Abstract:
A changeable pipette tip includes a first end having a fluid opening and a second end having a pipe elastic in the radial direction having an orifice. The orifice and the fluid opening are in fluid connection. The first end is designed to be coupled to a matching coupling unit of a pipetting unit such that liquid may be sucked into the fluid area through the orifice by an actuating unit in the pipetting unit. In order to eject liquid as free-flying droplets or as a jet from the orifice of the pipe elastic in the radial direction, a volume change of a portion of the pipe elastic in the radial direction is effected.

Description:
CROSS-REFERENCE TO THE RELATED APPLICATION  
       [0001]     This is a continuing application, under 35 U.S.C. §120, of copending international application No. PCT/EP2005/013671, filed on Dec. 19, 2005, which designated the U.S.; this application also claims the priority, under 35 U.S.C. §119, of German patent application No. DE 10 2005 002 525.0, filed Jan. 19, 2005; the prior applications are herewith incorporated by reference in their entirety. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a changeable pipette tip, a pipetting device, a pipette tip actuating device and a method for pipetting which allow to take in liquid and to eject liquid volumes in the nanoliter range.  
         [0004]     2. Description of the Related Art  
         [0005]     According to prior art, pipetting methods with changeable tips only allow to dose volumes in the range of some microliters (10 −9  m 3 ) to milliliters (10 −6  m 3 ).  
         [0006]     A typical hand pipette  10  with a changeable pipette tip  12  is illustrated in  FIG. 5 . The hand pipette  10  includes a coupling means  14  onto which the rear part of the pipette tip  12  may be plugged so that there is a fluid connection of the internal fluid areas of the pipette tip with internal fluid areas of the hand pipette  10  via the fluid opening  16 . The hand pipette  10  includes means (not shown) for generating a negative pressure and/or a positive pressure in its internal fluid areas so that liquid may be sucked into the pipette tip and/or ejected therefrom through an orifice opening  18  in the pipette tip  12 .  
         [0007]     Automatic pipetting devices generally provide a moveable mount  20  ( FIG. 6 ) comprising coupling means  22  for receiving one or more pipette tips  24 . Here, the pipette tips  24  are connected to the pipetting means comprising the moveable mount  20  such that liquid is sucked in and/or ejected through the orifice openings of the pipette tips  24  by corresponding actuating means in the pipetting means. For this purpose, fluid areas in the pipette tip are generally in fluid connection with fluid areas in the pipetting means.  
         [0008]     In such automatic pipetting devices, the pipette tip  24  is taken from a carrier and clamped into the moveable mount  20 . For aspirating, the orifice opening of the pipette tip is then immersed in a vessel. After the liquid has been taken in, which is achieved by means of negative pressure in the pipette, the pipette tip is moved over the target where then, by means of a positive pressure in the pipette, either its whole contents or a small part thereof is released into the target vessel. In the case of large volumes, this may be done in a free jet, in the case of small volumes there may have to be a contact between target and pipette tip since there will be no drop break due to adhesion forces at the pipette tip.  
         [0009]     On the one hand, the above process limits the minimum volume to be released, on the other hand, there may also occur a carry-over of substances already present in the target. Once the dosing is completed, the pipette tip is released into a waste box by means of an automatic ejection mechanism. In the example shown in  FIG. 6 , the automatic pipetting device, as it is used by the company Eppendorf, for example, includes coupling means for eight pipette tips.  
         [0010]     For the release of liquid volumes of less than one microliter, the prior art knows free jet methods, as described in DE 19802367 C1 and DE 19802368 C1. There, a pressure chamber is respectively bounded by a membrane on one side, so that liquid droplets may be ejected from an ejection opening fluidically connected to the pressure chamber by deflecting the membrane.  
         [0011]     A method allowing to release liquid amounts in the range of some 10 nanoliters is known as so-called “mosquito” method by the company TP Labtech, wherein here, however, the part to be exchanged in fluid contact involves a lot of manufacturing effort and is correspondingly expensive. Other systems, such as one described in EP 1093856 A1, are based on adapted pipettes into which a membrane is inserted. By means of an actuator pushing it, it allows higher dynamics than air cushion pipettes, whereby smaller release amounts may be achieved.  
