The interest in hollow structures with defined porosities has promoted the fabrication of colloidosomes,
i.e. capsules from spherical colloids. The hierarchically organized architectures were built from
microparticles 01' multiple layers of nanoparticles to make sure that the capsule walls were sufficiently
robust. Herein, we present [or the first time a strategy towards submicron-sized capsules with walls that
consist of a single layer of nanoscopic inorganic constituents. Nanopartieies and oppositely charged
polymer colloids were joined at the surface of evaporating emulsion droplets. The heteroaggregates
exhibited well-defined core-shell morphologies, with clusters of the polymer colloids as the core and
a dense monolayer of nanoparticles as the shel!. Various complex yet well-defined global shapes can be
obtained in respect to the number of polymer particles. Subsequent removal of the polymer core led to
capsules, which exhibited regular compartmentalized shapes. A high density of nanopores was obtained
on objects with dimensions of less than half a micron. Regardless of the fact that the capsules consisted
of a single layer of nanoparticles with tiny contacts keeping them together, they did not collapse or
break apart. Monte Carlo computer simulations demonstrated that the nanoscopie constituents can be
trapped into structurally arrested states.