Patent Publication Number: US-9429276-B2

Title: Flow channel device, particle sorting apparatus, particle outflow method, and particle sorting method

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Japanese Priority Patent Application JP 2013-049983 filed Mar. 13, 2013, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     The present technology relates to a flow channel device, a particle sorting apparatus, a particle outflow method, and a particle sorting method for circulating particles such as cells. 
     As apparatuses that sort particles such as cells, a fluorescence flow cytometer and a cell sorter are known. In those apparatuses, under an appropriate vibration condition (generally, an exit flow velocity of several m/s and a vibration count of tens of kHz), cells are closed in a gas-liquid interface at an ejection opening by a fluid, and charges are given to the cells at the same time. The cells fly as droplets in a direction in accordance with a charge quantity in air to which a static electric field is applied and are eventually sorted into a sorting container provided outside a flow channel. 
     The technology is useful in the case where the flow velocity is relatively high as described above. For a flow cytometer for a low flow velocity or a dielectric cytometer, it is difficult to make droplets and satisfy an ejection condition for the droplets. In view of this, it is desirable to perform a sorting operation in a flow channel having branches and hold cells on a rear stage. 
     As a sorting mechanism in the flow channel, a method for changing a flow direction of a fluid by using a piezoelectric element or the like and indirectly driving cells in the fluid has been proposed. However, the responsiveness of the mechanical element is an approximately millisecond. In consideration of the responsiveness of a pressure wave of the flow channel, a sorting speed for the cells has a limitation. 
     On the other hand, as a method for directly driving the cells, a dielectrophoresis method has been proposed. Japanese Patent Translation Publication No. 2003-507739 discloses that a difference of a dielectrophoretic force between cell types and a difference of a sedimentation rate therebetween are used, thereby separating cells by type which flow in a flow channel in which an electrode is provided. Further, Japanese Patent Application Laid-open No. 2012-98075 discloses a cell sorting method by which cells that flow in a flow channel are analyzed to determine whether the cells are targets to be sorted or not, and in accordance with a sorting signal transmitted on the basis of the determination result, an electric field is applied. By the method, it is possible to sort the cells as the sorting targets by a sufficient dielectrophoretic force. 
     SUMMARY 
     Concerning the sorting method for the cells disclosed in Japanese Patent Translation Publication No. 2003-507739, the difference of the dielectrophoretic force caused by the difference of particle types is significantly smaller as compared to the difference of the dielectrophoretic force caused by the difference of the size, the shape, or the like between particles. Therefore, it is expected that the sorting method disclosed in Japanese Patent Translation Publication No. 2003-507739 does not work well in the case where a particle group with a small difference which is practically demanded is used as a target. The sorting method disclosed in Japanese Patent Application Laid-open No. 2012-98075 is expected to fulfill the function well, but further improvement in accuracy is demanded. 
     In view of the above-mentioned circumstances, it is desirable to provide a flow channel device, a particle sorting apparatus, a particle outflow method, and a particle sorting method capable of sorting particles with high accuracy. 
     According to an embodiment of the present technology, there is provided a flow channel device including an inflow unit, a first outflow unit, and a second outflow unit. 
     Into the inflow unit, a transfer fluid that transfers particles is caused to flow. 
     The first outflow unit includes an inflow port into which a part of the transfer fluid caused to flow from the inflow unit is caused to flow, a holding unit that is connected to the inflow port and holds particles, and a particle outflow port from which the particles held in the holding unit are caused to flow out to a predetermined flow channel area by the transfer fluid caused to flow from the inflow port. 
     The second outflow unit includes a peripheral outflow channel through which another part of the transfer fluid caused to flow from the inflow unit is caused to flow out to a peripheral flow channel area that surrounds the predetermined flow channel area, the peripheral outflow channel surrounding at least the particle outflow port. 
     In the flow channel device, the part of the transfer fluid caused to flow from the inflow unit is caused to flow to the holding unit from the inflow port of the first outflow unit. Then, the particles in the holding unit are caused to flow out to the predetermined flow channel area from the particle outflow port. Around the particle outflow port, the peripheral outflow port of the second outflow unit is provided. Through the peripheral outflow channel, another part of the transfer fluid caused to flow from the inflow unit is caused to flow out to the peripheral flow channel area that surrounds the predetermined flow channel area. As a result, it is possible to cause the particles to stably flow out in the predetermined flow channel area. Consequently, it is also possible to sort the particles with high accuracy. 
     The first and second outflow units may respectively cause the particles and the transfer fluid to flow out as a laminar flow having a Reynolds number of 1 or less. 
     In the case where the particles and the transfer fluid are caused to flow as the laminar flow having the Reynolds number of 1 or less as described above, it is also possible to cause the particles to stably flow in the predetermined flow channel area. 
     The first and second outflow units may respectively cause the particles and the transfer fluid to flow out in such a manner that a ratio between a flow rate in the predetermined flow channel area and a flow rate in the peripheral flow channel area falls within a range of 1:2 to 1:100. 
     By causing the particles and the transfer fluid to flow out with the flow rate ratio that falls within the range as described above, it is possible to cause the particles to stably flow out. 
     The peripheral outflow channel may be disposed concentrically with the particle outflow port as a center. 
     As a result, it is possible to sufficiently surround the particles caused to flow out to the predetermined flow channel area by the transfer fluid caused to flow out to the peripheral flow channel area, with the result that the particles can be caused to stable flow out. 
     The holding unit may include a supply port for supplying the particles and a main body unit having a funnel-like shape. The supply port has a diameter larger than that of the particle outflow port, and the main body unit includes a tapered unit which connects the supply port and the particle outflow port with each other and a diameter of which is reduced from the supply port toward the particle outflow port. 
     By providing the main body unit having the funnel-like shape, it is possible to guide the particles to the particle outflow port smoothly and thus cause the particles to flow out to the predetermined flow channel area with high accuracy. 
     The supply port may be sealed by a sealing member. 
     In this way, the supply port may be sealed by the sealing member. By appropriately setting the structure or the like of the sealing member, it is also possible to adjust the pressure in the holding unit. 
     The supply port may be in a state of being released to an atmosphere. 
     In this way, the supply port may be in the state of being released to the atmosphere. As a result it is possible to simplify the structure of the holding unit. 
     The particle outflow port may have a diameter that is smaller than ten times a diameter of the particle. 
     With this structure, it is possible to cause the particles to flow out to the predetermined flow channel area with high accuracy. 
     According to another embodiment of the present disclosure, there is provided a particle sorting apparatus including the flow channel device, a flow channel, a plurality of branch units, and an electrical field application unit. 
     The flow channel is connected to the flow channel device, and in the flow channel, the particles and the transfer fluid caused to flow out from the flow channel device are caused to flow. 
     The plurality of branch channels are branched from the flow channel. 
     The electrical field application unit is capable of forming a guide electrical field in the flow channel in accordance with a sorting signal that gives an instruction to sort the particles. The guide electrical field guides the particles to a predetermined branch channel out of the plurality of branch channels. 
     According to another embodiment of the present disclosure, there is provided a particle outflow method including causing a transfer fluid that transfers particles to flow into an inflow unit. 
     A part of the transfer fluid caused to flow from the inflow unit is caused to flow into a holding unit that holds particles, thereby causing the particles held in the holding unit to flow out to a predetermined flow channel area through a particle outflow port. 
     Another part of the transfer fluid caused to flow from the inflow unit is caused to flow out to a peripheral flow channel area that surrounds the predetermined flow channel area via a peripheral outflow channel that surrounds the particle outflow port. 
     According to another embodiment of the present disclosure, there is provided a particle sorting method including causing a transfer fluid that transfers particles to flow into an inflow unit. 
     A part of the transfer fluid caused to flow from the inflow unit is caused to flow into a holding unit that holds particles, thereby causing the particles held in the holding unit to flow out to a predetermined flow channel area through a particle outflow port. 
     Another part of the transfer fluid caused to flow from the inflow unit is caused to flow out to a peripheral flow channel area that surrounds the predetermined flow channel area via a peripheral outflow channel that surrounds the particle outflow port. 
     The particles caused to flow out from the particle outflow port and the transfer fluid caused to flow out through the peripheral outflow channel are caused to flow to a flow channel; and 
     A guide electrical field in the flow channel is formed in accordance with a sorting signal that gives an instruction to sort the particles by an electrical field application unit provided to the flow channel. The guide electrical field guides the particles to a predetermined branch channel out of a plurality of branch channels. 
     As described above, according to the embodiments of the present technology, it is possible to provide a flow channel device capable of sorting the particles with high accuracy. 
