Near-infrared Surface Plasmon Resonance Research Articles

Infrared surface plasmon resonance of AZO-Ag-AZO sandwich thin films

Near-infrared surface plasmon resonance (SPR) spectra were collected of thin multilayer films of aluminum-doped zinc oxide (AZO) / silver (Ag) / AZO on BK-7 glass in the Kretschmann configuration in air, with the silver layer thickness varying from 5 nm to 50 nm. The SPR results were interpreted by modeling the reflectance with a five-layer transfer-matrix method, with the aid of a simplex algorithm. The model indicated that the Ag plasma frequency was significantly higher than the bulk value, possibly due to Schottky effect charge transfer from the AZO to the Ag layer. Continuous silver films were made as thin as 10 nm, indicating an inhibition of metal island formation for Ag deposited on AZO.

Controllable Synthesis of Chitosan-Mediated Gold Nanoplate and the Growth Mechanisms

By chitosan as a stabilizer and reducing agent, the tunable surface plasmon resonance (SPR) ab- sorption peak of gold nanoplate has been successfully fabricated by water bath heating of solution containing HAuCl4, chitosan and gold nanoseeds. The SEM images indicated that the gold nanoplates were mainly composed of triangular and truncated triangular shape. The edge is about 170 nm. X-ray diffraction analyses indicated that the gold nameplates were pure single crystals with {111} planes as their basal planes. The growth mechanisms on synthesis of chitosan-mediated gold nanoplate were discussed. Under optimum con- ditions the SPR absorption peak of gold nanoplate in-plane dipolar is 920 nm. The experiment results showed that the near-infrared SPR absorption peak and the absorption intensity can be effectively controlled by controlling the amounts of chitosan and gold seeds, water bath temperature and bath time.

Planar near-infrared surface plasmon resonance sensor with Si prism and grating coupler

We have developed a silicon-microfabrication-based surface plasmon resonance (SPR) sensor with Si prisms and an optical grating. Since this sensor is compatible with microelectromechanical systems technology, it can be further miniaturized and integrated with optical parts or fluidic components for the realization of a one-chip SPR sensor. The Si prism structure, transparent in the near-infrared range, was used to lead the 1550-nm measuring light to the sensing surface where the evanescent light was generated. Smooth prism slopes were obtained by using anisotropic etching to utilize the (1 1 1) planes on the (1 0 0) surface plane of single-crystalline Si wafer. The result was a 200-μm-pitch array of prisms with 54.74° slope angles. In this configuration the range of incident angles at which near-infrared light produces an SPR dip is from 38.26° to 71.24°. Because the SPR angles for major specimens (16.60° for air, 22.06° for water, and 22.79° for ethanol) are out of range, we used an optical grating with a roughly 400-nm-pitch to make an SPR dip position move to fit within the available angle range by the diffraction effect. SPR measurements with several specimens confirmed that the combination of Si prisms and the optical grating excited surface plasmons. The measured SPR dip positions and their sensitivity to refractive index were compared with the theoretical values, and their consistency confirmed the utility of this device as an SPR sensor.

540 Siプリズムと回折格子を備えたMEMS近赤外用SPRセンサ(T04 MEMS技術を用いたヒューマンインターフェース,大会テーマセッション,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

540 Siプリズムと回折格子を備えたMEMS近赤外用SPRセンサ(T04 MEMS技術を用いたヒューマンインターフェース,大会テーマセッション,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

Near-infrared surface plasmon resonance sensing on a Si platform with nanoparticle-based signal enhancement

A Si-based surface plasmon resonance (SPR) system is examined in conditions of the nanoparticle-enhanced sensing. The system is equipped with near IR pumping light and a silicon coupling prism, used with SPR-supporting gold film in the Kretschmann– Raether geometry. Using Maxwell–Garnett (MG) effective medium theory, we modeled the SPR-related response of the system to the absorption of colloidal nanoparticles of different materials (Au, Cu, Pt, Ag, Al, Ti, Pd) on gold. We show that this response strongly depends on the nanoparticle fill factor, associated with a relative volume of nanoparticles in the absorbed layer. For low fill factors (fm � 0.1), corresponding to relatively low concentrations of small nanoparticles, the absorption of nanoparticles of different materials leads to almost identical angular shifts of the SPR dip, but to a quite different intensity damping at the dip point. In contrast, the increase of the fill factor results in quite different angular and intensity SPR characteristics for the materials used, with the most pronounced sensing responses for Pt, Pd and Ti. The proposed analysis enables to estimate the efficiency of nanoparticles of different materials as markers in nanoparticle-enhanced SPR sensing. 2004 Elsevier B.V. All rights reserved.

Near-infrared surface plasmon resonance sensing on a silicon platform

A novel surface plasmon resonance (SPR) sensing configuration equipped with a silicon coupling prism is described. Theoretical results and experimental data are obtained to establish essential conditions of SPR excitation using infrared light in the Kretschmann–Raether geometry with a thin gold layer as the supporting metal. We also compare sensitivities of different angular and spectral interrogation Si-based schemes in models of bio- and chemical sensing. Possibilities for the miniaturization of SPR sensors using the proposed Si-based configuration are discussed.

