Genosensor on gold films with enzymatic electrochemical detection of a SARS virus sequence

Electrochemical biosensor for sensitive detection of SARS-CoV-2 gene fragments using Bi2Se3 topological insulator

In this study, we have designed an electrochemical biosensor based on topological material Bi2Se3 for the sensitive detection of SARS-CoV-2 in the COVID-19 pandemic. Flake-shaped Bi2Se3 was obtained directly from high-quality single crystals using mechanical exfoliation, and the single-stranded DNA was immobilized onto it. Under optimal conditions, the peak current of the differential pulse voltammetry method exhibited a linear relationship with the logarithm of the concentration of target-complementary-stranded DNA, ranging from 1.0 × 10-15 to 1.0 × 10-11 M, with a detection limit of 3.46 × 10-16 M. The topological material Bi2Se3, with Dirac surface states, enhanced the signal-to-interference plus noise ratio of the electrochemical measurements, thereby improving the sensitivity of the sensor. Furthermore, the electrochemical sensor demonstrated excellent specificity in recognizing RNA. It can detect complementary RNA by amplifying and transcribing the initial DNA template, with an initial DNA template concentration ranging from 1.0 × 10-18 to 1.0 × 10-15 M. Furthermore, the sensor also effectively distinguished negative and positive results by detecting splitting-synthetic SARS-CoV-2 pseudovirus with a concentration of 1 copy/μL input. Our work underscores the immense potential of the electrochemical sensing platform based on the topological material Bi2Se3 in the detection of pathogens during the rapid spread of acute infectious diseases.

Nanomaterial-based sensors for microbe detection: a review

Airborne microorganisms pose a significant health threat, causing various illnesses. Traditional detection methods are often slow and complex. This review highlights the potential of nanomaterial-based biosensors, particularly colorimetric sensors, for rapid and on-site detection of airborne microbes. Colorimetric sensors offer real-time visual detection without complex instrumentation. We explore the integration of these sensors with Lab-on-a-Chip technology using PDMS microfluidics. This review also proposes a novel PDMS-based colorimetric biosensor for real-time detection of airborne microbes. The sensor utilizes a color change phenomenon easily observable with the naked eye, simplifying analysis and potentially enabling point-of-care applications.

Dual-Target Additively Manufactured Electrochemical Sensor for the Multiplexed Detection of Protein A29 and DNA of Human Monkeypox Virus

Herein, we present the first 3D-printed electrochemical portable biodevice for the detection of monkeypox virus (MKPV). The electrochemical device consists of two biosensors: an immunosensor and a genosensor specifically designed for the detection of the protein A29 and a target DNA of MKPV, respectively. The electrodes were manufactured using lab-made ultraflexible conductive filaments composed of carbon black, recycled PLA from coffee pods, and castor oil as a plasticizer. The sensors created through 3D printing technology exhibited good reproducibility and repeatability of analytical responses. Furthermore, both the immunosensor and genosensor demonstrated excellent MKPV detection capabilities, with a linear range from 0.01 to 1.0 μmol L-1 for the antigen and 0.1 to 20.0 μmol L-1 for the DNA target. The biosensors achieved limits of detection of 2.7 and 29 nmol L-1 for the immunosensor and genosensor, respectively. Interference tests conducted with the biosensors demonstrated their selectivity for MKPV. Moreover, analyses of fortified human serum samples showed recoveries close to 100%, confirming the absence of significant matrix effects for MKPV analysis. Therefore, the 3D-printed multiplex device represents a viable and highly promising alternative for on-site, portable, and rapid point-of-care MKPV monitoring.

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.

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.

Genosensors as an alternative diagnostic sensing approaches for specific detection of various certain viruses: a review of common techniques and outcomes

Viral infections are responsible for the deaths of millions of people throughout the world. Since outbreak of highly contagious and mutant viruses such as contemporary sars-cov-2 pandemic, has challenged the conventional diagnostic methods, the entity of a thoroughly sensitive, specific, rapid and inexpensive detecting technique with minimum level of false-positivity or -negativity, is desperately needed more than any time in the past decades. Biosensors as minimized devices could detect viruses in simple formats. So far, various nucleic acid, immune- and protein-based biosensors were designed and tested for recognizing the genome, antigen, or protein level of viruses, respectively; however, nucleic acid-based sensing techniques, which is the foundation of constructing genosensors, are preferred not only because of their ultra-sensitivity and applicability in the early stages of infections but also for their ability to differentiate various strains of the same virus. To date, the review articles related to genosensors are just confined to particular pathogenic diseases; In this regard, the present review covers comprehensive information of the research progress of the electrochemical, optical, and surface plasmon resonance (SPR) genosensors that applied for human viruses' diseases detection and also provides a well description of viruses' clinical importance, the conventional diagnosis approaches of viruses and their disadvantages. This review would address the limitations in the current developments as well as the future challenges involved in the successful construction of sensing approaches with the functionalized nanomaterials and also allow exploring into core-research works regarding this area.

