Severe respiratory syndrome COVID-19 (SARS-CoV-2) outbreak has became the most important global health issue, and simultaneous efforts to fast and low-cost diagnosis of this virus were performed by researchers. One of the most usual tests was colorimetric methods based on the change of color of gold nanoparticles in the presence of viral antibodies, antigens, and other biological agents. This spectral change can be due to the aggregation of the particles or the shift of localized surface plasmon resonance due to the electrical interactions of surface agents. It is known that surface agents could easily shift the absorption peak of metallic nanocolloids which is attributed to the localized surface plasmon resonance. Experimental diagnosis assays for colorimetric detection of SARS-CoV-2 using Au NPs were reviewed, and the shift of absorption peak was studied from the viewpoint of numerical analysis. Using the numerical method, the refractive index and real and imaginary parts of the effective relative permittivity of the viral biological shell around Au NPs were obtained. This model gives a quantitative description of colorimetric assays of the detection of SARS-CoV-2 using Au NPs.

Coronavirus disease (COVID-19) pandemic outbreak is being investigated by severe respirational syndrome coronavirus-2 (SARS-CoV-2) as a global health issue. It is crucial to propose sensitive and rapid coronavirus detectors. Herein, we propose a biosensor based on surface plasmon resonance (SPRE) for the detection of SARS-CoV-2 virus. To achieve improved sensitivity, a BiFeO layer is inserted between a metal (Ag) thin film and a graphene layer in the proposed SPRE device so that it has the structure BK7 prism/ Ag/ BiFeO/ graphene/ analyte. It has been demonstrated that a small variation in the refractive index of the analyte can cause a considerable shift in the resonance angle caused by the remarkable dielectric properties of the BiFeO layer, which include a high index of refraction and low loss. The proposed device has shown an extremely high sensitivity of 293 deg/RIU by optimizing the thicknesses of Ag, BiFeO, and the number of graphene sheets. The proposed SPRE-based sensor is encouraging for use in various sectors of biosensing because of its high sensitivity.

A novel surface plasmon resonance-based biosensor for SARS-CoV-2 virus is proposed in this article. The biosensor is a Kretschmann configuration-based structure that consists of CaF prism as base, at which silver (Ag), TiO, and MXene nanolayers are used to enhance the performance. Theoretically, the performance parameters have been investigated by means of Fresnel equations and transfer matrix method (TMM). The TiO nanolayer not only prevents oxidation of Ag layer but also enhances the evanescent field in its vicinity. The sensor provides an ultrahigh angular sensitivity of 346°/RIU for the detection of SARS-CoV-2 virus. Some other performance parameters, including FWHM (full width at half maxima), detection accuracy (DA), limit of detection (LOD), and quality factor (QF) have also been calculated for proposed SPR biosensor with their optimized values 2.907°, 0.3439 deg, 1.445 × 10, and 118.99 RIU, respectively. The obtained results designate that the proposed surface plasmon resonance (SPR) based biosensor has notably enhanced angular sensitivity as compared to previous results reported in the literatures till date. This work may facilitate a significant biological sample sensing device for fast and accurate diagnosis at early stage of SARS-CoV-2 virus.

In this paper, four individual structures based on graphene-plasmonic nano combinations are proposed for detection of corona viruses and especially COVID-19. The structures are arranged based on arrays in the shapes of half-sphere and one-dimensional photonic crystal formats. The half-sphere and plate shaped layers are made of , , and graphene. The one-dimensional photonic crystals lead the wavelength and peak corresponding to the absorption peak to lower and higher amounts, respectively. In order to improve the functionality of the proposed structures, effects of structural parameters and chemical potentials are considered. A defect layer of is positioned in the middle of one-dimensional photonic crystal layers to shift the absorption's peak wavelength to the appropriate wavelength range for diagnosing corona viruses (~ to 600 nm). The last proposed structure is considered as a refractive bio-sensor for detection of corona viruses. In the final proposed structure (based on different layers of , , , and graphene), corona viruses are considered as the biomolecule layer and the results are obtained. The proposed bio-sensor can be a good and functional candidate for detection of corona viruses and especially COVID-19 in photonic integrated circuits with the satisfying sensitivity of ~ (refractive index unit).

