Surface-enhanced Raman spectroscopy (SERS) relies on strong amplification of the local electromagnetic field within plasmonic hotspots formed around metallic nanostructures. In this study, we present a computational framework that models a silver nanoparticle (AgNP) dimer placed on a ZnO dielectric spacer, supported by a base substrate, to investigate hotspot-enhancement mechanisms. Finite-difference time-domain (FDTD) simulations were employed to systematically examine the combined influence of ZnO layer thickness, base substrate, interparticle gap, and nanoparticle (NP) radius on the plasmonic response and the enhancement factor (EF) arising from the local electric field. The simulations reveal two distinct plasmonic modes, the single-particle (SP) mode and the gap mode, whose resonance wavelengths and enhancement strengths are highly sensitive to the dielectric spacer, base substrate, and NP configuration. The EF for both modes varies non-monotonically with the ZnO layer thickness, initially increasing, reaching a maximum at intermediate thicknesses, and then decreasing, highlighting the tunability of EF through the dielectric layer. Further analysis confirms that interparticle separation and NP size play dominant roles in governing hotspot intensity and spectral position. Validation of the model against SERS experiments performed at an excitation wavelength of 785 nm shows good agreement, confirming the reliability of the simulations. These findings provide useful design guidelines for hybrid spacer-base substrate architectures and underscore the critical role of ZnO-base substrate synergy in optimizing plasmonic hotspots to improve SERS performance.
By adjusting composite films with different refractive indices, the coupling conditions of surface plasmon resonance (SPR) can be precisely controlled, thereby inducing a controllable redshift in the sensing bandwidth of the sensor. This feature provides a reliable means for effectively separating the dual-channel sensing bandwidths. In this study, we propose a sensor modulated by composite films for the simultaneous and independent measurement of refractive index (RI) and temperature. The RI sensing channel is realized by depositing Ag/MgF2 films onto the surface of the no-core fiber (NCF), while the temperature sensing channel is implemented by coating the NCF with the Ag/MoS2/ polydimethylsiloxane (PDMS) films. Experimental results show that the sensor achieves a maximum sensitivity of 7300 nm/RIU in the RI range of 1.33–1.39, and a maximum sensitivity within the temperature range of 30–100 ℃ can reach 4.4 nm/℃. The sensing bandwidth are effectively separated around 800 nm. Through rational design of the film structure, this study provides a feasible solution for achieving high-performance multi-parameter sensing.
A highly sensitive photonic crystal fiber surface plasmon resonance (PCF-SPR) magnetic sensor assisted by statistical optimization and machine learning is proposed and numerically investigated. The sensor consists of a silica-based PCF incorporating two gold-coated elliptical channels filled with magnetic fluid, enabling efficient coupling between the guided core mode and surface plasmon polaritons. Finite element method (FEM) simulations were performed over a magnetic-field range of 30–300 Oe. The air-hole diameter, pitch, and gold layer thickness were optimized using the Taguchi method and analysis of variance (ANOVA), identifying the pitch as the dominant design parameter. The optimized sensor achieves a wavelength sensitivity of 500 pm/Oe, an amplitude sensitivity of 0.0361 Oe− 1, and a resolution of 2 × 10− 2 Oe within the 30–90 Oe operating range. To accelerate sensor analysis, a multilayer perceptron (MLP) model was developed to predict the complete confinement-loss spectrum directly from the wavelength and magnetic-field intensity. The model was trained using a FEM-generated dataset and rigorously validated through a Leave-One-H-Configuration-Out (LOCO) cross-validation strategy. The MLP achieved an average R2 of 0.9878 ± 0.0101, outperforming Support Vector Regression and Random Forest models under the same validation protocol. Furthermore, robustness analysis considering ± 5
This paper proposes a high-sensitivity and compact plasmonic refractive index sensor based on a metal–insulator-metal (MIM) waveguide and two MIM ring resonators. The optimal radii of the resonators are determined via a parameter sweep to achieve near-zero transmission and strong resonance at 1550 nm. The sensor exhibits a refractive index sensitivity of 1540 nm/RIU, a figure of merit of 91 RIU−1, and a quality-factor of 121 for refractive indices near n = 1.33. Using ethanol as a thermos-optic material, the presented sensor can detect small temperature changes with a temperature sensitivity of 0.61 nm/°C. Compared to previous MIM-based sensors, the proposed structure achieves competitive refractive index sensitivity and superior temperature sensitivity while maintaining structural simplicity. Due to its compact footprint of 2.5 μm2 and remarkable sensing capabilities, the proposed sensor has high potential for use in a wide range of industrial, medical, and environmental applications.
