The optical properties of gold nanoparticles with dopamine at different hydrogen ion concentration.

In this work, gold nanoparticles (Au NPs) were prepared by citrate reduction method, and the Surface-Enhanced Raman Scattering (SERS) intensities of these colloidal solutions with dopamine (DA) were compared at different hydrogen ion concentration (pH). The charged states of Au NPs and DA molecules at different pH were critical factors for the SERS intensity by affecting NPs aggregation degree via DA bridging-effect. The results showed that the SERS enhancement was strongest at intermediate pH ranges (pH 7-9), in which the Au NPs was sufficiently stable and the electrostatic interaction between the Au NPs and the DA molecules was appropriate, together with a slightly aggregating.