SUCTION DEVICE

Abstract: The object of the invention is a suction device (1) for dispensing a liquid, such as pipette, comprising a body and associated end portion (3), the open end (6) of which being directed away from the body for removably attaching a tip (8) enclosing a sample space (9) for receiving a liquid sample (10) whereby the end portion (3) of the suction device (1) defines an air space (4) containing means (5) for changing the volume of the said air space (4) for drawing and dispensing a sample. It is characterizing for the invention that in the air space (4) within the end portion (3) there is sealingly mounted a barrier means (11, 12), which is permeable to air but impermeable to liquids, such as porous plug-like sieve, which is self-sealing under the influence of liquid, or a porous, hydrophobic membrane.

Description: 1 Suction device The object of this invention is a suction device intended for dispensing, transferring, diluting, titrating, mixing or a combination of all or some of these, of a li- quid, such as a mechanical or electronic pipette comprising a body and associated end portion, the open end of which being directed away from the body for removably attaching a tip enclosing a sample space for receiving a liquid sample whereby the end portion of the suction device defines an air space containing means for changing the volume of the said air space for drawing and dispensing a samp- le. Over approximately the past three decades pipettes have been in use having attached liquid reservoirs, that is pipette tips, from which liquid has escaped to the inner parts of the pipette, for example due to careless operation of the pipette or in form of liquid molecules vaporized from the liquid. The contamination of the inner parts of the pipette has jeopardized the labour safety and reduced the reliable operation of the pipette itself or even completely eliminated it. Naturally this cannot be accepted in precise laboratory work. Due to these problems pipette manufacturers recommend that the pipettes are disassembled and cleaned at regular intervals by the pipette users. In this procedure almost always also the plunger and the gasket of the pipette are re-lubπcated and often also the pipette has to be re-calibrated, i.e. the pipetted, dispensed etc. liquid volumes are set to correspond to the volumes set on the scale of the pipette. This disassembling and reassembling of the pipette, in addition to being inconvenient and laborious procedure, does not guarantee that the pipette would not contain infection agents or other contamination such as DNA- and RNA-contamina- tion which interferes with PCR-work. Therefore some pipette manufacturers have started to manufacture pipettes, which are claimed to be sterilizable in an autocla- ve. Sterilization in the autoclave does not, however, remove DNA- and RNA- contamination from the pipette parts. It is a very tedious operation and often the operation itself damages parts of the pipette in such a way that the pipette will not function sufficiently accurately and reliably any more. When the pipette is used 2 after the sterilization, it is possible that it will be contaminated already with the first pipetting. US Patent publication 5,156,811 discloses a suction device using disposable pipet- te tips removably attachable to the end portion of the suction device and containing a plug-like sieve at a location between the open ends of the tip. This solution is not only expensive, because with every disposed pipette tip, also the porous sieve therein is discarded, but the porous sieve in the pipette tip contaminates easily and is damaged by the liquid taken into the tip. When the sieve is damaged, the liquid sample in the tip is often lost, which loss can sometimes be very costly. The disadvantages cited above can be avoided using the solution according to the invention. It is characterising to the invention that the air space within the end portion is provided with a barrier means which is permeable to air but self-sealing under the influence of a liquid. The suction device as such can be prior known, manually or e.g. electrically operated and it can be independently operated or function as a part of other equipment, e.g. a pipette. When in the following description the word 'pipette' is used, it is used to generally mean all kinds of suction devices defined above which are utilized for pipetting, dispensing, diluting, titrating or mixing or in addition for a combination of all or for some of these operations. Thus, according to the invention a barrier means, which is self-sealing under the influence of a liquid, which can be a porous sieve, or a combination structure of a porous sieve and a membrane, which is permeable to air but impermeable to liquids, is mounted in the suction device itself, to its end portion and not in the tip used with the suction device. The barrier means to be used according to the invention, in the air space of the suction device, can be a porous sieve which is self-sealing under the influence of 3 a liquid. The sieve which acts as a barrier means, is preferably mounted on the open end, or in the vicinity of the open end of the end portion. The shape of the sieve functioning as the barrier means is naturally dependent of the form of the air space. According to a preferred embodiment of the invention, it is essential that it can be sealingly mounted into the air space and that it stays there by means of friction force, preferably without separate fastening means. According to a preferred embodiment it is formed as a plug and tightly pushed into the open end of the end portion. The sieve can be completely situated in the air space of the end portion, or it can also at least partially protrude from the open end