Abstract: A stable protein-coated nickel particle useful in biological assays contains a nickel particle having removed from the surface thereof nickel oxide; a linker attached to said nickel particle, the linker having a free amino group; and a protein attached to said linker by covalently bonding to the free amino group. Methods of producing and using these oxide-free nickel-protein conjugates are disclosed.

Abstract: A stable colloidal particle comprises a colloidal-sized core substrate having amine-reactive functional groups thereon with an aminodextran coating over its peripheral surface and a layer of colloidal-sized metallic solid overlaying the aminodextran coating. A linker comprising aminotrithiolate attached to the metallic solid has a free amino group to which a protein is attached by covalent bonding to the free amino group. Such novel particles are useful in flow cytometry, particularly useful in the simultaneous analyses of subpopulations of leukocytes. Methods of preparation of such particles, as well as methods of use are provided. These conjugates enable the simultaneous analyses of at least two different mutually exclusive subsets of white blood cells, based on the binding affinity of the conjugated protein.