H₂O₂-induced green synthesis of EGCG-flavonoid carrier-free nanoparticles:The role of hydroxyl group number governing formation and function

Nanoparticles are successfully constructed by a green H₂O₂ oxidation strategy. • Formation entails EGCG oxidation, Mannich cross-linking and H-bonding/π-π stacking. • Nanoparticles show excellent antioxidant activity and enhanced stability. • The greater the number of hydroxyl groups, the stronger the interaction force. This study developed a green, carrier-free EGCG-flavonoid nanoparticle assembly strategy driven by H₂O₂. This approach overcomes the drawbacks of traditional formaldehyde-induced methods, including solvent toxicity and poor biocompatibility. It further investigated how the number of flavonoid hydroxyl groups regulates the assembly process and properties of EGCG-flavonoid nanoparticles. The formation involves H₂O₂-mediated oxidation of EGCG hydroxyl groups to generate aldehyde and carboxyl groups, which then undergo covalent bonding with the amino group of glycine. Flavonoids are embedded into the EGCG–glycine network through noncovalent interactions, resulting in spherical nanoparticles (200–260 nm, PDI ≈ 0.3). Increasing hydroxyl groups on flavonoids enhanced their loading capacity and interaction with EGCG. Nanoparticles with polyhydroxylated flavonoids exhibited strong antioxidant activity (>85% DPPH•/ABTS• + scavenging), high storage stability (>70% retention after 60 days), and improved thermal stability. This work provides a theoretical foundation for green synthesis of polyphenol-flavonoid nanosystems in functional foods and targeted delivery. Download: Download high-res image (114KB) Download: Download full-size image