Surface Plasmon Resonance Device Research Articles

ВПЛИВ ОПТИЧНОГО СКЛА ЯК ПІДКЛАДКИ В ППР-СЕНСОРАХ НА ТЕМПЕРАТУРНУ СТАБІЛЬНІСТЬ РЕЗУЛЬТАТІВ ВИМІРЮВАННЯ

The influence of the properties of the substrate made from optical glass of surface plasmon resonance (SPR) sensors on the temperature stability of measurements at a temperature change from 20 to 30°C, in which research is most often carried out, was studied. The phenomenon of surface plasmon resonance is very sensitive to any changes at the metal-dielectric interface, so studying the influence of the temperature factor is an actual task. Research in the infrared region of the spectrum is important because in this case the possible thickness of the research object increases, and it is also possible to reduce the thickness of the gold layer that is sprayed to the glass substrate of the sensory element from 50 nm to 30 nm. But heating the sensitive element with an IR laser can introduce an additional error into the measurement results. The sensitive element of the SPR device consists of a plate made of optical glass and a thin layer of gold deposited on it. It is known that materials expand when heated. The difference in temperature coefficients of linear expansion of glass and gold applied to it can lead to unequal expansion of glass (74x10 -7 ) and gold (14.2x10 -6 ), respectively, causing elastic stresses in the gold sensitive layer of the sensor. Sensory elements with a 30 nm gold layer are used for the IR range of measurements, and 50 nm for the visible range. Therefore, we investigated the stability of the results of measuring the angle of surface plasmon resonance minimum at a wavelength of 650 nm (Plasmon-6 device). It was determined that the optical glass of the substrate affects the stability of measurements of the SPR index of air from temperature fluctuations. The period of stabilization of measurement results in the visible range when the temperature changes from 20 to 30 °C to the change in the angle of the SPR minimum changes from 0.0006 degrees/min for Zerodur to 0.0032 degrees/min for flints, i.e. almost 5 times with the thickness of the gold nanolayer 50 nm, and for a thickness of 30 nm it varies from 0.0010 deg/min for crowns and quartz to 0.0013 deg/min for flints. The lowest value corresponds to Zerodur substrates with practically zero temperature coefficient of linear expansion and quartz in this temperature range. To ensure the stability of the results of measurements of SPR characteristics against temperature fluctuations in the range of 20-30°С, it is recommended to use Zerodur, quartz and crowns for the substrates of SPR sensors

A Point-of-Care Testing Device Utilizing Graphene-Enhanced Fiber Optic SPR Sensor for Real-Time Detection of Infectious Pathogens.

Timely detection of highly infectious pathogens is essential for preventing and controlling public health risks. However, most traditional testing instruments require multiple tedious steps and ultimately testing in hospitals and third-party laboratories. The sample transfer process significantly prolongs the time to obtain test results. To tackle this aspect, a portable fiber optic surface plasmon resonance (FO-SPR) device was developed for the real-time detection of infectious pathogens. The portable device innovatively integrated a compact FO-SPR sensing component, a signal acquisition and processing system, and an embedded power supply unit. A gold-plated fiber is used as the FO-SPR sensing probe. Compared with traditional SPR sensing systems, the device is smaller size, lighter weight, and higher convenience. To enhance the detection capacity of pathogens, a monolayer graphene was coated on the sensing region of the FO-SPR sensing probe. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was used to evaluate the performance of the portable device. The device can accurately detect the SARS-CoV-2 spike S1 protein in phosphate-buffered saline (PBS) and artificial saliva within just 20 min, and the device successfully detected cultured SARS-CoV-2 virus. Furthermore, the FO-SPR probe has long-term stability, remaining stable for up to 8 days. It could distinguish between the SARS-CoV-2 spike protein and the MERS-CoV spike protein. Hence, this FO-SPR device provides reliable, rapid, and portable access to test results. It provides a promising point-of-care testing (POCT) tool for on-site screening of infectious pathogens.

