Method of measuring interaction between molecules

Abstract

The present invention relates to methods of measuring interaction between a first and a second molecule, for example a protein and an antibody, by conjugation of one of these molecules with nanoparticles, and measuring the interaction between the first and second molecule via changes in the optical properties of the nanoparticles. The present invention further relates to methods of coating nanoparticles.

What is claimed is: 
     
         1 . A method of coating a metal nanoparticle with a compound, comprising:
 i) providing a liquid composition comprising metal nanoparticles at least partially coated with cetyl trimethyl ammonium bromide (CTAB);   ii) adding a thiol-polyethylene glycol to said composition of step i), thereby obtaining a liquid composition comprising metal nanoparticles coated with thiol-polyethylene glycol;   iii) purification of said composition obtained in step ii) by separating said nanoparticles from free thiol-polyethylene glycol and free CTAB;   iv) adding a mercaptocarboxylic acid to said composition obtained in step iii), thereby obtaining a liquid composition comprising metal nanoparticles coated with mercaptocarboxylic acid, and   v) contacting said metal particles obtained in step iv) with said compound.   
     
     
         2 . The method according to  claim 1 , wherein step iv) further comprises providing said metal nanoparticles coated with mercaptocarboxylic acid with one or more functional groups. 
     
     
         3 . The method according to  claim 2 , wherein said functional groups are selected from the group consisting of carboxyl, amino, azido, alkynyl, carbonyl, hydroxyl and maleimides. 
     
     
         4 . The method according to  claim 1 , wherein said liquid composition in steps i), ii), iii) and iv), is an aqueous composition. 
     
     
         5 . The method according to  claim 4 , wherein said liquid composition in step v) is an aqueous composition. 
     
     
         6 . The method according to  claim 1 , wherein the mercaptocarboxylic acid added in step iv) is a compound of formula (I) 
       
         
           
           
               
               
           
         
       
       wherein n is an integer from 6 to 16. 
     
     
         7 . The method according to  claim 3  wherein the mercaptocarboxylic acid is 11-mercaptoundecanoic acid. 
     
     
         8 . The method according to  claim 1 , wherein the thiol-polyethylene glycol added in step ii) is a compound of formula (IV) 
       
         
           
           
               
               
           
         
       
       wherein nc is such that the molecular weight of compound (IV) is between 100 Da and 10 kDa; and R 1  is C 1-4 alkoxy, wherein said C 1-4 alkoxy is optionally substituted by one or more groups such as hydroxyl. 
     
     
         9 . The method according to  claim 8  wherein the thiol-polyethylene glycol is methoxy-PEG-thiol or ethoxy-PEG thiol. 
     
     
         10 . The method according to  claim 1 , wherein said metal nanoparticles comprise a metal selected from the group consisting of Au, Ag, Cu, Ta, Pt, Pd, and Rh. 
     
     
         11 . The method according to  claim 1 , wherein said metal nanoparticles are nanorods 
     
     
         12 . The method according to  claim 11 , wherein said nanorods have an aspect ratio between 1.5 and 5. 
     
     
         13 . The method according to  claim 1  wherein said compound is a biomolecule. 
     
     
         14 . The method according to  claim 13  wherein said biomolecule is a peptide, protein, amino acid or a nucleic acid. 
     
     
         15 . The method according to  claim 1  wherein the amount of said compound coated onto the metal nanoparticles is less than 70% of the minimum amount required for full coverage of said metal nanoparticles with said compound. 
     
     
         16 . The method according to  claim 15 , wherein the amount of said compound coated onto the metal nanoparticles is more than 30% of the minimum amount required for full coverage of said metal nanoparticles with said compound. 
     
     
         17 . The method according to  claim 1 , wherein said compound is provided with at least one functional group, prior to the step v) of contacting said metal particles obtained in step iv) with said compound, to thereby conjugate said compound to the metal nanoparticles.