of the end portion, in which case it will be preferably located at least partly in the gas passage between the air space and the sample space of the tip. It is obvious that the barrier means is placed in the air space of the end portion in such a way that any means for changing the volume of the air space, typically the plunger of the pipette, can move freely back and forth in the said air space to aspirate a liquid sample into the sample space and to dispense it therefrom. Materials suitable for use in a sieve according to the invention are such porous materials, which are self-sealing under the influence of liquid, e.g. such where the sieve is formed from a porous polymer (base polymer) with pores containing particulate, hydrophilic material, the particle size of which in a "dry", non-hydra- ted state is smaller than the pore size of the base polymer. Thus in a normal state air can flow through the sieve means from the sample space to the air space, and vice versa. A suitable base polymer is a polyolefin, e.g. polyethylene or polypropylene, or polytetrafluorethylene, or other similar materials. Suitable porous polymers are manufactured e.g. by the Porex Technologies Corp., U.S.A. The pore size of the polymer can vary according to the application, and can be e.g. some microns or more. A suitable pore size range for many applications is about 10- 150 microns, e.g. 25-60 microns. The hydrophilic material in the pores can be any such material that in its dry, non-hydrated state is in the form of particles, but which under the influence of a liquid swells and closes the pores of the base polymer. Typically such materials are swelling cellulose, starch, and rubber derivatives. The material for the sieve can be manufactured by expanding a powdery 4 mixture of the base polymer and the hydrophilic material in a known way to obtain a porous sieve material containing hydrophilic particles, which material is then formed to sieve bodies of a suitable size. According to an alternative way of manufacturing, the porous base material can be impregnated with a solution of the hydrophilic material, and then the solvent is evaporated. As sieve material also such a porous polymer material can be used, which is permeable to air in its dry state, but which having absorbed liquid swells to a state where it is impermeable to liquids. In normal use the sieve mounted in the air space is permeable to air in both directions, but if for some reason liquid, e.g. water or blood, passes from the pipette tip acting as a liquid or sample space into the end portion and from there into the sieve, the flow of liquid into the pipette is barred by the sieve and the sieve thereby prevents the contamination of the inner parts of the pipette. The pore size of the sieve can be chosen to be of a certain size to prevent materials of a desired molecule size from entering the pipette and from exiting it. The suction device according to the invention is applicable also to laboratory work based on the PCR-technique because the porous sieve mounted in the end portion of the pipette prevents DNA- and RNase-contamination of the inner parts of the pipette and thus cross-contamination of different samples and reaction mixtures. According to the invention the barrier means can consist of a porous hydrophobic membrane in combination with a sieve, the membrane letting through only air but preventing liquids, such as aqueous solutions, aerosols, particles and microbes from passing through. For such a material different hydrophobic porous polymers, such as polyethylenes and polypropylenes are appropriate, and especially so-called expanded polytetrafluorethylene (e.g. Gore-tex, manufacturer W.L. Gore & Associates, Inc.) are suitable. The membrane can be mounted e.g. in a special frame, which is mounted, e.g. using a snap-fit attachment, on the outer surface of the end of the end portion, so that the membrane covers the open end of the end portion. 5 The frame for the membrane can also be suitably supported on a shoulder formed e.g. in the vicinity of the end portion, preferably on its outer surface. According to another preferred embodiment of the invention the barrier means can consist of a combination of a self-sealing sieve and a membrane, e.g. in the form of a membrane sieve or in the form of a sandwich structure, wherein the sieve can be protected with a membrane on those parts, for example on that surface that is susceptible to come into contact with the liquid in the sample space. In this case the liquid cannot get into direct contact with the sieve, but already the membrane means prevents the liquid from advancing from the tip into the air space of the end portion. In this case it is necessary to replace only the membrane means and the sieve is saved from damage and from replacement. The barrier means, whether it be a sieve, a membrane sieve or simply a membrane means, can be mounted in the end portion of the suction device or onto it from a suitably designed protective tray without touching it by hand. The end portion of the suction device can be provided with a releasing means for releasing from the end portion means, preferably barrier means, removably attached to the end portion of the suction device. The barrier means can also be removed without touching it by hand from the end portion of the suction device directly into a waste bin, e.g. by pushing the sieve or the membrane means with an extension member of the plunger and which is movable in relation thereto. When using a sieve, a membrane sieve, or a membrane means in the suction devi- ce, the calibration of a mechanical pipette can be checked by using a special calibrating means so that the desired liquid volume to be pipetted corresponds to the value of the volume indicated