The coronavirus (COVID-19) pandemic has put the entire world at risk and caused an economic downturn in most countries. This work provided theoretical insight into a novel fiber optic-based plasmonic biosensor that can be used for sensitive detection of SARS-CoV-2. The aim was always to achieve reliable, sensitive, and reproducible detection. The proposed configuration is based on Ag-Au alloy nanoparticle films covered with a layer of graphene which promotes the molecular adsorption and a thiol-tethered DNA layer as a ligand. Here, the combination of two recent approaches in a single configuration is very promising and can only lead to considerable improvement. We have theoretically analyzed the sensor performance in terms of sensitivity and resolution. To highlight the importance of the new configuration, a comparison was made with two other sensors. One is based on gold nanoparticles incorporated into a host medium; the other is composed of a bimetallic Ag-Au layer in the massive state. The numerical results obtained have been validated and show that the proposed configuration offers better sensitivity (7100 nm\RIU) and good resolution (figure of merit; FOM = 38.88 and signal-to-noise ratio; SNR = 0.388). In addition, a parametric study was performed such as the graphene layers' number and the size of the nanoparticles.

Since the coronavirus pandemic began, research groups worldwide developed diagnostic tests. One of the promising platforms for testing is an optical and plasmonic biosensor. Localized surface plasmon resonances owing to their highly concentrated field intensity provide highly sensitive devices. A beneficial approach to excite localized surface plasmon modes for field-based applications is using photonic crystal fibers while photonic quasi-crystals demonstrate a higher order of symmetry, the more isotropic Brillouin zone, and the easier achievement of photonic bandgap as compared with conventional photonic crystals. In this work, by exploiting a photonic quasi-crystal fiber, we are designing a surface plasmon resonance biosensor for the on-chip and real-time detection of coronaviruses. In our miniaturized design, a thin gold layer is employed on the outer layer of an air hole of a photonic quasi-crystal fiber with a 12-fold symmetry where the leakage of the fiber core mode can excite the surface plasmon resonance mode on the gold. According to three-dimensional finite-difference time-domain simulations, the proposed biosensor shows the sensitivity of 1172 nm/RIU in the detection of coronaviruses within the saliva. Moreover, the smallest detection limit obtained in the simulation is about 12 nm. These promising results altogether indicate that this reconfigurable and lab-on-a-chip platform can potentially be used in the detection of all kinds of coronaviruses.

The surface plasmon resonance (SPR) is a phenomenon based on the combination of quantum mechanics and electromagnetism, which leads to the creation of charge oscillations on a metal-dielectric interface. The SPR phenomenon creates a signal which measures refractive index change at the metal-dielectric interface. SPR-based sensors are being developed for real-time and label-free detection of water pollutants, toxins, disease biomarkers, etc., which are highly sensitive and selective. Smartphones provide hardware and software capability which can be incorporated into SPR sensors, enabling the possibility of economical and accurate on-site portable sensing. The camera, screen, and LED flashlight of the smartphone can be employed as components of the sensor. The current article explores the recent advances in smartphone-based SPR sensors by studying their principle, components, application, and signal processing. Furthermore, the general theoretical and practical aspects of SPR sensors are discussed.

As developed countries' ability to control infectious diseases increases, it has become clear that genetic diseases are a major cause of disability, death, and human tragedy. Coronavirus has recently spread throughout the world, and the capacity to detect low concentrations and virus changes can help to prevent the sickness from spreading further. In this paper, a surface plasmon resonance sensor based on nanostructured thin films and graphene as a 2D material has been designed with high sensitivity and accuracy to identify DNA-based infectious diseases such as SARS-CoV-2. The transfer matrix method assesses the effects of different structural factors, including nanolayer thickness on the sensor's performance. The results demonstrated that the sensor with the Kretschmann configuration has ultra-high sensitivity (192.19 deg/RIU) and a high figure of merit (634.68 RIU).

In the present study, we report giant extra-ordinary transmission of near infrared (NIR) light, more than 90%, through a seemingly opaque plasmonic metasurface, which consists of two metal nano-slits arrays (MNSAs) with alternate opening arrangements. By using perfect coupling of the plasmonic modes formed between the sharp edges of the upper and lower MNSAs of silver, a giant, wavelength selective transmission could be obtained. The study is accompanied by optimization of electromagnetic (EM) field coupling for different interlayer spacings and lateral overlap between the two MNSAs to understand their significance in light transmission through the metasurface. The interlayer spacing between the MNSAs works as the transmitting channel for light. The optimization of performance with different fill factors and plasmonic metals was performed as well. Because of the excitation of extended surface plasmons (ESPs) generated at both the MNSAs, the metasurface can be used for refractive index (RI) sensing as one of its applications by using a transparent and flexible polymer, such as polydimethylsiloxane (PDMS), as substrate. The maximum sensitivity which could be achieved for the optimal configuration of the metasurface was 1435.71 nm/RIU, with a figure of merit (FOM) of 80 RIU for 90.45% optical transmission of light for the refractive index variation of analyte medium from 1.33 to 1.38 RIU. The present study strengthens the concept of light funneling through subwavelength structures due to plasmons, which are responsible for light transmission through this seemingly opaque metasurface and finds use in highly sensitive, flexible, and cost-effective EOT-based sensors.

