Bottom nanotechnology

Nanomaterials can be manufactured by one of two groups of methods, one physical and one chemical. In top-down approaches, nanoscale materials are carved into shape by the use of physical nanotechnology methods such as lithography (Fig. 15.30). In bottom-up approaches, molecules are encouraged to assemble themselves into desired patterns chemically by making use of specific... 

Nanotechnology is the branch of engineering that deals with the manipulation of individual atoms, molecules, and systems smaller than 100 nanometers. Two different methods are envisioned for nanotechnology to buUd nanostructured systems, components, and materials. One method is the top-down approach and the other method is called the bottom-up approach. In the top-down approach the idea is to miniaturize the macroscopic structures, components, and systems toward a nanoscale of the same. In the bottom-up approach the atoms and molecules constituting the building blocks are the starting point to build the desired nanostmcture [96-98]. 

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]. 

Considering that nanoparticles have much higher specific surface areas, in their assembled forms there are large areas of interfaces. One needs to know in detail not only the structures of these interfaces, but also their local chemistries and the effects of segregation and interaction between MBBs and their surroundings. The knowledge of ways to control nanostructure sizes, size distributions, compositions, and assemblies are important aspects of bottom-up nanotechnology [97]. 

The Nobel laureate Richard P. Feynman described, in a lecture delivered in 1959, the future of miniaturization. The published version of his lecture is called There s Plenty of Room at the Bottom and in it can be found a recipe for putting the entire Encyclopedia Britan-nica on the very small head of a very small pin. Feynman s comments set into motion an entirely new area of study and have lead to what have become known as the fields of nanoscience and nanotechnology. Chemists, physicists, materials scientists, and engineers have come together over the past several decades to produce with high accuracy and precision materials that have dimensions measured in nanometers (nm, 10 meters, about 1/100 000 the width of a human hair). Specifically, materials with one, two, or three dimensions of 100 nm or less (called, respectively, nanofilms, nanotubes, and nanoparticles) qualify as products of nanotechnology. It appears that almost any chemical substance that is a solid under ordinary conditions of temperature... 

The ideal scenario would be to have the power of a traditional IR analyzer but with the cost and simplicity of a simple filter device, or even better to reduce the size down to that of a sensor (such as the spectral detector mentioned earlier) or a simple handheld device. This is not far-fetched, and with technologies emerging from the telecommunications industry, the life science industry and even nanotechnology, there can be a transition into analyzer opportunities for the future. There is definitely room for a paradigm shift, with the understanding that if an analyzer becomes simpler and less expensive to implement then the role of analyzers/sensor can expand dramatically. With part of this comes the phrase good enough is OK - there is no need for the ultimate in versatility or sophistication. Bottom line is that even in process instrumentation, simple is beautiful. 

As in all active areas of research, there are several approaches to the development of nanotechnology. One approach involves techniques similar to sculpting, where one starts with a large piece of material and cuts away what is not needed. The problem is that a lot of the material winds up wasted on the cutting room floor. An alternative approach, described in the following section, starts at the bottom or lower end of the scale and builds up from there. An important feature of this approach is the bonding of molecules to make even larger, more complex molecules—supramolecular chemistry. 

Table 1.1 summarizes the types of processes for generating nanoparticles that are currently involved in the top-down and bottom-up approaches (or their mixed variants). It should be noted that many of these processes have their origin and primary applications predominantly in the pharmaceutical industry so far the commercial food applications of nanotechnology are still in their infancy. For each of the processes mentioned in Table 1.1, the kinds of nanoparticles involved are listed along with a brief indication of their characteristic properties and their approximate particle dimensions. Also presented are some recent literature sources on these various topics (mainly review-type articles) where the interested reader can obtain further background material. 

Table 1.1 Examples of processes involved in nanotechnological top-down and bottom-up approaches.

Modern nanotechnology and nanofabrication processes are advancing towards manipulation of structure and functions on the molecular scale [19-23]. Many innovations and strategic areas of research which have appeared during the last 5-10 years corroborate the famous opinion of R. Feynman there is a plenty of space on the bottom [471]. Some prominent examples include self-assembly of small molecules and their ordering at interfaces [8,220,472,473 ], three-dimensional macromolecules with a defined shape, interior and surface structure [34-38], and templating of biomolecules [39-41,474]. Most of these concepts follow a biomimetic approach, where synthetic structures mimic organisation princi-... 

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