A nanozyme–enzyme hybrid electrochemical platform based on CeO₂–MoS₂/Au for selective lactate monitoring in human sweat

This study reports a nanozyme-enhanced electrochemical platform for quantifying lactate in exercise-induced sweat, constructed by modifying a glassy carbon electrode with a CeO₂–MoS₂ composite decorated with Au nanoparticles and immobilized lactate oxidase. Structural characterization confirmed crystalline CeO₂ (8 nm) with mixed Ce³ ⁺/Ce⁴⁺ states, layered MoS₂ (0.62 nm spacing), and uniformly distributed AuNPs, forming a conductive, high-surface-area catalytic interface. The composite significantly reduced the H₂O₂ reduction overpotential, enabling sensor operation at 0.0 V vs Ag/AgCl and minimizing interference from coexisting sweat metabolites. Electrochemical impedance spectroscopy showed a reduction in charge transfer resistance from ∼580 Ω (bare electrode) to ∼220 Ω after nanozyme modification, supporting accelerated electron transport. The sensor exhibited rapid amperometric response (<10 s), a broad linear range of 0.05–20 mM, and a sensitivity of 25.0 µA·mM⁻¹ ·cm⁻², with a detection limit of 0.02 mM, fully encompassing physiological sweat lactate levels from rest to intense exercise. High selectivity was demonstrated, with responses to 5 mM lactate remaining within 97–103 % in the presence of 0.2 mM ascorbate, 0.2 mM urate, and 5 mM glucose, while D -lactate produced < 2 % of the L -lactate signal. The device showed excellent reproducibility (RSD 4.7 %), repeatability (RSD 3.2 %), and long-term stability, retaining ∼90 % sensitivity after four weeks of storage at 4 °C. Recovery tests in artificial sweat yielded 96–97 %, and real-sample analysis agreed within 4 % of a reference colorimetric assay. These results establish a laboratory-validated nanozyme–enzyme catalytic interface on a rigid glassy carbon electrode and provide a reproducible foundation for subsequent integration and validation on flexible, epidermal-relevant platforms for wearable sweat monitoring.