Synthesis and characterization of superparamagnetic iron oxide nanoparticles covered with methylene blue and hypericin molecules

The present study is focused on the synthesis and characterization of methylene blue and hypericin-containing silica-coated superparamagnetic nanoparticles with great potential for photodynamic therapy (PDT). The photoactive molecule (PM) when exposed to light reacts with molecular oxygen and generates singlet oxygen (1O2) which is cytotoxic. Superparamagnetic iron oxide nanoparticles (SPIONs) were prepared with a mixture of iron (II) and (III) chlorides in the presence of a base by co-precipitation and its surface was covered with tetraethylammonium. SPIONs were coated with a double layer of silica, tetraethylortosilicate (TEOS) and sodium silicate (Na2SiO3), generating the SPIONs-Na2SiO3-TEOS-PM compound, as shown below. As-synthesized nanoparticles were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, and SQUID magnetic measurements. X-ray powder diffraction technique confirmed the formation of the magnetite. By using the Scherrer equation for 311 reflection, it was observed that the average crystallite sizes were 18 nm. By infrared spectroscopy, it is possible to note characteristics bands of iron- oxygen, besides others bands associated to silicate groups. The nanocomposites presented magnetic behavior at room temperature due to the presence of magnetite (Fe3O4) core. Indirect measurements of 1O2 release were performed using a red light (630-650nm, P=25mW) and reagent, 1,3-Diphenylisobenzophuran, with SPIONs-Na2SiO3-TEOS-PH, observing the absorption decay in UV-vis. 1O2 is spontaneously released in aqueous solution at levels required for biomedical applications and tests with bacteria show promising nanoparticles applications.