Localized Surface Plasmon Resonance Spectra Research Articles

Magneto-Plasmons in Periodic Nanoporous Structures

AbstractWe report on ordered nanoporous films exhibiting a unique magneto-plasmon based response, fabricated by nanosphere-assisted physical deposition. This work focuses on multi-layer Ag/CoFeB/Ag films as examples of such structures. Their microstructure dependent magnetic properties, localized surface plasmon resonance (LSPR) and magneto-optical Kerr effect were investigated. The observed effects of nanopores and Ag layers on the magnetic properties indicate the synergistic interaction between nanopores and Ag layers leading to an enhancement of the ferromagnetic character of the CoFeB film. LSPR spectra reveal that the introduction of Ag layers enhances the light transmission in the nanoporous CoFeB films (having pore sizes exceeding the wavelength of light) due to an enhanced interaction of light with surface plasmons. Periodic nanoporous Ag/CoFeB/Ag films covered by Ag capped nanospheres show a much larger extinction than uncovered nanoporous Ag/CoFeB/Ag films. The correlation between the magneto-optical Kerr effect and the nanostructures suggests a field-tunable Kerr effect owing to the magneto-electric coupling between the magnetic layer and the Ag layers, which is enhanced by the nanopores. These hybrid nanostructures are expected to offer potential applications in photovoltaic cells and for magneto-optic sensors.

Finite-Difference Time-Domain (FDTD) design of gold nanoparticle chains with specific surface plasmon resonance

We employ Finite-Difference Time-Domain (FDTD) simulations to analyze the electromagnetic far- and near-field response of gold nanoparticles (NPs) organized in chain-like structures as function of the number of particles and inter-particle distance in structures. As a result an empirical formula to predict the position of collective localized surface plasmon resonance (LSPR) as function of number of particles in the chain is devised. On the other hand the experimental LSPR spectrum recorded from a colloidal solution exhibiting a certain degree of aggregation has been effectively reconstructed by linear combination of individual LSPR contribution as calculated for NP ensembles of different size (monomers, dimers, trimers, etc.). Notably, we find that the maximum of electric field intensity (E2) in between adjacent NPs increases from dimeric to trimeric and tetrameric ensembles, followed by a steady state decrease as the number of NPs per chain further increases. The central gap in a long chain of NPs accommodate the highest field enhancement (‘hot-spots’). Our findings are relevant for designing effective substrates for Surface-Enhanced Raman Scattering (SERS) and plasmonic waveguides.

Localized surface plasmon resonance nanosensing of C-reactive protein with poly(2-methacryloyloxyethyl phosphorylcholine)-grafted gold nanoparticles prepared by surface-initiated atom transfer radical polymerization.

Highly sensitive and selective protein nanosensing based on localized surface plasmon resonance (LSPR) of gold nanoparticles (AuNPs) on which polymerized specific ligands were grafted as an artificial protein recognition layer for the target protein were demonstrated. As a model, optical nanosensing for C-reactive protein (CRP), a known biomarker for chronic inflammation that predicts the risk of arteriosclerosis or heart attacks, was achieved by measuring the shift of LSPR spectra derived from the change of permittivity of poly(2-methacryloyloxyethyl phosphorylcholine)-grafted AuNPs (PMPC-g-AuNPs) upon interacting with CRP, in which the PMPC-g-AuNPs layer were grafted on AuNPs by surface-initiated atom transfer radical polymerization (ATRP). This nanosensing system was effective even for detecting CRP concentrations in a human serum solution diluted to 1% (w/w), at which point a limit of detection was ~50 ng/mL and nonspecific adsorption of other proteins was negligible. The nanosensing system using specific ligand-grafted AuNPs has several strengths, such as low preparation cost, avoiding the need for expensive instruments, no necessary complex pretreatments, and high stability, because it does not contain biobased molecules. We believe this novel synthetic route for protein nanosensors, composed of AuNPs and a polymerized specific ligand utilizing surface-initiated controlled/living radical polymerization, will provide a foundation for the design and synthesis of nanosensors targeting various other biomarker proteins, paving the way for future advances in the field of biosensing.

