analysis of multiple substances in vivo. Besides biosensors, nanotechnology also
aims to exploit biomolecules and the processes carried out by them for the
development of novel functional materials and devices and more speculatively,
nanomachines and perhaps nanorobots. In the long term, the earliest molecular
machine systems and nanodevices may be effective in scientific and medical
applications, giving scientists and physicians the most potent tools imaginable to
conquer scientific problems, human disease, ill health, and aging.
Hence, one of the questions arising from nanotechnology development is:
‘‘How to provide energy for nanodevices?’’ Similar to conventional equipments
and devices, nanodevices also need energy to function properly and
consistently. This leads to the idea of constructing nanomotors from biological
molecules. So far, several types of nanomotors have been developed based on
protein, DNA, and RNA molecules, and their efficiency to convert biological
or chemical energy into mechanical energy has been demonstrated and
characterized.
Ideal for engineering purposes, proteins represent fertile territory for
nanotechnology. They possess sophisticated architectures at nanoscale dimen-
sions, rich chemistry, and versatile enzymatic activities. They are also capable
of carrying out complex tasks in cells. Nanodevices could use motor proteins to
move linearly, by rotation, or in a more complex three-dimensional manner.
Nanodevices might also respond to the environment through proteins with
built-in switches that operate in a simple onoff way or through more finely
tuned and complex logic gates with graded or multiple inputs. In this way,
nanodevices will be able to sense their environment.
More advanced functions might include transport (uptake, movement,
and delivery of cargoes utilizing protein transporters and pores) and chemical
transformation, by enzymatic catalysis, for example. Most molecular
motor proteins perform actual physical work by actively transporting or
moving other molecules or proteins within cellular systems. Examples of
these type of proteins are the kinesin motor proteins that ‘‘walk’’ on
‘‘tubulin-rails’’ transporting vesicles along given pathways in the cell.
Similarly, certain members of the myosin family transport cargo using actin
filaments as a track to run on. In addition to intracellular transport directed
by microtubule tracks, proteins like dynein together with tubulin are
also involved in the movement of whole, free cells like sperm cells and
protozoa [2].
Besides proteins, nanomotors can be constructed with various biomotifs. In
this chapter, we mainly focus on DNA nanomotors. Despite its central
importance in biology, the ap plications of DNA are not restricted to biological
sciences. DNA functions successfully as genetic material because of its
chemical properties. Its capabilities to form duplex via WastonCrick base
pairing, as well as its diversity in adopting different conformations due to
external stimuli, which can be mediated by small molecules or ions [3], promise
its potential in the development of nanomotors.
50 BIOMEDICAL NANOSTRUCTURES