JP6551149B2 - Fine particle capturing method and optical tweezers device - Google Patents

Description

  The present invention relates to a fine particle capturing method and an optical tweezer device.

  For example, an optical tweezer technology is known as a technology for capturing and moving fine particles of about 1 μm (see, for example, Patent Document 1). In the optical tweezer technology, laser light is collected by a lens, and the fine particles can be captured by light pressure acting on the fine particles brought close to the focal point. In this optical tweezers technology, there is a difference in refractive index between the fine particle and its surroundings, and the combined force of the light pressure acting on the fine particle can be directed to the focal point to keep capturing the fine particle.

  In order to capture particulates by such an optical tweezers technique, the particulates have optical transparency (laser light permeability), and the refractive index (n2) of the particulates is the refractive index (n1) around it. Greater than (n2> n1) is required.

JP 2006-235319 A

  The conventional optical tweezers technology targets light-transmissive particles as the particles to be handled, but it may be necessary to capture and move even non-light-transmissive particles, for example, metal particles. . For example, when performing physical measurement such as frictional force and elastic force of a microscopic metal material, it is necessary to capture and move such fine particles made of metal.

  In the conventional optical tweezers technology, even when trying to capture metal particles, the light pressure generated when the laser beam is collected is in the direction away from the light collection point, that is, metal particles are collected at the light collection point On the other hand, it becomes impossible to capture because it repels. Therefore, conventionally, there is a technique in which at least four laser beams are used, and the metal fine particles are surrounded by the condensing points of these laser beams to capture. However, since the fine particles repel each focusing point, it is difficult to control the position of the fine particles, and in order to move the captured fine particles, it is necessary to simultaneously operate at least four laser beams. The operation becomes very difficult.

  Therefore, an object of the present invention is to provide a particle capturing method and an optical tweezers device using an optical tweezers technique that can capture even metal particles, for example.

  The particle capturing method of the present invention is a particle capturing method using an optical tweezers technique in which a laser beam is condensed by a lens and the particles brought close to the focusing point of the laser beam are captured, and have light transmittance. One particle is charged to one of positive and negative, the second particle having a light transmitting property lower than that of the first particle is charged to the other of the positive and negative, and the first particle is charged by a laser beam collected by the lens. Is captured, and the second particle is captured by the Coulomb force generated between the first particle and the captured first particle.

  According to this particle capturing method, even if the second particle is, for example, a metal particle, the light transmitting first particle is charged to one of positive and negative, and the metal particle (second particle) is By charging to the other side, it is possible to capture metallic microparticles (second microparticles) due to the Coulomb force generated between the first microparticles captured close to the focal point by the lens.

Further, in the particle capturing method, each of the plurality of first particles is charged to one of positive and negative, the laser beam is focused at different focusing points, and the laser beam is focused on the different focusing points. It is preferable that the plurality of first particles be separately captured and the second particles be captured by the Coulomb force generated between each of the plurality of first particles captured.
In this case, for example, the two first microparticles are divided and captured by laser beams collected at two different focusing points, and the two first microparticles thus trapped separate the second microparticles located between them. Capturing is possible. Thereby, the capture power of the second particulates can be enhanced, and the freedom of operation of the second particulates can be increased.

  Moreover, it is preferable that the first fine particles have a volume larger than that of the second fine particles. For example, when the first particle and the second particle have the same charge, and the first particle has a volume larger than that of the second particle, the first particles are separated from each other by the volume difference as compared with the case of the same volume. Can do. This makes it possible to avoid contact between the respective particles.

  Further, according to the optical tweezers device of the present invention, a light source for emitting laser light, a lens for condensing laser light from the light source, and a predetermined first position provided between the light source and the lens as the light source And optical means for setting a condensing point of laser light from the light source, and the laser light condensed at the first position by the optical means has light transparency and is charged to one of positive and negative. The first particle is captured, and the second particle charged to the other of positive and negative is captured at a second position different from the first position by the Coulomb force generated between the first particle and the second particle.