An Insight Into Detection Pathways/Biosensors of Highly Infectious Coronaviruses

The outbreak of COVID-19 pandemic and its consequences have inflicted a substantial damage on the world. In this study, it was attempted to review the recent coronaviruses appeared among the human being and their epidemic/pandemic spread throughout the world. Currently, there is an inevitable need for the establishment of a quick and easily available biosensor for tracing COVID-19 in all countries. It has been known that the incubation time of COVID-19 lasts about 14 days and 25% of the infected individuals are asymptomatic. To improve the ability to determine SARS-CoV-2 precisely and reduce the risk of eliciting false-negative results produced by mutating nature of coronaviruses, many researchers have established a real-time reverse transcriptase-polymerase chain reaction (RT-PCR) assay using mismatch-tolerant molecular beacons as multiplex real-time RT-PCR to distinguish between pathogenic and non-pathogenic strains of coronaviruses. The possible mechanisms and pathways for the detection of coronaviruses by biosensors have been reviewed in this study.

Smartphone-Based Biosensor Devices for Healthcare: Technologies, Trends, and Adoption by End-Users

Smart biosensors are becoming an important support for modern healthcare, even more so in the current context. Numerous smartphone-based biosensor developments were published in recent years, some highly effective and sensitive. However, when patents and patent applications related to smart biosensors for healthcare applications are analyzed, it is surprising to note that, after significant growth in the first half of the decade, the number of applications filed has decreased considerably in recent years. There can be many causes of this effect. In this review, we present the state of the art of different types of smartphone-based biosensors, considering their stages of development. In the second part, a critical analysis of the possible reasons why many technologies do not reach the market is presented. Both technical and end-user adoption limitations were addressed. It was observed that smart biosensors on the commercial stage are still scarce despite the great evolution that these technologies have experienced, which shows the need to strengthen the stages of transfer, application, and adoption of technologies by end-users.

Rapid electrochemical detection of COVID-19 genomic sequence with dual-function graphene nanocolloids based biosensor

Discovered in December 2019, the Severe Acute Respiratory Syndrome Coronavirus 2 (aka SARS-CoV-2 or 2019-nCoV) has attracted worldwide attention and concerns due to its high transmissibility and the severe health consequences experienced upon its infection, particularly by elderly people. Over 329 million people have been infected till date and over 5.5 million people could not survive the respiratory illness known as COVID-19 syndrome. Rapid and low-cost detection methods are of utmost importance to monitor the diffusion of the virus and to aid in the global fight against the pandemic.

We propose here the use of graphene oxide nanocolloids (GONC) as an electroactive nanocarbon material that can act simultaneously as a transducing platform as well as the electroactive label for the detection of 2019-nCoV genomic sequences. The ability of GONC to provide an intrinsic electrochemical signal arising from the reduction of the electrochemically reducible oxygen functionalities present on its surface, allows GONC to be used as a simple and sensitive biosensing platform. Different intrinsic electroactivity of the material was obtained at each step of the genosensing process, starting from the immobilization of a short-stranded DNA probe and followed by the incubation with different concentrations of the target 2019-nCoV DNA strand. Monitoring such variations enabled the quantification of the target analyte over a wide dynamic range between 10⁻¹⁰ and 10⁻⁵ M.

All in all, this proof-of-concept system serves as a stepping stone for the development of a rapid, sensitive and selective analytical tool for the detection of 2019-nCoV as well as other similar viral vectors. The use of cost-effective electrochemical detection methods coupled with the vast availability and suitability of carbon-based nanomaterials make this sensing system a valid candidate for low-cost and point-of-care analysis.

Advanced Point-of-Care Testing Technologies for Human Acute Respiratory Virus Detection

The ever-growing global threats to human life caused by the human acute respiratory virus (RV) infections have cost billions of lives, created a significant economic burden, and shaped society for centuries. The timely response to emerging RVs could save human lives and reduce the medical care burden. The development of RV detection technologies is essential for potentially preventing RV pandemic and epidemics. However, commonly used detection technologies lack sensitivity, specificity, and speed, thus often failing to provide the rapid turnaround times. To address this problem, new technologies are devised to address the performance inadequacies of the traditional methods. These emerging technologies offer improvements in convenience, speed, flexibility, and portability of point-of-care test (POCT). Herein, recent developments in POCT are comprehensively reviewed for eight typical acute respiratory viruses. This review discusses the challenges and opportunities of various recognition and detection strategies and discusses these according to their detection principles, including nucleic acid amplification, optical POCT, electrochemistry, lateral flow assays, microfluidics, enzyme-linked immunosorbent assays, and microarrays. The importance of limits of detection, throughput, portability, and specificity when testing clinical samples in resource-limited settings is emphasized. Finally, the evaluation of commercial POCT kits for both essential RV diagnosis and clinical-oriented practices is included.

