Real-time in-situ H₂O₂ quantification in high-biomass marine environments with a robust NiCo-MOF nanosheet electrode

Electrochemical sensors are widely investigated for H₂O₂ detection, but real-time in-situ quantification in complex biological media remains challenging. Most sensors require sample dilution or operation under non-physiological conditions, which compromises true in-situ analysis. Alternative approaches detecting H₂O₂ from stimulated cells rely on short-term amperometric monitoring, offering only qualitative insights into transient fluctuations rather than continuous quantitative concentration profiles, and cannot support long-term tracking.

Here, we report a fouling-resistant H₂O₂ sensor based on a hierarchically porous two-dimensional NiCo-MOF nanosheet array. The engineered nanopores are proposed to act as a molecular sieve, potentially limiting the access of large biomolecules and organic interferents, enabling stable and direct detection in complex biological media-including HCT116 cell suspensions, Escherichia coli cultures, and Skeletonema costatum seawater medium. Benefiting from cooperative effects between Ni-Co centers and hydrophilic carboxyl groups, the sensor achieves a wide linear range (0.05-5000 μM) with low detection limits (25-45 nM) across all tested systems. Notably, this work demonstrates the first six-day continuous real-time in-situ monitoring of H₂O₂ dynamics in a live, high-density S. costatum seawater culture, reliably capturing diurnal fluctuations as well as sustained H₂O₂ accumulation during the late-growth phase, with excellent agreement with parallel UV-Vis spectrophotometry (σ = 0.046).

This work addresses a key technological challenge by enabling long-term, in-situ quantitative electrochemical monitoring in complex biological media, validating the potential of the NiCo-MOF material and establishing a versatile platform for environmental dynamics and life process research.