Gold (Au), silver (Ag), and Ag core Au shell nanoparticles (NPs) were explored as optical sensing agents for the sensitive detection of dopamine (DA) neurotransmitters in surface-enhanced Raman scattering (SERS) measurements. In these colloidal systems, dopamine (DA) molecules played as a cross-linker between M NPs (Au or Ag NPs), allowing them to reside in the confined junctions (i.e., hot spots) between aggregated NPs. The progressive addition of DA molecules (from 1 × 10 −6 to 1 × 10 −3 M) consequently decreased a primary absorption peak attributed to the characteristic M NPs and generated a secondary absorption peak at longer wavelengths attributed to heavily aggregated M NPs formed by molecular bridging effects of DA molecules at high concentrations. The aggregation degree of M NPs was also dependent on the surface states of Au and Ag NPs, i.e., DA molecules with positive amine groups induced more aggregations of Au NPs in comparison to Ag NPs with less negative charges. As the final outcome, Au NPs demonstrated higher sensitivity in SERS detection of DA at low concentrations (1 × 10 −7 to 1 × 10 −5 M), whereas Ag NPs exhibited the stronger Raman signals of DA molecules at high concentrations (1 × 10 −4 to 1 × 10 −3 M). Besides, Ag core Au shell NPs with the lowest surface coverage of Au shell exhibited more sensitive and stronger SERS activity for DA molecules than that of singular Au NPs, probably due to the combined contribution by Ag core with strong SERS intensity and Au shell with high SERS sensitivity.

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Silver nanoparticles (Ag NPs) prepared by the citrate reduction method were examined as surface-enhanced Raman scattering (SERS) substrates in the detection of dopamine (DA) molecules at different hydrogen ion concentrations. The aggregation of Ag NPs was influenced by the crosslinking effect of DA molecules as the function of pH of colloidal solution. Somewhat clustering of Ag NPs in a limited pH range (pH 7-9) exhibited the strong red-shift of absorption peak and maximal SERS activity to DA molecules, highlighting the importance of strong electrostatic adsorption and cross-linking effect that allowed DA molecules to reside in the junctions (hot spots) between aggregated Ag NPs. Furthermore, Ag NPs with DA molecules at strongly basic condition (> pH 9) exhibited the relatively high SERS activity as compared to negligible SERS activity at acidic condition (< or = pH 5), indicating the important role of oxidized surface of silver NPs which can interact with hydroxyl groups of DA molecules.

Patterned copper oxide (CuO) microprotrusions have been developed by combining facile wet-chemical oxidation, photolithography and e-beam evaporation processes.

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.

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Flower-like gold nanostructures (so called gold nanoflowers) were electrodeposited on indium tine oxide (ITO) glass and served as a SERS-active substrate for sensing dopamine. A double-potential method was applied for the deposition of gold nanostructures on the glass. The density, size, and morphology of the gold nanostructures were controlled by adjusting parameters such as deposition potentials, duration, and concentrations of gold precursors. The particle density on the glass was controlled by changing the overvoltage potentials, while the size and morphology were controlled by changing the concentration of gold precursors and growth times of Gold crystal seeds. The intensity of the Raman spectrum of dopamine was distinctly enhanced on the gold nanostructures with unique flower-like topography, thereby demonstrating the utility of this SERS-active substrate that is facilely obtained by the double-potential deposition method without supporting electrolytes.