Periodic 3-D nanoparticle arrays by protein crystallization

直径只有几纳米的非常小的颗粒（纳米是比一米小1000万倍的长度单位）可以具有与大块材料完全不同的特性。如果这种大小的粒子被组装成一个周期阵列，即粒子的简单排列被重复多次，粒子之间的电和磁相互作用可以进一步改变其性质。这就是纳米大小的粒子（简称为纳米粒子）的周期性阵列的有趣之处。这个项目是开发一种新的方法，使纳米粒子的三维周期阵列，具有新颖和有用的磁性和光学性质。人们已经找到了许多方法来制造纳米颗粒的二维周期性阵列，但制造一个真正的三维阵列，比几个纳米颗粒厚，要困难得多。我们提出的方法有望比目前的替代方法更快、更灵活，目前的替代方法是一种被称为胶体结晶的纯化学技术。我们的方法引入了生物学和化学的元素，因为我们将在蛋白质内部合成纳米颗粒，然后使蛋白质结晶。由于蛋白质晶体是分子的周期性阵列，每个分子包含一个纳米粒子，因此结果将是期望的纳米粒子的三维周期性阵列。我们将从使用铁蛋白制造纳米粒子开始。铁蛋白分子的形状像一个空心球体，细胞用它来储存铁。我们将合成用于磁性研究的磁性金属和氧化物纳米粒子，以及用于光学研究的其他金属纳米粒子。我们将找到生长含纳米颗粒的铁蛋白大晶体的最佳条件，并使用非常敏感的技术，如扫描探针显微镜和动态光散射来研究阵列生长的最早阶段。我们将通过改变结晶条件来改变我们的三维周期阵列的对称性，我们还将研究其他蛋白质，包括Dps，它具有与铁蛋白相似的结构，但用于保护DNA。我们将测量纳米颗粒阵列在不同温度下的磁性，并将结果与计算机模拟结果进行比较。这将帮助我们更深入地了解所有单个粒子的磁场如何相互作用，从而确定整个阵列的磁性行为。理解磁相互作用对于开发用于磁数据记录的新材料以及本身的兴趣是重要的。我们还将测量光如何通过银、金和合金纳米粒子的三维周期性阵列进行传输和反射。事实上，阵列的周期将比光的波长小得多，这使得这些系统特别有趣。他们的研究将有助于未来奇异光学设备的发展，如完美的透镜或屏蔽，可以使物体隐形。

Very small particles with diameters of only a few nanometres (a nanometre is a unit of length 1000 000 000 times smaller than a metre) can have properties quite different from bulk materials. If particles of this size are assembled to form a periodic array, that is one in which a simple arrangement of particles is repeated many times, electrical and magnetic interactions between the particles can further change the properties. This is what makes periodic arrays of nanometre-sized particles, known as nanoparticles for short, interesting.This project is to develop a new way of making 3-dimensional periodic arrays of nanoparticles, with novel and useful magnetic and optical properties. Many ways have been found to make 2-dimensional periodic arrays of nanoparticles, but making a truly 3-dimensional array, more than a few nanoparticles thick, is much more difficult. The approach we propose promises to be faster and more flexible than the current alternative, which is a purely chemical technique known as colloidal crystallization. Our method introduces elements of biology as well as chemistry, because we will synthesize nanoparticles inside proteins, then crystallize the protein. Since a protein crystal is a periodic array of molecules, and each molecule contains a nanoparticle, the result will be the desired 3-dimensional periodic array of nanoparticles.We will start by using the protein ferritin to make nanoparticles. The ferritin molecule is shaped like a hollow sphere and cells use it to store iron. We will synthesize magnetic metal and oxide nanoparticles for magnetic studies, and other metal nanoparticles for optical studies. We will find the best conditions for growing large crystals of ferritin with nanoparticles inside, and use very sensitive techniques such as scanning probe microscopy and dynamic light scattering to study the very earliest stages of array growth. We will change the symmetry of our 3-dimensional periodic arrays by changing the crystallization conditions and we will also study other proteins, including Dps, which has a similar structure to ferritin, but is used to protect DNA.We will measure the magnetic properties of our nanoparticle arrays at different temperatures and compare the results with computer simulations. This will help us gain a deeper understanding of how the magnetic fields of all the individual particles interact to determine the magnetic behaviour of the array as a whole. Understanding magnetic interactions is important for developing new materials for magnetic data recording as well as being of interest in itself.We will also measure how light is transmitted through and reflected from 3-dimensional periodic arrays of silver, gold and alloy nanoparticles. The fact that the period of the array will be much smaller than the wavelength of light makes these systems particularly interesting. Their study will contribute to the future development of exotic optical devices such as perfect lenses or shields that can make an object invisible.