Conventional Surface Plasmon Resonance Sensor Research Articles

Hybrid magneto-plasmonic structure consisting of hexagonal periodic nanodisks array with giant transverse magneto-optical Kerr effect for sensing application

The present study proposes a theoretical design of the magneto-optical surface plasmon resonance (MOSPR) refractive index sensor that utilizes a magnetic field for modulating the dispersion of surface plasmon. This sensor based on the transverse magneto-optical Kerr effect (TMOKE) is constructed using a hybrid magneto-plasmonic film covered with an array of hexagonal periodic Au nanodisks. The structural parameters were optimized to obtain the Fano shape TMOKE response characterized by an extremely narrow bandwidth (0.00997°) and remarkably high amplitude (0.99). The excitation of the optimal surface plasmon resonance (SPR) and the resonance enhancement effect of multi-mode coupling enables us to achieve a surface sensitivity of 207.5 deg RIU−1 and a high figure of merit of the order of 104 RIU−1, surpassing conventional SPR and MOSPR sensors by at least one order of magnitude. The present study offers a comprehensive guideline for the design of high-performance magneto-plasmonic sensors, facilitating instrument miniaturization and manufacturing cost reduction.

Analytical Design of a Portable Surface Plasmon Resonance Sensor by Using a Divergence Beam for Measuring Multiple Heavy Metals and Other Contamination Simultaneously

The study proposes a surface plasmon resonance (SPR) sensor for measuring water quality by detecting the presence of heavy metal ions and other contamination. The proposed SPR sensor operates in the Kretschmann configuration, which employs the divergence beam produced by the Powell lens. The beam is diverged to eliminate mechanical scanning, indicating that the sensor can measure water quality from deionized water (DIW) with refractive index (RI) of 1.3317, diluted DIW with multiple heavy metal ion such as Hg[II], Pb[II], Ni[II], Zn[II], Cu[II] at concentration of 100 μM and other pollutant with the RI of 1.34 without any mechanical movement. The proposed SPR sensor has a theoretical sensitivity of 399.45˚/RIU and resolution of 1.3456×10-8 and 8.3790×10-10RIU with 8-bits (ATmega1284) and 12-bits (STM32F401RE) ADC of the controller, respectively. The CCD sensor (TCD1304AP) and microcontroller data sheets were used to calculate the theoretical in which all these components are very chip. The reported sensitivity and resolution were achieved because of the proper application and optimization of TiO2 and BaTiO3. In comparison to a conventional SPR sensor, the proposed SPR improved sensitivity and figure of merits by 50.98 % and 13.93 %, respectively. Furthermore, the proposed SPR sensor outperforms recently published research in terms of performance

Lossy Mode Resonance Sensors Based on Anisotropic Few-Layer Black Phosphorus.

Lossy mode resonance (LMR) sensors offer a promising avenue to surpass the constraints of conventional surface plasmon resonance (SPR) sensors by delivering enhanced label-free detection capabilities. A notable edge of LMR over SPR is its excitation potential by both transverse electric (TE) and transverse magnetic (TM) polarized light. Yet this merit remains underexplored due to challenges to achieving high sensing performance under both TM and TE polarization within a singular LMR model. This study introduces a theoretical model for an LMR prism refractive index sensor based on a MgF2-few layer black phosphorus-MgF2 configuration, which can achieve angular sensitivity nearing 90° refractive index unit-1 (RIU-1) for both polarizations. Leveraging the distinct anisotropic nature of black phosphorus, the figure of merit (FOM) values along its two principal crystal axes (zigzag and armchair) show great difference, achieving an impressive FOM of 1.178 × 106 RIU-1 along the zigzag direction under TE polarized light and 1.231 × 104 RIU-1 along the armchair direction under TM polarized light. We also provide an analysis of the electric field distribution for each configuration at its respective resonant conditions. The proposed structure paves the way for innovative applications of anisotropic-material-based LMR sensors in various applications.

