Homogeneous binding assay

A method of determining the presence of a member of a chemical binding pair in an aqueous sample comprising the steps of:

• selecting a material which is chemically stable in aqueous solution and which has a complex refractive index n-ik wherein a real part n of the index approaches zero when an imaginary part k approaches .sqroot.2, thereby yielding a resonant optical extinction in a wavelength region where water is optically transparent;
• producing an aqueous solution of colloidal particles of the material, the colloidal particles being spherical single particles with diameters less than a wavelength of visible light;
• attaching first members of a first chemical binding pair to the surfaces of the colloidal particles;
• adding an aqueous sample to be analyzed to the colloidal particles having said attached chemical binding member, and mixing thoroughly;
• and
• measuring a resonant wavelength of the colloidal particles without any bound-free separation step, an extinction change at the resonant wavelength being indicative of changes in particle-particle association which is related to the presence and amount, in the sample, of a substance bearing a second member of the first chemical binding pair.

A method of determining the presence of an inhibitor of a chemical binding interaction, the method comprising the steps of:

• selecting a material which is chemically stable in aqueous solution and which has a complex refractive index n-ik wherein a real part n of the index approaches zero when an imaginary part k approaches .sqroot.2, thereby yielding a resonant optical extinction in a wavelength region where water is optically transparent;
• producing an aqueous solution of colloidal particles of the material, the colloidal particles being spherical single particles with diameters less than a wavelength of visible light;
• attaching a first member of a chemical binding pair to the surfaces of the colloidal particles in a first aliquot;
• attaching a second member of a chemical binding pair to the surfaces of the colloidal particles in a second aliquot;
• combining the two aliquots so that the binding interaction leads to particle-particle association;
• adding as a sample a chemical compound with unknown activity as an inhibitor of the binding interaction;
• and
• measuring a resonant wavelength of the colloidal particles without any bound-free separation step, an extinction change at the resonant wavelength being related to the presence and activity, in the sample, of an inhibitor of the binding interaction.

A method of assaying the presence of a specific polynucleotide sequence, the method comprising the steps of:

• selecting a material which is chemically stable in aqueous solution and which has a complex refractive index n-ik wherein a real part n of the index approaches zero when an imaginary part k approaches .sqroot.2, thereby yielding a resonant optical extinction in a wavelength region where water is optically transparent;
• producing an aqueous solution of colloidal particles of the material, the colloidal particles being spherical single particles with diameters less than a wavelength of visible light;
• attaching first polynucleotide sequences complementary to one region of said specific polynucleotide sequence to the surfaces of the colloidal particles in a first aliquot;
• attaching second polynucleotide sequences complementary to a different region of said specific polynucleotide sequence to the surfaces of the colloidal particles in a second aliquot;
• combining the two aliquots with an aqueous sample to be analyzed for said specific polynucleotide sequence so that the binding interaction between said specific polynucleotide sequence and the complementary regions on the first and second polynucleotide sequences leads to particle-particle association;
• and
• measuring a resonant wavelength of the colloidal particles without any bound-free separation step, an extinction change at the resonant wavelength being related to the presence, in the sample, of said specific polynucleotide sequence.