Conjugated Polyelectrolyte Blend as Photonic Probe of Biomembrane Organization

A PEDOT based graft copolymer with enhanced electronic stability

Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) remains the most investigated conjugated polymer in bioelectronics, due to its biocompatibility, high conductivity, and commercial availability. Despite these advantages, it suffers from structural and electronic instability, associated with the PSS component. Here, a graft copolymer based on ionised sulfonic modified PEDOT, poly(EDOTS-g-EDOT), was electrochemically synthesised with demonstrated structural and electronic stability and enhanced electrochemical performance. The graft copolymer was insoluble in water without crosslinking, and exhibited enhanced ion diffusion upon electrochemical switching, as revealed by its volumetric capacitance (159 ± 8 F cm-3), which was significantly higher than that of spin-coated PEDOT:PSS films (41 ± 5 F cm-3). Similarly, its performance as an active channel material in organic electrochemical transistors (OECTs) was superior to the spin-coated PEDOT:PSS, as shown for instance by its high normalised transconductance (273 ± 79 S cm-1) and a significantly high ION/IOFF ratio (19 345 ± 1205). Its short- and long-term electronic stability were also confirmed with no drop in its output drain current, despite its high swelling degree. In contrast, the spin-coated PEDOT:PSS experienced a significant deterioration in its performance over the same operational time. The facile synthesis and improved performance of poly(EDOTS-g-EDOT) highlight the importance of innovative material design in overcoming existing operational shortcomings in electronic devices.

Self-doped conducting polymers in biomedical engineering: Synthesis, characterization, current applications and perspectives

Recent studies willingly agree that conducting polymers (CPs) are attractive materials for biomedical engineering purposes, mainly because of their unique physicochemical characteristics combining electrical conductivity and high biocompatibility. Nevertheless, the applicability of CPs is restricted by their limited stability under physiological conditions, associated with a decrease in electrical conductivity upon dedoping. Accordingly, modifying chemical structure of CPs to exhibit a self-doping effect seems to be an appealing approach aimed to enhance their functionality. The aim of this review is to provide a current state-of-the-art in the research concerning self-doped CPs, particularly those with potential biomedical applications. After presenting a library of available structure modifications, we describe their physicochemical characteristics, focusing on achievable conductivities, electrochemical, optical and mechanical behaviour, as well as biological properties. To highlight high applicability of self-doped CPs in biomedical engineering, we elaborate on biomedical areas benefiting most from using this type of conducting materials.

A One Step Procedure toward Conductive Suspensions of Liposome-Polyaniline Complexes

Interaction of conjugated polymers with liposomes is an attractive approach that benefits from both systems' characteristics such as electroactivity and enhanced interaction with cells. Conjugated polymer-liposome complexes have been investigated for bioimaging, drug delivery, and photothermal therapy. Their fabrication has largely been achieved by multistep procedures that require first the synthesis and processing of the conjugated polymer. Here, a new one step fabrication approach is reported based on in situ polymerization of a conjugated monomer precursor around liposomes. Polyaniline (PANI) doped with phytic acid is synthesized via oxidative polymerization in the presence of 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine (DOPC) vesicles to produce a conductive aqueous suspension of Liposome-PANI complexes. PANI interacts with liposomes without disrupting the bilayer as shown using differential scanning calorimetry and fluorescence quenching studies of the hydrophobic Nile red probe. The electronic conductivity of the Liposome-PANI complexes, which stems from the doped PANI accessible on the liposome surface, is confirmed using conductive atomic force microscopy and electrochemical impedance spectroscopy. Further, short-term in vitro cell studies show that the complexes colocalize with the cell membrane without reducing cell proliferation. This study presents a novel fabrication route to conductive suspensions of conjugated polymer-liposome complexes suitable for potential applications at the biointerface.

A DNA and Self-Doped Conjugated Polyelectrolyte Assembled for Organic Optoelectronics and Bioelectronics

Deoxyribonucleic acid (DNA) and a self-doped conjugated polyelectrolyte, poly(4-(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl-methoxy)-1-butanesulfonic acid (PEDOT-S), are assembled for organic optoelectronics and bioelectronics. The DNA's helix-coil phase transition in water is studied as a function of composition by thermo-optical analysis. DNA and PEDOT-S are functionalized by using a surfactant, cetyltrimethylammonium chloride (CTMA), and DNA:CTMA, PEDOT-S:CTMA, and DNA:CTMA:PEDOT-S:CTMA complexes were characterized regarding thermal, optical, morphological, and structural properties. Finally, DNA and DNA:PEDOT-S mixtures are processed in water for fabricating organized films through brushing. The electrical properties of these films are characterized using an interdigitated electrode. The films show an electronic conductivity of ∼10^-6-10^-5 S/cm in a range of semiconductors.

Conjugated Polymers for Assessing and Controlling Biological Functions

The field of organic bioelectronics is advancing rapidly in the development of materials and devices to precisely monitor and control biological signals. Electronics and biology can interact on multiple levels: organs, complex tissues, cells, cell membranes, proteins, and even small molecules. Compared to traditional electronic materials such as metals and inorganic semiconductors, conjugated polymers (CPs) have several key advantages for biological interactions: tunable physiochemical properties, adjustable form factors, and mixed conductivity (ionic and electronic). Herein, the use of CPs in five biologically oriented research topics, electrophysiology, tissue engineering, drug release, biosensing, and molecular bioelectronics, is discussed. In electrophysiology, implantable devices with CP coating or CP-only electrodes are showing improvements in signal performance and tissue interfaces. CP-based scaffolds supply highly favorable static or even dynamic interfaces for tissue engineering. CPs also enable delivery of drugs through a variety of mechanisms and form factors. For biosensing, CPs offer new possibilities to incorporate biological sensing elements in a conducting matrix. Molecular bioelectronics is today used to incorporate (opto)electronic functions in living tissue. Under each topic, the limits of the utility of CPs are discussed and, overall, the major challenges toward implementation of CPs and their devices to real-world applications are highlighted.

Highly Stable Conjugated Polyelectrolytes for Water-Based Hybrid Mode Electrochemical Transistors

Hydrophobic, self-doped conjugated polyelectrolytes (CPEs) are introduced as highly stable active materials for organic electrochemical transistors (OECTs). The hydrophobicity of CPEs renders films very stable in aqueous solutions. The devices operate at gate voltages around zero and show no signs of degradation when operated for 10⁴ cycles under ambient conditions. These properties make the produced OECTs ideal devices for applications in bioelectronics.