控制纳米结构以调控氧化锌的发光、磁性和细胞毒性

氧化锌(ZnO) 纳米材料因其在UV 激光器、发光二极管、太阳能电池、稀磁半导体、生物荧光标示、靶向药物等领域中的广泛应用而成为最热门的研究课题之一. 调节和优化ZnO 纳米结构的性质是ZnO 的实际应用迫切所需. 在此, 通过发展聚乙烯吡咯烷酮导向结晶法、微波加热强制水解法、表面活性剂后处理法, 成功地制备出了尺寸、表面电荷或成分可调的球、半球、棒、管、T 型管、三脚架、片、齿轮、两层、多层、带盖罐子、碗等一系列ZnO 纳米结构. 通过简单地改变ZnO 纳米粒子的尺寸、形貌和表面电荷或成分, 有效地调控ZnO 本身的发光强度和位置, 并近90 倍地增强了荧光素染料的荧光强度; 诱使了强度可调的室温铁磁性; 实现了对ZnO纳米颗粒的细胞毒性的系统性调控.

Tuning the photoluminescence,magnetism and cytotoxicity of ZnO by tailoring the nanostructures

ZnO nanomaterials have been extensively investigated for its broad applications such as room-temperature UV lasers, light-emitting diodes, solar cells, dilute magnetic semiconductors, bio-labeling, and target medicines. Tuning and optimizing the properties of ZnO nanostructures are urgent for the practical applications. Here, the photoluminescence, magnetism, and cytotoxicity of ZnO nanparticles have been effectively tuned by adjusting the nanostructures. Firstly, by developing the novel polyvinylpyrrolidone(PVP)-directed crystallization route, microwave heating-assisted forced hydrolysis method, and post-treating with surfactants, a series of high pure ZnO nanostructures including spheres, semispheres, rods, tubes, T-type tubes, tripods, wafers, gears, double layers, multilayer, capped pots, and bowls with tunable size and surface component/charge has been successfully prepared. The PVP can greatly promote the ZnO nucleation by binding water, and direct the ZnO growth by forming a variety of soft-templates and/or selectively capping the specific ZnO facet which is confirmed by the infrared absorption spectra. Secondly, the band-edge UV emission of ZnO has been greatly modified in both intensity and peak position by simply changing the sizes, shapes, and surface component of the ZnO nanoparticles. However, changing the surface charge of ZnO nanoparticles can only vary the intensity of the band-edge UV emission of ZnO. Significantly, the fluorescence of fluorescein isothiocyanate (FITC) is increased by up to 90 fold through doping the FITC molecules into the ZnO naoncrystals, which can effectively separate the FITC molelcules and avoid the energy transfer and the resulting fluorescence self-quenching. Thirdly, the room temperature ferromagnetism with tunable intensity is induced in the ZnO nanoparticles by coating them with different surfactants at different concentrations. As confirmed by the x-ray photoemission spectra, the coated surfactant molecules can donate electrons to the ZnO nanoparticles and induce the ferromagnetism. The electron number varies with the surfactant and the surfactant concentration, leading to the fluctuant ferromagnetism. The theoretical calculation further reveal the fluctuant nature of ferromagnetism in the ZnO nanoparticles coated with surfactants. This explains the previously reported seemingly irreconcilable ZnO ferromagnetism induced by capping surfactants, and provides a general chemical approach to tuning the ferromagnetism of ZnO nanoparticles by modifying the capping-surfactant concentration. Finally, it is revealed that the shape, size, surface charge/composition, and band-gap of ZnO nanostructures have different influences on the ZnO-induced cytotoxicity. The surface composition or adsorbed species of NPs may contain the toxic matter such as OH-ions that determine the NP-induced cytotoxicity, and should be detected before cytotoxicity assays are conducted. The rod-like NPs are more toxic than the spherical NPs. The positive surface charge can accelerate the nanoparticle-induced toxic action and enhance the cytotoxicity. Compared with the effects of shape and surface composition/charge, the influence of the nanoparticle-size variation on the nanparticle-induced cytotoxicity is less significant, and can be overwhelmed by other factors. These results will be conducible to the cytotoxicity assay and safe usage of ZnO NPs.