C Scotson Soil Waters Screen 06.04.17(1367) 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.

本研究构建了一种在土壤环境下具备良好胶体稳定性的金纳米颗粒体系，可作为X射线计算机断层成像（X-ray computed tomography, XCT）造影剂。金纳米颗粒在生物学实验中具备诸多优势特性：相对较低的植物毒性、出色的X射线衰减能力，以及可进行功能化修饰的潜力。然而，土壤的盐度、酸度以及表面电荷会诱导金纳米颗粒团聚并使其失稳，因此在生物医学应用中，通常会通过聚合物涂层修饰金纳米颗粒，以提升其在体内（in vivo）环境中的稳定性。本研究首先证实，未包覆的金纳米颗粒会在土壤水溶液中发生团聚；随后证实，包覆聚乙二醇（polyethylene glycol, PEG）层可有效抑制此类团聚现象。为验证这一结论，研究团队使包覆PEG的金纳米颗粒流过装填有土壤的流动柱，证实其仍保持稳定；这一结果与使用二氧化硅和氧化铝装填的对照实验形成鲜明反差。进一步研究发现，完全浸透土壤的包覆型金纳米颗粒悬浮液至少可在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，估算出金纳米颗粒的扩散特性与其他典型植物养分在水中的扩散特性相近。综上，上述研究结果证实，PEG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。