Eco-friendly synthesis of Cu nanoparticles using agave syrup: antifungal activity and molecular mechanism against plant pathogenic fungus

Abstract

Background Nanotechnology offers sustainable strategies for modern agriculture, particularly through nanopesticides that enhance crop protection and yield. Among them, copper nanoparticles (Cu-NPs) are of special interest because of their potent antimicrobial activity, which is closely linked to their size and morphology during synthesis. Methods We present a green synthesis route for Cu-NPs using agave syrup as a natural reducing agent and gum Arabic as a stabilizer. The antifungal efficacy of the Cu-NPs was assessed in vitro against several fungal phytopathogens. Morphological alterations in fungal hyphal upon Cu-NPs were analyzed by scanning electron microscopy. Additionally, all-atom molecular dynamics simulations combined with well-tempered metadynamics were conducted to elucidate the molecular mechanism underlaying Cu-NPs interactions with model fungal membrane, focusing on deformation, pore formation, and penetration mechanisms. For practical applicability, the S60/50 (97% Cu) formulation was selected for antifungal assays due to its high stability and representative physicochemical properties, whereas the highly reduced S90/50 (≈100% Cu) sample was employed in molecular simulations to elucidate the antifungal mechanism at the nanoscale. Significant Findings Transmission electron microscopy revealed polyhedral Cu nanocrystals with sizes ranging from 50 to 70 nm. The Cu-NPs exhibited strong antifungal activity, significantly inhibiting fungal radial growth even at low concentrations. Quantum mechanics/molecular mechanics calculations further indicated that favorable energetic interactions promote nanoparticle penetration into membranes, accompanied by protein oxidation as a secondary effect. These findings demonstrate that the green synthesized Cu-NPs possess broad-spectrum antifungal properties and offer a promising, eco-friendly alternative for sustainable crop protection.