Silver nanoclusters (AgNC) and polytetrafluoroethylene (PTFE) were employed as the nanomatrix of positive and negative electrodes respectively, ammonium pentadecafluorooctanoate (APO) as the template molecule, and trialdehyde resorcinol (Tp) and biphenylamine (BD) as functional monomers to synthesize two new surface molecularly imprinted covalent organic framework nanoprobes (MCOFP and MCOFN). The slope procedure was used to evaluate the catalysis of those nanoprobes for the gold nanoparticle (AuNP) reaction of sodium formate (SF)-HAuCl₄ with surface-enhanced Raman scattering (SERS) monitoring. The piezoelectric nanocatalysis of MCOFP was observed firstly. The mixture of two probes exhibited molecular recognition, nanocatalytic, piezoelectric nanocatalysis and triboelectric nanogenerator tetra-functions. Upon addition of APO, the catalytic performance of the mixture system was further enhanced, mainly due to TENG amplification. Based on these findings, a new TENG-based SERS quantitative analytical method was developed for trace detection of 0.05–0.50 nmol/L APO.
Pathogenic Escherichia coli (E. coli) contamination in food and water supplies poses a severe threat to global public health, necessitating the development of rapid and ultra-sensitive detection methods. The present work proposes a high-performance surface plasmon resonance (SPR) biosensor based on BK7/Ag/Pd/ZnO heterostructure specially designed to detect E. coli in high-refractive-index conditions (ns = 1.388). The sensor design employs a bimetallic Ag/Pd stack to incorporate the best plasmonic characteristics of silver and the chemical stability of palladium, with a zinc oxide (ZnO) dielectric overlayer to improve the confinement of the evanescent fields. Based on numerical analysis through finite-difference time-domain (FDTD) simulations, the optimal structure, which consists of 45 nm Ag, 15 nm Pd, and 1 nm ZnO layers, achieves an angular sensitivity of 256.34 deg/RIU, Quality Factor (QF) of 163.45 RIU⁻¹, and Detection Accuracy (DA) of 8.66. The simpler structure not only surpasses more complicated multi-layer structures but is also easier to fabricate since it still follows the layer-by-layer approach despite being a simpler configuration for detecting Escherichia coli, making it more practical in terms of scalable production. Moreover, the device showed excellent reliability, achieving a linear regression coefficient (R2) value of 0.9943 throughout the whole refractive index spectrum. The high sensitivity, practicality, and reliability of the proposed sensor confirm its applicability real-time monitoring to ensure food safety and safeguard public health.
This paper designs a surface plasmon resonance dual-parameter sensor based on a dual-core D-type photonic crystal fiber, and proposes a hybrid deep learning prediction model. The sensor constructs two independent sensing channels for refractive index and temperature detection. The upper channel uses an Au-TiO _2 composite coating for refractive index detection, and the lower channel uses an Au-Polydimethylsiloxane (PDMS) composite structure for temperature detection. From the structural perspective, the sensor achieves complete physical decoupling of the two parameters and the crosstalk between the channels is less than 1 nm. The sensor has a maximum sensitivity of 19000 nm/RIU within the refractive index range of 1.30 1.41 RIU, and a maximum sensitivity of 27.1 nm/ ^∘ C within the temperature range of -19 - 100 ^∘ C. Moreover, the structural parameters such as the radius of the air holes, the hole spacing, and the polishing depth all have excellent tolerance. In response to the low computational efficiency problem of the traditional finite element method, this paper further proposes a hybrid deep learning model named HybridOpticalNet, which integrates a residual multi-layer perceptron and a one-dimensional convolutional neural network. The model adopts a dual-branch parallel architecture to extract global structural features and local spectral features, achieving deep complementary fusion of the two types of information. The prediction coefficient R^2 of the model for the dual-channel loss spectrum is above 0.998, the average absolute error is less than 30 dB/m, and the spectral prediction can be completed within milliseconds, with a significant improvement in efficiency compared to traditional numerical methods. This sensor has high sensitivity, low crosstalk, and good process tolerance. Combined with the deep learning model, it can complete the rapid design and performance optimization of multi-parameter PCF-SPR sensors, and has broad application prospects in biochemical detection and environmental monitoring fields.
