(2cx) Advancing Next-Generation Bioelectronics through Rational Omiec Design

Organic mixed ionic–electronic conductors (OMIECs) are soft, often polymeric, organic materials that solvate/transport ionic species and transport electronic charges, enabling ionic–electronic coupling. OMIEC materials are therefore attractive for many next-generation bioelectronic, optoelectronic, and energy storage applications. Despite recent progress and a rapidly expanding library of OMIECs, there are many material limitations that complicate their widespread adoption. The most significant limitation of polymeric OMIECs is the imprecise synthetic control of important parameters such as molecular weight, dispersity, and end groups under traditional cross-coupling methodologies operating under step-growth kinetics. While the organic electronic community has identified molecular weight as a critical parameter dictating charge transport for conjugated materials, its effect on mixed conduction remains largely unknown. Shedding light on this relationship is important, not just to optimize performance of known polymer systems, but to improve our understanding of mixed charge transport in OMIECs. To elucidate the effect of molecular weight on mixed transport, a series of glycolated thiophene based polymers were synthesized via Kumada catalyst transfer polymerization, a chain-growth method, to obtain polymers with molecular weights ranging from 13.9 to 32.5 kg/mol. This range had previously been found to contain the entanglement threshold of P3HT molecular weights in organic thin film transistors (OTFTs). Organic electrochemical transistors (OECTs), a common test bed for OMIECs, were tested in both aqueous NaCl and KTFSI electrolytes, which are the most ubiquitous salts in aqueous metal halide electrolytes as well as ionic liquids and battery electrolytes, respectively. To help explain origins of observed differences in electronic performance, we performed operando grazing-incidence wide angle x-ray scattering (GIWAXS) and electrochemical quartz crystal microbalance (EQCM) experiments. We discovered a mobility threshold around 20 kg/mol when OECTs were operated in KTFSI, which was absent in devices operated in NaCl. Leveraging operando characterization techniques, we found that this absence could be explained by a more unstable microstructure of the material in NaCl, as observed via larger modulation of the lamellar spacing during doping and dedoping. This work suggests percolation thresholds in OMIECs may only be accessible in suitable electrolytes, which can help guide materials choices for given applications. Work is currently underway in the Rivnay lab to understand the role of OMIEC structural features on performance.

Another limitation within this class of materials is ion-selective doping/dedoping. OMIECs are common active materials for electrolyte-gated transistors due to their changes in conductivity upon redox reaction with ions. However, this process generally relies upon gate modification, ion-selective membranes, molecular imprinted polymers, or other technologies to provide ion-selectivity. These methodologies are not only unwieldly but reduce long-term use and can limit application in complex aqueous environments. We address this challenge using a supramolecular approach, through the direct incorporation of an ion-selective macrocycle into the active material. A phosphate-selective macrocycle was directly blended with a diketopyrrolopyrrole (DPP)-based conjugated polymer. The blend was investigated via UV-vis-NIR and EPR spectroscopy to ascertain the origin of the electronic coupling between the polymer and receptor, which suggested the formation of a ground-state charge-transfer complex. The polymer-receptor blend was then used as an active material within an electrolyte-gated OFET (EGOFET), which displayed remarkable selectivity for the detection of phosphate over other anions. The direct incorporation of the supramolecular receptor within the active layer afforded a device with remarkably low limits of detection (LOD) of 178 pM (17.3 ppt), and stable operation in seawater environments. This work features a new concept where the receptor enhances the stability and transport characteristics of the semiconductor via doping effects; a method that can be broadly used for a wide variety of different analytes. Current work in the Rivnay and Azoulay labs are underway to leverage this concept within other device architectures.

Research Interests

I am currently a postdoctoral research associate in Biomedical Engineering at Northwestern University, working with Prof. Jonathan Rivnay. I received a Ph.D. in Polymer Science & Engineering at the University of Southern Mississippi in 2020 under the guidance of Prof. Jason D. Azoulay. My vision is to establish a multidisciplinary laboratory at the intersection of chemistry (organic, polymer, and analytical), engineering, and biology. As an assistant professor I plan to utilize my expertise in in p-conjugated polymer/materials synthesis and organic (bio)electronics to enable (1) bioelectronic interfacing for precision control of biological functions and (2) chemical sensing in complex aqueous media for medical, environmental, and defense applications. These research interests rely on precision control of semiconductor electronic structure which will be achieved through advancements in both polymer synthesis and engineering.

Teaching Interests

I am also passionate about teaching and mentorship, an often-overlooked responsibility that is essential for the development of our next-generation of scientists and leaders. Innovative projects within my group will provide excellent, rigorous, and highly interdisciplinary research opportunities and training for undergraduates, graduate students, and postdoctoral researchers. I consistently engage with the educational literature and pursue evidence-based pedagogies (pedagogical methods) to enhance student learning, an interest that I will further pursue as a faculty member. I am comfortable teaching introductory and advanced chemistry (organic, methods, analytical), chemical engineering (design, separations, kinetics), and specialty courses (polymer science, materials science, nanotechnology, biochemical engineering). In the process of earning my CIRTL Practitioner certification at Northwestern University, I have developed a polymer science course that can be adapted and integrated within most chemistry and chemical engineering curricula.