PIPETTING PROBE WITH REDUCED REAGENT CARRYOVER

Abstract: The present invention embraces an improved pipetting probe wherein a portion of the interior of said probe is etched so as to create fluid turbulence therewithin during use to improve the washing out of residual sample fluid. More particularly, the pipetting probe of the present invention comprises a rigid tubular sheath (11) tightly circumscribing a tubular polymeric liner (12) wherein a portion of the interior of said polymeric liner is etched, particularly that portion excluding the sample region portion. The present invention also embraces a method of improving the internal washing efficiency of a pipetting probe by etching a portion of the interior of the pipetting probe. In addition, the invention embraces a method of making an improved pipetting probe by pulling a tubular polymeric liner, which has a narrowed liner portion formed by a narrowing die, into a rigid tubular sheath, and allowing the narrowed liner portion to expand against screw threads in the tip portion of the sheath so as to become immovably fixed therein.

Description: PIPETTING PROBE WITH REDUCED REAGENT CARRYOVER Background of the Invention This invention relates to an improved pipetting probe. Pipetting probes are generally used in automatic diagnostic or analytical equipment and serve to extract measured quantities of reagents of various types from the containers which store them and to dispense these reagents as required to conduct the test or analysis which is to be performed. After each extraction and dispensing of a particular reagent, the pipetting probe must be carefully washed, both inside and out, to remove all traces of that reagent in order to prevent contamination of the other reagents and carryover of that reagent into subsequent tests. Since many diagnostic and analytical tests conducted in automatic equipment are capable of making precise measurements in the parts per million range, it is imperative that the pipetting probe which dispenses the reagents for such tests be designed such that it can be efficiently washed to remove all potential contaminants to a level below the normal measurement range of the instrument. Accordingly, it is an object of the present invention to provide a pipetting probe which can be efficiently washed so as to reduce reagent carryover. It is also an object to provide a method of making such a pipetting probe. Summary of the Invention The present invention embraces an improved pipetting probe wherein a portion of the interior of said probe is etched so as to create fluid turbulence therewithin during use to improve the washing out of residual sample fluid. More particularly, the pipetting probe of the present invention comprises a rigid tubular sheath tightly circumscibing a tubular polymeric liner, wherein a portion of the interior of said polymeric liner is etched, particularly that portion excluding the sample region portion. The present invention also embraces a method of improving the internal washing efficiency of a pipetting probe by etching a portion of the interior of the pipetting probe. In addition, the invention embraces a method of making an improved pipetting probe by pulling a tubular polymeric liner, which has a narrowed liner portion formed by a narrowing die, into a rigid tubular sheath, and allowing the narrowed liner portion to expand against screw threads in the tip portion of the sheath so as to become immovably fixed therein. Brief Description of the Drawings Fig. 1 is a perspective view of the pipetting probe of the present invention and depicts both the rigid sheath, with its tip portion, and the polymeric liner. Fig. 2a is an enlarged cross-section of the tip portion of the rigid sheath and depicts the threaded section (shown by dashed lines) and the polymeric liner portion. Fig. 2b is an enlarged cross-section of the opposite end of the rigid sheath and depicts the polymeric liner portion tightly circumscribed by the main portion of the rigid sheath and extending out therefrom. Fig. 2c is an even further enlarged cross-section of a fragment of the tip portion and depicts the threaded section therewithin. Fig. 3 is a cross-section of a narrowing die and depicts a portion of polymeric liner being drawn therethrough. Description of the Preferred Embodiments Throughout the specification and claims the terms reagent and sample fluid are used interchangeably and are intended to include any fluid material used in a diagnostic or analytical test instrument. Such fluid materials include the sample being tested, for example patient samples, such as blood or urine or extracts thereof, as well as standardized test samples, and the reagents utilized to conduct the test(s) to be performed, for example chemical, biochemical or biological reagents, including immunological reagents such as solutions of antibodies