     These and other objects, features and advantages of the present technology will become more apparent in light of the following detailed description of best mode embodiments thereof, as illustrated in the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram showing the structure of a particle sorting apparatus according to an embodiment of the present technology; 
         FIG. 2  is a perspective view showing an example of a sorting flow channel unit shown in  FIG. 1 ; 
         FIG. 3  is a schematic diagram showing the structure of a particle outflow unit according to this embodiment; 
         FIG. 4  is a schematic top view of an entire outflow unit shown in  FIG. 3 ; 
         FIG. 5  is a diagram showing a more specific structural example of the particle outflow unit shown in  FIG. 3 ; 
         FIG. 6  is a diagram showing an example in which the particle outflow unit shown in  FIG. 5  is expanded to a shape of an actual device with a main flow channel (micro flow channel) for causing the particles to flow, and a fluid numerical analysis is performed; 
         FIG. 7  is a perspective view showing a schematic structure of a sorting unit shown in  FIG. 2 ; 
         FIG. 8  is a plan view showing the sorting unit; 
         FIG. 9  is a cross-sectional diagram of the sorting unit shown in  FIG. 8  which is taken along the line A-A; 
         FIG. 10  is a diagram for explaining an operation of the sorting unit in a flow channel device; 
         FIG. 11  is an example showing sizes of parts of a sorting electrode unit; 
         FIG. 12A  is a diagram showing an electrical field intensity distribution on an x-y plane at the position of z=10 μm, and  FIG. 12B  is a diagram showing an electrical field intensity distribution on a y-z plane at the position of x=50 μm; 
         FIG. 13A  is a diagram showing an intensity distribution of a dielectrophoretic force generated in a rightward y direction on a y-z plane at a position of x=50 μm, and  FIG. 13B  is a diagram showing an intensity distribution of a dielectrophoretic force generated in a leftward y direction thereon; 
         FIG. 14A  is a diagram showing an intensity distribution of a dielectrophoretic force generated in an upward z direction on a y-z plane at a position of x=50 μm, and  FIG. 14B  is a diagram showing an intensity distribution of a dielectrophoretic force generated in a downward z direction thereon; 
         FIG. 15  is a diagram showing a degree of the dielectrophoretic force that operates in the y direction on a boundary where positive and negative dielectrophoretic forces in the z direction are switched at a position of a height z; 
         FIG. 16  is a diagram showing a simulation result of tracks of particles in the case where the particles flow into a flow channel area of a guide electrode structure from different positions in the y direction; 
         FIG. 17  is a schematic perspective view showing another structural example of a sorting flow channel unit; 
         FIG. 18  is a schematic plan view showing the sorting flow channel unit shown in  FIG. 17 ; 
         FIG. 19  is a diagram showing a simulation result of tracks of the particles with the sorting flow channel unit; 
         FIGS. 20A and 20B  are diagrams showing design examples of approach sections of the guide electrode structures according to the two structural examples, respectively; 
         FIG. 21  is a diagram showing another structural example of the sorting flow channel unit for sorting the particles caused to flow out from the flow channel device; 
         FIG. 22  is a diagram showing a simulation result of tracks of the particles that are caused to flow into a narrow channel from different positions in a flow channel width direction of a first flow channel; 
         FIG. 23  is a schematic diagram of a track of a cell and a velocity distribution in a height direction of a second flow channel in the sorting flow channel unit; 
         FIG. 24  is a schematic diagram showing another structural example of a sealing member for sealing a particle supply port of a middle outflow unit; and 
         FIGS. 25A to 25C  are schematic diagrams each showing another structural example of the middle outflow unit to a particle outflow port. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an embodiment of the present technology will be described with reference to the drawings. 
     (Structure of Particle Sorting Apparatus) 
       FIG. 1  is a schematic diagram showing the structure of a particle sorting apparatus according to an embodiment of the present technology.  FIG. 2  is a perspective view showing an example of a sorting flow channel unit shown in  FIG. 1 .  FIG. 3  is a schematic diagram showing the structure of a particle outflow unit as a flow channel device according to this embodiment. 
     As shown in  FIG. 1 , a particle sorting apparatus  100  is provided with a sorting flow channel unit  55 , a measurement unit  60 , and an analysis unit  70 . In the sorting flow channel unit  55 , from the upstream side thereof, an input unit  3 , a flow channel (main flow channel)  2 , a measurement electrode unit  4 , a sorting unit  5 , branch channels  2   a  and  2   b , particle takeout units  6  and  7 , and a discharge unit  10  are provided. 
     Into the input unit  3 , a fluid (liquid) containing cells as particles C sampled is input through a particle outflow unit  20  shown in  FIG. 3 . In the flow channel  2 , the liquid that is input from the input unit  3  flows. A direction of a main stream of the liquid is an x direction in  FIG. 1 . 
     In the measurement unit  60 , an AC voltage having an arbitrary frequency within a predetermined frequency range is applied to the measurement electrode unit  4 . For example, with respect to individual cells that flow in the flow channel  2 , a complex dielectric constant that depends on each cell is measured for multipoint frequencies (three or more points, typically, about 10 to 20 points) within a frequency range (for example, 0.1 MHz to 50 MHz) of an AC voltage, in which a dielectric relaxation phenomenon occurs. It should be noted that the measurement unit  60  measures an impedance from a detection signal obtained from the measurement electrode unit  4  and obtains, from the impedance measured, the complex dielectric constant by a known electric conversion expression. 
     Examples of an amount electrically equivalent to the complex dielectric constant include a complex impedance, a complex admittance, a complex capacitance, a complex conductance, and the like. Those can be converted to each other by a simple electrical quantity conversion. Further, the measurement of the complex impedance or the complex dielectric constant includes a measurement of only a real part or only an imaginary part. 
     The analysis unit  70  receives information of the complex dielectric constant of the particles C measured by the measurement unit  60 , determines whether the particles C have to be sorted or not on the basis of the complex dielectric constant, and in the case where the particles have to be sorted, generates a sorting signal. In this case, the analysis unit  70  functions as a signal generation unit. 
     Out of the plurality of kinds of particles C input from the input unit  3 , the sorting unit  5  sorts particles C as targets into the particle takeout unit  6  and sorts remaining particles C into the particle takeout unit  7 . The sorting unit  5  has a sorting electrode unit  8 . A position on which the sorting electrode unit  8  is provided is a downstream side from a position on which the measurement electrode unit  4  is provided. The sorting unit  5  functions as an electrical field application unit in this embodiment. 
     The measurement unit  60  and the analysis unit  70  may be formed of hardware or formed of both of hardware and software. The measurement unit  60  and the analysis unit  70  may be one apparatus physically. 
     To the sorting electrode unit  8 , a DC or AC drive voltage in accordance with the sorting signal output from the analysis unit  70  is applied. As a result, the sorting electrode unit  8  generates a guide electrical field in the flow channel  2 . The guide electrical field is such an electrical field that the particles C are guided to predetermined one of the plurality of branches  2   a  and  2   b.    
     The branches  2   a  and  2   b  are flow channels that are branched from the flow channel  2 . The branch channel  2   a  is connected to the particle takeout unit  6 , and the branch channel  2   b  is connected to the particle takeout unit  7 . For example, in the case where the guide electrical field is not generated by the sorting electrode unit  8 , the particles C flow to the particle takeout unit  7  through the branch channel  2   b . On the other hand, in the case where the guide electrical field is generated in the flow channel  2  by the sorting electrode unit  8 , the particles C flow to the particle takeout unit  6  through the branch channel  2   a.    
     The particle takeout units  6  and  7  are communicated with the discharge unit  10 . The liquid that has passed through the particle takeout units  6  and  7  is discharged to the outside from the discharge unit  10  by using a pump or the like. 
     Here, when the electrical field is applied to the particles C that exist in the liquid, an induced dipole moment is generated due to a difference of a polarizability between a medium (liquid) and the particles C. In the case where a space distribution of the applied electrical field, that is, a space distribution of an electrical flux density is not uniform, the electrical field intensity differs in the vicinity of the particles C, so a dielectrophoretic force expressed by the expression (1) is generated due to the induced dipole. 
     In the expression (1), ∈′m, ∈v, R, and Erms represent the real part of a complex relative permittivity (complex relative permittivity is defined by the expression (2)) of the medium, a vacuum dielectric constant, a particle radius, and an RMS (room mean square) value of the electrical field applied, respectively. Further, K is Clausius-Mossotti function expressed by the expression (3), and ∈*p and ∈*m represent dielectric constants of the particles C and the medium, respectively. 
     
       
         
           
             
               
                 
                   
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     As described above, in Japanese Patent Translation Publication No. 2003-507739, an attention is focused on a difference of K between particle types, and the particles are sorted by using only a dielectrophoresis method. In contrast, the particle sorting apparatus  100  according to the present technology does not use the difference of the dielectrophoretic force between particle types (frequency dependency). In accordance with the sorting signal transmitted from the analysis unit  70 , the particle sorting apparatus  100  turns on and off the guide electrical field or performs an amplitude modulation and application, and performs sorting only for the particles C as the sorting targets by a sufficient dielectrophoretic force even if the particle groups have variations in particle size or physicality. 
     The particles C as the targets to be guided to the branch channel  2   a  by generating the guide electrical field by the sorting electrode unit  8  are referred to as target particles hereinafter. The particles C guided to the branch channel  2   b  without generating the guide electrical field are referred to as non-target particles hereinafter. The target particles and the non-target particles are normal cells and dead or cancerous cells, respectively, for example. 
     In advance, a storage device (not shown) only has to store information (and/or information of a range of the complex dielectric constant of the non-target particles) of a range of the complex dielectric constant of the target particles. The storage device is a device that is accessible by at least the analysis unit  70 . On the basis of the information stored in the storage device, the analysis unit  70  determines whether the complex dielectric constant of the particles C which is measured by the measurement unit  60  falls within the range of the complex dielectric constant of the target particles or not (whether the complex dielectric constant of the particles C falls within the range of the complex dielectric constant of the non-target particles). The determination is performed in real time immediately after the measurement of the complex dielectric constant by the measurement unit  60 . Then, in the case where the analysis unit  70  determines that the particles C as the measurement targets are target particles, the analysis unit  70  outputs the sorting signal and applies a predetermined drive voltage to the sorting electrode unit  8 . 
