Cost-Effective and Handmade Paper-Based Immunosensing Device for Electrochemical Detection of Influenza Virus

Recent Trends of Bioanalytical Sensors with Smart Health Monitoring Systems: From Materials to Applications

Smart biosensors attract significant interest due to real-time monitoring of user health status, where bioanalytical electronic devices designed to detect various activities and biomarkers in the human body have potential applications in physical sign monitoring and health care. Bioelectronics can be well integrated by output signals with wireless communication modules for transferring data to portable devices used as smart biosensors in performing real-time diagnosis and analysis. In this review, the scientific keys of biosensing devices and the current trends in the field of smart biosensors, (functional materials, technological approaches, sensing mechanisms, main roles, potential applications and challenges in health monitoring) will be summarized. Recent advances in the design and manufacturing of bioanalytical sensors with smarter capabilities and enhanced reliability indicate a forthcoming expansion of these smart devices from laboratory to clinical analysis. Therefore, a general description of functional materials and technological approaches used in bioelectronics will be presented after the sections of scientific keys to bioanalytical sensors. A careful introduction to the established systems of smart monitoring and prediction analysis using bioelectronics, regarding the integration of machine-learning-based basic algorithms, will be discussed. Afterward, applications and challenges in development using these smart bioelectronics in biological, clinical, and medical diagnostics will also be analyzed. Finally, the review will conclude with outlooks of smart biosensing devices assisted by machine learning algorithms, wireless communications, or smartphone-based systems on current trends and challenges for future works in wearable health monitoring.

The use of biological fluids in microfluidic paper-based analytical devices (μPADs): Recent advances, challenges and future perspectives

The use of microfluidic paper-based analytical devices (μPADs) for aiding medical diagnosis is a growing trend in the literature mainly due to their low cost, easy use, simple manufacturing, and great potential for application in low-resource settings. Many important biomarkers (proteins, ions, lipids, hormones, DNA, RNA, drugs, whole cells, and more) and biofluids are available for precise detection and diagnosis. We have reviewed the advances μPADs in medical diagnostics have achieved in the last few years, focusing on the most common human biofluids (whole blood/plasma, sweat, urine, tears, and saliva). The challenges of detecting specific biomarkers in each sample are discussed, along with innovative techniques that overcome such limitations. Finally, the difficulties of commercializing μPADs are considered, and future trends are presented, including wearable devices and integrating multiple steps in a single platform.

Advances in paper-based electrochemical immunosensors: review of fabrication strategies and biomedical applications

Cellulose paper-based sensing devices have shown promise in addressing the accuracy, sensitivity, selectivity, analysis time and cost of current disease diagnostic tools owing to their excellent physical and physiochemical properties, high surface-area-to-volume ratio, strong adsorption capabilities, ease of chemical functionalization for immobilization, biodegradability, biocompatibility and liquid transport by simple capillary action. This review provides a comprehensive overview of recent advancements in the field of electrochemical immunosensing for various diseases, particularly in underdeveloped regions and globally. It highlights the significant progress in fabrication techniques, fluid control, signal transduction and paper substrates, shedding light on their respective advantages and disadvantages. The primary objective of this review article is to compile recent advances in the field of electrochemical immunosensing for the early detection of diseases prevalent in underdeveloped regions and globally, including cancer biomarkers, bacteria, proteins and viruses. Herein, the critical need for new, simplistic early detection strategies to combat future disease outbreaks and prevent global pandemics is addressed. Moreover, recent advancements in fabrication techniques, including lithography, printing and electrodeposition as well as device orientation, substrate type and electrode modification, have highlighted their potential for enhancing sensitivity and accuracy.