Surface plasmon resonance sensor with photodiode integrated beneath plasmonic layer

Surface plasmon resonance (SPR)-based sensors have demonstrated exceptional sensitivity in detecting changes in the refractive index (RI) occurring near the sensor surface due to variations in concentration within the medium, chemical reactions, analyte binding with its ligand, and similar factors. However, most conventional SPR sensors rely on an external photodiode system and a complex mechanical system to measure changes in both intensity and position of reflected light. This is the main limitation of typical SPR sensors, making them non-portable and challenging to apply in experiments beyond the laboratory. Here, we propose SPR sensor chips integrated with a photodiode that eliminates the disadvantage of conventional SPR sensors. The photodiode is based on an n-type Silicon (nSi)-intrinsic Silicon (iSi) junction, sandwiched between a transparent conductive oxide layer, specifically Indium Tin Oxide (ITO), and a plasmonic material, namely Gold (Au). The working principle of our photodiode-integrated SPR sensors was revealed, and the impact of nSi and iSi film thicknesses on sensor sensitivity was investigated. Our SPR sensors enhance the efficiency of SPR-based sensors across diverse applications and facilitate integration into completed electronic devices.

Detection of fat concentration milk using TMDC-based surface plasmon resonance sensor

In this paper, a TMDC-based surface plasmon resonance (SPR) sensor for detecting fat concentration milk, incorporating an Ag-Pt (bimetallic) layer, is presented. The Pt (Platinum) layer provides chemical stability and increases sensitivity with the TMDC layer. Compared to the conventional SPR sensor, the maximum sensitivity, detection accuracy (DA), and figure of merit (FoM) of 314∘/RIU, 0.142/degree, and FoM 44.05/RIU are achieved with the WS2 layer. The sensor’s increased sensitivity is due to the increased field intensity and depth of penetration into the sensor layer, resulting in a larger interaction volume. The presence of the WS2 layer, with its significant imaginary part of the dielectric constant, helps improve sensitivity and broadens the SPR curves. This broadening SPR curve ultimately affects the DA and FoM of the sensor. The capability of the proposed sensor to detect various biological analytes with a refractive index (1.3452–1.3657) can be demonstrated.

Mode Coupling and Sensing in Plasmonic Layered Structures

Optical sensors based on a plasmonic multilayer stack, such as metal-insulator-metal (MIM), have attracted considerable attention over the past decades owing to their high resolution and high performance compared to conventional surface plasmon resonance (CSPR) sensors for bulk sensing (BS) applications. In this paper we show that CSPR is better than MIM sensors for thin film sensing, i.e. when a dielectric sensing layer (SL) is deposited on the outermost metal layer of the structure. We demonstrate that the deposition of a thin film SL on the top of the outermost-layer of an optimized multilayer structure, i.e. MIM, strongly decreases the evanescent electric field and the field enhancement at metal-SL interface and decreases the sensor’s sensitivity for MIM versus CSPR. By considering the theoretical and experimental results we demontrated that CSPR is more suitable than MIM for thin films sensing applications.

Advancing Sensitivity in Guided-Wave Surface Plasmon Resonance Sensor through Integration of 2D BlueP/MoS2 Hybrid Layers.

The surface plasmon resonance (SPR) signal, generated from the Kretschmann configuration, has been developed as an effective detection technology in chemical and biological sensors. The sensitivity of SPR signals to changes in the surrounding media makes it a valuable tool, as even a slight variation in refractive index can cause a significant change in SPR signals, such as phase, intensity, and resonance angle. However, the detection of ultralow changes in refractive index, which occur in chemical reactions or biological actions, remains a challenge for conventional SPR sensors due to their limited sensitivity. To overcome this limitation, we theoretically propose a novel guided-wave SPR (GWSPR) configuration coated with a few-layer blue phosphorene (blueP)/MoS2 hybrid structure. This configuration aims to enhance the electric field and subsequently achieve a significant improvement in sensitivity. The results of our study demonstrate that the proposed blueP/MoS2-based GWSPR sensor exhibits a high sensitivity of 290°/RIU, which represents an impressive enhancement of approximately 82.4% compared to the conventional Au-based SPR sensor. This advancement addresses the challenge of detecting ultralow changes in refractive index and offers significant potential for enhancing the performance of chemical and biological sensors.

