One-step synthesis and assembly of gold nanochains using the Langmuir monolayer of long-chain ionic liquids and their applications to SERS

Gold nanochains were prepared at the air/water interface under the Langmuir monolayer of a long-chain ionic liquid 1-hexadecyl-3-methylimidazolium bromide (C(16)mimBr) through the reduction of AuCl4- ions by UV-light irradiation. It is revealed that these nanochains are self-assembled from gold nanoparticles about an average diameter of 15 nm. The synthesis and assembly of the Au nanoparticles can be achieved in one step. It is found that the structures of the nanochains are mainly dependent on reaction temperature. Both the pi-pi interactions and the steric hindrance play important roles in the formations of the nanochains. The application of the thin film of Au nanochains as a substrate for surface-enhanced Raman scattering (SERS) was demonstrated. Interestingly, the enhancement property depended on the temperature. This means the effective hot spot'' of the metal nanochains are dependent on their lengths, which may be controlled by the temperature.