Layered material platform for surface plasmon resonance biosensing

2D material-based surface plasmon resonance biosensors for applications in different domains: an insight

The design of surface plasmon resonance (SPR) sensors has been greatly enhanced in recent years by the advancements in the production and integration of nanostructures, leading to more compact and efficient devices. There have been reports of novel SPR sensors having distinct nanostructures, either as signal amplification tags like gold nanoparticles (AuNPs) or as sensing substrate-like two-dimensional (2D) materials including graphene, transition metal dichalcogenides (TMDCs), MXene, black phosphorus (BP), metal-organic frameworks (MOFs), and antimonene. Such 2D-based SPR biosensors offer advantages over conventional sensors due to significant increases in their sensitivity with a good figure of merit and limit of detection (LOD). Due to their atomically thin structure, improved sensitivity, and sophisticated functionalization capabilities, 2D materials can open up new possibilities in the field of healthcare, particularly in point-of-care diagnostics, environmental and food monitoring, homeland security protection, clinical diagnosis and treatment, and flexible or transient bioelectronics. The present study articulates an in-depth analysis of the most recent developments in 2D material-based SPR sensor technology. Moreover, in-depth research of 2D materials, their integration with optoelectronic technology for a new sensing platform, and the predicted and experimental outcomes of various excitation approaches are highlighted, along with the principles of SPR biosensors. Furthermore, the review projects the potential prospects and future trends of these emerging materials-based SPR biosensors to advance in clinical diagnosis, healthcare biochemical, and biological applications.

Highly oriented single-crystalline gold quantum-dot metamaterials as prospective materials for photonics

Miniaturization of optical devices is a modern trend essential for optoelectronics, optical sensing, optical computing and other branches of science and technology. To satisfy this trend, optical materials with a small footprint are required. Here we show that extremely thin, flat, nanostructured gold films made of highly oriented single-crystalline gold quantum-dots can provide elements of topological photonics in visible light and be used as high-index dielectric materials in the infrared part of the spectra. We measure and theoretically confirm the presence of topological darkness and associated phase singularities in studied gold films of thickness of below 10 nm placed on MgO substrates in the red part of the spectrum. At telecom wavelengths, the fabricated gold metasurface behaves as a dielectric with the refractive index of n≈2.75 and the absorption coefficient of k≈0.005.

Unleashing the potential of tungsten disulfide: Current trends in biosensing and nanomedicine applications

The discovery of graphene ignites a great deal of interest in the research and advancement of two-dimensional (2D) layered materials. Within it, semiconducting transition metal dichalcogenides (TMDCs) are highly regarded due to their exceptional electrical and optoelectronic properties. Tungsten disulfide (WS2) is a TMDC with intriguing properties, such as biocompatibility, tunable bandgap, and outstanding photoelectric characteristics. These features make it a potential candidate for chemical sensing, biosensing, and tumor therapy. Despite the numerous reviews on the synthesis and application of TMDCs in the biomedical field, no comprehensive study still summarizes and unifies the research trends of WS2 from synthesis to biomedical applications. Therefore, this review aims to present a complete and thorough analysis of the current research trends in WS2 across several biomedical domains, including biosensing and nanomedicine, covering antibacterial applications, tissue engineering, drug delivery, and anticancer treatments. Finally, this review also discusses the potential opportunities and obstacles associated with WS2 to deliver a new outlook for advancing its progress in biomedical research.

Topological Darkness in Optical Heterostructures: Prediction and Confirmation

Topological darkness is a new phenomenon that guarantees zero reflection/transmission of light from an optical sample and hence provides topologically nontrivial phase singularities. Here we consider topological darkness in an optical heterostructure that consists of an (unknown) layer placed on a composite substrate and suggest an algorithm that can be used to predict and confirm the presence of topological darkness. The algorithm is based on a combination of optical measurements and the Fresnel equations. We apply this algorithm to ultrathin Pd films fabricated on a Si/SiO2/Cr substrate and extract four different points of topological darkness. Our results will be useful for topological photonics and label-free optical biosensing based on phase interrogation.

