Showing papers on "Surface plasmon resonance published in 2001"

Variations in Coupled Water, Viscoelastic Properties, and Film Thickness of a Mefp-1 Protein Film during Adsorption and Cross-Linking: A Quartz Crystal Microbalance with Dissipation Monitoring, Ellipsometry, and Surface Plasmon Resonance Study

Abstract: We have measured the time-resolved adsorption kinetics of the mussel adhesive protein (Mefp-1) on a nonpolar, methyl-terminated (thiolated) gold surface, using three independent techniques: quartz crystal microbalance with dissipation monitoring (QCM-D), surface plasmon resonance, and ellipsometry. The QCM-D and ellipsometry data shows that, after adsorption to saturation of Mefp-1, cross-linking of the protein layer using NaIO4 transforms it from an extended (∼20 nm), water-rich, and hydrogel-like state to a much thinner (∼5 nm), compact, and less water-rich state. Furthermore, we show how quantitative data about the thickness, shear elastic modulus, and shear viscosity of the protein film can be obtained with the QCM-D technique, even beyond the Sauerbrey regime, if frequency (f) and energy dissipation (D) measurements measured at multiple harmonics are combined with theoretical simulations using a Voight-based viscoelastic model. The modeling result was confirmed by substituting H2O for D2O. As expect...

Chain Length Dependence and Sensing Capabilities of the Localized Surface Plasmon Resonance of Silver Nanoparticles Chemically Modified with Alkanethiol Self-Assembled Monolayers

Abstract: In this paper, we explore the optical properties of Ag nanoparticles chemically modified with alkanethiol self-assembled monolayers (SAMs) by measuring the localized surface plasmon resonance (LSPR) spectrum using UV−vis extinction spectroscopy. For all the experiments presented here, the Ag nanoparticles were fabricated using the technique of nanosphere lithography (NSL) and had in-plane widths of 100 nm and out-of-plane heights of 50 nm. We first demonstrate that unmodified nanoparticles are extremely susceptible to slight changes in 3-dimensional structure when exposed to various solvents. These structural effects can have dramatic effects on the extinction maximum, λmax, of the LSPR shifting it to the blue by over 100 nm. The significant discovery reported here is that λmax for NSL fabricated Ag nanoparticles is extremely sensitive to the SAM properties. We will demonstrate the following new features: (1) λmax of the LSPR linearly shifts to the red 3 nm for every carbon atom in the alkane chain; (2) ...

The effect of surface probe density on DNA hybridization

Abstract: The hybridization of complementary strands of DNA is the underlying principle of all microarray-based techniques for the analysis of DNA variation. In this paper, we study how probe immobilization at surfaces, specifically probe density, influences the kinetics of target capture using surface plasmon resonance (SPR) spectroscopy, an in situ label-free optical method. Probe density is controlled by varying immobilization conditions, including solution ionic strength, interfacial electrostatic potential and whether duplex or single stranded oligonucleotides are used. Independent of which probe immobilization strategy is used, we find that DNA films of equal probe density exhibit reproducible efficiencies and reproducible kinetics for probe/target hybridization. However, hybridization depends strongly on probe density in both the efficiency of duplex formation and the kinetics of target capture. We propose that probe density effects may account for the observed variation in target-capture rates, which have previously been attributed to thermodynamic effects.

Metal Nanoparticles: Synthesis, Characterization, and Applications

Abstract: Introduction to particle synthesis, optical, and electronic properties solution-phase nanocluster synthesis and mechanisms of formation magic number metal clusters electrochemical synthesis of high aspect ratio gold particles template synthesis of metal nanostructures synthesis of metal nanoclusters using dendrimer templates nanosphere lithography electrochemistry of monolayer protected gold clusters modelling of nanoparticle optical properties hyper-Raleigh scattering of nanoparticles nanoparticle single electron devices DNA detection using gold nanoparticles conductance-based nanoparticle chemical sensors surface plasmon resonance detection of biomolecules synthesis of conductive polymer-gold particle composites optical properties of complex metal nanostructures si-coated nanoparticles nanoparticle arrays mixed particle arrays nanoparticles in electronic devices.

