Localized Surface Plasmon Resonance Spectra Research Articles

Reconfigurable localized surface plasmon resonance spectrum based on acousto-dynamic coupling in arrays gold nanoparticles induced by shear horizontal vibration

Reconfigurable localized surface plasmon resonance (LSPR) is an essential characteristic for various applications to support Society 5.0. However, many LSPR spectrum have poor reconfigurability. As a novelty, we proposed a reconfigurable LSPR spectrum by acousto-dynamic coupling in arrays of gold nanoparticles (AuNPs) induced by shear-horizontal vibrations. The vibrations were produced by piezoelectric phenomena especially shear horizontal surface acoustic waves (SH-SAWs) on a 36XY-LiTaO3 substrate after applying an electric signal, the ON-condition. The experimental results demonstrated that the ON-condition produced a blueshift effect on the peak position (λP) with an adjustment quality factor compared to the OFF-condition. Moreover, in order to perform the finite-difference time-domain (FDTD) analysis, we reproduced the morphological structure of AuNPs base on scanning electron microscope (SEM) images. The different coupling distances and different arrays structures were utilized as ON-condition approaches for dimer AuNPs and arrays AuNPs, respectively. The FDTD simulation obtained a blueshift effect compared to the initial structure. Finally, the proposed structure successfully combines piezoelectric phenomena with plasmonic phenomena to produce reconfigurable LSPR. The LSPR spectrum can be switched comfortably and reverses easily. The proposed method can be applied for multifunctional sensors with the high possibility of integration into a wireless network.

Scanning probe microscopy by localized surface plasmon resonance at fiber taper tips.

Plasmonic antenna probes have been widely investigated for detecting electrical permittivity changes on the nanometer scale by employing high-sensitivity localized surface plasmon resonance (LSPR). Although it is intuitive to integrate such a probe onto an atomic force microscope (AFM) to add one more measurable quantity to the family of scanning probe microscopy techniques, the strong scattering background of the AFM tip overwhelms the LSPR scattering signal. To solve this problem, we combined evanescent coupling, polarization and spatial filtering, confocal spectroscopy, and numerical methods to extract clean LSPR spectra from a gold nanosphere-antenna probe attached to the tip of a fiber taper. By mounting the fiber taper on a custom quartz-tuning-fork SPM, we achieved high-quality nanometer-scale imaging of gold nanospheres on glass slides by mapping the LSPR wavelength shift. In addition, we reported an LSPR wavelength shift enhancement by more complicated probe designs and the consequent promise for higher-sensitivity microscopy. Our optical system and spectral processing method provide an effective solution to the long-standing quest for LSPR scanning microscopy.

Alkaline Phosphatase-Triggered Etching of Au@FeOOH Nanoparticles for Enzyme Level Assay under Dark-Field Microscopy.

In clinical diagnosis, the level of biological enzymes in serum has been generally regarded as markers of human diseases. In this work, a kind of simple and sensitive plasmonic probe (indicated as Au@FeOOH) has been synthesized with the guidance of plasmonic imaging and subsequently developed for the alkaline phosphatase (ALP) level detection under dark-field microscopy (DFM). As a kind of hydrolysis enzyme, ALP can promote the hydrolysis of l-ascorbic acid 2-phosphate to ascorbic acid (AA). AA further acts as a strong reduction reagent for the decomposition of the FeOOH shell, which results in a blue shift of localized surface plasmon resonance spectra and an obvious color change under DFM. RGB analyses show that using a ΔR/G value instead of scattering wavelength or R/G value as the analytical signal, the deviation attributed to the size distribution of the initial Au NPs is greatly suppressed, and a linear range from 0.2 to 6.0 U/L (R2 = 0.99) and a limit of detection of 0.06 U/L are acquired with various concentrations of ALP during the detection. Besides, this approach exhibits excellent selectivity in complex biological serum samples, which is expected to be applied for the early diagnosis of clinical diseases by monitoring various biomarkers in the future.

Gold Nanostar Spatial Distribution Impacts the Surface-Enhanced Raman Scattering Detection of Uranyl on Amidoximated Polymers.