Rapid Direct Detection of SARS-CoV-2 Aerosols in Exhaled Breath at the Point of Care

Airborne transmission via virus-laden aerosols is a dominant route for the transmission of respiratory diseases, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Direct, non-invasive screening of respiratory virus aerosols in patients has been a long-standing technical challenge. Here, we introduce a point-of-care testing platform that directly detects SARS-CoV-2 aerosols in as little as two exhaled breaths of patients and provides results in under 60 s. It integrates a hand-held breath aerosol collector and a llama-derived, SARS-CoV-2 spike-protein specific nanobody bound to an ultrasensitive micro-immunoelectrode biosensor, which detects the oxidation of tyrosine amino acids present in SARS-CoV-2 viral particles. Laboratory and clinical trial results were within 20% of those obtained using standard testing methods. Importantly, the electrochemical biosensor directly detects the virus itself, as opposed to a surrogate or signature of the virus, and is sensitive to as little as 10 viral particles in a sample. Our platform holds the potential to be adapted for multiplexed detection of different respiratory viruses. It provides a rapid and non-invasive alternative to conventional viral diagnostics.

Paper-based electrochemical biosensors for the diagnosis of viral diseases

Paper-based electrochemical analytical devices (ePADs) have gained significant interest as promising analytical units in recent years because they can be fabricated in simple ways, are low-cost, portable, and disposable platforms that can be applied in various fields. In this sense, paper-based electrochemical biosensors are attractive analytical devices since they can promote diagnose several diseases and potentially allow decentralized analysis. Electrochemical biosensors are versatile, as the measured signal can be improved by using mainly molecular technologies and nanomaterials to attach biomolecules, resulting in an increase in their sensitivity and selectivity. Additionally, they can be implemented in microfluidic devices that drive and control the flow without external pumping and store reagents, and improve the mass transport of analytes, increasing sensor sensitivity. In this review, we focus on the recent developments in electrochemical paper-based devices for viruses' detection, including COVID-19, Dengue, Zika, Hepatitis, Ebola, AIDS, and Influenza, among others, which have caused impacts on people's health, especially in places with scarce resources. Also, we discuss the advantages and disadvantages of the main electrode's fabrication methods, device designs, and biomolecule immobilization strategies. Finally, the perspectives and challenges that need to be overcome to further advance paper-based electrochemical biosensors' applications are critically presented.

Paper-based diagnostic chips for viral detection

Viruses cause various diseases in humans, and pose serious health risks to individuals and populations worldwide. As a result, various diagnostic procedures and methods have been developed to prevent, manage, and reduce the burden of viral diseases, each with its own benefits and drawbacks. Among these, paper-based diagnostic chips are becoming increasingly common because of their speed, accuracy, convenience, and economical and environmental friendliness. These paper-based diagnostic tests have ideal point-of-care (POC) diagnostic applications, particularly in personalized healthcare. Paper-based diagnostics have emerged as innovative and low-cost solutions for diagnosing viral diseases in remote and underdeveloped regions where traditional diagnostic methods are not readily available. These tests are easy to use, require minimal equipment, and can be performed by nonspecialized personnel, making them accessible even in resource-constrained settings. In this review, we discuss recent developments in paper-based diagnostic chips, the importance of improved methods for identifying viral pathogens, drawbacks of traditional detection techniques, and challenges and prospects of paper-based diagnostic chips for the detection of viruses.

Advances on microfluidic paper-based electroanalytical devices

Since the inception of the first electrochemical devices on paper substrates, many different reports of microfluidic paper-based electroanalytical devices (μPEDs), innovative hydrophobic barriers and electrode fabrication processes have allowed the incorporation of diverse materials, resulting in different applications and a boost in performance. These advancements have led to the creation of paper-based devices with comparable performance to many standard conventional devices, with the added benefits of pumpless fluidic transport, component separation and reagent storage that can be exploited to automate and handle sample preprocessing. Herein, we review μPEDs, summarize the characteristics and functionalities of μPEDs, such as separation, fluid flow control and storage, and outline the conventional and emerging fabrication and modification approaches for μPEDs. We also examine the recent application of μPEDs in biomedicine, the environment, and food and water safety, as well as some limitations and challenges that must be addressed.