Surface Plasmon Resonance Imaging Measurements of DNA and RNA Hybridization Adsorption onto DNA Microarrays

Abstract: Surface plasmon resonance (SPR) imaging is a surface-sensitive spectroscopic technique for measuring interactions between unlabeled biological molecules with arrays of surface-bound species. In this paper, SPR imaging is used to quantitatively detect the hybridization adsorption of short (18-base) unlabeled DNA oligonucleotides at low concentration, as well as, for the first time, the hybridization adsorption of unlabeled RNA oligonucleotides and larger 16S ribosomal RNA (rRNA) isolated from the microbe Escherichia coli onto a DNA array. For the hybridization adsorption of both DNA and RNA oligonucleotides, a detection limit of 10 nM is reported; for large (1500-base) 16S rRNA molecules, concentrations as low as 2 nM are detected. The covalent attachment of thiol-DNA probes to the gold surface leads to high surface probe density (1012 molecules/cm2) and excellent probe stability that enables more than 25 cycles of hybridization and denaturing without loss in signal or specificity. Fresnel calculations are...

Ultrafast Electron Dynamics and Optical Nonlinearities in Metal Nanoparticles

Abstract: The femtosecond optical response of noble metal nanoparticles and its connection to the ultrafast electron dynamics are discussed in light of the results of high-sensitivity femtosecond pump−probe experiments. The physical origins of the nonlinear responses in the vicinity of the surface plasmon resonance and interband transition threshold are analyzed using extension of the theoretical models used in the bulk materials. These responses contain information on the electron interaction processes (electron−electron and electron−phonon scattering) that can thus be directly investigated in the time domain. Their size and environment dependences are discussed, and the results are compared to the ones in the bulk materials. Time-resolved techniques also permit direct study of the vibrational modes of metal nanoparticles and, in particular, the determination of their damping, which is a sensitive probe of the nature of the surrounding matrix and of the interface quality.

Plasmon resonances of silver nanowires with a nonregular cross section

Abstract: We investigate numerically the spectrum of plasmon resonances for metallic nanowires with a nonregular cross section, in the 20‐50 nm range. We first consider the resonance spectra corresponding to nanowires whose cross sections form different simplexes. The number of resonances strongly increases when the section symmetry decreases: A cylindrical wire exhibits one resonance, whereas we observe more than five distinct resonances for a triangular particle. The spectral range covered by these different resonances becomes very large, giving to the particle-specific distinct colors. At the resonance, dramatic field enhancement is observed at the vicinity of nonregular particles, where the field amplitude can reach several hundred times that of the illumination field. This near-field enhancement corresponds to surface-enhanced Raman scattering~SERS! enhancement locally in excess of 10 12 . The distance dependence of this enhancement is investigated and we show that it depends on the plasmon resonance excited in the particle, i.e., on the illumination wavelength. The average Raman enhancement for molecules distributed on the entire particle surface is also computed and discussed in the context of experiments in which large numbers of molecules are used.

Nanosphere Lithography: Effect of Substrate on the Localized Surface Plasmon Resonance Spectrum of Silver Nanoparticles

Abstract: In this paper, we explore the optical contributions of the substrate to the localized surface plasmon resonance (LSPR) spectrum of surface confined Ag nanoparticles produced by nanosphere lithography (NSL). We present optical extinction spectra of Ag nanoparticles fabricated on the following substrates: fused silica, borosilicate optical glass, mica, and SF-10a high refractive index specialty glass. For all the experiments discussed here, the Ag nanoparticles were approximately 100 nm in in-plane width and 25 nm in out-of-plane height. In a controlled N2 environment, the wavelength corresponding to the extinction maximum, λmax, shifts to the red with increasing refractive index of the substrate, nsubstrate. The sensitivity factor, Δλmax/Δnsubstrate, was measured to be 87 nm per refractive index unit (RIU). Experimental extinction spectra were modeled using the discrete dipole approximation (DDA). The DDA theory qualitatively predicts the experimentally observed trend that λmax is linearly dependent on ns...

