Abstract:
A microplate liquid handling system requiring minimum installation area, helping to avoid waste of various reagents, and making it possible to perform dispensing the various reagents in the shortest possible time. The microplate liquid handling system has a main frame body provided with a moving mechanism, a dispensing mechanism, and a stage. On the stage, a microplate, two dispensing tip containers, and two reagent vessels are mounted. Formed in the microplate are 12×8 wells, i.e., 96 wells in total, arranged in matrix. The microplate, the dispensing tip containers, and the reagent vessels are substantially of the same, rectangular configuration. Each of the two dispensing tip containers is capable of accommodating 12×8 dispensing tips in total in a matrix fashion.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a microplate liquid handling system and, more particularly, to a microplate liquid handling system for simultaneously delivering liquid reagent, liquid specimen, etc. to a plurality of desired wells for specimen/reagent reaction arranged in a microplate in n×m matrix. 
     2. Description of the Related Art 
     A microplate liquid handling system has conventionally been known which is used to deliver reagent, specimen, etc. to desired ones of a plurality of wells formed in a microplate. The microplate liquid handling system has a dispensing mechanism and a moving mechanism, and the dispensing mechanism is equipped with a cylinder having a nozzle. Mounted to the nozzle is a dispensing tip, through which liquid can be sucked and discharged. The cylinder is equipped with a plunger for sucking liquid into the dispensing tip mounted to the nozzle and for discharging liquid from the interior of the dispensing tip. 
     As disclosed, for example, in JP 8-271528 A and JP 5-232124 A, the moving mechanism is capable of moving the nozzle to an appropriate position above a desired well in the microplate, and the dispensing mechanism can be moved in the lateral, longitudinal, and vertical directions (the X-, Y-, and Z-axis directions) above the microplate. Generally speaking, arranged in the microplate are 96 wells in 12×8 matrix, and so-called dispensing is conducted, that is, reagent or specimen is delivered to a desired well from a dispensing tip mounted to the nozzle of the cylinder of the dispensing mechanism, so that reagent-specimen reaction or the like is effected in the well. 
     There are four types of microplate liquid handling system: 12-gang type, 8-gang type, single-gang type, and 96-gang type. In a 12-gang type microplate liquid handling system, the nozzles of twelve cylinders arranged in parallel and in a straight line in the longitudinal direction of the microplate are operated in synchronism with each other, and it is possible to perform suction or discharge of liquid such as reagent collectively on the dispensing tips mounted to the twelve nozzles. For example, it is possible to simultaneously discharge reagent onto each of the specimens in the plurality of wells arranged longitudinally in a row in the microplate.  
     Similarly, in an 8-gang type microplate liquid handling system, eight nozzles arranged in parallel and in a straight line in the lateral direction of the microplate are operated in synchronism with each other, and it is possible to perform suction or discharge of liquid such as reagent collectively on the dispensing tips mounted to the eight nozzles. In a 96-gang type microplate liquid handling system, 96 nozzles arranged in 12×8 matrix are operated in synchronism with each other, and it is possible to perform suction or discharge of liquid such as reagent collectively on the dispensing tips mounted to the 96 nozzles and to discharge reagent or the like simultaneously onto all the 96 wells in the microplate. In a single-gang type microplate liquid handling system, a single nozzle is solely operated. 
     For example, regarding enzyme reaction tests, such as drug metabolic reaction tests, there are a number of kinds of test using a microplate with wells arranged in a n×m in matrix. In these testing, m kinds of samples are poured into all the longitudinally arranged wells and n kinds of enzyme reagents are poured into all the laterally arranged wells to collectively effect n×m enzyme reactions. 
     To perform dispensing row by row both longitudinally and laterally, the conventional 96-gang type microplate liquid handling system, in which 96 nozzles collectively perform ganged operation, solely requires attachment of dispensing tips to a certain row of the 96 nozzles. However, a tip container must require an area n-times or m-times as large as the requisite area for containing the 96 tips. That is, a large installation place is required. Further, a critical error may occur in the test results due to attachment of the row of dispensing tips to an erroneous row of the nozzles. Further, the reagent vessel for containing sample and reagent also has to exhibit a similar largeness. This requires a large amount of sample or reagent, which is valuable in itself, resulting in a marked deterioration in test efficiency. 
     In the case of a n- or m-gang type microplate liquid handling system fixed in terms of direction, n or m nozzles collectively perform ganged operation, so that it is possible to collectively dispense sample or reagent in the arrangement direction of the microplate liquid handling system with a microplate in which the wells are arranged in matrix. However, in a direction perpendicular thereto, dispensing has to be performed with a single dispensing tip attached to a certain one of the n or m nozzles, as in the case of the 96-gang type microplate liquid handling system, so that it takes long time to complete dispensing, resulting in a deterioration in test efficiency. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a microplate liquid handling system requiring a minimum installation area, helping to avoid waste of various reagents, and capable of performing dispensing of various reagents in minimum time. 
