JPH04210231A - Fine particle behavior pattern - Google Patents

Abstract

PURPOSE:To control the fine particle behavior in a specified pattern and to fixe, process and modify the fine particle by repeatedly scanning the focus position of a laser beam at a high rate and capturing the fine particles on the track to form a pattern. CONSTITUTION:A trapping laser beam is biaxially polarized with two galvanomirrors 2 and matched with the numerical aperture and focus position of a microscopic optical system with two lens systems 3. The beams are reflected by a dichroic mirror 4 in the microscope and condensed on a sample with an oil immersion lens 5. The laser beam is repeatedly scanned at a rate sufficiently higher than the mechanical speed of response determined by the diameter of the particle and the viscosity of the medium, hence each particle is trapped just the same as the particle being captured by stationary light, and many particles are captured on the track of the focus. Accordingly, the behavior of the particle is controlled in a specified pattern, and the particle is processed and modified.

Description

[Detailed description of the invention]

[00011

[Industrial Field of Application] This invention relates to a fine particle dynamic pattern and a method for forming the same. For more details,
The present invention relates to a new particle dynamic pattern that can be formed by a laser beam and a method therefor, which is useful for microfabrication technology and the creation of new material structures. [0002] [Prior Art and its Problems] In recent years, the development of micro-modification of chemical substances, such as polymeric substances and inorganic substances, at the fine particle level and their processing techniques have attracted attention, and the manipulation of elementary processes of material conversion has attracted attention. Research and development efforts are underway to make this possible. Furthermore, microprocessing, which performs micromanipulations such as transplantation, transfer, and even fusion of living cells, has become extremely important. [0003] Regarding such microparticle manipulation, various methods using chemical manipulation have been proposed, but in the case of chemical methods, it is necessary to control the reaction between the microparticles to be treated and the reaction treatment agent. It is very difficult to control the particles, their aggregation state, position, etc., and there are limits to accuracy in applying operations to predetermined particles. On the other hand, in the field of biological cell manipulation, it has become possible to reliably perform the transfer process using manual methods such as microinjection, and it has become possible to improve expression efficiency to about 10-2. ing. However, in this method, the practitioner directly contacts individual cells with a micropipette under a microscope, so processing in a clean bench is essential, and automation of the processing is not possible. Therefore, processing efficiency and processing amount depend on the skill level and labor of the person performing the processing, and there is a problem in that it is difficult to perform precise processing in a short time. [00041] In recent years, in contrast to the conventional methods described above,
Processing that uses laser light to micromanipulate particles has been proposed. Laser light has excellent monochromaticity, directionality, brightness, and controllability, so it is possible to concentrate light energy on a minute area of particles.
It becomes possible to perform fine local operations without contact with high precision, which was impossible with conventional methods. [0005] However, in the conventional methods, it is difficult to position the stage of a microscope etc. in order to adjust the laser beam irradiation area, and even if it is operated, the positioning accuracy is poor and there are practical problems, especially However, it has been impossible to control a plurality of fine particle groups into a predetermined spatial arrangement and then process them. That is, with conventional laser microprocessing, there has been a problem in that it is difficult to control the dynamic pattern of microparticles or a group of microparticles to enable highly accurate manipulation. [0006] The present invention has been made in view of the above circumstances, and it solves the drawbacks of conventional microparticle microprocessing and freely controls spatial dynamic patterns for high-precision processing of microparticles or groups of microparticles. The aim is to provide new means that can be used. More specifically, we aim to provide this dynamic pattern itself and methods for forming and utilizing it. [0007]

