静电组装金纳米粒子制备局域表面等离子体共振传感膜

采用聚电解质自组装技术制备局域表面等离子体共振(LSPR)传感膜的方法, 在玻璃基片上依次沉积聚电解质PDDA, PSS和PVTC, 并通过静电吸附构建胶体金纳米粒子自组装膜形成LSPR传感膜. 利用扫描电镜对LSPR传感膜表面形貌以及膜中金纳米粒子的粒径进行了表征, 同时通过紫外-可见消光光谱对其灵敏度和渗透深度等重要参数进行检测. 研究结果表明, 所制备的LSPR传感膜粒子分布均匀、单分散性好、稳定性高、重现性好; 消光峰位对样品溶液折射率的检测灵敏度为71 nm/RIU, 相应的峰强检测灵敏度为0.21 AU/RIU, 对表面吸附层的渗透深度约为16 nm.     

A nanoscale optical biosensor: sensitivity and selectivity of an approach based on the localized surface plasmon resonance spectroscopy of triangular silver nanoparticles

Triangular silver nanoparticles ( approximately 100 nm wide and 50 nm high) have remarkable optical properties. In particular, the peak extinction wavelength, lambda(max) of their localized surface plasmon resonance (LSPR) spectrum is unexpectedly sensitive to nanoparticle size, shape, and local ( approximately 10-30 nm) external dielectric environment. This sensitivity of the LSPR lambda(max) to the nanoenvironment has allowed us to develop a new class of nanoscale affinity biosensors. The essential characteristics and operational principles of these LSPR nanobiosensors will be illustrated using the well-studied biotin-streptavidin system. Exposure of biotin-functionalized Ag nanotriangles to 100 nM streptavidin (SA) caused a 27.0 nm red-shift in the LSPR lambda(max). The LSPR lambda(max) shift, DeltaR/DeltaR(max), versus [SA] response curve was measured over the concentration range 10(-)(15) M < [SA] < 10(-)(6) M. Comparison of the data with the theoretical normalized response expected for 1:1 binding of a ligand to a multivalent receptor with different sites but invariant affinities yielded approximate values for the saturation response, DeltaR(max) = 26.5 nm, and the surface-confined thermodynamic binding constant K(a,surf) = 10(11) M(-)(1). At present, the limit of detection (LOD) for the LSPR nanobiosensor is found to be in the low-picomolar to high-femtomolar region. A strategy to amplify the response of the LSPR nanobiosensor using biotinylated Au colloids and thereby further improve the LOD is demonstrated. Several control experiments were performed to define the LSPR nanobiosensor's response to nonspecific binding as well as to demonstrate its response to the specific binding of another protein. These include the following: (1) electrostatic binding of SA to a nonbiotinylated surface, (2) nonspecific interactions of prebiotinylated SA to a biotinylated surface, (3) nonspecific interactions of bovine serum albumin to a biotinylated surface, and (4) specific binding of anti-biotin to a biotinylated surface. The LSPR nanobiosensor provides a pathway to ultrasensitive biodetection experiments with extremely simple, small, light, robust, low-cost instrumentation that will greatly facilitate field-portable environmental or point-of-service medical diagnostic applications.     

Second harmonic excitation spectroscopy of silver nanoparticle arrays

Frequency-scanned excitation profiles of coherent second harmonic generation (SHG) were measured for silver nanoparticle arrays prepared by nanosphere lithography. The frequency of the fundamental beam did not coincide with the localized surface plasmon resonance (LSPR) of the nanoparticles and was tuned so that the coherent second harmonic (SH) emission was in the region of the LSPR at 720-750 nm. The SH emission from the arrays was compared with a smooth silver film to identify an enhancement of SH emission efficiency that peaks near approximately 650 nm for nanoparticles 50 nm in height. The polarization and orientation dependence of this enhancement suggests that it is related to a dipolar LSPR mode polarized normal to the plane of the substrate. Linear extinction spectra are dominated by in-plane dipoles and do not show this weak out-of-plane LSPR mode. The nanoparticle arrays are truncated tetrahedrons symmetrically oriented by nanosphere lithography to cancel SH from in-plane dipoles which allows observation of the weak out-of-plane component.     

