antigens, neurotransmitters, enzyme substrates, DNA fragments, and drug metabolites.

These polymeric biosensors can be examined by electrochemical, optical, or piezo­

gravimetric detectors with very high sensitivities, and low detection limits.

18.2.1 Conducting Polymer–Based Hydrogels

Conducting hydrogels are often synthesized by mixing insulating polymer matrices

(providing structural support and water holding properties) with conducting polymer or

filler material (providing electrical conductivity). Metallic nanoparticles, carbon nano­

tubes, graphene, and their derivatives have been extensively employed to prepare con­

ducting hydrogel due to their electrical and mechanical properties. However, the rigid

and fragile nature of conducting polymers hampers the long-time stability of hydrogels

and restrains the wider applications in emerging flexible electronic devices. Synthesis of

conducting hydrogel along with excellent biocompatibility is highly required for the

development of bioelectronics and energy devices.

Several electrically conductive polymers including PPy, PANI, PEDOT, and PTH-based

hydrogels with their synthetic flexibility have gained widespread interest in bioelec­

tronics applications. Conducting polymer-based hydrogels has the additional benefit of

electrical conductivity over conventional hydrogels. Conducting polymers such as PPy

have also been widely employed along with dopants for conductive hydrogels designing

as they provide conductive pathways for bio-electrocatalysis of enzymes. The first con­

ducting hydrogel was synthesized by Gilmore and group by direct electropolymerization

of PPy on pre-prepared polyacrylamide hydrogel in the cylindrical gel cell [2], while the

Wallace group has prepared a range of conducting polymer-based electroactive hydrogel

composites bearing excellent rehydration levels up to 80–95% [3]. The composites based

on the growth of conducting film of PPy or PANI throughout hydrogel were investigated.

Excellent water-retaining capacity and the stimuli-responsive electrochemical release of

larger incorporated counterions provide an open porous structure of the resultant hy­

drogel materials. The hydrogel composites, with retained properties of hydrogel, present

newer electrochemical applications of these materials. An enzyme-based biosensor was

fabricated by an electrosynthetic approach of conducting PPy with alginate as co-dopant

of laccase (an oxydoreductase enzyme) and 2,2′-and-bis(3-ethyl benzothiazoline-6-

sulfonic acid) (a redox mediator) [4]. The catalytic effect of PPy film as a function of

several cycles at various ratios of alginate doped laccase was examined. The catalytic

effect was found to enhance the number of cycles from 0 to 10, and further decreased as

the number of cycles increased.

PEDOT is a widely used conducting polymer in the field of bioelectronics and has en­

abled improvements in the electrical conductivity of metallic electrodes and provided

functional versatility of biomolecules. Doping of PEDOT with several counterions was

reported. A biocompatible polyurethane hybrid composite (PUHC) hydrogel formed by

dispersion of polyurethane with PEDOT:PSS and liquid crystalline graphene oxide shows

high conductivity, stretchability, and good mechanical performance. Certain organogels of

PEDOT:PSS with polyacrylamide (PAAm) allowed electronic transport within organogel.

Conducting polymers incorporated hybrid hydrogels are promising materials for bioactive

electrode coatings. A blending of conducting polymers into hydrogels helped in improving

the electrical, mechanical, and biological properties of inherent hydrogels, e.g., flexible

conducting polymer PEDOT-based sodium alginate hydrogel coated neural electrodes.

PEDOT: PSS was added to CS/PVA scaffolds causing a significant enhancement in

the mechanical and electrical properties for cardiovascular engineering. Chitosan (CS), a

Conductive Hydrogels for Bioelectronics

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