Estimation of organic molecular film structures using surface–plasmon resonance spectroscopy

Near-infrared surface–plasmon resonance (SPR) spectroscopy can be used to determine the thickness of single organic molecular films and the permittivities of organic materials with a high degree of sensitivity. The two-wavelength SPR method with one NIR and one visible light probes was used to improve the accuracy of our experiment. Structures of organic molecules on various substrates were investigated. Particular attention was focused on the error in the measuring of thickness, which was caused by the surface roughness of the substrate. The effect of this was determined by AFM observations. The error in measurement caused by a rough substrate was, thus, estimated.

Near-Infrared Surface Plasmon Resonance Measurements of Ultrathin Films. 1. Angle Shift and SPR Imaging Experiments

The application of surface plasmon resonance (SPR) measurements to the study of ultrathin organic and inorganic films adsorbed onto gold surfaces utilizing near-infrared (NIR) excitation from 800 to 1152 nm is described. SPR scanning angle measurements of film thickness are demonstrated at 814 and 1152 nm using low-power diode and HeNe laser sources, respectively. Several advantages of SPR in the NIR are noted. The in situ reflectivity versus angle of incidence curves sharpen greatly (as compared to 632.8 nm) at longer wavelengths so that there is no loss in sensitivity in the measurement of film thickness despite a doubling of the excitation wavelength. The sharper resonance and longer wavelengths also allow for the measurement of thicker films. Examples of SPR thickness measurements for self-assembled alkanethiol monolayers and composite biopolymer/SiO2 nanoparticle electrostatic multilayer films are given. SPR imaging experiments are also performed at various NIR wavelengths using an incoherent white light source and narrow band-pass filters. The incoherent white light source eliminates laser fringes that have been observed in previous SPR imaging experiments, and the use of narrow band-pass filters allows for the easy selection and variation of excitation wavelength. The narrowness of the reflectivity versus angle curves leads to greater contrast in NIR SPR images compared to the same features examined with excitation from visible light. The combination of these changes results in nearly 1 order of magnitude enhancement in the SPR differential reflectivity image, indicating that SPR imaging is best conducted with incoherent NIR excitation. One disadvantage of using NIR wavelengths for SPR imaging is that the surface plasmon propagation length increases in the NIR so that the lateral image resolution is reduced; however, image features larger than 50 μm can easily be resolved. A NIR SPR image of a DNA array onto which single-stranded DNA binding protein has bound is shown as an example of how NIR SPR imaging experiments have sufficient sensitivity to monitor DNA−protein interactions.

Assembly of polymer/lipid composite films on solids based on hairy rod LB-films

The present work deals with the assembly of multilayers or rod-like polymers with hydrophobic side chains (called hairy rods) and their potential application as ultrathin polymer cushions for the build-up of self healing supported membranes on various solids (Si/SiO(2)-wafer, gold covered substrates). Three types of hairy rods were studied: Isopentyl cellulose (IPC), phtalocyaniatopolysiloxane with mixed alkane side chains (PCPS) and trimethylsilane cellulose (TMCS). Detailed analysis of the thickness of supported multilayers as a function of the number of deposited monolayers with ellipsometry, near infrared surface plasmon resonance (NIR-SPR), a quartz crystal microbalance (QCM) and reflection interference contrast microscopy (RICM), show that the basic building blocks of hairy rod multilayers are bilayers with the hydrophobic surfaces of the monolayers facing each other. Continuous and stable firms of hairy rods can be deposited if the hydrophobicities of the solid surface and the monolayer are matched. It is demonstrated by lateral diffusion measurements (using photobleaching techniques) that continuous phospholipid bilayers can be deposited onto multilayers of rigid rods of TMCS after hydrophilization by cleavage of trimethylsilane side chains in HCl-vapour, while stable lipid monolayers can be deposited onto hydrophobic surfaces of rigid rod layers. NIR-SPR allows the observation of double band reflectivity curves at interfaces separating different surface layers and thus offers the possibility of differential detection of ligand binding at the interface of differently functionalized domains.

Near-infrared surface plasmon resonance in silicon-based sensor: new opportunities in sensitive detection of biomolecules from aqueous solutions by applying microstep for discriminating specific and non-specific binding

We report the application of near-infrared surface plasmon spectroscopy to study the sensitive detection of the binding of proteins to functionalized surfaces. Working at 300 nm, where both water and silicon are transparent, the method is of particular interest for biosensors based on silicon technology. We describe the application of thin functionalization layers forming a step on the sensor surface. Employment of such a step for discriminating specific and non-specific binding of biomolecules is suggested: measuring surface plasmon resonance (SPR) with a single near-infrared laser and detector chip on a single sensor spot shows simultaneously adsorption to one surface in comparison to a reference surface. As a model for this step, a few monolayers of phthalocyaninatopolysiloxane a 'hairy' rod-like polymer, are deposited by the Langmui-Blodgett technique. As a model system, we use the binding behaviour of bovine serum albumin to two different kinds of surface.

Self assembly of covalently anchored phospholipid supported membranes by use of DODA-Suc-NHS-lipids

We present a novel preparation method for the self assembly of covalently anchored phospholipid supported membranes. The surface is gold covered by cysteamine. Vesicles containing DMPC and activated DODA-Suc-NHS-lipids assembled on this surface. The whole self-assembly process is monitored conveniently by Near Infrared Surface Plasmon Resonance (NIR-SPR). Comparing the data to those obtained by Ca2+-mediated vesicle fusion, confirmed this interpretation.