         [0012]     Finally, a method for dosing liquids in the nanoliter range is known from the German application 10337484.1, which was not prepublished. Such a method is schematically shown in  FIGS. 7   a  to  7   c . As shown in  FIG. 7   a , a flexible tube  30  includes an end  32  on the inlet side serving for the connection to a liquid reservoir, and an end  34  on the outlet side at which micro drops and/or micro jets may be released. Respective walls  36  of the elastic tube  30  are illustrated by dashed lines. An actuating means  38  is provided in the form of a displacer, which comprises a connecting part  40  with which the displacer  38  may be attached to an actuating member for driving the displacer  38 .  
         [0013]     The elastic tube may, for example, have a substantially constant cross-section, which will generally be circular, from its inlet end  32  to its outlet end  34 . An area  42  arranged below the displacer  38  may be referred to as dosing chamber area and is defined by the position of the displacer with respect to the elastic tube. An area  44  essentially starting at the right end of the displacer  38  represents an outlet channel, while an area  46  essentially starting at the left end of the displacer  38  represents an inlet channel. The displacer  38  may comprise a displacer surface  50  extending in an inclined way with respect to the wall  36  of the flexible tube  30 , which, during operation of the micro dosing device, allows the generation of a preferred direction in the direction of the outlet opening  34 .  
         [0014]     Assume that, in the state shown in  FIG. 7   a , the flexible tube  30  is filled with a liquid, wherein such a filling may be done, for example, by capillary forces. Starting from this state, the displacer  38  is moved quickly downwards in the direction of the arrows  52 , so that a reduction of the duct volume between inlet opening and outlet opening is caused. This results in a liquid flow  54  towards the outlet end  34  and a liquid flow  56  towards the inlet end  32 . Due to the forward flow  54 , there is a liquid ejection in the form of a micro drop  60  and/or micro jet at the outlet opening  34 . The portion of the liquid released through the outlet opening  34  as jet and/or drop depends on the position, type and dynamics of the volume change. Furthermore, the amount of liquid released as drop depends on the size of the displacer and on the stroke of the displacer  38 , i.e. how much the tube is compressed.  
         [0015]     After the ejection process, there is a refilling phase in which the displacer  38  is moved away from the tube in the direction of arrow  61  so that the volume of the inlet opening  32  and the outlet opening  34  is increased again and thus liquid flows through the inlet channel  46 , see arrow  64  in  FIG. 7   c.    
         [0016]     The details regarding this dosing method are described, as mentioned above, in the German application 10337484, whose related disclosure is incorporated by reference.  
         [0017]     U.S. Pat. No. 5,032,343 discusses a micro pipette tip for locations that are hard to reach. For this purpose, the front portion of the micro pipette tip is extended and ultra thin. This causes flexibility allowing the placement of the pipette tip at locations that are hard to reach. The opposing end of the pipette tip is rigid and allows to attach the pipette tip to conventional tools.  
         [0018]     U.S. Pat. No. 6,180,061 discusses a cartridge pump and dispensing arrangement for applications in which cartridges containing liquid reagents are changed frequently. The cartridge pump includes a reservoir in which there is arranged a moveable piston. A lower open end of the reservoir empties directly into a dosing chamber in the form of a flexible pipe line. An actuating means in the form of a rubber mallet is provided by which the volume of the dosing chamber may be reduced to thereby cause an outflow of liquid through a nozzle connected to an end of the dosing chamber on the ejection side. Two valves are further arranged in the dosing chamber which allow only a unidirectional flow from the end on the reservoir side to the end on the nozzle side of the dosing chamber.  
         [0019]     WO 02/092228 A2 discusses a dispensing means in which a conventional syringe pump is used to eject liquid volumes of less than 5 μl. According to this document, there is provided a syringe pump that is connected to a dispenser  2  via a tube line. The dispenser includes a system liquid reservoir separated from a sample liquid reservoir by an elastomer membrane. A nozzle comprising a nozzle bore is connected to the sample liquid reservoir. The system liquid reservoir is connected to the syringe pump via the tube line so that, by actuating the syringe pump, the membrane may be deflected via the system liquid to thereby eject sample liquid through the nozzle. Sample liquid may also be sucked in through the nozzle, wherein, in order to disconnect a droplet hanging at the nozzle after sucking in the sample liquid, an electric field is applied between the nozzle and a suitably arranged counterelectrode. One embodiment alternatively provides an actuating means to cause an axial expansion and/or compression of the nozzle to thereby disconnect droplets adhering to the tip after the sucking.  
