Binding assays using optical resonance of colloidal particies

Abstract

A device and a method enable the rapid, quantitative evaluation of a large collection of ligands for binding affinity with a certain immobilized receptor, the improvements being that binding pan be detected without the need for a label and that binding is carried out in solution phase at a high rate. The instrument has at least two embodiments, one is based on a sensitive absorption photometer and the other on a sensitive light scatter photometer operating at a specific resonance wavelength, λ R , of small, metallic, colloidal particles. The resonance is present in small particles having a complex refractive index with real part n(λ) approaching 0 and imaginary part k(λ) approaching {square root}2 simultaneously at a specific wavelength λ R . The particles are substantially spherical and substantially smaller than λ R . The receptor is immobilized on a suspension of such particles and ligand binding is detected by a change in optical absorption or light scatter at the resonance wavelength.

We claim:  
     
         1 . A method for determining binding of a ligand comprising the steps of: 
 providing colloidal particles having a complex index of refraction and showing optical resonance at a resonant wavelength, said particles coated with a receptor for the ligand, wherein the resonant wavelength is a wavelength at which a real part n(λ) of the index of refraction approaches zero while an imaginary part n(λ) of the index of refraction simultaneously approaches {square root}2, and wherein diameter of said particles is less than about {fraction (1/10)} of the resonant wavelength;    contacting the colloidal particles with a sample solution; and    measuring light scatter and/or light absorption at the resonant wavelength whereby a decrease in light scatter and/or light absorption at the resonant wavelength is representative of binding of the ligand to the colloidal particles.    
     
     
         2 . A system for determining binding of a ligand comprising: 
 a sample container;    colloidal particles having a complex index of refraction and showing optical resonance at a resonant wavelength, said particles coated with a receptor for the ligand, wherein the resonant wavelength is a wavelength at which a real part n(λ) of the index of refraction approaches zero while an imaginary part n(λ) of the index of refraction simultaneously approaches {square root}2, and wherein diameter of said particles is less than about {fraction (1/10)} of the resonant wavelength;    means for contacting the colloidal particles with a sample liquid to form a mixture thereof;    means for placing the mixture into the sample container; and    means for measuring light absorption and/or light scatter of mixture in the sample container at a resonant wavelength, whereby a decrease in light scatter and/or light absorption at the resonant wavelength is representative of binding of the ligand to the particles.    
     
     
         3 . A method for determining binding of a ligand comprising the steps of: 
 providing colloidal silver particles coated with a receptor for the ligand, said silver particles having a diameter less than about 70 nanometers;    contacting the colloidal particles with a sample solution; and    measuring light scatter and/or light absorption at a resonant wavelength between 350 and 500 nanometers whereby a decrease in light scatter and/or light absorption at the resonant wavelength is representative of binding of the ligand to said colloidal particles.    
     
     
         4 . A system for determining binding of a ligand comprising: 
 a sample container;    colloidal silver particles coated with a receptor for the ligand and having a diameter of less than about 70 nanometers;    means for contacting said particles with a sample liquid to form a mixture thereof;    means for placing the mixture into the sample container; and    means for measuring light absorption and/or light scatter of mixture in the sample container at a resonant wavelength between 350 nanometers and 500 nanometers, whereby a decrease in light scatter and/or light absorption at the resonant wavelength is representative of binding of the ligand to the colloidal silver particles.