Evaluation of kinetics and thermodynamics of interaction between immobilized SARS-CoV-2 nucleoprotein and specific antibodies by total internal reflection ellipsometry

Comparison of the ACE2 receptor and monoclonal antibodies immobilisation strategies for the sensitive detection of SARS-CoV-2 variants of concern

Investigation of antibody or receptor immobilisation and binding to the target analyte is essential for the development of effective immunoassays. In our research, we applied the combination of two surface-sensitive methods: spectroscopic ellipsometry and quartz crystal microbalance with dissipation. It enabled quantitative investigation of optical and mechanical properties of formed biomolecule layers consisting of monoclonal antibodies (mAb) or angiotensin-converting enzyme 2 (ACE2) receptors coupled with the Fc fragment, in complex with severe acute respiratory syndrome coronavirus 2 spike Omicron variant (SCoV2-oS). Random and site-directed immobilisation of ACE2 receptor gave 1.8 and 2.4 times higher dry surface mass density compared to random and site-direct mAbs immobilisation, respectively. Therefore, ACE2 had better potential for more sensitive detection of the target analyte SCoV2-oS. However, the binding of SCoV2-oS to site-directed ACE2 resulted in a low 80 ng/cm2 surface mass compared to other samples. Moreover, ΔD/ΔF data revealed two-step binding of SCoV2-oS to ACE2 and mAbs. Furthermore, calculated affinity constants (KD) showed that both ACE2 and mAb have high affinity to SCoV2-oS (in the range of 10-10 to 10-11 M), and their orientation on the surface had only a minor impact on KD values. Our findings in this investigation indicated that ACE2 coupled with the Fc fragment is as effective in the recognition of SARS-CoV-2 as mAbs and it can be successfully applied for the development of immunoassays. Considering SARS-CoV-2 mutates for a better S protein binding to the ACE2 receptor, using ACE2 as a biorecognition element is useful.

The second life for unused COVID-19 vaccines: Towards biosensing application

Many vaccines have been produced during the COVID-19 pandemic. Currently, an increasing number of vaccines have reached an expiration date without being used. Therefore, expired vaccines (EXVAX) based on virus-like particles (VLP) recombinant SARS-CoV2-S protein can be repurposed for biosensing application and provide a use, even though they are past their expiration date for vaccination. In the current study, we applied EXVAX based on VLP for gold sensor chip modification to use such surface for specific antibody detection from diluted human serum. For this purpose, we used total internal reflection ellipsometry for real-time kinetics measurement and mathematical modelling for the calculation of affinity constants. Moreover, we cross-validated the results obtained with a widely applied ELISA method. EXVAX was tested and compared with commercially available recombinant S proteins analogues that are commonly used for immunosensing. The results suggest that the EXVAX functionalisation is thermodynamically favoured. The interaction analysis of polyclonal antibodies from human serums shows that the EXVAX SARS-CoV2-S proteins retain their biological activity more than one year after the expiration date as the calculated values of the affinity constant fall in a nM range of (10-11 > KD > 10-9), suggesting a high affinity interaction and thus could be used for biosensing and meet sustainable development goal.

Detection of the SARS-CoV-2 nucleoprotein by electrochemical biosensor based on molecularly imprinted polypyrrole formed on self-assembled monolayer

Herein, we report the development and characterisation of an electrochemical biosensor with a polypyrrole (Ppy)-based molecularly imprinted polymer (MIP) for the serological detection of the recombinant nucleocapsid protein of SARS-CoV-2 (rN). The electrochemical biosensor utilises a Ppy-based MIP formed on a self-assembled monolayer (SAM) at the gold interface to enhance Ppy layer stability on the screen-printed electrode (SPE). Electrochemical impedance spectroscopy (EIS) and square wave voltammetry (SWV) were employed for the electrochemical characterisation of screen-printed gold electrodes (SPGEs) modified with MIP or non-imprinted polymer (NIP) layers. Removing the rN protein template from the MIP layer increased electron transfer and decreased impedance, indicating the specificity of molecular imprinting. The electrochemical biosensor with a Ppy-based MIP exhibited higher sensitivity than the NIP counterpart, demonstrating its potential for selective rN protein detection. The limit of detection 0.4 nM and 0.2 nM and the limit of quantification 1.3 nM and 0.66 nM values obtained through SWV and EIS, respectively, highlight the biosensor's ability to detect low target protein concentrations. The specificity test confirmed minimal nonspecific binding, reinforcing the reliability of the novel electrochemical sensor with a Ppy-based MIP.

Kinetics of Macroion Adsorption on Silica: Complementary Theoretical and Experimental Investigations for Poly-l-arginine

A comprehensive approach enabling a quantitative interpretation of poly-l-arginine (PARG) adsorption kinetics at solid/electrolyte interfaces was developed. The first step involved all-atom molecular dynamics (MD) modeling of physicochemical characteristics yielding PARG molecule conformations, its contour length, and the cross-section area. It was also shown that PARG molecules, even in concentrated electrolyte solutions (100 mM NaCl), assume a largely elongated shape with an aspect ratio of 36. Using the parameters derived from MD, the PARG adsorption kinetics at the silica/electrolyte interface was calculated using the random sequential adsorption approach. These predictions were validated by optical reflectometry measurements. It was confirmed that the molecules irreversibly adsorbed in the side-on orientation and their coverage agreed with the elongated shape of the PARG molecule predicted from the MD modeling. These theoretical and experimental results were used for the interpretation of the quartz crystal microbalance measurements carried out under various pH conditions. A comprehensive analysis unveiled that the results stemming from the hydrodynamic theory postulating a lubrication-like (soft) contact of the macroion molecules with the sensor adequately reflect the adsorption kinetics. The range of validity of the intuitively used Sauerbrey model was also estimated. It was argued that acquired results can be exploited to control macroion adsorption at solid/liquid interfaces. This is essential for the optimum preparation of their supporting layers used for bioparticle immobilization and shell formation at nanocapsules in targeted drug delivery.

