The functionality, assembly, and fabrication of functional nanoparticles, such as magnetic materials, noble metals, and quantum dots, are of increasing interest for a wide range of application areas and there is currently a strong scientific focus on the fundamental properties of such particles. Magnetite (Fe₃O₄) nanoparticles are especially useful in a wide range of fields, including drug delivery systems, diagnostics, gene analysis, proteomics, separation, purification, hyperthermia therapy, in vivo imaging, photonics and the like. In many cases the individual nanoparticles themselves are not desired, since they generally do not respond strongly to magnetic fields, and it is necessary to form small clusters of these nanoparticles that are more responsive to moderate magnetic fields. The establishment of well defined methods for the fabrication of highly ordered, two- and three dimensional nanoparticle assemblies (superlattices) is crucial if various future applications based on functional nanoparticles are to be realized.  We will discuss three different approaches we have adopted to investigate these phenomena:  

(i)         The synthesis of responsive Janus nanoparticles that can be induced to self assemble reversibly into stable, small clusters on application of appropriate stimuli, such as pH and temperature. 

(ii)       The formation of magnetite nanoparticle clusters of varying geometry and internal packing structure in which the processing conditions determine the morphology and crystallinity of dense clusters of monodisperse magnetite nanoparticles, or the arrangement of nanoparticles on the surfaces of ~100-200 nm polymer beads.   String-like clusters with very high aspect ratios can be formed during processing of these materials by the application of high magnetic fields. 

(iii)     The self-assembly of nanoparticles on liquid surfaces and surfactant assemblies for the generation of homogeneous, relatively defect-free, large-area, nanoparticle films and tubules.