Rapid detection of SARS-CoV-2 antibodies using electrochemical impedance-based detector

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.

An overview of electrochemical biosensors used for COVID-19 detection

This short review presents the latest advances in the field of electrochemical biosensors, focusing particularly on impedimetric biosensors for the direct measurement of analytes. As a source of study we have chosen to describe these advances in the latest global health crisis originated from the COVID-19 pandemic, initiated by the SARS-CoV-2 virus. In this period, the necessity for swift and precise detection methods has grown rapidly due to an imminent need for the development of an analytical method to identify and isolate infected patients as an attempt to control the spreading of the disease. Traditional approaches such as the enzyme-linked immunosorbent assay (ELISA), were extensively used during the SARS-CoV-2 pandemic, but their drawbacks, including slow response time, became evident. In this context, the potential of electrochemical biosensors as an alternative for COVID-19 detection was emphasized. These biosensors merge electrochemical technology with bioreceptors, offering benefits such as rapidity, accuracy, portability, and real-time result provision. Additionally, we present instances of electrochemical biosensors modified with conductive polymers, eliminating the necessity for an electrochemical probe. The adaptability of the developed materials and devices facilitated the prompt production of electrochemical biosensors during the pandemic, creating opportunities for broader applications in infectious disease diagnosis.

Wide-range and selective detection of SARS-CoV-2 DNA via surface modification of electrolyte-gated IGZO thin-film transistors

The 2019 coronavirus pandemic resulted in a massive global healthcare crisis, highlighting the necessity to develop effective and reproducible platforms capable of rapidly and accurately detecting SARS-CoV-2. In this study, we developed an electrolyte-gated indium-gallium-zinc-oxide (IGZO) thin-film transistor with sequential surface modification to realize the low limit of detection (LoD <50 fM) and a wide detection range from 50 fM to 5 μM with good linearity (R2 = 0.9965), and recyclability. The surface chemical modification was achieved to anchor the single strand of SARS-CoV-2 DNA via selective hybridization. Moreover, the minute electrical signal change following the chemical modification was investigated by in-depth physicochemical analytical techniques. Finally, we demonstrate fully recyclable biosensors based on oxygen plasma treatment. Owing to its cost-effective fabrication, rapid detection at the single-molecule level, and low detection limit, the proposed biosensor can be used as a point-of-care platform to perform timely and effective SARS-CoV-2 detection.

Hydroxyapatite-Gold Modified Screen-Printed Carbon Electrode for Selective SARS-CoV-2 Antibody Immunosensor

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), or coronavirus disease 2019 (COVID-19), is still spreading worldwide; therefore, the need for rapid and accurate detection methods remains relevant to maintain the spread of this infectious disease. Electrochemical immunosensors are an alternative method for the rapid detection of the SARS-CoV-2 virus. Herein, we report the development of a screen-printed carbon electrode immunosensor using a hydroxyapatite-gold nanocomposite (SPCE/HA-Au) directly spray-coated with the immobilization receptor binding domain (RBD) Spike to increase the conductivity and surface electrode area. The HA-Au composite synthesis was optimized using the Box-Behnken method, and the resulting composite was characterized by UV-vis spectrophotometry, TEM-EDX, and XRD analysis. The specific interaction of RBD Spike with immunoglobulin G (IgG) antibodies was evaluated by differential pulse voltammetry and electrochemical impedance spectroscopy methods in a [Fe(CN)6]4-/3- solution redox system. The IgG was detected with a detection limit of 0.0561 pg mL-1, and the immunosensor had selectivity and stability of 103-122% and was stable until week 7 with the influence of storage conditions. Also, the immunosensor was tested using real samples from human serum, where the results were confirmed using the chemiluminescent microparticle immunoassay (CMIA) method and showed satisfactory results. Therefore, the developed electrochemical immunosensor can rapidly and accurately detect SARS-CoV-2 antibodies.

Clinical evaluation of a new COVID-19 antigen rapid test kit for detection of SARS-CoV-2

The antigen rapid diagnostic test (Ag-RDT) is an assay kit for detecting the SARS-COV-2 nucleocapsid proteins, based on the colloidal gold method.Accurate diagnosis has an important role in limiting the transmission of SARS-COV-2, and also helps patients to receive earlier treatment .The object of this study was to perform the clinical evaluation of a novel Ag-RDTs with samples collected from two different swabs.DEEPBLUE®COVID-19 antigen detection kit used for the examination of the subjects in the experiment.For antigen testing on samples collected with nasal swabs, sensitivity was 91.7 % (95 % CI 83.6-96.6 %) and specificity was 100 %(95 %CI 98.1-100 %).For nasopharyngeal swabs, the sensitivity was 96.8 % (95 % CI 93.6-98.7 %) and the specificity was 100 % (95 % CI 98.2-100 %).Fisher Precision test showed a significant correlation between nasopharyngeal swab Ag-RDTs and nasal swab Ag-RDTs and RT-qPCR test (p-value <0.001).The results showed that the patients use the kit for testing were comparable to the RT-qPCR.

Capacitive biosensors for label-free and ultrasensitive detection of biomarkers

Capacitive biosensors are label-free capacitors that can detect biomarkers with the outstanding advantages of simplicity, low cost, and ultrahigh sensitivity. A typical capacitive biosensor consists of a bioreceptor and a transducer, where the bioreceptor captures the biomarker to form a bioreceptor/biomarker conjugate and the transducer generates a detectable signal. In general, antibodies, aptamers, or proteins are exploited as the bioreceptor, while various electrodes including carbon electrodes (CEs), gold electrodes (AuEs), or interdigitated electrodes (IDEs) may serve as the transducer. Because the formation of bioreceptor/biomarker conjugates often leads to a change in capacitance, the capacitive signal is then employed for biomarker detection. This review summarizes recent advances in capacitive biosensors for the detection of biomarkers over the last five years. With a focus on the three common types of bioreceptors, i.e., antibodies, aptamers, and proteins, capacitive biosensors using CEs, AuEs, and IDEs as the transducers are discussed in detail. The immobilization of bioreceptors and signal amplification strategies are described to provide a robust overview of capacitive biosensors for biomarker detection. In addition, analytical methods and future prospects are given to support the application of capacitive biosensors.

Carbon Nanostructured Immunosensing of Anti-SARS-CoV-2 S-Protein Antibodies

The rampant spread and death rate of the recent coronavirus pandemic related to the SARS-CoV-2 respiratory virus have underscored the critical need for affordable, portable virus diagnostics, particularly in resource-limited settings. Moreover, efficient and timely monitoring of vaccine efficacy is needed to prevent future widespread infections. Electrochemical immunosensing poses an effective alternative to conventional molecular spectroscopic approaches, offering rapid, cost-effective, sensitive, and portable electroanalysis of disease biomarkers and antibodies; however, efforts to improve binding efficiency and sensitivity are still being investigated. Graphene quantum dots (GQDs) in particular have shown promise in improving device sensitivity. This study reports the development of a GQD-functionalized point-of-contamination device leveraging the selective interactions between SARS-CoV-2-specific Spike (S) Protein receptor binding domain (RBD) antigens and IgG anti-SARS-CoV-2-specific S-protein antibodies at screen-printed carbon electrode (SPCE) surfaces. The immunocomplexes formed at the GQD surfaces result in the interruption of the redox reactions that take place in the presence of a redox probe, decreasing the current response. Increased active surface area, conductivity, and binding via EDC/NHS chemistry were achieved due to the nanomaterial inclusion, with 5 nm, blue luminescent GQDs offering the best results. GQD concentration, EDC/NHS ratio, and RBD S-protein incubation time and concentration were optimized for the biosensor, and inter- and intra-screen-printed carbon electrode detection was investigated by calibration studies on multiple and single electrodes. The single electrode used for the entire calibration provided the best results. The label-free immunosensor was able to selectively detect anti-SARS-CoV-2 IgG antibodies between 0.5 and 100 ng/mL in the presence of IgM and other coronavirus antibodies with an excellent regression of 0.9599. A LOD of 2.028 ng/mL was found, offering comparable findings to the literature-reported values. The detection sensitivity of the sensor is further compared to non-specific IgM antibodies. The developed GQD immunosensor was compared to other low-oxygen content carbon nanomaterials, namely (i) carbon quantum dot (CQD), (ii) electrochemically reduced graphene oxide, and (iii) carbon black-functionalized devices. The findings suggest that improved electron transfer kinetics and increased active surface area of the CNs, along with surface oxygen content, aid in the detection of anti-SARS-CoV-2 IgG antibodies. The novel immunosensor suggests a possible application toward monitoring of IgG antibody production in SARS-CoV-2-vaccinated patients to study immune responses, vaccine efficacy, and lifetime to meet the demands for POC analysis in resource-limited settings.

