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applications. A very intense research effort is currently being developed to solve nanostructures in the bulk of liquids. Solubilization and biocompatibilization of light emitting and magnetic nanoparticles are currently a hot topic for nanomedicine studies.
mass. From the point of view of Materials Science, the most important challenges to meet are the chemical functionalization of graphene (to control its solubility, open a semiconducting gap and control the sign and concentration of charge carriers by doping) and the epitaxial growth of graphene sheets with reduced defect concentration. An analysis of the scientific papers published in the field of graphene research in the last few years (2007-2009), shows that Spain has played a major role in this scientific enterprise, occupying the 7th position in the ranking of countries, according to Web of Science.
New experimental non-invasive imaging techniques and therapies for a number of diseases, which are currently being developed, relay on the capability of these nanostructures to get incorporated into the blood stream without triggering immune responses, and get into target cells and organs.
2. State of the Art For this purpose a major challenge that must be tackled in the next few years is finding the proper chemical functionalizations that would enable the nanostructures to bind selectively to the targeted organs.
As described above, we will limit ourselves to the Materials Science aspects of current Nanoscience and Nanotechnology, i.e. to materials that contain distributions of nanoscale motifs that control or affect their macroscopic properties. Since their preparation methods and final properties are very different, we will classify nanostructured materials depending on whether the nanoscale motifs are distributed all over the bulk of the material or at its surface.
One possible alternative to incorporate the nanostructures into a bulk material without the need of a matrix could be the direct crystallization of nanoparticles. The interactions between the nanoparticles that steer the selfassembly processes are dictated, and thus can be controlled, by the proper choice of the ligands that cover their surfaces.
2.1 Embedding nanostructures at the bulk of a material Nanostructures can be embedded in typically amorphous matrices, very often polymeric matrices, resulting usually in random spatial distribution and the nanoscale structural motifs. Typical examples are polymeric matrices with incorporated carbon nanotubes, which have very interesting effects in their elastic and thermal conduction properties, or semiconducting nanoparticles (quantum dots) dispersed in polymeric matrices with very interesting photovoltaic properties.
It was already described in the literature that nanoparticles can be embedded into larger colloidal particles, for which crystallization methods have been long known. The resulting photonic crystals have very interesting optical properties. Nanoporous materials, such as zeolites or organometallic coordination networks, can act as molecular sieves with very promising applications in the fields of catalysis and water purification. The directionality of the bonds that hold the 3D structure of these materials, leads to the formation of ordered arrays of holes with well
Recently, hybrid CNT-QD systems have been synthesized, holding promise for photovoltaic
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