Shift Of Surface Plasmon Resonance Research Articles

Formation of core-shell Au@Ag nanorods induced by catecholamines: A comparative study and an analytical application

Gold nanorods (AuNRs) stabilized by cetyltrimethylammonium bromide (CTAB) were synthesized and an interaction of catecholamines (CAs) with silver ions in the presence of the obtained AuNRs was studied. The reaction results into formation of core-shell Au@Ag nanorods (Au@AgNRs) and leads to a hypsochromic shift of the long-wave surface plasmon resonance (SPR) band in the absorption spectrum of AuNRs. The influence of a CA structure, excess of CTAB, interaction time, pH, concentration of AuNRs, silver ions and CAs on this interaction was studied. Based on correlation of the NRs spectral characteristics with the concentration of CAs, a method for spectrophotometric determination of dobutamine, epinephrine, norepinephrine and dopamine with detection limits 27, 18, 16 and 13 μg L−1, respectively, has been developed. The method can be applied to the analysis of medicines.

Synthesis of oxocarbon-encapsulated gold nanoparticles with blue-shifted localized surface plasmon resonance by pulsed laser ablation in water with CO2 absorbers

Colloidal suspensions of oxocarbon-encapsulated gold nanoparticles have been synthesized in a one-step procedure by pulsed-laser ablation (PLA) at 532 nm of a solid gold target placed in aqueous solution containing CO2 absorbers, but without any stabilizing agent. Multi-wavelength surface enhanced Raman spectroscopy allows the identification of adsorbed amorphous carbon and graphite, Au-carbonyl, Au coordinated CO2-derived bicarbonates/carbonates and hydroxyl groups around the AuNPs core. Scanning electron microscopy, energy dispersive x-ray analysis and high resolution transmission electron microscopy highlight the organic shell structure around the crystalline metal core. The stability of the colloidal solution of nanocomposites (NCs) seems to be driven by solvation forces and is achieved only in neutral or basic pH using monovalent hydroxide counter-ions (NaOH, KOH). The NCs are characterized by a blue shift of the localized surface plasmon resonance (LSPR) band typical of metal-ligand stabilization by terminal π-back bonding, attributed to a core charging effect caused by Au-carbonyls. Total organic carbon measurements detect the final content of organic carbon in the colloidal solution of NCs that is about six times higher than the value of the water solution used to perform PLA. The colloidal dispersions of NCs are stable for months and are applied as analytical probes in amino glycoside antibiotic LSPR based sensing.

Shift of localized surface plasmon resonance in monolayer of small gold nanoparticles: Simulation predictions of interparticle coupling

Localized surface plasmon resonance of gold nanoparticle layer is investigated by the experiment as well as theoretical calculations. The limits of analytical models are illustrated for compact nanoparticle film revealing signify cant discrepancy between experimental and simulated results while the numerical calculations based on finite-difference time-domain using thin film optical parameters are shown as suitable. There it is shown that 3D finite-difference time-domain simulation can be replaced by 2D simulation without losing accuracy of the calculation of localized surface plasmon resonance. The dependence of the localized surface plasmon resonance wavelength on the nanoparticle size, separation as well as local dielectric constant of surrounding environment is presented and applied for the real nanoparticle size and separation distributions observed in the experiment. Tuning of plasmon resonance in a wide range is demonstrated as a promising way for further applications.

Dispersion curve-based sensitivity engineering for enhanced surface plasmon resonance detection

Manipulation of dispersion curve for enhancing surface plasmon resonance (SPR) detection is proposed. Based on strong correlation between slope of dispersion curve and SPR angle shift, it is confirmed that dispersion curve characteristics can be employed as an analysis tool to evaluate SPR sensor performance and to predict anomalous plasmonic behaviors. Complicated resonance shift in SPR angle, especially in the presence of metallic nanograting, such as negative shift, can be controlled reliably by engineering the dispersion curve. As it has a dependence on geometrical parameters of metallic films and gratings, dispersion relation engineering is also useful in optimizing the sensor sensitivity. For a wavelength of λ=630nm, introduction of a gold nanograting shows a significant improvement in sensitivity by more than 5 times, compared to a traditional thin-film-based SPR structure. In addition, we find that use of a longer wavelength in near-infrared region can be advantageous for avoiding a negative SPR shift and obtaining a narrow and deep SPR curve. Our approach is expected to extend the applicability of dispersion-based sensitivity engineering technique to a variety of SPR platforms for highly enhanced SPR detection.