Localized surface plasmon resonance spectroscopy near molecular resonances

The peak location of the localized surface plasmon resonance (LSPR) of noble metal nanoparticles is highly dependent upon the refractive index of the nanoparticles' surrounding environment. In this study, new phenomena are revealed by exploring the influence of interacting molecular resonances and nanoparticle resonances. The LSPR peak shift and line shape induced by a resonant molecule vary with wavelength. In most instances, the oscillatory dependence of the peak shift on wavelength tracks with the wavelength dependence of the real part of the refractive index, as determined by a Kramers-Kronig transformation of the molecular resonance absorption spectrum. A quantitative assessment of this shift based on discrete dipole approximation calculations shows that the Kramers-Kronig index must be scaled in order to match experiment.     

Raman scattering of 4-aminobenzenethiol sandwiched between Ag nanoparticle and macroscopically smooth Au substrate: effects of size of Ag nanoparticles and the excitation wavelength

A nanogap formed by a metal nanoparticle and a flat metal substrate is one kind of "hot site" for surface-enhanced Raman scattering (SERS). Accordingly, although no Raman signal is observable when 4-aminobenzenethiol (4-ABT), for instance, is self-assembled on a flat Au substrate, a distinct spectrum is obtained when Ag or Au nanoparticles are adsorbed on the pendent amine groups of 4-ABT. This is definitely due to the electromagnetic coupling between the localized surface plasmon of Ag or Au nanoparticle with the surface plasmon polariton of the planar Au substrate, allowing an intense electric field to be induced in the gap even by visible light. To appreciate the Raman scattering enhancement and also to seek the optimal condition for SERS at the nanogap, we have thoroughly examined the size effect of Ag nanoparticles, along with the excitation wavelength dependence, by assembling 4-ABT between planar Au and a variable-size Ag nanoparticle (from 20- to 80-nm in diameter). Regarding the size dependence, a higher Raman signal was observed when larger Ag nanoparticles were attached onto 4-ABT, irrespective of the excitation wavelength. Regarding the excitation wavelength, the highest Raman signal was measured at 568 nm excitation, slightly larger than that at 632.8 nm excitation. The Raman signal measured at 514.5 and 488 nm excitation was an order of magnitude weaker than that at 568 nm excitation, in agreement with the finite-difference time domain simulation. It is noteworthy that placing an Au nanoparticle on 4-ABT, instead of an Ag nanoparticle, the enhancement at the 568 nm excitation was several tens of times weaker than that at the 632.8 nm excitation, suggesting the importance of the localized surface plasmon resonance of the Ag nanoparticles for an effective coupling with the surface plasmon polariton of the planar Au substrate to induce a very intense electric field at the nanogap.     

Interaction of plasmon and molecular resonances for rhodamine 6G adsorbed on silver nanoparticles

Localized surface plasmon resonance (LSPR) is a key optical property of metallic nanoparticles. The peak position of the LSPR for noble-metal nanoparticles is highly dependent upon the refractive index of the surrounding media and has therefore been used for chemical and biological sensing. In this work, we explore the influence of resonant adsorbates on the LSPR of bare Ag nanoparticles (lambda(max,bare)). Specifically, we study the effect of rhodamine 6G (R6G) adsorption on the nanoparticle plasmon resonance because of its importance in single-molecule surface-enhanced Raman spectroscopy (SMSERS). Understanding the coupling between the R6G molecular resonances and the nanoparticle plasmon resonances will provide further insights into the role of LSPR and molecular resonance in SMSERS. By tuning lambda(max,bare) through the visible wavelength region, the wavelength-dependent LSPR response of the Ag nanoparticles to R6G binding was monitored. Furthermore, the electronic transitions of R6G on Ag surface were studied by measuring the surface absorption spectrum of R6G on an Ag film. Surprisingly, three LSPR shift maxima are found, whereas the R6G absorption spectrum shows only two absorption features. Deconvolution of the R6G surface absorption spectra at different R6G concentrations indicates that R6G forms dimers on the metal surface. An electromagnetic model based on quasi-static (Gans) theory reveals that the LSPR shift features are associated with the absorption of R6G monomer and dimers. Electronic structure calculations of R6G under various conditions were performed to study the origin of the LSPR shift features. These calculations support the view that the R6G dimer formation is the most plausible cause for the complicated LSPR response. These findings show the extreme sensitivity of LSPR in elucidating the detailed electronic structure of a resonant adsorbate.     

