Search Results (1,407)

2,4-Dichlorophenoxyacetic acid (2,4-D) is an extensively applied organic compound, primarily for agricultural weed control and plant growth agents. Although 2,4-D usually exists in the environment in low volumes, the detection of 2,4-D is critical for human health and environmental safety. In this work, a biophotonic biosensor was fabricated by coating the surface of a tapered optical fiber with gold nanoparticles (AuNPs) to excite the localized surface plasmon resonance (LSPR) and functionalizing the fiber with molybdenum disulfide nanosheets (MoS₂-NSs)/zinc oxide nanowires (ZnO-NWs) to extend the effective sensing area. Due to the inhibitory effect of 2,4-D on the hydrolytic activity of ALP, the refractive index (RI) around the sensor surface changes, leading to a shift in the LSPR peak wavelength. According to this sensing technique, the sensor can detect concentrations in the range of 1–10 mg/L, with a limit of detection (LOD) of 0.29 mg/L. The stability, repeatability and selectivity tests show that the sensor has good stability and selectivity. In the actual sample detection experiment, the recovery rates of apples and Chinese cabbage were 96.2–100.4% and 83.8–108.8%, respectively, which indicated that the detection method had good accuracy for the detection of target substances in actual samples. Thus, the proposed sensor has an important application in the detection of 2,4-D herbicides. Full article

Optical fiber multi-analyte biosensors have become an important cutting-edge technology for the simultaneous detection of multiple biochemical substances in complex samples due to their unique advantages such as small size, anti-interference capability, and remote and label-free detection. This paper systematically reviews the recent research progress of optical fiber multi-analyte biosensors in the field of simultaneous detection of various types of targets. The review is organized by detection target type and elaborates on the simultaneous detection of biomarkers and proteins, viruses and bacteria, biological metabolites and nutrients, heavy metal ions, gases, organic pollutants, cells, and mixed detection of different types of biochemical substances. The advantages and disadvantages of existing optical fiber multi-analyte biosensors are summarized. Key technical challenges are also discussed, including issues of selectivity, long-term stability, real-sample validation, and system integration that currently hinder practical deployment. Finally, the future challenges and development directions of optical fiber multi-analyte biosensors are briefly discussed, providing references for relevant research teams. Full article

A highly sensitive surface plasmon resonance (SPR) sensor is theoretically presented, including Silver (Ag), Tin Diselenide (SnSe₂), Zirconium Diselenide (ZrSe₂) and a sensing layer using the Kretschmann configuration. At the optimized thickness of the Ag layer, the sensitivity was measured using the angular interrogation method with a refractive index (RI) of 1.33–1.35. The sensitivity of the sensor was found to be 337.98°/RIU for a 2 nm SnSe₂ layer thickness at RI of 1.34 and 320.94°/RIU for a 1 nm SnSe₂ layer thickness at RI of 1.35 throughout with remarkable figure of merit (FoM) of 60.78/RIU and 64.57/RIU at 633 nm wavelength. The maximum sensitivity was achieved with 1 nm thickness of the SnSe₂ layer. By systematically optimizing the Ag thickness, significant improvements in sensitivity, minimum reflectance (R_min), detection accuracy (DA), and figure of merit (FoM) were achieved compared with the conventional Ag-only configuration. These additional SnSe₂ layers increase the confinement of the electromagnetic field, increase the number of adsorption sites for biomolecules, and increase the effective change in the RI, resulting in larger shifts in the resonance angles. The proposed multilayer sensor provides a promising platform for high-performance, stable, and repeatable biosensing applications in chemical detection, environmental monitoring, and medical diagnostics, according to the results obtained. Full article