Photoluminescence-based biosensor for the detection of antibodies against SARS-CoV-2 virus proteins by ZnO tetrapod structure integrated within microfluidic system

This paper reports on development of an optical biosensor for the detection of antibodies against SARS-CoV-2 virus proteins in blood serum. ZnO nanotetrapods with high surface area and stable room temperature photoluminescence (PL) were selected as transducers. Structure and optical properties of the ZnO tetrapods have been studied by XRD, SEM and Raman spectroscopy. Crystallinity, dimensions and emission peaks of the ZnO tetrapods were determined. The ZnO tetrapods were fixed on glass chip. Silanization of ZnO tetrapods surface resulted in forming of functional surface groups suitable for the immobilization of bioselective layer. Two types of recombinant proteins (rS and rN) have been used to form bioselective layer on the surface of the ZnO tetrapods. Flow through microfluidic system, integrated with optical system, has been used for the determination of antibodies against SARS-CoV-2 virus proteins present in blood samples. The SARS-CoV-2 probes, prepared in PBS solution, have been injected into the measurement chamber with a constant pumping speed. Steady-state photoluminescence spectra and photoluminescence kinetics have been studied before and after injection of the probes. The biosensor signal has been tested to anti-SARS-CoV-2 antibodies in the range of 0.001 nM-1 nM. Control measurements have been performed with blood serum of healthy person. ZnO-SARS-CoV-2-rS and ZnO-SARS-CoV-2-rN biosensors showed high stability and sensitivity to anti-SARS-CoV-2 antibodies in the range of 0.025-0.5 nM (LOD 0.01 nM) and 0.3-1 nM (LOD 0.3 nM), respectively. Gibbs free energy of interaction between ZnO/SARS-CoV-2-rS and ZnO/SARS-CoV-2-rN bioselective layers with anti-SARS-CoV-2 antibodies showed -35.5 and -21.4 kJ/mol, respectively. Average detection time of biosensor integrated within microfluidic system was 15-20 min. The detection time and pumping speed (50 μL/min) were optimized to make detection faster. The developed system and ZnO-SARS-CoV-2-rS nanostructures have good potential for detection of anti-SARS-CoV-2 antibodies from patient's probes.

Surface Plasmon Resonance Immunosensor for Direct Detection of Antibodies against SARS-CoV-2 Nucleocapsid Protein

The strong immunogenicity of the SARS-CoV-2 nucleocapsid protein is widely recognized, and the detection of specific antibodies is critical for COVID-19 diagnostics in patients. This research proposed direct, label-free, and sensitive detection of antibodies against the SARS-CoV-2 nucleocapsid protein (anti-SCoV2-rN). Recombinant SARS-CoV-2 nucleocapsid protein (SCoV2-rN) was immobilized by carbodiimide chemistry on an SPR sensor chip coated with a self-assembled monolayer of 11-mercaptoundecanoic acid. When immobilized under optimal conditions, a SCoV2-rN surface mass concentration of 3.61 ± 0.52 ng/mm2 was achieved, maximizing the effectiveness of the immunosensor for the anti-SCoV2-rN determination. The calculated KD value of 6.49 × 10-8 ± 5.3 × 10-9 M confirmed the good affinity of the used monoclonal anti-SCoV2-rN antibodies. The linear range of the developed immunosensor was from 0.5 to 50 nM of anti-SCoV2-rN, where the limit of detection and the limit of quantification values were 0.057 and 0.19 nM, respectively. The immunosensor exhibited good reproducibility and specificity. In addition, the developed immunosensor is suitable for multiple anti-SCoV2-rN antibody detections.

Central Countries' and Brazil's Contributions to Nanotechnology

Abstract:

Nanotechnology is a cornerstone of the scientific advances witnessed over the past few years. Nanotechnology applications are extensively broad, and an overview of the main trends worldwide can give an insight into the most researched areas and gaps to be covered. This document presents an overview of the trend topics of the three leading countries studying in this area, as well as Brazil for comparison. The data mining was made from the Scopus database and analyzed using the VOSviewer and Voyant Tools software. More than 44.000 indexed articles published from 2010 to 2020 revealed that the countries responsible for the highest number of published articles are The United States, China, and India, while Brazil is in the fifteenth position. Thematic global networks revealed that the standing-out research topics are health science, energy, wastewater treatment, and electronics. In a temporal observation, the primary topics of research are: India (2020), which was devoted to facing SARS-COV 2; Brazil (2019), which is developing promising strategies to combat cancer; China (2018), whit research on nanomedicine and triboelectric nanogenerators; the United States (2017) and the Global tendencies (2018) are also related to the development of triboelectric nanogenerators. The collected data are available on GitHub. This study demonstrates the innovative use of data-mining technologies to gain a comprehensive understanding of nanotechnology's contributions and trends and highlights the diverse priorities of nations in this cutting-edge field.

Electrochemical biosensor for the evaluation of monoclonal antibodies targeting the N protein of SARS-CoV-2 virus

The emergence of COVID-19 caused by the coronavirus SARS-CoV-2 has prompted a global pandemic that requires continuous research and monitoring. This study presents a design of an electrochemical biosensing platform suitable for the evaluation of monoclonal antibodies targeting the SARS-CoV-2 nucleocapsid (N) protein. Screen-printed carbon electrodes (SPCE) modified with gold nanostructures (AuNS) were applied to design a versatile and sensitive sensing platform. Electrochemical techniques, including electrochemical impedance spectroscopy (EIS) and square wave voltammetry (SWV), were used to investigate the interactions between immobilised recombinant N (rN) protein and several monoclonal antibodies (mAbs). The electrochemical characterisation of SPCE/AuNS/rN demonstrated a successful immobilisation of rN, enhancing the electron transfer kinetics. Affinity interactions between immobilised rN and four mAbs (mAb-4B3, mAb-4G6, mAb-12B2, and mAb-1G5) were explored. Although mAb-4B3 showed some non-linearity, the other monoclonal antibodies exhibited specific and well-defined interactions followed by the formation of an immune complex. The biosensing platform demonstrated high sensitivity in the linear range (LR) from 0.2 nM to 1 nM with limits of detection (LOD) ranging from 0.012 nM to 0.016 nM for mAb-4G6, mAb-12B2, and mAb-1G5 and limits of quantification (LOQ) values ranging from 0.035 nM to 0.139 nM, as determined by both EIS and SWV methods. These results highlight the system's potential for precise and selective detection of monoclonal antibodies specific to the rN. This electrochemical biosensing platform provides a promising route for the sensitive and accurate detection of monoclonal antibodies specific to the rN protein.