or antigens. In its broadest application, the present invention embraces a pipetting probe comprising a polymeric tube having a discharge end into or from which a quantity of sample fluid may be drawn or discharged, wherein a portion of the interior of said tube is etched so as to create fluid turbulence therewithin during use to improve the washing efficiency thereof. Preferably that portion of the polymeric tube interior which is etched excludes at least about the first 20% of said tube at the discharge end, more preferably about the first 30% to 70% of said tube at the discharge end. Normally, the pipetting probe will comprise a sample region portion which extends from the discharge end to a predetermined length of the polymeric tube. This is the portion which will hold a predetermined measured volume of sample fluid. It is most preferred to exclude the sample region portion from that portion of the polymeric tube interior which is etched. It has been found that etching a portion of the polymeric tube interior substantially increases the washing efficiency of the probe interior. It is theorized that when wash solution is passed through the probe interior, it becomes turbulent as a result of contact with the etched interior wall. This turbulence then carries through the non-etched portion, which includes the sample region portion, and assists in the removal of any traces of sample fluid which otherwise might adhere to the smooth wall of the probe. Without such etching, the interior wall is substantially smooth throughout, which results in a substantially laminar flow of wash fluid through the probe (near-zero fluid velocity at the wall surface) . Such laminar flow is not very effective at removing sample fluid that adheres to the interior wall. The washing efficiency of the pipetting probe can be .further improved by altering the inner diameter of the probe in certain sections. For example, it is particularly advantageous where the tip portion of the polymeric tube (i.e. at the discharge end) has an inner diameter which is narrower, preferably about 40 to 60% narrower, than the inner diameter of the major part of the polymeric tube. Most preferably, the polymeric tube will also have an intermediate portion, with an intermediate inner diameter, between the tip portion and the major part of the polymeric tube. This intermediate inner diameter is preferably about 20 to 30% narrower than the major part of the polymeric tube. The particulars of this geometry will be discussed in greater detail later. The invention will now be more specifically described by reference to the accompanying drawings, with particular emphasis on its most preferred embodiments. The pipetting probe 10, in its most practical form, comprises a rigid tubular sheath 11, preferably fabricated of stainless steel, and a tubular polymeric liner 12, preferably fabricated of polyfluoroethylene. The rigid tubular sheath comprises a main portion 13 and a tip portion 14 at one end thereof, said main portion 13 having a first inner diameter and said tip portion 14 having a second inner diameter, with said second inner diameter being equal to or less than said first inner diameter. Preferably said second inner diameter is less than said first inner diameter, most preferably about 25% less. It is also preferred that the tip portion 14 will have an outer diameter which is less than the outer diameter of the main portion 13 and will be connected to said main portion through angularly inclined neck portion 15, which serves as a transition between the tip portion and the main portion. The tip portion 14 has a discharge end 16, into or from which sample fluid may be drawn or discharged. This discharge end 16 is preferably cut at an angle (or beveled) to facilitate the puncturing of sealed cartridges and the dispensing of fluid. It is also especially preferred that a portion of the tip portion contain internal screw threads 20 for gripping the liner as will be discussed later. In a typical pipetting probe which is proposed for use in the SRI instrument sold by Serono-Baker Diagnostics Inc. , the rigid tubular sheath is fabricated from 15 gauge type 304 stainless steel tubing and has the following dimensions: Tip Portion Length - 14.0 mm (0.55 in) I.D. - 1.14 mm (0.045 in) O.D. - 1.45 mm (0.057 in) Main Portion Length - 124 mm (4.88 in) I.D. - 1.52 mm (0.060 in) O.D. - 1.83 mm (0.072 in) Neck Portion Inclined at 13° angle from longitudinal axis Discharge End Beveled at 30° angle from perpendicular axis Screw Threads Extend 5 mm (0.2 in) from discharge end Thread size/pitch - M 1.2 x 0.25 The tubular polymeric liner 12 is the more critical part of the invention since that is the part which holds the sample fluid and which is the most difficult to wash of residual sample fluid after it is dispensed. Generally, the polymeric liner is constructed of