Surface Plasmon States Research Articles

Surface Plasmon Coupling Electrochemiluminescence Immunosensor Based on Polymer Dots and AuNPs for Ultrasensitive Detection of Pancreatic Cancer Exosomes.

Polymer dots (Pdots) have become attractive electrochemiluminescence (ECL) luminophores due to their facile synthesis, easy modification, and stable electrochemical and optical properties. However, their ECL efficiency is not high enough for practical applications. In this work, we proposed an ECL immunosensor based on localized surface plasmon resonance (LSPR) between AuNPs and Pdots for the determination of pancreatic cancer exosomes. Based on the finite-difference time-domain simulations and the band energy of Pdots and AuNPs, we proposed the possible LSPR mechanism. The hot electrons of plasmonic AuNPs were photoexcited to surface plasmon states by ECL emission of Pdots, and then the excited hot electrons were transferred to the conduction band of Pdots, which significantly improved the ECL efficiency of Pdots. The ECL immunosensor displayed a wide calibration range of 1.0 × 103 to 1.0 × 106 particles/mL with a detection limit of 400 particles/mL. Cancer-related protein profiling revealed high selectivity toward different expressions of exosomal surface proteins from PANC-01, HeLa, MCF-7, and HPDE6-C7 cell lines. The proposed ECL system exhibits a promising prospect for protein biomarker profiling and early cancer-related diagnosis.

Wavelength-Tunable Purcell Effect in a Surface Plasmon Polariton State on a Metamaterial Edge

Layered metal-dielectric structures are easy-to-fabricate one-dimensional plasmonic metamaterials. Using the effective media approach, we consider surface plasmons that appear on an interface between such metamaterial and a dielectric. We have shown that two types of surface plasmon states appear on an interface. The frequency of the peak in the local density of states of these states is dependent on the fraction of metal in the metamaterial. By reducing the fraction, the frequency can be shifted towards longer wavelengths. There the losses of light in metal are reduced, which, as we have shown, leads to the increase in peak value of the Purcell factor.

Resonant Optical Phenomena in Heterogeneous Plasmon Nanostructures of Noble Metals: A Review

The interaction of electromagnetic radiation with ordered and disordered arrays of noble metal nanoparticles, leading to the excitation of various modes of surface plasmon states in them, is analyzed. The dipole localized surface plasmon resonance in isolated nanoparticles and the influence of various size effects on its optical response are considered. The effect of dipole-dipole interaction between gold and silver nanoparticles on the optical properties of various nanosized and nanostructured objects is discussed. It is shown that both localized and delocalized (propagated) surface plasmon modes can be excited in composite gold and silver nanosystems, in particular, in porous films. The prospects for the practical application of nanostructures with arrays of gold and silver nanoparticles in sensor technology, surface-enhanced Raman spectroscopy, and modern optoelectronics are examined.

Fano resonance in the CsPbBr3 nanocrystal/Ag nanostructure through the exciton-plasmon coupling

Fano resonance (FR) has attracted more attention recently due to its outstanding properties, such as coherent interference at the resonant energy and intense changes in the spectral lines. Here, we studied the FR effects in the CsPbBr3 nanocrystal (NC)/Ag nanostructure coupling structure. The FR effects cause asymmetric line shapes in both the reflection and transmission spectra. A sharp variation was observed in the spectral line at the exciton energy of CsPbBr3 NC. The FR in this coupling structure is attributed to the configuration interaction between the exciton state and the surface plasmon (SP) states. From the coupling theory, we suggest that it is necessary to consider multiSP states in the interaction Hamiltonian, instead of a single SP state, which will induce more interesting effects. Moreover, we demonstrate that the FR effects are sensitively dependent on the spacing in the coupling structure. The sharp variation of the spectral line shape at the resonant energy and its sensitivity on the spacing in the coupling structure make the FR effects an important candidate as the optical monitoring methods in the application of real time artificial tunable optoelectronic device at the nanoscale.

