irradiated from above the liquid toward the specific surface area. Figure 1 (a) Figure 2 Such direct irradiation is shown in (a) by dashed arrows 32 and 34. It should be noted that direct irradiation can be implemented in a manner such that the angle between the optical axis of the laser and the gas-liquid interface (i.e., the incident angle) is 90° as shown in the figure, and more preferably, the incident angle is inclined at an angle less than 90° as shown in the figure, thereby increasing the irradiation cross-sectional area of ​​the liquid surface and efficiently heating the vicinity of the surface.

[0050] As described above, the method for forming a fluid flow of the present invention can be implemented as long as the liquid side of the boundary surface between the liquid containing particles and the gas phase adjacent to the liquid, that is, the specific surface area of ​​the liquid is locally irradiated with laser light to locally heat the specific surface area. Local irradiation means that only the specific surface area of ​​the liquid is irradiated, for example, by focusing the laser light on the specific surface area to heat the area. Such a method for forming a liquid flow can be used as a pump for moving the liquid in the sense of making the liquid flow.

[0051] In the method for forming a liquid flow of the present invention, by Figure 1 Methods and references for explanation Figure 2 The combination of methods described above can change the direction of the liquid flow. Specifically, Figure 1 As shown, the laser is incident from the end face of the container in a manner such that the optical axis is parallel to the gas-liquid interface, and a specific surface area adjacent to the end face is heated to form a rightward liquid flow (arrow 20), and then, as shown in FIG. Figure 2 As shown, the laser is irradiated obliquely from the end face 16 of the container in such a way that the laser is totally reflected at the gas-liquid interface, and a specific surface area near the reflection point 24 is heated to form a leftward liquid flow (arrow 28). Therefore, by changing the incident angle of the laser irradiated from the same end face 16 of the transparent container, a rightward liquid flow and a leftward liquid flow can be formed, that is, the flow direction of the liquid flow can be switched, that is, a transition can be made.

[0052] It should be noted that, in order to form a rightward liquid flow when the liquid flow changes, direct irradiation using the laser 32 and direct irradiation using the laser 34 may be used. Of course, indirect irradiation and direct irradiation may also be combined.

[0053] In one scenario, initially Figure 3 As shown in (a), laser light 42 is incident from the end face 16 of the transparent container in such a manner that the optical axis becomes parallel to the gas-liquid interface 40, and irradiates in such a manner that the upper edge of the beam area reaches a position millimeter-level deeper than the surface of the specific surface area 44 adjacent to the end face, and irradiates in such a manner that the upper edge of the laser beam area does not directly irradiate the liquid surface. As a result, the particles contained in the specific surface area 44 absorb light energy and become relatively high temperature, and their surface tension becomes relatively small, resulting in the formation of a rightward liquid flow (arrow 46). When the object 48 is suspended in the specific surface area 44 or in the vicinity thereof (for example, adjacent thereto), the object 48 is carried by the formed liquid flow to move in the right direction, and for example, when the laser irradiation is stopped, or when the irradiation is performed for a short time under the condition of total reflection, it stops at the position shown by the object 48'.

[0054] Therefore, the present invention also provides a method for moving an object by being carried on a liquid flow formed by the method for forming a liquid flow of the present invention. That is, the method for moving an object of the present invention is characterized in that, in the method for forming a liquid flow of the main purpose of the present invention, in a state where the object intended to be moved is suspended in the surface area of ​​the liquid, such a suspended area or the surface area of ​​the liquid located near it (for example, adjacent to it) is regarded as a "specific surface area of ​​the liquid", and a liquid flow is formed by laser irradiation, so that the suspended object is carried on the flow of the formed liquid to move it. It should be noted that the term "suspended area" refers to the surface area of ​​the liquid where the object exists, and the surface area of ​​the liquid in its area or its vicinity (for example, an area adjacent to it or away from it) is irradiated with laser. In this case, the surface area of ​​the liquid in the suspended area or its vicinity corresponds to the specific surface area of ​​the liquid.

[0055] Such a method of moving an object of the present invention can be used in the case where a liquid containing particles is contained in a microscopic space portion (e.g., a microchannel) of a microchip, by irradiating a specified portion of the microscopic space portion (equivalent to a specific surface area of ​​the liquid) with a laser to form a liquid flow, and causing the specified object to be carried on the liquid flow to move. For example, the moving method of the present invention can be used as a method for operating a microchip as follows: by irradiating a specific surface area of ​​a liquid containing a specified object (e.g., an antigen) contained in a microscopic space portion of a microchip with a laser, causing the object to be carried on the formed liquid flow to move. Moreover, by moving it in this way, the antigen can be bound to the antibody embedded in the chip, so the moving method of the present invention can be used in an analysis method using a microchip.