a flexible, inert, non-wettable material such as polyfluoroethylene. Its length and inner diameter are selected so as to hold a predetermined quantity of sample fluid as a minimum (i.e. the sample region portion) , plus some excess to serve as a buffer between the sample region portion and the operative machinery to which the liner is connected (e.g. Cavro syringe) . While the dimensions may be varied inversely without affecting a change in the absolute volume of material held, there is a practical range of values that is constrained by a need to measure and deliver accurate volumes, reduce pressure drop, minimize surface area, and fit within the instrument and sheath in which it is utilized. This practical range of values may be readily determined and optimized by the skilled practitioner. The outer diameter of the polymeric liner should be approximately equal to or slightly greater than the inner diameter of the rigid sheath (particularly the main portion of the sheath) so that, upon insertion, it is tightly circumscribed and, preferably, immovably fixed therein. It will be longer than the rigid sheath and will extend from the discharge end 16, to which it is preferably cut flush, through and beyond the opposite end of the sheath. A preferred method of inserting and affixing the polymeric liner in the rigid sheath is now described, with particular reference to dimensions and materials that are characteristic of those proposed for use in the aforementioned SRI diagnostic instrument. The sheath to which the liner is inserted is the one previously described. The polymeric liner utilized consists of polyfluoroethylene tubing (FEP tubing manufactured by Fluortek Medical Inc. , Easton, PA) with an inner diameter of 1.07 mm (0.042 in) and an outer diameter of 1.74 mm (0.068 in). As will be apparent, the outer diameter of this liner is slightly greater than the inner diameter of the main portion of the stainless steel sheath, which is 1.52 mm (0.060 in) . A portion of the liner is drawn through a narrowing die 17, as illustrated in Fig. 3, to provide a narrowed liner portion 18 of 1.07 mm (0.042 in) outer diameter and 0.41 mm (0.016 in) inner diameter. The outer diameter of the narrowed liner portion 18 is somewhat less than the inner diameter of the tip portion 14, which is 1.13 mm (0.045 in), to facilitate easy insertion of the liner within the sheath. For this reason the length of the narrowed liner portion is advantageously greater than the length of the sheath. Upon insertion of the narrowed liner portion through the sheath, so that it extends through the discharge end thereof, it is pulled with the necessary force so as to draw the liner into the sheath, thereby narrowing that portion of the liner which enters the main portion of the sheath so as to form an intermediate liner portion 19 until that intermediate liner portion abuts against the interior wall of the neck portion. The intermediate liner portion 19 will thus be tightly circumscribed by the main portion 13 of the rigid sheath and will have a length and outer diameter equal to the length and inner diameter of the main portion of the rigid sheath. The inner diameter of the intermediate liner portion is thus reduced to 0.71 mm (0.028 in). The probe is then heated to about 200°F (93°C) for approximately two hours to allow the narrowed liner portion to expand (due to memory characteristics of the material) and become tightly circumscribed by the tip portion. This expansion increases the inner diameter of the liner within the tip portion to 0.46 mm (0.018 in). This expansion also causes the narrowed liner portion to expand against the screw threads 20 and become immovably fixed within the tip portion. This is an important feature of the present invention since it substantially prevents movement of the liner away from the discharge end of the probe, which is a problem with conventionally lined probes. After expansion of the narrowed liner portion, the liner is cut flush with the discharge end of the sheath and to a suitable length for the intended use of the probe, which in this case is 585 mm (23.0 in) . To further insure that the liner is immovably fixed within the sheath, it is preferred to apply adhesive to either the interior of the sheath or the exterior of the liner prior to pulling the liner into the sheath, then subsequently curing the adhesive. It is most preferred to use an epoxy adhesive, such as Smooth-On MT-13. To insure good bonding of the adhesive to the polyfluoroethylene liner, the exterior surface of the liner which will come in contact with the adhesive should be etched with a chemical etchant, such as Chemgrip Treating Agent (Norton Company) . The pipetting probe described above is intended to measure samples of approximately 100 μL to 225 μL volume. Accordingly, the sample region of the probe consists of about the first 335 