Testing and diagnosis of SARS-CoV-2 infection

The recent outbreak of the coronavirus disease 2019 (COVID-19) has rapidly spread around the world since its discovery in China, in December 2019. The current standard method for determining whether a patient is infected with the SARS-CoV-2 virus involves taking a nasal or throat swab sample, which is then sent to laboratories for testing. The laboratories then use polymerase chain reaction (PCR)-based technology on respiratory specimens remain the gold standard to determine if the genetic material of the virus is present in the sample and use this information to diagnose the patient. However, serologic immunoassays and point-of-care technologies are rapidly emerging with high specificity and sensitivity as well. Even if there are excellent techniques for diagnosing symptomatic patients with COVID-19 in equipped laboratories, critical gaps still exist in the screening of asymptomatic individuals who are in the incubation phase of the virus, as well as in the accurate determination of live virus shedding during convalescence to inform decisions for ending isolation.

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

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

Emerging materials for the electrochemical detection of COVID-19

The SARS-CoV-2 virus is still causing a dramatic loss of human lives worldwide, constituting an unprecedented challenge for the society, public health and economy, to overcome. The up-to-date diagnostic tests, PCR, antibody ELISA and Rapid Antigen, require special equipment, hours of analysis and special staff. For this reason, many research groups have focused recently on the design and development of electrochemical biosensors for the SARS-CoV-2 detection, indicating that they can play a significant role in controlling COVID disease. In this review we thoroughly discuss the transducer electrode nanomaterials investigated in order to improve the sensitivity, specificity and response time of the as-developed SARS-CoV-2 electrochemical biosensors. Particularly, we mainly focus on the results appeard on Au-based and carbon or graphene-based electrodes, which are the main material groups recently investigated worldwidely. Additionally, the adopted electrochemical detection techniques are also discussed, highlighting their pros and cos. The nanomaterial-based electrochemical biosensors could enable a fast, accurate and without special cost, virus detection. However, further research is required in terms of new nanomaterials and synthesis strategies in order the SARS-CoV-2 electrochemical biosensors to be commercialized.

Laboratory detection methods for the human coronaviruses

Coronaviruses are a group of envelop viruses which lead to diseases in birds and mammals as well as human. Seven coronaviruses have been discovered in humans that can cause mild to lethal respiratory tract infections. HCoV-229E, HCoV-OC43, HCoV-NL63, and HCoV-HKU1 are the low-risk members of this family and the reason for some common colds. Besides, SARS-CoV, MERS-CoV, and newly identified SARS-CoV-2, which is also known as 2019-nCoV, are the more dangerous viruses. Due to the rapid spread of this novel coronavirus and its related disease, COVID-19, a reliable, simple, fast, and low-cost detection method is necessary for patient diagnosis and tracking worldwide. Human coronaviruses detection methods were classified and presented in this article. The laboratory detection techniques include RT-PCR, RT-LAMP, electrochemical and optical biosensors for RNA detection, and whole virus or viral proteins detection assays.

Trends in biosensing platforms for SARS-CoV-2 detection: A critical appraisal against standard detection tools

In this ongoing theme of coronavirus disease 2019 (COVID-19) pandemic, highly sensitive analytical testing platforms are extremely necessary to detect SARS-CoV-2 RNA and antiviral antibodies. To limit the viral spread, prompt and precise diagnosis is crucial to facilitate treatment and ensure effective isolation. Accurate detection of antibodies (IgG and IgM) is imperative to understand the prevalence of SARS-CoV-2 in public and to inspect the proportion of immune individuals. In this review, we demonstrate and evaluate some tests that have been used commonly to detect SARS-CoV-2. These include nucleic acid and serological tests for the detection of SARS-CoV-2 RNA and specific antibodies in infected people. Moreover, the vitality of biosensing technologies emphasizing on optical and electrochemical biosensors toward the detection of SARS-CoV-2 has also been discussed here. The early diagnosis of COVID-19 based on detection of reactive oxygen species overproduction because of virus-induced dysfunctioning of lung cells has also been highlighted.

