Real-time Thermal Imaging of Microwave Accelerated Metal-Enhanced Fluorescence (MAMEF) Based Assays on Sapphire Plates

In this paper, we describe an optical geometry that facilitates our further characterization of the temperature changes above silver island films (SiFs) on sapphire plates, when exposed to microwave radiation. Since sapphire transmits IR, we designed an optical scheme to capture real-time temperature images of a thin water film on sapphire plates with and without SiFs during the application of a short microwave pulse. Using this optical scheme, we can accurately determine the temperature profile of solvents in proximity to metal structures when exposed to microwave irradiation. We believe that this optical scheme will provide us with a basis for further studies in designing metal structures to further improve plasmonic-fluorescence clinical sensing applications, such as those used in microwave accelerated metal-enhanced fluorescence (MAMEF).     

Microwave-Triggered Chemiluminescence with Planar Geometrical Aluminum Substrates: Theory,Simulation and Experiment

Previously we combined common practices in protein detection with chemiluminescence, microwave technology, and metal-enhanced chemiluminescence to demonstrate that we can use low power microwaves to substantially increase enzymatic chemiluminescent reaction rates on particulate silvered substrates. We now describe the applicability of continuous aluminum metal substrates to potentially further enhance or "trigger" enzymatic chemiluminescence reactions. Furthermore, our results suggest that the extent of chemiluminescence enhancement for surface and solution based enzyme reactions critically depends on the surface geometry of the aluminum film. In addition, we also use FDTD simulations to model the interactions of the incident microwave radiation with the aluminum geometries used. We demonstrate that the extent of microwave field enhancement for solution and surface based chemiluminescent reactions can be ascribed to "lightning rod" effects that give rise to different electric field distributions for microwaves incident on planar aluminum geometries. With these results, we believe that we can spatially and temporally control the extent of triggered chemiluminescence with low power microwave (Mw) pulses and maximize localized microwave triggered metal-enhanced chemiluminescence (MT-MEC) with optimized planar aluminum geometries. Thus we can potentially further improve the sensitivity of immunoassays with significantly enhanced signal-to-noise ratios.     

Metal-Enhanced Fluorescence from Gold Surfaces: Angular Dependent Emission

The first observation of Metal-Enhanced Fluorescence (MEF) from large gold colloids is presented. Gold colloids, 40 and 200 nm diameter, were deposited onto glass substrates in a homogeneous fashion. The angular-dependent fluorescence emission of FITC-HSA, adsorbed onto gold colloids, was measured on a rotating stage which was used to evaluate MEF at all spatial angles. The emission intensity of FITC-HSA was found to be up to 2.5-fold brighter than the emission on bare glass substrates at an angle of 270 degrees. This is explained by the Radiating Plasmon Model, whereby the combined system, composed of the fluorophore and the metal colloids, emits with the photophysical characteristics of the fluorophore, after the excitation and the partial radiationless energy transfer between the excited states of the fluorophore and the surface plasmons of the gold colloids. The fluorescence enhancement was found to be higher with 200 nm gold colloids as compared to 40 nm colloids due to the increased contribution of the scattering portion of the 200 nm gold colloid extinction spectrum. These observations suggest that gold colloids could be used in MEF applications, offering more stable surfaces than the commonly used silvered surfaces, for applications requiring longer term storage and use.     

Quenching of TiO2 photo catalysis by silver nanoparticles

The plasmon resonance of metal nanostructures affects neighboring semiconductors, quenching or enhancing optical transitions depending on various parameters. These plasmonic properties are currently investigated with respect to topics such as photovoltaics and optical detection and could also have important consequences for photocatalysis. Here the effect of silver nanoparticles of a size up to 30 nm and at maximum 0.50 monolayers on the photocatalytic oxidation of ethylene on TiO₂ is studied. Since the plasmon resonance energy of silver nanoparticles is comparable with the TiO₂ band gap, dipole-dipole interaction converts excitons into heat at the silver nanoparticle. This indicates that plasmonic interaction with TiO₂ semiconductor catalysts can reduce the photo catalytic activity considerably.     

