Salvia hydrangea-derived carbon quantum dots via sustainable synthesis: Unraveling physicochemical properties, biocompatibility, and biological efficacy

Carbon quantum dots (CQDs) are biocompatible, water-soluble nanoparticles with tunable photoluminescence properties. Their green synthesis from medicinal plants offers an eco-friendly and cost-effective approach while enabling surface functionalization with plant-derived bioactive compounds. Salvia hydrangea and its cell cultures have recently been reported as rich sources of rosmarinic acid. In this study, plant aerial parts and cell cultures (as renewable precursors) were employed for the first time to synthesize CQDs via a one-step hydrothermal method. The nanoparticles were characterized by FTIR, EDX, XRD, TEM, Zeta potential, and UV–Vis spectroscopy, and their antimicrobial, antioxidant, and cytotoxic activities were evaluated. The average size of CQDs synthesized from plant aerial parts (pCQDs) and cell cultures (cCQDs) were 3.7 ± 2.3 nm and 2.9 ± 1.9 nm, respectively, showing distinct particle size distributions. With abundant N-containing and O-rich groups on their surfaces, the CQDs exhibited good solubility in water. Moreover, zeta potential values for pCQDs (+15.7 mV) and cCQDs (–54.9 mV) indicated a significant difference in surface charge. Despite the higher colloidal stability and superior optical properties of cCQDs (QY = 8.3%), pCQDs demonstrated stronger antibacterial activity, particularly against Staphylococcus aureus . pCQDs also showed greater free radical scavenging activity compared with Trolox. Both types of CQDs exhibited low cytotoxicity toward fibroblast cells and did not cause significant hemolytic effects in human red blood cells. These findings highlight the influence of different plant tissues on the physicochemical and biological properties of CQDs and suggest their diverse application potential. • First green synthesis of CQDs from Salvia hydrangea aerial parts (pCQDs) and cell cultures (cCQDs). • pCQDs showed superior antibacterial activity (30 mm zone vs S. aureus , MIC=0.0625 mg/mL). • cCQDs exhibited higher quantum yield (8.3%) and excellent colloidal stability (-54.9 mV). • Both CQDs demonstrated remarkable biocompatibility (<10% hemolysis at 1000 μg/mL). • pCQDs displayed strong antioxidant capacity (86% scavenging), outperforming Trolox.