Localized Surface Plasmon Resonance Sensor of Gold Nanoplates for Detection of Boric Acid

Localized surface plasmon resonance (LSPR) peak wavelength of nanostructures metallic materials, such as gold and silver, is very sensitive to the dielectric environment of the materials; hence widely used as sensors to detect various types of chemicals. In this study, high - yield gold nanoplates ca. 63% have been grown on the quartz substrate using the seed - mediated growth method. The grown gold nanoplates exhibit variety of shapes such as triangular, hexagonal, truncated hexagonal and flat rod. The LSPR spectrum of Au nanoplates sample has two absorption bands; centring at 543 nm and 710 nm, which are associated with transverse SPR (t-SPR) and longitudinal SPR (l-SPR) respectively. The intensities and peaks position of these two bands were found to linearly change with the concentration of boric acid solutions.

Wavelength-position correspondent plasmon resonance of planar Au/In2O3 bilayered nanostructures on quartz

The localized surface plasmon resonance (LSPR) of individual Au/In2O3 bilayered nanowires on a quartz substrate is investigated using dark-field scattering spectroscopy. The In2O3 nanowires are grown along the [422] direction via a self-forming process by surface diffusion, and the zone axis is found to be in the [111] direction. The samples are coated with a 20 nm-thick Au film, and position-dependent LSPR spectra along the length of a single Au/In2O3 bilayered nanowire on a quartz substrate are obtained with dark-field scattering spectroscopy for nanowires of various diameters. A shift of the LSPR peak wavelength for nanowires with different diameters is observed, which ranges from 605 to 640 nm. This fact, and the non-uniform scattering of light around the nanowire caused by asymmetry in its geometrical cross-section, suggests that the plasmon resonance wavelength may also be position dependent. This study on the LSPR property of a bilayered Au/In2O3 nanostructure provides an insight for understanding the wavelength dependence of plasmonic bilayered nanostructures.

Photothermal therapy of cancer cells using novel hollow gold nanoflowers.

This article presents a new strategy for fabricating large gold nanoflowers (AuNFs) that exhibit high biological safety under visible light and very strong photothermal cytotoxicity to HeLa cells under irradiation with near-infrared (NIR) light. This particular type of AuNF was constructed using vesicles produced from a multiamine head surfactant as a template followed by depositing gold nanoparticles (AuNPs) and growing their crystallites on the surface of vesicles. The localized surface plasmon-resonance spectrum of this type of AuNF can be easily modulated to the NIR region by controlling the size of the AuNFs. When the size of the AuNFs increased, biosafety under visible light improved and cytotoxicity increased under NIR irradiation. Experiments in vitro with HeLa cells and in vivo with small mice have been carried out, with promising results. The mechanism for this phenomenon is based on the hypothesis that it is difficult for larger AuNFs to enter the cell without NIR irradiation, but they enter the cell easily at the higher temperatures caused by NIR irradiation. We believe that these effects will exist in other types of noble metallic NPs and cancer cells. In addition, the affinity between AuNPs and functional biomolecules, such as aptamers and biomarkers, will make this type of AuNF a good recognition device in cancer diagnosis and therapy.

Single Gold Nanoparticle Localized Surface Plasmon Resonance Spectral Imaging for Quantifying Binding Constant of Carbohydrate–Protein Interaction

Quantifying carbohydrate-protein (ligand-receptor) interactions is important to understand diverse biological processes and to develop new diagnostic and therapeutic methods. We develop an approach to quantitatively study carbohydrate-protein interactions by Au nanoparticle localized surface plasmon resonance (LSPR) peak position shift at the single particles level. Unlike the previous techniques for single particle LSPR spectral imaging, only the first-order streak of an individual nanoparticle is needed to extract a LSPR spectrum, which has great potential to increase throughput to 500 single particle spectra in each frame. LSPR peak shift of protein modified single Au nanoparticles is found to be a function of its ligand concentration, which can be used to fit the binding constants of the interactions. The moderate interactions of Antithrombin III (AT III) and heparins including low molecular weight heparin (LMWH) are determined as well as the strong interaction of transferrin and antitransferrin and the weak interaction of bovine serum album (BSA) and heparin. The measured binding constants of transferrin to antitransferrin, heparin and LMWH to AT III, and BSA to heparin are (3.0 ± 0.6) × 10(9) M(-1), (3.1 ± 0.3) × 10(6) M(-1), (8.0 ± 0.5) × 10(5) M(-1), and (5.1 ± 0.1) × 10(3) M(-1), respectively, which are in good agreement with the reported values.

