BIOMEDICAL APPLICATIONS VI: CARBON NANOTUBES AS BIOSENSING AND BIO-INTERFACIAL MATERIALS - Carbon Nanotubes: From Bench Chemistry to Promising Biomedical Applications - page 194

hydrophobic functionalities. The microscope equipped with these tips
showed images with phase contrast reversed for the same materials because
the tips have different afinity towards the CH 3 and COOH area. Furthermore,
the CNT tip functionalised with biotin was able to detect the adhesion with
streptavidin protein receptor. Those studies suggested that it is feasible to
modify CNT tips with different functional groups, active ligands or other
macromolecules to create chemical and biological maps.
7.2.2.2.6 Liquid flow sensor: transfer momentum to current
Most interestingly, CNTs can be used as liquid low sensors. Král and Shapiro 43
predicted theoretically that lowing a liquid may generate an electric current
in a metallic CNT and suggested that the voltage may be caused by momentum
transfer from the lowing liquid or by the scattering of free charge carriers in
the lowing liquid. Ghosh et al. 44 observed that the lowing liquid induced a
voltage on the CNT along the direction of the low. The voltage response to
low velocity was almost logarithmic (Fig. 7.6), indicating that the current was
dependent on a direct forcing of the free charge carriers in the nanotubes by
the luctuating Coulombic ield of the lowing liquid. In addition, the voltage
was also strongly correlated with the ionic and polar nature of the lowing
liquid: liquids with higher ionic strength could induce a higher voltage along
the low direction. Meanwhile, a high viscosity did not result in a higher
induced voltage. Although the voltage-inducing mechanisms suggested by
different groups were not the same, the novel momentum-current change
property hints CNTs as possible candidates to modulate the voltage and
current source in a lowing liquid environment, which may have interesting
biomedical applications.
Figure 7.6 The scheme of the device to measure lowing-induced voltage.
7.2.3 Fluorescence Emission, Quenching and Detecon
CNTs have shown many novel electroluminescence properties. They can be
functionalised to become both luorescence emitters and detectors. Light