         [0020]     EP 0028478 B1 discusses a pipetting means in which an elastic pipe line is housed in a block such that a pipe-shaped recess in the block has a larger diameter than the outer diameter of the elastic pipe line. An end of the elastic pipe line on the ejection side is connected to a connection piece which, in turn, is connected to a pipette tip. Sucking in and ejecting liquid through the pipette tip is done by applying a positive pressure or a negative pressure to the internal bore of the block to cause corresponding volume changes of the elastic pipe line. In one embodiment, an end of the described squeeze tube means spaced apart from the pipette tip is connectable to a syringe via a three-way valve so that sample liquid and a diluting agent that was drawn into the syringe beforehand may be ejected into an outflow vessel through the pipette tip by actuating the syringe and by pressurizing the internal bore of the block.  
       SUMMARY OF THE INVENTION  
       [0021]     It is the object of the present invention to provide a pipette tip, a micro pipetting device, a pipette tip actuating device and a method for pipetting allowing the release of small amounts of liquid.  
         [0022]     In accordance with a first aspect, the present invention provides a changeable pipette tip having a first end having a fluid opening; and a second end having a pipe elastic in the radial direction having an orifice, wherein the elastic pipe is designed such that it behaves substantially rigid with respect to bending along the pipe axis, but flexible and elastic with respect to radial deformations, wherein the orifice and the fluid opening are in fluid connection, and wherein the first end is designed to be coupled to a matching coupling unit of a pipetting unit such that liquid may be sucked into the fluid area through the orifice by an actuating unit in the pipetting unit.  
         [0023]     In accordance with a second aspect, the present invention further provides a pipetting device having a coupling unit for coupling to a pipette tip having a first end with a fluid opening and a second end having a pipe elastic in the radial direction with an orifice, wherein the orifice and the fluid opening are in fluid connection, and wherein the first end is designed to be coupled to the coupling unit; a first actuating unit for generating a negative pressure at the fluid opening at the first end of the pipette tip to suck in liquid through the orifice of the pipe elastic in the radial direction; and a second actuating unit for changing the volume of a portion of the pipe elastic in the radial direction in time to thereby eject liquid as droplets or as a free-flying jet from the orifice of the pipe elastic in the radial direction.  
         [0024]     In accordance with a third aspect, the present invention further provides a pipette tip actuating device for a pipetting device having a pipette tip having a first end with a fluid opening and a second end, wherein the second end has a pipe elastic in the radial direction having an orifice, wherein the fluid opening and the orifice are in fluid connection, having a fixing unit having a first state in which the pipe elastic in the radial direction is fixed in a predetermined position, and a second state in which the pipe elastic in the radial direction is not fixed; a fixing unit driver for changing the state of the fixing unit; and an actuating unit for changing the volume of a portion of the pipe elastic in the radial direction in time to thereby eject liquid as droplets or as a free-flying jet from the orifice of the pipe elastic in the radial direction, when the fixing unit is in the first state.  
         [0025]     In accordance with a fourth aspect, the present invention further provides a method for pipetting liquid using a pipette tip having a first end having a fluid opening and a second end, wherein the second end has a pipe elastic in the radial direction having an orifice, wherein the fluid opening and the orifice are in fluid connection, the method having the steps of filling the pipette tip by immersing the orifice of the pipe elastic in the radial direction into a liquid and generating a negative pressure at the fluid opening of the first end of the pipette tip; and causing a volume change of a portion of the pipe elastic in the radial direction to eject liquid as free-flying droplets or as a jet from the orifice of the pipe elastic in the radial direction by the volume change.  
         [0026]     The present invention is based on the finding that a pipette tip both representing a low-cost exchange member and allowing the dosing of very small liquid volumes may be implemented by providing it with a flexible tube comprising an orifice end serving for liquid ejection and for liquid intake.  
