Surface-enhanced infrared absorption spectra of eicosanoic acid on confeito-like Au nanoparticle

• Confeito-like Au nanoparticles enhanced IR absorption of eicosanoic acid.
• Enhancing factors of IR absorption reached around 200.
• Citrate on confeito-like Au nanoparticles anchored eicosanoic acid on hot-sites.

Surface-enhanced infrared absorption spectra of eicosanoic acid were measured with transmission mode using citrate-protected confeito-like Au nanoparticles on a CaF2 substrate. The absorption bands of the alkyl chain in eicosanoic acid were significantly enhanced around 200-fold of the control. This enhancing effect decreased, when the Au nanoparticles were dialyzed to remove excess citrate, suggesting that the citrate covering the Au nanoparticles played the role of anchoring the eicosanoic acid on the Au nanoparticles. It was also confirmed that the eicosanoic acid on the Au nanoparticles with the citrate was more ordered than that on the Au nanoparticles without the coverage of citrate. These findings are useful to design the plasmonics devices with ultrasensitive assay using the surface-enhanced infrared absorption spectroscopy based on the simple procedure.