Porous Structural Microfluidic Device for Biomedical Diagnosis: A Review

Microfluidics has recently received more and more attention in applications such as biomedical, chemical and medicine. With the development of microelectronics technology as well as material science in recent years, microfluidic devices have made great progress. Porous structures as a discontinuous medium in which the special flow phenomena of fluids lead to their potential and special applications in microfluidics offer a unique way to develop completely new microfluidic chips. In this article, we firstly introduce the fabrication methods for porous structures of different materials. Then, the physical effects of microfluid flow in porous media and their related physical models are discussed. Finally, the state-of-the-art porous microfluidic chips and their applications in biomedicine are summarized, and we present the current problems and future directions in this field.

Electrochemical biosensor based on antibody-modified Au nanoparticles for rapid and sensitive analysis of influenza A virus

To cope with the easy transmissibility of the avian influenza A virus subtype H1N1, a biosensor was developed for rapid and highly sensitive electrochemical immunoassay. Based on the principle of specific binding between antibody and virus molecules, the active molecule-antibody-adapter structure was formed on the surface of an Au NP substrate electrode; it included a highly specific surface area and good electrochemical activity for selective amplification detection of the H1N1 virus. The electrochemical test results showed that the BSA/H1N1 Ab/Glu/Cys/Au NPs/CP electrode was used for the electrochemical detection of the H1N1 virus with a sensitivity of 92.1 µA (pg/mL)^-1 cm², LOD of 0.25 pg/ml, linear ranges of 0.25-5 pg/mL, and linearity of (R ² = 0.9846). A convenient H1N1 antibody-based electrochemical electrode for the molecular detection of the H1N1 virus will be of great use in the field of epidemic prevention and raw poultry protection.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s11581-023-04944-w.

Electrochemical Biosensors Based on Carbon Nanomaterials for Diagnosis of Human Respiratory Diseases

In recent years, respiratory diseases have increasingly become a global concern, largely due to the outbreak of Coronavirus Disease 2019 (COVID-19). This inevitably causes great attention to be given to the development of highly efficient and minimal or non-invasive methods for the diagnosis of respiratory diseases. And electrochemical biosensors based on carbon nanomaterials show great potential in fulfilling the requirement, not only because of the superior performance of electrochemical analysis, but also given the excellent properties of the carbon nanomaterials. In this paper, we review the most recent advances in research, development and applications of electrochemical biosensors based on the use of carbon nanomaterials for diagnosis of human respiratory diseases in the last 10 years. We first briefly introduce the characteristics of several common human respiratory diseases, including influenza, COVID-19, pulmonary fibrosis, tuberculosis and lung cancer. Then, we describe the working principles and fabrication of various electrochemical biosensors based on carbon nanomaterials used for diagnosis of these respiratory diseases. Finally, we summarize the advantages, challenges, and future perspectives for the currently available electrochemical biosensors based on carbon nanomaterials for detecting human respiratory diseases.

Identification of Serum Ferritin-Specific Nanobodies and Development towards a Diagnostic Immunoassay

Serum ferritin (SF) is an iron-rich protein tightly connected with iron homeostasis, and the variations are frequently observed in diseased states, including iron-deficiency anemia, inflammation, liver disease, and tumors, which renders SF level an indicator of potential malignancies in clinical practice. Nanobodies (Nbs) have been widely explored and developed into theranostic reagents. Surprisingly, no reports stated the identification of anti-SF Nbs, nor the potential of such Nbs as a diagnostic tool. In this study, we generated SF-specific Nbs and provided novel clinical diagnostic approaches to develop an immunoassay. An immune library was constructed after immunizing an alpaca with SF, and five Nbs specifically targeting human SF were retrieved. The obtained Nbs exhibited robust properties including high stability, affinity, and specificity. Then, an ELISA-based test using a heterologous Nb-pair was developed. The calibration curve demonstrated a linear range of SF between 9.0 to 1100 ng/mL, and a limit of detection (LOD) of 1.01 ng/mL. The detecting recovery and coefficient variation (CV) were determined by spiking different concentrations of SF into the serum sample, to verify the successful application of our selected Nbs for SF monitoring. In general, this study generated SF-specific Nbs and demonstrated their potential as diagnostic immunoassay tools.

