JPS6333661B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to an electrophoresis measuring device.

When measuring the electrophoretic movement speed, that is, the mobility of visible particles by applying an electric field to a liquid in which visible particles are suspended, the following problems arise. One of them is the convection of liquid due to the generation of Joule heat.
The other is electroosmotic flow, which will be described later.

When a solution in which visible particles are suspended contains an electrolyte and is conductive, when an electric field is applied to the solution to cause the visible particles to undergo electrophoresis, a current flows and Joule heat is generated. Therefore, the liquid temperature is different between the center of the electrophoresis cell and near the surface, and convection is formed. Since suspended particles perform electrophoresis while flowing along with this convection, the movement of suspended particles is confused, making it difficult to extract and measure purely the movement due to electrophoresis. This convection due to Joule heat will be reduced if the temperature difference between the center of the solution and near the surface is small, so to avoid the effect of convection, the cell is made into a thin tube shape and an electric field is applied in the direction of the tube axis. . However, if this is done, the influence of the electroosmotic flow becomes noticeable.

Electroosmotic flow is the following phenomenon.
When two types of dielectric materials come into contact, the side with a larger dielectric constant becomes positively charged and the side with a smaller dielectric constant becomes negatively charged at the contact surface. Since the electrophoresis cell is glass and the solution is usually water, water has a higher dielectric constant, and at the contact surface between the cell and the solution, the solution side is positively charged and the cell side is negatively charged. The positive charge on the solution side is due to hydrogen ions collecting at the contact surface with the cell. 1 in Figure 1
is an electrophoresis cell, and 2 and 3 are electrodes. electrode 2,
When a voltage is applied between 3, the hydrogen ions gathered near the contact surface of the solution in the cell with the cell are drawn toward the negative electrode 2, and as a result, the region of the solution in contact with the inner surface of the cell moves toward the negative electrode 2. Flow. Since the cell 1 is a closed tube and the amount of solution penetrating any cross section of the tube must be zero, as the surface layer of the solution flows toward the electrode 2, the center of the solution flows towards the electrode 3 and horizontal convection occurs within the cell. This is an electroosmotic flow, and when the cell is elongated to reduce convection due to Joule heat, the electroosmotic flow becomes more pronounced. The electrophoresis of suspended particles and the electroosmotic flow are in the same direction, and suspended particles perform electrophoresis while flowing along with the electroosmotic flow, so simply measuring the moving speed of the particles does not indicate their true mobility. Not asked for. Conventionally, therefore, a method has been adopted in which an optical device is focused on a layer in which electroosmotic flow is 0 within a cell, and only suspended particles in that layer are optically selected and their moving speeds are measured. Since the direction of the electroosmotic flow is opposite between the surface and the center of the solution, a layer exists where the flow velocity of the osmotic flow is 0. However, with this method, it is difficult to improve the accuracy of mobility measurement because the number of particles observed is small.

The present invention aims to provide a cell for electrophoresis measurement in which convection and electroosmotic flow due to the generation of Joule heat described above are small and the effects thereof can be ignored.

The present invention provides an electrophoresis measurement cell in which plate-shaped electrodes whose width in the narrowest direction within a container is larger than the facing interval are arranged to face each other in parallel. Here, the width in the narrowest direction is the diameter for a disk, the short axis for an elliptical plate, and the length of the short side for a rectangle. This also includes cases where it is familiar. The present invention will be explained below with reference to Examples.

FIG. 3 shows an embodiment of the invention. Reference numeral 4 denotes a rectangular parallelepiped container, and disc-shaped electrodes 2 and 3 are arranged in the container 4 so as to face each other in parallel. The distance d between the electrodes is approximately 1/2 of the diameter D of the electrodes 2 and 3. electrode 2,
Through holes 5 and 6 are bored at the center of the container 3, and a beam L of laser light is guided from the outside of the container 4 through the through holes 5 and 6. The container 4 is filled with a solution, and the electrodes 2,
A sample is injected between electrodes 2 and 3, a voltage is applied between electrodes 2 and 3, and the particles illuminated by the laser beam are transferred to electrodes 2 and 3.
Optical observation is made from a direction perpendicular to the laser beam between 3 and 3.

FIG. 4 is a plan view of the above-mentioned embodiment, and electric lines of force as shown by arrows are generated between the electrodes 2 and 3. In other words, the electric field is approximately uniform between the electrodes 2 and 3 facing each other, rapidly weakens outside the periphery of the electrodes, and becomes weaker outside the periphery of the electrodes 2 and 3.
The electric field strength along the inner wall of the container is extremely low, and therefore the electroosmotic flow generated is extremely weak. Since the cross-sectional area of the flow in the direction is wide, the electroosmotic flow in the space between the electrodes 2 and 3 can be considered to be practically zero. Considering the convection caused by the generation of Joule heat in this structure, the container 4
accommodates a wide electrode, and considering its width, electrode 2,
Since the distance between 3 is small, the container 4 has a flat shape, and the surface area is large compared to the meat volume, so cooling is effective, and the temperature difference in the solution in the container 4 depending on the location is small, so convection is weak. .

