ИСТИНА

Nowadays, nanodiamonds (NDs) are widely used in the different areas of science and industry. In biomedicine, they can be used as fluorescent biomarkers, drug carriers, adsorbents, basses of various bioconjugates. Their fluorescence is one of the properties that define the effectiveness of NDs in biomedical applications. Florescence of the undoped nanodiamonds significantly depends on their surface state, in particular on its purification from the sp2-hybridized carbons formed during synthesis. However, while most studies of the methods of purification of NDs from the graphitized carbon focuses on the degree of purification and colloidal stability of purified nanodiamonds, the influence of purification on the fluorescent properties of NDs is poorly reported, although it is especially important for verification of hypotheses on surface mechanisms of ND fluorescence. In this work the changes in fluorescence of NDs in result of various surface purification treatments are studied. Two types of NDs, synthesized by the laser ablation and milled CVD diamonds, were treated with four methods of surface purification: annealing, ozonation, treatment by perchloric acid, treatment by a mixture of nitric and sulfuric acids. To study the influence of the purification method on the surface and fluorescent properties of NDs the methods of fluorescent, Raman and FTIR spectroscopies were used. It was found that fluorescence of both powders and water suspensions of NDs is significantly intensifies upon the purification in the perchloric acid compared to other methods. Additionally, the intensity of the fluorescence depends on the purification duration. On the obtained results recommendations on the purification of nanodiamonds for their use in specific areas have been developed, a hypothesis on the mechanisms of the observed changes in fluorescence has been proposed. The work was founded by Russian Science Foundation (project №17-12-01481), Russian Foundation for Basic Research (grant №18-32-00779), Basis Foundation.