Utilisation of molecularly imprinting technology for the detection of glucocorticoids for a point of care surface plasmon resonance (SPR) device

Herein, we describe the synthesis and characterisation of four synthetic recognition materials (nanoMIPs) selective for the glucocorticoid steroids – prednisolone, prednisone, dexamethasone, and cortisone. Using a solid-phase synthesis approach, these materials were then applied in the development of a surface plasmon resonance (SPR) sensor for the detection of these four targets in doped urine, to mimic the routine testing of agricultural waste for possible environmental exposure. The synthesised particles displayed a range of sizes between 104 and 160 nm. Affinity studies were performed, and these synthetic materials were shown to display nanomolar affinities (15.9–62.8 nM) towards their desired targets. Furthermore, we conducted cross-reactivity studies to assess the materials selectivity towards their desired target and the materials showed excellent selectivity when compared to the non-desired target, with selectivity factors calculated. Furthermore, through the use of 3D visualisation it can be seen that small changes between structures (such as a hydroxyl to ketone transformation) there is excellent selectivity between the compounds in the ranges of 100 fold plus. Using Surine™ doped samples the materials offered comparable nanomolar affinities (10.7–75.7 nM) towards their targets when compared to the standardised buffer preparation. Detection levels in urine for all compounds was in the nanomolar range. The developed sensor offers potential for these devices to be used in the prevention of these pharmaceutical compounds to enter the surrounding environment through agricultural waste through monitoring at source. Likewise, they can be used to monitor use in clinical samples.

Separation of shifts in surface plasmon resonance into refractive index and thickness of deposited layers

Routine Surface Plasmon Resonance (SPR) measurements, which are widely applied in affinity (bio)sensors and surface science, do not allow one to separate the obtained SPR signals into the change of the refractive index and thickness of deposited layers. For thin layers the signal is proportional to the product of the layer thickness and the difference in the refractive indices of this layer and of the aqueous media. In this study, we suggest an approach to separate these parameters. It is performed by subsequent measurements in the presence and in the absence of polyethylene glycol (PEG), an inert additive which modifies the refractive index of the liquid phase but do not penetrate into the adsorbed layer. Both parameters were successively determined for human serum albumin (HSA) as well as for anti-HSA IgG in three different settings: i) HSA adsorbed directly onto a gold surface, ii) HSA chemically immobilized on a gold surface coated with a self-assembled monolayer of 1,16 mercaptohexadecanoic acid and iii) chemically immobilized HSA with additional monomolecular layer of anti-HSA IgG antibodies bond to this protein layer. The suggested approach can be applied in most SPR devices with a flow cell for analysis of various adsorbed layers.

Development of a biosensor based on a surface plasmon resonance structure comprising strontium titanate, graphene and affinity layers for malaria diagnosis

This paper investigates the numerical analysis of a highly performed surface plasmon resonance (SPRE)-based sensor employing a hybrid structure of SrTiO3 (STO) and graphene for rapid detection of malaria. The investigation is performed using the angular interrogation technique and transfer matrix method. The SPRE device has a glass prism, silver (Ag), STO, graphene, affinity layer and sensing medium (SGM). Four coupling prisms are examined and we found the prism N-FK51A corresponds to the highest sensitivity. The sensitivity of the structure N-FK51A/Ag/STO/graphene/affinity layer/SGM is found to be 205.405, 222.222 and [Formula: see text]/RIU for Schizont, Trophozoite and Ring malaria stages. The layer thicknesses are then optimized and it is found that the proposed SPRE sensor can achieve a sensitivity of 278.378, 227.027 and [Formula: see text]/RIU for Schizont, Trophozoite and Ring malaria stages with 30 nm (silver), 1[Formula: see text]nm (STO), mono-sheet of graphene and 5[Formula: see text]nm of the affinity layer. These findings demonstrate that the proposed method and structure can be used efficiently for biomedical applications.

A surface plasmon resonance nanostructure containing graphene and BaTiO3 layers for sensitive defection of organic compounds.

Organic compound-based sensors are used in a variety of significant fields, including medical research, azeotropic calibration, vegetable oil extraction, the shoe industry and geothermal power plants. Here, a high-performance, two-dimensional material-based organic compound sensor has been proposed using a surface plasmon resonance (SPR) nanostructure consisting of a BK7 glass prism, Ag, BaTiO3, Ag, graphene and sensing layer. The reflectivity curves of the SPR device have been investigated when the sensing media are Pentane, n-Hexane, n-Heptane and n-Octane. The thickness of the BaTiO3 layer and the number of graphene sheets have been optimized to maximize the sensitivity. The highest sensitivity attained is 220.83 deg/RIU for n-Octane with 45 nm silver/10 nm BaTiO3/8 nm silver and four layers of graphene. We believe that the SPR-based sensors are simple and can replace the spectrometry, chromatography and electrochemical based sensors. The proposed design is extremely effective for diverse applications in biological, industrial and chemical detection because of its simple structure and great performance.

