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Background: Superparamagnetic iron oxide nanoparticles (SPION) are widely used in various biomedical technologies, in particular, as carriers for drug delivery to the target. Since SPION-drug complexes are planned to be used in vivo, it is necessary to find out if competitive binding of nanoparticles with biologically important macromolecules (nucleic acids and proteins) is possible. Objectives: To investigate the possibility of complexation of iron oxide nanoparticles with DNA and serum albumin. Materials and methods: Bare and sodium citrate coated SPION with different surface charges, bovine serum albumin (BSA) and calf thymus DNA were used. The complexes of SPION and macromolecules were precipitated by an external magnetic field. The research was carried out by spectrophotometry in visible and ultraviolet ranges. Results: To study SPION interactions with DNA and BSA, the spectra of supernatants of the binary systems were compared with the spectra of the corresponding control macromolecules solutions. In the DNA-SPION systems, a decrease in the DNA absorption is observed only for bare nanoparticles. Our estimation shows that the maximum possible concentration ratio of bound DNA to SPION is about 2.5×10-4 mol/g. The addition of sodium citrate coated SPION to the DNA solution does not cause any spectral changes of the supernatant. The interaction of BSA with SPION, coated with sodium citrate, leads to a slight increase in supernatant absorption compared with the one of the control protein solution. It can be caused by the fact that the resulting complexes are not precipitated by a magnetic field. No difference between the spectrum of the supernatant of BSA-bare SPION system and the control protein solution was observed. Conclusions: The obtained spectrophotometric results demonstrate the formation of complexes between DNA and bare iron oxide nanoparticles as well as between BSA and the nanoparticles, coated with sodium citrate. The maximum concentration ratio of bound DNA and bare SPION was obtained for the investigated system. It is necessary to take into account when SPION are used as carriers for drug delivery.

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