Investigation of Purcell Factor for an Activator Ion due to Surface Plasmon Modes

We considered earlier the role of the surface plasmon states in the spontaneous decay of an optically active ion in proximity to a flat, metallic surface. In this work we have extended our earlier results to obtain an expression for the density of plasmon states accessible to the ion. We express the spontaneous decay rate of the ion into the surface plasmon field in terms of the density of final states and the appropriate “Einstein” B-coefficient, which depends on the matrix elements of the ion-surface plasmon interaction. Next we derive an expression for the contribution of the surface plasmons to the total radiative decay rate, and determine the Purcell factor of this system. Finally, calculations are presented showing how the Purcell factor for an optically active ion near a silver surface depends on the wavelength of the transition and distance of the ion from the surface.

The Role of Metal Nanostructures in CO2 Photoreduction

Process of CO2 reduction requires substantial decrease of the energy barriers. Consequently, one of the promising way to approach this problem is using use of metal nanoparticles to accelerate electrons and make them more electronegative at the end of this process. Better understanding of the photo-induced phenomena enables to improve design & construction of semiconductor architectures governing the efficiency of CO2 reduction and its selectivity. The objective of this presentation will rely onto use of semiconductor photocathode with co-assembly of plasmonic and catalytic metal nanoparticles, such as silver or gold with other metal electrocatalysts which decrease the energy barriers of the CO2 reduction process through interaction of photo-excited surface plasmon states with adsorbed reaction intermediates. The significance to investigate reduction of CO2 with gold, silver and copper nanoparticles, enhanced by the extra activation of the process provided by the illuminated, incorporated plasmonic metallic nanostructures is supported by the occurrence of the photo-emission process associated with the decay of photo-excited surface plasmons. The occurrence, and contribution of this process to the overall efficiency of the CO2 reduction process as well as its impact on the distribution of the products will be investigated and discussed in detail. Moreover, the tradeoff between CO2 and water reduction will be continuously investigated and discussed in view of choice of the best metal-based catalyst designed for high efficiency and best selectivity CO2 reduction process.

Photoluminescence enhancement of tris(8-hydroxyquinolinato)aluminum thin film by plasmonic Ag nanotriangle array fabricated by nanosphere lithography

Enhancement of 4.4-fold photoluminescence (PL) of tris(8-hydroxyquinolinato)aluminum (Alq3) thin film was observed in the presence of 50-nm thick Ag nanotriangles (NTs) compared with bare Alq3 film at room temperature. According to the temperature dependence of integrated PL intensity and the PL lifetime obtained from time-resolved PL measurements, an increase in radiative recombination rate was observed over a wide temperature range. Because the absorption peak originated from localized surface plasmon (LSP) states and the emission spectra are well overlapped, the observed enhancement can be explained by efficient coupling of the LSP of the Ag NTs with the emission from the Alq3.

Photo/ Catalytic Activation of Carbon Dioxide through Implementation of Plasmonic Metal Nanoparticles

Investigations of the photo-induced phenomena enabling to improve and understand fundamental processes involved in CO2 reduction includes co-assembly of plasmonic and catalytic metal nanoparticles to the build-up of a semiconductor photocathode. Combination of the nanostructures of plasmonic metals, such as silver or gold with other metal electrocatalysts will substantially decrease the energy barriers of the CO2 reduction process through interaction of photo-excited surface plasmon states with adsorbed reaction intermediates. The significance to investigate reduction of CO2 at gold, silver and copper surfaces enhanced by the extra activation of the process provided by the illuminated, incorporated plasmonic metallic nanostructures is supported by the occurrence of the photo-emission process associated with the decay of photo-excited surface plasmons. Of particular interest will be a strong influence of the Ag/FTO electrode roughness upon the photo-emissive cathodic currents of electro-reduction of CO2 dissolved in aqueous solution. Actually, two metals Ag and Au, the nanostructures of which exhibit strong excitation of surface plasmon resonance through interaction with near UV and visible photons are also catalytically active toward electro-reduction of CO2. Besides the photo-emission, another property of plasmonic NPs – heat generation resulting from the absorption of incident photons and their influence on the reduction of CO2 at composite cathodes will be the objectives of this presentation.

