Plasmonic Properties Research Articles

Magnesium Nanoparticles for Surface-Enhanced Raman Scattering and Plasmon-Driven Catalysis.

Nanostructures of some metals can sustain localized surface plasmon resonances, collective oscillations of free electrons excited by incident light. This effect results in wavelength-dependent absorption and scattering, enhancement of the incident electric field at the metal surface, and generation of hot carriers as a decay product. The enhanced electric field can be utilized to amplify the spectroscopic signal in surface-enhanced Raman scattering (SERS), while hot carriers can be exploited for catalytic applications. In recent years, cheaper and more earth abundant alternatives to traditional plasmonic Au and Ag have gained growing attention. Here, we demonstrate the ability of plasmonic Mg nanoparticles to enhance Raman scattering and drive chemical transformations upon laser irradiation. The plasmonic properties of Mg nanoparticles are characterized at the bulk and single particle level by optical spectroscopy and scanning transmission electron microscopy coupled with electron energy-loss spectroscopy and supported by numerical simulations. SERS enhancement factors of ∼102 at 532 and 633 nm are obtained using 4-mercaptobenzoic acid and 4-nitrobenzenethiol. Furthermore, the reductive coupling of 4-nitrobenzenethiol to 4,4'-dimercaptoazobenzene is observed on the surface of Mg nanoparticles under 532 nm excitation in the absence of reducing agents, indicating a plasmon-driven catalytic process. Once decorated with Pd, Mg nanostructures display an enhancement factor of 103 along with an increase in the rate of catalytic coupling. The results of this study demonstrate the successful application of plasmonic Mg nanoparticles in sensing and plasmon-enhanced catalysis.

Reuseable Fe3O4@PEI-DTC-Au@Ag magnetic nanocomposites: A versatile and sensitive SERS substrate for food safety assessment

A novel recyclable SERS substrate with magnetic manipulation capability and surface-enhanced Raman scattering (SERS) effect based on Fe3O4@PEI-DTC-Au@Ag (FPDAA) core-shell nanocomposites has been successfully prepared by engineered hydrothermal deposition and seed deposition techniques. The uniformity and SERS efficacy of these substrates, incorporating various Au@Ag core-shell nanocomposites with differing Ag shell thicknesses, were evaluated using 4-aminothiophenol (4-ATP) molecules. The optimal SERS substrate, Fe3O4@PEI-DTC-Au@Ag-3 (FPDAA-3), exhibited an enhancement factor (EF) of up to 1.121×106. This remarkable performance can be attributed to the synergistic effect between the magnetic plasmon of the Fe3O4 nanoparticles (NPs) core and the surface plasmonic resonance properties of Au@Ag core-shell nanocomposites, which create abundant interparticle hotspots within the FPDAA nanocomposites. Furthermore, the FPDAA-3 nanocomposite was employed as a SERS substrate for rapid thiram detection, achieving a minimum detectable concentration of 1×10−9 M. Notably, the relative standard deviation of SERS measurements from 50 randomly selected points was found to be less than 12.13 %, and the SERS spectra intensity showed minimal variation after 5 cycling tests, underscoring the excellent uniformity and recyclability of the FPDAA-3 substrate. The highly reusable and reliable FPDAA-3 nanocomposites enable direct on-site detection of thiram pesticide residues on fruit skins, thereby offering significant implications for food safety assessment and spectroscopic identification.

Optically controllable deformation and phase change in VO2/Si3N4/Au hybrid nanostructures with polarization selectivity

Optically spatial displacement and material modification hold great potential for the appealing applications in nanofabrication and reconfiguration of functional optical devices. Here, we propose and demonstrate a scheme to achieve simultaneous deformation and phase change in vanadium dioxide (VO2)/Si3N4/Au hybrid nanostructures by laser stimuli. Low triggering threshold and significant deformation characteristics of VO2, based on controllable phase transition, are demonstrated in microscale cantilevers. The plasmonic properties of the nanostructure array are further utilized to achieve a polarization-selective dynamic response. The persistence of deformation and dynamical optical modulation are further demonstrated. Such high-precision fabrication methods and non-contact reconfiguration methods are useful for future applications in dynamic optical manipulation.