A flexible polyvinyl alcohol (PVA)-based surface-enhanced Raman spectroscopy (SERS) substrate was fabricated by solution casting, followed by Ag deposition using DC magnetron sputtering and controlled thermal annealing. X-ray diffraction analysis confirmed the formation of face-centered cubic (fcc) Ag with a dominant (111) orientation after thermal treatment, indicating improved crystallinity. The hydroxyl groups present in the PVA matrix, as identified by FTIR analysis, may promote the adsorption of analyte molecules through hydrogen-bonding interactions. Morphological analysis revealed substantial restructuring of the Ag layer after annealing, resulting in a finer, and more densely distributed Ag nanoisland morphology. Elemental analysis confirmed the presence and distribution of Ag on the polymer substrate. The SERS performance was evaluated using crystal violet (CV) as a model analyte over a concentration range of 10− 2–10− 6M. The fabricated substrate achieved a limit of detection (LOD) of 6.4 × 10− 6 M and exhibited a linear response with R² = 0.91785. An enhancement factor of 3.659 × 107 was achieved, demonstrating substantial Raman signal enhancement. The substrate also exhibited good spatial reproducibility, with a relative standard deviation (RSD) of 9.9
Localized surface plasmon resonance (LSPR) sensing commonly interprets a resonance red shift as interfacial binding, although bulk-medium drift, nonspecific dielectric loading and metal-surface transformation can produce similar spectral displacement. Here, spherical Au and Ag reference particles are used to compare these mechanisms with the Discrete Dipole Scattering code (DDSCAT), spatial-resolution and polarizability checks, and exact coated-sphere Mie benchmarks. The Au bulk-index calibration gave an endpoint sensitivity of approximately 176 nm per refractive-index unit (RIU). A 5 nm protein-like shell with refractive index 1.45 produced a 4.42 nm shift, equivalent to an apparent 0.0250 RIU change; a 10 nm shell produced an 8.38 nm shift and 0.0475 RIU. For a 30 nm-radius Ag core in water, the corrected Bennett et al. composite tarnish-film model gave exact-Mie shifts of 15.31, 33.27 and 48.24 nm for 1–3 nm shells. At 3 nm, the full width at half maximum (FWHM) increased from 48.14 to 81.50 nm, the quality factor (Q) decreased from 8.67 to 5.71, the scattering fraction decreased from 85.23
Effective porphyrin-mediated electrosyntheses of nanocomposites of silver and palladium nanoparticles (AgNPs and PdNPs) with tetraphenylporphyrin (TPP), as well as its complex with cobalt(II) (TPPCo(II)) were carried out in the absence and presence of a stabilizer poly(N-vinylpyrrolidone) (PVP), in dimethylsulfoxide (DMSO) medium at room temperature. Silver or palladium ions were in situ generated directly during electrolysis by dissolving the corresponding metal anodes. The synthesis results were universal hybrid organo-inorganic nanocomposites of mainly spherical AgNPs and PdNPs, stabilized by the coordination interaction of pyrrole nitrogen atoms with metal(0) in the porphyrin matrix or by polymer PVP The X-ray photoelectron spectroscopy (XPS) of obtained samples also confirms a presence of metallic palladium as nanocomposite with porphyrin. The fluorescence spectroscopy study of the obtained nanocomposites ability to bind the antitumor drug doxorubicin (DOX) demonstrated the presence of almost 100
Plasmonic integration provides an opportunity to improve light control in perovskite solar cells (PSCs) based on localized surface plasmon resonances (LSPRs). In this study, perovskite thin films integrated with Au, Ag, Al, and Ti metal layers were systematically investigated under identical processing conditions. Ultrathin metal films ( 10 nm) were annealed at 500 °C and 700 °C to induce nanoparticle formation by solid-state dewetting and to test the resulting structural and optical evolution. The UV-Vis results indicate a clear metal-dependent optical response, with Au-integrated films showing the most pronounced enhancment in visible-region absorption ( 4
We theoretically propose a triple-narrowband perfect absorber based on graphene-embedded asymmetric Fabry–Pérot cavity for visible-to-near-infrared spectral range. By physically pre-determining the Ag thickness via critical-coupling theory, a simple stochastic search in the reduced parameter space is employed to optimize the graphene positions, achieving simultaneous perfect absorption (> 99