Effects of graphene layer addition on sensitivity of surface plasmon resonance sensor for immunoglobulin M detection

A novel technique is proposed for detecting immunoglobulin M (IgM) using differential Mueller matrix polarimetry and a surface plasmon resonance (SPR) sensor enhanced through the addition of multiple (1–10) thin layers of graphene on the sensing surface. Simulations are first performed to optimize the structure of the SPR device. The feasibility of the proposed sensor is then demonstrated by measuring the principal fast axis angle (α) of linear birefringence (LB) of human IgM serum aqueous solution samples with known concentrations in the range of 0–250 ng/ml. The results shows that α increases linearly over the considered concentration range. However, α reduces with an increasing number of graphene layers. The finest resolution of 7.8 ng/ml is obtained from the sensor incorporating three graphene layers.

SPECTRA: A Novel Compact System for Surface Plasmon Resonance Measurements.

Surface plasmon resonance (SPR) is a common and useful measurement technique to perform fast and sensitive optical detection. SPR instrumentations usually comprise optical systems of mirrors and lenses which are quite expensive and impractical for point-of-care applications. In this work, we presented a novel and compact SPR device called SPECTRA, designed as a spectrophotometer add-on with a grating coupling configuration. The device is conceived as a marketable solution to perform quick SPR measurements in grating configuration without the requirement of complex instrumentation. The device can be customized either in a vertical structure to reach lower incident light angles, or in a horizontal configuration, which is suitable for SPR analysis using liquid solutions. The SPECTRA performance was evaluated through SPR measurements in typical applications. The vertical SPECTRA system was employed to detect different functionalization molecules on gold 720 nm-period grating devices. Meanwhile, the horizontal SPECTRA configuration was exploited to carry out fluid-dynamic measurements using a microfluidic cell with glycerol solutions at increasing concentrations to account for different refractive indexes. The experimental tests confirmed that the SPECTRA design is suitable for SPR measurements, demonstrating its capability to detect the presence of analytes and changes in surface properties both in static and dynamic set-ups.

Portable Surface Plasmon Resonance Detector for COVID-19 Infection.

Methods based on nucleic acid detection are currently the most commonly used technique in COVID-19 diagnostics. Although generally considered adequate, these methods are characterised by quite a long time-to-result and the necessity to prepare the material taken from the examined person-RNA isolation. For this reason, new detection methods are being sought, especially those characterised by the high speed of the analysis process from the moment of sampling to the result. Currently, serological methods of detecting antibodies against the virus in the patient's blood plasma have attracted much attention. Although they are less precise in determining the current infection, such methods shorten the analysis time to several minutes, making it possible to consider them a promising method for screening tests in people with suspected infection. The described study investigated the feasibility of a surface plasmon resonance (SPR)-based detection system for on-site COVID-19 diagnostics. A simple-to-use portable device was proposed for the fast detection of anti-SARS-CoV-2 antibodies in human plasma. SARS-CoV-2-positive and -negative patient blood plasma samples were investigated and compared with the ELISA test. The receptor-binding domain (RBD) of spike protein from SARS-CoV-2 was selected as a binding molecule for the study. Then, the process of antibody detection using this peptide was examined under laboratory conditions on a commercially available SPR device. The portable device was prepared and tested on plasma samples from humans. The results were compared with those obtained in the same patients using the reference diagnostic method. The detection system is effective in the detection of anti-SARS-CoV-2 with the detection limit of 40 ng/mL. It was shown that it is a portable device that can correctly examine human plasma samples within a 10 min timeframe.

Application of the surface plasmon resonance phenomenon to controlling suspensions

Represented in this paper are the results of investigations aimed at checking up the capabilities of devices based on the surface plasmon resonance (SPR) phenomenon to be applied for studying the properties of water suspensions. As an example, the authors used here the suspensions of tooth pastes Sensodyne and Colgate in distilled water. For measurements, we used the SPR device Plasmon-71 operating in the near infrared spectral range. Results of these measurements were compared to those obtained using the spectrophotometric ones. The measured values of the sedimentation velocity obtained using both the applied methods confirmed availability to efficiently apply SPR devices for studying the opaque multi-component suspensions.

