Conventional Surface Plasmon Resonance Research Articles

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.

Biofilm growth monitoring using guided wave ultralong-range Surface Plasmon Resonance: A proof of concept

Unwelcomed biofilms are problematic in food industries, surgical devices, marine applications, and wastewater treatment plants, essentially everywhere where there is moisture. Very recently, label-free advanced sensors such as localized and extended surface plasmon resonance (SPR) have been explored as tools for monitoring biofilm formation. However, conventional noble metal SPR substrates suffer from low penetration depth (100–300 nm) into the dielectric medium above the surface, preventing the reliable detection of large entities of single or multi-layered cell assemblies like biofilms which can grow up to a few micrometers or more. In this study, we propose using a plasmonic insulator-metal-insulator (IMI) structure (SiO2–Ag–SiO2) with a higher penetration depth based on a diverging beam single wavelength format of Kretschmann configuration in a portable SPR device. An SPR line detection algorithm for locating the reflectance minimum of the device helps to view changes in refractive index and accumulation of the biofilm in real-time down to 10−7 RIU precision. The optimized IMI structure exhibits strong penetration dependence on wavelength and incidence angle. Within the plasmonic resonance, different angles penetrate different depths, showing a maximum near the critical angle. At the wavelength of 635 nm, a high penetration depth of more than 4 μm was obtained. Compared to a thin gold film substrate, for which the penetration depth is only ∼200 nm, the IMI substrate provides more reliable results. The average thickness of the biofilm after 24 h of growth was found to be between 6 and 7 μm with ∼63% live cell volume, as estimated from confocal microscopic images using an image processing tool. To explain this saturation thickness, a graded index biofilm structure is proposed in which the refractive index decreases with the distance from the interface. Furthermore, when plasma-assisted degeneration of biofilms was studied in a semi-real-time format, there was almost no effect on the IMI substrate compared to the gold substrate. The growth rate over the SiO2 surface was higher than on gold, possibly due to differences between surface charge effects. On the gold, the excited plasmon generates an oscillating cloud of electrons, while for the SiO2 case, this does not happen. This methodology can be utilized to detect and characterize biofilms with better signal reliability with respect to concentration and size dependence.

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.

SARS-CoV-2 proteins monitored by long-range surface plasmon field-enhanced Raman scattering with hybrid bowtie nanoaperture arrays and nanocavities.

The identification of biomacromolecules by using surface-enhanced Raman scattering (SERS) remains a challenge because of the near-field effect of traditional substrates. Long-range surface plasmon resonance (LRSPR) is a special type of surface optical phenomenon that provides higher electromagnetic field enhancement and longer penetration depth than conventional surface plasmon resonance. To break the limit of SERS detection distance and obtain a SERS substrate with increased enhancement ability, a bowtie nanoaperture array was sandwiched between two symmetric dielectric environments. Then, an Au mirror was inserted to form a metal-insulator-metal configuration. Finite-difference time-domain simulations revealed that numerous hybrid modes can be provided by this novel configuration (denoted as long-range SERS [LR-SERS] substrate). In particular, the LRSPR mode can be excited and reach the maximum value through the regulation of the polarizations of the incident light and the geometrical parameters of the LR-SERS substrate. The optimized LR-SERS substrate was then applied to detect SARS-CoV-2 spike (S) and nucleocapsid (N) proteins. This substrate displayed ultralow detection limits of ∼9.2 and ∼11.3 pg mL-1 for the S and N proteins, respectively. Moreover, with the help of principal component analysis and receiver operating characteristic methods, our fabricated sensors exhibited excellent selectivity and hold great potential for the diagnosis of SARS-CoV-2 proteins in real samples.

High-sensitivity long-range surface plasmon resonance sensing assisted by gold nanoring cavity arrays and nanocavity coupling.

