Understanding and manipulating cellular function at the level of individual molecules is within reach. One of the requirements of single molecule techniques is the ability to follow an individual molecule for sufficiently long times in solution. However, it is a challenge to cope with the effects of Brownian motion (the random motion of small particles suspended in a gas or liquid) on this time scale. To meet this challenge, more recently, biomolecules have been encapsulated inside lipid vesicles, which are themselves tethered to a surface. Now, a novel nanocontainer offers controlled permeability functionality which not only is desirable for single molecule imaging but also is a very important property for micro- and nanodevices and for delivery of drugs or imaging agents in vitro and in vivo.
You have seen the effect: if you splash water on your car it leaves wet areas; if you do this with your freshly polished car the drops just pearl off. Materials scientists are very interested in designing surfaces that allow them to control this effect - called wetting - because it enables them to fabricate things like more comfortable contact lenses, better prosthetics, and self-cleaning materials. The primary measurement to determine wettability is the angle between the solid surface and the surface of a liquid droplet on the solid's surface. For example, a droplet of water on a hydrophobic surface would have a high contact angle, but a liquid spread out on a hydrophilic surface would have a small one. Maintaining the position of a drop of water on a hydrophobic surface (e.g. your newly waxed car) appears to be impossible - it will just move across the surface. Scientists in Israel have managed to fabricate a nanostructured, highly hydrophobic surface that allows them to pin a nearly spherical drop of water in place. A droplet sitting on one class of these substrates did not fall even after the substrate was turned upside-down! An important application for this novel fabrication technique could be as a tool in single-molecule spectroscopy: a water drop, containing molecules to be probed, could be pinned down for an extended time, allowing to spectroscopically probe it for long periods without affecting the properties of molecules, or even just one molecule, dissolved in the water drop.
'Field evaporation' is the phenomenon by which surface atoms are ionized (evaporated) under an applied, extremely high electric field of the order of several volts per nanometer. Electric fields of this magnitude can only be achieved by applying a high field to an extremely sharp needle such as the specimen tip in a Field Ion Microscope. Field evaporation was first reported over 50 years ago and has since developed into the powerful Atom Probe Field Ion Microscopy which is able to reproduce the atomic structure of a piece of material in three dimensions. Today, field evaporation is mainly used for material characterization, and the behavior of nanomaterials at extremely strong electric fields is of great scientific and technological interest. In principle, the field evaporation phenomenon can be utilized not only for materials characterization, but also for materials processing and morphology control with extremely high precision because of its unique atom-by-atom removal capability. However, detailed structural evolution of nanomaterials during field evaporation has never been directly observed and this limitation has greatly restricted the potential applications of field evaporation as a materials-processing tool. Now, researchers in Beijing have reported the first direct observation of field evaporation phenomena using a transmission electron microscopy (TEM) technique. By conducting in situ TEM field evaporation experiments on individual carbon nanotubes (CNTs), the researchers were able to reveal details about the structural evolution of the nanomaterials via direct observation. Using this technique, they have been able to perform controlled engineering of the CNTs with atomic precision, for example, grinding and shortening of CNTs, shaping of the open ends of CNTs, and opening of CNT caps.
When two surfaces approach each other in air, they attract. A phenomenon that is explained by van der Waals forces that affect molecules' interaction. Without these - very weak - intermolecular forces, life as we know it would be impossible. They are responsible for a number of properties of molecular compounds, including crystal structures, condensing, melting and boiling points, surface tension, and densities. Intermolecular forces form molecules like enzymes, proteins, and DNA into the shapes required for biological activity. Van der Waals forces can also be repulsive, for instance when two surfaces approach each other in liquid: the same force which causes attraction in air (and which is responsible for so called stiction and adhesion) can be made repulsive by choosing the right combination of surface materials and intervening liquid. This force has the characteristic that it increases very rapidly with very small changes in separation when the surfaces are close to each other. Researchers now have shown that if repulsive van der Waals forces exist between two surfaces prior to their contact then friction is essentially precluded and supersliding is achieved. This opens the possibility that, in certain material systems, the controlled use of repulsive van der Waals forces could be a way to reduce, if not eliminate, friction.