Dual synergistic response for the electrochemical detection of H1N1 virus and viral proteins using high affinity peptide receptors

Identifying alternatives to antibodies as bioreceptors to test samples feasibly is crucial for developing next-generation in vitro diagnostic methods. Here, we aimed to devise an analytical method for detecting H1N1 viral proteins (hemagglutinin [HA] and neuraminidase [NA]) as well as the complete H1N1 virus with high sensitivity and selectivity. By applying biopanning of M13 peptide libraries, high affinity peptides specific for HA or NA were successfully identified. After selection, three different synthetic peptides that incorporated gold-binding motifs were designed and chemically synthesized on the basis of the original sequence identified phage display technique with or without two repeat. Their binding interactions were characterized by enzyme-linked immunosorbent assay (ELISA), square wave voltammetry (SWV), Time of flight-secondary ion mass spectroscopy (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS). The binding constants (K_d) of HA BP1, HA BP2 and NA BP1 peptides were found to be 169.72 nM, 70.02 nM and 224.49 nM for HA or NA proteins by electrochemical measurements (SWV). The single use of HA BP2 peptide enabled the detection of either H1N1 viral proteins or the actual H1N1 virus, while NA BP1 peptide exhibited lower binding for real H1N1 virus particles. Moreover, the use of both HA BP1 and BP2 as a divalent capturing reagent improved sensor performance as well as the strength of the electrochemical signal, thereby exhibiting a dual synergistic effect for the electrochemical detection of H1N1 antigens with satisfactory specificity and sensitivity (limit of detection of 1.52 PFU/mL).

Recent Advances in Electrochemical Tools for Virus Detection

Virus detection at the point-of-care facility has become an alarming topic in the research community. The latest coronavirus pandemic has highlighted the limitations of current conventional virus detection methods. Compared to nonelectrochemical sensors, electrochemical sensors provide the ideal platform for rapid, cheap, fast, sensitive, and selective diagnosis of several viruses, particularly at point-of-care facilities. This article highlights the most promising studies reported over the past decade to detect a broad spectrum of viruses using voltammetry, amperometry, and electrochemical impedance spectroscopy.

Multiwalled carbon nanotube nanofiller-polyindole polymer matrix-based efficient biosensor for the rapid detection of swine flu

Pictorial representation of the synthesis of the electrode material, fabrication and electrochemical response of the biosensing platform for swine flu detection.

Micro/nanotechnology-inspired rapid diagnosis of respiratory infectious diseases

Humans have suffered from a variety of infectious diseases since a long time ago, and now a new infectious disease called COVID-19 is prevalent worldwide. The ongoing COVID-19 pandemic has led to research of the effective methods of diagnosing respiratory infectious diseases, which are important to reduce infection rate and help the spread of diseases be controlled. The onset of COVID-19 has led to the further development of existing diagnostic methods such as polymerase chain reaction, reverse transcription polymerase chain reaction, and loop-mediated isothermal amplification. Furthermore, this has contributed to the further development of micro/nanotechnology-based diagnostic methods, which have advantages of high-throughput testing, effectiveness in terms of cost and space, and portability compared to conventional diagnosis methods. Micro/nanotechnology-based diagnostic methods can be largely classified into (1) nanomaterials-based, (2) micromaterials-based, and (3) micro/nanodevice-based. This review paper describes how micro/nanotechnologies have been exploited to diagnose respiratory infectious diseases in each section. The research and development of micro/nanotechnology-based diagnostics should be further explored and advanced as new infectious diseases continue to emerge. Only a handful of micro/nanotechnology-based diagnostic methods has been commercialized so far and there still are opportunities to explore.