In many of the existing refractive index (RI) sensing works, only the shape and size of plasmonic structures are usually taken into account, while the parameters of spacer layers are ignored. In this publication, we explored the long-range surface plasmon resonance (LRSPR) and Fabry-Pérot resonance coupling effects of our proposed gold nanoring cavity array/spacer layer/Au mirror/glass substrate. Both the RI sensitivity and full width at half-maximum (FWHM) values were superior than those of conventional surface plasmon resonance substrates. We discussed the tunability of the RI sensitivity through changing the RI and thickness of the spacer layer. Then, under the optimized parameter conditions of the spacer layer, the geometry parameters (including size, gap and periodicity) of gold nanoring cavity arrays were tuned to optimize the best RI sensitivity. Finally, we broke the structural symmetry of a nanoring cavity to introduce Fano resonances into our system, and a high RI sensitivity and figure-of-merit (FOM) of 695 nm per RIU (refractive index unit) and 96.5, respectively, were achieved when the breaking angle θ was 30°. This study opens up many possibilities for boosting the FOM of RI sensing by taking into account the hybridization effects of localized surface plasmon resonance, LRSPR, and Fabry-Pérot and Fano resonances.

DNA-Directed Protein Anchoring on Oligo/Alkanethiol-Coated Gold Nanoparticles: A Versatile Platform for Biosensing Applications

Herein, we report on a smart biosensing platform that exploits gold nanoparticles (AuNPs) functionalized through ssDNA self-assembled monolayers (SAM) and the DNA-directed immobilization (DDI) of DNA-protein conjugates; a novel, high-sensitivity optical characterization technique based on a miniaturized gel electrophoresis chip integrated with online thermal lens spectrometry (MGEC-TLS), for the high-sensitivity detection of antigen binding events. Specifically, we characterized the physicochemical properties of 20 nm AuNPs covered with mixed SAMs of thiolated single-stranded DNA and bio-repellent molecules, referred to as top-terminated oligo-ethylene glycol (TOEG6), demonstrating high colloidal stability, optimal binder surface density, and proper hybridization capacity. Further, to explore the design in the frame of cancer-associated antigen detection, complementary ssDNA fragments conjugated with a nanobody, called C8, were loaded on the particles and employed to detect the presence of the HER2-ECD antigen in liquid. At variance with conventional surface plasmon resonance detection, MGEC-TLS characterization confirmed the capability of the assay to titrate the HER2-ECD antigen down to concentrations of 440 ng/mL. The high versatility of the directed protein-DNA conjugates immobilization through DNA hybridization on plasmonic scaffolds and coupled with the high sensitivity of the MGEC-TLS detection qualifies the proposed assay as a potential, easily operated biosensing strategy for the fast and label-free detection of disease-relevant antigens.

Modeling of surface plasmon resonance biosensor based on Ag/BiFeO3/Ni using 2D nanomaterial perovskite MAPbBr3

In the present work, the sensing performance analysis of a surface plasmon resonance (SPR) sensor for biological and chemical applications is reported. The structure studied consists of a silver nanofilm, the hybrid nanostructure of bismuth ferrite material (BiFeO 3 ), and a nickel nanofilm covered by a layer of perovskite CH 3 NH 3 PbBr 3 (MAPbBr 3 ) nanomaterial. Our analyses are based on the finite element method (FEM) and a monochromatic excitation of wavelength 633 nm. We numerically analyzed performance parameters such as angular sensitivity, sensitivity enhancement, factor of merit (FoM) and electric field distribution. We have shown that the proposed SPR biosensor exhibits very good detection performance in terms of sensitivity and FoM. Compared with the conventional SPR structure, the 2D nanomaterials have excellent properties, such as stronger absorption capacity, which improves the biological and chemical sensing ability of the sensor. The sensitivity and FoM of the optimized biosensor reaches 408 deg/RIU with 240% enhancement, and 93.12 RIU −1 with 138.78% improvement respectively, when the perovskite material layer covered the BK7/Ag/BiFeO 3 /Ni hybrid nanostructure; for a 0.005 RIU variation in the refractive index of the sensing medium. Therefore, our proposed design and study would be practically suitable for bio/chemical sensing and in biomedical application has excellent performance, with the available fabrication technologies. • We proposed a SPR nanostructured as a high multi-functional detection biosensor by the MAPbBr 3 perovskite nanomaterial layer: BK7/Ag/BiFeO 3 /Ni/MAPbBr 3 . • The optimized nanostructure shows the highest angular sensitivity of 408 deg/RIU. • Highest sensitivity enhancement 240% for bimetallic/nanomaterials based SPR biosensor. • This study demonstrated high FoM of 105.78 RIU {-1} with an enhancement of 171.23%.