[0056] In the moving method of the present invention, since the object is carried on the formed liquid flow, it is possible to carry the object on the starting point of the liquid flow (the specific surface area of ​​the liquid irradiated with the laser), or it is possible to carry it on the way of the liquid flow (the liquid flow in the specific surface area formed by the irradiation of the laser moves, and other liquid flows are generated as a result (in a chain)). In the former case, the suspended area of ​​the object coincides with the specific surface area. In the latter case, the suspended area of ​​the object is located near the specific surface area of ​​the liquid (including an adjacent state), in which case the object suspended in the surface area of ​​the liquid is away from the specific surface area of ​​the liquid in the direction in which it is desired to move, and is located in the vicinity thereof. In order to be carried on the flow, it is necessary to avoid being too far away from the specific surface area.

[0057] Next, the object 48' becomes a reflection point 50 just to the right, and the laser 56 is irradiated to the specific surface area 52 at an incident angle θ from a position lower than the incident position of the laser 42 on the end surface 16 in such a manner that total reflection occurs at the reflection point. As a result, the particles contained in the specific surface area 52 absorb the light energy and become relatively hot, and their surface tension becomes relatively small, resulting in a leftward liquid flow (arrow 54). As a result, the object 48' suspended in the specific surface area 52 on the left side of the reflection point 50 moves to the left.

[0058] exist Figure 3 In the figure, the state of the object 48 adjacent to the specific surface areas 44 and 52 and floating on the surface areas is shown, and it can also be suspended in the specific surface areas. The object can be any appropriate object contained in the specific surface area. For example, the object can be a dispersed substance, a granular substance, a dissolved substance, etc. (such as a drug, a cell, an antibody, etc. contained in a biochip) contained in the specific surface area and / or adjacent to it. The object may only exist in a specific surface area on the surface of the liquid and / or in the vicinity thereof, but in other schemes, it may also exist in the entire liquid. In the case where the object is suspended only in a specific surface area, it is equivalent to the former scheme. It should be noted that the term "suspended" refers to the situation of floating on the liquid surface of a specific surface area and / or the situation of existing in the surface area.

[0059] In the method for forming a liquid flow of the present invention, since the flow of the liquid itself is formed, a larger object can be moved. Specifically, the object floating on the liquid surface can have a size of micrometer to millimeter, for example, a plastic sheet of 2mm×2mm (thickness 1μm to 1mm) can be moved.

[0060] In one embodiment, when various treatments are performed on cells, etc. in the field of life sciences, cells, etc. can be operated as the object in the method of the present invention, and the liquid of the present invention containing cells, etc. can be moved in a microchannel, and the required treatment is performed on the cells, etc. during the movement. For example, when a microchip is used for analysis, in order to react a sample with a specific reagent, the sample can be moved to a predetermined location in a microchannel and treated there, and the object movement method of the present invention is used.

[0061] In another embodiment, the method for forming a liquid stream of the present invention can be used for screening a mixture containing substances of various sizes. Figure 1 As shown, a mixture to be screened is added near the end face 16 of a transparent container 12 containing a liquid, and the surface area of ​​the end is irradiated with a laser 14 as a "specific surface area of ​​the liquid" 18, forming a flow of the liquid from the end to the other side as shown by arrow 20.

[0062] A plurality of meshes are pre-arranged so that the flow passes through the plurality of meshes, and the mesh size of the plurality of meshes is gradually reduced during the flow (arrow 20) in the transparent container. The mesh size of the mesh that the substance can pass through is determined according to the size, so the mixture can be sieved according to each size according to the mesh size of the mesh.

[0063] Example 1

[0064] Gold nanoparticles were contained as fine particles in a rectangular glass transparent container 12 (8 mm (width) × 100 mm (length) × 18 mm (depth), end face size: 8 mm × 13 mm), and water was added as liquid 10. It should be noted that the container was an open container without a cover, and the water depth was 13 mm. It should be noted that the transparent container was composed of a glass sheet with a thickness of 2 mm.

