Propolis-Derived Carbon Dots: Structural, Optical, and Physicochemical Characterization Coupled with Antioxidant, Antimicrobial, Cytocompatibility, Anti-Aging, and Anti-Inflammatory Activities

Propolis, a resinous substance produced by stingless bees, is rich in polyphenols and exhibits diverse biological activities. However, its application in aqueous formulations is limited by poor water dispersibility, intense coloration, and compositional variability. This study converted propolis into carbon dots (P-CDs) using a one-step hydrothermal method and evaluated their physicochemical and biological properties. P-CDs are quasi-spherical nanoparticles (4.76 nm) with oxygen-bearing surface functionalities and a negative zeta potential (−17.34 mV). They showed antioxidant activity, with DPPH and ABTS IC50 values of 48.79 and 44.10 µg/mL, respectively, and metal-chelating activity with an IC50 of 49.70 µg/mL. Antibacterial activity was observed against Staphylococcus aureus and Pseudomonas aeruginosa (minimum bactericidal concentration, ≥7 mg/mL). HaCaT keratinocyte viability remained 94.01% at 1.25 mg/mL after 24 h, while significant cytotoxicity occurred at 2.5 and 5 mg/mL. In lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophages, P-CD at 1.25 mg/mL reduced nitric oxide from 70.96 µM to 29.76 µM in the LPS control. P-CD also reduced SA-β-gal-positive human dermal fibroblasts following H2O2-induced oxidative stress, providing preliminary anti-senescence evidence. Collectively, these findings highlight the potential of P-CD as nanomaterials for further investigation in cosmetic formulations, particularly for oxidative stress, inflammation, and skin aging.