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.
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.