Increasing the spectral shifts in LSPR biosensing using DNA-functionalized gold nanorods in a competitive assay format for the detection of interferon-γ

We demonstrate an approach that utilizes DNA-functionalized gold nanorods (AuNRs) in an indirect competitive assay format to increase the spectra shift in localized surface plasmon resonance (LSPR) biosensing. We use interferon gamma (IFN-γ) as a model analyte to demonstrate the feasibility of our detection method. The LSPR chips with periodic gold nanodot arrays are fabricated using a thermal lithography process and are functionalized with IFN-γ aptamers for detection. The DNA-functionalized AuNRs and IFN-γ compete with each other to bind to the aptamers during detection, and the spectra shifts are mainly caused by the AuNRs rather than IFN-γ. When using our approach, the target molecules do not need to be captured by two capture ligands simultaneously during detection and thus do not require multiple binding sites. Both experiments and finite-difference time-domain (FDTD) simulations show that making the AuNRs as close to the chip surface as possible is very critical for increasing LSPR shifts, and the simulated results also show that the orientation of the AuNR affects the plasmon coupling between the gold nanodots on the chip surface and the nearby AuNRs. Although only the detection of IFN-γ is demonstrated in this study, we expect that the LSPR biosensing method can be applied to label-free detection of a variety of molecules as long as suitable aptamers are available.

Ex Vivo and In Vivo Imaging and Biodistribution of Aptamers Targeting the Human Matrix MetalloProtease-9 in Melanomas.

The human Matrix MetalloProtease-9 (hMMP-9) is overexpressed in tumors where it promotes the release of cancer cells thus contributing to tumor metastasis. We raised aptamers against hMMP-9, which constitutes a validated marker of malignant tumors, in order to design probes for imaging tumors in human beings. A chemically modified RNA aptamer (F3B), fully resistant to nucleases was previously described. This compound was subsequently used for the preparation of F3B-Cy5, F3B-S-acetylmercaptoacetyltriglycine (MAG) and F3B-DOTA. The binding properties of these derivatives were determined by surface plasmon resonance and electrophoretic mobility shift assay. Optical fluorescence imaging confirmed the binding to hMMP-9 in A375 melanoma bearing mice. Quantitative biodistribution studies were performed at 30 min, 1h and 2 h post injection of 99mTc-MAG-aptamer and 111In-DOTA-F3B. 99mTc radiolabeled aptamer specifically detected hMMP-9 in A375 melanoma tumors but accumulation in digestive tract was very high. Following i.v. injection of 111In-DOTA-F3B, high level of radioactivity was observed in kidneys and bladder but digestive tract uptake was very limited. Tumor uptake was significantly (student t test, p<0.05) higher for 111In-DOTA-F3B with 2.0%ID/g than for the 111In-DOTA-control oligonucleotide (0.7%ID/g) with tumor to muscle ratio of 4.0. Such difference in tumor accumulation has been confirmed by ex vivo scintigraphic images performed at 1h post injection and by autoradiography, which revealed the overexpression of hMMP-9 in sections of human melanomas. These results demonstrate that F3B aptamer is of interest for detecting hMMP-9 in melanoma tumor.

Kinetically Selective Inhibitors of Human Carbonic Anhydrase Isozymes I, II, VII, IX, XII, and XIII.

