Electroosmosis pump and liquid feeding device

The present invention relates to an electroosmotic pump (electroosmosis pump) suitable for use in controlling movement of a liquid in a microfluid chip for use in biotechnology, analytical chemistry, or the like, or for controlling movement of a fluid in a mobile electronic device, as well as to a liquid feeding device incorporating such an electroosmotic pump therein.

Electroosmotic pumps are pumps for transporting a fluid based on an electroosmotic phenomenon, and are used as fluid moving means in capillaries and microfluid chips, for example.

Based on the fact that an electroosmotic phenomenon manifests itself within a very narrow fluid passage having a width of several hundreds [μm] or less, the capillary diameter is set to several hundreds [μm] or less, or the width of the fluid passage within a microfluid chip is set to several tens [μm], for example, and two electrodes (positive and negative electrodes) are disposed in the capillary or the fluid passage, thereby turning the capillary or the fluid passage into a pump.

FIG. 38 shows an electroosmotic pump 200 including reservoirs 202, 204, each containing an electrolytic solution, which are connected to each other by a capillary 206 filled with the electrolytic solution. When a DC power supply 208 applies a DC voltage between electrodes 210, 212 disposed respectively in the reservoirs 202, 204, the electrolytic solution is transported from the reservoir 202 to the reservoir 204 through the capillary 206.

The electroosmotic pump 200 is advantageous in that (1) the electroosmostic pump can flow electrolytic solution without pulsations, (2) the electroosmotic pump 200 is easy to use since the electrolytic solution can be displaced simply by inserting the electrodes 210, 212 into the reservoirs 202, 204 and applying a DC voltage therebetween, and (3) the electroosmotic pump 200 has no mechanically movable parts and is simple in structure. Therefore, use of the electroosmotic pump in macroscopic applications of about several [mm], which are constructed of only narrow fluid passages, has been considered.

FIG. 39 shows an electroosmotic pump 214, which is a smaller version of the electroosmotic pump 200 (see FIG. 38). The electroosmotic pump 214 comprises an electroosmotic member 220 of an electroosmotic material (hereinafter referred to as an EO material) disposed in a fluid passage 218 defined in a pump case 216, and electrodes 222, 224 disposed on upstream and downstream sides, respectively, of the electroosmotic member 220 and having a plurality of pores defined therein along the direction of the fluid passage. The electrodes are not limited to the illustrated structure, but may also be in the form of wires.

If porous material or a filled structure of minute particles or fibers, or the like, which exhibit electroosmosis, are used as the EO material, then it is possible to transport an electrolytic solution at a flow rate within a range of from [μL/min] to [mL/min] or higher without the need for a capillary 206 (see FIG. 38) and/or a fluid passage within the microfluid chip (see non-patent Documents 1 through 3).

Concerning the DC voltage applied to the electrodes 210, 212, 222, 224 from the DC power supply 208, while the electroosmotic pump 200 (see FIG. 38) needs to have a DC voltage of several tens [kV], the electroosmotic pump 214 allows the electrolytic solution to be moved under a DC voltage of only about several [V].

If the electrolytic solution can be transported under a low voltage at a large flow rate under a desired drive pressure, then electroosmotic pumps are free of the limitations imposed by using the small-diameter capillary 206 and the fluid passage in the microfluid chip, and hence the electroosmotic pump 214 can be used in an increased range of applications.

FIG. 40 shows an electroosmotic pump 230 devised by the present applicant. The electroosmotic pump 230 includes a reservoir 232 disposed in an upper portion thereof and containing an electrolytic solution. The electroosmotic pump 230 has a lower portion connected to a fluid passage 236 of a microfluid chip 234. When a DC voltage in the range from several [V] to 30 [V] is applied between electrodes 222, 224, the electrolytic solution is supplied from the reservoir 232 to the fluid passage 236, at a maximum rate of about several tens [μL/min] and under a maximum pressure of 100 [kPa] or higher.

Non-patent Document 1: U.S. Published Application No. 2003/0068229

Non-patent Document 2: U.S. Pat. No. 3,923,426

Non-patent Document 3: U.S. Published Application No. 2004/0234378

Since electroosmosis is an electrochemical phenomenon, when the DC voltage is applied between the electrodes 222, 224 by the DC power supply 208, gas is produced in the vicinity of the electrodes 222, 224. Any gas which has not been dissolved into the electrolytic solution floats as bubbles in the electrolytic solution, wherein such floating bubbles tend to cause the flow within the fluid passage 236 to become unstable, thus causing an operational failure of the electroosmotic pump 214, and greatly affecting various measurements, such as chemical reactions and chemical analyses that take place downstream from the fluid passage 236.

More specifically, the electroosmotic pump 214 is generally a system wherein ionic electrical conduction in the electrolytic solution and electronic conduction at the electrodes 222, 224 exist together. At the electrodes 222, 224, a gas is produced upon charge exchange therebetween.

For example, in FIG. 39, if the drive liquid is an aqueous solution, wherein the zeta potential of the electroosmotic member 220 has a negative potential, the upstream electrode 222 is a positive electrode, and the downstream electrode 224 is a negative electrode, then when a DC voltage is applied between the electrodes 222, 224 by the DC power supply 208, an electrochemical reaction brings about the following reaction in the vicinity of the electrodes 222, 224:

2H₂O→2H₂+O₂  (1)

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