Abstract:
A chemical analysis apparatus is equipped with analysis sections having openings, means for supplying samples or reagents from the openings, means for combining and mixing samples with reagents to obtain droplets as liquids to be measured, and means for measuring the physical properties of the liquids to be measured during reaction or after completion of reaction. Furthermore, plate members are provided facing each other in analysis sections and a plurality of electrodes are provided on the plate member faces that face each other. Voltage is applied from the plurality of electrodes to the droplets of the samples and the reagents.

Description:
[0001]     The present application claims priority from Japanese application JP2004-237479 filed on Aug. 17, 2004, the content of which is hereby incorporated by reference into this application.  
       BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to a chemical analysis apparatus appropriate for analyzing small quantities of substances contained in vivo.  
         [0003]     The specification of U.S. Pat. No. 6,565,727 discloses a method by which: a plate member having rows of a plurality of electrodes that are insulated from each other is provided facing a single common electrode plate; and droplets of small volume in a filling liquid that fills the gap between 2 plates are transported along the electrode rows by consecutively applying voltage to the electrode rows so as to generate attraction between the electrode faces and droplets.  
         [0004]     The following problems exist concerning the application of the technology disclosed in the specification of U.S. Pat. No. 6,565,727 to a chemical analysis apparatus for analyzing small quantities of substances contained in vivo.  
         [0005]     First, the range of small volumes of liquids (liquids for analysis such as samples and reagents) is determined based on the gap between 2 plate members and electrode size at the time of composing electrode rows, so that it is difficult to handle wide-ranging liquid volumes of liquids for analysis.  
         [0006]     Second, each liquid for analysis has a different specific gravity. Thus, depending on the size of the specific gravity of a liquid for analysis compared with the filling liquid, the location of a droplet is biased towards either one of the electrode plates. Attraction between electrode faces and droplets is obtained by a change in hydrophilicity and/or water-repellency of liquids. Hydrophilicity and/or water-repellency of electrodes on either one of the plates alone can be controlled. Thus, handling thereof may be difficult.  
         [0007]     Third, to dispense a liquid that is temporarily retained in a reservoir for a liquid for analysis, a droplet is separated and formed from the liquid in the reservoir. States of liquid separation differ depending on the physical properties of various liquids, so that droplets vary in liquid volume to greater extent. Thus, there is a concern in this case that dispensing accuracy may be lowered.  
         [0008]     Fourth, there is a concern that mixing efficiency is poor because a sample is mixed with a reagent only by transporting a droplet so that it collides with the reagent and swinging the mixture.  
       BRIEF SUMMARY OF THE INVENTION  
       [0009]     In view of the above problems, an object of the present invention is to provide a chemical analysis apparatus whereby liquids for analysis varying in volumes can be analyzed, a liquid for analysis having a specific gravity lower than that of a filling liquid can be analyzed, dispensing with high accuracy is realized, and higher mixing accuracy is achieved.  
         [0010]     To achieve the above object, the chemical analysis apparatus of the present invention is equipped with analysis sections having openings, means for supplying samples and reagents from the openings, means for combining and mixing the samples with the reagents to obtain droplets as liquids to be measured, and means for measuring the physical properties of the liquids to be measured during reaction or after completion of reaction. Furthermore, analysis sections are composed of plate members provided facing each other, wherein a plurality of electrodes are provided on plate member faces that face each other, and voltage is applied from the plurality of electrodes to the droplets of the samples and the reagents so as to control the wettability of the droplets.  
         [0011]     The droplets containing the samples and the reagents are located between the plate members provided facing each other. The contact angles of the droplets vary by application of electric fields to the electrodes, thereby enabling the movement of the droplets on the plurality of electrodes. Furthermore, the samples and the reagents supplied from the openings of the analysis sections can move in the form of droplets with volumes smaller than those of the reagents and the samples when they are in the vicinity of the openings.  
