Localized Surface Plasmon Resonance Of Nanoparticles Research Articles

Research on the adsorption-photocatalytic synergistic degradation of tetracycline by Au nanoparticles/TiO2 nanorods/biochar

As a persistent antibiotic, tetracycline is widely used in medical and livestock farming fields. However, the long-term accumulation effect of tetracycline has a significant impact on the ecosystem. In this research, we integrated the processes of adsorption-photocatalytic degradation for organic pollutants by combining Sichuan Pepper shell biochar adsorption, TiO2 Nanorods photocatalytic oxidation, and Au nanoparticles Localized Surface Plasmon Resonance. The findings demonstrated that the specific surface area of Au nanoparticles/TiO2 nanorods/biochar has increased by 1287.6 m2/g compared to TiO2. Furthermore, when TiO2 is compounded with biochar, its particle size reduces by approximately half and forms C-Ti and N-Ti bonds. The composite catalyst exhibited the highest removal rate for tetracycline, nearly four times that of commercial TiO2 (P25), showing excellent application prospects. The enhanced composite structure improved its ability to capture sunlight, leading to more effective photocatalysis. This research explains the composite and synergistic mechanism of biochar, TiO2 nanorods, and Au nanoparticles, which could guide the removal of organic pollutants.

Study of Metal–Graphene Aerogel for Efficient Solar Energy Interface Evaporation Based on One‐Step Thermal Reduction Method

Freshwater resources can be sustainably harvested through interfacial evaporation by solar energy. To enhance the efficiency of solar interfacial evaporation, a metal–graphene alcohol gel is synthesized using a one‐step thermal reduction technique. Subsequently, a metal–graphene aerogel (GA) is produced using freeze‐drying technology. The hydrothermal treatment method is applied to introduce asymmetric moisture and roughness on the upper and lower surfaces of the aerogel. The unique structure of the aerogel plays a significant role in facilitating continuous water transport to the interface for evaporation. The top layer, being hydrophobic, and the bottom layer, being hydrophilic, contribute to this process. Importantly, the top layer's design ensures that an excessively thick water film does not form, thereby preventing any adverse effects on light‐absorption efficiency. The aerogel exhibits that an outstanding water‐evaporation rate is 1.75 kg m−2 h−1 and a remarkable photothermal conversion efficiency (PTCE) is 93.17% under one solar radiation intensity. This is because the aerogel has a unique 3D structure. This special 3D structure has an interconnected microporous‐like appearance inside, which increases the evaporation area. Metal–GA is based on the electric field dielectric evaporation mechanism of metal nanoparticles localized surface plasmon resonance effect and the thermal mediated evaporation mechanism of graphene full spectrum. Under the double action, the PTCE is significantly improved. The meticulously created metallic GA performs exceptionally well at evaporating water. As a result, it presents a promising and practical avenue for exploring effective solar interfacial evaporation.

Innovative utilization of silver nanoparticles localized surface plasmon resonance for green and sensitive spectrofluorimetric analysis of sildenafil and xipamide in pure forms and pharmaceutical preparations

A green, novel, simple and sensitive spectrofluorimetric approach was investigated and validated for the analysis of two important cardiovascular drugs namely; sildenafil citrate and xipamide using silver nanoparticles as a fluorescence probe (Ag-NPs).Silver nanoparticles were prepared through chemical reduction of silver nitrate using sodium borohydride in distilled water without using non-green organic stabilizer. These nanoparticles were stable, water soluble and had high fluorescence. After addition of the studied drugs, noticeable quenching of Ag-NPs fluorescence occurred. The intensity of Ag-NPs fluorescence was measured at 484 nm (λex 242 nm) before and after complex formation with these studied drugs. The difference between these values (ΔF) were linear with the concentrations in the following ranges (1.0–10.0 μg/mL), (0.5–5.0 μg/mL) for sildenafil and xipamide, respectively. The formed complexes did not need to be separated by solvent extraction before measurement. For proving the complex formation between the two studied drugs and silver nanoparticles, stern volmer method was applied. The suggested method was perfectly validated in compliance with the international conference on harmonization (ICH) Guidelines and the outcomes were acceptable. Furthermore, suggested technique was perfectly applied for the assay of each drug in its pharmaceutical dosage form. Eventually assessment of method greenness was performed using different tools and found that the suggested method was safe and eco-friendly.