Microfluidically Partitioned Dual Channels for Accurate Background Subtraction in Cellular Binding Studies by Surface Plasmon Resonance Microscopy.

Unlike conventional surface plasmon resonance (SPR) using an antifouling film to anchor biomolecules and a reference channel for background subtraction, SPR microscopy for single-cell analysis uses a protein- or polypeptide-modified gold substrate to immobilize cells and a cell-free area as the reference. In this work, we show that such a substrate is prone to nonspecific adsorption (NSA) of species from the cell culture media, resulting in false background signals that cannot be correctly subtracted. To obtain accurate kinetic results, we patterned a dual-channel substrate using a microfluidic device, with one channel having poly-l-lysine deposited in situ onto a preformed polyethylene glycol (PEG) self-assembled monolayer for cell immobilization and the other channel remaining as PEG-covered for reference. The two 2.0 mm-wide channels are separated by a 75 μm barrier, and parts of the channels can be readily positioned into the field of view of an SPR microscope. The use of this dual-channel substrate for background subtraction is contrasted with the conventional approach through the following binding studies: (1) wheat germ agglutinin (WGA) attachment to the N-acetyl glucosamine and N-acetyl-neuraminic acid sites of glycans on HFF cells, and (2) the S1 protein of the COVID-19 virus conjugation with angiotensin-converting enzyme 2 (ACE2) on the HEK293 cells. Both studies revealed that interferences by NSA and the surface plasmon polariton wave diffracted by cells can be excluded with the dual-channel substrate, and the much smaller refractive index changes caused by the injected solutions can be correctly subtracted. Consequently, sensorgrams with higher signal-to-noise ratios and shapes predicted by the correct binding model can be obtained with accurate kinetic and affinity parameters that are more biologically relevant. The affinity between S1 protein and ACE2 is comparable to that measured with recombinant ACE2, yet the binding kinetics is different, suggesting that the cell membrane does impose a kinetic barrier to their interaction.

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.

Recent Advances in Lossy Mode Resonance-Based Fiber Optic Sensors: A Review.

Fiber optic sensors (FOSs) based on the lossy mode resonance (LMR) technique have gained substantial attention from the scientific community. The LMR technique displays several important features over the conventional surface plasmon resonance (SPR) phenomenon, for planning extremely sensitive FOSs. Unlike SPR, which mainly utilizes the thin film of metals, a wide range of materials such as conducting metal oxides and polymers support LMR. The past several years have witnessed a remarkable development in the field of LMR-based fiber optic sensors; through this review, we have tried to summarize the overall development of LMR-based fiber optic sensors. This review article not only provides the fundamental understanding and detailed explanation of LMR generation but also sheds light on the setup/configuration required to excite the lossy modes. Several geometries explored in the literature so far have also been addressed. In addition, this review includes a survey of the different materials capable of supporting lossy modes and explores new possible LMR supporting materials and their potential applications in sensing.

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.

