Carbon quantum dots by submerged arc discharge in water: Synthesis, characterization, and mechanism of formation

Carbon quantum dots (CQDs) are novel nanostructures that have great potential as fluorescent markers due to their multi-fluorescence, down and up converted emission, resistance to photobleaching, and biocompatibility. Here, we report the synthesis of fluorescent CQDs by the submerged arc discharge in water method. We discuss the method's simplicity, natural phases' separation, and scalability. The produced CQDs size distribution was in the range of 1-5nm. High-resolution transmission electron microscopy images and their fast Fourier transformation allowed the analysis of the CQDs' internal structure. The absorption and fluorescence spectra of the as-produced CQDs were analyzed. The UV-Vis spectrum shows a single band with a maximum located at 356nm. The photoluminescence emission presents two consistent bands with maxima located in the ranges of 320-340nm (band A) and 400-410nm (band B). To these emission bands correspond two bands in the excitation spectra located at 275nm (band A) and 285nm (band B). The fluorescence quantum yield was assessed as similar to 16% using Rhodamine 6G as reference. The capabilities of the produced CQDs as fluorescent markers for in vitro studies were also evaluated by setting them in contact with a cell culture of L929 murine fibroblasts. Control and CQD-treated cell cultures were visualized under a fluorescence microscope. Finally, the mechanism of formation of these nanostructures by top-down methods is discussed, and a general model of formation is proposed.

Automated summary

This study reported the synthesis of fluorescent CQDs using the submerged arc discharge method, with a size distribution of 1-5nm. The internal structure and spectra of the produced CQDs were analyzed, showing dual-band fluorescence emission characteristics. The CQDs were evaluated as fluorescence markers for in vitro studies, demonstrating their potential biocompatibility and application in cell culture visualization.