The plasmonic properties of carboxylated gold nanostars distributed on amidoximated polyacrylonitrile (AO PAN) electrospun polymer films scale with surface-enhanced Raman scattering (SERS) intensities for coordinated uranium(VI) oxide (uranyl) species. This two-step plasmonic sensor first isolates uranyl from solution using functionalized polymers; then carboxylated gold nanostars are subsequently deposited for SERS. Spatially resolved localized surface plasmon resonance (LSPR) and SERS facilitate correlated nanostar optical density and uranyl quantification. To reduce sampling bias, gold nanostars are deposited in an inverted drop-coating geometry and measurements are conducted inside resulting nanoparticle coffee rings that form on the polymer substrates. This approach naturally preserves the plasmonic properties of gold nanostars while reducing the deposition of nanoparticle aggregates in active sensing regions, thereby maximizing both the accuracy and the precision of SERS measurements. Several advances are made. First, second-derivative analysis of LSPR spectra facilitates the quantification of local nanostar density across large regions of the sensor substrate by reducing background variations caused by the polymeric and gold materials. Second, local nanostar densities ranging from 140 to 200 pM·cm are shown to result in uranyl signals that are independent of nanostar concentration. Third, the Gibbs free energy of uranyl adsorption to carboxylated nanostars is estimated at 8.4 ± 0.2 kcal/mol. Finally, a linear dynamic range from ∼0.3 to 3.4 μg U/mg polymer is demonstrated. Signals vary by 10% or less. As such, the uniformity of the plasmonic activity of distributed gold nanostars and the employment of spatially resolved spectroscopic measurements on the composite nanomaterial sensor interface facilitate the quantitative detection of uranyl while also reducing the dependence on user expertise and the selected sampling region. These important advances are critical for the development of a user-friendly SERS-based sensor for uranyl.

Cu-Sb-S Ternary Semiconductor Nanoparticle Plasmonics.

Semiconductor plasmonics is a recently emerging field that expands the chemical and physical bandwidth of the hitherto well-established noble metallic nanoparticles. Achieving tunable plasmonics from colloidal semiconductor nanocrystals has drawn enormous interest and is promising for plasmon-related applications. However, realizing this goal of tunable semiconductor nanocrystals is currently still a synthetic challenge. Here, we report a colloidal synthesis strategy for highly dispersed, platelet-shaped, antimony-doped copper sulfide semiconductor nanocrystals (Sby-CuxS NCs) with a dominant localized surface plasmon resonance (LSPR) band tunable from the near-infrared into the midvisible spectral range. This work presents the synthesis and quantifies the resulting plasmonic features. It furthermore elucidates the underlying carrier concentration requirements to realize a continuum of LSPR spectra. Building on our previous work on binary plasmonics CuxS, CuxSe, and CuxTe NCs, the present method introduces a much wider and finer tunability with ternary semiconductor plasmonics.

Localized surface plasmon resonance in deep ultraviolet region below 200\xa0nm using a nanohemisphere on mirror structure

Localized surface plasmon resonance (LSPR) was performed in the deep ultraviolet (UVC) region with Al nanohemisphere structures fabricated by means of a simple method using a combination of vapor deposition, sputtering, and thermal annealing without top-down nanofabrication technology such as electron beam lithography. The LSPR in the UV region was obtained and tuned by the initial metal film thickness, annealing temperature, and dielectric spacer layer thickness. Moreover, we achieved a flexible tuning of the LSPR in a much deeper UVC region below 200 nm using a nanohemisphere on a mirror (NHoM) structure. NHoM is a structure in which a metal nanohemisphere is formed on a metal substrate that is interposed with an Al2O3 thin film layer. In the experimental validation, Al and Ga were used for the metal hemispheres. The LSPR spectrum of the NHoM structures was split into two peaks, and the peak intensities were enhanced and sharpened. The shorter branch of the LSPR peak appeared in the UVC region below 200 nm. Both the peak intensities and linewidth were flexibly tuned by the spacer thickness. This structure can contribute to new developments in the field of deep UV plasmonics.

Preface to the special issue dedicated to Professor Richard P. Van Duyne (1945–2019)

Preface to the special issue dedicated to Professor Richard P. Van Duyne (1945–2019)

Tuning gold nanostar morphology for the SERS detection of uranyl.