Topological Darkness: How to Design a Metamaterial for Optical Biosensing with Ultrahigh Sensitivity

Due to the absence of labels and fast analyses, optical biosensors promise major advances in biomedical diagnostics, security, environmental, and food safety applications. However, the sensitivity of the most advanced plasmonic biosensor implementations has a fundamental limitation caused by losses in the system and/or geometry of biochips. Here, we report a "scissor effect" in topologically dark metamaterials which is capable of providing ultrahigh-amplitude sensitivity to biosensing events, thus solving the bottleneck sensitivity limitation problem. We explain how the "scissor effect" can be realized via the proper design of topologically dark metamaterials and describe strategies for their fabrication. To validate the applicability of this effect in biosensing, we demonstrate the detection of folic acid (vitamin important for human health) in a wide 3-log linear dynamic range with a limit of detection of 0.22 nM, which is orders of magnitude better than those previously reported for all optical counterparts. Our work provides possibilities for designing and realizing plasmonic, semiconductor, and dielectric metamaterials with ultrasensitivity to binding events.

Label-free optical biosensing: going beyond the limits

Label-free optical biosensing holds great promise for a variety of applications in biomedical diagnostics, environmental and food safety, and security. It is already used as a key tool in the investigation of biomolecular binding events and reaction constants in real time and offers further potential additional functionalities and low-cost designs. However, the sensitivity of this technology does not match the routinely used but expensive and slow labelling methods. Therefore, label-free optical biosensing remains predominantly a research tool. Here we discuss how one can go beyond the limits of detection provided by standard optical biosensing platforms and achieve a sensitivity of label-free biosensing that is superior to labelling methods. To this end we review newly emerging optical implementations that overcome current sensitivity barriers by employing novel structural architectures, artificial materials (metamaterials and hetero-metastructures) and using phase of light as a sensing parameter. Furthermore, we elucidate the mechanism of plasmonic phase biosensing and review hyper-sensitive transducers, which can achieve detection limits at the single molecule level (less than 1 fg mm-2) and make it possible to detect analytes at several orders of magnitude lower concentrations than so far reported in literature. We finally discuss newly emerging layouts based on dielectric nanomaterials, bound states in continuum, and exceptional points.

A Genetic Algorithm for Universal Optimization of Ultrasensitive Surface Plasmon Resonance Sensors with 2D Materials

We present a general optimization technique for surface plasmon resonance, (SPR) yielding a range of ultrasensitive SPR sensors from a materials database with an enhancement of ∼100%. Applying the algorithm, we propose and demonstrate a novel dual-mode SPR structure coupling SPP and a waveguide mode within GeO2 featuring an anticrossing behavior and an unprecedented sensitivity of 1364 deg/RIU. An SPR sensor operating at wavelengths of 633 nm having a bimetal Al/Ag structure sandwiched between hBN can achieve a sensitivity of 578 deg/RIU. For a wavelength of 785 nm, we optimized a sensor as a Ag layer sandwiched between hBN/MoS2/hBN heterostructures achieving a sensitivity of 676 deg/RIU. Our work provides a guideline and general technique for the design and optimization of high sensitivity SPR sensors for various sensing applications in the future.

MoS2-Nanoflower and Nanodiamond Co-Engineered Surface Plasmon Resonance for Biosensing

Surface plasmon resonance (SPR) based sensors play an important role in the biological and medical fields, and improving the sensitivity is a goal that has always been pursued. In this paper, a sensitivity enhancement scheme jointly employing MoS₂ nanoflower (MNF) and nanodiamond (ND) to co-engineer the plasmonic surface was proposed and demonstrated. The scheme could be easily implemented via physically depositing MNF and ND overlayers on the gold surface of an SPR chip, and the overlayer could be flexibly adjusted by controlling the deposition times, thus approaching the optimal performance. The bulk RI sensitivity was enhanced from 9682 to 12,219 nm/RIU under the optimal condition that successively deposited MNF and ND 1 and 2 times. The proposed scheme was proved in an IgG immunoassay, where the sensitivity was twice enhanced compared to the traditional bare gold surface. Characterization and simulation results revealed that the improvement arose from the enhanced sensing field and increased antibody loading via the deposited MNF and ND overlayer. At the same time, the versatile surface property of NDs allowed a specifically-functionalized sensor using the standard method compatible with a gold surface. Besides, the application for pseudorabies virus detection in serum solution was also demonstrated.

