Abstract:
Disclosed herein is a volume displacement pipette that includes a channel within the piston. The channel allows for cleaning fluids to be continuously run through the pipette tip for cleaning the tip. One end of the channel may be closed during normal operation of the pipette. Multiple pipettes may be combined into an array pipetter.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to the field of scientific instrumentation. More specifically, the present invention relates to pipettes and array pipetters.  
         [0003]     2. Description of the Related Art  
         [0004]     The widespread adoption by the biotech, pharmaceutical, and life science industry of 96-well plates and its denser 384- and 1536-well descendants has stimulated the concomitant demand for pipetters that can take advantage of these formats. Indeed, there are a variety of fluid-handling devices on the market that are designed to pipette in and out of 96 or 384 wells simultaneously. These array pipetters have 96 or 384 tips arranged in rectangular arrays of 8×12 or 16×24, with 9-mm or 4.5-mm pitch, respectively. There are also devices that only address one column of the plate at a time; this allows for more flexibility at the cost of reduced throughput.  
         [0005]     Array pipetters typically are volume displacement devices designed to work in the aspirate-and-dispense mode. Typically a tip, or cannula, is mated to a piston-and-barrel structure with appropriate seals to achieve air-tightness. As the piston moves up, liquid is drawn into the cannula. As the piston moves down, liquid is expelled from the same cannula. This combination of a cannula and piston-barrel is repeated across the array (e.g., 96 or 384 times) to give a pipetting head. For convenience, the cannulae are often assembled into a single tip-carrier to facilitate exchanging one set for another.  
         [0006]     This basic design has proved its worth in terms of simplicity, manufacturability, robustness, and versatility. It is adopted by virtually all manufacturers of array pipetters. Yet it suffers from one major defect. Once a reagent has been delivered, the only way to clean out the cannulae is by repeated aspiration and dispensing of a cleaning fluid. Sometimes, sonication is applied to ameliorate the cleaning action. The inside of the cannulae can also be coated with Teflon to reduce adhesion. Despite all these measures, currently available cleaning methods are often not thorough enough and carry-over of reagents becomes a significant problem. When carry-over of reagents must be limited to an absolute minimum, the only existing solution is to replace fixed cannulae with disposable pipette tips. While this is a workable solution, it entails significant cost increases. In addition, throughput is decreased because replacing an entire tip-array is time consuming, especially since it must usually be done manually.  
       SUMMARY OF THE INVENTION  
       [0007]     Disclosed herein is a pipette comprising: a piston barrel coupled to a fluid dispenser/aspirator; a piston disposed within the barrel; and a cleaning channel having a first end in fluid communication with the fluid dispensor/aspirator and a second end in fluid communication with a source of cleaning fluid. In some embodiments a plurality of these pipettes are present in an array pipetter.  
         [0008]     Also disclosed herein is a pipette comprising a piston barrel and a piston, wherein the piston comprises a channel extending along its length.  
         [0009]     Also disclosed herein is a method of cleaning a pipette that has a barrel and a piston, wherein the method comprises flushing a cleaning fluid through a channel disposed within the piston. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  shows a traditional volume displacement pipette.  
         [0011]      FIG. 2  shows a volume displacement pipette including a channel allowing for cleaning of the cannula.  
         [0012]      FIG. 3  shows a portion of an array pipetter that includes cleaning channels and a flexible membrane.  
         [0013]      FIG. 4  shows the operation of an array pipetter with cleaning channels and a flexible membrane. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0014]     A typical pipette design used in array pipetters is depicted in  FIG. 1 . In this design, a piston barrel  100  is provided. A piston  102  is disposed within the piston barrel  100 . The piston barrel  100  typically contains barrel openings  104  and  106  on the ends. The body of the piston  102  extends through opening  104 . A seal  108  is provided at opening  104  to ensure that an airtight seal is formed between piston  104 , seal  108 , and pipette body  110 . A cannula  112  is disposed at opening  106  to act as a fluid dispenser/aspirator. Optionally, the cannula  112  may be held in a tip carrier  114 . A seal  116  may be used to provide an airtight seal between the seal  116 , tip carrier  114 , pipette body  110 , and cannula  112 . In operation, piston  102  can move up, as in position B in  FIG. 1 , to draw fluid  118  into cannula  112 . Movement of the piston  102  down, as in position A in  FIG. 1 , will expel fluid  118  out of cannula  112 .  