To get a better understanding of the possibility of developing selective carbonic anhydrase (CA) inhibitors, interactions between 17 benzenesulphonamide ligands and 6 human CAs (full-length CA I, II, VII, and XIII and catalytic domains of CA IX and XII) were characterized using surface plasmon resonance and fluorescent-based thermal shift assays. Kinetics revealed that the strongest binders had subnanomolar affinities with low dissociation rates (i.e., kd values around 1 × 10(-3) s(-1)) or were essentially irreversible. Chemodynamic analysis of the interactions highlighted an intrinsic mechanism of the CA-sulphonamide interaction kinetics and showed that slow dissociation rates were mediated by large hydrophobic contacts. The studied inhibitors demonstrated a high cross-reactivity within the protein family. However, according to chemical phylogenetic analysis developed for kinetic data, several ligands were found to be selective against certain CA isozymes, indicating that it should be possible to develop selective CA inhibitors suitable for clinical use.

Surface plasmon resonance for characterization of large-area atomic-layer graphene film

Characterization of large-area thin films with atomic-scale resolution is challenging but in great demand for diverse applications (e.g., nanotechnology and sensing). Here, we use the Surface Plasmon Resonance (SPR) method to characterize both the thickness and refractive index of chemical-vapor-deposition (CVD)-grown graphene films. The measured refractive index and extinction coefficient values of the CVD-grown graphene monolayer at 670 nm wavelength are 3.135 and 0.897, respectively. Our results demonstrate that SPR shifts generated by graphene films are large (i.e., ∼1°/nm), almost tenfold larger than that observed in SPR measurements of organic monolayers. We find that this significantly large SPR shift easily enables the thickness of a large area sample (i.e., ∼mm2) to be determined with subnanometer-scale resolution. We show that the SPR method can identify thickness of different graphene layers and give an estimate of ∼0.37 nm for the thickness of the CVD-grown graphene layer, which agrees extremely well with the 0.335 nm reported for layer-to-layer carbon atom distance of graphite crystals. Our results open the avenue to fast and cost-effective simultaneous characterization of various parameters (including thickness and optical constants) of thin films at the atomic-scale resolution. The presented characterization method can be applied both to physical characterizations of various two-dimensional layered materials as well as to the use of these layered materials for biosensing applications as shown earlier, due to the favorable properties of graphene plasmons.

Gold nanoparticles in aqueous solutions: influence of size and pH on hydrogen dissociative adsorption and Au(iii) ion reduction.

The shift of the localized surface plasmon resonance (LSPR) band of gold nanoparticles to shorter wavelengths upon saturation of the hydrosol with hydrogen is used as a tool to study the electrochemical processes on the particle surface. It is shown that dissociative adsorption of hydrogen takes place on the surface of a particle and results in the migration of a proton into the dispersion medium, while the electron remains on the nanoparticle, i.e., a hydrogen-like nanoelectrode is formed. It is shown that Au(iii) ions can be reduced on the gold nanoelectrodes. A thermodynamic scheme explaining the shift of the LSPR band is used to explain the peculiarities of the Au(iii) ion reduction. The reduction rate does not depend on the ion concentration and varies linearly with pH. The observed correlations are explained in terms of a simple model of electrochemical processes taking place on the nanoparticle as an electrode. It is shown that with an increase in the particle size, its capacity for dissociative adsorption of hydrogen decreases and the Au(iii) reduction slows down.

Colorimetric SNP genotyping utilizing colloidal stability of double-stranded DNA-functionalized gold nanoparticles having a dangling end