Magnetic field is intimately linked to human life and modern technology across diverse areas, including biomedical, industrial power system monitoring, geoscience exploration, and so on. Consequently, the development of high-sensitivity magnetic field sensors has become a research priority. First, a magnetic field photonic crystal fiber sensor based on the surface plasmon resonance effect is proposed, encompassing three-layer air holes and an elliptical open ring. The linear proportional method employed in the sensor structural design can facilitate independent adjustment of the phase-matched wavelength and reduce manufacturing complexity. Based on the physical mechanisms, a material composition including TiO2, Au, and graphene is employed as the plasmonic material. Subsequently, to achieve optimal performance, the influence of each structural parameter on the sensing performance is analyzed individually by utilizing the finite element method. The results show that the proposed sensor can detect the magnetic field from 40Oe to 170Oe, with a maximum sensitivity of 13 nm/Oe and an average sensitivity of 1.85 nm/Oe. Finally, comparison of different material combinations verifies the feasibility of the material configuration of the proposed sensor from the standpoint of the numerical data. Such a process of structural design, optimization, and material comparison paves the way for the future proposal of high-sensitivity magnetic sensors.
The active medium in the random laser consisted of an active material, the kiton red dye, and scattering centers. In the current study, two types of scattering centers were used: perovskite nanoparticles and Au nanoparticles. The thermal relaxation time and thermal diffusivity of this medium are significant factors that affect the stability of the structure and output coefficients. Thermal lens spectroscopy, which relies on the use of two types of lasers, was used to measure these two factors. The pumping laser had a wavelength of 532 nm and a power of 20 mW, whereas the probe laser was of the helium-neon type with a wavelength of 632 nm and a stable power of 1 mW. The results showed a clear effect of the dye solution concentration, as increasing the dye concentration increased the thermal relaxation time and decreased the thermal diffusivity. A significant effect was also observed when nanoparticles were added. The also of perovskite nanoparticles led to nonlinear behavior, which created an ideal volumetric ratio for heat leakage. The results also showed that the addition of Au nanoparticles led to an increase in the thermal relaxation time and a deterioration in the thermal diffusivity. The reason for the increased thermal relaxation time in the case of nano-gold is its strong absorption of light and its conversion into heat via the photothermal effect, which increases the overall heat capacity of the system, while perovskite allows the possibility of controlling heat leakage through the optimal volume ratio. These findings can be used to design thermally stable random laser devices for biomedical imaging and remote sensing applications. A future horizon for this work is to develop a theoretical model that links the geometric structure of the scattering centers and the parameters that were measured.
This study presents a D-shaped photonic crystal fiber (PCF) surface plasmon resonance (SPR) sensor based on an Au/Al2O3 hyperbolic metamaterial (HMM) stack. By depositing a three-period Au/ Al2O3 HMM stack, consisting of six alternating layers, on the polished PCF surface, strong localized field enhancement is achieved through hyperbolic dispersion characteristics. Key structural parameters (Λ = 2.25 μm, d = 1.0 μm, f = 9.7 μm, t1 = 4.5 nm, t2 = 10.0 nm) are optimized via COMSOL simulations. The sensor exhibits a broad refractive-index (RI) detection range of 1.20–1.42 RIU, achieving a maximum wavelength sensitivity (WS) of 53,600 nm/RIU and a figure of merit (FOM) of 420.39 RIU− 1. Compared with conventional Au-film structures, the HMM integration provides a clear enhancement in RI sensitivity, especially in the high-RI region. A feasible fabrication route, including fiber drawing, side polishing, and sequential deposition of the Au/Al₂O₃ multilayer, is also discussed. This work provides a numerically promising design for wide-range bulk RI sensing.
