Longitudinal Plasmon Resonance Research Articles

Gold nanorods as performance enhancers in planar perovskite solar cells: A numerical study

The quest for efficient and sustainable energy sources calls for an optimized optical design in photovoltaic technologies, particularly in perovskite solar cells (PSCs). This study focuses on the numerical analysis of integrating plasmonic non-spherical gold nanorods into realistic n-i-p MAPbI3 PSCs. The research addresses the light-harvesting enhancement, especially in near-infrared (NIR), a known limitation of metal halide PSCs. Nanorods were the selected nanostructures, as their longitudinal plasmon resonance has the potential to cover the NIR spectral limitation. The study aims to optimize the size, aspect ratio, orientation, and distance between nanorods, as well as provide insights into practical solutions for the positioning and encapsulation of the nanorods. The findings reveal that the aspect ratio and orientation of the nanorods significantly impact the absorption enhancement. Optimal outcomes are achieved with the vertical orientation of the nanorods, parallel to the stacking direction of the solar cell films. The most promising results from this study demonstrate that the incorporation of gold nanorods with small aspect ratios close to 1.5 leads to the potential enhancement of the perovskite photocurrent by at least 5 % (for spherical nanoparticles the maximum is 4.4 %). Additionally, it is also possible to reduce the layer thickness and the associated lead amount by at least 33 %, while maintaining the solar cell performance.

Anisotropic Plasmon Resonance Enables Spatially Controlled Photothermal and Photochemical Effects in Hot Carrier‐Driven Catalysis

Comprehensive SummaryLocalized surface plasmon resonance has been demonstrated to provide effective photophysical enhancement mechanisms in plasmonic photocatalysis. However, it remains highly challenging for distinct mechanisms to function in synergy for a collective gain in catalysis due to the lack of spatiotemporal control of their effect. Herein, the anisotropic plasmon resonance nature of Au nanorods was exploited to achieve distinct functionality towards synergistic photocatalysis. Photothermal and photochemical effects were enabled by the longitudinal and transverse plasmon resonance modes, respectively, and were enhanced by partial coating of silica nanoshells and epitaxial growth of a reactor component. Resonant excitation leads to a synergistic gain in photothermal‐mediated hot carrier‐driven hydrogen evolution catalysis. Our approach provides important design principles for plasmonic photocatalysts in achieving spatiotemporal modulation of distinct photophysical enhancement mechanisms. It also effectively broadens the sunlight response range and increases the efficacy of distinct plasmonic enhancement pathways towards solar energy harvesting and conversion.

Biodistribution and Targeted Antitumor Effects of Trastuzumab-Modified Gold Nanorods in Mice with Gastric Cancer.

Targeted drug is often engulfed and cleared by the reticuloendothelial system in vivo, resulting in reduced treatment efficacy. This study aimed to explore the biodistribution and HER-2-targeted antitumor effects of trastuzumab-modified gold nanorods (Tra-AuNRs) in a gastric cancer animal model. Gold nanorods were synthesized using a seed-mediated growth method, and then subjected to trastuzumab-targeted modification. Elemental analysis, Fourier transform infrared spectroscopy, and Xray photoelectron spectroscopy were performed; UV-visible absorption peak, photothermal effects, morphology, and size distribution of Tra-AuNRs were characterized. The targeted killing effect of Tra- AuNRs on gastric cancer cells was assessed in vitro. Tra-AuNRs were injected intravenously and intratumorally into gastric cancer-bearing nude mice in vivo and their distribution was detected. Tumor growth inhibition rate and tumor apoptosis-related protein expression were compared between groups. Tra-AuNRs presented a relatively uniform morphology with an average particle size of 59.9 nm and a longitudinal plasmon resonance absorption peak of 790 nm. The targeted killing rate of gastric cancer cells in vitro by Tra-AuNRs was 87.9%. After intravenous injection, Tra-AuNRs were mainly distributed in the liver, tumor, spleen, and lungs. Comparatively, Tra-AuNRs were mainly distributed in the tumor when intratumorally injected, with a tumor concentration of 6.42 μg/g after 24 h. The tumor growth inhibition rate reached 78.3% in the intratumoral injection group, with significantly higher BAX, BAD, and CASPASE-3 expression than that in the intravenous injection group. The findings suggest that Tra-AuNRs can be used for HER-2-positive gastric cancer treatment. Intratumoral injection of Tra-AuNRs significantly increased the local tumor drug concentration and improved the molecular targeted antitumor growth effect in gastric cancer-bearing nude mice.

