Magnetic beads combined with carbon black-based screen-printed electrodes for COVID-19: A reliable and miniaturized electrochemical immunosensor for SARS-CoV-2 detection in saliva

Graphene derivative-based ink advances inkjet printing technology for fabrication of electrochemical sensors and biosensors

The field of biosensing would significantly benefit from a disruptive technology enabling flexible manufacturing of uniform electrodes. Inkjet printing holds promise for this, although realizing full electrode manufacturing with this technology remains challenging. We introduce a nitrogen-doped carboxylated graphene ink (NGA-ink) compatible with commercially available printing technologies. The water-based and additive-free NGA-ink was utilized to produce fully inkjet-printed electrodes (IPEs), which demonstrated successful electrochemical detection of the important neurotransmitter dopamine. The cost-effectiveness of NGA-ink combined with a total cost per electrode of $0.10 renders it a practical solution for customized electrode manufacturing. Furthermore, the high carboxyl group content of NGA-ink (13 wt%) presents opportunities for biomolecule immobilization, paving the way for the development of advanced state-of-the-art biosensors. This study highlights the potential of NGA inkjet-printed electrodes in revolutionizing sensor technology, offering an affordable, scalable alternative to conventional electrochemical systems.

Rapid detection of SARS-CoV-2 spike protein using a magnetic-assisted electrochemical biosensor based on functionalized CoFe2O4 magnetic nanomaterials

The outbreak of novel coronavirus pneumonia (COVID-19) in 2019 has garnered widespread attention. The virus exhibits high contagiousness, and in certain cases, it can lead to recurrent infections. Therefore, it is imperative to develop portable, sensitive, and accurate sensors to promptly detect infected individuals, control the virus's transmission, and determine suitable treatment strategies. In this study, we proposed a magnetically-assisted method employing CFO@CS-Au MNP as the substrate material, which was functionalized with human angiotensin-converting enzyme (ACE2) for efficient capture of SARS-CoV-2 spike protein in solution. Subsequently, the captured protein was sensitively detected through differential pulse voltammetry (DPV) electrical analysis. The linear detection range of the labeled GCE/MNP/GA/ACE2/BSA electrochemical sensor is from 1 pg/mL to 10 μg/mL, with a minimum detection limit of 0.15 pg/mL. Furthermore, the fabricated GCE/MNP/GA/ACE2/BSA sensor achieved satisfactory recoveries of SARS-CoV-2 spike protein in saliva and nasal swab samples within 10 min. These results indicate that this magnetically-assisted biosensor has established a solid foundation for the swift on-site detection of COVID-19.

Nanomaterials-based electrochemical biosensors for diagnosis of COVID-19

Since the outbreak of corona virus disease 2019 (COVID-19), this pandemic has caused severe death and infection worldwide. Owing to its strong infectivity, long incubation period, and nonspecific symptoms, the early diagnosis is essential to reduce risk of the severe illness. The electrochemical biosensor, as a fast and sensitive technique for quantitative analysis of body fluids, has been widely studied to diagnose different biomarkers caused at different infective stages of COVID-19 virus (SARS-CoV-2). Recently, many reports have proved that nanomaterials with special architectures and size effects can effectively promote the biosensing performance on the COVID-19 diagnosis, there are few comprehensive summary reports yet. Therefore, in this review, we will pay efforts on recent progress of advanced nanomaterials-facilitated electrochemical biosensors for the COVID-19 detections. The process of SARS-CoV-2 infection in humans will be briefly described, as well as summarizing the types of sensors that should be designed for different infection processes. Emphasis will be supplied to various functional nanomaterials which dominate the biosensing performance for comparison, expecting to provide a rational guidance on the material selection of biosensor construction for people. Finally, we will conclude the perspective on the design of superior nanomaterials-based biosensors facing the unknown virus in future.