Event Abstract Back to Event Colorimetric SNP genotyping utilizing colloidal stability of double-stranded DNA-functionalized gold nanoparticles having a dangling end Yoshitsugu Akiyama1, 2, Hiroto Shikagawa1, Shota Shiraishi1, Guoqing Wang1, Naoki Kanayama1, Tohru Takarada1 and Mizuo Maeda1 1 RIKEN, Bioengineering Laboratory, Japan 2 Tokyo University of Science, Faculty of Industrial Science and Technology, Japan Introduction: Facile and reliable analytical methods to discriminate single nucleotide polymorphisms (SNPs) are of great importance for the realization of personalized medicine. We have already reported a colorimetric SNP genotyping method using salt-induced, non-crosslinking aggregation of double-stranded DNA-modified gold nanoparticles (dsDNA-GNPs)[1]. To develop a more reliable method, the present study exploited a large difference in colloidal stability of dsDNA-GNPs with and without a dangling end is described (Figure 1). Experimental: According to a reported procedure[1], GNP with a diameter of 15 nm was functionalized with 16-nucleotide (nt) ssDNA. The base sequence of ssDNA was designed to be complementary to an SNP typing primer. A chemically synthesized fragment (56 base pairs) of the cytochrome P450 2C19*2 gene including the SNP site (G→A) was used as a model target. Single base extension of the 16-nt typing primer for the SNP site was carried out with the model target, DNA polymerase, and each ddNTP. To this reaction solution was added ssDNA-GNP (final conc. 5 nM) and NaCl (final conc. 1 M). The as-prepared mixture was incubated for 10 min at room temperature to induce non-crosslinking aggregation. The color change attributed to a surface plasmon resonance shift was detected with the naked eye. Results and Discussion: When the single base extension reaction using the model target of a homozygous mutant (the SNP site: T) in the presence of ddATP, ddGTP, or ddCTP, the distinct color change from red to purple through non-crosslinking aggregation of dsDNA-GNP was observed (Figure 1, left). This is due to the formation of fully matched dsDNA between ssDNA on the GNP surface and the unextended 16-nt typing primer. On the other hand, it showed no color change (red) with ddTTP (Figure 1, right), because the dsDNA having a dangling end was formed on the surface with the single-base-extended 17-nt typing primer, leading to the nanoparticle’s dispersion by the entropic repulsion. In addition, the corresponding color changes were also obtained when using the model target of the homozygous wild-type gene, as well as that of the heterozygous gene[2]. Conclusion: Colorimetric SNP genotyping of the cytochrome P450 2C19*2 gene by unique colloidal stability of dsDNA-GNP with a dangling end was successfully demonstrated. It will be potentially achievable to develop a clinical sample analysis. This work was supported by a Grant-in-Aid for Scientific Research (S) (No. 25220204) from the Ministry of Education, Culture, Sports, Science, and Technology of Japan, and by a Grant for Molecular Systems Research provided by RIKEN.

Iodine-mediated etching of gold nanorods for plasmonic sensing of dissolved oxygen and salt iodine.

Here, we have carefully investigated iodine-mediated etching of gold nanorods (AuNRs) in the presence of iodate and applied this phenomenon to on-site detection of dissolved oxygen (DO). Under given conditions, the quantitative conversion of target analytes DO to iodine leads to the etching of AuNRs along the longitudinal direction with the aid of cetyltrimethylammonium. As a result, the longitudinal localized surface plasmon resonance shifts to a short wavelength. The peak-shift can be used for quantitative determination of DO and iodate by a spectrophotometer. The satisfactory results from DO detection in different water samples and iodate detection in table salt indicate the feasibility of the proposed methods. Moreover, the as-prepared colorimetric test paper would make the detection more economical and simpler.

A Localized Surface Plasmon Resonance (LSPR)-based, simple, receptor-free and regeneratable Hg2+ detection system

A simple, receptor-free and regeneratable Hg2+ sensor, which utilizes localized surface plasmon resonance (LSPR) shifts of a gold nanorod (GNR), has been developed. Precipitation induced by coordination of Hg2+ to citrate alters the local refractive index (RI) around the GNR surface on glass slide, promoting a red-shift in its LSPR absorption peak. This phenomenon is used to design a sensor that enables quantitative detection of Hg2+ in the 1nM to 1mM concentration range with good linearity (0.9507 correlation coefficient) and limit of detection (LOD) is reached to 0.38nM. A high selectivity of this sensor for Hg2+ is demonstrated by the specific LSPR red-shift of 27.67nm promoted by Hg2+ in comparison to those caused by other metal ions. In addition, the reusability of the new sensor chip is shown by its successful reuse eight-times following successive washing/precipitation steps. Lastly, the sensor displays excellent recoveries in spiking test with real water samples, such as tap water, lake and river. The simple combination of precipitation of Hg2+-citrate complex and the LSPR red-shift has led to the design of a novel sensing strategy for Hg2+ detection.