Plasmonic magnesium arrays with nanosphere lithography

Magnesium is a rising alternative plasmonic metal that is potentially cheaper, more biocompatible, and less lossy in the ultraviolet-blue region of the visible spectrum than the commonly used gold and silver. Recent studies of colloidal magnesium nanoparticles demonstrated the plasmonic resonances of a variety of faceted shapes. However, applications such as refractive index sensing benefit from well-defined arrays, which have been developed for all other plasmonic metals. Here, we implement nanosphere lithography to fabricate metallic magnesium arrays that display attractive plasmonic properties. The deposition process was found to be highly vulnerable to oxidation, recrystallization, kinetic energy of the metal vapor, and substrate properties. The resulting structures obtained with 350, 500, and 750 nm hexagonally packed nanosphere masks exhibit the hallmark light–matter interactions of plasmonic metals, including strong extinction and resonance energy dependence on feature size, further securing Mg’s place as an alternative plasmonic metal.

Polydopamine-mediated facile Silver grown on ZnO Thin Films as High Performance SERS Substrates for R6G Detection

Surface-enhanced Raman spectroscopy (SERS) is a widely known technique that uses plasmonic structures (silver, gold, etc.) to detect low-concentration molecules. However, the limited number of metallic elements with plasmonic properties leads to limitations in their application. The qualitative detection method of SERS holds considerable promise in providing novel platforms for diverse applications, owing to its utilization of hybrid structures. Mussel-inspired polydopamine offers a promising avenue for the fabrication and integration of hybrid structures suitable for the SERS platform. Here, sputtered ZnO thin films were modified with Ag Nanostructures using polydopamine to fabricate a homogeneous Ag@ZnO hybrid high-performance SERS substrate. Ag/ZnO hybrid nanostructures were analyzed by FESEM and XRD to investigate their morphological and structural characterizations. SERS measurements were performed for all silver growth times to understand the effect of the silver growth process and hybrid structure synergy on SERS performance. The Ag@ZnO hybrid structure, cultivated with 24-hour silver growth, exhibited remarkable detectability even at an ultra-low R6G concentration of 10 pM

Janus Fe3O4-Au@Pt nanozymes based lateral flow assay for enhanced-sensitive colorimetric detection of influenza A virus

The traditional colloidal gold-based lateral flow assay (LFA) is widely applied in point-of-care testing (POCT) for pathogens. However, its disadvantage of low sensitivity greatly limits its effectiveness in early detection. In this work, we developed an enhanced-sensitive colorimetric nucleic acid lateral flow assay (NALFA) based on Janus Fe3O4-Au@Pt nanoparticles (Fe3O4-Au@Pt NPs) for H1N1 influenza virus detection. Dumbbell-like heterodimer Fe3O4-Au@Pt NPs were prepared by a seed-mediated method, and their unique Janus structure endowed them with both good plasmonic property and high peroxidase-like activity. With the Fe3O4-Au@Pt NPs as NALFA signal labels, qualitative detection was achieved by observing the color change with the naked eyes, and quantitative results were obtained by measuring the gray values on test strips. Due to the strong peroxidase-like activity of Fe3O4-Au@Pt NPs, they could quickly catalyze 3,3′,5,5′-tetramethylbenzidine (TMB) to oxidize to the dark blue chelate (oxTMB), thus resulting in greatly enhanced color on the strips. The limit of detection (LOD) of NALFA reached as low as 50 pM, which was 20-fold lower than that of before catalysis. Therefore, the constructed Janus Fe3O4-Au@Pt NPs could effectively improve the performance of traditional colloidal gold LFA and provide a potential tool for the development of sensitive sensing platforms.

Tuning Overbias Plasmon Energy and Intensity in Molecular Plasmonic Tunneling Junctions by Atomic Polarizability.