A unified view of propagating and localized surface plasmon resonance biosensors

The intense colors of noble metal nanoparticles have inspired artists and fascinated scientists for hundreds of years. In this review, we describe refractive index sensing platforms based on the tunability of the localized surface plasmon resonance (LSPR) of arrays of silver nanoparticles and of single nanoparticles. Specifically, the color associated with single nanoparticles and surface-confined nanoparticle arrays will be shown to be tunable and useful as platforms for chemical and biological sensing. Finally, the LSPR nanosensor will be compared to traditional, flat surface, propagating surface plasmon resonance sensors.     

LSPR Biosensor Signal Enhancement Using Nanoparticle-Antibody Conjugates

A method to amplify the wavelength shift observed from localized surface plasmon resonance (LSPR) bioassays is developed using gold nanoparticle-labeled antibodies. The technique, which involves detecting surface-bound analytes using gold nanoparticle conjugated antibodies, provides a way to enhance LSPR shifts for more sensitive detection of low-concentration analytes. Using the biotin and antibiotin binding pair as a model, we demonstrate up to a 400% amplification of the shift upon antibody binding to analyte. In addition, the antibody-nanoparticle conjugate improves the observed binding constant by 2 orders of magnitude, and the limit of detection by nearly 3 orders of magnitude. This amplification strategy provides a way to improve the sensitivity of plasmon-based bioassays, paving the way for single molecule-based detection and clinically relevant diagnostics.     

Widely tuning optical properties of nanoporous gold-titania core-shells

Widely shifting localized surface plasmon resonance (LSPR) bands of nanoporous metals is essential for light manipulation within small volumes. In this work, nanoporous gold-titania core-shells fabricated by atomic layer deposition exhibit tunable LSPR of gold skeletons in comparison with nanoporous gold-alumina developed before. Extremely large red-shift of LSPR band in nanoporous gold-titania from 537 to 751 nm results from high refractive index of titania and its dielectric medium dependence of LSPR, and the well-controlled thickness of titania shell at the nanometer scale will benefit to integrate optical nanodevices with supreme performances.     

Measurement of antibody binding to protein immobilized on gold nanoparticles by localized surface plasmon spectroscopy

Antibody binding to bovine serum albumin (BSA) and human serum albumin (HSA) immobilized onto gold nanoparticles was studied by means of localized surface plasmon resonance (LSPR) spectroscopy. Amine-modified glass was prepared by self-assembly of amine-terminated silane on substrate, and gold (Au) nanoparticles were deposited on the amine-modified glass substrate. Au nanoparticles deposited on the glass surface were functionalized by BSA and HSA. BSA immobilization was confirmed by LSPR spectroscopy in conjunction with surface-enhanced Raman scattering spectroscopy. Then, LSPR response attributable to the binding of anti-BSA and anti-HSA to BSA- and HSA-functionalized Au nanoparticles, respectively, was examined. Anti-HSA at levels larger than ∼10 nM could be detected by HSA-immobilized chips with LSPR optical response, which was saturated at concentrations greater than ∼650 nM of anti-HSA. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible to authorized users.     

A comparative analysis of localized and propagating surface plasmon resonance sensors: the binding of concanavalin a to a monosaccharide functionalized self-assembled monolayer

A comparative analysis of the properties of two optical biosensor platforms: (1) the propagating surface plasmon resonance (SPR) sensor based on a planar, thin film gold surface and (2) the localized surface plasmon resonance (LSPR) sensor based on surface confined Ag nanoparticles fabricated by nanosphere lithography (NSL) are presented. The binding of Concanavalin A (ConA) to mannose-functionalized self-assembled monolayers (SAMs) was chosen to highlight the similarities and differences between the responses of the real-time angle shift SPR and wavelength shift LSPR biosensors. During the association phase in the real-time binding studies, both SPR and LSPR sensors exhibited qualitatively similar signal vs time curves. However, in the dissociation phase, the SPR sensor showed an approximately 5 times greater loss of signal than the LSPR sensor. A comprehensive set of nonspecific binding studies demonstrated that this signal difference was not the consequence of greater nonspecific binding to the LSPR sensor but rather a systematic function of the Ag nanoparticle's nanoscale structure. Ag nanoparticles with larger aspect ratios showed larger dissociation phase responses than those with smaller aspect ratios. A theoretical analysis based on finite element electrodynamics demonstrates that this results from the characteristic decay length of the electromagnetic fields surrounding Ag nanoparticles being of comparable dimensions to the ConA molecules. Finally, an elementary (2 x 1) multiplexed version of an LSPR carbohydrate sensing chip to probe the simultaneous binding of ConA to mannose and galactose-functionalized SAMs has been demonstrated.     

