Copper nanowire network as a breathable anti-biofouling layer on gas-permeable membranes for long-term electrochemical dissolved oxygen monitoring.

Dissolved oxygen (DO) is a central metric of aquatic ecosystem function, yet long-term, in situ electrochemical DO monitoring remains limited by biofouling: microbial colonization and biofilm growth progressively block oxygen access and destabilize amperometric currents over time. Copper is an attractive antifouling material because it can inactivate bacteria through contact-mediated membrane damage coupled with Cu+/Cu2+ release and redox-driven oxidative stress. However, conventional Cu film layers often restrict analyte diffusion due to their dense or aggregated morphologies, accelerating sensitivity loss. Here, we demonstrate that film morphology enables controlling parameters, by engineering a self-supported, interconnected copper nanowire (CuNW) network as a breathable protective layer on gas-permeable membranes. Comparative morphology archetypes (sputtered Cu, Cu nanoparticle, CuNW) reveal that oxygen permeability and sensor output are regulated by porosity rather than copper content alone. The open CuNW framework minimizes diffusion resistance in a transport assay and sustains amperometric sensitivity at -0.8 V vs Ag/AgCl. Tuning CuNW loading reveals a transition from breathable skin to diffusion barrier, with an optimum at 75 μg cm-2 that maintains fast response (t90 = 10 s) while maintaining high sensitivity of 0.55 ± 0.03 μA ppm-1 under marine-relevant biofouling exposure for three weeks. Additionally, CuNW-protected sensors retain 98.6% of their initial sensitivity, whereas unprotected sensors drop to 79.1%. Our study proposed a scalable strategy for antifouling gas-exchange membranes that enables durable DO sensing in a fouling-prone environment.