     This and other objects of the present invention will be attained by a microplate liquid handling system including a main frame body, a dispensing mechanism, a moving mechanism, a microplate, first and second dispensing tip containers, and first and second reagent vessels. The dispensing mechanism includes a plurality of cylinders extending side by side and in parallel with each other by an even interval to provide a linear cylinder array. Each cylinder has a nozzle and a plunger and each dispensing tip is attachable to each nozzle for performing suction and discharge of liquid reagent or specimen through the dispensing tips by way of each plunger. Each dispensing tip is detachably connectable to each nozzle. The moving mechanism is supported to the main frame body for moving the dispensing mechanism in X-axis, Y-axis, and Z-axis directions directed perpendicular to each other. The microplate is placed in the main frame body and has a plurality of wells arranged in an n×m in matrix fashion. The plurality of cylinders are provided in a number that is equal to the larger of n and m. The liquid sucked into each dispensing tip is discharged onto each well through each dispensing tip simultaneously with each other. The first dispensing tip container is capable of containing n×m dispensing tips in a matrix fashion for permitting the nozzles to be attached with a first dispensing tip array directing in the Y-axis direction. The first dispensing tip container provides a longitudinal direction in parallel with the Y-axis direction. The second dispensing tip container is capable of containing n×m dispensing tips in a matrix fashion for permitting the nozzles to be attached with a second dispensing tip array directing in the X-axis direction. The second dispensing tip container provides a lateral direction in parallel with the X-axis direction. The first reagent vessel stores a reagent to be supplied to the dispensing tips of the cylinder array directed in the Y-axis direction. The first reagent vessel provides a longitudinal direction in parallel with the Y-axis direction. The second reagent vessel stores a reagent to be supplied to the dispensing tips of the cylinder array directed in the X-axis direction. The second reagent vessel provides a lateral direction in parallel with the X-axis direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG. 1  is a perspective view of a microplate liquid handling system according to a first embodiment of the present invention; 
         FIG. 2A  is a schematic diagram showing a rotating mechanism and a dispensing mechanism in the microplate liquid handling system of the first embodiment of the present invention, and shows a state in which the dispensing mechanism is at the origin; 
         FIG. 2B  is a schematic diagram showing a rotating mechanism and a dispensing mechanism in the microplate liquid handling system of the first embodiment, and shows a state in which the dispensing mechanism is at a 90-degrees position; 
         FIG. 3  is a flowchart illustrating dispensing process  1  conducted by the microplate liquid handling system of the first embodiment of the present invention; 
         FIG. 4  is a flowchart illustrating dispensing process  2  conducted by the microplate liquid handling system of the first embodiment of the present invention; 
         FIG. 5  is a plan view showing the on-stage layout of the microplate liquid handling system of the first embodiment of the present invention; 
         FIG. 6  is a perspective view of an essential portion of a microplate liquid handling system according to a second embodiment of the present invention; 
         FIG. 7  is a view showing an essential portion of a modification to the second embodiment for description of how an abutment member and a pulley in a microplate liquid handling system of the modification are opposed to each other; and 
         FIG. 8  is a partial perspective view showing two moving mechanisms in a microplate liquid handling system according to a modification. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A microplate liquid handling system according to a first embodiment of the present invention will now be described with reference to  FIGS. 1 through 5 . A microplate liquid handling system  1  has a main body  10 , which is equipped with a moving mechanism  20 , a rotating mechanism  30 , a dispensing mechanism  40 , and a stage  50 . The main body  10  has a substantially rectangular box-like outward configuration, and defines therein a substantially rectangular chamber  10   a  which is substantially geometrically similar to the outward configuration of the main body  10 . Partially formed in an upper surface  10 A and a front surface  10 B of the main body  10  are openings  10   b  and  10   c  outwardly open from within the chamber  10   a . The openings  10   b  and  10   c  have rectangular configurations which are respectively substantially geometrically similar to those of the upper surface  10 A and the front surface  10 B. The stage  50  is provided on an inner peripheral surface defining the chamber  10   a , on a bottom surface  10 C of the main body  10 . Further, the main body  10  is equipped with a switch group  11 , a control device (not shown), etc. for effecting, starting, stopping, etc. of the microplate liquid handling system  1 . The above-mentioned control device (not shown) controls the movements of the moving mechanism  20  in the X-, Y-, and Z-axis directions described later, rotation of the dispensing mechanism  40 , and suction/discharge by dispensing tips  60  attached to nozzles  46 . Further, this control device allows arbitrary storage of a test process by an external input device (not shown). 
     X-axis members  21 A and  21 B forming the moving mechanism  20  are fixedly provided on the upper sides of the front surface and the rear surface of the main body  10 , respectively, The X-axis members  21 A and  21 B are formed into substantially square pillars, and are immovable with respect to the main body  10 . These two X-axis members  21 A and  21 B extend along the upper sides of the front surface and the rear surface and are parallel to each other. Between the two X-axis members  21 A and  21 B, there is provided a Y-axis member  22  substantially in the form of a square pillar and extending across the two X-axis members  21 A and  21 B. The Y-axis member  22  is capable of moving in the longitudinal direction (X-axis direction) of the X-axis members  21 A and  21 B while being kept perpendicular to the X-axis members  21 A and  21 B. Further, on the Y-axis member  22  and at a position between the two X-axis members  21 A and  21 B, there is provided a Z-axis member  23  substantially in the form of a square pillar and extending vertically and perpendicular to the Y-axis member  22 . The Z-axis member  23  is capable of moving in the Y-axis direction while being kept perpendicular to the Y-axis member  22 . Thus, the X-axis members  21 A and  21 B allow the Y-axis member  22  to move to the right and left with respect to the main body  10 , and the Y-axis member  22  allows the Z-axis member  23  to move forwards and backwards with respect to the main body  10 . The Y-axis member  22  and the Z-axis member  23  constitute the moving mechanism  20  together with the X-axis members  21 A and  21 B. 
     The rotating mechanism  30  and the dispensing mechanism  40  are connected to the Z-axis member  23 . As shown in  FIGS. 2A and 2B , the rotating mechanism  30  is equipped with a rotating mechanism main body  31 , a stepping motor  32  provided in the main body  31 , an origin detection photo sensor  33 , and a coupling  34 . The rotating mechanism main body  31  is mounted so as to be movable on the Z-axis member  23  in the longitudinal direction of the Z-axis member  23 . The stepping motor  32  and the dispensing mechanism  40  are connected through the coupling  34 , and the rotation of the stepping motor  32  is transmitted to the dispensing mechanism  40  through the coupling  34 . The origin detection photo sensor  33  is firmly attached to the rotating mechanism main body  31 , and has a light emitting portion and a light receiving portion (those not shown). An origin position ( FIG. 2A ) of the dispensing mechanism  40  can be detected when the light receiving portion is shielded by an origin detection dog  43  provided on the dispensing mechanism  40  described later. 