Duplex Electrochemical Microfluidic Sensor for COVID-19 Antibody Detection: Natural versus Vaccine-Induced Humoral Response

The rapid transmission and resilience of coronavirus disease 2019 (COVID-19) have led to urgent demands in monitoring humoral response for effective vaccine development, thus a multiplex co-detection platform to discriminate infection-induced from vaccine-induced antibodies is needed. Here a duplex electrochemical immunosensor for co-detection of anti-nucleocapsid IgG (N-IgG) and anti-spike IgG (S-IgG) is developed by using a two-working electrode system, via an indirect immunoassay, with antibody quantification obtained by differential pulse voltammetry. The screen-printed electrodes (SPEs) are modified by carbon black and electrodeposited gold nanoflowers for maximized surface areas, enabling the construction of an immunological chain for S-IgG and N-IgG electrochemical detection with enhanced performance. Using an optimized immunoassay protocol, a wide linear range between 30-750 and 20-1000 ng mL-1 , and a limit of detection of 28 and 15 ng mL-1 are achieved to detect N-IgG and S-IgG simultaneously in serum samples. This duplex immunosensor is then integrated in a microfluidic device to obtain significantly reduced detection time (≤ 7 min) while maintaining its analytical performance. The duplex microfluidic immunosensor can be easily expanded into multiplex format to achieve high throughput screening for the sero-surveillance of COVID-19  and other infectious diseases.

Advances in Simple, Rapid, and Contamination-Free Instantaneous Nucleic Acid Devices for Pathogen Detection

Pathogenic pathogens invade the human body through various pathways, causing damage to host cells, tissues, and their functions, ultimately leading to the development of diseases and posing a threat to human health. The rapid and accurate detection of pathogenic pathogens in humans is crucial and pressing. Nucleic acid detection offers advantages such as higher sensitivity, accuracy, and specificity compared to antibody and antigen detection methods. However, conventional nucleic acid testing is time-consuming, labor-intensive, and requires sophisticated equipment and specialized medical personnel. Therefore, this review focuses on advanced nucleic acid testing systems that aim to address the issues of testing time, portability, degree of automation, and cross-contamination. These systems include extraction-free rapid nucleic acid testing, fully automated extraction, amplification, and detection, as well as fully enclosed testing and commercial nucleic acid testing equipment. Additionally, the biochemical methods used for extraction, amplification, and detection in nucleic acid testing are briefly described. We hope that this review will inspire further research and the development of more suitable extraction-free reagents and fully automated testing devices for rapid, point-of-care diagnostics.

Portable microfluidic impedance biosensor for SARS-CoV-2 detection

Pandemics as the one we are currently facing, where fast-spreading viruses present a threat to humanity, call for simple and reliable methods to perform early diagnosis, enabling detection of very low pathogen loads even before symptoms start showing in the host. So far, standard polymerase chain reaction (PCR) is the most reliable method for doing so, but it is rather slow and needs specialized reagents and trained personnel to operate it. Additionally, it is expensive and not easily accessible. Therefore, developing miniaturized and portable sensors which perform early detection of pathogens with high reliability is necessary to not only prevent the spreading of the disease but also to monitor the effectiveness of the developed vaccines and the appearance of new pathogenic variants. Thus, in this work we develop a sensitive microfluidic impedance biosensor for the direct detection of SARS-CoV-2, towards a mobile point-of-care (POC) platform. The operational parameters are optimized with the aid of design-of-experiment (DoE), for an accurate detection of the viral antigens using electrochemical impedance spectroscopy (EIS). We perform the biodetection of buffer samples spiked with fM concentration levels and validate the biosensor in a clinical context of relevance by analyzing 15 real patient samples up to a Ct value (cycle threshold) of 27. Finally, we demonstrate the versatility of the developed platform using different settings, including a small portable potentiostat, using multiple channels for self-validation, as well as with single biosensors for a smartphone-based readout. This work contributes to the rapid and reliable diagnostics of COVID-19 and can be extended to other infectious diseases, allowing the monitoring of viral load in vaccinated and unvaccinated people to anticipate a potential relapse of the disease.

Emerging trends in point-of-care biosensing strategies for molecular architectures and antibodies of SARS-CoV-2

COVID-19, a highly contagious viral infection caused by the occurrence of severe acute respiratory syndrome coronavirus (SARS-CoV-2), has turned out to be a viral pandemic then ravaged many countries worldwide. In the recent years, point-of-care (POC) biosensors combined with state-of-the-art bioreceptors, and transducing systems enabled the development of novel diagnostic tools for rapid and reliable detection of biomarkers associated with SARS-CoV-2. The present review thoroughly summarises and discusses various biosensing strategies developed for probing SARS-CoV-2 molecular architectures (viral genome, S Protein, M protein, E protein, N protein and non-structural proteins) and antibodies as a potential diagnostic tool for COVID-19. This review discusses the various structural components of SARS-CoV-2, their binding regions and the bioreceptors used for recognizing the structural components. The various types of clinical specimens investigated for rapid and POC detection of SARS-CoV-2 is also highlighted. The importance of nanotechnology and artificial intelligence (AI) approaches in improving the biosensor performance for real-time and reagent-free monitoring the biomarkers of SARS-CoV-2 is also summarized. This review also encompasses existing practical challenges and prospects for developing new POC biosensors for clinical monitoring of COVID-19.

Integrating Water Purification with Electrochemical Aptamer Sensing for Detecting SARS-CoV-2 in Wastewater

Wastewater analysis of pathogens, particularly SARS-CoV-2, is instrumental in tracking and monitoring infectious diseases in a population. This method can be used to generate early warnings regarding the onset of an infectious disease and predict the associated infection trends. Currently, wastewater analysis of SARS-CoV-2 is almost exclusively performed using polymerase chain reaction for the amplification-based detection of viral RNA at centralized laboratories. Despite the development of several biosensing technologies offering point-of-care solutions for analyzing SARS-CoV-2 in clinical samples, these remain elusive for wastewater analysis due to the low levels of the virus and the interference caused by the wastewater matrix. Herein, we integrate an aptamer-based electrochemical chip with a filtration, purification, and extraction (FPE) system for developing an alternate in-field solution for wastewater analysis. The sensing chip employs a dimeric aptamer, which is universally applicable to the wild-type, alpha, delta, and omicron variants of SARS-CoV-2. We demonstrate that the aptamer is stable in the wastewater matrix (diluted to 50%) and its binding affinity is not significantly impacted. The sensing chip demonstrates a limit of detection of 1000 copies/L (1 copy/mL), enabled by the amplification provided by the FPE system. This allows the integrated system to detect trace amounts of the virus in native wastewater and categorize the amount of contamination into trace (<10 copies/mL), medium (10-1000 copies/mL), or high (>1000 copies/mL) levels, providing a viable wastewater analysis solution for in-field use.

Enzymatic Electrochemical/Fluorescent Nanobiosensor for Detection of Small Chemicals

The detection of small molecules has attracted enormous interest in various fields, including the chemical, biological, and healthcare fields. In order to achieve such detection with high accuracy, up to now, various types of biosensors have been developed. Among those biosensors, enzymatic biosensors have shown excellent sensing performances via their highly specific enzymatic reactions with small chemical molecules. As techniques used to implement the sensing function of such enzymatic biosensors, electrochemical and fluorescence techniques have been mostly used for the detection of small molecules because of their advantages. In addition, through the incorporation of nanotechnologies, the detection property of each technique-based enzymatic nanobiosensors can be improved to measure harmful or important small molecules accurately. This review provides interdisciplinary information related to developing enzymatic nanobiosensors for small molecule detection, such as widely used enzymes, target small molecules, and electrochemical/fluorescence techniques. We expect that this review will provide a broad perspective and well-organized roadmap to develop novel electrochemical and fluorescent enzymatic nanobiosensors.

