N-(1-(2,3-dioleoyloxy)propyl)-N,N,N-trimethylammonium chloride (DOTAP) lipid molecules were used to drive the self-assembly of pre-fabricated Fe3O4 nanoparticles (similar to 10 nm in size) into a tightly packed hexagonal array by spin coating. In spite of the relatively wide particle size distribution of the pre-fabricated nanoparticles, the nanoparticles encapsulated by the DOTAP lipid molecules were self-assembled into a two-dimensional superlattice over a large area because the monolayer of DOTAP molecules attached to the particles surface provided the force necessary to anchor the nanoparticles on the substrate surface during spin coating as well as the force necessary to hold the particles together. It is expected that the proposed method can be easily scalable to an industrial process and be also adapted to different nanoparticle systems by appropriate selection of the encapsulating lipid molecules. (C) 2010 Elsevier B.V. All rights reserved.