Stabilizing gold nanoparticles for use in X-ray computed tomography imaging of soil systems

Abstract

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.

Developing a system for in vivo imaging of maize roots containing iodinated contrast media in soil using synchrotron XCT and XRF

“…1c) -the roots extending from the base were thus submerged in the contrast media. This concentration was determined by previous work (Scotson et al 2020) and was confirmed as appropriate with the use of a phantom containing the contrast media and soil which displayed sufficient contrast between materials. The phantom consisted of a length of syringe identical to those used for the root growth chamber.…”

“…3). Additionally, with the development of nanoparticulate contrast media for use in soil (Scotson et al 2019), it is possible that in future the in vivo anatomical imaging achievable with our experimental system could be further enhanced with the use of nanoparticles functionalised to accumulate on particular plant tissues or organs. Particularly with the use of nanoparticles of approximately 3.5 nm in size, which have previously been observed to pass into roots and then be translocated throughout the plant to the leaves (Sabo-Attwood et al 2012).…”

“…This could be achieved by applying the contrast agent through a partially saturated soil rather than submerging the root in a contrast media solution. Such an approach of application via partially saturated soil could be paired with studies which seek to capture root-water interactions, such as Scotson et al, (2020), to monitor effects of root water uptake on soil pore water. Table 2 Pearson Correlation Coefficient of average grey value of root stele versus aerenchyma cross sectional are over depth.…”

“…Iodinated contrast media has been used previously to study larger soil and plant systems and one future avenue for exploration could be upscaling the experimental system developed in this study and using it to capture solute movement through roots in considerably larger soil systems. Previous studies have investigated fluid flow through soil cores of 10 cm in diameter or larger using radiographic contrast media (Heijs et al 1996;Larsbo et al 2014;Scotson et al 2020) and, were such methodologies to be combined with the principles of the experimental system used in this study, fluid flow and nutrient movement through both the soil and through the root system could be studied simultaneously. Such data could then be used to parameterise mathematical models of solute movement through soil to roots and then transport within the plants.…”

Linking root structure to functionality: the impact of root system architecture on citrate‐enhanced phosphate uptake

“…The organic matter contents were 2.3% and 5.5%, and the pH was 6.35 and 6.5 for the LS and CL, respectively. The water‐extractable phosphorus (P) was 530 ppb for the LS (Scotson et al , 2019). No P information was available for the clay‐loam; however, both soils were taken from the same field.…”