JP2008096373A - Method and apparatus for measuring nanoparticles - Google Patents

Abstract

An object of the present invention is to form a diffraction grating by a measured particle group by forming an electric field having a spatial period by applying a voltage to an electrode in a sample in which the measured particle group is dispersed in a medium, and then stop the voltage application. In the method of calculating the particle diameter by extinguishing the diffraction grating due to particle diffusion and obtaining the particle diffusion coefficient from the time change of the diffracted light from the diffraction grating in the annihilation process, it is caused by Joule heat due to voltage application to the electrode The present invention provides a method that enables accurate particle diameter measurement by eliminating the effect of temperature rise.
An applied voltage to an electrode is changed over a plurality of times, diffusion coefficients D1 to Dn based on the applied voltages V1 to Vn are obtained, and the applied voltage is reduced to 0 V from the relationship of the applied voltage Vi and the diffusion coefficient Di. Correspondingly, in other words, the diffusion coefficient D ′ when the temperature rise due to Joule heat does not occur is calculated, and the particle diameter is calculated using the diffusion coefficient D ′.
[Selection] Figure 1

Description

  The present invention relates to a method and an apparatus for measuring the particle diameter of so-called nanoparticles having a diameter of 100 nm or less.

  Particles having a particle size of 100 nm or less are generally referred to as nanoparticles, and even if they are the same material, they exhibit properties different from ordinary bulk materials, and thus are beginning to be used in various fields. Various methods are known for measuring the particle size, including the laser diffraction / scattering method. Nanoparticles having a particle size of 100 nm or less are mainly referred to as the dynamic scattering method (photon correlation method). A method based on the measurement method is used (see, for example, Patent Documents 1 and 2).

  The dynamic scattering method uses the Brownian motion of particles, irradiates the particles that are in Brownian motion in the medium with a light beam, and measures the intensity of the scattered light from the particles at a predetermined position. The fluctuation of the scattered light intensity caused by the Brownian motion of the particle, that is, the change with time of the scattered light is captured, and the particle size of the particle to be measured is measured by using the Brownian motion with the intensity according to the particle size. The particle size distribution of the particle group is calculated.

  In such a dynamic scattering method (photon correlation method), it is necessary to measure small fluctuations in large scattered light, in other words, it is necessary to measure fluctuations in light intensity in a bright field of view. Therefore, in principle, problems such as low measurement sensitivity and poor S / N are inevitable.

  Therefore, in order to solve such problems, the present inventors have applied a voltage to electrodes of a predetermined pattern in a sample in which particles to be measured are dispersed so as to be movable in a medium. An electric field having a period is formed, and the particles are dielectrophoresised or electrophoresed to generate a pseudo diffraction grating based on the density distribution of the particles, and then the voltage application to the electrodes is stopped to diffuse the particles. The diffraction grating is extinguished, and the temporal change of the diffracted light obtained by irradiating the diffraction grating with light in the process of extinction of the diffraction grating is detected, and the diffusion coefficient of the particle group to be measured is calculated from the detection result. Furthermore, a method of calculating the particle diameter of the particle group to be measured from the diffusion coefficient is proposed (see, for example, Patent Document 3).

In this proposed technology, the diffracted light generated by irradiating light on the pseudo diffraction grating by the particle group travels at an angle corresponding to the wavelength of the light and the distance between the diffraction gratings with respect to the light transmitted through the particle group. In addition, since it is stronger than the light scattered by individual particles obtained by the dynamic scattering method, the signal to be measured is strong, and the S / N and sensitivity are greatly improved as compared with the dynamic scattering method.
US Pat. No. 5,094,532 JP 2001-159595 A JP 2006-84207 A

  By the way, in the proposal of above-mentioned patent document 3, the sample suspension which dispersed the to-be-measured particle group in the medium (medium liquid) is accommodated in a container as a concrete apparatus structure, and the inner surface of the container is accommodated. The electrode is configured to form an electric field. However, if the sample is conductive, when a voltage that generates dielectrophoresis is applied, current flows and Joule heat is generated, and the temperature in the container rises. To do.