A plasmonic colorimetric strategy for biosensing through enzyme guided growth of silver nanoparticles on gold nanostars

A plasmonic colorimetric strategy was designed for sensitive detection of biomolecules through enzyme guided silver nanoparticles (AgNPs) growth on gold nanostars (AuNS). The growth of AgNPs on AuNS led to a substantial blue shift of the localized surface plasmon resonance (LSPR) peak and the color change of AuNS from blue to dark blue, purple and ultimately orange. Both the LSPR blueshift wavelength and the color of detection solution containing AuNS, Ag+ and ascorbic acid 2-phosphate (AAP) depend on the amount of enzyme that catalyzed the dephosphorylation of AAP to reduce Ag+ on AuNS surface. Thus this strategy could be used for LSPR and naked-eye detections of both the enzyme such as alkaline phosphatase (ALP) and other biomolecules involved in biorecognition events using ALP as a tag. The LSPR detection method for ALP showed a linear range from 1.0pM to 25nM with a detection limit of 0.5pM. Using DNA as a mode target molecule, this technique showed a detection range from 10fM to 50pM DNA with a detection limit of 2.6fM through the convenient combination with hybridization chain reaction amplification. The proposed plasmonic colorimetric strategy could be extended as a general analytical platform for design of immunosensors and aptasensors with ALP as a label.

Resonant Optical Properties of Single Out-Diffused Silver Nanoislands

An ensemble of hemiellipsoidally shaped silver nanoislands was grown on a soda-lime glass substrate using the combination of ion exchange, thermal poling, and out-diffusion techniques. The nanoislands were characterized using scanning electron and atomic force microscopy, and their dipole and quadrupole plasmonic properties were studied using dark-field spectroscopy and numerical modeling using discrete dipole approximation and finite element analysis. Numerically simulated scattering spectra demonstrate good correspondence with the single-particle dark-field measurements. The maps of the dipole surface plasmon resonance (SPR) wavelength and intensity are plotted in nanoisland height-diameter coordinates. It is shown that SPR shifts to the red spectral region with the increase of nanoisland width and with the decrease in the nanoisland base diameter. The quadrupole resonance observed at shorter wavelengths demonstrates higher Q-factor, and stronger enhancement and localization in the near-field.

Effect of Ag Templates on the Formation of Au-Ag Hollow/Core-Shell Nanostructures.

Au-Ag alloy nanostructures with various shapes were synthesized using a successive reduction method in this study. By means of galvanic replacement, twined Ag nanoparticles (NPs) and single-crystalline Ag nanowires (NWs) were adopted as templates, respectively, and alloyed with the same amount of Au+ ions. High angle annular dark field-scanning TEM (HAADF-STEM) images observed from different rotation angles confirm that Ag NPs turned into AuAg alloy rings with an Au/Ag ratio of 1. The shifts of surface plasmon resonance and chemical composition reveal the evolution of the alloy ring formation. On the other hand, single-crystalline Ag NWs became Ag@AuAg core-shell wires instead of hollow nanostructure through a process of galvanic replacement. It is proposed that in addition to the ratio of Ag templates and Au ion additives, the twin boundaries of the Ag templates were the dominating factor causing hollow alloy nanostructures.

Bi-nanorod/Si-nanodot hybrid structure: surface dewetting induced growth and its tunable surface plasmon resonance

Hybrid nanostructures composed of plasmonic metal and semiconductor are receiving increasing attentions, owing to their unique optical features that are induced by the co-existence of localized surface plasmon resonance (SPR) and semiconduction as well as the synergistic interactions between these two components. Other than the structures based on conventional noble metals, a cost-effective structure based on non-noble metal is studied in this work. Utilizing the surface dewetting in Bi-Si system, the Bi-nanorod/Si-nanodots hybrid structure (BSHS) is prepared by alternated sputtering of Bi and Si at low rate. The shift, split, and high order excitation of SPRs in BSHS are studied combining numerical and theoretical simulation. Calculations of the optical extinction performed as a function of the size of BSHS show a guideline to tune its spectra.