Label-free integrated microfluidic plasmonic biosensor from vertical-cavity surface-emitting lasers for SARS-CoV-2 receptor binding domain protein detection

The nanoplasmonic sensor of the nanograting array has a remarkable ability in label-free and rapid biological detection. The integration of the nanograting array with the standard vertical-cavity surface-emitting lasers (VCSEL) platform can achieve a compact and powerful solution to provide on-chip light sources for biosensing applications. Here, a high sensitivity and label-free integrated VCSELs sensor was developed as a suitable analysis technique for COVID-19 specific receptor binding domain (RBD) protein. The gold nanograting array is integrated on VCSELs to realize the integrated microfluidic plasmonic biosensor of on-chip biosensing. The 850 nm VCSELs are used as a light source to excite the localized surface plasmon resonance (LSPR) effect of the gold nanograting array to detect the concentration of attachments. The refractive index sensitivity of the sensor is 2.99 × 10⁶ nW/RIU. The aptamer of RBD was modified on the surface of the gold nanograting to detect the RBD protein successfully. The biosensor has high sensitivity and a wide detection range of 0.50 ng/mL - 50 µg/mL. This VCSELs biosensor provides an integrated, portable, and miniaturized idea for biomarker detection.

New, fast, and precise method of COVID-19 detection in nasopharyngeal and tracheal aspirate samples combining optical spectroscopy and machine learning

Fast, precise, and low-cost diagnostic testing to identify persons infected with SARS-CoV-2 virus is pivotal to control the global pandemic of COVID-19 that began in late 2019. The gold standard method of diagnostic recommended is the RT-qPCR test. However, this method is not universally available, and is time-consuming and requires specialized personnel, as well as sophisticated laboratories. Currently, machine learning is a useful predictive tool for biomedical applications, being able to classify data from diverse nature. Relying on the artificial intelligence learning process, spectroscopic data from nasopharyngeal swab and tracheal aspirate samples can be used to leverage characteristic patterns and nuances in healthy and infected body fluids, which allows to identify infection regardless of symptoms or any other clinical or laboratorial tests. Hence, when new measurements are performed on samples of unknown status and the corresponding data is submitted to such an algorithm, it will be possible to predict whether the source individual is infected or not. This work presents a new methodology for rapid and precise label-free diagnosing of SARS-CoV-2 infection in clinical samples, which combines spectroscopic data acquisition and analysis via artificial intelligence algorithms. Our results show an accuracy of 85% for detection of SARS-CoV-2 in nasopharyngeal swab samples collected from asymptomatic patients or with mild symptoms, as well as an accuracy of 97% in tracheal aspirate samples collected from critically ill COVID-19 patients under mechanical ventilation. Moreover, the acquisition and processing of the information is fast, simple, and cheaper than traditional approaches, suggesting this methodology as a promising tool for biomedical diagnosis vis-à-vis the emerging and re-emerging viral SARS-CoV-2 variant threats in the future.

CeO2@NH2 functionalized electrodes for the rapid detection of SARS-CoV-2 spike receptor binding domain

A detection method based on an electrochemical aptasensor has been developed as an alternative fast, portable, simple, inexpensive, and high-accuracy detection method for detecting the SARS-CoV-2 Spike Receptor Binding Domain (spike RBD). The CeO₂@NH₂ functionalized Screen Printed Carbon Electrode (SPCE) was used to immobilize an aminated aptamer of spike RBD protein via glutaraldehyde as a linker. The aptamer's interaction with the SARS-CoV-2 Spike RBD was measured via the [Fe(CN)₆]^4-/3- redox system signal. Experimental conditions were optimized using a Box-Behnken experimental design and showed that the optimal conditions of the SARS-CoV-2 aptasensor were 1.5 ng mL^-1 of aptamer, immobilization of aptamer for 60 minutes, and Spike RBD incubation for 10 minutes. The developed aptasensor was able to detect the standard SARS-CoV-2 Spike RBD with a detection limit of 0.017 ng mL^-1 in the range of 0.001-100 ng mL^-1. This aptasensor was used to detect salivary and oropharyngeal swab samples of normal individuals with the addition of Spike RBD, and the recoveries were 92.96% and 96.52%, respectively. The testing on nasopharyngeal swab samples of COVID-19 patients showed that the aptasensor results were comparable with the qRT-PCR results. Thus, the developed aptasensor has the potential to be applied as a SARS-CoV-2 rapid test method for clinical samples.

Impedimetric Sensing: An Emerging Tool for Combating the COVID-19 Pandemic

The COVID-19 pandemic revealed a pressing need for the development of sensitive and low-cost point-of-care sensors for disease diagnosis. The current standard of care for COVID-19 is quantitative reverse transcriptase polymerase chain reaction (qRT-PCR). This method is sensitive, but takes time, effort, and requires specialized equipment and reagents to be performed correctly. This make it unsuitable for widespread, rapid testing and causes poor individual and policy decision-making. Rapid antigen tests (RATs) are a widely used alternative that provide results quickly but have low sensitivity and are prone to false negatives, particularly in cases with lower viral burden. Electrochemical sensors have shown much promise in filling this technology gap, and impedance spectroscopy specifically has exciting potential in rapid screening of COVID-19. Due to the data-rich nature of impedance measurements performed at different frequencies, this method lends itself to machine-leaning (ML) algorithms for further data processing. This review summarizes the current state of impedance spectroscopy-based point-of-care sensors for the detection of the SARS-CoV-2 virus. This article also suggests future directions to address the technology's current limitations to move forward in this current pandemic and prepare for future outbreaks.

Point-of-Care Diagnostic Biosensors to Monitor Anti-SARS-CoV-2 Neutralizing IgG/sIgA Antibodies and Antioxidant Activity in Saliva

Monitoring biomarkers is a great way to assess daily physical condition, and using saliva instead of blood samples is more advantageous as the process is simple and allows individuals to test themselves. In the present study, we analyzed the titers of neutralizing antibodies, IgG and secretory IgA (sIgA), in response to the SARS-CoV-2 vaccine, in saliva. A total of 19 saliva and serum samples were collected over a 10-month period 3 weeks after the first vaccine, 8 months after the second vaccine, and 1 month after the third vaccine. The ranges of antibody concentrations post-vaccination were: serum IgG: 81-15,000 U/mL, salivary IgG: 3.4-330 U/mL, and salivary IgA: 58-870 ng/mL. A sharp increase in salivary IgG levels was observed after the second vaccination. sIgA levels also showed an increasing trend. A correlation with trends in serum IgG levels was observed, indicating the possibility of using saliva to routinely assess vaccine efficacy. The electrochemical immunosensor assay developed in this study based on the gold-linked electrochemical immunoassay, and the antioxidant activity measurement based on luminol electrochemiluminescence (ECL), can be performed using portable devices, which would prove useful for individual-based diagnosis using saliva samples.

Investigation and comparison of graphene nanoribbon and carbon nanotube based SARS-CoV-2 detection sensors: An ab initio study

The rapid detection of SARS-CoV-2, the pathogen of the Covid-19 pandemic, is obviously of great importance for stopping the spread of the virus by detecting infected individuals. Here, we report the ab initio analysis results of graphene nanoribbon (GNR) and carbon nanotube (CNT) based SARS-CoV-2 detection sensors which are experimentally demonstrated in the literature. The investigated structures are the realistic molecular models of the sensors that are employing 1-pyrenebutyric acid N-hydroxysuccinimide ester as the antibody linker. Density functional theory in conjunction with non-equilibrium Green's function formalism (DFT-NEGF) is used to obtain the transmission spectra, current-voltage and resistance-voltage characteristics of the sensors before and after the attachment of the SARS-CoV-2 spike protein. The operation mechanism of the GNR and CNT based SARS-CoV-2 sensors are exposed using the transmission spectrum analysis. Moreover, it is observed that GNR based sensor has more definitive detection characteristics compared to its CNT based counterpart.