         [0012]     Furthermore, specifically, steps are created on electrode plates or electrodes are made in the form of projections, so that the electrodes can be in contact with even small volumes of liquids. Alternatively, dotted electrodes are distributed and provided, so that the electrodes can always be in contact with liquids. Hence, it becomes possible to control the hydrophilicity and/or water-repellency of even small volumes of liquids and an apparatus capable of analysis even when liquid volume is small can be provided.  
         [0013]     Furthermore, through provision of ground electrodes and applicator electrodes in a manner such that the order thereof on the top plate and that on the bottom plate are opposite, an apparatus for analyzing liquids for analysis having specific gravities smaller than those of filling liquids can be provided. Moreover, a chemical analysis apparatus whereby highly accurate dispensing is realized can be provided by dividing liquids for analysis into a large number of small droplets and dispensing the droplets at many separate times, processing electrodes in the shape of droplets, correcting data by image processing, producing dispensing nozzles with electrodes, and the like.  
         [0014]     The chemical analysis apparatus of the present invention can realize analysis of liquids for analysis varying in liquid volume, analysis of liquids for analysis having specific gravities smaller than those of filling liquids, highly accurate dispensing, and chemical analysis with high mixing accuracy. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0015]      FIG. 1  is a perspective view in an embodiment of the chemical analysis apparatus according to the present invention.  
         [0016]      FIG. 2  is a top view of substrates for analysis to be used for the chemical analysis apparatus.  
         [0017]      FIG. 3  and  FIG. 6  are sectional views of the substrates for analysis.  
         [0018]      FIG. 7  and  FIG. 8  are top views in an embodiment of electrodes to be used for substrates for analysis.  
         [0019]      FIG. 9  explains how droplets become deformed on electrode rows.  
         [0020]      FIG. 10  is a figure explaining how droplets become deformed. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]     Embodiments of the present invention will be described below based on figures.  
         [0022]     Embodiments are described using FIGS.  1  to  7 .  FIG. 1  is a schematic perspective view of the entire system.  FIG. 2  shows a top view of substrates for analysis.  FIG. 3  is a sample-dispensing section and shows a sectional view taken along the line B-B′ in  FIG. 2 .  FIG. 4  is a reagent-dispensing section and shows a sectional view taken along the line C-B′ in  FIG. 2 .  FIG. 5  is a detection section and shows a sectional view taken along the line D-D′ in  FIG. 2 .  FIG. 6  is a waste fluid section and shows a sectional view taken along the line E-E′ in  FIG. 2 .  
         [0023]     The chemical analysis apparatus is composed of, as shown in  FIG. 1 , sample cups  101  containing biological samples such as sera, a sample disc  102  that rotationally moves the sample cups  101 , substrates for analysis  104  for analyzing samples placed on an analysis disc  103 , a sample-dispensing probe  105  for dispensing samples from the sample cups to the substrates for analysis, and a waste-fluid shipper  106  for removing liquids that have been analyzed by suction and discarding the liquids outside. A reagent bottle  108  and an oil bottle  109  placed on a bottle table  107  having a cooling function are piped via a tube  110  to each substrate for analysis  104  with a piping connector  111  provided with an electromagnetic valve. On the upper surface of each substrate for analysis  104 , a detection unit  114  is provided. Each substrate for analysis  104  is opened to the outside via two openings including a sample port  112  and a waste-fluid port  113 .  
         [0024]     Procedures for analysis are as described below. Samples are dispensed from the sample cups  101  using the sample-dispensing probe  105  to the substrates for analysis  104  and reagents are dispensed from the reagent bottles  108  through the tubes  110 . In each substrate for analysis  104 , the two liquids are mixed, and the mixed liquid is subjected to absorbance analysis and the like. After such analysis, the liquid is discharged to the outside using a waste-fluid shipper  106 .  
         [0025]     As shown in  FIGS. 2 and 3 , each substrate for analysis consists of two substrates including an upper substrate  201  and a lower substrate  202 . At a part of the lower substrate  202 , a large number of electrodes having sides with lengths between approximately several millimeters and several micrometers are aligned to form, for example, a sample electrode row  115  or a reagent electrode row  116  and are coated with water-repellent and insulating film  208 . The electrodes are each connected via a switching circuit  204 . Here, a case is shown wherein the mixed liquid volume ratio of a sample to a reagent indicates that the reagent is greater than the sample. Electrode sizes differ in accordance with liquid volume ratios. The gap between the two substrates is maintained by a spacer  205 , so that the substrates have a specific distance from each other. Oil is supplied from the oil port  206  according to need. The water-repellent and insulating film may be separated into water-repellent film and insulating film.  