Carbon-based biosensors from graphene family to carbon dots: A viewpoint in cancer detection

According to the latest report by International Agency for Research on Cancer, 19.3 million new cancer cases and 10 million cancer deaths were globally reported in 2020. Early diagnosis can reduce these numbers significantly, and biosensors have appeared to be a solution to this problem as, unlike the traditional methods, they have low cost, rapid process, and do not need experts present on site for use. These devices have been incorporated to detect many cancer biomarkers and measure cancer drug delivery. To design these biosensors, a researcher must know about their different types, properties of nanomaterials, and cancer biomarkers. Among all types of biosensors, electrochemical and optical biosensors are the most sensitive and promising sensors for detecting complicated diseases like cancer. The carbon-based nanomaterial family has attracted lots of attention due to their low cost, easy preparation, biocompatibility, and significant electrochemical and optical properties. In this review, we have discussed the application of graphene and its derivatives, carbon nanotubes (CNTs), carbon dots (CDs), and fullerene (C60), for designing different electrochemical and optical cancer-detecting biosensors. Furthermore, the application of these carbon-based biosensors for detecting seven widely studied cancer biomarkers (HER2, CEA, CA125, VEGF, PSA, Alpha-fetoprotein, and miRNA21) is reviewed. Finally, various fabricated carbon-based biosensors for detecting cancer biomarkers and anticancer drugs are comprehensively summarized as well.

Chimeric Peptide-Based Biomolecular Constructs for Versatile Nucleic Acid Biosensing

Nucleic acid biomarkers hold great potential as key indicators for the diagnosis and monitoring of diseases. Herein we design and implement bifunctional chimeric biomolecules composed of a solid-binding peptide (SBP) domain that specifically adsorbs onto solid sensor surfaces and a peptide nucleic acid (PNA) moiety that facilitates anchoring of antisense oligonucleotide (ASO) probes for the detection of nucleic acid targets. A gold-binding peptide, AuBP1, previously selected by directed evolution to specifically bind to gold, served as the basis for immobilizing nucleic acid probes onto gold substrates. Using surface plasmon resonance (SPR) spectroscopy and quartz crystal microbalance (QCM) analyses, we demonstrate the sequential biomolecular assembly of the heterofunctional solid-binding peptide-antisense oligomer (SBP-ASO) construct onto a sensor surface and the subsequent detection of DNA in an aqueous environment. The effect of steric hindrance on optimal probe assembly is observed, establishing that less packing density results in greater target capture efficacy. In addition, an adsorbed layer of chimeric solid-binding peptide-peptide nucleic acid (SBP-PNA) undergoes viscoelastic changes at the solid-liquid interface upon probe immobilization and DNA target capture, whereby the rigid biofunctional layer becomes more flexible. The dual nature of the chimeric construct is highly amenable to a variety of platforms allowing for both specific recognition and probe immobilization on the sensor surface, while the modular design of the solid-binding peptide-antisense oligonucleotide provides facile functionalization of a wide diversity of solid substrates.

Topological phase singularities in atomically thin high-refractive-index materials

Atomically thin transition metal dichalcogenides (TMDCs) present a promising platform for numerous photonic applications due to excitonic spectral features, possibility to tune their constants by external gating, doping, or light, and mechanical stability. Utilization of such materials for sensing or optical modulation purposes would require a clever optical design, as by itself the 2D materials can offer only a small optical phase delay - consequence of the atomic thickness. To address this issue, we combine films of 2D semiconductors which exhibit excitonic lines with the Fabry-Perot resonators of the standard commercial SiO2/Si substrate, in order to realize topological phase singularities in reflection. Around these singularities, reflection spectra demonstrate rapid phase changes while the structure behaves as a perfect absorber. Furthermore, we demonstrate that such topological phase singularities are ubiquitous for the entire class of atomically thin TMDCs and other high-refractive-index materials, making it a powerful tool for phase engineering in flat optics. As a practical demonstration, we employ PdSe2 topological phase singularities for a refractive index sensor and demonstrate its superior phase sensitivity compared to typical surface plasmon resonance sensors.

All-optical control of phase singularities using strong light-matter coupling

Strong light-matter coupling occurs when the rate of energy exchange between an electromagnetic mode and a molecular ensemble exceeds competing dissipative processes. The study of strong coupling has been motivated by applications such as lasing and the modification of chemical processes. Here we show that strong coupling can be used to create phase singularities. Many nanophotonic structures have been designed to generate phase singularities for use in sensing and optoelectronics. We utilise the concept of cavity-free strong coupling, where electromagnetic modes sustained by a material are strong enough to strongly couple to the material’s own molecular resonance, to create phase singularities in a simple thin film of organic molecules. We show that the use of photochromic molecules allows for all-optical control of phase singularities. Our results suggest what we believe to be both a new application for strong light-matter coupling and a new, simplified, more versatile means of manipulating phase singularities.

Phase singularities are known to have applications in various branches of optics. Here the authors demonstrate that phase singularities can be created and controlled, all optically, in a simple thin film of organic molecules using cavity-free strong light-matter coupling.

2D Material-Based Optical Biosensor: Status and Prospect

The combination of 2D materials and optical biosensors has become a hot research topic in recent years. Graphene, transition metal dichalcogenides, black phosphorus, MXenes, and other 2D materials (metal oxides and degenerate semiconductors) have unique optical properties and play a unique role in the detection of different biomolecules. Through the modification of 2D materials, optical biosensor has the advantages that traditional sensors (such as electrical sensing) do not have, and the sensitivity and detection limit are greatly improved. Here, optical biosensors based on different 2D materials are reviewed. First, various detection methods of biomolecules, including surface plasmon resonance (SPR), fluorescence resonance energy transfer (FRET), and evanescent wave and properties, preparation and integration strategies of 2D material, are introduced in detail. Second, various biosensors based on 2D materials are summarized. Furthermore, the applications of these optical biosensors in biological imaging, food safety, pollution prevention/control, and biological medicine are discussed. Finally, the future development of optical biosensors is prospected. It is believed that with their in-depth research in the laboratory, optical biosensors will gradually become commercialized and improve people's quality of life in many aspects.

Ultrathin Metals on a Transparent Seed and Application to Infrared Reflectors

Ultrathin metal films (UTMFs) are widely used in optoelectronic applications, from transparent conductors to photovoltaic cells, low emissivity windows, and plasmonic metasurfaces. During the initial deposition phase, many metals tend to form islands on the receiving substrate rather than a physically connected (percolated) network, which eventually evolves into continuous films as the thickness increases. For example, in the case of Ag and Au on dielectric surfaces, percolation begins when the thickness of the metal film is at least about 5 nm. It is known that the type of growth can be changed when a proper seed layer is used. Here, we show that a CuO layer directly deposited on a substrate can dramatically influence surface wetting and promote early percolation of polycrystalline Ag and Au UTMFs. We demonstrate that the proposed seed is effective even when its thickness is sub-nanometric, in this way maintaining the full transparency of the receiving substrate. The Ag and Au films seeded with CuO showed a percolation thickness close to 1 nm and were morphologically and optically characterized from an ultraviolet (λ = 300 nm) to a midinfrared (λ = 15 μm) wavelength. Infrared reflectors, a mirror and a resonant plasmonic structure, were also demonstrated and uniquely tuned by electrical gating, this being possible owing to the small thickness of the constituting Au UTMF.

Design and Optimization of Surface Plasmon Resonance Spectroscopy for Optical Constant Characterization and Potential Sensing Application: Theoretical and Experimental Approaches

The best surface plasmon resonance (SPR) signal can be generated based on several factors that include the excitation wavelength, the type of metal used, and the thickness of the metal layer. In this study, the aforementioned factors have been investigated to obtain the best SPR signal. The excitation wavelength of 633 nm and gold metal with thickness of 50 nm were required to generate the SPR signal before the SPR was used for optical constant characterization by fitting of experimental results to the theoretical data. The employed strategy has good agreement with the theoretical value where the real part refractive index, n value, of the gold thin film was 0.1245 while the value for the imaginary part, k, was 3.6812 with 47.7 nm thickness. Besides that, the optical characterization of nanocrystalline cellulose (NCC)-based thin film has also been demonstrated. The n and k values found for this thin film were 1.4240 and 0.2520, respectively, with optimal thickness of 9.5 nm. Interestingly when the NCC-based thin film was exposed to copper ion solution with n value of 1.3333 and k value of 0.0060 to 0.0070 with various concentrations (0.01–10 ppm), a clear change of the refractive index value was observed. This result suggests that the NCC-based thin film has high potential for copper ion sensing using SPR with a sensitivity of 8.0052°/RIU.

Nanophotonic biosensors harnessing van der Waals materials

Low-dimensional van der Waals (vdW) materials can harness tightly confined polaritonic waves to deliver unique advantages for nanophotonic biosensing. The reduced dimensionality of vdW materials, as in the case of two-dimensional graphene, can greatly enhance plasmonic field confinement, boosting sensitivity and efficiency compared to conventional nanophotonic devices that rely on surface plasmon resonance in metallic films. Furthermore, the reduction of dielectric screening in vdW materials enables electrostatic tunability of different polariton modes, including plasmons, excitons, and phonons. One-dimensional vdW materials, particularly single-walled carbon nanotubes, possess unique form factors with confined excitons to enable single-molecule detection as well as in vivo biosensing. We discuss basic sensing principles based on vdW materials, followed by technological challenges such as surface chemistry, integration, and toxicity. Finally, we highlight progress in harnessing vdW materials to demonstrate new sensing functionalities that are difficult to perform with conventional metal/dielectric sensors.

This review presents an overview of scenarios where van der Waals (vdW) materials provide unique advantages for nanophotonic biosensing applications. The authors discuss basic sensing principles based on vdW materials, advantages of the reduced dimensionality as well as technological challenges.

Nano-layered surface plasmon resonance-based highly sensitive biosensor for virus detection: A theoretical approach to detect SARS-CoV-2

The outbreak of the coronavirus disease (COVID-19) pandemic has become a worldwide health catastrophe instigated by Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2). Countries are battling to slow the spread of this virus by testing and treating patients, along with other measures such as prohibiting large gatherings, maintaining social distance, and frequent, thorough hand washing, as no vaccines or medicines are available that could effectively treat infected people for different types of SARS-CoV-2 variants. However, the testing procedure to detect this virus is lengthy. This study proposes a surface plasmon resonance-based biosensor for fast detection of SARS-CoV-2. The sensor employs a multilayered configuration consisting of TiO₂-Ag-MoSe₂ graphene with a BK7 prism. Antigen-antibody interaction was considered the principle for this virus detection. Immobilized CR3022 antibody molecules for detecting SARS-CoV-2 antigens (S-glycoprotein) are used for this sensor. It was found that the proposed sensor's sensitivity (194°/RIU), quality factor (54.0390 RIU^-1), and detection accuracy (0.2702) outperformed those of other single and multilayered structures. This study could be used as a theoretical base and primary step in constructing an actual sensor.

State-of-the-Art Optical Devices for Biomedical Sensing Applications—A Review

Optical sensors for biomedical applications have gained prominence in recent decades due to their compact size, high sensitivity, reliability, portability, and low cost. In this review, we summarized and discussed a few selected techniques and corresponding technological platforms enabling the manufacturing of optical biomedical sensors of different types. We discussed integrated optical biosensors, vertical grating couplers, plasmonic sensors, surface plasmon resonance optical fiber biosensors, and metasurface biosensors, Photonic crystal-based biosensors, thin metal films biosensors, and fiber Bragg grating biosensors as the most representative cases. All of these might enable the identification of symptoms of deadly illnesses in their early stages; thus, potentially saving a patient’s life. The aim of this paper was not to render a definitive judgment in favor of one sensor technology over another. We presented the pros and cons of all the major sensor systems enabling the readers to choose the solution tailored to their needs and demands.

Understanding breast cancer heterogeneity through non-genetic heterogeneity

Intricacy in treatment and diagnosis of breast cancer has been an obstacle due to genotype and phenotype heterogeneity. Understanding of non-genetic heterogeneity mechanisms along with considering role of genetic heterogeneity may fill the gaps in landscape painting of heterogeneity. The main factors contribute to non-genetic heterogeneity including: transcriptional pulsing/bursting or discontinuous transcriptions, stochastic partitioning of components at cell division and various signal transduction from tumor ecosystem. Throughout this review, we desired to provide a conceptual framework focused on non-genetic heterogeneity, which has been intended to offer insight into prediction, diagnosis and treatment of breast cancer.

Emerging graphene-based sensors for the detection of food adulterants and toxicants - A review

The detection of food adulterants and toxicants can prevent a large variety of adverse health conditions for the global population. Through the process of rapid sensing enabled by deploying novel and robust sensors, the food industry can assist in the detection of adulterants and toxicants at trace levels. Sensor platforms which exploit graphene-based nanomaterials satisfy this requirement due to outstanding electrical, optical and thermal properties. The materials' facile conjugation with linkers and biomolecules along with the option for further enhancement using nanoparticles results in highly sensitive and selective sensing characteristics. This review highlights novel applications of graphene derivatives for detection covering three important approaches; optical, electrical (field-effect) and electrochemical sensing. Suitable graphene-based sensors for portable devices as point-of-need platforms are also presented. The future scope of these sensors is discussed to showcase how these emerging techniques will disrupt the food detection sector for years to come.

Strong second-harmonic response from semiconductor-dielectric interfaces

In this study, an analysis of the second-harmonic generation (SHG) response from surfaces containing dielectric-semiconductor interfaces with sub-wavelength features is presented. The investigated medium is a metamaterial where the SHG response is governed by the symmetry breaking between consecutive layers. The examined material is composed of a periodic structure based on 50 nm silicon nitride and 10 nm indium gallium zinc oxide (IGZO) fabricated on a quartz glass substrate. The elementary cell consists of a pair of materials in an exchangeable order. The preliminary results show a promising application of the amorphous IGZO as a nonlinear optical material, whose optical characteristics can be controlled by the fabrication process itself. Prepared structures give a remarkably high SHG response. For an effective thickness of the structure equal to 240 nm, a more than 250-fold increase in SHG compared to the reference substrate is observed.

A Review of Graphene-Based Surface Plasmon Resonance and Surface-Enhanced Raman Scattering Biosensors: Current Status and Future Prospects

The surface plasmon resonance (SPR) biosensor has become a powerful analytical tool for investigating biomolecular interactions. There are several methods to excite surface plasmon, such as coupling with prisms, fiber optics, grating, nanoparticles, etc. The challenge in developing this type of biosensor is to increase its sensitivity. In relation to this, graphene is one of the materials that is widely studied because of its unique properties. In several studies, this material has been proven theoretically and experimentally to increase the sensitivity of SPR. This paper discusses the current development of a graphene-based SPR biosensor for various excitation methods. The discussion begins with a discussion regarding the properties of graphene in general and its use in biosensors. Simulation and experimental results of several excitation methods are presented. Furthermore, the discussion regarding the SPR biosensor is expanded by providing a review regarding graphene-based Surface-Enhanced Raman Scattering (SERS) biosensor to provide an overview of the development of materials in the biosensor in the future.