[0065] Water contains 2.2×10 －8 The absorption coefficient of the gold nanoparticles was measured using a UV-vis device, and the result was Figure 4 The absorption coefficient showed a maximum value (13.8×10 8 M －1 cm －1 ). It should be noted that the measurement of the absorption coefficient was carried out using UH5300 (manufactured by HITACHI).

[0066] like Figure 1 As shown, at room temperature (25°C), the laser 14 is incident from the end face 16 of the container in such a way that the optical axis is substantially parallel to the liquid surface. The incident position is set to be about 3 mm below the liquid surface. It should be noted that as a laser light source, (OXIDE, product name: CW three-wavelength laser, output: 730mW) is used. A green laser (wavelength: 532nm) is used among the three wavelengths.

[0067] As a result, if Figure 1 As shown, almost simultaneously with the irradiation, a liquid flow is generated as shown by arrow 20. The maximum flow rate of the liquid flow is about 0.63 mm / sec. In addition, the surface temperature of the liquid was measured using a thermocamera, and the result was that the temperature of a specific surface area adjacent to the end face 16 was 32°C, which was about 5°C higher than the surrounding temperature (for example, a portion about 30 mm away from the end face 16 to the right).

[0068] Example 2

[0069] As in Example 1, water containing gold nanoparticles was added to the container. Figure 2As shown, the laser light 14 is incident obliquely upward from the end surface 16 of the container and is totally reflected from the liquid surface at the incident point 24. The incident angle θ of the laser light is 84°.

[0070] As a result, if Figure 2 As shown, almost simultaneously with the irradiation, a liquid flow is generated from the reflection point 24 to the left as shown by arrow 28, and a liquid flow is generated from the reflection point 24 to the right as shown by arrow 30. The flow rate of the liquid flow is about 0.7 mm / sec at the maximum in the left direction and about 0.3 mm / sec at the maximum in the right direction. In addition, the surface temperature of the liquid was measured using a thermal camera, and the result was that it was 32°C near the reflection point, 27°C at the surface area about 30 mm away from the reflection point 24 to the right and left, and 25°C at the surface area adjacent to the two end faces.

[0071] Example 3

[0072] and Figure 1 Similarly, as in Example 1, water containing gold nanoparticles was added to the container. Figure 5 As shown in (a) of FIG. 1 , a commercially available plastic sheet (2 mm×2 mm, 0.25 mm thick) as an object is floated on the liquid surface at the position of the object 60 shown in the figure.

[0073] As in Example 2, the laser beam 61 is incident obliquely from the end surface 16 so as to cause total reflection at the reflection point 62 just to the right of the plastic sheet 60. It should be noted that the incident angle θ is 84°. As a result, the temperature of the area near the reflection point 62 rises, and the surface tension around it becomes smaller, so that as shown by the arrow 64, a leftward liquid flow is generated and the plastic sheet 60 moves to the left. The distance moved by the plastic sheet 60 in 20 seconds is about 7 mm.

[0074] Then, if Figure 5 As shown in (b), the laser 66 is incident obliquely from the end face 16 in the same manner as in Example 2 so that total reflection occurs at the reflection point 68 just to the left of the plastic sheet 60. It should be noted that the incident angle θ is 84°. As a result, the temperature of the area near the reflection point 68 rises, and the surface tension around it becomes smaller, so that as shown by the arrow 70, a rightward liquid flow is generated and the plastic sheet 60 moves to the right. The distance moved by the plastic sheet 60 in 20 seconds is about 5.5 mm.

[0075] This result means that the flow direction of the liquid flow can be changed, that is, it can be converted. When the piercing method is used, the object can be moved by forming a liquid flow in a desired flow direction with laser light.

[0076] Industrial Applicability

[0077] As can be clearly seen from the above description, in the formation method of liquid flow of the present invention, by irradiating a laser to a specific surface area of ​​the liquid contained in a transparent container, a liquid flow can be formed. And, forming a liquid flow in this way means that the liquid can be moved as specified in the transparent container. When utilizing this method, the liquid contained in the transparent container is moved to implement the required treatment, and after the treatment, the laser is irradiated again to form a liquid flow, which can thus be moved non-contactly as required. For example, in the field of life sciences, in order to properly process a trace amount of sample, it is necessary to move the sample. If the sample is carried on the liquid flow formed by the formation method of liquid flow of the present invention, the sample can be easily moved.