Disposable paper electrodes for detection of changes in dopamine concentrations in rat brain homogenates

Dopamine, the main catecholamine neurotransmitter plays an important role in renal, cardiovascular, central nervous systems, and pathophysiological processes. The abnormal dopamine levels can result in neurological disorders such as Parkinson's, Alzheimer's, schizophrenia, acute anxiety, neuroblastoma and also contribute to cognitive dysfunctions. Given the widespread importance of dopamine concentration levels, it is imperative to develop sensors that are able to monitor dopamine. Herein, we have developed pre-anodized disposable paper electrode modified with 1-pyrenebutyric acid, for the selective and sensitive determination of dopamine. The sensor was characterized with Fourier transform infrared spectroscopy, Energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and electrochemical techniques for addressing the robust formation and electrochemical activity. The modified electrode exhibited excellent electrocatalytic activity towards dopamine without the common interference from ascorbic acid. The calibration plot for the dopamine sensor resulted linear range from 0.003 μM to 0.5 μM with a detection limit of 0.11 nM. The sensor's potential utility was tested by monitoring dopamine concentration changes in rat brain homogenates when subjected to neurotoxicity. The developed sensor was validated with gold-standard UV-Vis spectroscopy studies and computational studies were performed to understand the interaction between 1-pyrenebutyric acid and dopamine.

Simultaneous electrochemical sensing of heavy metal ions (Zn2+, Cd2+, Pb2+, and Hg2+) in food samples using a covalent organic framework/carbon black modified glassy carbon electrode

In this study, for the first time, a selective electrochemical sensor by glassy carbon electrode (GCE) modified with the covalent organic framework (COF) and carbon black (CB) was introduced and applied to simultaneous sensing of Zn2+, Cd2+, Pb2+, and Hg2+ via differential pulse anodic stripping voltammetry (DPASV). The COF is supplied through a condensation reaction between melamine and trimesic acid. The COF and CB, which are used to modify the GCE surface, increase electrochemical activity. The linearity to determine ions was achieved as Zn2+: 0.009-1100 nM, Cd2+: 0.005-1100 nM, Pb2+: 0.003-1100 nM, and Hg2+: 0.001-1100 nM. Besides, the detection limits for Zn2+, Cd2+, Pb2+, and Hg2+ have obtained 0.003, 0.002, 0.001 and 0.0003 nM, respectively. The CB-COF/GCE was applied to simultaneously measure the ions in food samples. For validation, atomic absorption spectrometry (AAS) was applied to measure the amount of target metal ions as a standard method in real samples.

Cutting-edge biorecognition strategies to boost the detection performance of COVID-19 electrochemical biosensors: A review

Electrochemical biosensors are known for their high sensitivity, selectivity, and low cost. Recently, they have gained significant attention and became particularly important as promising tools for the detection of COVID-19 biomarkers, since they offer a rapid and accurate means of diagnosis. Biorecognition strategies are a crucial component of electrochemical biosensors and determine their specificity and sensitivity based on the interaction of biological molecules, such as antibodies, enzymes, and DNA, with target analytes (e.g., viral particles, proteins and genetic material) to create a measurable signal. Different biorecognition strategies have been developed to enhance the performance of electrochemical biosensors, including direct, competitive, and sandwich binding, alongside nucleic acid hybridization mechanisms and gene editing systems. In this review article, we present the different strategies used in electrochemical biosensors to target SARS-CoV-2 and other COVID-19 biomarkers, as well as explore the advantages and disadvantages of each strategy and highlight recent progress in this field. Additionally, we discuss the challenges associated with developing electrochemical biosensors for clinical COVID-19 diagnosis and their widespread commercialization.

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.

Electrochemical Sensors and Biosensors for Identification of Viruses: A Critical Review

Due to their life cycle, viruses can disrupt the metabolism of their hosts, causing diseases. If we want to disrupt their life cycle, it is necessary to identify their presence. For this purpose, it is possible to use several molecular-biological and bioanalytical methods. The reference selection was performed based on electronic databases (2020-2023). This review focused on electrochemical methods with high sensitivity and selectivity (53% voltammetry/amperometry, 33% impedance, and 12% other methods) which showed their great potential for detecting various viruses. Moreover, the aforementioned electrochemical methods have considerable potential to be applicable for care-point use as they are portable due to their miniaturizability and fast speed analysis (minutes to hours), and are relatively easy to interpret. A total of 2011 articles were found, of which 86 original papers were subsequently evaluated (the majority of which are focused on human pathogens, whereas articles dealing with plant pathogens are in the minority). Thirty-two species of viruses were included in the evaluation. It was found that most of the examined research studies (77%) used nanotechnological modifications. Other ones performed immunological (52%) or genetic analyses (43%) for virus detection. 5% of the reports used peptides to increase the method's sensitivity. When evaluable, 65% of the research studies had LOD values in the order of ng or nM. The vast majority (79%) of the studies represent proof of concept and possibilities with low application potential and a high need of further research experimental work.

