Showing papers on "Surface plasmon resonance published in 2009"

Plasmon coupling of gold nanorods at short distances and in different geometries.

Abstract: The experimentally determined scattering spectra of discrete, crystalline, gold nanorod dimers arranged side-to-side, end-to-end, at right angles in different orientations and also with longitudinal offsets are reported along with the electron micrographs of the individual dimers. The spectra exhibit both red- and blue-shifted surface plasmon resonances, consistent with the plasmon hybridization model. However, the plasmon coupling constant for gold dimers with less than a few nanometers separation between the particles does not obey the exponential dependence predicted by the Universal Plasmon Ruler equation. The experimentally determined spectra are compared with electrodynamic calculations and the interactions between the individual rod plasmons in different dimer orientations are elucidated.

Laser ablation synthesis in solution and size manipulation of noble metal nanoparticles

Abstract: In the past years, laser ablation synthesis in solution (LASiS) emerged as a reliable alternative to traditional chemical reduction methods for obtaining noble metal nanoparticles (NMNp). LASiS is a “green” technique for the synthesis of stable NMNp in water or in organic solvents, which does not need stabilizing molecules or other chemicals. The so obtained NMNp are highly available for further functionalization or can be used wherever unprotected metal nanoparticles are desired. Surface functionalization of NMNp can be monitored in real time by UV-visible spectroscopy of the plasmon resonance. However LASiS has some limitations in the size control of NMNp, which can be overcome by “chemical free” laser treatments of NMNp. In this paper we provide an overview of LASiS, size manipulation by laser irradiation and functionalization of NMNp, with special care in pointing out some of the main issues about this research area.

A unified view of surface-enhanced Raman scattering.

Abstract: In the late 1970s, signal intensity in Raman spectroscopy was found to be enormously enhanced, by a factor of 106 and more recently by as much as 1014, when an analyte was placed in the vicinity of a metal nanoparticle (particularly Ag). The underlying source of this huge increase in signal in surface-enhanced Raman scattering (SERS) spectroscopy has since been characterized by considerable controversy. Three possible contributions to the enhancement factor have been identified: (i) the surface plasmon resonance in the metal nanoparticle, (ii) a charge-transfer resonance involving transfer of electrons between the molecule and the conduction band of the metal, and (iii) resonances within the molecule itself. These three components are often treated as independently contributing to the overall effect, with the implication that by properly choosing the experimental parameters, one or more can be ignored. Although varying experimental conditions can influence the relative degree to which each resonance influ...

Chemical Synthesis of Novel Plasmonic Nanoparticles

Abstract: Under the irradiation of light, the free electrons in a plasmonic nanoparticle are driven by the alternating electric field to collectively oscillate at a resonant frequency in a phenomenon known as surface plasmon resonance. Both calculations and measurements have shown that the frequency and amplitude of the resonance are sensitive to particle shape, which determines how the free electrons are polarized and distributed on the surface. As a result, controlling the shape of a plasmonic nanoparticle represents the most powerful means of tailoring and fine-tuning its optical resonance properties. In a solution-phase synthesis, the shape displayed by a nanoparticle is determined by the crystalline structure of the initial seed produced and the interaction of different seed facets with capping agents. Using polyol synthesis as a typical example, we illustrate how oxidative etching and kinetic control can be employed to manipulate the shapes and optical responses of plasmonic nanoparticles made of either Ag or Pd. We conclude by highlighting a few fundamental studies and applications enabled by plasmonic nanoparticles having well-defined and controllable shapes.

Highly Efficient Visible-Light Plasmonic Photocatalyst Ag@AgBr

Abstract: Visible improvements: Owing to the plasmon resonance of silver nanoparticles deposited on the surface of AgBr, the newly-prepared plasmonic photocatalyst Ag§AgBr has a strong absorption in the visible region (see picture) and shows high efficiency in the photodegradation of organic pollutants under visible light.

Tunable light trapping for solar cells using localized surface plasmons

Abstract: Effective light management is imperative in maintaining high efficiencies as photovoltaic devices become thinner. We demonstrate a simple and effective method of enhancing light trapping in solar cells with thin absorber layers by tuning localized surface plasmons in arrays of Ag nanoparticles. By redshifting the surface plasmon resonances by up to 200 nm, through the modification of the local dielectric environment of the particles, we can increase the optical absorption in an underlying Si wafer fivefold at a wavelength of 1100 nm and enhance the external quantum efficiency of thin Si solar cells by a factor of 2.3 at this wavelength where transmission losses are prevalent. Additionally, by locating the nanoparticles on the rear of the solar cells, we can avoid absorption losses below the resonance wavelength due to interference effects, while still allowing long wavelength light to be coupled into the cell. Results from numerical simulations support the experimental findings and show that the fraction ...