         [0026]     A method of producing the aforementioned lower substrate  202  involves, for example, thin-film electrodes having conductivity, such as those composed of Cr, Ti, Al, or ITO on an insulated substrate such as glass or quartz by vapor deposition, sputtering, CVD, or the like. On the resultant electrodes, organic insulating film such as Parylene (trade name) of Three Bond Co., Ltd. or inorganic insulating film such as SiO 2  is formed by vapor deposition, sputtering, CVD, or the like. The insulating film is then coated with fluorobase water-repellent film so as to produce the lower substrates  202 . As a material for water-repellent film, Teflon AF1600 (trade name) of Du Pont Kabushiki Kaisha, Cytop (trade name) of ASAHI GLASS CO., LTD., or the like can be used. Furthermore, the upper substrates  201  are produced by forming transparent conductive film such as ITO on one side as counter electrodes  211 , and the resultant electrodes are coated with the above water-repellent film.  
         [0027]     Between the substrates (of each substrate for analysis  104 ), for example, inert oil  207  with high chemical resistance, such as silicon oil, FOMBLIN (trade name), or KRYTOX OIL (trade name), is supplied. At this time, film composed of the oil  207  covers the upper and the lower substrates, so that it becomes difficult for a sample droplet  213  or the like to be in contact with the substrates. The substrates for analysis  104 , between which there exists a gap to be filled with oil  207 , are placed on plane plates, so that oil  207  does not naturally flow out. Oil  207  can be supplied at relatively low cost based on head differences and there is no need to supply oil  207  in every analysis. At this time, it becomes difficult for liquids to remain at positions with which the liquids are in contact. Thus, carry-over, which has been a problem of conventional analysis apparatuses, is addressed, enabling analysis with high accuracy.  
         [0028]     Operations concerning the substrates for analysis  104  will be described in detail. First, a sample dispensed to each sample port  112  by the sample-dispensing probe  105  not shown in  FIG. 2  is in a state of being stored in each sample port  112 . At this time, a dispensed sample  210  on a sample electrode A 209  exists on water-repellent and insulating film, so that the sample  210  is repelled from the surfaces of the upper and lower substrates and is round in shape. Next, switching circuits  204  are operated to apply voltage between the sample-dispensing electrode A 209  and the counter electrodes  211 . After the wetting status of the sample changes, the sample liquid develops and extends so as to come into contact with a sample electrode B 212 . Next, the switching circuits are operated to turn off the sample electrode A 209  to eliminate an electric field and to apply voltage between the sample electrode B 212  and the counter electrodes  211 . The dispensed sample  210  is partially constricted at an appropriate position, moves away from the sample-dispensing electrode A 209 , develops, and then extends to the sample-dispensing electrode B 212 . Next, the switching circuits  204  are operated to turn off the sample-dispensing electrode B 212  to eliminate an electric field and to apply voltage to a sample-dispensing electrode C 214 . The liquid is divided at an appropriate position so as to form a sample droplet  213 . The sample droplet  213  moves onto the sample-dispensing electrode C 214 . In this manner, through switching the switching circuits  204  successively, the sample droplet  213  is transported in each substrate for analysis  104  along each sample electrode row  115 . Furthermore, the sample droplet  213  is successively separated from each sample port  112 . Thus, the entire sample is dispensed in the form of a large number of sample droplets  213 .  
