JP2544520B2 - Fine particle dynamics pattern - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fine particle dynamic pattern and a method for forming the same. For more information,
The present invention relates to a new fine particle dynamic pattern that can be formed by a laser beam and a method therefor, which are useful for microfabrication technology and creation of new material structures.

[0002]

2. Description of the Related Art In recent years, attention has been focused on micromodification of chemical substances such as polymer substances and inorganic substances at the fine particle level and the development of processing techniques therefor, enabling manipulation of the elementary process of substance return. Research and development have been energetically pursued as things. Further, in living cells, microprocessing for performing micromanipulation such as transplantation, transfer, and fusion has become very important.

Various methods have been proposed so far for the operation of such microparticles by chemical operations. In the case of chemical methods, the reaction control between the particles to be treated and the reaction treatment agent is controlled. However, there is a limit in accuracy in controlling the fine particles, their aggregate state, position, etc., and applying the operation to predetermined fine particles. On the other hand, in the field of biological cell manipulation, it has become possible to reliably carry out the transfer process by a manual method such as microinjection method, and it is possible to improve the expression efficiency to about 10 ^-2. ing. However, in this method, the practitioner directly treats individual cells with a micropipette or the like under a microscope, and therefore treatment in a clean bench is indispensable, and the treatment cannot be automated. Therefore, the processing efficiency and the processing amount depend on the skill and labor of the practitioner, and it is difficult to perform precise processing in a short time.

In contrast to the above conventional methods, in recent years,
Processing for performing micromanipulation of fine particles using laser light has been proposed. Since laser light is excellent in monochromaticity, directivity, light brightness, and controllability, it is possible to irradiate light energy in a minute region of fine particles in a concentrated manner.
It becomes possible to perform a local fine operation with high accuracy in a non-contact manner, which is impossible with the conventional method.

However, according to the conventional methods, it is difficult to position the stage of a microscope or the like because the laser light irradiation site is adjusted, and the positioning accuracy is poor even if the stage is operated, and there is a problem in practical use. It was impossible to control the fine particle group to a predetermined spatial arrangement and to process it. That is, there has been a problem that it is difficult to control a dynamic pattern of fine particles or a group of fine particles to enable highly accurate operation by the conventional laser microprocessing.

The present invention has been made in view of the above circumstances, solves the drawbacks of the conventional fine particle microprocessing, and freely controls the spatial dynamic pattern for high-precision processing of fine particles or a group of fine particles. It aims to provide a new means of doing things. More specifically, it is intended to provide this dynamic pattern itself and a method for forming and utilizing it.

[0007]

In order to solve the above problems, the present invention irradiates a fine particle dispersion medium with laser light and repeatedly scans the focal position of the laser light at high speed, and There is provided a fine particle dynamics pattern, characterized in that a plurality of fine particles are captured and patterned. This fine particle dynamics pattern has been made based on the operation of optical trapping that has been studied by the inventor of the present invention, and has been completed based on new knowledge that further develops this optical trapping method.

That is, as one of the operations to be performed on fine particles, due to the excellent coherent characteristics of laser light, the momentum of the field of light is transferred as a mechanical momentum acting on an object, and a force is applied to the fine particles. There is an optical trapping operation that captures or moves the object. In this light trapping operation, since only the force generated by the laser light acts on the object, a completely non-contact and non-destructive operation is possible. For this reason, there are great expectations for this optical trapping technique as an operation for fine particles.

Explaining the principle of such optical trapping, first, the laser light is incident on the fine particles through the lens and is reflected / refracted, and the momentum of the laser light is transferred to the fine particles. Since the reflectance is usually small, the momentum transferred by refraction becomes dominant, and the force due to this is applied to the particles. Due to this force, the fine particles are in a state of being captured by the laser light. Therefore, when the laser light is moved, the fine particles also follow it.

In such laser trapping, by narrowing the laser light to the wavelength order, it is possible to lift it against the gravity of the particles and capture it three-dimensionally. By manipulating the beam and moving the sample stage,
Non-contact manipulation of target particles can be realized. Therefore, application in the fields of biology and chemistry has been studied, and manipulation of living cells, cell sorters, microsurgery, etc. have been reported. The inventor of the present invention is also trying to apply microchemistry such as laser ablation of polymer latex.