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

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

The potential application of electrochemical biosensors in the COVID-19 pandemic: A perspective on the rapid diagnostics of SARS-CoV-2

Electrochemical biosensors combine the selectivity of electrochemical signal transducers with the specificity of biomolecular recognition strategies. Although they have been broadly studied in different areas of diagnostics, they are not yet fully commercialized. During the COVID-19 pandemic, electrochemical platforms have shown the potential to address significant limitations of conventional diagnostic platforms, including accuracy, affordability, and portability. The advantages of electrochemical platforms make them a strong candidate for rapid point-of-care detection of SARS-CoV-2 infection by targeting not only viral RNA but antigens and antibodies. Herein, we reviewed advancements in electrochemical biosensing platforms towards the detection of SARS-CoV-2 through studying similar viruses.

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The complicated nature of conventional tests restricted the availability and distribution of COVID-19 tests.

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Electrochemical detection methods can stand as potential rapid tests for the diagnosis of COVID-19.

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Electrochemical biosensors combine signal selectivity and molecular specificity for rapid accurate detection of SARS-CoV-2.

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The electrochemical biosensors demonstrate trail-blazing sensitivity and specificity, outmatching conventional assays.

The potential of electrochemistry for the detection of coronavirus-induced infections

Human coronaviruses (HCoV) are no stranger to the global environment. The etiology of previous outbreaks with reported symptoms of respiratory tract infections was attributed to different coronavirus strains, with the latest global pandemic in 2019 also belonging to the coronavirus family. Timely detection, effective therapeutics and future prevention are stake key holders in the management of coronavirus-induced infections. Apart from the gold standard clinical diagnostics, electrochemical techniques have also demonstrated their great potentials in the detection of different viruses and their correlated antibodies and antigens, showing high sensitivities and selectivities, and faster times for the analysis. This article aims to critically review the multifaceted electrochemical approaches, not only in the development of point-of-care portable devices but also as alternative detection strategies that can be coupled with traditional methods for the detection of various strains of coronaviruses.

Nanobiosensors for the Detection of Novel Coronavirus 2019-nCoV and Other Pandemic/Epidemic Respiratory Viruses: A Review

The coronavirus disease 2019 (COVID-19) pandemic is considered a public health emergency of international concern. The 2019 novel coronavirus (2019-nCoV) or severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that caused this pandemic has spread rapidly to over 200 countries, and has drastically affected public health and the economies of states at unprecedented levels. In this context, efforts around the world are focusing on solving this problem in several directions of research, by: (i) exploring the origin and evolution of the phylogeny of the SARS-CoV-2 viral genome; (ii) developing nanobiosensors that could be highly effective in detecting the new coronavirus; (iii) finding effective treatments for COVID-19; and (iv) working on vaccine development. In this paper, an overview of the progress made in the development of nanobiosensors for the detection of human coronaviruses (SARS-CoV, SARS-CoV-2, and Middle East respiratory syndrome coronavirus (MERS-CoV) is presented, along with specific techniques for modifying the surface of nanobiosensors. The newest detection methods of the influenza virus responsible for acute respiratory syndrome were compared with conventional methods, highlighting the newest trends in diagnostics, applications, and challenges of SARS-CoV-2 (COVID-19 causative virus) nanobiosensors.

Diagnostic methods and potential portable biosensors for coronavirus disease 2019

Timely detection and diagnosis are urgently needed to guide epidemiological measures, infection control, antiviral treatment, and vaccine research. In this review, biomarkers/indicators for diagnosis of coronavirus disease 2019 (COVID-19) or detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in the environment are summarized and discussed. It is concluded that the detection methods targeting antibodies are not suitable for screening of early and asymptomatic cases since most patients had an antibody response at about 10 days after onset of symptoms. However, antibody detection methods can be combined with quantitative real-time reverse transcriptase-polymerase chain reaction (RT-qPCR) to significantly improve the sensitivity and specificity of diagnosis, and boost vaccine research. Fast, sensitive and accurate detection methods targeting antigens need to be developed urgently. Various specimens for diagnosis or detection are compared and analyzed. Among them, deep throat saliva and induced sputum are desired for RT-qPCR test or other early detection technologies. Chest computerized tomography (CT) scan, RT-qPCR, lateral flow immunochromatographic strip (LFICS) for diagnosis of COVID-19 are summarized and compared. Specially, potential electrochemical (EC) biosensor, surface enhanced Raman scattering (SERS)-based biosensor, field-effect transistor (FET)-based biosensor, surface plasmon resonance (SPR)-based biosensor and artificial intelligence (AI) assisted diagnosis of COVID-19 are emphasized. Finally, some commercialized portable detection device, current challenges and future directions are discussed.