  According to this optical tweezers device, even if the second fine particle is, for example, a fine particle made of metal, the first fine particle having light transparency is charged to one of positive and negative, and the fine particle (second fine particle) made of metal is Of the metal particles (second particles) with the first position by the Coulomb force generated between the first particles captured close to the focusing point (first position) of the lens. It is possible to capture at a different second position.

Further, it is preferable that the optical unit includes an optical unit that disperses the laser light from the light source, and condenses each of the plurality of laser beams separated by the optical unit at different first positions.
In this case, a plurality of focusing points are obtained by the laser light divided into a plurality of parts, and a plurality of first particles are divided and captured at these focusing points, and Coulomb force generated between each of the plurality of captured first particles The second particle can be captured by the That is, although a plurality of first microparticles are divided and captured at a plurality of focusing points, only one light source is sufficient.

  According to the present invention, optical tweezers technology can be used to capture particulates, for example made of metal.

It is explanatory drawing explaining the whole structure of an optical tweezers apparatus. It is explanatory drawing of an optical means, a lens, and a holding member. It is explanatory drawing of the microparticles | fine-particles currently hold | maintained at the holding member.

Hereinafter, embodiments of the present invention will be described based on the drawings.
FIG. 1 is an explanatory view for explaining the entire configuration of the optical tweezers 1. The optical tweezers 1 includes a light source 10 for laser light, light guiding means (21 to 27), an optical means 40, a first lens 28, a light source 30 for illumination, a second lens 31, an apparatus base 45, a stage 46, and driving. Means 48, imaging means 50, and control means 60 are included.

  In this optical tweezer device 1, as will be described later, a stage 46 is configured to be movable by a driving unit 48 with respect to a device base 45 that is fixed to the work floor. The imaging means 50 and the like are provided in a fixed state on the device base 45, and these do not move relative to the device base 45.

  The light source 10 for laser light is a laser device that emits laser light (laser beam) L, and emits laser light L of a first wavelength based on a control signal from the control means 60. By the optical tweezer technology based on the laser light L, fine particles held on a holding member (for example, a preparation) 47 mounted on the stage 46 are captured (light trapped).

The light guiding means (21 to 27) are for guiding the laser light L emitted from the light source 10 to the optical means 40. The light guiding means (21 to 27) will be described in order.
The first reflection mirror 21 reflects the laser light L from the light source 10 and causes the laser light L to be incident on the first stop 22. The first aperture stop 22 narrows the diameter of the incident laser beam L and emits it to the first collimator lens 23. The first collimating lens 23 enlarges the diameter of the laser light L and emits it to the second collimating lens 24. The second collimator lens 24 converts the laser beam L whose diameter is expanded into parallel light and emits the parallel light. The second diaphragm 25 narrows the diameter of the collimated laser light L and emits it toward the first mirror 26. The first mirror 26 reflects the incident laser light L toward the second mirror 27. The second mirror 27 reflects the incident laser light L toward the optical means 40.

  The optical means 40 is configured to include, for example, an acousto-optic modulator (AOM) as the optical device 40a, and the optical device (acousto-optic modulator) 40a includes a plurality of laser beams L incident from the second mirror 27. It has a function to categorize. In the present embodiment, the optical device 40a divides the incident single laser beam L into two laser beams L1 and L2 based on the control signal from the control means 60. Then, as shown in FIG. 2, these laser beams L1 and L2 both enter the first lens. FIG. 2 is an explanatory view of the optical means 40, the lens 28 and the holding member 47.

  The first lens 28 condenses one laser beam L1 incident from the optical means 40 toward the (first) focal position set on the holding member 47 and the other lens incident from the optical means 40. The laser beam L2 is condensed toward another (second) focal position set in the holding member 47. The position at which one of the split laser beams L1 is focused is the first focusing point Q1, and the position at which the other split laser beam L2 is focused is the second focusing point Q2.

  In FIG. 1, the light source 30 for illumination is, for example, an LED illumination, and emits illumination light S of a second wavelength based on a control signal from the control means 60. The illumination light S serves as illumination for the imaging unit 50 that observes the state of the particles held by the holding member 47. The second lens 31 condenses the illumination light S emitted from the light source 30 for illumination in a region including the condensing points Q1 and Q2.

