Laser-written high-entropy metal-oxy patch for non-enzymatic lactate-pH sweat sensing

Wearable sweat analytics demands sensing interfaces that remain catalytically active in biofluids yet are manufacturable in flexible formats. Here we report a one-step CO₂-laser writing strategy that converts chitosan-multimetal precursor on polyimide into a porous N-doped graphene (NG) network uniformly anchored with high-entropy multimetal (oxy)nanoparticles (HEMO). The laser process yields a high-entropy (oxy)surface where metallic ensemble sites coexist with oxygenated motifs (M-O/M-OH), generating mixed-valence catalytic centers electronically coupled to the conductive graphene. Leveraging this architecture, the flexible electrode enables lactate-pH co-sensing under neutral conditions. Non-enzymatic lactate detection proceeds via adsorption-assisted electrocatalytic oxidation on multimetal ensemble sites, where the mixed-valence (oxy)surface accelerates interfacial charge transfer and turnover, delivering a linear range of 0.05-20 mM with a detection limit of 8.83 μM. Concurrently, potentiometric pH sensing arises from reversible proton-coupled conversion between -OH and -O^-∗ on oxygenated surface groups, producing a linear open-circuit potential (OCP)-pH relationship. Finally, integrating the laser-written electrodes into a skin-conformal patch with microfluidics and wireless electronics enables real-time exercise monitoring, tracking sweat lactate dynamics with pH shifts and agreeing well with standard reference assays. Collectively, this work establishes a scalable, laser-enabled route to high-entropy metal-oxy electrocatalytic interfaces for pH-assisted lactate quantification and multiplexed wearable sweat sensing.