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Specific ion effects ranking in theHofmeister sequence are ubiquitousin biochemical, industrial, and atmospheric processes. In this experimentalstudy specific ion effects inexplicable by the classical DLVO theoryhave been investigated at curved water–metal interfaces ofgold nanoparticles synthesized by a laser ablation process in liquidin the absence of any organic stabilizers. Notably, ion-specific differencesin colloidal stability occurred in the Hückel regime at extraordinarilylow salinities below 50 μM, and indications of a direct influenceof ion-specific effects on the nanoparticle formation process arefound. UV–vis, zeta potential, and XPS measurements help toelucidate coagulation properties, electrokinetic potential, and theoxidation state of pristine gold nanoparticles. The results clearlydemonstrate that stabilization of ligand-free gold nanoparticles scalesproportionally with polarizability and antiproportionally with hydrationof anions located at defined positions in a direct Hofmeister sequenceof anions. These specific ion effects might be due to the adsorptionof chaotropic anions (Br–, SCN–, or I–) at the gold/water interface, leading torepulsive interactions between the partially oxidized gold particlesduring the nanoparticle formation process. On the other hand, kosmotropicanions (F–or SO42–) seem to destabilize the gold colloid, whereas Cl–and NO3–give rise to an intermediatestability. Quantification of surface charge density indicated thatparticle stabilization is dominated by ion adsorption and not by surfaceoxidation. Fundamental insights into specific ion effects on ligand-freeaqueous gold nanoparticles beyond purely electrostatic interactionsare of paramount importance in biomedical or catalytic applications,since colloidal stability appears to depend greatly on the type ofsalt rather than on the amount. [ABSTRACT FROM AUTHOR]