However, conventional laser trapping is intended for manipulation of single fine particles. On the other hand, a method has been proposed in which a large number of fine particles are arranged in a place having a high light intensity by using an interference pattern of laser light to form a spatial pattern of the fine particles. By using this method, it is possible to pseudo-crystallize fine particles by light, and open a way to construct a highly efficient and highly selective substance conversion system by arranging minute functional sites spatially. However, naturally, there is a limit to the pattern that can be drawn only by using the interference pattern of laser light. On the other hand, in the trapping laser optical system, a method is conceivable in which a mask pattern is placed at a position having an image-forming relationship with the sample surface and projected onto the sample to form a fine particle pattern. In this case, the degree of freedom of the pattern increases, but the energy utilization efficiency of the laser light is very low, and it is difficult to manufacture a mask that can withstand high-power laser light. Also,
Since the image is formed by a laser beam having high coherence, there are problems such as speckle noise. (Furthermore, the fine particle pattern can be formed only two-dimensionally on the substrate.) Therefore, the inventor of the present invention irradiates the fine particle dispersion medium with laser light, and repeats the focal position of the laser light at high speed. We propose a new particle dynamics pattern by capturing a plurality of particles on the trajectory by operation and forming a pattern, and its method.

That is, the first feature of the present invention as described above is that when the laser beam is repeatedly scanned sufficiently faster than the mechanical response speed of the fine particles determined by the particle diameter of the fine particles and the viscosity of the medium, each fine particle is This is because the trap state is the same as when the constant light is irradiated, and therefore it is possible to capture a large number of fine particles on the locus of the focus.
By making the locus of this focus a predetermined graphic pattern, a large number of fine particles are arranged in this predetermined pattern. At this time, each fine particle can be in a stationary state or a moving state (along a pattern). In any case, the plurality of fine particles are trapped in a predetermined pattern. Then, when the irradiation of the laser beam is stopped, the fine particles start moving irregularly in the medium by thermal motion (Brownian motion). Therefore, in the present invention, the pattern formation itself of fine particles is called a "fine particle dynamics pattern", as being clearly distinguished from the irregular thermal motion. The dynamic patterns of such trapped particles are the galvano-mirror, polygon-mirror,
This can be easily achieved by using the technology used in laser printers and laser scanning microscopes such as photoacoustic deflectors.
It is possible to form an arbitrary fine particle pattern, and almost all energy of laser light can be used. Also,
As discussed in laser scanning microscopy, despite the use of laser light, it does not suffer from coherent noise as well as incoherent imaging systems.

As described above, in the "fine particle dynamics pattern" of the present invention, looking at individual fine particles, there are cases of static state in the medium and cases of movement along the pattern. The second feature of the above is that when a predetermined dynamic pattern is formed by capturing with a laser beam, the individual fine particles can be made to stand still in the medium, and all the fine particles forming the spatial pattern It is also possible to move and move at the same time, to transport so as to flow in a pattern, and to control the flow velocity. This utilizes the fact that when a laser beam scans fine particles, it exerts a slight force on the fine particles in the scanning direction, and the force becomes larger as the scanning speed becomes slower.

The formed particle dynamics pattern can be arranged along an image of any shape. In this case, the dynamic pattern can be freely and continuously changed.
A variety of patterns can be formed by imparting the intensity of light. With respect to the above-described fine particle dynamics pattern provided by the present invention, it is also possible to perform a photoreaction, a thermal reaction, and a chemical reaction to add modification or processing scanning to the captured fine particles under a predetermined condition. . The most typical and important operations in the present invention include fine particle decomposition, division, local conversion, chemical modification, fine particle mutual connection, fusion, and cross-linking with a functional reactive group.

There is no particular limitation on the kind of the target fine particles or fine particle groups, and for example, various types of polymer latex, microcapsules, titanium dioxide, other inorganic particles, biological cells, viruses, or various types. Molecular assemblies can be used. As the laser beam, the fundamental wave of the Nd: YAG laser (1064 nm)
Various items such as can be used. Further, when the dispersion cell is used, as the dispersion medium, various media such as water, organic substances, and other conditions satisfying a higher refractive index of the captured fine particles than the dispersion medium are used.