Structural properties of immune complexes formed by viral antigens and specific antibodies shape the inflammatory response of macrophages

Data on the course of viral infections revealed severe inflammation as a consequence of antiviral immune response. Despite extensive research, there are insufficient data on the role of innate immune cells in promoting inflammation mediated by immune complexes (IC) of viral antigens and their specific antibodies. Recently, we demonstrated that antigens of human polyomaviruses (PyVs) induce an inflammatory response in macrophages. Here, we investigated macrophage activation by IC. We used primary murine macrophages as a cell model, virus-like particles (VLPs) of PyV capsid protein as antigens, and a collection of murine monoclonal antibodies (mAbs) of IgG1, IgG2a, IgG2b subclasses. The inflammatory response was investigated by analysing inflammatory chemokines and activation of NLRP3 inflammasome. We observed a diverse pattern of chemokine secretion in macrophages treated with different IC compared to VLPs alone. To link IC properties with cell activation status, we characterised the IC by advanced optical and acoustic techniques. Ellipsometry provided precise real-time kinetics of mAb-antigen interactions, while quartz crystal microbalance measurements showed changes in conformation and viscoelastic properties during IC formation. These results revealed differences in mAb-antigen interaction and mAb binding parameters of the investigated IC. We found that IC-mediated cell activation depends more on IC characteristics, including mAb affinity, than on mAb affinity for the activating Fc receptor. IC formed by the highest affinity mAb showed a significant enhancement of inflammasome activation. This may explain the hyperinflammation related to viral infection and vaccination. Our findings demonstrate that IC promote the viral antigen-induced inflammatory response depending on antibody properties.

Engineered two-dimensional nanomaterials based diagnostics integrated with internet of medical things (IoMT) for COVID-19

More than four years have passed since an inimitable coronavirus disease (COVID-19) pandemic hit the globe in 2019 after an uncontrolled transmission of the severe acute respiratory syndrome (SARS-CoV-2) infection. The occurrence of this highly contagious respiratory infectious disease led to chaos and mortality all over the world. The peak paradigm shift of the researchers was inclined towards the accurate and rapid detection of diseases. Since 2019, there has been a boost in the diagnostics of COVID-19 via numerous conventional diagnostic tools like RT-PCR, ELISA, etc., and advanced biosensing kits like LFIA, etc. For the same reason, the use of nanotechnology and two-dimensional nanomaterials (2DNMs) has aided in the fabrication of efficient diagnostic tools to combat COVID-19. This article discusses the engineering techniques utilized for fabricating chemically active E2DNMs that are exceptionally thin and irregular. The techniques encompass the introduction of heteroatoms, intercalation of ions, and the design of strain and defects. E2DNMs possess unique characteristics, including a substantial surface area and controllable electrical, optical, and bioactive properties. These characteristics enable the development of sophisticated diagnostic platforms for real-time biosensors with exceptional sensitivity in detecting SARS-CoV-2. Integrating the Internet of Medical Things (IoMT) with these E2DNMs-based advanced diagnostics has led to the development of portable, real-time, scalable, more accurate, and cost-effective SARS-CoV-2 diagnostic platforms. These diagnostic platforms have the potential to revolutionize SARS-CoV-2 diagnosis by making it faster, easier, and more accessible to people worldwide, thus making them ideal for resource-limited settings. These advanced IoMT diagnostic platforms may help with combating SARS-CoV-2 as well as tracking and predicting the spread of future pandemics, ultimately saving lives and mitigating their impact on global health systems.

Electrochemical biosensing based comparative study of monoclonal antibodies against SARS-CoV-2 nucleocapsid protein

In this study, we are reporting an electrochemical biosensor for the determination of three different clones of monoclonal antibodies (mAbs) against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) recombinant nucleocapsid protein (rN). The nucleocapsid protein was chosen as a system component identifying and discriminating antibodies that occur after virus infection instead of S protein used in serological tests to measure antibodies raised after vaccination and infection. The sensing platform was based on a screen-printed carbon electrode (SPCE) covered with gold nanoparticles (AuNP) and subsequently modified with a self-assembled monolayer (SAM) to ensure the covalent immobilization of the rN. The interaction between the protein and three clones of mAbs against SARS-CoV-2 rN with clone numbers 4G6, 7F10, and 1A6, were electrochemically registered in the range of concentrations. Three techniques, cyclic voltammetry (CV), differential pulse voltammetry (DPV), and pulse amperometric detection (PAD) were used for the detection. A gradual change in the responses with an increase in mAbs concentration for all techniques was observed. To assess the performance of the developed electrochemical biosensor, 'complexation constant' (KC), limit of detection (LOD), and limit of quantification (LOQ) were calculated for all assessed clones of mAbs and all used techniques. Our results indicated that DPV possessing higher fitting accuracy illustrated more significant differences in KC constants and LOD/LOQ values. According to the DPV results, 7F10 clone was characterized with the highest KC value of 1.47 ± 0.07 μg/mL while the lowest LOD and LOQ values belonged to the 4G6 clone and equaled 0.08 ± 0.01 and 0.25 ± 0.01 μg/mL, respectively. Overall, these results demonstrate the potential of electrochemical techniques for the detection and distinguishing of different clones of mAbs against SARS-CoV-2 nucleocapsid protein.