         [0029]     If the viscosity of a sample liquid is high or the surface tension of the same is small, the effect of changing wettability by switching of electric fields will be small. Thus, it becomes difficult for the liquid to develop and extend to the next electrode and to be constricted. Therefore, it becomes also difficult for sample droplets to be separated from the dispensed sample. At this time, the position at which a droplet is separated from a liquid differs at every separation, so that sample droplets will vary in size. Hence, there is a concern that sample dispensing accuracy would become lowered. As shown in  FIG. 7A , an electrode at a position where a liquid is constricted ( 221 ), such as a sample electrode B 212 , is shaped to have a crevice conforming to the shape of the constricted liquid  221 . Thus, the constricted portion of the liquid  221  can be made larger, thereby facilitating separation of droplets from the liquid. Alternatively, as shown in  FIG. 7B , an electrode for the formation of a sample droplet  213 , such as a sample electrode C 214 , is shaped in conformation with the droplet size. Thus, the formation of the sample droplet  213  can be promoted. In this manner, it becomes easier to separate droplets from a dispensed sample  210 , so as to be able to improve sample dispensing accuracy. Regarding the curved part of such an electrode with a shape conforming to droplet size, for example, it is desirable that the curvature radius be smaller than that of an electrode  112  closest to the opening so that the electrode can conform to the curve of a constricted liquid. Conversely, if the curvature radius is too small, the tolerance of the droplet deformation degree is exceeded. Thus, it is desirable that such a curved part have a curvature radius larger than the size of the adjacent electrode.  
         [0030]     In the present invention, as described above, a sample dispensed from the sample-dispensing probe is dispensed in small volumes. Generally, dispensing of a sample in small volumes results in improved dispensing accuracy. For example, according to Non-patent document 1, accuracy is improved in inverse proportion to the square root of N in a case where a sample is dispensed N separate times, where the sample is dispensed always in the same volume with the same dispensing accuracy. When dispensing a sample using a conventional analysis apparatus, the minimum volume of a sample to be dispensed is approximately 1 μl. Thus, it has been impossible to dispense 1 μl or less of a sample in smaller volumes. However in the present invention, through the use of a smaller electrode, a sample can be dispensed in the form of droplets in even smaller volumes and dispensing accuracy can be improved by dispensing the sample in such smaller volumes.  
         [0031]     As described above and as shown in  FIG. 3 , the sample-dispensing probe  105  is also coated with water-repellent and insulating film  208  similar to the case of the substrate, so that the probe has water repellency. Furthermore, an electric field is applied through the switching circuits  204 , so that wettability can be controlled. First, a dispensed sample  210  is dispensed from the sample-dispensing probe  105  between the substrates (of each substrate for analysis  104 ). Next, the sample-dispensing probe  105  is lifted. In the case of a conventional analysis apparatus, when a sample-dispensing probe is lifted, the sample liquid  210  is partially moved away by such probe. Thus, the liquid should be dispensed in consideration of the volume of such a liquid that is moved away by a probe. Hence, one problem was that the volume of a sample to be used tends to increase. It has also been problematic that analysis accuracy is also lowered because the volume of a sample that is moved away by a probe is unstable. However, with the composition as shown in  FIG. 3 , when the sample-dispensing probe  105  is lifted, voltage is controlled between the counter electrode  211  of the sample-dispensing probe  105  and a sample electrode A, so that a role equivalent to that of the counter electrode  211  of the upper substrate  201  can be played. Hence, the wettability of a dispensed sample liquid is controlled so that a droplet can be separated more easily from the liquid. Thus, the problem of a sample liquid being partially moved away by a probe is addressed, because no sample liquids remain attached to the sample-dispensing nozzle. Furthermore, it becomes possible to reduce the volume of a sample to be used and to improve analysis accuracy. Moreover, when electric current is monitored by providing an ammeter (not shown) between the sample-dispensing probe  105  and the sample electrode A 209 , an extremely small electric current flows in the presence of droplets. Thus, whether or not droplets are attached can be confirmed, thereby contributing to improvement of dispensing accuracy.  
