Nanoparticles of Au. Ag. CdS, and CdSe have been linked together by a chemical reaction to form controlled assemblies of similar or different types of nanoparticles through amido or azo linkage. The capping of nanoparticles was exchanged with bifunctional groups containing active functional groups at the tails. The reaction between the tails of the capping agents resulted in the formation of amido or azo linkages. These reactions were carried out Under very dilute conditions to control the assembly and avoid the polymerization. The assemblies Formed included the dimers, trimers, tetramers, and hexa- or heptamers. These reactions Eire the first examples for the systematic approach to establish the chemical route for the controlled assembly of nanoparticles and open the way for the Fabrication of nanoparticle based devices for various application.