Controlled dispersion of polystyrene‐capped Au nanoparticles in P3HT:PC61BM 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     

Wavelength-scanned surface-enhanced Raman excitation spectroscopy

A detailed wavelength-scanned surface-enhanced Raman excitation spectroscopy (WS SERES) study of benzenethiol adsorbed on Ag nanoparticle arrays, fabricated by nanosphere lithography (NSL), is presented. These NSL-derived Ag nanoparticle array surfaces are both structurally well-characterized and extremely uniform in size. The WS SERES spectra are correlated, both spatially and spectrally, with the corresponding localized surface plasmon resonance (LSPR) spectra of the nanoparticle arrays. The surface-enhanced Raman scattering (SERS) spectra were measured in two excitation wavelength ranges: (1) 425-505 nm, and (2) 610-800 nm, as well as with the 532-nm line from a solid-state diode-pumped laser. The WS SERES spectra have line shapes similar to those of the LSPR spectra. The maximum SERS enhancement factor is shown to occur for excitation wavelengths that are blue-shifted with respect to the LSPR lambda(max) of adsorbate-covered nanoparticle arrays. Three vibrational modes of benzenethiol (1575, 1081, and 1009 cm(-1)) are studied simultaneously on one substrate, and it is demonstrated that the smaller Raman shifted peak shows a maximum enhancement closer to the LSPR lambda(max) than that of a larger Raman shifted peak. This is in agreement with the predictions of the electromagnetic (EM) enhancement mechanism of SERS. Enhancement factors of up to approximately 10(8) are achieved, which is also in good agreement with our previous SERES studies.     

Localized surface plasmon resonance: nanostructures, bioassays and biosensing--a review

Localized surface plasmon resonance (LSPR) is an optical phenomena generated by light when it interacts with conductive nanoparticles (NPs) that are smaller than the incident wavelength. As in surface plasmon resonance, the electric field of incident light can be deposited to collectively excite electrons of a conduction band, with the result being coherent localized plasmon oscillations with a resonant frequency that strongly depends on the composition, size, geometry, dielectric environment and separation distance of NPs. This review serves to describe the physical theory of LSPR formation at the surface of nanostructures, and the potential for this optical technology to serve as a basis for the development bioassays and biosensing of high sensitivity. The benefits and challenges associated with various experimental designs of nanoparticles and detection systems, as well as creative approaches that have been developed to improve sensitivity and limits of detection are highlighted using examples from the literature.     

Localized surface plasmon resonance interfaces coated with poly[3-(pyrrolyl)carboxylic acid] for histidine-tagged peptide sensing

The paper reports on a novel localized surface plasmon resonance (LSPR) substrate architecture for the immobilization and detection of histidine-tagged peptides. The LSPR interface consists of an ITO (indium tin oxide) substrate coated with gold nanostructures. The latter are obtained by thermal deposition of a thin (2 nm thick) gold film followed by post-annealing at 500 °C. The LSPR interface was coated with poly[3-(pyrrolyl)carboxylic acid] thin films using electrochemical means. The ability of the LSPR interfaces coated with poly[3-(pyrrolyl)carboxylic acid] to chelate copper ions was investigated. Once loaded with metal ions, the modified LSPR interface was able to bind specifically to histidine-tagged peptides. The binding process was followed using LSPR.     

