JP2006007120A - Method and device for transporting droplet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make it possible to transport a droplet in an electrode system which can be manufactured by means of a simple single wiring. <P>SOLUTION: A pair of comb-line electrodes 2 are patterned such that one side becomes +45° and another side becomes -45° with respect to the center line X on a flat substrate 1, and are coated with an insulating layer 3 and, further, surface hydrophobic treatment 4 is applied thereon. In the initial state, the droplet has a shape 6 approximate to a sphere. When an alternate voltage is applied to the droplet, an inductive charge is generated on the surface of the droplet and is interacted with an applied electric field and, as a result, the droplet is deformed and is moved to the right side. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a field of performing a small amount of transfer operation on the order of several microliters to nanoliters on a substrate, such as a microchemical analysis apparatus and a microchemical synthesis apparatus.

  The technique for manipulating micro liquids on the chip is an important technique used for mixing micro liquids and transporting the liquid as a sample to the target analytical apparatus, particularly in micro chemical analysis systems and micro chemical synthesis devices. .

  As a conventional liquid manipulation technique on a chip, there is a technique in which a closed flow path is formed and liquid is driven using pressurization or electroosmotic flow. However, this method has disadvantages such that an open system cannot be operated, it is difficult to move only a part of the fluid in the continuous flow path, and a dead volume cannot be avoided.

  Therefore, as a solution to such a problem, there is a technology that does not completely cover the flow path, that is, a technique that handles the liquid as a droplet in a semi-open system. For this method, a voltage is applied to the strip electrode on the substrate to create a movement along the electrode by the dielectrophoretic force acting on the liquid, thereby developing a means to drive and drop the liquid and mix it. (See Non-Patent Document 1). However, this method has a problem that when the conductivity of the sample is increased, heat generation is increased and driving becomes difficult.

In addition, a method of moving a droplet to an arbitrary position on an XY plane by sequentially applying a voltage to an electrode array formed in a tile shape using electrowetting (see Non-Patent Document 2). ) And a method of moving the liquid droplets so as to roll by arranging a multiphase electrode having a hydrophobic surface on the substrate and sequentially applying a voltage on the surface (see Non-Patent Document 3). Has been developed. However, these methods have a problem that the electrical connection becomes complicated and it is necessary to use a multilayer wiring technique.
TB Jones, M. Gunji, M. Washizu and MJ Feldman: "Dielectrophoretic liquid actuation and nanodroplet formation", JAP, Vol. 89, No.2, p.1441-1448 (2001) J. Lee, H. Moon, J. Fowler, T. Schoellhammer and C.-J. Kim, "Electrowetting on Dielectric for Microscale Liquid Handling," Sensors and Actuators A, 2002, vol. 95, pp. 259-268. Masao Washizu: "Electrostatic Actuation of Liquid Droplets for Micro-Reactor Applications", IEEE Transaction IA, Vol.34, No.4, p.732-737 (1998)

  An object of the present invention is to provide a method and an apparatus for transporting droplets in an electrode system that can be manufactured with a simple single-layer wiring.

  The present invention relates to a droplet transport apparatus in which a patterned transport electrode is formed on a substrate, the transport electrode is covered with an insulating film, and a droplet is transported on the insulating film, and the transport electrode Consists of a pair of electrodes arranged on both sides along the droplet traveling direction with a smaller interval than the droplet, each electrode having an angle smaller than 90 degrees with respect to the droplet traveling direction and smaller than the droplet The present invention relates to a droplet transport device having conductor patterns arranged parallel to each other at an interval, wherein an alternating voltage is applied to the transport electrode.

A large number of electrodes are arranged on the substrate such that one is + θ ₁ and the other is −θ ₂ with respect to the traveling direction from the center line of the direction in which the droplet is to be transported. The electrode is placed near the center line of one end. Here, θ ₁ and θ ₂ may be equal or different. When an AC voltage is applied to the electrodes, the droplets are flattened by an electric force in the vicinity of the peak of the AC voltage, and vibration is generated such that the deformation is released near the moment when the voltage becomes zero. In the cycle in which flattening occurs, deformation beyond the electrode shape is less likely to occur due to the electric field concentration created by the edge of the electrode, whereas in the released cycle, the shape returns to a nearly spherical shape. Since the electrode shape is asymmetric with respect to the front and rear in the traveling direction, the droplet moves in a direction in which it easily moves each time a deformation cycle occurs. That is, the inch worm mechanism causes the droplets to be transported in one direction.