Spectroscopic studies of conformational changes of β-lactoglobulin adsorbed on gold nanoparticle surfaces

In this work, we investigated the conformational changes of a globular protein (β-lactoglobulin, β-lg) coated on the surface of 200nm gold nanoparticles (GNPs) using a number of analytical techniques: dynamic light scattering (DLS); particle electrophoresis (ζ-potential); localized surface plasmon resonance (LSPR) spectroscopy; transmission electron microscopy (TEM); and surface-enhanced Raman scattering (SERS). The β-lg (pH 3) concentration had a pronounced effect on the aggregation and surface charge of β-lg-coated GNPs. The surface charge of GNPs changed from negative to positive as increasing amounts of β-lg molecule were added, indicating that the globular protein molecules adsorbed to the surfaces of the particles. Extensive particle aggregation occurred when β-lg did not saturate the GNP surfaces, which was attributed to electrostatic bridging flocculation. Modifications in LSPR and SERS spectra after addition of β-lg to the GNP suspensions supported the adsorption of β-lg to the particle surfaces. Moreover, SERS highlighted the importance of a number of specific molecular groups in the binding interaction, and suggested conformational changes of the globular protein after adsorption. This research provides useful information for characterizing and understanding the interactions between globular proteins and colloidal particles.

Layer-by-Layer Structured AuNP Sensors for Terpene Vapor Detection

A localized surface plasmon resonance (LSPR) sensor based on self-assembled Au nanoparticle (AuNP) multilayers is developed for the detection of volatile terpenes that are considered to be biomarker gases during the growth process of plants. The sensor is fabricated by an alternate deposition of a bifunctional dithiol cross-linker and AuNPs. UV-vis spectra, atomic force microscopy images, and scanning electron microscope images of AuNP multilayers are investigated to analyze their LSPR spectra and refractive index sensitivity to terpene vapors. The results show that the optical properties of NP multilayers are jointly decided by the molecular length and chemical nature of dithiol linkers. The electric field coupling of AuNPs occurred in inter- and intra-layers determined by the refractive index sensitivity (RIS) of the sensor. The normalized RIS of the AuNP multilayer is about three times higher than that of the monolayer. The responses of AuNP multilayer sensors to changes in terpene vapor concentration are rapid, reversible, and reproducible.

Silica-Coated Gold Nanorod Arrays for Nanoplasmonics Devices

A facile method for growing silica layer on lithographically designed gold nanorod arrays (GNRAs) using a convenient sol-gel method is presented herein. The silica layer thickness was controlled on GNRAs with the reaction time. The localized surface plasmon resonance (LSPR) spectra of these hybrid metal/dielectric nanoparticles were recorded before and after the coating and the effect of different solvents on the LSPR were also assessed. The change in the fluorescence and SERS intensities of a probe molecule (Rh6G) deposited on GNRAs and silica-coated GNRAs revealed that the as-fabricated silica layer does inhibit the quenching of molecular excited states and enhances photophysical/photochemical processes. This kind of hybrid metal/dielectric nanoparticle arrays hence turn out to be real good candidates to design new "plasmonic-active" devices.

The Last Step in Converting the Surface Plasmonic Energy into Heat by Nanocages and Nanocubes on Substrates

The phonons of the vibrationally excited nanoparticle lattice couple to the environment on a time scale of tens to hundreds of picoseconds. The dynamics of electron–phonon, phonon–phonon, and vibrational processes in plasmonic nanoparticles may be followed optically through time-resolved pump–probe spectroscopy. [ 3–7 ] Vibrational motion of the lattice causes instantaneous modulation of the nanoparticle size, which modulates the electron density and results in periodic variations of the localized surface plasmon resonance (LSPR) spectrum at the lattice vibration frequency. The relaxation of these oscillations by coupling the nanoparticle lattice phonons to the phonons of the surrounding medium could lead to observed coherent oscillation of the medium phonons. The oscillations thus modulate the dielectric function of the medium around the nanoparticle resulting in modulations in the LSPR spectrum. In this manner, the excited medium phonons can be optically determined. The strength of the signal depends, among other factors, on the coupling between the nanoparticle and the medium as well as the coherence lifetime of the medium phonons produced. We recently reported on the lattice oscillations of gold nanocages having single and double shells [ 8 ] and showed that the value of the frequencies of the totally symmetric coherent oscillations observed refl ected the mechanical strength of these hollow nanoparticles. In the present study, we extend our time scale to that beyond the phonon–phonon relaxation

Localized Surface Plasmon Resonance Sensor Using Gold Nanoparticles for Detection of Bisphenol A