Surface plasmon propagation in microscale metal stripes

Abstract: Addressing the fundamental question of miniaturization of light guiding and routing towards nanoscale optics, we study experimentally surface plasmon propagation in silver and gold thin films of finite widths in the micrometer range. Spatially confined excitation of surface plasmons is realized by a prism coupling arrangement involving an opaque aluminum screen for a distinct separation of excitation and propagation (measurement) region. The surface plasmon propagation length as a function of film widths is measured by detecting stray light due to surface plasmon scattering with a conventional optical microscope.

Plasmon resonant coupling in metallic nanowires

Abstract: We investigate the plasmon resonances of interacting silver nanowires with a 50 nm diameter. Both non–touching and intersecting configurations are investigated. While individual cylinders exhibit a single plasmon resonance, we observe much more complex spectra of resonances for interacting structures. The number and magnitude of the different resonances depend on the illumination direction and on the distance between the particles. For very small separations, we observe a dramatic field enhancement between the particles, where the electric field amplitude reaches a hundredfold of the illumination. A similar enhancement is observed in the grooves created in slightly intersecting particles. The topology of these different resonances is related to the induced polarization charges. The implication of these results to surface enhanced Raman scattering (SERS) are discussed.

Long-range surface plasmons for high-resolution surface plasmon resonance sensors

Abstract: We present the application of long-range surface plasmons to a wavelength-modulated surface plasmon resonance sensor. Theoretical design parameters and experimental data are presented for two sensor designs, using either magnesium fluoride or Teflon AF-1600 as a dielectric buffer layer. The demonstrated sensitivity of the long-range surface plasmon resonance sensor in refractometric experiments is up to seven times higher than that of an equivalent conventional surface plasmon resonance (SPR) sensor, while the measured resolution is comparable. According to theoretical design calculations presented, further optimization of materials and layer thickness could reduce the resonance width while achieving even higher sensitivities, thereby creating a sensor with significantly better resolution than conventional SPR sensors.

Surface plasmon resonance biosensor based on integrated optical waveguide

Abstract: We report a sensor based on spectral interrogation of surface plasmon resonance (SPR) in an integrated optical waveguide-coupled SPR sensing device. We present theoretical analysis of the integrated optical SPR sensor structure leading to a device design optimized for operation in aqueous environments. We demonstrate that the fabricated laboratory prototype of the sensor is capable of measuring bulk refractive index changes smaller than 1.2×10 −6 . In conjunction with specific biomolecular recognition elements (monoclonal antibodies against human chorigonadotropin (hCG)) the sensor is used for the detection of hCG. The sensor is demonstrated to be capable of detecting 2 ng of hCG present in 1 ml of 1% bovine serum albumin solution.

Detection of foodborne pathogens using surface plasmon resonance biosensors

Abstract: Salmonella enteritidis and Listeria monocytogenes were detected in real time using a surface plasmon resonance (SPR) sensor based on prism excitation of surface plasmons and spectral interrogation. The respective antibodies against the pathogens were immobilized on the gold sensor surface as a covalently crosslinked double-layer or covalently bound on a crosslinked albumin layer. Salmonella and Listeria could be detected by the sensor at concentrations down to 10 6 cell/ml. The sensor sensitivity was comparable with that of standard ELISA in which the same antibodies were used.

Novel spectral fiber optic sensor based on surface plasmon resonance

Abstract: A novel fiber optic surface plasmon resonance (SPR) sensing device based on spectral interrogation of SPR in a miniature fiber optic sensing element using depolarized light is reported. Optimization analysis of the sensor based on the equivalent planar waveguide approach and the mode expansion and propagation method is presented. A laboratory prototype of the sensor has been proved to be able to measure refractive index variations as small as 5×10 −7 . Suitability of the sensor for biosensing has been demonstrated by detecting IgG via respective monoclonal antibodies immobilized on the SPR sensor surface.