  In order to calculate the particle diameter from the particle diffusion coefficient obtained from the diffraction grating method using the dielectrophoretic phenomenon, the temperature in the situation where the diffusion coefficient is obtained is required. However, it is difficult to accurately measure the local temperature increase in the vicinity of the electrode in the container, and there is a problem that an accurate particle diameter excluding the influence of temperature cannot be calculated.

  The present invention has been made in view of such a situation, and even when measuring a conductive sample, the influence of the temperature rise of the sample due to Joule heat is excluded without measuring the temperature of a minute region near the electrode. An object of the present invention is to provide a nanoparticle measurement method and apparatus that can always calculate an accurate particle diameter.

  In order to solve the above-mentioned problems, the nanoparticle measurement method of the present invention applies a voltage to an electrode having a predetermined pattern in a sample in which a group of particles to be measured is movably dispersed in a medium. By forming an electric field having a period, the above-mentioned particle group has a spatial periodic concentration change to generate a pseudo diffraction grating, and diffracted light obtained by irradiating the particle group with laser light in that state In this method, the voltage applied to the electrode is calculated by calculating the particle coefficient of the particle group from the diffusion coefficient obtained from the time change of the diffracted light from the time when the formation of the electric field is stopped. The diffusion coefficient is obtained by changing the number of particles to a plurality of values, the diffusion coefficient corresponding to the applied voltage of 0 V is obtained by extrapolation using the relationship between each voltage and the diffusion coefficient, and the particle group is obtained using the obtained diffusion coefficient. Particle size Characterized by calculating (claim 1).

  The nanoparticle measurement apparatus of the present invention is a measurement apparatus to which the above-described method of the present invention is applied, and a container for holding a sample in which a group of particles to be measured is movably dispersed in a medium, and the container An electrode for forming an electric field having a spatial period therein, a power source for applying a selectable voltage to the electrode, a laser light source for irradiating the sample in the container with a laser beam, and the laser beam passing through the sample A detection optical system for detecting the diffracted light generated by the operation, a data processing means for performing data processing using the output of the detection optical system after the application of the voltage to the electrode is stopped, and a measurement operation are controlled. The control means changes the voltage applied to the electrode into a plurality of voltages, and the data processing means obtains a diffusion coefficient based on each applied voltage, and then applies each applied voltage and diffusion coefficient. No seki From the diffusion coefficient corresponding to the applied voltage 0V extrapolated, characterized by calculating the particle diameter of the particles to be measured using the diffusion coefficients in the applied voltage 0V (claim 2).

  In the present invention, the applied voltage to the electrode for forming the electric field is changed to a plurality of values, the diffusion coefficient is obtained based on each applied voltage, and the applied voltage is 0 V from the relationship between the applied voltage and the diffusion coefficient. The problem is to be solved by estimating and calculating the diffusion coefficient, that is, the diffusion coefficient when no Joule heat is generated.

  That is, when the sample has conductivity, when a voltage is applied to the electrode to form an electric field, the temperature in the vicinity of the electrode rises due to the generation of Joule heat as described above. The amount of temperature rise depends on the magnitude of the applied voltage, and the temperature rise increases as the applied voltage increases. Therefore, the magnitude of the applied voltage is changed over a plurality of times, the diffusion coefficient is obtained under each applied voltage, the relationship between the applied voltage and the diffusion coefficient is obtained, and the diffusion coefficient when the applied voltage is 0 V is obtained by extrapolation. . The diffusion coefficient calculated in this way for an applied voltage of 0 V can be regarded as a diffusion coefficient under the initial temperature without Joule heat being 0, and thus without increasing the temperature of the sample. If the particle diameter is calculated using, a particle diameter that is not affected by the temperature rise caused by Joule heat can be obtained.

  According to the present invention, it is possible to calculate an accurate particle diameter of a conductive sample that is not affected by the temperature rise due to Joule heat without measuring the temperature in the vicinity of the electrode. The effect of temperature rise due to Joule heat, which is peculiar to diffraction grating methods using dielectrophoresis and electrophoresis, can be accurately corrected by simply changing the applied voltage over several points, requiring special measurements. do not do. In addition, it is easy to automatically perform a series of measurement operations, and simple and accurate particle size measurement of nanoparticles can be realized.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. It should be noted that the present invention is not limited to the embodiments described below, and it goes without saying that various aspects are included without departing from the spirit of the present invention. In the following explanation, the migration force is described on the premise of a positive migration force that collects particles by suction. However, even in the case of a negative migration force having a repulsive force, particles near the electrode by migration will be closer than the surroundings. A particle density modulation is formed where the density is reduced and similarly functions as a diffraction grating.