on the scale of the pipette. In a mechanical pipette the calibrating means (a screw) can be adjusted to a position corresponding to each sieve or membrane alternative. When the sieve or the membrane means is changed, the pipette has to be recalibrated to correspond to the alternative taken into use. On the calibrating scale there can thus for example be a different marking for each of the alternatives, and there is no need for calibrating the pipette 6 e.g. by weighing distilled water. In an electronic pipette a microprocessor can contain the necessary parameters corresponding to each alternative, so that the operation of the pipette is controlled by the processor to pipet or dispense correctly the desired amounts and so that these correspond to the programmed data. The microprocessor can take into consideration in addition to the said alternatives also the effect of the following factors: air pressure and humidity, the temperature of the ambient air (pipette) and the temperature of the liquid to be pipetted as well as the density and the viscosity of the liquid. These factors and in addition the type of the pipette tip and its characteristics, the angle of the pipette tip and its depth in relation to the liquid considered all together or each factor separately, can be taken into consideration also by re-calibrating a mechanical pipette e.g. by weighing the liquid or by taking into account the effect of these factors from a table compiled for each pipette, or by using a special calculator. According to an alternative embodiment for use in an electronic pipette, the pipette is equipped with sensing means for identifying the barrier means alternative in use and with means for transferring this data to the microprocessor of the pipette so that the corresponding correction is effected in the dispensed volumes. In the following the invention is described with working examples with reference to the appended drawings wherein Fig. 1 is a lenghtwise cross-sectional view of a pipette functioning as a suction device with attached replacable tip, Fig. 2 is a view of the end portion of the pipette of Fig. 1 and the attached tip in a larger scale and, Fig. 3 and Fig. 4 illustrate an alternative embodiment for the barrier means of Fig. 2. 7 In the Fig. 1-4 like reference numbers are used for like parts. In Fig. 1 of the drawing, the suction device, or pipette, as a whole is referred to with number 1, and it comprises a body portion 2 and an associated end portion 3. In the cylindrical air space 4 within the end portion 3, in its lengthwise direction, a plunger means 5 is moving slidably to change the volume of the air space 4 for drawing a sample. The end part 6 of the end portion 3 is provided with an opening 7, which forms a gas passage to the sample space 9 defined by the pipette tip 8 to be attached to the end portion 3. The plunger means 5 is sealed so that the air space 4 is gas tight except for the opening 7. In the embodiments shown in the drawings there is a liquid sample 10 in the sample space 9 of the pipette tip 8. In Fig. 1 and 2 a barrier means 11 according to the invention is illustrated in the form of a sieve. In the illustrated embodiment the sieve 11 is essentially a cylin- drically shaped plug, which is sealingly arranged into the opening 7 of the end portion 3 and where it stays in place by friction force. The sieve 11 extends a distance into the sample space 9 of the tip 8, clearly above the surface of the liquid sample 10, however. The sieve 11 is mounted in the air space 4 of the end portion 3 so, that there is sufficiently empty space between the surface of the liquid sample 10 and the surface of the sieve 11 facing the sample space 9, preferably approximately 10-50 % of the total length of the tip 8. Fig. 3 shows an alternative embodiment of the invention, where the barrier means is a hydrophobic membrane in form of a membrane means 12. In this embodiment the membrane is mounted in a suitable way, e.g. on a frame 13 on the end part 6 of the end portion 3 so that the membrane 12 covers the opening 7 of the end portion 3. In the illustrated embodiment, shoulders are provided on the outer surface of the end portion 3 in the vicinity of its end part 6 onto which the frame 13 is supported. The frame 13 can also be mounted on the end part 6 of the end portion 3 by using a suitable snap-fit connection. According to one alternative embodiment, which is not illustrated, the barrier means is a combination of a sieve and a membrane. In this case the membrane 12 8 is arranged to protect that surface of the sieve 11 that faces the sample space 9. The membrane 12 can be permanently fastened to the sieve 11, preferably to a surface part thereof, or it can cover the sieve 11 as a loose or removable membrane. The last-mentioned embodiment has the advantage that if the membrane 12 is damaged by liquid or something else, the whole barrier means does not need to be changed, but a change of only the membrane 12 is sufficient. In the preferred embodiments according to the invention illustrated in the drawings, the barrier means 11 can be removed from the pipette in a very simple way without touching it by hand. One alternative solution of realizing it is shown in Fig. 4, where an extension 14 is associated with the plunger 5, this extension 14 being telescopically movable in relation to the plunger 5 in the air space 4 in the longitudinal direction of the plunger 5 towards the end part 6 of the end portion 3 and away therefrom. To remove the barrier means 11 the extension 14 is made to move by using suitable operating means operated from the body of the suction device, towards the end part 6 of the end portion 3, where the extension 14 releases the barrier means 11 from the end portion 3.