This paper reports an attempt to develop an optical sensor system to detect Bisphenol A (BPA) in water based on plasmonic property of Gold Nanoparticles (GNPs). Spherical GNPs of the average size of ca. 31±7 nm were grown on quartz substrate using seed mediated growth. An optical sensor system was setup, comprises a tungsten lamp light source, a duplex fiber optic probe, a spectrometer and a sensor chamber. Detection of BPA was done by comparing the Localized Surface Plasmon Resonance (LSPR) spectra of the GNPs film immersed in the deionised water and in BPA solutions by varying the concentration of BPA solutions from 58 mg/L to 0.003 ng/L. The LSPR spectra of GNPs sample were very sensitive to the presence of BPA where the shifted of their peaks position and the changed of their intensities are increases with the concentration of the BPA solutions.

A novel gold nanorod-based spectrographic method for evaluating the curcumin inhibitory action on HepG2 cells

A versatile and facile strategy for detecting the inhibitory action of curcumin on cancer cells has been developed by using the specific recognition between folic acid conjugated-gold nanorods (F-AuNRs) and folate receptors on the cell surface, based on the localized surface plasmon resonance (LSPR) and fluorescence spectra of gold nanorods (AuNRs). The F-AuNR probe was used to detect cancer cells with a detection limit down to 10 cells per mL, and it could replace traditional organic dyes as it has a better detection limit. Combined MTT, flow cytometry, fluorescence images and high-resolution AFM images further confirmed the feasibility of the spectroscopy methods. This approach can be used as a simple, rapid and sensitive tool to study the inhibitory action of drugs on cancer cells.

LSPR properties of metal nanoparticles adsorbed at a liquid–liquid interface

Unlike the solid-air and solid-liquid interfaces, the optical properties of metal nanoparticles adsorbed at the liquid-liquid interface have not been theoretically exploited to date. In this work, the three dimensional finite difference time domain (3D-FDTD) method is employed to clarify the localized surface plasmon resonance (LSPR) based optical properties of gold nanoparticles (NPs) adsorbed at the water-oil interface, including near field distribution, far field absorption and their relevance. The LSPR spectra of NPs located at a liquid-liquid interface are shown to differ significantly from those in a uniform liquid environment or at the other interfaces. The absorption spectra exhibit two distinct LSPR peaks, the positions and relative strengths of which are sensitive to the dielectric properties of each liquid and the exact positions of the NPs with respect to the interface. Precise control of the particles' position and selection of the appropriate wavelength of the excitation laser facilitates the rational design and selective excitation of localized plasmon modes for interfacial NPs, a necessary advance for the exploration of liquid-liquid interfaces via surface enhanced Raman spectroscopy (SERS). According to our calculations, the SERS enhancement factor for Au nanosphere dimers at the water-oil interface can be as high as 10(7)-10(9), implying significant promise for future investigations of interfacial structure and applications of liquid-liquid interfaces towards chemical analysis.

Fiber-Optic Refractive Index Sensor Based on the Cone-Based Round Structure

Fiber-optic refractive index (RI) sensors have the advantages of low cost, simple optical setup, remote sensing, and simple fabrication. A cone-based round structure, which is the combined structure of the cone structure and the round structure, is successively fabricated by using a cleaving method, a chemical glass etching method, and an electrical arc discharge method. In order to examine the possibility of the RI sensor, the fabricated cone-based round structure is used for the detection of various RIs by measuring the reflected intensities in the target sensing media. In addition, a fiber-optic localized surface plasmon resonance (LSPR) sensor based on the cone-based round structure is fabricated to enhance the sensitivity regarding RI changes. The fabricated fiber-optic LSPR sensor is used to detect the change of the RIs using the shift of peak wavelengths, as well as the change of reflected resonance intensities, by measuring LSPR spectra for gold nanoparticles on it.

