The DELFIA® Assay Buffer is a buffered protein and detergent solution intended for use in DELFIA® assays that include lanthanide-labelled proteins. It is optimised to give a minimum fluorescence background and non-specific binding in solid phase DELFIA® assays. The formulation includes ready-to-use Tris-HCl buffered NaCl solution (pH 7.8) containing 0.05% NaN3, bovine serum albumin (BSA), bovine gamma globulins, Tween 40, diethylenetriaminpentaacetic acid (DTPA) and an inert red dye.