The TEM image on the left shows citrate-stabilized Au nanoparticles prepared in solution using literature methods. The SEM image on the right shows that these particles can be uniformly adsorbed in porous alumina membranes using the layer-by-layer method. The density of particles in the membranes pores is about 500 colloids/μm2, and when catalyzing the reduction of p-nitrophenol, these immobilized particles exhibit the same rate constants as particles in solution.