Nanoparticles (NPs) are a new class of advanced materials with sizes ranging from 1 nm to 100 nm. They have special physicochemical properties that are very different from those of bulk materials. For example, metal nanoparticles smaller than 5 nm show remarkable quantum size effects, which endow them with peculiar physical and chemical properties. The superlattices of metal nanoparticles exhibit novel electronic and optical properties that are not present in the isolated particles. The sizes of the nanoparticles are close to those of biomolecules, which allows an integration of nanotechnology and biotechnology, leading to major advances in multiplexed bioassays [1-3], clinical therapies , ultrasensitive biodetection, and bioimaging [5,6]. Moreover, nanoparticles can be used as building blocks for the fabrication of micro/nanoscale constructs with highly ordered architectures.
Increasing interest has been attracted to building close-packed solids of nanoparticles, controlling their microstructure, and engineering their properties on a nanometer scale. There are a number of strategies available for the ordering of nanoparticles into structured assemblies, and construction of large and complex systems, for example, shape-directed assembly and programmed assembly of nanoparticles comprising surface-attached molecules, ligands, and recognition sites, the formation of complex hybrid nanostructures by in situ transformation of unstable nanoparticle-based precursors, and template-directed assembly using nanoparticle building blocks . These materials can bring new and unique capabilities to a variety of biomedical applications ranging from diagnostics to therapies.
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