This manuscript aims to analyze the effect of tin selenide (SnSe) on the sensing application of SPR biosensors. Tin selenide is the 2-dimensional transition metal dichalcogenide material. The proposed multilayer structure has a BK7 prism, a bimetallic layer of Au, tin selenide, and a graphene layer. Tin selenide is used to improve the performance parameters of the biosensor. The nanosheet is placed in between two layers of gold (Au) in the Kretschmann configuration. The proposed configuration has a maximum sensitivity of 214 deg/RIU, 93.81% higher than the conventional sensor. The performance parameters like full width half maximum, detection accuracy, and quality factor have been analyzed. The material is an air-stable 2-D. The proposed sensor is suitable for the analysis of chemical, medical, and biological analytes.

With continuous mutations of SARS-CoV-2 virus, new highly contagious and fast-spreading variants have emerged, including Delta and Omicron. The popular label-free immunosensor based on surface plasmon resonance (SPR) technique can be used for real-time monitoring of the ligand-analyte or antibody-antigen interactions occurring on the sensor surface. In this work, an SPR-based biosensor combined with a nanodisk array was presented to enhance the sensitivity toward virus detection. The nanodisk arrays were employed to enhance the adsorption of molecules for better detection by increasing the SPR field. Four optimal sensing configurations of silver or gold nanodisks on gold thin films with different aspect ratios were achieved through systematic optimization of all parameters to yield the best sensor performance. The resonance angle can be modulated simply by the aspect ratio of nanodisk array. The sensitivity of the optimized sensors has been improved, and the detection limit is smaller than that of bare gold-based sensor. The multi-jump resonance angle curves at tiny refractive index can clearly distinguish the difference of trace concentrations, which is very important for the accurate detection of trace substances.

The sensing performance parameters of the SPR sensors are sensitivity, detection accuracy, the figure of merit (FOM), and full-width half maximum (FWHM), and it has been discussed with refractive indexes of analyte 1.33, 1.35, 1.38, and 1.39. In this, we proposed a multilayer structure comprising nanofilms of Ag, Silicon, and PtSe for the early diagnosis of chikungunya virus. The suggested sensor structure consists of a BK7 (borosilicate crown) coupling prism over which the nanofilm of silver metal is present. The layer thicknesses and the number of silicon and PtSe sheets are optimized for high performance. At the operating wavelength of 633 nm, a Kretschmann-based SPR sensor has been proposed, which gives the highest sensitivity of 287.3 Deg/RIU. The principle of attenuated total reflection has been employed for the performance analysis of the sensor.

The major challenge in today's world is that medical research is facing the existence of a vast number of viruses and their mutations, which from time to time cause outbreaks. Also, the continuous and spontaneous mutations occurring in the viruses and the emergence of resistant virus strains have become serious medical hazards. So, in view of the growing number of diseases, like the recent COVID-19 pandemic that has caused the deaths of millions of people, there is a need to improve rapid and sensitive diagnostic strategies to initiate timely treatment for such conditions. In the cases like COVID-19, where a real cure due to erratic and ambiguous signs is not available, early intervention can be life-saving. In the biomedical and pharmaceutical industries, nanotechnology has evolved exponentially and can overcome multiple obstacles in the treatment and diagnosis of diseases. Nanotechnology has developed exponentially in the biomedical and pharmaceutical fields and can overcome numerous challenges in the treatment and diagnosis of diseases. At the nano stage, the molecular properties of materials such as gold, silver, carbon, silica, and polymers get altered and can be used for the creation of reliable and accurate diagnostic techniques. This review provides insight into numerous diagnostic approaches focused on nanoparticles that could have been established for quick and early detection of such diseases.

In this article, we propose a simple method to calculate electrical permittivity and refractive index of surface agents of gold nanoparticles (Au NPs), in which it is possible to find the refractive index of surface agents shell by using the absorption peak of the gold nano-colloid. One of the usual tests for detection of surface agents is colorimetric methods based on the change of color of Au NPs. The color change is mainly due to the shift of localized surface plasmon resonance which is related to electrical interactions of surface agents. Although there are many mathematical models for simulating the absorption spectrum and calculating the plasmonic peak, using them is not simple and possible for everyone due to the need for programming. Here, the necessary simulations have been performed for different values ​​of refractive index of surface agents and particle size, and absorption peaks have been obtained. Using numerical methods, a simple formula is obtained between the wavelength of plasmonic peak, the ratio of hydrodynamic diameter to Feret size of the particles, and the refractive index of the surface agents. This method can help researchers to obtain the refractive index and consequently the type or concentration of surface agents around Au NPs without the need for programming or complex mathematical operations. It can also open new horizons in analyzing colorimetric diagnosis of biological agents such as viral antibodies, antigens, and other biological agents.

