In addition to the ultrathin layers, nanoparticles are interesting both as materials and for nanostructure technology. Nanocomposite materials and nanoparticles are already established in materials sciences in several areas. Thus, the special properties relating to the small size, such as size-dependent light adsorption or the huge specific surface area, are utilized, when a large number of particles will be involved.
In addition, the individual particles are of interest in nanostructure technology. Therefore, methods are being developed to manipulate small ensembles and even individual nanoparticles. One approach is based on the principle of reducing the dimensions. Nanoparticles are deposited in mono- or submono-layers on planar solidstate surfaces, where they bind on the surface in a similar manner to molecules. However, larger particles form non-specific bonds when in contact with surfaces, based on their relatively large contact area, and these numerous non-specific forces overcome the few specific bonds; smaller particles exhibit a greater influence of individual chemical bonds compared with ensembles of weak and non-specific bonds. This enables the controlled deposition of nanoparticles onto microstructured areas, resulting in microchips with spots covered with nanoparticle monolayers. A prerequisite for this specific binding is the existence of complementary-reactive groups on the surface of both the nanoparticle and substrate.
The reactions of nanoparticles with each other is also possible with appropriate functionalization of the surface. This extends the surface chemistry with nanoparti-cles in solution to synthetic chemistry. The specific hybridization of single-stranded DNA can be used for the connection of gold nanoparticles exhibiting thiol-functiona-lized oligonucleotides with complementary sequences . These structures can be deposited as synthetic nanoparticle modules. Analogous operations are possible with organic nanoparticles, e. g., polymeric nanoparticles.
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