Plasmonic Photocatalysis Driven by Indirect Gold Excitation Via Upconversion Nanoparticle Emission Monitored In Situ by Surface-Enhanced Raman Spectroscopy

Lanthanide-doped upconversion nanoparticles (UCNPs) absorb low-energy photons, in the near-infrared region (NIR), and emit high-energy photons, in the visible or ultraviolet region (UV/Vis). The higher energy radiation emissions can be used to promote plasmonic photocatalytic reactions by coupling UCNPs with plasmonic nanoparticles. Thus, in this work, highly crystalline β-NaYF4:Yb3+,Er3+@NaYF4:Nd3+@NaYF4 UCNPs capped with an amino-modified nanosized silica shell were coupled with Au nanospheres (13 ± 2 nm). The plasmonic-driven dimerization of 4-aminothiophenol (4-ATP) to 4,4′-dimercaptoazobenzene (DMAB) was carried out solely by using the UCNP visible emissions to excite the Au nanoparticle localized surface plasmon resonance band. The reaction was monitored in situ through surface-enhanced Raman spectroscopy (SERS) and optimal conditions were achieved in order to eliminate secondary influences during spectra acquisition. The SERS substrates containing either UCNPs@SiO2-NH2/Au or SiO2-NH2/Au nanoparticles were prepared by the drop-cast method in silicon substrates. In the studied reaction conditions, plasmonic photocatalytic activity was observed only in the substrates containing UCNPs and Au nanoparticles. The plasmonic-driven reaction was achieved by UCNPs excitation with a 980 nm laser (25.7 mW), aligned in a Raman spectrometer, only after 5 s of exposition. Interactive document mapping (IDMAP), which is an unsupervised pattern recognition method, was applied to analyze the numerous SERS spectra acquired during the plasmonic photocatalytic measurements. The high values found for the silhouette coefficient (0.88 for the Si_SiO2-NH2/Au and 0.76 for the Si_NYF@SiO2-NH/Au substrate) indicate that strong discrimination among the Raman spectra was achieved. Thus, through IDMAP, it was observed that the SERS spectra obtained for the substrates containing either UCNPs@SiO2-NH2/Au or SiO2-NH2/Au corresponded to spectral features, respectively, from the DMAB product and the 4-ATP reagent, evidencing that, in the optimized reaction conditions, the dimerization occurred only through the interaction of the UCNPs with the Au nanospheres.

Multispectral Localized Surface Plasmon Resonance (msLSPR) Reveals and Overcomes Spectral and Sensing Heterogeneities of Single Gold Nanoparticles.

Metal nanoparticles can be sensitive molecular sensors due to enhanced absorption and scattering of light near a localized surface plasmon resonance (LSPR). Variations in both intrinsic properties such as the geometry and extrinsic properties such as the environment can cause heterogeneity in nanoparticle LSPR and impact the overall sensing responses. To date, however, few studies have examined LSPR and sensing heterogeneities, due to technical challenges in obtaining the full LSPR spectra of individual nanoparticles in dynamic assays. Here, we report multispectral LSPR (msLSPR), a wide-field imaging technique for real-time spectral monitoring of light scattering from individual nanoparticles across the whole field of view (FOV) at ∼0.5 nm spectral and ∼100 ms temporal resolutions. Using msLSPR, we studied the spectral and sensing properties of gold nanoparticles commonly used in LSPR assays, including spheres, rods, and bipyramids. Complemented with electron microscopy imaging, msLSPR analysis revealed that all classes of gold nanoparticles exhibited variations in LSPR peak wavelengths that largely paralleled variations in morphology. Compared with the rods and spheres, gold nanobipyramids exhibited both more uniform and stronger sensing responses as long as the bipyramids are structurally intact. Simulations incorporating the experimental LSPR properties demonstrate the negative impact of spectral heterogeneity on the overall performance of conventional, intensity-based LSPR assays and the ability of msLSPR in overcoming both particle heterogeneity and measurement noise. These results highlight the importance of spectral heterogeneity in LSPR-based sensors and the potential advantage of performing LSPR assays in the spectral domain.

Gold-Silver Core-Shell Nanoparticle Crosslinking Mediated by Protease Activity for Colorimetric Enzyme Detection.

