BİYOMEDİKAL UYGULAMALAR İÇİN ÇOK-İŞLEVLİ DEMİR OKSİT-GADOLİNYUM BORAT KOMPOZİT NANOPLATFORMLARIN GELİŞTİRİLMESİ

Abstract

In the first part of this PhD study, Fe3O4-GdBO3 nanocomposites were prepared via a hydrothermal route using simple and biocompatible inorganic chemicals. Borax (BX) and boric acid (BA) were used as the boron precursors; plain and PEGylated magnetite were used as the source precursors for Fe3O4 and Gd(NO3)3.6H2O as the source of Gd(III). The experimental conditions were systematically varied to link the properties of the final composites with the methodology. The products obtained by depositing gadolinium borate over magnetite were analyzed by powder X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDS), Transmission Electron Microscopy (TEM), Thermogravimetric Analysis (TGA) and magnetization measurements. The XRD patterns of the nanocomposites showed a bi-phase pattern with reflections matching with those of Fe3O4 and GdBO3. The results showed that the experimental parameters e.g. using either BX or BA, uncoated- or polyethylene glycol (PEG) coated-Fe3O4 as the precursors, changing reactant concentrations and the pH, all influence the structure of the borate coating, coverage type, size and morphology of the nanocomposites and saturation magnetization values to some extent. The coating was yielded in the form of vaterite-type orthoborate [Gd3(B3O9)] with BA and iclinic-GdBO3 with BX, both having the Gd/B ratio of 1/1. PEGylated Fe3O4 appeared to be a preferable support for coating with the borate layer to obtain smaller size and uniform composite structures. The composites prepared with BX displayed typical TEM images where a bunch of spherical 20-40 nm size magnetite nanoparticles were surrounded with a gadolinium borate cloud while nearly cubic, pseudo core-shell nanocomposite particles of 100-150 nm size were obtained with BA at pH 9. The prepared Fe3O4-GdBO3 nanocomposites all displayed soft ferromagnetic properties that might be relevant for applications in biotechnology and medicine. Hydrothermal synthesis offered the advantages of simplicity, efficiency and allowed for the preparation of controlled nanocomposite structures by carefully tuning the experimental conditions. The second part of this study involves the bioconjugation of GdBO3-Fe3O4 nanocomposites. The bioconjugation processes were performed with citric acid (CA) and floresceinisothiocyanate-doped silica (FITC-SiO2), followed by the treatment with folic acid (FA). The successful functionalization of the nanocomposite particles was demonstrated by qualitative and quantitative (X-Ray Photoelectron Spectroscopy/XPS, SEM, TEM, Inductively Coupled Plasma-Optical Emission Spectroscopy/ICP-OES) analytical data. All bioconjugates displayed soft ferromagnetic properties and zeta potential values that are appropriate for biological applications. The 10B and 157Gd contents were ca. 1014 atom/g making them promising agents for Boron Neutron Capture Therapy (BNCT), Gadolinium Neutron Capture Therapy (GdNCT) and the combined GdBNCT. The Gd/Fe molar ratios (0.27-0.63) provided capability for T1- or dual (T1+T2) magnetic resonance imaging (MRI). Finally, to examine the biocompatibility and possible applicability of these particles for NCT and MRI imaging, in vitro tests were performed. Flow cytometry results with MIA-Pa-CA- 2 cells demonstrated that there is a dose-dependent increase in cellular uptake of all nanocomposites. The dot-plot analysis of MIA-PaCA-2 cells showed that all nanocomposite particles penetrated into MIA-Pa-CA-2 cells after incubation at 10 μg/mL. The cells began to show fluorescence intensity after incubated with 1 μg/mL concentration and the green dots due to FITC were clearly observed at the 10 μg/mL incubation. Overall, a 10g of FAconjugated nanocomposite containing 1015 atoms of 10B and 157Gd was found effective for 0.125x106 cancer cells making 1010 atoms per cell. The boron and gadolinium contents exceed the required concentrations to sustain a neutron capture reaction for BNCT and GdNCT by tenfold also providing an appropriate Gd/10B ratio for GdBNCT. The bioconjugated nanoplatforms of GdBO3-Fe3O4 composites, introduced herein, proved to have potential features of next generation agents for theranostic applications like “magnetically targeted therapy, fluorescence imaging, magnetic resonance imaging/diagnosis and neutron capture therapy”.