Search Results (205)

Finding high-performance and low-cost materials is essential for high-quality photocatalytic water purification to expand the spectral response and improve light utilization. In this paper, we used relatively inexpensive materials such as Ag and TiO₂. The influence of particle spacing, core radius, shell thickness, environmental refractive index, and incident light direction angle on the light absorption and scattering properties, local electric field enhancement, and photothermal effect of the Ag@TiO₂ core–shell nanosphere dimer is investigated by using the finite element method and the finite difference time domain. The formation mechanism of multipole resonance mode of the dimer is revealed by means of the multipole decomposition theory and the internal current distribution of the particles. The results show that light absorption and scattering of the dimer can be tuned within the visible light range by changing the particle spacing, core radius, and shell thickness. With the azimuth angle of incident light increases, the longitudinal local surface plasmon resonance (L-LSPR) mode will transform into the transverse local surface plasmon resonance (T-LSPR) mode, and the L-LSPR mode makes the dimer have better local electric field enhancement. Strong light absorption can easily cause a sharp increase in the temperature around the dimer, accelerating the rate of catalytic oxidation reactions and the elimination of bacteria and viruses in water. Strong light scattering causes a significant enhancement of the electric field between the particles, making the generation of hydroxyl and other active oxides more efficient and convenient. This work establishes a theoretical basis for designing efficient water purification photocatalysts. Full article

Plasmonic metasurfaces that convert hydrogen-induced dielectric changes into optical signals hold promise for next-generation hydrogen sensors. Here, we employ simulations and theoretical analysis to systematically assess single-layer, bilayer, and trilayer nanodisk arrays comprising magnesium, palladium, and noble metals. Although monolithic Mg nanodisks show strong optical contrast after hydrogenation, the corresponding surface plasmon resonance disappears completely, preventing quantitative spectral tracking. In contrast, bilayer heterostructures, particularly those combining Mg and Au, achieve a resonance red-shift of Δλ = 62 nm, a narrowed full width at half maximum (FWHM) of 207 nm, and a figure of merit (FoM) of 0.30. Notably, the FoM is boosted by up to 15-fold when tuning both material choice and stacking sequence (from Mg-Ag to Au-Mg), underscoring the critical role of interface engineering. Trilayer “sandwich” architectures further amplify performance, achieving a max 10-fold and 13-fold enhancement in Δλ and FoM, respectively, relative to its bilayer counterpart. Particularly, the trilayer Mg-Au-Mg reaches Δλ = 120 nm and FoM = 0.41, outperforming most previous plasmonic hydrogen sensors. These enhancements arise from maximized electric-field overlap with dynamically changing dielectric regions at noble-metal–hydride interfaces, as confirmed by first-order perturbation theory. These results indicate that multilayer designs combining Mg and noble metals can simultaneously maximize hydrogen-induced spectral shifts and signal quality, providing a practical pathway toward high-performance all-optical hydrogen sensors. Full article

Mid-infrared molecular sensing faces challenges in simultaneously achieving high-resolution qualitative identification and quantitative analysis of multiple biomolecules. To address this, we present a tunable mid-infrared sensing platform, integrating the simulation of a single-layer graphene square-aperture array sensor with a machine learning algorithm called principal component analysis for advanced spectral processing. The graphene square-aperture structure excites dynamically tunable localized surface plasmon resonances by modulating the graphene’s Fermi level, enabling precise alignment with the vibrational fingerprints of target molecules. This plasmon–molecule coupling amplifies absorption signals and serves as discernible “molecular barcodes” for precise identification without change in the structural parameters. We demonstrate the platform’s capability to detect and differentiate carbazole-based biphenyl molecules and protein molecules, even in complex mixtures, by systematically tuning the Fermi level to match their unique vibrational bands. More importantly, for mixtures with unknown total amounts and different concentration ratios, the principal component analysis algorithm effectively processes complex transmission spectra and presents the relevant information in a simpler form. This integration of tunable graphene plasmons with machine learning algorithms establishes a label-free, multiplexed mid-infrared sensing strategy with broad applicability in biomedical diagnostics, environmental monitoring, and chemical analysis. Full article

Materials’ plasmon activity is defined by their electronic structure. Nowadays, the application of plasmonic materials is increasingly determined by the possibilities to control the electronic processes in them. The electronic structure’s design is of particular importance for tuning the plasmon frequency and the excitation of hot electrons, which are important parameters determining the interaction of the nanostructures with the environment. The effective control of these parameters is important for the improvement of the efficiency and sensitivity of various processes, diagnostic methods and technologies in the field of photocatalysis and surface enhancement spectroscopies. This review is focused on the characterization techniques and the approaches for tuning the electronic states of plasmonic media. The diversity of materials and their electronic structure determine the approach for the engineering of the electronic structure. In the case of noble metals, the possibility for tuning the energy for interband transitions from their d band is considered by using intermetallic alloys (between noble metals themselves and with an addition of post-transition metals in them), while in semiconductor materials—the effect of charge transfer is mainly used. Such knowledge is not only essential from a practical point of view, but also contributes to understanding the processes in the field of new materials such as 2D noble metals and intermetallics. Full article

