Localized Surface Plasmon Resonance Phenomenon Research Articles

Influence of Shape on the Surface Plasmon Resonance of Tungsten Bronze Nanocrystals

Localized surface plasmon resonance phenomena have recently been investigated in unconventional plasmonic materials such as metal oxide and chalcogenide semiconductors doped with high concentrations of free carriers. We synthesize colloidal nanocrystals of CsxWO3, a tungsten bronze in which electronic charge carriers are introduced by interstitial doping. By using varying ratios of oleylamine to oleic acid, we synthesize three distinct shapes of these nanocrystals—hexagonal prisms, truncated cubes, and pseudospheres—which exhibit strongly shape-dependent absorption features in the near-infrared region. We rationalize these differences by noting that lower symmetry shapes correlate with sharper plasmon resonance features and more distinct resonance peaks. The plasmon peak positions also shift systematically with size and with the dielectric constant of the surrounding media, reminiscent of typical properties of plasmonic metal nanoparticles.

Controllable Localized Surface Plasmonic Resonance Phenomena in Reduced Gold Oxide Films

In this study, we used reactive sputtering to prepare large-area, homogeneous gold oxide (AuOx) films, which we then subjected to reduction processes under ambient conditions at room temperature to obtain reduced AuOx films featuring embedded Au nanoparticles (NPs). We analyzed these films in terms of both their material characteristics and optical properties. For the first time, we obtained the optical constants of AuOx films directly deposited on glass and Si substrates. Moreover, we observed localized surface plasmon resonance (LSPR) phenomena from the visible to the near-infrared (NIR) during the formation of the Au NPs in the AuOx film. The plasmonic properties of the Au NPs embedded in the AuOx films were much different from those of chemically synthesized Au NPs. We found that the LSPR wavelength of the Au NPs embedded in the AuOx films could be tuned from 700 to 980 nm by varying the duration of the reduction process. Moreover, the reduced AuOx films could be applied as surface-enhanced Raman spectroscopy (SERS)-active substrates. The minimum detection was achieved down to a concentration of 10–10 M (R6G) when using the reduced AuOx film-based substrate–a level comparable with those of other kinds of SERS substrates prepared using more complicated methods. The rapid method proposed herein provides large-areas films with tunable resonance wavelengths for applications as SERS-active substrates in optical and chemical sensing.

Nanoparticle device for biomedical and optoelectronics applications

Purpose – In this contribution, the aim is to present a nanoparticle device, operating in the visible regime based on the localized surface plasmon resonance (LSPR) phenomenon. Design/methodology/approach – The nanoparticle electromagnetic properties are evaluated by a new analytical model and compared to the results obtained by numerical analysis. Findings – A near-field enhancement is obtained by arranging the nanoparticles in a linear array. Analytical formulas, describing such enhancement, are presented. Originality/value – The results demonstrate the possibility to use the proposed device for medical diagnostics and optoelectronics applications.

Automation Highlights from the Literature

Automation Highlights from the Literature

Protein Integrated, Functionally Active Silver Nanoplanar Structures for Enhanced SPR

In an alternative approach to achieving nanoparticle-based enhanced surface plasmon resonance (SPR), we present a simple protein seeding-based method for the synthesis of a protein integrated, surface active silver nanoplanar structure, where the protein is cocrystallized with silver. The growth kinetics of this integrated structure has been probed by X-ray diffraction and Raman spectroscopy, which show a spherical to prismatic transition within a three minute growth span. The SPR activity is directly proportional to the tip sharpness of the nanostructure due to the localized surface plasmon resonance (LSPR) phenomenon. This biometallization process depends on the size, shape, and chemical nature of the interacting protein as demonstrated by comparing the results for different model proteins. Moreover, the protein remains functionally intact when embedded in the nanostructured SPR surface. Taking horseradish peroxidase (HRP) as a model protein, we have demonstrated a very high SPR binding profile against ...

Peak shift measurement of localized surface plasmon resonance by a portable electronic system

In recent years, the characterization of surface molecular layers by localized surface plasmon resonance (LSPR) has attracted a lot of interest thanks to its ability to provide a higher spatial resolution with respect to standard SPR. LSPR can be observed as a peak in the extinction spectrum of metal nanoparticles such as gold non-connected surface patterns. A plasmon peak red shift is caused both by the presence of molecular layers on the gold surface and by molecular binding events. The current study presents a portable transmission system to observe the LSPR phenomenon that extracts the peak location employing a discrete number of light sources. The peak location extraction is performed by an algorithm that takes into account the spectral characteristics of all the components. The performance of our LSPR measurement system has been characterized on a set of Fluorinated Tin Oxide-coated slides covered with nanoislands with a diameter of approximately 30 nm. The samples have been modified with a single-stranded DNA layer and the plasmonic peak location has been determined before and after surface treatment. The samples have been characterized in parallel with a high-end spectrophotometer. The results presented demonstrated the performance of our measurement system in determining the peak location with 1 nm precision. (C) 2012 Elsevier B.V. All rights reserved.