  FIG. 1 is a configuration diagram of an embodiment of the present invention, and is a diagram illustrating a schematic diagram showing an optical configuration and a block diagram showing an electrical configuration. FIG. 2 is an external view showing an example of the sample container 1 in FIG.

  The apparatus includes a sample container 1 for storing a sample in which particles are movably dispersed in a liquid and a sample made of a gel in which particles are movably dispersed, and an electrode pair 2 provided in the sample container 1. A power source 3 for applying a voltage to the light source, an irradiation optical system 4 for irradiating the sample container 1 with light, and a diffraction grating based on a density distribution of particle groups generated in the sample container 1 by applying a voltage to the electrode pair 2 Main components are a detection optical system 5 that measures the diffracted light from the light source, a calculation unit 6 that takes in an output from the detection optical system 5 via an amplifier 6a and performs a calculation described later, and a control unit 7 that controls the entire apparatus. It is said.

  As shown in the perspective view of FIG. 2 and the schematic enlarged cross-sectional view of FIG. 3, the sample container 1 has wall bodies 11 and 12 that are at least parallel to each other and each made of a transparent material, and one of the walls. An electrode pair 2 is formed on the surface (inner surface) of the body 11.

As illustrated in FIG. 4, the electrode pair 2 includes, as the electrodes 21 and 22, a plurality of electrode pieces 21 a or 22 a that are parallel to each other, and connection portions that electrically connect the electrode pieces 21 a or 22 a to each other. It is comprised by the comb-shaped electrode which has 21b and 22b. Each of the electrodes 21 and 22 has a shape in which an electrode uneven distribution region in which two linear electrode pieces 21a or 22a are arranged adjacent to each other and an electrode absence region in which no electrode pieces are present are alternately formed. Then, the two electrode pieces 21a or 22a in one electrode piece unevenly distributed region enter the other electrode piece non-existing region, and the electrode pieces 21a and 22a as a whole are parallel to each other with a certain distance therebetween. In this state, two are alternately positioned.
An AC voltage from the power source 3 is applied to the electrode pair 2 described above, and an electric field distribution is generated in the sample accommodated in the sample container 1 by the application of this voltage, and the particles in the sample are generated by the electric field distribution. The group migrates and a diffraction grating is generated by the density distribution of the particle group. The output voltage of the power source 3 is controlled by the control unit 6 as described later.

  In the irradiation optical system 4, monochromatic light such as a laser or LED is used as a light source, and light shaped into a substantially parallel light beam is irradiated into the sample container 1 as probe light.

  The detection optical system 5 is arranged in the direction in which, for example, the first-order diffracted light diffracted by the diffraction grating based on the density distribution of the particle group in the sample container 1 out of the light from the irradiation optical system 4 is emitted. The detection optical system 5 includes, for example, a pinhole 5a and a photodetector 5, and the detection optical system 5 detects the diffracted light intensity by the diffraction grating due to the density distribution of the particle group in the sample container 1 every moment. . The output is amplified by the amplifier 6a, and then digitized and captured by the arithmetic unit 6.

  The control unit 7 applies a specified alternating voltage from the power source 3 to the electrode pair 2 for a preset time to cause the particle group to undergo dielectrophoresis and generate a diffraction grating based on the density distribution of the particle group. The application of is stopped. The calculation unit 6 calculates the diffusion coefficient as described later, using the diffracted light intensity after the time point when the application of the voltage is stopped. Such an operation is repeated by changing the applied voltage to a plurality.

