A disposable device suitable for performing automated solid-state diagnostic assays which employs microparticles to complex an analyte and where the microparticle complex becomes retained and immobilized on a fibrous matrix such that the presence of analyte on the microparticles can be detected by an optical device. A device is disclosed having a shallow sample well for receiving a sample and reagents for forming a reaction mixture, a read well having (a) an entrance port and wash receiving structure for receiving a quantity of sample and assay reagents, (b) a fibrous matrix for retaining and immobilizing microparticle/analyte complexes for detection, the fibrous matrix positioned below the wash receiving structure, and having an average spatial separation of fibers greater than the average diameter of the microparticles and (c) a structure below the fibrous matrix for assisting the flow of sample and assay reagents through the fibrous matrix, such as an absorbent material or vacuum below the fibrous matrix and a passage means communicating between the shallow sample well and the read well where the sample and reaction mixtures can be transferred and washed from the shallow sample well into the read well without being contacted by any apparatus.