Enhancing the conductivity of PEDOT:PSS films for biomedical applications via hydrothermal treatment

This paper reports a new biocompatible conductivity enhancement of poly (3,4-ethylenedioxythiophene):poly (styrene sulfonate) (PEDOT:PSS) films for biomedical applications. Conductivity of PEDOT:PSS layer was reproducibly from 0.495 to 125.367 S cm⁻¹ by hydrothermal (HT) treatment. The HT treatment employs water (relative humidity > 80%) and heat (temperature > 61 °C) instead of organic solvent doping and post-treatments, which can leave undesirable residue. The treatment can be performed using the sterilizing conditions of an autoclave. Additionally, it is possible to simultaneously reduce the electrical resistance, and sterilize the electrode for practical use. The key to conductivity enhancement was the structural rearrangement of PEDOT:PSS, which was determined using atomic force microscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and ultraviolet–visible spectroscopy. It was found that PEDOT inter-bridging occurred as a result of the structural rearrangement. Therefore, the conductivity increased on account of the continuous conductive pathways of the PEDOT chains. To test the biocompatible enhancement technique for biomedical applications, certain demonstrations, such as the monitoring of joint movements and skin temperature, and measuring electrocardiogram signals were conducted with the hydrothermal-treated PEDOT:PSS electrode. This simple, biocompatible treatment exhibited significant potential for use in other biomedical applications as well.