Self-assembly is Nature's way of building stuff. This fundamental principle that governs natural structures on all scales, from molecules to galaxies, generates structural organization from pre-existing parts or components. In nanotechnology, self-assembly is seen as a key technique that will one day allow the fabrication of materials and devices from the bottom up. Still only tinkering with the basics, scientists so far have designed and created simple systems that could mimic natural functions by connecting biological components to abiotic materials to understand the workings of the biological system or to take advantage of the unique properties of the nonbiological components in a natural setting. Most nanotechnologist, even if they manage to self-assemble functional nanodevices, still operate exclusively at the nanoscale (it will be a while before you can order "Tea. Earl Grey. Hot" from your food replicator in the wall). Bridging the gap between the nano- and the macroworld has proven to be a huge hurdle. In a novel approach that merges material chemistry, biology and medicine, researchers in Germany have used living bacteria to show that self-assembly of functional materials and living systems is possible through a chemically programmed construction.
Throughout human history, technologies usually involved some kind of "top-down" approach, whether it was breaking a stone axe from a larger rock or using micro- or nanolithography to etch smaller structures from larger entities. In contrast, the self-assembly of nano-objects is an example of the principally new "bottom-up" technological approach which soon may provide novel fabrication processes and products with drastically improved properties. In particular the self-assembly of colloidal nanocrystals makes it possible to obtain structures with a high level of ordering and permit construction of patterns to be used in optoelectronics, photonics and biosensing. What makes nanocrystals so attractive to researchers is the fact that the properties essential to allow the arrangement process, including their size, shape, surface protection, stabilization and charge, can be controlled along with the electronic structure of each nanocrystal. As an example, we developed a "lab-in-a-drop" technique where a variety of nanostructures with desired properties may be produced.
Strong and highly directional hydrogen-bonding networks are of fundamental importance in nature. Their efficiency in assisting electron-transfer processes makes them increasingly appealing for technological application inspired by biomimetic principles, i.e. the application of methods and systems found in nature to the study and design of engineering systems and modern technology. Attempting to move from microelectronics to nanoelectronics, engineers are faced with the growing difficulty of manufacturing ever tinier devices with top-down engineering approaches. They are therefore looking at possible ways for bottom-up engineering approaches with the goal of achieving the holy grail of nanotechnology - molecular self-assembly. For some time now researchers have been able to design molecules in such a way that they attach themselves to each other in alternating order, and under certain circumstances - for example on surfaces - create chains. Unfortunately the chains are not very long, because all surfaces, even extremely smooth ones, show unevenness at the atomic level. Step edges, although only a few atomic layers high, represent insurmountable hurdles to the self-assembly process, and since they are distributed randomly over the surface, the molecules form themselves into very irregular patterns. Overcoming this problem, researchers were recently able to formulate two organic molecules in such a way that they organized themselves spontaneously into long parallel chains (nanowires) on a specially prepared gold surface. Selective self-assembly on surfaces and the fundamental processes which control this phenomenon are, however, not only critical in the area of molecular electronics but also in heterogeneous catalysis - a process used in automotive catalytic converters - and in sensor technologies.
The controllable fabrication of highly ordered homogeneous nanostructures on surfaces remains a difficult challenge. Nevertheless, motivated by potential applications in micro- and optoelectronic devices, the problem of organic nanoscale structures on surfaces with long-range order and uniform size has attracted considerable attention in recent years. Researchers in Switzerland have now grown ordered arrays of fullerene nanochains on a gold surface. This demonstration constitutes a successful proof-of-principle for the concept of site-selective molecular anchoring on nanostructured template surfaces, and provides the perspective of fabricating complex supramolecular nanostructures being of potential technological relevance by site-selective anchoring and selfassembly methods using properly designed functional molecular building blocks.
Back in 2005, Dr. Pu-Chun Ke conducted an experimental study ("Coating Single-Walled Carbon Nanotubes with Phospholipids") where he discovered a very efficient method of solubilizing nanotubes using lysophospholipids, or the so-called single-tailed phospholipids. The solubility provided by lysophospholipid LPC is at least one order of magnitude better than that provided by SDS, a routine surfactant people use to solubilize nanomaterials in aqueous solutions. Ke and his colleagues showed that superior solubility was due to the formation of lipid 'striations' coated on the nanotubes. The underling principle of this superior solubility of nanotubes by lysophospholipids is supramolecular assembly, a topic of common interest to researchers in nanoscience, chemistry, materials, and biophysics. New results obtained during recent follow-up research provide useful insight on the binding mechanism of amphiphiles and one-dimensional nanostructures. This knowledge may facilitate the bottom-up design of supramolecular assembly, nanotechnology, nanotoxicology, and gene and drug delivery.
Semiconductor photonics, electronics and optoelectronics infrastructure is at the core of the information society. As the length scales of electronic devices continue to shrink, the cost of traditional approaches to device fabrication involving lithography is becoming excessive. It is regarded that self-assembled growth methods are a solution to the problem of fabricating smaller devices at a lower cost. Self-assembled quantum dots (QDs) are providing the possibility of new devices for this infrastructure in the short, medium and long term. QDs are ideal for the study of the fundamental properties of nanostructures, which is applicable across the nanotechnology and nanoscience sector. Research in self-assembled semiconductor QDs is therefore characterized by a remarkably well-matched combination of the two main motivations for scientific research, namely academic interest and the potential for industrial applications. As a consequence, there is an intense scientific activity in materials growth, structural characterization, optical and transport spectroscopy, device engineering and computational modeling. The field of self-assembled semiconductor nanostructures started in 1985 in Europe by a French group at the Centre National d'Etudes des Telecommunications - CNET.
With the recent development in nanoscience and nanotechnology, a large variety of single-component nanomaterials (such as carbon nanotubes, nanoparticles, and quantum dots) and devices have been reported. There is now a pressing need to integrate multicomponent nanoscale entities into multifunctional systems and to connect these nano-systems to the micro/macro-world. This connection from the nano world to the macro world has been one of the long-standing problems in nanotechnology and still remains a big challenge. A novel approach of growing aligned carbon nanotubes (CNTs) around microsized carbon fibers should provide a useful platform technology for the development of various multidimensional and multifunctional nanomaterials and devices.
The fabrication of ultrafine structures beyond the limits of conventional lithography is a topic of tremendous importance and is expected to play a significant role in the realization of futuristic nanotechnology. It is also equally important to develop functional material systems of ultrafine dimensions in order to achieve this goal. An important step towards realization of nanodevices is self-organized nanopatterning of functional structures. A new technique, which might be called chemical lithography, enables the regular assembly of optically active nanoparticles on a silicon surface.