         [0015]     The pipette design depicted in  FIG. 1  may be used in a single stand alone pipette whose piston  102  is actuated either manually or automatically. Alternatively, a plurality of pipettes such as shown in  FIG. 1  may be provided to form an array of pipettes. In such a case, a single pipette body  110  may be used with piston barrels  100  formed therein. Furthermore, a single tip carrier  116  may hold all of the cannulae  112 . In some embodiments of this array pipetter, each individual piston  102  may be actuated individually. In other embodiments, the pistons  102  are actuated simultaneously. Usually, the pipettes of an array are simultaneously actuated.  
         [0016]     As used herein, “array pipetter” refers to any system that comprises more than one pipette assembly. For example, an array pipetter may comprise 96 or 384 pipettes. The multiple pipettes may be arranged in any geometric arrangement.  
         [0017]     As discussed above, the design of  FIG. 1 , whether as a single pipette or an array of pipettes, suffers from the drawback that it only allows for cleaning of the cannula  112  by repeated aspiration and dispensing of a cleaning fluid.  
         [0018]     In some embodiments, the present invention provides for effective cleaning of pipette cannulae by enabling sustained fluid flow of a cleaning fluid from one end of the cannula and out the other. In some embodiments, this sustained fluid flow is accomplished by providing a channel within the piston of the pipette. The channel allows fluid to flow through the piston and into the cannula. The channel may comprise an opening on the end of the piston near the cannula to enable fluid flow between the cannula and the channel in the piston. An opening on the other side of the piston allows for fluid flow between the channel and a fluid source or sink.  
         [0019]     One embodiment of such a pipette is depicted in  FIGS. 2A and 2B . The pipette comprises piston  200  disposed within piston barrel  202 . A channel  204  runs through piston  200 . Piston barrel  202  comprises two openings,  206  and  208 . The body of piston  200  extends through opening  206 . A cannula  210  is disposed on opening  208 . Opening  208  allows for fluid communication between the interior of piston barrel  202  and cannula  210 . Channel  204  comprises openings  212  and  214 . Opening  212  allows for fluid communication between channel  204  and cannula  210 . Opening  214  is connected to valve  216 . Valve  216  is connected to a cleaning fluid source  218  and an air source  220 . Valve  216  may be positioned to allow fluid communication between cleaning fluid source  218  and channel  204  or to allow fluid communication between air source  220  and channel  204 . Alternatively, valve  216  may be closed such that neither cleaning fluid  218  nor air source  220  is in fluid communication with channel  204 .  
         [0020]     For normal pipette operation, depicted in  FIG. 2A , valve  216  is advantageously closed. The seal formed by closed valve  216  allows reagent fluid  222  to be drawn into cannula  210  when piston  200  is raised. Similarly, when piston  200  is lowered, reagent fluid  222  will be expelled from cannula  210  as long as valve  216  is closed.  
         [0021]     For cleaning operation, depicted in  FIG. 2B , valve  216  may be opened to cleaning fluid source  218  allowing cleaning fluid  224  to flow through channel  204  into and out of cannula  210  in order to clean the cannula  210 . After sufficient cleaning, valve  216  may be opened to air source  220  to allow any cleaning fluid  224  remaining in cannula  210  to be dried. Alternatively, air source  220  may be used without prior use of cleaning fluid  224  to dry reagent fluid  222  in cannula  210 . It is advantageous that piston  200  be driven all the way down during cleaning as in  FIG. 2B  to prevent cleaning fluid from contaminating the sides of piston barrel  202 .  
