Localized surface plasmon resonance and atomic force microscopy study of model lipid membranes and their interactions with amyloid and melatonin

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by the accumulation of amyloid plaques in the brain. The toxicity of amyloid to neuronal cell surfaces arises from interactions between small intermediate aggregates, namely amyloid oligomers, and the cell membrane. The nature of these interactions changes with age and disease progression. In our previous work, we demonstrated that both membrane composition and nanoscale structure play crucial roles in amyloid-membrane interactions. In our previous work, we demonstrated that both membrane composition and nanoscale structure play crucial roles in amyloid toxicity, and that membrane models mimicking healthy neuron were less affected by amyloid than model membranes mimicking AD neuronal membranes. This understanding introduces the possibility of modifying membrane properties with membrane-active molecules, such as melatonin, to protect them from amyloid-induced damage. In the present study, we employed atomic force microscopy (AFM) and localized surface plasmon resonance (LSPR) to investigate the protective effects of melatonin. We utilized synthetic lipid membranes that mimic the neuronal cellular membrane at various stages of AD and explored their interactions with amyloid-β (1-42) in the presence of melatonin. Our findings reveal that the early diseased membrane model is particularly vulnerable to amyloid binding and subsequent damage. However, melatonin exerts its most potent protective effect on this early-stage membrane. These results suggest that melatonin could act at the membrane level to alleviate amyloid toxicity, offering the most protection during the initial stages of AD.

Concurrent Mechanisms of Hot Electrons and Interfacial Water Molecule Ordering in Plasmon-Enhanced Nitrogen Fixation

The participation of high-energy hot electrons generated from the non-radiative decay of localized surface plasmons is an important mechanism for promoting catalytic processes. Herein, another vital mechanism associated with the localized surface plasmon resonance (LSPR) effect, significantly contributing to the nitrogen reduction reaction (NRR), is found. That is to say, the LSPR-induced strong localized electric fields can weaken the intermolecular hydrogen bonds and regulate the arrangement of water molecules at the solid-liquid interface. The AuCu pentacle nanoparticles with excellent light absorption ability and the capability to generate strong localized electric fields are chosen to demonstrate this effect. The in situ Raman spectra and theoretical calculations are employed to verify the mechanism at the molecular scale in a nitrogen fixation process. Meanwhile, due to the promoted electron transfer at the interface by the well-ordered interfacial water, as well as the participation of high-energy hot electrons, the optimal catalyst exhibits excellent performance with an NH3 yield of 52.09 µg h-1 cm-2 and Faradaic efficiency (FE) of 45.82% at ─0.20 V versus RHE. The results are significant for understanding the LSPR effect in catalysis and provide a new approach for regulating the reaction process.

Localized Surface Plasmon Resonance-Enhanced Photocatalytic Antibacterial of In-situ Sprayed 0D/2D Heterojunction Composite Hydrogel for Treating Diabetic Wound

Chronic diabetic wounds pose significant challenges due to uncontrolled bacterial infections, prolonged inflammation, and impaired angiogenesis. The rapid advancement of photo-responsive antibacterial therapy showed promise in addressing these complex issues, particularly utilizing 2D heterojunction materials, which offer unique properties. Herein, we designed an in situ sprayed Bi/BiOCl 0D/2D heterojunction composite fibrin gel with the characteristics of rapid formation and effective near-infrared activation for the treatment of non-healing diabetes-infected wounds. The sprayed composite gel can provide protective shielding for skin tissues and promote endothelial cell proliferation, vascularization, and angiogenesis. The Bi/BiOCl 0D/2D heterojunction, with its localized surface plasmon resonance (LSPR), can overcome the wide bandgap limitation of BiOCl, enhancing the generation of local heat and reactive oxygen species under near-infrared irradiation. This facilitated bacterial elimination and reduced inflammation, supporting the accelerated healing of diabetes-infected wounds. Our study underscores the potential of LSPR-enhanced heterojunctions as advanced wound therapies for chronic diabetic wounds. This article is protected by copyright. All rights reserved.

Programming Intracellular Clustering of Spiky Nanoparticles via Liposome Encapsulation

The intracellular clustering of anisotropic nanoparticles is crucial to the improvement of the localized surface plasmon resonance (LSPR) for phototherapy applications. Herein, we programmed the intracellular clustering process of spiky nanoparticles (SNPs) by encapsulating them into an anionic liposome via a frame-guided self-assembly approach. The liposome-encapsulated SNPs (lipo-SNPs) exhibited distinct and enhanced lysosome-triggered aggregation behavior while maintaining excellent monodispersity, even in acidic or protein-rich environments. We explored the enhancement of the photothermal therapy performance for SNPs as a proof of concept. The photothermal conversion efficiency of lipo-SNPs clusters significantly increased 15 times compared to that of single lipo-SNPs. Upon accumulation in lysosomes with a 2.4-fold increase in clustering, lipo-SNPs resulted in an increase in cell-killing efficiency to 45% from 12% at 24 μg/mL. These findings indicated that liposome encapsulation provides a promising approach to programing nanoparticle clustering at the target site, which facilitates advances in the development of smart nanomedicine with programmable enhancement in LSPR.

Boosting the Efficiency of High-Resolution Quantum Dot Light-Emitting Devices Based on Localized Surface Plasmon Resonance

With pixel miniaturization, the performance of high-resolution quantum dot light-emitting diodes (QLEDs) usually degrades. Considering the dimension of ultrasmall pixels, herein, a barrier architecture based on localized surface plasmon resonance (LSPR) that promotes the radiative recombination of neighboring quantum dots is rationally designed to improve the device performance. Au nanoparticles (NPs) are embedded in an insulating polymer to form a honeycomb-patterned barrier layer via the nanoimprint process. Each pixel fabricated in the void area (average diameter of 1.5 μm) of the barrier layer is surrounded by a number of LSPR-NPs to enhance the luminescence. The resultant green QLEDs with a resolution of 9027 pixels per inch show a maximum external quantum efficiency of 11.1%, a 42.8% enhancement compared to the control device. Additionally, the lifetime of high-resolution QLEDs is obviously improved by the LSPR effect.

Metal Films on Two-Dimensional Materials: van der Waals Contacts and Raman Enhancement

Electronic devices based on two-dimensional (2D) materials will need ultraclean and defect-free van der Waals (vdW) contacts with three-dimensional (3D) metals. It is therefore important to understand how vdW metal films deposit on 2D surfaces. Here, we study the growth and nucleation of vdW metal films of indium (In) and non-vdW metal films of gold (Au), deposited on 2D MoS2 and graphene. In follows a 2D growth mode in contrast to Au that follows a 3D growth mode. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to image the morphology of metal clusters during growth and quantify the nucleation density. As compared to Au, In atoms exhibit nearly 50 times higher diffusivity (3.65 × 10-6 μm-2 s-1) and half the nucleation density (64.9 ± 2.46 μm-2), leading to larger grain sizes (∼60 nm for 5 nm In on monolayer MoS2). The grain size of In can be further increased by reducing the 2D surface roughness, while the grain size for Au is limited by its high nucleation density due to the creation of interface defects during deposition. The vdW gap between In and MoS2 and graphene leads to strong enhancement (>103) in their Raman signal intensity due to localized surface plasmon resonance. In the absence of a vdW gap, the plasmon-mediated enhancement in Raman does not occur.

