Abstract: A method for making composite nanoparticles comprises a) providing an amount of a polyelectrolyte having a charge, b) providing an amount of a counterion having a valence of at least 2, the counterion having a charge opposite the charge of the polyelectrolyte, c) combining the polyelectrolyte and the counterion in a solution such that the polyelectrolyte self-assembles to form a plurality of polymer aggregates, the plurality of polymer aggregates having an average diameter less than about 100 nm, d) adding a precursor to the solution, wherein the precursor has a charge opposite the charge of the polyelectrolyte, and e) allowing the precursor to infuse each polymer aggregate and polymerize so as to produce composite nanoparticles. The composite nanoparticles comprise a polymer aggregate containing at least one polyelectrolyte and at least one counterion and a polymer network crosslinked throughout the polymer aggregate. The polymer network may be inorganic, e.g silicon-containing.