On the Challenges for the Diagnosis of SARS-CoV-2 Based on a Review of Current Methodologies

Diagnosis of COVID-19 has been challenging owing to the need for mass testing and for combining distinct types of detection to cover the different stages of the infection. In this review, we have surveyed the most used methodologies for diagnosis of COVID-19, which can be basically categorized into genetic-material detection and immunoassays. Detection of genetic material with real-time polymerase chain reaction (RT-PCR) and similar techniques has been achieved with high accuracy, but these methods are expensive and require time-consuming protocols which are not widely available, especially in less developed countries. Immunoassays for detecting a few antibodies, on the other hand, have been used for rapid, less expensive tests, but their accuracy in diagnosing infected individuals has been limited. We have therefore discussed the strengths and limitations of all of these methodologies, particularly in light of the required combination of tests owing to the long incubation periods. We identified the bottlenecks that prevented mass testing in many countries, and proposed strategies for further action, which are mostly associated with materials science and chemistry. Of special relevance are the methodologies which can be integrated into point-of-care (POC) devices and the use of artificial intelligence that do not require products from a well-developed biotech industry.

Exploring Graphene and MoS2 Chips Based Surface Plasmon Resonance Biosensors for Diagnostic Applications

Until now, two-dimensional (2D) nanomaterials have been widely studied and applied in the biosensor field. Some of the advantages offered by these 2D materials include large specific surface area, high conductivity, and easy surface modification. This review discusses the use of 2D material in surface plasmon resonance (SPR) biosensor for diagnostic applications. Two-dimensional material reviewed includes graphene and molybdenum disulfide (MoS2). The discussion begins with a brief introduction to the general principles of the SPR biosensor. The discussion continues by explaining the properties and characteristics of each material and its effect on the performance of the SPR biosensor, in particular its sensitivity. This review concludes with some recent applications of graphene- and MoS2-based SPR biosensor in diagnostic applications.

Graphene Plasmonics in Sensor Applications: A Review

Surface plasmon polaritons (SPPs) can be generated in graphene at frequencies in the mid-infrared to terahertz range, which is not possible using conventional plasmonic materials such as noble metals. Moreover, the lifetime and confinement volume of such SPPs are much longer and smaller, respectively, than those in metals. For these reasons, graphene plasmonics has potential applications in novel plasmonic sensors and various concepts have been proposed. This review paper examines the potential of such graphene plasmonics with regard to the development of novel high-performance sensors. The theoretical background is summarized and the intrinsic nature of graphene plasmons, interactions between graphene and SPPs induced by metallic nanostructures and the electrical control of SPPs by adjusting the Fermi level of graphene are discussed. Subsequently, the development of optical sensors, biological sensors and important components such as absorbers/emitters and reconfigurable optical mirrors for use in new sensor systems are reviewed. Finally, future challenges related to the fabrication of graphene-based devices as well as various advanced optical devices incorporating other two-dimensional materials are examined. This review is intended to assist researchers in both industry and academia in the design and development of novel sensors based on graphene plasmonics.

Multi-band MIM refractive index biosensor based on Ag-air grating with equivalent circuit and T-matrix methods in near-infrared region

In this paper, a multi-band metal-insulator-metal (MIM) perfect absorber with refractive index sensing capability has been investigated in near-infrared region. The proposed structure has been studied for biomedical applications such as detection of solution of glucose in water, diagnosis of different stages of malaria infection, bacillus bacteria and cancer cells. The MIM configuration improves the sensing parameters of the biosensor due to the good interaction with the analyte. The high sensitivity and figure of merit of 2000 nm/RIU and 100 RIU⁻¹ have been achieved, respectively. Also, the Ag-air grating in the suggested plasmonic sensor helps the localized surface plasmons excitation and makes the structure sensitive to the incident lightwave polarization. Therefore, the presented biosensor behaves like a polarization switch with the high extinction ratio and fast response time of 25.15 dB and 100 fs, respectively. The methods of equivalent circuit model and transmission matrix have been utilized to verify the simulation results, as a new challenge in near-infrared region. The new idea of multi-application plasmonic devices, the feasibility of fabrication for the presented structure and utilizing mentioned analytical methods in near-infrared region could pave the way for the future of plasmonic structures.

Grafting of Diazonium Salts on Surfaces: Application to Biosensors

This review is divided into two parts; the first one summarizes the main features of surface modification by diazonium salts with a focus on most recent advances, while the second part deals with diazonium-based biosensors including small molecules of biological interest, proteins, and nucleic acids.