Surface Plasmon Resonance Dip Research Articles

High-performance portable grating-based surface plasmon resonance sensor using a tunable laser at normal incidence

Surface plasmon resonance (SPR) sensors are among the most sensitive sensors. In such devices, a grating is a compelling alternative to a prism for the excitation of a surface plasmon, especially in the development of sensors for point-of-care applications due to their compactness and cost-effectiveness. Here, we demonstrate the use of a tunable laser in a grating-based SPR system for further miniaturization and integration. The tunable laser working at normal incidence replaces spectral and moving components, while also simplifying the optical setup. Normal incidence is conventionally avoided due to the complexity of the control of degenerated SPR modes. We investigate, both computationally and experimentally, the splitting of the SPR modes at small nonzero incidences, which is lacking in previously reported studies. By optimizing the grating configuration, we were able to diminish the SPR mode splitting phenomenon when the excitation was feasible with the normal incidence configuration. The fabricated sensor showed a high sensitivity of 1101.6 nm/RIU. Notably, the figure of merit of the sensor, defined as the ratio between the sensitivity and bandwidth of the SPR dip, was 229.5. The experimental results were consistent with the simulation results. We also demonstrate its capability for detecting low concentrations of glucose and creatinine with the limit of detection of 14.2 and 19.1 mmol/L, respectively.

Evaluations of ethylene glycol and polyethylene glycol aqueous solutions using a hybrid sensor of surface plasmon resonance and quartz crystal microbalance

A hybrid sensor based on surface plasmon resonance (SPR) and quartz crystal microbalance (QCM) was prepared. One of the electrodes of the QCM sensor had a grating structure to enable SPR excitation. The SPR property was investigated through the transmission of the visible-light spectrum. The theoretical calculation showed that the experimental values almost corresponded to the theoretical ones; this suggests that the transmitted light dips were due to SPR. In order to investigate the usefulness of this hybrid sensor, the characteristics of SPR and the oscillation frequency drops of QCM (ΔF QCM) were investigated for aqueous solutions of ethylene glycol and polyethylene glycols with various degrees of polymerization. The position and slope of the SPR dip wavelength and the ΔF QCM curves depended on the degree of polymerization, suggesting that the sensor can be used to evaluate a solution property and/or discriminate a solute material.

High-sensitivity optical fiber SPR sensor with cascaded biconical fiber and hetero-core structure for simultaneous measurement of seawater salinity and temperature

A novel dual-channel optical fiber surface plasmon resonance (SPR) sensor, which achieves high-sensitivity simultaneous measurement of seawater salinity and temperature, was designed and verified. The hetero-core structure based on no-core fiber (NCF) with 40 nm thick Au film and polydimethylsiloxane (PDMS) overlaying was utilized to excite the SPR effect and serve as the temperature sensing channel. In order to effectively separate from the temperature SPR dip, a silver/gold bimetallic film was deposited on the surface of the biconical fiber with a grinding angle of 14° to construct the salinity channel cascaded with the temperature channel, where the metal thickness was determined as Ag/Au: 30 nm/10 nm. The simulation and experimental results showed that the bimetallic film used in this article can significantly improve the figure of merit (FOM) of the sensor compared with the optical fiber SPR sensor deposited with a single kind of metal film. In addition, further experimental results on salinity and temperature indicated that the proposed sensor had a salinity sensitivity of 0.73 nm/‰ and a temperature sensitivity of −2.43 nm/℃, and demonstrated the advantages of ease of manufacturing, acceptable repeatability, and good stability. Therefore, the proposed dual-channel optical fiber SPR sensor has high research value and application prospects in the field of ocean measurement.

Ag/CdS surface plasmon simulation systems for gas sensor

In this work, the Surface Plasmon Resonance (SPR) sensor simulated for a wide range of wavelengths and refractive index. The Kretschmann configuration of the suggested sensor is Silver (Ag) with a thickness of 45 ​nm, and Cadmium Sulfide (CdS) dielectric with variable thickness (10 ​nm–80 nm) that deposited on FD60 Dense flint prism. The sensing medium is gas which includes air and different refractive indexes (Δn ​= ​0, 0.02, 0.05, and 0.1) to consider most gas cases. The wavelength light range studied from 100 nm to 1000 ​nm. The results show that SPR appeared strongly in the Infrared range between 900 ​nm and 1000 ​nm. It is weakly appeared in the visible range and cannot be noticed in the ultraviolet region. The sharpest and longest SPR dip occurred in the Infrared range. The smallest value of full-width half maxima (FWHM) was 0.4° at CdS thickness of 10 ​nm, and the longest SPR dip has 0.97° at CdS thickness of 60 ​nm. The smallest and longest value of FWHM dip occurred at wavelength 1000 ​nm and n ​= ​0.02. Hence, the better detection accuracy and sensitivity of the SPR sensor were in the infrared region at wavelength 1000 ​nm and n ​= ​0.02 for the suggested sample. So, the range of working wavelengths depending on the sample design.

