Vol.48,No.10,2021
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Cover Story：The nucleolus is an important subnuclear structure in the cell, which plays an important role in the
evolution of malignancies and the diagnosis of cancer. Although the nucleolus is critical, so far, there are really
few fluorescent probes for the nucleolus. In this paper, salicylic acid and 1,8-diaminonaphthalene were used as
carbon and nitrogen sources, and a novel fluorescent carbon nanoparticles (FCNs) were synthesized by
microwave digestion system. Its physical, chemical and optical properties of FCNs were characterized and
analyzed by using transmission electron microscope (TEM), dynamic light scattering instrument (DLS), Fourier
infrared spectrometer, ultraviolet spectrophotometer, fluorescence spectrometer, etc. The experimental results
demonstrated that the synthesized carbon nanoparticles were uniform in size and rich with amino groups on
surface. Its best excitation wavelength was 348 nm, the corresponding maximum emission peak was 432 nm. Its
fluorescence quantum yield was 17.8% and fluorescence lifetime was 1.13 ns. Moreover, the photostability and
cytotoxicity of FCNs were investigated with illumination and MTT assays. Our results suggest that FCNs exhibit
to be a really photostable and low toxic probe. To confirm the potential application of this fluorescence FCNs in
bioimaging, the FCNs were designed to stain human cervical cancer HeLa cells. After incubation, we found that
FCNs enable the function of selectively staining the nucleolus of living cells due to its positive chargeability. Its
cellular uptake mechanism and intracellular distribution in HeLa cells were explored further by using confocal
laser scanning microscopy and TEM. It was interesting to observe that more FCNs entered the cell, and lighted the
nucleolus more obviously with the extension of the co-incubation time. In addition, after investigating the cells’
uptake path of FCNs, we found that FCNs were endocytosed via caveolae-mediated pathway rather than clathrin
mediated pathways or macropinocytosis. Our study provided a potential probe for nucleolus and this finding is of
great significance for the development of functional nanomaterials targeting subcellular organelles.
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