Graphene and carbon nanotubes interfaced electrochemical nanobiosensors for the detection of SARS-CoV-2 (COVID-19) and other respiratory viral infections: A review

Recent COVID-19 pandemic has claimed millions of lives due to lack of a rapid diagnostic tool. Global scientific community is now making joint efforts on developing rapid and accurate diagnostic tools for early detection of viral infections to preventing future outbreaks. Conventional diagnostic methods for virus detection are expensive and time consuming. There is an immediate requirement for a sensitive, reliable, rapid and easy-to-use Point-of-Care (PoC) diagnostic technology. Electrochemical biosensors have the potential to fulfill these requirements, but they are less sensitive for sensing viruses/viral infections. However, sensitivity and performance of these electrochemical platforms can be improved by integrating carbon nanostructure, such as graphene and carbon nanotubes (CNTs). These nanostructures offer excellent electrical property, biocompatibility, chemical stability, mechanical strength and, large surface area that are most desired in developing PoC diagnostic tools for detecting viral infections with speed, sensitivity, and cost-effectiveness. This review summarizes recent advancements made toward integrating graphene/CNTs nanostructures and their surface modifications useful for developing new generation of electrochemical nanobiosensors for detecting viral infections. The review also provides prospects and considerations for extending the graphene/CNTs based electrochemical transducers into portable and wearable PoC tools that can be useful in preventing future outbreaks and pandemics.

Nanomaterials-Based Sensors for Respiratory Viral Detection: A Review

Contagious diseases are the principal cause of mortality, particularly respiratory viruses, a real menace for public health and economic development worldwide. Therefore, timely diagnosis and treatments are the only life-saving strategy to overcome any epidemic and particularly the ongoing prevailing pandemic COVID-19 caused by SARS-CoV-2. A rapid identification, point of care, portable, highly sensitive, stable, and inexpensive device is needed which is exceptionally satisfied by sensor technology. Consequently, the researchers have directed their attention to employing sensors targeting multiple analyses of pathogenic detections across the world. Nanostructured materials (nanoparticles, nanowires, nanobundles, etc.), owing to their unique characteristics such as large surface-to-volume ratio and nanoscale interactions, are widely employed to fabricate facile sensors to meet all the immediate emerging challenges and threats. This review is anticipated to foster researchers in developing advanced nanomaterials-based sensors for the increasing number of COVID-19 cases across the globe. The mechanism of respiratory viral detection by nanomaterials-based sensors has been reported. Moreover, the advantages, disadvantages, and their comparison with conventional sensors are summarized. Furthermore, we have highlighted the challenges and future potential of these sensors for achieving efficient and rapid detection.

Physical collection and viability of airborne bacteria collected under electrostatic field with different sampling media and protocols towards rapid detection

Electrostatic samplers have been increasingly studied for sampling of viral and bacterial aerosols, and bioaerosol samplers are required to provide concentrated liquid samples with high physical collection and biological recovery, which would be critical for rapid detection. Here, the effects of sampling media and protocols on the physical collection and biological recovery of two airborne bacteria (Pseudomonas fluorescens and Micrococcus luteus) under electrostatic field were investigated using a personal electrostatic particle concentrator (EPC). Deionized (DI) water with/without sodium dodecyl sulfate (SDS) and phosphate buffered saline were tested as sampling media. A polystyrene container was mounted onto the collection electrode of the EPC for stable storage and vortexing after capture. Many bacterial cells were found to be deposited on the bottom surface of the container submerged in the media via electrophoresis, and among the tested sampling protocols, wet sampling with a container and subsequent vortexing offered the most bacteria in the collection suspension. Experiments with several sampling media showed that 0.001-0.01% SDS-DI water demonstrated the highest recovery rate in the EPC. These findings would be valuable in the field of sampling and subsequent rapid detection of bioaerosols.

