Abstract: The invention relates to microparticles incorporating a series of two or more fluorescent dyes having overlapping excitation and emission spectra allowing efficient energy transfer from the excitation wavelength of the first dye in the series, transfer through the dyes in the series and re-emitted as an optical signal at the emission wavelength of last dye in the series, resulting in a desired effective Stokes shift which is controlled through selection of appropriate dyes.

Abstract: The subject invention concerns novel compositions for use in immunoassays, as well as immunoassays employing such novel compositions. The compositions comprise discrete charged colloidal particles comprised of small molecules which particles are capable of retaining their discrete character in an aqueous medium and composed of aggregates of lipophilic and/or amphiphilic organic molecules to which are bound non-covalently a label capable of producing a detectible signal and a ligand or an analog of the ligand capable of competing with a ligand for a ligand receptor. The discrete colloidal particle serves as a hub or nucleus for retaining the ligand or its analog and the label within a limited locus.The compositions are prepared by individually covalently bonding the ligand and the label, when not naturally lipophilic, to a lipophilic (includes amphiphilic) compound, normally a phospholipid.