Indium tin oxide nanoparticles with compositionally tunable surface plasmon resonance frequencies in the near-IR region.

Abstract: Here we report the synthesis of conducting indium tin oxide (ITO) nanoparticles (NPs) and their surface plasmon resonance (SPR) properties. The SPR peaks of the ITO NPs can be easily tuned by changing the concentration of Sn doping from 3 to 30 mol %. The shortest SPR wavelength of 1618 nm in 10% Sn-doped ITO NPs may reflect the highest electron carrier density in the ITO NPs. The controllable SPR frequencies of metal oxides may offer a novel approach for noble-metal-free SPR applications. Unlike noble-metal nanostructures, ITO has no inter- and intraband transitions in the vis−near-IR region and represents a free-electron conduction, allowing us to systematically study the origin of optical effects arising from the SPRs of conduction electrons.

Heterogenous Catalysis Mediated by Plasmon Heating

Abstract: We introduce a new method for performing and miniaturizing many types of heterogeneous catalysis involving nanoparticles. The method makes use of the plasmon resonance present in nanoscale metal catalysts to provide the necessary heat of reaction when illuminated with a low-power laser. We demonstrate our approach by reforming a flowing, liquid mixture of ethanol and water over gold nanoparticle catalysts in a microfluidic channel. Plasmon heating of the nanoparticles provides not only the heat of reaction but the means to generate both water and ethanol vapor locally over the catalysts, which in turn allows the chip and the fluid lines to remain at room temperature. The measured products of the reaction, CO2, CO, and H2, are consistent with catalytic steam reforming of ethanol. The approach, which we refer to as plasmon-assisted catalysis, is general and can be used with a variety of endothermic catalytic processes involving nanoparticles.

Multiwavelength photoacoustic imaging and plasmon resonance coupling of gold nanoparticles for selective detection of cancer.

Abstract: Gold nanoparticles targeting epidermal growth factor receptor via antibody conjugation undergo molecular specific aggregation when they bind to receptors on cell surfaces, leading to a red shift in their plasmon resonance frequency. Capitalizing on this effect, we demonstrate the efficacy of the molecular specific photoacoustic imaging technique using subcutaneous tumor-mimicking gelatin implants in ex-vivo mouse tissue. The results of our study suggest that highly selective and sensitive detection of cancer cells is possible using multiwavelength photoacoustic imaging and molecular specific gold nanoparticles.

Surface Plasmon Resonance-Based Fiber Optic Sensors: Principle, Probe Designs, and Some Applications

Abstract: Surface plasmon resonance technique in collaboration with optical fiber technology has brought tremendous advancements in sensing of various physical, chemical, and biochemical parameters. In this review article, we present the principle of SPR technique for sensing and various designs of the fiber optic SPR probe reported for the enhancement of the sensitivity of the sensor. In addition, we present few examples of the surface plasmon resonance- (SPR-) based fiber optic sensors. The present review may provide researchers valuable information regarding fiber optic SPR sensors and encourage them to take this area for further research and development.

Selective release of multiple DNA oligonucleotides from gold nanorods.

Abstract: Combination therapy, or the use of multiple drugs, has been proven to be effective for complex diseases, but the differences in chemical properties and pharmacokinetics can be challenging in terms of the loading, delivering, and releasing multiple drugs. Here we demonstrate that we can load and selectively release two different DNA oligonucleotides from two different gold nanorods. DNA was loaded on the nanorods via thiol conjugation. Selective releases were induced by selective melting of gold nanorods via ultrafast laser irradiation at the nanorods’ longitudinal surface plasmon resonance peaks. Excitation at one wavelength could selectively melt one type of gold nanorods and selectively release one type of DNA strand. Releases were efficient (50−80%) and externally tunable by laser fluence. Released oligonucleotides were still functional. This proof of concept is potentially a powerful method for multiple-drug delivery strategies.

Strong polarization dependence of plasmon-enhanced fluorescence on single gold nanorods.

