Fig. 3. (a and c) Temporal evolution of σ for the grafting process of HS-PEG on GNPs and plot of σ at full coverage against (b) the diameter of NPs and (d) HS-PEG molecular weight. The polymer molecular weight, original capping ligand and NP size were as follows: (a and b) 5.0 kg mol^–1 HS-PEG grafted to CTAB-capped NPs in various sizes, and (c and d) various molecular weights of HS-PEG grafted to 13 nm citrate-capped NPs. Dotted circles in (a) and (c) highlight σ at the grafting time of 3 min. The error bars in (b) represent standard deviation from three replicas each measurement.