Estimation of surface oxide on surfactant-free gold nanoparticles laser-ablated in water

Surfactant-free gold nanoparticles were prepared by laser ablation of a gold metal plate in water. The nanoparticles were characterized by absorption spectroscopy, zeta-potential measurements, and XPS spectroscopy. The nanoparticles are negatively charged because the surface atoms are partially oxidized to Au-O-, according to the literature by Sacher and co-workers (J. Phys. Chem. B, 2004, 108, 16864). We further examined electrostatic interactions between nanoparticle and cationic surfactants. It was found that the surfactant cations attach to the particle surface, neutralizing the particle charge. Taking advantage of the electrostatic interactions, we estimated that 3.3-6.6% of the surface gold atoms was oxidized in water.