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A bottom-up method, using monoethanolamine (MEA) as both a passivation agent and a solvent, has been developed for rapid and massive synthesis of nitrogen-doped carbon dots (N-C-dots) from citric acid under heating conditions. This method requires relative mild temperature (170 °C) without special equipment, and affords one-pot large-scale production (39.96 g) of high-quality N-C-dots (quantum yield 10 of 40.3%) in a few minutes (10 minutes). Significantly, an interesting formation process of N-C-dots, for the first time, has been monitored by transmission electron microscopy, ultraviolet-visible absorbance spectroscopy, photoluminescence spectroscopy, Fourier transformed infrared spectroscopy, and thermogravimetric analysis, and a corresponding formation mechanism including polymerization, aromatization, nucleation, and growth, is proposed. It is important that the MEA-based synthesis of N-C-15 dots can be extended to various precursors, such as glucose, ascorbic acid, cysteine, and glutathione, which show general university. Furthermore, the N-C-dots with strong fluorescence, excellent optical stability, and low cytotoxicity, are successfully applied as fluorescent probes for bioimaging.

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In this work we designed a MoS2 nanoplate-based nanoprobe for fluorescence imaging of intracellular ATP and photodynamic therapy (PDT) via ATP-mediated controllable release of (1)O2. The nanoprobe was prepared by simply assembling a chlorine e6 (Ce6) labelled ATP aptamer on MoS2 nanoplates, which have favorable biocompatibility, unusual surface-area-to-mass ratio, strong affinity to single-stranded DNA, and can quench the fluorescence of Ce6. After the nanoprobe was internalized into the cells and entered ATP-abundant lysosomes, its recognition to ATP led to the release of the single-stranded aptamer from MoS2 nanoplates and thus recovered the fluorescence of Ce6 at an excitation wavelength of 633 nm, which produced a highly sensitive and selective method for imaging of intracellular ATP. Meanwhile, the ATP-mediated release led to the generation of (1)O2 under 660 nm laser irradiation, which could induce tumor cell death with a lysosomal pathway. The controllable PDT provided a model approach for design of multifunctional theranostic nanoprobes. These results also promoted the development and application of MoS2 nanoplate-based platforms in biomedicine.