Patent Publication Number: US-6702990-B1

Title: Spot picker

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to pipettes and pipette tips. 
     2. Prior Art 
     An air pipette is a laboratory tool for transferring small but precise quantities of fluids between containers. A typical pipette shown in FIG. 1 is comprised of a hand-held housing  10  with a suction tube  11  attached to a lower end. An actuation button  12  and a tip eject button  13  are positioned at the top of housing  10 . Actuation button  12  is connected to a piston  14  inside tube  11 , and is biased by a spring to the uppermost or retracted position shown. Tip eject button  13  is connected to an ejection arm  15  positioned around the lower end of suction tube  11 . A disposable tubular pipette tip  16  is attached to suction tube  11  by fitting an open proximal end of pipette tip  16  around the lower end of suction tube  11 . A porous hydrophobic filter  17  is positioned within pipette tip  16 . Typical filters are disclosed in U.S. Pat. No. 6,117,394 to Smith, U.S. Pat. No. 6,045,757 to Moriarty et al., and U.S. Pat. No. 5,496,523 to Gazit et al. Such filters are made of incompressible materials and immovably fixed inside their pipette tips. 
     To transfer a fluid from one container to another, actuation button  12  is depressed to a first stop to move piston  14  downward inside suction tube  11 . Pipette tip  16  is dipped into the fluid, and actuation button  12  is released and allowed to retract. When piston  14  is moved upward, a low pressure within pipette tip  16  is generated to draw in the fluid. Filter  17  has pores which allow air to pass through for sucking in the fluid, but which are fine enough to prevent the fluid from passing through at the working pressure of the pipette. Therefore, filter  17  prevents the fluid from contaminating suction tube  11 . 
     After the fluid is drawn in, pipette tip  16  is positioned over another container, and actuation button  12  is depressed to move piston  14  past the first stop to a second stop and discharge the fluid. Tip eject button  13  is depressed to push the used pipette tip  16  off suction tube  11  with ejection arm  15 . A clean pipette tip is attached to suction tube  11  for transferring another fluid to avoid contaminating the second fluid with the first fluid. 
     Sometimes semi-solids, such as gels, are also transferred in laboratory work. Although a conventional pipette can cut a gel spot by pressing the tip into a gel sheet, the gel spot tends to get sucked up fairly high in the tip. When the piston is depressed, the gel spot is moved downward unevenly and break the air seal between the gel spot and the tip before the gel spot is ejected. 
     BRIEF SUMMARY OF THE INVENTION 
     The objects of the present spot picker are: 
     to provide a pipette with a disposable cutting tip for cutting a spot from a semi-solid material; 
     to protect the pipette from being contaminated by the material; and 
     to reliably eject the spot from the cutting tip. 
     The present spot picker is comprised of a pipette and a disposable cutting tip. The pipette is comprised of a housing with a suction tube projecting from a lower end. An actuation button is positioned at the top end of the housing. The actuation button is connected to a piston inside the suction tube. A plunger attached to the piston has a lower end positioned outside the suction tube. The cutting tip is comprised of a hollow tube with an open proximal end attached to the suction tube. A compressible porous hydrophobic filter is securely but movably positioned within the hollow tube. The cutting tip cuts a gel spot when its open lower end is pushed into a sheet of gel. The plunger pushes the filter outward to discharge the gel spot from the cutting tip when the actuation button is fully depressed. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     FIG. 1 is a partial sectional side view of a prior art pipette and filtered pipette tip. 
     FIG. 2 is a partial sectional side view of the present spot picker before assembly. 
     FIG. 3 is a partial sectional side view thereof about to be inserted into a sheet of gel. 
     FIG. 4 is a partial sectional side view thereof inserted into the sheet of gel. 
     FIG. 5 is a partial sectional side view thereof drawing the gel into the cutting tip. 
     FIG. 6 is a partial sectional side view thereof lifting the gel spot from the sheet of gel. 
     FIG. 7 is a partial sectional side view thereof ejecting the gel spot from the cutting tip. 
     FIG. 8 is a partial sectional side view thereof ejecting the used cutting tip from the pipette. 
    