Revealing the SARS-CoV-2 Spike Protein and Specific Antibody Immune Complex Formation Mechanism for Precise Evaluation of Antibody Affinity

The profound understanding and detailed evaluation of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike (SCoV2-S) protein and specific antibody interaction mechanism is of high importance in the development of immunosensors for COVID-19. In the present work, we studied a model system of immobilized SCoV2-S protein and specific monoclonal antibodies by molecular dynamics of immune complex formation in real time. We simultaneously applied spectroscopic ellipsometry and quartz crystal microbalance with dissipation to reveal the features and steps of the immune complex formation. We showed direct experimental evidence based on acoustic and optical measurements that the immune complex between covalently immobilized SCoV2-S and specific monoclonal antibodies is formed in two stages. Based on these findings it was demonstrated that applying a two-step binding mathematical model for kinetics analysis leads to a more precise determination of interaction rate constants than that determined by the 1:1 Langmuir binding model. Our investigation showed that the equilibrium dissociation constants (KD) determined by a two-step binding model and the 1:1 Langmuir model could differ significantly. The reported findings can facilitate a deeper understanding of antigen-antibody immune complex formation steps and can open a new way for the evaluation of antibody affinity towards corresponding antigens.

Nano-biosensor for SARS-CoV-2/COVID-19 detection: methods, mechanism and interface design

The epidemic of coronavirus disease 2019 (COVID-19) was a huge disaster to human society. The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which led to COVID-19, has resulted in a large number of deaths. Even though the reverse transcription-polymerase chain reaction (RT-PCR) is the most efficient method for the detection of SARS-CoV-2, the disadvantages (such as long detection time, professional operators, expensive instruments, and laboratory equipment) limit its application. In this review, the different kinds of nano-biosensors based on surface-enhanced Raman scattering (SERS), surface plasmon resonance (SPR), field-effect transistor (FET), fluorescence methods, and electrochemical methods are summarized, starting with a concise description of their sensing mechanism. The different bioprobes (such as ACE2, S protein-antibody, IgG antibody, IgM antibody, and SARS-CoV-2 DNA probes) with different bio-principles are introduced. The key structural components of the biosensors are briefly introduced to give readers an understanding of the principles behind the testing methods. In particular, SARS-CoV-2-related RNA mutation detection and its challenges are also briefly described. We hope that this review will encourage readers with different research backgrounds to design SARS-CoV-2 nano-biosensors with high selectivity and sensitivity.

Polyaniline-based electrochemical immunosensor for the determination of antibodies against SARS-CoV-2 spike protein

In this work, we report an impedimetric system for the detection of antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Spike protein. The sensing platform is based on recombinant Spike protein (SCoV2-rS) immobilized on the phytic acid doped polyaniline films (PANI-PA). The affinity interaction between immobilized SCoV2-rS protein and antibodies in the physiological range of concentrations was registered by electrochemical impedance spectroscopy. Analytical parameters of the sensing platform were tuned by the variation of electropolymerization times during the synthesis of PANI-PA films. The lowest limit of detection and quantification were obtained for electropolymerization time of 20 min and equalled 8.00 ± 0.20 nM and 23.93 ± 0.60 nM with an equilibrium dissociation constant of 3 nM. The presented sensing system is label-free and suitable for the direct detection of antibodies against SARS-CoV-2 in real patient serum samples after coronavirus disease 2019 and/or vaccination.

Investigation of Biomolecule Interactions: Optical-, Electrochemical-, and Acoustic-Based Biosensors

Today, optical, electrochemical, and acoustic affinity biosensors; immunosensors; and immunoanalytical systems play an important role in the detection and characterization of a number of biological substances, including viral antigens, specific antibodies, and clinically important biomarkers [...].

Recent Advances in Synthesis and Application of Metal Oxide Nanostructures in Chemical Sensors and Biosensors

Nanostructured materials formed from metal oxides offer a number of advantages, such as large surface area, improved mechanical and other physical properties, as well as adjustable electronic properties that are important in the development and application of chemical sensors and biosensor design. Nanostructures are classified using the dimensions of the nanostructure itself and their components. In this review, various types of nanostructures classified as 0D, 1D, 2D, and 3D that were successfully applied in chemical sensors and biosensors, and formed from metal oxides using different synthesis methods, are discussed. In particular, significant attention is paid to detailed analysis and future prospects of the synthesis methods of metal oxide nanostructures and their integration in chemical sensors and biosensor design.

Photonic Sensors in Chemical and Biological Applications

Biosensors are described as analytical devices in which biological substances are detected by using various physicochemical detection systems [...].

Investigation of SARS-CoV-2 nucleocapsid protein interaction with a specific antibody by combined spectroscopic ellipsometry and quartz crystal microbalance with dissipation

Detailed evaluations of the antigen and antibody interaction rate and strength of the immune complex formed are very important for medical and bioanalytical applications. These data are crucial for the development of sensitive and fast immunosensors suitable for continuous measurements. Therefore, combined spectroscopic ellipsometry (SE) and quartz crystal microbalance with dissipation (QCM-D) technique (SE/QCM-D) was used for the evaluation: (i) of covalent immobilization of SARS-CoV-2 nucleocapsid protein (SCoV2-N) on QCM-D sensor disc modified by self-assembled monolayer based on 11-mercaptoundecanoic acid and (ii) interaction of immobilized SCoV2-N with specific polyclonal anti-SCoV2-N antibodies followed by immune complex formation process. The results show that the SCoV2-N monolayer is rigid due to the low energy dissipation registered during the QCM-D measurement. In contrast, the anti-SCoV2-N layer produced after interaction with the immobilized SCoV2-N formed a soft and viscous layer. It was determined, that the sparse distribution of SCoV2-N on the surface affected the spatial arrangement of the antibody during the formation of immune complexes. The hinge-mediated flexibility of the antibody Fab fragments allows them to reach the more distantly located SCoV2-N and establish a bivalent binding between proteins in the formed SCoV2-N/anti-SCoV2-N complex. It was noted that the SE/QCM-D method can provide more precise quantitative information about the flexibility and conformational changes of antibody during the formation of the immune complex on the surface over time.

