Showing papers on "Surface plasmon resonance published in 2012"
TL;DR: This work investigates the plasmon resonances of individual ligand-free silver nanoparticles using aberration-corrected transmission electron microscope imaging and monochromated scanning TEM electron energy-loss spectroscopy, and presents an analytical quantum mechanical model that describes this shift due to a change in particle permittivity.
Abstract: The plasmon resonances of metallic nanoparticles have received considerable attention for their applications in nanophotonics, biology, sensing, spectroscopy and solar energy harvesting. Although thoroughly characterized for spheres larger than ten nanometres in diameter, the plasmonic properties of particles in the quantum size regime have been historically difficult to describe owing to weak optical scattering, metal-ligand interactions, and inhomogeneity in ensemble measurements. Such difficulties have precluded probing and controlling the plasmonic properties of quantum-sized particles in many natural and engineered processes, notably catalysis. Here we investigate the plasmon resonances of individual ligand-free silver nanoparticles using aberration-corrected transmission electron microscope (TEM) imaging and monochromated scanning TEM electron energy-loss spectroscopy (EELS). This technique allows direct correlation between a particle's geometry and its plasmon resonance. As the nanoparticle diameter decreases from 20 nanometres to less than two nanometres, the plasmon resonance shifts to higher energy by 0.5 electronvolts, a substantial deviation from classical predictions. We present an analytical quantum mechanical model that describes this shift due to a change in particle permittivity. Our results highlight the quantum plasmonic properties of small metallic nanospheres, with direct application to understanding and exploiting catalytically active and biologically relevant nanoparticles.
1,075 citations
TL;DR: RET from a plasmonic metal to a semiconductor is a viable and efficient mechanism that can be used to guide the design of photocatalysts, photovoltaics, and other optoelectronic devices.
Abstract: Plasmonic metal nanostructures have been incorporated into semiconductors to enhance the solar-light harvesting and the energy-conversion efficiency. So far the mechanism of energy transfer from the plasmonic metal to semiconductors remains unclear. Herein the underlying plasmonic energy-transfer mechanism is unambiguously determined in Au@SiO2@Cu2O sandwich nanostructures by transient-absorption and photocatalysis action spectrum measurement. The gold core converts the energy of incident photons into localized surface plasmon resonance oscillations and transfers the plasmonic energy to the Cu2O semiconductor shell via resonant energy transfer (RET). RET generates electron–hole pairs in the semiconductor by the dipole–dipole interaction between the plasmonic metal (donor) and semiconductor (acceptor), which greatly enhances the visible-light photocatalytic activity as compared to the semiconductor alone. RET from a plasmonic metal to a semiconductor is a viable and efficient mechanism that can be used to ...
1,026 citations
TL;DR: Gold nanoclusters have discrete electronic energy levels as opposed to the continuous band in plasmonic nanoparticles, and show multiple optical absorption peaks in the optical spectrum versus a single surface plAsmon resonance (SPR) peak at 520 nm for spherical gold nanocrystals.
Abstract: Gold nanoparticles typically have a metallic core, and the electronic conduction band consists of quasicontinuous energy levels (i.e. spacing δ ≪ kBT, where kBT is the thermal energy at temperature T (typically room temperature) and kB is the Boltzmann constant). Electrons in the conduction band roam throughout the metal core, and light can collectively excite these electrons to give rise to plasmonic responses. This plasmon resonance accounts for the beautiful ruby-red color of colloidal gold first observed by Faraday back in 1857.On the other hand, when gold nanoparticles become extremely small (<2 nm in diameter), significant quantization occurs to the conduction band. These quantum-sized nanoparticles constitute a new class of nanomaterial and have received much attention in recent years. To differentiate quantum-sized nanoparticles from conventional plasmonic gold nanoparticles, researchers often refer to the ultrasmall nanoparticles as nanoclusters.In this Account, we chose several typical sizes of ...
798 citations
TL;DR: This article surveys various plasmonic photocatalysts that have been prepared and characterized in recent years and describes the metal-semiconductor composite photocatalysis, in which noble metal nanoparticles are deposited on the surface of polar semiconductor or insulator particles.