Abstract: We report on the strong polarization dependence of the plasmon-enhanced fluorescence on single gold nanorods. The fluorescence from the organic fluorophores that are embedded in a mesostructured silica shell around individual gold nanorods is enhanced by the longitudinal plasmon resonance of the nanorods. Our electrostatic calculations show that under an off-resonance excitation, the electric field intensity contour around a nanorod rotates away from the length axis as the excitation polarization is varied. The polarization dependence of the plasmon-enhanced fluorescence is ascribed to the dependence of the averaged electric field intensity enhancement within the silica shell on the excitation polarization. The measured fluorescence enhancement factor is in very good agreement with that obtained from the electrostatic calculations. The fluorescence enhancement factor increases as the longitudinal plasmon wavelength is synthetically tuned close to the excitation wavelength. In addition, the polarization de...

Noble Metals on the Nanoscale: Optical and Photothermal Properties and Some Applications in Imaging, Sensing, Biology, and Medicine

Abstract: Noble metal nanostructures attract much interest because of their unique properties, including large optical field enhancements resulting in the strong scattering and absorption of light. The enhancement in the optical and photothermal properties of noble metal nanoparticles arises from resonant oscillation of their free electrons in the presence of light, also known as localized surface plasmon resonance (LSPR). The plasmon resonance can either radiate light (Mie scattering), a process that finds great utility in optical and imaging fields, or be rapidly converted to heat (absorption); the latter mechanism of dissipation has opened up applications in several new areas. The ability to integrate metal nanoparticles into biological systems has had greatest impact in biology and biomedicine. In this Account, we discuss the plasmonic properties of gold and silver nanostructures and present examples of how they are being utilized for biodiagnostics, biophysical studies, and medical therapy. For instance, takin...

Wave–particle duality of single surface plasmon polaritons

Abstract: When light interacts with metal surfaces, it excites electrons, which can form propagating excitation waves called surface plasmon polaritons. These collective electronic excitations can produce strong electric fields localized to subwavelength distance scales 1 , which makes surface plasmon polaritons interesting for several applications. Many of these potential uses, and in particular those related to quantum networks 2 , r equire a deep understanding of the fundamental quantum properties of surface plasmon polaritons. Remarkably, these collective electron states preserve many key quantum mechanical properties of the photons used to excite them, including entanglement 3,4 and sub-Poissonian statistics 5 . Here, we show that a single-photon source coupled to a silver nanowire excites single surface plasmon polaritons that exhibit both wave and particle properties, similar to those of single photons. Furthermore, the detailed analysis of the spectral interference pattern provides a new method to characterize the dimensions of metallic waveguides with nanometre accuracy.

Controlling Nanoparticles with Atomic Precision: The Case of Au144(SCH2CH2Ph)60

Abstract: We report a facile, two-step synthetic method for preparing truly monodiserse Au144(SCH2CH2Ph)60 nanoparticles with their formula determined by electrospray mass spectrometry in conjunction with other characterization. A remarkable advantage of our synthetic approach lies in that it solely produces Au144(SCH2CH2Ph)60 nanoparticles, hence, eliminating nontrivial, postsynthetic steps of size separation, which has proven to be very difficult. This advantage makes the approach and the type of nanoparticles generated by it of broad utility for practical applications. Unlike their larger counterparts, Au nanocrystals (typically >2 nm) that are crystalline and show a prominent surface plasmon resonance band at ∼520 nm (for spherical particles), the Au144(SCH2CH2Ph)60 nanoparticles instead exhibit a stepwise, multiple-band absorption spectrum, indicating quantum confinement of electrons in the particle. In addition, these ultrasmall nanoparticles do not adopt face-centered cubic structure as in Au nanocrystals or...

Electron energy-loss spectroscopy (EELS) of surface plasmons in single silver nanoparticles and dimers: influence of beam damage and mapping of dark modes

Abstract: We demonstrate the use of a scanning transmission electron microscope (STEM) equipped with a monochromator and an electron energy loss (EEL) spectrometer as a powerful tool to study localized surface plasmons in metallic nanoparticles We find that plasmon modes can be influenced by changes in nanostructure geometry and electron beam damage and show that it is possible to delineate the two effects through optimization of specimen preparation techniques and acquisition parameters The results from the experimental mapping of bright and dark plasmon energies are in excellent agreement with the results from theoretical modeling

Shape-Controlled Synthesis of Silver Nanoparticles for Plasmonic and Sensing Applications

Abstract: The localized surface plasmon resonance of a silver nanoparticle is responsible for its ability to strongly absorb and scatter light at specific wavelengths. The absorption and scattering spectra (i.e., plots of cross sections as a function of wavelength) of a particle can be predicted using Mie theory (for a spherical particle) or the discrete dipole approximation method (for particles in arbitrary shapes). In this review, we briefly discuss the calculated spectra for silver nanoparticles with different shapes and the synthetic methods available to produce these nanoparticles. As validated in recent studies, there is good agreement between the theoretically calculated and the experimentally measured spectra. We conclude with a discussion of new plasmonic and sensing applications enabled by the shape-controlled nanoparticles.