High linearity temperature-compensated SPR fiber sensor for the detection of glucose solution concentrations

In the realm of optical fiber sensing, conventional surface plasmon resonance (SPR) sensors often face challenges due to their low linearity, broad resonance, and susceptibility to external temperature changes. To that end, we evaluate a groundbreaking approach with a temperature-compensating SPR biosensor based on the Mach-Zehnder interferometer (MZI), featuring a novel tapered multimode fiber-single mode fiber-multimode fiber (MMF-SMF-MMF) architecture. Specifically, the SPR is excited on a silver film modified by reduced graphene oxide (rGO) and π-π stacked pyrene-1-boric acid providing specific glucose binding ability. The MZI effect compensating for ambient temperature influence on the SPR is realized with the MMF-SMF-MMF structure. The study also explores the use of Fast Fourier Transform (FFT) for separate, granular analysis of the MZI and SPR signals and improves the linearity of the sensor using a novel centroid-fitting technique. This method utilizes the shift of calculated centroid coordinates rather than the single dip resonance wavelength from SPR, enhancing the overall performance of the sensor. The experimental results demonstrate excellent glucose sensitivity of 2.819 nm/mM, a linear range of 0–10 mmol/L, a LOD of 0.12 mM/L and concurrent temperature compensation. Compact and easy to fabricate, the proposed SPR sensor provides a novel solution for accurate glucose concentration detection in human blood.

Refractive index SPR sensor with high sensitivity and wide detection range using tapered silica fiber and photopolymer coating.

This paper introduces a surface plasmon resonance (SPR) sensor using tapered silica fiber and photopolymer coating for enhanced refractive index (RI) detection. Tapering the silica fiber to a diameter of 10 µm ensures the evanescent wave leaks into a 1.8-µm thick photopolymer film, which increases the average waveguide RI and broadens the RI detection range accordingly. A 50-nm thick single-side gold film is coated on the photopolymer film, exciting SPR and causing less light transmission loss than a double-side gold film. The method avoids the complex microfabrication processes of conventional polymer optical fiber SPR sensors, while the waveguide RI can be controlled by altering the curing time of the photopolymer during fabrication. The sensor has an overall sensitivity of 3686.25 nm/RIU, enabling RI detection of 1.333 - 1.493. Moreover, the sensor has an ultrahigh sensitivity of 6422.9 nm/RIU in the RI range of 1.423 - 1.493. The temperature response is about 1.43 nm/°C at 20 - 50 °C, which has little impact on RI detection. Finally, we demonstrate that the sensor can grade the severity of hepatic steatosis by measuring the RIs of cytoplasm/triglyceride emulsions with superior sensing performance.

A high-performance long-range surface plasmon resonance sensor based on the co-modification of carbon nanotubes and gold nanorods

In order to solve the problem that the sensitivity of the optical fiber surface plasmon resonance (SPR) sensor is limited and the full width at half maxima (FWHM) is greatly increased after modification of two-dimensional materials such as carbon nanotubes (CNTs), this paper proposes a Long-Range Surface Plasmon Resonance (LRSPR) Sensors co-modified by CNTs and gold nanorods. Gold nanorods were used to further enhance the sensitivity, and a simple and convenient method was used to excite the LRSPR by using low refractive index UV glue as a dielectric matching layer (DML). Compared with SPR sensor, the FWHM is reduced. The LRSPR sensor produced in this paper has a sensitivity of 5056.35 nm/RIU and a figure of merit (FOM) of 23.52 RIU−1, which are 150.64% and 24.38% higher than conventional SPR sensors, providing a method to achieve high sensitivity and FOM of the sensor. At the same time, the large specific surface area of CNTs and gold nanorods can also improve the biocompatibility of the sensor surface, which makes it have the potential of biosensing. In this paper, the use of UV glue as a DML to excite LRSPR is proposed for the first time.

