compute flux 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 in vivo 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，该体系在土壤环境下可作为X射线计算机断层扫描（X-ray computed tomography, XCT）造影剂，展现出良好的胶体稳定性。金纳米颗粒在生物学实验中具备诸多优良特性，包括相对较低的植物毒性、优异的X射线衰减能力，以及可功能化的特点。然而，土壤中的盐度、酸度以及表面电荷会诱导金纳米颗粒团聚，使其失去稳定性，因此在生物医学应用中，通常会通过聚合物涂层对金纳米颗粒进行修饰，以增强其在生物体内环境中的稳定性。本研究首先证实了未包覆的金纳米颗粒会在土壤水溶液中发生团聚。随后，我们证明了聚乙二醇（polyethylene glycol, PEG）涂层可有效阻止这一团聚现象。为验证这一点，研究人员将聚乙二醇包覆的金纳米颗粒通过填充有土壤的流动柱进行渗流实验，结果显示纳米颗粒保持了稳定；这与使用二氧化硅和氧化铝填充柱的对照实验结果形成鲜明对比。我们进一步发现，完全浸润土壤的聚乙二醇包覆金纳米颗粒悬浮液至少可在5天内保持稳定。最后，我们借助时间分辨XCT成像技术以及基于图像的模型，近似估算出纳米颗粒的扩散行为与其他典型植物养分在水中的扩散行为相似。综上，上述研究结果证实了聚乙二醇修饰的金纳米颗粒可作为潜在的土壤XCT成像造影剂。