         [0022]     In some embodiments, the general pipette design described above may be repeated to form an array pipetter. In some embodiments, valves such as depicted in  FIGS. 2A and 2B  may be used for each pipette within the array pipetter. In other embodiments, a single valve may operate to open and close all piston channels. Such a design is depicted in  FIGS. 3A and 3B . In this design, a control mechanism to open and close the piston channels is provided by a flexible membrane  300 . The top portions of a plurality of pistons  302 ,  304 , and  306  are secured within holes in a piston end plate  308 . The lower part of the pistons  302 ,  304 , and  306  extend into piston barrels (not shown). Piston channels  308 ,  310 , and  312  run through pistons  302 ,  304 , and  306  respectively. The piston channels  308 ,  310 , and  312  have top openings  314 ,  316 , and  318 . The ends of a curved top plate  320  secures the top plate  320  to the ends of membrane  300  and the piston end plate  308 . While a curved top plate is advantageous in order to minimize trapped air bubbles, top plate  320  may have any shape. A seal is formed between top plate  320  and membrane  300  and between piston end plate  308  and membrane  300 . A pressure-based control inlet  322  is provided through top plate  320 .  
         [0023]     The flexible membrane  300  operates to close channels  308 ,  310 , and  312  when pressure is applied through pressure control inlet  322 , as depicted in  FIG. 3A . Pressure may be applied by directing pressurized air through pressure control inlet  322 . When this occurs, membrane  300  is pressed against channel openings  314 ,  316 , and  318 , forming a seal over the openings  314 ,  316  and  318 . The array pipetter may then be used for normal pipette operation.  
         [0024]     Flexible membrane  300  may be opened by applying a vacuum to pressure control inlet  322 , as depicted in  FIG. 3B . The vacuum causes flexible membrane  300  to be pulled up against top plate  320 , thus breaking the seal between the membrane  300  and the channel openings  314 ,  316 , and  318 . This operation also defines a cavity  324  that is in fluid communication with piston channels  308 ,  310 , and  312 . An inlet  326  that extends through piston end plate  308  is also in fluid communication with cavity  324 . The inlet  326  may be connected to a valve  328  that operates to close inlet  326  or open it to cleaning fluid source  330  or air source  332 . For cleaning operation, cleaning fluid can flow from cleaning fluid source  330  through inlet  326  to flood cavity  324  and flow through pipette channels  308 ,  310 , and  312 , thus forcing cleaning fluid through the pipette cannulae (not shown). Similarly, air can flow from air source  332  through inlet  326 , into cavity  324 , and through channels  308 ,  310 , and  312  to dry the cannulae (not shown). It will be appreciated that the design of  FIGS. 3A and 3B  allows for a single fluid inlet for all pipettes within the array pipetter.  
         [0025]     A single pipette within an array pipetter according to  FIGS. 3A and 3B  is depicted in  FIG. 4 . A piston barrel  400  is formed within pipette body  402 . The pipette cavity  400  has openings  403  and  405 . A piston  404  is disposed within the pipette cavity  400  and extends through opening  405 . A channel  406  runs through piston  404 . An opening  408  in channel  406  is provided on the end of piston  404  that is within piston barrel  400 . A second opening  410  in channel  406  is provided on the opposite end of piston  404 . As in the design of  FIG. 1 , a seal  412  is provided to maintain an airtight seal between piston  404 , pipette body  402 , and seal  412 . A cannula  414  is disposed over opening  403  to act as a fluid dispenser/aspirator. A tip carrier  416  may hold the cannula  414 . A seal  418  may be provided to form an airtight seal between seal  418 , tip carrier  416 , cannula  414 , and pipette body  402 .  