Determining Transmission Characteristics from Shot-Noise-Driven Electroluminescence in Single-Molecule Junctions

Biased metal-molecule-metal junctions emit light through electroluminescence, a phenomenon at the intersection of molecular electronics and nanoplasmonics. This can occur when the junction plasmon mode is excited by inelastic electron current fluctuations. Here, we simultaneously measure the conductance and electroluminescence intensity from single-molecule junctions with time resolution in a solution environment at room temperature. We use current versus bias data to determine the molecular junction transport parameters and then relate these to the expected current shot noise. We find that the electroluminescence signal accurately matches the theoretical prediction of shot-noise-driven emission in a large fraction of the molecular junctions studied. This introduces a novel experimental method for qualitatively estimating finite-frequency shot noise in single-molecule junctions under ambient conditions. We further demonstrate that electroluminescence can be used to obtain the level alignment of the frontier orbital dominating transport in the molecular junction.

Spatially Uniform and Quantitative Surface-Enhanced Raman Scattering under Modal Ultrastrong Coupling Beyond Nanostructure Homogeneity Limits

We developed a substrate that enables highly sensitive and spatially uniform surface-enhanced Raman scattering (SERS). This substrate comprises densely packed gold nanoparticles (d-AuNPs)/titanium dioxide/Au film (d-ATA). The d-ATA substrate demonstrates modal ultrastrong coupling between localized surface plasmon resonances (LSPRs) of AuNPs and Fabry-Pérot nanocavities. d-ATA exhibits a significant enhancement of the near-field intensity, resulting in a 78-fold increase in the SERS signal for crystal violet (CV) compared to that of d-AuNP/TiO2 substrates. Importantly, high sensitivity and a spatially uniform signal intensity can be obtained without precise control of the shape and arrangement of the nanoscale AuNPs, enabling quantitative SERS measurements. Additionally, SERS measurements of rhodamine 6G (R6G) on this substrate under ultralow adsorption conditions (0.6 R6G molecules/AuNP) show a spatial variation in the signal intensity within 3%. These findings suggest that the SERS signal under modal ultrastrong coupling originates from multiple plasmonic particles with quantum coherence.

Light Absorption Analysis and Optimization of Ag@TiO2 Core-Shell Nanospheroid and Nanorod

For photothermal therapy of cancer, it is necessary to find Ag @TiO2 core-shell nanoparticles that can freely tune the resonance wavelength within the near-infrared biological window. In this paper, the finite element method and the size-dependent refractive index of metal nanoparticles were used to theoretically investigate the effects of the core material, core length, core aspect ratio, shell thickness, refractive index of the surrounding medium, and the particle orientation on the light absorption properties of Ag@TiO2 core-shell nanospheroid and nanorod. The calculations show that the position and intensity of the light absorption resonance peaks can be freely tuned within the first and second biological windows by changing the above-mentioned parameters. Two laser wavelengths commonly used in photothermal therapy, 808 nm (first biological window) and 1064 nm (second biological window), were selected to optimize the core length and aspect ratio of Ag@TiO2 core-shell nanospheroid and nanorod. It was found that the optimized Ag@TiO2 core-shell nanospheroid has a stronger light absorption capacity at the laser wavelengths of 808 nm and 1064 nm. The optimized Ag@TiO2 core-shell nanoparticles can be used as ideal therapeutic agents in photothermal therapy.

Recent Advances in the 3D Chiral Plasmonic Nanomaterials

From the view of geometry, chirality is that an object cannot overlap with its mirror image, which has been a fundamental scientific problem in biology and chemistry since the 19th century. Chiral inorganic nanomaterials serve as ideal templates for investigating chiral transfer and amplification mechanisms between molecule and bulk materials, garnering widespread attentions. The chiroptical property of chiral plasmonic nanomaterials is enhanced through localized surface plasmon resonance effects, which exhibits distinctive circular dichroism (CD) response across a wide wavelength range. Recently, 3D chiral plasmonic nanomaterials are becoming a focal research point due to their unique characteristics and planar-independence. This review provides an overview of recent progresses in 3D chiral plasmonic nanomaterials studies. It begins by discussing the mechanisms of plasmonic enhancement of molecular CD response, following by a detailed presentation of novel classifications of 3D chiral plasmonic nanomaterials. Finally, the applications of 3D chiral nanomaterials such as biology, sensing, chiral catalysis, photology, and other fields have been discussed and prospected. It is hoped that this review will contribute to the flourishing development of 3D chiral nanomaterials.

High-Throughput Synthesis of Nanogap-Rich Gold Nanoshells Using Dual-Channel Infusion System

Gold nanoshells have been actively applied in industries beyond the research stage because of their unique optical properties. Although numerous methods have been reported for gold nanoshell synthesis, the labor-intensive and time-consuming production process is an issue that must be overcome to meet industrial demands. To resolve this, we report a high-throughput synthesis method for nanogap-rich gold nanoshells based on a core silica support (denoted as SiO2@Au NS), affording a 50-fold increase in scale by combining it with a dual-channel infusion pump system. By continuously dropping the reactant solution through the pump, nanoshells with closely packed Au nanoparticles were prepared without interparticle aggregation. The thickness of the gold nanoshells was precisely controlled at 2.3-17.2 nm by regulating the volume of the reactant solution added dropwise. Depending on the shell thickness, the plasmonic characteristics of SiO2@Au NS prepared by the proposed method could be tuned. Moreover, SiO2@Au NS exhibited surface-enhanced Raman scattering activity comparable to that of gold nanoshells prepared by a previously reported low-throughput method at the same reactant ratio. The results indicate that the proposed high-throughput synthesis method involving the use of a dual-channel infusion system will contribute to improving the productivity of SiO2@Au NS with tunable plasmonic characteristics.

Wavelength Tunable Infrared Perfect Absorption in Plasmonic Nanocrystal Monolayers

The ability to efficiently absorb light in ultrathin (subwavelength) layers is essential for modern electro-optic devices, including detectors, sensors, and nonlinear modulators. Tailoring these ultrathin films' spectral, spatial, and polarimetric properties is highly desirable for many, if not all, of the above applications. Doing so, however, often requires costly lithographic techniques or exotic materials, limiting scalability. Here we propose, demonstrate, and analyze a mid-infrared absorber architecture leveraging monolayer films of nanoplasmonic colloidal tin-doped indium oxide nanocrystals (ITO NCs). We fabricate a series of ITO NC monolayer films using the liquid-air interface method; by synthetically varying the Sn dopant concentration in the NCs, we achieve spectrally selective perfect absorption tunable between wavelengths of two and five micrometers. We achieve monolayer thickness-controlled coupling strength tuning by varying NC size, allowing access to different coupling regimes. Furthermore, we synthesize a bilayer film that enables broadband absorption covering the entire midwave IR region (λ = 3-5 μm). We demonstrate a scalable platform, with perfect absorption in monolayer films only hundredths of a wavelength in thickness, enabling strong light-matter interaction, with potential applications for molecular detection and ultrafast nonlinear optical applications.

Deciphering the Mechanisms of Photo-Enhanced Catalytic Activities in Plasmonic Pd-Au Heteromeric Nanozymes for Colorimetric Analysis

The growing demand for highly active nanozymes in various fields has led to the development of several strategies to enhance their activity. Plasmonic enhancement, a strategy used in heterogenous catalysis, represents a promising strategy to boost the activity of nanozymes. Herein, Pd-Au heteromeric nanoparticles (Pd-Au dimers) with well-defined heterointerfaces have been explored as plasmonic nanozymes. As a model system, the Pd-Au dimers with integrated peroxidase (POD)-like activity and plasmonic activity are used to investigate the effect of plasmons on enhancing the activity of nanozymes under visible light irradiation. Mechanistic studies revealed that the generation of hot electron-hole pairs plays a dominant role in plasmonic effect, and it greatly enhances the decomposition of H2 O2 to the reactive oxygen species (ROS) intermediates (•OH, •O2 - and 1 O2 ), leading to elevated POD-like activity of the Pd-Au dimers. Finally, the Pd-Au dimers are applied in the plasmon-enhanced colorimetric method for the detection of alkaline phosphatase, exhibiting broad linear range and low detection limit. This study not only provides a straightforward approach for regulating nanozyme activity through plasmonic heterostructures but also sheds light on the mechanism of plasmon-enhanced catalysis of nanozymes.