     The dispensing mechanism  40  is provided at the vertical lower end of the rotating mechanism main body  31 , and the dispensing mechanism  40  is supported by the Z-axis member  23  through the intermediation of the rotating mechanism  30 . Thus, the Z-axis member  23  is capable of vertically moving the dispensing mechanism  40  through the rotating mechanism  30 , with the result that the dispensing mechanism  40  is movable by the moving mechanism  20  in the directions of the X-axis members  21 A and  21 B, the Y-axis member  22 , and the Z-axis member  23 , that is, up and down, to the right and left, and forward and backwards with respect to the main body  10 . 
     The dispensing mechanism  40  is composed of a cylinder retaining portion  41  and a supported portion  42 . The supported portion  42  is substantially in the form of a cylinder, the longitudinal direction of which is parallel to the Z-axis direction (vertical direction). The upper vertical end of the supported portion  42  is detachably connected to the coupling  34  of the rotating mechanism  30 , and the rotation of the stepping motor  32  is transmitted to the supported portion  42  through the coupling  34 , rotating the supported portion  42  about a vertically directed rotation axis. Since the upper vertical end of the supported portion  42  is detachable with respect to the coupling  34  of the rotating mechanism  30 , the dispensing mechanism  40  is detachable with respect to the rotating mechanism  30 . Thus, when the cylinder, nozzles, etc. are damaged, the operation of the microplate liquid handling system can be resumed quickly by replacing the dispensing mechanism portion alone. The origin detection dog  43  protrudes horizontally from the upper vertical end of the supported portion  42 , making it possible, as stated above, to detect the origin position of the dispensing mechanism  40  is at the origin position, which will be described below. Further, a motor  44  for vertically operating a plunger  47  described later is provided inside the supported portion  42 . 
     The cylinder retaining portion  41  is provided at the lower vertical end of the supported portion  42 . The cylinder retaining portion  41  is rotatable integrally with the supported portion  42 . Thus, the dispensing mechanism  40 , which is composed of the cylinder retaining portion  41  and the supported portion  42 , is rotatable about a vertically directed rotation axis. The cylinder retaining portion  41  is equipped with twelve cylinders  45 . The twelve cylinders  45  are of the same cylindrical configuration, and, as shown in  FIGS. 1 ,  2 A and  2 B, their axes are vertically directed, provided at equal intervals and parallel to each other, and linearly arrayed in a horizontal row. 
     The position of the midpoint of the length of the array of twelve cylinders  45 , that is, the position between the sixth and seventh cylinders  45 A and  45 B, as counted from one end of the array, coincides with the position of the rotation axis of the dispensing mechanism  40 . As shown in  FIG. 2A , the rotating position of the dispensing mechanism  40  at which the cylinders  45  are arrayed in a direction in parallel with the Y-axis member  22 , is referred to as the origin position of the dispensing mechanism  40 , and this direction is referred to as the origin direction. Further, as shown in  FIG. 2B , the rotating position of the dispensing mechanism  40  at which the cylinders  45  are arrayed in a direction perpendicular to the Y-axis member  22  is referred to as the 90-degrees position of the dispensing mechanism  40 , and this direction is referred to as the 90 degrees direction. 
     Since the rotation axis is at the center of the row of the plurality of cylinders  45  arrayed linearly, movement of the dispensing mechanism  40  by the moving mechanism  20  and positioning of the dispensing mechanism  40  vertically above a desired wells can be performed with reference to the rotation axis, facilitating each dispensing tip to face each target well. Further, the number of cylinders  45  is twelve. This number is in conformity with the longitudinal number of wells of an ordinarily available microplate having 12×8 wells, i.e., ninety-six wells in total. 
     The nozzles  46  are provided at the lower ends of the cylinders  45 . The nozzles  46  have discharge holes which are open directly downwards. In the state in which the dispensing tips  60  ( FIG. 5 ) described later have been mounted to the lower ends of the nozzles  46 , air in the dispensing tips  60  is sucked or discharged into the nozzles  46  through the discharge holes, whereby reagent or the like can be sucked into or discharged from the dispensing tips  60 . A plunger  47  is provided at the upper end of each cylinder  45 . All the plungers  47  are supported by a plunger support member  47 A. The plunger support member  47 A has an inverted-T-shaped configuration, the horizontal portion  47 B of which is connected to all the plungers  47  and the vertical portion  47 C of which extends into the supported portion  42 . The vertical portion  47 C has a spiral teeth which is in meshing engagement with a gear  44 A which is drive-connected to the motor  44  provided in the supported portion  42 . Thus, by driving the motor  44 , the plungers  47  can move vertically, and through this vertical movement, the air in the dispensing tips  60  is sucked or discharged into the cylinders  45  through the discharge holes, whereby liquid can be sucked into the interiors of the dispensing tips  60  mounted to the nozzles  46 , or liquid inside the dispensing tips  60  can be discharged therefrom. 
     The dispensing tips  60 , mounted to the forward ends of the nozzles  46 , will now be described. The dispensing tips  60 , which are well-known in the art, are substantially in the form of tapered short pipes having a larger diameter open end and a smaller diameter open end. One dispensing tip is mounted to one nozzle such that the forward end of the nozzle  46  is covered with the larger diameter opening. Since the dispensing tips  60  are tapered, the tapered portions are brought into press contact with the nozzles  46  when the dispensing tips  60  are fitted onto the nozzles  46 , whereby the dispensing tips  60  are retained by the nozzles  46 . More specifically, in the state in which they have not been mounted to the nozzles  46  yet, the dispensing tips  60  are contained in a dispensing tip container, with the larger diameter opening being directed vertically upwards. The nozzles  46  are brought above the dispensing tips  60  by the X-axis members  21 A and  21 B and the Y-axis member  22  of the moving mechanism  20 , and are moved vertically downwards by the Z-axis member  23 . Thus, the larger diameter opening of the dispensing tip  60  gradually covers the nozzles  46 , and the nozzles  46  are covered by the dispensing tips  60  until the tapered portions of the dispensing tips  60  are brought into press contact with the nozzles  46  to thereby mount the dispensing tips  60  to the nozzles  46 . 