Plasmon excitation in molecular tunnel junctions is interesting because the plasmonic properties of the device can be, in principle, controlled by varying the chemical structure of the molecules. The plasmon energy of the excited plasmons usually follows the quantum cutoff law, but frequently overbias plasmon energy has been observed, which can be explained by quantum shot noise, multielectron processes, or hot carrier models. So far, clear correlations between molecular structure and the plasmon energy have not been reported. Here, we introduce halogenated molecules (HS(CH2)12X, with X = H, F, Cl, Br, or I) with polarizable terminal atoms as the tunnel barriers and demonstrate molecular control over both the excited plasmon intensity and energy for a given applied voltage. As the polarizability of the terminal atom increases, the tunnel barrier height decreases, resulting in an increase in the tunneling current and the plasmon intensity without changing the tunneling barrier width. We also show that the plasmon energy is controlled by the electrostatic potential drop at the molecule-electrode interface, which depends on the polarizability of the terminal atom and the metal electrode material (Ag, Au, or Pt). Our results give new insights in the relation between molecular structure, electronic structure of the molecular junction, and the plasmonic properties which are important for the development of molecular scale plasmonic-electronic devices.

Gold-Hydrogel Nanocomposites for High-Resolution Laser-Based 3D Printing of Scaffolds with SERS-Sensing Properties.

Although visible light-based stereolithography (SLA) represents an affordable technology for the rapid prototyping of 3D scaffolds for in vitro support of cells, its potential could be limited by the lack of functional photocurable biomaterials that can be SLA-structured at micrometric resolution. Even if innovative photocomposites showing biomimetic, bioactive, or biosensing properties have been engineered by loading inorganic particles into photopolymer matrices, main examples rely on UV-assisted extrusion-based low-resolution processes. Here, SLA-printable composites were obtained by mixing a polyethylene glycol diacrylate (PEGDA) hydrogel with multibranched gold nanoparticles (NPs). NPs were engineered to copolymerize with the PEGDA matrix by implementing a functionalization protocol involving covalent grafting of allylamine molecules that have C═C pendant moieties. The formulations of gold nanocomposites were tailored to achieve high-resolution fast prototyping of composite scaffolds via visible light-based SLA. Furthermore, it was demonstrated that, after mixing with a polymer and after laser structuring, gold NPs still retained their unique plasmonic properties and could be exploited for optical detection of analytes through surface-enhanced Raman spectroscopy (SERS). As a proof of concept, SERS-sensing performances of 3D printed plasmonic scaffolds were successfully demonstrated with a Raman probe molecule (e.g., 4-mercaptobenzoic acid) from the perspective of future extensions to real-time sensing of cell-specific markers released within cultures. Finally, biocompatibility tests preliminarily demonstrated that embedded NPs also played a key role by inducing physiological cell-cytoskeleton rearrangements, further confirming the potentialities of such hybrid nanocomposites as groundbreaking materials in laser-based bioprinting.

Engineering the Internal Structure of Hollow Nanostructures for Enhanced Plasmonic Properties

Engineering the Internal Structure of Hollow Nanostructures for Enhanced Plasmonic Properties

Plasmonic properties and stability of Au and Cu nanoparticles embedded in cerium oxide

With the aim of sensitizing cerium oxide—a very important catalytic material—to visible light, its coupling with Au and Cu nanoparticles is investigated. The samples are grown by physical synthesis by embedding a layer of nanoparticles between two cerium oxide films. The films are controlled in composition by in-situ x-ray photoemission spectroscopy and in morphology by ex-situ scanning electron microscopy. The optical properties as a function of the oxide thickness, investigated by spectrophotometry in the UV-Vis range, are interpreted based on the results of the morphological characterization and of simulations based on the Maxwell Garnett model. The stability of chemical and optical properties after air exposure is also investigated. The results, indicating that stable materials with tuneable optical properties can be obtained, are important in view of the potential application of the investigated systems in photocatalysis.

