Abstract: An analytical element can be used to sensitively and rapidly detect a wide variety of specific binding ligands in either a competitive or sandwich assay format. The assays are carried out using a vanadium bromoperoxidase-labeled immunoreactant and a chemiluminescent signal-providing wash composition which comprises a 2,3-dihydro-1,4-phthalazinedione derivative; a halogen, pseudohalogen, halogen-providing source or pseudohalogen-providing source; and a peroxide or a peroxide-generating reagent composition.

Abstract: The present invention provides a novel dry analytical element for determination of an analyte in a fluid sample in thin film immunoassay, particularly chemiluminescence, fluorescence and colorimetry immunoassay. There is provided an analytical element comprising a support member, a reagent matrix comprised of at least one layer of a porous material carried on the support member, the matrix including a read area, an absorbent material in contact with the matrix, and light absorbing or reflecting means integral to the absorbent material and/or positioned between the absorbant material and the read area for absorbing or blocking background signal generated by washed, removed label and other interferents from outside the read area prior to it moving back into the read area. The analytical element can comprises a cover depending on the type of immunoassay to be conducted.