A method for producing a composite nanoparticle, including the steps of: changing the conformation of a dissolved polyelectrolyte polymer from a first extended conformation to a more compact conformation by changing a solution condition so that at least a portion of the polyelectrolyte polymer is associated with a precursor moiety to form a composite precursor moiety with a mean diameter in the range between about 1 nm and about 100 nm; and cross-linking the polyelectrolyte polymer of the composite precursor moiety to form a composite nanoparticle.