Synthesis and characterization of mixed monolayer protected gold nanorods and their Raman activities

The cetyltrimethylammonium bromide (CTAB) gold nanorods (AuNRs) were prepared by seed-mediated route followed by the addition of a Raman active compound (HS-(CH2)11-NHCO-coumarin) on the gold nanorods surfaces. Different stoichiometric mixtures of HS-(CH2)11-NHCO-coumarin and HS-PEG-(CH2)11COOH were evaluated for their Raman activities. The lowest stoichiometric ratio HS-(CH2)11-NHCO-coumarin adsorbed on gold nanorods surface was detected and enhanced by Raman spectroscopy. The produced mixed monolayer protected gold nanorods were characterized by UV-vis spectrometer for optical properties, transmission electron microscope (TEM) for structural properties (shape and aspect ratio) and their zeta potentials (charges) were obtained from ZetaSizer to determine the stability of the produced mixed monolayer protected gold nanorods. The Raman results showed a surface enhanced Raman scattering (SERS) enhancement at the lowest stoichiometric ratio of 1% HS-(CH2)11-NHCO-coumarin compared to high ratio of 50% HS-(CH2)11-NHCO-coumarin on the surface of gold nanorods.