Green preparation of nitrogen-doped carbon dots derived from silkworm chrysalis for cell imaging

Carbon dots (CDs) with a high quantum yield have been synthesized by a facile and green one-pot approach under microwaves with silkworm chrysalis (SC) as the natural carbon source, without using any other chemicals/reagents. The morphology and optical properties of the resultant CDs are characterized by TEM, XRD, FT-IR, XPS, UV-vis and photoluminescence (PL). The SC-CDs have an average size of 19 nm, and contain C, O and N with relative contents of ca. 71.32%, 22.96% and 5.72%, respectively. A significant emission at 420 nm at an excitation wavelength of 350 nm is recorded, resulting in a quantum yield of 46% with quinine sulfate (quantum yield 54%) as a reference. In addition to excellent solubility and stability in aqueous medium, the SC-CDs exhibit excitation-dependent photoluminescence with a large Stokes shift of 70 nm. It is further demonstrated that the SC-CDs exhibit a low cytotoxicity at a higher concentration of 15 mg mL^-1 and they are able to display bright blue, green and red colors under an inverted fluorescence microscope during cell imaging experiments, showing their vast potential in bioimaging.