1. Field of the invention
Heterogeneous immunoassays such as the solid phase enzyme linked immunosorbent assay (ELISA), have numerous advantages for assaying low level analytes.
Despite these advantages, present assay methods suffer from a number of difficulties. For example, the ELISA uses a relatively large volume of reagents, which impacts the cost of the assay, and also uses relatively large volumes of wash solution, which presents a disposal problem. Additionally, the washing operation itself is awkward in terms of the plumbing required.
Another disadvantage of heterogeneous assays is that, in order to produce a result in a reasonable time, a high ratio of the surface of the solid phase to the volume of reactants is required. One of the ways to achieve this high ratio has been the use of beads or microspheres as the solid phase. To measure the result of the assay's signal producing system requires some means of separating the liquid from the solid phase.
It is the purpose of this invention to obviate these difficulties associated with heterogenous assays such as the ELISA and other similar assay techniques.
2. Description of the Related Art
The enzyme linked immunosorbent assay (ELISA) is described in numerous patents, for example, Shuurs, et al., U.S. Pat. Nos. 3,654,090; 3,850,752; 3,839,153; 4,016,043; and Shuurs, et al., U.S. Pat. No. Re. 31,006.
Capillary tubes have been used for immunoassays in several different ways.
In one scheme, a capillary tube is used to simply transfer assay components from one cuvette to another, as in Johnson, U.S. Pat. No. 4,454,235; or to deliver a controlled volume onto an absorbent test pad, as in Hewett, U.S. Pat. No. 5,110,724.
In a more involved technique, analyte bound to the inner surface of the tube, is detected by examining the tube through its clear or transparent surface. Hibino, et al., U.S. Pat. No. 4,690,907, describes an assay where the capillary tube is divided into several zones, with each zone containing a different assay reagent. Heelies, U.S. Pat. No. 4,883,760, discloses an immunoassay where sample and assay reagents are added to the top of a reagent-coated tube and withdrawn by means of absorbent material positioned at the bottom of the tube. Grenner, U.S. Pat. No. 4,918,025, describes a self contained assay device where a capillary tube functions as the reaction zone.
Another technique uses an optical fiber coated with an immunoreactant that is positioned within a capillary tube to detect the presence of analyte by fluorescence, such as described in Hirschfeld, U.S. Pat. No. 4,447,546 and Glass, U.S. Pat. No. 4,844,869.
Some techniques utilize a plurality of capillary tubes. In Chandler, et al., U.S. Pat. No. 4,590,157, numerous tubes are positioned in series or in sequence, each capable of binding with a different analyte so that a single sample can be screened against a number of antibodies or antigens in one test sequence. Kenoff, U.S. Pat. No. 4,116,638 describes using both the interior and exterior surfaces of a plurality of capillary tubes as the solid support for immunoassays. Morin, et al., U.S. Pat. No. 5,110,431 discloses a technique where two capillaries are aligned end to end with a small gap between them and placed in a buffer solution. Under an applied voltage a sample liquid can be coupled in the gap and tagged with a label.