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

Abstract

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.