Much has been written about the fascinating properties of spider silk, a biopolymer that is stronger than steel and more elastic than rubber. The silken threads possess a unique combination of mechanical properties: strength, extensibility and toughness. Of course this begs the obvious question: How is it possible that spider silk, produced by little creatures that evolved about 400 million years ago, can be as strong as steel - a modern alloy that plays a critical role in our infrastructure and which still attracts considerable R&D investments in its production technology? What is perplexing is that the atomic interactions (H-bonds) in spider silk are actually 100 to 1,000 times weaker than those in steel, or than those in the superfiber Kevlar, where covalent bonds are used. Hydrogen bonds are the basic chemical bonds that hold together proteins, similar to trusses and beams in buildings, and play a key role in controlling the behavior of these structures. In order to reach silk's mechanical properties, most synthetic materials must be much denser, thus much heavier and consume much more energy during their synthesis and transport. New analysis performed at MIT's Laboratory for Atomistic and Molecular Mechanics shows that the intriguing strength of spider silk may be made possible by precisely controlling the number and the geometry of H-bonds at a characteristic length scale. The physical concept is that by making many small elements work together cooperatively, the weaknesses of the individual components can be overcome. All this must happen at the nanoscale in order to be effective.
Electron microscopy is a delicate balancing act between using the highest energy electrons possible in order to obtain the best image while avoiding destruction of the sample under investigation. Trouble is, the electron beam does not just observe, it also interacts with the structure that is observed. This can be critical for fragile samples such as nanostructures: the transfer of energy from the electron beam can be sufficient that atoms are knocked right out of the material. In the worst case the sample is destroyed in front of your eyes. Scientists in Orsay, France have turned this problem to their advantage. They have developed a new approach to shaping nanomaterials atom by atom, using a scanning transmission electron microscope (STEM) as a nanometrically precise cutting tool. In this way they 'carve' their materials, such as carbon nanotubes, by removing individual atoms from specifically chosen locations. This technique has the added advantage that scientists can observe what they are doing at the same time. The new technique demonstrates a 'nanoelectron- lithography' of single walled nanotubes, a top down approach to locally control their nanostructures.
Diatoms are a major group of hard-shelled algae and one of the most common types of phytoplankton. A characteristic feature of diatom cells is that they are encased within a unique cell wall made of silica. Silicate materials are very important in nature and they are closely related to the evolution of living organisms. Diatom walls show a wide diversity in form, some quite beautiful and ornate, but usually consist of two symmetrical sides with a split between them, hence the group name. There is great potential for the use of diatoms in nanotechnology. This potential lies in the pores and channels which give rise to a greatly increased surface area, and the silica structure which lends itself to chemical modification. In addition there is a huge variety in the sizes and shapes of diatoms available, providing scope for the selection of a particular species of diatom tailored to a particular requirement. Researchers in the UK have demonstrated that the silica walls of diatoms can be used for the attachment of active biomolecules, such as antibodies, using either primary amine groups or the carbohydrate moiety. These modified structures can, therefore, be used for antibody arrays or for use in techniques such as immunoprecipitation.
The vision of revolutionary bottom-up nanotechnology is based on a concept of molecular assembly technologies where nanoscale materials and structures self-assemble to microscale structures and finally to macroscopic devices and products. We are a long way from realizing this vision but researchers are busily laying the foundation for nanoscale engineering. Assembling nanoscopic components into macroscopic materials is an appealing goal but one of the enormous difficulties lies in bridging approximately six orders of magnitude that separate the nanoscale from the macroscopic world. Until machinery capable of automated and industrial-scale nano-assembly can be built, the parallelism of chemical synthesis and self-assembly is necessary when controlling materials at the nanoscale. An obvious direct approach to molecular nanotechnology therefore is to start with organic molecules as building blocks. Modest from the viewpoint of molecular manufacturing visionaries, but quite fascinating to a lot of scientists, research into nanofibers, as a modification of organic crystals, is making good progress. New research results coming out of Denmark offer the basis for a novel organic-molecule-based nanotechnological concept that allows for a multitude of applications in fundamental research and in device applications. Essentially, this concept is based on three steps: 1) directed self-assembled surface growth of nanofibers from functionalized molecules; 2) transfer and manipulation of individual fibers as well as of ordered arrays; and 3) device integration.