Development of Liquid-Phase Plasmonic Sensor Platforms for Prospective Biomedical Applications

Localized Surface Plasmon Resonance (LSPR) is an optical method for detecting changes in refractive index by the interaction between incident light and delocalized electrons within specific metal thin films' localized "hot spots". LSPR-based sensors possess advantages, including their compact size, enhanced sensitivity, cost-effectiveness, and suitability for point-of-care applications. This research focuses on the development of LSPR-based nanohole arrays (NHAs) as a platform for monitoring probe/target binding events in real time without labeling, for low-level biomolecular target detection in biomedical diagnostics. To achieve this objective, this study involves creating a liquid-phase setup for capturing target molecules. Finite-difference time-domain simulations revealed that a 75 nm thickness of gold (Au) is ideal for NHA structures, which were visually examined using scanning electron microscopy. To illustrate the functionality of the liquid-phase sensor, a PDMS microfluidic channel was fabricated using a 3D-printed mold with a glass slide base and a top glass cover slip, enabling reflectance-mode measurements from each of four device sectors. This study shows the design, fabrication, and assessment of NHA-based LSPR sensor platforms within a PDMS microfluidic channel, confirming the sensor's functionality and reproducibility in a liquid-phase environment.

Manipulating Coupled Field Enhancement in Slot-under-Groove Nanoarrays for Universal Surface-Enhanced Raman Scattering

Surface-enhanced Raman scattering (SERS) is an ultrasensitive spectroscopic technique that can identify materials and chemicals based on their inelastic light-scattering properties. In general, SERS relies on sub-10 nm nanogaps to amplify the Raman signals and achieve ultralow-concentration identification of analytes. However, large-sized analytes, such as proteins and viruses, usually cannot enter these tiny nanogaps, limiting the practical applications of SERS. Herein, we demonstrate a universal SERS platform for the reliable and sensitive identification of a wide range of analytes. The key to this success is the prepared "slot-under-groove" nanoarchitecture arrays, which could realize a strongly coupled field enhancement with a large spatial mode distribution via the hybridization of gap-surface plasmons in the upper V-groove and localized surface plasmon resonance in the lower slot. Therefore, our slot-under-groove platform can simultaneously deliver high sensitivity for small-sized analytes and the identification of large-sized analytes with a large Raman gain.

Structural Control of Plasmon Resonance in Molecularly Linked Metal Oxide Nanocrystal Gel Assemblies

Nanocrystal gels exhibit collective optical phenomena based on interactions among their constituent building blocks. However, their inherently disordered structures have made it challenging to understand, predict, or design properties such as optical absorption spectra that are sensitive to the coupling between the plasmon resonances of the individual nanocrystals. Here, we bring indium tin oxide nanocrystal gels under chemical control and show that their infrared absorption can be predicted and systematically tuned by selecting the nanocrystal sizes and compositions and molecular structures of the link-mediating surface ligands. Thermoreversible assemblies with metal-terpyridine links form reproducible gel architectures, enabling us to derive a plasmon ruler that governs the spectral shifts upon gelation, predicated on the nanocrystal and ligand compositions. This empirical guide is validated using large-scale, many-bodied simulations to compute the optical spectra of gels with varied structural parameters. Based on the derived plasmon ruler, we design and demonstrate a nanocrystal mixture whose spectrum exhibits distinctive line narrowing upon assembly.

Tuning Chemical Interface Damping: Competition between Surface Damping Pathways in Amalgamated Gold Nanorods Coated with Mesoporous Silica Shells

The mechanism of mercury (Hg) amalgamation in gold nanorods coated with a mesoporous silica shell (AuNRs@mSiO2) and the effect of chemical treatments on the localized surface plasmon resonance (LSPR) spectral changes in single amalgamated AuNRs@mSiO2 remains unclear. In this study, we investigated Hg amalgamation and inward Hg diffusion in single AuNRs@mSiO2 without structural deformation via dark-field scattering spectroscopy and X-ray photoelectron spectroscopy. Then, we investigated the chemisorption of thiol molecules on single amalgamated AuNRs@Hg-mSiO2. Unlike previous studies on single AuNRs, the thiolation on single AuNRs@Hg-mSiO2 resulted in a redshift and line width narrowing of the LSPR peak within 1 h. To determine the chemical effect, we investigated the competition between two surface damping pathways: metal interface damping (MID) and chemical interface damping (CID). When we exposed amalgamated AuNRs@Hg-mSiO2 to 1-alkanethiols with three different carbon chain lengths for 1 h, we observed an increase in the line width broadening with longer chain lengths owing to enhanced CID, demonstrating the tunability of CID and LSPR properties upon chemical treatments. We also investigated the competition between the two surface damping pathways as a function of the time-dependent Au-Hg surface properties in AuNRs@Hg-mSiO2. The 24-h Hg treatment resulted in increased line width broadening compared to the 1-h treatment for the same thiols, which was attributed to the predominance of CID. This was in contrast to the predominance of MID under the 1-h treatment, which formed a core-shell structure. Therefore, this study provides new insights into the Hg amalgamation process, the effect of chemical treatments, competition between surface decay pathways, and LSPR control in AuNRs@mSiO2.

Plasmonic Nanoparticle-Enhanced Optical Techniques for Cancer Biomarker Sensing

This review summarizes recent advances in leveraging localized surface plasmon resonance (LSPR) nanotechnology for sensitive cancer biomarker detection. LSPR arising from noble metal nanoparticles under light excitation enables the enhancement of various optical techniques, including surface-enhanced Raman spectroscopy (SERS), dark-field microscopy (DFM), photothermal imaging, and photoacoustic imaging. Nanoparticle engineering strategies are discussed to optimize LSPR for maximum signal amplification. SERS utilizes electromagnetic enhancement from plasmonic nanostructures to boost inherently weak Raman signals, enabling single-molecule sensitivity for detecting proteins, nucleic acids, and exosomes. DFM visualizes LSPR nanoparticles based on scattered light color, allowing for the ultrasensitive detection of cancer cells, microRNAs, and proteins. Photothermal imaging employs LSPR nanoparticles as contrast agents that convert light to heat, producing thermal images that highlight cancerous tissues. Photoacoustic imaging detects ultrasonic waves generated by LSPR nanoparticle photothermal expansion for deep-tissue imaging. The multiplexing capabilities of LSPR techniques and integration with microfluidics and point-of-care devices are reviewed. Remaining challenges, such as toxicity, standardization, and clinical sample analysis, are examined. Overall, LSPR nanotechnology shows tremendous potential for advancing cancer screening, diagnosis, and treatment monitoring through the integration of nanoparticle engineering, optical techniques, and microscale device platforms.

