Absorption Spectra of Model Single Chains of Conducting Polyaniline

Electrochemical Soft Actuator: Deciphering the Difference in the Characteristics of Polaronic and Bipolaronic Forms of Polyaniline

Polyaniline (PANI) has been projected as an efficient electrochemical actuator due to its ease of synthesis, lightweight, biocompatibility, low cost, and possible low operating potential and high stress generation. However, challenges such as low inherent ionic and electronic conductivity of the polymer lead to small accumulation of ions and high ionic diffusion path length inside the polymer remain. In the present study, a highly conjugated, planar, conducting polaronic form of PANI with a nanofiber morphology is synthesized using in situ electrochemical polymerization on a reduced graphene oxide (rGO) electrode. The polymerization is carried out in the Schaefer mode at the air-water interface under controlled surface pressure in a Langmuir trough. Electrochemical, UV-visible, XPS, and Raman spectroscopic studies confirm the formation of the planar polaronic PANI form. Polymerization without surface pressure leads to the bipolaronic form of PANI. The two forms are subsequently used to understand their contributions toward electrochemical actuation in a bilayer configuration. The conducting polaronic PANI/EGO (exfoliated graphene oxide) exhibits a remarkably larger total angular displacement of 220° in aqueous 1 M NaClO₄ during a potential scan in the range ±0.9 V than the bipolaronic counterpart which exhibits a total angular displacement of 125°. Current imaging in the scanning electrochemical microscopy mode confirms a high volumetric expansion in the case of the polaronic form as compared to its bipolaronic counterpart. Raman spectroscopy reveals the oxidation to the emeraldine form in the polaronic PANI and to the pernigraniline form in the bipolaronic form during actuation. Electrochemical impedance spectroscopy study evidences the existence of a small charge transfer resistance with high bulk capacitance for the polaronic structure.

Application of an enzymatic cascade reaction for the synthesis of the emeraldine salt form of polyaniline

The synthesis of the emeraldine salt form of polyaniline (PANI-ES) from aniline with Aspergillus sp. glucose oxidase (GOD), d-glucose, dissolved O2, and horseradish peroxidase isoenzyme C (HRPC) in the presence of large unilamellar vesicles of AOT (sodium bis-(2-ethylhexyl)sulfosuccinate) as templates at pH = 4.3 and T ~ 25 °C was investigated in a systematic way. In this cascade reaction mixture, the oxidation of aniline is catalyzed by HRPC with H2O2 that is formed in situ as byproduct of the GOD-catalyzed oxidation of d-glucose with O2. Under the elaborated experimental conditions which we considered ideal, the formation of PANI-ES products is evident, as judged by UV/Vis/NIR and EPR measurements. Comparison was made with a reference reaction, which was run under similar conditions with added H2O2 instead of GOD and d-glucose. Although the reference reaction was found to be superior, with the cascade reaction, PANI-ES products can still be obtained with high aniline conversion (> 90%) within 24 h as stable dark green PANI-ES/AOT vesicle dispersion. Our results show that the in situ formation of H2O2 does not prevent the inactivation of HRPC known to occur in the reference reaction. Moreover, the GOD used in the cascade reaction is inactivated as well by polymerization intermediates.

Tyrosinase based amperometric biosensor for determination of tyramine in fermented food and beverages with gold nanoparticle doped poly(8-anilino-1-naphthalene sulphonic acid) modified electrode

The aim of the present work was to develop an amperometric biosensor for tyramine (Tyr) measurement in food and beverages. The biosensor architecture is based on tyrosinase (Tyr_ase) immobilization on glassy carbon electrode modified by a nanocomposite consisting of gold nanoparticles (AuNP) synthesized by a green method and poly(8-anilino-1-naphthalene sulphonic acid) modified glassy carbon electrode. Under optimized experimental conditions for fixed potential amperometric detection, the biosensor exhibited a linear response to tyramine in the range 10-120 µM and the limit of detection was estimated to be 0.71 µM. The novel platform showed good selectivity, long-term stability, and reproducibility. The strong interaction between tyrosinase and the nanocomposite was revealed by the high value of the Michaelis-Menten constant (79.3 μM). The fabricated biosensor was successfully applied to the determination of Tyr in dairy products and fermented drinks with good recoveries, which makes it a promising biosensor for quantification of tyramine.

Density Functional Theory Assessment of the Environment Polarity Effect on Polyaniline-Water Coupling

Crystallization water plays an important role in the self-organization of oligomer chains in conducting polyaniline. In order to quantify the interaction between emeraldine salt and such a water, models containing a tetramer in bipolaronic or polaronic form, chloride counterions, and an explicit water molecule are used. Different initial positions of water with respect to the oligomer chain-tangential and vertical-are considered. Various media are simulated by introducing an implicit solvent continuum of decreasing polarity. The DFT-D3/PCM computational approach is employed to examine the behavior of the systems in several aspects-the role of the explicit water position and the effect of the environment polarity on the spatial structure, energetics, charge distribution, and the frontier molecular orbital energies. The strength of hydrogen bonding and the patterns of charge redistribution invoked by the water molecule are discussed. The study establishes trend lines in the variation of the molecular characteristics upon change of milieu as a tool for control of the self-assembly process. The results show that chains interact more efficiently with tangentially placed water. The influence of the environment polarity is minor and is mainly expressed in slight shortening of the intermolecular distances and mild decrease of the group charges of the system components with reduction of polarity.

Biologically derived soft conducting hydrogels using heparin-doped polymer networks

The emergence of flexible and stretchable electronic components expands the range of applications of electronic devices. Flexible devices are ideally suited for electronic biointerfaces because of mechanically permissive structures that conform to curvilinear structures found in native tissue. Most electronic materials used in these applications exhibit elastic moduli on the order of 0.1-1 MPa. However, many electronically excitable tissues exhibit elasticities in the range of 1-10 kPa, several orders of magnitude smaller than existing components used in flexible devices. This work describes the use of biologically derived heparins as scaffold materials for fabricating networks with hybrid electronic/ionic conductivity and ultracompliant mechanical properties. Photo-cross-linkable heparin-methacrylate hydrogels serve as templates to control the microstructure and doping of in situ polymerized polyaniline structures. Macroscopic heparin-doped polyaniline hydrogel dual networks exhibit impedances as low as Z = 4.17 Ω at 1 kHz and storage moduli of G' = 900 ± 100 Pa. The conductivity of heparin/polyaniline networks depends on the oxidation state and microstructure of secondary polyaniline networks. Furthermore, heparin/polyaniline networks support the attachment, proliferation, and differentiation of murine myoblasts without any surface treatments. Taken together, these results suggest that heparin/polyaniline hydrogel networks exhibit suitable physical properties as an electronically active biointerface material that can match the mechanical properties of soft tissues composed of excitable cells.