The manuscript presents a thorough study of mixed pegylated self-assembled monolayers (SAMs) on gold nanoparticles (NPs). The authors have successfully attempted to address some deficiencies in NP surface modification studies, in particular by gaining insight into the affinities of different bioconjugates for the NP surface.
In my view, the manuscript could benefit from a few clarifications. In particular,
1. Some acronyms used in the manuscript appear field-specific and might need to be spelled out for a broader readership, e.g. SH-PEG and DMEM
2. Showing the exact chemical structures for the two bioconjugates, MUA and SH-PEG, might be useful for further MD simulation and NP surface modification studies
3. The most interesting observation of the present study is the effect of increasing MUA grafting density on PEG conformation. For comparison, it would be helpful to show how the increase in grafting density of PEG alone (in a single component SAM) affects the PEG conformation
4. The authors conclude that PEG conformation changes with increasing MUA density. However, on page 5, when quantifying “PEG to MUA ratio” in the SAMs, the authors appear to ignore the change in the PEG “footprint” associated with the change in PEG conformation. A brief discussion concerning the effect of change in PEG conformation on “PEG to MUA ratio” in SAMs would be useful
5. First line on page 7 refers to Figure 2b, where abscissa is “ Ratio SH-PEG/MUA”. The text on page 7 reads “… 0.7 [MUA]added/[SH-PEG]added…”, which is confusing
6. To strengthen the argument on changes in PEG conformation from mushroom to brush, a comparison of NP hydrodynamic diameter values for SH-PEG/MUA ratios below and above 0.7 would be useful. Quite a few values for NP hydrodynamic diameters are mentioned in the manuscript, yet there appears to be no clear comparison of NP hydrodynamic diameter in relation to change in PEG conformation