Growth Mechanism of Metal–Organic Frameworks: Insights into the Nucleation by Employing a Step-by-Step Route

Abstract: One step at a time: The in situ monitoring of the step-by-step formation of metal-organic frameworks (MOFs) by using surface plasmon resonance (SPR), allows the nucleation process and the formation of the secondary building units to be investigated. Growth rates on functionalized organic surfaces with different crystallographic orientations can also be studied.

Magnetic−Plasmonic Core−Shell Nanoparticles

Abstract: Nanoparticles composed of magnetic cores with continuous Au shell layers simultaneously possess both magnetic and plasmonic properties. Faceted and tetracubic nanocrystals consisting of wustite with magnetite-rich corners and edges retain magnetic properties when coated with a Au shell layer, with the composite nanostructures showing ferrimagnetic behavior. The plasmonic properties are profoundly influenced by the high dielectric constant of the mixed iron oxide nanocrystalline core. A comprehensive theoretical analysis that examines the geometric plasmon tunability over a range of core permittivities enables us to identify the dielectric properties of the mixed oxide magnetic core directly from the plasmonic behavior of the core−shell nanoparticle.

Dynamic light scattering as a powerful tool for gold nanoparticle bioconjugation and biomolecular binding studies.

Abstract: Dynamic light scattering (DLS) is an analytical tool used routinely for measuring the hydrodynamic size of nanoparticles and colloids in a liquid environment. Gold nanoparticles (GNPs) are extraordinary light scatterers at or near their surface plasmon resonance wavelength. In this study, we demonstrate that DLS can be used as a very convenient and powerful tool for gold nanoparticle bioconjugation and biomolecular binding studies. The conjugation process between protein A and gold nanoparticles under different experimental conditions and the quality as well as the stability of the prepared conjugates were monitored and characterized systematically by DLS. Furthermore, the specific interactions between protein A-conjugated gold nanoparticles and a target protein, human IgG, can be detected and monitored in situ by measuring the average particle size change of the assay solution. For the first time, we demonstrate that DLS is able to directly and quantitatively measure the binding stoichiometry between a protein-conjugated GNP probe and a target analyte protein in solution.

Refractometric sensing using propagating versus localized surface plasmons: a direct comparison.

Abstract: We present a direct experimental comparison between the refractive index sensing capabilities of localized surface plasmon resonances (LSPRs) in gold nanodisks and propagating surface plasmon resonances (SPRs) on 50 nm gold films. The comparison is made using identical experimental conditions, and for the same resonance wavelength, λSP ≅ 700 nm. Biosensing experiments with biotin−avidin coupling reveal that the two sensing platforms have very similar performance, despite a superior bulk refractive index sensing figure of merit for the SPR sensor. The results demonstrate that LSPR sensing based on simple transmission or reflection measurements is a highly competitive technique compared to the traditional SPR sensor.

Plasmonic-enhanced polymer photovoltaic devices incorporating solution-processable metal nanoparticles

Abstract: We have explored the effect of gold nanoparticle (Au NP)-induced surface plasmons on the performance of organic photovoltaic devices (OPVs). The power conversion efficiency of these OPVs was improved after blending the Au NPs into the anodic buffer layer. The addition of Au NPs increased the rate of exciton generation and the probability of exciton dissociation, thereby enhancing the short-circuit current density and the fill factor. We attribute the improvement in device performance to the local enhancement in the electromagnetic field originating from the excitation of the localized surface plasmon resonance.

Synthesis of rod-shaped gold nanorattles with improved plasmon sensitivity and catalytic activity.

Abstract: We prepared rod-shaped gold nanorattles solid gold nanorods surrounded by a thin gold shell using a galvanic replacement process starting with silver-coated gold nanorods. These structures are very promising candidates for catalytic applications and optimized plasmon sensors. They combine the advantages of rods (low plasmon resonance frequency, large polarizability, small damping) with the high surface area of hollow structures. The plasmon sensitivity to changes in the dielectric environment is up to 50% higher for gold nanorattles compared to gold nanorods with the same resonance frequency and 6x higher than for plasmons in spherical gold nanoparticles. The catalytic activity measured for the reduction of p-nitrophenol is 4x larger than for bare gold nanorods.

