Nanoparticle suspensions were transferred to zetasizer cuvettes (DTS1061, Malvern), flushed with filtered deionised water. Zeta potential measurements were made in triplicate for nanoparticle suspensions in deionised water and PBS (0.001 M) (parameters used for dispersant deionised water dispersant; refractive index: 1.330, viscosity: 0.8872 cP, dielectric constant: 78.5 εr, Model Smoluchowski F (Ka) 1.5). All samples were equilibrated to 25 °C for 120 seconds prior to measurement. All measurements were conducted in triplicate.