     In the state in which the dispensing tips  60  have been mounted to the nozzles  46 , the nozzles  46  exhibit larger longitudinal length. When the nozzles  46  are vertically lowered through operation of the Z-axis member  23  to place the nozzles at lower position, the dispensing tips  60  can reach the surface of liquid reagent that has been existing vertically below the nozzles  46 . In contrast, in the state in which no dispensing tips  60  are mounted to the nozzles, the nozzles  46  exhibit an accordingly smaller longitudinal length, so that even if the nozzles  46  are brought to the vertically lowermost position through operation of the Z-axis member  23 , the forward ends of the nozzles  46  cannot reach the liquid surface. In this way, only the selected nozzles (equipped with the dispensing tips) can reach the liquid surface. Thus, when the dispensing tips  60  are mounted to the nozzles  46  of all the twelve cylinders  45 , it is possible to suck/discharge liquid reagent collectively through the entire row of dispensing tips  60  mounted to all the nozzles  46  of the twelve cylinders  45 . As stated above, in the suction/discharge process, the liquid reagent is sucked into the dispensing tips  60 . Thus, there is no fear of the reagent coming into contact with the nozzles  46  or the cylinders  45 . Thus, even when dispensing is performed several times with a plurality of kinds of reagent, there is no need to clean the cylinders  45  and the nozzles  46 , and it is only necessary to replace the dispensing tips  60  with new dispensing tips  60 . 
     As shown in  FIGS. 1 and 5 , arranged on the stage  50  of the main body  10  are first and second dispensing tip containers  51 A and  51 B containing dispensing tips  60  which are to be attached to the nozzles  46  of the dispensing mechanism  40 , a microplate  53  formed in a rectangular outer configuration with 12×8 wells  53   a , i.e., 96 in total, arranged in matrix, first and second reagent vessels  52 A and  52 B containing liquid reagent to be dispensed to the plurality of wells  53   a  in the microplate  53 , and a dispensing tip disposal container  54  for temporarily containing used dispensing tips  60 . The first and second dispensing tip containers  51 A and  51 B are collectively referred to as the dispensing tip containers, and the first and second reagent vessels  52 A and  52 B are collectively referred to as the reagent vessels. 
     The microplate  53 , the first and second dispensing tip containers  51 A and  51 B, the first and second reagent vessels  52 A and  52 B, and the dispensing tip disposal container  54  have substantially the same, rectangular outer configuration. Further, on the stage  50 , the microplate  53  is arranged on the front, right-hand side, the first reagent vessel  52 A is arranged on the front, middle side, the first dispensing tip container  51 A is arranged on the front, left-hand side, the dispensing tip disposal container  54  is arranged on the right-hand, depth side, the second reagent vessel  52 B is arranged on the middle, depth side, and the second dispensing tip container  51 B is arranged on the left-hand, depth side. The components arranged on the front side and those arranged on the depth side are aligned with their right and left longitudinal sides for orderly arrangement. Similarly, on the front and depth sides, the components arranged on the right-hand, middle, and left-hand sides are aligned with their lateral sides for orderly arrangement. Thus, these components including the microplate  53  are all arranged such that their longitudinal direction is parallel to the origin direction. 
     As shown in  FIG. 1 , on the stage  50 , the microplate  53 , the dispensing tip containers  51 A,  51 B, the reagent vessels  52 A,  52 B, and the dispensing tip disposal container  54  are placed on predetermined stands  55  and  56 . A cooling device (not shown) is connected to the stand  55  on which the reagent vessels are placed for cooling the stand  55 , making it possible to cool the reagent vessels  52 A,  52 B on the stand  55  and to maintain them at a desired temperature. Thus, the stand  55  constitutes a cooler. Because the reagent vessels  52 A,  52 B can be placed on the cooler with which the reagent can be stored at a predetermined low temperature, can be eliminated a process for cooling the reagent by keeping the reagent vessel in a separate reagent insulating container. 
     Further, the microplate  53  is placed on the stand  56  through the intermediation of an aluminum plate (not shown). In the stand  56 , there are provided a vibrating device and a heating device, making it possible to agitate specimen and reagent in the wells  53   a  of the microplate  53  in a heated state. The stand  56  on which the microplate  53  is placed constitutes a thermomixer. Since the microplate  53  is arranged above the thermomixer for vibrating the microplate  53  in order to promote the stirring of the specimen and reagent in the wells while maintaining the interior of the wells heated to a predetermined temperature, can be eliminated a process of extracting the microplate from the microplate liquid handling system and rearranging the same above a separate thermomixer. 
     The first dispensing tip container  51 A and the second dispensing tip container  51 B are respectively equipped with 12×8, i.e., 96 in total, dispensing tip containing holders  51 C so that they can respectively contain 12×8, i.e., 96 in total, dispensing tips  60 . The first dispensing tip container  51 A serves to contain the dispensing tips  60  to be mounted to the nozzles  46  when the dispensing mechanism  40  is at the origin position. As shown in  FIG. 5 , a desired number of dispensing tips  60  are contained in a state in which they are arranged in a row in the origin direction. 
     The second dispensing tip container  51 B serves to contain the dispensing tips  60  to be mounted to the nozzles  46  when the dispensing mechanism  40  is at the 90-degrees position. As shown in  FIG. 5 , a desired number of dispensing tips  60  are contained in a state in which they are arranged in a row in the 90-degrees direction. Thus, with the first dispensing tip container  51 A, it is possible to mount dispensing tips  60  to all the twelve nozzles  46  of the dispensing mechanism  40 , and it is also possible to mount dispensing tips  60  to arbitrary nozzles  46 . With the second dispensing tip container  51 B, it is possible to mount dispensing tips  60  to arbitrary ones of the third to the tenth nozzles  46  as counted from one end of the row of twelve nozzles  46 , and it is possible to mount up to eight dispensing tips. 