Probing the Interaction between Individual Metal Nanocrystals and Two-Dimensional Metal Oxides via Electron Energy Loss Spectroscopy.

Metal nanoparticles can photosensitize two-dimensional metal oxides, facilitating their electrical connection to devices and enhancing their abilities in catalysis and sensing. In this study, we investigated how individual silver nanoparticles interact with two-dimensional tin oxide and antimony-doped indium oxide using electron energy loss spectroscopy (EELS). The measurement of the spectral line width of the longitudinal plasmon resonance of the nanoparticles in absence and presence of 2D materials allowed us to quantify the contribution of chemical interface damping to the line width. Our analysis reveals that a stronger interaction (damping) occurs with 2D antimony-doped indium oxide due to its highly homogeneous surface. The results of this study offer new insight into the interaction between metal nanoparticles and 2D materials.

Exploring the photophysical interaction of xanthene dyes with gold nanorods by optical spectroscopic techniques and in-vitro cytotoxicity studies of dye-nano conjugates

The current study investigates the photophysical interactions of xanthene dyes such as fluorescein (FL) and rose bengal (RB) dyes with cetyltrimethylammonium bromide stabilized gold nanorods (CTAB-AuNRs) using optical spectral techniques, and computational interaction analyses. When xanthene dyes are conjugated with CTAB-AuNRs, significant modifications in their optical spectroscopic characteristics are found. In the absorption spectrum analyses of dye-AuNRs systems, the appearance of longitudinal plasmon resonance bands and the hypochromic behavior of xanthene dyes were observed in response to the interaction of CTAB-AuNRs. The gathered extinction spectral results indicated that there were significant electrostatic interactions between the positively charged CTAB-AuNRs and the negatively charged xanthene dye molecules. At the same time, the substantial quenching with a reduced quantum yield of the dye molecules is shown in the emission spectra of xanthene dyes with CTAB-AuNRs. The strong electrostatic interactions and ground state complex between xanthene dyes and CTAB-AuNRs have been suggested as the mechanism of emission quenching. The results of the emission quenching are supported by the calculated high binding constant values. Additionally, the results of computational interaction investigations also demonstrate the near closeness of xanthene dye molecules and CTAB-AuNRs. Finally, the cytotoxicity of free dyes and dye-nanoconjugates was next tested against breast (MCF-7) and lung (A-549) cancer cells. All the tested samples exhibit significant antiproliferative activity against MCF-7 and A-549 cancer cells. These cytotoxic study results showed that cells treated with xanthene dyes were less sensitive than FL-AuNRs and RB-AuNRs dye nanoconjugates.

Thermal Effect during Laser-Induced Plasmonic Heating of Polyelectrolyte-Coated Gold Nanorods in Well Plates

We examined the generation and transfer of heat when laser irradiation is applied to water containing a suspension of gold nanorods coated with different polyelectrolytes. The ubiquitous well plate was used as the geometry for these studies. The predictions of a finite element model were compared to experimental measurements. It is found that relatively high fluences must be applied in order to generate biologically relevant changes in temperature. This is due to the significant lateral heat transfer from the sides of the well, which strongly limits the temperature that can be achieved. A 650 mW continuous-wave (CW) laser, with a wavelength that is similar to the longitudinal plasmon resonance peak of the gold nanorods, can deliver heat with an overall efficiency of up to 3%. This is double the efficiency achievable without the nanorods. An increase in temperature of up to 15 °C can be achieved, which is suitable for the induction of cell death by hyperthermia. The nature of the polymer coating on the surface of the gold nanorods is found to have a small effect.

