Superparamagnetic magnetite colloidal nanocrystal clusters
Superparamagnetic magnetite colloidal nanocrystal clusters
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DOI：
10.1002/anie.200700197
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发表时间：
2007-01-01
影响因子：
16.6
通讯作者：
Yin, Yadong
中科院分区：
文献类型：
--
作者：
Ge, Jianping;Hu, Yongxing;Yin, Yadong
胶体合成的最新进展使得能够制备具有可控尺寸和形状的高质量纳米晶体。[1-5]合成工作的重点似乎转移到创建纳米晶体的二级结构，无论是通过自组装或通过直接溶液生长。过去两年出版的一些有趣的著作证明了这一趋势。[6-10]需要操纵纳米晶体的二级结构，以便将利用单个纳米晶体的尺寸依赖性质的能力与由于子单元之间的相互作用而调节集体性质的可能性联合收割机结合起来。在这里，我们报告的高度水分散性的磁铁矿（Fe 3 O 4）的胶体纳米粒子簇（CNCs）的合成与统一的大小从约30至约180 nm，其中每个是由许多单一的磁铁矿微晶约10 nm的大小。在室温下，CNCs表现出超顺磁性，而在相同尺寸范围内的单晶磁铁矿颗粒将表现出铁磁行为。显然，CNC内微晶之间的磁相互作用从单晶颗粒的情况下被充分扰动，从而抑制了超顺磁性-铁磁性转变。超顺磁性纳米晶体具有超顺磁性、高磁化强度和高亲水性等特点，在药物输送、生物分离和磁共振成像等领域有着广泛的应用前景。超顺磁性纳米晶体在分散过程中不受强磁相互作用的影响，在生物医学领域具有广阔的应用前景。[11氧化铁纳米晶体由于其在生理条件下的生物相容性和稳定性而为此目的受到最多关注。已经开发了几种稳健的方法来合成具有严格控制的尺寸分布的磁性氧化铁（例如，g-Fe 2 O3或Fe 3 O 4）纳米晶体，通常通过在非极性溶剂中在升高的温度下的有机金属过程。[13-16]附加步骤
Recent advances in colloidal synthesis have enabled the preparation of high-quality nanocrystals with controlled size and shape.[1–5] The focus of synthetic efforts appears to be shifting to creation of secondary structures of nanocrystals, either by self-assembly or through direct solution growth. This trend is evidenced by a number of interesting works published in the past two years.[6–10] Manipulation of the secondary structures of nanocrystals is desired in order to combine the ability to harness the size-dependent properties of individual nanocrystals with the possibility to tune collective properties due to interactions between the subunits. Herein we report the synthesis of highly water dispersible magnetite (Fe3O4) colloidal nanocrystal clusters (CNCs) with uniform size from about 30 to about 180 nm, each of which is composed of many single magnetite crystallites approximately 10 nm in size. The CNCs show superparamagnetic properties at room temperature, whereas a single-crystalline magnetite particle within the same size range would exhibit ferromagnetic behavior. Apparently, the magnetic interactions among crystallites within a CNC are perturbed sufficiently from the case of a single-crystalline particle that the superparamagnetic–ferromagnetic transition is suppressed. The superparamagnetic behavior, high magnetization, and high water dispersibility make these CNCs ideal candidates for various important applications such as drug delivery, bioseparation, and magnetic resonance imaging.Superparamagnetic nanocrystals have proved to be very promising for biomedical applications, as they are not subject to strong magnetic interactions in dispersion.[11, 12] Iron oxide nanocrystals have received the most attention for this purpose because of their biocompatibility and stability under physiological conditions. Several robust approaches have been developed for synthesizing magnetic iron oxide (eg, g-Fe2O3 or Fe3O4) nanocrystals with tightly controlled size distribution, typically by organometallic processes at elevated temperatures in nonpolar solvents.[13–16] Additional steps of