     The first reagent vessel  52 A is evenly divided into eight equal longitudinal sections, each of which serves as a reagent vessel, and it is possible to put different reagents in these sections. The second reagent vessel  52 B is evenly divided into twelve equal lateral sections, each of which serves as a reagent vessel, and it is possible to put different reagents in these sections. In the first reagent vessel  52 A, when the dispensing mechanism  40  is at the origin position, it is possible to suck one specific kind of reagent simultaneously and collectively with the entire nozzle row through all the dispensing tips  60  mounted to the nozzles  46 . In the second reagent vessel  52 B, when the dispensing mechanism  40  is at the 90-degrees position, it is possible to suck one specific kind of reagent simultaneously and collectively with the entire nozzle row through all the dispensing tips  60  mounted to the nozzles  46 . The dispensing tip disposal container  54  serves as a space in which used dispensing tips  60  are temporarily placed after removal of the dispensing tips  60  from the nozzles  46  before the dispensing tips being disposed of. 
     As described above, the second dispensing tip container  51 B, the second reagent container  52 B, and the microplate  53  are of the same outer configuration, and the same lateral length. Further, as shown in  FIG. 5 , in the second dispensing tip container  51 B, there are laterally eight dispensing tip containing holders A through H, and in the microplate  53 , there are laterally formed eight wells  53   a  represented by A through H for coincidence in numbers. Thus, when the dispensing mechanism  40  equipped with the twelve nozzles  46  is at the 90-degrees position, it is possible to prevent dispensing tips  60  from being erroneously mounted in a number in excess of eight, which is the number of laterally arranged wells  53   a  of the microplate  53 . Further, it is possible to prevent reagent from being sucked through dispensing tips  60  in a number in excess of eight, which is the number of the laterally arranged wells  53   a  of the microplate  53 . Thus, it is possible to prevent reagent from being discharged from a dispensing tip  60  to a position on the stage  50  where there is no well  53   a.    
     Further, since the first and second reagent vessels  52 A and  52 B are respectively divided into eight and twelve sections, it is possible to store a plurality of kinds of reagent in the first and second reagent vessels  52 A and  52 B. Thus, even in the case in which the dispensing mechanism  40  is operated exclusively at the origin position, or in the case in which the dispensing mechanism  40  is operated exclusively at the 90-degrees position, or in the case in which the dispensing mechanism  40  is operated both at the origin position and the 90-degrees position, it is possible to conduct experiments using various kinds of reagent. 
     Further, due to the provision of the rotating mechanism  30  rotating the dispensing mechanism  40  about the vertically directed rotation axis, both a longitudinal row of wells  53   a  and a lateral row of wells  53   a  can be subjected to automatic dispensing by a single microplate liquid handling system with regard to the 12×8, i.e., 96 in total, wells  53   a  in the microplate  53  arranged on the stage  50 . In performing this dispensing, it is possible to discharge liquid reagent simultaneously and collectively through the entire row of nozzles onto the longitudinal row of wells  53   a . Further, it is also possible to discharge liquid reagent collectively and simultaneously through the entire nozzle row onto the lateral row of wells  53   a . Further, it is possible to collectively suck liquid reagent from the reagent vessel into the dispensing tips  60  mounted to the plurality of nozzles  46  with regard to the entire row of nozzles. Thus, drug metabolic reaction can be performed easily. 
     Because of the provision of the first and second dispensing tip containers  51 A,  51 B, the first and second reagent vessels  52 A,  52 B, it is possible to contain in a classified manner the dispensing tips  60  to be used when discharging reagent to desired wells  53   a  arranged in one and the other directions, thereby preventing any mistake between dispensing tips  60  for one direction and those for the other direction when automatically attaching the dispensing tips  60  to the nozzles  46 . Further, it is also possible to store in a classified manner liquid reagents to be discharged to desired wells  53   a  arranged in one and the other directions, making it possible to automatically suck reagent into dispensing tips  60  without involving any mistake between tips for one direction and those for the other direction. Furthermore, increased kinds of reagents can be stored in the reagent vessels, and amount of reagent can be minimized. 
     Due to the accommodation of the dispensing tips  60  in two dispensing tip containers  51 A,  51 B, it is possible to separately arrange beforehand on the dispensing tip container the following two kinds of dispensing tips: longitudinal-arrangement dispensing tips to be attached to the nozzles of the dispensing mechanism when the cylinders are arrayed longitudinally, and lateral-arrangement dispensing tips to be attached to the nozzles of the dispensing mechanism when the cylinders are arrayed laterally. Thus, it is possible to mount the longitudinal-arrangement dispensing tips and lateral-arrangement dispensing tips without involving any mistake between the two kinds of tips. 
     Next, the dispensing operation will be described with reference to a drug metabolic reaction test conducted by the microplate liquid handling system  1  constructed as described above. Here, for convenience of illustration, as shown in  FIG. 5 , each of the components: the microplate  53 , the first dispensing tip container  51 A, and the second dispensing tip container  51 B, is longitudinally divided into portions  1  through  12  and laterally divided into portions A through H, indicating positions where dispensing tips  60  are received through coordinates, as A 1 , B 3 , etc. Further, the sub reagent vessels obtained through division of the first reagent vessel  52 A are indicated by symbols A through H, from the left to the right, and the sub reagent vessels obtained through division of the second reagent vessel  52 B are indicated by numbers  01  through  12 , from the front to the depth side. 
