539Chemical Nanosensors
For this purpose, several functionalization methods have been developed.
These include doping or inserting atoms or functional groups into nano-
tube structures, which constitutes a type of covalent functionalization.
Functionalization can also be noncovalent. This consists of depositing
particles or coating the surface of the CNT with a material that interacts
with the analyte of interest. In the latter case, the nanotubes still act as a
transducer system, while the material deposited on the surface becomes
the sensing part of the device. The sensitivity of some sensors has been
dramatically enhanced from ppm to ppb level after surface modication
or functionalization and doping.
What attempts have been made ...