Оптическая анизотропия пленок из поливилового спирта с металлическими наностержнями при одноосном растяжении

The possibility of obtaining macroscale anisotropic thin films from polyvinyl alcohol with included metal nanorods under uniaxial tension under conditions that do not lead to a change in the morphology of metal nanoparticles is shown. Silver and gold nanorods were obtained by directed growth from nuclei and then embedded in a polymer matrix based on polyvinyl alcohol. Initially isotropic films with absorption independent of the polarization of the probing light became anisotropic after stretching, which manifested itself in the dependence of the extinction spectra on the polarization of the probing radiation. The weakening of the longitudinal dipole plasmon resonance mode with the simultaneous enhancement of the transverse dipole plasmon resonance when the light polarization is rotated from 0 to 90 degree indicates the orientation of the nanorods in the film along the direction of its stretching. In addition to the change in absorption in the bands of dipole modes, a strong orientational dependence of absorption in the band of the quadrupole mode of the plasmon resonance of metal nanorods was found.

Spray-Deposited Anisotropic Assemblies of Plasmonic Nanowires for Direction-Sensitive Strain Measurement.

The development of nanoscale composites with hierarchical architecture and complex anisotropies enables the fabrication of new classes of devices. Stretchable strain sensors have been developed in the past for applications in various fields such as wearable electronics and soft robotics, yet the sensing capacities of most of these sensors are independent of the direction of deformation. In the present work, we report on the preparation of a direction-sensitive strain sensor using the anisotropic optical properties of a monolayer of oriented plasmonic 1D nano-objects. Grazing incidence spraying (GIS) is used for depositing a monolayer of in-plane aligned silver nanowires with a controlled density on a deformable and transparent substrate. Using the selective excitation of transverse and longitudinal localized plasmon resonance modes of silver nanowires by polarized UV-visible-NIR spectroscopy, we show that the macroscopic anisotropic properties of the monolayer upon stretching are highly dependent on the stretching direction and light polarization. Measuring the polarized optical properties of the anisotropic thin films upon stretching thus allow for retrieving both the local strain and the direction of the deformation using a simple model.

Low-intensity near-infrared light-tunable gold nanorod-incorporated hydrogel actuator system for remotely controlled human–robot interface applications

Light-responsive soft actuators have recently drawn attention as the need for lightweight remotely controlled actuator systems with high environmental adaptability and safe human–robot interaction interface characteristics has increased. In this study, we focused on a near-infrared (NIR) light-tunable hydrogel soft actuator system capable of fast and precisely controllable mechanical actuation even under the irradiation of NIR light with low intensity. We designed a bilayer type hydrogel soft actuator consisting of a poly(N-isopropylacrylamide) (PNIPAAm) active layer containing gold nanorods (AuNRs) as a photothermal agent and poly(acrylamide) (PAAm) passive layer. AuNRs with an aspect ratio of 4.12 showed the largest longitudinal plasmon resonance absorption peak in the NIR 880 nm range, which was used as a photothermal agent. The AuNR-incorporated PNIPAAm/PAAm hydrogel with a bilayer structure (PNIPAAm-AuNR/PAAm) exhibited more than 70% gel fraction and temperature-sensitive swelling behaviors. In particular, rod-shaped PNIPAAm-AuNR/PAAm hydrogels showed rapid bending deformation by a photothermally induced phase transition of PNIPAAm upon 880 nm laser irradiation, but a PNIPAAm/PAAm bilayer hydrogel without AuNRs did not show a light-induced bending movement. The NIR-responsive bending actuation of the hydrogel can be precisely controlled by cross-linking density, content of photothermal agent, NIR laser intensity, and thickness ratio of the active/passive layer. It was observed that the full bending deformations of the hydrogel into a ring shape through an arc occurred within a minute under NIR irradiation with a lower intensity of less than 1.0 W/cm2. Hydrogels showed a cell viability of more than 95% in the biocompatibility test, indicating no significant cytotoxicity. Therefore, these PNIPAAm-AuNR/PAAm hydrogels are promising soft actuator materials that can be controlled by low-intensity NIR irradiation for remotely controlled human–robot interaction interface applications.

Investigation of Plasmonic-Enhanced Solar Photothermal Effect of Au NR@PVDF Micro-/Nanofilms.