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

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

Methane-Induced SPR Shifts of Cryptophane A-Doped Polymer Layers

The macromolecular cage cryptophane A can host methane molecules in its cavity and is thus suited as methane-sensing molecules for sensors based on refractive index (RI) sensitive analytical methods such as surface plasmon resonance (SPR). In this work, we assessed the methane response of different cryptophane A-doped polymer membranes by using a custom-made, angular-based SPR device with an RI resolution of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.4\cdot 10\,\,^{\mathrm{ -5}}$ </tex-math></inline-formula> . We show that cryptophane A needs to be dissolved in doped polymer coatings for successful methane detection. For membranes made of poly(methylmethacrylate) (PMMA), polycarbonate (PC), polystyrene (PS), and polymethylpentene (PMP), cryptophane A could be dissolved, and the solution could not be achieved with polydimethylsiloxane (PDMS) polymers, irrespective of the solvent used. Signal responses and response times toward a methane atmosphere were quantified for different layer thicknesses and cryptophane A contents. The best results were observed for thin but highly doped polymer layers, which could be achieved best for PS layers.

ПЕРСПЕКТИВИ ТА ТЕНДЕНЦІЇ РОЗВИТКУ ПРИЛАДІВ ТА МЕТОДІВ НА ОСНОВІ ЯВИЩА ПОВЕРХНЕВОГО ПЛАЗМОННОГО РЕЗОНАНСУ В ІНФРАЧЕРВОНОМУ ДІАПАЗОНІ (ОГЛЯД)

On the phenomenon of surface plasmon resonance (SPR) and its use for the study of gaseous and liquid substances, more and more papers are published in professional journals. These studies are used in clinical diagnostics, food industry, environmental monitoring. The advantages of SPR sensors include quick results, a small amount of analyte, the possibility of real-time measurement of such reactions as antigen-antibody, protein-protein, enzyme-substrate or inhibitor, protein-DNA, receptor-drug, protein-polysaccharide , virus protein and reactions of external stimulation of a living cell. The high sensitivity of the method is due to the properties of its resonant nature of plasmon-polariton oscillation. SPR devices are used in laboratory conditions and there is a potential possibility of further reduction of overall dimensions for use in field conditions. The use of SPR in the IR region of the spectrum has a number of advantages, namely: the laser light penetrates deeper into the sample, it becomes possible to study substances that are not transparent in the visible region, but transparent in the infrared, which allows working with larger research objects, provides a narrower characteristic of the SPR, which allows to more accurately determine the angle of the minimum of the SPR, and also requires the application of a thinner layer of gold on the glass chip, which reduces the cost of the analysis. The review analyzed literary sources and determined prospects for the development of devices and methods based on IR SPR, considered prospective materials of the sensitive element and prisms of the total internal reflection device according to the Kretchman scheme. It was determined that, in addition to precious metals (gold and silver), conductive metal oxides ITO, ZnO, CdO:Dy have the prospect of being used as materials for manufacturing the sensitive element of the sensor. Their compliance with the requirements for materials for maintaining the SPR was analyzed. It is shown that CdO:Dy has the greatest potential due to sufficient mobility and density of charge carriers. But in practice, the most common use is gold and silver, for which it is necessary to determine the optimal thicknesses for the IR range of SPR. Total internal reflection prisms (hereafter prisms) in SPR devices according to the Kretchman scheme are usually made of glass, but for the IR range it is advisable to consider other materials that are less sensitive to the temperature effect of the IR laser. The paper analyzes the dependence of the plasmon resonance parameters on the prism material. The possibility of using not only different brands of traditional glass, but also glass ceramics with practically zero coefficient of thermal expansion, semiconductor silicon and chalcogenide glass for the manufacture of prisms is shown.

Advanced Lab-on-Fiber Optrodes Assisted by Oriented Antibody Immobilization Strategy.