LSPR Imaging: Simultaneous Single Nanoparticle Spectroscopy and Diffusional Dynamics

A wide-field localized surface plasmon resonance (LSPR) imaging method using a liquid crystal tunable filter (LCTF) is used to measure the scattering spectra of multiple Ag nanoparticles in parallel. This method provides the ability to characterize moving Ag nanoparticles by measuring the scattering spectra of the particles while simultaneously tracking their motion. Consequently, single particle diffusion coefficients can be determined. As an example, several single Ag nanoprisms are tracked, the LSPR scattering spectrum of each moving particle is obtained, and the single particle diffusion coefficient is determined from its trajectory. Coupling diffusion information with spectral information in real time is a significant advance and addresses many scientific problems, both fundamental and biological, such as cell membrane protein diffusion, functional plasmonic distributions, and nanoparticle growth mechanisms.     

Gold nanoparticle dimers for plasmon sensing

In this study, gold nanoparticles (GNP) were stabilized for the first time as dimers by a conducting polymer (CP). The morphology of kissing particles was examined by high-resolution transmission electronic microscopy (HRTEM). The broad-band localized surface plasmon resonance (LSPR) tunable by solvent variation and molecular binding was demonstrated by UV-vis measurement. The sensitivity of the longitudinal LSPR to the surrounding media or the binding of a biomolecule was 6 times higher than that of the transversal LSPR. A homogeneous bioassay was directly developed from the highly stable GNP-CP dimers with LSPR as prober, and protein sensing with detection limit well below 100 ng/mL was achieved.     

A calcium-modulated plasmonic switch

A plasmonic switch based on the calcium-induced conformational changes of calmodulin is shown to exhibit reversible wavelength modulations in response to changing calcium concentration. The extinction maximum (lambdamax) of a localized surface plasmon resonance (LSPR) sensor functionalized with a novel calmodulin construct, cutinase-calmodulin-cutinase (CutCaMCut), reversibly shifts by 2-3 nm. A high-resolution (HR) LSPR spectrometer with a wavelength resolution (3sigma) of 1.5 x 10-2 nm was developed to detect these wavelength modulations in real-time, providing information about the dynamics and structure of the protein. The rate of conversion from open (Ca2+-bound) to closed (Ca2+-free) calmodulin is shown to be 4-fold faster than the reverse process, with a closing rate of 0.127 s-1 and opening rate of 0.034 s-1. As far as we are aware, this plasmonic switch marks the first use of LSPR spectroscopy to detect reversible conformational changes in an unlabeled protein.     

A visual photothermal paper sensor for H_2S recognition through rational modulation LSPR wavelength of plasmonics

It is known that the localized surface plasmon resonance(LSPR) wavelength of plasmonics is highly dependent on compositions and geometry of plasmonics as well as the surrounding environments. Here, monodispersed Au@Ag core-shell nanoparticles(Au@Ag NPs) were prepared by carefully optimizing the shell thickness of Au@Ag NPs, and the presence of hydrogen sulfide(H_2 S) would significantly alter the LSPR wavelength. On the basis of this, a photothermal paper sensor for on-site recognition of H_2 S was constructed with a visual detection limit of 12.8 ng/L.     

Recent advances in analytical and bioanalysis applications of noble metal nanorods

In the last decade the use of anisotropic nanoparticles in analytical and bioanalytical applications has increased substantially. In particular, noble metal nanorods have unique optical properties that have attracted the interest of many research groups. The localized surface plasmon resonance (LSPR) generated by interaction of light at a specific wavelength with noble metal nanoparticles was found to depend on particle size and shape and on the constituting material and the surrounding dielectric solution. Because of their anisotropic shape, nanorods are characterized by two LSPR peaks: the transverse, fixed at approximately 530 nm, and the longitudinal, which is in the visible–near infra-red region of the spectrum and varies with nanorod aspect ratio. The intense surface plasmon band enables nanorods to absorb and scatter light in the visible and near infra-red regions, and fluorescence and two-photon induced luminescence are also observed. These optical properties, with the reactivity towards binding events that induce changes in the refractive index of the surrounding solution, make nanorods a useful tool for tracking binding events in different applications, for example assembly, biosensing, in-vivo targeting and imaging, and single-molecule detection by surface-enhanced Raman spectroscopy. This review presents the promising strategies proposed for functionalizing gold nanorods and their successful use in a variety of analytical and biomedical applications.