[Means for Solving the Problems] This invention solves the above problems by repeatedly scanning the focal position of a laser beam at high speed, capturing a plurality of fine particles on the trajectory, and forming a pattern. The present invention provides a particle dynamics pattern characterized by the following. This particle dynamic pattern was created based on the optical trapping operations studied by the inventor of the present invention, and was completed based on new findings that further develop this optical trapping method. [0008] In other words, one of the methods that has attracted attention as a method for manipulating fine particles is that, due to the excellent coherent properties of laser light, the momentum of the field of light is transferred as mechanical momentum acting on an object, and force is applied to the fine particles. There is an optical trapping operation that captures or moves the object by adding . In this optical trapping operation, only the force produced by the laser beam acts on the object, making it possible to perform completely non-contact and non-destructive operation. For this reason, there are great expectations for this optical trapping technology as a means of manipulating fine particles. [0009] To explain the principle of such optical trapping, first, a laser beam enters a fine particle through a lens, is reflected and refracted, and the momentum of the laser beam is transferred to the fine particle. Since the reflectance is usually low, the momentum transferred by refraction becomes dominant, and the resulting force is applied to the particles. This force causes the particles to be captured by the laser beam. Therefore, when the laser beam moves, the particles will follow it. [0010] In this type of laser trapping, by narrowing down the laser light to the wavelength order, it is possible to lift particles against gravity and capture them three-dimensionally.By manipulating the beam and moving the sample stage,
Non-contact manipulation of only the target particles can be achieved. Therefore, applications in the fields of biology and chemistry are being considered, and applications such as manipulation of living cells, cell sorters, and microsurgery have been reported. The inventor of this invention is also attempting to apply microchemistry such as laser ablation of polymer latex. [0011] However, conventional laser trapping is aimed at the manipulation of single microparticles. On the other hand, a method has been proposed in which a large number of fine particles are arranged in a place where the light intensity is high using an interference pattern of laser light to form a spatial pattern of fine particles. Using this method, it is possible to pseudo-crystallize microparticles using light, and it also opens the door to constructing highly efficient and highly selective material conversion systems by spatially arranging microscopic functional sites. However, there are naturally limits to the patterns that can be drawn just by using the interference pattern of laser light. On the other hand, in a trapping laser optical system, a method can be considered in which a mask pattern is placed at a position in image formation relation to the sample surface, and the mask pattern is projected onto the sample to form a particle pattern. In this case, the degree of freedom in patterning increases, but the energy utilization efficiency of laser light is extremely low, and it is difficult to produce a mask that can withstand high-power laser light. Furthermore, since the image is formed using highly coherent laser light, problems such as speckle noise occur. (Furthermore, a fine particle pattern can only be created two-dimensionally on a substrate.) Therefore, the inventor of this invention has developed a method for creating a plurality of fine particles on the trajectory by repeatedly controlling the focal position of a laser beam at high speed. We propose a new particle dynamic pattern and its method by capturing and forming a pattern. [0012] This invention provides that when a laser beam is repeatedly scanned sufficiently faster than the mechanical response speed of the particles determined by the particle size of the particles and the viscosity of the medium, each particle will be in the same trap state as when irradiated with steady light. Therefore, it takes advantage of the fact that a large number of particles can be captured on the trajectory of the focal point. The dynamic pattern of such captured particles is
Galvano mirrors, polygon mirrors, photoacoustic deflectors, etc.
This can be easily achieved using technology used in laser printers and laser scanning microscopes. It is possible to form any pattern of fine particles, and almost all of the energy of laser light can be used. Furthermore, as discussed in laser scanning microscopes, despite the use of laser light, there is no effect of coherent noise, similar to incoherent imaging systems. [0013] Furthermore, another major feature of pattern formation using scanning laser trapping is that
All particles forming a spatial pattern are moved simultaneously,
It may be possible to transport the material in a flowing manner over a pattern and control the flow rate. This utilizes the fact that when a laser beam scans a particle, it exerts a slight force on the particle in the scanning direction, and the slower the scanning speed, the greater this force becomes. [00141 The formed particulate movement pattern can be arranged along an arbitrary-shaped image. In this case, the dynamic pattern can be freely and continuously changed. By varying the intensity of light, even more diverse patterns can be formed. The patterned particles are subjected to photoreactions, thermal reactions, and even chemical reactions to fix the pattern, and the captured particles are scanned for modification and processing under predetermined conditions. You can also add The most representative and important operations in this invention include decomposition, division, local conversion, chemical modification of fine particles, adhesion of fine particles to each other, fusion, and crosslinking with functional reactive groups. [0015] There are no particular limitations on the type of target fine particles or fine particle groups, such as various types of polymer latex, microcapsules, titanium dioxide, other inorganic particles, biological cells, viruses, or various types. Molecular tissues can be used. As a laser beam, the fundamental wave (1064
A variety of materials including nanometer (nm) can be used. When a dispersion cell is used, the dispersion medium may be water, an organic substance, or any other medium that satisfies the condition that the refractive index of the fine particles to be captured is higher than that of the dispersion medium. [0016]