         [0026]     The array pipetter in  FIG. 4  comprises the flexible membrane  419  and pipette end plate  422  that is depicted in more detail in  FIGS. 3A and 3B . As described above, when pressure is exerted against membrane  419 , as depicted in positions A and B in  FIG. 4 , a seal is formed between membrane  419  and piston  404 . When pressure is reduced on membrane  419 , such as by using a vacuum as depicted in position C in  FIG. 4 , the seal is broken allowing fluid communication between channel  406  and the space above channel opening  410 . The pressure on membrane  419  may be controlled by any suitable means. Some means include controlling the air pressure above membrane  419  as depicted in  FIGS. 3A and 3B  or providing a mechanism for applying mechanical pressure to membrane  419 .  
         [0027]     When the pipette of  FIG. 4  is to be used for normal pipette fluid withdrawing and dispensing, membrane  418  advantageously forms a seal over piston channel opening  410 . Thus, as depicted in position B of  FIG. 4 , the piston  404  can be moved up to draw fluid  420  into cannula  414 . Similarly, when membrane  419  forms a seal, the piston can be moved down, as in position A of  FIG. 4  to expel fluid from cannula  414 . Because piston end plate  422  is fixed to piston  404 , piston end plate  422 , membrane  419 , and the rest of the assembly as described in  FIGS. 3A and 3B  moves with the piston  404 .  
         [0028]     When the cannula  414  is to be cleaned, the seal formed by membrane  418  is broken by reducing pressure on membrane  418  as described above. Cleaning fluid can then be forced through channel  406  and cannula  414 . It is preferable during cleaning to drive piston  406  all the way down, as in position C in  FIG. 4 , such that there is no empty space within piston barrel  400 . Such a position inhibits cleaning fluid from contacting and contaminating the sides of piston barrel  400 . It will be recognized that in general, cleaning fluid may either flow from opening  410  through the cannula  414  or from cannula  414  to opening  410 . When used as depicted in  FIGS. 3A and 3B , cleaning fluid flows from opening  410  through cannula  414 .  
         [0029]     As depicted in  FIGS. 3A and 3B , the array pipetter may have a single fluid inlet to supply cleaning fluid to all channels  406 . The flow rate in channels  406  having the same diameter has been found to vary by less than two times regardless of the location of the single fluid inlet. In some embodiments, the resistance to flow in the channels  406  may be varied between the channels  406  such that the flow rate through the channels  406  is substantially uniform. Methods of varying fluid resistance include varying the diameter of the channels  406  or varying the diameter of channel openings  410  or  408 .  
         [0030]     In an alternative embodiment, the pipette array may be constructed such that pressure may be applied to membrane  410  individually over each channel opening  410  to provide individual control to piston channels  406 . In some alternative embodiments, each individual piston  404  may be actuated individually.  
         [0031]     Cleaning substances for use herein include any of those known in the art and may be varied depending on the substance to be cleaned from the cannulae. Typical cleaning substances include water, detergent, acid, acetone, or other organic solvents. Multiple cleaning substances may be used in series to achieve the desire level of decontamination. Furthermore, a gas may be used to dry the cannulae, either as the sole means of cleaning or after applying a liquid cleaning substance. Typical gases that may be used include air, nitrogen, or argon.  
         [0032]     It will be recognized to those of skill in the art that the cleaning channel described herein may be used for purposes other than cleaning fluids. For example, reagents may be dispensed through the channels. The pipette may be connected to multiple supplies of reagents with appropriate switching valves for selecting the appropriate reagent source.  
         [0033]     It will be further recognized to those of skill in the art that geometries other than that depicted in  FIGS. 2-4  may be used. For example, the pistons and piston barrels may have shapes other than cylindrical. Similarly, the piston channels need not be cylindrical. In some embodiments, the channel could be a groove in the side of the piston or could be drilled through the pipette body. In addition, the piston channel openings may be located in positions other than on the ends of the pistons. For example, the openings may be located on the side of the pistons. While the flexible membrane described herein is advantageous, any suitable valve means may be used for closing piston channel opening.