Lab-on-fiber (LoF) optrodes offer several advantages over conventional techniques for point-of-care platforms aimed at real-time and label-free detection of clinically relevant biomarkers. Moreover, the easy integration of LoF platforms in medical needles, catheters, and nano endoscopes offer unique potentials for in vivo biopsies and tumor microenvironment assessment. The main barrier to translating the vision close to reality is the need to further lower the final limit of detection of developed optrodes. For immune-biosensing purposes, the assay sensitivity significantly relies on the capability to correctly immobilize the capture antibody in terms of uniform coverage and correct orientation of the bioreceptor, especially when very low detection limits are requested as in the case of cancer diagnostics. Here, we investigated the possibility to improve the immobilization strategies through the use of hinge carbohydrates by involving homemade antibodies that demonstrated a significantly improved recognition of the antigen with ultra-low detection limits. In order to create an effective pipeline for the improvement of biofunctionalization protocols to be used in connection with LoF platforms, we first optimized the protocol using a microfluidic surface plasmon resonance (mSPR) device and then transferred the optimized strategy onto LoF platforms selected for the final validation. Here, we selected two different LoF platforms: a biolayer interferometry (BLI)-based device (commercially available) and a homemade advanced LoF biosensor based on optical fiber meta-tips (OFMTs). As a clinically relevant scenario, here we focused our attention on a promising serological biomarker, Cripto-1, for its ability to promote tumorigenesis in breast and liver cancer. Currently, Cripto-1 detection relies on laborious and time-consuming immunoassays. The reported results demonstrated that the proposed approach based on oriented antibody immobilization was able to significantly improve Cripto-1 detection with a 10-fold enhancement versus the random approach. More interestingly, by using the oriented antibody immobilization strategy, the OFMTs-based platform was able to reveal Cripto-1 at a concentration of 0.05 nM, exhibiting detection capabilities much higher (by a factor of 250) than those provided by the commercial LoF platform based on BLI and similar to the ones shown by the commercial and well-established bench-top mSPR Biacore 8K system. Therefore, our work opened new avenues into the development of high-sensitivity LoF biosensors for the detection of clinically relevant biomarkers in the sub-ng/mL range.

Synthesis of Molecularly Imprinted Polymer Nanoparticles for SARS-CoV-2 Virus Detection Using Surface Plasmon Resonance

COVID-19 caused by a SARS-CoV-2 infection was first reported from Wuhan, China, and later recognized as a pandemic on March 11, 2020, by the World Health Organization (WHO). Gold standard nucleic acid and molecular-based testing have largely satisfied the requirements of early diagnosis and management of this infectious disease; however, these techniques are expensive and not readily available for point-of-care (POC) applications. The COVID-19 pandemic of the 21st century has emphasized that medicine is in dire need of advanced, rapid, and cheap diagnostic tools. Herein, we report on molecularly imprinted polymer nanoparticles (MIP-NPs/nanoMIPs) as plastic antibodies for the specific detection of SARS-CoV-2 by employing a surface plasmon resonance (SPR) sensor. High-affinity MIP-NPs directed against SARS-CoV-2 were manufactured using a solid-phase imprinting method. The MIP-NPs were then characterized using dynamic light scattering (DLS) and atomic force microscopy (AFM) prior to their incorporation into a label-free portable SPR device. Detection of SARS-CoV-2 was studied within a range of 104–106 PFU mL−1. The MIP-NPs demonstrated good binding affinity (KD = 0.12 pM) and selectivity toward SARS-CoV-2. The AFM, cyclic voltammetry, and square-wave voltammetry studies revealed the successful stepwise preparation of the sensor. A cross-reactivity test confirmed the specificity of the sensor. For the first time, this study demonstrates the potential of molecular imprinting technology in conjunction with miniaturized SPR devices for the detection of SARS-CoV-2 particles with high-affinity and specificity. Such sensors could help monitor and manage the risks related to virus contamination and infections also beyond the current pandemic.

A Review of Apta-POF-Sensors: The Successful Coupling between Aptamers and Plastic Optical Fibers for Biosensing Applications

Aptamers represent the next frontier as biorecognition elements in biosensors thanks to a smaller size and lower molecular weight with respect to antibodies, more structural flexibility with the possibility to be regenerated, reduced batch-to-batch variation, and a potentially lower cost. Their high specificity and small size are particularly interesting for their application in optical biosensors since the perturbation of the evanescent field are low. Apart from the conventional plasmonic optical sensors, platforms based on silica and plastic optical fibers represent an interesting class of devices for point-of-care testing (POCT) in different applications. The first example of the coupling between aptamers and silica optical fibers was reported by Pollet in 2009 for the detection of IgE molecules. Six years later, the first example was published using a plastic optical fiber (POF) for the detection of Vascular Endothelial Growth Factor (VEGF). The excellent flexibility, great numerical aperture, and the large diameter make POFs extremely promising to be coupled to aptamers for the development of a sensitive platform easily integrable in portable, small-size, and simple devices. Starting from silica fiber-based surface plasmon resonance devices, here, a focus on significant biological applications based on aptamers, combined with plasmonic-POF probes, is reported.