     As shown in  FIG. 2 , in this embodiment, the sorting flow channel unit  55  has a chip shape and includes a substrate  12  and a sheet-shaped member  13  formed of a polymer film or the like. On the substrate  12 , the flow channel  2 , the branch channels  2   a  and  2   b , a liquid input unit  3   a  serving as the input unit  3 , the particle takeout units  6  and  7 , and the discharge unit  10  are provided. Those are configured by forming grooves or the like on the surface of the substrate  12  and covering the surface with the sheet-shaped member  13 . 
     A particle input unit  3   b  to which the liquid containing the particles C is input has a minute input hole  3   c  formed on the sheet-shaped member  13 . Into the input hole  3   c , the liquid containing the particles C is caused to flow by using the particle outflow unit  20  shown in  FIG. 3 . Then, the liquid caused to flow out is merged with the liquid that flows from the upstream side and flows to the downstream of the flow channel  2 . By using the particle outflow unit  20  according to this embodiment, it is possible to cause the particles C to stably flow into the flow channel  2  with the particles C aligned. 
     A pair of measurement electrodes  4   a  and  4   b  is provided so that the input hole  3   c  is disposed therebetween. The measurement electrode  4   a  is provided on a front surface of the sheet-shaped member  13 , and the measurement electrode  4   b  is provided on a back surface of the sheet-shaped member  13 . 
     Upper portions of the particle takeout units  6  and  7  are covered with the sheet-shaped member  13 . The sheet-shaped member  13  is stuck with a pipette, and the particles C are taken out via the pipette. 
     The measurement electrode unit  4  is electrically connected to electrode pads  14 . The electrode pads  14  are connected to the measurement unit  60 . The measurement unit  60  applies an AC voltage to the measurement electrode unit  4  through the electrode pads  14  and receives a detection signal from the measurement electrode unit  4  through the electrode pads  14 . 
     The sorting electrode unit  8  in the sorting unit  5  is electrically connected to electrode pads  15 . The analysis unit  70  applies a drive voltage to the sorting electrode unit  8  through the electrodes pads  15 . 
     Through holes  26  are holes for fixation. 
     (Structure of Particle Outflow Unit (Flow Channel Device)) 
     As shown in  FIG. 3 , the particle outflow unit  20  is disposed above the input hole  3   c  of the input unit  3  for a liquid. The particle outflow unit  20  causes the particles C to flow out to the input hole  3   c  in a direction of gravity. The particle outflow unit  20  is fixed to the sorting flow channel unit  55  by any fixation method. The sorting flow channel unit  55  and the particle outflow unit  20  may be integrally formed. 
     The particle outflow unit  20  includes an entire outflow unit  21  and an entire flow channel  22 . The entire outflow unit  21  causes the particles C and a transfer fluid (also called as working fluid) that transfers the particles C to flow out. The entire flow channel  22  is connected to the entire outflow unit  21  and guides the particles C and the transfer fluid to the sorting flow channel unit  55 . As shown in  FIG. 3 , the entire outflow unit  21  and the entire flow channel  22  are provided in such a manner that long axes thereof are along the direction of gravity. Further, the entire outflow unit  21  and the entire flow channel unit  22  each have an approximately columnar outside shape having a circular cross section taken along a plane in a direction (x-y plane direction) perpendicular to the long axis direction. 
     An upper surface  23  of the entire outflow unit  21  is a circular shape having the largest diameter. In contrast, a cross section of a connection part  24  between the entire outflow unit  21  and the entire flow channel  22 , that is, a cross section of the entire flow channel  22  on the uppermost side is a circular shape, the diameter of which is smaller than the upper surface  23 . A tapered unit  26  is formed in such a manner that a diameter thereof is gradually reduced from a part  25  in the middle of the entire outflow unit  21  in the z direction to the connection part  24 . The shapes of the entire outflow unit  21  and the entire flow channel  22  are not limited and may be appropriately designed so as to be fit for the outflow of the particles C and the transfer fluid to be described later. 
     The entire outflow unit  21  includes an inflow unit  27  and a middle outflow unit  29  (first outflow unit). Into the inflow unit  27 , the transfer fluid is caused to flow. The middle outflow unit  29  holds the particles C therein and causes the particles C to flow out to a middle flow channel area  28  (predetermined flow channel area) of the entire flow channel  22 . The entire outflow unit  21  further includes a peripheral outflow unit (second outflow unit)  31  that causes the transfer fluid to flow out to a peripheral flow channel area  30  that surrounds the middle flow channel area  28 . 
       FIG. 4  is a schematic top view of the entire outflow unit  21 . The upper surface  23  having the circular outer shape includes an opening  32  formed on the center thereof and an upper surface portion  33  that surrounds the opening  32 . On a predetermined position of the upper surface portion  33 , a transfer fluid inflow port  34  into which the transfer fluid is caused to flow is formed as the inflow unit  27 . The other structure of the inflow unit  27  may be arbitrarily designed in such a manner that the transfer fluid can be appropriately caused to flow in the transfer fluid inflow port  34 . 
     As shown in  FIG. 3 , the middle outflow unit  29  includes a main body  36  (holding unit) and a diverting route  37 . The main body  36  has a space unit  35  therein. The diverting route  37  causes a part of the transfer fluid caused to flow from the transfer fluid inflow port  34  to send to the space unit  35  of the main body  36 . The middle outflow unit  29  further includes a particle supply port  38  for supplying the particles C to the space unit  35  and a particle outflow port  39  for causing the particles C held in the space unit  35  to flow out to the middle flow channel area  28 . 
     Above the main body  36 , the particle supply port  38  is formed. In this embodiment, the opening  32  shown in  FIG. 1  corresponds to the particle supply port  38 . The particle supply port  38  is sealed by a sealing member  40  such as a movable stopper made of rubber or the like. Below the main body  36 , the particle outflow port  39  is formed. The particle supply port  38  and the particle outflow port  39  are formed in such a manner that center axes P of the ports approximately coincide with each other in a direction in which the ports are opposed to each other in the z direction. Further, the particle supply port  38  is desired to have a larger diameter than the particle outflow port  39 . 
     The shapes and the sizes of the particle supply port  38  and the particle outflow port  39  and the positional relationship therebetween are not limited to the above. The diameter of the particle outflow port  39  is designed in accordance with the diameter of the particle C caused to flow out, for example. For example, the particle outflow port  39  may be formed to have a diameter smaller than ten times the diameter of the particle C. In this case, it is possible to cause the particles C to flow out to the middle flow channel area  28  with high accuracy. 
     The main body  36  includes a main body unit  41  that connects the particle supply port  38  and the particle outflow port  39  with each other. The main body unit  41  includes a side wall unit  42  and a tapered unit  43  and has a funnel-like shape. The side wall unit  42  is extended downward so as to have a diameter which is approximately the same as the particle supply port  38 . The tapered unit  43  has a diameter which is gradually reduced from the side wall unit  42  toward the particle outflow port  39 . It should be noted that the shape of the main body  36  may be appropriately designed. By forming the funnel-shaped main body unit  41  as in this embodiment, it is possible to guide the particles C to the particle outflow port  39  smoothly. Further, as shown in  FIG. 3 , by disposing the particle outflow port  39  above the middle flow channel area  28  of the entire flow channel  22  relatively in the vicinity thereof, it is possible to cause the particles C to flow out to the middle flow channel area  28  with high accuracy. 
     In this embodiment, a part that is extended in the z direction so as to have a constant diameter from the lower end portion of the tapered unit  43  to the particle outflow port  39  is formed. Hereinafter, the part is referred to as a middle outflow channel  44 . The particles C are caused to pass through the middle outflow channel  44  and flow out from the particle outflow port  39  to the middle flow channel area  28 . 
     The diverting route  37  is connected to the side wall unit  42  of the main body  36 . A tip of the diverting route  37  corresponds to an inflow port  45 . The inflow port  45  and the main body  36  are communicated with each other via the diverting route  37 . The inflow port  45  is opened upward so as to be opposed to the transfer fluid inflow port  34 . Thus, when the transfer fluid is caused to flow in the transfer fluid inflow port  34 , a part thereof is caused to flow in the inflow port  45  and is sent to the space unit  35  of the main body  36  via the diverting route  37 . The shape and the size of the inflow port  45 , the size of the diameter of the diverting route  37 , and the like are not limited. For example, in order to set a flow channel resistance of the diverting route  37 , a flow channel resistance from the inflow port  45  to the particle outflow port  39 , or a flow rate ratio of the middle flow channel area  28  and the peripheral flow channel area  30  to be desirable, the diameter and the like of the diverting route  37  are designed appropriately. 
     The peripheral outflow unit  31  includes a peripheral outflow channel  46  that surrounds at least the particle outflow port  39 . In this embodiment, the peripheral outflow channel  46  is formed so as to surround the entire main body  36 . That is, an entire lower side part of the upper surface portion  33  shown in  FIG. 1  forms the peripheral outflow channel  46 . The peripheral outflow channel  46  is connected to the transfer fluid inflow port  34 . Therefore, another part of the transfer fluid caused to flow from the transfer fluid inflow port  34 , that is, the transfer fluid excluding the part that is caused to flow in the inflow port  45  of the main body  36  is caused to flow in the peripheral outflow channel  46  and then is caused to flow out to the peripheral flow channel area  30  of the entire flow channel  22  via the peripheral outflow channel  46 . 