Abstract: The efforts to produce photocatalysts operating efficiently under visible light have led to a number of plasmonic photocatalysts, in which noble metal nanoparticles are deposited on the surface of polar semiconductor or insulator particles. In the metal–semiconductor composite photocatalysts, the noble metal nanoparticles act as a major component for harvesting visible light due to their surface plasmon resonance while the metal–semiconductor interface efficiently separates the photogenerated electrons and holes. In this article, we survey various plasmonic photocatalysts that have been prepared and characterized in recent years.
714 citations
TL;DR: The plasmonic detection of single molecules in real time without the need for labelling or amplification is reported, and the binding of single proteins is detected by monitoring the plAsmon resonance of the nanorod with a sensitive photothermal assay.
Abstract: Existing methods for the optical detection of single molecules require the molecules to absorb light to produce fluorescence or direct absorption signals. This limits the range of species that can be detected, because most molecules are purely refractive. Metal nanoparticles or dielectric resonators can be used to detect non-absorbing molecules because local changes in the refractive index produce a resonance shift. However, current approaches only detect single molecules when the resonance shift is amplified by a highly polarizable label or by a localized precipitation reaction on the surface of a nanoparticle. Without such amplification, single-molecule events can only be identified in a statistical way. Here, we report the plasmonic detection of single molecules in real time without the need for labelling or amplification. Our sensor consists of a single gold nanorod coated with biotin receptors, and the binding of single proteins is detected by monitoring the plasmon resonance of the nanorod with a sensitive photothermal assay. The sensitivity of our device is ∼700 times higher than state-of-the-art plasmon sensors and is intrinsically limited by spectral diffusion of the surface plasmon resonance.
669 citations
TL;DR: It is demonstrated that metallic phases of WO(3-δ) nanoparticles exhibit a strong and tunable localized surface plasmon resonance, which opens up the possibility of rationally designing plasMonic tungsten oxide nanoparticles for light harvesting, bioimaging, and sensing.
Abstract: Transition-metal oxide nanocrystals are interesting candidates for localized surface plasmon resonance hosts because they exhibit fascinating properties arising from the unique character of their outer-d valence electrons. WO3−δ nanoparticles are known to have intense visible and near-IR absorption, but the origin of the optical absorption has remained unclear. Here we demonstrate that metallic phases of WO3−δ nanoparticles exhibit a strong and tunable localized surface plasmon resonance, which opens up the possibility of rationally designing plasmonic tungsten oxide nanoparticles for light harvesting, bioimaging, and sensing.
629 citations
TL;DR: Signals from a G-SERS substrate were demonstrated to have interesting advantages over normal SERS, in terms of cleaner vibrational information free from various metal-molecule interactions and being more stable against photo-induced damage, but with a comparable enhancement factor.
Abstract: Surface enhanced Raman spectroscopy (SERS) is an attractive analytical technique, which enables single-molecule sensitive detection and provides its special chemical fingerprints. During the past decades, researchers have made great efforts towards an ideal SERS substrate, mainly including pioneering works on the preparation of uniform metal nanostructure arrays by various nanoassembly and nanotailoring methods, which give better uniformity and reproducibility. Recently, nanoparticles coated with an inert shell were used to make the enhanced Raman signals cleaner. By depositing SERS-active metal nanoislands on an atomically flat graphene layer, here we designed a new kind of SERS substrate referred to as a graphene-mediated SERS (G-SERS) substrate. In the graphene/metal combined structure, the electromagnetic “hot” spots (which is the origin of a huge SERS enhancement) created by the gapped metal nanoislands through the localized surface plasmon resonance effect are supposed to pass through the monolayer graphene, resulting in an atomically flat hot surface for Raman enhancement. Signals from a G-SERS substrate were also demonstrated to have interesting advantages over normal SERS, in terms of cleaner vibrational information free from various metal-molecule interactions and being more stable against photo-induced damage, but with a comparable enhancement factor. Furthermore, we demonstrate the use of a freestanding, transparent and flexible “G-SERS tape” (consisting of a polymer-layer-supported monolayer graphene with sandwiched metal nanoislands) to enable direct, real time and reliable detection of trace amounts of analytes in various systems, which imparts high efficiency and universality of analyses with G-SERS substrates.
