ИСТИНА

Surface-functionalized carbon nanoparticles of different carbon hybridizations exhibit fluorescence that varies in both intensity and spectrum shape not only between different types of carbon nanoparticles but even in the nanoparticles of the same type and synthesis. Of all carbon nanoparticles, nanodiamonds (NDs) are best suited for the role of the base of biomedical conjugates, due to the combination of their fluorescence properties with mechanical stability, non-toxicity, cheap production and easily modifiable surface. However, the exact origin of the surface fluorescence of nanodiamonds is highly debatable. It was proven that NDs’ surface fluorescence is dependent on the surface functionalization. However, there are results of studies, according to which the diversity of the fluorescence intensity in the different NDs’ batches with same surface functionalization is observed. Very bright fluorescence of NDs with a large amount of sp2-hybridized carbon on their surfaces (so called carbon dots (CDs)-decorated nanodiamonds) as well as the fact that such type of carbon almost always present on the surfaces of NDs allow the hypothesis that the source of surface fluorescence of NDs is not just NDs surface’ functionalization but the functionalized non-diamond carbon phase on their surface. To verify this hypothesis, we prepared different carbon nanoparticles with different sp2/sp3 carbon hybridization ratio – CDs, NDs, CDs-decorated NDs, and produced various purifications of these samples. The analysis of their surfaces by Raman and IR adsorption spectroscopies as well as the analysis of their fluorescence in aqueous suspensions confirmed that the increase in the amount of non-diamond carbon on the surfaces of NDs corresponds to the increase of NDs’ surface fluorescence. This study has been performed at the expense of Russian Science Foundation (grant number 17-12-01481) (A.L., T.D. – data acquisition, data analysis) and of Russian Foundation for Basic Research (grant number 18-32-00779 mol_a) (A.V. – data processing).