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

Abstract

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.