Design and finite element modeling of two-dimensional nanomechanical biosensors for SARS-CoV-2 detection

SARS-CoV-2 is the causative agent of COVID-19 disease. The development of different variants has increased the prevalence, pathogenicity, and mortality of the SARS-CoV-2. Prompt diagnosis and timely initiation of therapy can undoubtedly minimize the damage caused by this virus. In this study, a wide range of emerging single layer two-dimensional materials (SL2DMs), including graphene, grapheme oxide (GO), reduced graphene oxide (rGO), hexagonal boron nitride (h-BN), Ti3C2Tx MXene, and MoS2that can be used to fabricate highly sensitive biosensors, are analyzed using the finite element method based on antigen-antibody interaction. Important design parameters including sensor size, sensor aspect ratio, number of viruses, and applying in-plane strain on sensor performance are analyzed using frequency shift technique. In the following, an analytical relationship that can predict the limit of detection (LOD) according to the above parameters is proposed. The results show that all the above materials have a good performance in detecting viruses in the sample range of 10-100 viruses. This range can be reduced significantly by applying strains of less than 0.1. Also, applying strain increases shift frequency index by 2 to 3 times, which is a significant result. The maximum and minimum sensor performance are obtained for GO and Ti3C2Tx, respectively. The results of this paper can be used to build a new generation of two-dimensional biosensors for rapid detection of COVID-19 and other viruses.

Single-particle detection of native SARS-CoV-2 virions by microfluidic resistive pulse sensing

Microfluidic resistive pulse sensing (MRPS) was used to determine the size -distribution of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) based on detecting nearly 30,000 single virions. However, the ultrastructure of SARS-CoV-2 is thoroughly described, but ensemble properties of SARS-CoV-2, e.g., its particle size distribution, are sparsely reported. According to the MRPS results, the size distribution of SARS-CoV-2 follows a log-normal function with a mean value of 85.1 nm, which corresponds to an approximate diameter of the viral envelope. This result also confirms the low number (< 50) of spike proteins on the surface of the virions.

Determination of rSpike Protein by Specific Antibodies with Screen-Printed Carbon Electrode Modified by Electrodeposited Gold Nanostructures

In this research, we assessed the applicability of electrochemical sensing techniques for detecting specific antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike proteins in the blood serum of patient samples following coronavirus disease 2019 (COVID-19). Herein, screen-printed carbon electrodes (SPCE) with electrodeposited gold nanostructures (AuNS) were modified with L-Cysteine for further covalent immobilization of recombinant SARS-CoV-2 spike proteins (rSpike). The affinity interactions of the rSpike protein with specific antibodies against this protein (anti-rSpike) were assessed using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods. It was revealed that the SPCE electroactive surface area increased from 1.49 ± 0.02 cm2 to 1.82 ± 0.01 cm2 when AuNS were electrodeposited, and the value of the heterogeneous electron transfer rate constant (k0) changed from 6.30 × 10-5 to 14.56 × 10-5. The performance of the developed electrochemical immunosensor was evaluated by calculating the limit of detection and limit of quantification, giving values of 0.27 nM and 0.81 nM for CV and 0.14 nM and 0.42 nM for DPV. Furthermore, a specificity test was performed with a solution of antibodies against bovine serum albumin as the control aliquot, which was used to assess nonspecific binding, and this evaluation revealed that the developed rSpike-based sensor exhibits low nonspecific binding towards anti-rSpike antibodies.

Total Internal Reflection Ellipsometry Approach for Bloch Surface Waves Biosensing Applications

A one-dimensional photonic crystal with an additional TiO₂ layer, supporting Bloch surface waves (BSW), was used for enhanced signal sensitivity for the detection of protein interaction. To compare the optical response of BSW and photonic crystals (PC), bovine serum albumin and specific antibodies against bovine serum were used as a model system. The results obtained show the enhanced sensitivity of p- and s-BSW components for the 1D PC sample with an additional TiO₂ layer. Furthermore, a higher sensitivity was obtained for the BSW component of p-polarization in the PC sample with an additional TiO₂ layer, where the sensitivity of the ellipsometric parameter Ψ was five times higher and that of the Δ parameter was eight times higher than those of the PC sample. The capabilities of BSW excitations are discussed from the sensitivity point of view and from the design of advanced biosensing.

Electrochemical Determination of Interaction between SARS-CoV-2 Spike Protein and Specific Antibodies

The serologic diagnosis of coronavirus disease 2019 (COVID-19) and the evaluation of vaccination effectiveness are identified by the presence of antibodies specific to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). In this paper, we present the electrochemical-based biosensing technique for the detection of antibodies specific to the SARS-CoV-2 proteins. Recombinant SARS-CoV-2 spike proteins (rSpike) were immobilised on the surface of a gold electrode modified by a self-assembled monolayer (SAM). This modified electrode was used as a sensitive element for the detection of polyclonal mouse antibodies against the rSpike (anti-rSpike). Electrochemical impedance spectroscopy (EIS) was used to observe the formation of immunocomplexes while cyclic voltammetry (CV) was used for additional analysis of the surface modifications. It was revealed that the impedimetric method and the elaborate experimental conditions are appropriate for the further development of electrochemical biosensors for the serological diagnosis of COVID-19 and/or the confirmation of successful vaccination against SARS-CoV-2.

Electrochemical Determination of Interaction between SARS-CoV-2 Spike Protein and Specific Antibodies

The serologic diagnosis of coronavirus disease 2019 (COVID-19) and the evaluation of vaccination effectiveness are identified by the presence of antibodies specific to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). In this paper, we present the electrochemical-based biosensing technique for the detection of antibodies specific to the SARS-CoV-2 proteins. Recombinant SARS-CoV-2 spike proteins (rSpike) were immobilised on the surface of a gold electrode modified by a self-assembled monolayer (SAM). This modified electrode was used as a sensitive element for the detection of polyclonal mouse antibodies against the rSpike (anti-rSpike). Electrochemical impedance spectroscopy (EIS) was used to observe the formation of immunocomplexes while cyclic voltammetry (CV) was used for additional analysis of the surface modifications. It was revealed that the impedimetric method and the elaborate experimental conditions are appropriate for the further development of electrochemical biosensors for the serological diagnosis of COVID-19 and/or the confirmation of successful vaccination against SARS-CoV-2.

