An All-Solid-State Calcium Ion-Selective Electrode with a Peptide-Based Interface Integrating Passive Antifouling and Active Photothermal Bactericidal Strategies for Long-Term Seawater Monitoring.

Biofouling significantly compromises the long-term stability of ion-selective electrodes operating in marine environments. In this work, we develop an all-solid-state calcium ion (Ca2+) selective electrode, featuring a multifunctional antifouling interface (PPA) constructed from phytic acid (PA), Prussian blue nanoparticles (PB), and an antimicrobial peptide (AMP). Through coordination and electrostatic interactions, hydrophilic PA-PB nanoparticles and the positively charged AMP cooperatively self-assemble to form a stable antifouling interface on the surface of the calcium ion-selective membrane. The novelty of this work lies in integrating PA-enabled hydrophilic antifouling, AMP-based contact killing, and PB-mediated near-infrared (NIR) photothermal sterilization into all-solid-state ion-selective electrodes. Under NIR irradiation, the coating exhibits efficient photothermal conversion capability, maintaining stable peak temperatures and baseline levels over six heating-cooling cycles. The PPA interface rapidly inactivates bacteria while effectively suppressing bacterial adhesion, with the relative bacterial adhesion rate decreasing to 0.23%-0.36% after NIR irradiation. Importantly, this antifouling modification does not compromise the sensing performance of the electrode. The electrode exhibits a near-Nernstian response with a slope of 28.82 ± 0.48 mV dec-1 in the concentration range from 10-5 to 10-1 M and demonstrates a fast response time (<4 s). Long-term immersion tests show that the sensor maintains stable response characteristics even after 50 days in seawater. Furthermore, accurate in-situ determination of Ca2+ in coastal seawater was achieved, with results that are in good agreement with those obtained by ICP-AES measurements. This work provides a simple and effective strategy for constructing long-term antifouling ion-selective electrodes suitable for marine sensing applications.