     The peripheral outflow channel  46  only has to surround at least the particle outflow port  39  and is not limited to such a structure as to entirely surround the main body  36  as in this embodiment. Further, typically, the peripheral outflow channel  46  is formed around the entire periphery of the particle outflow port  39 . However, a plurality of peripheral outflow channels may be formed at intervals around the particle outflow port  39 . In this case, around the particle outflow port  39 , a plurality of outflow ports for causing the transfer fluid to flow out are formed. 
     The entire flow channel  22  includes a side wall unit  47  that is extended downward in the z direction, with the diameter of the connection part  24  with the entire outflow unit  21  maintained. The connection part  24  is a part where the particles C from the middle outflow unit  29  merge with the transfer fluid from the peripheral outflow channel  46 . Hereinafter, the connection part may be referred to as a merged part  24 . An area in the vicinity of a center axis P along a long-axis direction of the entire flow channel  22  corresponds to the middle flow channel area  28  to which the particles C are caused to flow out. An area in the vicinity of the side wall unit  47  which surrounds the center flow channel area  28  corresponds to the peripheral flow channel area  30 . As shown in  FIG. 3 , on the outflow port  48  on the lower side of the entire flow channel  22 , the particle outflow unit  20  is fixed to the sorting flow channel unit  55  in such a manner that the middle flow channel area  28  is disposed approximately on the center of the input hole  3   c.    
     (Operation of Particle Outflow Unit (Flow Channel Device)) 
     First, a sample containing the particles C is injected into the space unit  35  in the main body  36  with a pipette or the like with the movable stop removed. Typically, the sample containing the particles C is a liquid in which the particles C and the transfer fluid are mixed. That is, in the space unit  35  of the main body  36 , the transfer fluid as the sample is injected in advance. The sample containing the particles C may be made of a material different from the transfer fluid. In this way, the main body  36  is used as a sample holder. 
     The way of injecting the sample into the main body  36  is not limited. As in this embodiment, in the case where the movable stop is removed, and the sample is injected with the pipette or the like, it is desirable that the pressure loss of the two flow channels (middle outflow channel  44  that is connected to the particle outflow port  39  and a narrow tube serving as the diverting route  37 ) that are connected with the space unit  35  is sufficiently increased. As a result, a flow caused by a pressure generated at the time of the injection with the pipette is directed upward, which is the atmosphere side, and thus leakage from the particle outflow port  39  or the like can be prevented. Upon completion of the injection of the sample to the main body  36 , the particle supply port  38  is sealed with the movable stop. 
     Subsequently, the transfer fluid is caused to flow from the transfer fluid inflow port  34  formed on the upper surface portion  33 . The transfer fluid caused to flow therein mostly passes through the peripheral outflow channel  46  and becomes an outer coaxial flow to be caused to flow out to the peripheral flow channel area  30  of the entire flow channel  22 . On the other hand, the transfer fluid that is caused to flow in the inflow port  45  of the middle outflow unit  29  is caused to flow to the space unit  35  of the main body  36 . By the pressure, the particles C held in the space unit  35  of the main body  36  are caused to flow out to the middle flow channel area  28  via the particle outflow port  39 . At this time, the transfer fluid caused to flow in the main body  36  and the flow containing the particles C and the transfer fluid injected in advance become an inner coaxial flow and go out to the middle flow channel area  28 . As a result, it is possible to cause the particles C to stably flow with the particles aligned in the middle flow channel area  28 . 
     A ratio between the flow rate of the flow (hereinafter, referred to as middle flow) to the middle flow channel area  28  and the flow rate of the flow (hereinafter, referred to as peripheral flow) to the peripheral flow channel area  30  is determined as a reciprocal ratio of the flow channel resistances of the routes. Here, the diameter of the entire flow channel  22  is set as a typical length L, and an average flow velocity with respect to a cross section of the entire flow channel which is taken along an x-y plane direction is set as a typical velocity u. Further, a fluid kinematic viscosity of a mixture fluid (middle flow and peripheral flow) caused to flow through the entire flow channel  22  is represented by ν. A Reynolds number Re is expressed by the following expression (4).
 
 Re=Lu/ν   (4)
 
     In this embodiment, by the middle outflow unit  29  and the peripheral outflow unit  31 , the particles C and the transfer fluid are caused to flow out as a laminar flow having the Reynolds number Re of 1 or less. In the case of the laminar flow area having a sufficiently small Reynolds number Re as described above, by sufficiently reducing the flow rate ratio of the middle flow to the peripheral flow, it is possible to stabilize the middle flow in the middle flow channel area  28  in the entire flow channel  22 . Generally, if the diameter of the particle C is sufficiently small, inertia thereof is small. Thus, by the fluid viscosity, a velocity vector of the peripheral flow and a velocity vector of the particles C quickly become identical (small relief time). As a result, the particles C follow the middle flow and align and flow in the middle channel area  28 . In this embodiment, the flow rate ratio between the middle flow and the peripheral flow is set to be approximately 1:9. Thus, it is possible to cause the particles C to stably flow in the middle flow channel area  28 . 
     The numerical value of the flow rate ratio is not limited and may be set as necessary within such a range as to make an appropriate flow possible. For example, the particles C and the transfer fluid may be respectively caused to flow out in such a manner that the flow rate ratio between the middle flow and the peripheral flow falls within the range from 1:2 (1/2) to 1:100 (1/100). If the flow rate ratio between the middle flow and the peripheral flow is smaller than 1:2, that is, the peripheral flow is smaller than a double of the middle flow, the middle flow is increased immediately after being merged, and the particles C occupy approximately half of the flow channel width. This makes the control of the positions of the particles C difficult. If the flow rate ratio of the peripheral flow to the middle flow becomes larger, a property of going straight of the middle flow becomes better. However, if the flow ratio therebetween is larger than 1:100, that is, the peripheral flow becomes larger than 100 times the middle flow, the density of the particles C that occupy the entire flow is decreased, resulting in reduction of time efficiency for the measurement and sorting. In addition, the entire flow rate is excessively increased, and it is difficult to satisfy a passing velocity condition for the measurement unit or the like. It should be noted that in the case where the flow ratio is set to be larger than 1:100 with the entire flow rate fixed, the middle flow becomes significantly small. As a result, it may be impossible to perform stable liquid transmission. 
     In consideration of the points described above, the setting range of the flow rate ratio may be selected as appropriate within the range mentioned above. For example, the setting range of the flow rate ratio such as 1:10 to 1:70 and 1:30 to 1:50 may be selected as appropriate. 
       FIG. 5  is a diagram showing a more specific structural example of the particle outflow unit  20  shown in  FIG. 3 . In  FIG. 5 , a structural example of a part corresponding to the entire outflow unit  21  shown in  FIG. 1  is mainly described. Further, in  FIG. 5 , a flux of the middle flow caused to go out from the middle outflow channel  44  and a flux of the peripheral flow caused to go out from the peripheral outflow channel  46  are indicated on the basis of a numeric value calculation. The flux of the middle flow is indicated by solid lines, and the flux of the peripheral flow is indicated by broken lines. The applicant of the present disclosure can disclose the flow line graph of  FIG. 5  (and flow line graph of  FIG. 6 ) as color diagrams in which the fluxes are distinguished with colors. 
     In the particle outflow unit  20  shown in  FIG. 5 , a part protruded in the x direction (horizontal direction) on the left-hand side in the figure corresponds to the inflow unit  27  in which a transfer fluid F is caused to flow. On the tip of the inflow unit  27 , the transfer fluid inflow port  34  is formed. From the port, the transfer fluid F is caused to flow therein. Advancing through the inside the inflow unit  27 , the fluid reaches a branch unit  49 . By the branch unit  49 , the transfer fluid F caused to flow from the inflow unit  27  is split. A part of the transfer fluid F flows straight as it is and flows into the space unit  35  of the main body  36  via the inflow port  45  of the middle outflow unit  29 . The transfer fluid F caused to flow in the space unit  35  is caused to flow along an inner surface of the main body unit  41  having a funnel-like shape. Then, the part of the transfer fluid F passes through the middle outflow channel  44  provided below the main body  36  and is caused to flow out as a middle flow F1 with particles (not shown) held in the space unit  35  from the particle outflow port  39 . 
     By the branch unit  49  of the inflow unit  27 , the other part of the transfer fluid F is split to the z direction. Then, the other part of the fluid is caused to flow into the peripheral outflow channel  46  of the peripheral outflow unit  31 . Then, the transfer fluid F advances along an inner surface of the peripheral outflow channel  46  and is caused to flow out as a peripheral flow F2 that surrounds the middle flow F1. 
     In the structural example shown in  FIG. 5 , a flow resistance of the middle flow F1 relative to the peripheral flow F2 (flow channel resistance between the branch unit  49  and the merged part  24 ) is set to be ten times. As shown in the flow line graph, the middle flow F1 that is branched from the inflow unit  27  is surrounded by the peripheral flow F2 also branched from the inflow unit  27  and is caused to stably flow out to the downstream side. 
       FIG. 6  is a diagram showing an example in which the particle outflow unit  20  shown in  FIG. 5  is expanded to a shape of an actual device with a main flow channel (micro flow channel)  50  for causing the particles C to flow, and a fluid numerical analysis is performed. The main flow channel  50  shown in the figure is a flow channel having a rectangular cross section which is perpendicular to the middle flow F1 and corresponds to the flow channel  2  shown in  FIG. 1 . That is,  FIG. 6  shows the analysis of how the middle flow F1 and the peripheral flow F2 that are caused to flow in the direction of gravity are transferred to the main flow channel  50  extended in the horizontal direction. 
