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

了解纳米颗粒在多孔地质材料中的运移是提供有效预测和减轻纳米颗粒污染的必要条件。通常，填充柱实验包含岩石，沉积物或土壤被用来量化纳米粒子如何通过这些介质。虽然信息量很大，但获得的数据是列中复杂且异构的交互数组的大量平均值。像自然系统一样，柱内的材料将在几何、流体动力学和微生物学方面显示出复杂的异质性。问题是，由于这种材料不是“透明的”，我们无法直接观察内部，以直观地看到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）是一种多功能的成像工具，可以对不透明地质物质中的孔隙结构和流体流动进行成像。此外，用顺磁标签标记的分子很容易被MRI看到，从而使它们通过多孔系统的运输能够实时成像。这种技术在医学科学中被大量用于跟踪人类和其他哺乳动物系统中感兴趣的分子的运输。在这项研究中，我们建议使用MRI和带有顺磁标签的纳米颗粒来成像纳米颗粒在填充柱中的运输和命运。在允许生物膜在孔隙网络中生长后，同样的材料也将进行实验（预计生物膜将作为纳米颗粒的主要吸收源）。至关重要的是，这将证明如何使用这种方法来揭示这些系统中复杂的非均质性如何促进纳米颗粒的整体运输。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，而且，开发出有充分基础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.