Clove-assisted green synthesis of propolis-polysaccharide-functionalized Ag/SeO₂ nanocomposites: Structural...

Polysaccharides from propolis were isolated, characterized structurally, and used as a natural biopolymeric matrix and surface-modifying agent for the biosynthesis of Ag/SeO₂ nanocomposites through Syzygium aromaticum (clove) extract. ¹H and ¹³C NMR analyses revealed a structurally heterogeneous polysaccharide, characterized by multiple anomeric proton and carbon signals, indicating diverse sugar residues and glycosidic environments. Characterization by means of XRD, XPS, HR-TEM, SEM, and EDX demonstrated that crystalline Ag/SeO₂ nanoparticles had been synthesized and incorporated in the polysaccharide matrix with retention of the crystallinity. Functionalization of the polysaccharide modified the surface properties of the nanoparticle with an improvement in polydispersity index from 0.458 to 0.331, indicating a narrower hydrodynamic size distribution. The results obtained by UV-Vis indicated a red shift in the absorption peak from 468 to 516 nm, and a reduction in the apparent optical energy of transition from 3.50 to 2.09 eV after functionalization of the polysaccharide. The Ag/SeO₂/polysaccharide nanocomposite demonstrated wide-spectrum antimicrobial activity against B. subtilis, S. aureus, E. coli, and S. typhi with MIC values of 0.0063, 0.025, 0.050, and 0.050 mg mL^-1, respectively. The preparation showed excellent antioxidant properties (DPPH IC₅₀ = 0.009 ± 0.001 mg mL^-1) and cytotoxic activity toward the tested cancer cells (IC₅₀ = 12.68-15.20 μg/mL), but a lower cytotoxic effect against normal WI-38 cells (IC₅₀ = 337.4 μg/mL; HCT116/WI-38 selectivity index = 26.6). Particularly, the findings demonstrate that propolis-polysaccharide functionalization provides a promising green strategy for developing multifunctional Ag/SeO₂ biohybrid nanocomposites with antioxidant, antibacterial, and anticancer potential.