Synthesis and characterization of carbon dots derived from spinach, green tea, and yerba mate for photodynamic therapy

Abstract

Photodynamic Therapy is a directed and minimally invasive treatment modality that requires efficient and biocompatible photosensitizers. In this work, we develop a green nanomedicine platform by synthesizing Carbon Dots (CDs) using a solvothermal method from extracts of three commercially available and carbon-rich sources: spinach, green tea, and yerba mate. This approach leverages the sustainability of the starting materials and highlights the versatility of carbon-based hybrid systems while evaluating their theranostic functionality and capability as Photodynamic Therapy (PDT) therapeutic effectors. The synthesized CDs were rigorously characterized by Dynamic Light Scattering, Zeta Potential, High-Resolution Transmission Electron Microscopy, Fourier-Transform Infrared Spectroscopy, 1H-Nuclear Magnetic Resonance Spectroscopy, Raman Spectroscopy, and Thermogravimetric Analysis. We found CDs populations with surface compositions rich in carboxyl, hydroxyl, and nitrogen-containing pyrrolic and pyridinic groups that contribute to their potential as nanoeffectors. We comprehensively evaluated the photogeneration of reactive oxygen species (ROS) through oxygen consumption kinetics and hydrogen peroxide quantification, identifying a clear predominance of Type I photosensitization mechanisms. A significant singlet oxygen quantum yield of nearly 29% was obtained for spinach-derived CDs when irradiating at 355 nm, supported by their characteristic chlorophyll-like absorption at 675 nm. Additionally, antioxidant capacity assays demonstrated that green tea and yerba mate derivatives retain high antioxidant properties, contrasting with the superior photosensitizing performance of spinach. Finally, light-exposed viability assays on HaCaT and 3T3 cell lines demonstrated significant photodynamic activity and established that spinach-derived particles are the most biocompatible, maintaining cell viability at 100 µg per ml. These results demonstrate the potential of these plant-derived CDs for targeted and non-invasive therapy applications against cancer cells or parasites. This study provides a sustainable and biocompatible approach for delivering photodynamic therapy agents. By balancing radiative and non-radiative electronic pathways, these plant-derived CDs offer a promising alternative for future nanomedicine platforms.