  The stage 46 mounts a holding member 47 that holds fine particles. The holding member 47 holds a fluid and particulates contained in the fluid and targeted for capture. The fluid may contain fine particles that are not to be captured. In this embodiment, the fluid is a liquid. The refractive index (n1) of this fluid is smaller than the refractive index (n2) of the fine particles (n1 <n2).

  The stage 46 is supported so as to be movable back and forth, left and right, up and down, and the driving means 48 moves the stage 46 back and forth, left and right, up and down. In FIG. 1, the front-rear direction, the left-right direction, and the up-down direction are shown as an X-axis direction, a Y-axis direction, and a Z-axis direction, respectively. The driving unit 48 moves the stage 46 in at least one of the X-axis direction, the Y-axis direction, and the Z-axis direction based on a control signal from the control unit 60, and moves the holding member 47 in the same direction. The driving means 48 is, for example, an actuator using a piezo element.

As described above, in the optical tweezers device 1 shown in FIG. 1, the focusing point Q1 and Q2 (lens 28) does not move (by the driving means 48) because the lens 28 is not moved. , Q 2, and the trapped particles do not move (by the driving means 48). On the other hand, since the stage 46 is moved together with the holding member 47 by the driving means 48, the particles trapped in the vicinity of the focusing points Q1 and Q2 are contained in the fluid (and in the surrounding fluid) Particulates that are not trapped will move.
Note that, unlike the mode shown in FIG. 1, the stage 46 may be fixed, and the focal point of the lens 28 (focus points Q1 and Q2) may be moved.
Further, in the present embodiment, since the optical means 40 is an acousto-optic modulator, the positions of the focusing points Q1 and Q2 may be changed by the optical means (acousto-optic modulator) 40. That is, by changing the voltage applied to the acousto-optic modulator, the incident positions of the laser beams L1 and L2 in the lens 28 are changed, thereby moving the focusing points Q1 and Q2, and the focusing points Q1 and Q2 The particle to be captured may be moved closer to the

The imaging unit 50 is, for example, a CCD camera or a CMOS camera, and images a region including the focusing points Q1 and Q2 and the periphery thereof. The imaging unit 50 outputs the image data obtained by imaging to the control unit 60.
The control means 60 is, for example, a personal computer, and outputs each control signal as described above, and also takes in image data from the imaging means 50.

  The optical tweezer device 1 of the present embodiment is configured as described above, but the light guide means (21 to 27) may have other configurations, for example. That is, the optical tweezers device 1 of the present invention (see FIG. 1) includes a light source 10 for emitting the laser light L, a lens 28 for condensing the laser light L from the light source 10, and a space between the light source 10 and the lens 28. And optical means 40 provided in a part of the above. As shown in FIG. 2, the optical unit 40 sets the predetermined positions (first positions P <b> 1-1 and P <b> 1-2) as the condensing points Q <b> 1 and Q <b> 2 of the laser beams L <b> 1 and L <b> 2 from the light source 10. The first microparticles C1-1 and C1-2 which are light transmissive and negatively charged are captured by the laser beams L1 and L2 condensed at the first positions P1-1 and P1-2 by the optical means 40. (Light trap). And this optical tweezers device 1 is the 1st position P1-1 by the Coulomb force which arises between the 1st fine particles C1-1 and C1-2 which negatively charged the 2nd fine particles C2 positively charged. , P1-2 is configured to capture at a second position P2 different from the second position P2.

Furthermore, in the present embodiment, as described above, the optical unit 40 includes an acousto-optic modulator as an optical unit 40a that splits the laser light L from the light source 10, and this optical unit (acousto-optic modulator) 40a In this configuration, the laser beams L1 and L2 that have been split are condensed at different first positions P1-1 and P1-2.
For this reason, a plurality of focusing points Q1 and Q2 are obtained by the laser beams L1 and L2 which are split into a plurality of pieces, and the plurality of first microparticles C1-1 and C1-2 are divided and captured at the focusing points Q1 and Q2. The second particle C2 can be captured by the Coulomb force generated between each of the plurality of captured first particles C1-1 and C1-2. That is, although the plurality of first microparticles C1-1 and C1-2 are separately captured at the plurality of focusing points Q1 and Q2, only one light source 10 and one lens 28 are required, and the configuration of the optical tweezers device 1 is simplified. Can be Further, according to the acousto-optic modulator, the first fine particles C1-1 and C1-2 can be optically trapped and operated simultaneously.