Gold nanospheres (Au NSs) and gold nanorods (Au NRs) are traditional noble metal plasmonic nanomaterials. Particularly, Au NRs with tunable longitudinal plasmon resonance from the visible to the near-infrared (NIR) range were suitable for highly efficient photothermal applications due to the extended light-receiving range. In this work, we synthesized Au NRs and Au NSs of similar volumes and subsequently developed them into Au NR/poly(vinylidene fluoride) (PVDF) and Au NS/PVDF nanofilms, both of which exhibited excellent solar photothermal performance evaluated by solar photothermal experiments. We found that the Au NR/PVDF nanofilm showed a higher solar photothermal performance than the Au NS/PVDF nanofilm. Through detailed analysis, such as morphological characterization, optical measurement, and finite element method (FEM) modeling, we found that the plasmonic coupling effects inside the aggregated Au NR nanoclusters contributed to the spectral blue shifts and intensified the photothermal performance. As compared to Au NS/PVDF nanofilms, the Au NR/PVDF nanofilm exhibited a higher efficient light-to-heat conversion rate because of the extended light-receiving range and high absorbance, as a result of the strong plasmonic interactions inside nanoclusters, which was further validated by monochromatic laser photothermal experiments and FEM simulations. Our work proved that the Au NRs have huge potential for plasmonic solar photothermal applications and are envisioned for novel plasmonic applications.

Theoretical simulation of nonlinear regulation of wall thickness dependent longitudinal surface plasmon in pentagonal gold nanotubes

In this paper, the longitudinal plasmon mode optical properties and localized electric field distribution of a single pentagonal gold nanotube are investigated for the first time by the discrete dipole approximation. It is found that pentagonal gold nanotube has stronger electric field distribution compared with circular gold nanotubes when the incident wavelength is located at the plasmon resonance peak. Additionally, we observed that the longitudinal plasmon resonance peak can blue shift nonlinearly with increasing wall thickness, but red shifts linearly with the increase of the length of the pentagonal gold nanotube. The localized electric field analysis reveals that the longitudinal plasmon peak of the pentagonal gold nanotube originates from the dipole resonance mode. The local electric field intensity is controlled by the wall thickness and length. Notably, the effect of wall thickness on the longitudinal plasmon resonance and electric field enhancement can be attributed to the change of the plasmon coupling position and intensity. This work has enriched the theoretical research of pentagonal gold nanotubes and provided ideas for the preparation of high sensitivity nanoprobes biosensors.

Achieving sub-diffraction spatial resolution using combined Fourier transform spectroscopy and nonlinear optical microscopy.

Fourier transform nonlinear optical microscopy is used to perform nonlinear spectroscopy of single gold nanorods in an imaging platform, which enables sub-diffraction spatial resolution. The nonlinear optical signal is detected as a function of the time delay between two phase-locked pulses, forming an interferogram that can be used to retrieve the resonant response of the nanoparticles. Detection of the nonlinear signal through a microscopy platform enables wide-field hyperspectral imaging of the longitudinal plasmon resonances in individual gold nanorods. Super-resolution capabilities are demonstrated by distinguishing multiple nanorods that are co-located within the optical diffraction limit and are spatially separated by only tens of nanometers. The positions and resonance energies obtained through Fourier transform nonlinear optical microscopy agree with the relative positions and aspect ratios deduced from electron microscopy.

Coating gold nanorods with silica prevents the generation of reactive oxygen species under laser light irradiation for safe biomedical applications.

Gold nanoparticles can produce reactive oxygen species (ROS) under the action of ultrashort pulsed light. While beneficial for photodynamic therapy, this phenomenon is prohibitive for other biomedical applications such as imaging, photo-thermal drug release, or targeted gene delivery. Here, ROS are produced in water by irradiating gold nanorods and silica-coated gold nanorods with near-infrared femtosecond laser pulses and are detected using two fluorescent probes. Our results demonstrate that a dense silica shell around gold nanorods inhibits the formation of singlet oxygen (1O2) and hydroxyl radical (˙OH) efficiently. The silica coating prevents the Dexter energy transfer between the nanoparticles and 3O2, stopping thus the generation of 1O2. In addition, numerical simulations accounting for the use of ultrashort laser pulses show that the plasmonic field enhancement at the nanoparticle vicinity is lessened once adding the silica layer. With the multiphotonic ejection of electrons being also blocked, all the possible pathways for ROS production are hindered by adding the silica shell around gold nanorods, making them safer for a range of biomedical developments.

Dual Plasmon Resonances and Tunable Electric Field in Structure-Adjustable Au Nanoflowers for Improved SERS and Photocatalysis.

