Devices and methods for performing receptor binding assays using magnetic particles

A method for performing an assay for an analyte in a fluid sample, comprising:

• (a) introducing said fluid sample into an assay device comprising:
• (i) a sample addition region to receive said fluid sample,
• (ii) a second device region discrete from, and in fluid communication with, said sample addition region, said second device region comprising a population of labeled conjugates corresponding to said analyte, and
• (iii) an analyte detection region discrete from, and in fluid communication with, both said sample addition region and said second device region,
• by applying said fluid sample to said sample addition region, wherein said assay device is configured to provide, upon application of said fluid sample to said sample addition region, fluid flow from said sample addition region to said second device region, thereby contacting said labeled conjugates in said second device region with at least a portion of said fluid sample, and fluid flow from said sample addition region to said analyte detection region;
• (b) contacting said labeled conjugates with a population of magnetically responsive particles in the presence of at least a portion of said fluid sample, thereby forming a reaction mixture in said second device region, wherein said magnetically responsive particles are configured to form a complex with said labeled conjugates in an amount related to the presence or amount of said analyte in said reaction mixture;
• (c) applying a magnetic field to said assay device, said magnetic field configured to induce movement of said magnetically responsive particles on a path from said second device region to said analyte detection region, wherein the direction of said movement is counter to the direction of said fluid flow from said sample addition region to said second device region for at least a portion of said path;
• and
• (d) detecting a signal from labeled conjugates in said analyte detection region.