Label-free impedimetric immunosensor for point-of-care detection of COVID-19 antibodies

The COVID-19 pandemic has posed enormous challenges for existing diagnostic tools to detect and monitor pathogens. Therefore, there is a need to develop point-of-care (POC) devices to perform fast, accurate, and accessible diagnostic methods to detect infections and monitor immune responses. Devices most amenable to miniaturization and suitable for POC applications are biosensors based on electrochemical detection. We have developed an impedimetric immunosensor based on an interdigitated microelectrode array (IMA) to detect and monitor SARS-CoV-2 antibodies in human serum. Conjugation chemistry was applied to functionalize and covalently immobilize the spike protein (S-protein) of SARS-CoV-2 on the surface of the IMA to serve as the recognition layer and specifically bind anti-spike antibodies. Antibodies bound to the S-proteins in the recognition layer result in an increase in capacitance and a consequent change in the impedance of the system. The impedimetric immunosensor is label-free and uses non-Faradaic impedance with low nonperturbing AC voltage for detection. The sensitivity of a capacitive immunosensor can be enhanced by simply tuning the ionic strength of the sample solution. The device exhibits an LOD of 0.4 BAU/ml, as determined from the standard curve using WHO IS for anti-SARS-CoV-2 immunoglobulins; this LOD is similar to the corresponding LODs reported for all validated and established commercial assays, which range from 0.41 to 4.81 BAU/ml. The proof-of-concept biosensor has been demonstrated to detect anti-spike antibodies in sera from patients infected with COVID-19 within 1 h. Photolithographically microfabricated interdigitated microelectrode array sensor chips & label-free impedimetric detection of COVID-19 antibody.

Achieving broad availability of SARS-CoV-2 detections via smartphone-based analysis

With the development of COVID-19, widely available tests are in great demand. Naked-eye SARS-CoV-2 test kits have recently been developed as home tests, but their sensitivity and accuracy are sometimes limited. Smartphones can convert various signals into digital information, potentially improving the sensitivity and accuracy of these home tests. Herein, we summarize smartphone-based detections for SARS-CoV-2. Optical detections of non-nucleic acids using various sensors and portable imaging systems, as well as nucleic acid analyses based on LAMP, CRISP, CATCH, and biosensors are discussed. Furthermore, different electrochemical detections were compared. We show results obtained using relatively complex equipment, complicated programming procedures, or custom smartphone apps, and describe methods for obtaining information with only simple setups and free software on smartphones. Then, the combined costs of typical smartphone-based detections are evaluated. Finally, the prospect of improving smartphone-based strategies to achieve broad availability of SARS-CoV-2 detection is proposed.

Amplification Free Detection of SARS-CoV-2 Using Multi-Valent Binding

We present the development of electrochemical impedance spectroscopy (EIS)-based biosensors for sensitive detection of SARS-CoV-2 RNA using multi-valent binding. By increasing the number of probe-target binding events per target molecule, multi-valent binding is a viable strategy for improving the biosensor performance. As EIS can provide sensitive and label-free measurements of nucleic acid targets during probe-target hybridization, we used multi-valent binding to build EIS biosensors for targeting SARS-CoV-2 RNA. For developing the biosensor, we explored two different approaches including probe combinations that individually bind in a single-valent fashion and the probes that bind in a multi-valent manner on their own. While we found excellent biosensor performance using probe combinations, we also discovered unexpected signal suppression. We explained the signal suppression theoretically using inter- and intra-probe hybridizations which confirmed our experimental findings. With our best probe combination, we achieved a LOD of 182 copies/μL (303 aM) of SARS-CoV-2 RNA and used these for successful evaluation of patient samples for COVID-19 diagnostics. We were also able to show the concept of multi-valent binding with shorter probes in the second approach. Here, a 13-nt-long probe has shown the best performance during SARS-CoV-2 RNA binding. Therefore, multi-valent binding approaches using EIS have high utility for direct detection of nucleic acid targets and for point-of-care diagnostics.

Colorimetric Detection of SARS-CoV-2 Using Plasmonic Biosensors and Smartphones

Low-cost, instrument-free colorimetric tests were developed to detect SARS-CoV-2 using plasmonic biosensors with Au nanoparticles functionalized with polyclonal antibodies (f-AuNPs). Intense color changes were noted with the naked eye owing to plasmon coupling when f-AuNPs form clusters on the virus, with high sensitivity and a detection limit of 0.28 PFU mL-1 (PFU stands for plaque-forming units) in human saliva. Plasmon coupling was corroborated with computer simulations using the finite-difference time-domain (FDTD) method. The strategies based on preparing plasmonic biosensors with f-AuNPs are robust to permit SARS-CoV-2 detection via dynamic light scattering and UV-vis spectroscopy without interference from other viruses, such as influenza and dengue viruses. The diagnosis was made with a smartphone app after processing the images collected from the smartphone camera, measuring the concentration of SARS-CoV-2. Both image processing and machine learning algorithms were found to provide COVID-19 diagnosis with 100% accuracy for saliva samples. In subsidiary experiments, we observed that the biosensor could be used to detect the virus in river waters without pretreatment. With fast responses and requiring small sample amounts (only 20 μL), these colorimetric tests can be deployed in any location within the point-of-care diagnosis paradigm for epidemiological control.

Recent Developments in Electrochemical-Impedimetric Biosensors for Virus Detection

Viruses, including influenza viruses, MERS-CoV (Middle East respiratory syndrome coronavirus), SARS-CoV (severe acute respiratory syndrome coronavirus), HAV (Hepatitis A virus), HBV (Hepatitis B virus), HCV (Hepatitis C virus), HIV (human immunodeficiency virus), EBOV (Ebola virus), ZIKV (Zika virus), and most recently SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2), are responsible for many diseases that result in hundreds of thousands of deaths yearly. The ongoing outbreak of the COVID-19 disease has raised a global concern and intensified research on the detection of viruses and virus-related diseases. Novel methods for the sensitive, rapid, and on-site detection of pathogens, such as the recent SARS-CoV-2, are critical for diagnosing and treating infectious diseases before they spread and affect human health worldwide. In this sense, electrochemical impedimetric biosensors could be applied for virus detection on a large scale. This review focuses on the recent developments in electrochemical-impedimetric biosensors for the detection of viruses.

Current trends in COVID-19 diagnosis and its new variants in physiological fluids: Surface antigens, antibodies, nucleic acids, and RNA sequencing

Rapid, highly sensitive, and accurate virus circulation monitoring techniques are critical to limit the spread of the virus and reduce the social and economic burden. Therefore, point-of-use diagnostic devices have played a critical role in addressing the outbreak of COVID-19 (SARS-CoV-2) viruses. This review provides a comprehensive overview of the current techniques developed for the detection of SARS-CoV-2 in various body fluids (e.g., blood, urine, feces, saliva, tears, and semen) and considers the mutations (i.e., Alpha, Beta, Gamma, Delta, Omicron). We classify and comprehensively discuss the detection methods depending on the biomarker measured (i.e., surface antigen, antibody, and nucleic acid) and the measurement techniques such as lateral flow immunoassay (LFIA), enzyme-linked immunosorbent assay (ELISA), reverse transcriptase-polymerase chain reaction (RT-PCR), reverse transcription loop-mediated isothermal amplification (RT-LAMP), microarray analysis, clustered regularly interspaced short palindromic repeats (CRISPR) and biosensors. Finally, we addressed the challenges of rapidly identifying emerging variants, detecting the virus in the early stages of infection, the detection sensitivity, selectivity, and specificity, and commented on how these challenges can be overcome in the future.

