Manipulation


The exploitation of macro-functional molecules will inherently involve the application of their natural characteristics. Taking advantage of those interesting properties of nanoscale particles will require the successful manipulation of their position and properties. For example, a self-assembling biological system could be employed in a bottom-up fabrication scheme. The fusion of biology with nanotechnology will not only result in technological innovation but will also encourage future research into natural biological nanosystems.

Current technology harnesses the ability to deform individual molecules such as proteins or DNA. DNA is a nanoscale, long-chain macromolecule and behaves like a mass-spring system. Placing a DNA molecule inside a viscous flow stretches the DNA molecule from its coiled position at equilibrium by applying stress across the length of the molecule. To stretch DNA molecules, Wong et al. (2003) designed microfluidic channels with two buffer streams that converge to sandwich a middle stream containing the DNA solution, effectively extending the DNA molecule, as shown in Figure 17-3. Such a method proves advantageous in that the DNA extensional rates depend upon the flow rate of the outer buffer streams, thereby minimizing the effect of the flow from the centerline on the DNA. Furthermore, the low mixing among the streams enabled independent DNA control.

Figure 17-3. Relaxation of a DNA molecule after stretching is shown here in 2.5-second increments (Wong et al. 2003).


DNA/RNA Characterization

A precursor to the use of nanoparticles for practical, beneficial purposes will be the ability to characterize their properties with respect to composition, structure, and so on. Biomolecular characterizationwith respect, for example, to proteinshas provided key information about three-dimensional structure as well as mechanistic behavior. Information gleaned from these studies serves as the foundation for current development of devices based purely on biomolecular function (Ho et al. 2004). Toward the realization of improving the human condition through nanotechnology, a full-scale characterization of DNA will elicit a broader understanding of the body of embedded information that governs this condition.

The mapping of the human genetic code as part of the Human Genome Project took ten years. Building on this foundation and developing a technology to quickly sequence an individual's DNA hold enormous potential for health maintenance and drug development. With specific respect to the interrogation of composition and structure, one pioneering methodology has been the use of nanoscale pores to characterize DNA molecules. For example, Meller et al. (2000) have monitored electrical conductance through an a-hemolysin channel from Staphylococcus aureus to yield important information regarding nucleotide composition and the effects of temperature on DNA transport.

Current results can discern transport events involving adenine polymers (poly dA100) as well as cytosine polymers (poly dC100) (Figure 17-4). These studies enable investigation of several characteristics of the analyzed molecule, from chain length to its exact composition and structure.

Figure 17-4. Translocation events of both poly(dA)100 and poly(dC)100. Differentiation between dA and dC translocation was determined using tD provided in ms10 (Meller et al. 2000).


The use of membrane proteins to examine DNA strands possessed certain limitations, including the range of conditions in which characterizations could be performed, because the a-hemolysin and lipid membranes possessed their own ranges of optimal conditions for preserved activity.

To build upon the groundwork that was established by protein- and lipid-based characterization, Chen et al. (2004) used Si3N4-based nanopores to serve as solid-state characterization systems. Not confined to the same set of limitations observed with a protein-based setup, the solid-state nanopores were able to successfully detect translocation, or movement, of DNA through the pore while possessing the versatility of varied pore diameters to decrease the chances of blockages to DNA translocation and so on. Furthermore, solid-state nanopores will withstand broader ranges of pH, temperature, and pressure, as well as voltages that would normally impair the protein/lipid assembly, thereby allowing the testing of a broader class of molecules in a wider range of environments.




Nanotechnology. Science, Innovation, and Opportunity
Nanotechnology: Science, Innovation, and Opportunity
ISBN: 0131927566
EAN: 2147483647
Year: 2003
Pages: 204

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