Introduction to Bionanotechnology

Today, researchers find themselves involved in cross-disciplinary science that a decade ago was simply inconceivable. Nowhere is this more apparent than at the cusp of two rapidly developing fields, nanoscience and biotechnology. But what is nanotechnology? The prefix nano means a billionth (1*10^-9). Nanotechnology is the study and application of unique structures having dimensions on the order of a billionth of a meter that exhibit novel size-controlled electronic, optical or catalytic properties. These structures can be metallic, semiconductor or magnetic nanoparticles, nanowires or nanotubes. The underlying basis for such nanoscale effects is that every property of a material has a characteristic and critical length associated with it. The fundamental physics and chemistry of a material will change when the dimensions of a solid become comparable to one or more of these characteristic lengths, many of which exist at the nanometer length scale.
One of the challenges of understanding nanotechnology is the vocabulary. The nanoscale is populated by a diverse group of players. If only one length of a three-dimensional structure is of a nanodimension, the structure is known as a quantum well. When a material exists on the nanoscale along two sides, the structure is referred to as a nanowire. A quantum dot has all three dimensions in the nanometer range. The assembly of these structures into hierarchical assemblies relies on both physical (e.g. lithography, scanning probe microscopy, electrophoretic strategies, ball milling or Langmuir–Blodgett films) and chemical methods (e.g. interparticle electrostatic interactions, covalent coordination, template recognition with subsequent crosslinking or crystal engineering).Although effective for the preparation of certain nanoscale architectures, many of the physical methods are limited because they tend to be slow, have a large infrastructural cost and do not lend themselves to preparing designed nanostructures which span the macroscopic dimension. In contrast, the advantages of chemical methods are that building blocks may be linked in a massively parallel fashion. This is particularly useful for the rapid construction of two- or three-dimensional structures. Unfortunately, current chemical methodologies, especially when compared with the above physical methods, are difficult to control. Increasingly, there has been interest in the use of biomolecules to overcome this challenge.
It is not surprising, then, to find that nanotechnology is interested in the realm of biology, for they share the nanoscale (Figure 1). Consider the tendon, whose function it is to attach muscle to bone. The principal building block of the tendon is the assemblage of amino acids (~0.6 nm) that form the gelatin-like protein collagen (~1 nm), that coils into a lefthanded triple helix (~2 nm). These individual helical proteins then assemble into a fibrillar nanostructure in which collagen assembles to form microfibrils (~3.5 nm), subfibrils (10–20 nm) and fibrils (50–500 nm). These fibers then form clusters of mesoscopic fibers called a fascicle (50–300 mm) and, finally, the macroscopic tendon itself (10–50 cm). A number of research groups are actively focusing on the use of biomolecules to direct the formation of nanostructures and extended nanoscale assemblies due to the inherent molecular recognition of such molecules.

In an emergent field such as nanobiotechnology, it is difficult to predict the ultimate achievements of the field. Today, the discipline is making significant progress in four broad areas: separations, imaging/ diagnostics, drug delivery and synthesis of new materials. As a testament to the true interdisciplinary nature of these endeavors, each of these areas is being driven by rapid advances in the other. Consequently, the resulting hybrid of bionanotechnology holds the promise of providing revolutionary insight into the many aspects of biology. However, it also represents a substantial challenge. Biological systems have been making functional nanoscale devices since the beginning of life and there is much to learn from biology about how to build nanostructured materials. Yet, how can a life scientist who is trying to develop new gene transfer methods, but who does not know the difference between a buckyball and a II–VI semiconductor core–shell quantum dot, gain entre´e into the field of nanotechnology?

Figure 1 Many proteins have dimensions and molecular weights that place them in
the nano-regime.