# What is the role of NaCl in the functionalization of gold nanoparticles?

In the functionalization of gold nanoparticles (GNPs) through the sulfur-metal bond, this article (among others) states that $\ce{NaCl}$ is slowly added in the GNPs solution after addition of thiol compound.

What is the role of $\ce{NaCl}$ in the functionalization step?