[0016]

The present invention will be described in more detail with reference to the following examples. <Experimental system> The configuration of the experimental system is shown in Fig. 1. The trapping laser light is a CWNd: YAG laser (Specron SL9
02T, wavelength 1064 nm) (1). This is deflected in two axial directions by two galvanometer mirrors (GSIG352DT) (2), and the numerical aperture and the focus position of the microscope optical system are adjusted by the two lens systems (3). Microscope (Nikon OptiphotX
In F), the light is reflected by the dichroic mirror (4) and focused on the sample by the oil immersion objective lens (x100, NA = 1.30) (5). The size of the focused spot is about 1 μm. Two
Both of the galvanometer mirrors (2) are at the aperture pupil and the image forming position of the microscope, and by the deflection by the galvanometer mirror (2),
The focal point scans the sample two-dimensionally. The galvanometer mirror (2) is controlled by the controller (Marubun) (6),
For example, in the case of a square pattern described later, it is possible to repeatedly draw 30 times per second. The shape of the drawing pattern is given from the computer (NECPC9801RA) (7) to the controller (6). The pattern formation of the fine particles is observed by a monitor (9) by forming an image on a CCD camera (NECNE-15M) (8) by illuminating from below the sample. The power of the laser light was 600 mW in this experiment.

Sample (10) was a 1 μm monodisperse polystyrene latex (refractive index 1.59) dispersed in ethylene glycol (refractive index 1.46, viscosity 17.3 cP), and this dispersion solution was sandwiched between two cover glasses. The thickness of the liquid layer was about 100 μm using a spacer. <Test Results> FIG. 2 is a drawing in which the letter "M" is drawn with a laser beam and the latex particles are arranged along the pattern. Approximately 60 latexes are arranged in a beaded pattern, and a beautiful "M" dynamic pattern is formed.
At the time when the irradiation of the laser beam was started, the latex particles did not exist on the observation surface, and the latex particles were attracted by the radiation pressure of the laser beam, except for a part of the latex that naturally dropped. The laser power irradiated per one was about 10 mW, and repeated scanning was performed 20 times per second. Similarly, "1", "C", "R",
It was also possible to form an "O" character pattern. One side of the character was about 15 μm, and the repetition frequencies were 40, 30, 15, and 30 times / second, respectively. These letters could be freely translated in the field of view as they were. The time required for the latex particles to be attracted by the laser beam to form one character was about 30 seconds. This is because ethylene glycol, which has a high viscosity, is used as a medium, and in the case of a smart case, the speed becomes significantly faster.

As another example, FIGS. 3, 4, 5, and 6 show observations at 20-second intervals of the entire fine particles being transported when a square is drawn. It can be seen that the particles with arrows in the figure are moving. One side of the square is 15 μm, and the drawing is repeated 30 times per second. This is 1.8 mm / s when converted to the moving speed of the laser beam focus position. The moving speed (flow speed) of the particles was estimated to be 2.0 μm / s.

In order to study the principle of the transport of latex fine particles in this manner, it is assumed that one fine particle is focused on and the laser beam is scanned once. When the particles are stationary and do not move at all, the force acting on the particles is related to the position of the laser spot.
It can be represented schematically as (a). This FIG.
In (a), the ordinate represents the force in the positive direction of the coordinate, that is, the force in the traveling direction of the laser spot, and the ordinate represents the force in the opposite direction. When the laser spot approaches the fine particles, first, a force that attracts the fine particles is exerted, and its size changes as shown in the figure due to the gradient of the electric field. When the laser light overlaps the particles, no force acts in the horizontal direction, and when the laser light passes by, the opposite phenomenon occurs. In this case, when the force acting on the particles is integrated with respect to time, the force in the traveling direction and the force in the opposite direction are canceled and become zero.