Tunable Au@SiO2/Au Film Metasurface as Surface Plasmon Resonance Enhancer for Direct and Ultrasensitive Detection of Exosomes.

Surface plasmon resonance (SPR) spectroscopy with non-labelling, sensitive, and real-time properties is critical for clinical diagnosis applications. However, conventional SPR sensors face the challenge of lower sensitivity and selectivity for trace exosomes assay in complex serum. We proposed a core-shell Au@SiO2-Au film (Au@SiO2-Au film) metasurface to enhance SPR signal based on systematic study on the relationship between gap modes and SPR enhancement. The self-assembled multifunctional peptide was designed as recognition layer with antifouling properties for ultrasensitive and selective detection of PD-L1+ exosomes in serum. The tuning electromagnetic (EM) field model by manipulating the gap was established to guide the preparation of Au@SiO2-Au film metasurface. The in-plane and out-of-plane coupling of Au@SiO2 nanoparticles (NPs) could greatly enlarge and enhance three-dimensional EM field to meet the size of exosomes located in the evanescent field. At the structural level, we achieved high sensitivity (0.16 particles/mL) and a broad response range (10-5 × 103 particles/mL) through optimizing the thickness of SiO2 and surface coverage of Au@SiO2. Furthermore, clinical sample assay achieved the optimal diagnostic accuracy (AUC = 0.97) for differentiating cancer patients from healthy controls. This work provides an opportunity for the construction of a tunable gap mode as SPR enhancer in a total internal reflection architecture. The systematic study on the relationship between gap modes and SPR sensitivity provides a broad scope for promoting direct, efficient, highly selective, and sensitive detection of SPR sensors for clinical application.

A Field-Enhancement Optical Fiber SPR Sensor Using Graphene, Molybdenum Disulfide, and Zinc Oxide

Graphene, molybdenum disulfide (MoS $$_2$$ ), and zinc oxide (ZnO) are proposed here to enhance the evanescent field of an optical fiber surface plasmon resonance (SPR) sensor. Gold and silver are the plasmonic materials, and the fiber core material is made of polymethylmethacrylate (PMMA). A Fresnel equations-based analysis is used, and the obtained results pointed out higher values of sensitivity, figure of merit, and FWHM (full-width at half maximum) when compared to conventional SPR sensors. In despite of silver-only based SPR sensor has a better performance, oxidation occurs, and the sensor’s lifetime is reduced. The addition of graphene layers leads to sensitivity values $$50\%$$ higher than the conventional sensor. On the other hand, the MoS $$_2$$ -based sensor improves the interaction of the sensor with the bio-recognition molecules, which is attractive for biomedical applications. When ZnO was added to the silver-based sensor, a highest sensitivity, 4740.9 nm/RIU, was obtained. Graphene-based silver SPR exhibit the highest FOM values.

A High-Sensitivity Sensor Based on Insulator-Metal-Insulator Structure

In this paper, a theoretical model of a surface plasmon resonance (SPR) biosensor based on the insulator-metal-insulator (IMI) structure is proposed. The sensor mainly consists of two IMI structures, MgF2/Au/Al2O3 and Al2O3/Au/sensing medium structure, respectively. Benefits from the symmetrical modes stimulated by the IMI structure, i.e., the electric field strength inside the sensing medium, are reinforced, resulting in a better overall performance in sensitivity and figure of merit (FOM). The influences of the thickness of the metal layers, the parameters of the dielectric layer materials, and the number of structural layers on the performance of this sensor are discussed. When the refractive index (RI) of the analyte varies in the range of 1.3494–1.3495, the optimized sensor could achieve a maximum wavelength sensitivity of 220 μm/RIU (refractive index unit) and a FOM of 3013.70 RIU−1. Compared with the conventional SPR sensor, the sensitivity and FOM of this structure are significantly improved.