Spiky Au-Ag nanostars offer intense plasmonic enhancement due to their sharp-tipped morphology, enabling powerful surface-enhanced Raman scattering (SERS). Here, we report a liquid-phase SERS platform that addresses current limitations in cancer biomarker detection, such as low sensitivity and dependence on Raman reporters. Nanostar concentration was tuned by simple centrifugation (10, 30, and 60 min), and their SERS performance was evaluated using methylene blue (MB) and mercaptopropionic acid (MPA) as probe molecules. Signal intensity scaled with nanostar content, enabling sensitive detection. Optimized nanostars were functionalized with MPA, 1-Ethyl-3-(3-dimethylamino1-Ethyl-3-(3dimethylaminopropyl1) carbodiimide (EDC), and N-Hydroxy succinimide (NHS) for covalent attachment of monoclonal anti-α-fetoprotein antibodies (AFP-Ab), facilitating the detection of AFP antigens across 167–38 ng/mL (antibody) and 500–0 ng/mL (antigen) ranges. The limit of detection (LOD) for the antigens was determined to be 16.73 ng/mL. Unlike conventional SERS systems, this aqueous, surfactant-free platform exploits the intrinsic vibrational modes of AFP, enabling sensitive and rapid biomarker detection with strong potential for early cancer diagnostics. Full article

Localized therapeutic action and targeted drug release offer compelling advantages over traditional systemic drug administration. This is particularly important for nitric oxide (NO), whose biological effects vary greatly depending on concentration and cellular environment. Light-sensitive NO donors are promising for achieving precise, on-demand NO release. However, their efficiency and photostability are limited by competing photophysical processes and the generation of reactive oxygen species (ROS). In this study, we investigate hybrid systems composed of photosensitive nitric oxide (NO) donors and silver island films (SIFs). The influence of localized surface plasmon on non-radiative relaxation pathways and ROS generation is the main focus of the paper. Upon excitation at 500 nm, we observed several-fold increase in NO release, attributed to resonant interactions between the plasmonic field and the dye molecules. By tuning the thickness of a SiO₂ buffer layer, we identified key parameters affecting process efficiency: the spectral overlap between the plasmon resonance and the sensitizer’s absorption band, and the distance between the nanoparticle and the molecule. Additionally, singlet oxygen generation increase was observed. These findings demonstrate the potential of plasmonic enhancement to controllably boost photochemical activity in organic systems, paving the way for advanced applications in phototherapy and biomedical diagnostics. Full article

Fast, spark-free detection of hydrogen leaks is indispensable for large-scale hydrogen deployment, yet electronic sensors remain power-intensive and prone to cross-talk. Optical schemes based on surface plasmons enable remote read-out, but single-metal devices offer either weak H2 affinity or poor plasmonic quality. Here we employ full-wave finite-difference time-domain (FDTD) simulations to map the hydrogen response of nanohole arrays (NAs) that can be mass-produced by colloidal lithography. Square lattices of 200 nm holes etched into 100 nm films of Pd, Mg, Ti, V, or Zr expose an intrinsic trade-off: Pd maintains sharp extraordinary optical transmission modes but shifts by only 28 nm upon hydriding, whereas Mg undergoes a large dielectric transition that extinguishes its resonance. Vertical pairing of a hydride-forming layer with a noble metal plasmonic cap overcomes this limitation. A Mg/Pd bilayer preserves all modes and red-shifts by 94 nm, while the predicted optimum Ag (60 nm)/Mg (40 nm) stack delivers a 163 nm shift with an 83 nm linewidth, yielding a figure of merit of 1.96—surpassing the best plasmonic hydrogen sensors reported to date. Continuous-film geometry suppresses mechanical degradation, and the design rules—noble-metal plasmon generator, buried hydride layer, and thickness tuning—are general. This study charts a scalable route to remote, sub-ppm, optical hydrogen sensors compatible with a carbon-neutral energy infrastructure. Full article