     In this example, the flow channel resistance of the middle flow F1 is set to be 20 times as large as that of the peripheral flow F2. Further, a connection unit  52  is formed between the particle outflow unit  20  and the main flow channel  50 . The connection unit  52  has a diameter larger than a diameter of an outflow port  51  from which the peripheral flow F2 is caused to flow out. On a position approximately the same as a bottom surface of the connection unit  52 , the main flow channel  50  is formed so as to be extended from a side surface of the connection unit  52 . As a result of the fluid numerical analysis with the structure as described above, it is found that the middle flow F1 is caused to flow into the main flow channel  50  having the rectangular cross section, with the middle flow F1 surrounded by the peripheral flow F2 while keeping a similar figure. 
     A description will be given on a result of experimental confirmation of the numerical analysis. In a particle outflow unit having the same structure as shown in  FIG. 6 , a diameter t1 of the particle outflow port  39  is set to 10 μm, and a diameter t2 of the peripheral outflow channel  46  is set to 100 μm. Then, a width t3 (size in the y direction) of the main flow channel  50  connected thereto is set to 250 μm, and a height t4 (size in the z direction) thereof is set to 50 μm. In the experiment, a sample obtained by suspending a great number of 10-μm polystyrene particles in water is injected to the main body  36 . After that, the transfer fluid F is caused to flow from the inflow unit  27  by a volume flow rate of 1 μm per minute. 
     In the case where the particle outflow unit  20  provided with the flow adjustment structure according to the present technology, a standard deviation of the width of a particle distribution in a width direction in the main flow channel  50  was 4 μm. On the other hand, in the case where the sample containing the particle was caused to flow in the main flow channel  50  at the same flow rate without using the particle outflow unit  20 , the particles flowed over approximately entire width direction. From this result, it is found that the particles can be caused to stably flow with the particles aligned by using the present technology. 
     As described above, in the particle outflow unit  20  as the flow channel device according to the present technology, the part of the transfer fluid F caused to flow from the transfer fluid inflow port  34  is caused to flow from the inflow port  45  of the middle outflow unit  29  into the main body  36 . Then, the particles C in the main body  36  are caused to flow from the particle outflow port  39  to the middle flow channel area  28 . Around the particle outflow port  39 , the peripheral outflow channel  46  of the peripheral outflow unit  31  is disposed. Via the peripheral outflow channel  46 , the other part of the transfer fluid F caused to flow from the transfer fluid inflow port  39  is caused to flow out to the peripheral flow channel area  30  that surrounds the middle flow channel area  28 . As a result, it is possible to cause the particles C to stably flow out in the middle flow channel area  28 . Consequently, it is possible to sort the particles with high accuracy in a sorting process of the particles (to be described later). 
     For example, it is thought that the middle flow F1 for causing the particles C to flow and the peripheral flow F2 for facilitating the flow adjustment of the particles are caused to flow in while being controlled independently of each other. That is, a flow called a sheath flow is caused to flow as the peripheral flow F2. However, in a minute flow rate area with approximately 1 μm per minute as in this embodiment, to configure an automatic control mechanism for maintaining the flow rate ratio between the middle flow F1 and the peripheral flow F2 to be constant or to measure the flow rate therefor is difficult, and thus precise control is difficult. 
     In this embodiment, the transfer fluid F caused to flow from the transfer fluid inflow port  34  is split and caused to flow into the middle outflow unit  29  and the peripheral outflow unit  31 . As a result, as described above, the middle flow F1 and the peripheral flow F2 are caused to flow out with the constant flow rate ratio. That is, it is possible to maintain the flow rate ratio to be constant passively only by the transfer fluid F caused to flow from the transfer fluid inflow opening  34 . Therefore, it is possible to stably align and cause the particles C to flow in the flow channel  50  without a specific flow rate automatic control method. By aligning the particles C, it is possible to improve analysis accuracy of an optical method, an electrical method, or the like for the particles C in the main flow channel  50  or on a later stage of the main flow channel  50 . In addition, in the case where, by using some drive forces in the main flow channel  50  or on the later stage of the main flow channel  50 , the particles C are sorted and extracted, it is possible to improve performance thereof. 
     Further, in the case where the particle outflow unit  20  according to the present technology is not used, it is difficult to exclude the possibility of mixture of a material derived from another sample, because the particles remain in a sample introduction tube in a sample introduction mechanism such as a particle analysis apparatus, or a particle suspension is brought into contact with the tube even once, for example. In contrast, in this embodiment, it is possible to cause the particles C to stably flow with the particles aligned and cause the sample suspension to stably flow in the middle flow channel area  28 , with the result that the problem described above can be prevented. 
       FIG. 7  is a perspective view showing a schematic structure of the sorting unit  5  shown in  FIG. 2 .  FIG. 8  is a plan view showing the sorting unit  5 .  FIG. 9  is a cross-sectional view of the sorting unit  5  taken along the linen A-A of  FIG. 8 . 
     The sorting electrode unit  8  is provided with a common electrode  81  having a first area and guide electrodes  83  and  84  each having a second area different from the first area. In this embodiment, the second area is smaller than the first area. In the following description, the pair of guide electrodes  83  and  84  is referred to as a “guide electrode structure  82 ”. 
     The common electrode  81  is provided on the back surface side of the sheet-shaped member  13 , for example, and the guide electrode structure  82  is provided on a bottom surface  2   d  in the flow channel  2 . End portions of the common electrode  81  and the guide electrode structure  82  on the upstream side are disposed on the downstream side in relation to the particle input unit  3   b , and end portions thereof on the downstream side are disposed on the upstream side in relation to the branch channels  2   a  and  2   b.    
     The common electrode  81  may be provided on the front surface side of the sheet-shaped member  13 , for example. 
     The common electrode  81  functions as a ground electrode. The common electrode  81  has a width in a y direction, which is substantially the same as the width of the flow channel  2  in the y direction, and has a length in the x direction to such an extent that the guide electrode structure  82  is covered therewith as shown in  FIG. 8 , for example. The common electrode  81  typically has a planar rectangular shape. The length of the common electrode  81  in the x direction may be longer or shorter than the length of the guide electrode structure  82  by a predetermined length. 
     The number of guide electrodes is multiple, for example, two. The guide electrodes  83  and  84  each have an elongated shape (band shape or rail shape) in a direction in which a liquid flows. One width of the guide electrode  83  or  84  in the y direction is formed to be smaller than that of the common electrode  81 . The guide electrode structure  82  includes a linear portion  82   a  provided along the x direction, which is a mainstream direction of the liquid, and a direction change portion  82   b  provided so that a direction is changed from the linear portion  82   a  toward the branch channel  2   a , that is, provided so as to be bent. A bend angle α (see,  FIG. 8 ) will be described later. The linear portion  82   a  functions as an approach section of particles up to the direction change portion  82   b.    
     As shown in  FIG. 8 , the linear portion  82   a  is disposed so as to be closer to the branch channel  2   b  side in the y direction in the flow channel  2 . More specifically, in the linear portion  82   a , an area between the guide electrode  83  on the inner side in the y direction in the flow channel  2  and the guide electrode  84  on the outer side is disposed on the branch channel  2   b  side in relation to a branch reference line J. The branch reference line J indicates a position of a branch point of the branch channels  2   a  and  2   b  in the y direction. The branch reference line J is substantially the center position in the flow channel  2  in the y direction. 
     To the common electrode  81  and the guide electrode structure  82 , an AC power source  75  operated by the analysis unit  70  applies an AC voltage, for example. The common electrode  81  is connected to the ground as described above and is kept 0 V substantially. The two guide electrodes  83  and  84  each function as an active electrode that is driven at substantially the same potential. To those electrodes, a drive voltage having an amplitude of 1 to 30 V is applied. The frequency of the AC drive voltage is 1 kHz to 100 MHz. 
     As shown in  FIG. 8 , the input hole  3   c  provided in the particle input unit  3   b  is provided on the branch channel  2   b  side in the y direction in relation to the branch reference line J. With this structure, the particles C input from the input hole  3   c  can pass on the branch channel  2   b  side in the y direction in relation to the branch reference line J and can pass above the guide electrode structure  82 . 
     (Sorting Operation by Sorting Flow Channel Unit) 
     Typically, intervals between particles C input through the particle input unit  3   b  are each set to at least a distance equal to or longer than a length of the sorting electrode unit  8  in the x direction. This is because the sorting unit  5  typically performs either one of an application of a guide electrical field for each particle C and a stop thereof, thereby performing sorting for each particle C. The flow velocity of the liquid (moving velocity of the particles C) can be set as appropriate, for example, set to approximately several mm/s. The velocity is capable of being controlled by a pump (not shown). 
     In the case where the drive voltage is not applied to the sorting electrode unit  8 , the guide electrical field is not formed. In this case, as shown in  FIG. 10 , non-target particles above the guide electrode structure  82  pass through the sorting electrode unit  8  while mostly maintaining the position in the y direction and flow into the branch channel  2   b  integrally with the flow of the liquid (see, particle C2). 
     In the case where the drive voltage is applied to the sorting electrode unit  8 , a dielectrophoretic force toward the y direction is given to the target particles above the guide electrode structure  82  by the guide electrical field. As will be described later, the guide electrical field gives the target particles such a dielectrophoretic force that the target particles are disposed between the two guide electrodes  83  and  84 . Thus, the target particles move along with the liquid so as to be disposed between the guide electrodes  83  and  84 . As a result, a target particle C1 flows into the branch channel  2   a.    