513 citations
TL;DR: A review of surface plasmon resonance-mediated photocatalysis can be found in this article, where the authors highlight diverse applications of plasmoric photocatalysts in mineralization of organic pollutants, organic synthesis and water splitting.
Abstract: Harvesting abundant and renewable sunlight in energy production and environmental remediation is an emerging research topic. Indeed, research on solar-driven heterogeneous photocatalysis based on surface plasmon resonance has seen rapid growth and potentially opens a technologically promising avenue that can benefit the sustainable development of global energy and the environment. This review briefly summarizes recent advances in the synthesis and photocatalytic properties of plasmonic composites (e.g., hybrid structures) formed by noble metal (e.g., gold, silver) nanoparticles dispersed on a variety of substrates that are composed of metal oxides, silver halides, graphene oxide, among others. Brief introduction of surface plasmon resonance and the synthesis of noble metal-based composites are given, followed by highlighting diverse applications of plasmonic photocatalysts in mineralization of organic pollutants, organic synthesis and water splitting. Insights into surface plasmon resonance-mediated photocatalysis not only impact the basic science of heterogeneous photocatalysis, but generate new concepts guiding practical technologies such as wastewater treatment, air purification, selective oxidation reactions, selective reduction reactions, and solar-to-hydrogen energy conversion in an energy efficient and environmentally benign approach. This review ends with a summary and perspectives.
464 citations
TL;DR: This work presents a facile approach to synthesize water-soluble noble metal coated SWNTs with a strong SERS effect suitable for labeling and fast Raman spectroscopic imaging of biological samples, which has been rarely realized before.
Abstract: Single-walled carbon nanotubes (SWNTs) with various unique optical properties are interesting nanoprobes widely explored in biomedical imaging and phototherapies. Herein, DNA-functionalized SWNTs are modified with noble metal (Ag or Au) nanoparticles via an in situ solution phase synthesis method comprised of seed attachment, seeded growth, and surface modification with polyethylene glycol (PEG), yielding SWNT-Ag-PEG and SWNT-Au-PEG nanocomposites stable in physiological environments. With gold or silver nanoparticles decorated on the surface, the SWNT-metal nanocomposites gain an excellent concentration and excitation-source dependent surface-enhanced Raman scattering (SERS) effect. Using a near-infrared (NIR) laser as the excitation source, targeted Raman imaging of cancer cells labeled with folic acid (FA) conjugated SWNT-Au nanocomposite (SWNT-Au-PEG-FA) is realized, with images acquired in significantly shortened periods of time as compared to that of using nonenhanced SWNT Raman probes. Owing to the strong surface plasmon resonance absorption contributed by the gold shell, the SWNTs-Au-PEG-FA nanocomposite also offers remarkably improved photothermal cancer cell killing efficacy. This work presents a facile approach to synthesize water-soluble noble metal coated SWNTs with a strong SERS effect suitable for labeling and fast Raman spectroscopic imaging of biological samples, which has been rarely realized before. The SWNT-Au-PEG nanocomposite developed here may thus be an interesting optical theranostic probe for cancer imaging and therapy.
425 citations
TL;DR: It is shown that the pH-responsive disassembly of the plasmonic vesicle, stimulated by the hydrophobic-to-hydrophilic transition of theHydrophobic brushes in acidic intracellular compartments, allows for triggered intrACEllular drug release.