The impact of tunable morphologies and plasmonic properties of gold nanostars are evaluated for the surface enhanced Raman scattering (SERS) detection of uranyl. To do so, gold nanostars are synthesized with varying concentrations of the Good's buffer reagent, 2-[4-(2-hydroxyethyl)-1-piperazinyl]propanesulfonic acid (EPPS). EPPS plays three roles including as a reducing agent for nanostar nucleation and growth, as a nanostar-stabilizing agent for solution phase stability, and as a coordinating ligand for the capture of uranyl. The resulting nanostructures exhibit localized surface plasmon resonance (LSPR) spectra that contain two visible and one near-infrared plasmonic modes. All three optical features arise from synergistic coupling between the nanostar core and branches. The tunability of these optical resonances are correlated with nanostar morphology through careful transmission electron microscopy (TEM) analysis. As the EPPS concentration used during synthesis increases, both the length and aspect ratio of the branches increase. This causes the two lower energy extinction features to grow in magnitude and become ideal for the SERS detection of uranyl. Finally, uranyl binds to the gold nanostar surface directly and via sulfonate coordination. Changes in the uranyl signal are directly correlated to the plasmonic properties associated with the nanostar branches. Overall, this work highlights the synergistic importance of nanostar morphology and plasmonic properties for the SERS detection of small molecules.

Random lasing based on plasmonic enhancement from dye-doped capillary tubes with Ag-TiO2 composite nanostructure

Plasmonics have allowed revolutionary progress in field of random lasers through improvement of the lasing property via surface plasmon resonance (SPR). However, localized surface plasmon resonance (LSPR) spectra of conventional metal nanostructures are too narrow to sufficiently cover both the absorption and emission spectra of dyes. Therefore, in this paper, we fabricate a typical Ag-TiO2 composite nanostructure by a solution-reduction method and dope it into a random-laser system with a dye solution. With the assistance of this new nanostructure with a broadened plasmon-resonance band, the random-lasing device shows a lower threshold, sharper peak, and higher intensity compared with devices with pure TiO2 nanoparticles (NPs) and mixtures of TiO2 and Ag NPs as scattering media. The results further stimulate consideration of the plasmon effects in random laser systems and help in the design of high-performance, cost-effective random laser devices.

Colorimetric Determination of Urinary Creatinine in Proteinuria Patients by Chromaticity Analysis of Gold Nanoparticle Colloidal Solutions.

Several scientific works have reported the use of colloidal gold nanoparticle (AuNP) solutions as a colorimetric probe for creatinine detection. Nonetheless, urinary protein is one of the primary chemical components that can interfere with creatinine detection. In this work, we developed a colorimetric probe using AuNP colloidal solution to detect creatinine in the urine of proteinuria patients. A microchamber array was prepared to minimize the sample volume and was used to simultaneously perform spectral recording and image acquisition of several samples. The analyzed volume for each sample was 15 μL. A camera coupled with liquid crystal tunable filters was used to record hyperspectral images, and the signals were then converted to localized surface plasmon resonance (LSPR) spectra. Color changes in the AuNP colloidal solution in the presence of varying concentrations of creatinine and human serum albumin (HSA) indicated different features and could be detected by a hyperspectral imaging technique. The relevant concentration ranges of creatinine and HSA were 5 - 200 and 50 - 250 mg dL-1, respectively. Furthermore, a smartphone camera was adopted to record a color mapping image of the AuNP colloidal solution in the presence of creatinine and HSA at these concentration ranges. Contour plots of red and blue chromaticity levels from color mappings were produced, and 2D fitting equations obtained from these contour plots were adopted to determine the creatinine concentration in the urine of proteinuria patients. This practical technique can be used for screening and can be further developed as a household biosensing device for urinalysis.

Influence of Saline Buffers over the Stability of High-Annealed Gold Nanoparticles Formed on Coverslips for Biological and Chemosensing Applications.

