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

Area of Science:

• Materials Science
• Analytical Chemistry
• Nanotechnology

Background:

• Carbon quantum dots (CQDs) are recognized for their low cytotoxicity, biocompatibility, and fluorescence, leading to applications in sensors, bio-imaging, and drug delivery.
• Understanding CQDs' core-surface structure is crucial for optimizing their properties for diverse applications.
• Conventional characterization methods like electron microscopy and spectroscopy have limitations in fully resolving CQDs' detailed structure.

Purpose of the Study:

• To investigate the utility of laser desorption/ionization mass spectrometry (LDI-MS) for analyzing the core-surface structure of CQDs.
• To compare the structural analysis of CQDs synthesized from citric acid (CA-CQDs), diammonium citrate (AC-CQDs), and spermidine trihydrochloride (Spd-CQDs) using LDI-MS.
• To explore the potential of LDI-MS in characterizing heteroatom-doped CQDs and their surface functional groups.

Main Methods:

• Utilized laser desorption/ionization mass spectrometry (LDI-MS) to analyze three model CQDs: CA-CQDs, AC-CQDs, and Spd-CQDs.
• Examined the formation of anionic carbon cluster ions ([C_n]^-) and heteroatom-containing fragments.
• Investigated shot-dependent fragmentation behavior of AC-CQDs to understand surface versus core composition.

Main Results:

• CA-CQDs and AC-CQDs produced anionic carbon cluster ions ([C_n]^-, n = 4-9).
• AC-CQDs yielded fragments containing C, N, and O, identified as [CNO]^-, [CH₃N₂O₃]^-, and [CH₃N₂O₄]^-.
• Spd-CQDs, doped with nitrogen and chlorine, showed chlorine-associated ions instead of carbon clusters, indicating homogeneous doping and the presence of chlorine.
• LDI-MS revealed shot-dependent fragmentation for AC-CQDs, differentiating surface groups from the core structure.

Conclusions:

• LDI-MS is a viable technique for analyzing the core-surface structure of CQDs.
• The method is particularly effective for characterizing CQDs with heteroatom doping (N, O, Cl) and diverse surface functional groups.
• LDI-MS provides insights into the homogeneous distribution of dopants and the nature of surface modifications in CQDs.