         [0027]     A pipe elastic in the radial direction is to be understood as one that is flexible and elastic with respect to radial deformations. For example, the pipe elastic in the radial direction may be formed by an elastic tube, i.e. a fluid duct that may also be flexible with respect to bending along the pipe axis, i.e. in the axial direction. For lengths typically used in a micro dosing device, such elastic tubes, however, behave more like a pipe, i.e. essentially rigid with respect to bending along the tube axis, but flexible and elastic with respect to radial deformations.  
         [0028]     Typical materials for the pipe elastic in the radial direction and/or the elastic tube include polyimide, polyamide or silicone. Typical diameters may be from 0.1 to 1 mm. The pipe elastic in the radial direction may be mounted to the pipette tip body, for example, by gluing, injecting, shrinking or by press-fitting. The pipe elastic in the radial direction may further comprise arbitrarily shaped, for example round or angular, constant or changing cross-sections.  
         [0029]     The present invention includes devices and a method that may be integrated into conventional automatic pipetting devices and offer the possibility to release volumes in the range from 0.1 nL to some μL. Preferably, the present invention further allows intermediate storage of the fluid in the pipette tip.  
         [0030]     Instead of conventional pipette tips, the invention uses an arrangement of a rigid part that may have the structure of a conventional pipette tip, and an elastic tube. The rigid part allows the reception of the pipette tip in the automatic pipetting device and allows the ejection by means of conventional devices installed in the automatic device. Alternatively, the rigid part may allow the reception in a hand pipette. The tube attached to the bottom of the pipette serves for the release of the fluid situated in the pipette tip according to the method as described above with respect to  FIGS. 7   a  to  7   c  and as discussed in the German application 10337484. The dosing volume released in a contact-free way may be in the range from 0.1 nL to 100 nL per individual dosing process. A higher dosing volume may be achieved by multiple dosing, wherein there may be achieved flow rates of up to 20 μL/s.  
         [0031]     The inventive micro pipette may be used with conventional automatic pipetting devices, for example air cushion pipettes or syringe pumps, which are capable of using conventional one-way pipette tips. Instead of the conventional one-way pipette tips, there are used the inventive pipette tips. Through them, liquid may be drawn into the inventive pipette tip by the conventional pipetting mechanism. The liquid taken in may then be released again in various ways. Dosing may be done by the conventional pipetting mechanism to eject large volumes. Such a conventional pipetting mechanism is generally a pressure generating means capable of generating a negative pressure and/or a positive pressure in a pressure chamber in fluid connection with the interior of the pipette tip to cause sucking in and/or ejecting of liquid into and/or at the pipette tip.  
         [0032]     However, in preferred embodiments of the present invention, the dosing is done according to the method described above with respect to  FIGS. 7   a  to  7   c . In preferred embodiments, the dosing tube is fixed using a fixing means, whereupon a volume displacement is caused in the tube and the dosing process is triggered thereby.  
         [0033]     The inventive changeable pipette tip and/or one-way pipette tip may be handled, i.e. taken up and put down, automatically by a pipetting device like conventional pipette tips.  
         [0034]     Using the inventive pipette tip, a liquid may be sucked in at a first position, wherein the pipette tip is then moved to a second position by the automatic pipetting device, where the dosing takes place. Alternatively, the pipette tip may also be removed from the automatic pipetting device after sucking in the liquid, wherein the dosing may be done at another place after the removal using a suitable actuating means for squeezing the tube.  
         [0035]     The present invention thus provides a novel pipette tip consisting of an arrangement of a rigid pipette tip part and a flexible tube. Such a pipette tip may automatically be received in an actuating device for squeezing the elastic tube to thereby cause liquid ejection. Preferably, a fixing means is provided to automatically clamp the tube in the actuating means, whereupon the actuating member is moved in the actuating means to squeeze the tube to reduce its volume to cause liquid ejection. Such an actuating means may be used combined with a conventional automatic pipetting device so that liquid may be released from a pipette tip using the tube squeezing method, which may also be used for conventional pipetting, such as according to the air cushion principle.  
         [0036]     The dimensions of the elastic tube may be such that a liquid may be intermediately stored in the pipette tip. In this respect, the dimensions of the tube and the orifice of the same may be so that liquid is retained in the tube by capillary forces and surface forces.  
