Periodic 3-D nanoparticle arrays by protein crystallization

直径只有几纳米的非常小的颗粒(纳米是小于一米的1000,000,000倍的长度单位)可以具有与大块材料完全不同的性质。如果这种大小的颗粒被组装成周期性阵列，即其中简单的颗粒排列重复多次，颗粒之间的电和磁相互作用可以进一步改变性质。这就是纳米粒子的周期性阵列，简称纳米粒子的有趣之处。这个项目旨在开发一种新的方法来制造具有新颖和有用的磁性和光学性质的纳米粒子的三维周期性阵列。人们已经发现了许多方法来制作纳米颗粒的二维周期性阵列，但要制作一个真正的三维阵列，而不仅仅是几个纳米颗粒的厚度，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，后者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和化学的元素，因为我们将在蛋白质中合成纳米颗粒，然后使蛋白质结晶。由于蛋白质晶体是一个周期性的分子阵列，每个分子都包含一个纳米颗粒，所以结果将是所需的纳米颗粒的三维周期性阵列。我们将首先使用蛋白质铁蛋白来制造纳米颗粒。铁蛋白分子的形状像一个中空球，细胞用它来储存铁。我们将合成磁性金属和氧化物纳米颗粒用于磁性研究，以及其他金属纳米颗粒用于光学研究。我们将找到生长内含纳米颗粒的铁蛋白大晶体的最佳条件，并使用扫描探针显微镜和动态光散射等非常敏感的技术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，它的结构类似于铁蛋白，但用于保护DNA。我们将测量不同温度下纳米颗粒阵列的磁性，并将结果与计算机模拟进行比较。这将帮助我们更深入地了解所有单个粒子的磁场是如何相互作用的，以确定阵列作为一个整体的磁性行为。了解磁相互作用对于开发用于磁数据记录的新材料以及其本身具有重要意义。我们还将测量光如何透过和反射银、金和合金纳米颗粒的三维周期性阵列。阵列的周期将比光的波长小得多，这一事实使这些系统特别有趣。他们的研究将有助于未来发展奇异的光学设备，如可以使物体看不见的完美透镜或屏蔽物。

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.