Nanoengineered plasmonics-enhanced photothermal tags for sensitive detection of cardiac biomarker troponin I using lateral flow immunoassay

In recent years, photothermal lateral flow immunoassay (LFIA) has gained widespread use as a point-of-care testing (POCT) technique because of its cost-effective portable instrumentation and easy-to-handle procedures. However, developing a highly sensitive photothermal LFIA platform with high photothermal efficiency remains challenging. In this study, we developed a portable smartphone-based plasmonics-enhanced photothermal LFIA (PPh-LFIA) platform to improve the photothermal LFIA sensitivity by engineering plasmonic-active gold nanostars (GNS) having large-sized sharp branches. We investigated the photothermal effect using various GNS engineered to have different sizes and spike lengths of GNSs (GNS-1, GNS-2, GNS-3, and GNS-4) in order to exhibit optimal plasmonics properties. The results showed that the GNS-3 having a broad plasmon band with a plasmon maximum band at 995 nm exhibited the strongest photothermal efficiency (80 %). As a proof-of demonstration, we have employed GNS-3 for the detection of the cardiac biomarker, troponin I (cTnI), used as the model system. The results show high sensitivity with a detection limit (LOD) of 5.5 pg/mL, which was around 1000 times more sensitive than traditional colorimetric LFIA based on gold nanospheres (GNSP). To verify the applicability of the PPh-LFIA platform, cTnI was spiked into human blood serum samples, enabling the detection of cTnI with an LOD of 6.7 pg/mL. Overall, this study offers insights for nanoengineering and fine-tuning the GNS morphology to increase the photothermal efficiency, consequently improving the PPh-LFIA detection sensitivity, which makes it suitable for use as a sensitive and portable POCT tool.

Synthesis and Characterization of Mesoporous Bismuth Nanopowders as a Stabilizer of 2‐Aminophenol under Ultraviolet Light

AbstractIn this paper, a mesoporous bismuth nanopowders (Bi‐NPWs) were synthesized by chemical method and used as photosbilizer agent. The formation and stability of Bi in the solution was monitored by UV‐Vis analysis, the results shows a strong plasmonic band near 270 nm, which confirms the reduction of bismuth ions to Bi0 in the aqueous phase.Also, after the precipitating process, the optical properties of Bi‐NPWs were measured with UV‐Vis spectroscopy, which showed an absorption peak around 290 and 470 nm, characteristic of the plasmonic response of Bi nanoparticles (Bi‐NPs). X‐ray diffraction (XRD) analysis have revealed a rhombohedral polycrystalline structure with a preferential orientation along the (012) plane for the Bi‐NPs. The surface states of the Bi‐NPs were evidenced by X‐ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR).The plasmonic properties the Bi‐NPWs was evaluated and exploited to photo‐stabilization of 2‐Aminophenol (2AP) in aqueous solutions under UV irradiation (365 nm). It was found that the Bi‐NPWs exhibited a remarkablephoto‐stabilization performance depending on the active surface.In the absence of Bi‐NPWs, a significant variation which increases to about (0.42 %) after 9 h of UV irradiation was noticed, with the presence of 6 and 45 Bi‐NPs the relative variation decreases to about (0.12 %) and to about 0.2 % respectively.

Nano-structured metamaterial absorber based on a plus-shaped resonator for optical wavelength applications

Metamaterial absorbers have sparked widespread interest due to their remarkable electromagnetic properties, which enable a wide range of applications in light absorption and manipulation. This study introduces a new three-layer nanomaterial absorber (NMA) unit cell composed of nickel (Ni), silicon dioxide (SiO2), and nickel (Ni) designed to operate across the entire visible spectrum (390–780 nm). We demonstrate the NMA’s exceptional absorption characteristics through rigorous numerical simulations using industry-standard software, achieving a mean absorption rate of 97.17% and a maximum absorption peak of 99.99% at 694.89 nm under standard angles. Furthermore, the NMA unit cell has good impedance matching, efficient coupling between capacitors and inductors, and significant plasmonic resonance properties. Fabrication feasibility and potential applications in solar energy harvesting, optical sensing, and light detection.

Synthesis of Au@Ag core-shell nanorods with tunable optical properties.