Silver Prism Interface Plasmon Resonance for Biosensor in Ir-Visible Spectrum Region

The performance of a surface Plasmon resonance (SPR) sensor with silver film was demonstrated. The Kretschmann setup's evanescent field, which can activate the sensor. The sensitivity and FWHM of the SPR sensor drop as the thickness of the silver layer in the metallic film increases. Using water as a sensing medium, it can create a simulation model at various thicknesses of the silver layers placed on the semicircular glass prism D-ZLAF50 with a thickness of dAg = 10–80 nm. The proposed sensor can function at wavelengths of up to 600,700nm in the visible area and the infrared region at wavelengths of 900 & 1000 nm. Optimum sensitivity (S = 100–140) may be observed in the visible and infrared spectrum with thicknesses ranging from dAg = (10–80) nm , ∆n = 0.1. At silver layer thicknesses, the values of SPR dip length and FWHM are excellent (40–60 nm).

A Numerical Study of Different Metal and Prism Choices in the Surface Plasmon Resonance Biosensor Chip for Human Blood Group Identification.

Optimized design of Surface plasmon resonance (SPR) based biosensor in terms of different metal choices and prisms are presented to the first time for the high precision detection of human blood group in near infrared wavelength range. The results are well compared with the earlier published gold coated silicon biosensor chip while discussing the pros and cons of various prism/metal choices. In this study buffer layer onto SPR active metal has been deployed to avoid the oxidation problem and contamination issue related with blood samples. Refractive index of blood samples has been considered in theoretical model based on the experimental data. Si prism has been found to be the best choice as a substrate material with combination of Al as a SPR active metal for blood group identification analysis. SPR dip slope (S), detection accuracy (D.A.) and blood group discrimination factor ( δθSPR ) have been studied with respect to different metal choices with their suitability to the next generation biosensor applications.

Dual plasmonic modes in the visible light region in rectangular wave-shaped surface relief plasmonic gratings

Rectangular wave-shaped surface-relief plasmonic gratings (RSR-PGs) have been fabricated from a hybrid polymer by employing a simple nanoimprint photocuring lithography technique using a silicon template, followed by gold nanolayer metallization on top of the formed replica structure. By forming a one-dimensional (1D) plasmonic grating with a periodicity of approximately 700 nm, a reflectance spectral dip was experimentally observed in the visible light region, from 600 to 700 nm, with increasing incident angle from 45° to 60°. This dip can be associated with surface plasmon resonance (SPR) wave excitation, which is coupled with the diffraction order m = − 2. The calculations of reflectance spectra simulation using the rigorous coupled wave analysis (RCWA) method have also been carried out, resulting in the appearance of an SPR dip in the range of 600–700 nm, for incident angles in the range of 45°–65°, which agrees with the experimental results. Interestingly, these RSR-PGs show richer plasmon characteristics than the sine-wave-shaped plasmonic gratings. The experimental and spectral simulation results revealed two different plasmonic excitation modes: long-range SPR and quasi-localized SPR (LSPR). While the long-range SPR was formed above the ridge sections along the grating structure surface, the quasi-localized SPR was locally formed inside the groove. In addition, for RSR-PGs with a narrow groove section, the long-range SPR seems to be coupled with the periodic structure of the grating, resulting in the appearance of plasmonic lattice surface resonance (LSR) that is indicated by a narrower plasmon resonance dip. These characteristics are quite different from those found in the sine wave-shaped plasmonic gratings. The present results may thus provide better insights for understanding the plasmon excitations in this type of rectangular plasmonic grating and might be useful for designing their structure for certain practical applications.

Simultaneous measurement of the refractive index and thickness of graphene oxide/gold multilayered structure for potential in dopamine sensing using surface plasmon resonance spectroscopy

Thin films have infinite potential uses in optics and other fields. They must be well suited to meet the requirements of its specific application in terms of thickness, optical properties, morphology and other characteristics. Herein, surface plasmon resonance (SPR) technique was employed to accurately determine the thickness and analyze the optical characteristics of graphene oxide/gold (GO/Au) multilayered structure in contact with the neurotransmitter dopamine (DA). Based on the theoretical fitting of the experimentally recorded SPR dips, n and k values of GO layer were 1.4400 and 0.0250, respectively, prior to DA injection. By increasing DA concentrations, SPR experimental curves were shifted to higher angles continuously. DA Binding to SPR chip which was confirmed by AFM and FTIR analysis has increased both n and thickness of GO film while decreased k. These results proved sensitivity enhancement of the modified chip towards DA and highlighted the technique's appropriate and sufficient potential to measure thickness and refractive index variations in real-time when 100 fM of DA was detected with sensitivity of 12.402°/RIU.