Next, the operation of the embodiment of the present invention having the above configuration will be described.
When an AC voltage is applied between the electrodes 21 and 22 constituting the electrode pair 2, an electric field corresponding to the electrode pattern is formed in the sample container 1, and the density distribution of the particle group is obtained by dielectrophoresis based on the distribution of the electric field. Occurs. That is, in the electrode pair 2 in FIG. 4, the electrode pieces 21 a of one electrode 21 and the electrode piece 22 a of the other electrode 22, as shown in FIG. A high-density region P of particles is formed in a portion adjacent to each other. The high-density region P of the particle group is repeatedly formed in parallel with the electrode pieces 21a and 22a and spatially at a pitch twice the arrangement pitch of the electrode pieces 21a or 22a. A diffraction grating is generated by the high-density region P of the particle group.

  When light from the irradiation optical system 4 is irradiated onto a diffraction grating having such a density distribution of particle groups, the light is diffracted by the diffraction grating. The grating spacing of the diffraction grating due to the density distribution of the particle group is twice the grating spacing of the diffraction grating formed by the electrode pieces 21a and 22a. The diffracted light of a specific order determined by the lattice constant of appears in an orientation where there is no diffracted light by the diffraction grating formed by the electrode pieces 21a and 22a.

  That is, in this embodiment, the [2m + 1] -order diffracted light (m is an integer) formed by the diffraction grating formed by the density distribution of particles is formed in an orientation where there is no diffracted light by the diffraction grating formed by the electrode piece. Is done. Therefore, by arranging the detection optical system 5 in that direction, the diffracted light from the diffraction grating due to the density distribution of the particle group can be measured under a good S / N.

  Now, as shown in the graph of FIG. 5 showing the voltage application to the electrode pair 2 and the intensity change of the diffracted light, when the voltage application to the electrode pair 2 is stopped, the particle group starts to diffuse in the medium, and The diffraction grating due to the density distribution of the collected particles starts to disappear. Since the temporal change of the diffracted light during the annihilation process of this diffraction grating depends on the diffusion speed of the particles, the diffusion coefficient of the group of particles to be measured can be obtained from the temporal change of the diffracted light during the annihilation process. . An example of the arithmetic expression is shown below.

この（１）式において、Ｉ₀ は電圧の印加停止時点の回折光強度で、ｔは電圧の印加停止からの経過時間、Ｉは時間ｔ経過後の回折光強度、Λは粒子群の密度分布による回折格子の格子間隔、Ｄは粒子の拡散係数である。

In this equation (1), I ₀ is the diffracted light intensity when the voltage application is stopped, t is the elapsed time from the voltage application stop, I is the diffracted light intensity after time t, and Λ is the density distribution of the particle group. The grating spacing of D, and D is the diffusion coefficient of the particles.

  When the diffusion coefficient D is obtained in this way, the particle diameter of the particle group can be calculated from the following Einstein-Stokes equation.

（２）式において、ｄは粒子径、ηは粒子群の分散媒である媒液の粘度で、ｋ_B はボルツマン定数であって、Ｔは絶対温度である。

In the formula (2), d is the particle diameter, η is the viscosity of the liquid medium that is the dispersion medium of the particle group, k _B is the Boltzmann constant, and T is the absolute temperature.

  As described above, the particle diffusion coefficient D obtained as described above is affected by the sample temperature. Therefore, in this embodiment, the voltage applied to the electrode pair 2 is differentiated into a plurality of magnitudes, and a diffraction grating based on the density distribution of the particle group is formed as described above under each applied voltage. The temporal change of the diffracted light during the extinction process is measured, and the calculation unit 6 obtains the diffusion coefficient D for each applied voltage. FIG. 6 is a flowchart showing the operation procedure. A plurality of preset voltages V1 to Vn are sequentially applied to the electrode pair 2, and diffracted light intensities after the time point when the application of each voltage is stopped are captured. Then, the diffusion coefficients D1 to Dn are calculated for each applied voltage V1 to Vn, and the diffusion coefficient D ′ corresponding to the applied voltage of 0 V is estimated and calculated from the relationship of the applied voltage Vi−the diffusion coefficient Di.