Bioactive hybrid metal-organic framework (MOF)-based nanosensors for optical detection of recombinant SARS-CoV-2 spike antigen

Fast, efficient, and accurate detection of SARS-CoV-2 spike antigen is pivotal to control the spread and reduce the mortality of COVID-19. Nevertheless, the sensitivity of available nanobiosensors to detect recombinant SARS-CoV-2 spike antigen seems insufficient. As a proof-of-concept, MOF-5/CoNi₂S₄ is developed as a low-cost, safe, and bioactive hybrid nanostructure via the one-pot high-gravity protocol. Then, the porphyrin, H₂TMP, was attached to the surface of the synthesized nanomaterial to increase the porosity for efficient detection of recombinant SARS-CoV-2 spike antigen. AFM results approved roughness in different ranges, including 0.54 to 0.74 μm and 0.78 to ≈0.80 μm, showing good physical interactions with the recombinant SARS-CoV-2 spike antigen. MTT assay was performed and compared to the conventional synthesis methods, including hydrothermal, solvothermal, and microwave-assisted methods. The synthesized nanodevices demonstrated above 88% relative cell viability after 24 h and even 48 h of treatment. Besides, the ability of the synthesized nanomaterials to detect the recombinant SARS-CoV-2 spike antigen was investigated, with a detection limit of 5 nM. The in-situ synthesized nanoplatforms exhibited low cytotoxicity, high biocompatibility, and appropriate tunability. The fabricated nanosystems seem promising for future surveys as potential platforms to be integrated into biosensors.

Design and simulation of a millifluidic device for differential detection of SARS-CoV-2 and H1N1 based on triboelectricity

Differential diagnosis of pathogenic diseases, presently coronavirus disease 2019 (COVID-19) and influenza, is crucial with due attention to their superspreading events, presumably long incubation period, particular complications, and treatments. In this paper, a label-free, self-powered, and ultrafast immunosensor device working based on triboelectric effect is proposed. Equilibrium constants of specific antibody-antigen reactions are accompanied by IEP-relevant electric charges of antigens to recognize SARS-CoV-2 and H1N1. Simulation attributes including fluid flow and geometrical parameters are optimized so that the maximum capture efficiency of 85.63% is achieved. Accordingly, antibody-antigen complexes form electric double layers (EDLs) across the channel interfaces. The resultant built-in electric field affects the following external electric field derived from triboelectricity, leading to the variation of open-circuit voltage as a sensing metric. The device is flexible to operate in conductor-to-dielectric single-electrode and contact-separation modes simultaneously. While the detection limit is reduced utilizing the single-electrode mode compared to the latter one, surface treatment of the triboelectric pair contributes to the sensitivity enhancement. A threshold value equal to −4.113 V is featured to discriminate these two viruses in a vast detectable region; however, further surface engineering can allow the on-site detection of any electrically-charged pathogen applying the emerging triboelectric immunosensor enjoying a lower detection limit.

Investigation and Comparison of Specific Antibodies' Affinity Interaction with SARS-CoV-2 Wild-Type, B.1.1.7, and B.1.351 Spike Protein by Total Internal Reflection Ellipsometry

SARS-CoV-2 vaccines provide strong protection against COVID-19. However, the emergence of SARS-CoV-2 variants has raised concerns about the efficacy of vaccines. In this study, we investigated the interactions of specific polyclonal human antibodies (pAb-SCoV2-S) produced after vaccination with the Vaxzevria vaccine with the spike proteins of three SARS-CoV-2 variants of concern: wild-type, B.1.1.7, and B.1.351. Highly sensitive, label-free, and real-time monitoring of these interactions was accomplished using the total internal reflection ellipsometry method. Thermodynamic parameters such as association and dissociation rate constants, the stable immune complex formation rate constant (kr), the equilibrium association and dissociation (KD) constants and steric factors (Ps) were calculated using a two-step irreversible binding mathematical model. The results obtained show that the KD values for the specific antibody interactions with all three types of spike protein are in the same nanomolar range. The KD values for B.1.1.7 and B.1.351 suggest that the antibody produced after vaccination can successfully protect the population from the alpha (B.1.1.7) and beta (B.1.351) SARS-CoV-2 mutations. The steric factors (Ps) obtained for all three types of spike proteins showed a 100-fold lower requirement for the formation of an immune complex when compared with nucleocapsid protein.

Spectroscopic Ellipsometry and Quartz Crystal Microbalance with Dissipation for the Assessment of Polymer Layers and for the Application in Biosensing

Polymers represent materials that are applied in almost all areas of modern life, therefore, the characterization of polymer layers using different methods is of great importance. In this review, the main attention is dedicated to the non-invasive and label-free optical and acoustic methods, namely spectroscopic ellipsometry (SE) and quartz crystal microbalance with dissipation (QCM-D). The specific advantages of these techniques applied for in situ monitoring of polymer layer formation and characterization, biomolecule immobilization, and registration of specific interactions were summarized and discussed. In addition, the exceptional benefits and future perspectives of combined spectroscopic ellipsometry and QCM-D (SE/QCM-D) in one measurement are overviewed. Recent advances in the discussed area allow us to conclude that especially significant breakthroughs are foreseen in the complementary application of both QCM-D and SE techniques for the investigation of polymer structure and assessment of the interaction between biomolecules such as antigens and antibodies, receptors and ligands, and complementary DNA strands.

