Pulse laser-induced fragmentation of carbon quantum dots: a structural analysis

摘要: Carbon quantum dots (CQDs) have attracted enormous interest in recent years owing to their low cytotoxicity, excellent biocompatibility and strong fluorescence. They been successfully employed sensor, bio-imaging, drug carrier applications. A complete understanding of core–surface structure is essential for tuning physical chemical properties various Conventional characterizations CQDs are conducted with electron microscopy or spectroscopy, such as transmission microscopy, X-ray photoelectron Fourier transform infrared spectroscopy Raman spectroscopy. However, these techniques cannot fully resolve the CQDs. In this study, we attempt analyze structures by laser desorption/ionization mass spectrometry (LDI-MS) using three model synthesized from citric acid (CA-CQDs), diammonium citrate (AC-CQDs) spermidine trihydrochloride (Spd-CQDs). Both CA-CQDs AC-CQDs produced anionic carbon cluster ions ([Cn]−, n = 4–9) during process. Additionally, fragments containing C, N, O that appeared at m/z values 41.999, 91.015, 107.008, which were identified 15N isotopes [CNO]−, [CH3N2O3]−, [CH3N2O4]−, respectively. By contrast, subjecting Spd-CQDs same analysis did not yield ([Cn]−); instead, chlorine-associated a unique isotopic pattern observed, strongly implying contain chlorine. The lack ion formation nitrogen- chlorine-doped indicates nitrogen chlorine abundantly homogenously doped We also found shot-dependent fragmentation behavior produces oxygen-containing ([Cn]−) initial surface, gradual destruction nanocrystalline core after additional shots. These results suggest LDI-MS can be used tool analyzing CQDs, particularly when it contains heteroatom surface functional groups nitrogen, oxygen halogens.