The transport electrode is preferably arranged at an angle of 10 degrees to 80 degrees with respect to the droplet traveling direction.
The preferred shape of such an electrode is a comb-like electrode.
The insulating film preferably has a thickness of 0.1 μm to 100 μm.
It is preferable that the apparatus is a droplet transport device in which the surface on the substrate side that comes into contact with the liquid forming the droplet is subjected to a hydrophobic treatment.
By arranging two or more transport electrode rows so as to gather at one point in the traveling direction, and gathering a plurality of droplets at the gathering point, a droplet transport device that mixes the droplets is provided. it can.
The transport method of the present invention is a method in which the droplet transport device described above is used, deformation deformation is caused in the droplet by application of the AC voltage, and the droplet is moved by the vibration.
It is preferable that the droplet transport device is selected so that the frequency of the applied voltage resonates with the natural frequency of the droplet particles.

  Since the device of the present invention includes a pair of electrodes, it can be manufactured by a simple single-layer process. Therefore, it is possible to manufacture and operate with high reliability and low cost, so that the chip itself can be made disposable. In addition, the power supply system for driving can be simplified and the cost can be reduced.

By making the electrodes comb-like, the connection to the power supply device can be simplified, and the configuration can be simplified.
By applying a hydrophobic treatment to the surface of the substrate in contact with the droplet, the droplet can be made more spherical in the vicinity of the alternating voltage 0, and the shape between the flat shape near the peak of the alternating voltage The amount of deformation can be increased, and the amount of droplet movement can be increased.
By selecting the frequency of the applied voltage so as to resonate with the natural frequency of the droplet particles, the amount of droplet movement can be further increased.

An embodiment of the present invention will be described in detail.
As shown in FIG. 1, a pair of comb-like electrodes 2 a and 2 b are formed on a glass substrate 1 which is a flat substrate so that one is +45 degrees and the other is −45 degrees with respect to the center line in the traveling direction X. It is formed as a pattern and is arranged so that the detection parts face each other. The electrodes 2a and 2b are coated with an insulating layer 3 thereon. A surface hydrophobic treatment layer 4 is provided on the insulating layer 3. The comb-like electrode 2 is connected to a power source 5.
An SiO ₂ film is used as the insulating layer 3, an amorphous Teflon (registered trademark) spin coat film is used as the hydrophobic treatment layer 4, and a power source 5 of 170 V at a frequency of 50 Hz is used as the power source.
The electrode 2 can be formed by forming a conductive film such as copper or aluminum on the substrate 1 and patterning it by photolithography and etching.

  The present invention is not limited to the above-described insulating layer, processing method, and the like, and in addition to the linear comb-shaped electrode having an angle of 45 degrees as an electrode shape, linear comb teeth other than 45 degrees such as 30 degrees and 60 degrees. Any electrode that can cause vibration with a center of gravity movement in a certain direction when an AC voltage is applied between the electrodes, such as a ring-shaped electrode, a curved comb-shaped electrode, or a spiral electrode Can be used.

In FIG. 1, when a droplet 6 is disposed so as to straddle two electrodes 2a and 2b at one end of electrodes 2a and 2b, and the electrodes 2a and 2b are excited by a power source 5, the droplet is generated by an electric force near the peak of the AC voltage. In the vicinity of the moment when 6 becomes flat and the voltage becomes zero, a vibration is generated so that the deformation is released.
Here, in the cycle in which flattening occurs, deformation beyond the comb teeth is unlikely to occur due to the electric field concentration created by the edges of the comb-like electrodes 2a and 2b, whereas in the cycle in which flattening is released, it is isotropic. Return to a shape close to a sphere. As a result, the droplet moves in the droplet traveling direction X on the right side shown in FIG.

FIG. 2 illustrates the mechanism of droplet movement in more detail. As shown in FIG. 2a), in the initial state where no deformation of the droplet occurs, the droplet takes a shape 7 that is almost spherical due to the hydrophobic surface treatment.
When an alternating voltage of frequency f is applied, if the dielectric constant or conductivity of the droplet is different from the dielectric constant or conductivity of the surrounding medium, an induced charge is generated on the surface of the droplet, and the applied electric field interacts therewith. As a result, an electric force having a frequency of 2f acts on the droplet, and the droplet is deformed.