Surface Plasmon Resonance Biosensor Chip for Human Blood Groups Identification Assisted with Silver-Chromium-Hafnium Oxide

Chromium (Cr), silver (Ag) and hafnium oxide (HfO2) are used in a surface plasmon resonance (SPR)-based biosensor with an optimized design for measuring blood groups at a wavelength of 633 nm. A buffer layer was placed on the SPR active metal in this investigation to avoid oxidation and contamination of blood samples. A theoretical model based on experimental data considered the refractive index of blood samples. The BK7 prism is the optimum substrate material for blood type identification analysis using a combination of Ag and Cr as an SPR active metal. The sensor’s performance is carefully researched in terms of its angular shift and curve width to predict the design aspects that provide precise blood-group identification. The SPR dip slope, detection accuracy and figure of merit (FOM) have been investigated concerning the subsequent generation of biosensor applications.

Simultaneous Measurement of Ultraviolet Irradiance and Temperature by Employing Optical Fiber SPR Sensor With Ag/ZnO/PDMS Coating

It is a challenging and valuable work to design and manufacture temperature-compensated all-fiber ultraviolet (UV) sensor. In this article, we creatively use a simple and compact optical fiber sensor based on surface plasmon resonance (SPR) for simultaneous detection of UV and ambient temperature. Different coatings [Ag/polydimethylsiloxane (PDMS) and Ag/ZnO/PDMS] are used to split a length of no-core optical fiber (NCF) into two sensing regions, which generates a transmission spectrum with two distinct SPR dips. The proposed sensor achieves a temperature sensitivity of −2.542 nm/°C in the 15 °C–35 °C range and a UV sensitivity of −0.605 nm/(mW/cm2) in the range of 0–17.20 mW/cm2. The matrix established by the wavelength shift of two dips can demodulate UV and temperature changes, and provide temperature compensation for UV detection. In addition, even in surroundings of complex and changeable UV intensity and ambient temperature, the sensor shows excellent stability and repeatability, as well as great potential in UV sensing, providing a reference for the development of multiparameter optical fiber sensors.

Surface plasmon resonance temperature sensor with tunable detection range based on a silver-coated multi-hole optical fiber.

A novel surface plasmon resonance (SPR) temperature sensor based on a silver-coated multi-hole optical fiber (SMHOF) is presented. The central and surrounding air holes of the SMHOF are filled with two kinds of thermosensitive liquid with high and low refractive index (RI), respectively. Two separated resonance dips, which are related to the high and low RI filled liquid respectively, are observed at different wavelength in the transmission spectrum. Advantageously, the two dips move towards opposite direction with the temperature variation. The interval between the two SPR dips is measured under different environmental temperature and exhibits a good linearity. The proposed sensor with different detection range is fabricated by changing the RIs of the filled thermosensitive liquids. The temperature sensitivity of 7.72 nm/°C and -7.81 nm/°C is obtained in the range of 20-60 °C and -20-20 °C, respectively. Owing to the high temperature sensitivity and tunable detection range, the proposed sensor is expected to find potential applications in biomedicine, health care and environmental monitoring.

Highly sensitive detection of nucleocapsid protein from SARS-CoV-2 using a near-infrared surface plasmon resonance sensing system

We report a near-infrared surface plasmon resonance (SPR) system to achieve highly sensitive, unlabeled detection of the SARS-CoV-2 nucleocapsid protein antigen. Use of the near-infrared light in SPR makes the SPR dip of the angular spectrum sharp and causes a large change of the reflected light intensity at a fixed incident angle. The present SPR system achieves the resolution of 10−5 refractive index unit in the refractive index measurement of glycerol solution samples. Additionally, we measured the nucleocapsid protein antigen of SARS-CoV-2 down to a molar concentration of 1 fM by immobilizing its corresponding antibody on the SPR sensor surface. This demonstration indicates a high potential of the present system for highly sensitive biosensing in medical diagnostics.

Fiber-Optic Vector-Magnetic-Field Sensor Based on Gold-Clad Bent Multimode Fiber and Magnetic Fluid Materials.