Based on the theory of optical sensing, we propose a high-precision plasmonic refractive index nanosensor, which consists of a symmetric rectangular waveguide and a circular ring containing a rectangular cavity. The designed novel tunable micro-resonant circular cavity filter based on surface plasmon excitations is able to confine light to sub-wavelength dimensions. The data show that different geometrical factors have different effects on sensing, with the geometry of the rectangular cavity and the radius of the circular ring being the key factors affecting the Fano resonance. Furthermore, the resonance bifurcation enables the structure to achieve a tunable dual Fano resonance system. The structure was tuned to obtain optimal sensitivity (S) and figure of merit values up to 3066 nm/RIU and 78. The designed structure has excellent sensing performance with sensitivities of 0.4767 nm·(mg/d${\mathrm{L}}^{-1}$) and 0.6 nm·(mg/d${\mathrm{L}}^{-1}$) in detecting Na⁺ and K⁺ concentrations in the electrolyte solution, respectively, and can be easily achieved by the spectrometer. The wavelength accuracy of 0.001 nm can be easily achieved by a spectrum analyzer, which has a broad application prospect in the field of optical integration. Full article

Titanium dioxide (TiO₂) is a benchmark photocatalyst for environmental applications, but its limited visible-light activity due to a wide band gap and fast charge recombination restricts its practical efficiency. This study presents the development of heterostructured Ag (Au)/MoS₂-TiO₂ inverse opal (IO) films that synergistically integrate photonic, plasmonic, and semiconducting functionalities to overcome these limitations. The materials were synthesized via a one-step evaporation-induced co-assembly approach, embedding MoS₂ nanosheets and plasmonic nanoparticles (Ag or Au) within a nanocrystalline TiO₂ photonic framework. The inverse opal architecture enhances light harvesting through slow-photon effects, while MoS₂ and plasmonic nanoparticles improve visible-light absorption and charge separation. By tuning the template sphere size, the photonic band gap was aligned with the TiO₂-MoS₂ absorption edge and the localized surface plasmon resonance of Ag, enabling optimal spectral overlap. The corresponding Ag/MoS₂-TiO₂ photonic films exhibited superior photocatalytic and photoelectrocatalytic degradation of tetracycline under visible light. Ultraviolet photoelectron spectroscopy and Mott–Schottky analysis confirmed favorable band alignment and Fermi level shifts that facilitate interfacial charge transfer. These results highlight the potential of integrated photonic–plasmonic-semiconductor architectures for efficient solar-driven water treatment. Full article

In this paper, we experimentally investigated the excitation of spoof surface plasmon polaritons (SSPPs) supported by a 1D subwavelength grating with a rectangular profile in the terahertz (THz) frequency range. Using the attenuated total reflection technique and the THz radiation of the Novosibirsk free electron laser, we carried out detailed studies of both angular and gap spectra at several wavelengths. A shallow grating supporting a fundamental mode was fabricated by means of multibeam X-ray lithography and used as a test sample. The results indicated that we achieved 1-THz tunability of resonance in the frequency range from 1.51 to 2.54 THz on a single grating, which cannot be obtained with active tunable metamaterials. The Q factors of the resonances in the angular spectra were within the range of 19.4–37.6, while the resonances of the gap spectra had a Q factor lying within the 1.17–2.03 range. The gap adjustment capability of the setup shown in the work has great potential in modulation of the absorption efficiency, whereas the angular tuning and recording data from each point of the grating will enable real-time monitoring of changes in the surrounding medium. All of this is highly important for enhanced terahertz real-time absorption spectroscopy and imaging. Full article

The early and accurate detection of cancer remains a critical challenge in biomedical diagnostics. In this work, we propose and investigate a novel surface plasmon resonance (SPR) biosensor platform based on a multilayer configuration incorporating copper (Cu), silicon nitride (Si₃N₄), and molybdenum disulfide (MoS₂) for the optical detection of various cancer types. Four distinct sensor architectures (Sys₁–Sys₄) were optimized through the systematic tuning of Cu thickness, Si₃N₄ dielectric layer thickness, and the number of MoS₂ monolayers to enhance sensitivity, angular shift, and spectral sharpness. The optimized systems were evaluated using refractive index data corresponding to six cancer types (skin, cervical, blood, adrenal, breast T1, and breast T2), with performance metrics including sensitivity, detection accuracy, quality factor, figure of merit, limit of detection, and comprehensive sensitivity factor. Among the configurations, Sys₃ (BK7–Cu–Si₃N₄–MoS₂) demonstrated the highest sensitivity, reaching 254.64 °/RIU for adrenal cancer, while maintaining a low detection limit and competitive figures of merit. Comparative analysis revealed that the MoS₂-based designs, particularly Sys₃, outperform conventional noble-metal architectures in terms of sensitivity while using earth-abundant, scalable materials. These results confirm the potential of Cu/Si₃N₄/MoS₂-based SPR biosensors as practical and effective tools for label-free cancer diagnosis across multiple malignancy types. Full article