     The drive voltage is applied to the guide electrode  83  at timing before the target particle flows into the sorting electrode unit  8 . The timing of the application of the drive voltage is preset in accordance with a distance from the input hole  3   c  to the sorting electrode unit  8 , the flow velocity of the liquid, and the like. 
     In this embodiment, by the particle outflow unit  20  having the flow adjustment structure, the particles C are input to the input hole  3   c  with the particles aligned. Therefore, it is possible to cause the particles C to stably flow on the appropriate position in the flow channel  2 . As a result, by applying the guide electrical field, the dielectrophoretic force of the target particle C1 can be appropriately generated. Consequently, it is possible to sort the particles C with high accuracy. 
     (Dielectrophoretic Force by Guide Electrical Field) 
     A. Generation Principle 
     The dielectrophoretic force has a property of being formed in a direction from an area having a stronger electrical field to an area having a weaker electrical field. The more abrupt difference in the intensity of the electrical field is caused, the larger the dielectrophoretic force becomes. In the present technology, an area having a weaker electrical field is formed between the guide electrodes  83  and  84 . As a result, in an area from, for example, an edge of the guide electrode  83  (or  84 ) to the center between the guide electrodes  83  and  84 , an abrupt difference in the intensity of the electrical field is generated. The guide electrical field is in such a state, thereby positioning the target particle C1 in the area in the guide electrode  83 . 
     B. Example of Sorting Electrode Unit 
       FIG. 11  is a diagram showing an example of sizes of parts of the sorting electrode unit.  FIGS. 12 to 14  are diagrams each showing a simulation result of an electrical field intensity distribution for explaining the guide electrical field generated by the sorting electrode unit shown in  FIG. 11 . In those figures, to make it easy to grasp the electrical field intensity distribution, auxiliary lines are drawn with broken lines. In actuality, the applicant of the present technology can disclose  FIGS. 12 to 14  as color figures. 
     As shown in  FIG. 11 , a flow channel  2 A having a rectangular parallelepiped shape is provided. As the sizes of the flow channel  2 A, a length in the mainstream direction (x direction), a width, and a height are set to Lch (=100 μm), Wch (=100 μm), and Hch (=50 μm), respectively. A length of the common electrode  81  in the mainstream direction and a width thereof are set to Lch and Wch, respectively. A length of each guide electrode in the mainstream direction and a width thereof are set to Lch and Wel (=10 μm), respectively. Further, a width of an area of a gap in the guide electrode structure  82  is set to Wgap (=30 μm). The unit of an electrical field E in this case is kV/m. 
       FIG. 12A  shows an electrical field intensity distribution on an x-y plane at a position of z=10 μm in the height direction.  FIG. 12B  shows an electrical field intensity distribution on a y-z plane at a position of x=50 μm in the mainstream direction. The guide electrodes ( 83  and  84 ) are disposed within ranges of 25 to 35 μm and 65 to 75 μm, respectively, in the range of 0 to 100 μm in the y direction. 
       FIG. 13A  shows an intensity distribution of a dielectrophoretic force generated only rightward in the figure, out of a dielectrophoretic force F DEPy  that operates in the y direction on the y-z plane at the position of x=50 μm. Similarly,  FIG. 13B  shows an intensity distribution of a dielectrophoretic force generated only leftward in the figure, out of the dielectrophoretic force F DEPy  on the y-z plane at the position of x=50 μm.  FIG. 14A  shows an intensity distribution of a dielectrophoretic force generated only upward in the figure, out of a dielectrophoretic force F DEPz  that operates in the z direction on the y-z plane at the position of x=50 μm.  FIG. 14B  shows an intensity distribution of a dielectrophoretic force generated only downward in the figure, out of the dielectrophoretic force F DEPz  on the y-z plane at the position of x=50 μm. 
       FIGS. 13A and 13B  show the distributions having forms obtained by inverting each other, and the same holds true for  FIGS. 14A and 14B . For example, the white area of  FIG. 13A  shows that the dielectrophoretic force that operates leftward is distributed, and the white area of  FIG. 13B  shows that the dielectrophoretic force that operates rightward is distributed. The same holds true for  FIGS. 14A and 14B . 
     The dielectrophoretic force can be calculated on the basis of the above expression (1). The unit of the dielectrophoretic force in this case is nN. 
     Out of those figures, for example, as can be seen from  FIG. 12B , the strongest electrical field is generated in the vicinity of the edge of each guide electrode, and the weakest electrical field is generated between the guide electrodes ( 83  and  84 ). Further, a weak electrical field also exists in the vicinity of 0 μm and 100 μm in the y direction. With reference to  FIGS. 14A and 14B , it is found that intensity gradients of the dielectrophoretic force are generated within a range of about 15 μm with respect to the center between the guide electrodes ( 83  and  84 ) and within a range of about 30 μm in the z direction. 
     As a result, by the guide electrical field formed, a steeper intensity gradient in the y direction than the intensity gradient in the z direction can give a dielectrophoretic force that is attracted to a direction toward the center between the guide electrodes  83  and  84 . 
     A movement performance in the y direction of the particles in the direction change portion  82   b  of the guide electrode structure  82  is mainly determined by the bend angle α of the direction change portion  82   b  the speed of the liquid in the mainstream direction. The movement performance is defined in accordance with the degree of the dielectrophoretic force that operates in the y direction on a region boundary (curved surface represented by F DEPz =0) where the dielectrophoretic force in the downward z direction operates. 
       FIG. 15  is a diagram showing the degree of the dielectrophoretic force F DEPy  (including rightward and leftward dielectrophoretic forces that are directed toward the center between the guide electrodes  83  and  84  in this case) that operates in the y direction on a boundary where positive and negative dielectrophoretic forces in the z direction are switched at a position of the height z. From  FIG. 15 , it is found that F DEPy  is significantly changed in the z direction and is stronger as the height position is lower. That is, depending on an equilibrium position in the height direction of the movement of the particles, performance to be obtained (that is, F DEPy  toward inside) is significantly changed. The equilibrium position in the height direction is significantly affected by the size of the particle or a force that acts on the particle from the liquid in proximity to a wall surface of the flow channel. 
     In this embodiment, it is possible to align the particles in the middle flow channel area and cause the particles to flow out into the input hole. Thus, it is possible to flow the particles with the particles aligned without positional variations also in the height direction of the flow channel. As a result, it is possible to stabilize the dielectrophoretic force F DEPy  that acts on the particles. 
       FIG. 16  is a diagram showing a simulation result of tracks of particles in the case where the particles flow into an area where the guide electrode structure  82  is disposed from different positions in the y direction. The upper diagram of  FIG. 16  is viewed in the y direction, and the lower diagram thereof is viewed in the z direction. 
     As shown in the lower graph of  FIG. 16 , out of the particles that flow into the area in the guide electrode  83 , particles other than particles (y p,0 =34 μm) having a track indicated by a dotted and dashed line move through a path along the guide electrodes  83  and  84 . Particles that pass through an area closer to the center between the guide electrodes  83  and  84  in the y direction are less likely to be affected by the dielectrophoretic force in the upward z direction, and stably move through a path along the guide electrode structure  82  by F DEPy  toward inside and the dielectrophoretic force in the downward z direction. Particles that pass through an area which is more distant from the center between the guide electrodes  83  and  84  in the y direction are more likely to be affected by the dielectrophoretic force in the upward z direction, but moves through the path along the guide electrode structure  82  by a force attracted to the center by F DEPy  toward inside. 
     The particles having the track indicated by the dotted and dashed line are brought into a state where the height in the z direction is relatively high in the vicinity of x=50 μm, and F DEPy  becomes small (see,  FIG. 15 ), and therefore the particles go straight in the x direction as they are. Further, the particles that flow into the area above the guide electrode  84  (particles having a track indicated by the solid line (y p,0 =30 μm)) also show the same result. By using the flow channel device (particle outflow unit) according to the present technology, it is possible to prevent generation of the particles that flow along such a track and achieve sorting of the particles with high accuracy. 
     As described above, by the sorting flow channel unit  55  according to this embodiment, because the area of the common electrode  81  and the area of the guide electrode  83  (and  84 ) are different from each other, the sorting electrode unit  8  is capable of forming the guide electrical field having the non-uniform electric flux density in the flow channel  2 . In addition, because the guide electrical field is formed so that the target particle C1 is guided to the branch channel  2   a  predetermined, the sorting flow channel unit  55  is capable of sorting the particles appropriately. 
     Further, the shapes of the guide electrodes  83  and  84  are elongated shapes. Therefore, as the width of the common electrode  81  is longer than those of the guide electrodes  83  and  84 , the degree of freedom of positioning of the guide electrodes  83  and  84  with respect to positioning of the common electrode  81  is increased in the manufacture of the sorting flow channel unit  55 . In other words, a precise alignment of the guide electrodes  83  and  84  with respect to the common electrode  81  is unnecessary. Furthermore, as a result, the productivity of the sorting flow channel unit  55  is improved, and thus it is possible to save the cost. 
     In this embodiment, the two elongated guide electrodes  83  and  84  are provided, with the result that the guide electrical field is easily formed, and the particles are easily guided to the branch channel  2   a . Thus, it is possible to increase the sorting accuracy. 
