Water and Organic Solvent Dispersible Gold Nanorods that are pH Responsive

Shape‐controlled gold nanorods are prepared in the presence of a capping agent, cetyltrimethylammonium bromide (CTAB), which controls their morphology and dispersibility in water. To control their dispersibility between water and another organic solvent, a pH‐responsive amphiphile C18AA was introduced on gold nanorods instead of CTAB. The C18AA‐capped gold nanorods were dispersed in both water and chloroform. These gold nanorods were pH‐responsive depending on the extent of C18AA deprotonation observed: deprotonation of the terminal amine above pH 9.5 increases the hydrophobicity of the nanorods, resulting in them being more soluble in chloroform than in water. C18AA‐capped gold nanorods can transfer from the water phase to the organic phase by changing the pH from 9.0 to 12.5. The morphology of the nanorods did not change as a result of ligand‐exchange, or phase transfer, due to the stabilizing effect of the C18AA capping molecule. C18AA‐capped gold nanorods can also be transferred to the water phase by evaporating the chloroform. We prepared water and organic solvent dispersible gold nanorods using long‐chain amidoamine derivative (C18AA) as a capping agent, which shows selective adsorption properties on gold surfaces. Furthermore, dispersion solvent of the C18AA‐capped gold nanorods were controlled by pH change.