Nanotechnology-Enabled Sensors

7.3 Surface Materials and Surface Modification 393
ICPs continue to find market niches as they emerge from the research
laboratory. Several of these aspiring applications can be found in
MacDiarmid’s lecture (one of the Nobel Prize winners in 2000 for his contributions
in the field of chemistry) on conductive polymers. 45 ICPs play a
significant role in the development of sensors as their electrical, mechanical
and optical properties change when they are exposed to different environments
and target analytes.
For a polymer to be conductive it has to alternate single and double
bonds along the backbone of the polymer, which is called conjugation,
and the resultant polymer is described as conjugated (Fig. 7.19). Generally,
the π bonds give the conjugated polymer the properties of a semiconductor.
46
(a) (b)
Fig. 7.19 The conjugated structure of polyacetylene: (a) cis and (b) trans forms.
Fig. 7.20 shows the degree of conductivity of different forms of polyaniline
in comparison with conventional materials.
Material Conductivity
(S/m)
Ag 10 6
In 10 3 Doped-polyaniline 10 5 (S/m)
Ge 1
Si 10 -6
Glass 10 -9 Polyaniline 10 -10 (S/m)
Diamond 10 -12
Quartz 10 -15
Fig. 7.20 Conductivity of polyaniline.
When dealing with ICPs for sensing applications, doping is an important
process as the user can tailor the conductivity of polymer to suit their
needs. The conductivity of ICPs can be manipulated by doping it with certain
certain atoms or molecules. 46,47 There are also other methods for doping
ICPs. The most common doping processes are as follows: