Angular Interrogation Research Articles

An Automated Platform for Surface Plasmon Resonance-Based Sensors

This article presents the design of an automated platform to quickly, efficiently, and accurately manipulate the components required for a typical surface plasmon resonance (SPR) sensing instrument. In traditional SPR platforms, such parts are at prearranged and fixed positions. The proposed solution enables individual and group component movements by adjusting the alignment and positioning to ensure either the proper excitation and detection of the SPR. The platform's mechanical chassis is constructed with an aluminum V-slot profile and trapezoidal thread spindles and nuts to guide the components' displacement. An L-shaped frame specially designed for this purpose holds all the parts. Besides mechanical chassis, microcontrollers, motors, distance sensors, temperature sensors, and a touch-screen compose the automated platform components. The use of the so-called PPBIO biochip operating in the angular interrogation mode (AIM) demonstrates the platform's functioning. The obtained experimental results agree with the ones acquired with a similar but manually adjusted test platform.

Design and comparative analysis of aluminum-MoS2 based plasmonic devices with enhanced sensitivity and Figure of Merit for biosensing applications in the near-infrared region

Aluminum (Al)-Molybdenum Disulfide (MoS2) based plasmonic structures act as excellent biosensors when exploited in the near-infrared region. While Al is economical as well as compatible with the optoelectronic devices, MoS2 is an emerging 2D nanomaterial with the promise of initiating better plasmonic activity. Based on Kretschmann's arrangement, we have explored angular interrogation over four different combinations of heterostructures with Al as the plasmonic metal layer, at a wavelength of 1550 nm. After studying the effect of Al thickness on the conventional configuration, the intermediate layers between the metal layer and the analyte were optimized. Inclusion of graphene along with MoS2 results in better interaction with the sensing medium. The effect of including silicon is also studied for sensitivity enhancement. In addition, a comparative analysis of sensor performances of the proposed devices is presented taking into account the two important parameters i.e. sensitivity as well as the Figure of Merit (FOM). Among the optimized multi-layered MoS2 based configurations, a maximum sensitivity of about 141°/RIU is obtained along with FOM of about 335.13 RIU−1. Finally, the single-stranded DNA sensing on the proposed devices shows that the structures can be used as a highly sensitive refractive index biosensor for bio-medical applications.

Highly sensitive antimonene-coated black phosphorous-based surface plasmon-resonance biosensor for DNA hybridization: design and numerical analysis

The design of an ultrasensitive surface plasmon resonance (SPR) sensor for the detection of deoxyribose nucleic acid (DNA) hybridization is highly desirable for biomedical applications. We have proposed an SPR sensor architecture (Prism-SF10/Al/Si/BP/Antimonene/phosphate buffer saline solution) and performed its numerical analysis for DNA hybridization using angular interrogation at 633 nm. Antimonene is used as a biorecognition element layer for better attachment of single stranded (ss), i.e., ss probe DNA on its surface, due to its higher binding energy for ssDNA (even greater than graphene). Silicon and black phosphorous are utilized to enhance the electromagnetic field at the sensing layer interface. Aluminum is used as an surface plasmon active metal and it also improves the quality factor. Remarkable sensitivity (202.37 deg / refractive index unit) is attained for this work, which is greater than any other SF10 prism-based SPR sensor proposed to date. The performance of the SPR biosensor is meticulously evaluated as limit-of-detection (0.0028 nM) and figure-of-merit (0.037 nM − 1) with respect to the concentration of complementary target ssDNA in the sensing medium. This versatile biosensor shows great application to detect deadly diseases via DNA hybridization in the biomedical field if developed as an SPR chip for experimental verification.

Sensitivity Analysis of GaAs-Metamaterial Nanocavity as a Tunable Surface Plasmon Resonance Sensor

Background: The paper reports on typical characteristics of resonant electromagnetic modes propagation through interfaces of a multilayer device. Methods: Using the transfer matrix method, p-reflectance is analyzed in angular interrogation for a symmetrical cavity performed with left-handed metamaterial layer mediated with GaAs. Results: An advantage of SPR sensor is demonstrated in terms of optimal performances by controlling thicknesses, refractive indices and dielectric gap layers of the media involved. Conclusion: The functionality of the proposed design, as a tunable filter, has been also identified.

Gaussian Beam Shaping and Multivariate Analysis in Plasmonic Sensing.

