Materials graduate student Xuchen Ren, with undergraduate researcher Alexandra Kuhlman-Schneider, found that adding chloride ions during electropolymerization of PEDOT:PSS thin films shifts their electrochromic response and reshapes voltage sensitivity across wavelengths. Using chloride-free films, the team achieved a voltage detection sensitivity of 2.8 µV, demonstrated through prolonged, label-free optical recordings of electrical and mechanical activity in developing embryonic chicken hearts, published in the Journal of Materials Chemistry B. The findings point toward more sensitive, stable and non-perturbative voltage sensors for cardiac research, drug screening and organ-on-chip systems.
Written by Jeni Bushman
Illinois researchers have used a tunable platform to produce label-free optical recording of embryonic chicken hearts
Researchers from the Department of Materials Science and Engineering at the University of Illinois Urbana-Champaign have demonstrated a new way to improve label-free optical recording of bioelectric signals using the electrochromic polymer PEDOT:PSS. Led by assistant professor Yuecheng “Peter” Zhou and featured in the Journal of Materials Chemistry B as the June 2026 cover story, the group’s materials-based optical platform establishes electropolymerization as a practical framework for engineering next-generation electrochromic materials for bioelectric signal detection.
The artwork featured as the June 2026 cover of Journal of Materials Chemistry B was created by Bri Hege and Alex Jerez of the Beckman Institute Visualization Laboratory.
Recording electrical activity in heart and brain cells usually requires electrodes or fluorescent dye indicators — interventions that can disturb living tissues and constrain recording time. To circumvent these issues, researchers have begun turning to label-free optical recording, a technique that tracks electrical activity using light without dyes. A promising material for this approach is PEDOT:PSS, a conductive polymer commonly used in flexible electronics. While trying to synthesize PEDOT:PSS, Zhou and graduate student Xuchen Ren noticed something curious: small, unexplained changes in the polymer that dramatically affected the material’s optical properties.
Wanting to understand the mechanism behind this change, the Illinois Grainger engineers began by hypothesizing and evaluating four electropolymerization factors that might affect the polymer’s sensitivity: the presence of competing counterions; the solution pH; the molecular weight of PSS; and the treatment of their substrate surface. Zhou’s team found that the addition of a second counter ion — sodium chloride — changed the sensitivity of their material, suggesting that the optical spectrum of the PEDOT polymer films is highly sensitive to both chloride and PSS ions.
“Without changing the general framework of PEDOT:PSS, an additional counter ion shifts the sensitivity of the materials significantly,” said Ren, the paper’s first author. “It’s not a simple mixture; these counter ions actually get into the backbone of these polymers.”
Further, applying different voltages to the polymer changed the material’s optical absorbance: a revelation that opens the door for long-term, non-perturbative optical recording that can be optimized for different laser wavelengths.
The researchers tested their tunable method by recording electrical activity from embryonic chicken hearts, observing a significant difference in electrical and mechanical signal development between day 10 and day 15. The latter produced an equivalent electrical signal of 1 - 1.3 mV, marking the first demonstration of this label-free framework in an embryonic chicken heart.
“This serves as a very nice model system for us and the future studies in our lab,” Zhou said. “We can use it to demonstrate other materials developed here for this type of work.”
Going forward, the researchers will explore different conjugated polymers that can better interface with heart cells, hoping to progress their platform’s application from ex vivo to in vivo.
“We’re not limiting ourselves,” Zhou said. “We are taking small steps toward our goals of applying this technique to more biological settings.”