An alternative ready-to-use electrochemical immunosensor for point-of-care COVID-19 diagnosis using graphene screen-printed electrodes coupled with a 3D-printed portable potentiostat

A severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a cause of worldwide Coronavirus 2019 (COVID-19) disease pandemic. It is thus important to develop ultra-sensitive, rapid and easy-to-use methods for the identification of COVID-19 infected patients. Herein, an alternative electrochemical immunosensor based on poly(pyrrolepropionic acid) (pPPA) modified graphene screen-printed electrode (GSPE) was proposed for rapid COVID-19 detection. The method was based on a competitive enzyme immunoassay process utilizing horseradish peroxidase (HRP)-conjugated SARS-CoV-2 as a reporter binding molecule to compete binding with antibody against the SARS-CoV-2 receptor binding domain (SARS-CoV-2 RBD) protein. This strategy enhanced the current signal via the enzymatic reaction of HRP-conjugated SARS-CoV-2 RBD antibody on the electrode surface. The modification, immobilization, blocking, and detection processes were optimized and evaluated by amperometry. The quantitative analysis of SARS-CoV-2 was conducted based on competitive enzyme immunoassay with amperometric detection using a 3D-printed portable potentiostat for point-of-care COVID-19 diagnosis. The current measurements at -0.2 V yielded a calibration curve with a linear range of 0.01-1500 ng mL^-1 (r² = 0.983), a low detection limit of 2 pg mL^-1 and a low quantification limit of 10 pg mL^-1. In addition, the analyzed results of practical samples using the developed method were successfully verified with ELISA and RT-PCR. Therefore, the proposed portable electrochemical immunosensor is highly sensitive, rapid, and reliable. Thus, it is an alternative ready-to-use sensor for COVID-19 point-of-care diagnosis.

Directly immersible silicon photonic probes: Application to rapid SARS-CoV-2 serological testing

Silicon photonic probes based on broad-band Mach-Zehnder interferometry are explored for the first time as directly immersible immunosensors alleviating the need for microfluidics and pumps. Each probe includes two U-shaped waveguides allowing light in- and out-coupling from the same chip side through a bifurcated fiber and a mechanical coupler. At the opposite chip side, two Mach-Zehnder interferometers (MZI) are located enabling real-time monitoring of binding reactions by immersion of this chip side into a sample. The sensing arm windows of the two MZIs have different length resulting in two distinct peaks in the Fourier domain, the phase shift of which can be monitored independently through Fast Fourier Transform of the output spectrum. The photonic probes analytical potential was demonstrated through detection of antibodies against SARS-CoV-2 in human serum samples. For this, one MZI was functionalized with the Receptor Binding Domain (RBD) of SARS-CoV-2 Spike 1 protein, and the other with bovine serum albumin to serve as reference. The biofunctionalized probes were immersed for 10 min in human serum sample and then for 5 min in goat anti-human IgG Fc specific antibody solution. Using a humanized rat antibody against SARS-CoV-2 RBD, a detection limit of 20 ng/mL was determined. Analysis of human serum samples indicated that the proposed sensor discriminated completely non-infected/non-vaccinated from vaccinated individuals, and the antibodies levels determined correlated well with those determined in the same samples by ELISA. These results demonstrated the potential of the proposed sensor to serve as an efficient tool for expeditious point-of-care testing.

Bipolar silica nanochannel array confined electrochemiluminescence for ultrasensitive detection of SARS-CoV-2 antibody

Ultrasensitive, specific, and early identification of Coronavirus Disease (2019) (COVID-19) infection is critical to control virus spread and remains a global public health problem. Herein, we present a novel solid-state electrochemiluminescence (ECL) platform targeting severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibody with rapidity and ultrahigh sensitivity, in which a bipolar silica nanochannel array (bp-SNA) is fabricated on indium tin oxide (ITO) electrode for the first time to stably confine the ECL probe of tris(2,2'-bipyridyl) ruthenium (Ru(bpy)₃²⁺) under dual electrostatic force. The bp-SNA consists of tightly packed bilayer silica nanochannel array (SNA) with asymmetric surface charges, namely an inner negatively charged SNA (n-SNA) and an outer positively charged SNA (p-SNA), serving as an "electrostatic lock" to enrich and stabilize the cationic Ru(bpy)₃²⁺ probe without leakage from the electrode surface. The detection of SARS-CoV-2 IgG antibody could be realized via immobilization of SARS-CoV-2 spike protein on the utmost of Ru(bpy)₃²⁺-confined solid-state ECL platform (Ru@bp-SNA). Upon the capture of target SARS-CoV-2 IgG by immune recognition, the formed immunocomplex will block the nanochannel, leading to the hindered diffusion of the co-reactant (tri-n-propylamine, TPrA) and further producing a decreased ECL signal. The developed solid-stated ECL immunosensor is able to determine SARS-CoV-2 IgG with a wide linear range (5 pg mL^-1 to 1 μg mL^-1), a low limit-of-detection (2.9 pg mL^-1), and a short incubation time (30 min). Furthermore, accurate analysis of SARS-CoV-2 IgG in real serum samples is also obtained by the sensor.

Novel approach based on GQD-PHB as anchoring platform for the development of SARS-CoV-2 electrochemical immunosensor

In the present work, we report an innovative approach for immunosensors construction. The experimental strategy is based on the anchoring of biological material at screen-printed carbon electrode (SPE) modified with electrodeposited Graphene Quantum Dots (GQD) and polyhydroxybutyric acid (PHB). It was used as functional substract basis for the recognition site receptor-binding domain (RBD) from coronavirus spike protein (SARS-CoV-2), for the detection of Anti-S antibodies (AbS). SEM images and EDS spectra suggest an interaction of the protein with GQD-PHB sites at the electrode surface. Differential pulse voltametric (DPV) measurements were performed before and after incubation, in presence of the target, shown a decrease in voltametric signal of an electrochemical probe ([Fe(CN)₆]^3/4-). Using the optimal experimental conditions, analytical curves were performed in PBS and human serum spiked with AbS showing a slight matrix effect and a relationship between voltametric signal and AbS concentration in the range of 100 ng mL^-1 and 10 μg mL^-1. The selectivity of the proposed sensor was tested against yellow fever antibodies (YF) and the selective layer on the electrode surface did not interact with these unspecific antibodies. Eight samples of blood serum were analyzed and 87.5% of these total investigated provided adequate results. In addition, the present approach showed better results against traditional EDC/NHS reaction with enhancements in time and the possibility to develop an immunosensor in a single drop, since the proteins can be anchored prior to the electrode modification step.

A comparison of conventional and advanced electroanalytical methods to detect SARS-CoV-2 virus: A concise review

Respiratory viruses are a serious threat to human wellbeing that can cause pandemic disease. As a result, it is critical to identify virus in a timely, sensitive, and precise manner. The present novel coronavirus-2019 (COVID-19) disease outbreak has increased these concerns. The research of developing various methods for COVID-19 virus identification is one of the most rapidly growing research areas. This review article compares and addresses recent improvements in conventional and advanced electroanalytical approaches for detecting COVID-19 virus. The popular conventional methods such as polymerase chain reaction (PCR), loop mediated isothermal amplification (LAMP), serology test, and computed tomography (CT) scan with artificial intelligence require specialized equipment, hours of processing, and specially trained staff. Many researchers, on the other hand, focused on the invention and expansion of electrochemical and/or bio sensors to detect SARS-CoV-2, demonstrating that they could show a significant role in COVID-19 disease control. We attempted to meticulously summarize recent advancements, compare conventional and electroanalytical approaches, and ultimately discuss future prospective in the field. We hope that this review will be helpful to researchers who are interested in this interdisciplinary field and desire to develop more innovative virus detection methods.

Label-free electrochemical immunosensor for highly sensitive COVID-19 spike protein detection

The ongoing coronavirus pandemic responsible for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has rapidly increased the rate of global death and infections due to variant mutations (such as Delta and Omicron). While specifically developed and approved vaccines can limit the spread of disease in a population and severity of resulting symptoms, none have been demonstrated to effectively prevent infection altogether. Thus, reliable early diagnosis of COVID-19 is critical to identify positive cases to help contain the outbreak. Herein we report a label-free electrochemical immunosensor for rapid diagnosis of COVID-19 by using nitrogen-doped holey graphene (N-HRGO) as a nanocarrier decorated with thionine (TH) molecules as electrochemical indicators. With the spike protein located on the surface of the COVID-19 particles as the model target, the as-prepared electrochemical immunosensor could detect the presence of the COVID-19 spike protein over a wide linear range (1 pg mL^-1-10 ng mL^-1) with a low detection limit (0.3 pg mL^-1). In addition, the developed electrochemical immunosensor exhibited an excellent selectivity (with insignificant current changes towards interfering proteins comparing with COVID-19 spike protein), a good reproducibility and long-term storage stability. Importantly, the electrochemical immunosensor thus developed could successfully and reliably detect the spike protein of COVID-19 in saliva and human serum complex samples. Thus, the as-prepared label-free electrochemical immunosensor can achieve rapid and sensitive detection of the COVID-19 spike protein, as a promising clinical diagnosis tool in monitoring the progression of COVID-19.

