CAPILLARY IMMUNOASSAY AND DEVICE
THEREFOR COMPRISING MOBILIZABLE
PARTICULATE LABELLED REAGENTS
This is a continuation of application Ser. No. 07/876,449 5 filed on Apr. 30, 1992, which was abandoned upon filing hereof, which is a Divisional of Appln. Ser. No. 07/795,266 filed Nov. 19,1991, now abandoned which is a continuation of Appln. Ser. No. 07/294,146, filed as PCT/GB88/00322, Apr. 26, 1988, now abandoned. 10
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to assays involving specific binding, especially immunoassays.
In particular, he invention relates to analytical devices which are suitable for use in the home, clinic or doctor's surgery and which are intended to give an analytical result 20 which is rapid and which requires the minimum degree of skill and involvement from the user.
2. Description of the Related Art The use of test devices in the home to test for pregnancy and fertile period (ovulation) is now commonplace, and a wide variety of test devices 25 and kits are available commercially. Without exception, the commercially-available devices all require the user to perform a sequence of operations before the test result is observable. These operations necessarily involve time, and introduce the possibility of error. 30
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a test 35 device which is readily usable by an unskilled person and which preferably merely requires that some portion of the device is contacted with the sample (e.g. a urine stream in the case of a pregnancy or ovulation test) and thereafter no further actions are required by the user before an analytical ^ result can be observed. Ideally the analytical result should be observable within a matter of minutes following sample application, e.g. ten minutes or less.
The use of reagent-impregnated test strips in specific binding assays, such as immunoassays, has previously been 45 proposed. In such procedures a sample is applied to one portion of the test strip and is allowed to permeate through the strip material, usually with the aid of an eluting solvent such as water. In so doing, the sample progresses into or through a detection zone in the test strip wherein a specific 50 binding reagent for an analyte suspected of being in the sample is immobilised. Analyte present in the sample can therefore become bound within the detection zone. The extent to which the analyte becomes bound in that zone can be determined with the aid of labelled reagents which can 55 also be incorporated in the test strip or applied thereto subsequently. Examples of prior proposals utilising these principles are given in Thyroid Diagnostics Inc GB 1589234, Boots-Celltech Diagnostics Limited EP 0225054, Syntex (USA) Inc EP 0183442, and Behringwerke AG EP 60 0186799.
The present invention is concerned with adapting and improving the known techniques, such as those referred to in the above publications, to provide diagnostic test devices especially suitable for home use which are quick and con- 65 venient to use and which require the user to perform as few actions as possible.
Atypical embodiment of the invention is an analytical test device comprising a hollow casing constructed of moistureimpervious solid material containing a dry porous carrier which communicates directly or indirectly with the exterior of the casing such that a liquid test sample can be applied to the porous carrier, the device also containing a labelled specific binding reagent for an analyte which labelled specific binding reagent is freely mobile within the porous carrier when in the moist state, and unlabelled specific binding reagent for the same analyte which unlabelled reagent is permanently immobilised in a detection zone on the carrier material and is therefore not mobile in the moist state, the relative positioning of the labelled reagent and detection zone being such that liquid sample applied to the device can pick up labelled reagent and thereafter permeate into the detection zone, and the device incorporating means enabling the extent (if any) to which the labelled reagent becomes in the detection zone to be observed.
Another embodiment of the invention is a device for use in an assay for an analyte, incorporating a porous solid phase material carrying in a first zone a labelled reagent which is retained in the first zone while the porous material is in the dry state but is free to migrate through the porous material when the porous material is moistened, for example by the application of an aqueous liquid sample suspected of containing the analyte, the porous material carrying in a second zone, which is spatially distinct from the first zone, an unlabelled specific binding reagent having specificity for the analyte, and which is capable of participating with the labelled reagent in either a "sandwich" or a "competition" reaction, the unlabelled specific binding reagent being firmly immobilised on the porous material such that it is not free to migrate when the porous material is in the moist state.
The invention also provides an analytical method in which a device as set forth in the proceeding paragraph is contacted with an aqueous liquid sample suspected of containing the analyte, such that the sample permeates by capillary action through the porous solid phase material via the first zone into the second zone and the labelled reagent migrates therewith from the first zone to the second zone, the presence of analyte in the sample being determined by observing the extent (if any) to which the labelled reagent becomes bound in the second zone.
In one embodiment of the invention, the labelled reagent is a specific binding partner for the analyte. The labelled reagent, the analyte (if present) and the immobilised unlabelled specific binding reagent cooperate together in a "sandwich" reaction. This results in the labelled reagent being bound in the second zone if analyte is present in the sample. The two binding reagents must have specificities for different epitopes on the analyte.
In another-embodiment of the invention, the labelled reagent is either the analyte itself which has been conjugated with a label, or is an analyte analogue, ie a chemical entity having the identical specific binding characteristics as the analyte, and which similarly has been conjugated with a label. In the latter case, it is preferable that the properties of the analyte analogue which influence its solubility or dispersibility in an aqueous liquid sample and its ability to migrate through the moist porous solid phase material should be identical to those of the analyte itself, or at least very closely similar. In this second embodiment, the labelled analyte or analyte analogue will migrate through the porous solid phase material into the second zone and bind with the immobolised reagent. Any analyte present in the sample will compete with the labelled reagent in this binding reaction. Such competition will result in a reduction in the amount of