Advances in Surface Plasmon Resonance-Based Biosensor Technologies for Cancer Cell Detection

Efforts have been made to enhance the surface sensitivity of the conventional surface plasmon resonance biosensor. To improve the sensitivity, a unique two-dimensional heterostructure layer of titanium disilicide and black phosphorus layer has been deposited over the metal surface. The titanium disilicide (TiSi2) nanosheet is placed in between silver (Ag) and black phosphorus (BP) films in the Kretschmann arrangement. This biosensor executes better over a wide range of refractive index variations, including biological cell distribution in individual blood. It may become a fast method of detecting cancerous cells and the several variants of corona and other viruses that become pandemic. Using the finite element method-based simulation technique, the sensitivity obtained as 195.4 degree/RIU, 167.6 degree/RIU, 212.4 degree/RIU, 168.4 degree/RIU, 212.4 degree/RIU, 186.6 degree/RIU, 218.6 degree/RIU, 195.4 degree/RIU, 203.6 degree/RIU, 202.6 degree/RIU 203.6 degree/RIU, and 202.6 for basal (skin cancer), basal (normal cell), HeLa (cervical cancer), MCF-7 (breast cancer), HeLa (normal cell), Jurkat (blood cancer), Jurkat (normal cell), PCI-2 (adrenal gland cancer), PCI-2 (normal cell), MDA-MB-231 (breast cancer), MDA-MB-231 (normal cell), MCF-7 (breast cancer), and MCF-7 (normal cell), respectively, and other performance parameters such as detection accuracy, figure of merit, and full width and half maximum (FWHM) are also evaluated.

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.

Magnetic field sensor with Fano resonance in resonant plasmonic and planar waveguide structures

By introducing a waveguide layer into the surface plasmon resonance (SPR)-supported Kretschmann configuration, a Fano resonance (FR) sensor has been proposed and suggested for magnetic field sensing. FR with higher quality factor (Q) can be manipulated through the coupling between surface plasmon polariton (SPP) and dielectric planar waveguide (PWG) modes. The design procedures for determining and optimizing the performance of the magnetic field sensor (MFS) are elaborated through the numerical calculation with rigorous coupled wave analysis (RCWA) method. The sensor’s performance has been analyzed by considering the intensity sensitivity and figure of merit (FOM). By optimizing the structural parameters, the intensity sensitivity and FOM can reach 3002∕T and 1.68 × 104/T, respectively, which have been greatly increased compared to that obtained using the conventional SPR technique in state of-the-art sensors.

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.

Simulation study to improve the sensitivity of surface plasmon resonance sensor by using ferric oxide, nickel and antimonene nanomaterials

In the present paper, a simulation work has been done to study about a hypersensitive Surface Plasmon Resonance (SPR) based sensor device created by the angular interrogation method based on Attenuated Total Reflection (ATR) phenomenon. The numerical analysis has been done by the method of transfer matrix and a plane polarised source of light of wavelength 633 nm approx (632.8 nm wavelength of He-Ne laser) has been used. In this device configuration, glass prism of Calcium fluoride (CaF2) has been used with Silver (Ag) metal using Kretschmann configuration, a diamagnetic material nanosheets of ferric oxide (Fe2O3), nickel (Ni) and a 2D material antimonene is used as a polymeric structure. All the important performing parameters of SPR sensor such as sensitivity, detection accuracy, quality factor has been calculated for different device configuration of SPR sensor. Fe2O3 and Ag layer thickness has been optimized by using genetic algorithms to obtain the highest sensitivity. The configuration gives the highest sensitivity 310°RIU−1 of projected SPR sensor when sensing medium RI varies from 1.330 to 1.335. For proposed design of SPR sensor the sensitivity and FWHM are high as compared to the conventional SPR senor having FWHM value 3.4995 (deg.). For the proposed device configuration bilayer of Ni and antimonene has been used as a polymeric substance to improve the sensitivity and protect device from corrosion. Penetration depth value of 110.5 nm and 3D plot of transverse electric (TM) field intensity has also been plotted. The numerical simulation is based on transfer matrix method and Fresnel equations and the used softwares are MATLAB and COMSOL multiphysics software. The proposed SPR sensor helps to detect the liquid analytes in the field of biomedical and environmental application.

