Nanotechnology-Enabled Sensors

390 Chapter 7: Organic Nanotechnology Enabled Sensors
7.3.4 Conductive and Non-Conductive Polymeric Surfaces
Polymers are large organic molecules that consist of repeating units,
called monomers, which are covalently connected together. They are attractive
materials for the development of sensors as their chemical and
physical properties can be tailored over a wide range. 27,28 Some of their
advantages include the following: low fabrication cost, an ability to take
different forms including nanosized formation, biocompatibility and their
ability for chemical and biosensing at different temperatures.
Both intrinsically-conducting and non-conducting polymers (ICPs and
NCPs) can be used for the development of sensors. They can be employed
in the sensor structure, they can directly participate as the sensitive layer,
and they can also be used as the media for immobilizing biomaterials on a
surface.
There are a multitude of possible polymeric materials which can be used
in sensing applications. As fabrication technologies such as nanoimprinting
are becoming more and more mature, and due to the emergence of new
thermal and UV-curable polymers, the attraction of working with polymers
is becoming increasingly favorable in nanotechnology.
Non Conducting Polymers (NCPs)
NCPs are becoming increasingly attractive in the fabrication of transducers
and sensors. They are inexpensive, simple to prepare and it is relatively
easy to manipulate their structure. Screen printing, molding and
stamping are generally employed to carry out such tasks. With a plethora
of photo and thermally curable NCPs available, there are many possible
sensor designs that can be formed. NCPs can also be employed as selective
layers in bio and ion selective sensing. In addition, NCPs have many applications
in biosensing. They can be used for the entrapment of biomolecules
and as a membrane for the formation of bio-selective layers in
order to immobilize biomolecules such as proteins and DNA. NCPs are
also very attractive in the fabrication of ion-selective membranes. This is
achieved by placing ionophores within polymeric membranes. These ionophores
can be organic salts, macrocyclic compounds such as crown ethers,
calixerenes, and antibiotics. The most commonly used polymeric matrix
for making ion selective membranes is polyvinyl chloride (PVC). The PVC
is mixed with a plasticizer in order to soften it and then the, ionophores are
added to provide selectivity towards the target ion. 29 An example of such
ion-selective membranes can be found in the report by Shamsipur et al
who fabricated a PVC membrane electrochemical sensor for monitoring