Optical properties of Ag and Au nanowire gratings

Abstract: The optical response of regularly arranged noble metal wires with nanoscopic cross sections (nanowire gratings) strongly depends on the polarization direction of the incident light. We use silver and gold nanowire gratings produced by electron beam lithography to study this effect by optical extinction spectroscopy. For a polarization direction perpendicular to the wire axis, the excitation of a dipolar plasmon mode dominates the extinction spectrum. The spectral position of the plasmon resonance can be tuned by an appropriate choice of nanowire geometry and material. For a polarization direction parallel to the wire axis, the profile of the extinction spectrum varies mainly as a function of the grating constant. In particular, a transmission maximum for small grating constants is found. By combining the surface plasmon excitation and grating effect for orthogonal polarization directions, a spectrally selective polarizer with an extinction ratio of 26 is demonstrated.

Strength of the electric field in apertureless near-field optical microscopy

Abstract: Enhancement γ of the electrical field at the end of a tip relative to the incident field in a focused radiation beam is calculated by the finite-element time-domain (FETD) method. First, the reliability of the FETD method is established by calculating the electric field on simple structures like thin cylinders, spheres, and ellipsoids, and comparing the results with analytical solutions. The calculations on these test structures also reveal that phase retardation effects substantially modify γ when the size of the structure is larger than approximately λ/4, λ being the radiation wavelength. For plasmon resonance, in particular, phase retardation severely reduces the resonance and the expected field enhancement for a gold tip. The small value of γ=4 calculated by FETD is about an order of magnitude smaller than the value found in recent published work. Resonance effects can be recovered for special tips, which have a discontinuity or a different material composition at the end of the tip. Some tuning of the discontinuity dimension is needed to maximize the resonance. Under optimal conditions for plasmon resonance, an enhancement in the electric field of about 50 is calculated at the end of a small gold protrusion mounted on a wider silicon or glass tip.

Electrostatic surface plasmon resonance: direct electric field-induced hybridization and denaturation in monolayer nucleic acid films and label-free discrimination of base mismatches.

Abstract: We demonstrate that in situ optical surface plasmon resonance spectroscopy can be used to monitor hybridization kinetics for unlabeled DNA in tethered monolayer nucleic acid films on gold in the presence of an applied electrostatic field. The dc field can enhance or retard hybridization and can also denature surface-immobilized DNA duplexes. Discrimination between matched and mismatched hybrids is achieved by simple adjustment of the electrode potential. Although the electric field at the interface is extremely large, the tethered single-stranded DNA thiol probes remain bound and can be reused for subsequent hybridization reactions without loss of efficiency. Only capacitive charging currents are drawn; redox reactions are avoided by maintaining the gold electrode potential within the ideally polarizable region. Because of potential-induced changes in the shape of the surface plasmon resonance curve, we account for the full curve rather than simply the shift in the resonance minimum.

Scanning of guanine-guanine mismatches in DNA by synthetic ligands using surface plasmon resonance.

Abstract: Here we have designed and synthesized ligands that specifically bind with high affinity (K(d) = 53 nM) to the guanine (G)-guanine mismatch, one of four types of single-nucleotide polymorphism (SNP). Detection of the G-G mismatch was performed by a surface plasmon resonance (SPR) assay using a sensor chip carrying the G-G specific ligand on its surface. The accuracy of the G-G mismatch detection by the SPR sensor was demonstrated by a marked SPR response obtained only for the DNA containing the G-G mismatch. DNAs containing G-A and G-T mismatches, as well as a fully matched duplex, produced only a weak response. Furthermore, this assay was found applicable for the detection of SNP existing in PCR amplification products of a 652-nucleotide sequence of the HSP70-2 gene.

Photochemical incorporation of silver quantum dots in monodisperse silica colloids for photonic crystal applications.

Abstract: We developed a novel method to fabricate nanocomposite monodisperse SiO2 spheres (approximately 100 nm) containing homogeneously dispersed Ag quantum dots (approximately 2 to 5 nm). The inclusion morphology is controlled through the timing of the photochemical reduction of silver ions during hydrolysis of tetraethoxysilane in a microemulsion. Depending on the timing, Ag quantum dots can be directed to different annuli within the SiO2 spheres, as well as onto the SiO2 sphere surfaces. The embedded Ag quantum dots show a plasmon resonance absorption band at 438 nm. These Ag@SiO2 particles have significant surface charge and readily self-assemble into crystalline colloidal array (CCA) photonic crystals which Bragg-diffract light in the visible region. The magnitude of the plasmon resonance absorption depends on the CCA Bragg diffraction condition. The negative dielectric constant of the silver nanoparticles may be decreasing the silica-silver nanodot composite refractive index below that of the water medium. We may be observing an analogue of the Borrmann effect previously observed in X-ray scattering, where the incident and diffracted electric field standing wave becomes localized in regions of small CCA crystal absorption.