  FIG. 7 is a graph showing an example of the results, in which the calculation results of the diffusion coefficients D1, D2,... Based on the actual measurement results using the applied voltages V1, V2,. The computing unit 6 further approximates the relationship between the applied voltage Vi and the diffusion coefficient Di by a polynomial or the like, and obtains the diffusion coefficient D ′ at the applied voltage V = 0 from the approximate expression. The diffusion coefficient D ′ obtained in this way is an estimated value of the diffusion coefficient that does not include the influence of the temperature rise due to Joule heat.

  If the temperature of the sample sealed in the sample container 1 is the same as the ambient temperature, the diffusion coefficient D ′ obtained as described above can be regarded as a diffusion coefficient under the ambient temperature. Therefore, when the particle size is calculated by the calculation unit 6 using the diffusion coefficient D ′ and the parameter in the Einstein-Stokes equation represented by the equation (2) is obtained from the ambient temperature, the obtained particle size is Accurate particle size not affected by Joule heat.

  Here, in the above embodiment, an example in which an alternating voltage is applied to the electrode pair to cause dielectrophoresis in the particle group to form a diffraction grating based on the density distribution has been shown. In some cases, a diffraction grating having a density distribution may be formed by applying a DC voltage to the electrode pair to cause electrophoresis.

  Further, the pattern of the electrode pair 2 is not limited to the above example, and of course, any pattern can be used as long as it can form an electric field having a spatial period in the sample.

In the block diagram of embodiment of this invention, it is the figure which writes together and shows the schematic diagram showing an optical structure, and the block diagram showing an electric structure. FIG. 2 is a diagram illustrating a perspective view of a specific example of a sample container 1 in FIG. 1 and a circuit diagram for applying a voltage to an electrode pair 2. It is a typical partial enlarged view of the sample container 1 in FIG. It is explanatory drawing of the example of a pattern of the electrode pair 2 provided in the sample container 1 of embodiment of this invention. FIG. 2 is a diagram illustrating an applied voltage waveform to an electrode pair 2 in the embodiment of FIG. 1 and a graft representing a temporal change in diffracted light intensity. It is a flowchart showing the measurement operation | movement in embodiment of this invention. Graph for explaining a method for obtaining a diffusion coefficient D ′ corresponding to an applied voltage of 0 V from values of diffusion coefficients obtained from measured values of diffracted light changes after application of a plurality of voltages obtained in the embodiment of the present invention. It is.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sample container 2 Electrode pair 21, 22 Electrode 21a, 22a Electrode piece 3 Power supply 4 Irradiation optical system 5 Detection optical system 6 Calculation part 7 Control part

Claims (2)

By applying a voltage to an electrode having a predetermined pattern to form an electric field having a spatial period in a sample in which a group of particles to be measured is movably dispersed in a medium, the particle group is spatially periodic. A pseudo diffraction grating is generated with a concentration change, and the diffracted light obtained by irradiating light to the particle group in that state is detected, and the time change of the diffracted light from the point when the formation of the electric field is stopped In the method of calculating the particle coefficient of the particle group from the diffusion coefficient, to determine the particle coefficient of the particle group from
While obtaining the diffusion coefficient by changing the voltage applied to the electrode to a plurality of values, the diffusion coefficient corresponding to the applied voltage of 0 V is obtained by extrapolation using the relationship between each voltage and the diffusion coefficient, and the obtained diffusion coefficient is obtained. A method for measuring nanoparticles, wherein the particle size of the particle group is calculated using a particle.   A container for holding a sample in which a group of particles to be measured are movably dispersed in a medium, an electrode for forming an electric field having a spatial period in the container, and a power source for applying a selectable voltage to the electrode A laser light source for irradiating the sample in the container with light, a detection optical system for detecting diffracted light generated by the light passing through the sample, and the above-mentioned after the time when the application of voltage to the electrode is stopped Data processing means for performing data processing using the output of the detection optical system, and control means for controlling the measurement operation. The control means changes the voltage applied to the electrode into a plurality of voltages, and the data processing means. After obtaining a diffusion coefficient based on each applied voltage, a diffusion coefficient corresponding to the applied voltage 0V is obtained by extrapolation from the relationship between each applied voltage and the diffusion coefficient, and the diffusion coefficient at the applied voltage 0V is used. Measuring device of nanoparticles and calculates the particle size of the particles to be measured.

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