This work investigates the performance enhancement of an aluminum (Al)-based plasmonic device in the near-infrared region by incorporating a metamaterial layer. The quantitative findings from angle interrogation reveal a notable improvement in quality factor and figure of merit when a metamaterial layer is incorporated over conventional structures. The proposed hybrid structure comprises a metal-dielectric-metal (MDM) configuration, with Al as the metal and barium titanate (BTO) as the high-dielectric material. A monolayer of molybdenum disulfide (MoS2) serves as the binding medium, increasing the adsorption of biomolecules on the sensor surface. Additionally, a titanium oxide (TiO2) nanolayer coating over the metamaterial layer has been shown to yield enhanced sensitivity due to its high refractive index and low loss. The proposed plasmonic device offers a quality factor of 3303 and a Figure of Merit of 5060 RIU− 1. This is further used to numerically assess refractive-index changes representative of cervical (HeLa), blood (Jurkat), and breast (MCF-7) cancer cell states. The integration of metamaterials into surface plasmon resonance (SPR) sensor design holds transformative potential for optical sensing. The ability of these materials to manipulate and intensify electromagnetic fields at the interface substantiates their use in next-generation high-performance SPR sensors for advanced biomedical diagnostics.
A novel angle-modulated surface plasmon resonance biosensor based on a Prism/Ag/BaTiO₃/antimonene/sensing medium multilayer in the Kretschmann configuration is proposed and analyzed at 633 nm. The influence of prism refractive index and BaTiO₃ spacer thickness on sensor performance is systematically investigated using the transfer matrix method. Results show that when a high-index BaTiO₃ spacer is employed to shift resonance toward higher incident angles, lower-index prisms achieve comparable sensitivity with significantly thinner dielectric layers and consequently narrower resonance widths. For the refractive index range of 1.33–1.34, the optimized CaF2-based structure requires only a 3 nm BaTiO₃ layer and achieves a sensitivity of 401.7 °/RIU, detection accuracy of 0.41 deg⁻¹, quality factor of 164.8 RIU⁻¹, and signal-to-noise ratio of 1.648, outperforming comparable reported sensors. Extending the analysis to a wider refractive index range of 1.33–1.36 demonstrates that the optimal prism is the lowest-index prism capable of sustaining SPR over the desired sensing interval, leading to an optimized SiO₂-based design with a sensitivity of 291.97 °/RIU, detection accuracy of 0.5463 deg⁻¹, quality factor of 159.5 RIU⁻¹ and signal-to-noise ratio of 4.785. The proposed sensor is further evaluated using antimonene, MXene Ti₃C₂Tₓ, and graphene as biorecognition layers. Concerning its low dielectric loss, antimonene provides superior performance, improving sensitivity, detection accuracy, and quality factor by up to 15.53
A dual-parameter sensor based on lossy mode resonance (LMR) using a D-shaped offset-core photonic quasicrystal fiber (PQF) is proposed in this paper, and a parallel-designed neural network structure combining the Patch Time Series Transformer (PatchTST) and Long Short-Term Memory Network (LSTM) is employed to optimize its structure. This sensor detects refractive index (RI) by coating a layer of titanium dioxide (TiO2) and a layer of indium tin oxide (ITO) on a D-shaped polished surface, and by coating a layer of ITO and filling polydimethylsiloxane (PDMS) on the pores on both sides of the core for temperature detection. Without the optimization of structural parameters by the neural network, the detection ranges of RI and temperature are 1.370 1.442 and − 25 ℃ 40 ℃, respectively, with the maximum RI sensitivity of 17,500 nm/RIU and the maximum temperature sensitivity of 2.8 nm/℃. The applied neural network predicts the sensitivity under different structural parameters with coefficient of determination (R²) scores of 0.99978 and 0.99992, respectively. After optimization of the structural parameters, the detection ranges of RI and temperature are 1.360 1.442 and − 30 ℃ 60 ℃, respectively, with maximum sensitivities of 73,000 nm/RIU and 2.9 nm/℃. This achieves a significant improvement in sensor performance and an effective reduction in computational complexity, providing a more efficient and reliable design method for sensor development.