Herein, coverslips were used as solid supports for the synthesis of gold nanoparticles (AuNPs) in three steps: (i) detergent cleaning, (ii) evaporation of 4 nm gold film and (iii) exposure at high annealing temperature (550 °C) for 3 h. Such active gold nanostructured supports were investigated for their stability performances in aqueous saline buffers for new assessments of chemical sensing. Two model buffers, namely saline-sodium phosphate-EDTA buffer (SSPE) and phosphate buffer saline (PBS), that are often used in the construction of (bio)sensors, are selected for the optical and microscopic investigations of their influence over the stability of annealed AuNPs on coverslips when using a dropping procedure under dry and wet media working conditions. A study over five weeks monitoring the evolution of the localized surface plasmon resonance (LSPR) chemosensing of 1,2-bis-(4-pyridyl)-ethene (BPE) is discussed. It is concluded that the optimal sensing configuration is based on annealed AuNPs exposed to saline buffers under wet media conditions (overnight at 4 °C) and functionalized with BPE concentrations (10−3–10−11 M) with the highest LSPR spectra after two weeks.

Simulating Plasmon Resonances of Gold Nanoparticles with Bipyramidal Shapes by Boundary Element Methods.

Computational modeling and accurate simulations of localized surface plasmon resonance (LSPR) absorption properties are reported for gold nanobipyramids (GNBs), a class of metal nanoparticle that features highly tunable, geometry-dependent optical properties. GNB bicone models with spherical tips performed best in reproducing experimental LSPR spectra while the comparison with other geometrical models provided a fundamental understanding of base shapes and tip effects on the optical properties of GNBs. Our results demonstrated the importance of averaging all geometrical parameters determined from transmission electron microscopy images to build representative models of GNBs. By assessing the performances of LSPR absorption spectra simulations based on a quasi-static approximation, we provided an applicability range of this approach as a function of the nanoparticle size, paving the way to the theoretical study of the coupling between molecular electron densities and metal nanoparticles in GNB-based nanohybrid systems, with potential applications in the design of nanomaterials for bioimaging, optics and photocatalysis.

The influence of gap spacing in localized surface plasmon resonance (LSPR) spectra of Ag nanorod-coupled with end-to-end assembly using boundary element method

We have systematically investigated the Localized Surface Plasmon Resonance (LSPR) of Ag nanorod-coupled with end-to-end assembly and influence distance between nanorod using metallic nanoparticle based on the boundary element method (MNPBEM). We focused on the extinction curve of LSPR spectra for investigating the effect of gap spacing for this work. It was found that the extinction curve showed two behaviours, for lower wavelength known as the transversal mode and higher wavelength as the longitudinal mode. For further understanding, we also analyzed the electric field related to LSPR spectra of Ag nanorod-coupled. In end-to-end assembly, the resonance peak of transversal mode shifted to lower wavelength (blue-shift) while for longitudinal mode shifted to higher wavelength (red-shift), both as the spacing gap decreased. Interestingly, for the case in parallel polarization, the peaks of wavelength decay as the gap spacing increased followed a plasmon ruler. We observed the dipole-dipole interaction was the influence in LSPR spectra of Ag nanorod-coupled. According to this result, it is essential to understand the distance dependence in LSPR spectra in coupled noble particle system.

The sensitivity calculation of localized surface plasmon resonance (LSPR) Au nanorod by applying a boundary element system simulation

