Antifungal Activity of Ag and ZnO Nanoparticles Co-Loaded in Zinc–Alginate Microparticles

Fungal infections caused by Fusarium solani demand sustainable alternatives to conventional fungicides and free nanoparticles, which often show poor stability and rapid release. This study developed zinc-crosslinked alginate microparticles containing silver (AgNPs), zinc oxide (ZnONPs), or both to improve nanoparticle stability, sustain release, and enhance antifungal efficacy. Microparticles were produced by ionic gelation and characterized by FTIR, microscopy, swelling analysis, encapsulation efficiency, and kinetic modeling. AgNPs weakened hydrogen bonding within alginate, yielding rough, porous structures, whereas ZnONPs strengthened COO−–Zn2+ interactions, forming smoother surfaces with smaller pores; co-loaded particles combined both characteristics. Encapsulation efficiencies were 77.9% (AgNPs) and 98.6% (ZnONPs), with co-loaded systems retaining 64.0% and 98.9%, respectively. Swelling was highest in AgNP-loaded microparticles (63.8%) and lowest in ZnONP and co-loaded systems (≈42%). AgNPs followed anomalous transport (n = 0.65), while ZnONPs transitioned from Fickian diffusion (n ≈ 0.36–0.38) to zero-order release (K0 = 1.00 for ZnONPs alone; 0.80 co-loaded). Antifungal tests showed strong inhibition: 80.7% for AgNPs, 91.4% for ZnONPs, and 99.7% for co-loaded formulations. Microscopy confirmed membrane disruption, hyphal collapse, and ROS-mediated damage, with the strongest effects in co-loaded samples. These results demonstrate a tunable, synergistic, sustained-release platform that outperforms single nanoparticles and offers a promising strategy for sustainable crop protection.