A novel delayed lateral flow immunoassay for enhanced detection of SARS-CoV-2 spike antigen

A new detection strategy was developed to improve the sensitivity of a lateral flow immunoassay platform utilizing a delayed hydrophobic barrier fabricated with trimethylsilyl cellulose (TMSC). The SARS-CoV-2 spike receptor-binding domain (SARS-CoV-2 SP RBD) antigen was chosen as a model analyte to demonstrate the superior detectability of this scheme. The novel device consists of 2 separate layers, so-called delayed lateral flow immunoassay (d-LFIA). The upper layer is intended for the analyte or sample flow path, where the test solution flows freely straight to the detection zone to bind with the primary antibody. The lower layer, located just underneath, is designed for the SARS-CoV-2 spike receptor-binding domain-conjugated gold nanoparticles (SARS-CoV-2 SP RBD-AuNPs) used for producing a colorimetric signal. This layer is fabricated with a TMSC barrier to time-delay the movement of SARS-CoV-2 SP RBD-AuNPs, thus allowing the antigen to bind with the primary antibody more efficiently. This platform exhibited a 2.6-fold enhancement in the sensitivity and 9.1-fold improvement in the limit of detection (LOD) as compared with the conventional LFIA. In addition, this d-LFIA device was satisfactorily applied to accurate screening of COVID-19 patients.

Point-of-care electrochemical testing of biomarkers involved in inflammatory and inflammatory-associated medical conditions

Recent years have shown that the diagnosis and monitoring of biomarkers involved in inflammatory-associated medical conditions such as cancer, neurological disorders, viral infections, or daily physical activities offer real benefits in increasing the quality of medical care and patient life quality. In this context, the use of integrated and portable platforms as point-of-care testing devices for biomedical analysis to enable early disease diagnosis and monitoring, which can be successfully used even at the patient's bed, is an emergency nowadays. The development of low-cost, miniaturized, and portable, user-friendly devices that provide an answer in a timely manner, such as electrochemical sensors, is relevant for the elaboration of point-of-care testing devices. This review focuses on the recent progress in bioanalysis of both specific biomarkers and inflammatory-associated biomarkers present in several diseases like neoplasia, severe neurological disorders, viral infections, and usual physical activity and provides an overview of the state of the art over the most recent electrochemical (bio)sensors for the detection of inflammation-related biomarkers. Future perspectives of point-of-care testing to improve healthcare management are also discussed.

Improving immunoassay detection accuracy of anti-SARS-CoV-2 antibodies through dual modality validation

A novel test strategy is proposed with dual-modality detection techniques for COVID-19 antibody detection. The full-length S protein of SARS-CoV-2 was chemically immobilized on a glass surface to capture anti-SARS-CoV-2 IgG in patient serum and was detected through either Electrochemical Impedance Spectroscopy (EIS) or fluorescence imaging with labeled secondary antibodies. Gold nanoparticles conjugated with protein G were used as the probe and the bound GNP-G was detected through EIS measurements. Anti-human-IgG conjugated with the fluorescent tag Alexa Fluor 488 was used as the probe for fluorescence imaging. Clinical SARS-CoV-2 IgG positive serum and negative controls were used to validate both modalities. For fluorescence-based detection, a high sensitivity was noticed with a quantification range of 0.01-0.1 A.U.C. and a LOD of 0.004 A.U.C. This study demonstrates the possibility of utilizing different measurement techniques in conjunction for improved COVID-19 serology testing.

Diagnosis Methods for COVID-19: A Systematic Review

At the end of 2019, the coronavirus appeared and spread extremely rapidly, causing millions of infections and deaths worldwide, and becoming a global pandemic. For this reason, it became urgent and essential to find adequate tests for an accurate and fast diagnosis of this disease. In the present study, a systematic review was performed in order to provide an overview of the COVID-19 diagnosis methods and tests already available, as well as their evolution in recent months. For this purpose, the Science Direct, PubMed, and Scopus databases were used to collect the data and three authors independently screened the references, extracted the main information, and assessed the quality of the included studies. After the analysis of the collected data, 34 studies reporting new methods to diagnose COVID-19 were selected. Although RT-PCR is the gold-standard method for COVID-19 diagnosis, it cannot fulfill all the requirements of this pandemic, being limited by the need for highly specialized equipment and personnel to perform the assays, as well as the long time to get the test results. To fulfill the limitations of this method, other alternatives, including biological and imaging analysis methods, also became commonly reported. The comparison of the different diagnosis tests allowed to understand the importance and potential of combining different techniques, not only to improve diagnosis but also for a further understanding of the virus, the disease, and their implications in humans.

Impedimetric Detection Based on Label-Free Immunoassay Developed for Targeting Spike S1 Protein of SARS-CoV-2

After the COVID-19 pandemic started all over the world, great importance was placed on the development of sensitive and selective bioanalytical assays for the rapid detection of the highly pathogenic SARS-CoV-2 virus causing COVID-19 disease. In this present work, an impedimetric immunosensor was developed and applied for rapid, reliable, sensitive and selective detection of the SARS-CoV-2 S1 protein. To detect the SARS-CoV-2 virus, targeting of the spike S1 protein was achieved herein by using S1 protein-specific capture antibody (Cab-S1) immobilized screen-printed electrode (SPE) in combination with the electrochemical impedance spectroscopy (EIS) technique. With the impedimetric immunosensor, the detection limit for S1 protein in buffer medium was found to be 0.23 ng/mL (equal to 23.92 amol in 8 µL sample) in the linear concentration range of S1 protein from 0.5 to 10 ng/mL. In the artificial saliva medium, it was found to be 0.09 ng/mL (equals to 9.36 amol in 8 µL sample) in the linear concentration range of S1 protein between 0.1 and 1 ng/mL. The selectivity of the impedimetric immunosensor toward S1 protein was tested against influenza hemagglutinin antigen (HA) in the buffer medium as well as in artificial saliva.

Performance of electrochemical immunoassays for clinical diagnostics of SARS-CoV-2 based on selective nucleocapsid N protein detection: Boron-doped diamond, gold and glassy carbon evaluation

The 21st century has already brought us a plethora of new threats related to viruses that emerge in humans after zoonotic transmission or drastically change their geographic distribution or prevalence. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was first spotted at the end of 2019 to rapidly spread in southwest Asia and later cause a global pandemic, which paralyzes the world since then. We have designed novel immunosensors targeting conserved protein sequences of the N protein of SARS-CoV-2 based on lab-produced and purified anti-SARS-CoV-2 nucleocapsid antibodies that are densely grafted onto various surfaces (diamond/gold/glassy carbon). Titration of antibodies shows very strong reactions up to 1:72 900 dilution. Next, we showed the mechanism of interactions of our immunoassay with nucleocapsid N protein revealing molecular recognition by impedimetric measurements supported by hybrid modeling results with both density functional theory and molecular dynamics methods. Biosensors allowed for a fast (in less than 10 min) detection of SARS-CoV-2 virus with a limit of detection from 0.227 ng/ml through 0.334 ng/ml to 0.362 ng/ml for glassy carbon, boron-doped diamond, and gold surfaces, respectively. For all tested surfaces, we obtained a wide linear range of concentrations from 4.4 ng/ml to 4.4 pg/ml. Furthermore, our sensor leads to a highly specific response to SARS-CoV-2 clinical samples versus other upper respiratory tract viruses such as influenza, respiratory syncytial virus, or Epstein-Barr virus. All clinical samples were tested simultaneously on biosensors and real-time polymerase chain reactions.