The ability to broaden the bandwidth of nanodevices holds significant promise for applications in modern science and technology. In this work, we demonstrate a tunable approach to the bandwidth modulation of nanoresonators by applying a direct current electric field. Quantum hydrodynamic theory reveals that the biased electric field redistributes surface charges, inducing positively and negatively charged regions on the metal surface. This charge asymmetry splits the plasmonic modes, resulting in bandwidth broadening. The optical response can be finely tuned by varying the amplitude and polarization direction of the bias field. This mechanism offers a versatile strategy for developing nanodevices, including metasurfaces with dynamically adjustable bandwidths. Full article

A straightforward and economical engraving diode laser with a 455 $\pm$$5$ nm visible wavelength was employed for the first time in a pulsed laser fragmentation in liquid (PLFL) technique coupled simultaneously with a chemical reduction method to synthesize silver nanoparticles (AgNPs) in an Origanum majorana extract liquid, as a natural reduction agent. The chemical reduction correlated with the PLFL method to control the NP size by examining the effect of irradiation times. The AgNPs were characterized by X-Ray diffraction (XRD), UV–vis spectrophotometry, dynamic light scattering (DLS), transmission electron microscopy (TEM), and Fourier transform infrared (FTIR) spectroscopy. The lattice diffraction Bragg’s planes (111), (200), (220), (311), and (222) were found by XRD. The AgNPs had a surface plasmon resonance (SPR) peak at around 432–409 nm. The position of this SPR peak moves toward shorter wavelengths, by around 23 nm, with increased laser irradiation. When exposure times were increased, a drop in Ag NP size was revealed, from 22 nm when only a chemical reduction approach was used to 12 nm when the PLFL technique was associated. The DLS and TEM confirmed the UV–vis results. Such consideration suggests that combining the chemical reduction and PLFL methods could enable the tuning of the Ag NP size to be tailored for specific applications. This work could open the field for synthesizing NPs and controlling their size using an easy and handy engraving laser. Full article

This paper presents a highly sensitive and tunable graphene-based metamaterial perfect absorber (MPA) operating in the near-terahertz band. The structure features a unique flower-like graphene pattern, consisting of a Au substrate, a SiO₂ dielectric layer, and the patterned graphene. Multiple reflections of incident light between the gold and graphene layers increase the duration and intensity of the interaction, resulting in efficient absorption at specific frequencies. The design utilizes surface plasmon resonance (SPR) to achieve near-perfect absorption of 99.9947% and 99.6079% at 11.7475 THz and 15.8196 THz, respectively. By tuning the Fermi level and relaxation time of graphene, it is possible to precisely control the frequency and absorptivity of the absorption peak, thereby demonstrating the dynamic tunability of the absorber. The high symmetry and periodic arrangement of the structure ensures insensitivity to the polarization angle of the incident light in the range of 0° to 90°, making it extremely valuable in practical applications. In addition, the absorber exhibits very high sensitivity to changes in ambient refractive index with a maximum sensitivity of 3.205 THz/RIU, a quality factor (FOM) of 11.3011 RIU⁻¹, and a Q-Factor of 48.61. It has broad application prospects in the fields of sensors, optoelectronic devices, and terahertz imaging. Full article

This research introduces a biosensor utilizing surface plasmon resonance in a photonic crystal fiber (PCF) configuration. PCF uses fused silica as the base material, with a layer of gold placed over the U-channels in the cross-section of the fiber to create a surface plasmon resonance. There are three different sizes of internal fiber optic air hole diameters, with a larger channel circle below the u-channel for the formation of an energy leakage window. COMSOL software 6.0 assisted us in tuning the fiber optic structure and performance for the study, and the structural parameters analyzed mainly include the channel circle diameter, the channel circle spacing, the profundity measurement of the polished layer, and the nanoscale size variation of metal films. The results of the simulation study show that the optical fiber sensor achieves refractive index (RI) responsiveness across the 1.30 to 1.41 range, and in the RI interval of 1.40 to 1.41, the sensor exhibits the largest resonance peak shift, and its highest sensitivity reaches 10,200 nm/RIU, and the smallest full width at half peak (FWHM) corresponds to the RI of 1.34 with a value of 4.8 nm, and the highest figure of merit (FOM) corresponds to the RI of 1.34 with a value of 895.83 (1/RIU). COMSOL 6.0 simulation software, was used to simulate the changes in blood refractive index corresponding to different glucose concentrations, and the detection performance of the sensor for different concentrations of glucose was tested. Then, the results show that the glucose concentration in 75 mg/dL–175 mg/dL with RI detection sensitivity is 3750 nm/RIU, where the maximum refractive index sensitivity is 5455 nm/RIU. It shows that the sensor can be applied in the field of biomedical applications, with its convenience, fast response, and high sensitivity, it has great potential and development prospect in the market. Full article