The disclosed invention relates to assays for detecting and quantifying Aβ peptide, using solid supports that are coated with heavy metal cations, such as zinc (II) or copper (II) form of a nitriloacetic acid. Further, diagnostic kits are described which are used to carry out the assays of the present invention. An improvement in an assay for detection of Aβ peptide is suggested which comprises forming a heavy metal cation/solid support complex. The preferred heavy metal cations for this improvement are zinc (II) or copper (II) form of a nitriloacetic acid. Finally, methods and kits for bulk purification of Aβ peptides from biological fluids are taught.