Coating processes – Nonuniform coating
Reexamination Certificate
2001-03-20
2002-07-02
Parker, Fred J. (Department: 1762)
Coating processes
Nonuniform coating
C427S287000
Reexamination Certificate
active
06413586
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the dispensing of liquids. More particularly, the invention provides an apparatus and method of use for spotting liquids, such as biological samples or reagents, onto a substrate.
BACKGROUND OF THE INVENTION
Target compounds, or analytes, present within a sample can often be identified through the controlled exposure of the sample to an appropriate probe, with subsequent detection of a resulting reaction. In a typical arrangement, a sample of a test solution containing an analyte of interest is exposed to a probe carrying a detectable reporter. The probe is chosen such that it can specifically bind the analyte, e.g., by hybridization of complementary nucleotide sequences, or antibody-antigen interactions. After excess probe material has been removed, e.g., washed away, specific binding of the probe to the analyte can be detected.
As the sensitivity of analytical techniques continues to improve, it is increasingly desirable to carry out such analyses using very small volumes of samples/reagents. This is especially true in situations involving expensive compounds. Accordingly, it is now popular to utilize very small volumes of such liquids laid down as “spots” on the surface of a substrate, such as a slide, microcard, or chip.
Not only is it often desirable to provide ultra-small volumes of individual samples and/or reagents in the form of spots, it is becoming increasingly popular to arrange numerous such spots in close proximity to one another as an array on a substrate. For example, a lab technician might need to evaluate a specimen for the presence of a wide assortment of target biological and/or chemical compounds, or to determine the reaction of many different specimens against one or more reagents, such as labeled probes. High-density array formats permit many reactions to be carried out in a substantially simultaneous fashion, saving space, time and money.
Both manual and automated devices for dispensing very small fluid volumes have been devised, including, for example, micropipettes, pins, quills and ink-jetting devices. While suitable for some purposes, each of these is associated with certain disadvantages. For example, micropipettes are generally incapable of accurately dispensing the extremely small volumes of liquid called for by many present-day protocols. With regard to pens and quills, a number of problems need to be resolved relating to the differences in size and shape of the spots which are placed (which can lead to differences in resulting signal intensity or overlap of spots), “missed spots” (where little or no sample is placed on the surface), and the overhead associated with cleaning and reloading. Ink-jet devices dispense a controlled volume of liquid onto a substrate by use of a pressure wave created within the cartridge. This approach is not acceptable for the spotting of samples containing relatively fragile macromolecules, as they can become sheered or otherwise damaged. Further, ink-jetting devices are associated with a high degree of splattering, thereby presenting a substantial risk of contamination, particularly for closely spaced spots.
As an additional disadvantage, most of the known spotting devices require very precise placement of the spotting head relative to the substrate surface. Variations in the distance between the spotting head and the substrate surface can result in inconsistent spot sizes and/or missed spots. With particular regard to contact-type devices, if placed to close to the substrate, the spotting tip can collide with the substrate surface with a force sufficient to damage the spotting tip and/or the substrate.
In view of the above, the need is apparent for a device and method useful for delivering a micro-volume of liquid onto a substrate in a quick and precise manner. Preferably, the device should be relatively easy to use, cost effective and readily adaptable for the production of micro-arrays having a great number of individual spots.
SUMMARY OF THE INVENTION
In one of its aspects, the present invention provides an apparatus for micro-spotting a predetermined volume of a liquid at a plurality of spaced regions on a substrate or substrates.
In one embodiment, the apparatus includes a tube adapted to contain a selected liquid, such as a biological sample, reagent, or the like. The lower end of the tube defines an orifice having a diameter of less than about 1 mm. In an exemplary construction, the diameter of the orifice is less than about 500 &mgr;m, and preferably less than about 200 &mgr;m. An elongate fiber is disposed within the tube for axial movement therein between raised and lowered positions. The fiber, which has a free distal end, is provided with a diameter that is less than the inner diameter of the tube's lower end. In one exemplary arrangement, the diameter of the fiber is between about 10-100 &mgr;m smaller than that of the orifice. For example, a fiber having a diameter of about 100 &mgr;m can be disposed within a tube having an inner diameter of between about 110 to 200 &mgr;m. A workpiece holder can be employed to hold a selected substrate or substrates for spotting. At its raised position, the fiber's free end is spaced from the surface of such a substrate. At its lowered position, the fiber's free end contacts the surface of the substrate.
Shifting means are operatively connected to the fiber for shifting the same between its raised and lowered positions. The shifting means can be, for example, an actuator, such as a linear or vertical actuator, or the like. Positioning means are provided for positioning the tube and associated fiber laterally with respect to the workpiece holder, at selected deposition positions with respect to the substrate. The positioning means can be adapted to move the substrate and/or the tube, fiber and shifting means. In one embodiment, for example, the positioning means is an x-y positioner (e.g., a robotically controlled x-y movable arm) operatively connected to the tube and the shifting means.
A control unit is operatively connected to the positioning means and shifting means for use in successively (i) positioning the tube and associated fiber at a selected deposition position with respect to a substrate, and (i) shifting the fiber to its lowered position, to deposit a selected volume of liquid upon such substrate. In a preferred embodiment, the fiber is (i) laterally flexible and (ii) substantially incompressible along its longitudinal axis. Suitable fibers having such characteristics include, for example, optical fibers. Advantageously, these characteristics permit efficient transfer of motion from the shifting means to the fiber, and the accommodation of variations in the distance between the tube's lower end and the substrate by flexing, or bowing, of the fiber.
According to one embodiment, the apparatus is adapted for use in micro-spotting a predetermined volume of a liquid at a preselected position on each of a plurality of different substrates in the workpiece holder. The control unit, in this embodiment, is operable to position the tube successively at such preselected position on each substrate.
In one embodiment, the tube has a substantially uniform diameter, and includes a larger-diameter upper reservoir for holding the selected liquid. The tube and reservoir can be separately formed and subsequently attached together, or they can be integrally formed.
In another embodiment, the tube's inner diameter tapers on progressing downwardly to a defined-volume tube end region having the diameter of the orifice. The diameter of the tube end region, in this embodiment, is substantially the same as that of the fiber. The fiber's end, with such in its raised position, is disposed above the tube end region, such that shifting of the fiber from its raised to its lowered position is effective to expel from the tube the volume of liquid contained in the tube end region.
One embodiment of the apparatus, particularly useful in micro-spotting a predetermined volume of one or more selected liquid
Bryning Zbigniew
Vann Charles S.
Frazier Jeffery D.
Parker Fred J.
PE Corporation (NY)
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