Electrochemical properties of diamond-like carbon film electrodes for Japanese sake sensing using cyclic voltammetry

Diamond-like carbon (DLC) films offer tunable electrical, optical, surface, and electrochemical properties through control of feed-gas composition during deposition. Reusable voltammetric platforms based on a single working electrode for beverage analysis remain insufficiently explored. In this study, DLC films were deposited by low-frequency plasma-enhanced chemical vapor deposition onto fluorine-doped tin oxide (FTO) substrates using CH₄/H₂ feed-gas mixtures containing 0 or 40 % H₂, denoted as DLC (H₂: 0 %) and DLC (H₂: 40 %). Electrochemical behavior was evaluated by cyclic voltammetry using DLC-coated FTO working electrodes in a three-electrode configuration. Fourier-transform infrared spectroscopy revealed lower C–H stretching intensity for DLC (H₂: 40 %), suggesting modified C–H bonding. Raman spectroscopy showed a shift of the G band toward lower wavenumbers, indicating changes in sp² carbon. X-ray photoelectron spectroscopy revealed lower relative sp² C–C fraction and higher relative sp³ C–C fraction for DLC (H₂: 40 %) than for DLC (H₂: 0 %). The refractive index and extinction coefficient were higher for DLC (H₂: 40 %), while both DLC films exhibited lower contact angles toward Japanese sake than bare FTO. DLC (H₂: 40 %) exhibited a wider potential window among the electrodes. Euclidean-distance analysis and principal component analysis of voltammetric fingerprints from five Japanese sake samples showed reproducible responses and distinct clustering. These results indicate that H₂ addition modifies the bonding and interfacial properties of DLC films and that DLC (H₂: 40 %) enables reproducible voltammetric discrimination of Japanese sake, highlighting potential for food analysis and quality monitoring.