  FIG. 2b) schematically shows a state in which the deformation is maximized. The electric lines of force 8 cause the droplets 9 to be deformed 9 such that they are attracted to the substrate and become flat. At this time, in the portion 10 where the edge of the comb-like electrode provided obliquely and the surface of the droplet come into contact with each other in parallel, the strong electrolysis at the edge attracts the droplet, so that the liquid moves beyond this edge. It becomes difficult to do. For this reason, the portion 10 is deformed so that the surface of the droplet is parallel to the electrode edge, whereas the portion 11 where the electrode edge and the surface of the droplet are orthogonal is not such a restriction and spreads along the electrode. Deform.

  As shown in FIG. 2 b), the deformation of the droplet becomes asymmetrical in the upper right and lower right in the figure, and the center of gravity shifts to the right in the figure than before the deformation. Since the electric force changes between 0 and the peak value at the frequency 2f, the deformation is released after a half period of the applied frequency as shown in FIG. 2c). The spheroidizing 13 is performed with the center of gravity at the time of deformation as the center. Accordingly, each time one cycle of deformation is reduced, the droplet moves by a distance of 14 in the right direction in the figure.

The movement distance by this mechanism is determined by (movement distance per step) × (number of deformation cycles), and the movement distance per step depends on the size of the deformation and is an integral multiple of the electrode pitch. If the deformation is small, no movement occurs, but if the deformation is large, it is possible to move one or more electrode pitches. In order to make this deformation large, it is effective to select an applied frequency so as to resonate with the natural vibration of the droplet, that is, select so that (power supply frequency) = (natural frequency of the droplet) / 2. is there.
Here, the natural frequency of the liquid droplet is a natural frequency of free vibration of deformation of the liquid surface caused by the surface tension and mass of the liquid constituting the liquid droplet. A water droplet having a diameter of 1 mm isolated in the space. For a mode that repeats flattening and lengthening, the natural frequency is about 340 Hz.

  The present invention can be used for microchemical analysis, microchemical synthesis apparatus, and the like.

It is a figure which shows one Example of this invention, (A) is a top view, (B) is sectional drawing in the A-A 'line position. (A)-(c) is operation | movement explanatory drawing of the Example, all are a top view in the left figure, and a right figure is sectional drawing in the droplet position.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Electrode 3 Insulating layer 4 Surface hydrophobic treatment 5 Power supply 6 Droplet 7 Droplet initial position and shape 8 Electric field lines 9 Droplet deformed by electric field application 10 Electrode edge and contact area of drop surface 11 Electrode edge Droplet shape at the time of deformation in the part 12 b) where the surface of the liquid droplet intersects at right angle 13 Droplet position when the deformation is restored 14 Droplet moving distance in one cycle

Claims (8)

A patterned transport electrode is formed on the substrate, and the transport electrode is covered with an insulating film,
A droplet transport device for transporting droplets on the insulating film,
The transport electrode comprises a pair of electrodes arranged on both sides with a smaller interval than the droplet along the droplet traveling direction,
Each electrode has an angle smaller than 90 degrees with respect to the droplet traveling direction, and has conductor patterns arranged in parallel to each other at an interval smaller than the droplet,
An apparatus for transporting droplets, wherein an alternating voltage is applied to the transport electrode.   The droplet transport device according to claim 1, wherein the transport electrode is a comb-like electrode.   The droplet transport device according to claim 1 or 2, wherein the transport electrode is installed at an angle of 10 degrees to 80 degrees with respect to a droplet traveling direction.   The droplet transport device according to claim 1, wherein the insulating film has a thickness of 0.1 μm to 100 μm.   The droplet transport device according to claim 1, wherein a hydrophobic treatment is applied to a surface on a substrate side that comes into contact with a liquid forming the droplet.   6. The liquid droplet mixing is performed by arranging two or more transport electrode arrays so as to gather at one point in the traveling direction and collecting a plurality of liquid droplets at the gathering point. The droplet transport device described.   A droplet transport method using the droplet transport device according to claim 1, causing deformation vibration to the droplet by application of the alternating voltage, and moving the droplet by the vibration. The droplet transport device according to claim 1, wherein the frequency of the applied voltage is selected so as to resonate with the natural frequency of the droplet particle.

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