Role of Metal Nanoparticles in Photo/ Catalytic Activation of Carbon Dioxide

Investigations of the photo-induced phenomena enabling to improve and understand fundamental processes involved in CO2 reduction includes co-assembly of plasmonic and catalytic metal nanoparticles to the build-up of a semiconductor photocathode. Combination of the nanostructures of plasmonic metals, such as silver or gold with other metal electrocatalysts will substantially decrease the energy barriers of the CO2 reduction process through interaction of photo-excited surface plasmon states with adsorbed reaction intermediates. The significance to investigate reduction of CO2 at gold, silver and copper surfaces enhanced by the extra activation of the process provided by the illuminated, incorporated plasmonic metallic nanostructures is supported by the occurrence of the photo-emission process associated with the decay of photo-excited surface plasmons. Of particular interest will be a strong influence of the Ag/FTO electrode roughness upon the photo-emissive cathodic currents of electro-reduction of CO2 dissolved in aqueous solution. Actually, the two metals Ag and Au, the nanostructures of which exhibit strong excitation of surface plasmon resonance through interaction with near UV and visible photons are also catalytically active toward electro-reduction of CO2. Besides the photo-emission, another property of plasmonic NPs – heat generation resulting from the absorption of incident photons and their influence on the reduction of CO2 at composite cathodes will be the objectives of this presentation.

Thin film based plasmon nanorulers

In this work, isolated metal nanoparticles are supported on a dielectric thin film that is placed on a conducting plane. The optical scattering characteristics of these metal nanoparticles are directly correlated with the localized surface plasmon states of the nanoparticle—image particle dimer, formed in the conducting plane below. Quantification of plasmon resonance shifts can be directly correlated with the application of the plasmon nanoruler equation. This simple geometry shows that direct optical techniques can be used to resolve thickness variations in dielectrics of only a few nanometers.

Laser-driven parametric instability and generation of entangled photon-plasmon states in graphene

We show that a strong infrared laser beam obliquely incident on graphene can experience a parametric instability with respect to decay into lower-frequency (idler) photons and THz surface plasmons. The instability is due to a strong in-plane second-order nonlinear response of graphene which originates from its spatial dispersion. The parametric decay leads to efficient generation of THz plasmons and gives rise to quantum entanglement of idler photons and surface plasmon states.

Effects of silver nanoparticles on Raman spectrum and fluorescence enhancement of nano-diamond

The nano-diamond has been a hot topic in the field of nano-science and nanotechnology for its optical properties. Much effort has been devoted to improving the fluorescence and Raman scattering intensity of nitrogen-vacancy (NV) center in nano-diamond by using plasmon resonance effect in sensing area. A combination of Ag nanoparticle and diamond can not only take advantage of the stability and biocompatibility of diamond, but also enhance the local electric field around NV center through the Ag nanoparticles, thereby speeding up the radiation of the fluorescent near the surface of the substrate, improving the strength and stability of the fluorescence, and greatly broadening the application areas of Raman spectroscopy. In this paper, we mix the nano-diamonds with Ag nanoparticles to improve the fluorescence and Raman scattering intensity on the basis of the localized surface plasmon resonance effect. The influences of Ag mass concentration on the Raman spectrum and fluorescence intensity are investigated. The results show that when the concentration of nano-Ag nanoparticles reaches up to 5 wt%, the light intensity becomes saturated, but the concentration further increases up to a value more than 7 wt% the light intensity begins to decline. Then the corresponding radiative transition rate and the fluorescence quantum efficiency are investigated, and based on these researches, influences and mechanism of surface plasmon resonance (SPR) enhancement are discussed thoroughly. We deduced that the fluorescence enhancement is mainly due to the enhanced surface plasmon field caused by transfer of surface plasmon resonance energy and the energy transfer between surface plasmon and excited state of NV centers. When the concentration of Ag nanoparticles reaches an appropriate value, a suitable distance between metal nanoparticles and diamond is obtained, thereby ensuring the strong local electric field forming on the metal surface, accelerating the emitting photons of diamond in the excited state, and also suppressing the transfer of non-radiative energy, eventually leading to the increase of diamond fluorescence emission intensity.