An Investigation on the Use of Au@SiO2@Au Nanomatryoshkas as Gap-Enhanced Raman Tags

Gap-enhanced Raman tags are a new type of optical probe that have wide applications in sensing and detection. A gap-enhanced Raman tag is prepared by embedding Raman molecules inside a gap between two plasmonic metals such as an Au core and Au shell. Even though placing Raman molecules beneath an Au shell seems counter-intuitive, it has been shown that such systems produce a stronger surface-enhanced Raman scattering response due to the strong electric field inside the gap. While the theoretical support of the stronger electric field inside the gap was provided in the literature, a comprehensive understanding of how the electric field inside the gap compares with that of the outer surface of the particle was not readily available. We investigated Au@SiO2@Au nanoparticles with diameters ranging from 35 nm to 70 nm with varying shell (2.5-10 nm) and gap (2.5-15 nm) thicknesses and obtained both far-field and near-field spectra. The extinction spectra from these particles always have two peaks. The low-energy peak redshifts with the decreasing shell thickness. However, when the gap thickness decreases, the low-energy peaks first blueshift and then redshift, producing a C-shape in the peak position. For every system we investigated, the near-field enhancement spectra were stronger inside the gap than on the outer surface of the nanoparticle. We find that a thin shell combined with a thin gap will produce the greatest near-field enhancement inside the gap. Our work fills the knowledge gap between the exciting potential applications of gap-enhanced Raman tags and the fundamental knowledge of enhancement provided by the gap.

High Freshwater Flux Solar Desalination via a 3D Plasmonic Evaporator with an Efficient Heat-Mass Evaporation Interface

Passive solar desalination with interfacial heating is a promising technique to utilize solar energy to convert seawater into fresh water through evaporation and condensation. However, the current freshwater flux of solar desalination is much below industrial requirements (> 20 L m-2  h-1 ). Herein, it is demonstrated that a 3D plasmonic evaporator with an efficient heat-mass evaporation interface (HM-EI) achieves a freshwater flux of 29.1 L m-2  h-1 for 3.5 wt.% NaCl, which surpasses the previous solar evaporators and approaches the level of reverse osmosis (the highest installed capacity in industrial seawater desalination technology). The realization of high freshwater flux solar desalination comes from the efficient HM-EI comprising a grid-like plasmonic macrostructure for enhanced energy utilization in heat properties and a large-pore microstructure for accelerated ion transport in mass properties. This work provides a new direction for designing next-generation solar evaporators with high freshwater flux for industrial requirements.

Facile and Low-Cost Fabrication of SiO2-Covered Au Nanoislands for Combined Plasmonic Enhanced Fluorescence Microscopy and SERS

An easy and low-cost way to fabricate monometallic Au nanoislands for plasmonic enhanced spectroscopy is presented. The method is based on direct thermal evaporation of Au on glass substrates to form nanoislands, with thicknesses between 2 and 15 nm, which are subsequently covered by a thin layer of silicon dioxide. We have used HR-SEM and AFM to characterize the nanoislands, and their optical transmission reveals strong plasmon resonances in the visible. The plasmonic performance of the fabricated substrates has been tested in fluorescence and Raman scattering measurements of two probe materials. Enhancement factors up to 1.8 and 9×104 are reported for confocal fluorescence and Raman microscopies, respectively, which are comparable to others obtained by more elaborated fabrication procedures.

Plasmon-Enhanced Perovskite Solar Cells Based on Inkjet-Printed Au Nanoparticles Embedded into TiO2 Microdot Arrays

The exceptional property of plasmonic materials to localize light into sub-wavelength regimes has significant importance in various applications, especially in photovoltaics. In this study, we report the localized surface plasmon-enhanced perovskite solar cell (PSC) performance of plasmonic gold nanoparticles (AuNPs) embedded into a titanium oxide (TiO2) microdot array (MDA), which was deposited using the inkjet printing technique. The X-ray (XRD) analysis of MAPI (methyl ammonium lead iodide) perovskite films deposited on glass substrates with and without MDA revealed no destructive effect of MDA on the perovskite structure. Moreover, a 12% increase in the crystallite size of perovskite with MDA was registered. Scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HR-TEM) techniques revealed the morphology of the TiO2_MDA and TiO2-AuNPs_MDA. The finite-difference time-domain (FDTD) simulation was employed to evaluate the absorption cross-sections and local field enhancement of AuNPs in the TiO2 and TiO2/MAPI surrounding media. Reflectance UV-Vis spectra of the samples comprising glass/TiO2 ETL/TiO2_MDA (ETL-an electron transport layer) with and without AuNPs in TiO2_MDA were studied, and the band gap (Eg) values of MAPI have been calculated using the Kubelka-Munk equation. The MDA introduction did not influence the band gap value, which remained at ~1.6 eV for all the samples. The photovoltaic performance of the fabricated PSC with and without MDA and the corresponding key parameters of the solar cells have also been studied and discussed in detail. The findings indicated a significant power conversion efficiency improvement of over 47% in the PSCs with the introduction of the TiO2-AuNPs_MDA on the ETL/MAPI interface compared to the reference device. Our study demonstrates the significant enhancement achieved in halide PSC by utilizing AuNPs within a TiO2_MDA. This approach holds great promise for advancing the efficiency and performance of photovoltaic devices.

Dipolar Ligands Tune Plasmonic Properties of Tin-Doped Indium Oxide Nanocrystals

Surface functionalization with dipolar molecules is known to tune the electronic band alignment in semiconductor films and colloidal quantum dots. Yet, the influence of surface modification on plasmonic nanocrystals and their properties remains little explored. Here, we functionalize tin-doped indium oxide nanocrystals (ITO NCs) via ligand exchange with a series of cinnamic acids with different electron-withdrawing and -donating dipolar characters. Consistent with previous reports on semiconductors, we find that withdrawing (donating) ligands increase (decrease) the work function caused by an electrostatic potential shift across the molecular layer. Quantitative analyses of the plasmonic extinction spectra reveal that varying the ligand molecular dipole affects the near-surface depletion layer, with an anticorrelated trend between the electron concentration and electronic volume fraction, factors that are positively correlated in as-synthesized NCs. Electronic structure engineering through surface modification provides access to distinctive combinations of plasmonic properties that could enable optoelectronic applications, sensing, and hot electron-driven processes.

Hybrid Metal-Ligand Interfacial Dipole Engineering of Functional Plasmonic Nanostructures for Extraordinary Responses of Optoelectronic Properties

Programmable manipulation of inorganic-organic interfacial electronic properties of ligand-functionalized plasmonic nanoparticles (NPs) is the key parameter dictating their applications such as catalysis, photovoltaics, and biosensing. Here we report the localized surface plasmon resonance (LSPR) properties of gold triangular nanoprisms (Au TNPs) in solid state that are functionalized with dipolar, conjugated ligands. A library of thiocinnamate ligands with varying surface dipole moments were used to functionalize TNPs, which results in ∼150 nm reversible tunability of LSPR peak wavelength with significant peak broadening (∼230 meV). The highly adjustable chemical system of thiocinnamate ligands is capable of shifting the Au work function down to 2.4 eV versus vacuum, i.e., ∼2.9 eV lower than a clean Au (111) surface, and this work function can be modulated up to 3.3 eV, the largest value reported to date through the formation of organothiolate SAMs on Au. Interestingly, the magnitude of plasmonic responses and work function modulation is NP shape dependent. By combining first-principles calculations and experiments, we have established the mechanism of direct wave function delocalization of electrons residing near the Fermi level into hybrid electronic states that are mostly dictated by the inorganic-organic interfacial dipole moments. We determine that both interfacial dipole and hybrid electronic states, and vinyl conjugation together are the key to achieving such extraordinary changes in the optoelectronic properties of ligand-functionalized, plasmonic NPs. The present study provides a quantitative relationship describing how specifically constructed organic ligands can be used to control the interfacial properties of NPs and thus the plasmonic and electronic responses of these functional plasmonics for a wide range of plasmon-driven applications.

