Patent ID: 8367399

Claim:
An optical method for determining a presence and strength of binding affinity of interacting molecular species, without requiring their labeling with fluorescent substances or with other kinds of luminescent or light absorbing probes, hereafter named receptor, being immobilized on a surface and the others, hereafter named ligands, being in a solution, or for determining a concentration of the ligands in the solution by using a measure of an intensity of a light reflected by a transparent assembly forming an interface between the solution and a solid material having a refractive index differing by no more than 0.1 from that of the solution, comprising the following steps: a) a bare surface, flat or rough, of a transparent solid material constituted by a hydrophobic amorphous polymer, having a refractive index between 1.3200 and 1.3500, is brought into contact with an aqueous or non-aqueous solution of a mixture containing from 1 nanogram/ml to 10 milligrams/ml in concentration of molecules with a function of receptor or reagent, or antibodies or other proteic or peptidic complexes, or nucleic acids, or lipids, or amphiphilic surfactants or block polymers ended with a receptor or reagent, optionally mixed to other molecules having no receptor function, optionally measuring at each addition the light intensity reflected from the interface between the aqueous solution and said solid material and reporting the measured value on a diagram as a function of time or as a function of the receptor concentration progressively added, optionally repeating this procedure by bringing the surface into contact with other aqueous or non-aqueous solutions of said molecules; b) addition to the solution obtained in step (a) of a sequence of known volumes of an aqueous solution of a ligand, measuring at each addition the light intensity reflected from the interface between the aqueous solution and the polymeric material and reporting the measured value on a diagram as a function of the time or as a function of the ligand concentration [T 0 ] progressively added, and fitting the reflected light intensity data I as a function of the ligand additions with Fresnel formulas for thin layer reflection to obtain the adhered mass, and with a Langmuir formula for adsorption to obtain the strength of binding affinity of the ligand and the receptor at equilibrium or, if the strength of the binding affinity is known, to obtain the ligand concentration [T 0 ].