Electrochemical detection of ACE2 as a biomarker for diagnosis of COVID-19 and potential male infertility

Knowing how heavily the body is burdened by SARS-CoV-2 infection is all important to avoid tragic outcomes. This demands fast and convenient assays with minimum requirement for instruments and reagents. Therefore, a short synthetic peptide is developed to perform direct serum assay, using portable hand-held potentiostat, in a reagent-less manner. The target is angiotensin converting enzyme 2 (ACE2), a protein secreted by the body into the blood to restrict viral invasion. Specifically, under electrochemical potential scanning, the peptide can covalently capture ACE2 from the serum, and then form a covalent gel-like 2D protein network with the serum proteins, in an ACE2-specific fashion. This formation of a covalent biosensing complex enables sensitive detection in serum samples of SARS-CoV-2 infected patients. The detected serum level of ACE2 can not only serve as an index of viral load, but may also hint at the associated risk of potential male infertility. These results may point to field application of this simple design in the clinical practice in treating COVID-19 in the near future.

Potential of Bacillus subtilis Against SARS-CoV-2 - A Sustainable Drug Development Perspective

The COVID-19 pandemic had anomalous yet inevitable impacts on the world's economies, healthcare systems, and all other aspects of life. Researchers began to uncover hidden routes to find a new horizon of hope using underrated resources. Biosurfactants are sustainable biomolecules with an active surface, unique characteristics, and extensive uses. Bacillus species showed the highest amount of biosurfactant activities and Bacillus subtilis is one of them. The antiviral, antimicrobial, and anti-inflammatory activity of B. subtilis was proven recently. The great advantage is its non-toxic nature. Pro-inflammatory cytokines including IL-1 β, 6, 8, 12, 18, and TNF-(α are secreted in higher amounts when neutrophils and monocytes are triggered by biosurfactant bacteria. This point of view furnishes the potential application of B. subtilis and its biomolecules against COVID-19, either in the form of a vaccine/therapeutic agent, for a greener environment, healthier life, and environmental sustainability. Further in vivo and clinical trials are needed to validate this hypothesis.

Magnet-assisted electrochemical immunosensor based on surface-clean Pd-Au nanosheets for sensitive detection of SARS-CoV-2 spike protein

Tracking and monitoring of low concentrations of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can effectively control asymptomatic transmission of current coronavirus disease 2019 (COVID-19) in the early stages of infection. Here, we highlight an electrochemical immunosensor for sensitive detection of SARS-CoV-2 antigen marker spike protein. The surface-clean Pd-Au nanosheets as a substrate for efficient sensing and signal output have been synthesized. The morphology, chemical states and excellent stable electrochemical properties of this surface-clean heterostructures have been studied. Functionalized superparamagnetic nanoparticles (MNPs) were introduced as sample separators and signal amplifiers. This biosensor was tested in phosphate buffered saline (PBS) and nasopharyngeal samples. The results showed that the sensor has a wide linear dynamic range (0.01 ng mL-1 to 1000 ng mL-1) with a low detection limit (0.0072 ng mL-1), which achieved stable and sensitive detection of the spike protein. Therefore, this immunosensing method provides a promising electrochemical measurement tool, which can furnish ideas for early screening and the reasonable optimization of detection methods of SARS-CoV-2.

PEDOT-AuNPs-based impedimetric immunosensor for the detection of SARS-CoV-2 antibodies

Electrochemical sensors and biosensors are useful techniques for fast, inexpensive, sensitive, and easy detection of innumerous specimen. In face of COVID-19 pandemic, it became evident the necessity of a rapid and accurate diagnostic test, so the impedimetric immunosensor approach can be a good alternative to replace the conventional tests due to the specific antibody-antigen binding interaction and the fast response in comparison to traditional methods. In this work, a modified electrode with electrosynthesized PEDOT and gold nanoparticles followed by the immobilization of truncated nucleoprotein (N aa160-406aa) was used for a fast and reliable detection of antibodies against COVID-19 in human serum sample. The method consists in analyzing the charge-transfer resistance (R_CT) variation before and after the modified electrode comes into contact with the positive and negative serum sample for COVID-19, using [Fe(CN)₆]^3-/4- as a probe. The results show a linear and selective response for serum samples diluted in a range of 2.5 × 10³ to 20 × 10³. Also, the electrode material was fully characterized by Raman spectroscopy, transmission electron microscopy and scanning electron microscopy coupled with EDS, indicating that the gold nanoparticles were well distributed around the polymer matrix and the presence of the biological sample was confirmed by EDS analysis. EIS measurements allowed to differentiate the negative and positive samples by the difference in the R_CT magnitude, proving that the material developed here has potential properties to be applied in impedimetric immunosensors for the detection of SARS-CoV-2 antibodies in about 30 min.

Biosensors for the Determination of SARS-CoV-2 Virus and Diagnosis of COVID-19 Infection

Monitoring and tracking infection is required in order to reduce the spread of the coronavirus disease 2019 (COVID-19), induced by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). To achieve this goal, the development and deployment of quick, accurate, and sensitive diagnostic methods are necessary. The determination of the SARS-CoV-2 virus is performed by biosensing devices, which vary according to detection methods and the biomarkers which are inducing/providing an analytical signal. RNA hybridisation, antigen-antibody affinity interaction, and a variety of other biological reactions are commonly used to generate analytical signals that can be precisely detected using electrochemical, electrochemiluminescence, optical, and other methodologies and transducers. Electrochemical biosensors, in particular, correspond to the current trend of bioanalytical process acceleration and simplification. Immunosensors are based on the determination of antigen-antibody interaction, which on some occasions can be determined in a label-free mode with sufficient sensitivity.