mm ('"13 in) starting from the discharge end. The remainder of the probe, which is about 250 mm (•~-10 in) long, should be etched on the interior surface with a chemical etchant, such as Chemgrip Treating Agent. Such etching changes the surface to a wettable carbonaceous layer which, as stated previously, creates fluid turbulence in the washing fluid which is passed through the probe between sampling, thereby increasing the washing efficiency and substantially lowering the carryover of sample fluid. The pipetting probe of the present invention, as described above, was tested for carryover of residual sample fluid after washing and the results compared to that from a control probe which was used prior to this invention. The control probe is very similar to the inventive probe except that the polyfluoroethylene liner is not etched and has an inner diameter of 0.58 mm (0.023 in) at the tip portion and 1.07 mm (0.042 in) throughout the remainder of the liner. The test used to measure sample carryover utilizes a sample well spiked with 1-2 x 10 mlU/ml of human chorionic gonadotropin (hCG) . Diagnostic testing of hCG is used to determine pregnancy. Generally, a measured hCG value above 25 mlU/ml is a positive indication of pregnancy. Since immunologic measurement of such levels of hCG is somewhat imprecise, it is extremely important to insure that the sample being measured is not contaminated with any hCG carried over in the probe from a previous test. Thus, the ability to efficiently wash out an especially sticky substance like hCG has been a difficult problem to overcome. The test protocol for sample carryover used to compare the performance of the inventive probe versus the control probe involved the use of each probe in a conventional SRI diagnostic instrument set up to read hCG levels from several control cartridge wells containing 10 mlU/ml hCG, followed by a spiked well containing 1-2 x 10 mlU/ml hCG, followed by a control well. The instrument was set to run its standard hCG assay under which the pipetting probe draws and dispenses 100 μl of hCG solution and is washed with about 1.4 ml (about 1.0-1.2 ml internally) of a buffered surfactant wash solution. The hCG carryover from the spiked well is the difference between the control reading after the spike and the control reading before the spike. The actual quantity of hCG carryover is converted to parts per million (that is, parts of hCG carried over per million parts in the spiked well) by dividing this difference by the amount of hCG in the spiked well. Following this protocol in repeated experiments, it has been found that the control probe produces an hCG carryover in the range of 30-40 ppm. In contrast thereto, the probe of the present invention has been found to reduce the hCG carryover to less than 10 ppm, and generally to about 2-6 ppm. This represents approximately a ten-fold improvement.

Claims: Claims 1. In a pipetting probe comprising a polymeric tube having a discharge end into or from which a quantity of sample fluid may be drawn or discharged, the improvement wherein a portion of the interior of said tube beginning a predetermined distance from said discharge end is etched so as to create fluid turbulence therewithin during use to improve the washing out of residual sample fluid. 2. The pipetting probe of claim 1 wherein the portion of the interior which is etched excludes about the first 30% to 70% of said tube at the discharge end. 3. The pipetting probe of claim 1 comprising a sample region portion extending from the discharge end to a predetermined length of said tube, wherein the portion of the interior which is etched excludes said sample region portion. 4. The pipetting probe of claim 1, 2 or 3 wherein said polymeric tube is fabricated of polyfluoroethylene. 5. In a pipetting probe comprising a rigid tubular sheath having a tip portion with a discharge end into or from which a quantity of sample fluid may be drawn or discharged, said sheath tightly circumscribing a tubular polymeric liner which is approximately flush with said discharge end and extends through and beyond the opposite end of said sheath, wherein said polymeric liner comprises a sample region portion extending from said discharge end to a predetermined length of said polymeric liner, the improvement wherein the interior of said polymeric liner excluding said sample region portion is etched so as to create fluid turbulence therewithin during use to improve the washing out of residual sample fluid. 6. The pipetting probe of claim 5 wherein said polymeric liner is fabricated of polyfluoroethylene and said rigid tubular sheath is fabricated of stainless steel. 