         [0037]     The present invention further allows the use of various driving units for aspirating and for dosing. The aspirating may be done, for example, by a conventional automatic pipetting device generating a negative pressure at the first end of the pipette tip. However, the aspirating may also be done driven only by capillary forces. Aspirating driven by capillary forces is described, for example, in GB 2353093 A. The dispensing may be done by an actuating means for generating a volume change of a pipe elastic in the radial direction, or may be caused by positive pressure or inertial forces, such as disclosed in GB 2353093 A or DE 19913076 A. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0038]     Preferred embodiments of the present invention will be explained in more detail below with respect to the accompanying drawings, in which:  
         [0039]      FIGS. 1   a  and  1   b  schematically show a cross-section and a full view of an inventive pipette tip;  
         [0040]      FIG. 2  is a schematic representation of an embodiment of an inventive pipetting device;  
         [0041]      FIGS. 3   a  and  3   b  are schematic representations of a pipette tip with an actuating means for dosing;  
         [0042]      FIGS. 4   a  to  4   c  are schematic cross-sectional views for explaining various operating phases of the actuating means shown in  FIGS. 3   a  and  3   b ;  
         [0043]      FIG. 5  schematically shows a conventional hand pipette;  
         [0044]      FIG. 6  schematically shows a moveable mount of a conventional automatic pipetting device; and  
         [0045]      FIG. 7   a  to  7   c  show schematic representations for explaining a preferred inventive used dosing method. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0046]     Schematic representations of an embodiment of an inventive pipette tip  100  are shown in  FIGS. 1   a  and  1   b . The pipette tip  100  includes a rigid pipette tip body  101  and an elastic tube  102  attached to a portion  104  on the pipette tip body  101 . The pipette tip  100  includes a first end  106  formed by the rigid pipette tip body  101  and adapted to be mounted removably onto an automatic pipetting device or a hand pipette. The first end  106  includes a fluid opening  106   a  fluidically connected to a fluid chamber  108  in the micro pipette. The interior of the tube  102  is also fluidically connected to the fluid chamber  108 . The elastic tube is arranged at a second end  110  of the pipette tip and comprises an orifice or fluid opening  112  through which liquid may enter or leave.  
         [0047]     The pipette tip body  101  may consist of the same material as conventional pipette tips, while the elastic tube  102  is preferably formed of an elastically deformable polymer material. Elastic tube or pipe means a fluid duct that recovers the original shape after deformation, e.g. by squeezing, due to the elasticity of its material. The dimensions of the tube are preferably so that liquid may be retained in the pipette tip by the capillary effect therein and the surface tension at the orifice opening  112 , so that the liquid may be intermediately stored in the pipette tip.  
         [0048]     A schematic representation of an embodiment of an inventive pipetting means is shown in  FIG. 2 . The pipetting means includes a pipetting unit  120  comprising a coupling means  122  to which a pipette tip  100 , for example one as explained above with respect to  FIGS. 1   a  and  1   b , may be replaceably attached. The pipetting unit may, for example, be structured comparable to the moveable mount of a conventional automatic pipetting device. A positioning means  126  is provided by which the pipetting unit  120  with the pipette tip  100  attached thereto may be moved between various operating positions. The pipetting unit further comprises a pressure generating means  128  to generate a negative pressure in the fluid chamber of the pipette tip  100  to thereby suck liquid into the pipette tip  100  through the orifice  112 . Furthermore, the pressure generating means may also be designed such that the pipette tip may be provided with positive pressure, if necessary, for example to eject liquid driven by pressure in the conventional method of air cushion pipettes. A controller  130  is provided and connected to the positioning means  126  and the pressure generating means  128  to control operation of the same.  
         [0049]     Furthermore, the inventive pipetting device does not only comprise the pressure generating means, but also an actuating means and/or driving means  132  to eject liquid from the elastic tube of the pipette tip  100 . The controller  130  is also connected to the actuating means  132  to control its operation.  
         [0050]     A complete pipetting cycle using a pipetting device as described above with respect to  FIG. 2  may take place, for example, as follows.  
