Flexible Conductive Paper-Based Sensors for On-Skin Electrophysiological Monitoring and Wearable Applications

Flexible, skin-conformable electrodes require materials that combine mechanical robustness, environmental stability, high electrical performance, and biocompatibility. Here, we present a flexible conductive composite film composed of poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS), cellulose nanofibers (CNF), and the ionic liquid 1-ethyl-3-methylimidazolium ethyl sulfate (EMIM ES). The composite is fabricated via a simple aqueous blending and filtration process, yielding a free-standing film with a robust fibrous microstructure. ATR-FTIR analysis confirms the successful integration of all components, while SEM imaging reveals a percolated nanofibrillar architecture that enhances interfacial adhesion and structural integrity. Mechanical testing reveals a tensile strength of up to 335 MPa, accompanied by a strain of 21%, attributed to the increasing CNF content. Composite films with low CNF content exhibit excellent electrical stability across humidity levels between 10% and 90% and temperatures of 15-55 °C, and maintain electrochemical performance after 100,000 cycles of mechanical fatigue testing. On-skin electrophysiological recordings from a rodent model demonstrate stable signal acquisition without skin irritation, establishing the hybrid films as a promising platform for soft, wearable bioelectronic interfaces.