Direct printing of metal oxide nanostructures for wearable electrochemical sensing

Metal oxides such as Zinc Oxide (ZnO) and Cerium Oxide (CeO₂) have emerged as promising materials for electrochemical sensing due to their redox activity, surface charge sensitivity, and chemical stability. We report the direct printing of ZnO and CeO₂ nanostructures on flexible screen-printed electrodes using an atmospheric plasma-aided technique, enabling binder-free printing from aqueous suspensions. The electrochemical sensing ability of ZnO was tested for pH sensing, while CeO₂ was tested for non-enzymatic Hydrogen Peroxide (H₂O₂) detection. Morphological and optical characterizations revealed voltage-dependent variations in nanoparticle distribution, thickness, and bandgap, with improved layer uniformity and substrate adhesion at higher plasma voltages. Electrochemical characterization demonstrated enhanced charge transfer and sensitivity, with ZnO showing a maximum pH response of 34.96 mV/pH when fabricated at 18 kV and CeO₂ reaching a peak H₂O₂ sensitivity of 1.03 µA/µM/cm² when fabricated at 24 kV. Our results establish plasma-assisted printing as a binder free, rapid, low-temperature method for directly printing high-performance metal oxide sensors on flexible polymer substrates for wearable applications.