Hybrid metal–insulator–semiconductor (MIS) nanostructures provide a powerful platform for enhancing solar-driven photocatalysis by combining plasmonic light concentration with controlled interfacial carrier dynamics. In this work, the optical response and solar-harvesting performance of a concentric Pd@SiO₂@TiO₂ core–shell nanostructure are systematically investigated using full-wave finite-difference time-domain (FDTD) simulations. The influence of key geometric parameters—including Pd core radius, SiO₂ spacer thickness, and TiO₂ shell thickness—is analyzed through spectral characteristics and solar-weighted metrics, namely the Solar Overlap Integral (SOI) and Absorbed Photon Flux (APF). The MIS architecture induces plasmon hybridization, giving rise to antibonding and bonding modes that extend absorption into the near-UV and visible regions. The SiO₂ spacer plays a dual role by suppressing interfacial losses while regulating near-field coupling, yielding an optimal thickness of 2 nm for maximizing solar-weighted performance. Increasing both the TiO₂ shell thickness and Pd core size leads to a monotonic enhancement in absolute SOI and APF, driven by increased absorption volume, stronger plasmonic response, and improved spectral alignment with solar irradiance. In contrast, volume-normalized metrics reveal different optimal conditions. Thinner TiO₂ shells exhibit higher intrinsic efficiency due to effective utilization of the active semiconductor region. Similarly, the normalized SOI and APF show a clear optimum at a Pd core radius of 30 nm, reflecting a balance between enhanced plasmonic coupling and efficient energy localization within the TiO₂ shell. The combined analysis of absolute and normalized performance metrics highlights a fundamental trade-off between total photon harvesting and intrinsic efficiency. These findings establish clear design guidelines for optimizing plasmon–semiconductor coupling in MIS nanostructures and provide a quantitative framework for evaluating and engineering solar-driven optical absorption and photon utilization, which are indicative of enhanced carrier generation potential rather than direct measures of photocatalytic efficiency.
The present research proposes a novel, sustainable, and eco-friendly method for the synthesis of gold nanoparticles using *Brassica oleracea* (cabbage) extract, which were subsequently employed for biomolecule detection through a surface plasmon resonance (SPR)-based colorimetric approach. The formation of the nanoparticles was confirmed by UV–Vis spectroscopy, which exhibited an SPR peak at 544 nm for the uncoated AuNPs. Upon surface modification, the SPR peak shifted to 540 nm and 533 nm for the PVA- and PEG-coated AuNPs, respectively, indicating improved particle dispersion and reduced agglomeration. FTIR results confirmed the presence of characteristic bands at 3400–3600 cm⁻¹ (O–H) and 1630–1650 cm⁻¹ (C = O), demonstrating the role of biomolecules in both the reduction and stabilization of the nanoparticles. XRD analysis revealed a face-centered cubic (fcc) crystal structure with diffraction peaks indexed to the (111), (200), (220), and (311) planes, confirming the high crystallinity and phase purity of the synthesized AuNPs. TEM images showed particle sizes ranging from 11 to 59 nm depending on the stabilization method. In the bacterial detection experiment, the SPR peak of the uncoated AuNPs shifted from 520 to 529 nm after interaction with Pseudomonas aeruginosa, while the PVA- and PEG-coated AuNPs exhibited redshifts to 550 nm and 554 nm, respectively, accompanied by a distinct color change. Furthermore, fluorescence measurements revealed an increase in the emission intensity at 518 nm with increasing bacterial concentration. These findings demonstrate the efficiency of the developed system as a rapid, low-cost, and environmentally friendly biosensor with promising potential for diagnostic applications.