A minireview on nanoparticle-based sensors for the detection of coronaviruses

Coronaviruses (CoVs) are a class of viruses that cause respiratory tract infections in birds and mammals. Severe acute respiratory syndrome and Middle East respiratory syndrome are pathogenic human viruses. The ongoing coronavirus causing a pandemic of COVID-19 is a recently identified virus from this group. The first step in the control of spreading the disease is to detect and quarantine infected subjects. Consequently, the introduction of rapid and reliable detection methods for CoVs is crucial. To date, several methods were reported for the detection of coronaviruses. Nanoparticles play an important role in detection tools, thanks to their high surface-to-volume ratio and exclusive optical property enables the development of susceptible analytical nanoparticle-based sensors. The studies performed on using nanoparticles-based (mainly gold) sensors to detect CoVs in two categories of optical and electrochemical were reviewed here. Details of each reported sensor and its relevant analytical parameters are carefully provided and explained.

In Silico Modeling as a Perspective in Developing Potential Vaccine Candidates and Therapeutics for COVID-19

The potential of computational models to identify new therapeutics and repurpose existing drugs has gained significance in recent times. The current ‘COVID-19’ pandemic caused by the new SARS CoV2 virus has affected over 200 million people and caused over 4 million deaths. The enormity and the consequences of this viral infection have fueled the research community to identify drugs or vaccines through a relatively expeditious process. The availability of high-throughput datasets has cultivated new strategies for drug development and can provide the foundation towards effective therapy options. Molecular modeling methods using structure-based or computer-aided virtual screening can potentially be employed as research guides to identify novel antiviral agents. This review focuses on in-silico modeling of the potential therapeutic candidates against SARS CoVs, in addition to strategies for vaccine design. Here, we particularly focus on the recently published SARS CoV main protease (Mpro) active site, the RNA-dependent RNA polymerase (RdRp) of SARS CoV2, and the spike S-protein as potential targets for vaccine development. This review can offer future perspectives for further research and the development of COVID-19 therapies via the design of new drug candidates and multi-epitopic vaccines and through the repurposing of either approved drugs or drugs under clinical trial.

A one-step, one-pot CRISPR nucleic acid detection platform (CRISPR-top): Application for the diagnosis of COVID-19

The existing CRISPR-mediated diagnostic tests require a two-step procedure (DNA or RNA amplification followed by CRISPR-mediated sequence-specific detection) for nucleic acid detection, which increases complexity and the risk of sample cross-contamination. Here, we report a new CRISPR-mediated test, called CRISPR-top (CRISPR-mediated testing in one-pot), which integrates simultaneous target pre-amplification with CRISPR/cas12b-mediated detection into a one-pot reaction mixture, performed at a constant temperature. The novel CRISPR-top assay was applied to detect severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent for COVID-19 (coronavirus disease 2019). COVID-19 CRISPR-top targets the ORF1ab (opening reading frame 1a/b) and NP (nucleoprotein) genes of SARS-CoV-2, and operates at 59 °C for 40 min with minimal instrument. The COVID-19 CRISPR-top assay can return results within 60-min and is easily interpreted by visual fluorescence or lateral flow readouts. The analytical limit of detection (LoD) for COVID-19 CRISPR-top is 10 copies (for each detection target) per reaction with no cross-reactivity observed from non-SARS-CoV-2 templates. Among clinically collected non-COVID-19 samples, the assay's specificity was 100% (80/80 oropharynx swab samples). Among 52 COVID-19 positive clinical samples collected, the COVID-19 CRISPR-top assay yielded 38 (73.1%) positive results using fluorescence readout and 35 (67.3%) positive results with lateral-flow readout. These diagnostic results were similar to those obtained using RT-PCR (34 positive (65.4%)). These data indicate that COVID-19 CRISPR-top is a simple, rapid, accurate and highly sensitive method for SARS-CoV-2 detection which can be used in the clinic, field laboratories and primary care facilities in resource-challenged settings.

Affinity Sensors for the Diagnosis of COVID-19

The coronavirus disease 2019 (COVID-19) outbreak caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was proclaimed a global pandemic in March 2020. Reducing the dissemination rate, in particular by tracking the infected people and their contacts, is the main instrument against infection spreading. Therefore, the creation and implementation of fast, reliable and responsive methods suitable for the diagnosis of COVID-19 are required. These needs can be fulfilled using affinity sensors, which differ in applied detection methods and markers that are generating analytical signals. Recently, nucleic acid hybridization, antigen-antibody interaction, and change of reactive oxygen species (ROS) level are mostly used for the generation of analytical signals, which can be accurately measured by electrochemical, optical, surface plasmon resonance, field-effect transistors, and some other methods and transducers. Electrochemical biosensors are the most consistent with the general trend towards, acceleration, and simplification of the bioanalytical process. These biosensors mostly are based on the determination of antigen-antibody interaction and are robust, sensitive, accurate, and sometimes enable label-free detection of an analyte. Along with the specification of biosensors, we also provide a brief overview of generally used testing techniques, and the description of the structure, life cycle and immune host response to SARS-CoV-2, and some deeper details of analytical signal detection principles.

Advances in Molecularly Imprinted Polymers Based Affinity Sensors (Review)

Recent challenges in biomedical diagnostics show that the development of rapid affinity sensors is very important issue. Therefore, in this review we are aiming to outline the most important directions of affinity sensors where polymer-based semiconducting materials are applied. Progress in formation and development of such materials is overviewed and discussed. Some applicability aspects of conducting polymers in the design of affinity sensors are presented. The main attention is focused on bioanalytical application of conducting polymers such as polypyrrole, polyaniline, polythiophene and poly(3,4-ethylenedioxythiophene) ortho-phenylenediamine. In addition, some other polymers and inorganic materials that are suitable for molecular imprinting technology are also overviewed. Polymerization techniques, which are the most suitable for the development of composite structures suitable for affinity sensors are presented. Analytical signal transduction methods applied in affinity sensors based on polymer-based semiconducting materials are discussed. In this review the most attention is focused on the development and application of molecularly imprinted polymer-based structures, which can replace antibodies, receptors, and many others expensive affinity reagents. The applicability of electrochromic polymers in affinity sensor design is envisaged. Sufficient biocompatibility of some conducting polymers enables to apply them as "stealth coatings" in the future implantable affinity-sensors. Some new perspectives and trends in analytical application of polymer-based semiconducting materials are highlighted.