Carbon quantum dots from silymarin extraction for multi-fluorescent sensors, photocatalysis, and anticancer activity applications

In this work, water-soluble fluorescent carbon quantum dots were prepared by a one-stage hydrothermal method via a green synthesis route using silymarin extract from milk thistle seeds as a single precursor. Various experimental techniques were used to characterize the synthesized silymarin-based carbon quantum dots (SM-CQDs), to confirm their structure and investigate their potential applications in fluorescent sensors, photocatalysis and anticancer activity. The prepared SM-CQDs exhibited amorphous graphitic structure with a spherical shape and an average particle size of 4.6 ± 0.7 nm, as indicated by XRD, Raman, and TEM measurements. The FTIR results indicate the presence of diverse functionalities on the surface of the SM-CQDs, which were further confirmed by XPS analysis. Fluorescence characterization of the prepared SM-CQDs revealed blue emission with a fluorescence quantum yield (QY) value of 4.9%. Furthermore, the prepared dots exhibit temperature-sensitive photoluminescence (PL) behavior, which has been interestingly used to design economical, green, and highly sensitive fluorescent probes for the detection of Fe³⁺ ions and H₂O₂ with a detection limit (DL) of 0.071 and 0.159 µM, respectively. A nano thermosensor has been demonstrated to have a wide temperature range of 10-90 °C and a good recovery, exhibiting a thermal sensitivity of 0.8% °C^{- 1} based on its temperature-sensitive behavior. Moreover, we demonstrated that the as-prepared SM-CQDs can serve as excellent photocatalysts for the degradation of methylene blue (MB) dye under direct visible light irradiation with a degradation efficiency of about 45% within 105 min. The obtained SM-CQDs have a zeta potential of -22.24 mV, indicating excellent stability in water. Finally the SM-CQDs exhibit anticancer activity showing cytotoxicity to Caco2 cells with IC₅₀ = 285.2 ± 11.9 µg/mL. These features of SM-CQDs indicate their potential in applications such as sensing, cell imaging, and optoelectronics.