Advancements in electrochemical biosensing for respiratory virus detection: A review

Respiratory viruses are real menace for human health which result in devastating epidemic disease. Consequently, it is in urgent need of identifying and quantifying virus with a rapid, sensitive and precise approach. The study of electrochemical biosensors for respiratory virus detection has become one of the most rapidly developing scientific fields. Recent developments in electrochemical biosensors concerning respiratory virus detection are comprehensively reviewed in this paper. This review is structured along common detecting objects of respiratory viruses, electrochemical biosensors, electrochemical biosensors for respiratory virus detection and future challenges. The electrochemical biosensors for respiratory virus detection are introduced, including nucleic acids-based, immunosensors and other affinity biosensors. Lastly, for Coronavirus disease 2019 (COVID-19) diagnosis, the future challenges regarding developing electrochemical biosensor-based Point-of-Care Tests (POCTs) are summarized. This review is expected to provide a helpful guide for the researchers entering this interdisciplinary field and developing more novel electrochemical biosensors for respiratory virus detection.

Portable Sensing Devices for Detection of COVID-19: A Review

The coronavirus pandemic is the most challenging incident that people have faced in recent years. Despite the time-consuming and expensive conventional methods, point-of-care diagnostics have a crucial role in deterrence, timely detection, and intensive care of the disease's progress. Hence, this detrimental health emergency persuaded researchers to accelerate the development of highly-scalable diagnostic devices to control the propagation of the virus even in the least developed countries. The strategies exploited for detecting COVID-19 stem from the already designed systems for studying other maladies, particularly viral infections. The present report reviews not only the novel advances in portable diagnostic devices for recognizing COVID-19, but also the previously existing biosensors for detecting other viruses. It discusses their adaptability for identifying surface proteins, whole viruses, viral genomes, host antibodies, and other biomarkers in biological samples. The prominence of different types of biosensors such as electrochemical, optical, and electrical for detecting low viral loads have been underlined. Thus, it is anticipated that this review will assist scientists who have embarked on a competition to come up with more efficient and marketable in-situ test kits for identifying the infection even in its incubation time without sample pretreatment. Finally, a conclusion is provided to highlight the importance of such an approach for monitoring people to combat the spread of such contagious diseases.

Biosensing strategies for the electrochemical detection of viruses and viral diseases - A review

Viruses are the causing agents for many relevant diseases, including influenza, Ebola, HIV/AIDS, and COVID-19. Its rapid replication and high transmissibility can lead to serious consequences not only to the individual but also to collective health, causing deep economic impacts. In this scenario, diagnosis tools are of significant importance, allowing the rapid, precise, and low-cost testing of a substantial number of individuals. Currently, PCR-based techniques are the gold standard for the diagnosis of viral diseases. Although these allow the diagnosis of different illnesses with high precision, they still present significant drawbacks. Their main disadvantages include long periods for obtaining results and the need for specialized professionals and equipment, requiring the tests to be performed in research centers. In this scenario, biosensors have been presented as promising alternatives for the rapid, precise, low-cost, and on-site diagnosis of viral diseases. This critical review article describes the advancements achieved in the last five years regarding electrochemical biosensors for the diagnosis of viral infections. First, genosensors and aptasensors for the detection of virus and the diagnosis of viral diseases are presented in detail regarding probe immobilization approaches, detection methods (label-free and sandwich), and amplification strategies. Following, immunosensors are highlighted, including many different construction strategies such as label-free, sandwich, competitive, and lateral-flow assays. Then, biosensors for the detection of viral-diseases-related biomarkers are presented and discussed, as well as point of care systems and their advantages when compared to traditional techniques. Last, the difficulties of commercializing electrochemical devices are critically discussed in conjunction with future trends such as lab-on-a-chip and flexible sensors.