Next, consider the case where fine particles move. When the laser light approaches, the fine particles are attracted and move, so that the waveform until the laser light overlaps the fine particles is compressed as shown in FIG. 7A, as shown in FIG. 7B. On the other hand, after the laser light has passed through the fine particles, the laser light is also attracted to widen the force waveform. Then, the force integrated over time has a value in the traveling direction of the laser. 1 for this power
The product obtained by multiplying the number of repeated scans per second acts on the fine particles as a work amount, and the moving speed of the fine particles is determined by the work amount, the viscous resistance due to the solvent, and the frictional resistance with the substrate.

When the moving speed of the fine particles is plotted as a function of the scanning speed of the laser spot by changing the number of times the square is drawn repeatedly in FIGS. 3 to 6, it is confirmed that the higher the scanning speed is, the lower the flow velocity is. This is shown in Figure 7.
In consideration of the principle of (1), it is considered that when the scanning speed of the laser light is high, the amount of movement of the fine particles becomes small and the difference between the force in the traveling direction and the force in the opposite direction becomes small.

From the result of measuring the laser power dependence of the moving speed of fine particles, it is confirmed that a square putter can be formed with a power of a minimum of about 100 mW, and the moving speed becomes faster when the laser power is increased. . In this way, the flow velocity for transporting the fine particles depends on the laser power,
It can be controlled by the scanning speed of the laser spot.

In principle, three-dimensional trapping is also possible, and the formed pattern can be lifted from the substrate. Also, taking advantage of the fact that fine particles that absorb at the wavelength of laser light cannot be trapped. For example, if two types of fine particles are mixed and one contains a substance that absorbs laser light, only one It is also possible to selectively form a pattern with the fine particles of the above, and to irradiate the other fine particles with laser beams of different wavelengths at the same time to form another pattern.

On the other hand, if the transport function is used, chemical process control on the order of micrometers can be performed.
By irradiating the two sides of the square pattern of 6 with light of different wavelengths, respectively, and incorporating a photoreactive substance in the latex, particles reacting with one light gradually react with the surrounding solvent while being transported, Furthermore, a system can be constructed in which the reaction occurs with another light. By constructing such a spatially minute reaction field, it is expected that highly efficient and highly selective conversion / transfer of materials / energy corresponding to the material circulation system of biological cells / living tissues will be possible.

FIG. 8 shows a star pattern formed in the same manner as in FIG. 2 by using titanium oxide particles having a particle size of 0.5 μm or less instead of latex. As described above, in the present invention, various fine particles or microcapsules can be used to form a specific dynamic pattern by laser light. Of course, the present invention is not limited to the above example. Various specific embodiments are possible.

[0026]

As described in detail above, according to the present invention, it is possible to control the dynamics of fine particles in a predetermined pattern, and it is also possible to process / modify fine particles having this dynamic pattern.

[Brief description of drawings]

FIG. 1 is an optical system block diagram showing an experimental system that can be used in the present invention.

FIG. 2 is a schematic plan view showing an example of a fine particle dynamics pattern according to the present invention.

FIG. 3

FIG. 4

[Figure 5]

FIGS. 3 to 6 are schematic plan views showing a transportation state of fine particles in a fine particle dynamic pattern according to the present invention.

7 (a) and 7 (b) are schematic diagrams of the action force which is shown in principle for the stationary state and transportation of fine particles.

FIG. 8 is a schematic plan view showing still another dynamic pattern of the present invention.

[Explanation of symbols]

 1 CWNd: YAG laser 2 Galvano mirror 3 Lens system 4 Dichroic mirror 5 Objective lens 6 Controller 7 Computer 8 CCD camera 9 Monitor 10 Sample

Continuation of the front page (56) References JP-A-64-34439 (JP, A) Tokuhyo 3-501364 (JP, A) SCIENCE, VOL. 235, PP. 1517-1520, (1987) CHEMISTRY LETTER S, NO. 8, PP. 1479-1482, (1990)

Claims (1)

(57) [Claims] 1. A method in which a fine particle dispersion medium is irradiated with laser light, the focal position of the laser light is repeatedly scanned at high speed, and a plurality of fine particles are captured on the locus to form a pattern. Fine particle dynamics pattern.