Flower-like metallic nanocrystals have shown great potential in the fields of nanophononics and energy conversion owing to their unique optical properties and particular structures. Herein, colloid Au nanoflowers with different numbers of petals were prepared by a steerable template process. The structure-adjustable Au nanoflowers possessed double plasmon resonances, tunable electric fields, and greatly enhanced SERS and photocatalytic activity. In the extinction spectra, Au nanoflowers had a strong electric dipole resonance located around 530 to 550 nm. Meanwhile, a longitudinal plasmon resonance (730~760 nm) was obtained when the number of petals of Au nanoflowers increased to two or more. Numerical simulations verified that the strong electric fields of Au nanoflowers were located at the interface between the Au nanosphere and Au nanopetals, caused by the strong plasmon coupling. They could be further tuned by adding more Au nanopetals. Meanwhile, much stronger electric fields of Au nanoflowers with two or more petals were identified under longitudinal plasmon excitation. With these characteristics, Au nanoflowers showed excellent SERS and photocatalytic performances, which were highly dependent on the number of petals. Four-petal Au nanoflowers possessed the highest SERS activity on detecting Rhodamine B (excited both at 532 and 785 nm) and the strongest photocatalytic activity toward photodegrading methylene blue under visible light irradiation, caused by the strong multi-interfacial plasmon coupling and longitudinal plasmon resonance.

Morphological Changes of Silica Shells Deposited on Gold Nanorods: Implications for Nanoscale Photocatalysts

Gold nanorods (GNRs) support strong localized surface plasmon resonances that can be exploited to enhance the fluorescence or catalytic properties of adjacent molecules. Coating GNRs with silica is frequently used to functionalize their surfaces, but full encapsulation limits the ability to control the spatial distribution of molecules and their related reactivity. For example, locating molecules near the ends of GNRs would enable their strong longitudinal plasmon resonance to be exploited, but such selectivity is challenging. So far, studies of anisotropic coating have been limited and the mechanism of the adsorption onto GNRs remains unclear. Here, we systematically investigated the anisotropic coating of the ends of GNRs with silica and the influence of growth conditions on the formation of silica shells. Three types of nanostructures have been observed and their origins are described: fully encapsulated core-shell GNRs, GNRs with only one end coated with silica, and dumbbell-like GNRs (dGNRs) with both ends coated. The study was performed at around room temperature, where the solubility and micellization of the surfactant cetyltrimethylammonium bromide (CTAB) can be tuned to affect the morphology, stability and density of resulting silica shells. Optimized parameters, in combination with an appropriate GNR aspect ratio, are shown to significantly improve the growth yield of dGNRs, which become the dominant product. A protocol for a high yield synthesis of dGNRs was developed, with a maximum yield exceeding 90 %. This study advances our understanding of the growth mechanism of anisotropic coating of GNRs and sheds light on the optimization of site-selective coating processes. The development of anisotropic GNR-based nanostructures for fluorescence/scattering amplifiers will be important in applications such as metal-enhanced fluorescence, surface-enhanced Raman scattering or plasmon-enhanced catalysis.

Computed Tomography Imaging Agent Based on Gold Nanoparticles for Internal Iliac Artery Embolization after Endovascular Abdominal Aortic Repair and CCN3 Protection Mechanism

Abdominal aortic aneurysm is more stressful and has more complications in many diseases. During treatment and repair, arteriosclerosis, abdominal congestion deposition, and abdominal swelling cannot be eliminated. In this paper, we used the seed growth method to obtain gold nanoparticles (AuNPs) with good morphology and dispersion. The AuNPs of larger aspect ratio synthesized in this experiment moved their longitudinal plasmon resonance absorption peak to the near-infrared region, which provided suitable materials for subsequent experiments and laid the foundation for the photothermal therapy of tumors. Experiments show that near-infrared rays can penetrate into deep tissues to overcome the shortcomings that visible light cannot penetrate abdominal aorta well. AuNPs absorb near-infrared rays, thereby generating heat energy to achieve the purpose of treating tumors. In addition, AuNPs also have fluorescent properties, combined with other forms of imaging methods, to achieve the purpose of multimodal imaging, and improve the diagnostic accuracy of studying the protection mechanism of the nephroblastoma overexpressed (NOV or CCN3) gene.