     First, before performing dispensing, 6 μl of specimen is put in the portions A 1  through E 1  of the microplate beforehand. Further, as shown in  FIG. 5 , dispensing tips  60  are received beforehand at positions A 2 –A 12  of the first tip container  51 A. Similarly, dispensing tips  60  are also received at positions B 1 –B 12  through G 1 –G 12  of the first tip container  51 A. Further, dispensing tips  60  are received at positions A 1 –E 1  and positions A 2 –E 2  of the second tip container. Further, reagent  1  constituting dilute solution A is put in the sub reagent vessel A of the first reagent vessel  52 A. The dilute solution implies the solution for diluting the specimen. Similarly, reagents  3  through  7  constituting reaction starting solutions A through E are put in the sub reagent vessels B–F of the first reagent vessel  52 A. Further, reagent  8  constituting a reaction stopping solution is put in the sub reagent vessel H of the first reagent vessel  52 A. Further, reagent  2  constituting dilute solution B is put in the sub reagent vessel  01  of the second reagent vessel  52 B. 
     Next, dispensing operation is conducted. The dispensing operation will be described with reference to two processes: process  1  in which dispensing is conducted with the dispensing mechanism  40  at the 90-degrees position, and process  2  in which the dispensing mechanism  40  is at the origin position. Note that, in process  1 , it is assumed that the dispensing mechanism  40  is at the origin position in the initial state, and in process  2 , it is assumed that the dispensing mechanism  40  is at the 90-degrees position in the initial state. 
     As shown in the flowchart of  FIG. 3 , in process  1 , the X-axis members  21 A and  21 B and the Y-axis member  22  of the moving mechanism  20  are first driven to bring the dispensing mechanism  40  to a position substantially vertically above the portions A 1  through E 1  of the second dispensing tip container  51 B ( 1   a ). Next, the rotating mechanism  30  rotates the dispensing mechanism  40  from the origin position to the 90-degrees position to situate the third through seventh nozzles  46 , as counted from one end of the row of twelve nozzles  46  of the dispensing mechanism  40  in vertical alignment with the portions A 1  through E 1  of the second dispensing tip container  51 B ( 1   b ). Next, the Z-axis member  23  is driven to move the dispensing mechanism  40  vertically downwards to the position where dispensing tips  60  can be attached to the nozzles  46 , whereupon the dispensing tips  60  contained in the portions A 1  through E 1  of the second dispensing tip container  51 B are attached to the nozzles  46  of the dispensing mechanism  40  ( 1   c ). While in this example the dispensing tips  60  are attached to the third through seventh nozzles  46  as counted from one end of the row of twelve nozzles  46  of the dispensing mechanism  40 , this should not be construed restrictively. The dispensing tips may be attached to any positions of the nozzles  46 . 
     Next, the Z-axis member  23  is driven to move the dispensing mechanism  40  vertically upwards ( 1   d ). Then, the X-axis members  21 A and  21 B and the Y-axis member  22  are driven to bring the dispensing mechanism  40  to a position vertically above the portion  01  of the second reagent vessel  52 B ( 1   e ). Subsequently, the Z-axis member  23  is driven to move the dispensing mechanism  40  vertically downwards until a level (i.e., suction level) is reached at which the smaller diameter forward ends of the dispensing tips  60  attached to the nozzles  46  reach the liquid surface and at which the forward ends of the nozzles  46  with no dispensing tips  60  attached thereto do not reach the liquid surface ( 1   f ). Then, 144 μl of reagent  2  constituting dilute solution B is sucked into the dispensing tips  60  ( 1   g ). 
     Next, the Z-axis member  23  is driven to move the dispensing mechanism  40  vertically upwards ( 1   h ), and the X-axis members  21 A and  21 B and the Y-axis member  22  are driven to situate those nozzles  46  of the dispensing mechanism  40  to which the dispensing tips  60  are attached at positions in alignment with the portions A 1  through E 1  of the microplate  53  ( 1   i ). Then, the Z-axis member  23  is driven to move the dispensing mechanism  40  vertically downwards to the reagent discharge position ( 1   j ). Then, reagent  2  which has been sucked into the dispensing tips  60  ( 1   g ) is discharged to the wells  53   a  A 1  through E 1  of the microplate  53  by an amount of 144 μl ( 1   k ). 
     Next, the Z-axis member  23  is driven to move the dispensing mechanism  40  vertically upwards ( 11 ), and the X-axis members  21 A and  21 B and the Y-axis member  22  are driven to position the dispensing mechanism  40  vertically above the dispensing tip disposal container  54 , and the dispensing tips  60  are detached by a dispensing tip detaching mechanism (not shown) ( 1   m ). With this, the process  1  is completed. 
     When rotating the dispensing mechanism  40  from the origin position to the 90-degrees position in step  1   b  of process  1 , a control device (not shown) controls the stepping motor  32 . More specifically, the origin position of the dispensing mechanism  40  is set when the origin detection dog  43  shields the light receiving portion (not shown) of the origin detection sensor  33 . A control device (not shown) controls the stepping motor  32  such that the dispensing mechanism  40  rotates toward the origin until the origin detection dog  43  shields the light receiving portion (not shown) of the origin detection sensor  33 . For rotating the dispensing mechanism  40  from the origin to the 90-degrees position, the control unit drives the stepping motor  32  by the requisite number of pulses for effecting rotation by 90 degrees from the origin position. The dispensing mechanism  40  is rotated by the motor  32 , so that, even when the dispensing mechanism  40  is moved to an arbitrary position on the X-axis, Y-axis, and Z-axis by the moving mechanism  20 , the dispensing mechanism  40  can be rotated at any arbitrary position. 
     Next, as shown in the flowchart of  FIG. 4 , in process  2 , the X-axis members  21 A and  21 B and the Y-axis member  22  of the moving mechanism  20  are first driven to bring the dispensing mechanism  40  to a position substantially vertically above the portions A 2  through A 12  of the first dispensing tip container  51 A ( 2   a ). Next, the rotating mechanism  30  rotates the dispensing mechanism  40  from the 90-degrees position to the origin position to situate all the nozzles  46 , except the nozzle  46  of one end of the row of twelve nozzles  46  of the dispensing mechanism  40 , in vertical alignment with the portions A 2  through A 12  of the first dispensing tip container  51 A ( 2   b ). Next, the Z-axis member  23  is driven to move the dispensing mechanism  40  vertically downwards to the position where dispensing tips  60  can be attached to the nozzles  46  of the dispensing mechanism  40  whereupon the dispensing tips  60  contained in the portions A 2  through A 12  of the first dispensing tip container  51 A are attached to the nozzles  46 , except the nozzle  46  of one end of the row of twelve nozzles  46  of the dispensing mechanism  40  ( 2   c ). 