Theoretical limit of localized surface plasmon resonance sensitivity to local refractive index change and its comparison to conventional surface plasmon resonance sensor

In this paper, the theoretical sensitivity limit of the localized surface plasmon resonance (LSPR) to the surrounding dielectric environment is discussed. The presented theoretical analysis of the LSPR phenomenon is based on perturbation theory. Derived results can be further simplified assuming quasistatic limit. The developed theory shows that LSPR has a detection capability limit independent of the particle shape or arrangement. For a given structure, sensitivity is directly proportional to the resonance wavelength and depends on the fraction of the electromagnetic energy confined within the sensing volume. This fraction is always less than unity; therefore, one should not expect to find an optimized nanofeature geometry with a dramatic increase in sensitivity at a given wavelength. All theoretical results are supported by finite-difference time-domain calculations for gold nanoparticles of different geometries (rings, split rings, paired rings, and ring sandwiches). Numerical sensitivity calculations based on the shift of the extinction peak are in good agreement with values estimated by perturbation theory. Numerical analysis shows that, for thin (≤10 nm) analyte layers, sensitivity of the LSPR is comparable with a traditional surface plasmon resonance sensor and LSPR has the potential to be significantly less sensitive to temperature fluctuations.

The Analysis of Ag Nanospheres and Arrays LSPR Phenomena Based on DDA and FDTD Method

The Discrete Dipole Approximation (DDA) method and the Finite Difference Time Domain (FDTD) method are used to analyze silver nanospheres with different radius and the coupling of nanospheres array complementarily. DDA method is used for simulating the extinction spectra of single silver nanosphere and nanospheres array; and the coupling of two nanospheres and their surrounding electric field distribution are simulated by FDTD method. Through these results, we got some important conclusions of nanoparticles’ Localized Surface Plasmon Resonance (LSPR) phenomenon.

Sensitivity‐enhancement methods for surface plasmon sensors

AbstractSurface plasmon resonance (SPR) sensors have been a mature technology for more than two decades now, however, recent investigations show continuous enhancement of their sensitivity and their lower detection limit. Together with the recent investigations in localized SPR phenomena, extraordinary optical transmission through nanoapertures in metals, and surface‐enhanced spectroscopies, drastic developments are expected to revolutionize the field of optical biosensing. Sensitivity‐enhancement (SE) techniques are reviewed focusing both on the physical transduction mechanisms and the system performance. In the majority of cases the SE is associated with the enhancement of the electromagnetic field overlap integral describing the interaction energy within the analyte. Other important mechanisms are the interaction between plasmons and excitons and between the analyte molecules and the metal surface. The lower detection limit can be reduced significantly if systems with high signal‐to‐noise ratio are used such as common‐path interferometry, ellipsometry or polarimetry systems.

Selective Aggregation of Polyanion-Coated Gold Nanorods Induced by Divalent Metal Ions in an Aqueous Solution

A simple, accurate method for detecting metal ions in an aqueous solution using functionalized gold nanorods (AuNRs) is described. The method involves the complexing of divalent metal ions with poly(acrylic acid) (PAA) and, the localized surface plasmon resonance (LSPR) phenomena of AuNRs. Changes in the longitudinal surface plasmon bands (LSPBs) were monitored using aggregates of PAA-coated AuNRs with various divalent metal ions via UV-vis spectroscope. Functionalized AuNRs underwent robust aggregate formation by chelation with divalent metal ions (e.g., Cu2+, Zn2+, Cd2+, and Fe2+). Copper ions formed largest aggregates within 2 h, because complexation between Cu2+ and dicarboxylate has the highest deltaH and -deltaG values. This process represents an easy and useful method for detecting certain divalent metal ions, and the aggregates are also, in some cases, clearly visible to the naked eye.

Binding of Ricinus communis agglutinin to a galactose-carrying polymer brush on a colloidal gold monolayer

A polymer with many pendent galactose residues was prepared by atom-transfer radical polymerization (ATRP) of galactose-carrying vinyl monomer, 2-lactobionamidoethyl methacrylate (LAMA), with a disulfide-carrying ATRP initiator, 2-(2′-bromoisobutyroyl)ethyl disulfide (DT-Br). The galactose-carrying polymer obtained (DT-PLAMA) was accumulated as a polymer brush via Au–S bond on a colloidal gold monolayer deposited on a cover glass. For comparison, a disulfide which carried one galactose residue at both ends (2-lactobionamidoethyl disulfide, Cys-Lac) was accumulated as a self-assembled monolayer (SAM) on the colloidal gold monolayer, too. The association and dissociation processes of galactose residues on the colloidal gold with a lectin, Ricinus communis agglutinin (RCA 120), were observed by the increase and decrease in absorbance at 550 nm corresponding to localized surface plasmon resonance (LSPR) phenomena. The Cys-Lac SAM-carrying glass chip showed a strong non-specific adsorption of the lectin, whereas the DT-PLAMA brush-carrying one reversibly associated with the lectin, indicating reusability of the latter device. The apparent association constant of the lectin with the galactose residues in the DT-PLAMA brush was much larger than the association constant for free galactose, and the detection limit of RCA 120 by the glycopolymer brush-modified device was satisfactorily low. Furthermore, a microscopic observation clearly indicated that the DT-PLAMA brush could reversibly associate with a HepG2 cell having galactose receptors, though these processes could not be observed spectrophotometrically due to a gigantic size of the cell.