The role of biosensors in coronavirus disease-2019 outbreak

Herein, we have summarized and argued about biomarkers and indicators used for the detection of severe acute respiratory syndrome coronavirus 2. Antibody detection methods are not considered suitable to screen individuals at early stages and asymptomatic cases. The diagnosis of coronavirus disease 2019 using biomarkers and indicators at point-of-care level is much crucial. Therefore, it is urgently needed to develop rapid and sensitive detection methods which can target antigens. We have critically elaborated key role of biosensors to cope the outbreak situation. In this review, the importance of biosensors including electrochemical, surface enhanced Raman scattering, field-effect transistor, and surface plasmon resonance biosensors in the detection of severe acute respiratory syndrome coronavirus 2 has been underscored. Finally, we have outlined pros and cons of diagnostic approaches and future directions.

Genosensor on gold films with enzymatic electrochemical detection of a SARS virus sequence

Biosensors are one of the best examples of miniaturization and simplification trends in analytical chemistry. Among them, DNA sensors, with oligonucleotides as recognition elements, are being widely utilized for many applications, mainly diagnosis of infectious diseases. In this experiment, a hybridization-based genosensor was designed on a 100-nm sputtered gold film. This material worked as an immobilization and transduction surface for the electrochemical diagnosis of a specific DNA sequence of SARS (severe acute respiratory syndrome) virus. The simplicity of the electrochemical instrumentation is combined with a selective methodology to detect the hybridization event enzymatically. This chapter explains all the necessary steps for the construction of the genosensor allowing a low detection limit for the chosen DNA sequence. Protocols for studying the influence of parameters affecting the methodology are given. This chapter also includes questions for students and indications for writing a lab report.

Micropipette Tip-Based Immunoassay with Electrochemical Detection of Antitissue Transglutaminase to Diagnose Celiac Disease Using Staples and a Paper-Based Platform

In this work, 1-200 μL polypropylene micropipette tips were used as platforms for performing immunoassays after converting their inner surfaces on a capture zone for the analyte of interest. We have used a micropipette-tip immunoelectroanalytical platform for the detection of antitissue transglutaminase (IgA), the main biomarker for celiac disease. Modification of the tip wall with poly-l-lysine allowed adsorption of tissue transglutaminase (tTG), which will capture later anti-tTG (IgA) antibodies developed in celiac-affected people. A sandwich-type format was followed, incubating simultaneously the analyte and the detection antibody, labeled with horseradish peroxidase. With this new application for an extremely common lab material, we can perform quantitative analysis by dispensing the liquid into a low-cost and miniaturized staple-based paper electrochemical platform. The analytical signal was the reduction of the enzymatically oxidized substrate, recorded chronoamperometrically (i-t curve). The intensity of the current obtained at a fixed time after the application of the cathodic potential followed a linear relationship with anti-tTG (IgA) concentration. The relative standard deviation obtained for immunoassays performed in different tips indicates the adequate precision of this new methodology, which is very promising for decentralized analysis. Negative and positive controls produced results that were in accordance with those obtained with spectrophotometric enzyme linked-immunosorbent assays.

In situ gold-nanoparticle electrogeneration on gold films deposited on paper for non-enzymatic electrochemical determination of glucose

This work describes the development and evaluation of a new electrochemical platform based on the sustainable generation of gold-nanoparticles on paper-based gold-sputtered electrodes. The disposable porous paper electrode is combined with screen-printed electrodes for ensuring a precise electrogeneration of nanoparticles and also for the evaluation of these simple, versatile and low-cost microfluidic devices. Two types of chromatographic paper with different thicknesses have been evaluated. Paper gold working electrodes modified with gold nanoparticles were characterized by scanning electron microscopy and cyclic voltammetry using potassium ferrocyanide as a common redox probe, showing an improved electrochemical performance when compared to bare gold electrodes. The platform has been applied to the non-enzymatic determination of glucose, molecule of enormous interest. The porous gold structure made by sputtering on paper, modified with electrogenerated nanoparticles allowed precise and accurate determination of the analyte in beverages at low potential.

Enzymatic amplification-free nucleic acid hybridisation sensing on nanostructured thick-film electrodes by using covalently attached methylene blue

Amplification-free (referring to enzymatic amplification step) detection methodologies are increasing in biosensor development due to the need of faster and simpler protocols. However, for maintaining sensitivity without this step, highly detectable molecules or very sensitive detection techniques are required. The nanostructuration of transducer surfaces with carbon nanotubes (CNTs), gold nanoparticles (AuNPs) or both in nanohybrid configurations has been employed in this work for DNA hybridisation sensing purposes. Methylene blue (MB), covalently attached to single stranded DNA, (ssDNA) was incubated with a complementary sequence immobilized on nanostructured screen-printed electrodes (AuSPEs). Although CNTs can increase notoriously the signal of the marker, adsorptive properties should also be considered when bioassays are performed because non-specific adsorption (NSA) phenomena are magnified. In this work, strategies for decreasing NSA were thoroughly evaluated for the detection of Mycoplasma pneumoniae (MP) on CNTs-nanostructured screen-printed electrodes. Among them, the employ of UV-radiation or long incubation times (72h) allowed obtaining higher signals for the complementary strand with respect to the non-complementary one. The use of CNTs/AuNPs nanohybrids, together with the use of streptavidin-biotin (ST-B) interaction allows the higher differentiation (with a 3.5 ratio) in the genosensing of M. pneumoniae.

