BIOMEDICAL APPLICATIONS VI: CARBON NANOTUBES AS BIOSENSING AND BIO-INTERFACIAL MATERIALS - Carbon Nanotubes: From Bench Chemistry to Promising Biomedical Applications - page 185

Moreover, the materials used to prepare nano-transistors are not limited
to semiconductive nanotubes. Because of their ultra-small and regular
structure, metal CNTs could be used to produce single-electron transistors
working at room temperature. 14 This was achieved by introducing two
buckles in an individual metallic SWNT using AFM. The conductance of the
resulting device was affected by the gate voltage and showed opening and
closing effects in a periodic manner, thus demonstrating Coulomb blockade
(single-electron tunneling) at room temperature.
However, it was a challenge to precisely connect CNTs to each part of
the nano-devices and assemble them into nano-transistors. Therefore,
Keren et al. 15 reported a novel method to precisely prepare those nano-
transistors. In their study, they used DNA-RecA protein as the template. Then
CNTs assembled with DNA by a lot of RecA/anti-RecA/biotin antimouse/
streptavidin linkers. The protruded terminals of DNA directed the deposition
of gold, which formed the electrodes linking the CNTs. This study made it
feasible to eficiently produce transistors with a precise structure.
In addition to the transistors, CNTs can be manipulated by various
techniques to prepare many types of functional molecular devices. For
example, CNTs can be used to produce wafers. 16 This was achieved by
assembling individual CNTs hierarchically by two self-assembly stages and
form closely packed and aligned nanotube ilms. Another example is the
preparation of serpentines using CNTs (Fig. 7.3) . 17 During the process of
CNT synthesis, the CNTs grew standing up from the surface and then fell on
the substrate surface. The structure of the serpentines could be controlled
and were dramatically dependent on the gas low: in fact, by changing the
direction and rate of the gas low, the structure of the serpentines could be
controlled precisely.
Further applications of these CNT-based nano-devices resulted in
inventions of several kinds of nano-machines, such as nano-sensors,
nano-antennas, heating and cooling elements, optoelectronic devices and
single-molecule dynamos. An interesting example of such applications is
the nanotube radio. 18 The four critical radio components, antenna, tuner,
ampliier and demodulator, can be implemented with a single CNT. Compared
with the traditional radio, a special point of the CNT radio was that it sensed
the electromagnetic waves and responded by physical vibration.
All of the studies and applications listed above suggested that, because
of their novel properties, CNTs could be used to produce functional nano-
electric devices in the areas of electronic transport as well as signal detection.
Therefore, CNTs have become more and more attractive in the area of
chemical/biological sensing and analysis.