         [0032]     Glass or the like is used as material for the upper substrates  201 , transparent electrodes (e.g., ITO) are used as the counter electrodes  211 , and cameras (not shown) are provided on the upper sides of the substrates for analysis  104 . Therefore, the shape of each sample droplet  213  dispensed from each sample port  112  can be monitored and a two-dimensionally-spreading image of a sample droplet can be obtained. At this time, cross-sections of droplets between plate members will be uniform. The volume of a droplet can be easily obtained with high accuracy by determining the area of the obtained droplet image as a cross-sectional area and then multiplying the distance between the plate members by such cross-sectional area. Accordingly, a problem of lowered monitoring accuracy when three-dimensional images of droplets are obtained, which has been a problem connected with monitoring with a conventional analysis apparatus, is addressed. Furthermore, dispensing of samples with high accuracy and analysis with high accuracy are enabled. Moreover, by producing a sample-dispensing electrode that has a size of several μm, it becomes possible to set the volume of a sample droplet on the nanoliter order. Therefore, adjustment with high accuracy is made possible by monitoring when excesses or deficiencies are generated.  
         [0033]     In the meantime, as shown  FIG. 4 , a reagent is distributed to each upper substrate  201  via each tube  110 . As shown in  FIG. 1 , the reagent bottles  108  are provided on the upper sides of the substrates for analysis  104 , so that reagents can be supplied based on head differences. Reagents are transported to reagent ports  121  via electromagnetic valves within connector units  111  by water-repellent piping connectors  219 . Necessary volumes of reagents are supplied to the substrates for analysis by controlling intervals of opening and closing of the electromagnetic valves. Similar to the sample ports  112 , the reagent ports  121  are provided with reagent electrode rows  116  connected from the switching circuits  204  (not shown in  FIGS. 1 and 4 ), so that a reagent droplet  122  is separated from a dispensed reagent  190  in a plurality of times and then transported. Subsequently, the reagents are combined with sample liquids at mixing electrodes A 216  to result in necessary volumes.  
         [0034]     A sample liquid and a reagent are mixed as follows. First, here the reagent droplet  122  is transported to a mixing electrode A. Next, the sample droplet  213  is transported and caused to collide at each mixing electrode A 216  with the reagent droplet  122  kept ready for mixing on the mixing electrode or with a mixed droplet  123  that has been previously mixed to some extent. Furthermore, the switching circuits  204  are switched to a mixing electrode B 217  and a mixing electrode C 218 . Thus the mixed droplet  123  is transported back and forth in horizontal direction, that is, in parallel with each substrate for analysis  104 , thereby generating flowing movement within the droplet and promoting mixing. The volume of a sample droplet to be collided with a reagent, that is, number of times a sample droplet is separated from a sample port, is determined depending on the mixing ratio as determined in analysis protocols.  
         [0035]     In general, when volumes of two liquids to be mixed are increased, it will be difficult for internal flowing movement to take place and mixing will also be difficult. For example, in the case of conventional analysis apparatuses, it has been attempted to address such a problem through longer mixing times. However, because of insufficient mixing even with longer mixing times, there has been a problem of lowered-analysis accuracy. However, as described above, in the present invention, mixing is greatly facilitated because of sufficient mixing at the droplet level. Thus, mixing efficiency is improved, so that it becomes possible to shorten analysis time and improve analysis accuracy.  
         [0036]     When the specific gravity of a liquid is lower than that of inert oil  207  that fills the gap between the substrates for analysis, a droplet floats and becomes attached to the upper substrate side. At this time, as with the sample electrode A in  FIG. 3  and the like, when electrodes are provided on the lower substrate  202  side of the droplet, followed by switching to the substrate, wettability will not change significantly. Conversely, by separately providing electrodes on the upper substrate  201  side and with the use of the lower substrate  202  side as counter electrodes, it becomes possible to handle droplets with high accuracy in a similar manner as above. Moreover, when the volume of a droplet is increased, the aspect ratio of the horizontal direction to the depth (vertical) direction of the cross-section of the substrates for analysis will be increased. Furthermore, resistance to the movement of droplets will increase. Thus, it becomes difficult to handle droplets only by control of surface tension through the application of an electric field. Furthermore, as in  FIGS. 3 and 4 , a step  215  is provided to change the depth (vertical) direction and to lower the aspect ratio, thereby reducing resistance to the movement of droplets. Thus, the effect of a change in surface tension will increase, making it possible to handle the mixed droplet  123  in a relatively larger volume. When such a change in the depth (vertical) direction is larger than, for example, the size of an electrode, it becomes difficult for a droplet to be in contact with both the top and bottom plates. It also becomes difficult to apply an electric field between droplets. Conversely, when a step is smaller than about a half of the distance between electrodes, almost no effect of such a step can be expected.  
