The invention provides a method of preparing nanoparticles having at least one polymer shell attached to them, each polymer shell having a selected property or properties. The method comprises attaching initiation monomers to the surfaces of the nanoparticles, contacting the nanoparticles having the initiation monomers attached to them with a transition metal ring-opening metathesis catalyst to activate the initiation monomers, and contacting the nanoparticles with one or more types of propagation monomers of the formula P--L--N under conditions effective so that the monomers are polymerized to form the one or more polymer shells. In the formula P--L--N, N is a cyclic olefin-containing group, P is a moiety which gives each polymer shell a selected property or properties, and L is a bond or linker. The invention also provides polymers formed by polymerizing the propagation monomers. The invention further provides the nanoparticles, the initiation monomers, and propagation monomers of formula P--L--N wherein P is a moiety having a property selected from the group consisting of redox activity, optical activity, electrical activity and magnetic activity, and L and N are defined above. The invention also provides binding monomers of formula B--L--N, wherein B is a binding moiety that binds specifically to an analyte, and N and L are defined above. Finally, the invention provides methods and kits for detecting or quantitating an analyte.