Measuring and testing – Sampler – sample handling – etc. – Capture device
Reexamination Certificate
2003-05-22
2004-10-19
Raevis, Robert (Department: 2856)
Measuring and testing
Sampler, sample handling, etc.
Capture device
C073S864130, C417S488000
Reexamination Certificate
active
06805015
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of Invention
The present invention relates to syringes which can accurately meter small volumes of fluid. In one embodiment, the syringe has dual resolution capability which enables the aspiration of a tiny sample and also the dilution of the tiny sample with a much larger-volume of reagent (or another sample) with the same syringe.
2. Discussion of Related Art
In recent years, diagnostic and analytic tests have required smaller and smaller samples to be accurately metered, both to mix or dilute the samples with larger volumes of various reagents (sometimes in high dilution proportions) and to transfer them separately. There is a demand for samples less than 1 microliter and even less than 100 nanoliters or even 10 nanoliters to be aspirated arid delivered using a syringe or pipette system. Unfortunately, positive displacement devices that can accurately pick up the minute volume of the sample cannot provide enough flow to completely transfer the sample and cannot also meter large reagent volumes. Often times when transferring the sample, the sample will hang onto the tip of the syringe, which requires touching the sample to another surface to free it from the capillary action and surface tension. A touchless transfer, where the sample is ejected out of the syringe with enough force to prevent the sample from hanging on the tip of the syringe, is desired. One way to increase the ejection force of a syringe is to use a syringe with a larger diameter. Yet when the diameter of a syringe is increased to be able to impart the flow rate needed to prevent the “hanging drop” occurrence, the accuracy of the size of the sample aspirated is compromised. While a larger diameter syringe can effect a touchless transfer, it cannot precisely aspirate a tiny sample, such as one as minute as 10 nanoliters.
Multiple pistons of different diameters contained within a single pipette chamber or cylinder such as described below have been known in the past. In such pipettes, spring means are used to keep the pistons in an upper position with a thumb-pressed button so that the pistons can be moved against the force of helical springs to a pre-determined lower position. These systems have been used for a variety of purposes, including the transfer of small volumes of fluids.
In U.S. Pat. No. 5,383,372, assigned to DRD Diluter Corporation, a design is provided with a plurality of pistons that move together and separately in a pipette chamber to measure a small sample and then dispense it with an air blowout to completely remove the sample. While these systems have provided the capability of dispensing small samples with some significant air blow-off or touchless transfer, the demand for using smaller and smaller samples require systems and devices which permit the aspiration and ejection of smaller and smaller samples. These requirements become more acute with the development of programs for genetic testing of patient's blood and blood derivatives. Minute aspirations of less than 100 nanoliters and often even 10 nanoliters are now becoming important.
In many instances, it is desirable to deliver the samples by a “touchless” system that does not require the samples to be touched by another surface, washed out by another liquid, or delivered beneath the surface of another liquid. Therefore new delivery and syringe means are required. Satisfying these developing requirements has been difficult because drops tend to hang onto the tip of the delivery tube forming a hanging drop. The size of the hanging drops can vary widely, and syringes or single piston devices with resolution fine enough to pick up tiny samples simply do not have the flow power to cleanly blow off the sample. A typical sample must be given a velocity when leaving the tip of the probe or pipette of at least approximately 1 meter per second to break free. The smaller the sample, the greater the inaccuracy caused by a hanging drop remaining on the syringe tip. For a variety of reasons, this escape velocity is particularly difficult to achieve with the very small syringes needed to handle very small samples. The problem is further complicated by the requirement that these transfer devices or pipettes be useful for materials that have a widely varied viscosity, from blood derivatives like serum to chemicals like DMSO to various viscous genetic brews. The viscosity variation introduces further variations in the ability of a given sample to escape a confining tip.
Past efforts to achieve desired results involve the miniaturization of syringes to meter smaller and smaller samples. However, small syringes lack the flow power necessary to expel tiny samples. Smaller and smaller probe and pipette tips were developed so that the lower flow rates and pressures the small syringes were able to deliver were artificially increased in an effort to achieve a tip escape velocity. Tips with internal diameters as small as 0.010 inches were developed and in recent years solenoid valve approaches have relied on sapphire drill channels as small as 0.002 inches to provide a sufficient velocity lift at the tip. These delivery tubes result in very long narrow columns of liquid passing through the syringe orifice, which exposes a significantly large proportion of the total fluid volume to damaging surfaces. As a result, genetically related assays which helped trigger the interest in smaller pipettes are compromised because the samples are damaged by the extensive surface area contact to which the assay material is subjected. Therefore, to prevent extensive surface area contact damage to the sample, it is beneficial to not use an excessively small probe tip.
The demand for means and methods for metering very small volumes of material with significant resolution is increasing the need for pumps and pipettes having resolution as fine as that provided by a 10 microliter or even 1 microliter syringe likely required in the future. These precise requirements for accurate metering of very small quantities of material present additional problems. For example, glass is a choice material because much diagnostic work benefits from clear glass for visual inspection. In addition, glass is chemically very inert. However, manufacturing glass tubes with very small internal diameters precise and accurate enough to achieve resolution equivalent to that of a traditional 10 microliter syringe is costly due to the small dimensions. Due to the rugged manufacturable larger sized components of the present invention, prior problems associated with manufacturing tiny syringes are obviated.
Furthermore, traditional syringes for metering small and minute volumes of fluid are troubled with sealing problems. Teflon seals are the industry standard due to its low coefficient of friction and Teflon is chemically inert. However, Teflon has the undesirable characteristic of a high coefficient of thermal expansion and its size can vary considerably with temperature. These slight changes in properties are negligible with a large syringe, but are physically noticeable with traditional syringes that can handle small volumes of fluid. At room temperature, a Teflon seal fit for the internal diameter of a glass syringe can slide smoothly within the housing and seal inside. However at cooler or warmer temperatures, the Teflon seal can be too loose or too tight and “stick” therefore the piston cannot be moved as smoothly within the housing or the seal leaks. Since the present invention is able to achieve the resolution of a small syringe with larger components, thermal variations of the sealing material are enormously reduced with the present invention.
Additional concerns not only center on the need to meter smaller and smaller samples with finer resolution, but also there is an increasing need for a more efficient method and means for delivering the selected sample in its entirety without damaging it. As noted, systems used heretofore commonly attempt to solve this problem by adopting probes and tips with artificially small diameters intended to increase the tip velocity o
Sabin Douglas G.
Schwartz H. Donald
Raevis Robert
Wolf Greenfield & Sacks P.C.
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