# 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?

$$\ce{NaCl}$$ acts as a charge suppressor so that the negatively charged gold nanoparticle and a negatively charged ligand (with thiol) are not longer charge repelled and can experience a chemical bond. $$\ce{NaCl}$$ is easily broken into $$\ce{Na+}$$ and $$\ce{Cl-}$$ so that the $$\ce{Na+}$$ can pacify the negative charge on the surface of the gold nanoparticle to become less negative and approach zero charge. Other higher charged salts such as $$\ce{Mg^2+}$$ impart even greater pacification.
in $$\pu{10 mM}$$ phosphate-buffered solution (pH 7.0) containing $$\pu{1.0 mmol L−1} ~\ce{NaCl}$$ at room …