This application is a continuation of U.S. patent application Ser. No. 11/359,666 filed Feb. 21, 2006, which is a continuation of U.S. patent application Ser. No. 10/686,548 filed Oct. 14, 2003, which is a continuation of U.S. patent application Ser. No. 09/835,304 filed Apr. 13, 2001, now U.S. Pat. No. 6,699,722, which claims priority from U.S. Provisional Application No. 60/197,365 filed Apr. 14, 2000, and U.S. Provisional Application No. 60/203,696 filed May 11, 2000, all of which are incorporated herein by reference. Priority is claimed to each of these applications.
The present invention relates to sensitive lateral-flow methods and devices for determining the presence and/or amount of small and large analytes in fluid samples. The present invention provides a direct or positive detection result (i.e. increasing signal with increasing analyte concentration) in a sequential binding format.
Analytical tests have been developed for the routine identification or monitoring of physiological and pathological conditions (e.g., pregnancy, cancer, endocrine disorders, infectious diseases) using different biological samples (e.g., urine, serum, plasma, blood, saliva), and for analysis of environmental samples (e.g., natural fluids and industrial plant effluents) for instance for contamination. Many of these tests are based on the highly specific interactions between specific binding pairs. Examples of such binding pairs include antigen/antibody, hapten/antibody, lectin/carbohydrate, apoprotein/cofactor and biotin/(strept)avidin. Furthermore, many of these tests involve devices (e.g., solid phase, lateral-flow test strips, flow-through tests) with one or more of the members of a binding pair attached to a mobile or immobile solid phase material such as latex beads, glass fibers, glass beads, cellulose strips or nitrocellulose membranes (U.S. Pat. Nos. 4,703,017; 4,743,560; 5,073,484).
Immunochromatographic assays fall into two principal categories: “sandwich” and “competitive.” In general, sandwich immunochromatographic procedures call for mixing the sample that may contain the analyte to be assayed with antibodies to the analyte. These antibodies are mobile and typically are linked to a label or another signaling reagent, such as dyed latex, a colloidal metal sol, or a radioisotope. This mixture is then applied to a chromatographic medium containing a band or zone of immobilized antibodies to the analyte of interest. The chromatographic medium often is in the form of a strip that resembles a dipstick. When the complex of the molecule to be assayed and the labeled antibody reaches the zone of the immobilized antibodies on the chromatographic medium, binding occurs and the bound, labeled antibodies are localized at the zone. This indicates the presence of the molecule to be assayed. This technique can be used to obtain quantitative or semi-quantitative results. Examples of sandwich immunoassays performed on test strips are described in U.S. Pat. Nos. 4,168,146 and 4,366,241, each of which is incorporated herein by reference.
In competitive immunoassays, the label is typically a labeled analyte or analyte analogue that competes with any unlabeled analyte present in the sample for binding to an antibody. In such competitive assays, the analyte and labeled tracer molecule are simultaneously introduced to the binding agent such that these molecules compete for binding sites. Competitive immunoassays are typically used for detection of analytes such as haptens, each hapten being monovalent and capable of binding only one antibody molecule. Examples of competitive immunoassay devices are those disclosed by U.S. Pat. Nos. 4,235,601, 4,442,204 and 5,208,535, each of which is incorporated herein by reference.
Solid phase immunoassay devices, whether sandwich- or competition-type, provide sensitive detection of an analyte in a biological fluid sample. Solid phase immunoassay devices incorporate a solid support to which one member of a ligand-receptor pair, usually an antibody, antigen, or hapten, is bound. Common early forms of solid supports were plates, tubes, or beads of polystyrene, which were known from the fields of radioimmunoassay and enzyme immunoassay. More recently, a number of porous materials such as nylon, nitrocellulose, cellulose acetate, glass fibers, and other porous polymers have been employed as solid supports.
In the more common forms of dipstick assays, as typified by home pregnancy and ovulation detection kits, immunochemical components such as antibodies are bound to a solid phase. The assay device is “dipped” for incubation into a sample suspected of containing the subject analyte. Enzyme-labeled antibody is then added, either simultaneously or after an incubation period. The device next is washed and then inserted into a second solution containing a substrate for the enzyme. The enzyme-label, if present, interacts with the substrate, causing the formation of colored products, which either deposit as a precipitate onto the solid phase or produce a visible color change in the substrate solution. EP-A 0 125 118 discloses such a sandwich type dipstick immunoassay. EP-A 0 282 192 discloses a dipstick device for use in competition type assays.
Flow-through type immunoassay devices (such as test strips) were designed to obviate the need for incubation and washing steps associated with dipstick assays. U.S. Pat. No. 4,632,901 discloses a sandwich immunoassay device wherein antibody (specific to a target antigen analyte) is bound to a porous membrane or filter to which a liquid sample is added. As the liquid flows through the membrane, target analyte binds to the antibody. The addition of sample is followed by addition of labeled antibody. The visual detection of labeled antibody provides an indication of the presence of target antigen analyte in the sample.
Migration assay devices usually incorporate within them reagents that have been attached to colored labels, thereby permitting visible detection of the assay results without addition of further substances. See, for example, U.S. Pat. No. 4,770,853; WO 88/08534; and EP-A 0 299 428.
