pH-controlled reversible assembly and disassembly of gold nanorods

A pH-controlled reversible assembly and disassembly of Au nanorods in aqueous solutions using 3-mercaptopropionic acid (MPA), 11-mercaptoundecanoic acid (MUA), glutathione (GSH), and cysteine (CYS) as the assembling agents was demonstrated. The bifunctional molecules were first dissolved in deionized water to make make stock solutions at relatively high concentrations in order to minimize the dilution of the nanorod solutions. MUA in its powder form was directly used due to its low solubility in water. Calculated volumes of the stock solutions were then added into the as-prepared nanorod solutions so that the concentrations of the bifunctional molecules reached desired values. The pH value of the nanorod solutions was adjusted using 1 M aqueous HCl or NaOH solutions. induce both EE and SS assembly. It was observed that in the presence of MPA and MUA, the assembly occurs at higher pH while the disassembly occurs at lower pH.