Excitation of localized surface plasmon resonance using a core–shell structurednanoparticle layer substrate and its application for label-free detection of biomolecularinteractions

The novel characteristics of nanomaterials enable highly sensitive and specific applicationsin electronics, optics and biotechnology. In particular, nanomaterials have become thepreferable tools for monitoring biomolecular interactions on a biochip withoutlabelling procedures using enzymes and fluorescent dyes. In this report, label-freedetection of hybridization between nucleic acids using localized surface plasmonresonance (LSPR) based on a core–shell structured nanoparticle layer substrate isdescribed. The core–shell structured nanoparticle layer substrate could be excitedusing LSPR phenomena, and its LSPR characteristics were controlled by applyingdifferent fabrication conditions. Using our LSPR label-free biochip, the opticalcharacteristics were monitored for the detection of specific DNA–DNA and PNA–DNAhybridization reactions. Furthermore, the detection limit of the LSPR label-free biochipwas 1 pM. The highly sensitive label-free detection of DNA hybridization waspossible in a short analysis time. As a result, the LSPR label-free biochip provides apromising platform with attractive advantages for the detection of biomolecularinteractions at low cost in a simplified experimental set-up with a low samplevolume.

A novel enhancement assay for immunochromatographic test strips using gold nanoparticles

The immunochromatographic assay is a well-known and convenient diagnostic system. In this report, the development of a novel enhancement assay for the test strips is described. Additionally, this highly sensitive immunochromatographic assay was applied to detect human chorionic gonadotropin hormone (HCG) as the model case. The primary antibody-conjugated gold nanoparticles were used as the enhancer of the standard method. The primary antibodies were immobilized within a defined detection zone (test line) on the diagnostic nitrocellulose membrane. The secondary antibodies were conjugated with colloidal gold nanoparticles. In combination with an effective sample pretreatment, the gold-conjugated antibodies and the primary antibodies formed a sandwich complex with the target protein. Within the test line, the sandwich complex was immobilized, and furthermore, concentrated by the enhancer resulting in a localized surface plasmon resonance (LSPR) phenomenon and a distinct red color on the test line. The intensity of color of the red test line (signal intensity), which correlated directly with the concentration of the target protein in the standard or spiked samples, was assessed visually and by computer image analysis using a three-determination analysis. Under optimum conditions, the limit of detection (LOD) for HCG assay was 1 pg/mL. When using human serum, 10 pg/mL of HCG could be detected. We have also spiked total prostate-specific antigen (TPSA) in female serum. The LOD for TPSA was determined as 0.2 ng/mL. With this method, the quantitative determination of the target protein could be completed in less than 15 min. Our novel immunochromatographic strips using the enhancing method based on LSPR of gold nanoparticles are useful as a rapid and simple screening method for the detection of important analytes for medical applications, environmental monitoring, food control, and biosecurity.

Localized Surface Plasmon Resonance Sensing of Lipid-Membrane-Mediated Biorecognition Events

Supported phospholipid bilayers (SPBs) have emerged as important model systems for studies of the natural cell membrane and its components, which are essential for the integrity and function of cells in all living organisms, and also constitute common targets for therapeutic drugs and in disease diagnosis. However, the preferential occurrence of spontaneous SPB formation on silicon-based substrates, but not on bare noble-metal surfaces, has so far excluded the use of the localized surface plasmon resonance (LSPR) sensing principle for studies of lipid-membrane-mediated biorecognition reactions. This is because the LSPR phenomenon is associated with, and strongly confined to, the interfacial region of nanometric noble-metal particles. This problem has been overcome in this study by a self-assembly process utilizing localized rupture of phospholipid vesicles on silicon dioxide in the bottom of nanometric holes in a thin gold film. The hole-induced localization of the LSPR field to the voids of the holes is demonstrated to provide an extension of the LSPR sensing concept to studies of reactions confined exclusively to SPB-patches supported on SiO2. In particular, we emphasize the possibility of performing label-free studies of lipid-membrane-mediated reaction kinetics, including the compatibility of the assay with array-based reading (approximately 7 x 7 microm2) and detection of signals originating from bound protein in the zeptomole regime.