Colloidal stability and controlled release of Au@SiO₂ and Ag@SiO₂ core–shell nanostructures from biopolymer-based hydrogels

Nanotechnology offers innovative strategies for developing multifunctional cosmetic ingredients. Here, we synthesize Au@SiO₂ and Ag@SiO₂ core-shell nanostructures with high shape and size uniformity, colloidal stability, and hydrophilicity. The silica shell stabilizes the metal core and enables surface functionalization, enhancing applicability in biopolymer-based formulations. We characterize the nanomaterials using UV-Vis spectroscopy, TEM, DLS, zeta potential, and contact angle measurements, confirming well-defined core-shell morphology and favorable surface properties. Both nanostructures display comparable antioxidant activity, while Ag@SiO₂ exhibits superior catalytic efficiency. To evaluate delivery performance, we incorporate the nanoparticles into sodium hyaluronate (HA) and hydroxyethylcellulose (HEC) hydrogels. The hybrid gels maintain homogenous morphology and enable tunable nanoparticle release profiles: HA gels promote rapid release and significantly improve skin hydration, whereas HEC gels provide sustained release suitable for prolonged action. These results demonstrate that Au@SiO₂ and Ag@SiO₂ nanostructures act as versatile, stable, and bioactive components for cosmetic and biomedical formulations. The study highlights the potential of core-shell nanomaterials at soft matter interfaces, combining antioxidant and antimicrobial functionality with controlled delivery and enhanced skin barrier performance.