         [0051]     First, the pipette tip  100  is received from a carrier using the pipetting unit  120  and particularly the coupling means  122 . Such a reception may take place according to conventional receiving methods provided by conventional automatic pipetting devices. After the reception of the pipette tip, the pipetting unit  120  is moved using the positioning means  126  to immerse the elastic tube of the pipette tip into the liquid. By means of negative pressure provided by the pressure generating means  128  as in conventional automatic pipetting devices, the liquid is drawn into the pipette tip through the tube. After the completion of the aspirating process, the dosing unit, together with the pipette tip, is moved to the release site by the positioning means  126 , i.e. to the position where the elastic tube may be actuated by the actuating means  132 . Subsequently, the actuating means  132  is actuated to squeeze the elastic tube to once or several times eject liquid as droplets or as a free-flying jet from the orifice of the elastic tube. The tube and the actuating means are preferably designed to eject a dosing of liquid volumes in the nanoliter range, for example between 0.1 and 100 nL per dosing process. There may also take place several dosing processes to different targets and/or into different vessels from the same pipette tip. After completing the dosing processes in the nanoliter range, a liquid volume that may have remained in the pipette tip may be ejected driven by pressure with the conventional method of air cushion pipettes to completely empty the pipette tip and maybe retrieve valuable liquid.  
         [0052]     After completing the dosing process and/or the dosing processes, the dosing unit may be moved to a storage container using the positioning means  126 , where the pipette tip is disconnected from the pipetting unit and the coupling unit  122  using an ejection mechanism that may correspond to that of conventional automatic pipetting devices, and is put into the storage container.  
         [0053]     As is apparent to someone skilled in the art, the positioning means may appropriately contain driving mechanisms, which may include motors and gears, to be able to effect the desired movements of the dosing unit  120 . The controller  130  may be designed in any suitable way, for example using a micro processor, to control the positioning means  126 , the pressure generating means  128  and the actuating means  132 .  
         [0054]     An exemplary embodiment of the actuating means  132  will be explained in more detail in the following with respect to  FIGS. 3 and 4 .  
         [0055]     For reasons of clarity,  FIGS. 3   a  and  3   b  only show the pipette tip  100  and the portions of the actuating means  132  necessary for the explanation. Furthermore, respective elements are illustrated at least partially transparent in  FIGS. 3   a  and  3   b  to simplify the explanation.  
         [0056]     As is to be seen from  FIGS. 3   a ,  3   b  and  4   a  to  4   c , the actuating means includes a first clamping jaw  134 , a second clamping jaw  136  and an actuating member  138 . The clamping jaws  134  and  136  are positioned on running rails  140 ,  142 , wherein a suitable driving mechanism  143  (schematically illustrated in  FIG. 4   b ) is provided to move the clamping jaws  134 ,  136  relative to each other along the running rails  140 ,  142 . For the actuating member  138 , which may also be referred to as ram or actuator, there is also provided a suitable driving mechanism  144  ( FIG. 4   b ) by which the actuating member  138  may be moved substantially in parallel to the running rails  140  and  142 . Furthermore, an auxiliary centering means  145  is provided in the shown embodiment that facilitates a centering of the pipette tip  100  relative to the actuating means  132 . The auxiliary centering means  145  includes a block in which a recess  146  is formed whose shape is adapted to the outer contours of the pipette tip body  101 . By inserting the pipette tip, as shown in  FIG. 3   a , its tube  102  is thus automatically centered with respect to the actuating means  132 . This state is illustrated in  FIG. 3   b  and in the expanded view of  FIG. 4   a .  
         [0057]     After this centering of the pipette tip and thus of its elastic tube  102 , the clamping jaws  134  and  136  are closed using the driving mechanism  143 , so that the elastic tube  102  is fixed between them. As is best seen in  FIGS. 3   b  and  4   a , the clamping jaws  134  and  136  preferably comprise reliefs  150  for this purpose, which are adapted to the shape of the flexible tube  102  to support secure fixing of the flexible tube. As is further best to be seen from  FIG. 3   b , the clamping jaw  136  includes a through-hole through which the actuating member  138  extends. The recesses  150  may preferably be designed such that areas thereof abut the tube and surround the same so that the tube is securely fixed in the areas surrounding the actuating member  138 .  
