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Abstract

Nanotechnology has revolutionized material science and biomedicine by enabling the eco-friendly synthesis of carbon nanodots using plant-based biomolecules like Eriobotrya japonica seeds, offering a sustainable alternative to conventional toxic methods. In this study, nitrogen–sulfur co-doped carbon nanodots (N–S CDs) were successfully synthesized from Eriobotrya japonica seed extract through a green hydrothermal route at 180 °C without using any hazardous chemicals. The resulting N–S CDs displayed a uniform quasi-spherical morphology with an average size of 4.2 ± 1.1 nm and excellent aqueous stability (zeta potential = –21.4 mV). Optical characterization revealed bright blue fluorescence at 450 nm under 360 nm excitation, with a high quantum yield of 32.4%, nearly twice that of undoped CDs. The nanodots retained over 91.7% fluorescence intensity after 120 minutes of UV exposure, demonstrating exceptional photostability. Structural analyses (TEM, XRD, Raman, and XPS) confirmed a partially graphitic carbon framework with successful nitrogen and sulfur incorporation, enhancing electronic conjugation and surface passivation. The synthesized N–S CDs exhibited remarkable sensitivity and selectivity toward Fe³⁺ ions with a detection limit of 0.04 µM and recovery of 96.8–103.4% in tap water, indicating strong analytical potential. Cytotoxicity studies confirmed >92% cell viability at 500 µg mL⁻¹, showing excellent biocompatibility, while antioxidant assays demonstrated up to 90% DPPH radical scavenging, comparable to ascorbic acid. Overall, Eriobotrya japonica-based N–S CDs represent a low-cost, sustainable, and multifunctional nanomaterial with promising applications in biosensing, bioimaging, and environmental monitoring, highlighting the potential of green nanotechnology for future biomedical innovations. Keywords:co-doping; Eriobotrya japonica seed extract; Hydrothermal synthesis; Photoluminescence; Fe³⁺ ion sensing

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