[Examples] Hereinafter, the present invention will be explained in more detail with reference to Examples. <Experimental system> The configuration of the experimental system is shown in Figure 1. The trapping laser beam was a CWNd:YAG laser (Spectro
n S L 902T, wavelength 101064n (1
). Connect this to two galvano mirrors (GSIG3
52DT) (2) to deflect in two axial directions, and two lens systems (3) to match the numerical aperture and focal position of the microscope optical system. Inside the microscope (Nikon 0ptiphot The size of the focused spot is approximately 1 μm. 2
Both galvano mirrors (2) are located at the aperture pupil and imaging position of the microscope, and due to the deflection by the galvano mirrors (2),
The focal position scans the sample two-dimensionally. The galvanometer mirror (2) is connected to the controller (Marubun) (6
), and for example, in the case of a square pattern to be described later, it is possible to repeatedly draw 30 times per second. The shape of the drawing pattern is created by a computer (NECPC9801RA)
An instruction is given from (7) to the controller (6). The pattern formation of fine particles was observed using a CCD camera (NECN (,-15M) (8)) by illuminating the sample from below.
An image is formed on top and observed on a monitor (9). The power of the laser light was 600 mW in this experiment. [0017] Sample (10) is 17 dispersed in ethylene glycol (refractive index 1.46, viscosity 17.3 cP).
xm monodispersed polystyrene latex (refractive index 1°59
), and this dispersion solution is sandwiched between two cover glasses,
The thickness of the liquid layer was set to about 100 μm using a spacer. <Test Results> In FIG. 2, the alphabet letter "M" is drawn with a laser beam, and latex fine particles are arranged on it. Approximately 60 pieces of latex are lined up in a rosary, neatly
A pattern of "M" is formed.When the laser beam irradiation was started, there were no latex particles on the observation surface, except for some latex particles that had fallen naturally. They were attracted by radiation pressure. The laser power irradiated per one was about 10 mW, and scanning was repeated 20 times per second. In the same way, ■°", "c", " It was also possible to form character patterns of “R” and “○゛.One side of the character is approximately 15 μm.
and the repetition frequency is 40.30.1, respectively.
It was 5.30 times/second. It was also possible to move these characters freely in parallel within the field of view in their original form. It took about 30 seconds for the latex fine particles to be attracted by the laser beam to form one character. This is because ethylene glycol, which has a high viscosity, is used as a medium, and water is much faster. [0018] FIG. 31 FIGS. 4, 5, and 6 are images of a 20-second observation of how the entire particulate is transported when a square is drawn. It can be seen that the particles marked with arrows in the figure are moving. One side of the square is 15 μm, and drawing is repeated 30 times per second. This is 1.8 mm/s when converted to the moving speed of the laser beam focal position.
It is. In addition, when estimating the moving speed (flow speed) of particles, it is 2.0μ
It was m/S. [0019] In order to consider the principle by which latex fine particles are transported in this way, let us now focus on one fine particle and assume that a laser beam scans over it once. Assuming that the particles are fixed and do not move at all, the force acting on the particles as a function of the position of the laser spot can be schematically expressed as shown in FIG. In FIG. 7, the upper part of the vertical axis represents the force in the positive direction of the coordinates, that is, the force in the advancing direction of the laser spot, and the lower part represents the force in the opposite direction. When the laser spot approaches a particle, a force that attracts the particle acts, and its size changes as shown in the figure, depending on the gradient of the electric field. When a laser beam overlaps with a particle, no horizontal force is exerted on it, and when it passes by, the exact opposite phenomenon occurs. In this case, when the force acting on the particle is integrated over time, the force in the direction of movement and the force in the opposite direction cancel and become zero. [o o 201 Next, consider the case where particles can move. When the laser beam approaches, the fine particles are attracted and move, so the waveform