Ag and Au Nanoparticles as Color Indicators for Monomer/Micelle-Nanoparticle Interactions

Ag and Au nanoparticles (NPs) were used as color indicators to determine the monomer/micelle adsorption on the NP surface. A simple methodology based on the color change of Ag/Au NPs upon interacting with surface-active molecules was developed. A contrasting color change occurred when NPs interact with the monomer/micelle. This was demonstrated by monitoring the adsorption behavior of a series of Gemini surfactants. UV-visible measurements showed a large change in the intensity and wavelength of Ag/Au NP absorbance upon the surface adsorption of the monomer/micelle of Gemini surfactants. The mechanism of surface adsorption and molecular orientation on the solid-liquid interface of NPs was determined by performing the FT-IR and XPS measurements. Results demonstrated that sharp color changes from yellow to red for Ag NPs and red to purple for Au NPs happened when the Gemini surfactant monomer/micelle adsorbs on the NP surface. This colorimeter-based methodology highlighted the applicability of Ag/Au NPs in complex media where such NPs frequently encounter surface-active molecules.

Automated summary

In this study, silver and gold nanoparticles were used as color indicators to determine the adsorption of monomers/micelles on the nanoparticle surface. A simple method based on color change was developed, and the adsorption behavior of Gemini surfactants was monitored. UV-visible measurements showed significant changes in the intensity and wavelength of absorbance when the monomer/micelle of Gemini surfactants adsorbed onto the silver/gold nanoparticles. FT-IR and XPS measurements were conducted to determine the mechanism of surface adsorption and molecular orientation. The results demonstrated distinct color changes for silver nanoparticles (yellow to red) and gold nanoparticles (red to purple) when the Gemini surfactant monomer/micelle adsorbed onto the nanoparticle surface. This colorimeter-based method highlights the applicability of silver and gold nanoparticles in complex media with surface-active molecules.