The accurate detection and quantification of electromagnetic radiation in the infrared (IR) and terahertz (THz) regions are critical for modern applications, yet they remain challenging due to the “THz gap” and the limitations of current room-temperature technologies. This paper proposes a novel uncooled IR–THz power sensor based on a hybrid graphene oxide (GO) and polydimethylsiloxane (PDMS) bilayer integrated into a surface plasmon resonance (SPR) architecture in the Kretschmann configuration. The device exploits the broadband optical absorption of GO to efficiently convert incident radiation into heat, while the high thermo-optic coefficient of the PDMS layer translates these thermal variations into measurable refractive index shifts. Finite Element Method (FEM) modeling was employed to optimize the sensor design, predicting a linear angular shift of 0.093 deg/mW. Experimental results confirm the theoretical expectations, demonstrating a high sensitivity of 0.083 deg/mW and an exceptionally low limit of detection and resolution on the order of 15 nW. By eliminating the need for cryogenic cooling or vacuum packaging, this platform offers a compact, low-cost, and high-performance solution for next-generation IR–THz metrology. Full article

Introduction: Heavy metal contamination in water represents a major environmental and public health challenge because toxic ions frequently occur as complex multi-species mixtures rather than isolated pollutants. This study presents a numerical design and optimization of a surface plasmon resonance (SPR) sensor based on a LaF/Au/BaTiO₃/WS₂ heterostructure for monitoring refractive-index changes associated with mixed heavy metal ions in aqueous media. Methodology: The optical response of the multilayer sensor was evaluated using the transfer matrix method under TM-polarized illumination at 633 nm. Systematic optimization was performed for the prism substrate, Au thickness, dielectric oxide layer, and 2D nanomaterial interface. The final configuration consisted of a LaF prism, 50 nm Au film, 2.0 nm BaTiO₃ spacer, and 0.80 nm WS₂ monolayer. Sensor performance was assessed using resonance-angle shift, sensitivity, detection accuracy, quality factor, figure of merit, FWHM, attenuation, and estimated limit of detection. Results and Discussion: The optimized LaF/Au/BaTiO₃/WS₂ configuration produced stable simulated SPR responses across single, binary, quaternary, and five-ion heavy metal matrices. The WS₂ monolayer provided the highest angular displacement among the evaluated 2D materials, while BaTiO₃ improved field confinement and limited optical damping in the numerical model. The configuration maintained attenuation near 1.6%, FWHM values around 7.9°, detection accuracy between 0.030 and 0.032 deg⁻¹, and model-based refractometric LoD values down to 3.49 × 10⁻⁵ RIU under the assumed angular-resolution criterion. Conclusions: The proposed LaF/Au/BaTiO₃/WS₂ SPR configuration provides a numerical framework for label-free monitoring of refractive-index changes associated with complex heavy-metal-ion mixtures in contaminated water. Experimental fabrication and testing are required to validate the simulated performance. Full article

We developed a smartphone-assisted digital image-based optical biosensor array using a planar glass slide with sensor spots in a 2 × 5 array format for point-of-care multiplex detection of biomarkers. The detection is based on the integration of the capture antibody (Ab^C)-functionalized sensor array with a detection antibody-conjugated gold nanoparticle bioconjugate (AuNP@Ab^D) in the presence of interleukin-8 (IL8) to form a sandwich-type AuNP@Ab^D–IL8–Ab^C nanocomplex on the sensing spot surface. Thus, the colorimetric detection method can be applied to the quantitative analysis of IL8, a clinically relevant pro-inflammatory and pro-angiogenic biomarker. The sensing strategy utilizes digital image-based analysis via ImageJ software (V 1.54 g; Java 1.8.0_345 [64 − bit], Windows 8) to quantify the colorimetric signals generated by the light absorbance of surface-bound gold nanoparticles in response to an IL8 droplet sample of merely 8 μL on the planar glass surface, achieving a low detection limit of 0.23 pg/mL (27 fM) and good reproducibility with a coefficient of variation of 0.95%. Validation using IL8-spiked serum at concentrations of 1 × 10⁻⁹ M and 1 × 10⁻¹⁰ M showed minimal matrix effects with a detection accuracy of 99.5% and 106.1%, respectively. Hence, this low-cost portable digital image-based plasmonic nanoparticle-linked immunosorbent assay serves as an alternative to traditional enzyme-linked immunosorbent assays. Full article