A kind of bent multimode fiber (MMF) vector magnetic sensor based on surface plasmon resonance (SPR) was proposed. By plating gold film on the curved part of the bent multimode fiber, the surface plasmon mode (SPM) was excited via a whispering gallery mode (WGM). Fabricating the structure only required bending the fiber and plating it with gold, which perfectly ensured the integrity of the fiber and made it more robust compared with other structures. The sensor used magnetic fluid (MF) as the magnetically sensitive material. Through monitoring the shift of the surface plasmon resonance dip, the as-fabricated sensor not only had a high magnetic field intensity sensitivity of 9749 pm/mT but could also measure the direction of a magnetic field with a high sensitivity of 546.5 pm/°. The additional advantages of the proposed sensor lay in its easy fabrication and good integrity, which make it attractive in the field of vector-magnetic-field sensing.

Surface Plasmon Resonance (SPR) Simulation of a Gold-Bismuth Bi-layer Gas Sensor

The features of plasmonic surface frequency sensor technology, such as the small number of sensor samples required, electromagnetic interference, and high sensitivity, have been found to be highly important.. In this paper, a simulation program was created in Matlab_b2018 by adopting Fresnel equations for calculating the reflectivity of the electromagnetic wave between different media. A surface plasmon resonance sensor based on electromagnetic wavelengths within the range (100 nm to 1000 nm) has been proposed. The transfer matrix was used for a system consisting of four different media. The first medium is a semicircular BK7 glass prism, the second medium is a gold layer (40 nm thick), then a bismuth layer of variable thicknes(10–80) nm, and the last medium is air as the sensing medium. The surface plasmon resonance (SPR) technique was adopted based on the Kretschmann configuration in the simulation of the proposed system. The simulation results showed that there is no SPR within the range of wavelengths (100-500nm), while SPR appears in the visible region and in the IR region at wavelengths (900 and 1000nm). The SPR phenomenon starts to weaken gradually with an increase in the thickness of the bismuth layer. The full width at half maximum (FWHM) decreases with the decrease of thickness of bismuth layer. The best value for it is (10) at thickness (d=10 nm) and wavelength (900 nm). While the height (H) of the SPR dip increased, with the best value of (0.95) at thickness (d=10 nm) and wavelength (700 nm). Also, the sensitivity increased with increasing the bismuth layer thickness at wavelengths (700 , 800, and 1000 ) nm. The highest obtained sensitivity(S) was (112.5 deg/RIU).

An optical sensor combining surface plasmon resonance, light extinction, and near-critical angle reflection, for thin liquid film biochemical sensing

We present a novel and low-cost optical sensor to obtain at the same time, fast and label-free optical information such as reflectivity, refractive index and extinction coefficient of biochemical samples. The sensor measures in around one minute optical internal reflectivity as a function of the angle of incidence at the interface between a glass prism covered by a gold nanofilm (≈20 nm) in contact with a liquid sample (≈10 µL). The nanofilm is thin enough that a large fraction of the incident light transmits through it at angles of incidence below the critical angle set by the prism and sample refractive indices (≈ 61°), but thick enough to present a Surface Plasmon Resonance dip for angles of incidence beyond that critical angle. The calculated sensitivity of SPR to the surface refractive index is 168.35 deg/RIU. We demonstrate that when a sample contains live bacteria (E. coli) the whole reflectivity curve including the SPR region is clearly affected, and to adjust a theoretical model to the experimental curves, it is necessary to assume a complex refractive index of the nanofilm appreciably different than that of gold. The optical curve of the sensor provides more information than a conventional SPR measurements offering a more complete strategy for the analysis of biochemical substances and bacterial cell suspensions.

Calculation of spectra and plasmon wave distribution in one-dimensional periodic structure

Surface Plasmon Resonance (SPR) is a resonance phenomenon between electromagnetic waves and electrons, which is formed on the interface between metal and dielectric surface. SPR waves can be generated by using a coupler element, such as prisms and gratings. In this study, we analyzed the effect of groove filling in nanograting structures using computation work based on Rigorous Coupled Wave Analysis (RCWA) method. The structure periodicity is 700 nm with a groove depth of around 350 nm. The reflectance spectra calculation by the RCWA method produces the appearance of SPR dip for an empty groove (with air inside the groove) at around 550 nm - 650 nm. The dip wavelength varies on the incident angles from 30 up to 60 degrees. In addition, the shifting of those dips is also predicted from the calculation results when the groove is filled by a medium with a refractive index of 1.5, which can be the basis of its utilization as optical sensing elements.

Direct and Sensitive Detection of Dopamine Using Carbon Quantum Dots Based Refractive Index Surface Plasmon Resonance Sensor.