Localized plasmons on a metal surface

This paper considers collective oscillations of electron density localized near a metal surface. Its description involves the wave equation of plasma oscillations. Assuming the axial symmetry of the problem, separation of variables in the equation is carried out and a set of analytical functions providing the variety of solutions is obtained. The solutions provide natural multipole quantization of surface plasmon states. Expressions are obtained for local potential fields formed by multipole plasmon modes at the interface. Their role in physical implementation of mechanisms of localization of excess electrons on the metal surface is discussed.

Coupling Behaviors of Surface Plasmon Polariton and Localized Surface Plasmon with an InGaN/GaN Quantum Well

Surface plasmon (SP) coupling behaviors of an InGaN/GaN quantum well (QW) with surface plasmon polariton (SPP) induced on a smooth Ag-film/GaN interface and localized surface plasmon (LSP) induced on randomly distributed surface Ag nanoparticles (NPs) are compared based on temperature-dependent, excitation power-dependent, and time-resolved photoluminescence (PL) measurements. By comparing the variations of PL excitation power-dependent emission at 10 and 300 K, the contribution of SP coupling to the increase of PL intensity can be differentiated from that of PL excitation-intensity increase at the QW due to the enhanced reflection at the Ag/GaN interface. The observed stronger SP coupling effect through SPP, when compared with that through LSP, is attributed to its larger available SP state number per unit area for coupling with the QW. Although the SP coupling strength through LSP on the surface Ag NPs is weakly dependent on PL excitation power, that through SPP at the smooth Ag-film/GaN interface increases significantly with PL excitation power. Such different behavior is due to the abundant SPP states available for coupling with the QW of a higher carrier density. It can also be attributed to the spectral blueshift of QW emission through the screening of the quantum-confined Stark effect and the band filling effect for QW coupling with SPP of a higher density of state.

Origami with negative refractive index to generate super-lenses

Negative refractive index materials (NRIM) enable unique effects including superlenses with a high degree of sub-wavelength image resolution, a capability that stems from the ability of NRIM to support a host of surface plasmon states. Using a generalized lens theorem and the powerful tools of transformational optics, a variety of focusing configurations involving complementary positive and negative refractive index media can be generated. A paradigm of such complementary media are checkerboards that consist of alternating cells of positive and negative refractive index, and are associated with very singular electromagnetics. We present here a variety of multi-scale checkerboard lenses that we call origami lenses and investigate their electromagnetic properties both theoretically and computationally. Some of these meta-structures in the plane display thin bridges of complementary media, and this highly enhances their plasmonic response. We demonstrate the design of three-dimensional checkerboard meta-structures of complementary media using transformational optics to map the checkerboard onto three-dimensional corner lenses, the only restriction being that the corresponding unfolded structures in the plane are constrained by the four color-map theorem.

Morphology-induced redistribution of surface plasmon modes in two-dimensional crystalline gold platelets

The 2D optical field intensity distribution in sub-micron, ultrathin, and crystalline gold platelets is investigated by two-photon luminescence (TPL) microscopy. In particular, the evolution of the TPL maps as the particle morphology undergoes a transition from triangular to hexagonal reveals that the signatures of the high-order surface plasmon states sustained by the platelets follows the same C3v to C6v symmetry redistribution. Experimental observations are precisely accounted for by theoretical simulations based on the Green dyadic method.