In this study, we have calculated the sensitivity of localized surface plasmon resonance (LSPR) Au nanorod by a public metallic particle simulation based on the boundary element method (Metallic Nano-Particle Boundary Element Method, MNPBEM). The diameter of nanorod D is 20 nm, 60 nm, and 80 nm. The variation of aspect ratio is 1.5 to 3.5. The dielectric of Au nanorod based on the Christine-Johnson experiment. To understand sensitivity sense, we have also varied the refractive index medium by Lorentz-Lorentz approximation from a mixture of water and glycerol concentration. The refractive medium index is n = 1.3334 (100 % water pure), n = 1.3605 (80 % water and 20 % glycerol), n = 1.3881 (60 % water and 40 % glycerol), n = 1.4164 (40 % water and 60 % glycerol), and n = 1.4452 (20 % water and 80 % glycerol). From MNPBEM simulation, we have produced LSPR spectra such as absorption, scattering, and extinction curve as the function of wavelength. Then, the sensitivity of LSPR Au nanorod is determined by the gradient of the peak of wavelength to the refractive index medium variation for all aspect ratio. Interestingly, we have found the LSPR Au nanorod consisted of longitudinal and transversal mode in LSPR Au nanorod curve. The longitudinal mode appeared a higher wavelength than the transversal mode in LSPR spectra. In longitudinal mode, the peak of wavelength increased as the aspect ratio increased (red-shift) while in transversal mode, the peak of wavelength was relatively constant. Furthermore, the sensitivity in longitudinal mode increased as the aspect ratio increased, whereas the sensitivity in transversal decreased as the aspect ratio increased. Increasing the sensitivity in longitudinal mode related to red-shift as the nanorod volume increased and the refractive medium index change. According to the results, the sensitivity determination is useful to understand the refractive index medium changes that it is important to design a sensor device.

The incident electrical field angle effect in localized surface plasmon resonance (LSPR) of bimetallic Ag-Au nanorod using MNPBEM simulation

In this study, we have performed the incident electrical field angle effect in localized surface plasmon resonance (LSPR) spectra of bimetallic Ag–Au nanorod using Metallic Nano-Particle Boundary Element Method (MNPBEM) based on the boundary element method. The diameter and length of nanorod are 40 nm and 100 nm, respectively. The fraction of Ag in bimetallic Agx, Au(100-x) are 0, 20, 40, 60, 80, and 100 within weight percent. The dielectric function of Ag–Au was generated by linear approximation and the incident angle used from 0 to 90 degrees. We found that the intensity of the extinction curve shows decreasing follow logistic type curve as the incident angle increases whereas the resonance peak is constant. For a given silver fraction in bimetallic Ag-Au, the resonance peak of LSPR shifted to higher energy or blue-shift and the intensity increased. Interestingly, the LSPR of bimetallic Ag–Au occurred in the visible range and the transition mode from longitudinal to transverse mode was observed at the angle greater than 60 degrees.

Gold Nanoparticles and Uricase Functionalized Tapered Fiber Sensor for Uric Acid Detection

In this paper, a tapered optical fiber-based sensor is developed for the detection of uric acid (UA) in human serum. The fiber probes were fabricated using single-mode fiber (SMF) with taper diameter of $40~\mu \text{m}$ . The diameter of taper section has culminated on the basis of excretion of evanescent waves and their handling capacity. To enhance the sensitivity, taper section (sensing region) was immobilized with synthesized gold nanoparticles (AuNPs). The AuNPs were used to initiate the excitation of surface plasmons (SP) at the fiber surface and ultimately leads to the localized surface plasmon resonance (LSPR) phenomenon. The comparative studies were also done to analyze the effect of size of AuNPs by immobilizing the sensor probes with ~10 nm and ~30 nm size of AuNPs. The UV-Vis spectrophotometry, high resolution-transmission electron microscopy (HR-TEM) and scanning electron microscopy (SEM) were used for the characterization of AuNPs solution and developed sensor probes. The sensing ability of sensors was authenticated by recording the transmitted intensity of LSPR spectrum for a wide range of UA from $10~\mu \text{M}$ to $800~\mu \text{M}$ . The detected range of UA completely covers its concentration available in human serum that is from $150~\mu \text{M}$ to $420~\mu \text{M}$ . Thereafter, the wavelength shift in LSPR spectrums was evaluated to determine the sensitivity and detection limit of sensors. The selectivity of the sensor probe was enhanced by functionalizing it with uricase enzyme (0.672 U/ml). The specificity of uricase functionalized sensor probes were also analyzed in the presence of other biomolecules found in human-serum.

Multiple Scattering from Electrospun Nanofibers with Embedded Silver Nanoparticles of Tunable Shape for Random Lasers and White-Light-Emitting Diodes.

