Opening the black box: Imaging nanoparticle transport with magnetic resonance imaging

了解纳米颗粒通过多孔地质材料的运输是必要的，以提供有效的预测和减轻纳米颗粒污染。通常，包含岩石、沉积物或土壤的填充柱实验用于量化纳米颗粒如何通过这些介质。虽然信息量很大，但获得的数据是色谱柱内复杂和异质相互作用阵列的整体平均值。像自然系统一样，柱内的材料将在几何形状、流体动力学和微生物学方面表现出复杂的异质性。问题是，因为这种材料不是“透明的”，我们不能看到内部直接可视化这些异质性如何影响纳米颗粒的运输。然而，这是可以改变的。磁共振成像（MRI）是一种高度通用的工具，它可以成像孔隙结构和流体流动在不透明的地质材料。此外，标记有顺磁性标签的分子对于MRI是容易可见的，使得它们通过多孔系统的运输能够被真实的实时成像。这种技术在医学科学中被大量使用，以跟踪感兴趣的分子在人类和其他哺乳动物系统中的运输。在这项研究中，我们建议使用磁共振成像和纳米粒子标记的顺磁性标签的图像纳米粒子的运输和命运的包装列。实验也将在允许生物膜在孔隙网络中生长后在相同的材料上进行（生物膜预计将表现为纳米颗粒的主要汇）。重要的是，这将展示如何使用这样的方法来揭示这些系统中的复杂的异质性如何有助于纳米颗粒的整体散装运输。最终，这项技术将使研究人员能够探测复杂系统中的纳米颗粒运输，并开发出有充分依据的纳米颗粒运输预测模型。

Understanding the transport of nanoparticles through porous geologic material is imperative to provide effective prediction and mitigation of nanoparticlulate pollution. Often, packed column experiments containing rock, sediment or soil are used to quantify how nanoparticles move through these media. Whilst highly informative, the data obtained is a bulk average of a complex and heterogeneous array of interactions within the column. Like natural systems, the material within the column will display complex heterogeneities in geometry, hydrodynamics and microbiology. Problematically, because this material is not 'see-through' we cannot look inside to directly visualize how these heterogeneities impact the transport of the nanoparticle. This, however, can change. Magnetic resonance imaging (MRI) is a highly versatile tool which can image pore structure and fluid flow in opaque geological material. Moreover, molecules labelled with a paramagnetic tag are readily visible to MRI enabling their transport through porous systems to be imaged in real time. Such technology is heavily used in the medical sciences to track the transport of molecules of interest in human and other mammalian systems. In this study we propose to use MRI and nanoparticles labelled with a paramagnetic tag to image nanoparticulate transport and fate in packed columns. Experiments will also be performed on the same material after biofilms have been allowed to grow in the pore networks (the biofilms are expected to behave as major sinks for the nanoparticles). Critically, this will demonstrate how such a method can be used to reveal how the complex heterogeneities in these systems contribute to the overall bulk transport of nanoparticulates. Ultimately, this technique will enable researchers to probe nanoparticulate transport in complex systems and moreover, to develop well-founded predictive models of nanoparticulate transport.