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We report on the synthesis of manganese oxide doped CDs (MnO x -CDs) by a hydrothermal strategy using manganese (III) acetylacetonate (Mn(III) (C 5 H 7 O 2) 3) as the only raw materials. The MnO x -CDs exhibit water solubility, favorable biocompatibility, low cytotoxicity, and show blue fluorescence with excitation/emission maxima at 326/442 nm with a quantum yield of 11.3%, allowing efficient cellular imaging. The MnO x -CDs have a reversible temperature-sensitive fluorescent property in vitro within 10–60 °C, which can also be used as a sensitive thermometer in living cells. By a scratch assay, the MnO x -CDs can restrain the migration of HepG2 cancer cells, which make the MnO x -CDs be attractive candidates for liver cancer adjuvant treatment. Besides, the fluorescence of the MnO x -CDs is quenched in the presence of Fe3+ due to the formation of a nonfluorescent MnO x -CDs-Fe3+ complex between oxygen-containing groups on the surface of MnO x -CDs and Fe3+, and the quenched fluorescence of MnO x -CDs can be turn-on by dissociation of MnO x -CDs-Fe3+ complexes by biothiols including L -cysteine, homocysteine and glutathione. Therefore, the Fe3+ and biothiols can be sequentially detected with high reliability and accuracy via exploiting the on-off-on nanosensor at room temperature, respectively. Further application to detection biothiols in human serum indicated that the probe was practicality and feasibility in medical field. Image 1 • First synthesis of manganese oxide doped CDs (MnO x -CDs) using manganese (III) acetylacetonate as the single precursor. • The MnO x -CDs have reversible temperature-sensitive fluorescent behaviors in vitro and can be used as a thermometer in vivo. • The MnO x -CDs can restrain the migration of HepG2 cancer cells, which facilitate liver cancer adjuvant treatment. • Fe3+ and biothiols can be sequentially detected with high reliability and accuracy based on the MnO x -CDs. [ABSTRACT FROM AUTHOR]

Fluorescent nitrogen and sulfur co-doped carbon dots (NSCDs) were synthesized by a one-step pyrolysis strategy using casein as carbon, nitrogen and sulfur sources, and characterized by UV-vis spectrum, fluorescent spectrum, X-ray photoelectron spectroscopy (XPS) and FT-IR, etc. The synthesized NSCDs displayed a blue emission under ultraviolet illumination with a quantum yield of 31.8%, and a good aqueous solubility, photostability and biocompatibility. It was found that the fluorescence intensity of NSCDs could be selectively quenched by Hg2+, so NSCDs was used as an effective probe for the detection of Hg2+. The linear range and the limit of detection (LOD) of the fluorescent sensor based on NSCDs for the detection of Hg2+ were 0.01-0.25 μM and 6.5 nM, respectively. Spiked water samples were detected by the sensor with the recovery of 95.4-106.3% and relative standard deviation (RSD) of 3.6-8.6%. It was also observed that the quenched NSCDs-Hg2+ system could be restored by the addition of biothiols such as l-cysteine (Lcy), homocysteine (Hcy) and glutathione (GSH), thus NSCDs-Hg2+ system was employed as a fluorescent sensor for the detection of biothiols. The linear range and LOD of the NSCDs-Hg2+ system were 1-10 μM and 23.6 nM for Lcy, 0.2-2.5 μM and 12.3 nM for Hcy, and 0.1-2.0 μM and 16.8 nM for GSH, respectively. The NSCDs-Hg2+ system was applied for the detection of biothiols in serum samples with satisfied results. In addition, the study in vitro imaging HeLa cells revealed that the synthesized NSCDs could be used as effective fluorescent probes in cellular imaging without noticeable cytotoxicity. [ABSTRACT FROM AUTHOR]