Pathogen detection with electrochemical biosensors: Advantages, challenges and future perspectives

Detection of pathogens, e.g., bacteria and viruses, is still a big challenge in analytical medicine due to their vast number and variety. Developing strategies for rapid, inexpensive, specific, and sensitive detection of the pathogens using nanomaterials, integrating with microfluidics devices, amplification methods, or even combining these strategies have received significant attention. Especially, after the health-threatening COVID-19 outbreak, rapid and sensitive detection of pathogens became very critical. Detection of pathogens could be realized with electrochemical, optical, mass sensitive, or thermal methods. Among them, electrochemical methods are very promising by bringing different advantages, i.e., they exhibit more versatile detection schemes and real-time quantification as well as label-free measurements, which provides a broader application perspective. In this review, we discuss the recent advances for the detection of bacteria and viruses using electrochemical biosensors. Moreover, electrochemical biosensors for pathogen detection were broadly reviewed in terms of analyte, bio-recognition and transduction elements. Different fabrication techniques, detection principles, and applications of various pathogens with the electrochemical biosensors were also discussed.

Recent progress in nanomaterial-based sensing of airborne viral and bacterial pathogens

Airborne pathogens are small microbes that can cause a multitude of diseases (e.g., the common cold, flu, asthma, anthrax, tuberculosis, botulism, and pneumonia). As pathogens are transmitted from infected hosts via a number of routes (e.g., aerosolization, sneezing, and coughing), there is a great demand to accurately monitor their presence and behavior. Despite such need, conventional detection methods (e.g., colony counting, immunoassays, and various molecular techniques) generally suffer from a number of demerits (e.g., complex, time-consuming, and labor-intensive nature). To help overcome such limitations, nanomaterial-based biosensors have evolved as alternative candidates to realize portable, rapid, facile, and direct on-site identification of target microbes. In this review, nano-biosensors developed for the detection of airborne pathogens are listed and discussed in reference to conventional options. The prospects for the development of advanced nano-biosensors with enhanced accuracy and portability are also discussed.

Survey of Saliva Components and Virus Sensors for Prevention of COVID-19 and Infectious Diseases

The United States Centers for Disease Control and Prevention considers saliva contact the lead transmission means of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which causes the coronavirus disease 2019 (COVID-19). Saliva droplets or aerosols expelled by heavy breathing, talking, sneezing, and coughing may carry this virus. People in close distance may be exposed directly or indirectly to these droplets, especially those droplets that fall on surrounding surfaces and people may end up contracting COVID-19 after touching the mucosa tissue on their faces. It is of great interest to quickly and effectively detect the presence of SARS-CoV-2 in an environment, but the existing methods only work in laboratory settings, to the best of our knowledge. However, it may be possible to detect the presence of saliva in the environment and proceed with prevention measures. However, detecting saliva itself has not been documented in the literature. On the other hand, many sensors that detect different organic components in saliva to monitor a person's health and diagnose different diseases that range from diabetes to dental health have been proposed and they may be used to detect the presence of saliva. This paper surveys sensors that detect organic and inorganic components of human saliva. Humidity sensors are also considered in the detection of saliva because a large portion of saliva is water. Moreover, sensors that detect infectious viruses are also included as they may also be embedded into saliva sensors for a confirmation of the virus' presence. A classification of sensors by their working principle and the substance they detect is presented. This comparison lists their specifications, sample size, and sensitivity. Indications of which sensors are portable and suitable for field application are presented. This paper also discusses future research and challenges that must be resolved to realize practical saliva sensors. Such sensors may help minimize the spread of not only COVID-19 but also other infectious diseases.

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.

