Figure 6. A model describing the prerequisites for the formation of DNA nanoparticles by macromolecular crowding.

Due to the electrostatic repulsive force, DNA molecules are separated from each other in normal buffer solution. The buffer context, which can neutralize the charge of the DNA, screens the repulsive forces between them. Macromolecular crowding, which causes a strong depletion effect, exerts an attractive force between the DNA molecules. With the presence of the two factors, the attractive force between the DNA molecules overcomes the repelling force and DNA form nanoparticles. However neither of them can do it alone.