     It should be noted that the structure of the sorting flow channel unit  55  is not limited, and various structures may be used therefor. By using the flow channel device according to the present technology, it is possible to cause the particles to flow in the flow channel with the particles aligned, so the particles can be sorted with high accuracy. 
     (Another Structural Example of Sorting Flow Channel Unit) 
       FIG. 17  is a schematic perspective view showing another structural example of the sorting flow channel unit  55 , and  FIG. 18  is a schematic plan view thereof. In the following description, the description of the same parts, functions, and the like as in the structural example described above will be simplified or omitted, and different points will be mainly described. 
     A guide electrode structure  182  according to this structural example has an entrance portion  182   c  provided at an end portion on the upstream side thereof. Here, a linear portion  182   a  and a direction change portion  182   b  are set as a main portion. In the entrance portion  182   c , a distance between the guide electrodes  183  and  184  is formed to be longer than a distance therebetween in the main portion. In this embodiment, the distance between the guide electrodes  183  and  184  in the entrance portion  182   c  is formed so as to be increased toward the upstream side. More specifically, both of the two guide electrodes  183  and  184  are bent so that directions thereof are changed from the mainstream direction toward the upstream side. 
     A common electrode (not shown) has the same shape and the like as the common electrode  81  according to the structural example described above. 
     Because of the shape of the entrance portion  182   c  of the guide electrode structure  182  as described above, the particles C are likely to be attracted into an area between the guide electrodes  183  and  184  in the main portion of the guide electrode structure  182 . Therefore, it is possible to provide a wide acceptable range for an outflow position of the particles by the flow channel device according to the present technology, that is, in relation to which part of the input hole  3   c  the middle flow channel area in which the particles flow is fit to. Further, the degree of freedom for disposition of the input hole  3   c  in the y direction is also increased. 
       FIG. 19  is a diagram showing a simulation result of tracks of the particles with the sorting flow channel unit shown in  FIGS. 17 and 18 . The intent of this simulation is the same as that described with reference to  FIG. 16 . In the simulation shown in  FIG. 19 , the particles having the same variations similar to the case of  FIG. 16  in the y direction are entirely attracted to the area between the guide electrodes  183  and  184 . 
     It should be noted that  FIGS. 20A and 20B  are diagrams showing design examples of approach sections of the guide electrode structures  82  and  182  according to the two structural examples described above, respectively. The values of those figures may be values shown in the table on the lower part of  FIG. 11 . 
     To efficiently guide the particles by the guide electrical field, the bend angle, the size, the shape of the entrance portion, and the like can be designed in consideration of a particle size, a height, a width of the flow channel in accordance with a liquid material, or the velocity of the particle, for example. 
     As an example, as shown in  FIG. 18 , a width t1 of the end portion of the entrance portion  182   c  on the upstream side is designed as follows. The width t1 is set to be larger than a distance from an inner side surface  2   g  provided on the branch channel  2   b  side in the y direction, out of an inner side surface  2   f  and the inner side surface  2   g  of the flow channel  2 , which are opposed to each other, to the branch position of the branch channel  2   a  and the branch channel  2   b  in the y direction (i.e., distance to the branch reference line J). 
     Alternatively, as shown in  FIG. 18 , the guide electrode structure  182  is designed so that at least a part of the entrance portion ( 182   c ) of the guide electrode  183  on the branch channel  2   a  side in the y direction, of the pair of the guide electrodes  183  and  184 , is disposed on the branch channel  2   a  side in the y direction from the branch position of the branch channels  2   a  and  2   b.    
     Alternatively, in consideration of the variation of positions where the particles exist in the y direction, the distance between the guide electrodes  183  and  184  of the entrance portion  182   c  may be designed. For example, when the variation in the y direction is represented in a normal distribution, in the case of a standard deviation σ, the width t1 of the end portion of the entrance portion  182   c  on the upstream side may set to have a width (that exceeds 1σ) larger than a width of σ. 
     In this embodiment, it is possible to cause the particles flow with the particles aligned by the particle outflow unit, with the result that a burden on the design for the guide electrode structure as described above can be reduced. That is, the variation of the particles in the y direction is small (i.e., the standard deviation σ takes a small value), so the particles can be efficiently guided without strictly setting the distance between the guide electrodes  183  and  184 . 
       FIGS. 21 to 23  are diagrams for explaining effectiveness of the flow channel device  20  (particle outflow unit  20 ) according to the present technology.  FIG. 21  is a diagram showing another structural example of a sorting flow channel unit  255  for sorting the particles C caused to flow out by the flow channel device  20 . The sorting flow channel unit  255  is provided with a flow channel  210  having two stages in a thickness direction (z direction) of the sorting flow channel unit  255 . In  FIG. 21 , a first flow channel  211  provided on an upper stage has a first inlet  211   a . On the first inlet  211   a , the flow channel device  20  according to the present technology is disposed, and the middle flow containing the particles C and the peripheral flow that surrounds the middle flow are caused to flow out to the first inlet  211   a . The particles C are caused to flow in a predetermined flow channel area (typically, middle flow channel area) of the first flow channel  211  with the particles aligned. 
     A second flow channel  212  provided on the lower stage has a second inlet  212   a . The transfer fluid that does not contain the particles C is caused to flow to the second flow channel  212  via the second inlet  212   a  with a pump (not shown) or the like. As shown in  FIG. 21 , the first flow channel  211  and the second flow channel  212  are communicated with each other through a narrow channel  213  formed on a predetermined position. The narrow channel  213  has such a size as to allow particles to pass therethrough one by one. The particles C caused to flow in the first flow channel  211  in the aligned state are caused to flow into the second flow channel  212  via the narrow channel  213 . 
     In the sorting flow channel unit  255  shown in  FIG. 21 , an area including the narrow channel  213  serves as a measurement unit  260 . The measurement unit  260  includes measurement electrodes  214   a  and  214   b  with the narrow channel  213  sandwiched therebetween. The measurement electrodes  214   a  and  214   b  corresponds to the measurement electrodes  4   a  and  4   b  shown in  FIG. 2  and are provided on the lower side of the first flow channel  211  and on the upper side of the second flow channel  212 , respectively. To the measurement electrodes  214   a  and  214   b , an AC voltage is applied, and an electrical characteristic at a time when the particles pass through the narrow channel  213  is measured. 
     On the downstream side of the second flow channel  212 , a guard unit  290  and a sorting unit  205  are provided in the stated order. The guard unit  290  includes guard electrodes  291   a  and  291   b  disposed so as to be opposed on the upper side and the lower side of the second flow channel  212 , respectively. The guard electrodes  291   a  and  291   b  form an electrode pair and are connected to ground. The guard unit  290  is disposed between the measurement unit  260  and the sorting unit  205  and exerts an electrical guard function therebetween. For example, by the guard unit  290 , it is possible to suppress a noise due to a voltage signal applied to the sorting unit  205  from being mixed in the measurement unit  260 . 
     The sorting unit  205  includes a sorting electrode unit  208  that forms a guide electrical field. As shown in  FIG. 21 , on the upper side of the second flow channel  212 , a common electrode  281  is disposed, and a guide electrode  283  is disposed on the lower side of the second flow channel  212  so as to be opposed to the common electrode  281 . The sorting electrode unit  208  forms the guide electrical field as necessary, and the dielectrophoretic force is given to the target particle. As a result, the target particle and the other particles are sorted, and the particles C are caused to flow to a predetermined particle obtaining unit  250 . 
       FIG. 22  is a diagram showing a simulation result of tracks of the particles that are caused to flow in the narrow channel  213  from different positions in a flow channel width direction of the first flow channel  211 . For example, in the flow channel width direction (y direction), the particle C that advances along a position significantly distanced from a reference line O that passes the center of the narrow channel  213  does not enter the narrow channel  213  but passes by the narrow channel  213 . As a result, it may be impossible to sort the particles C. Further, for even the particles C that enter the narrow channel  213 , if positions thereof vary in the flow channel width direction, positions of the particles C at a time when the particles C pass through the narrow channel  213  vary. 
     In the simulation shown in  FIG. 22 , the particle that advances along the reference line O directly flows in and passes through the narrow channel  213  and then flows into the second flow channel  212 . Therefore, in this case, along the reference line O (at an angle of O degree with respect to the reference line O), the particle C flows in the narrow channel  213 . The particle that advances along a position distanced from the reference line O by 25 μm in the flow channel width direction flows in the narrow channel  213  at an angle of approximately 30 degrees with respect to the reference line O. The particle C that advances along a position distanced therefrom by 35 μm flows in the narrow channel  213  at an angle of approximately 45 degrees. The particle C that advances along a position distanced therefrom by 50 μm flows in the narrow channel  213  at an angle of approximately 90 degrees. In this way, when the angles at which the particles flow in the narrow channel  213  are different, the positions along which the particles C advance in the narrow channel  213  are also different. Thus, due to the variation of the position in the flow channel in the flow channel width direction, the variation in passing positions in the narrow channel is caused. The occurrence of the variation in passing positions in the narrow channel results in a reduction of accuracy of the measurement by the measurement unit  260  and the analysis for a signal measured. As a result, accuracy of determining the target particles is also degraded. 
     In addition, as described above, in association with the variation in the passing positions in the narrow channel, if the positions of the particles vary in the flow channel width direction and the height direction in the second flow channel  212 , it becomes difficult to appropriately generate the dielectrophoretic force by the guide electrical field. 
