Eco-friendly synthesis of polychromatic carbon dots as an efficient fluorescent probe for multicolor cell imaging

Polychromatic carbon dots (PCDs) were synthesized using Cornus officinalis fruits as natural sources of carbon and aqueous ammonia as sources of nitrogen, as well as a pH adjuster. Hydrothermally synthesized PCDs were systematically investigated by various analytical tools to determine their structural and optical properties. The resulting PCDs exhibited a modest degree of graphitization, which is demonstrated by XRD and Raman spectroscopy techniques. We employed FESEM with EDX, HRTEM, FTIR, and XPS techniques to characterize the structural morphology and elemental composition of the eco-friendly synthesized PCDs. These results reveal that the synthesized PCDs were nearly spherical in shape, with an average diameter of 3.5 nm, and were rich in surface functional moieties, exhibiting satisfactory dispersibility. The obtained PCDs exhibited polychromatic emission as the excitation wavelength varied from lower to higher values. The fluorescence wavelength of maximum excitation is ~365 nm, and the wavelength of maximum emission is ~441 nm, complemented by an impressive quantum yield of 21 %. PCDs exhibit extraordinary strength, retaining their fluorescence characteristics under different ecological (environmental) conditions, together with exposure to UV light and prolonged storage. Additionally, the synthesized PCDs exhibited excellent biocompatibility, maintaining over 95 % cell viability in RAW 264.7 (macrophage) and SVEC4-10 (endothelial) cells, even at high concentrations. Fluorescence imaging confirmed efficient cellular uptake and strong multicolor emission, supporting their potential as safe and effective probes for live-cell imaging. Moreover, polychromatic fluorescent, biocompatible PCDs can be used as fluorophores for efficient multicolor cell imaging under varying excitation light conditions. They can be further developed as cellular targeting probes for drug delivery.