UvVis Coated And Uncoated AuNPs Actual 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粒子体系，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。金纳米粒子在生物学实验中具备诸多优良特性：相对较低的植物毒性、良好的X射线衰减能力，以及可功能化修饰的特性。然而，土壤的盐度、酸碱度与表面电荷易诱导金纳米粒子聚集并破坏其胶体稳定性，因此在生物医学应用中，通常会对金纳米粒子施加聚合物涂层，以提升其在体内（in vivo）环境中的稳定性。本研究首先证实了未涂层的金纳米粒子会在土壤水溶液中发生聚集，随后证明聚乙二醇（polyethylene glycol, PEG）涂层可有效阻止此类聚集。为验证这一结论，研究人员将PEG涂层金纳米粒子通过填充有土壤的流动柱进行渗流实验，结果显示其保持稳定；而以二氧化硅和氧化铝填充的对照柱实验则呈现相反结果。本研究还进一步发现，完全浸润土壤的涂层金纳米粒子悬浮液至少可在5天内保持稳定。最后，本研究利用时间分辨XCT成像技术与基于图像的模型，近似估算出金纳米粒子的扩散行为与其他典型植物养分在水中的扩散行为相近。综上，上述研究结果证实，聚乙二醇化金纳米粒子有望成为土壤环境中XCT成像的潜在造影剂。