Strategy to Synthesize Tunable Multiemission Carbon Dots and Their Multicolor Visualization Application

Studies on multiemission fluorescent carbon dots (CDs) excited at one wavelength are extremely promising because of their label-free property, facile synthesis, multicolor visualization, and prevention of background interference. In this study, a novel template strategy to develop multiemission carbon dots (M-CDs) using fluorescent precursors has emerged. We attempted to elucidate the relationship between precursor substances and luminescence origins. The M-CDs prepared by calcein demonstrate three emissions, ultraviolet (UV), blue, and green, which are attributed to the solvent, surface defect, and precursor aromatic ring luminophores, respectively. Also, through a regular adjustment of the amount of NaOH or the solvothermal synthesis time, the expected optical requirements were successfully met by the M-CDs, which is a better capability than that of previously reported M-CDs. In addition, a multicolor sensor designed with M-CDs and rhodamine B (RhB) has been successfully applied in cell imaging. When exposed to different pH media, the fluorescence (FL) emission shows a linear relationship with the pH value, displaying a profuse color evolution from dark blue to light blue, cyan, green, yellow, and finally, orange.

Automated summary

Research on multiemission fluorescent carbon dots excited at one wavelength has shown great promise due to their label-free property, easy synthesis, multicolor visualization, and ability to prevent background interference. A new template strategy using fluorescent precursors has been developed for the synthesis of multiemission carbon dots (M-CDs), which show three different emissions attributed to solvent, surface defect, and precursor luminophores. The M-CDs can meet optical requirements by adjusting the amount of NaOH or solvothermal synthesis time, demonstrating better capabilities than previously reported M-CDs. Additionally, a multicolor sensor using M-CDs and rhodamine B has been successfully utilized for cell imaging, showing a color evolution from dark blue to orange based on the pH value of the medium.