Design and Simulation of Au/SiO2 Nanospheres Based on SPR Refractive Index Sensor

In this paper, three different structures of surface plasmon resonance (SPR) sensors based on the Kretschmann configuration: Au/SiO2 thin film structure, Au/SiO2 nanospheres and Au/SiO2 nanorods are designed by adding three different forms of SiO2 materials behind the gold film of conventional Au-based SPR sensors. The effects of SiO2 shapes on the SPR sensor are investigated through modeling and simulation with the refractive index of the media to be measured ranging from 1.330 to 1.365. The results show that the sensitivity of Au/SiO2 nanospheres could be as high as 2875.4 nm/RIU, which is 25.96% higher than that of the sensor with a gold array. More interestingly, the increase in sensor sensitivity is attributed to the change in SiO2 material morphology. Therefore, this paper mainly explores the influence of the shape of the sensor-sensitizing material on the performance of the sensor.

Highly sensitive short-range mode resonance sensor with multilayer structured hyperbolic metamaterials.

Hyperbolic metamaterial (HMM) based sensors can achieve superior sensing performance than conventional surface plasmon resonance sensors. In this work, the operator approach to effective medium approximation (OEMA) is used to characterize the HMM dielectric constant properties of metal-dielectric multilayer structures, which are classified into short-range (SR) mode and long-range (LR) mode according to the propagation length of the bulk high K waves in HMM. The dispersion relations of SR modes are derived, and a high-sensitivity refractive index sensor is designed for the near-infrared SR mode resonance. The effects of the number of periods, cell thickness, metal fill rate and incidence angle on the SR mode resonance were analyzed for the multilayer structured HMM. Our designed sensing structure achieves a maximum sensitivity of 330 µm/RIU in the near-infrared band with a quality factor of 492 RIU-1. In addition, the simulations show that the SR mode resonance wavelength is flexible and tunable. We believe that the study of HMM-based SR mode resonance sensors offers potential applications for high-sensitivity biochemical detection.

Terahertz Biosensor Based on Mode Coupling between Defect Mode and Optical Tamm State with Dirac Semimetal.

Bulk Dirac semimetal (BDS) has emerged as a "3D graphene" material for the development of optical devices in the past few years. In this study, a BDS-based tunable highly sensitive terahertz (THz) biosensor is proposed by using a Dirac semimetal/Bragg reflector multilayer structure. The high sensitivity of the biosensor originates from the sharp Fano resonance peak caused by coupling the Optical Tamm State (OTS) mode and defect mode. Besides, the sensitivity of the proposed structure is sensitive to the Fermi energy of Dirac semimetal and the refractive index of the sensing medium. The maximum sensitivity of 1022°/RIU is obtained by selecting structural and material parameter appropriately, which has certain competitiveness compared to conventional surface plasmon resonance (SPR) sensors. From the standpoint of the fabrication facility and integration, we judged that the BDS-based layered structure has the potential application in biosensor field.

Highly sensitive MXene-immobilized long range SPR sensor for biomolecule detection

In this article, a long-range surface plasmon resonance (LRSPR) sensor is proposed using the dielectric (Teflon)-metal (Silver)-Ti3C2Tx (MXene) layer for imaging sensitivity enhancement. MXene shows excellent properties, such as larger surface area, hydrophilic nature, high metallic conductivity, chemical stability, and strong biocompatibility for detection of biomolecules. The MXene layer is used here to improve imaging sensitivity and prevent unwanted silver oxidation. The proposed sensor takes advantage of the high adsorption efficiency of MXene for biomolecules and high resolution due to the LRSPR technique. Long-range SPPs are used to improve the imaging sensitivity, detection accuracy (DA), figure of merit (FoM) and penetration depth (PD) up to 4998/RIU, 12.5/°, 199.1/RIU and 546.65 nm, respectively, which are much higher than the present state of the art. The field intensity enhancement factor at the interface of the constituent layer of the proposed sensor and the conventional surface plasmon resonance (cSPR) sensor is also verified. The penetration depth (PD) of the field into the sensing layer for the LRSPR sensor is 2.5 times greater than that of the cSPR sensor. Thus, the proposed sensor offers potential benefits for sensing of large-sized biomolecules in the area of medical diagnostics.

