Thermal Processing Creates Water‐Stable PEDOT:PSS Films for Bioelectronics
Siddharth Doshi, Margaux O. A. Forner, Pingyu Wang, Salim El Hadwe, Amy Jin, Gerwin Dijk, Kenneth Brinson, Juhwan Lim, Antonio Dominguez‐Alfaro, Carina Yi Jing Lim, Alberto Salleo, Damiano G. Barone, Guosong Hong, Mark L. Brongersma, Nicholas A. Melosh, George G. Malliaras, Scott T. Keene
Abstract
Organic mixed ionic-electronic conductors have emerged as a key material for the development of bioelectronic devices due to their soft mechanical properties, biocompatibility, and high volumetric capacitance. In particular, PEDOT:PSS has become a choice material because it is highly conductive, easily processible, and commercially available. However, PEDOT:PSS is dispersible in water, leading to delamination of films when exposed to biological environments. For this reason, chemical cross-linking agents such as (3-glycidyloxypropyl)trimethoxysilane (GOPS) are used to stabilize PEDOT:PSS films in water, but at the cost of decreased electrical performance. Here, it is shown that PEDOT:PSS thin films become water-stable by simply baking at high temperatures (>150 °C) for a short time (≈ 2 min). It is shown that heat-treated PEDOT:PSS films are as stable as their chemically-cross-linked counterparts, with their performance maintained for >20 days both in vitro and in vivo. The heat-treated films eliminate electrically insulating cross-linkers, resulting in a 3× increase in volumetric capacitance. Applying thermal energy using a focused femtosecond laser enables direct patterning of 3D PEDOT:PSS microstructures. The thermal treatment method is compatible with a wide range of substrates and is readily substituted into existing workflows for manufacturing devices, enabling its rapid adoption in the field of bioelectronics.