A method for purifying a suspension containing colloid-seeded nanoparticles and
excess colloids is provided that includes adding to the suspension a filter aid
comprising a salt. The method further includes filtering the suspension with a
filter of a pore size intermediate between the average colloid-seeded nanoparticle
size and the average excess colloid size, so as to form a retentate that includes
the majority of the colloid-seeded nanoparticles and a filtrate that includes the
majority of the excess colloids. Still further, the method includes collecting
the retentate. The method may be incorporated into a method of making metallized
nanoparticles, such as nanoshells, by reduction of metal ions onto the purified
colloid-seed nanoparticles so as to form the metallized nanoparticles.