Although optical fiber-based surface plasmon resonance (SPR) sensors have revolutionized real-time, label-free biosensing, conventional designs suffer from limited multi-analyte detection capabilities. This study utilizes the novel Pi (π)-configured dual SPR optical fiber sensor with two opposing side-polished surfaces, enabling plasmonic excitation for simultaneous multi-analyte detection. The proposed sensor leverages asymmetric metallic thin films such as Ag, Au, Cu, and hybrid configurations (metal + TiO₂) to generate two distinct resonance peaks, significantly enhancing detection versatility. Numerical simulations using the finite element method in COMSOL Multiphysics v6.3 demonstrate that the π-configuration achieves dual resonance dips at 982 nm and 1276 nm for Ag and Ag–TiO₂ films, 1040 nm and 1317 nm for Au and Au–TiO₂ films, and 977 nm and 1249 nm for Cu and Cu–TiO₂ films, respectively, for an analyte refractive index of 1.42. A peak spectral separation >125 nm was achieved for all the sensors for a refractive index range of 1.37–1.42, ensuring that the two dips are resolvable since the change in SPR wavelength is greater than or equal to the full width at half maximum, preserving dual-analyte capability and minimizing potential crosstalk. The results indicate that the π-configured dual SPR sensor utilizing silver and silver–TiO₂ sensing layers had the highest wavelength sensitivity of 12,600 nmRIU⁻¹ and 20,000 nmRIU⁻¹, respectively, slightly outperforming its gold and copper counterpart. The optimized metallic and hybrid nanostructured films ensure dual distinct peaks with high sensitivity, while maximizing refractive index resolution. This work presents the design of a π-configured SPR-based optical fiber sensor utilizing dielectric and multi-metallic thin films, thereby offering a breakthrough in multiplexed biosensing for applications in medical diagnostics, environmental monitoring, and chemical detection. Full article

Due to the limited application of sensors in the low-refractive-index range, accurate detection of certain low-refractive-index objects remains challenging. To address this limitation, this study proposes a novel D-shaped photonic crystal fiber (PCF) operating on the surface plasmon resonance (SPR) principle. Distinct from conventional D-type PCF designs, the proposed structure employs an open-loop channel coated with a gold film to enable efficient excitation. Finite element analysis shows that the sensor’s detection range of refractive index is between 1.23 and 1.32. With increasing analyte refractive index, the loss peak exhibits progressive broadening and eventual stabilization. A maximum spectral sensitivity of 18,500 nm/RIU and a resolution of 5.41 × 10⁻⁶ RIU are attained at a refractive index of 1.32. The sensor features a straightforward design and exhibits excellent performance characteristics. Its exceptional sensing capabilities make it highly competitive for use in applications with a low refractive index. At the same time, to optimize the sensing performance, this study investigates how structural parameters affect the resonant spectrum. Full article

In this work, we propose a hyperbolic metamaterials (HMMs)-based coreless fiber surface plasmon resonance (SPR) sensor. Leveraging the absence of a core in coreless fibers, the evanescent waves at the cladding–external solution interface couple more effectively into the solution, enabling surface plasmon resonance without any additional processing. To enhance sensitivity, we adopted a multimode–coreless–multimode (MCM) structure and grew layered hyperbolic metamaterials as the SPR-excitation-sensitive layer within the coreless region. Through finite element simulations, we optimized HMM parameters and fabricated high-performance HMM-SPR sensors. Test results demonstrate that the fabricated HMM-SPR sensor achieves an optimal refractive index sensitivity of 3703.33 nm/RIU, representing a 49.68% improvement over single-layer gold film SPR sensors. It successfully detects glucose solutions at varying concentrations with a sensitivity of 2671.25 nm/RIU. The high-sensitivity, structurally simple HMM-SPR sensor we proposed demonstrates broad application prospects in biosensing, environmental monitoring, food safety, and other fields. Full article