Abstract: We report the development of bioconjugated plasmonic vesicles assembled from SERS-encoded amphiphilic gold nanoparticles for cancer-targeted drug delivery. This new type of plasmonic assemblies with a hollow cavity can play multifunctional roles as delivery carriers for anticancer drugs and SERS-active plasmonic imaging probes to specifically label targeted cancer cells and monitor intracellular drug delivery. We have shown that the pH-responsive disassembly of the plasmonic vesicle, stimulated by the hydrophobic-to-hydrophilic transition of the hydrophobic brushes in acidic intracellular compartments, allows for triggered intracellular drug release. Because self-assembled plasmonic vesicles exhibit significantly different plasmonic properties and greatly enhanced SERS intensity in comparison with single gold nanoparticles due to strong interparticle plasmonic coupling, disassembly of the vesicles in endocytic compartments leads to dramatic changes in scattering properties and SERS signals, which can serve as independent feedback mechanisms to signal cargo release from the vesicles. The unique structural and optical properties of the plasmonic vesicle have made it a promising platform for targeted combination therapy and theranostic applications by taking advantage of recent advances in gold nanostructure based in vivo bioimaging and photothermal therapy and their loading capacity for both hydrophilic (nucleic acids and proteins) and hydrophobic (small molecules) therapeutic agents.
398 citations
TL;DR: The recent development of SPR biosensor techniques, including bulk SPR and localized SPR (LSPR) biosensors, for detecting interactions between an analyte of interest in solution and a biomolecular recognition are reviewed.
Abstract: Optical Surface plasmon resonance (SPR) biosensors represent the most advanced and developed optical label-free biosensor technology. Optical SPR biosensors are a powerful detection and analysis tool that has vast applications in environmental protection, biotechnology, medical diagnostics, drug screening, food safety and security. This article reviews the recent development of SPR biosensor techniques, including bulk SPR and localized SPR (LSPR) biosensors, for detecting interactions between an analyte of interest in solution and a biomolecular recognition. The concepts of bulk and localized SPs and the working principles of both sensing techniques are introduced. Major sensing advances on biorecognition elements, measurement formats, and sensing platforms are presented. Finally, the discussions on both biosensor techniques as well as comparison of both SPR sensing techniques are made.
TL;DR: An SPR biosensor was developed by employing highly stable Au-protected Ag nanoplates (NP) as enhancers and retaining the strong surface plasmon resonance (SPR) of the silver nanoplate.
Abstract: An SPR biosensor was developed by employing highly stable Au-protected Ag nanoplates (NP) as enhancers (see picture). Superior performance was achieved by depositing a thin and uniform coating of Au on the Ag surface while minimizing disruptive galvanic replacement and retaining the strong surface plasmon resonance (SPR) of the silver nanoplates.
TL;DR: Yen-Hsun Su et al. as discussed by the authors showed that the efficiency of a plasmon-sensitized solar cell can be improved by depositing gold nanoparticles on the cell's surface.
Abstract: Layer-by-layer gold nanoparticles are used to generate photocurrent in an environmentally-friendly plasmon-sensitized solar cell towing to surface plasmon resonance. The efficiency of the photoelectric conversion of gold nanoparticle layers is increased as the intensity of surface plasmon resonance increases. We also explain the experimental results by modeling the phenomenon of charge separation and photocurrent formation, and the relationship between surface plasmon resonance and photocurrent formation, which has potential application in plasmon-sensitized solar cells and plasmonic solar cells in the future. The efficiency of a plasmon-sensitized solar cell can be improved by depositing gold nanoparticles on the cell’s surface. Achieving a high energy-conversion efficiency—the percentage of incident solar energy converted into electrical energy—is the primary goal for any solar cell technology. Yen-Hsun Su and colleagues at National Dong Hwa University in Hualien have now demonstrated that depositing multiple layers of gold nanoparticles on the surface of a plasmon-sensitized solar cell increases the amount of light scattered across its surface, boosting the amount of light absorbed and thus improving its efficiency. Once optimized, such gold-covered plasmonic solar cells have the potential to replace the more popular dye-sensitized solar cells.
TL;DR: In this paper, the authors exploit the uniquely strong and gate-tunable optical transitions of graphene to significantly modulate both the resonance frequency and quality factor of gold nanorod plasmon.