Recent advances in airborne pathogen detection using optical and electrochemical biosensors

The world is currently facing an adverse condition due to the pandemic of airborne pathogen SARS-CoV-2. Prevention is better than cure; thus, the rapid detection of airborne pathogens is necessary because it can reduce outbreaks and save many lives. Considering the immense role of diverse detection techniques for airborne pathogens, proper summarization of these techniques would be beneficial for humans. Hence, this review explores and summarizes emerging techniques, such as optical and electrochemical biosensors used for detecting airborne bacteria (Bacillus anthracis, Mycobacterium tuberculosis, Staphylococcus aureus, and Streptococcus pneumoniae) and viruses (Influenza A, Avian influenza, Norovirus, and SARS-CoV-2). Significantly, the first section briefly focuses on various diagnostic modalities applied toward airborne pathogen detection. Next, the fabricated optical biosensors using various transducer materials involved in colorimetric and fluorescence strategies for infectious pathogen detection are extensively discussed. The third section is well documented based on electrochemical biosensors for airborne pathogen detection by differential pulse voltammetry, cyclic voltammetry, square-wave voltammetry, amperometry, and impedance spectroscopy. The unique pros and cons of these modalities and their future perspectives are addressed in the fourth and fifth sections. Overall, this review inspected 171 research articles published in the last decade and persuaded the importance of optical and electrochemical biosensors for airborne pathogen detection.

A Low-Cost Handheld Impedimetric Biosensing System for Rapid Diagnostics of SARS-CoV-2 Infections

Current laboratory diagnostic approaches for virus detection give reliable results, but they require a lengthy procedure, trained personnel, and expensive equipment and reagents; hence, they are not a suitable choice for home monitoring purposes. This paper addresses this challenge by developing a portable impedimetric biosensing system for the identification of COVID-19 patients. This sensing system has two main parts: a throwaway two-working electrode (2-WE) strip and a novel read-out circuit, specifically designed for simultaneous signal acquisition from both working electrodes. Highly reliable electrochemical signal tracking from multiplex immunosensors provides a potential for flexible and portable multi-biomarker detection. The electrodes' surfaces were functionalized with SARS-CoV-2 Nucleocapsid Antibody enabling the selective detection of Nucleocapsid protein (N-protein) along with self-validation in the clinical nasopharyngeal swab specimens. The proposed programmable highly sensitive impedance read-out system allows for a wide dynamic detection range, which makes the sensor capable of detecting N-protein concentrations between 0.116 and 10,000 pg/mL. This lightweight and economical read-out arrangement is an ideal prospect for being mass-produced, especially during urgent pandemic situations. Also, such an impedimetric sensing platform has the potential to be redesigned for targeting not only other infectious diseases but also other critical disorders.

A gold nanoparticle-protein G electrochemical affinity biosensor for the detection of SARS-CoV-2 antibodies: a surface modification approach

As COVID-19 waves continue to spread worldwide, demand for a portable, inexpensive and convenient biosensor to determine community immune/infection status is increasing. Here we describe an impedance-based affinity biosensor using Interdigitated Electrode (IDE) arrays to detect antibodies to SARS-CoV-2 in serum. We created the biosensor by functionalizing the IDEs' surface with abaculaovirus-expressed and purified Spike (S) protein to bind anti-SARS CoV-2antibodies. Gold nanoparticles (GNP) fused to protein G were used to probe for bound antibodies. An ELISA assay using horseradish peroxidase-protein G to probe for bound IgG confirmed that the purified S protein bound a commercial source of anti-SARS-CoV-2 antibodies specifically and bound anti-SARS-CoV-2 antibodies in COVID-19 positive serum. Then we demonstrated that our biosensor could detect anti-SARS-CoV-2 antibodies with 72% sensitivity in 2 h. Using GNP-protein G, the affinity biosensor had increased impedance changes with COVID-19positive serum and minimal or decreased impedance changes with negative serum. This demonstrated that our biosensor could discriminate between COVID-19 positive and negative sera, which were further improved using poly(vinyl alcohol)as a blocking agent.

Smart Immunosensors for Point-of-Care Serological Tests Aimed at Assessing Natural or Vaccine-Induced SARS-CoV-2 Immunity

Innovative and highly performing smart voltammetric immunosensors for rapid and effective serological tests aimed at the determination of SARS-CoV-2 antibodies were developed and validated in human serum matrix. Two immunosensors were developed for the determination of immunoglobulins directed against either the nucleocapsid or the spike viral antigen proteins. The immunosensors were realized using disposable screen-printed electrodes modified with nanostructured materials for the immobilization of the antigens. Fast quantitative detection was achieved, with analysis duration being around 1 h. Signal readout was carried out through a smart, compact and battery-powered potentiostat, based on a Wi-Fi protocol and devised for the Internet of Things (IoT) paradigm. This device is used for the acquisition, storage and sharing of clinical data. Outstanding immunosensors' sensitivity, specificity and accuracy (100%) were assessed, according to the diagnostic guidelines for epidemiological data. The overall performance of the sensing devices, combined with the portability of the IoT-based device, enables their suitability as a high-throughput diagnostic tool. Both of the immunosensors were validated using clinical human serum specimens from SARS-CoV-2 infected patients, provided by IRCCS Ospedale San Raffaele.

Progress in Electrochemical Biosensing of SARS-CoV-2 Virus for COVID-19 Management

Rapid and early diagnosis of lethal coronavirus disease-19 (COVID-19) caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is an important issue considering global human health, economy, education, and other activities. The advancement of understanding of the chemistry/biochemistry and the structure of the SARS-CoV-2 virus has led to the development of low-cost, efficient, and reliable methods for COVID-19 diagnosis over “gold standard” real-time reverse transcription-polymerase chain reaction (RT-PCR) due to its several limitations. This led to the development of electrochemical sensors/biosensors for rapid, fast, and low-cost detection of the SARS-CoV-2 virus from the patient’s biological fluids by detecting the components of the virus, including structural proteins (antigens), nucleic acid, and antibodies created after COVID-19 infection. This review comprehensively summarizes the state-of-the-art research progress of electrochemical biosensors for COVID-19 diagnosis. They include the detection of spike protein, nucleocapsid protein, whole virus, nucleic acid, and antibodies. The review also outlines the structure of the SARS-CoV-2 virus, different detection methods, and design strategies of electrochemical SARS-CoV-2 biosensors by highlighting the current challenges and future perspectives.

A Review on Potential Electrochemical Point-of-Care Tests Targeting Pandemic Infectious Disease Detection: COVID-19 as a Reference

Fast and accurate point-of-care testing (POCT) of infectious diseases is crucial for diminishing the pandemic miseries. To fight the pandemic coronavirus disease 2019 (COVID-19), numerous interesting electrochemical point-of-care (POC) tests have been evolved to rapidly identify the causal organism SARS-CoV-2 virus, its nucleic acid and antigens, and antibodies of the patients. Many of those electrochemical biosensors are impressive in terms of miniaturization, mass production, ease of use, and speed of test, and they could be recommended for future applications in pandemic-like circumstances. On the other hand, self-diagnosis, sensitivity, specificity, surface chemistry, electrochemical components, device configuration, portability, small analyzers, and other features of the tests can yet be improved. Therefore, this report reviews the developmental trend of electrochemical POC tests (i.e., test platforms and features) reported for the rapid diagnosis of COVID-19 and correlates any significant advancements with relevant references. POCTs incorporating microfluidic/plastic chips, paper devices, nanomaterial-aided platforms, smartphone integration, self-diagnosis, and epidemiological reporting attributes are also surfed to help with future pandemic preparedness. This review especially screens the low-cost and easily affordable setups so that management of pandemic disease becomes faster and easier. Overall, the review is a wide-ranging package for finding appropriate strategies of electrochemical POCT targeting pandemic infectious disease detection.

