Abstract: Novel metal-lipid molecules have the formula M-Or-L. M represents a cluster or colloid of atoms of Au, Ag, Pt, Pd, or combinations thereof. Or is an organic group covalently attached to the metal atoms. L represents a lipid moiety. In a preferred embodiment, M represents a cluster of about 50-70 gold atoms having a diameter of about 1.4 nm in diameter and L represents dipalmitoyl phosphatidyl ethanolamine.

Abstract: Small organometallic probes comprise a core of metal atoms bonded to organic moieties. The metal atoms are gold, silver, platinum, palladium, or combinations thereof. In one embodiment, a multifunctional organometallic probe comprises a core of metal atoms surrounded by a shell of organic moieties covalently attached to the metal atoms, a fluorescent molecule, e.g., fluorescein, covalently attached to one of the organic moieties, and a targeting molecule, e.g., an antibody, covalently attached to another of the organic moieties.

Abstract: Antibody- or antibody fragment-gold cluster conjugates are shown wherein the conjugate size can be as small as 5.0 nm. Methods and reagents are disclosed in which antibodies, Fab' or F(ab').sub.2 fragments thereof are covalently bound to a stable cluster of gold atoms. The gold clusters may contain 6, 8, 9, 11, 13, 55 or 67 gold atoms in their inner core. The clusters may also contain radioactive gold. The antibody-cluster conjugates are useful in electron microscopy applications as well as in clinical applications that include imaging, diagnosis and therapy.