The Application of Plasmonic Nanostructures for Quantitative Measurements of Cell Secretions

The localized surface plasmon resonance (LSPR) of lithographically patterned gold nanostructures was utilized for the quantitative measurement of anti-c-myc antibodies as harvested from a cultured 9E10 hybridoma cell line. The fact that the technique is label-free allowed for the antibody detection to be made without the need for further purification or processing. The simultaneous acquisition of CCD imagery and LSPR spectra enabled the calibration of hundreds of individual nanostructures in parallel. From the calibration we mapped the fractional occupancy of surface-bound receptors at individual nanostructures with nanomolar sensitivity and a temporal resolution of 225 ms. The setup is integrated on to an inverted microscope and fully compatible with other imaging techniques such as fluorescence and DIC.View Large Image | View Hi-Res Image | Download PowerPoint Slide

Correct Spectral Conversion between Surface‐Enhanced Raman and Plasmon Resonance Scattering from Nanoparticle Dimers for Single‐Molecule Detection

Simultaneous measurement of surface-enhanced Raman scattering (SERS) and localized surface plasmon resonance (LSPR) in nanoparticle dimers presents outstanding opportunities in molecular identification and in the elucidation of physical properties, such as the size, distance, and deformation of target species. SERS-LSPR instrumentation exists and has been used under limited conditions, but the extraction of SERS and LSPR readouts from a single measurement is still a challenge. Herein, the extraction of LSPR spectra from SERS signals is reported and a tool for measuring the interparticle distance from Raman enhancement data by the standardization of the SERS signal is proposed. The SERS nanoruler mechanism incorporates two important aspects (the LSPR scattering peak shift and the Raman shift for measuring interparticle distance), and signifies their exact one-to-one correspondence after spectral correction. The developed methodology is applied to calculate the interparticle distance between nanoparticle dimers from SERS signals, to detect and quantify DNA at the single-molecule level in a base-pair-specific manner. It is also shown that the SERS nanoruler concept can be used in structural analysis for the specific detection of the interaction of immunoglobulin G (IgG) with its target from bianalyte Raman signals with identical shaping at single-molecule resolution. The SERS profile shaping approach not only offers a new detection mechanism for single molecules, but also has excellent potential for studying protein interactions and the intracellular detection of mRNA.

Plasmon‐enhanced photoluminescence from TiO2:Sm3+:Au nanostructure

AbstractIn this paper, a novel plasmon‐enhanced photoluminescence (PL) hybrid system is presented based on metal–semiconductor nanostructure, in which TiO2:Sm3+ works as luminophor while the gold nanoparticle (NP) as the promoter of plasmon resonance. The plasmon‐enhanced PL is obtained by optimizing the plasmon resonance peak of gold NP employed in the system, and it is deduced that there is energy transfer from TiO2:Sm3+ to Au NPs during the process of light emitting. When the localized surface plasmon resonance (LSPR) spectra of Au NPs overlap with the PL spectra of TiO2:Sm3+, the Au NPs absorb the energy transferred from TiO2:Sm3+, and then the plasmonic mode confined around Au NPs can be excited to bring out the PL enhancement. magnified imageSchematic illustration of the process of plasmon‐enhanced emission. The different steps are (a) light emitting of TiO2:Sm3+, (b) energy transferred from TiO2:Sm3+ to the Au NPs, and (c) enhanced emitting of the hybrid system.

Unusual optical properties of the Au/Ag alloy at the matching mole fraction

Optical properties of localized surface plasmon resonance (LSPR) in Au/Ag alloy were investigated experimentally and numerically. It was found that LSPR spectra of nanostructures at near-infrared wavelengths changed drastically at the 50% Au/Ag mole fraction. Both the experimental results and the finite-difference time-domain simulations using experimentally obtained n, k values showed a similar tendency. At 50% molar fraction, electromagnetic field enhancement reached almost the same value as in pure Au.

Spectrally-Resolved Polarization Anisotropy of Single Plasmonic Nanoparticles Excited by Total Internal Reflection

Polarization-resolved optical studies of individual plasmonic nanoparticles are valuable for providing orientation information about anisotropic plasmonic nanostructures, such as nanorods and nanoparticle dimers, but are less useful for structures such as nanoprisms. In this study, the anisotropic polarization-dependent excitation field generated by through-the-objective total internal reflection (TIR) is used to probe the orientation of single gold nanorods and single silver triangular nanoprisms with spectral and polarization resolution. By correlating localized surface plasmon resonance (LSPR) and polarization-resolved spectra with scanning electron microscopy (SEM) imaging, we show that both nanorods and nanoprisms show anisotropic polarization-sensitive scattering. While the polarization response of the nanorods is consistent with previous reports, the nanoprisms show an unexpected anisotropy that is related to their orientation in the x–y plane. Exploiting the anisotropic polarization-dependent excitation field offered by TIR allows us to access orientational information about a variety of nanostructures through a nonperturbative optical technique.