  In addition, the optical means 40 may be comprised from another means other than an acousto-optic modulator, and the structure obtained by combining various light guide means may be sufficient as it. Also, a plurality of light sources 10 and lenses 28 for condensing the laser light L from the light sources 10 may be provided, and a configuration in which a plurality of condensing points are obtained by these may be employed.

[Regarding the particle capture method]
A particle capturing method performed by the optical tweezers device 1 having the above configuration will be described.
FIG. 3 is an explanatory view of the particles held by the holding member 47. As shown in FIG. In the holding member 47, the first microparticles C1-1 and C1-2 charged negatively (negative) and the second microparticles C2 charged positively (plus) are mixed. In the present embodiment, the first particles C1-1 and C1-2 are resin-made particles, and have light transmittance (laser light transmittance). On the other hand, the second particles C2 are metal particles and do not have light transmittance (laser light transmittance).
Further, the particles C1-1, C1-2, and C2 are held in the liquid W. That is, in the present embodiment, the liquid W is held by the holding member 47, and the particles C1-1, C1-2, and C2 exist in the liquid W.

The method (one example) for negatively charging the resin-made first fine particles C1-1 and C1-2 is as follows. For example, it can be a corona charging method, and can be a method of charging by releasing a negative (negative) ion ionized by corona discharge to an object. In addition, it is preferable to set it as non-contact type charging here.
Moreover, the method (an example) which positively charges the metal 2nd microparticles | fine-particles C2 is as follows. For example, a corona discharge method can be used. Here, in addition to the non-contact type, a contact type method can also be adopted. For example, movement of electrons may occur by bringing a plate of the same metal into contact with an object and applying a voltage, and charging may be performed by separating the plate from the object.

In FIG. 2, as described above, the optical means 40 is configured to include an acousto-optic modulator as an optical unit 40 a that splits the laser light L from the light source 30 side, and this optical unit (acousto-optic modulator) 40 a is A single incident laser beam L is divided into two laser beams L1 and L2. The laser beams L1 and L2 are incident on a single lens 28, and are condensed by the lens 28 at different condensing points Q1 and Q2, respectively. That is, one laser beam L1 is focused at the first focusing point Q1, and the other laser beam L2 is focused at the second focusing point Q2 different from the first focusing point Q1.
Thereby, one first particle C1-1 can be captured close to the first focusing point Q1, and the other first particle C1-2 can be captured closer to the second focusing point Q2. .

  As shown in FIG. 3, since the resin-made first fine particles C1-1 and C1-2 are negatively charged as described above, the first fine particles C1-1 and C1-2 are charged. The second metallic fine particles C2 that are present near and positively charged (positive) are captured by the first fine particles C1-1 and C1-2 at the position where the Coulomb force is suspended. In addition, the Coulomb force F which arises between each of 1st microparticles | fine-particles C1-1 and C1-2 and 2nd microparticles | fine-particles C2 is following Formula (1).

  As described above, in the particle capturing method performed by the optical tweezers device 1 shown in FIG. 1, the first particle C1-1, in which the laser beam L is condensed by the lens 28 and brought close to the focusing points Q1 and Q2 of the laser beam. This is a method using optical tweezer technology (optical trap technology) for capturing C1-2. Further, this fine particle capturing method further uses an attractive force acting between charged fine particles.

  Although the said embodiment demonstrated the case where 1st microparticles | fine-particles C1-1 and C1-2 were negatively charged and 2nd microparticles | fine-particles C2 were positively charged, it may be contrary. That is, in the particle capturing method of the present invention, the first particles C1-1 and C1-2 having light transmittance may be charged to one of positive and negative, and the second particles C2 may be charged to the other of positive and negative. The first fine particles C1-1 and C1-2 are captured by the laser beams L1 and L2 condensed at the condensing points Q1 and Q2, and are generated between the captured first fine particles C1-1 and C1-2. This is a method of capturing the second microparticles C2 by the Coulomb force.

