Direct read lateral flow assay for small analytes

A process for determining the presence or amount of an analyte in a sample comprising:

• a) contacting said sample with a preparation containing
• i) anti-analyte antibodies, which bind to analyte or to both analyte and an analyte analog, and
• ii) an assay tracer, wherein said assay tracer comprises a detectable particulate substance having immobilized on its surface, analyte or analyte analog and a first member of a binding pair, to provide a sample/preparation mixture containing analyte/anti-analyte antibody complexes and/or assay tracer/anti-analyte complexes;
• b) contacting said sample/preparation mixture with a sample addition area of a lateral flow device, wherein said device comprises a solid support containing, in sequence,
• i) said sample addition area,
• ii) a capture area, wherein analyte or analyte analog is immobilized, to capture said analyte/anti-analyte antibody complexes and/or assay tracer/anti-analyte complexes,
• iii) a read-out area comprising at least one zone, wherein a second member of said binding pair, which binds to said first member, is immobilized, to bind assay tracer not captured in said capture area, in proportion to the amount of analyte in said sample;
• c) allowing said sample/preparation mixture to flow through said lateral flow device;
• and
• d) detecting the presence or amount of assay tracer bound in said at least one zone of said read-out area as a measure of analyte in said sample.