Ge[formula omitted]Sb[formula omitted]Te[formula omitted]-coated fiber optic SPR sensor: Improving sensitivity

This paper proposes and demonstrates a fiber optic surface plasmon resonance (SPR) sensor based on Au–Ge2 Sb2Te5 (GST). The GST is deposited on the Au film, which increases the dielectric constant of the metal layer due to the high refractive index (RI) of GST. Therefore, compared with conventional Au SPR sensor, the resonance wavelength of the Au–GST SPR sensor red-shifts, and the sensitivity is improved. When environmental RI varies in the range of 1.333∼1.403, the experimental results show that the sensor performs the best when the thicknesses of Au film is 50 nm and the GST layer’s thickness is 25 nm. The proposed sensor’s sensitivity is 5210 nm/RIU (refractive index unit), which is much higher than that of the conventional Au-based SPR sensor (2418 nm/RIU). The sensor achieves relatively high sensitivity based on a very simple structure, and it has potential applications in biological and biochemical such as DNA hybridization, cancer screenings, environmental temperature and humidity detection, and chemical analysis.

A Temperature Sensor Exploiting Plasmonic Phenomena Changes in Multimode POFs

A novel sensing method for temperature measurements of liquids, exploiting plasmonic resonance in multimode plastic optical fibers (POFs), has been devised. The possibility to measure the temperature is useful in several application fields of plasmonic sensors, such as when a binding test between a receptor and an analyte occurs, considering that the binding parameters are a function of the temperature. The novel temperature sensor consists of two different D-shaped POF connected in a cascade. The first element is a thermosensitive platform with a thin silicone layer on the POF core, whereas the second is a conventional surface plasmon resonance (SPR) D-shaped POF sensor. The operating principle of the novel temperature sensor is based on the variations of light launch conditions in the SPR-POF sensor as a consequence of the temperature changes in the solution covering the thermosensitive platform. In this way, the input light ray angle changes with the temperature, producing a shift in resonance wavelength conditions. The proposed sensor has been tested, as proof of concept, in a temperature range from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$20^{\circ }\text{C}$ </tex-math></inline-formula> to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$38^{\circ }\text{C}$ </tex-math></inline-formula> with a step size of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3^{\circ }\text{C}$ </tex-math></inline-formula> , to establish the role of the silicone layer on the thermosensitive platform and the best configuration in terms of sensitivity.

Performance Enhancement of SPR Biosensor Using Graphene-MoS2 Hybrid Structure.

We investigate a high-sensitivity surface plasmon resonance (SPR) biosensor consisting of a Au layer, four-layer MoS2, and monolayer graphene. The numerical simulations, by the transfer matrix method (TMM), demonstrate the sensor has a maximum sensitivity of 282°/RIU, which is approximately 2 times greater than the conventional Au-based SPR sensor. The finite difference time domain (FDTD) indicates that the presence of MoS2 film generates a strong surface electric field and enhances the sensitivity of the proposed SPR sensor. In addition, the influence of the number of MoS2 layers on the sensitivity of the proposed sensor is investigated by simulations and experiments. In the experiment, MoS2 and graphene films are transferred on the Au-based substrate by the PMMA-based wet transfer method, and the fabricated samples are characterized by Raman spectroscopy. Furthermore, the fabricated sensors with the Kretschmann configuration are used to detect okadaic acid (OA). The okadaic acid–bovine serum albumin bioconjugate (OA-BSA) is immobilized on the graphene layer of the sensors to develop a competitive inhibition immunoassay. The results show that the sensor has a very low limit of detection (LOD) of 1.18 ng/mL for OA, which is about 22.6 times lower than that of a conventional Au biosensor. We believe that such a high-sensitivity SPR biosensor has potential applications for clinical diagnosis and immunoassays.