This work demonstrates a novel strategy to improve the sensing performance of a prism-coupled surface plasmon resonance system by Gaussian beam shaping and multivariate data analysis. The propagation of the beam along the optical system has been studied using the Gaussian beam approximation to design the incident beam such that the beam waist is aligned precisely and that stability is assured at the metal-dielectric interface. This renders a collimated incident beam, hence least angular dispersion, yielding a stronger and sharper plasmonic resonance. Moreover, we use the multivariate analysis method partial least squares that combines multiple features of the surface plasmon resonance curve and allows for a more precise analysis of the plasmonic response. Compared to univariate analysis, partial least squares improves typical sensing performance parameters remarkably. The combination of both aspects, beam shaping and multivariate analysis, overcomes current limitations of plasmonic detection systems. Thereby, we improve analytical sensitivity by a factor of 16, decrease the prediction error of the concentration of an unknown analyte by a factor of 11, and enhance resolution to the order of 5 × 10-7 RIU in angular interrogation.

Sensitivity enhancement with anti-reflection coating of silicon nitride (Si3N4) layer in silver-based Surface Plasmon Resonance (SPR) sensor for sensing of DNA hybridization

This work presents a highly sensitive silver (Ag) based Surface Plasmon Resonance (SPR) sensor with graphene-coated over Silicon nitride (Si3N4) for sensing of Deoxyribonucleic acid (DNA) hybridization. The design consists of five layers namely Ag, Si3N4, graphene, and sensing medium along with BK7 glass prism that couple light at the metal–dielectric interface. The performance of the present structure has been evaluated using the angular interrogation method. The present investigation reveals the difference in complementary DNA strands and mismatched DNA strands as well as single-nucleotide polymorphisms (SNP) event by examining the variation of resonance angle in the reflectivity spectrum. The performance of the present structure is compared with the contemporary structures and found better than existing sensors. Therefore, the proposed structure is suitable in the biochemical field for the detection of biomolecules interactions.

Hyperchromatic structural color for perceptually enhanced sensing by the naked eye

Colorimetric sensors offer the prospect for on-demand sensing diagnostics in simple and low-cost form factors, enabling rapid spatiotemporal inspection by digital cameras or the naked eye. However, realizing strong dynamic color variations in response to small changes in sample properties has remained a considerable challenge, which is often pursued through the use of highly responsive materials under broadband illumination. In this work, we demonstrate a general colorimetric sensing technique that overcomes the performance limitations of existing chromatic and luminance-based sensing techniques. Our approach combines structural color optical filters as sensing elements alongside a multichromatic laser illuminant. We experimentally demonstrate our approach in the context of label-free biosensing and achieve ultrasensitive and perceptually enhanced chromatic color changes in response to refractive index changes and small molecule surface attachment. Using structurally enabled chromaticity variations, the human eye is able to resolve ∼0.1-nm spectral shifts with low-quality factor (e.g., Q ∼ 15) structural filters. This enables spatially resolved biosensing in large area (approximately centimeters squared) lithography-free sensing films with a naked eye limit of detection of ∼3 pg/mm2, lower than industry standard sensors based on surface plasmon resonance that require spectral or angular interrogation. This work highlights the key roles played by both the choice of illuminant and design of structural color filter, and it offers a promising pathway for colorimetric devices to meet the strong demand for high-performance, rapid, and portable (or point-of-care) diagnostic sensors in applications spanning from biomedicine to environmental/structural monitoring.

Smart Noise Reduction in SPR Sensors Response Using Multiple-ANN Design

Surface plasmon resonance (SPR) based sensors are commonly applied to detect molecular interactions from features extracted of the so-called SPR curve. The SPR curve represents the position of the resonance occurrence, and reflects the quality of the sensor measurements. The instrumentation used in the SPR sensors require very specific coupling conditions for optical-electronic, mechanical, and fluidic components to properly excitate the surface plasmons. Noise sources inherent to the sensor instrumentation are reflected in the SPR curve and affect the quality of its extracted features. A smart-filter based on multilayer artificial neural networks is designed to eliminate the main instrumental noise sources and noise due to sensing proceedings at the SPR sensor usage, which are perceived as distortions in the SPR curves. The filter, called NNSF, is embedded to SPR sensors operating in both spectral (WIM) and angular (AIM) interrogation modes, and achieved responses with a mean square error of 10−5, and tested model correlation indexes over 90%. The filter redressed noises, including artifacts such as metal-layer roughness, light source input angle/wavelength disagreements, prism birefringence and general oscillations in amplitude and phase of the curve due to no-rigorous control process in the environment and experimental routines. Thus, the NNSF delivers curves with enhanced features and consequently increases the sensor performances in the monitoring of the resonance features (Width, Energy, Phase, Asymmetry, and minimum Position). Furthermore, the proposed filter avoids replacement or incorporation of new components that cause considerable instrumental maintenance cost.

