HYDROTHERMAL SYNTHESIS AND MULTIFACETED CHARACTERIZATION OF FLUORESCENT NITROGEN-DOPED CARBON DOTS FOR PHARMACEUTICAL AND BIOMEDICAL APPLICATIONS

Carbon dots (CDs) have emerged as an important class of carbon-based nanomaterials owing to their excellent photoluminescence, biocompatibility, low toxicity, aqueous dispersibility, and versatile surface chemistry. The present study focused on the synthesis and physicochemical characterization of nitrogen-doped carbon dots prepared through a simple hydrothermal method using citric acid monohydrate as the carbon source and polyethyleneimine (PEI) as the nitrogen-doping agent. The synthesis was carried out at 200°C for 7 hours in a Teflon-lined autoclave, followed by purification through dialysis and membrane filtration to obtain highly purified carbon dot suspensions. The synthesized carbon dots were comprehensively characterized using Transmission Electron Microscopy (TEM), Dynamic Light Scattering (DLS), Zeta Potential Analysis, Fourier Transform Infrared Spectroscopy (FTIR), Fluorescence Spectroscopy, UV–Visible Spectroscopy, and Thermogravimetric Analysis (TGA). TEM analysis revealed uniformly distributed quasi-spherical nanoparticles with an average particle size of 4.8 ± 1.2 nm. DLS measurements indicated a hydrodynamic diameter of 7.2 ± 0.8 nm and a polydispersity index of 0.18 ± 0.03, confirming a monodisperse system. The positive zeta potential value of +32.5 ± 2.1 mV demonstrated excellent colloidal stability. FTIR studies confirmed the presence of hydroxyl, carboxyl, and amine functional groups on the carbon dot surface. Fluorescence studies showed strong excitation-dependent emission with a maximum emission wavelength at 450 nm and a quantum yield of 42.3 ± 3.1%. UV–Visible analysis demonstrated characteristic absorption at 340 nm, while TGA confirmed good thermal stability. The results indicate that the synthesized nitrogen-doped carbon dots possess favorable physicochemical and optical properties suitable for pharmaceutical, bioimaging, biosensing, drug delivery, and diagnostic applications.