Abstract: Surface plasmon has the unique capability to concentrate light into subwavelength volume Active plasmon devices using electrostatic gating can enable flexible control of the plasmon excitations, which has been demonstrated recently in terahertz plasmonic structures Controlling plasmon resonance at optical frequencies, however, remains a significant challenge because gate-induced free electrons have very weak responses at optical frequencies Here we achieve efficient control of near-infrared plasmon resonance in a hybrid graphene-gold nanorod system Exploiting the uniquely strong and gate-tunable optical transitions of graphene, we are able to significantly modulate both the resonance frequency and quality factor of gold nanorod plasmon Our analysis shows that the plasmon-graphene coupling is remarkably strong: even a single electron in graphene at the plasmonic hotspot could have an observable effect on plasmon scattering intensity Such hybrid graphene-nanometallic structure provides a powerful way for electrical control of plasmon resonances at optical frequencies and could enable novel plasmonic sensing down to single charge transfer events
TL;DR: In this review, a special emphasis will be given to techniques used to link plasmonic nanostructures to surfaces, and the difference between colorimetric and refractive index sensing approaches will be briefly described.
TL;DR: The development of a point-of-care immunosensor for the detection of the cancer biomarker (total prostate-specific antigen, tPSA) using surface plasmon resonance (SPR) and quartz crystal microbalance (QCM) sensor platforms in human serum samples demonstrates the high potential of the developed sensor devices as platforms for clinical prostate cancer diagnosis and prognosis.
Abstract: Early detection of cancer is vital for the successful treatment of the disease. Hence, a rapid and sensitive diagnosis is essential before the cancer is spread out to the other body organs. Here we describe the development of a point-of-care immunosensor for the detection of the cancer biomarker (total prostate-specific antigen, tPSA) using surface plasmon resonance (SPR) and quartz crystal microbalance (QCM) sensor platforms in human serum samples. KD of the antibody used toward PSA was calculated as 9.46 × 10–10 M, indicating high affinity of the antibody used in developing the assay. By performing a sandwich assay using antibody-modified nanoparticles concentrations of 2.3 ng mL–1 (Au, 20 nm) and 0.29 ng mL–1 (8.5 pM) (Au, 40 nm) tPSA in 75% human serum were detected using the developed assay on an SPR sensor chip. The SPR sensor results were found to be comparable to that achieved using a QCM sensor platform, indicating that both systems can be applied for disease biomarkers screening. The clinical ap...
TL;DR: Experimental results reveal that these Au-BiVO(4) heterogeneous nanostructures exhibit much higher visible-light photocatalytic activities than the individual BiVO( 4) microtubes and nanosheets for both dye degradation and water oxidation.
Abstract: Au-BiVO4 heterogeneous nanostructures have been successfully prepared through in situ growth of gold nanoparticles on BiVO4 microtubes and nanosheets via a cysteine-linking strategy. The experimental results reveal that these Au-BiVO4 heterogeneous nanostructures exhibit much higher visible-light photocatalytic activities than the individual BiVO4 microtubes and nanosheets for both dye degradation and water oxidation. The enhanced photocatalytic efficiencies are attributed to the charge transfer from BiVO4 to the attached gold nanoparticles as well as their surface plasmon resonance (SPR) absorption. These new heteronanostructures are expected to show considerable potential applications in solar-driven wastewater treatment and water splitting.
TL;DR: An overview of surface plasmon resonance (SPR) sensing technology in Laboratory of Science and Technology of Micro-Nano Optics (LMNO) at the University of China is presented in this article.
Abstract: An overview of recent researches of surface plasmon resonance (SPR) sensing technology in Laboratory of Science and Technology of Micro-Nano Optics (LMNO), University of Science and Technology of China, is presented. Some novel SPR sensors, such as sensors based on metallic grating, metal-insulator-metal (MIM) nanoring and optical fiber, are designed or fabricated and tested. The sensor based on localized surface plasmon resonance (LSPR) of metallic nanoparticles is also be summarized. Because of the coupling of propagating surface plasmons and localized surface plasmons, the localized electromagnetic field is extremely enhanced, which is applied to surface-enhanced Raman scattering (SERS) and fluorenscence enhancement. Future prospects of SPR and/or LSPR sensing developments and applications are also discussed.