  According to this fine particle capturing method, even if the second fine particle C2 is a metal fine particle and does not have light transmittance, the resin-made first fine particles C1-1 and C1-2 having positive and negative properties are positive and negative. By charging the second particle C2 made of metal to the other of positive and negative, the first particle C1-1 and C1- made of resin captured close to the focusing points Q1 and Q2 by the lens 28 are captured. The Coulomb force generated between 2 and 2 makes it possible to capture the metal second microparticles C2.

  In this embodiment, by moving the stage 46 together with the holding member 47, the metal second fine particles C2 captured via the resin first fine particles C1-1 and C1-2, and the periphery thereof. It can be moved relatively. When the positions of the focusing points Q1 and Q2 are changed by the optical means 40 including the acousto-optic modulator, the first particles C1-1 and C1-2 made of resin are made to follow the focusing points Q1 and Q2. The metal second fine particles C2 can be moved so as to follow the first fine particles C1-1 and C1-2.

  In particular, in the present embodiment, as shown in FIGS. 2 and 3, each of the two resin-made first fine particles C1-1 and C1-2 is negatively charged, and the laser light L is collected at different condensing points Q1, Q2. Each Q2 is condensed. And two first microparticles | fine-particles C1-1 and C1-2 are divided | segmented and captured by laser beam L1, L2 condensed on each of these different condensing points Q1, Q2. Then, the metal second fine particles C2 are captured by the Coulomb force generated between the captured two first fine particles C1-1 and C1-2.

  Thus, the two second microparticles C1-1 and C1-2 are divided and captured by the laser beams L1 and L2 condensed at two different condensing points Q1 and Q2, and these two first microparticles captured C1-1 and C1-2 make it possible to capture the second fine particle C2 located therebetween. As a result, the capturing power of the second particle C2 is enhanced, and the degree of freedom in the operation (position control) of the second particle C2 can be increased. That is, the second fine particles C2 can be moved not only linearly but also two-dimensionally and three-dimensionally and moved two-dimensionally and three-dimensionally.

Further, in the present embodiment, one first particle C <b> 1-1 and the other first particle C <b> 1-2 are the same and have the same size. Thereby, the charge amount (q1) of the first fine particles C1-1 and C1-2 can be made the same. As a result, the balance of the electric field can be prevented from being lost, and the capture performance of the second fine particles C2 can be improved.
Further, in the present embodiment, the first fine particles C1-1 (C1-2) have a larger volume than the second fine particles C2. For example, when the first particle C1-1 (C1-2) and the second particle C2 have the same charge, and the first particle C1-1 (C1-2) has a larger volume than the second particle C2 The first fine particles C1-1 and C1-2 can be separated from each other by a volume difference as compared with the case of the same volume. This can avoid contact between the respective fine particles.

  In the above-described embodiment, the first particles C1-1 and C1-2 have light transmission, whereas the second particles C2 do not have light transmission (metal particles). As described above, the second particles C2 may be particles with low light transmittance. Fine particles with low light transmittance are difficult to be captured by laser light, but can be captured by using fine particles with low light transmittance as the second fine particles as in the above embodiment. That is, the particle capturing method of the present invention can be applied to the case where the second particle does not have light permeability, but also when the light transmittance is lower than that of the first particle.

In the above embodiment, the first particles C1-1 and C1-2 are made of resin and the second particles C2 are metal, but the first particles C1-1 and C1-2 are It may be made of other than resin as long as it has optical transparency, for example, it may be made of glass. The second particles C2 may be made of other than metal, for example, may be made of ceramics.
Furthermore, in the above-described embodiment, the first particles C1-1 and C1-2 are negatively charged, and the second particles C2 are positively charged. If the first particles C1-1 and C1-2 are likely to be positively charged, the first particles C1-1 and C1-2 may be positively charged and the second particles C2 may be negatively charged. The polarity may be determined according to the ease of charging of the particles.