Claims: 9 CLAIMS 1. A suction device (1) for dispensing a liquid, such as pipette, comprising a body (2) and associated end portion (3), the open end (6) of which being directed away from the body (2) for removably attaching a tip (8) enclosing a sample space (9) for receiving a liquid sample (10) whereby the end portion (3) of the suction device (1) defines an air space (4) containing means (5) for changing the volume of the said air space (4) for drawing and dispensing a sample (10), characterized in that in the air space (4) of the end portion (3) there is sealingly mounted a bar- rier means (11, 12) which is permeable to air but self-sealing under the influence of a liquid. 2. The suction device according to the claim 1, characterized in that the barrier means (11,12) is arranged to at least partially protrude from the open end of the end portion (3). 3. The suction device according to the claim 1 or 2, characterized in that the sieve (11) is made of a porous plastic, which is self-sealing under the influence of a liquid, e.g. a porous polyolefin, which has in its pores particles of hydrophilic material, the size of the particles in dry state being smaller than the size of the pores in the plastic. 4. The suction device according to the claim 3, characterized in that the hydrophilic material is a material that swells under the influence of water, for exam- pie a cellulose derivative. 5. The suction device according to one of the claims 1-4, characterized in that the barrier means (11, 12) comprises a combination of a membrane (12) and a sieve (11) of a material which is sealing or non-sealing under the inluence of li- quid, whereby the membrane (12) covers the surface of the sieve (11) facing the sample space (9), or a part thereof. 10 6. The suction device according to the claim 5, characterized in that the said membrane (12) is made of expanded polytetrafluorethylene plastic. 7. The suction device according to the claim 5, characterized in that the mem- brane (12) is mounted on the end part (6) of the end portion (3) of the suction device (1) to cover the opening (7) in the end portion (3), suitably supported by a frame (13) with a snap-fit closure to the outer surface of the end portion (3). 8. The suction device according to one of the claims 1-7, characterized in that it has means (14) for releasing the barrier means (11, 12) from the end portion (3). 9. The suction device according to the claim 8, characterized in that the means for changing the volume of the air space (4) is a plunger (5) movable back and forth in the said air space (4), and the means for releasing the barrel means (11, 12) comprises an extension (14) of the plunger (5) telescopically movable in the air space (4) in relation to the plunger (5) towards and away from the end part (6) of the end portion (3). 10. The suction device according to one of the foregoing claims characterized in that it comprises means for effecting calibration or a calibration change due to the barrier means (11, 12) employed. 11. The suction device according to the claim 10, characterized in that it is a mechanical pipette wherein the means for effecting calibration or a calibration change is a calibration screw and a corresponding calibration scale with indications for each of the barrier means (11, 12) alternative. 12. The suction device according to the claim 10, characterized in that it is an electronic pipette, having the regulation parameters corresponding to each of the barrier means (11, 12) alternatives preprogrammed in the microprocessor of the pipette. 11 13. The suction device according to the claim 10 or 12, characterized in that it is an electronic pipette with means for sensing the barrier means (11, 12) alternative employed and for inputting the corresponding data in the microprocessor of the pipette. 14. The suction device according to the claim 10, characterized in that said means also allow for taking into account other factors than those resulting from the choice of barrier means (11, 12) alternative, which influence the pipetting result and create a need for calibration. 15. The suction device according to the claim 14 characterized in that it is a mechanical pipette comprising a means or having as additional means a table compiled for the said pipette or a calculator which contains or which is employed for determining the calibrating caused by said other factors.

Inventors: SUOVANIEMI OSMO, SUOVANIEMI, OSMO
Applicants: BIOHIT OY, SUOVANIEMI OSMO ANTERO, SUOVANIEMI, OSMO
Application year: 1999
Main classification: B01L3
IPC codes: B01L3