A synthetic route is presented for the realization of ultrathin freestanding nanoparticle membranes that are built of gold nanoparticles protected with trimethoxysilane-bearing ligands. The mechanism relies on interfacial assembly in an oil-water mixture. Upon shaking, nanoparticles are transported to the liquid-liquid interface of the oil droplets and form a network through the formation of Si-O-Si bridges. Reticulation of the nanoparticles during the dynamic process of droplet coalescence allows the formation of ultrathin membranes of only a few nanoparticle layers in thickness and square centimeters in dimension. The membranes can be manipulated, such as locally perforated, without causing their collapse. Furthermore they can be transferred onto solid or holey substrates. The synthetic route is compatible with a coassembly of dopants. As an example, membranes were doped with single walled carbon nanotubes, which resulted in a sizable increase of their electric conductivity.