Takumi Sannomiya

Single binding events of nanoparticle-labeled DNA strands were detected as stepwise peak shifts in localized surface plasmon resonance by single particle measurement. We confirmed the number of binding events by observing label particles by scanning electron microscopy. Our simulation based on a multiple multipole program showed that the peak shift is dependent on interparticle gap size and binding position. The experimental peak shift distribution was also reproduced by simulation.

Biosensing with nanoholes is one of the most promising applications of nanoplasmonic devices. The sensor properties, however, are complex due to coupled resonances through propagating and localized surface plasmons. This Full Paper demonstrates experimental and simulation studies on different plasmonic hole systems, namely various patterns of circular holes in gold films. In contrast to most previous work, here, the challenging situation of optically thin films is considered. The refractive-inde

The optical signal of a localized surface plasmon resonance (LSPR)-based sensor combined with electrochemistry was investigated. Gold nanoparticles were immobilized on an indium tin oxide (ITO) substrate, which functioned as working electrode. Using cyclic voltammetry synchronized with LSPR sensing, surface reactions on gold were detected both electrically and optically. In the capacitive charging regime, optical signals linear to the applied potential were detected. Gold was found to be dissolv

Densely packed plasmonic particle arrays are investigated for biosensing applications. Such particle arrays exhibit interparticle optical coupling creating a strong field between the particles, which is useful for sensing purposes. The sensor properties, such as bulk sensitivity, layer sensitivity, and the depth of sensitivity are investigated with the aid of a multiple multipole program. Sensitivity to the analyte with low concentration is also examined by a dynamic adsorption processes. The de

Circularly polarized light (CPL) is currently receiving much attention as a key ingredient for next-generation information technologies, such as quantum communication and encryption. CPL photon generation used in those applications is commonly realized by coupling achiral optical quantum emitters to chiral nanoantennas. Here, we explore a different strategy consisting in exciting a nanosphere-the ultimate symmetric structure-to produce CPL emission along an arbitrary direction. Specifically, we

Control of the optical properties of nano-plasmonic structures is essential for next-generation optical circuits and high-throughput biosensing platforms. Realization of such nano-optical devices requires optical couplings of various nanostructured elements and field confinement at the nanoscale. In particular, symmetric coupling modes, also referred to as dark modes, have recently received considerable attention because these modes can confine light energy to small spaces. Although the coupling

Nanoscale gaps between metals can strongly confine electromagnetic fields that enable efficient electromagnetic energy conversion and coupling to nanophotonic structures. In particular, the gap formed by depositing a metallic particle on a metallic substrate produces coupling of localized particle plasmons to propagating surface plasmon polaritons (SPPs). Understanding and controlling the phase of such coupling is essential for the design of devices relying on nanoparticles coupled through SPPs.

A change of the optical coupling of plasmonic particles was observed upon deformation of a matrix elastomer where 50 nm gold particles were embedded. The coupling mode showed higher extinction at the polarization perpendicular to the strain direction than the parallel polarization, as deformation induces interparticle distance change. Simulation by a multiple multipole program confirmed such a spectral change when the orientation of a coupled particle cluster is deformed. The strain vector map w

Interference of electromagnetic multipoles can result in strong directionality of the electromagnetic waves from a single-object antenna, which is essential to realize directional optical nanoantennas below the wavelength of light. Beaming even from a spherically symmetric nanoantenna can be achieved when magnetic modes are utilized in dielectric antennas. More tuning parameters become available by including modes with multiple nodes in the radial direction inside the structure, which we call “r

Shape-dependent sensitivity of localized surface plasmon-based biosensing was investigated by combining single-particle protein-sensing and multiple multipole program simulation. Significantly higher sensitivity was observed for tetrahedral particles than spherical ones, which was revealed by careful structural analysis of individually measured particles. The simulation of the corresponding particles with layered protein adsorption model showed consistent optical property and sensitivity, which

The combination of interferometry and plasmonic structure, which consists of gold nanoparticle layer, sputter coated silicon oxide spacer layer, and aluminum mirror layer, was studied in transmission mode for biosensing and refractive index sensing applications. Because of the interferometric nature of the system, the information of the reflection amplitude and phase of the plasmonic layer can be deduced from one spectrum. The modulation amplitude in the transmission spectrum, caused by the inte

The Multiple multipole program (MMP) is one of the most reliable and accurate simulation methods for plasmonic structures. However, proper MMP modelling is not always trivial since the setting of the multipoles by automatic routines may fail or be inefficient. In such difficult cases, good understanding and experience of the user is needed. In order to illustrate this, four examples are considered and their efficient MMP modelling is explained. In the first two examples a non-spherical particle

A spherical metallic nanoparticle is the simplest and most frequently used example of plasmonic nanostructures. In such a highly symmetric structure the plasmon modes consist of degenerate multipoles, which cannot be separately observed by only utilizing energy resolved means. We here demonstrate nanoscale optical field mappings of degenerate multipole modes in spherical silver nanoparticles using an angle- and polarization-resolved cathodoluminescence technique combined with scanning transmissi

Differential phase contrast (DPC) scanning transmission electron microscopy was applied to investigate the magnetic structures of Fe granular films. The DPC images showed a cluster-like contrast of 200 nm in the lateral size, which could not be observed by Lorentz transmission electron microscopy in the Fresnel mode. The magnetization vector map reproduced from the DPC images indicated that a magnetization loop generally intersects several isolated particles of 20–40 nm in diameter. The films co