Blue luminescent amorphous carbon nanoparticles synthesized by microplasma processing of folic acid

Environmentally friendly synthesis of carbon nanoprticles (C-NPs) from folic acid (FA) is realized with the assistance of microplasma. TEM shows that the synthesized FA C-NPs are amorphous and of diameter around 47 nm. The produced FA C-NPs exhibit an excitation independent emission around 445 nm with the fluorescence quantum yield 13% at excitation wavelength of 370 nm. X-ray photoelectron spectroscopy (XPS) shows the FA C-NPs are composed of carbon (64.15%), nitrogen (6.04%), and oxygen (29.81%). Raman spectroscopy shows that the intensity ratio between the sp³ and sp² hybridizations of Carbon is 0.35. UV-Vis absorption, Fourier Transform Infrared Spectroscopy (FTIR), and Nuclear Magnetic Resonance (NMR) spectra provide a deep insight into the fluorescence of FA C-NPs. With plasma processing of FA, carbon atoms are involved in sp² hybridization and amine (NH₂), NH and COOH groups are converted into ROOCNHCOOR group. As a consequence, the electron donating ability of aromatic ring is enhanced, which plays an important role in the fluorescence of FA C-NPs. Finally, the promising application of FA C-NPs in bioimaging is also demonstrated by fluorescence labeling of MCF-7 cancer cells.