Uniform Gold Nanostructure Formation via Weakly Adsorbed Gold Films and Thermal Annealing for Reliable Localized Surface Plasmon Resonance-Based Detection of DNase-I

Deoxyribonuclease-I (DNase-I), a representative endonuclease, is an important biomarker for the diagnosis of infectious diseases and cancer progression. However, enzymatic activity decreases rapidly ex vivo, which highlights the need for precise on-site detection of DNase-I. Here, a localized surface plasmon resonance (LSPR) biosensor that enables the simple and rapid detection of DNase-I is reported. Moreover, a novel technique named electrochemical deposition and mild thermal annealing (EDMIT) is applied to overcome signal variations. By taking advantage of the low adhesion of gold clusters on indium tin oxide substrates, both the uniformity and sphericity of gold nanoparticles are increased under mild thermal annealing conditions via coalescence and Ostwald ripening. This ultimately results in an approximately 15-fold decrease in LSPR signal variations. The linear range of the fabricated sensor is 20-1000 ng mL-1 with a limit of detection (LOD) of 127.25 pg mL-1 , as demonstrated by spectral absorbance analyses. The fabricated LSPR sensor stably measured DNase-I concentrations from samples collected from both an inflammatory bowel disease (IBD) mouse model, as well as human patients with severe COVID-19 symptoms. Therefore, the proposed LSPR sensor fabricated via the EDMIT method can be used for early diagnosis of other infectious diseases.

Investigation of Performance Parameters of Spherical Gold Nanoparticles in Localized Surface Plasmon Resonance Biosensing

In this paper, we present numerical and experimental results on Localized Surface Plasmon Resonance (LSPR) refractive index (RI) sensitivity, Figure of Merit (FoM), and penetration depth (dp) dependence on spherical gold nanoparticles (AuNPs) size, and the effects of AuNP dimer interparticle distance (ds) studied numerically. These parameters were calculated and observed for d = 20, 40, 60, 80, and 100 nm diameter spherical AuNPs. Our investigation shows d = 60 nm AuNPs give the best FoM. The AuNP dimer interparticle distance can significantly influence the RI sensitivity. Therefore, the effect of distances between pairs of d = 20 nm and 60 nm AuNPs is shown. We discuss the importance of penetration depth information for AuNPs functionalized with aptamers for biosensing in the context of aptamer size.

Machine Learning Techniques for Effective Pathogen Detection Based on Resonant Biosensors

We describe a machine learning (ML) approach to processing the signals collected from a COVID-19 optical-based detector. Multilayer perceptron (MLP) and support vector machine (SVM) were used to process both the raw data and the feature engineering data, and high performance for the qualitative detection of the SARS-CoV-2 virus with concentration down to 1 TCID50/mL was achieved. Valid detection experiments contained 486 negative and 108 positive samples, and control experiments, in which biosensors without antibody functionalization were used to detect SARS-CoV-2, contained 36 negative samples and 732 positive samples. The data distribution patterns of the valid and control detection dataset, based on T-distributed stochastic neighbor embedding (t-SNE), were used to study the distinguishability between positive and negative samples and explain the ML prediction performance. This work demonstrates that ML can be a generalized effective approach to process the signals and the datasets of biosensors dependent on resonant modes as biosensing mechanism.

Fountain Pen-Inspired 3D Colloidal Assembly, Consisting of Metallic Nanoparticles on a Femtoliter Scale

The 3D colloidal assemblies composed of nanoparticles (NPs) are closely associated with optical properties such as photonic crystals, localized surface plasmon resonance, and surface-enhanced Raman scattering. However, research on their fabrication remains insufficient. Here, the femtoliter volume of a 3D colloidal assembly is shown, using the evaporation of a fine fountain pen. A nano-fountain pen (NPF) with a micrometer-level tip inner diameter was adopted for the fine evaporation control of the ink solvent. The picoliters of the evaporation occurring at the NFP tip and femtoliter volume of the 3D colloidal assembly were analyzed using a diffusion equation. The shape of the 3D colloidal assembly was dependent on the evaporation regarding the accumulation time and tip size, and they exhibited random close packing. Using gold-, silver-, and platinum-NPs and mixing ratios of them, diverse 3D colloidal assemblies were formed. The spectra regarding a localized surface plasmon resonance of them were changed according to composition and mixing ratio. We expect that this could be widely applied as a simple fabrication tool in order to explore complex metamaterials constructed of nanoparticles, as this method is highly flexible in varying the shape as well as composition ratio of self-assembled structures.

Hierarchically Doped Plasmonic Nanocrystal Metamaterials

Assembling plasmonic nanocrystals in regular superlattices can produce effective optical properties not found in homogeneous materials. However, the range of these metamaterial properties is limited when a single nanocrystal composition is selected for the constituent meta-atoms. Here, we show how continuously varying doping at two length scales, the atomic and nanocrystal scales, enables tuning of both the frequency and bandwidth of the collective plasmon resonance in nanocrystal-based metasurfaces, while these features are inextricably linked in single-component superlattices. Varying the mixing ratio of indium tin oxide nanocrystals with different dopant concentrations, we use large-scale simulations to predict the emergence of a broad infrared spectral region with near-zero permittivity. Experimentally, tunable reflectance and absorption bands are observed, owing to in- and out-of-plane collective resonances. These spectral features and the predicted strong near-field enhancement establish this multiscale doping strategy as a powerful new approach to designing metamaterials for optical applications.

Computational analysis of efficient organic solar cell-based retinal prosthesis using plasmonic gold nanoparticles

Introduction

Photovoltaic restoration of vision, especially in conjunction with the use of silicon photodiodes, has gained attention for use in patients affected by blindness due to retinal layer disease. Although the use of silicon photodiodes offers miniaturization of the implant unit and increase in the stimulation channel, the implant unit may suffer from the fracture of these brittle photodiodes when mechanical pressure exerted.

Methods

We present an organic solar cell (OSC)-based retinal prosthesis in which spherical gold nanoparticles (AuNPs) are embedded into the active layer to increase the efficiency of the bioelectric interface.

Results

We demonstrate computationally that a modeled OSC incorporating spherical AuNPs has three times higher efficiency than that of a bare OSC presented before for retinal prostheses. Our AuNP based OSC was able to activate the neuron at the minimum light intensity of 0.26 mW/mm2, which is lower than that of the bare OSC.

Discussion

The use of AuNPs in OSC allows device miniaturization or lowering of the light exposure required for neural activation using a photovoltaic retinal prosthesis, which can generally be applied in a broad range of neural prostheses.

High Efficiency over 15% by Breaking the Theoretical Efficiency Limit of Fluorescent Organic Light-Emitting Diodes with Localized Surface Plasmon Resonance Effects

The theoretical efficiency limit of fluorescence organic light-emitting diodes (OLEDs) was successfully surpassed by utilizing the localized surface plasmon resonance (LSPR) effect with conventional emissive materials. The interaction between polaritons and plexcitons generated during the LSPR process was also analyzed experimentally. As a result, the external quantum efficiency (EQE) increased dramatically from 6.01 to 15.43%, significantly exceeding the theoretical efficiency limit of fluorescent OLEDs. Additionally, we introduced a new concept of the LSPR effect, called "LSPR sensitizer", which allowed for simultaneous improvement in color conversion and efficiency through cascade transfer of the LSPR effect. To the best of our knowledge, the EQE and the current efficiency of our LSPR-OLED are the highest among LSPR-based fluorescent OLEDs to date.