     Next, the Z-axis member  23  is driven to move the dispensing mechanism  40  vertically upwards ( 2   d ). Then, the X-axis members  21 A and  21 B and the Y-axis member  22  are driven to bring the dispensing mechanism  40  to a position vertically above the section A of the first reagent vessel  52 A ( 2   e ). Subsequently, the Z-axis member  23  is driven to move the dispensing mechanism  40  vertically downwards to the suction level where the smaller diameter forward ends of the dispensing tips  60  attached to the nozzles  46  reach the liquid surface and the forward ends of the nozzles  46  with no dispensing tips  60  attached thereto do not reach the liquid surface ( 2   f ). Then, reagent  1  constituting dilute solution A is sucked into the dispensing tips  60  attached to the nozzles  46  ( 2   g ). 
     Next, the Z-axis member  23  is driven to move the dispensing mechanism  40  vertically upwards ( 2   h ), and the X-axis members  21 A and  21 B and the Y-axis member  22  are driven to situate those nozzles  46  of the dispensing mechanism  40  to which the dispensing tips  60  are attached vertically above the portions A 2  through A 12  of the microplate  53  ( 2   i ). Then, the Z-axis member  23  is driven to move the dispensing mechanism  40  vertically downwards to the reagent discharge position ( 2   j ). And, reagent  1  which has been sucked into the dispensing tips  60  is discharged to the wells  53   a  of the portions A 2  through A 12  of the microplate  53  ( 2   k ). Further, as in the series of steps surrounded in box A of  FIG. 4 , the reagent  1  is also discharged to portions B 2 –B 12  through portions E 2 –E 12 . 
     Next, the Z-axis member  23  is driven to move the dispensing mechanism  40  vertically upwards, and the X-axis members  21 A and  21 B and the Y-axis member  22  are driven to position the dispensing mechanism  40  vertically above the dispensing tip disposal container  54 , and the dispensing tips  60  are detached by the dispensing tip detaching mechanism (not shown) ( 2   m ). With this, the process  2  is completed. 
     Next, in process  3 , similar to the process  1 , the dispensing tips  60  contained in the portions A 2  through E 2  of the second dispensing tip container  51 B are attached to the nozzles  46  of the dispensing mechanism  40 , and after suction of 50 μl from the wells A 1  through E 1  of the microplate  53 , discharge of the sucked liquid to the portions A 2  through E 2  of the microplate  53  is effected. After the completion of the discharge, suction of 50 μl is effected from the wells A 2  through E 2 , and discharge to A 3  through E 3  is effected. This operation is repeated up to the wells A 8  through E 8 , preparing dilute specimen solutions diluted stepwise in the microplate  53 . Next, the dispensing tips  60  are detached by the dispensing tip detaching mechanism (not shown) to complete process  3 . 
     Next, in process  4 , similar to the series of steps of process  2  shown in  FIG. 4 , the dispensing tips  60  contained in the portions B 1  through B 12  of the first dispensing tip container  51 A are attached to the nozzles  46  of the dispensing mechanism  40 , and 100 μl of reagent  3  constituting reaction starting solution A is sucked from the section B of the reagent vessel  52 A, and is discharged to the wells A 1  through A 12  of the microplate  53 . Next, the dispensing tips  60  are detached by the dispensing tip detaching mechanism (not shown). Then, the dispensing tips  60  contained in the portions C 1  through C 12  of the first dispensing tip container  51 A are attached to the nozzles  46 , and 100 μl of reagent  4  constituting reaction starting solution B is sucked from the section C of the reagent vessel  52 A, and is discharged to the wells B 1  through B 12  of the microplate  53 . Next, the dispensing tips  60  are detached by the dispensing tip detaching mechanism (not shown). 
     Similarly, reagents  5  through  7  constituting reaction starting solutions C through E are respectively poured into the wells C 1 –C 12 , D 1 –D 12 , and E 1 –E 12  of the microplate  53 , and reaction test is started on each well  53   a.    
     Next, in process  5 , the dilute specimen solution mixed with the reaction starting solution in the microplate  53  undergo reaction at a fixed temperature for a fixed period of time. 
     Next, in process  6 , after elapse of a previously set arbitrary period, the dispensing tips  60  contained in the portions G 1  through G 12  of the first dispensing tip container  51 A are attached to the nozzles  46  of the dispensing mechanism  40  as in process  2 , and 75 μl of reagent  8  constituting reaction stopping solution is sucked from the section H of the reagent vessel  52 A, and is discharged to the wells A 1  through A 12  of the microplate  53 . As in the series of steps enclosed in box A in  FIG. 4 , reagent  8  is poured successively into wells B 1 –B 12  through E 1 –E 12  to stop reaction in each well  53   a.    
     As described above, in the first embodiment, since the rotating mechanism  30  for rotating the dispensing mechanism  40  abut the rotation axis is provided, automatic liquid dispensing operation can be performed with the single dispensing mechanism  40  with respect to the row of wells extending in the longitudinal direction of the microplate  53  and the row of wells extending in the lateral direction thereof. In the dispensing operation, simultaneous fluid discharge can be performed with the wells linearly arrayed. Further, simultaneous fluid suction into dispensing tips can be performed. Accordingly, drug metabolic reaction test can be easily performed. 
     Next, a microplate liquid handling system according to a second embodiment of the present invention will be described with reference to  FIGS. 6 and 7 . The microplate liquid handling system of the second embodiment only differs from that of the first embodiment in that the rotating mechanism is equipped with a pulley  48  and an abutment member  12  instead of the stepping motor  32 . The dispensing mechanism  40  is rotated by the pulley  48  and the abutment member  12 . 