Active control of multi-mode light–matter interactions is crucial for advancing quantum photonic technologies. Although triple-mode plasmon–exciton systems involving two distinct excitonic transitions offer a pathway to multi-level polaritonic states, achieving reversible electrical tuning at room temperature remains challenging. Here, we numerically investigate an electrically tunable triple-mode strong-coupling system comprising a J-aggregate-coated Au@Ag nanorod coupled with monolayer WS₂. The simulated spectra show a UPB–LPB energy separation of approximately 239 meV near the zero-detuning condition. A modest gate voltage (2.0 V to 3.8 V) selectively modulates the middle and lower polariton branches over ∼46 meV, while the upper branch remains largely unaffected. This selective control is elucidated via a triple-mode coupled-oscillator model and Hopfield coefficient analysis, linking the polariton response to the excitonic composition. These results establish a framework for electrically reconfigurable multi-level polaritonic devices, offering potential for ultracompact optical modulators, high-sensitivity multiplexed sensors, and programmable quantum photonic circuits. Full article

We demonstrate a mechanism-oriented Surface-Enhanced Raman Scattering (SERS) platform based on a hybrid structure integrating monolayer molybdenum disulfide (MoS₂) and gold nanospheres (AuNSs) on an optical microfiber (MF). The microfiber serves as a whispering-gallery-mode (WGM) microcavity. Monolayer MoS₂, grown directly on the microfiber surface via chemical vapor deposition (CVD), provides a chemically active interface for molecular adsorption and charge-transfer-related chemical enhancement. Subsequently deposited AuNSs couple with the microfiber-supported WGM, leading to the formation of hybrid photonic–plasmonic modes. This coupling results in a narrowed scattering resonance and a localized electromagnetic hotspot near the AuNS–microfiber interface. The combined contribution of electromagnetic enhancement from the microfiber–AuNS hybrid cavity and chemical enhancement from the MoS₂ layer produces discernible Raman enhancement for Rhodamine 6G (R6G) molecules under proof-of-concept measurement conditions. This work provides a useful platform for studying SERS enhancement mediated by hybrid photonic–plasmonic modes and offers guidance for the future development of optimized fiber-based SERS sensors. Full article

This study proposes a novel anti-resonant fiber sensing structure based on a composite “egg-shaped” configuration with surface plasmon resonance (SPR) effect. By designing a novel anti-resonant structure consisting of a semicircle and a semi-ellipse and coating its inner surface with a gold film, the optimal structural parameters are determined through three sets of simulation experiments using temperature sensitivity as the criterion. The optimal sensing structure was applied to the simulated detection and analysis of cancer cells, aiming to provide value and reference for the application of high-sensitivity optical fiber sensor in the field of cancer cell detection. Simulation results show that the proposed sensing structure achieves a maximum temperature sensitivity (TS) of 3.86 nm/°C. For the detection of six different types of cancer cells, the maximum wavelength sensitivity (WS), optimal resolution (R), maximum figure of merit (FOM), maximum signal-to-noise ratio (SNR), and best limit of detection (LOD) reach 12,142.86 nm/RIU, 8.24 × 10⁻⁶, 3035.72 RIU⁻¹, 65.50, and 0.94 nm, respectively. Owing to its unique detection mechanism, the proposed sensing structure exhibits label-free characteristics and demonstrates balanced and excellent performance across all metrics for both temperature and cancer cell detection, showing broad application prospects and great potential in the fields of environmental monitoring and medical prevention and treatment. Full article

