Diagnostic detection device using colloidal gold particles and polymerized streptavidin

Disclosed is a device for detecting an analyte in a liquid sample deposited on a first portion of the device for transport to a second portion of the device. The disclosed device comprises: a) a release medium formed of a first material and comprising: i. a labelled conjugate comprising a binding member reactive with a first epitope of the analyte and a label comprising colloidal gold particles having a mean particle size of at least about 50 nm prior to formation of the labelled conjugate; and ii. a biotinylated capturable component having a site reactive with a second epitope of the analyte, such that if the analyte is present in the sample, the analyte produces a complex comprising the labelled conjugate, the analyte for detection, and the biotinylated capturable component; and b) a capture medium in fluid communication with the release medium and formed of a second, different material, the capture medium comprising a capture site for capturing the complex, the capture site having immobilized thereon a capture component comprising polymerized streptavidin.