Conic hyperspectral dispersion mapping applied to semiconductor plasmonics

The surface plasmon resonance tracking over metal surfaces is a well-established, commercially available, biochemical quantification tool primarily applied in research. The utilization of such a tool is, however, constrained to highly specialized industries, capable of justifying the human and instrumental resource investments required by the characterization method. We have proposed to expand the field of application of this biosensing approach by redesigning this method through the integration and miniaturization within a semiconductor platform. Uncollimated and broadband emission from a light-emitting semiconductor is employed to couple a continuum of surface plasmon modes over a metal–dielectric architecture interfaced with a GaAs–AlGaAs substrate. A tensor version of rigorous coupled wave theory is employed to optimize the various fabrication specifications and to predict the light scatterings over a wide range of variables. We then present a hyperspectral characterization microscope capable of directly mapping the dispersion relation of scattered light, including diffracted surface plasmons, as an intensity distribution versus photon energy and surface wavevectors. Measurements carried out in a buffered solution demonstrate the accurate description of the uncollimated and broadband surface plasmon states. Finally, we introduce a simplified method of dispersion mapping, in which quasi-conic cross-sections of the light's scattering can be acquired directly, thus monitoring surficial responses in as fast as 1.2 s. This is over 300 times faster than required by implementing full dispersion mapping. While compromising on the volume of collected information, this method, combined with the solid-state integration of the platform, shows great promise for the fast detection of biochemical agents. Researchers have miniaturized surface plasmon resonance experiments by using microchips embedded with gallium arsenide ‘quantum wells’. One of the best ways to track biochemical agents is through surface plasmon resonance spectroscopy, a technique that uses vibrations from a thin metal layer to detect specific molecular adsorption events. However, observing surface plasmons for biosensing traditionally requires the use of large, precisely tuned light sources. The scheme developed by Dubowski and co-workers employs hyperspectral imaging—a means of measuring data from hundreds of different spectral bands—to record how the broadband light of quantum well nanostructures scatters after striking a metal film. Advanced algorithms then pick out surface plasmons from the light-scattering data and enable near real-time analysis. Solid-state integration and pre-analysed output make this device ideal for future commercial ventures that could go beyond the application of surface plasmon resonance for biosensing.

Surface–plasmon-coupled photoluminescence from CdS nanoparticles with Au films

The enhancement of surface–plasmon-coupled photoluminescence from CdS nanoparticles was examined for various thicknesses of sputtered Au films. The improved luminescence with thickness control of Au correlated well with the increased density of surface–plasmon states, which was modified by the plasmon-dispersion relation at the planar Au/PMMA interface. By annealing the Au films to form a rough surface morphology, the emission in the CdS nanoparticles was further enhanced by the improved excitation and coupling of the surface–plasmon modes.

Surface Plasmon States in Inhomogeneous Media at Critical and Subcritical Metal Concentrations

Semicontinuous metal-dielectric films are composed of a wide range of metal clusters of various geometries—sizes as well as structures. This ensures that at any given wavelength of incident radiation, clusters exist in the film that will respond resonantly, akin to resonating nanoantennas, resulting in the broad optical response (absorption) that is a characteristic of semicontinuous films. The physics of the surface plasmon states that are supported by such systems is complex and can involve both localized and propagating plasmons. This chapter describes near-field experimental and numerical studies of the surface plasmon states in semicontinuous films at critical and subcritical metal concentrations and evaluates the local field intensity statistics to discuss the interplay between various eigenmodes.

Gold nanoring trimers: a versatile structure for infrared sensing

In this work we report on the observation of surface plasmon properties of periodic arrays of gold nanoring trimers fabricated by electron beam lithography. It is shown that the localized surface plasmon resonances of such gold ring trimers occur in the infrared spectral region and are strongly influenced by the nanoring geometry and their relative positions. Based on numerical simulations of the optical extinction spectra and of the electric near-field intensity maps, the resonances are assigned to surface plasmon states arising from the strong intra-trimer electromagnetic interaction. We show that the nanoring trimer configuration allows for generating infrared surface plasmon resonances associated with strongly localized electromagnetic energy, thus providing plasmonic nanoresonators well-suited for sensing and surface enhanced near-infrared Raman spectroscopy.