IBM1
TL;DR: In this paper, an infrared spectroscopy study of plasmon excitations in graphene in high magnetic fields is presented, showing that the edge plasmons develop increasingly longer lifetimes in high fields due to the suppression of backscattering.
Abstract: We present infrared spectroscopy study of plasmon excitations in graphene in high magnetic fields The plasmon resonance in patterned graphene disks splits into edge and bulk plasmon modes in magnetic fields Remarkably, the edge plasmons develop increasingly longer lifetimes in high fields due to the suppression of backscattering Moreover, due to the linear band structure of graphene, the splitting of the edge and bulk plasmon modes develops a strong doping dependence, which differs from the behavior of conventional semiconductor two-dimensional electron gas (2DEG) systems We also observe the appearance of a higher order mode indicating an anharmonic confinement potential even in these well-defined circular disks Our work not only opens an avenue for the investigation of the properties of Dirac magnetoplasmons but also supports the great potential of graphene for tunable terahertz magneto-optical devices
TL;DR: It is demonstrated that noble metal NPs such as Ag NPs function as visible-light harvesting and electron-generating centers during the daylight photocatalysis of AgBr@Ag.
Abstract: Noble metal nanoparticles (NPs) are often used as electron scavengers in conventional semiconductor photocatalysis to suppress electron-hole (e(-)-h(+) ) recombination and promote interfacial charge transfer, and thus enhance photocatalytic activity of semiconductors. In this contribution, it is demonstrated that noble metal NPs such as Ag NPs function as visible-light harvesting and electron-generating centers during the daylight photocatalysis of AgBr@Ag. Novel Ag plasmonic photocatalysis could cooperate with the conventional AgBr semiconductor photocatalysis to enhance the overall daylight activity of AgBr@Ag greatly because of an interesting synergistic effect. After a systematic investigation of the daylight photocatalysis mechanism of AgBr@Ag, the synergistic effect was attributed to surface plasmon resonance induced local electric field enhancement on Ag, which can accelerate the generation of e(-)-h(+) pairs in AgBr, so that more electrons are produced in the conduction band of AgBr under daylight irradiation. This study provides new insight into the photocatalytic mechanism of noble metal/semiconductor systems as well as the design and fabrication of novel plasmonic photocatalysts.
TL;DR: It is shown that atomically precise nanocrystal molecules are achievable and that the factor of atomic shell closing contributes to their extraordinary stability compared to other sizes, which opens up new opportunities for investigating many fundamental issues of nanocrystals.
Abstract: Since Faraday’s pioneering work on gold colloids, tremendous scientific research on plasmonic gold nanoparticles has been carried out, but no atomically precise Au nanocrystals have been achieved. This work reports the first example of gold nanocrystal molecules. Mass spectrometry analysis has determined its formula to be Au333(SR)79 (R = CH2CH2Ph). This magic sized nanocrystal molecule exhibits fcc-crystallinity and surface plasmon resonance at approximately 520 nm, hence, a metallic nanomolecule. Simulations have revealed that atomic shell closing largely contributes to the particular robustness of Au333(SR)79, albeit the number of free electrons (i.e., 333 - 79 = 254) is also consistent with electron shell closing based on calculations using a confined free electron model. Guided by the atomic shell closing growth mode, we have also found the next larger size of extraordinarily stability to be Au∼530(SR)∼100 after a size-focusing selection—which selects the robust size available in the starting polydisperse nanoparticles. This work clearly demonstrates that atomically precise nanocrystal molecules are achievable and that the factor of atomic shell closing contributes to their extraordinary stability compared to other sizes. Overall, this work opens up new opportunities for investigating many fundamental issues of nanocrystals, such as the formation of metallic state, and will have potential impact on condensed matter physics, nanochemistry, and catalysis as well.
TL;DR: Chemosensing based on angle-resolved surface plasmon resonance is demonstrated on intact cell phones using a disposable optical coupler and software to configure illumination and acquisition.