Ag/AgBr/WO3·H2O: Visible-Light Photocatalyst for Bacteria Destruction

Abstract: A new composite photocatalyst Ag/AgBr/WO3·H2O was synthesized by reacting Ag8W4O16 with HBr and then reducing some Ag+ ions in the surface region of AgBr particles to Ag nanoparticles via the light-induced chemical reduction. Ag nanoparticles are formed from AgBr by the light-induced chemical reduction reaction. The Ag/AgBr particles are on the surface of WO3·H2O and have irregular shapes with sizes varying between 63 and 442 nm. WO3·H2O appears as flakes about 31 nm thick and 157−474 nm wide. The as-grown Ag/AgBr/WO3·H2O sample shows strong absorption in the visible region because of the plasmon resonance of Ag nanoparticles in Ag/AgBr/WO3·H2O. The ability of this compound to destroy E. coli and oxidize methylic orange under visible light was compared with those of other reference photocatalysts. Ag/AgBr/WO3·H2O is a highly efficient photocatalyst under visible light. The Ag/AgBr/WO3·H2O samples recovered from repeated photooxidation experiments are almost identical to the as-prepared samples, proving th...

Fano resonances in plasmonic nanoparticle aggregates.

Abstract: We investigate the plasmonic properties of a symmetric silver sphere septamer and show that the extinction spectrum exhibits a narrow Fano resonance. Using the plasmon hybridization approach and group theory we show that this Fano resonance is caused by the interference of two bonding dipolar subradiant and superradiant plasmon modes of E(1u) symmetry. We investigate the effect of structural symmetry breaking and show that the energy and shape of the Fano resonance can be tuned over a broad wavelength range. We show that the wavelength of the Fano resonance depends very sensitively on the dielectric permittivity of the surrounding media with one of the highest LSPR sensitivities reported for a finite nanostructure.

Surface plasmon resonance enhanced magneto-optics (SuPREMO): Faraday rotation enhancement in gold-coated iron oxide nanocrystals.

Abstract: We report enhanced optical Faraday rotation in gold-coated maghemite (γ-Fe2O3) nanoparticles. The Faraday rotation spectrum measured from 480−690 nm shows a peak at about 530 nm, not present in eit...

Enhancement of optical absorption in thin-film solar cells through the excitation of higher-order nanoparticle plasmon modes

Abstract: Recent research in the rapidly emerging field of plasmonics has shown the potential to significantly enhance light trapping inside thin-film solar cells by using metallic nanoparticles In this article it is demonstrated the plasmon enhancement of optical absorption in amorphous silicon solar cells by using silver nanoparticles Based on the analysis of the higher-order surface plasmon modes, it is shown how spectral positions of the surface plasmons affect the plasmonic enhancement of thin-film solar cells By using the predictive 3D modeling, we investigate the effect of the higher-order modes on that enhancement Finally, we suggest how to maximize the light trapping and optical absorption in the thin-film cell by optimizing the nanoparticle array parameters, which in turn can be used to fine tune the corresponding surface plasmon modes

Phase and amplitude sensitivities in surface plasmon resonance bio and chemical sensing

Abstract: We consider amplitude and phase characteristics of light reflected under the Surface Plasmon Resonance (SPR) conditions and study their sensitivities to refractive index changes associated with biological and chemical sensing. Our analysis shows that phase can provide at least two orders of magnitude better detection limit due to the following reasons: (i) Maximal phase changes occur in the very dip of the SPR curve where the vector of probing electric field is maximal, whereas maximal amplitude changes are observed on the resonance slopes: this provides a one order of magnitude larger sensitivity of phase to refractive index variations; (ii) Under a proper design of a detection scheme, phase noises can be orders of magnitude lower compared to amplitude ones, which results in a much better signal-to-noise ratio; (iii) Phase offers much better possibilities for signal averaging and filtering, as well as for image treatment. Applying a phase-sensitive SPR polarimetry scheme and using gas calibration model, we experimentally demonstrate the detection limit of 10(-8) RIU, which is about two orders of magnitude better compared to amplitude-sensitive schemes. Finally, we show how phase can be employed for filtering and treatment of images in order to improve signal-to-noise ratio even in relatively noisy detection schemes. Combining a much better physical sensitivity and a possibility of imaging and sensing in micro-arrays, phase-sensitive methodologies promise a substantial upgrade of currently available SPR technology.