Nanomedicine: swarming towards the target.

objective of all system providers, as it is for all power-generation systems. It can be achieved by increasing the system efficiency (that is, reducing the collection area, which is a major cost driver) and by reducing materials, production and installation costs. For example, owing to an impressive materials and production cost reduction in the past few years, the LEC of flat non-concentrating photovoltaics is at present lower than that of concentrated photovoltaics, although the efficiency of the latter is significantly higher. Some developers of future photovoltaic systems are striving for further cost reductions, even if their efficiency would be reduced. Developers of concentrated photovoltaics hope to become more competitive in the near future by improving their system efficiency while keeping sufficiently low production and installation costs. Among the solar thermal systems, linear Fresnels are competitive because of their low production costs, whereas dish-engine developers strive for higher annual-average efficiency (at reasonable cost). Parabolic-trough and solar-tower developers try to find the best trade-off between efficiency and cost for reaching the optimum LEC point. As Fig. 1 shows, the efficiency of thermoelectric systems is relatively low compared with the other systems. Yet, following the direction pointed out by Kraemer et al. 7 , the system efficiency of thermoelectrics could be similar to that of flat non-concentrating photovoltaics. These photovoltaic systems provide the best present solution for highly distributed, domestic power generation, which is also the most fitting market for thermoelectrics. However, to become competitive with photovoltaic systems, thermoelectric systems must demonstrate a potential for significant cost reduction — similar to that achieved by photovoltaic systems over the past few years — in addition to the increase of efficiency. An efficiency increase and cost reduction may enable other applications for thermoelectrics, for example, utilization of waste heat exhausted from solar thermal or other power-generation systems. T he power of nanomedicine — a subfield of nanotechnology that uses nanomaterials for the diagnosis and treatment of disease 1 — stems from our ability to tailor the properties of materials. This can be achieved by engineering their compositions, structures, sizes and shapes, modifying their surfaces with ligands, and integrating different functions for multi-modal imaging or theranostic applications. The full promise of nanomedicine is unlikely to arrive until we can selectively deliver nanomaterials to particular sites of interest, with minimal accumulation in off-target regions. Writing in Nature Materials, von Maltzahn et al. report a giant leap forward …