Biosensors for the detection of respiratory viruses: A review

The recent events of outbreaks related to different respiratory viruses in the past few years, exponentiated by the pandemic caused by the coronavirus disease 2019 (COVID-19), reported worldwide caused by SARS-CoV-2, raised a concern and increased the search for more information on viruses-based diseases. The detection of the virus with high specificity and sensitivity plays an important role for an accurate diagnosis. Despite the many efforts to identify the SARS-CoV-2, the diagnosis still relays on expensive and time-consuming analysis. A fast and reliable alternative is the use of low-cost biosensor for in loco detection. This review gathers important contributions in the biosensor area regarding the most current respiratory viruses, presents the advances in the assembly of the devices and figures of merit. All information is useful for further biosensor development for the detection of respiratory viruses, such as for the new coronavirus.

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.

Electrochemical paper-based devices: sensing approaches and progress toward practical applications

Paper-based sensors offer an affordable yet powerful platform for field and point-of-care (POC) testing due to their self-pumping ability and utility for many different analytical measurements. When combined with electrochemical detection using small and portable electronics, sensitivity and selectivity of the paper devices can be improved over naked eye detection without sacrificing portability. Herein, we review how the field of electrochemical paper-based analytical devices (ePADs) has grown since it was introduced a decade ago. We start by reviewing fabrication methods relevant to ePADs with more focus given to the electrode fabrication, which is fundamental for electrochemical sensing. Multiple sensing approaches applicable to ePADs are then discussed and evaluated to present applicability, advantages and challenges associated with each approach. Recent applications of ePADs in the fields of clinical diagnostics, environmental testing, and food analysis are also presented. Finally, we discuss how the current ePAD technologies have progressed to meet the analytical and practical specifications required for field and/or POC applications, as well as challenges and outlook.

Suppressing Non-Specific Binding of Proteins onto Electrode Surfaces in the Development of Electrochemical Immunosensors

Electrochemical immunosensors, EIs, are systems that combine the analytical power of electrochemical techniques and the high selectivity and specificity of antibodies in a solid phase immunoassay for target analyte. In EIs, the most used transducer platforms are screen printed electrodes, SPEs. Some characteristics of EIs are their low cost, portability for point of care testing (POCT) applications, high specificity and selectivity to the target molecule, low sample and reagent consumption and easy to use. Despite all these attractive features, still exist one to cover and it is the enhancement of the sensitivity of the EIs. In this review, an approach to understand how this can be achieved is presented. First, it is necessary to comprise thoroughly all the complex phenomena that happen simultaneously in the protein-surface interface when adsorption of the protein occurs. Physicochemical properties of the protein and the surface as well as the adsorption phenomena influence the sensitivity of the EIs. From this point, some strategies to suppress non-specific binding, NSB, of proteins onto electrode surfaces in order to improve the sensitivity of EIs are mentioned.

Recent advances in and potential utilities of paper-based electrochemical sensors: beyond qualitative analysis

Paper based electrochemical sensors (PESs) are simple, low-cost, portable and disposable analytical sensing platforms that can be applied in clinical diagnostics, food quality control and environmental monitoring.

Development of an Electrochemical Paper-Based Analytical Device for Trace Detection of Virus Particles

Viral pathogens are a serious health threat around the world, particularly in resource limited settings, where current sensing approaches are often insufficient and slow, compounding the spread and burden of these pathogens. Here, we describe a label-free, point-of-care approach toward detection of virus particles, based on a microfluidic paper-based analytical device with integrated microwire Au electrodes. The device is initially characterized through capturing of streptavidin modified nanoparticles by biotin-modified microwires. An order of magnitude improvement in detection limits is achieved through use of a microfluidic device over a classical static paper-based device, due to enhanced mass transport and capturing of particles on the modified electrodes. Electrochemical impedance spectroscopy detection of West Nile virus particles was carried out using antibody functionalized Au microwires, achieving a detection limit of 10.2 particles in 50 μL of cell culture media. No increase in signal is found on addition of an excess of a nonspecific target (Sindbis). This detection motif is significantly cheaper (∼$1 per test) and faster (∼30 min) than current methods, while achieving the desired selectivity and sensitivity. This sensing motif represents a general platform for trace detection of a wide range of biological pathogens.