【作者】 马铭；

【导师】 刘祖黎；

【作者基本信息】 华中科技大学 ， 材料物理与化学， 2011， 博士

【摘要】 氧化铁纳米颗粒具有超顺磁性和良好的稳定性,是作为磁共振造影剂的最佳材料。磁共振成像(Magnetic Resonance Imaging, MRI)是一项先进的医学成像诊断技术,已广泛应用于人体多种疾病的检测和早期诊断,磁共振成像造影剂(MRI Contrast Agent)是该技术的重要组成部分,它可以缩短成像时间,提高成像的对比度和清晰度。本文以超顺磁性氧化铁(Superparamagnetic Iron Oxide, SPIO)纳米颗粒为核心,以葡聚糖为分散剂,通过水相共沉淀法制备了葡聚糖包覆的SPIO,然后在表氯醇的催化作用下,加入乙二胺,让氨基官能团取代葡聚糖表面的羟基基团,最终得到氨基官能团修饰的SPIO (SPIO-NH2)纳米颗粒。在制备工艺方面,对于SPIO氨基化的实验工艺进行了探讨,找到了最佳的实验工艺,该工艺可让SPIO-NH2表面的氨基含量达到最大。我们通过晶体结构、磁性测量结果发现,SPIO-NH2在室温下具有较好的超顺磁性,在磁共振仪下能够有效缩短家兔肝脏组织信号的驰豫时间；另外,将SPIO-NH2纳米颗粒和带有荧光的多肽Tat (FITC)进行偶联,得到了具有磁性/荧光双功能的纳米颗粒探针,它不仅能够进入神经干细胞内进行细胞标记,还能够缩短神经干细胞的磁共振信号驰豫时间,做为磁性标记物。多铁材料是指在一定温度范围内共存的铁电有序和磁性有序的材料,并且铁电相和铁磁相的耦合作用还可以产生磁电效应,该材料在半导体器件方面具有重要的应用前景,近几年来受到了全世界的广泛关注。多铁材料分为单相多铁材料和复合多铁材料。复合多铁材料除了具有单相多铁材料所具有的优点之外,还能产生更强的磁电耦合效应,因而其应用也更加广泛,受到的关注也越来越多。本文利用纯相的铁磁性材料和纯相的多铁材料来制备复合的多铁材料。镧锶锰氧(La0.67Sr0.33MnO3, LSMO)是一种钙钛矿结构的铁磁性材料,而铁酸铋(BiFeO3, BFO)也是一种典型的钙钛矿型的多铁材料,其居里温度为TC=1103K,奈尔温度为TN=643K,在室温下表现出共存的铁电性和很弱的反铁磁性。我们正是利用了LSMO的室温铁磁性和BFO的室温铁电性,通过溶胶-凝胶法而制备了LSMO/BFO复合的多铁薄膜,并研究了不同BFO层数的LSMO(7层)/BFO复合多铁薄膜的结构、形貌、铁电性、介电性等性质,研究发现复合多铁薄膜的铁电性较单纯的BFO薄膜有明显的增强。另外,我们还通过A位Ca掺杂,制备了不同Ca掺杂比例的Bi1-xCaxFeO3 (BCFO)多铁薄膜；之后再和LSMO层进行复合,制备出了LSMO/BCFO复合的多铁薄膜,同时也研究了上述两类薄膜的结构形貌、铁电性、介电性等性质,研究结果发现Ca掺杂可以明显提高BCFO薄膜的铁电性,这来源于BCFO薄膜的晶格结构变化,并且还发现复合了LSMO层的BCFO薄膜,比单纯BCFO薄膜的铁电性要好,表现为具有较大剩余极化强度和饱和极化强度,这来源于LSMO铁磁层和BCFO铁电层的磁电耦合作用。更多还原

【Abstract】 Superparamagnetic iron oxide (SPIO) nanoparticles show superparamagnetism and good stability, which make them the best candidate for the widely used as a magnetic resonance imaging (MRI) contrast agent. MRI is a powerful clinical diagnostic modality for the detection and diagnosis of a wide varity of diseases. MRI contrast agent is a diagnostic agent that could be administered to a patient in order to shorten the relaxation times of protons in tissues in which the agent accumulates, enhancing the imaging contrast between normal and diseased tissue. In this thesis, as the SPIO is core, the dextran is dispersant, we synthezise the dextran-coated SPIO nanoparticles by coprecipitation technique at first; under the catalysis of epichlorohydrin, the ethylenediamine was added, the hydroxyl on the surface of dextran is replaced by the amino-group, finally amino-group functionalized SPIO (SPIO-NH2) was obtained. In preparation process, we focus on the functionalization of SPIO with amino-group, and optimize the preparation technology, in which the amount of surface amino-group of the SPIO-NH2 nanoparticles is highest. The structure and magnetism of these SPIO-NH2 nanoparticles were also studied, it found that SPIO-NH2 nanoparticles possess superparamagnetic behavior. In a 1.5 T MR system, SPIO-NH2 nanoparticles can shorten the T2 signal relaxation time of liver tissue dramatically. Furthermore, Tat (FITC) peptide was choosen to conjugated with SPIO-NH2 nanoparticles, we obtain the magnetic/fluorescent bifunctional labeling prode; The obtained probe not only can enter the neural stem cells for cells labeling, but also result in significant negative T2 signal contrast enhancement, and can be used for magnetically labeling in a MR system.In a certain temperature range, multiferroics shows coexistent ferroelectric order and magnetic order, the coexistent ferroelectricity and magnetism can couple with each other and result in magneto-electric effects, so the multiferroics was considered to have important potential application in the semi-conductor devices, such as sensors, switches and modulators et al. In recent years, much attention were paid on multiferroics, which can be divided into single-phase multiferroics and composite multiferroics. The composite multiferroics prior to single-phase counterpart since they can produce stronger magneto-electric effects, which makes them possess widely application value, and also evokes more and more attention. In this thesis, single-phase ferromagnetic material and single-phase ferroelectric material were adopted to prepare multiferroic composite thin films. La0.67Sr0.33MnO3 (LSMO) is a typical ferromagnetic material with perovskite structure; while BiFeO3 (BFO) is also a perovskite typed multiferroics, which ferroelectric-paraelectric transition Curie temperature is Tc= 1103 K and its antiferromagnetic-paramagnetic transition Neel temperature is TN= 643 K, so BFO shows coexistent ferroelectricity and weak magnetism at room temperature. Based on the above, the ferromagnetic material LSMO (at room temperature) and the ferroelectric material BFO (at room temperature) were choosen to fabricate LSMO (7 layers)/BFO multiferroic composite thin films with different BFO layers by sol-gel technique, and further focus on its structure, morphology, ferroelectricity, dielectric properties et al, we found that the ferroelectricity of LSMO/BFO multiferroic thin films is enhanced when compared with that of BFO films. In addition, A site Ca substituted Bi1-xCaxFeO3 (BCFO) single-phase thin films was prepared by adding Ca(NO3)2*4H2O as starting material, and LSMO/BCFO multiferroic thin films was also obtained; the structure, morphology, ferroelectricity, dielectric properties et al of BCFO thin films and LSMO/BCFO composite thin films were also analysed. The results show that the doping of Ca can dramatically enhance the ferroelectricity of BCFO multiferroic thin films, which arises from the structure evolution of BFO. In addition, the remnant polarization and saturated polarization of LSMO/BCFO thin films are higher than that of pure BCFO thin films, shows enhanced ferroelectricity in LSMO/BCFO thin films, which originate from the magneto-electric coupled effects between LSMO layer and BCFO layer.更多还原