Synthesis Of Drug Loaded Magnetic Silica Nanocarriers

Photodynamic therapy （PDT） is an emerging modality for the treatment of a variety of diseases. In contrast to other conventional medical treatments, PDT is unnecessary to release the loaded drug, and the diffusion of surrounding oxygen molecules for the generation of reactive oxygen species （ROSs） is sufficient for therapeutic effects. In details, PDT is based on the concept that photosensitizers （PSs） are irradiated by visible or near-infrared lights of appropriate wavelength, resulting in the formation of ROSs, such as singlet oxygen （¹O₂） or free radicals. ROSs are responsible for oxidizing various cellular compartments, leading to an irreversible damage of pathological cells. Combining the photosensitizer with Fe₃O₄ magnetic nanoparticles can help to minimize the generation of cytotoxic substances in the surrounding normal tissues. Therefore, under appropriate conditions, PDT offers an effective and selective method for destroying diseased tissues without damaging adjacent healthy ones. Typically, most of the PDT drugs are poisonous and porphyrin-based and have an extensive system of conjugated double bonds. This property makes them ideal for absorbing light, but normally renders the molecule somewhat hydrophobic. Such features are difficult to formulate into an effective drug and then various encapsulation strategies have been studied to protect the molecules from the aqueous environment, and this shell structure also can protect the drug from the degradation by digestive enzymes during the transportation process. Silica nanoparticles have a number of advantages over organic polymeric ones as widely known. Their preparative processes involved are quite simple and these particles are extremely stable and can be easily obtained with the desired size, shape, and porosity. Silica is also known for its biocompatibility and ease of surface modification with a variety of functional groups using silane chemistry and commercially available organosilicon reagents for biotargeting.The objective of this work was to develop a novel photodynamic drug nanocarriers consisting of magnetite core/silica shell （Fe₃O₄/SiO₂） structure by sol-gel method and micro-emulsion method, respectively. The magnetic nanocarriers prepared were characterized by transmission electron microscopy （TEM）, fourier transform infrared spectroscopy （FT-IR）, and X-ray diffraction （XRD）. These nanocarriers were approximately spherical, sized in the range of 30-50 nm. From the FT-IR spectrum of nanocarriers, the presences of these characteristic peaks of the drug clearly indicated the drug existed in the nanocarriers. The SiO₂ layer was amorphous corresponding to the XRD.The ultraviolet absorption peak of the drug existing in those of the nanocarriers indicateed that the drug was enwrapped in the magnetite nanocarriers. The generation of singlet oxygen （¹O₂） was measured by the use of N, N-Dimethyl-4-nitrosoaniline （RNO） as a selective scavenger. Using laser to irradiate the nanocarriers and RNO system, the decrease in the absorption peak of RNO at 440 nm was due to the ¹O₂ released from the nanocarriers, which proved that the photodynamic drug could work normally.These two methods could be widely used to prepare other drug nanocarriers. The results showed that the magnetic silica nanocarriers may have potential applications in photodynamictherapy.