In this paper, the optical and thermoplasmonics properties of nanocomposites consisting of spherical gold nanoparticles (AuNPs) integrated in matrix are determined using the Finite Element Method (FEM). Firstly, the refractive index , extinction coefficient , absorption coefficient , and optical conductivity are calculated from the effective complex permittivity obtained by solving the Laplace's equation for different size and concentration of nanoparticles. The surface plasmon resonance (SPR) properties of AuNPs are optimized from the peak presented in the absorption coefficient spectrum. The results show that the optical parameters , and undergo a strong variation around the wavelength corresponding to the SPR phenomenon. The value of increases from to when the radius of the particles varies between and . The effect of the AuNP concentration on the band gap energy of Au- nanocomposites is also studied, a shift from to is observed when the concentration of the AuNPs increases from to . The electric field enhancement induced by the AuNPs at plasmonic resonance is also determined depending to the particle size; the results show that the enhancement factor increases from to when the radius of the AuNPs increases from to . The thermal dissipation of the plasmonic energy of spherical of our system dispersed in the matrix is determined considering the Joule effect which occurs by the oscillation of the charges at the plasmonic resonance. The generated thermal power by particles is calculated for different sizes, which allows to calculate the thermal power per gram of particles depending on the intensity of the incident electric field. The results show that the plasmonic thermal power is almost identical for small particles when the radius is less than and increases considerably when the size increases from to . For a fixed size and incident field amplitude, we calculated the temperature change in the nanocomposites Au- depending of time for different particle concentrations; the temperature variation curves obtained are linear as a function of time.

In this study, we propose a surface plasmon resonance (SPR)-based biosensor using silicon nitride (SiN), black phosphorous (BP), and thiol-tethered DNA as a ligand for fast detection of the SARS-CoV-2 virus. In the proposed biosensor, we have deposited silver (Ag), SiN, and BP on the base of the BK-7 prism and investigated the performance parameters on the probe in different combinations of the mentioned materials. Herein, three (Ag, SiN, and BP) different configurations are introduced and compared for the detection of SARS-CoV-2. Furthermore, with the help of the transfer matrix method (TMM), all the three configurations have been analyzed. Notably, the combination of Ag, SiN, and BP shows better sensitivity (154°/RIU) when compared with other configurations for the detection of SARS-CoV-2. This work may facilitate a new sensing device to detect SARS-CoV-2, based on the hybrid materials.

Coronavirus disease (COVID-19) is a worldwide health emergency caused by the coronavirus 2 (severe acute respiratory illness) (SARS-CoV-2). COVID-19 has a wide range of symptoms, making a definitive diagnosis difficult. The shortage of equipment for testing technology COVID-19 has resulted in long queues for COVID-19 testing, which is a major problem. COVID-19 testing is currently performed using sluggish and costly technology like single-photon emission computed tomography (SPECT), computed tomography (CT), positron emission tomography (PET), and enzyme-linked immunosorbent assay (ELISA). The gold standard test for diagnosing COVID-19 is real-time reverse transcriptase-polymerase chain reaction (RT-PCR), which necessitates highly skilled workers and has a lengthy turnaround time. However, rapid and affordable immunodiagnostic techniques (antigen or antibody tests) are also available with some trade off accuracy. Optical sensors are frequently employed in a variety of applications, because of their increased sensitivity, strong selectivity, rapid reaction times, and outstanding resolution. The use of photonic crystal fibre (PCF) is advantageous for the quick detection of the new coronavirus and is suggested with the use of a PCF-based (Au/BaTiO3/graphene) multilayered surface plasmon resonance (SPR) biosensor. The proposed sensor can quickly detect the COVID-19 virus in two different ligand-analyte environments: (i) the virus spike receptor-binding domain (RBD) as an analyte and monoclonal antibodies (mAbs) as a probe ligand, and (ii) monoclonal antibodies (IgG or IgM) as an analyte and the virus spike RBD as a probe ligand. The finite element method (FEM) is used to quantitatively examine the performance of the PCF-based multilayered SPR sensor.

