title: Particle size dependence of the surface-enhanced Raman scattering properties of densely arranged two-dimensional assemblies of Au(core)-Ag(shell) nanospheres.
abstract: We investigated the dependence of the surface-enhanced Raman scattering (SERS) activity of densely arranged two-dimensional assemblies of spherical Au(core)-Ag(shell) nanoparticles (Au/AgNSs) on the nanoparticle diameter. The size-controlled Au/AgNSs were synthesized using the Au nanosphere seed-mediated growth method without any bulky stabilizers. The diameters of the Au/AgNSs were 38, 53, and 90 nm and the ratio of the total diameter to the Au core diameter was adjusted to ca. 2.0. Extinction spectra of the colloidal solutions of these nanoparticles exhibited the prominent peak of the localized surface plasmon resonance (LSPR) of Ag and therefore the Au/AgNSs exhibited LSPR properties almost the same as Ag nanospheres. It was confirmed from SEM observation that the organic solvent-mediated liquid-liquid interface assembly technique easily generated densely arranged two-dimensional assemblies of the nanospheres. The extinction spectra of all the assemblies exhibited a prominent broad peak ranging from 500 nm to the near-infrared region, which is assigned to the longitudinal LSPR mode of the coupling nanospheres. The extinction intensity increased with increasing nanosphere diameter. The SERS activities of these assemblies were investigated using p-aminothiophenol as a probe molecule. The result revealed that the enhancement factor (EF) of the Raman signal dramatically increased upon increasing the particle diameter. The maximum EF obtained with a laser excitation wavelength of 785 nm was 1.90 × 10(6) for a nanosphere diameter of 90 nm. This renders the two-dimensional assemblies of the plasmonic Au/AgNSs promising for the development of highly sensitive SERS sensor platforms due to their strong electromagnetic effect.
authors.affiliation: College of Science and Technology, Nihon University, 1-8-14 Kanda Surugadai, Chiyoda-ku, Tokyo 101-8308, Japan. sugawa.kosuke@nihon-u.ac.jp.
authors.forename: Kosuke
authors.initials: K
authors.lastname: Sugawa
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Akiyama
authors.forename: Yoshimasa
authors.initials: Y
authors.lastname: Tanoue
authors.forename: Takashi
authors.initials: T
authors.lastname: Harumoto
authors.forename: Sayaka
authors.initials: S
authors.lastname: Yanagida
authors.forename: Atsuo
authors.initials: A
authors.lastname: Yasumori
authors.forename: Shohei
authors.initials: S
authors.lastname: Tomita
authors.forename: Joe
authors.initials: J
authors.lastname: Otsuki
mesh_terms: D000814:Aniline Compounds / Q000737:chemistry; D006046:Gold / Q000737:chemistry*; D054118:Nanospheres / Q000737:chemistry*; D010316:Particle Size; D012834:Silver / Q000737:chemistry*; D013059:Spectrum Analysis, Raman; D013438:Sulfhydryl Compounds / Q000737:chemistry; D020349:Surface Plasmon Resonance
chemical_list: D000814:Aniline Compounds; D013438:Sulfhydryl Compounds; D012834:Silver; D006046:Gold; C064316:4-aminothiophenol