In the above embodiment, although the particles (C1-1, C1-2, C2) to be captured are contained in the liquid, they may be present in the air. However, when in the liquid, it becomes easy to suspend the fine particles and handling is easy.
In the case where the particles (C1-1, C1-2, C2) are contained in the solution, one laser beam L may be used in particular. It can be trapped, and the first microparticle and the second microparticle are separated to some extent, and the drag force (by the liquid) and the attractive force by the coulomb force in the direction in which the second microparticle approaches the first microparticle The second particle can be captured (stopped) at a position where it is balanced. Then, when the first particle is moved linearly in one direction (the direction away from the second particle), the second particle can move following it.

As mentioned above, according to the said optical tweezers apparatus and the microparticles | fine-particles trapping method, it becomes possible to capture | acquire 2nd microparticles | fine-particles, such as metal, for example by laser light of the number as small as possible. Furthermore, the second particulates can be easily captured nondestructively and nondestructively, and position control of the second particulates becomes possible.
In addition, when performing physical measurement such as frictional force or elastic force of a microscopic metal substance, it is necessary to capture and move fine particles made of metal, for example, but according to the optical tweezers device and the fine particle capturing method It becomes possible.

  Moreover, in the said embodiment, since the mode of microparticles C1-1, C1-2, and C2 is imaged by the imaging means 50, in order to clarify the mode, the first microparticles C1-1 and C1-2 and It is preferable to color at least one of the two microparticles C2. The first particles C1-1 and C1-2 may be made into chargeable microcapsules, and dyes and pigments may be contained therein.

  Then, according to the optical tweezers device and the particle capturing method, as shown in FIG. 3, an electrostatic field is created by the particles (C1-1, C1-2, C2), and, for example, (positive or The present invention can be applied to techniques for performing negative (negative) discrimination, and sorting of the size and type of fine particles. Further, the present invention can be applied to a technique in which the deposit on the material surface is the second fine particle, and the second fine particle is peeled off from the material surface by the first fine particle.

  The embodiments disclosed above are illustrative in all respects and not restrictive. That is, the optical tweezers and the fine particle capturing method of the present invention are not limited to the illustrated forms, and may be in other forms within the scope of the present invention.

1: Optical tweezers 10: Light source for laser light 28: Lens 40: Optical means 40a: Optical device C1-1: First particulate C1-2: First particulate C2: Second particulate L1: Laser light L2: Laser light P1-1: First position P2: Second position Q1: First focusing point Q2: Second focusing point

Claims (5)

A particulate capturing method using an optical tweezers technique in which laser light is collected by a lens and the fine particles brought close to the focusing point of the laser light are captured,
Charge one of the light-transmissive first particles positively and negatively;
Charging the second particle, which has lower light transmittance than the first particle, to the other of positive and negative,
The first particle is captured by a laser beam condensed at a condensing point by the lens,
A particulate capturing method, comprising capturing the second particulate by Coulomb force generated between the captured first particulate and the first particulate. Charging each of the plurality of first particles to one of positive and negative,
Condensing the laser light at different focusing points,
A plurality of the first fine particles are divided and captured by the laser light condensed to each of the different condensing points;
The particulate capturing method according to claim 1, wherein the second particulates are captured by Coulomb force generated between each of the plurality of captured first particulates.   The particulate capturing method according to claim 1, wherein the first particulates have a larger volume than the second particulates. A light source for emitting laser light,
A lens for condensing laser light from the light source;
Optical means provided between the light source and the lens for setting a predetermined first position as a focusing point of the laser light from the light source;
By the laser beam condensed at the first position by the optical means, the first fine particles having optical transparency and charged to one of positive and negative are captured.
The second particle charged to the other of positive and negative is captured at a second position different from the first position by the Coulomb force generated with the first particle,
Optical tweezers device. The optical means includes an optical device that disperses the laser light from the light source,
5. The optical tweezers device according to claim 4, wherein each of the plurality of laser beams separated by the optical device is focused at different first positions.