Küçük süperparamanyetik demir oksit nanoparçacıkların fototermal ısınma potansiyellerinin incelenmesi

Superparamagnetic iron oxide nanoparticles (SPIONs) are the most studied nanoparticles for biomedical applications due to its FDA approved formulations and superbiocompatibility. They are clinically used as a contrast agent in magnetic resonance imaging (MRI). They have also provided successful results in magnetic dragging and magnetic hyperthermia owing to their strong response to external magnetic field. SPIONs may be prepared with different surface coatings and in various sizes and hence, may be utilized for gene and drug delivery as well as for targeted delivery to diseased sites or cells for specific medical imaging and therapy. SPIONs are also utilized in non-medical fields such as cell sorting, magnetic damping or magnetic refrigeration. In addition to these application areas, there has been a various number of reports showing that SPIONs may be effective sensitizers in photothermal therapy (PTT). Such potential of SPIONs is very exciting for people working with SPIONs in the field of biotechnology and medicine since this means another way of utilizing SPIONs in PTT which is a local and less invasive treatment for cancer and bacterial infections. SPIONs has an important role in PTT studies because they induce temperature increase when they are irradiated with 808 and 1064 nm laser. Yet, the origin of the photothermal effect in case of SPIONs is still not clearly understood. A systematic study was not ever performed to understand the mechanism. It has been suggested that this effect depends on the absorption and hence to agglomerate sizes; however, SPIONs do not have any strong absorbance at these wavelengths. The agglomerate sizes are not appropriate for in in vivo and clinical studies. In the first part of this thesis, PTT potential of SPIONs was investigated based on irradiation wavelength, laser power and laser intensity. Influence of laser irradiation on the properties of SPIONs were also determined. The dependence of the temperature increase on the laser irradiation wavelength was tested over 728-838 nm with 10 nm steps and it was found that there is no relation between temperature increase and attenuation within this wavelength range. This result suggested that longer wavelength which provides deeper penetration could not cause any temperature loss. Intensity dependent experiments, where the power was kept constant and the spot size was changed, indicated that the temperature increase does not depend on the laser intensity. But the temperature increase changed with the laser power. Hence, factors affecting the temperature increase were determined. These laser treatments did not provide even 1 ◦C temperature increase in water within this irradiation wavelength range. This suggested that these laser powers are clinically applicable and safe in the absence of SPIONs. Detailed characterization showed that there is no change on particle properties. Lastly, PTT using small and stable SPIONs were successfully achieved on HeLa cells. Combination of PTT with other techniques enhanced the therapeutic outcome. Photodynamic therapy, another type of phototherapy, is widely used in clinical applications. Combined PTT and PDT became a very popular in recent years. It is very valuable to perform combined therapy with single irradiation at the same wavelength. In the second part of the thesis, the combined therapy potential of indocyanine green (ICG) and 3-aminopropyltrimethoxysilane (APTMS) coated SPIONs were investigated. ICG was electrostatically loaded to SPIONs and its phototherapy experiments were performed with single irradiation at 795 nm (700 mW) for 10 min. The therapeutic effect of PTT, PDT and combined PTT+PDT was examined on both colon (HT29) and breast (MCF7) cancer cells. PTT experiments with APTMS@SPIONs did not induce any important cell death at these conditions; however, it caused mild hyperthermia. PDT experiments performed with ICG caused more cell death in MCF7 cells compared to HT29 cells. Combined therapy with ICG-APTMS@SPIONs caused near complete cell death on both cell lines with a single laser treatment. In recent years, phototherapy emerged as an effective option in fight against bacterial infections. In the third part of this thesis, the antibacterial activity of free ICG, APTMS@SPIONs, and ICG-APTMS@SPIONs was tested on both planktonic cells and biofilms of Pseudomonas aeruginosa, Klebsiella pneumoniae, Escherichia coli and Staphylococcus epidermidis under laser irradiation. An important growth inhibition was observed on both planktonic cells and biofilms after laser treatment, proving use of SPION based PTT with or without other photosensitizers as an effective antibacterial treatment method. Chemotherapy is widely used in cancer treatment; however, poor drug accumulation and serious side effects limit the effective therapy. Encapsulation of drug into nanoparticles usually enhances the therapeutic outcome. Further improvement may be achieved via combined chemotherapy and PTT. In the fourth part of this thesis, etoposide (Eto) was electrostatically loaded to BSA@PAA@SPIONs to treat three different prostate cancer cells (PC3, LNCaP, and DU145) with and without laser treatment. High drug accumulation was achieved with nanoparticles and an important cell death was observed as a function of NP dose and laser power. Overall, this thesis aimed to investigate the factors affecting the photothermal potential of "small" SPIONs and combine the PTT potential of SPIONs with other therapeutic methods to provide enhanced therapeutic outcomes.