Graphene monolayer of sub-nanometer thickness shows strong metallic and plasmonic behavior in terahertz (THz) frequency range. This plasmonic effect varies considerably when graphene layer is placed under a magnetic field of appropriate strength. The strong adsorption characteristic of graphene layer is another advantage. In this work, a photonic spin Hall effect (PSHE)-based plasmonic sensor consisting of germanium prism, organic dielectric layer, and graphene monolayer is simulated and analyzed in THz aiming at highly sensitive and reliable sensing under variable magnetic field. Modified Otto configuration and magneto-optic effect in graphene are considered. The sensor's performance is examined in terms of sensitivity, limit of detection (LOD), and figure of merit (FOM). The analysis indicates that LOD of the order of 10 RIU for gas sensing is achievable, which is finer than recently reported gas sensors based on different techniques. Further, the FOM improves when a larger magnitude of magnetic field is applied. The FOM is even greater for rarer gaseous media, which can make the sensor extremely useful in early detection of airborne viruses such as SARS-Cov-2 (while using appropriate specificity method) and to measure the concentration of a particular gas in a given gaseous mixture. The results further indicate that the same sensor design can be used for magnetic field detection while the FOM of magnetic field detection is significantly greater for rarer gaseous medium (e.g., air), which may enable the probe to be used in early detection of radiation leakage in nuclear reactors. For larger magnitudes of magnetic field, the corresponding LOD becomes finer.

Coronavirus is an ongoing global pandemic caused by severe acute respiratory syndrome coronavirus 2. Coronavirus disease 2019 known as COVID-19 is the worst pandemic since World War II. The outbreak of COVID-19 had a significant repercussion on the health, economy, politics, and environment, making coronavirus-related issues more complicated and becoming one of the most challenging pandemics of the last century with deadly outcomes and a high rate of the reproduction number. There are thousands of different types - or variants - of COVID circulating across the world. Viruses mutate all the time; it emphasizes the critical need for the designing of efficient vaccines to prevent virus infection, early and fast diagnosis, and effective antiviral and protective therapeutics. In this regard, the use of nanotechnology offers new opportunities for the development of novel strategies in terms of prevention, diagnosis, and treatment of COVID-19. This review presents an outline of the platforms developed using plasmonic nanoparticles in the detection, treatment, and prevention of SARS-CoV-2. We select the best strategies in each of these approaches. The properties of metallic plasmon NPs and their relevance in the development of novel point-of-care diagnosis approaches for COVID-19 are highlighted. Also, we discuss the current challenges and the future perspectives looking towards the clinical translation and the commercial aspects of nanotechnology and plasmonic NP-based diagnostic tools and therapy to fight COVID-19 pandemic. The article could be of significance for researchers dedicated to developing suitable plasmonic detection tools and therapy approaches for COVID-19 viruses and future pandemics.

Light enhancement occurs strongly within the plasmonic clusters by interaction with surface plasmons. Surface-enhanced Raman spectroscopic (SERS) characteristics of a series of silver@silica trimer core-shell (CS) nanosphere (NS) clusters are investigated in this paper. It is significant to understand the electric field (EF) enhancement mechanism behind the SERS technique. The effect of symmetry breaking is studied for the series starting from the highly symmetric trimer cluster and transformed to linear dimer geometry which progresses through the gradual reduction in the vertex NS. The optical activity such as the evolution of LSPR peak is discussed, the formation of hot spots is demonstrated and the strength of the local EF enhancement is calculated and correlated with the plasmon dipolar modes by using plasmon hybridization theory to understand the underlying physical concepts.

The current COVID-19 pandemic has resulted in an urgent need for methods to decontaminate respirators masks for reuse while keeping them intact and functional. The severe shortage of professional masks such as N95 and FFP2 has necessitated their reuse over long periods. A very promising method is the pasteurization of these masks by thermoplasmonic heat generated by plasmonics nanoparticles when they are irradiated by light. Under illumination at its plasmonic resonance, a metal nanoparticle features enhanced light absorption, turning it into an ideal nano-source of heat, remotely controllable using light. In this work, we propose a numerical study based on the finite element method (FEM) of the thermoplasmonic properties of silver nanoparticles (AgNPs) decorating polypropylene (PP) fibers which is a basic material for the manufacture of these masks. The surface plasmon resonance (SPR) of these nanostructures was investigated through the computation of the complex effective dielectric permittivity and the absorption cross section in the near UV-visible (NUV-Vis) range. First, the SPR characteristics of AgNPs for different morphologies are determined from the absorption spectra, including the SPR-peak position λ and the electric field enhancement. Second, we determine the power absorbed by an individual AgNP of different morphologies. From this, we calculate the internal temperature increase of the particle at the plasmonic resonance. The last step is devoted to the determination of the temperature profile in the surrounding medium in order to better understand and design the plasmon-assisted heating processes at the nanometric scale.