One-to-One Correlation between Structure and Optical Response in a Heterogeneous Distribution of Plasmonic Constructs

Assemblies of coupled plasmonic nanoparticles are used as sensors and rulers for the measurement of nanoscale distances and dynamic distance changes in biological and macromolecular systems. Since such rulers are employed at the single-device level, variations from one construct to another can greatly influence their reliability as sensors. In this work, we performed an experimental and simulation-based analysis of the structural and functional heterogeneity in model assemblies consisting of a Au nanosphere (NS) attached to a highly polarizable Au nanoplate (NP). Spectral characteristics, including the number, nature, and energy position of plasmon modes, varied significantly from one construct to another. The coupling-induced localized surface plasmon resonance (LSPR) shift, which can be the optical readout for sensing applications, ranged over an order of magnitude across the set of constructs measured. By correlating scattering spectra with construct morphologies obtained from scanning electron microsc...

Super-Period Gold Nanodisc Grating-Enabled Surface Plasmon Resonance Spectrometer Sensor.

We experimentally demonstrate a surface plasmon resonance spectrometer sensor by using an e-beam-patterned super-period gold nanodisc grating on a glass substrate. The super-period gold nanodisc grating has a small subwavelength period and a large diffraction grating period. The small subwavelength period enhances localized surface plasmon resonance, and the large diffraction grating period diffracts surface plasmon resonance radiation into different directions corresponding to different wavelengths. Surface plasmon resonance spectra are measured in the first order diffraction spatial profiles captured by a charge-coupled device (CCD) in addition to the traditional way of measurement using an external optical spectrometer in the zeroth order transmission. A surface plasmon resonance sensor for the bovine serum albumin protein nanolayer bonding is demonstrated by measuring the surface plasmon resonance shift in the first order diffraction spatial intensity profiles captured by the CCD.

Large dynamic range SPR measurements using a ZnSe prism

Large dynamic index measurement range (n = 1 to n = 1.7) using surface plasmon resonance (SPR) shifts is demonstrated with a ZnSe prism at 632.8 nm, limited by the available high index liquid hosts. In contrast to borosilicate based SPR measurements where angular limitations restrict solvent use to water and requires considerable care dealing with Fresnel reflections, the ZnSe approach allows SPR spectroscopies to be applied to a varied range of solvents An uncertainty in angular resolution between 1.5 and 6 deg, depending on the solvent and SPR angle, was estimated. The refractive index change for a given glucose concentration in water was measured to be n = (0.114 to 0.007) per precentage C6H12O6 conc. Given the transmission properties of ZnSe the processes can be readily extended into the mid infrared.

Green-synthesized gold nanoparticles from Plumeria alba flower extract to augment catalytic degradation of organic dyes and inhibit bacterial growth

Bio-inspired eco-friendly gold nanoparticles were synthesized by a green method using aqueous Plumeria alba flower extract (PAFE). The use of 1% and 5% concentrations of PAFE resulted in two different sizes of P. alba gold nanoparticles, PAGNPs1 and PAGNPs2, with surface plasmon resonance (SPR) peaks at 552 and 536nm, respectively. Size-controlled formation of gold nanoparticles was indicated by the SPR shift observed with increasing concentration of PAFE. The accurate size and morphology of PAGNPs1 and PAGNPs2 were determined by transmission electron microscope (TEM) analysis is found to be 28±5.6 and 15.6±3.4nm, respectively, and those are spherical in shape. The antibacterial activity of PAGNPs1 and PAGNPs2 was tested against Escherichia coli; the small-sized PAGNPs2 exhibited better antibacterial activity with a 16-mm zone of inhibition at a concentration of 400μg/mL. Furthermore, the catalytic activity of PAGNPs1 and PAGNPs2 was analyzed on six hazardous dyes; PAGNPs2 exhibited more pronounced catalytic activity than PAGNPs1. Among all of the dyes, 4-nitrophenol was most rapidly degraded to 4-aminophenol by PAGNPs2 within 5min. The mechanism of catalysis in the presence of PAGNPs1 and PAGNPs2 can be described as an electron transfer process from donor NaBH4 to an acceptor. The facile green synthesis of such eco-friendly nanoparticles in bulk suggests this method has potential industrial applications.