    
     DRAWING REFERENCE NUMERALS 
     
       
         
           
               
               
               
               
             
               
                   
               
             
            
               
                 12. 
                 Actuation Button 
                 13. 
                 Tip Eject Button 
               
               
                 14. 
                 Piston 
                 15. 
                 Ejection Arm 
               
               
                 16. 
                 Pipette Tip 
                 17. 
                 Filter 
               
               
                 20. 
                 Pipette 
                 21. 
                 Cutting Tip 
               
               
                 22. 
                 Housing 
                 23. 
                 Suction Tube 
               
               
                 24. 
                 Actuation Button 
                 25. 
                 Tip Eject Button 
               
               
                 26. 
                 Piston 
                 27. 
                 Plunger 
               
               
                 28. 
                 Ejection Arm 
                 29. 
                 Barrier 
               
               
                 30. 
                 Gel Sheet 
                 31. 
                 Gel Spot 
               
               
                 32. 
                 Area 
               
               
                   
               
            
           
         
       
     
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG.  2 : 
     A preferred embodiment of a spot picker is shown in a partial sectional side view in FIG.  2 . It is comprised of a pipette  20  and a disposable cutting tip  21 . Pipette  20  is comprised of a housing  22  with an open ended suction tube  23  projecting from a lower end. In this example, suction tube  23  is attached to a hand-held housing, but it may be attached to a robotic arm instead. An actuation button  24  and a tip eject button  25  are arranged on housing  22 . Actuation button  24  is connected to a piston  26  inside suction tube  23 . The connection between actuation button  24  and piston  26  is well known in the art. The upper end of an elongated plunger  27  is attached to the lower end of piston  26 , and the lower end of plunger  27  is positioned outside suction tube  23 . In FIG. 2, plunger  27  and actuation button  24  are biased by a spring (not shown) inside housing  22  to the uppermost or retracted position. Tip eject button  25  is connected to an ejection arm  28  positioned around suction tube  23  above its lower end. The connection between tip eject button  25  and ejection arm  28  is also well known in the art. Tip eject button  25  and ejection arm  28  are also biased by a spring (not shown) inside housing  22  to the uppermost or retracted position. 
     Disposable cutting tip  21  is comprised of a tube with open opposite ends. Cutting tip  21  is arranged to be detachably connected to suction tube  23  by snugly fitting the upper end of cutting tip  21  around the lower end of suction tube  23 . A compressible, porous hydrophobic barrier  29  is securely but movably positioned within cutting tip  21  and spaced upwardly from its lower end. Barrier  29  is preferably slightly wider than cutting tip  21 , so that it is slightly compressed when fitted inside for staying in position, but is still free to slide along cutting tip  21  when pushed. Barrier  29  is preferably comprised of a polyethylene barrier, but it may be comprised of another suitable material. Cutting tip  21  may also be attached to the suction tube of a material handling robot instead of a hand-held pipette. 
     FIG.  3 : 
     Cutting tip  21  is shown attached to pipette  20  in FIG. 3 for transferring a portion of a gel sheet  30  to another area. As shown by the arrows, actuation button  24  is depressed to a first stop to position plunger  27  slightly above or in light contact with barrier  29 . Cutting tip  21  is positioned over gel sheet  30 . 
     FIG.  4 : 
     Cutting tip  21  is shown inserted into gel sheet  30  in FIG. 4. A gel spot  31  is cut in gel sheet  30  by the open lower end of cutting tip  21  when it is pushed into gel sheet  30 . 
     FIG.  5 : 
     Actuation button  24  is shown released in FIG. 5 to retract piston  26  and plunger  27 , as shown by the arrows. Since barrier  29  is porous, the suction generated by the retraction of piston  26  and plunger  27  above filter  29  is transmitted to gel spot  31 , which is slightly sucked into cutting tip  21  and fully released from gel sheet  30 . Since barrier  29  is also hydrophobic, material from gel spot  31  cannot pass through barrier  29  and is prevented from reaching plunger  27 . Therefore, plunger  27  is protected from contamination by cutting tip  21 . 
     FIG.  6 : 
     In FIG. 6, pipette  20  and cutting tip  21  are shown lifted from gel sheet  30  to remove gel spot  31 . 
     FIG.  7 : 
     Pipette  20  is positioned over an area  32  away from the gel sheet for receiving gel spot  31 , as shown in FIG.  7 . Actuation button  24  is depressed past the first stop to a second stop to push barrier  29  downward with plunger  27  until gel spot  31  is pushed out of cutting tip  21  by barrier  29 , as shown by the arrow. Barrier  29  stays inside cutting tip  21  after gel spot  31  is ejected. Actuation button  24  is released and allowed to return its uppermost or retracted position. 
     FIG.  8 : 
     After use, cutting tip  21  is ejected and discarded by depressing tip eject button  25  to advance ejection arm  28  against cutting tip  21 , as shown in FIG.  8 . Cutting tip  21  is arranged to require a greater force to dislodge from suction tube  23  than is required to push barrier  29  and the gel spot through cutting tip  21 , so that cutting tip  21  cannot be dislodged when actuation button  24  is depressed. 
     In addition to gels, the present spot picker can be used for cutting spots from any other semi-solid materials in addition to gels. 
     Although the foregoing description is specific, it should not be considered as a limitation on the scope of the invention, but only as an example of the preferred embodiment. Many variations are possible within the teachings of the invention. Therefore, the scope of the invention should be determined by the appended claims and their legal equivalents, not by the examples given.