     More specifically, in a portion of the dispensing mechanism  40  and at the position where the cylinder retaining portion  41  and the supported portion  42 ′ are connected, there is provided a disc-shaped pulley  48 . The axis of the pulley  48  is in alignment with the rotation axis of the dispensing mechanism  40 , and the pulley  48 , the cylinder retaining portion  41 , and the supported portion  42 ′ are integrally rotatable. 
     Further, the abutment member  12  in the form of a rectangular plate is provided in the inner peripheral surface which defines the chamber  10   a  of the main body  10  and which is parallel to the X-axis member  21 A. The abutment member  12  is provided in the vicinity of the X-axis member  21 A, with its plate-like surface being horizontal, and one long side  12 B of the abutment member  12  is firmly attached to the above-mention ed inner peripheral surface. Thus, another longitudinal side  12 A of the other longitudinal side  12 A of the abutment member  12  is spaced apart from the inner peripheral surface and extends in parallel to the longitudinal direction of the X-axis member. 
     When rotating the dispensing mechanism  40 , the Z-axis member  23  is driven so as to align the vertical height of the pulley  48  with the abutment member  12 , and the dispensing mechanism  40  is moved along the X-axis members  21 A and  21 B so as to confront an outer peripheral surface  48 A of the pulley  48  with the other longitudinal side  12 A of the abutment member  12 . Next, the dispensing mechanism  40  is moved along the Y-axis member  22  to bring the outer peripheral surface  48 A of the pulley  48  into contact with the other longitudinal side  12 A of the abutment member  12 . While maintaining this contact state, the dispensing mechanism  40  is moved along the X-axis members  21 A and  21 B, whereby the pulley  48  receives a force due to the friction between the peripheral surface  48 A and the longitudinal side  12 A of the abutment member  12 , thereby rotating the dispensing mechanism  40 . 
     The control to the rotation angle of the dispensing mechanism  40  is effected by controlling moving amount of the dispensing mechanism  40  along the X-axis members  21 A and  21 B. Alternatively, the control can be made by detecting the rotation angle by way of an angle sensor provided in the dispensing mechanism  40 . Since the dispensing mechanism  40  can be rotated by the pulley  48  and the abutment member  12  instead of the stepping motor  32 , a less expensive microplate liquid handing system with a simple construction results. 
     While the invention has been described in detail and with reference to the specific embodiments thereof, it would be apparent to those skilled in the art that various changes and modifications can be made therein without depart from the scope of the invention. For example, while in the above-described first and second embodiments, the microplate  53  has 12×8 wells  53   a , i.e., ninety-six wells in total, this should not be construed restrictively. Generally speaking, the number of wells arranged is a multiple of four in both the longitudinal and lateral directions. For example, it is also possible to double (24 wells) or triple (36 wells) the number of wells arrayed in the longitudinal direction of the microplate. 
     Further, while in the above embodiments the X-axis members  21 A and  21 B are immovably fixed to the main body  10 , two Y-axis members can be immovably fixed to the main body  10 , whereas an X-axis member extends across the two Y-axis members. In the latter case, the X-axis member is movable in the longitudinal direction of the Y-axis members (Y-axis direction) while being maintained at right angles with respect to the Y-axis members. 
     Further, in the second embodiment the abutment member  12  is provided on the inner peripheral surface defining the chamber  10   a  inside the main body  10  and extending in parallel to the X-axis member  21 A. However, the abutment member can be provided on another inner peripheral surface extending in parallel to the Y-axis member  22 . 
     Further, in order to provide constant pressure between the pulley  48  and the abutment member  12 , as shown in  FIG. 7 , a support stand  13  can extend from the main body  10 , and the abutment member  12  is supported on the support stand  13 . Further, a spring  14  is interposed between the abutment member  12  and the inner peripheral surface of the main body  10 , for urging the abutment member  12  toward the pulley  48 . 
     Further, in order to prevent the pulley  48  from slipping with respect to the abutment member  15  during rotation of the dispensing mechanism  40 , as shown in  FIG. 7 , a resilient member  15  formed of a rubber or the like can be laid on the entire longitudinal side  12 A of the abutment member  12 . This can increase a coefficient of friction between the pulley  48  and the abutment member  12 . For a similar purpose, a resilient member can also be formed upon the entire peripheral surface  48 A of the pulley  48 . 
     Further, while in the above described embodiments the dispensing mechanism  40  is rotatable by the rotating mechanism, and reagent can be collectively discharged to the plurality of wells  53   a  arranged longitudinally and laterally, it is also possible to adopt a construction with no rotating mechanism. In this case, as shown in  FIG. 8 , two dispensing mechanisms  40 - 1  and  40 - 2  are provided, that is, a first dispensing mechanism  40 - 1  constantly at the origin position and a second dispensing mechanism  40 - 2  constantly at the 90-degrees position. Further, two moving mechanisms  20 ,  20 ′ are provided to allow separate movement of these dispensing mechanisms  40 - 1 ,  40 - 2 . X-axis members  21 A,  21 B are used commonly for the moving mechanisms  20 ,  20 ′. Each moving mechanism  20 ,  20 ′ also includes Y-axis members  22 ,  22 ′, Z-axis members  23 ,  23 ′, vertically movable members  130 ,  130 ′ movable along the Z-axis members  23 , 23 ′ and supporting the dispensing mechanisms  40 - 1  and  40 - 2  at their fixed orientation. 
     In this case, the numbers of cylinders  45  of the longitudinal dispensing mechanism and the lateral dispensing mechanisms are equal to the larger one of n and m, so that whether, of n and m, which are the numbers of wells in the longitudinal and lateral directions of the microplate, m is smaller or larger than n, it is possible to discharge liquid to an arbitrary position on the microplate by using the longitudinal dispensing mechanism and the lateral dispensing mechanism.