Plant-derived N, S-Co-doped carbon dots enable reductive engineering of Ag–Fe bimetallic nanocomposites with broad-spectrum bioactivity

N, S-co-doped carbon dots (N, S-CDs) were synthesized from Calotropis gigantea leaves via a green hydrothermal method and used as dual-function reducing and stabilizing agents for the in situ fabrication of Ag–Fe bimetallic nanocomposites (Ag–Fe@N, S-CDs). Thus, this study presents a sustainable nanoplatform that combines heteroatom-doped carbon dots with bimetallic systems without the use of external chemical reducing agents. The N, S-CDs exhibited effective antioxidant activity with IC₅₀ values of 39.17 µg mL⁻¹ (DPPH), 42.26 µg mL⁻¹ (FRAP), and 15.30 µg mL⁻¹ (ABTS). In contrast, Ag–Fe@N, S-CDs showed improved anti-inflammatory activity with albumin denaturation inhibition of 59.48–77.38% and proteinase inhibition up to 93.63%, along with enhanced cytotoxicity against MCF-7 cells (IC₅₀ = 90.15 µg mL⁻¹). Both nanomaterials exhibited effective antimicrobial activity with minimum inhibitory concentration (MIC) values ranging from 31.25 to 250 µg mL⁻¹ against tested pathogens. These results indicate that N, S-CDs are more effective as antioxidant agents due to their rich surface functional groups, whereas Ag–Fe@N, S-CDs show superior anti-inflammatory and cytotoxic performance due to synergistic interactions between the metal components and the carbon framework. Therefore, the present study revealed a green and efficient strategy for designing multifunctional nanocomposites with potential biomedical applications.