Magnetic particle tagged reagents and techniques

Methods for separating, in a continuous, multizone fluid medium, cells, particles, or other molecules of interest (MOI) from associated or contaminating unwanted materials not of interest (MNOI). The invention involves forced movement of MOI into certain zones having properties which deter the entry of unwanted materials. Differential movement of MOI and MNOI occurs by active counterforces that move MNOI but not MOI. MOI are tagged with magnetic particles and moved with a magnetic field through a fluid, or zones, of higher specific gravity that prevents, by flotation counterforce, unwanted less dense materials from entering.Surfaces specifically coated with reactants are reactive with the MOI in the tagged magnetic particle complex and of buoyant or other forces are used to remove any unbound material from the surface before reading. Readable labels, in addition to the magnetic particle tagged complex itself, such as enzymes, fluorophors, chemiluminescent materials, radioactive isotopes, chromogenic and fluorogenic substrates and other labels may be used. In most embodiments, materials of interest are delivered to a special final zone for reading or harvesting. The invention applies to many assays, diagnostic tests, separative procedures and chemical syntheses.