A Biosensor Platform for Point-of-Care SARS-CoV-2 Screening

The COVID-19 pandemic remains a constant threat to human health, the economy, and social relations. Scientists around the world are constantly looking for new technological tools to deal with the pandemic. Such tools are the rapid virus detection tests, which are constantly evolving and optimizing. This paper presents a biosensor platform for the rapid detection of spike protein both in laboratory conditions and in swab samples from hospitalized patients. It is a continuation and improvement of our previous work and consists of a microcontroller-based readout circuit, which measures the capacitance change generated in an interdigitated electrode transducer by the presence either of sole spike protein or the presence of SARS-CoV-2 particles in swab samples. The circuit efficiency is calibrated by its correlation with the capacitance measurement of an LCR (inductance (L), capacitance (C), and resistance (R)) meter. The test result is made available in less than 2 min through the microcontroller’s LCD (liquid-crystal display) screen, whereas at the same time, the collected data are sent wirelessly to a mobile application interface. The novelty of this research lies in the potential it offers for continuous and effective screening of SARS-CoV-2 patients, which is facilitated and enhanced, providing big data statistics of COVID-19 in terms of space and time. This device can be used by individuals for SARS-CoV-2 testing at home, by health professionals for patient monitoring, and by public health agencies for monitoring the spatio-temporal spread of the virus.

Debulking different Corona (SARS-COV-2 delta, omicron, OC43) and influenza (H1N1, H3N2) virus strains by plant viral trap proteins in chewing gums to decrease infection and transmission

Because oral transmission of SARS-CoV-2 is 3–5 orders of magnitude higher than nasal transmission, we investigated debulking of oral viruses using viral trap proteins (CTB-ACE2, FRIL) expressed in plant cells, delivered through the chewing gum. In omicron nasopharyngeal (NP) samples, the microbubble count (based on N-antigen) was significantly reduced by 20 μg of FRIL (p < 0.0001) and 0.925 μg of CTB-ACE2 (p = 0.0001). Among 20 delta or omicron NP samples, 17 had virus load reduced below the detection level of spike protein in the RAPID assay, after incubation with the CTB-ACE2 gum powder. A dose-dependent 50% plaque reduction with 50–100 ng FRIL or 600–800 μg FRIL gum against Influenza strains H1N1, H3N2, and Coronavirus HCoV-OC43 was observed with both purified FRIL, lablab bean powder or gum. In electron micrographs, large/densely packed clumps of overlapping influenza particles and FRIL protein were observed. Chewing simulator studies revealed that CTB-ACE2 release was time/dose-dependent and release was linear up to 20 min chewing. Phase I/II placebo-controlled, double-blinded clinical trial (IND 154897) is in progress to evaluate viral load in saliva before or after chewing CTB-ACE2/placebo gum. Collectively, this study advances the concept of chewing gum to deliver proteins to debulk oral viruses and decrease infection/transmission.

Utilizing Electrochemical-Based Sensing Approaches for the Detection of SARS-CoV-2 in Clinical Samples: A Review

The development of precise and efficient diagnostic tools enables early treatment and proper isolation of infected individuals, hence limiting the spread of coronavirus disease 2019 (COVID-19). The standard diagnostic tests used by healthcare workers to diagnose severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection have some limitations, including longer detection time, the need for qualified individuals, and the use of sophisticated bench-top equipment, which limit their use for rapid SARS-CoV-2 assessment. Advances in sensor technology have renewed the interest in electrochemical biosensors miniaturization, which provide improved diagnostic qualities such as rapid response, simplicity of operation, portability, and readiness for on-site screening of infection. This review gives a condensed overview of the current electrochemical sensing platform strategies for SARS-CoV-2 detection in clinical samples. The fundamentals of fabricating electrochemical biosensors, such as the chosen electrode materials, electrochemical transducing techniques, and sensitive biorecognition molecules, are thoroughly discussed in this paper. Furthermore, we summarised electrochemical biosensors detection strategies and their analytical performance on diverse clinical samples, including saliva, blood, and nasopharyngeal swab. Finally, we address the employment of miniaturized electrochemical biosensors integrated with microfluidic technology in viral electrochemical biosensors, emphasizing its potential for on-site diagnostics applications.

Electrochemical Impedance-Based Biosensors for the Label-Free Detection of the Nucleocapsid Protein from SARS-CoV-2

Diagnosis of coronavirus disease (COVID-19) is important because of the emergence and global spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Real-time polymerase chain reaction (PCR) is widely used to diagnose COVID-19, but it is time-consuming and requires sending samples to test centers. Thus, the need to detect antigens for rapid on-site diagnosis rather than PCR is increasing. We quantified the nucleocapsid (N) protein in SARS-CoV-2 using an electro-immunosorbent assay (El-ISA) and a multichannel impedance analyzer with a 96-interdigitated microelectrode sensor (ToAD). The El-ISA measures impedance signals from residual detection antibodies after sandwich assays and thus offers highly specific, label-free detection of the N protein with low cross-reactivity. The ToAD sensor enables the real-time electrochemical detection of multiple samples in conventional 96-well plates. The limit of detection for the N protein was 0.1 ng/mL with a detection range up to 10 ng/mL. This system did not detect signals for the S protein. While this study focused on detecting the N protein in SARS-CoV-2, our system can also be widely applicable to detecting various biomolecules involved in antigen-antibody interactions.

Quantification of a COVID-19 Antibody Assay Using a Lateral Flow Test and a Cell Phone

Although several biomedical assays have been developed to screen for antibodies against SARS-CoV-2, very few can be completed without drawing blood. We developed a rapid lateral flow screening tool that used saliva samples and yielded rapid results that could be quantified using a cell phone. This assay provided the sensitive detection of IgG antibodies against SARS-CoV-2 within 10 min. We started by synthesising, modifying, and characterising gold nanoparticles. Using these particles as a coloured label, we developed a lateral flow strip made of nitrocellulose, glass fibre, and cellulose material. We quantified our visual results using pictures acquired with a cell phone and calculated a limit of detection of 4 ng/mL of antibodies against the SARS-CoV-2 spike protein.

An impedimetric biosensor for COVID-19 serology test and modification of sensor performance via dielectrophoresis force

Coronavirus disease 2019 (COVID-19) has caused significant global morbidity and mortality. The serology test that detects antibodies against the disease causative agent, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has often neglected value in supporting immunization policies and therapeutic decision-making. The ELISA-based antibody test is time-consuming and bulky. This work described a gold micro-interdigitated electrodes (IDE) biosensor for COVID antibody detection based on Electrochemical Impedance Spectroscopy (EIS) responses. The IDE architecture allows easy surface modification with the viral structure protein, Spike (S) protein, in the gap of the electrode digits to selectively capture anti-S antibodies in buffer solutions or human sera. Two strategies were employed to resolve the low sensitivity issue of non-faradic impedimetric sensors and the sensor fouling phenomenon when using the serum. One uses secondary antibody-gold nanoparticle (AuNP) conjugates to further distinguish anti-S antibodies from the non-specific binding and obtain a more significant impedance change. The second strategy consists of increasing the concentration of target antibodies in the gap of IDEs by inducing an AC electrokinetic effect such as dielectrophoresis (DEP). AuNP and DEP methods reached a limit of detection of 200 ng/mL and 2 μg/mL, respectively using purified antibodies in buffer, while the DEP method achieved a faster testing time of only 30 min. Both strategies could qualitatively distinguish COVID-19 antibody-positive and -negative sera. Our work, especially the impedimetric detection of COVID-19 antibodies under the assistance of the DEP force presents a promising path toward rapid, point-of-care solutions for COVID-19 serology tests.

Microfluidic particle dam for direct visualization of SARS-CoV-2 antibody levels in COVID-19 vaccinees

Various COVID-19 vaccines are currently deployed, but their immunization varies and decays with time. Antibody level is a potent correlate to immune protection, but its quantitation relies on intensive laboratory techniques. Here, we report a decentralized, instrument-free microfluidic device that directly visualizes SARS-CoV-2 antibody levels. Magnetic microparticles (MMPs) and polystyrene microparticles (PMPs) can bind to SARS-CoV-2 antibodies simultaneously. In a microfluidic chip, this binding reduces the incidence of free PMPs escaping from magnetic separation and shortens PMP accumulation length at a particle dam. This visual quantitative result enables use in either sensitive mode [limit of detection (LOD): 13.3 ng/ml; sample-to-answer time: 70 min] or rapid mode (LOD: 57.8 ng/ml; sample-to-answer time: 20 min) and closely agrees with the gold standard enzyme-linked immunosorbent assay. Trials on 91 vaccinees revealed higher antibody levels in mRNA vaccinees than in inactivated vaccinees and their decay in 45 days, demonstrating the need for point-of-care devices to monitor immune protection.