Abstract: Chemosensing based on angle-resolved surface plasmon resonance is demonstrated on intact cell phones using a disposable optical coupler and software to configure illumination and acquisition. This ...
TL;DR: This cavity–nanoparticle system effectively combines the advantages of Fabry–Perot microresonators with those of plasmonic nanoparticles, providing interesting features such as remote-sensing ability, incident-angle independent resonances, strong polarization dependence, lateral ultra small sensing volume and strongly improved detection resolution.
Abstract: Plasmonic nanoparticles are useful as optical sensors, but their spectral resolution is hindered by the linewidth of the plasmon resonance. Schmidt et al. find that coupling this resonance to a microcavity creates hybrid modes with enhanced sensing figure-of-merit and improved frequency resolution.
TL;DR: In this paper, a direct experimental comparison of the sensitivity and figure of merit of biosensors based either on surface plasmon polaritons on metal layers or on Bloch surface waves on one dimensional photonic crystals was conducted.
Abstract: We report on the direct experimental comparison of the sensitivity and figure of merit of biosensors based either on surface plasmon polaritons on metal layers or on Bloch surface waves on one dimensional photonic crystals. The comparison was carried out by making use of a commercial surface plasmon resonance platform that was slightly adapted for these experiments. Although the experimental conditions are not optimized for Bloch surface waves, our experiments demonstrate that both types of biosensors show a similar figure of merit for biochips deposited on low cost molded plastic substrates. For glass substrates with better optical quality, the increased homogeneity of the photonic crystals results in the Bloch surface wave sensors outperforming the surface plasmon polariton sensors by a factor 1.7 in terms of figure of merit. Considerations on the illumination bandwidth indicate options to further increase such a factor.
TL;DR: In this article, the authors proposed a Au/TiO2/Au nanostructure with the thickness of the middle layer TiO2 nanosheets around 5 nm, which satisfies the distance needed for the coupling effect between the opposite and nearly touching Au nanoparticles, and thus, it can be used as a "plasmonic coupling photocatalyst".
Abstract: The enhanced near-field amplitude of localized surface plasmon resonance in the proximity of metal nanoparticles can boost the photocatalytic activity of the neighboring semiconductor, which has been proven and has attracted wide interest recently. Since the plasmon resonance energy strongly depends on the metal particle size and shape, interparticle spacing, and dielectric property of the surrounding medium, it is available to improve the photocatalytic activity of the neighboring semiconductor by designing and synthesizing targeted metal nanoparticles or assembled nanostructures. In this paper, we propose a Au/TiO2/Au nanostructure with the thickness of the middle layer TiO2 nanosheets around 5 nm, which satisfies the distance needed for the coupling effect between the opposite and nearly touching Au nanoparticles, and thus, it can be used as a “plasmonic coupling photocatalyst”. Compared with the bare TiO2 nanosheet films, the photocurrent density of this favorable nanostructure exhibited a significant...
TL;DR: In this article, a model system composed of hybrid graphene-gold nanorod structure is presented, where the strong optical transitions in graphene can be switched on and off, which leads to significant modulation of both the resonance frequency and quality factor of plasmon resonance in gold nanorods.
Abstract: Surface plasmon, with its unique capability to concentrate light into sub-wavelength volume, has enabled great advances in photon science, ranging from nano-antenna and single-molecule Raman scattering to plasmonic waveguide and metamaterials. In many applications it is desirable to control the surface plasmon resonance in situ with electric field. Graphene, with its unique tunable optical properties, provides an ideal material to integrate with nanometallic structures for realizing such control. Here we demonstrate effective modulation of the plasmon resonance in a model system composed of hybrid graphene-gold nanorod structure. Upon electrical gating the strong optical transitions in graphene can be switched on and off, which leads to significant modulation of both the resonance frequency and quality factor of plasmon resonance in gold nanorods. Hybrid graphene-nanometallic structures, as exemplified by this combination of graphene and gold nanorod, provide a general and powerful way for electrical control of plasmon resonances. It holds promise for novel active optical devices and plasmonic circuits at the deep subwavelength scale.
