1. Field of the Invention
The present invention relates to a solution stirring or transfer method for stirring or transferring a solution by Lorentz force generated by the interaction between an electric current generated through electrochemical reaction and a magnetic field. The present invention also relates to a treatment apparatus for efficiently performing at least one of the detection of a biologically relevant substance and the transfer of a solution using this stirring or transfer.
2. Description of the Related Art
In recent years, significantly evolving life science has required processing an enormous amount of information typified by genomes with a high throughput at a high speed. Against this backdrop, DNA or protein analysis techniques using micromachined DNA or protein chips have been established.
In this context, to hybridize target DNAs to probe DNAs in a DNA chip, a trace amount of a sample containing targets is added dropwise to an array of the DNA chip. Similarly, to immune-react target antigens with antibody probes in a protein chip, a sample is added dropwise to an array of the protein chip. Then, sufficient hybridization or antigen-antibody reaction must occur in the DNA or protein chip. Thus, the acquirement of reliable hybridization or immune reaction results requires lengthening a hybridization or antigen-antibody reaction time or promoting hybridization or immune reaction.
Examples of general approaches for promoting chemical reaction include the following two approaches: (1) an approach by which a reaction rate is improved; and (2) an approach by which the collision frequency of a substrate involved in reaction is improved.
Examples of specific methods for conducting these two approaches include the following methods: (1) a rise in reaction temperature and the addition of a catalyst; and (2) improvement in reaction temperature, an increase in substrate concentration and improvement in stirring strength.
In this context, the possible methods for promoting the general chemical reaction might be applied to hybridization or immune reaction. In such a case, the rise in reaction temperature incurs DNA dissociation in hybridization. Alternatively, this rise in reaction temperature incurs protein denaturation in immune reaction. Thus, this method did not simply serve as a reaction promotion unit. The same holds true for the other methods such as the addition of a catalyst and an increase in substrate concentration.
Thus, a promising method as a reaction promotion unit is the stirring or transfer of a solution. However, the DNA or protein chip is constructed in the form of a microcontainer array. Therefore, it was impossible to directly apply thereto a conventional stirring or transfer method using a stirrer or stirring blade. Thus, Patent Document 1 discloses a method for stirring a reaction solution in this microcontainer. Specifically, Patent Document 1 discloses a method comprising applying a magnetic field from outside to magnetic beads contained in a reaction solution.
For DNA or protein analysis, it has heretofore been demanded to establish a technique for stably transferring a solution in a very small area. Furthermore, the utilization of a microchannel in DNA or protein chips has been studied actively for the purpose of achieving a decrease in sample amount, reduction in treatment time and a high throughput. Thus, Patent Document 2 discloses a method for transferring a fluid in a capillary channel.
On the other hand, electrochemical reaction in a magnetic field generally generates Lorentz force by the interaction between an electrolytic current generated through the electrochemical reaction and the magnetic field. This Lorentz force causes a solution flow. Effects produced by this Lorentz force are called MHD (MagnetoHydroDynamic) effects and have been studied in various ways in recent years. In electrochemical reaction, this flow increases or decreases substrate supply to electrode surface. As a result, changes in electric current value are observed. For example, Katz et al. have reported the enhanced properties of biofuel cells utilizing MHD effects (Non-Patent Document 1).    (Patent Document 1) Japanese Patent Application Laid-Open No. 2003-248008    (Patent Document 2) Japanese Patent Application Laid-Open No. 2002-371954    (Non-Patent Document 1) J. Am. Chem. Soc. 2005, 127, p. 3979-3988
Patent Document 1 discloses a method for stirring a reaction solution using magnetic beads contained in the reaction solution, as described above. These magnetic beads allow the reaction solution to flow by a magnetic field changed from outside so as to stir the reaction solution. However, this stirring using the magnetic beads causes the aggregation of the magnetic beads or causes the uneven distribution of the magnetic beads depending on a container shape, an application pattern of the magnetic field and the dynamic properties of the magnetic beads. Therefore, it was difficult to perform effective and stable stirring.
Patent Document 2 discloses a method comprising introducing a magnetic fluid to a capillary channel so as to allow the magnetic fluid to occupy the whole cross section of the channel in the partial region of the channel, and transferring, in this state, the fluid in this channel by magnetism imparted from outside. However, for the construction disclosed in Patent Document 2, it was difficult to transfer the magnetic fluid stably and efficiently in the state that allows the magnetic fluid to occupy the whole cross section of the channel. It was also difficult to continue, in a solution, the stable dispersion of a ferromagnetic solid used as a magnetic fluid.
Thus, in the previous techniques, magnetic substances dispersed in a solution are controlled for stirring or transfer by the control of outside magnetic force. Therefore, a great challenge for the techniques was to maintain the dispersion stability of the magnetic substances. In this context, the present inventor has found that such dispersion stability does not have to be considered if substances for causing the solution flow are already dissolved in the solution.