Long- and short-ranged chiral interactions in DNA-assembled plasmonic chains

Circular dichroism (CD) has long been used to trace chiral molecular states and changes of protein configurations. In recent years, chiral plasmonic nanostructures have shown potential for applications ranging from pathogen sensing to novel optical materials. The plasmonic coupling of the individual elements of such metallic structures is a crucial prerequisite to obtain sizeable CD signals. We here identify and implement various coupling entities—chiral and achiral—to demonstrate chiral transfer over distances close to 100 nm. The coupling is realized by an achiral nanosphere situated between a pair of gold nanorods that are arranged far apart but in a chiral fashion using DNA origami. The transmitter particle causes a strong enhancement of the CD response, the emergence of an additional chiral feature at the resonance frequency of the nanosphere, and a redshift of the longitudinal plasmonic resonance frequency of the nanorods. Matching numerical simulations elucidate the intricate chiral optical fields in complex architectures.

Complex Resonant Scattering Behavior in the Surface Plasmon Resonance Imaging Microscopy of Single Gold Nanorods.

Diffraction patterns observed in surface plasmon resonance imaging (SPRI) microscopy measurements of single gold nanorods (AuNRs) exhibit a complex behavior at wavelengths near the longitudinal plasmonic resonance band. SPRI microscopy measurements at 814 nm from AuNRs in three samples with resonance extinction maxima at 670, 816, and 980 nm reveal a variety of diffraction patterns with central peaks that are either positive, negative, or biphasic. A unitless ratio parameter MR (-1 ≤ MR ≤ 1) is created to describe the distribution of diffraction patterns. A purely negative (MR = -1) central peak is observed for 30%, 57%, and 98% of the diffraction patterns in the 670, 816, and 980 nm samples, respectively. These results along with a theoretical modeling of the diffraction patterns with an anisotropic complex scattering coefficient suggests that this behavior only occurs for AuNRs when the laser wavelength used in SPRI experiments is shorter than the AuNR plasmonic resonance maxima, that is, in the anomalous dispersion region.

Size-modulated optical property of gold nanorods for sensitive and colorimetric detection of thiourea in fruit juice

As an important sulfur compound, thiourea (TU) has caused great concern because of its wide application as well as its serious toxicity and hazard to the environment. Thus, it is necessary to develop a sensitive and selective method for TU analysis. In this work, gold nanorods (AuNRs) acted as an optical probe to realize the sensitive and colorimetric detection of TU. In HCl medium, Fe3+ at low concentration was difficult to oxide Au0 to form Au+ because of the high redox potential or the positive Gibbs free energy change. However, this process was possible when TU was present since the association constant between Au+ and TU is great enough to bind with TU to form a stable complex to further promote the etching of AuNRs, resulting in the lower aspect ratio of AuNRs with the blue shift and intensity decrease in extinction spectra, accompanied by the divisive colors of AuNRs solution or colorful dark-field light scattering imaging of single AuNR. The blue-shift of AuNRs longitudinal plasmon resonance absorption (LPRA) band was proportional to the concentration of TU in the range of 1–250 nM and the limit of detection (3σ/k) was as low as 0.4 nM. In addition, the colorimetric method was proven with high selectivity in the presence of potential interfering compounds, which was successfully applied to the detection of TU in fruit juice samples. This proposed colorimetric method provides a simple, sensitive yet selective measurement tool for TU sensing, which may offer new opportunities in the development of colorimetric sensors for food safety in the future.

Deposited ultra-thin titanium nitride nanorod array as a plasmonic near-perfect light absorber

The transmittance, reflectance, and extinctance that correspond to the localized plasmonic resonance within TiN nanorods were investigated. The obliquely deposited TiN nanorod array shows polarization-independent admittance matching to air. Unlike noble metal nanorods, the near-field localized longitudinal and transverse plasmonic resonance of TiN nanorod arrays present polarization-dependent light extinction in the far field. The longitudinal plasmonic mode presents stronger extinction than transverse plasmonic mode. In order to have high efficient light absorption, an ultra-thin two-layered TiN nanorod array was fabricated with orthogonal deposition planes for upper layer and bottom layer to absorb different polarized light energy. The measured spectrum shows broadband and wide-angle light extinction.