Method of separation employing magnetic particles and second medium

A method for separating cells from a mixture containing said cells and other components, which method comprises:

• layering an aqueous medium containing said cells and said other components with a second liquid medium that is of different density and/or viscosity than said aqueous medium, said cells being non-specifically bound to superparamagnetic or paramagnetic particles wherein said superparamagnetic particles and paramagnetic particles are selected from the group consisting of uncoated pure metals, alloys, complex salts, oxides, borides, and sulfides of iron, cobalt, nickel and rare earth elements;
• and coated particles containing a core selected from the group consisting of pure metals, alloys, complex salts, oxides, borides, and sulfides of iron, cobalt, nickel and rare earth elements and a coating selected from the group consisting of proteins, carbohydrates and amphiphilic substances and,
• subjecting said aqueous medium and said second liquid medium to a magnetic field gradient sufficient to cause said coaggregate to migrate into said second medium.

A composition comprising:

• (a) a first liquid medium containing magnetic particles wherein said magnetic particles are selected from the group consisting of uncoated pure metals, alloys, complex salts, oxides, borides, and sulfides of iron, cobalt, nickel and rare earth elements;
• and coated particles containing a core selected from the group consisting of pure metals, alloys, complex salts, oxides, borides, and sulfides of iron, cobalt, nickel and rare earth elements and a coating selected from the group consisting of proteins, carbohydrates and amphiphilic substances, to which are non-specifically bound a particulate biologic material (PBM), selected from the group consisting of microorganisms, cells, and organelles, and
• (b) a second liquid medium having a different density and/or viscosity than said first liquid medium and in contact but substantially unmixed therewith.

In an assay for a particulate biologic material PBM, selected from the group consisting of microorganisms, cells, and organelles, wherein said assay comprises the step of separating said PBM from other components in a mixture, the improvement comprising:

• contacting a first liquid medium containing said PBM with a second liquid medium that is of different density and/or viscosity than said first liquid medium without mixing said media, said PBM being non-specifically bound to magnetic particles wherein said magnetic particles are selected from the group consisting of uncoated pure metals, alloys, complex salts, oxides, borides, and sulfides of iron, cobalt, nickel and rare earth elements;
• and coated particles containing a core selected from the group consisting of pure metals, alloys, complex salts, oxides, borides, and sulfides of iron, cobalt, nickel and rare earth elements and a coating selected from the group consisting of proteins, carbohydrates and amphiphilic substances and
• subjecting said media to a magnetic field gradient whereby said magnetic particles migrate into said second liquid medium.

The method of claim 79 wherein said label is conjugated to a member of a specific binding pair (sbp).