Random lasers (RLs) are convenient, tunable, and widely applicable. However, the influence of fluorescence lifetime on the scattering and nanofiber distribution of nanofibers with various shapes of silver nanoparticles (Ag NPs) embedded within is unclear. We prepared poly(vinyl alcohol) (PVA) nanofibers with Ag NPs through electrospinning (ES) and pyrromethene 597 dye doping. We determined the influences of the particles on scattering enhancement and localized surface plasmon resonance (LSPR) in RLs. The distinct scattering rates and LSPR can be used to control optical properties for sensing devices and other applications. Compared with traditional films, the threshold of the nanofibers with Ag NPs is 35% lower. In addition to improved matching between the LSPR and emission spectra, enhanced coupling of the electric field with nonradiative energy amplifies the radiative emission. Furthermore, the luminescence lifetime shortened by increasing the scattering rate. An excessive scattering rate may accelerate radiative recombination and convert some recombination into nonradiative recombination to produce a more sensitive device. Finally, we applied the prepared nanofibers to a backlight display and fabricated a white-light-emitting diode (LED) with a distinct thickness of nanofibers. The fabricated device is suitable for application in other LEDs and RL devices.

Revealing Lectin-Sugar Interactions with a Single Au@Ag Nanocube.

An individual nanoparticle-based plasmonic nanotechnology was used for real-time monitoring of lectin-sugar interactions, which could be designed as novel plasmonic nanobiosensors for the detection of trace concanavalin A (ConA) with high sensitivity and selectivity. The localized surface plasmon resonance (LSPR) spectra of Au@Ag nanocubes (NCs) are linearly shifted to a long wavelength with an increasing concentration of ConA. In fact, each Au@Ag NC can act as a nanobiosensor for the quantified detection of trace ConA, which enables the miniaturization of the biosensor system to nanoscale. Furthermore, the results demonstrated the perfect biosensing ability with the dual channel of dark-field microscopy images and LSPR spectra. We expect that this nanobiosensor system can provide an alternative important method for monitoring the specific binding of lectin-sugar at a single nanoparticle surface.

Investigating of LSPR spectra on a hybrid Fe3O4-Au within core-shell structure

In this study, we have investigated the tunability of localized surface plasmon resonance (LSPR) spectra of the magneto-plasmonic system composed of Au-coated Fe3O4 (Fe3O4@Au) by public optical simulation, MNPBEM based on boundary element method calculation. The magneto-plasmonic system is modeled nanorod core-shell structure with three different core’s aspect ratio: 2.3, 4.3, and 6.3. The nanoparticle was immersed in water (1.33+0i). Then, we applied the electromagnetic field in parallel and perpendicular to the long axis of nanorod. Interestingly, the peak of LSPR spectra Fe3O4@Au shows blue-shifted at gold thickness toward around ∼50 nm and as the gold-shell keep growing, a red-shifted can be occurred on greater than ∼50 nm of thick gold-shell. The peak of LSPR spectra shows to shift to lower wavelength or blue-shift and produce narrow width spectra. Based on the result, we believe our observation can be utilized for tuning LSPR spectra from visible range to near-infrared such as photocatalysis application and biosensing with well-controlled of thicknesses.

Optimizing the Sensing Performance of SiO2-Au Nanoshells

The localized surface plasmon resonance (LSPR) extinction spectrum and its dependence with permittivity of the surrounding medium have been broadly explored for molecular sensing applications. The sensing performance is governed by the bulk sensitivity and the linewidth of the LSPR peak. Therefore, a sensor needs to attend both requisites: a high bulk sensitivity and a sharp LSPR spectrum, related by the ηb ×FoM parameter. Complex plasmonic structures are proposed for sensing applications due to their high sensitivity values without considering the broad nature of the LSPR peak, that decrease the detection limit of the plasmonic sensor. In this article, we report the optical properties of SiO2 core/Au nanoshell (Au-NS) particles and the feasibility of exploring it as a sensor platform. On tuning the geometric parameters of the Au-NS, we have obtained the optimized the ηb ×FoM parameter with a value of 2057.4 nm/RIU2, which is the highest reported in the literature with spherical shapes. Moreover, for molecular adsorption sensing, Campbell’s model was exploited on a size-dependence approach. Finally, we have studied the influence of a dielectric substrate on the Au-NS sensing performance. Our results provide new bases for the development of high-performance nanostructures for bulk and molecular LSPR sensing.