State-of-the-art of (bio)chemical sensor developments in analytical Spanish groups

(Bio)chemical sensors are one of the most exciting fields in analytical chemistry today. The development of these analytical devices simplifies and miniaturizes the whole analytical process. Although the initial expectation of the massive incorporation of sensors in routine analytical work has been truncated to some extent, in many other cases analytical methods based on sensor technology have solved important analytical problems. Many research groups are working in this field world-wide, reporting interesting results so far. Modestly, Spanish researchers have contributed to these recent developments. In this review, we summarize the more representative achievements carried out for these groups. They cover a wide variety of sensors, including optical, electrochemical, piezoelectric or electro-mechanical devices, used for laboratory or field analyses. The capabilities to be used in different applied areas are also critically discussed.

Emerging molecular assays for detection and characterization of respiratory viruses

This article describes several emerging molecular assays that have potential applications in the diagnosis and monitoring of respiratory viral infections. These techniques include direct nucleic acid detection by quantum dots, loop-mediated isothermal amplification, multiplex ligation-dependent probe amplification, amplification using arbitrary primers, target-enriched multiplexing amplification, pyrosequencing, padlock probes, solid and suspension microarrays, and mass spectrometry. Several of these systems already are commercially available to provide multiplex amplification and high-throughput detection and identification of a panel of respiratory viral pathogens. Further validation and implementation of such emerging molecular assays in routine clinical virology services will enhance the rapid diagnosis of respiratory viral infections and improve patient care.

Trends and Perspectives of Biosensors for Food and Environmental Virology

Food and environmental virology has become a very important and interesting area of research because of food safety and public health concerns. During the last few decades, increasing foodborne diseases and environmental generated illnesses are considered to be highly challenging issues. Biosensor technology holds great promise for the healthcare market, and the security sector. Similar to clinical diagnostic tools, biosensors are being developed for the rapid, reliable, yet inexpensive identification and enumeration of pathogenic viruses which are adulterating environment, food and feed commodities. In this modern era, bio-and nano-technologies play a pivotal role in virological diagnostics of food industry, environmental and veterinary samples. This review covers the recent advances and future prospects of nanotechnology-based bioanalytical microsystems for food and environmental virology.

Detection of severe acute respiratory syndrome (SARS) coronavirus nucleocapsid protein in human serum using a localized surface plasmon coupled fluorescence fiber-optic biosensor

In order to enhance the sensitivity of conventional immunoassay technology for the detection of SARS coronavirus (SARS-CoV) nucleocapsid protein (N protein), we developed a localized surface plasmon coupled fluorescence (LSPCF) fiber-optic biosensor that combines sandwich immunoassay with the LSP technique. Experimentally, a linear relationship between the fluorescence signal and the concentration of recombinant SARS-CoV N (GST-N) protein in buffer solution could be observed from 0.1 pg/mL to 1 ng/mL. In addition, the concentration of GST-N protein in diluted serum across a similar range could also be measured. The correlation coefficients (linear scale) for these two measurements were 0.9469 and 0.9624, respectively. In comparison with conventional enzyme linked immunosorbent assay (ELISA), the detection limit of the LSPCF fiber-optic biosensor for the GST-N protein was improved at least 10⁴-fold using the same monoclonal antibodies. Therefore, the LSPCF fiber-optic biosensor shows an ability to detect very low concentration (∼1 pg/mL) of SARS-CoV N protein in serum. The biosensor should help with the early diagnosis of SARS infection.

Sensitive detection of lip genes by electrochemical DNA sensor and its application in polymerase chain reaction amplicons from Phanerochaete chrysosporium

An electrochemical DNA sensor based on the sandwich hybridization recognition of target sequence of lignin peroxidase (lip) genes on a gold electrode was developed. A monolayer of thiolated capture probe was formed on a gold electrode through self-assembling. Following hybridizations with target nucleic acid and biotinylated detection probe, streptavidin-horseradish peroxidase (HRP) conjugate was applied to the electrode. The DNA conformation and surface coverage on electrode were characterized by impedance spectroscopy and square wave voltammetry. The experimental variables were optimized to maximize the hybridization efficiency, detection sensitivity and speed up the assay time. The amperometric current response to HRP-catalyzed reaction was linearly related to the natural logarithm of the target nucleic acid concentration in the range from 0.6 to 30 nM, with the correlation coefficient of 0.9722. The detection limit was 0.03 nM. Synthesized oligonucleotide as well as Phanerochaete chrysosporium lip gene fragments amplified using polymerase chain reaction and digested by restriction endonucleases were tested. The DNA sensor exhibited good precision, stability, sensitivity, and selectivity, and discriminated satisfactorily against mismatched nucleic acid samples of similar lengths.

