Facile synthesis of ultrahigh fluorescence N,S-self-doped carbon nanodots and their multiple applications for H2S sensing, bioimaging in live cells and zebrafish, and anti-counterfeiting

Green-emissive N,S-self-doped carbon nanodots (N,S-self-CNDs) with an ultrahigh fluorescence (FL) quantum yield (QY) of 60% were synthesized using methyl blue as the only source by a facile hydrothermal approach. The -NH- and -SOx- groups of methyl blue were simultaneously used as nitrogen and sulfur co-dopants to dope into CNDs. The prepared N,S-self-CNDs have an extremely large Stokes shift (similar to 130 nm) and excitation-independent fluorescence, and are demonstrated to have multiple applications for H2S sensing, bioimaging and anti-counterfeiting. Taking advantage of their excellent optical properties, N,S-self-CNDs could act as a label-free nanoprobe for the detection of H2S. The FL of N,S-self-CNDs could be significantly quenched by H2S because of dynamic quenching, along with excellent selectivity toward H2S from 0.5-15 mu M with a detection limit of 46.8 nM. They were successfully employed for the analysis of H2S content in actual samples. Additionally, the nanoprobe was extended to bioimaging in both living PC12 cells and zebrafish, and monitoring H2S in live cells. Furthermore, N,S-self-CNDs have been used to prepare highly fluorescent polymer films by incorporating N,S-self-CNDs in polyvinyl alcohol (PVA). The as-prepared N,S-self-CNDs/PVA films show a prominent dual-mode FL property, implying that they are potential nanomaterials in the anti-counterfeiting field.