Thermo‐plasmonics: using metallic nanostructures as nano‐sources of heat

Recent years have seen a growing interest in using metal nanostructures to control temperature on the nanoscale. Under illumination at its plasmonic resonance, a metal nanoparticle features enhanced light absorption, turning it into an ideal nano‐source of heat, remotely controllable using light. Such a powerful and flexible photothermal scheme is the basis of thermo‐plasmonics. Here, the recent progress of this emerging and fast‐growing field is reviewed. First, the physics of heat generation in metal nanoparticles is described, under both continuous and pulsed illumination. The second part is dedicated to numerical and experimental methods that have been developed to further understand and engineer plasmonic‐assisted heating processes on the nanoscale. Finally, some of the most recent applications based on the heat generated by gold nanoparticles are surveyed, namely photothermal cancer therapy, nano‐surgery, drug delivery, photothermal imaging, protein tracking, photoacoustic imaging, nano‐chemistry and optofluidics.     

Spontaneous radiation of a two-level atom into multipole modes of a plasmonic nanoparticle

We consider the relaxation of an excited two-level system (TLS) positioned near a spherical plasmonic nanoparticle (NP). The transition frequency of the TLS is assumed to coincide with the frequency of the condensation point of NP plasmonic resonances. We show that the relaxation of the TLS excitation is a two-step process. Following an initial exponential decay, the TLS breaks in to Rabi oscillations. Depending upon the distance between the TLS and NP, the probability of the TLS being in the excited state exhibits either chaotic or nearly regular oscillations. In the latter case, the eigenfrequency of the TLS-NP system coincides with one of NP multipole modes.     

隧道电子激发的辛硫醇条纹相自组装膜上卟啉单分子荧光

利用扫描隧道显微镜诱导发光技术,对单个卟啉分子的电致荧光现象进行了研究. 为了避免金属衬底对单个卟啉分子的荧光淬灭,利用条纹状辛硫醇自组装膜作为脱耦合层,实现了单个中性卟啉分子的电致荧光,并且发现分子荧光的产生呈现双极性特征. 另外,分子瓣上的荧光强度要强于分子中心的荧光强度.     

Design and analysis of a vertical directional coupler between a three-dimensional plasmonic slot waveguide and a silicon waveguide

The design of a vertical directional coupler between a three-dimensional plasmonic slot waveguide and a silicon waveguide is theoretically investigated in detail. It consists of two steps: the design of isolated plasmonic slot waveguide and silicon waveguide and the determination of the gap between the two waveguides and the length of a coupling region. The designed structure transfers 70.8% of the power carried by the silicon waveguide mode to the plasmonic slot waveguide mode when the gap is 150 nm and the coupling length is 2.14 μm. The wavelength dependence of our vertical directional coupler is also studied. The analysis shows that the amount of the transferred power changes slightly over a very wide wavelength range between 1.40 μm and 1.61 μm. Moreover, if we employ the fabrication technology for silicon photonics, it is quite tolerant to the variation of the length of its coupling section. Finally, the vertical directional coupler is considered for a polarizer.     

Dispersive characteristics of surface plasmon polaritons on negative refractive index gratings

The dispersive characteristics of surface plasmon polaritons (SPPs) supported by a periodically corrugated boundary between vacuum and a negative refractive index, isotropic material were studied theoretically by numerical solution of a dispersion equation. SPP dispersion curves were correlated with the optical response of the corrugated boundary in frequency regions where SPPs can be excited by a normally incident plane wave. Abrupt reflectivity variations, characterized by the presence of a near unity maximum and an almost zero minimum, were found in regions where the boundary without corrugation exhibits low reflectivity and rather featureless reflectivity curves.     

Surface-plasmon wave at the planar interface of a metal film and a structurally chiral medium

The solution of a boundary-value problem formulated for a modified Kretschmann configuration shows that a surface-plasmon wave can be excited at the planar interface of a sufficiently thin metal film and a nondissipative structurally chiral medium, provided the exciting plane wave is p-polarized. An estimate of the wavenumber of the surface-plasmon wave also emerges thereby.