DNA hybridization biosensors using polylysine modified SPCEs

Two electrochemical DNA hybridization biosensors (genosensors) for the detection of a 30-mer sequence unique to severe acute respiratory syndrome (SARS) virus are described in this work. Both genosensors rely on the hybridization of the oligonucleotide target with its complementary probe, which is immobilized on positively charged polylysine modified screen-printed carbon electrodes (SPCEs), through electrostatic interactions. In one design, a biotinylated target is used and the detection of the hybridization reaction is monitored using alkaline phosphatase labeled streptavidin (S-AP). This enzyme catalyzes the hydrolysis of the substrate 3-indoxyl phosphate (3-IP) to indigo, which is then solubilized to indigo carmine and detected by means of cyclic voltammetry (CV). In the other design, the target is labeled using an Au(I) complex, sodium aurothiomalate, and the duplex formation is detected by measuring, for first time, the current generated by the hydrogen evolution catalyzed by the gold label. Using 30 min of hybridization time, a detection limit of 8 pM is calculated for the enzymatic genosensor. Although this good sensitivity cannot be reached with the metal label (0.5 nM), the use of this label allows a considerable decrease of the analysis time. Both genosensors do not require the modification of the oligonucleotide probe and using stringent experimental conditions (60 min of hybridization time and 50% formamide in the hybridization buffer) can discriminate between a complementary oligonucleotide and an oligonucleotide with a three-base mismatch.

Assembling Amperometric Biosensors for Clinical Diagnostics

Clinical diagnosis and disease prevention routinely require the assessment ofspecies determined by chemical analysis. Biosensor technology offers several benefits overconventional diagnostic analysis. They include simplicity of use, specificity for the targetanalyte, speed to arise to a result, capability for continuous monitoring and multiplexing,together with the potentiality of coupling to low-cost, portable instrumentation. This workfocuses on the basic lines of decisions when designing electron-transfer-based biosensorsfor clinical analysis, with emphasis on the strategies currently used to improve the deviceperformance, the present status of amperometric electrodes for biomedicine, and the trendsand challenges envisaged for the near future.

Oriented immobilisation of anti-pneumolysin Fab through a histidine tag for electrochemical immunosensors

Orientation of reagents is a key step in the construction of immunosensors. When the immunoreagent is a recombinant protein, this can be achieved by employing hexahistidine tags. The orientation of recombinant histidine-tagged Fab fragments of monoclonal anti-pneumolysin antibodies on gold films is evaluated. Using histidine as a chelator of Ni or employing an anti-polyhistidine antibody for capturing the His6 residue is considered. Measurements are based in the signal of indigo, which comes from the hydrolysis of 3-indoxylphosphate by alkaline phosphatase (AP). The attachment of the enzyme occurs through the interaction of biotin with AP-labelled streptavidin or employing AP-conjugated immunoreagents. In the case of the interaction Ni-histidine, for the study of the self-assembling process a His-tagged and biotinylated protein (His6-GST-B) was employed. General conditions were studied and non-specific adsorption was avoided with the use of 1-hexanethiol. Improvements of the signal compared with the direct adsorption were only achieved by the use of histidine capturing antibodies. With an optimised ratio anti-polyhis:His6-Fab the signal increases approximately a 100%. Precision is adequate and the response is linear with the concentration of pneumolysin between 0.1 and 10 ng/mL.

Alkaline Phosphatase-Catalyzed Silver Deposition for Electrochemical Detection

Alkaline phosphatase (AP) is one of the most used enzymatic labels for the development of ELISAs, immunosensors, DNA hybridization assays, etc. This enzyme catalyzes the dephosphorylation of a substrate into a detectable product usually quantified by optical or electrochemical measurements. This work is based on a substrate (3-indoxyl phosphate) that produces a compound able to reduce silver ions in solution into a metallic deposit, which is localized where the enzymatic label AP is attached. The deposited silver is electrochemically stripped into solution and measured by anodic stripping voltammetry. Its application to an enzymatic genosensor on streptavidin-modified screen-printed carbon electrodes for the detection of virulence nucleic acid determinants of autolysin gene, exclusively present on the genome of the human pathogen Streptococcus pneumoniae, is described. Compared with the direct voltammetric detection of indigo carmine, the anodic stripping voltammetry of silver ions is 14-fold more sensitive.