         [0058]     The  FIGS. 4   a  to  4   c  represent cross-sectional views with a sectional axis extending through the centers of the recesses  150  in the clamping jaws  134  and  136 .  
         [0059]      FIG. 4   b  shows the actuating device after the automatic closing of the. clamping jaws  134  and  136 . After closing the clamping jaws, the actuating member  138  is moved through the opening of the clamping jaw  136  provided for this purpose using the driving mechanism  144  to reduce the volume of the elastic tube  102  to thereby eject liquid as a free-flying droplet or as a free-flying jet from the orifice  112  of the elastic tube  102 . Here, the clamping jaw  134  acts as a counterholding element. The phase in which the volume of the tube is reduced is shown in  FIG. 4   c . In the position shown in  FIG. 4   b  the clamping jaw  136  and the actuating member  138  are preferably moved together, whereupon the actuating member is actuated into the position shown in  FIG. 4   c .  
         [0060]     At this point, it is to be noted that, in this respect,  FIGS. 3   a  to  4   c  are purely schematic, wherein the actuating member and the counterholding element may be formed in a suitable way to allow only partial squeezing of the tube or also complete squeezing of the tube. In this respect, it is further to be noted that the stroke of the driving means  144  of the actuating member  138  may be adjustable so that, by adjusting the stroke, different drop volumes may be ejected from the orifice  112  of the flexible tube  102 . With respect to the ejecting method, see again the above description of  FIGS. 7   a  to  7   c  and further the German application 10337484.1.  
         [0061]     In the described embodiment, there is provided an auxiliary centering means  145  to center the pipette tip in the actuating means  145 . It is apparent for those skilled in the art that such an auxiliary centering means is optional, for example if a sufficiently accurate positioning means is provided for the pipetting unit. The clamping jaws may, for example, be closed using an electromagnetic drive to fix the flexible tube. The actuating member may be driven electromagnetically or piezoelectrically to allow the desired dosing in the nanoliter range. If necessary, multiple dosing to various targets or into various vessels may optionally be performed. After the dosing process, the clamping jaws may be opened and the pipette tip may be removed by a conventional automatic pipetting device with a corresponding mechanism. The pipette tips may be placed in a waste box or in a storage carrier by means of an ejection mechanism (not shown) located in the automatic pipetting device. In the case of placement in a storage carrier, the dosing cycle may later be resumed by moving the pipette tip to the release position. As an alternative to the method described above, the pipette tip may also be put into a storage carrier immediately after aspirating and taken from the same only at a later time to perform a release of a volume of the aspirated liquid.  
         [0062]     In preferred embodiments of the inventive pipetting device, the nozzle opening does not have any contact to the actuating means (driving unit) during centering, closing, dosing and opening, so that a carry-over of the liquid is prevented. The pipette tips may further be given from the pipetting unit (for example  120  in  FIG. 2 ) to the actuating means including the fixing means, so that the liquid release may be done at another place than the intake, wherein the pipette tip does not have to be coupled to the pipette unit and/or the automatic pipetting device for the liquid release. Thus the automatic pipetting device and/or the pipetting unit may be used otherwise during the dosing by the actuating means for ejecting a liquid from the tube. By putting in series several driving units either driven by individual actuators or by a common actuator, it is very easy to achieve parallelization. In this respect, an actuating member driven by a corresponding driving mechanism may be designed to actuate several flexible tubes at the same time. On the other hand, several actuating members separate from each other may be provided, which may be actuated by a common driving unit or by separately controllable driving units.  
         [0063]     As explained above, the present invention provides a novel pipetting device and/or components for a pipetting device. In this respect, a conventional automatic pipetting device may be used together with inventive pipette tips and an inventive actuating means for such pipette tips.  
         [0064]     Alternatively, it is also possible to use the inventive pipette tips without the inventive actuating means. In this case, the dispensing may be done by conventional methods, such as pressure-driven in air cushion pipettes.  
         [0065]     While this invention has been described in terms of several preferred embodiments, there are alterations, permutations, and equivalents which fall within the scope of this invention. It should also be noted that there are many alternative ways of implementing the methods and compositions of the present invention. It is therefore intended that the following appended claims be interpreted as including all such alterations, permutations, and equivalents as fall within the true spirit and scope of the present invention.