When the electrodes 2 and 3 are made concave so that the counterflow flows as shown in Fig. 5, the lines of electric force become as shown by the arrows.
Concentrates near the center of electrodes 2 and 3. Since there are through holes 5 and 6 at the center of the electrodes 2 and 3 through which the laser beam passes, in the case of flat plate electrodes, the electric field becomes weaker on the line connecting the through holes 5 and 6, but if the electrodes 2 and 3 are made concave, Since the electric lines of force are concentrated in the vicinity of the line connecting the centers of the electrodes 2 and 3, a decrease in the electric field strength in the vicinity due to the opening of the through holes 5 and 6 is prevented.

FIG. 6 shows an embodiment in which the present invention is applied to a flow cell. A flow cell is a measurement container that allows floating particles to be observed while flowing a sample suspension. In this case, the direction of the flow of the solution in the flow cell must be perpendicular to the direction of electrophoresis of the suspended particles so that the speed of this flow is not observed to be superimposed on the electrophoresis speed of the particles. The water flows into the cell from the bottom of the container 4 and flows out from the top. FIG. 7 is an exploded perspective view of the cell of the embodiment shown in FIG. 2 and 3 are disc-shaped electrodes with through holes 5 and 6 in the center for passing the laser beam, 7 and 8 are glass discs that form the container wall behind the electrode plates 2 and 3, and 9 is an electrode. A sample solution inlet _Io and an outlet Ex are formed by a glass cylinder which serves as a spacer between the two and a side wall of the container. The above-mentioned parts are housed in a mantle tube 11, and a cap 12 is screwed onto the mantle tube 11 to form a sealed container that is pressed against each other. 13 is glass disks 7, 8 and electrode plate 2,
3 and between the electrodes 2, 3 and the glass disk 9. The mantle tube 11 has a window 1 on the side for observing suspended particles.
4 is worn.

FIG. 8 shows an electrophoresis measurement cell of the present invention in which electrophoresis of suspended particles is observed using a heterodyne Doppler optical system. This is structurally the same as the embodiment shown in FIG. In this embodiment, two pinholes 5, 6 and 5', 6' are bored in the electrode plates 2, 3, respectively. The line connecting the pinholes 5 and 6 and the line connecting the pinholes 5' and 6' intersect exactly at the center between the electrode plates 2 and 3. The sample liquid is irradiated with a laser beam l through pinholes 5 and 6. A light receiving element P is placed in the direction in which the pinholes 5' and 6' are arranged to receive the light scattered by the floating particles of the laser beam. Further, the second laser beam l' is made incident on the light receiving element P through the pinholes 5' and 6'. The second laser beam l' is attenuated by an attenuator An to the extent that the laser beam l is scattered by floating particles. Since the electrophoretic movement direction of the suspended particles makes only a small angle with the laser beam l, the wavelength of the scattered light of the laser beam l by the suspended particles is very small depending on the moving speed of the suspended particles. The wavelength is different from that of Since the laser beams l and l' are coherent with each other, when the scattered light in the same direction as l' interferes with the light of the beam l', the wavelength of the scattered light is slightly shifted, causing a beat, and the light receiving element P The output fluctuates periodically. Since there are a large number of floating particles, the output of the light-receiving element P fluctuates irregularly due to the superimposition of alternating currents with various periods and phases. By frequency-analyzing this output, the mobility distribution of suspended particles can be determined.

The electrophoresis measurement cell of the present invention has the above-described structure, and the electrodes with a wide area are opposed to each other in parallel at intervals narrower than the minimum width of the electrodes, so that the cell wall near the electrode periphery is Even if electroosmotic flow occurs in the contacting solution layer, the cross-sectional area of the solution between the electrodes is much larger than the total cross-sectional area of that layer, so the flow velocity of the electroosmotic flow in the opposite direction between the electrodes is almost negligible. In addition, since the container is flat, the cooling effect is large, and the difference in solution temperature in each part of the container is small.The electrode area is large and the distance between the electrodes is small, so the applied voltage can be low, and the generation of Joule heat itself is reduced. Therefore, convection is weak and can be ignored. Since the electroosmotic flow can be ignored, the number of particles that can be observed increases and the accuracy of mobility measurement can be improved compared to the conventional method in which suspended particles were observed only in a layer with zero electroosmotic flow.

In each of the above-mentioned embodiments, the electrodes 2 and 3 have a circular peripheral shape, but it goes without saying that they may also be square or rectangular.

[Brief explanation of the drawing]

Figure 1 is a side view of a conventional electrophoresis measurement cell.
FIG. 2 is a side view of a model of the above cell, FIG. 3 is a perspective view of one embodiment of the present invention, FIG. 4 is a plan view of the same embodiment, and FIG. 5 is a diagram of another embodiment of the present invention. Side view,
FIG. 6 is a longitudinal sectional side view of still another embodiment of the present invention;
FIG. 7 is an exploded perspective view of the same embodiment, and FIG. 8 is a plan view of a cell according to an embodiment of the present invention in which mobility is measured by a heterodyne Doppler optical system. 2, 3... Electrode, 4... Container, 5, 6... Through hole through which the laser beam passes.

Claims (1)

[Claims] 1 A pair of planar electrodes having a wide area and facing each other in parallel with an interval narrower than the minimum width or having a concave surface on the opposite side is housed in a flat container, and An electrophoresis measurement device characterized in that an illumination light beam is transmitted so as to pass through both opposing electrodes near the center, and suspended particles in a region illuminated by the light beam between the two electrodes is observed.