Amplifying the macromolecular crowding effect using nanoparticles.

The melting temperature (T(m)) of DNA is affected not only by salt but also by the presence of high molecular weight (MW) solutes, such as polyethylene glycol (PEG), acting as a crowding agent. For short DNAs in a solution of low MW PEGs, however, the change of excluded volume upon melting is very small, leading to no increase in T(m). We demonstrate herein that by attaching 12-mer DNAs to gold nanoparticles, the excluded volume change was significantly increased upon melting, leading to increased T(m) even with PEG 200. Larger AuNPs, higher MW PEGs, and higher PEG concentrations show even larger effects in stabilizing the DNA. This study reveals a unique and fundamental feature at nanoscale due to geometric effects. It also suggests that weak interactions can be stabilized by a combination of polyvalent binding and the enhanced macromolecular crowding effect using nanoparticles.