The synthesis of noble metal nanostructures with adjustable optical properties is essential due to their potential applications in various fields such as imaging, (bio) sensors, and catalysis. In this study, Au@Ag core-shell nanorods were synthesized with tunable optical properties. The synthesis process includes a two-stage approach: first, gold nanorods were synthesized through seed-mediated growth, and in the second stage, these gold nanorods were used as seeds to synthesize Au@Ag core-shell nanorods through the silver deposition process. Tunable core-shell nanorods were produced by changing the concentration of silver ions, reducing agent, stabilizing agent, seeds, and buffer as well as pH and the reaction time. Transmission electron microscopy (TEM) images demonstrated the formation of the Au@Ag core-shell nanorod structure. In addition, UV-visible spectroscopy revealed the peak height and its shift towards shorter wavelengths, demonstrating the tunable optical properties of the synthesized nanorods. Overall, in this study, we demonstrated the synthesis of Au@Ag core-shell nanorods with adjustable plasmonic optical properties that could be changed by precisely controlling the thickness of the silver shell on the surface of the gold core.&#xD.

Structure of plasmonic multi spectral Apta sensor and analyzing of bulk and surface sensitivity

In this work, a multispectral aptasensor structure, including a sub-layer and two side walls, was presented. The cells are positioned at the down and top of the structure, with the down cells oriented perpendicular to the walls and the top cells aligned parallel to the walls. The validity of the findings was verified by the utilization of a numerical simulation technique known as 3D Finite Difference Time Domain (FDTD). The biosensor under consideration exhibits sensitivities of 1093.7 nm/RIU, 754 nm/RIU, and 707.43 nm/RIU in mode III, mode II, and mode I, respectively. In the majority of instances, the quantity of analyte available is insufficient to coat the surface of the sensor thoroughly. Consequently, in this study, the evaluation of surface sensitivity was undertaken alongside bulk sensitivity. The surface sensitivity of the suggested structure for mode II in the sensor layer, with thicknesses of 10, 20, 30, and 70 nm, is measured to be 25, 78, 344, and 717.636 nm/RIU, respectively. Our design incorporates a unique arrangement of sub-layer and side walls, with cells positioned to maximize interaction with the target analyte. This innovative configuration, combined with Ag for its superior plasmonic properties, enables the detection of E. coli O157 with remarkable sensitivity.

Enhanced Molecular Interaction of 3D Plasmonic Nanoporous Gold Alloys by Electronic Modulation for Sensitive Molecular Detection.

Three-dimensional gold and its alloyed nanoporous structures possess high surface areas and strong local electric fields, rendering them ideal substrates for plasmonic molecular detection. Despite enhancing plasmonic properties and altering molecular interactions, the effect of alloy composition on molecular detection capability has not yet been explored. Here, we report molecular interactions between nanoporous gold alloys and charged molecules by controlling the alloy composition. We demonstrate enhanced adsorption of negatively charged molecules onto the alloy surface due to positively charged gold atoms and a shifted d-band center through charge transfer between gold and other metals. Despite similar EM field intensities, nanoporous gold with silver (Au/Ag) achieves SERS enhancement factors (EF) up to 6 orders of magnitude higher than those of other alloys for negatively charged molecules. Finally, nanoporous Au/Ag detects amyloid-beta at concentrations as low as approximately 1 fM, with SERS EF up to 10 orders of magnitude higher than that of a monolayer of Au nanoparticles.

Hyperbolic response and low-frequency ultra-flat plasmons in inhomogeneous charge-distributed transition-metal monohalides.

Plasmon, the collective oscillations of free electron gas in materials, determines the long-wavelength excitation spectrum and optical response, are pivotal in the realm of nanophotonics and optoelectronics. In this study, using the first-principles calculations, we systematically investigated the dielectric response and plasmon properties of bulk transition-metal monohalides MXs (M = Zr, Mo; X = Cl, F). Due to the strong electronic anisotropy, MXs exhibit a broadband type-II hyperbolic response and direction-dependent plasmon modes. Particularly, local field effect (LFE) driven by the charge distribution inhomogeneity, significantly modifies the optical response and excitation spectra in MX along the out-of-plane direction. Taking into account LFE, the energy dissipation along the out-of-plane direction is almost completely suppressed, and an ultra-flat and long-lived plasmon mode with a slow group velocity is introduced. This finding reveals the role of charge density in modifying the optical response and excitation behavior, shedding light on potential applications in plasmonics.