TL;DR: The complete plasmonic spectrum of silver nanodisks is mapped by electron energy loss spectroscopy and it is shown that the mode which couples strongest to the electron beam has radial symmetry with no net dipole moment.
Abstract: We map the complete plasmonic spectrum of silver nanodisks by electron energy loss spectroscopy and show that the mode which couples strongest to the electron beam has radial symmetry with no net dipole moment. Therefore, this mode does not couple to light and has escaped from observation in optical experiments. This radial breathing mode has the character of an extended two-dimensional surface plasmon with a wavenumber determined by the circular disk confinement. Its strong near fields can impact the hybridization in coupled plasmonic nanoparticles as well as couplings with nearby quantum emitters.
TL;DR: In this paper, a surface plasmon resonance based affinity biosensor comprising of 2S2G (Ge20Ga5Sb10S65) chalcogenide prism, graphene-multilayer and gold as a plasm active metal is proposed for sensing over a broad wavelength range in visible and near infrared regime.
Abstract: Surface plasmon resonance based affinity biosensor comprising of 2S2G (Ge20Ga5Sb10S65) chalcogenide prism, graphene-multilayer and gold as a plasmon active metal is proposed for sensing over a broad wavelength range in visible and near infrared regime. We have investigated and carried out detailed analysis to design high performance affinity biosensor by exploiting the unique optical properties of chalcogenide glass and graphene. The performance of the biosensor has been quantified in terms of sensitivity and detection accuracy. The sensitivity of proposed biosensor increases significantly due to the presence of graphene where as the detection accuracy increases by more than 100% because of high index chalcogenide glass as compared to silica glass. Also, the detection accuracy of the proposed sensor in near IR is 16 times more as compared to that in visible. Adequate values of crucial design parameters have been optimized to achieve the best possible sensing performance over a broad wavelength range.
TL;DR: The SERS performance of nanoparticle-functionalized paper can be optimized by controlling the 3D distribution of the metallic nanoparticles, and such control is critical if these systems are to be implemented as a low-cost and highly sensitive bioassay platform.
Abstract: This work investigates the effect of gold nanoparticle (AuNP) addition to paper substrate and examines the ability of these composite materials to amplify the surface enhanced Raman scattering (SERS) signal of a dye adsorbed. Paper has a three-dimensional (3D), porous, and heterogeneous morphology. The manner in which paper adsorbs the nanoparticles is crucial to its SERS properties, particularly with regards to aggregation. In this work, we sought to maintain the same degree of aggregation, while changing the concentration of nanoparticles deposited on paper. We achieved this by dipping paper into AuNP solutions of different, known concentration and found that the initial packing density of AuNPs in solutions was retained on paper with the same degree of aggregation. The surface coverage of AuNPs on paper was found to scale linearly to their concentration profile in solutions. The SERS performances of the AuNP-treated papers were evaluated with 4-aminothiophenol (4-ATP) as the Raman molecule, and their SERS intensities increased linearly with the AuNPs' concentration. Compared to AuNP-treated silicon, the Raman enhancement factor (EF) from paper was relatively higher due to a more uniform and greater degree of adsorption of AuNPs. The effect of the spatial distribution of AuNPs in their substrates on SERS activity was also investigated. In this experiment, the number of AuNPs was kept constant (a 1 μL droplet of AuNPs was deposited on all substrates), and the distribution profile of AuNPs was controlled by the nature of the substrate: paper, silicon, and hydrophobized paper. The AuNP droplet on paper showed the most reproducible and sensitive SERS signal. This highlighted the role of the z-distribution (through film) of AuNPs within the bulk of the paper, producing a 3D multilayer structure to allow inter- and intralayer plasmon coupling, and hence amplifying the SERS signal. The SERS performance of nanoparticle-functionalized paper can thus be optimized by controlling the 3D distribution of the metallic nanoparticles, and such control is critical if these systems are to be implemented as a low-cost and highly sensitive bioassay platform.