Dual-Function Meta-Grating Based on Tunable Fano Resonance for Reflective Filter and Sensor Applications

Localized surface plasmon resonance (LSPR)-based sensors exhibit enormous potential in the areas of medical diagnosis, food safety regulation and environmental monitoring. However, the broadband spectral lineshape of LSPR hampers the observation of wavelength shifts in sensing processes, thus preventing its widespread applications in sensors. Here, we describe an improved plasmonic sensor based on Fano resonances between LSPR and the Rayleigh anomaly (RA) in a metal-insulator-metal (MIM) meta-grating, which is composed of silver nanoshell array, an isolation grating mask and a continuous gold film. The MIM configuration offers more freedom to control the optical properties of LSPR, RA and the Fano resonance between them. Strong couplings between LSPR and RA formed a series of narrowband reflection peaks (with a linewidth of ~20 nm in full width at half maximum (FWHM) and a reflectivity nearing 100%) within an LSPR-based broadband extinction window in the experiment, making the meta-grating promising for applications of high-efficiency reflective filters. A Fano resonance that is well optimized between LSPR and RA by carefully adjusting the angles of incident light can switch such a nano-device to an improved biological/chemical sensor with a figure of merit (FOM) larger than 57 and capability of detecting the local refractive index changes caused by the bonding of target molecules on the surface of the nano-device. The figure of merit of the hybrid sensor in the detection of target molecules is 6 and 15 times higher than that of the simple RA- and LSPR-based sensors, respectively.

Size Control of the Mechanism of Exciton Polarization in Metal Oxide Nanocrystals through Fermi Level Pinning

Light-matter interaction in certain aliovalently doped metal oxide nanocrystals (NCs) results in the generation of localized surface plasmon resonance (LSPR) in the near- to mid-infrared, allowing for their implementation in various technologies, including photovoltaics, sensing, and electrochromics. These materials could also facilitate coupling between plasmonic and semiconducting properties, making them highly interesting for electronic and quantum information technologies. In the absence of dopants, free charge carriers can arise from native defects such as oxygen vacancies. Here we show using magnetic circular dichroism spectroscopy that the exciton splitting in In₂O₃ NCs is induced by both localized and delocalized electrons and that contributions from the two mechanisms are strongly dependent on the NC size, owing to Fermi level pinning and the formation of a surface depletion layer. In large NCs, the angular momentum transfer from delocalized cyclotron electrons to the excitonic states is the dominant mechanism of exciton polarization. This process diminishes with decreasing NC size, owing to the rapidly reduced volume of the plasmonic core. On the other hand, exciton polarization in small NCs is dominated by localized electron-spin-induced splitting of the excitonic states. This mechanism is independent of NC size, suggesting that wave functions of localized spin states on NC surfaces do not overlap with the excitonic states. The results of this work demonstrate that the effects of individual and collective electronic properties on excitonic states can be simultaneously controlled by NC size, making metal oxide NCs a promising class of materials for quantum, spintronic, and photonic technologies.

Nanoplasmonic biosensors for precision medicine

Nanoplasmonic biosensors have a huge boost for precision medicine, which allows doctors to better understand diseases at the molecular level and to improve the earlier diagnosis and develop treatment programs. Unlike traditional biosensors, nanoplasmonic biosensors meet the global health industry's need for low-cost, rapid and portable aspects, while offering multiplexing, high sensitivity and real-time detection. In this review, we describe the common detection schemes used based on localized plasmon resonance (LSPR) and highlight three sensing classes based on LSPR. Then, we present the recent applications of nanoplasmonic in other sensing methods such as isothermal amplification, CRISPR/Cas systems, lab on a chip and enzyme-linked immunosorbent assay. The advantages of nanoplasmonic-based integrated sensing for multiple methods are discussed. Finally, we review the current applications of nanoplasmonic biosensors in precision medicine, such as DNA mutation, vaccine evaluation and drug delivery. The obstacles faced by nanoplasmonic biosensors and the current countermeasures are discussed.

Optical Control of the Localized Surface Plasmon Resonance in a Heterotype and Hollow Gold Nanosheet

The remote excitation and remote-controlling of the localized surface plasmon resonance (LSPR) in a heterotype and hollow gold nanosheet (HGNS) is studied using FDTD simulations. The heterotype HGNS contains an equilateral and hollow triangle in the center of a special hexagon, which forms a so-called hexagon-triangle (H-T) heterotype HGNS. If we focus the incident-exciting laser on one of the vertexes of the center triangle, the LSPR could be achieved among other remote vertexes of the outer hexagon. The LSPR wavelength and peak intensity depend sensitively on factors such as the polarization of the incident light, the size and symmetry of the H-T heterotype structure, etc. Several groups of the optimized parameters were screened out from numerous FDTD calculations, which help to further obtain some significant polar plots of the polarization-dependent LSPR peak intensity with two-petal, four-petal or six-petal patterns. Remarkably, based on these polar plots, the on-off switching of the LSPR coupled among four HGNS hotspots could be remote-controlled simply via only one polarized light, which shows promise for its potential application in remote-controllable surface-enhanced Raman scattering (SERS), optical interconnects and multi-channel waveguide switches.

Rational Synthesis of Au-CdS Composite Photocatalysts for Broad-Spectrum Photocatalytic Hydrogen Evolution

Incorporation of plasmonic metal nanomaterials can significantly enhance the visible light response of semiconductor photocatalysts via localized surface plasmon resonance (LSPR) mechanisms. However, the surfaces of plasmonic metal nanomaterials are often covered with surfactant molecules, which is undesired when the nanomaterials are used for photocatalytic hydrogen evolution, since surfactant molecules could significantly compromise the nanomaterials' cocatalyst functionalities by blocking the active sites and/or by inhibiting the surface charge transfer process. Herein, we demonstrate a method that assembles Au nanoparticles (NPs) into Au colloidosomes (AuCSs) without modifying their surfaces with surfactants. The resulting AuCSs were then coupled with CdS for the formation of Au-CdS composite photocatalysts through an in situ deposition method. The assembly of Au NPs induced a broader and stronger LSPR response for AuCSs, while the absence of surfactants allowed them to act efficiently as cocatalysts. This essentially enhanced the electron-hole pair generation rate and further their utilization efficiency, leading to an extremely high hydrogen evolution rate of 235.8 mmol·g^-1·h^-1 under simulated sunlight excitation.

Catalytic Boosting by Surface-Plasmon-Driven Hot Electrons on Antenna-Reactor Schottky Nanodiodes

Significant research has focused on enhancing catalytic performance through solar energy conversion, and the design of photocatalysis incorporating surface plasmons is drawing considerable attention as a highly competitive catalyst system. Although the hot electron process is the primary mechanism in plasmonic photocatalysis, the precise function of hot electron transport in catalytic reactions remains unclear due to the absence of direct measurement. Here, we demonstrate the intrinsic relationship between surface-plasmon-driven hot electrons and catalytic activity during hydrogen oxidation, utilizing catalytic Schottky nanodiodes (Pt/Ag/TiO₂) for antenna-reactor plasmonic photocatalysis. The simultaneous and independent measurements of hot electron flow and catalytic turnover rate show that the plasmonic effect amplifies the flow of reaction-induced hot electrons (chemicurrent), leading to enhanced catalytic activity. Plasmonic photocatalytic performance can be controlled with light wavelengths, intensity, surface temperature, and structures. These results elucidate the hot electron flow on photocatalysis and offer improved strategies for efficient catalytic devices.