         [0037]     The mixed droplet  123  is transported to a detection section provided at a mixing electrode row  118 . For example, when detection is conducted by absorbance analysis, it is difficult to irradiate a droplet with light so that light passes through the droplet, because each substrate for analysis is very narrow in depth (vertical) direction. Furthermore, the droplet is short in the horizontal direction, so that the light path is shortened and analysis accuracy is lowered. Irradiation is also difficult because of the presence of electrodes in the vertical direction of each substrate for analysis. Furthermore, since each substrate is short in depth (vertical) direction, the light path is short and analysis accuracy is lowered. Hence, in the present invention, as shown in  FIG. 5 , irradiation is performed such that light enters at an angle with respect to each substrate from a light source  119  such as an LED, so as to cause light to reflect a plurality of times between the mixing electrode row  118  on the upper substrate  201  and the counter electrode  211  on the lower substrate  202 . Thus the light path is made longer so as to prevent analysis accuracy from being lowered. The electrodes of the analysis sections are preferably composed of opaque material with good reflecting properties, such as Cr or Au. Moreover, the light source  119  and a light receiving section  120  can be provided on the same upper surface side of each substrate for analysis, enabling facilitation of optical alignment.  
         [0038]     Generally, in the case of absorbance analysis, the larger the droplet volume, the longer the light path. Thus, detection accuracy is improved. Hence, in the present invention, droplets are combined on the mixing electrodes  118  to increase the volumes of the combined droplets, and then the droplets are transported to the detection sections. In this case, small droplets are all previously mixed appropriately at the micro level without dispersion. Thus, the final mixing at the macro level can also be conducted relatively easily. Moreover, when a droplet with a large volume is handled by controlling surface tension, the transportation rate is lowered. However, in the case of the present invention, small droplets are handled at positions other than those where handling of large droplets is required, so as to be able to prevent analysis time from decreasing.  
         [0039]     As shown in  FIG. 6 , a droplet  125  that has been detected is transported to a waste fluid port  113  by switching of the mixing electrode row  118  and then discharged outside each substrate for analysis  104  by a waste fluid probe  220 . When the specific gravity of inert oil  207  filling a gap is larger than that of a liquid for analysis, the droplet  125  floats and can be easily removed by suction by placing the tip of a probe at the upper portion of the waste fluid port  113 . Alternatively, as shown in the same figure, when a droplet remains in the gap, the droplet can be removed by suction by bending the waste fluid probe  220  into an L shape. In this case, by also providing the waste fluid probe  220  with water-repellent and insulating film and electrodes, it becomes possible to transport droplets from analysis electrodes to the waste fluid probe. Furthermore, electric current is monitored in a manner similar to that of the case of dispensing. Electric current does not flow in the presence of the tip of a waste fluid probe in inert oil, but it flows very weakly when it is in contact with a droplet. By the use of this phenomenon as a trigger, suction can be initiated. A waste fluid contains both a liquid for analysis and inert oil, but they can easily be separated from each other after the piping of the waste fluid probe. This can lead to a shortened total analysis time.  