Plasmonic nanoparticles produce a localized surface plasmon resonance (LSPR) under optical excitation. The LSPR of nanoparticles can shift in response to changes in the local dielectric environment and produce a color change. This color change can be observed by the naked eye due to the exceptionally large extinction coefficients (108-1011 M-1 cm-1) of plasmonic nanoparticles. Herein, we investigate the optical shifts (i.e., color change) of three unique gold-silver core-shell nanoparticle structures in response to changes in their dielectric environment upon nanoparticle aggregation. Aggregation is induced by a cysteine-containing peptide that has a sulfhydryl near its N and C termini, which crosslinks nanoparticles. Furthermore, we demonstrate that adding proline spacers between the cysteines impacts the degree of aggregation and, ultimately, the color response. Using this information, we construct a colorimetric enzyme assay, where the signal produced from nanoparticle aggregation is modulated by proteolysis. The degree of aggregation and the resulting optical shift can be correlated with enzyme concentration with high linearity (R2 = 0.998). Overall, this study explores the optical properties of gold-silver core-shell nanoparticles in a dispersed vs aggregated state and leverages that information to develop an enzyme sensor with a spectral LOD of 0.47 ± 0.09 nM.

Sensitivity enhancement of nanoparticle localized surface plasmon resonance pressure sensor based on the MoS2 monolayer for ultra-wide range pressure detection

The next generation of optical pressure sensors should be highly sensitive, and have wide-ranging pressure sensing detection. The monolayer MoS2 has been considered as an excellent material with exceptional mechanical, physical, electronic and chemical properties, which is significantly different from the properties of graphene. In this paper, the properties of the MoS2 monolayer according to the placement of silver nanoparticles on the surface have been used to design a pressure sensor that can act based on localized surface plasmon resonance. The MoS2 monolayer sensitivity to stress and variations the properties in proportion to the applied pressure, increases the possibility of using it as a pressure sensor. High pressure range, nanoscale and integration capabilities are important features of this sensor. In this sensor the change in the resonance frequency is proportional to the pressure range which the structure parameters including the shape of the nanoparticles, the material and radius of the nanoparticles, the angle of the incoming light and the presence of the mos2 monolayer by considering and optimizing are provided. For mechanics section calculation, we used the FEM method, and for optical behavior, the FDTD method. Measurable pressure range is less than 1 Gpa with 11 nm/GPa sensitivity for this sensor.

Formula omitted]-Carrageenan-capped core–shell gold@silver nanoparticles: Optical device for hydrogen peroxide detection

Metallic nanoparticles have outstanding properties that can be used to design optical detection devices, such as their high surface area and localized surface plasmon resonance (LSPR) effect. Despite these properties, metallic nanoparticles have low stabilities against aggregation and silver nanoparticles are quickly oxidized even in aqueous suspensions. To overcome these disadvantages, this study reports a new κ-carrageenan-stabilized core–shell gold@silver nanoparticles (κ-CAR-Au@AgNPs) composite. The κ-carrageenan (κ-CAR) was used as a reducing and stabilizing agent toward Au(III)/Ag(I) and Au0/Ag0, respectively. A pre-synthesized κ-CAR-capped gold nanoparticle (κ-CAR-AuNPs) suspension was mixed with Ag(I) ions and ascorbic acid to produce the κ-CAR-Au@AgNPs composite. The as-synthetized composite had an average hydrodynamic radius of 122 nm and a Zeta potential of −24 mV. The composite suspension had an LSPR band with high intensity after 15 days of storage. The κ-CAR stabilized the nanoparticles against aggregation and environmental oxidation. The physiochemical properties of κ-CAR-Au@AgNPs were compared to the properties of κ-CAR-capped silver nanoparticles (κ-CAR-AgNPs). The core–shell nanoparticle LSPR intensity was higher (10-fold) than that of the monometallic sample. Therefore, its optical response is improved for sensing applications. Thus, core–shell nanoparticles were used to detect hydrogen peroxide (H2O2). The H2O2 can almost completely oxidize the Ag shell of the Au@AgNPs after 4 h, altering the optical absorption intensity of the nanoparticles. Therefore, the κ-CAR-Au@AgNPs LSPR intensity can be used as an optical signal to assess H2O2 concentration in aqueous solutions.