until the laser beam overlaps the fine particles is compressed compared to that in FIG. 7(a), as shown in FIG. 7(b). On the other hand, after the laser beam passes through a particle, the force waveform is broadened due to the same attraction. Then, the force integrated over one hour has a certain value in the direction of travel of the laser. This force multiplied by the number of repeated scans per second acts on the particles as work, and the movement speed of the particles is determined by this work, viscous resistance due to the solvent, and frictional resistance with the substrate. [00211 When the number of repetitions of drawing the squares in FIGS. 3 to 6 is changed and the moving speed of the particles is plotted as a function of the scanning speed of the laser spot, it is confirmed that the faster the scanning speed is, the lower the flow speed is. This is shown in Figure 7.
Considering this principle, it is thought that when the scanning speed of the laser beam is high, the amount by which the particles move becomes smaller, and the difference between the force in the forward direction and the force in the opposite direction becomes smaller. (0022) Furthermore, the results of measuring the laser power dependence of the particle movement speed confirm that a square pattern can be formed with a minimum power of 100 mW, and that the movement speed increases as the laser power is increased. In this way, the flow rate when transporting fine particles can be controlled by the laser power and the scanning speed of the laser spot. [0023] In principle, three-dimensional wrapping is also possible, The formed pattern can also be lifted off the substrate.Also, by taking advantage of the fact that fine particles that absorb the wavelength of laser light cannot be trapped, for example, when two types of fine particles are mixed, one of them absorbs the laser beam. If a material is included in the material, it is possible to selectively form a pattern using only one type of fine particles, and it is also possible to form another pattern by simultaneously irradiating the other fine particles with laser light of a different wavelength. [0024] On the other hand, if the transport function is used, chemical process control on the micrometer order can be performed, for example, as shown in FIGS.
When light of different wavelengths is irradiated on each side of the square pattern 6 and a photoreactive substance is contained in the latex, the particles that reacted with one side of the light are transported and gradually react with the surrounding solvent. Furthermore, it is possible to construct a system in which a reaction occurs with another type of light. By constructing such a spatially minute reaction field, it is expected that highly efficient and highly selective conversion and transfer of substances and energy will be possible, which corresponds to the material circulation system of biological cells and tissues. [00251 In Figure 8, instead of latex, 0.5 μm
A star-shaped pattern was formed in the same manner as in FIG. 2 using titanium oxide particles having the following particle sizes. In this way, in the present invention, a specific dynamic pattern can be formed using laser light using various types of fine particles or microcapsules. Of course, the invention is not limited to the above examples. Various specific embodiments are possible. [0026]

[Effects of the Invention] As explained in detail above, according to the present invention, it is possible to control the movement of fine particles into a predetermined pattern, and it is also possible to fix, process and modify the fine particles in this movement pattern.

[Brief explanation of the drawing]

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 particle dynamic pattern according to the present invention.

[Figure 3]

[Figure 4]

51 [FIG. 6] FIGS. 3 to 6 are schematic plan views showing the transport state of fine particles in the fine particle movement pattern according to the present invention.

FIG. 7 is a schematic diagram of acting forces showing the principle of transport of fine particles.

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

[Explanation of symbols]

I 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 Wiping material

Claims (1)

[Claims] 1. A particulate dynamic pattern characterized by forming a pattern by repeatedly scanning the focal position of a laser beam at high speed and trapping a plurality of particulates on the trajectory.