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 Jackson Brunner
Research from the Department of Materials Science and Engineering at The Grainger College of Engineering, University of Illinois Urbana-Champaign, was published as cover story for the June 2026 edition of the Journal of Materials Chemistry B.
The research
Recording the electrical signals that drive the heart and brain often relies on fluorescent voltage dye, which are useful, but prone to perturbing cells and fading over time from photobleaching. A new study led by graduate student Xuchen Ren, with contributions from undergraduate researcher Alexandra Kuhlman-Schneider (recently named a Darin Butz Foundation Research Scholar, offers a way around these limits using PEDOT:PSS, an electrochromic material whose optical absorbance changes with applied voltage. Because the response is intrinsic to the material rather than a chemical label, it enables non-perturbative, long-term optical recording of bioelectric activity.
The team's central finding is that this electrochromic behavior can be tuned by controlling how the PEDOT:PSS film is electropolymerized. They tested several factors — counterions, solution pH, PSS molecular weight and substrate surface treatment — and found counterion competition to be the dominant one. Adding chloride ions alongside PSS during EDOT electropolymerization blue-shifted the film's absorption peak by about 120 nm, altered its morphology, increased its optical anisotropy and reshaped its voltage sensitivity across wavelengths: weaker at blue-green wavelengths, stronger at red. Using films grown without chloride and a 561 nm laser, the team reached a voltage detection sensitivity of 2.8 µV at a 10 kHz bandwidth under shot-noise-limited conditions.
To show the platform in action, the researchers performed prolonged label-free optical recordings of isolated embryonic chicken hearts, simultaneously capturing cardiac field potentials and mechanical contractions. Both signals increased from embryonic day 10 to day 15, while the latency between electrical and mechanical activity stayed constant. While prior PEDOT:PSS research has mostly focused on tuning its conductivity, this work establishes electropolymerization as a strategy for engineering its optical response instead, providing design principles for more sensitive, stable, non-perturbative voltage sensors that could support long-term studies of cardiac development and disease, drug screening and future bioelectronic or organ-on-chip systems.