Simultaneous visible and ultraviolet photoresponse improvement of MoS2/ZnO heterostructure photodetector via direct resonant coupling of Au nanoparticles localized surface plasmon resonance

Localized surface plasmon resonance (LSPR) as a unique property of metal nanoparticles (NPs) has been widely applied to enhance the performance of optoelectronic devices. However, limited by the specific resonance frequency of plasmonic NPs, the LSPR of NPs can only improve the photoresponse performance of photodetectors at specific wavelength. In this work, a simple strategy is proposed to simultaneously improve the performance of the p-MoS2/n-ZnO heterostructure photodetector in visible and ultraviolet (UV) light regions by modifying Au NPs. The Ilight/Idark ratio of the photodetector is considerably increased after the functionalization with plasmonic Au NPs under visible and UV light illumination due to the direct resonant coupling of LSPR. In particular, the photocurrent of the photodetector increases 14.8 times after Au NPs modification under 532 nm illumination, giving rise to an obvious increase in responsivity, external quantum efficiency and specific detectivity. Moreover, the modification of Au NPs facilitates the rapid separation of electrons and holes due to the generation of surface depletion regions located at Au/MoS2 and Au/ZnO interfaces. Consequently, the photoresponse speed is also drastically improved after Au NPs decoration in both visible and ultraviolet light regions. The strategy of direct resonant coupling of Au NPs LSPR with two photosensitive materials proposed in this work will provide a new avenue for optimizing the performance of optoelectronic devices.

Theoretical approach for calculation of dielectric functions of plasmonic nanoparticles of noble metals, magnesium and their alloys

Plasmonic nanoparticles of gold, silver, their alloys, and of the promising magnesium and its alloys with noble metals, find increasing applications due to the valuable optical properties, based on the presence of localized surface plasmon resonance (LSPR) in the spectra of optical extinction. To suggest effective synthesis routes of such nanoparticles with tunable in the wide wavelength range characteristics of LSPR, it is necessary to have a reliable approach for calculation of dielectric functions for these particles with complicated atomic architecture, which can provide the description of experimental optical spectra. Such approach is also required for the implementation of the suggested earlier original technique for the solution of the inverted problem – determination of structural parameters of particles arrays from their optical spectra. With the aim to suggest such computational procedure, calculations of dielectric functions for gold, silver, magnesium and their alloys are performed using alternative density functional theory approaches: local density approximation (LDA), generalized gradient approximation (GGA) in the form of GLLBSC functional, meta-GGA in the form of TB09 potential and Hubbard-corrected local density approximation (LDA+U). Using the calculated dielectric functions, the LSPR of nanoparticles are simulated within the T-matrix approach. We show that the application of LDA+U approach is promising for the description of optical properties of bulk samples, their alloys and nanoparticles, including particles with core–shell atomic architecture. The advantage of magnesium–gold core–shell nanoparticles as a broadband nanosized plasmonic material is illustrated.

Low‐Power Phase Transition of Chalcogenide Glass Using Au Nanoparticle Plasmon Resonance

AbstractChalcogenide materials are attractive for all‐photonic phase‐change memories owing to their large optical contrast between amorphous and crystalline structural phases. However, high‐power heating pulses are required to switch these structural phases, which can limit the cyclability. To reduce power, Au nanoparticles (NPs) are embedded in a typical chalcogenide phase‐change material, Ge2Sb2Te5 (GST). Raman analysis shows that a GST film crystallizes at a low optical power of 2 mW, which is almost 10 times lower than that of materials not embedded with NPs. This lower power is owing to the enhanced light absorptance through the strongly localized surface plasmon resonance (LSPR) of the Au NPs. The Au NPs embedded in the GST film scatter light at λ = 587 nm, which is close to Au NP's LSPR of ≈535 nm. Laser light at 532 nm is used to measure Raman scattering from the Au–GST system. The Raman scattering is enhanced by a factor 12 compared with a bare GST film. This study indicates that the GST film–Au NP system is suitable for high‐speed, low‐power, phase‐change memory and for a new type of tunable surface‐enhanced Raman scattering substrate.

Understanding Electromagnetic Interactions and Electron Transfer in Ga Nanoparticle–Graphene–Metal Substrate Sandwich Systems

Plasmonic metal nanoparticle (NP)–graphene (G) systems are of great interest due their potential role in applications as surface-enhanced spectroscopies, enhanced photodetection, and photocatalysis. Most of these studies have been performed using noble metal NPs of silver and gold. However, recent studies have demonstrated that the noble metal–graphene interaction leads to strong distortions of the graphene sheet. In order to overcome this issue, we propose the use of Ga NPs that, due to their weak interaction with graphene, do not produce any deformation of the graphene layers. Here, we analyze systems consisting of Ga NP/G/metal sandwich coupling structures, with the metal substrate being, specifically, copper (Cu) and nickel (Ni), i.e., Ga NP/G/Cu and Ga NPs/G/Ni. We experimentally show through real-time plasmonic spectroscopic ellipsometry and Raman spectroscopy measurements of the quenching of the Ga NP localized surface plasmon resonance (LSPR) depending on the wetting of the graphene by the Ga NPs and on the electron transfer through graphene. Theoretical finite-difference time-domain (FDTD) simulations supportively demonstrate that the LSPR in such sandwich structures strongly depends on the contact angle of the NP with graphene. Finally, we also provide evidence of the electron transfer from the Ga NPs into the graphene and into the metal substrate according to the work function alignments. These considerations about the contact angle and, consequently, geometry and wetting of the metal NPs on graphene, are useful to guide the design of those plasmonic systems to maximize electromagnetic enhancement.