Surface Characterization of Mixed Self-Assembled Monolayers Designed for Streptavidin Immobilization

Abstract: The self-assembly of streptavidin onto biotinylated alkylthiolate monolayers on gold has served as an important model system for protein immobilization at surfaces. Here, we report a detailed study of the surface composition and structure of mixed self-assembled monolayers (SAMs) containing biotinylated and diluent alkylthiolates and their use to specifically immobilize streptavidin. X-ray photoelectron spectroscopy (XPS), angle-resolved XPS (ARXPS), near-edge X-ray absorption fine structure (NEXAFS), and surface plasmon resonance (SPR) have been used to characterize the films produced on gold from a range of binary mixtures of a biotinylated alkylthiol (BAT) and either a C16 methyl-terminated thiol (mercaptohexadecane, MHD) or a C11-oligo(ethylene glycol)-terminated (OEG) thiol in ethanol. The correlation between the solution mole fraction of BAT and its surface mole fraction (χBAT,sur) indicates that it adsorbs ∼4-fold faster than OEG but slightly slower than MHD. ARXPS analysis demonstrates that the bi...

An integrated optic hydrogen sensor based on SPR on palladium

Abstract: A small and efficient hydrogen sensor using surface plasmon resonance in an integrated optical waveguide is reported. The waveguide properties are influenced by a thin palladium layer whose optical constants depend on concentration of hydrogen in surrounding gaseous medium. A modal analysis of the sensor structure is performed and a simple sensor model is proposed. Finally, experimental results are presented; detection of hydrogen concentration as low as 4% is demonstrated.

Preparation of AucoreAgshell Nanorods and Characterization of Their Surface Plasmon Resonances

Abstract: The surface of gold nanorods is coated with thickness-controlled silver by reducing AgCl43- exclusively on the metallic surface to form AucoreAgshell nanorods and then restored by selectively remov...

Strategies in the preparation of DNA oligonucleotide arrays for diagnostic applications.

Abstract: This report emphasizes the interfacial chemistry that is required to ensure proper attachment of oligonucleotides onto the surface of microarrays. For example, strategies for the covalent attachment of pre-synthesized oligonucleotides to glass slides, gold films, polyacrylamide gel pads, polypyrrole films, and optical fibers are surveyed in an attempt to better define the parameters for optimal formation and detection of DNA hybrids. These parameters include among others, the nature and length of the linkers attaching oligonucleotides to the arrays, and the surface density of oligonucleotides required for unhindered hybridization with DNA targets. Sensitive detection methods such as the use of light-scattering techniques, molecular beacons, surface plasmon resonance, attenuated total internal reflection-FTIR, and the evanescent field excitation of fluorescence from surface-bound fluorophores have been developed to study the kinetics and specificity of hybridization events. Finally, the synthesis of oligonucleotides directly on glass surfaces and polypropylene sheets has been investigated to enable DNA sequencing by hybridization and achieve oligonucleotide densities of ca. 10(6) sequences per cm(2) on DNA chips.

Surface-enhanced magneto-optics in metallic multilayer films

Abstract: The magneto-optical properties of noble-metal--ferromagnetic-metal multilayer thin films have been investigated as a function of the incidence angle, including the total reflection range, in the polar, longitudinal, and equatorial geometries, and for different values of the photon energy in the near-infrared and visible spectrum. The experimental and theoretical results are obtained on a Au/Co/Au model system. They demonstrate that the resonant coupling of the p component of the light electric field with the gold surface plasmon, which occurs in the total reflection range, yields a strong enhancement of the magneto-optical response and signal-to-noise ratio of the system for the three magnetization directions. This resonant coupling and the resulting enhancement of the relevant magneto-optical quantities are achieved for any photon energy in the near infrared and visible range simply by tuning the incidence angle. The efficiency of this enhancement effect is shown to increase towards the infrared region of the spectrum following the rise of the quality factor of the surface plasmon resonance.

