Nitrogen and sulphur doped carbon dot: An excellent biocompatible candidate for in-vitro cancer cell imaging and beyond

Carbon dots (CDs) are an exquisite class of carbon allotrope that is already well nourished for their good biocompatibility, water-solubility, excellent photostability, and magnificent photoluminescence property. Doping strategy with heteroatoms is an efficacious way to modify the physicochemical and optical properties, making the carbon dots an exceedingly potential candidate. This work reports the fabrication and cancer cell imaging application of photoluminescent heteroatom-doped carbon dots by use of cysteine and urea as carbon, nitrogen, and sulphur sources through a straightforward and highly productive hydrothermal procedure. The fabricated luminescent carbon dots are spherical in shape, with an average diameter of 3.5 nm. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) characterization revealed key facts about the surface functional groups and chemical compositions of carbon dots. The excitation-dependent photoluminescence (PL) peak appeared at around 445 nm against the excited wavelength of 350 nm. Moreover, under the provided experimental conditions, all the carbon dots are non-toxic and safe. The cytotoxicity and the safety profiles of the carbon dots were found to be in the bearable range under normal in-vitro experimental circumstances. Cellular uptake was observed by the green fluorescence of carbon dots inside cells. Likewise, the carbon dots did not alter the cell viability of the normal glial cell line. Again, when treated with the carbon dots, there was no notable increase of apoptotic cells in the G2/M phase of cell cycle analysis that confirmed the imaging-trackable ability of the carbon dots.