Sensitivity enhanced D-type large-core fiber SPR sensor based on Gold nanoparticle/Au film co-modification

A D-type large core optical fiber sensor with high sensitivity and good stability based on the coupling of gold nanoparticles and Au film was proposed and demonstrated by simulation and experiments. The proposed sensor is numerically simulated based on the finite element method. The simulation shows that the electric field intensity of the gap coupling between gold nanoparticles and Au film is 4–5 times higher than that of Au film, and the electric field intensity on the surface of gold nanoparticles is twice as strong as that on the surface of Au films. The electric field coupling effect between the Au film surface plasmon resonance (SPR) and the gold nanoparticle localized surface plasmon resonance (LSPR) can improve the refractive index sensitivity of the sensor. Experimental results show that the refractive index sensitivity of D-type optical fiber/Au film/gold nanoparticles sensor reaches 3074 nm/refraction index unit (RIU), which is 1.4 times that of D-type optical fiber/Au film sensor. SPR–LSPR coupling effect is a good method to improve the sensing performance of optical fiber sensors, especially for detecting the refractive index changes of surrounding media. Compared with existing similar biosensors, the designed biosensor has higher sensitivity and the sensor proposed in this paper has great application prospects in the field of biological detection.

Rapid Removal and Mineralization of Bisphenol A by Heterosupramolecular Plasmonic Photocatalyst Consisting of Gold Nanoparticle-Loaded Titanium(IV) Oxide and Surfactant Admicelle.

The establishment of technology for rapid and complete removal and mineralization of harmful phenolic compounds from water is of great importance for environmental conservation. Visible-light irradiation (λ > 430 nm, light intensity integrated from 420 to 485 nm = 6.0 mW cm-2) of Au nanoparticle (NP)-loaded TiO2 (Au/TiO2) in dilute aqueous solutions of bisphenol A (BPA) and p-cresol (PC) causes degradation of the phenols. The addition of trimethylstearylammonium chloride (C18TAC) enhances the adsorption of BPA on Au/TiO2 to greatly increase the rate of reaction. Consequently, 10 μM phenols are completely removed from the solutions within 2.5 h irradiation, and prolonging irradiation time to 24 h quantitatively oxidizes BPA to CO2. Dynamic light scattering ζ-potential measurements indicate that a C18TAC bilayer or admicelle is formed on the Au/TiO2 particle surface at C18TAC concentration >50 μM. The action spectrum for reaction shows that this reaction is driven by the Au NP localized surface plasmon resonance excitation-induced interfacial electron transfer from Au to TiO2. We propose a possible reaction scheme on the basis of the experimental results including intermediate analysis.

Controlled dispersion of polystyrene‐capped A u nanoparticles in P 3 HT : PC 61 BM and consequences upon active layer nanostructure

Numerous recent publications detail higher absorption and photovoltaic performance within organic photovoltaic (OPV) devices which are loaded with Au or Ag nanoparticles to leverage the light management properties of the localized surface plasmon resonance (LSPR). This report details the impact upon film morphology and polymer/nanoparticle interactions caused by incorporation of polystyrene-coated Au nanoparticles (Au/PS) into the P3HT:PC61BM bulk heterojunction film. Nanostructural analysis by transmission electron microscopy and X-ray scattering reveals tunable Au/PS particle assembly that depends upon the choice of casting solvent, polymer chain length, film drying time, and Au/PS particle loading density. This Au/PS particle assembly has implications on the spectral position of the Au nanoparticle LSPR, which shifts from 535 nm for individually dispersed particles in toluene to 650 nm for particles arranged in large clusters within the P3HT:PC61BM matrix. These results suggest a critical impact from PS/P3HT phase separation, which causes controlled assembly of a separate Au/PS phase in the nanoparticle/OPV composite; controlled Au/PS phase formation provides a blueprint for designing AuNP/OPV hybrid films that impart tunable optical behavior and potentially improve photovoltaic performance. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 709–720