7. A pipetting probe comprising a rigid tubular sheath comprising a main portion and a tip portion at one end thereof, said tip portion connected to said main portion through an angularly inclined neck portion and having a discharge end into or from which a quantity of sample fluid may be drawn or discharged, said tip portion having outer and inner diameters which are less, respectively, than the outer and inner diameters of said main portion, and a tubular polymeric liner tightly circumscribed by said sheath, said polymeric liner being approximately flush with said discharge end and extending through said main portion and beyond the opposite end of said sheath, a portion of said liner, beginning at said discharge end and extending for a predetermined length therefrom, comprising a sample region portion for holding a predetermined volume of sample fluid, the interior of said liner, excluding said sample region portion, being etched so as to create fluid turbulence within said liner during use to improve the washing out of residual sample fluid. 8. The pipetting probe of claim 7 wherein said tip portion comprises internal screw threads and said polymeric liner is embedded therein so as to prevent longitudinal movement of said liner within said tip portion. 9. The pipetting probe of claim 8 wherein the inner diameter of said polymeric liner within the tip portion is about 40 to 60% less than the inner diameter of said polymeric liner which extends out of the sheath. 10. The pipetting probe of claim 9 wherein the inner diameter of said polymeric liner within the main portion is about 20 to 30% less than the inner diameter of said polymeric liner which extends out of the sheath. 11. The pipetting probe of claim 10 wherein said polymeric liner is adhesively bound to said sheath. 12. The pipetting probe of claim 11 wherein said discharge end is bevelled. 13. The pipetting probe of claim 7, 10 or 12 wherein said polymeric liner is fabricated of polyfluoroethylene and said rigid tubular sheath is fabricated of stainless steel. 14. A method of improving the internal washing efficiency of a pipetting probe which comprises etching a portion of the interior of said pipetting probe. 15. The method of claim 14 wherein said pipetting probe comprises a sample region portion extending from the discharge end thereof to a predetermined length of said probe, said sample region portion being excluded from said etching. 16. The method of claim 15 wherein said pipetting probe is fabricated of polyfluoroethylene. 17. A method of making a pipetting probe which comprises: providing a rigid tubular sheath comprising a main portion and a tip portion at one end thereof, said main portion having a first inner diameter and said tip portion having a second inner diameter, said second inner diameter being equal to or less than said first inner diameter; providing a tubular polymeric liner longer than said sheath and having an outer diameter greater than said second inner diameter; forming screw threads within said tip portion; drawing at least a portion of said liner through a narrowing die so as to form a narrowed liner portion with an outer diameter less than said second inner diameter; pulling said liner into said sheath so that it extends from each end thereof, with said narrowed liner portion aligned with and extending from said tip portion; allowing said narrowed liner portion to expand against said screw threads so as to become immovably fixed within said tip portion; and cutting said liner flush with said tip portion. 18. The method of claim 17 additionally comprising applying adhesive to a portion of the interior of said sheath or the exterior of said liner prior to pulling said liner into said sheath and curing said adhesive after pulling said liner into said sheath. 19. The method of claim 18 additionally comprising etching that portion of the exterior of said liner which will come in contact with said adhesive to improve the bonding thereof. 20. The method of claim 19 wherein said tip portion has outer and inner diameters which are less, respectively, than the outer and inner diameters of said main portion and is connected to said main portion through an angularly inclined neck portion, and said liner is pulled into said sheath until that portion of the liner which was not narrowed abuts said neck portion. 21. The method of claim 20 wherein said liner initially has an outer diameter greater than said first inner diameter. 22. The method of claim 21 wherein said liner comprises a sample region portion extending from the end which is cut flush with the tip portion to a predetermined length thereof, and wherein the liner interior, excluding said sample region portion, is etched. 23. The method of claim 22 wherein said sheath is fabricated of stainless steel and said liner is fabricated of polyfluoroethylene.

Inventors: CLAFLIN ALFRED JAMES JR, CLAFLIN, ALFRED, JAMES, JR.
Applicants: APPLIED RESEARCH SYSTEMS, APPLIED RESEARCH SYSTEMS ARS HOLDING N.V.
Application year: 1991
Main classification: B05B1
IPC codes: B01L3, G01N35