Numerical modeling of MoS2–graphene bilayer-based high-performance surface plasmon resonance sensor: structure optimization for DNA hybridization

We present a MoS2–graphene bilayer-based high-performance refractive index surface plasmon resonance (SPR) sensor applying an angular interrogation technique. We used it for inspecting the reflected optical signal from the sensing medium. For enhancing the sensor angular sensitivity (S), signal-to-noise ratio (SNR), and quality factor (QF), we undertook some steps sequentially. First, the impact of gold layer thickness was investigated and optimized to 40 nm. Second, the MoS2 and graphene coating layers were optimized to four and three, respectively. Finally, the minimum reflectance and SPR angle were identified with this optimum structure. It is seen that the angular sensitivity of this optimum structure improved to an excellent value of 130 deg-RIU − 1 along with an improved angular SNR of 1.37 and QF of 17.02 RIU − 1. Then we compared the proposed sensor with the existing works in terms of angular sensitivity, SNR, and QF to prove its effective application. Finally, an analysis of DNA hybridization is presented as an application of the proposed structure. Our offered configuration is capable of recognizing absorption of DNAs by means of the attenuated total reflection method. The effective refractive index of the sensing medium alters because of the absorption of various concentrated DNAs. Computational investigation demonstrates that the change of SPR angle and minimum reflectance for mismatched DNA strands is inconsiderable, though it is significant for complementary DNA strands, which is crucial for the sensing of accurate DNA hybridization.

Predicting the Performance of Surface Plasmon Resonance Sensors Based on Anisotropic Substrates

The aim is to investigate how the sensing features of a surface plasmon resonance sensor based on the Kretschmann configuration are affected when the optical substrate is an anisotropic medium. The investigation considers the use of two different uniaxial anisotropic crystals, one made of barium titanate and another made of lithium niobate, as the optical substrate. It also considered that the sensor operates in the angular interrogation mode at the gold–water interface. The Fresnel equations and the finite element method were employed to determine the sensing features. The present study revealed that both formulations provide almost identical results for the resonance angle (difference less than 1%). On the other hand, the two formulations provide results with significant differences for additional features like the sensitivity and the full width at half maximum.

Waveguide controlled long range surface plasmon-polariton refractive index sensor

A long range surface plasmon-polariton resonance (LRSPPR) based refractive index sensor (for biomolecular interaction study applications) with ultrahigh sensitivity and extremely narrow resonance dips with very small full width at half maximum (FWHM, w) is proposed. The theoretical analysis of the sensitivity for spectral and angular interrogations is presented. The structure consists of a MgF2 prism and a plasmonic waveguide (consisting of a metal cladded high index dielectric waveguide) separated by a low index dielectric layer. It is shown that both angular and spectral sensitivities increase nonlinearly with increase in analyte index. Angular sensitivity with FWHM = 0.009°, ranges from 340°/RIU to 505°/RIU for analyte index variation from 1.360 to 1.368 and spectral sensitivity with FWHM = 3 nm, ranges from 1.79 × 105 nm RIU−1 to 2.60 × 105 nm RIU−1 for analyte index variation from1.361 00 to 1.361 10. The sensitivities (S) and the figures of Merit of the proposed sensor are the highest obtained so far (to our knowledge).

Performance analysis of Bloch surface wave-based sensor using transition metal dichalcogenides

In this manuscript, a highly sensitive Bloch surface wave (BSW)-based sensor is proposed for refractive index sensing analysis. The structure is designed using an one-dimensional photonic crystal (1D-PhC) structure. A top defective layer of transition metal dichalcogenides (TMDC) material with atomic layer thickness is introduced to confine a Bloch mode analogues to surface plasmon-like mode at the top interface. The detailed analysis is carried out to investigate the impact of number of TMDC monolayers on sensing performance. The wavelength (angular) interrogation provides the significant higher sensitivity of around 9650 nm/RIU (or 231°/RIU). Besides the sensitivity, the rigorous analysis of full-width-half-maximum (FWHM) and figure-of-merit (FOM) is also carried out and a FOM of around 48,250/RIU (38,500/RIU) has been reported. The proposed design possesses the advantage in terms of easy fabrication and integration capability to develop handheld senor systems, especially for biological and chemical sensing.

