Controllable Fabrication, Photoluminescence Mechanism, and Novel Application of Green–Yellow–Orange Fluorescent Carbon-Based Nanodots

Carbon-based nanodots (CBNs), as spick-and-span carbon nanomaterials, have been widely studied and applied in numerous fields. However, the controlled fabrication and photoluminescence (PL) mechanism remains an incompletely understood and widely debated topic. Herein, green, yellow, and orange light-emitting CBNs were fabricated by a one-step hydrothermal process with 4-aminobenzoic acid and 1,3-diaminobenzene, 1,2-diaminobenzene, and 1,4-diaminobenzene as precursors, respectively; the resulting CBNs were named gCBNs, yCBNs, and oCBNs, respectively. By adjusting the reaction conditions, including precursor, solvent, atmosphere, and dissolved solvent, the controllable fabrication of CBNs can be realized. We speculate that the PL of CBNs is dominated by the degrees of oxidation and amidation, which, together, cause the differences in the density of N-states and quantum size, ultimately manifesting as changes in three CBNs' fluorescence behaviors. Finally, the CBNs were used as agents to image four model cells, demonstrating that CBNs are potentially useful in biological labeling and multicolor bioimaging. More importantly, CBNs can be conjugated to the targeted micromolecule, DNA, RNA, and/or anticarcinogen groups to construct nanocomposite materials, which could be applied to identify target materials and/or execute the sustained release of drugs. We want to offer a guide for controllable fabrication of CBNs and further expanding the application depth and breadth in the biomedical field.