In biomedical imaging many labs have sought to develop gold nanoparticles that are functionalized with biomolecules, as X-CT contrast agents that are targeted specifically to label cancerous tissue. Despite success in preclinical studies, these have not yet been translated into clinical practice . In the different context of soil science, however, their highly tailorable and non-toxic nature makes them an ideal candidate as a contrast agent. Assynthesized gold nanoparticles made by standard methods such as citrate reduction cannot, however, be used for this application. This is because their colloidal stability relies on electrical charge, meaning that they will flocculate (stick together) under the electrolyte conditions present in soil . Equally, they will non-specifically adhere to the solid surfaces of soil minerals. In a bionanoscience context, the analogous issues are typically addressed by a multi-step process whereby gold nanoparticles are first synthesized using small-molecule surfactants, and then these surfactants are displaced from the nanoparticle surface by the application of thiol-functionalized poly(ethylene glycol) (PEG). The PEG forms an antifouling corona that protects the nanoparticle from flocculation and/or surface interactions, and its biocompatiblility ensures the non-toxic nature of the resulting nanostructure. In a recent preliminary study, we demonstrated that gold nanoparticles created using this standard method are stable in soil and can be used as a flow tracer . This was achieved by functionalizing commercially available citrate-reduced gold nanoparticles with a heterobifunctional PEG reagent (α-methoxy-ω-mercapto PEG(CH3O-PEG-SH), which must be done under dilute solution conditions, and then intensively concentrating to generate the high concentrations required for soil X-CT imaging. Hence while technically successful, this method generates a reagent cost of the order of thousands of dollars per soil sample imaged, precluding practical application in environmental sciences.