Copper-Zinc Bimetallic Single-Atom Catalysts with Localized Surface Plasmon Resonance-Enhanced Photothermal Effect and Catalytic Activity for Melanoma Treatment and Wound-Healing

Nanomaterials with photothermal combined chemodynamic therapy (PTT-CDT) have attracted the attention of researchers owing to their excellent synergistic therapeutic effects on tumors. Thus, the preparation of multifunctional materials with higher photothermal conversion efficiency and catalytic activity can achieve better synergistic therapeutic effects for melanoma. In this study, a Cu-Zn bimetallic single-atom (Cu/PMCS) is constructed with augmented photothermal effect and catalytic activity due to the localized surface plasmon resonance (LSPR) effect. Density functional theory calculations confirmed that the enhanced photothermal effect of Cu/PMCS is due to the appearance of a new d-orbital transition with strong spin-orbit coupling and the induced LSPR. Additionally, Cu/PMCS exhibited increased catalytic activity in the Fenton-like reaction and glutathione depletion capacity, further enhanced by increased temperature and LSPR. Consequently, Cu/PMCS induced better synergistic anti-melanoma effects via PTT-CDT than PMCS in vitro and in vivo. Furthermore, compared with PMCS, Cu/PMCS killed bacteria more quickly and effectively, thus facilitating wound healing owing to the enhanced photothermal effect and slow release of Cu2+ . Cu/PMCS promoted cell migration and angiogenesis and upregulated the expression of related genes to accelerate wound healing. Cu/PMCS has potential applications in treating melanoma and repairing wounds with its antitumor, antibacterial, and wound-healing properties.

Microfluidic-Generated Seeds for Gold Nanotriangle Synthesis in Three or Two Steps

Nanoparticle synthesis has drawn great attention in the last decades. The study of crystal growth mechanisms and optimization of the existing methods lead to the increasing accessibility of nanomaterials, such as gold nanotriangles which have great potential in the fields of plasmonics and catalysis. To form such structures, a careful balance of reaction parameters has to be maintained. Herein, a novel synthesis of gold nanotriangles from seeds derived with a micromixer, which provides a highly efficient mixing and simple parameter control is reported. The impact of the implemented reactor on the primary seed characteristics is investigated. The following growth steps are studied to reveal the phenomena affecting the shape yield. The use of microfluidic seeds led to the formation of well-defined triangles with a narrower size distribution compared to the entirely conventional batch synthesis. A shortened two-step procedure for the formation of triangles directly from primary seeds, granting an express but robust synthesis is further described. Moreover, the need for a thorough study of seed crystallinity depending on the synthesis conditions, which - together with additional parameter optimization - will bring a new perspective to the use of micromixers which are promising for scaling up nanomaterial production is highlighted.

Hot Spot Engineering in Hierarchical Plasmonic Nanostructures

The controllable nanogap structures offer an effective way to obtain strong and tunable localized surface plasmon resonance (LSPR). A novel hierarchical plasmonic nanostructure (HPN) is created by incorporating a rotating coordinate system into colloidal lithography. In this nanostructure, the hot spot density is increased drastically by the long-range ordered morphology with discrete metal islands filled in the structural units. Based on the Volmer-Weber growth theory, the precise HPN growth model is established, which guides the hot spot engineering for improved LSPR tunability and strong field enhancement. The hot spot engineering strategy is examined by the application of HPNs as the surface-enhanced Raman spectroscopy (SERS) substrate. It is universally suitable for various SERS characterization excited at different wavelengths. Based on the HPN and hot spot engineering strategy, single-molecule level detection and long-range mapping can be realized simultaneously. In that sense, it offers a great platform and guides the future design for various LSPR applications like surface-enhanced spectra, biosensing, and photocatalysis.

Application of the Nicoya OpenSPR to Studies of Biomolecular Binding: A Review of the Literature from 2016 to 2022

The Nicoya OpenSPR is a benchtop surface plasmon resonance (SPR) instrument. As with other optical biosensor instruments, it is suitable for the label-free interaction analysis of a diverse set of biomolecules, including proteins, peptides, antibodies, nucleic acids, lipids, viruses, and hormones/cytokines. Supported assays include affinity/kinetics characterization, concentration analysis, yes/no assessment of binding, competition studies, and epitope mapping. OpenSPR exploits localized SPR detection in a benchtop platform and can be connected with an autosampler (XT) to perform automated analysis over an extended time period. In this review article, we provide a comprehensive survey of the 200 peer-reviewed papers published between 2016 and 2022 that use the OpenSPR platform. We highlight the range of biomolecular analytes and interactions that have been investigated using the platform, provide an overview on the most common applications for the instrument, and point out some representative research that highlights the flexibility and utility of the instrument.

Plasmonic Metamaterial Ag Nanostructures on a Mirror for Colorimetric Sensing

In this study, we demonstrate the localized surface plasmon resonance (LSPR) in the visible range by using nanostructures on mirrors. The nanohemisphere-on-mirror (NHoM) structure is based on random nanoparticles that were obtained by heat-treating silver thin films and does not require any top-down nanofabrication processes. We were able to successfully tune over a wide wavelength range and obtain full colors using the NHoM structures, which realized full coverage of the Commission Internationale de l'Eclairage (CIE) standard RGB (sRGB) color space. Additionally, we fabricated the periodic nanodisk-on-glass (NDoG) structure using electron beam lithography and compared it with the NHoM structure. Our analysis of dark-field microscopic images observed by a hyperspectral camera showed that the NHoM structure had less variation in the resonant wavelength by observation points compared with the periodic NDoG structure. In other words, the NHoM structure achieved a high color quality that is comparable to the periodic structure. Finally, we proposed colorimetric sensing as an application of the NHoM structure. We confirmed the significant improvement in performance of colorimetric sensing using the NHoM structure and succeeded in colorimetric sensing using protein drops. The ability to fabricate large areas in full color easily and inexpensively with our proposed structures makes them suitable for industrial applications, such as displays, holograms, biosensing, and security applications.

Tunable Nonlinear Optical Response of ITO Films with Au@Ag Bimetallic Nanoparticles

The nonlinear optical (NLO) response of indium tin oxide films covered with Au@Ag colloid layer was characterized by a femtosecond single-beam open aperture (OA) Z-scan technique in this study. As the Au@Ag thickness increased, the transition from saturated absorption (SA) to reverse saturated absorption (RSA) was found in these ITO matrix composites. The nonlinear absorption coefficient for these composite materials can be regulated from -6.85 × 10^-7 m/W to 26.06 × 10^-7 m/W. In addition, this work also characterized the structure, morphology, and other optical properties of the specimen, and the finite-difference time-domain (FDTD) results were consistent with the experimental results. The NLO response of the ITO/Au@Ag composites can be attributed to the phase properties, synergistic competition effect, strong interaction based on the epsilon-near-zero (ENZ) mode, and localized surface plasmon resonance (LSPR) between the indium tin oxide films and Au@Ag.