A Comparative Performance Evaluation of 2D Nanomaterials for Applications in Plasmonic Biosensing

Plasmonic sensing relies on the interaction between the electromagnetic light wave and free electrons that reside at the interface of two materials, one of them being a metal. Surface plasmon resonance (SPR)‐based biosensing has distinct advantages of providing real‐time and label‐free detection technique that is capable of giving accurate and repeatable results. 2D nanomaterials (graphene and transition metal dichalcogenides [TMDCs] such as MoS2 and WS2) have recently gained high popularity in the field of biomedical sciences. Using Biacore commercial SPR machine manufactured by GE Healthcare, the efficacy of various combinations of these materials coated on the plasmonic metal gold (Au) (Au + MoS2, Au + WS2, Au + graphene, Au + graphene + MoS2, and Au + graphene + WS2) is evaluated, in enhancing the sensitivity of the biosensor as compared with the standard Kretschmann configuration (only Au). Some simulation results are also presented at incident light wavelengths of 633 and 785 nm that are based on the angular interrogation method. To conclude, it is found that the sensitivity in the increasing order is: only Au < Au + MoS2 < Au + WS2 ≈ Au + graphene < Au + graphene + MoS2 < Au + graphene + WS2.

Sensitivity Improvement of Surface Plasmon Resonance Sensor on Using BlueP/MoS2 Heterostructure and Antimonene

Here, an ultrasensitive surface plasmon resonance (SPR) sensor based on angular interrogation using antimonene and BlueP/MoS2 heterostructure is proposed. Antimonene is used as an interacting layer for analytes due to its higher binding energy for analyte adsorption. BlueP/MoS2 enhances the sensitivity by manipulating charge transfer to metal/dielectric interface. Sensitivity for the proposed SPR is analyzed by tuning the number of heterostructure, as well as antimonene layers for wide range of refractive index. Highest sensitivity of 198.4°/RIU is achieved for three layers of BlueP/MoS2. Results show significant sensitivity for proposed design in comparison to conventional and graphene based SPR sensor. Proposed SPR sensor can be successfully developed as SPR chip for biomolecule/analyte detection in visible range.

Numerical analysis of sensitivity enhancement of surface plasmon resonance biosensors using a mirrored bilayer structure

A mirrored bilayer structure incorporating layers of Graphene and MoS2 is proposed here for Surface Plasmon Resonance (SPR) biosensing and its performance is evaluated numerically. Starting from the basic configuration, the structure with graphene and MoS2 layers is gradually developed for enhanced performance. Reflectance is the main considered parameter for performance analysis. A theoretical framework based on Fresnel's equations is presented and by measuring reflectance versus angle of incidence, sensitivity is calculated from the displacement of SPR angle using finite-difference time-domain (FDTD) technique. Our numerical analysis shows that using the proposed approach, about 4.2 times enhanced sensitivity can be achieved compared to the basic Kretschmann configuration. Notably, the structure provides enhancement for both angular and wavelength interrogations. Furthermore, simulations have been repeated for various ligate–ligand pairs and consistent enhancement has been observed which proves the robustness of the structure. So, the proposed sensor architecture clearly provides pronounced improvement in sensitivity which can be significant in various practical applications.

Aluminum-Based Deep-Ultraviolet Surface Plasmon Resonance Sensor

An aluminum-based deep-ultraviolet surface plasmon resonance (DUV-SPR) sensor is promising for biological applications. Design aspects of a DUV-SPR sensor are here considered by using Fresnel multilayer model. Angular and wavelength interrogation modes are used, where fused silica, sapphire, and acrylic solacryl ultraviolet transmittance (acrylic SUVT) are used as optical substrates. Aluminum at its oxidized state (alumina) is also considered as an aluminum overlayer. Our 4-layer Kretschmann-Raether-based SPR sensor is applied for gaseous and aqueous solutions, where some figures of merit are used to analyze the sensor performance. Values for sensitivity, linewidth (FWHM, full width at half maximum), and FOM (figure of merit or quality factor) are calculated. Resolution is also found and compared with other devices by using a known formulation. The results indicate that our sensor has a higher sensitivity for both gaseous and aqueous solutions when compared with the visible light-based sensor. For aqueous solutions, analyte is simulated as a bulk or a monolayer. Therefore, DUV-SPR sensors are a good alternative to the conventional visible-based SPR devices, where the performance is similar or higher for some conditions, having a higher affinity for some proteins.