Tuning of Spectral and Angular Distribution of Scattering from Single Gold Nanoparticles by Subwavelength Interference Layers

Localized surface plasmon resonance (LSPR) as the resonant oscillation of conduction electrons in metal nanostructures upon light irradiation is widely used for sensing as well as nanoscale manipulation. The spectral resonance band position can be controlled mainly by nanoparticle composition, size, and geometry and is slightly influenced by the local refractive index of the near-field environment. Here we introduce another approach for tuning, based on interference modulation of the light scattered by the nanostructure. Thereby, the incoming electric field is wavelength-dependent modulated in strength and direction by interference due to a subwavelength spacer layer between nanoparticle and a gold film. Hence, the wavelength of the scattering maximum is tuned with respect to the original nanoparticle LSPR. The scattering wavelength can be adjusted by a metallic mirror layer located 100-200 nm away from the nanoparticle, in contrast to near-field gap mode techniques that work at distances up to 50 nm in the nanoparticle environment. Thereby we demonstrate, for the first time at the single nanoparticle level, that dependent on the interference spacer layer thickness, different distributions of the scattered signal can be observed, such as bell-shaped or doughnut-shaped point spread functions (PSF). The tuning effect by interference is furthermore applied to anisotropic particles (dimers), which exhibit more than one resonance peak, and to particles which are moved from air into the polymeric spacer layer to study the influence of the distance to the gold film in combination with a change of the surrounding refractive index.

Influences of gold/silver nanoparticles on fluorescence of europium-doped films

Spherical silver (Ag) nanoparticles, triangular Ag nanoprisms, and triangular gold (Au) nanoparticles were separately deposited on the Eu(TTFA)3-doped Su8 films. Compared with the fluorescence of films without nanoparticles, the fluorescence of the doped films was greatly enhanced by the two kinds of the Ag nanoparticles, the enhancement is greater for the spherical Ag nanoparticles than that for the triangular Ag nanoprisms. The fluorescence was quenched for the film with Au nanoparticles. Results show that the nanoparticles can both enhance and quench the fluorescence of the films, which depend mainly on the local surface plasmon resonance (LSPR) of the nanoparticles. When the LSPR of nanoparticles overlaps with the excitation or the emission spectrum of the films, the fluorescence would be enhanced. Otherwise the fluorescence of the films would be quenched.

Using the Localized Surface Plasmon Resonance of Gold Nanoparticles to Monitor Lipid Membrane Assembly and Protein Binding.

Gold nanoparticles provide a template for preparing supported lipid layers with well-defined curvature. Here, we utilize the localized surface plasmon resonance (LSPR) of gold nanoparticles as a sensor for monitoring the preparation of lipid layers on nanoparticles. The LSPR is very sensitive to the immediate surroundings of the nanoparticle surface and it is used to monitor the coating of lipids and subsequent conversion of a supported bilayer to a hybrid membrane with an outer lipid leaflet and an inner leaflet containing hydrophobic alkanethiol. We demonstrate that both decanethiol and propanethiol are able to form hybrid membranes and that the membrane created over the shorter thiol can be stripped from the gold along with the lipid leaflet using β-mercaptoethanol. The sensitivity of the nanoparticle LSPR to the refractive index (RI) of its surroundings is greater when the shorter thiol is used (37.8 ± 1.5 nm per RI unit) than when the longer thiol is used (27.5 ± 0.5 nm per RI unit). Finally, C-reactive protein binding to the membrane is measured using this sensor allowing observation of both protein-membrane and nanoparticle-nanoparticle interactions without chemical labeling of protein or lipids.

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.

Advances in Localized Surface Plasmon Resonance Spectroscopy Biosensing

In recent years, localized surface plasmon resonance (LSPR) spectroscopy advancements have made it a sensitive, flexible tool for probing biological interactions. Here, we describe the basic principles of this nanoparticle-based sensing technique, the ways nanoparticles can be tailored to optimize sensing, and examples of novel LSPR spectroscopy applications. These include detecting small molecules via protein conformational changes and resonance LSPR spectroscopy, as well as coupling LSPR with mass spectrometry to identify bound analytes. The last few sections highlight the advantages of single nanoparticle LSPR, in that it lowers limits of detection, allows multiplexing on the nanometer scale, and enables free diffusion of sensors in solution. The cases discussed herein illustrate creative ways that LSPR spectroscopy has been improved to achieve new sensing capabilities.