[0078] Description of Reference Numerals

[0079] 10: liquid containing particles; 12: container; 14: laser; 16: end face of container; 18: specific surface area; 20: flow direction of liquid; 22: gas-liquid interface; 24: reflection point; 26: specific surface area; 28: flow direction of liquid; 30: flow direction of liquid; 32, 34: direct irradiation with laser; 40: gas-liquid interface (or liquid surface); 42: laser; 44: specific surface area; 46: flow direction of liquid; 48, 48': object; 50: reflection point; 52: specific surface area; 54: flow direction of liquid; 56: laser; 60: object; 61: laser; 62: reflection point; 64: flow direction of liquid; 66: laser; 68: reflection point; 70: flow direction of liquid.

Claims

1. A method for forming a liquid flow, characterized in that: is a method of forming a liquid flow in the surface area of ​​the liquid, A specific surface area of ​​a liquid containing dispersed particles is irradiated with a parallel beam of laser light, so that the temperature of the specific surface area of ​​the liquid is relatively higher than that of other surrounding surface areas, thereby forming a temperature gradient between the two surface areas of the liquid. The liquid containing dispersed particles has a maximum absorption coefficient within the range of ±40nm of the wavelength of the laser used. The liquid containing dispersed particles has a 9.5×10 8 M －1 cm －1 ~14×10 8 M －1 cm －1 The absorption coefficient of .

2. The method for forming a liquid flow according to claim 1, characterized in that: Laser light is directed onto a specific surface area of ​​a liquid containing dispersed particles.

3. The method for forming a liquid flow according to claim 1, characterized in that: The laser is irradiated indirectly onto a specific surface area of ​​the liquid through the wall material of a container into which the liquid containing dispersed particles is placed.

4. The method for forming a liquid flow according to claim 3, characterized in that: The laser is irradiated in such a way that it is totally reflected at the air-liquid interface in a specific surface area of ​​the liquid.

5. The method for forming a liquid flow according to claim 1, characterized in that: The microparticles are gold nanoparticles.

6. The method for forming a liquid flow according to claim 5, characterized in that: The average particle diameter of the microparticles based on length is 1 nm to 100 nm.

7. The method for forming a liquid flow according to claim 6, characterized in that: Liquid at 0.5×10 －8 Mass%~10.0×10 －8 The content of mass % includes fine particles.

8. The method for forming a liquid flow according to claim 1, characterized in that: The liquid containing the microparticles is contained in a microchip as a container.

9. The method for forming a liquid flow according to claim 8, characterized in that: The microchip is a biochip, a tissue chip or an ex vivo human model.

10. A moving method, characterized in that: A method for moving an object. In the method for forming a liquid flow described in claim 1, an object to be moved is suspended in a surface area of ​​a liquid, the surface area where the object is suspended, or a surface area located near the surface area, is used as a "specific surface area of ​​the liquid", and a liquid flow is formed by laser irradiation, so that the suspended object is carried by the flow of the formed liquid and is moved.

11. The moving method according to claim 10, characterized in that: The object floats on the surface of the liquid.

12. The moving method according to claim 11, characterized in that: The object exists inside the surface area of ​​the liquid.

13. The moving method according to any one of claims 10 to 12, characterized in that: The object is a millimeter-level object.

14. A liquid flow forming device, characterized in that: A device for forming a liquid flow on the surface area of ​​a liquid, wherein the liquid flow forming device has: A container holding a liquid containing dispersed particles; and a laser source configured to irradiate a specific surface area of ​​the liquid with a laser having a parallel beam, so that the temperature of the specific surface area of ​​the liquid is relatively higher than that of other surface areas around it, thereby forming a temperature gradient between both surface areas of the liquid, thereby forming a liquid flow, The liquid containing dispersed particles has a maximum absorption coefficient within the range of ±40nm of the wavelength of the laser used. The liquid containing dispersed particles has a 9.5×10 8 M －1 cm －1 ~14×10 8 M －1 cm －1 The absorption coefficient of .

15. The liquid flow forming device according to claim 14, characterized in that: The container has an end surface through which laser energy irradiated from a laser source is incident and transmitted.

16. The liquid flow forming device according to claim 15, characterized in that: The container has an end surface through which laser light irradiated from a laser source can be incident obliquely upward and transmitted.

17. The liquid flow forming device according to claim 16, wherein: The laser source is configured so that the laser light is reflected on the liquid surface after being incident.

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