Nanoparticles were synthesised by separately adjusting aqueous solutions of copolymer and gold (III) chloride to pH7.5, before mixing. Concentrations were selected to give a final polymer concentration of 1% w/w, with the molar ratio of HAuCl4 to DEAEMA varied as follows: 0.1, 0.3, 0.5 and 0.7, with the concept that the number of amine groups that can be successfully complexed is probably < 100%. The reaction mixture was incubated at room temperature for 48h with shaking, during which time gold nanoparticle formation was visible via a colour change to intense wine-red. This was confirmed by ultraviolet-visible spectroscopy (UV-vis) showing a single peak at 520 nm (Fig. ), increasing over time (Fig ). The hydrodynamic size of the gold nanoparticles, including the polymer corona, was determined by dynamic light scattering (DLS), and was found to be in the vicinity of 40 nm for all levels of gold-loading. We also note the presence of some free polymer molecules (Figure ). In parallel, the zeta potential was measured (Table ). The expectation was that there must be some positive charge in the DEAEMA-rich micelle core, due the secondary amine groups. The impact of this charge on the zeta potential, which reflects the effective surface charge experienced at the outer hydrodynamic edge, will however reduce substantially due to the PEGMA bottlebrush corona, which creates a significant distance between the amine charges and the hydrodynamic edge. Measurements indeed showed a positive charge, and this increased significantly with the size of the gold particle, which may be attributed to the larger gold core displacing the amine groups closer to the outer edge of the overall particle. Given that all tested HAuCl4:DEAEMA ratios generated viable nanoparticles, the 0.7 ratio was selected for use, in order to give the largest quantity of gold per nanoparticle and hence the greatest contrast in X-CT imaging. Finally, to confirm that the gold nanoparticles do indeed sit within polymer micelle coronas as predicted, negative staining by uranyl acetate was used to visualize the polymer corona around each nanoparticle (Fig. ). The visualized corona size was ~2 times greater than the gold core, consistent with the expectation from DLS measurements (albeit the negative staining measurement used a dried sample). Micelle-templated gold nanoparticles are stable at high ionic strength and in the soil environment Since the soil environment contains significant, and highly varying, quantities of salt, we first confirmed that the polyPEGMA bottlebrush corona is adequate to stabilize the nanoparticles against flocculation at high ionic strength, I. This was tested using 1M solutions of NaCl (I = 1 M) and MgCl2 (I = 4 M). UV-vis data show that no discernible aggregation has occurred, with the traces the same as in salt-free water (Fig ). This confirms that the stabilizing effect of the polyPEGMA bottlebrush is extremely strong, and clearly sufficient for the ionic strengths typically found in the soil environment, e.g. 127 mM for an Australian soil sample (calculated from data in Ref ).