Physical Modifications of Kombucha‐Derived Bacterial Nanocellulose: Toward a Functional Bionanocomposite Platform

AbstractSustainable functionalization of bacterial cellulose for cost‐effective bionanocomposites with desired properties has received growing attention in recent years. This article presents the results of work aimed at obtaining bionanocomposite materials based on bacterial cellulose, a natural and eco‐friendly material. Bacterial cellulose obtained from the Kombucha symbiotic culture of bacteria and yeast (SCOBY) fermentation process is functionalized by embedding with diatom frustules, silver nanoparticles (AgNPs), and poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS). The effects of functionalization on mechanical, optical, plasmonic, electrical, chemiluminescent, and antimicrobial properties are evaluated. Morphological characteristics of the nanocomposites are studied using electron microscopy. Addition of diatom frustules introduced into the SCOBY culture media results in bionanocomposite materials with enhanced tensile strength and increased ultraviolet (UV) blockage properties. In situ functionalization of bacterial cellulose with AgNPs tunes plasmonic and chemiluminescent properties, revealing the biosensing potential of the material. Modified bacterial cellulose shows antimicrobial activity in experiments with gram‐positive and gram‐negative bacteria. Dual functionalization of bacterial cellulose with PEDOT:PSS and AgNPs results in improved electrical conductivity of the bionanocomposite. Overall, bottom‐up physical functionalization approaches and the resulting bionanocomposite materials will open up new opportunities for the low‐cost production of green materials and contribute to the development of a sustainable economy.

Multishaped bio-gold polyphenols bearing nanoparticles to promote inflammatory suppression

Green synthesis from plant waste involves the generation of functional nanoparticles (NPs), offering significant potential for a wide range of applications. Numerous studies have focused on the use of plant extracts to produce AuNPs suitable for various applications in the medical field, particularly in photothermal therapy and cancer therapy, owing to their plasmonic properties. Moreover, NP-mediated immunostimulation and immunosuppression is an intriguing field of research, focusing on how manipulation of NP physicochemical properties can influence their inter-action with immune cells and immune modulation. However, to date, few investigations have been conducted on the modulation of the inflammatory response mediated by green-synthesized nanostructures. To this aim, we synthesized AuNPs using extracts of Laurus nobilis, which exhibit high crystallinity and are inherently coated by a dense network of polyphenols, thus maintaining stability on their surface through the green synthesis approach. Then, in order to explore how these green-synthesized nanostructures can enhance or suppress the inflammatory cellular responses, we investigated the response of free polyphenols and AuNPs@polyphenols in murine bone marrow derived dendritic cells (BMDCs), by means of morphomechanical analysis and biochemical assays. Our findings demonstrated that DCs exposed to both free polyphenol extract and AuNPs@polyphenols were able to inhibit the secretion of crucial inflammatory mediators in response to lipopolysaccharide (LPS) administration. Therefore, polyphenols immobilized on Au surface were more effective in the inflammation suppression. These evidence paving the way for a powerful strategy to develop edible anti-inflammatory adjuvants, overcoming the limitations associated with the use of free polyphenols in clinical practice.

Reduced-Dimensionality Al Nanocrystals: Nanowires, Nanobars, and Nanomoustaches.

Aluminum nanocrystals created by catalyst-driven colloidal synthesis support excellent plasmonic properties, due to their high level of elemental purity, monocrystallinity, and controlled size and shape. Reduction in the rate of nanocrystal growth enables the synthesis of highly anisotropic Al nanowires, nanobars, and singly twinned "nanomoustaches". Electron energy loss spectroscopy was used to study the plasmonic properties of these nanocrystals, spanning the broad energy range needed to map their plasmonic modes. The coupling between these nanocrystals and other plasmonic metal nanostructures, specifically Ag nanocubes and Au films of controlled nanoscale thickness, was investigated. Al nanocrystals show excellent long-term stability under atmospheric conditions, providing a practical alternative to coinage metal-based nanowires in assembled nanoscale devices.