Phycocyanin-mediated silver nanoparticle/PDMS nanocomposite coatings: Field-validated antifouling performance in the marine environment of the Persian Gulf.

Marine biofouling poses severe operational and ecological challenges, driving the demand for sustainable, high-performance antifouling strategies. In this study, silver nanoparticles (AgNPs) were biosynthesized using phycocyanin (PC) extracted from Spirulina platensis as a green reducing and stabilizing agent, and incorporated into polydimethylsiloxane (PDMS) to produce multifunctional nanocomposite coatings. The biosynthesized PC-AgNPs were extensively characterized by UV-Vis spectroscopy, FTIR, XRD, FESEM-EDS, and TEM, confirming well-dispersed spherical nanoparticles (mean diameter 22.32 ± 8.39 nm, PDI = 0.14) with crystalline Ag0 cores and a biogenic capping layer. Antibacterial assays revealed strong, concentration-dependent inhibition of Escherichia coli, Staphylococcus aureus, and Pseudomonas stutzeri, with >93% growth suppression at optimal doses. The nanoparticles also demonstrated potent anti-algal activity against Nannochloropsis oculata and variable toxicity toward Artemia salina and Amphibalanus amphitrite larvae. Incorporation of PC-AgNPs into PDMS enhanced surface hydrophobicity (contact angle up to 110.3°) and reduced surface free energy to 14.9 mJ/m2, improving resistance to microbial adhesion. In 90-day marine field trials, PDMS/PC-AgNP coatings exhibited markedly reduced biofouling, particularly at a 2 wt% loading, achieving more than 70% lower coverage than uncoated substrates and over 50% less than pristine PDMS. This green nanotechnology approach offers an environmentally responsible and effective pathway for next-generation marine antifouling coatings.