6
D. K. Subbiah et al.
the interaction with polar solvents and play a major role in various fields such as
supercapacitors, catalysis, batteries and it is expected to be an active material for
next generation electronics. For example, negative charges of GO have the tendency
to interact with functional groups of cotton fabrics and leads to better fixation with
fabrics. This could be a prominent solution to fabricate a wearable and flexible etextile sensor at least for continuous health monitoring [25]. In overall, the feasibility
and potential of graphene-based materials make it a good candidate in the race of
active material for flexible electronics.
Apart from graphene as a sheet, it is necessary to recognize the potential of another
carbon allotrope, CNTs. When the graphene sheet is rolled along a particular axis,
it forms 1-D carbon nano tubes (CNTs) and further processing of CNTs leads to the
formation of carbon quantum dots (CQDs). It is classified into single walled CNTs
and multi-walled CNTs depending on the layer of carbon atoms rolled over, with the
diameter in the range of <1 nm and >100 nm respectively. CNTs offer high carrier
mobility of more than 10,000 cm
2 V
−1 s
−1 [26] and tensile strength of about 63 GPa
[27], which is somewhat lesser than that of graphene. Employing these mobility
characteristics of CNTs in transistor technology helps in designing a high electron
mobility transistor [28]. In terms of sensing, large surface to volume ratio features
enable highly sensitive response towards target analytes.
2.2 Conducting Polymers
Repetition of monomer units in all possible directions leads to the formation of
polymers. In earlier stages, polymers were used as an electrically insulating material, whereas a series of conducting polymers (CPs) like polyacetylene, polyaniline
(PANI), poly (3,4-ethylenedioxythiophene) (PEDOT), poly (styrenesulfonate) and
polypyrrole (PPy) were discovered later. It can be synthesized either by the process of oxidative polymerization or by electrochemical polymerization. Basically,
CPs exhibit one-dimensional (1-D) delocalized conjugated structure with remarkable electrical, optical properties and tunable bandgap nature. An interesting fact
about them is that their conductivity could be tuned either by the process of doping
or de-doping, which will influence its electrical and optical properties [29].
Based on the charge transport phenomena, conducting polymers have been classified based on the electron and proton conductivity. Further, the electron conducting polymers are subdivided into redox and intrinsically conducting polymers on
the basis of electron transport via hopping mechanism and delocalized electrons
through conjugated systems respectively. In summary, the conduction in CPs is
mainly dictated by the presence of conjugated bonds [30].
With regard to applications, several studies have been reported on biomedical
applications, where it was found that CPs response to the electric fields arise from
biological samples like tissues, epithelium, muscles and retain its biocompatibility [31]. In addition, CPs of high electroactive nature have the tendency to catalyse the reduction/oxidation (redox) reaction-based applications like biosensing, fuel
D. K. Subbiah et al.
the interaction with polar solvents and play a major role in various fields such as
supercapacitors, catalysis, batteries and it is expected to be an active material for
next generation electronics. For example, negative charges of GO have the tendency
to interact with functional groups of cotton fabrics and leads to better fixation with
fabrics. This could be a prominent solution to fabricate a wearable and flexible etextile sensor at least for continuous health monitoring [25]. In overall, the feasibility
and potential of graphene-based materials make it a good candidate in the race of
active material for flexible electronics.
Apart from graphene as a sheet, it is necessary to recognize the potential of another
carbon allotrope, CNTs. When the graphene sheet is rolled along a particular axis,
it forms 1-D carbon nano tubes (CNTs) and further processing of CNTs leads to the
formation of carbon quantum dots (CQDs). It is classified into single walled CNTs
and multi-walled CNTs depending on the layer of carbon atoms rolled over, with the
diameter in the range of <1 nm and >100 nm respectively. CNTs offer high carrier
mobility of more than 10,000 cm
2 V
−1 s
−1 [26] and tensile strength of about 63 GPa
[27], which is somewhat lesser than that of graphene. Employing these mobility
characteristics of CNTs in transistor technology helps in designing a high electron
mobility transistor [28]. In terms of sensing, large surface to volume ratio features
enable highly sensitive response towards target analytes.
2.2 Conducting Polymers
Repetition of monomer units in all possible directions leads to the formation of
polymers. In earlier stages, polymers were used as an electrically insulating material, whereas a series of conducting polymers (CPs) like polyacetylene, polyaniline
(PANI), poly (3,4-ethylenedioxythiophene) (PEDOT), poly (styrenesulfonate) and
polypyrrole (PPy) were discovered later. It can be synthesized either by the process of oxidative polymerization or by electrochemical polymerization. Basically,
CPs exhibit one-dimensional (1-D) delocalized conjugated structure with remarkable electrical, optical properties and tunable bandgap nature. An interesting fact
about them is that their conductivity could be tuned either by the process of doping
or de-doping, which will influence its electrical and optical properties [29].
Based on the charge transport phenomena, conducting polymers have been classified based on the electron and proton conductivity. Further, the electron conducting polymers are subdivided into redox and intrinsically conducting polymers on
the basis of electron transport via hopping mechanism and delocalized electrons
through conjugated systems respectively. In summary, the conduction in CPs is
mainly dictated by the presence of conjugated bonds [30].
With regard to applications, several studies have been reported on biomedical
applications, where it was found that CPs response to the electric fields arise from
biological samples like tissues, epithelium, muscles and retain its biocompatibility [31]. In addition, CPs of high electroactive nature have the tendency to catalyse the reduction/oxidation (redox) reaction-based applications like biosensing, fuel