Hyperbolic-Metamaterials-Based SPR Temperature Sensor Enhanced by a Nanodiamond-PDMS Hybrid for High Sensitivity and Fast Response.

A high-performance surface plasmon resonance (SPR) fiber sensor is proposed with hyperbolic metamaterials (HMMs), nanodiamonds (NDs), and polydimethylsiloxane (PDMS) to enhance the temperature sensitivity and response time. The HMM with tunable dispersion can break through the structural limitations of the optical fiber to improve the refractive index (RI) sensitivity, while NDs and PDMS with large thermo-optic coefficients enable to induce significant RI change under varied thermal fields. The ternary composite endows the sensor with a high temperature sensitivity of -9.021 nm/°C, which is 28.6 times higher than that of the conventional gold film-based SPR sensor. Furthermore, NDs with high thermal conductivity (2200 W/mK) effectively expedite the thermal response of PDMS, which reduces the response time from 80 to 6 s. It is believed that the proposed sensors with high sensitivity, fast response time, and compact size have great potential for applications in industrial production, healthcare, environmental monitoring, etc.

A High-FOM surface plasmon resonance sensor based on MMF-TUMMF-MMF structure of optical fiber

The figure of merit (FOM) of conventional surface plasmon resonance (SPR) sensors is low due to the low sensitivity and wide full width at half maxima (FWHM) caused by many low-intensity high-order cladding modes. To address this problem, this paper proposes a SPR sensor based on U-shaped tapered arm cascade of multimode fiber (TUMMF). The U-shaped macro-bend increases the intensity of the light field leaking into the cladding, and the tapered area makes the number of higher-order modes smaller to achieve high sensitivity and narrow FWMH sensing performance. Through simulation and experimental verification, the sensitivity of the sensor is proportional to the fiber curvature and taper ratio, and the FWMH is inversely proportional. Therefore, the parameters of the sensor are optimized by integrating the FOM and the mechanical strength of the sensor. The optimized sensor parameters are 3 mm bending diameter, 0.85 taper ratio, and 152 nm gold film thickness. The sensor was tested in the refractive index (RI) sensing range of 1.3324–1.3731 and showed a sensitivity of 4816.092 nm/RIU and a FWMH of 97.54 nm. The FOM of the proposed sensor is 49.37 /RIU, which is 3.18 times higher than that of the U-shaped multimode fiber SPR sensor. The probe has the advantages of simple fabrication, high environmental stability and easy modification, and has a wide range of applications in bioenvironmental and other fields.

Performance evaluation of multifunctional SPR bimetallic sensor using hybrid 2D-nanomaterials layers

In this paper, we analyzed the sensing performance of the multifunctional surface plasmon resonance (SPR) biosensors based on bimetallic film (Ag/Al2O3), and a hybrid nanostructure of BaTiO3 and 2D nanomaterials (Ti3C2Tx, black phosphorus and BlueP/MoS2 heterostructure). Using excitation light at 633 nm, we numerically analyze performance such as angular sensitivity, peak sensitivity, figure of merit, and electric field strength. The study shows the proposed biosensor design exhibits a highest sensitivity of 504 deg/RIU with a 320% improvement over the conventional SPR sensor reported so far on similar 2D nanomaterials, and can also maintain a good quality SPR curve. The results of different proposed and optimized nano-configurations show that the improved angular sensitivity of 120%, 60%, 290% and 80% for BaTiO3, Ti3C2Tx, Black phosphorus and BlueP/MoS2, respectively, for a change in the refractive index (RI) of the sensing medium of 5×10−3 RIU. Similarly, the variation in field intensity at the sensing interface further confirms the high sensitivity obtained for our proposed SPR biosensor. Therefore, our proposed design would be practically suitable for biosensing with higher performance with the available fabrication technologies.