AIEgens-enhanced rapid sensitive immunofluorescent assay for SARS-CoV-2 with digital microfluidics

BACKGROUND

Sensitive and rapid antigen detection is critical for the diagnosis and treatment of infectious diseases, but conventional ELISAs including chemiluminescence-based assays are limited in sensitivity and require many operation steps. Fluorescence immunoassays are fast and convenient but often show limited sensitivity and dynamic range.

RESULTS

To address the need, an aggregation-induced emission fluorgens (AIEgens) enhanced immunofluorescent assay with beads-based quantification on the digital microfluidic (DMF) platform was developed. Portable DMF devices and chips with small electrodes were fabricated, capable of manipulating droplets within 100 nL and boosting the reaction efficiency. AIEgen nanoparticles (NPs) with high fluorescence and photostability were synthesized to enhance the test sensitivity and detection range. The integration of AIEgen probes, transparent DMF chip design, and the large magnetic beads (10 μm) as capture agents enabled rapid and direct image-taking and signal calculation of the test result. The performance of this platform was demonstrated by point-of-care quantification of SARS-CoV-2 nucleocapsid (N) protein. Within 25 min, a limit of detection of 5.08 pg mL-1 and a limit of quantification of 8.91 pg mL-1 can be achieved using <1 μL sample. The system showed high reproducibility across the wide dynamic range (10-105 pg mL-1), with the coefficient of variance ranging from 2.6% to 9.8%.

SIGNIFICANCE

This rapid, sensitive AIEgens-enhanced immunofluorescent assay on the DMF platform showed simplified reaction steps and improved performance, providing insight into the small-volume point-of-care testing of different biomarkers in research and clinical applications.

Detection of SARS-CoV-2 N protein using AgNPs-modified aligned silicon nanowires BioSERS chip

The SARS-CoV-2 (COVID-19) pandemic had a strong impact on societies and economies worldwide and tests for high-performance detection of SARS-CoV-2 biomarkers are still needed for potential future outbreaks of the disease. In this paper, we present the different steps for the design of an aptamer-based surface-enhanced Raman scattering (BioSERS) sensing chip capable of detecting the coronavirus nucleocapsid protein (N protein) in spiked phosphate-buffered solutions and real samples of human blood serum. Optimization of the preparation steps in terms of the aptamer concentration used for the functionalization of the silver nanoparticles, time for affixing the aptamer, incubation time with target protein, and insulation of the silver active surface with cysteamine, led to a sensitive BioSERS chip, which was able to detect the N protein in the range from 1 to 75 ng mL-1 in spiked phosphate-buffered solutions with a detection limit of 1 ng mL-1 within 30 min. Furthermore, the BioSERS chip was used to detect the target protein in scarcely spiked human serum. This study demonstrates the possibility of a clinical application that can improve the detection limit and accuracy of the currently commercialized SARS-CoV-2 immunodiagnostic kit. Additionally, the system is modular and can be applied to detect other proteins by only changing the aptamer.

Saliva-based detection of SARS-CoV-2: a bibliometric analysis of global research

Saliva has emerged as a promising noninvasive biofluid for the diagnosis of oral and systemic diseases, including viral infections. During the coronavirus disease 2019 (COVID-19) pandemic, a growing number of studies focused on saliva-based detection of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Taking advantage of the WoS core collection (WoSCC) and CiteSpace, we retrieved 1021 articles related to saliva-based detection of SARS-CoV-2 and conducted a comprehensive bibliometric analysis. We analyzed countries, institutions, authors, cited authors, and cited journals to summarize their contribution and influence and analyzed keywords to explore research hotspots and trends. From 2020 to 2021, research focused on viral transmission via saliva and verification of saliva as a reliable specimen, whereas from 2021 to the present, the focus of research has switched to saliva-based biosensors for SARS-CoV-2 detection. By far, saliva has been verified as a reliable specimen for SARS-CoV-2 detection, although a standardized procedure for saliva sampling and processing is needed. Studies on saliva-based detection of SARS-CoV-2 will promote the development of saliva-based diagnostics and biosensors for viral detection. Collectively, our findings could provide valuable information to help scientists perceive the basic knowledge landscapes on saliva-based detection of SARS-CoV-2, the past and current research hotspots, and future opportunities.

