Collantes-Goicochea, Yesusa K.

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    Synthesis and characterization of ZnO-based nanostructures for potential biomedical applications
    (2013) Collantes-Goicochea, Yesusa K.; Perales-Pérez, Oscar J.; College of Arts and Science - Science; López, Jóse R.; Jiménez, Héctor J.; Department of Physics; Benítez, Jaime
    Zinc Oxide (ZnO) is a high quality semiconductor material that has been studied for several decades due to its applications in optics and optoelectronics. Currently, ZnO-based nanoparticles (NPs) are being widely studied because of their unique physico-chemical properties at the nanoscale and consequent potential applications in biology and medicine, including tissue imaging, biological fluorescence labeling, and diagnosis and photodynamic cancer therapy. ZnO is an excellent candidate for biological applications due to its non-toxicity and ability to biodegrade coupled with high thermal and chemical stabilities. However, some of the fundamental properties of ZnO remain unclear. A detailed study of the dependence of the optical properties on the crystal size in NPs of similar shape and synthesis process has not been properly carried out yet. On this basis, the present work was focused on the size-controlled synthesis and characterization of ZnO NPs through a modified polyol approach where heterogeneous nucleation conditions were promoted by using nanometric ZnO seeds. The polyol medium acts as the solvent for the formation of NPs while enhancing their water solubility. The corresponding structural and optical properties are discussed as a function of the crystallite size at the nanoscale. In turn, the doping of ZnO NPs has also been explored as an attempt to enhance and/or tune their functional properties. Although the doping of ZnO with different transition metal ions has been reported elsewhere, the effect of the dopant oxidation state on the materials’ properties at the nanoscale has not been altogether addressed. Accordingly, the present research focused on the controlled synthesis and characterization of Fe (II and III) and Mn (II and III)-doped ZnO NPs through a modified polyol-based approach. The corresponding structural, optical and magnetic properties are discussed as a function of the dopant concentration in the 0-2 at.% range. The potential use of ZnO-based nanostructures in photodynamic therapy for cancer treatment is based on their capability to produce reactive oxygen species (ROS) for cancer-cell killing, which relies on their semiconductor properties at the nanoscale. This work specifically focused on the effect of the nanoparticle size, the effect of the composition (Fe and Mn doping) and the effect of the oxidation state (3+ and 2+) of the dopant species on the yield of singlet oxygen, which is a widely-used type of reactive oxygen in photodynamic therapy.