19.3.4 Polypyrrole

Polypyrrole (Figure 19.3e) is a doped polymer that shows good stability in chemical and

room temperature, with comparably higher conductivity under physiological conditions

and environmental stability. Polypyrrole undergoes polymerization during synthesis, in

the presence of n-type dopants, which act as electron donors, or p-type dopants, which act

as electron acceptors. Dopants have been reported to confer some good level of con­

ductivity which ranges from 2 to 100 S/cm. Surfactants and nanoparticles are also used to

improve the conductivity, catalytic activity as well as crystallinity of the polypyrrole.

Methyl orange (MO) is one of the azo dyes used in the preparation of polypyrrole, because

of its planar hydrophobic region as well as hydrophilic point group, which interacts by

stacking flattened in aqueous solution.

In addition, FeSO4 and FeCl3 are types of oxidants introduced into the reaction en­

vironment during synthesis, to counter the electrostatic force repellent between the ne­

gatively charged MO aggregates in solution, which results in a complex formation of

MO–FeSO4. The outstanding electrical conductivity of polypyrrole has been assigned to

the redox interaction of electrostatic cross-linking between the conducting polymer, and

the metallic oxidant, as well as the characteristic stacking of the acidic azo dye which

enhances the electrical and optical properties of the polypyrrole. Also, the overlapping

orbitals of conjugated π-electrons run over the entire backbone of the polypyrrole matrix

resulting in the formation of valence bands as well as conduction bands, which runs

through the entire polymeric molecules; hence, their presence on the list of first choice

conductive and redox-active materials for use in biosensors [8].

19.3.5 Polyfuran

Polyfuran is a type of conducting polymer that consists of furan aromatic rings. Furan is a

five-membered heteroaromatic compound whose properties have been studied for ap­

plication in technology utilization in resins. Polyfuran is a conjugated polymer that is

different from non-conjugated resins. Polymerization of furan monomers leads to the

formation of polyfuran. Figure 19.3f illustrates the chemical structure of polyfuran.

Polyfuran can be synthesized by chemical and electrochemical polymerization.

The electrochemical process of fabricating polyfuran can be done using cyclic voltam­

metric technique at a constant potential, at constant current density, or by colorimetry.

Sherberla et al. [9] used the electrochemical polymerization method to synthesize polyfuran

from oligofuran. According to the authors, the use of furan monomers requires a high

potential of 1.8 V to achieve oxidation but the use of oligofuran reduces the potential to

below 1.0 V required to achieve oxidation. The reduction in oxidation potential by using

oligofuran produces a polyfuran of good quality and relevant for their applications. The

chemical polymerization method of fabricating polyfuran was used by McConnel et al. [10]

to synthesize polyfuran using a mild oxidizing agent, pyridium chlorochromate. The use of

nucleophilic agents such as water makes polyfuran less stable. Therefore, the authors of this

article reported the use of anhydrous conditions to fabricate a stable polyfuran. The syn­

thesized conducting polymer was characterized using proton nuclear magnetic resonance

(¹H NMR), infrared (IR) spectroscopy, and electron resonance spectroscopy (ESR). The

1H NMR spectra for polyfuran showed primary aromatic signals at δ 7.40, 7.740, 8.066, and

8.581. The IR spectra showed characteristic bands of the monomers of polyfuran at

1,585 cm⁻¹, 1,535 cm⁻¹, 1,438 cm⁻¹, 1,200 cm⁻¹, 1,160 cm⁻¹, 1,060 cm⁻¹, 940 cm⁻¹, and

730 cm⁻¹. The ESR spectra of polyfuran showed a Gaussian signal (∆HPP = 0.79 G) with a

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Bioelectronics