Abnormality of dopamine (DA), a vital neurotransmitter in the brain’s neuronal pathways, causes several neurological diseases. Rapid and sensitive sensors for DA detection are required for early diagnosis of such disorders. Herein, a carbon quantum dot (CQD)-based refractive index surface plasmon resonance (SPR) sensor was designed. The sensor performance was evaluated for various concentrations of DA. Increasing DA levels yielded blue-shifted SPR dips. The experimental findings revealed an excellent sensitivity response of 0.138°/pM in a linear range from 0.001 to 100 pM and a high binding affinity of 6.234 TM−1. The effects of varied concentrations of DA on the optical characteristics of CQD thin film were further proved theoretically. Increased DA levels decreased the thickness and real part of the refractive index of CQD film, according to fitting results. Furthermore, the observed reduction in surface roughness using AFM demonstrated that DA was bound to the sensor layer. This, in turn, explained the blue shift in SPR reflectance curves. This optical sensor offers great potential as a trustworthy solution for direct measurement due to its simple construction, high sensitivity, and other sensing features.

Simulation of surface plasmon resonance (SPR) layers of gold with silicon nitride as a Bi-layer biosensor

Surface Plasmon Resonance (SPR) has gotten a lot of attention in biomedical sensing. Many applications in medical diagnostics and single molecule detection have sparked interest in bio-sensing techniques. Surface Plasmon resonance (SPR) is an important phenomenon used for building sensors especially in the Biological fields. Simulation analysis (in Mat lab) has been made for SPR for gold (Au) layer with thickness (40 nm) and layer of silicon nitride (Si3N4) with different thickness (10- 70 nm) step 10, deposited on glass prism type N-LASF9_ glass with the sensitive layer was water at refractive index (∆n = 0, 0.01, 0.05 and 0.1). The analysis was taken for different wavelengths from UltraViolet wavelength 100 nm to Near Infra- Red wavelength 1000 nm. The properties of the surface Plasmon resonance angle (θSPR) have been calculated from plotted reflectance against incident angle θincid shows sharper resonance dip, narrower full width half maximum (FWHM), SPR dip length (Ld) increased so that improve in properties SPR and system. The SPR sensitivity (S) was calculated and recorded higher sensitivity about 134.

Micro-Lab on Tip: High-Performance Dual-Channel Surface Plasmon Resonance Sensor Integrated on Fiber-Optic End Facet

It is a challenging and valuable work to realize the simultaneous sensing of two or more parameters at the end of optical fiber. In this paper, we implemented an ultra compact dual-channel surface plasmon resonance (SPR) sensor on fiber-optic end facet. A dual-layer polymer microcap based on different refractive index (RI) films was used to segment a single Cu/TiO2 coated micro-cone on single mode fiber (SMF) end facet for producing a sensing spectrum with two separated SPR dips. The SPR dip (channel-II) generated by Polydimethylsiloxane (PDMS) microcap can reach high sensitivity temperature measurement of 2.935 nm/°C in the range of 30–70 °C, and the SPR dip (channel-I) generated by polyvinyl alcohol (PVA) microcap can achieve high sensitivity humidity measurement of 1.08 nm/%RH in the range of 20%RH-70%RH. Finally, the simultaneous detection of humidity and temperature can be realized by the matrix established by channel-I and channel-II. This is a simple, effective and reproducible micro laboratory on optical fiber end facet for dual parameter sensing.

Sensitivity enhancement of a fiber plasmonic sensor based on rolled-up Ag/TiO2 hyperbolic metamaterials

A novel, to the best of our knowledge, optical fiber plasmonic sensor based on a tapered coreless fiber (TCF) coating with rolled-up hyperbolic metamaterials (HMMs) is proposed and theoretically studied. The HMMs are composed mainly of A g / T i O 2 multi-layer composite materials. We can effectively control the surface plasmon resonance (SPR) wavelengths by adjusting the ratio of metal in two-layer ( R ), the number ( N ), and thickness ( T ) of two-layer on the HMMs. Spectral quality can be improved by changing the core diameter of TCF. According to the effective medium theory and finite element method, HMMs of R = 0.3 , T = 30 n m , N = 3 , and D = 20 µ m can provide an average sensitivity of 9127.86 nm/RIU (refractive index unit) in an external refractive index (ERI) of 1.33–1.40 and have a depth of SPR dip figure of merit of 65.32 R I U − 1 , which is an order of magnitude higher than 50 nm silver, for an ERI of 1.34–1.35. Also, the optical fiber plasmonic sensor integrated with roll-up HMMs shows performance superior to normal HMMs, thus providing certain guidance for future research.