       FIG. 23  is a schematic diagram of a track of a cell and a velocity distribution in the height direction of the second flow channel  212  in the sorting flow channel unit  255 . As shown in  FIG. 23 , in the height direction of the second flow channel  212 , the flowing velocity of the particle C differs. The velocity is increased in the middle portion of the second flow channel  212  in the height direction, and is reduced toward the upper side and the lower side. Due to the variation in the passing position in the narrow channel of the particles, the height position of the particles C that flow in the second flow channel  212  varies, with the result that the flowing velocity of the particles varies. If the velocity of the particles C that advance in the second flow channel  212  varies, it becomes difficult to adjust a sorting timing (timing at which the guide electrical field is generated) by the sorting unit  205 , which degrades the sorting accuracy. 
     As described above, if the particles C caused to flow out in the first flow channel  211  vary in the flow channel width direction, various factors that degrade the sorting accuracy are caused. In view of this, it is very effective that the flow channel device  20  according to the present technology is used to cause the particles C to flow out in the first flow channel  211  with the particles C aligned. As a result of experimental confirmation of the simulation described above, by using the flow channel device  20 , the positional variation in the first flow channel  211  in the flow channel width direction is reduced. Further, the particles pass through the narrow channel  213  at a constant height, with the result that the particle velocity in the second flow channel  212  is stabilized. As a result, it is possible to sort the particles with high accuracy. 
     Other Embodiments 
     The present technology is not limited to the above embodiments, and various other embodiments can be implemented as follows. 
     For example,  FIG. 24  is a schematic diagram showing another structural example of a sealing member  340  for sealing a particle supply port  338  of a middle outflow unit  329 . For example, in a sample injection process as shown in  FIG. 24 , a valve or the like made of elastomer, which is opened and closed by an insertion operation (arrow A) of a pipette, may be used as the sealing member  340 . When the pipette is inserted in an insertion hole  341 , by the insertion pressure, an opening and closing unit  342  is opened, and the pipette is inserted therein. In this state, a sample is supplied to a space unit  335  in the middle outflow unit  329  via the pipette. After the sample is supplied, the pipette is removed, and thus the opening and closing unit  342  is closed, thereby sealing the particle supply port  338 . Even if a pressure is applied from the inside of the sealing member  340  (arrow B), the opening and closing unit  342  is not opened and closed, and the particle supply port  38  is appropriately sealed. Such a device as to have the structure like a check valve may be used. Further, a member having a function of adjusting the pressure in the space unit  335  may be used as the sealing member  340 . 
     In addition, the particle supply port  338  is not sealed but opened to the atmosphere, and the middle flow and the peripheral flow may be flow out. For example, by appropriate container configuration design and pressure loss design, it is possible to achieve such a structure that the sample is not leaked to the outside (atmosphere side) of the device. For example, a negative pressure is given to the merged part and the downstream side of the main flow channel to perform operation, such a structure can be achieved. As a result, it is possible to simplify the structure of the holding unit. 
     By appropriately designing the structure of the sealing member as described above or designing the container configuration or the like with the supply port opened, for example, when the middle flow and the peripheral flow can be caused to flow out in the micro flow channel without splitting the transfer fluid from the transfer fluid inflow port, the same effect as described above can be exerted. The flow channel device having such a structure can be considered as a device conceptually having the same technical idea as the flow channel device according to the present technology. That is, it can be considered that the above technology is contained as the technology for maintaining the flow rate ratio between the middle flow and the peripheral flow to be constant in the small flow rate area with approximately 1 μL per minute. Further, the flow channel devices as described above (for example, flow channel device that splits the transfer fluid to make the flow rate ratio constant, flow channel device that makes the flow rate ratio constant with a different structure, or the like) can be used as interchangeable devices as necessary. 
       FIGS. 25A to 25C  are schematic diagrams showing other structural examples of a middle outflow channel up to particle outflow ports ( 439 ,  539 , and  639 ), respectively. As shown in  FIG. 25A , in a tapered unit  443  the diameter of which is gradually reduced from a side wall unit  442  to the particle outflow port  439 , an inner surface  451  and an outer surface  452  may have different tilt angles. The tilt angles of the inner surface  451  and the outer surface  452  may be individually designed in accordance with the flow of the transfer fluid in a space unit  435  and the flow of the transfer fluid in a peripheral outflow channel  446 . 
     In  FIG. 25B , a tapered unit  543  is formed as a middle outflow channel as it is. That is, at a lowermost end part of the tapered unit  543 , the particle outflow port  539  is formed. With this structure, it is possible to simplify the structure of the middle outflow unit. In this case, as shown in  FIG. 25C , a tapered unit  634  may be designed to have a thickness which is gradually reduced toward the particle outflow port  639 . 
     As shown in  FIGS. 3 and 4 , as described above, the peripheral outflow channel  46  is formed concentrically with the particle outflow port  39  as the center. With this structure, the particles C can be caused to stably flow out with the particles C aligned in the middle flow channel area  28 . However, for example, the peripheral outflow channel  46  may not be formed concentrically. That is, the particle outflow port  39  may be disposed at an eccentric position with respect to the annular peripheral outflow channel  46 . With this structure, it is possible to appropriately set the position to which the particles C are desired to be caused to flow. It should be noted that in the above description, the predetermined area to which the particles C are desired to be caused to flow is set as the middle flow channel area  28 . However, the predetermined area is not limited to the middle of the flow channel. The position of the particle outflow port  39  may be appropriately fitted to the position to which the particles C are desired to be caused to flow. 
     The direction in which the particles in the flow channel device according to the present technology are caused to flow out is not limited to the direction of gravity. For example, the flow channel device may be disposed along a horizontal direction, and the particles may be caused to flow in the horizontal direction. In addition to this, the angle at which the particles are caused to flow out may be set arbitrarily. Further, the extended direction of the flow channel as an outflow destination is not also limited. There is no limitation on the use of the flow channel device according to the present technology in order to cause the particles to flow to the main flow channel that is extended in the horizontal direction as described above. Further, the direction of the route to the outflow destination of the sorting apparatus, the flow channel device, or the like and the structures thereof are not also limited (for example, connection unit  52  shown in  FIG. 6 ). 
     In the above description, to cause the particles to flow out to the particle sorting apparatus, the flow channel device according to the present technology is used. However, the structure is not limited to this. The flow channel device according to the present technology may be used for an apparatus for analyzing the particles or another apparatus. That is, the use purpose of causing the particles to flow out, the kind of the particles, and the like are not limited. 
     As the guide electrode structure according to the above structural example, two guide electrodes are given as an example. However, three or more guide electrodes may be provided. 
     In addition, the drive voltage which is applied to the sorting electrode unit is the AC voltage but may be a DC voltage. 
     The flow channel, the branch channel, and the like described above each have the linear shape but may have a curved shape. The cross section of the flow channel has the rectangular shape but may have a circular shape, an oval shape, a polygonal shape other than the rectangle, or a shape obtained by combining those shapes. 
     The common electrode has the rectangular shape but may have a circular shape, an ellipse, an oval shape, a polygonal shape, or any other shape. Further, the shape of the common electrode can differ depending on the shape of the flow channel  2 . 
     The measurement unit measures impedance depending on the particles but may measure a fluorescent intensity or a scattered light intensity depending on the particles. The analysis unit generates a sorting signal on the basis of the values measured. 
     At least two of the features of the embodiments described above can be combined. 
     It should be noted that the present technology can take the following configurations. 
     (1) A flow channel device, including: 
     an inflow unit into which a transfer fluid that transfers particles is caused to flow; 
     a first outflow unit including an inflow port into which a part of the transfer fluid caused to flow from the inflow unit is caused to flow, a holding unit that is connected to the inflow port and holds particles, and a particle outflow port from which the particles held in the holding unit are caused to flow out to a predetermined flow channel area by the transfer fluid caused to flow from the inflow port; and 
     a second outflow unit including a peripheral outflow channel through which another part of the transfer fluid caused to flow from the inflow unit is caused to flow out to a peripheral flow channel area that surrounds the predetermined flow channel area, the peripheral outflow channel surrounding at least the particle outflow port. 
     (2) The flow channel device according to Item (1), in which 
     the first and second outflow units respectively cause the particles and the transfer fluid to flow out as a laminar flow having a Reynolds number of 1 or less. 
     (3) The flow channel device according to Item (1) or (2), in which 
     the first and second outflow units respectively cause the particles and the transfer fluid to flow out in such a manner that a ratio between a flow rate in the predetermined flow channel area and a flow rate in the peripheral flow channel area falls within a range of 1:2 to 1:100. 
     (4) The flow channel device according to any one of Items (1) to (3), in which 
     the peripheral outflow channel is disposed concentrically with the particle outflow port as a center. 
     (5) The flow channel device according to any one of Items (1) to (4), in which 
     the holding unit includes
         a supply port for supplying the particles, the supply port having a diameter larger than that of the particle outflow port, and   a main body unit having a funnel-like shape, the main body unit including a tapered unit which connects the supply port and the particle outflow port with each other and a diameter of which is reduced from the supply port toward the particle outflow port.       

     (6) The flow channel device according to Item (5), in which 
     the supply port is sealed by a sealing member. 
     (7) The flow channel device according to Item (5), in which 
     the supply port is in a state of being released to an atmosphere. 
     (8) The flow channel device according to any one of Items (1) to (7), in which 
     the particle outflow port has a diameter that is smaller than ten times a diameter of the particle. 
     It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.