This work presents an intrinsic optical fiber sensor based on plasmonic phenomena in modified plastic optical fibers (POFs). The sensing area is achieved by replacing the polymethyl methacrylate (PMMA) core with a molecularly imprinted polymer (MIP) containing gold nanorods (GNRs). Thus, in the sensing area, the MIP acts as both a selective recognition element and an optically sensitive guiding medium where plasmonic phenomena occur. This optical–chemical configuration has been developed as a proof-of-concept for the detection of furfural in aqueous solution. The proposed sensor achieves a limit of detection (LOD) of 27 pM, demonstrates high selectivity for the analyte of interest, and is applicable even in real-world scenarios, as demonstrated by experimental results (a commercially available infant milk). The proposed sensor presents a significant enhancement of the sensor response, of about six orders of magnitude, compared to a conventional configuration where the same (or a similar) mixture of MIP/GNRs is spun over the exposed PMMA of a D-shaped POF area for comparison. Notably, even if this study has been carried out via a proof-of-concept in furfural detection, this substantial improvement is achieved while preserving a simple, portable, and cost-effective optical setup, highlighting the potential of this sensing strategy for the development of highly selective sensors by changing the MIP template. Full article

Smart manufacturing, Industry 4.0, and cyber-physical systems (CPSs) require sensing architectures capable of resolving both spatially distributed asset behavior and highly localized process states. This review examines optical fiber sensors (OFSs) and integrated photonic sensors for industrial monitoring through a deployment-oriented, multi-scale perspective. The discussion covers five major application regimes: continuous infrastructure surveillance, structural health monitoring (SHM) of load-bearing composites, dynamic condition monitoring of machinery, in situ observability in advanced manufacturing, and localized chemical or gas sensing. Extended fiber-optic networks, including distributed fiber-optic sensing (DFOS) based on Rayleigh, Raman, and Brillouin scattering, together with multiplexed fiber Bragg grating (FBG) sensors, provide passive, embeddable, and remotely interrogated monitoring for large-scale assets and harsh environments. Photonic integrated circuits (PICs) shift transduction to compact node-level devices for localized thermal, mechanical, refractive-index, absorption, vibration, and inertial measurements, while plasmonic and dielectric nanophotonic sensors extend optical monitoring toward surface-selective and chemically specific detection. Across these platforms, digital signal processing (DSP), machine learning (ML), sensor fusion, and digital-twin (DT) coupling are treated as artificial-intelligence-enabled (AI-enabled) layers for signal recovery, inverse mapping, uncertainty reduction, and predictive maintenance. The review argues that scalable industrial adoption is less limited by sensing physics than by the complete deployment chain: packaging, fiber–chip interfacing, calibration stability, interrogation robustness, and AI-enabled data interpretation. This manuscript is structured as a deployment-oriented narrative review of optical fiber and integrated photonic sensors for industrial monitoring and smart manufacturing. Full article

An optical sensor based on a polymethacrylate matrix (PMM) with immobilized gold nanoparticles (Au⁰ NPs) has been developed for the determination of pollutants in environmental samples. The nanoparticles are synthesized by chemical reduction of Au(III) to Au⁰ using sodium borohydride, which yields conglomerates of spherical particles with an absorption maximum at 530 nm. The time stability of the nanocomposite is demonstrated, as well as the ability to control the nanoparticle loading in the matrix by varying the concentration of the HAuCl₄ solution. The analytical capability of the PMM–Au⁰ system is demonstrated for the direct determination of tetracycline in river water in two linear concentration ranges: 0.001–0.010 mg/L and 0.025–0.100 mg/L, with detection limits of 0.0005 mg/L and 0.012 mg/L, respectively. The determination of tetracycline is based on the enhancement of its intrinsic fluorescence at 520 nm by gold nanoparticles in the solid phase following solid-phase extraction from water in the anionic form H₂TC⁻ using PMM–Au⁰. The colorimetric determination of thiocyanate anions is based on a color change of the PMM–Au⁰ nanocomposite from red to blue, corresponding to a shift in the plasmon absorption maximum from 530 nm to 630 nm. The sensor exhibits a linear response in the thiocyanate concentration range of 0.3–50.0 mg/L, with a detection limit of 0.1 mg/L. Thus, the multifunctional PMM–Au⁰ sensor has been used for the determination of various analytes employing different modes of analytical signal readout after minimal sample preparation. Full article