Plasmonic Nanopillars-A Brief Investigation of Fabrication Techniques and Biological Applications

Nanopillars (NPs) are submicron-sized pillars composed of dielectrics, semiconductors, or metals. They have been employed to develop advanced optical components such as solar cells, light-emitting diodes, and biophotonic devices. To integrate localized surface plasmon resonance (LSPR) with NPs, plasmonic NPs consisting of dielectric nanoscale pillars with metal capping have been developed and used for plasmonic optical sensing and imaging applications. In this study, we studied plasmonic NPs in terms of their fabrication techniques and applications in biophotonics. We briefly described three methods for fabricating NPs, namely etching, nanoimprinting, and growing NPs on a substrate. Furthermore, we explored the role of metal capping in plasmonic enhancement. Then, we presented the biophotonic applications of high-sensitivity LSPR sensors, enhanced Raman spectroscopy, and high-resolution plasmonic optical imaging. After exploring plasmonic NPs, we determined that they had sufficient potential for advanced biophotonic instruments and biomedical applications.

Fiber Optic Localized Surface Plasmon Resonance Sensor Based on Carboxymethylated Dextran Modified Gold Nanoparticles Surface for High Mobility Group Box 1 (HMGB1) Analysis

Rapid, sensitive, and reliable detection of high mobility group box 1 (HMGB1) is essential for medical and diagnostic applications due to its important role as a biomarker of chronic inflammation. Here, we report a facile method for the detection of HMGB1 using carboxymethyl dextran (CM-dextran) as a bridge molecule modified on the surface of gold nanoparticles combined with a fiber optic localized surface plasmon resonance (FOLSPR) biosensor. Under optimal conditions, the results showed that the FOLSPR sensor detected HMGB1 with a wide linear range (10^-10 to 10^-6 g/mL), fast response (less than 10 min), and a low detection limit of 43.4 pg/mL (1.7 pM) and high correlation coefficient values (>0.9928). Furthermore, the accurate quantification and reliable validation of kinetic binding events measured by the currently working biosensors are comparable to surface plasmon resonance sensing systems, providing new insights into direct biomarker detection for clinical applications.

Plasmon-enhanced photoluminescence and Raman spectroscopy of silver nanoparticles grown by solid state dewetting

The growth of the metallic nanoparticles on the solid substrate with the desired shape and size is a critical issue for application of these nanoparticles in solid-state devices. Solid state dewetting (SSD) technique is simple, low cost and can be used to fabricate the metallic nanoparticles with control on the shape and size on different substrates. In this work, silver nanoparticles (Ag NPs) were grown on corning glass substrate by solid-state dewetting (SSD) of silver precursor thin film deposited at different substrate temperatures by rf sputtering. The influence of the substrate temperature on the growth of Ag NPs and their several properties like localized surface Plasmon resonance (LSPR), photoluminescence, and Raman spectroscopy is studied. The size of the nanoparticles was found to vary from 25 nm to 70 nm with the variation in substrate temperature from room temperature (RT) to 400℃. For the RT films, the LSPR peak position of Ag NPs is around 474 nm. A red shift in LSPR peak for films deposited at higher temperature is observed due to change in the particle size and interparticle separation. Photoluminescence spectra suggests the presence of two photoluminescence bands at 436 and 474 nm corresponding to Ag NPs radiative interband transition and LSPR band. An intense Raman peak was observed at 1587 cm-1. Enhancement in PL peak intensity and Raman peak intensity is found to be in accordance with the LSPR of Ag NPs.

Localized Surface Plasmon Resonance-Based Nanosensor for Rapid Detection of Glyphosate in Food Samples

In this study, we developed a biosensor based on the localized surface plasmon resonance (LSPR) phenomenon of gold nanoparticles (AuNPs) to detect the widely used herbicide glyphosate in food samples. To do so, either cysteamine or a specific antibody for glyphosate were conjugated to the surface of the nanoparticles. AuNPs were synthesized using the sodium citrate reduction method and had their concentration determined via inductively plasma coupled mass spectrometry. Their optical properties were analyzed using UV-vis spectroscopy, X-ray diffraction, and transmission electron microscopy. Functionalized AuNPs were further characterized via Fourier-transform infrared spectroscopy, Raman scattering, Zeta potential, and dynamic light scattering. Both conjugates succeeded in detecting the presence of glyphosate in the colloid, although nanoparticles functionalized with cysteamine tended to aggregate at high concentrations of the herbicide. On the other hand, AuNPs functionalized with anti-glyphosate functioned at a broad concentration range and successfully identified the presence of the herbicide in non-organic coffee samples and when it was added to an organic coffee sample. This study demonstrates the potential of AuNP-based biosensors to detect glyphosate in food samples. The low-cost and specificity of these biosensors make them a viable alternative to current methods for detecting glyphosate in foodstuffs.

Reflective Fiber Temperature Probe Based on Localized Surface Plasmon Resonance towards Low-Cost and Wireless Interrogation

Reflection fiber temperature sensors functionalized with plasmonic nanocomposite material using intensity-based modulation are demonstrated for the first time. Characteristic temperature optical response of the reflective fiber sensor is experimentally tested using Au-incorporated nanocomposite thin films deposited on the fiber tip, and theoretically validated using a thin-film-optic-based optical waveguide model. By optimizing the Au concentration in a dielectric matrix, Au nanoparticles (NP) exhibit a localized surface plasmon resonance (LSPR) absorption band in a visible wavelength that shows a temperature sensitivity ~0.025%/°C as a result of electron-electron and electron-phonon scattering of Au NP and the surrounding matrix. Detailed optical material properties of the on-fiber sensor film are characterized using scanning electron microscopy (SEM) and focused-ion beam (FIB)-assisted transmission electron microscopy (TEM). Airy's expression of transmission and reflection using complex optical constants of layered media is used to model the reflective optical waveguide. A low-cost wireless interrogator based on a photodiode transimpedance-amplifier (TIA) circuit with a low-pass filter is designed to integrate with the sensor. The converted analog voltage is wirelessly transmitted via 2.4 GHz Serial Peripheral Interface (SPI) protocols. Feasibility is demonstrated for portable, remotely interrogated next-generation fiber optic temperature sensors with future capability for monitoring additional parameters of interest.

Quantum-Coherence-Enhanced Hot-Electron Injection under Modal Strong Coupling

Modal strong coupling between localized surface plasmon resonance and a Fabry-Pérot nanocavity has been studied to improve the quantum efficiency of artificial photosynthesis. In this research, we employed Au nanodisk/titanium dioxide/Au film modal strong coupling structures to investigate the mechanism of quantum efficiency enhancement. We found that the quantum coherence within the structures enhances the apparent quantum efficiency of the hot-electron injection from the Au nanodisks to the titanium dioxide layer. Under near-field mapping using photoemission electron microscopy, the existence of quantum coherence was directly observed. Furthermore, the coherence area was quantitatively evaluated by analyzing the relationship between the splitting energy and the particle number density of the Au nanodisks. This quantum-coherence-enhanced hot-electron injection is supported by our theoretical model. Based on these results, applying quantum coherence to photochemical reaction systems is expected to effectively enhance reaction efficiencies.

Enhancement of luminous efficacy of polymer light-emitting diodes with silver-nanoparticles by oxygen-plasma treatment

Silver-nanoparticles deposited on indium tin oxide (AgNPs/ITO) with different O₂ -plasma treatment times are used as the anode window substrate for polymer light-emitting diodes (PLED). When AgNPs/ITO with an O₂ -plasma treatment time of 10 min is used for PLED, a maximum current efficiency of 3.33 cd/A is realized, which is notably higher than that of a reference PLED (1.00 cd/A). Compared to those of the reference PLED, the mean current efficiency and electroluminescence intensity of the optimal PLED are enhanced by 3.24 times and 480%, respectively. O₂ -plasma treatment is an easy method for optimizing the localized surface plasmon resonance effect of metal nanoparticles, exhibiting advantages of scalable mass production and high suitability for applications in related optoelectronic components.