       Another Embodiment  
       [0040]     Another embodiment is explained using FIGS.  8  to  10 .  FIGS. 8 and 9  are expanded top views of the substrates for analysis and  FIG. 10  is an expanded side view. The distribution ratio of a sample to a reagent when they are mixed differs depending on analysis protocols. Thus, mixed droplet size may significantly differ depending on analysis protocols. At this time, if electrodes of the same size are placed so as to be evenly spaced apart, droplets may be too small so as not to be able to be in contact with adjacent droplets, or may be too large, so as to extend over a plurality of electrodes. Therefore no electric fields can be applied, it will be impossible to control surface tension, and liquid handling will be difficult. Hence, as shown in  FIG. 8 , by miniaturizing electrodes to result in dotted microelectrodes  300  having, for example, sides with lengths between approximately several nanometers and several micrometers, and by providing a large number of such microelectrodes, it becomes possible for both a small-volume mixed liquid  303  and a large-volume mixed liquid  304  to be always in contact with electrodes. To which electrode switching should be directed is validated when a liquid volume is previously determined. This can also be performed by monitoring images or electric current, the method of which is described in Embodiment 1. An electrode group  302  to which an electric field should be applied comprises electrodes on the under surface of a droplet or in the vicinity of such droplet. By applying an electric field to these electrodes, it becomes possible to control surface tension and cause any small droplets to come into contact with electrodes. In the case of small droplets, the surface tension of such droplets can be effectively controlled and transportation of such droplets can be facilitated, so as to be able to contribute to a shortened analysis time. Preferably, the size of each of dotted electrode is, for example, equivalent to that of the gap between every two electrodes among the plurality of electrodes, so that a droplet has a shape that causes a change in wettability.  
         [0041]     Excessive liquids are transported by an excessive-liquid-discharging electrode row  301  connected to a dispensing port to an excessive-liquid-discharging port (not shown) provided in each substrate for analysis and then discharged outside. In this manner, in embodiments according to the present invention, liquids unnecessary for analysis can be easily discharged. This makes it possible to select a relatively low-cost liquid-sending method, such as a method that utilizes head differences as described above where the accuracy of the liquid volume to be sent is poor.  
         [0042]     A droplet moves on a large number of microelectrodes  300 . At this time, in general, unless voltage is applied to a plurality of electrodes with which the droplet comes into contact, no change in surface tension that is sufficient to cause the movement of the entire droplet can be generated. However, as shown in  FIG. 9A , for example, an electric field is applied only to longitudinal deformation electrodes  305  consisting of upper and lower electrodes (as shown in the figure) that are among the electrodes with which a droplet comes into contact. The surface tension of this part alone changes and a droplet is partially deformed and extends longitudinally. Next, by switching only to lateral deformation electrodes  306  consisting of a left electrode and a right electrode, a droplet extends laterally. By causing such extension and contraction of a droplet, flowing movement can be generated within the droplet. Internal uniformity of the droplet can thus be achieved, thereby significantly promoting mixing. Such extension and contraction may be caused when the motion of a droplet stops. Alternatively, as shown in  FIG. 9B , flowing movement for mixing may also be generated by applying an electric field to lateral deformation electrodes while laterally deforming and transporting a droplet. In this manner, it becomes possible to obtain high mixing efficiency. Thus, shortening of analysis time and improvement in analysis accuracy are enabled.  
         [0043]     Depending on differences in droplet size due to different analysis protocols, droplet deformation may differ into not only the horizontal direction of each substrate for analysis, but also the depth (vertical) direction of the same. On such an occasion, a small-volume mixed droplet  303  does not come into contact with only one substrate, so that it becomes impossible to apply electric fields. Hence, as shown in  FIG. 10 , microelectrodes are processed to result in microelectrodes  307  in the form of projections that are upright and vertical with respect to the substrates.  FIG. 10A  is a longitudinal cross-sectional view observed from the side along which a droplet is transported and  FIG. 10B  is a cross-sectional view observed from the end face that is vertical with respect to the direction along which a droplet is transported. Such electrodes in the form of projections preferably project from the periphery, such that the projection is, for example, larger than the gap provided between every two electrodes among the plurality of electrodes but small enough so as not to be in contact with both plate members provided facing each other. In this manner, the small-volume mixed droplet  303  comes into contact with microelectrodes  307  in the form of projections, enabling application of an electric field. Structurally, such microelectrodes  307  in the form of projections also come in contact with the large-volume mixed liquid  304 , so that an electric field can be applied also to a large droplet without any difficulties. This makes it possible to handle small droplets and can contribute to the improvement of analysis accuracy while shortening analysis time.