Smartphone-assisted paper-based electrochemical immunosensor for SARS-CoV-2 detection in saliva

Herein, we developed a new waste solution-free paper-based electrochemical immunosensor for SARS-CoV-2 detection in saliva, by combining vertical and lateral flow. In detail, the device was constituted of a reservoir containing all reagents for the construction of the immunological chain onto the magnetic beads and a lateral flow holder which contained a polyester-based electrode, a magnet, and an adsorbent pad. The measurement was carried out by adding the saliva sample into the reservoir, followed by the addition of this solution in the hole present in the lateral flow holder. The successive additions of washing buffer and TMB solution in the lateral flow holder allowed the detection of N protein in saliva in the range of 0.06 to 4 µg/mL with a detection limit equal to 30 ng/mL. The analysis of several saliva samples with the sensing tool and the reference method, demonstrated the effectiveness of this device, being able to identify positive patients with high values of CT e.g. 35. This new configuration paves the way for the realization of any magnetic beads-based immunosystem without waste solution production, enlarging the application of paper-based devices.

Boron nanosheets as a phosphatase mimicking nanozyme with ultrahigh catalytic activity for prodrug-based cancer therapy

Boron nanosheets (BNSs) are reported as a new phosphatase mimicking nanozyme. Surprisingly, the catalytic rate of BNSs is up to 17 times those of known phosphatase mimicking nanozymes. By adding polyols and Lewis bases, the catalytic activity of BNSs was attributed to the Lewis acidity of the B centers of the BNSs. Theoretical investigation shows that the B centers are responsible for the catalytic hydrolysis of phosphoesters. Moreover, the biomimetic activity of the BNSs was further explored for enhancing anticancer therapy through nanozyme-catalyzed prodrug conversion.

Simple, Visual, Point-of-Care SARS-CoV-2 Detection Incorporating Recombinase Polymerase Amplification and Target DNA-Protein Crosslinking Enhanced Chemiluminescence

The ongoing COVID-19 pandemic, driven by persistent SARS-CoV-2 transmission, threatens human health worldwide, underscoring the urgent need for an efficient, low-cost, rapid SARS-CoV-2 detection method. Herein, we developed a point-of-care SARS-CoV-2 detection method incorporating recombinase polymerase amplification (RPA) and DNA-protein crosslinking chemiluminescence (DPCL) (RPADPCL). RPADPCL involves the crosslinking of biotinylated double-stranded RPA DNA products with horseradish peroxidase (HRP)-labeled streptavidin (SA-HRP). Modified products are captured using SA-labeled magnetic beads, and then analyzed using a chemiluminescence detector and smartphone after the addition of a chemiluminescent substrate. Under optimal conditions, the RPADPCL limit of detection (LOD) was observed to be 6 copies (within the linear detection range of 1-300 copies) for a plasmid containing the SARS-CoV-2 N gene and 15 copies (within the linear range of 10-500 copies) for in vitro transcribed (IVT) SARS-CoV-2 RNA. The proposed method is convenient, specific, visually intuitive, easy to use, and does not require external excitation. The effective RPADPCL detection of SARS-CoV-2 in complex matrix systems was verified by testing simulated clinical samples containing 10% human saliva or a virus transfer medium (VTM) spiked with a plasmid containing a SARS-CoV-2 N gene sequence or SARS-CoV-2 IVT RNA. Consequently, this method has great potential for detecting targets in clinical samples.

An ultra-sensitive SARS-CoV-2 antigen optical biosensor based on angiotensin converting enzyme 2 (ACE-2) functionalized magnetic-fluorescent silica nanoparticles

