Copy of Liquid Phase Area Values Flow Columns Jan 19 Ratio from Stabilizing gold nanoparticles for use in X-ray computed tomography imaging of soil systems

This investigation establishes a system of gold nanoparticles that show good colloidal stability as an X-ray computed tomography (XCT) contrast agent under soil conditions. Gold nanoparticles offer numerous beneficial traits for experiments in biology including: comparatively minimal phytotoxicity, X-ray attenuation of the material and the capacity for functionalization. However, soil salinity, acidity and surface charges can induce aggregation and destabilize gold nanoparticles, hence in biomedical applications polymer coatings are commonly applied to gold nanoparticles to enhance stability in the <i>in vivo</i> environment. Here we first demonstrate non-coated nanoparticles aggregate in soil-water solutions. We then show coating with a polyethylene glycol (PEG) layer prevents this aggregation. To demonstrate this, PEG-coated nanoparticles were drawn through flow columns containing soil and were shown to be stable; this is in contrast with control experiments using silica and alumina-packed columns. We further determined that a suspension of coated gold nanoparticles which fully saturated soil maintained stability over at least 5 days. Finally, we used time resolved XCT imaging and image based models to approximate nanoparticle diffusion as similar to that of other typical plant nutrients diffusing in water. Together, these results establish the PEGylated gold nanoparticles as potential contrast agents for XCT imaging in soil.

本研究构建了一种金纳米颗粒体系，该体系在土壤环境中可作为X射线计算机断层扫描（XCT）造影剂，且具备优异的胶体稳定性。金纳米颗粒在生物学实验中具备诸多优良特性：相对较低的植物毒性、优异的X射线衰减能力，以及具备功能化修饰的能力。然而，土壤的盐度、酸度与表面电荷会诱导金纳米颗粒聚集，破坏其胶体稳定性；因此在生物医学应用中，通常会对金纳米颗粒施加聚合物涂层，以提升其在体内（in vivo）环境中的稳定性。本研究首先证实，未涂层的金纳米颗粒会在土壤水溶液中发生聚集行为；随后证实，聚乙二醇（polyethylene glycol, PEG）涂层可有效阻止此类聚集。为验证这一结论，本研究将PEG涂层金纳米颗粒通过填充土壤的流动柱进行渗滤实验，结果显示其仍保持稳定；这与使用二氧化硅、氧化铝填充柱的对照实验结果形成显著差异。本研究进一步发现，完全浸润饱和土壤的涂层金纳米颗粒悬浮液，至少可在5天内保持胶体稳定。最后，本研究采用时间分辨XCT成像技术与基于图像的扩散模型，对纳米颗粒的扩散行为进行近似分析，发现其扩散特性与水中常见的典型植物养分相似。综上，上述研究结果证实，经聚乙二醇修饰的金纳米颗粒有望成为土壤环境中XCT成像的潜在造影剂。