Facile layered structure of sensing chip of a prism–based surface plasmon resonance device

Surface plasmon resonance (SPR) is a popular optical phenomenon for sensing application owing to its capability for label-free measurement which offers very high resolution and sensitivity. The traditional prism based Kretschmann configuration employs a sensing chip consists of a glass substrate deposited with 50 nm thick gold/silver layer. The parameters of the figure-of-merit (FOM) of an SPR sensor are a quality factor, signal-to-noise ratio, and the strength of the plasmonic field over the gold surface. In this article, we present a simulation work on a facile SPR sensor chip that yields a high FOM as compared to the traditional SPR sensor chip. We introduced a metallic intermediate layer (IML) in the traditional SPR chip and optimized the performance with respect to the material and thickness of IML. We optimized the thickness of the glass substrate such that the plasmonic field generated in the IML can couple with the outer gold film (OGF). Such coupling enhances the overall plasmonic field over the OGF by 112%.

Development of SarS-Cov-2 antigen Detection Kit Based on Immunoglobulin Y (Igy) Using Surface Plasmon resonance (SPr)

SARS disease reappeared at the end of 2019 with a new name as Coronavirus Disease 2019 (COVID-19) caused by a new virus called SARS-CoV-2. This virus has spread throughout the world until recently and caused massive deaths and losses. The nucleic acid test in the form of real-time reverse transcriptase-polymerase chain reaction (RT-PCR) is very important to diagnose COVID-19 in patients, but this method has several drawbacks such as operators who have to be trained, the diagnosis results appear in a relatively long time, and the examination price relatively expensive. This research was conducted to produce immunoglobulin Y (IgY) extracted from chicken egg yolk targeting the S-protein receptor-binding domain (RBD) on SARS-CoV-2 as a component of the surface plasmon resonance (SPR) SARS-CoV-2 antigen detection kit. This research was started by extracting IgY from hyperimmune chicken egg yolks with the polyethylene glycol (PEG) precipitation method and continued with dialysis. The extracted IgY was further purified using thiophilic adsorption chromatography and concentrated by using Amicon® Ultra-15 ultrafiltration. The IgY activity against SARS-CoV-2 RBD was tested qualitatively using the agar gel precipitation test (AGPT) technique and the total protein content was determined using the Lowry method. IgY was tested for its affinity against SARS-CoV-2 RBD using SPR. The IgY concentration obtained was 11 mg/mL. The AGPT result showed the presence of IgY activity against SARS-CoV-2 RBD isolated from egg yolk and chicken serum after 8 weeks after the first vaccination of chickens. The SDS-PAGE results showed a very clear band of IgY characters. The obtained IgY showed adequate interaction with commercial SARS-CoV-2 RBD on an SPR device. The purified IgY was able to bind with protein-S RBD and showed a fairly good affinity for the SARS-CoV-2 antigen sample. The results of these observations indicate that IgY anti-S-protein SARS-CoV-2 can be produced and purified from chicken egg yolk and can be used as a diagnostic component to detect SARS-CoV-2 antigen, especially on SPR.

Silver nanoplates paved PMMA cuvettes as a cheap and re-usable plasmonic sensing device

Surface plasmon resonance (SPR) sensors find wide applications due to their prompt responses and because they do not need sophisticated instrumentation. One of the most explored effects is the high sensitivity of the plasmon band position due to refractive index changes in the medium. In the following, we present a cost-effective, reusable, and high-responsive SPR device based on silver nanoplate paved PMMA cuvettes. The nanostructures were obtained by the seed-growing approach. The localized surface plasmon resonance (LSPR) features, observed in the colloidal state, were successfully transferred to the paved cuvettes and their plasmon sensitivities with liquids of different refractive index were recorded. We observed refractive index sensitivities up to 280 nm/refractive index units, using nanoplates with plasmon resonances in the near-infrared region. The experimental results find correspondence and agreement with extinction cross-section calculated with a Boundary Element Method (BEM) approach. This work addresses how to build a simple, cost-effective optical device, which is suitable for integration and miniaturization.

Si grating structure for surface plasmon resonance excitation by back-side normal incidence illumination

We propose a structure suitable for surface plasmon resonance (SPR) excitation with light incident on the back-side of the device, which has affinity with the semiconductor process. We constructed a diffraction grating on the top layer of a silicon-on-insulator wafer and completely embedded the grating in a polymer. According to a reflectance measurement, SPR could be efficiently excited, and its behavior presented consistency with the calculations. Since this structure is semiconductor fabrication based and allows elimination of both the prism and the light receiver commonly used in SPR experiments, it will contribute to realization of a thin one-chip SPR device.