Detection of Leptospirosis Bacteria in Rodent Urine by Surface Plasmon Resonance Sensor Using Graphene

In this paper, a graphene-coated surface plasmon resonance sensor is designed for the examination of Rodent urine which is responsible for Leptospirosis bacteria. Rodent urine is considered as sensing medium. Graphene surface is activated by phosphate-buffered saline solution for better attachment of Leptospirosis bacteria on its surface. Oliguria and Polyuria are the Rodent urine with high and low concentrations of Leptospirosis bacteria, respectively. The transfer matrix method is used for the formulation of reflection intensity of p-polarized light. The reflectance curves for angular interrogation are plotted and the results are obtained in terms of sensitivity, detection accuracy, and quality factor. The significantly high sensitivity and detection accuracy for Oliguria distinguishes it from Polyuria having lower sensitivity.

Simulation and analysis of 2D material/metal carbide based fiber optic SPR probe for ultrasensitive cortisol detection

Cortisol, a steroid hormone, plays a vital part in regulating various activities such as metabolism and immune response. It is a well-known stress biomarker and should be measured with as high precision as possible. In this work, a non-invasive fiber optic surface plasmon resonance (FOSPR) based sensor probe is proposed for detection of salivary cortisol at the w avelength (λ) of 830 nm. Proposed sensor design consists of chalcogenide glass core, polymer clad, silver (Ag) layer with two-dimensional (2D) materials such as conventional (graphene, WS2 and MoS2) and transition metal carbides (MXenes) based layered materials considered one at a time. Angular and intensity interrogation methods have been envisaged for simulation and analysis purpose. The sensing performance analysis is carried out in terms of figure of merit (FOM) and combined performance factor (CPF). A comprehensive analysis of all the probe variants reveals that among all the sensor design variants, the Ti3C2O2-based probe is able to provide superior overall sensing performance including a detection limit as fine as 15.7 fg/mL, which is finer compared to existing cortisol sensors based on diverse techniques.

Enabling selective absorption in perovskite solar cells for refractometric sensing of gases

Perovskite solar cells are currently considered a promising technology for solar energy harvesting. Their capability to deliver an electrical signal when illuminated can sense changes in environmental parameters. We have numerically analyzed the variation of the current delivered by a perovskite cell as a function of the index of refraction of air, that is in contact with the front surface of the cell. This calculation identifies which geometrical and material structures enhance this behavior. After replacing the top transparent electrode of a solar cell by an optimized subwavelength metallic grating, we find a large variation in the responsivity of the cell with respect to the change in the index of refraction of the surrounding medium. Such a refractometric sensor can be interrogated electronically, avoiding the cumbersome set-ups of spectral or angular interrogation methods. We present an adaptation of the performance parameters of refractometric sensors (sensitivity and figure of merit) to the case of opto-electronic interrogation methods. The values of sensitivity and Figure of Merit are promising for the development of refractometric perovskite-based sensors.

Theoretical and experimental study of a surface plasmon sensor based on Ag-MgF2 grating coupler

To achieve a high-sensitivity surface plasmon resonance sensor, a sensor based on Ag-MgF2 grating was designed and fabricated. A suitable-thickness MgF2 was suggested to prevent the oxidation of silver while avoiding reducing its plasmonic properties. The combination of an interference lithography approach, the material used for the fabrication of grating, and angular interrogation method led to a less costly sensor. The sensitivity and figure of merit of the proposed sensor approached 85.61 deg/RIU and 51 RIU−1, respectively, which is higher than the experimental values reported so far for grating-based sensors. It was shown that by optimization of the silver-based structure, it has great potential for use in sensor applications. It was observed that based on the made grating pattern, the numerical results were closer to experimental results by considering the grating pattern in a sine form. The effect of temperature on sensor performance was experimentally investigated. It was demonstrated that the change in the resonance angle with the temperature in this structure was equal to 0.02 deg/°C and it was also experimentally shown that temperature changes in the analyte refractive index had the most effect on the variations of the SPR response with temperature.