Nanotechnology defined

In this chapter we describe the basic principles involved in the controlled production and modification of two-dimensional protein crystals. These are synthesized in nature as the outermost cell surface layer (S-layer) of prokaryotic organisms and have been successfully applied as basic building blocks in a biomolecular construction kit. Most importantly, the constituent subunits of the S-layer lattices have the capability to recrystallize into iso-porous closed monolayers in suspension, at liquid-surface interfaces, on lipid films, on liposomes, and on solid supports (e.g., silicon wafers, metals, and polymers). The self-assembled monomolecular lattices have been utilized for the immobilization of functional biomolecules in an ordered fashion and for their controlled confinement in defined areas of nanometer dimension. Thus, S-layers fulfill key requirements for the development of new supramolecular materials and enable the design of a broad spectrum of nanoscale devices, as required in molecular nanotechnology, nanobiotechnology, and biomimetics [1-3]. 

The building blocks of all materials in any phase are atoms and molecules. Their arrangements and how they interact with one another define many properties of the material. The nanotechnology MBBs, because of their sizes of a few nanometers, impart to the nanostructures created from them new and possibly preferred properties and characteristics heretofore unavailable in conventional materials and devices. These nanosize building blocks are intermediate in size, lying between atoms and microscopic and macroscopic systems. These building blocks contain a hmited and countable number of atoms. They constitute the basis of our entry into new realms of bottom-up nanotechnology [97, 98]. 

Atomic force microscope (AFM) is a powerful nanotechnology tool for molecular imaging and manipulations. One major factor limiting resolution in AFM to observe individual biomolecules such as DNA is the low sharpness of the AFM tip that scans the sample. Nanoscale 1,3,5,7-tetrasubstituted adamantane is found to serve as the molecular tip for AFM and may also find application in chemically well-defined objects for calibration of commercial AFM tips [113]. 

Figure 1.4. Catalysts are nanomaterials and catalysis is nanotechnology. If we define nanotechnology as the branch of materials science aiming to control material properties on the nanometer scale, then catalysis represents a field where nanomaterials have been applied commercially for about a century. Many synthetic techniques are available to...

Today s massive efforts in nanotechnology will certainly provide more well-defined, regular-shaped particles in the submicron range, and mini fixed-bed technology wiU profit from that. 

Stang, P. J. Olenyuk, B. Transition-metal-mediated self assembly of discrete manoscopic species with well-defined structures and shapes. In Handbook of Nanostructured Materials and Nanotechnology, Nalwa, H. S.. Ed. Academic Press San Deigo, 2000, Vol. 5, 167-224. 

Nucleic acids, DNA and RNA, are attractive biopolymers that can be used for biomedical applications [175,176], nanostructure fabrication [177,178], computing [179,180], and materials for electron-conduction [181,182]. Immobilization of DNA and RNA in well-defined nanostructures would be one of the most unique subjects in current nanotechnology. Unfortunately, a silica surface cannot usually adsorb duplex DNA in aqueous solution due to the electrostatic repulsion between the silica surface and polyanionic DNA. However, Fujiwara et al. recently found that duplex DNA in protonated phosphoric acid form can adsorb on mesoporous silicates, even in low-salt aqueous solution [183]. The DNA adsorption behavior depended much on the pore size of the mesoporous silica. Plausible models of DNA accommodation in mesopore silica channels are depicted in Figure 4.20. Inclusion of duplex DNA in mesoporous silicates with larger pores, around 3.8 nm diameter, would be accompanied by the formation of four water monolayers on the silica surface of the mesoporous inner channel (Figure 4.20A), where sufficient quantities of Si—OH groups remained after solvent extraction of the template (not by calcination). 

Synthesis of DNA-Au hybrid nanocomposites holds promise for applications in nanotechnology. Following the pioneering work of Mirkin et al., these modified Au nanopartides can act as useful building blocks to form spatially well-defined superstructures, including nanocrystals [108], binary and multilayered nanoparticle assemblies [109,110] and also well-ordered 3D nanoclusters [111]. 

There is a very bright future for these electronically well-defined NW building blocks both in fundamental science and in new nanotechnologies. Specifically, we believe that only the very edge of a broad range of ideas has been touched on and that many fascinating fundamental problems remain in these... 

Pores are found in many solids and the term porosity is often used quite arbitrarily to describe many different properties of such materials. Occasionally, it is used to indicate the mere presence of pores in a material, sometimes as a measure for the size of the pores, and often as a measure for the amount of pores present in a material. The latter is closest to its physical definition. The porosity of a material is defined as the ratio between the pore volume of a particle and its total volume (pore volume + volume of solid) [1]. A certain porosity is a common feature of most heterogeneous catalysts. The pores are either formed by voids between small aggregated particles (textural porosity) or they are intrinsic structural features of the materials (structural porosity). According to the IUPAC notation, porous materials are classified with respect to their sizes into three groups microporous, mesoporous, and macroporous materials [2], Microporous materials have pores with diameters < 2 nm, mesoporous materials have pore diameters between 2 and 50 nm, and macroporous materials have pore diameters > 50 nm. Nowadays, some authors use the term nanoporosity which, however, has no clear definition but is typically used in combination with nanotechnology and nanochemistry for materials with pore sizes in the nanometer range, i.e., 0.1 to 100 nm. Nanoporous could thus mean everything from microporous to macroporous. 

For advanced electrochemical applications of SAMs in this area, their design is, therefore, a key issue. While SAMs are often perceived to form easily well-defined structures, a closer look into the literature reveals that thiol SAMs, in fact, very often lack the structural quality anticipated. Contrasting their ease of preparation, orga-nosulfur SAMs represent systems whose structure is determined by a complex interplay of interactions and if those are not properly taken into account, a SAM of limited structural quality and performance will result. To optimize SAMs for electrochemical applications and to exploit their properties for electrochemical nanotechnology it is, therefore, crucial to identify the factors controlling their structure. For this reason we start with an account of the structural aspects of SAMs. 

The interest in polymer brushes and defined polymer coatings prepared via SIP is not at all restricted to the polymer community or the surface science community. The demand for tailored, fimctionahzed and adaptive surfaces comes from a multitude of scientific branches and also from industry. Possible applications are already discussed in many of the contributions compiled here. Besides polymer science, surface chemistry and physics, they include catalysis, biomedical applications, microfluidics and nanotechnology. This creates a highly interdisciplinary, Hvely and fruitful environment. 

---