Organic semiconductors are increasingly employed in electrochemical devices for energy conversion and storage and chemical sensing. In these systems, the conductivity can be modulated with electrochemical doping with substantial variation in electronic charge densities (10 16 to 10 21 cm −3 ) stabilized by electromigration of counterions from the electrolyte phase. Herein, we focus on the model system of regioregular poly(3hexylthiophene) to determine the structural evolution at the onset of conductivity arising from electrochemical doping, specifically targeting elucidation of structural relaxation that precedes volumetric swelling. Using spectroelectrochemical methods, a 20% electrochemical active fraction of the film volume comprised of a nanocrystallite subpopulation serves as a high doping efficiency charge nucleation site with an increase from 10 16 to 10 20 carriers/cm −3 . A small carrier density window is observed where structural reversion of J-to-H aggregates occurs due to electrostatic repulsion of neighboring charges (bipolarons) on the nanocrystallites. After this conformational change, further increase in doping leads to generation of free volume for counterion diffusion in the nanocrystallites along with doping of the amorphous fraction and J-aggregate recovery. This result advances the structural knowledge of conductive polymer electrodes for electrochemical devices beyond what has been reported using X-ray scattering and provides a benchmark for synthetic structural changes to control hybrid electrical−ionic transport, emphasizing the need to control structural conformation relaxations in addition to volumetric swelling.

Real-time sensing of proteins, especially in wearable devices, remains a substantial challenge due to the need to convert a binding event into a measurable signal that is compatible with the chosen analytical instrumentation. Impedance spectroscopy enables real-time detection via either measuring electrostatic interactions or electron transfer reactions while simultaneously being amenable to miniaturization for integration into wearable form-factors. To create a more robust methodology for optimizing impedance-based sensors, additional fundamental studies exploring components influencing the design and implementation of these sensors are needed. This investigation addresses a sub-set of these issues by combining optical and electrochemical characterization to validate impedance-based sensor performance as a function of (1) biorecognition element density, (2) self-assembled monolayer chain length, (3) self-assembled monolayer charge density, (4) the electrochemical sensing mechanism and (5) the redox reporter selection. Using a pre-existing lysozyme aptamer and lysozyme analyte combination, we demonstrate a number of design criteria to advance the state-of-the-art in protein sensing. For this model system we demonstrated the following: First, denser self-assembled monolayers yielded substantially improved sensing results. Second, self-assembled monolayer composition, including both thickness and charge density, changed the observed peak position and peak current. Third, single frequency measurements, while less informative, can be optimized to replace multi-frequency measurements and in some cases (such as that with zwitterionic self-assembled monolayers) are preferred. Finally, various redox reporters traditionally not used in impedance sensing should be further explored. Collectively, these results can help limit bottlenecks associated with device development, enabling realization of next-generation impedance-based biosensing with customize sensor design for the specific application.

Electrochemically deposited conductive polymers, with their ion imprinted channels, can increase ion transport speed by three orders of magnitude over their spin coated counterparts by eliminating energetic traps for ion movement.