Cytocompatible and photoluminescent nitrogen-doped carbon dots derived from grape seed flour for enhanced fluorescence bioimaging in breast cancer cells

Official URL: https://dx.doi.org/10.1039/d6ra02360f

Carbon dots (CDs) have attracted significant attention as fluorescent nanomaterials due to their tunable optical properties, low toxicity, and versatile surface chemistry. However, the development of sustainable and cost-effective synthesis routes remains an ongoing challenge. In this study, nitrogen-doped carbon dots (N-CDs) were synthesized via a simple and green solid-state method using grape seed flour as a renewable carbon source, together with citric acid and urea. The obtained N-CDs exhibited bright green photoluminescence with an emission maximum at 539 nm, a high quantum yield of 62.6%, and a large Stokes shift (∼89 nm). Structural and surface analyses (FTIR, XRD, STEM, and XPS) confirmed the formation of well-dispersed, nearly spherical nanoparticles (9–18 nm) with abundant oxygen- and nitrogen-containing functional groups. These surface functionalities contributed to excellent aqueous dispersibility and colloidal stability. In vitro cytotoxicity studies demonstrated that the N-CDs maintained high cell viability (>70%) in MCF-7 and SK-BR-3 cells up to 400 µg mL−1, indicating good biocompatibility. Confocal microscopy revealed efficient cellular uptake, which was further enhanced after folic acid conjugation, suggesting receptor-mediated internalization. Overall, this work presents a sustainable approach for producing biocompatible, highly luminescent carbon dots from biomass resources and highlights their potential as fluorescent probes for bioimaging applications.