ИСТИНА

Compared with organic dyes, semiconductor nanocrystals, known as quantum dots (QDs), offer several unique advantages, such as size- and composition-tunable emission from visible to infrared wavelengths, large absorption coefficients across a wide spectral range, and high levels of brightness and photostability1. QDs based on CdSe are the most used for cell and intracellular processes imaging, due to the established synthesis protocol. However, it is known that Cd is a cytotoxic element because it can attach to various intracellular proteins through sulfhydryl groups, causing disturbances in intracellular processes. It is important to note that during the application of QDs as intracellular labels, they fall into acidic compartments of cells, which can lead to the destruction of QDs shells with the subsequent release of the core ions into the cytoplasm. One of the solutions to solve the problem of cytotoxicity is the application of "cadmium-free" QDs, for example, based on InP. It was found that complexes based on InP-PEG and CPP proteins are identified in cells without causing toxic effects up to a QDs concentration 1 μM2. Since there are only a small number of works on the application of InP QDs in biology, the purpose of this study was to assess the possibilities of using InP QDs in biological imaging. In this paper we compared InP QDs with widely used CdSe QDs. The optical properties of commercial QDs samples based on CdSe/ZnS and InP/ZnS in aqueous solutions and in cells were compared. QDs CdSe/ZnS were coated with a PEG shell, InP/ZnS QDs were coated with a PEG shell with -NH2 or -COOH reactive groups. Cellular models were the cells of human epithelial carcinoma HeLa and macrophage-like cells of line J774. Analysis of spectral-luminescent properties showed that the quantum yield in water for CdSe/ZnS QDs is 31%, and for both types of InP/ZnS QDs is about 5%. The extinction coefficient is 5.5 ∙ 105 M-1 cm-1 and 3.3 ∙ 105 M-1 cm-1, respectively for CdSe QDs and InP QDs. Next, the effect of changing the pH of the environment was evaluated. Analysis of the spectra shows that when the pH is changed, the position of the maximum of the luminescence of all kinds of QDs is not shifted. According to the data of spectral-luminescence analysis, the luminescence quantum yield of CdSe QDs at pH 7.4 and 4.0 was 31% and 8%, respectively. On the other hand the luminescence quantum yield of both types of InP QDs at a neutral pH was 4.5% for QD-PEG-NH2 and 5.6% for QD-PEG-COOH, in the case of an acidic pH the quantum yield drops to 2.9% and 4.4%, respectively. The interaction of InP QDs with cultured cells was studied by confocal microscopy and flow cytometry. During the studying of the cell uptake of all three types of QDs, it was established that the fluorescence spectra of QDs do not change in comparison with those in solution. Analysis of luminescence properties of QDs showed the possibility of visualization of cells using InP QDs. Then this study was focuses on the effect of reactive groups on the efficiency of cellular uptake. Fluorescence shows the predominant uptake of InP QD-PEG-COOH in comparison with QD-PEG-NH2. However, since it is necessary to take into account the possible decay of QDs inside the intracellular compartments, further studies are needed to accurately assess the cellular uptake efficiency. Evaluation of cytotoxicity was performed on HeLa cells by cytometric analysis using propidium iodide (PI). It was shown that after 24 hours after the addition of QDs to the nutrient medium, the viability of the cells was more than 90% (less than 10% of the cells were stained with PI). It is demonstrated that InP QDs are an effective tool for biological research.