Mapping Infrared Enhancement around Gold Nanoparticles Using Polyelectrolytes

Abstract

Enhancement of infrared signals from polyelectrolyte adsorbed on gold nanoparticles (GNPs) was studied in situ by attenuated total reflection infrared spectroscopy. Nanoparticles and polyelectrolytes were deposited using layer-by-layer techniques, and the infrared signal was studied as a function of particle size, particle density, and distance from particle surface. It was observed that enhancement is more pronounced for larger nanoparticles and it decreases with increasing distance from the particle surface. Furthermore, at high GNP coverage, the signal from the first polyelectrolyte layer is particularly enhanced, and the signal increases slowly with time, in contrast to subsequent layers. We assign this to polyelectrolyte adsorption within narrow gaps between nanoparticles, where the electric field is enhanced. Furthermore, enhanced absorption was observed in the gap between the GNPs and the germanium internal reflection element, which was confirmed by polarized measurements. This enhancement is more pronounced for silver particles, and it represents a promising route for analysis of surfaces by infrared spectroscopy.

In‐Situ Infrared Spectroscopy Applied to the Study of the Electrocatalytic Reduction of CO2: Theory, Practice and Challenges

“…Noticeable enhancements are found to start when d ≤2 R , where d is the center to center distance between nanostructures and R is the particle radius, and increases as the gap between nanostructures shrinks . This is in line with experimental data, since the maximum enhancements are usually observed when the nanostructures are closely packed but are not completely merged together …”

“…It has been firmly established that the degree of enhancement is dramatically influenced by the distance between the metal particles . For instance, Figures c and 3d show simulations of the electric field strength between two gold particles separated by 10 nm and 0 nm, respectively .…”

“…It has been firmly established that the degree of enhancement is dramatically influenced by the distance between the metal particles. [36,69,86,87] For instance, Figures 3c and 3d show simulations of the electric field strength between two gold particles separated by 10 nm and 0 nm, respectively. [71] The strength of the electric field is at least one order of magnitude larger around the contact point of the particles when compared to spheres with larger separation.…”

Nanoscale image of the drug/metal mono-layer interaction: Tapping AFM-IR investigations

“…As confirmed [7,47], the surface enhancement observed in IR spectroscopy is associated with the morphology of the metal structure and strongly increases with the size and thickness of the metal island. Thus, mono-layers with a high degree of nanoparticle coverage are expected to ensure large absorption enhancements.…”

“…The cationic polyelectrolyte poly(allylamine hydrochloride) (PAH) with a molar mass of 70 kDa was used for modification of the CaF2 surface. It should be noted that PAH does not give a strong IR spectral signal; thus, it has been used for such experiments [47]. For the appropriate modification, freshly clean CaF2 windows were placed in the vertical position into 20 mg/L PAH solutions with an ionic strength of 0.01 M and pH 5.6.…”