Characteristics of localized surface plasmons excited on mixed monolayers composed of self-assembled Ag and Au nanoparticles

Abstract

The fundamental characteristics of localized surface plasmon resonance (LSPR) excited on mixed monolayers composed of self-assembled Ag and Au nanoparticles (AgNPs and AuNPs, respectively) were investigated. Mixed monolayered films were fabricated at the air-water interface at different mixing ratios. The films retained their phase-segregated morphologies in which AuNPs formed several 10 to 100 nm island domains in a homogeneous AgNP matrix phase. The LSPR bands originating from the self-assembled domains shifted to longer wavelengths as the domain size increased, as predicted by a finite-difference time-domain (FDTD) simulation. The FDTD simulation also revealed that even an alternating-lattice-structured two-dimensional (2D) AgNP/AuNP film retained two isolated LSPR bands, revealing that the plasmon resonances excited on each particle did not couple even in a continuous 2D sheet, unlike in the homologous NP system. The fluorescence quenching test of Cy3 and Cy5 dyes confirmed that the independent functions of AuNPs and AgNPs remained in the mixed films, whereas the AuNPs exhibited significantly higher quenching efficiency for the Cy3 dye compared with AgNPs due to the overlap of the excitation/emission bands of the dyes with the AuNP LSPR band. Various applications can be considered using this nanoheterostructured plasmonic assembly to excite spatially designed, high-density LSPR on macroscopic surfaces.

Tuning the Resonant Frequency of a Surface Plasmon by Double-Metallic Ag/Au Nanoparticles for High-Efficiency Green Light-Emitting Diodes

“…The resonant wavelength of the LSP mode for NPs 1, which was composed of only Ag, corresponded to ~516 nm, whereas that of NPs 5, which was composed of only Au, corresponded to ~630 nm. These values were similar to those obtained in previous research reports [35,36]. Additionally, the resonant wavelength of the LSP mode can be tuned by adjusting the ratio of Ag to Au in the NPs within the wavelength range of 516 nm to 630 nm.…”

“…Thus, we could match the resonant wavelength of the LSP to green-and yellow-emitting LEDs by tuning them. In addition, when the Ag NPs and Au NPs were separately formed, dual peaks in the absorption spectrum were observed, i.e., one corresponding to Ag NPs and the other corresponding to Au NPs, as presented in Reference [36]. However, we observed only a single peak in the absorption spectrum, as shown in Figure 3a.…”

High-resolution imaging of a cell-attached nanointerface using a gold-nanoparticle two-dimensional sheet

“…The SET theory predicts the energy transfer independently of the spectral overlap between the dyes and LSPR of the metal NPs, which instead depends on the dielectric constant of the bulk metal 28, 33 . However, as we reported in our previous study, the efficiency of energy transfer between fluorescent dyes and metal NPs certainly depends on the spectrum overlap 35, 36 . Therefore, plasmon-induced resonance energy transfer (PIRET) should be a more accurate explanation of this quenching phenomenon according to the most recent publications 37, 38 .…”

Electromagnetically induced transparency of a plasmonic metamaterial light absorber based on multilayered metallic nanoparticle sheets

“…The diameter of the silver core was approximately 5 nm. Stable, close-packed two-dimensional sheet structures of AgMy were fabricated at an air–water interface via hydrophobic interactions in a Langmuir Blodgett (LB) trough (KSV NIMA small trough, Biolin Scientific, Sweden) at room temperature111213141534. The AgMy nanosheet was transferred via the Langmuir–Schaefer (LS) technique onto hexamethyldisilazane (HMDS)-treated quartz substrates or dodecane thiol-functionalized thermally evaporated gold or silver thin films (200-nm thick) on quartz.…”

“…The intensity, wavelength, and linewidth of the absorption peak were changed by the number of layers and resulted in a colour change of the sample if they were placed on a metal substrate. We previously reported the unique optical properties of multilayered metallic nanoparticle sheets up to 5 layers12 and proposed several new applications, such as imaging13, colorimetric sensing14, and fluorescence controlling using Ag-Au nanosheets15. However, we had not noticed the peak splitting due to the EIT effect for multilayered metallic nanoparticle sheets until we have tried the layer deposition more than 5 layers.…”