A method for making hollow 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, c) combining the polyelectrolyte and the counterion in a solution such that the polyelectrolyte self-assembles to form spherical aggregates, and d) adding nanoparticles to the solution such that nanoparticles arrange themselves around the spherical aggregates. The polyelectrolyte may have a positive or negative charge. The charge ratio R of total charge of the counterions to the total charge of the polyelectrolyte is greater than 1.0.