DNA hybridization sensor based on aurothiomalate electroactive label on glassy carbon electrodes

In this work, a gold complex is used as electroactive label for monitoring hybridization assays on glassy carbon electrodes. Ionic gold is bound to a 30-mer sequence of the SARS (severe acute respiratory syndrome) virus, responsible for the atypical pneumonia, using sodium aurothiomalate. In order to label this single strand, a mixture of sodium aurothiomalate and the strand is prepared. Then, it is incubated for 24 h at 37 degrees C and, finally, free gold is separated from the labeled strand by a dialysis against a 0.15M NaCl solution (pH 7.5). The DNA hybridization sensor is designed immobilizing the complementary probe on the pre-treated electrode surface and, then, the hybridization reaction takes place with the gold labeled strand. The electrochemical determination is based on the catalytic effect of electrodeposited gold on the reduction of silver ions. In non-stringent experimental conditions, a limit of detection of 15 fmol (30 microL) is obtained, and discrimination between a complementary oligonucleotide and a three-based mismatch complementary oligonucleotide is achieved. For the discrimination of a single-base mismatch, is needed to use stringent conditions (50% of formamide in the hybridization buffer).

Chapter 29 Rapid detection of organophosphates, Ochratoxin A, and Fusarium sp. in durum wheat via screen printed based electrochemical sensors

Most of the inhibition bioassays or biosensors for organophosphate and carbamate pesticides are based on the amperometric detection of the enzymatic product of the reaction. Applications of amperometric biosensing strategies for pesticide detection in real or spiked food samples have been recently reported. Most of the applications have been developed for vegetable matrices. Different formats of biosensors have been used: disposable screenprinted choline oxidase biosensors using acetylcholinesterase (AChE) in solution were utilized to detect pesticides. Screen-printed sensor developed using photolithographic conducting copper track, graphite–epoxy composite, and either AChE or butirrylcholinesterase was also used in the analysis of spiked (paraoxon and carbofuran) samples of tap water and fruit juices at sub-nanomolar concentration. Additionally, the developed device, which consists of the hand-held potentiostat, the multiplexer for eight-channel control and a dedicated software, can be used to detect organophosphates pesticides, such as dichlorvos and pirimiphos methyl at contamination level below the maximum residue limit settled by the European Union and also amplified DNA of F. culmorum.

Chapter 26 Thick- and thin-film DNA sensors

The use of thick- and thin film electrodes as supports for genosensor devices offers enormous opportunities for their application in molecular diagnosis. The technologies used in the fabrication of both thick- and thin-film electrodes allow the mass production of reproducible, inexpensive and mechanically robust strip solid electrodes. Other important advantages of these electrodes are the possibility of miniaturization as well as their ease of manipulation in a disposable manner and therefore the use of small volumes. To detect transcriptional profiling and single nucleotide polymorphism thin-film arrays of 14, 20, 25, 48, and 64 electrodes have been fabricated, using lithographic techniques. Readout systems for these arrays based on electrical detection have also been developed. Moreover, a thick-film sensor array suitable for automation combined to readout based on intermittent pulse amperometry (IPA) has been commercialized. These genosensors and the readout instruments provide a simple, accurate and inexpensive platform for patient diagnosis. It is more than probable that arrays for 50–100 DNA sequences will be needed for some clinical applications. Although it is not difficult to design electrode pads with reproducible dimensions of a micron or less, the electrochemical readout requires mechanical connections to each individual electrode.

Procedure 36 Genosensor on gold thin-films with enzymatic electrochemical detection of a SARS virus sequence

This chapter presents a procedure for the construction of a hybridization-based genosensor for a SARS (severe acute respiratory syndrome) virus sequence on a 100nm sputtered gold film, which works as immobilization and transduction surface. The chapter tests the sensitivity and the selectivity of the SARS genosensor using complementary strands of SARS virus and three-base mismatch strands. Genosensor construction include following steps: a drop of 5 mL of 1.02 mM thiolated probe deposited on the gold film and maintain at 37°C for 20 min or at 41°C for 12 h; it is cleaned with 0.1M Tris-HCl buffer; further a15 mL drop of a 2% 1-hexanethiol solution is deposited on the gold film and maintained for 10 min and again cleaned with a 2×SSC buffer solution pH 7. From the results of hybridization assay and recording of the analytical signal no significant difference found between the analytical signal obtained for a 3.03nM solution of the complementary target strand and three-base mismatch strand. The limit of detection, calculated as the concentration corresponding to a signal which is three times the standard deviation of the intercept, results to be 5 pM. This means an improvement of various orders of magnitude when compared with limits of detection reported in the bibliography for DNA assays.