The color of finely dispersed nanoparticles

Abstract: We discuss the dependence of the color of low-concentrated nanoparticle systems on particle size and mass concentration for Ag, Au and TiN nanoparticles, which exhibit a surface plasmon polariton resonance in extinction spectra. Comparison is made with color data obtained for Ag and Au colloidal suspensions. When particles lump into aggregates, the splitting of the surface plasmon resonance into new resonances affects the extinction of light and, hence, the color of the particle assembly. This is demonstrated for aggregated colloidal suspensions of Ag and Au nanoparticles. Finally, for highly concentrated assemblies such as pigment films, we discuss the dependence of the color in diffuse reflectance and transmittance according to Kubelka and Munk (P. Kubelka, F. Munk: Z. Techn. Phys. 12, 593 (1931)), and extend this model by using optical properties of aggregates of spheres.

Surface plasmon polaritons on metal cylinders with dielectric core

Abstract: Metal-cladded dielectric cylinders with submicron diameters may serve to model coated tips used in nearfield scanning optical microscopy. The signal measured may be greatly influenced by resonance effects due to eigenmodes of the probe. Especially, using a photon scanning tunneling microscope setup, gold-coated tips have been found to detect a signal proportional to the magnetic field distributions [E. Devaux et al.. Phys. Rev. B 62, 10 504 (2000)]. This effect is attributed to cylindrical surface plasmons. We present here fully retarded calculations of the dispersion and field patterns of the nonradiative plasmon modes in cylindrical geometry. We study the effect of varying the cylinder radius on the surface plasmon dispersion, thus justifying that the cylinder is a useful model for near-field probes in spite of their slightly conical shape.

Using receptor conformational change to detect low molecular weight analytes by surface plasmon resonance.

Abstract: Small molecules are difficult to directly detect using commercially available surface plasmon resonance (SPR) instruments. This is because low molecular weight compounds do not have sufficient mass to cause a measurable change in refractive index. Refractive index is sensitive, however, to other properties besides the mass of the analyte. Recently the detection of substantial conformational changes for immobilized proteins using SPR has been reported. However, this property has not yet been exploited for the detection of low molecular weight ligand binding to immobilized protein receptors. Here we demonstrate that ligand-induced conformational changes can be used to monitor the binding of small molecules to immobilized maltose-binding protein and tissue transglutaminase. Ligand binding to a receptor that decreases in hydrodynamic radius yielded a net decrease in refractive index. A net positive change in refractive index was observed for a receptor that increases in hydrodynamic radius. Refractive index c...

Interfacial Phase Transition of an Environmentally Responsive Elastin Biopolymer Adsorbed on Functionalized Gold Nanoparticles Studied by Colloidal Surface Plasmon Resonance

Abstract: The change in optical properties of colloidal gold upon aggregation has been used to develop an experimentally convenient colorimetric method to study the interfacial phase transition of an elastin-like polypeptide (ELP), a thermally responsive biopolymer. Gold nanoparticles, functionalized with a self-assembled monolayer (SAM) of mercaptoundecanoic acid onto which an ELP was adsorbed, exhibit a characteristic red color due to the surface plasmon resonance (SPR) of individual colloids. Raising the solution temperature from 10 degrees C to 40 degrees C thermally triggered the hydrophilic-to-hydrophobic phase transition of the adsorbed ELP resulting in formation of large aggregates due to interparticle hydrophobic interaction. Formation of large aggregates caused a change in color of the colloidal suspension from red to violet due to coupling of surface plasmons in aggregated colloids. The surface phase transition of the ELP was reversible, as seen from the reversible change in color upon cooling the suspension to 10 degrees C. The formation of colloidal aggregates due to the interfacial phase transition of adsorbed ELP was independently verified by dynamic light scattering of ELP-modified gold colloids as a function of temperature. Colloidal SPR provides a simple and convenient colorimetric method to study the influence of the solution environment, interfacial properties, and grafting method on the transition properties of ELPs and other environmentally responsive polymers at the solid-water interface.