Robust and flexible electrochemical lactate sensors for sweat analysis based on nanozyme-enhanced electrode

In this work, nickel oxide (NiO) nanostructures deposited by glancing angle deposition (GLAD) are fabricated to achieve highly specific catalytic electrooxidation of lactate, replacing the natural enzyme lactate oxidase for electrochemical detection of lactate in sweat. GLAD NiO electrodes exhibit high sensitivity (412 μA mM−1 cm−2), wide linear detection range (1–45 mM), low detection limit (3 μM), and excellent specificity in artificial sweat samples. The unique microporous structure of the GLAD NiO electrodes, combined with their high surface area, high catalytic activity, and excellent conductivity, enhance the performance of the sensor and demonstrate their exceptional effectiveness in the sensitive detection of lactate. In-house fabricated gold counter, and stable solid-state Ag/AgCl reference electrodes, all fabricated on a flexible PET substrate along with the GLAD NiO working electrode, demonstrate performance comparable to commercial Pt auxiliary and Ag/AgCl (1M KCl) reference electrodes in lactate detection, along with outstanding flexibility, tested at various radii of curvature (15 mm, 7.5 mm, and 5 mm). The durable and long-lasting GLAD NiO electrode chips overcome numerous challenges in transport, storage, and operation, paving the way for the development of wearable lactate sensors that can detect lactate levels in sweat.