NaHS Induces Complete Nondestructive Ligand Displacement from Aggregated Gold Nanoparticles

Ligand displacement from gold is important for a series of gold nanoparticle (AuNP) applications. Complete nondestructive removal of organothiols from aggregated AuNPs is challenging due to the strong Au–S binding, the steric hindrance imposed by ligand overlayer on AuNPs, and the narrow junctions between the neighboring AuNPs. Presented herein is finding that monohydrogen sulfide (HS – ), an anionic thiol, induces complete and nondestructive removal of ligands from aggregated AuNPs. The model ligands include aliphatic (ethanethiol(ET)) and aromatic monothiols, methylbenzenethiol (MBT), organodithiol (benzenedithiol (BDT)), thioamides (mercaptobenzimidazole (MBI) and thioguanine (TG)), and nonspecific ligand adenine. The threshold HS – concentration to induce complete ligand displacement varies from 105 μM for MBI and TG to 60 mM for BDT. Unlike using HS –, complete ligand displacement does not occur when mercaptoethanol, the smallest water-soluble organothiol, is used as the incoming ligand. Mechanistically, HS – binding leads to the formation of sulfur monolayer on AuNPs that is characterized with S–S bonds and S–Au bonds, but with no detectable S–H spectral features. The empirical HS – saturation packing density and Langmuir binding constant on AuNPs are 960 ± 60 pmol/cm 2 and (5.5 ± 0.8) × 10 6 M –1, respectively. The successful identification of an effective ligand capable of inducing complete and nondestructive removal of ligands from AuNPs should pave the way for using AuNP for capture-and-release enrichment of biomolecules that have high affinity to AuNP surfaces.