This work reports on the design and synthesis of an angiotensin-converting enzyme 2 (ACE-2) functionalized magnetic fluorescent silica nanoparticles (Fe-FSNP) as a biosensing platform to detect severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antigen. Iron oxide (Fe3O4) nanoparticles were synthesized via ultrasonic-assisted coprecipitation and then coated with fluorescent silica nanoparticles (FSNP) through thesol-gelmethod forming the Fe-FSNP samples. Silica obtained from local geothermal powerplant was used in this work and Rhodamine B was chosen as the incorporated fluorescent dye, hence this reports for the first time ACE-2 was immobilized on the natural silica surface. The Fe-FSNP nanoparticle consists of a 18-25 nm magnetic core and a silica shell with a thickness of 30 nm as confirmed from the transmission electron microscopy image. Successful surface functionalization of the Fe-FSNP with ACE-2 as bioreceptor was conducted through hydrosylilation reaction and confirmed through the Fourier transform infrared spectroscopy. The detection of SARS-Cov-2 antigen by Fe-FSNP/ACE2 was measured through the change in its maximum fluorescence intensity at 588 nm where fluorescence- quenching had occurred. The biosensing platform showed a rapid response at 30 min with a linear range of 10-6to 10-2μg ml-1. The magnetic-fluorescent properties of the nanoparticle enables an ultra-sensitive detection of SARS-Cov-2 antigen with the limit of detection as low as 2 fg ml-1.

Detection of antibodies against SARS-CoV-2 Spike protein by screen-printed carbon electrodes modified by colloidal gold nanoparticles

In this work, electrochemical bioanalytical systems for the determination of antibodies against the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Spike protein (anti-rS) is reported. Environmentally friendly chemicals were applied in the synthesis of gold nanoparticles (AuNPs). The AuNPs were integrated onto the screen-printed carbon electrodes (SPE), and the biological recognition part was based on recombinant SARS-CoV-2 Spike protein (rS), which during the immobilization was cross-linked by glutaraldehyde. Immobilized rS protein based biological recognition part enabled selective recognition of anti-rS antibodies. The current flux of AuNPs reduction (at +200 mV) in a pure phosphate buffer (PB) was employed as the transduction signal. It has been reported that the formation of anti-rS layers on the surface of AuNPs delays the electrode response time (ts), tracked at the current flux density values of 80 μA cm-2. Using the AuNP-modified SPE, we demonstrated a rapid anti-rS detection within a detection limit of 2 ng mL-1 (0.125 binding antibody units mL-1, 17 pM). This system can be applied to track the response of immune system towards SARS-CoV-2 infection and monitoring of Coronavirus Disease 2019 (COVID-19).

Recent advances in SERS-based immunochromatographic assay for pathogenic microorganism diagnosis: A review

Infectious diseases caused by bacteria, viruses, fungi, and other pathogenic microorganisms are among the most harmful public health problems in the world, causing tens of millions of deaths and incalculable economic losses every year. The establishment of rapid, simple, and highly sensitive diagnostic methods for pathogenic microorganisms is important for the prevention and control of infectious diseases, guidance of timely treatment, and the reduction of public safety risks. Lateral flow immunoassay (LFA) based on the colorimetric signal of colloidal gold is the most popular point-of-care testing technology at present, but it is limited by poor sensitivity and low throughput and hardly meets the needs of the highly sensitive screening of pathogenic microorganisms. In recent years, the combination of surface-enhanced Raman scattering (SERS) and LFA technology has developed into a novel analytical platform with high sensitivity and multiple detection capabilities and has shown great advantages in the detection of pathogenic microorganisms and infectious diseases. This review summarizes the working principle, design ideas, and application of the existing SERS-based LFA methods in pathogenic microorganism detection and further introduces the effect of new technologies such as Raman signal encoding, magnetic enrichment, novel membrane nanotags, and integrated Raman reading equipment on the performance of SERS-LFA. Finally, the main challenges and the future direction of development in this field of SERS-LFA are discussed.

Advances in nanobiosensors during the COVID-19 pandemic and future perspectives for the post-COVID era

The unprecedented threat of the highly contagious virus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which causes exponentially increased infections of coronavirus disease 2019 (COVID-19), highlights the weak spots of the current diagnostic toolbox. In the midst of catastrophe, nanobiosensors offer a new opportunity as an alternative tool to fill a gap among molecular tests, rapid antigen tests, and serological tests. Nanobiosensors surpass the potential of antigen tests because of their enhanced sensitivity, thus enabling us to see antigens as stable and easy-to-access targets. During the first three years of the COVID-19 pandemic, a substantial number of studies have reported nanobiosensors for the detection of SARS-CoV-2 antigens. The number of articles on nanobiosensors and SARS-CoV-2 exceeds the amount of nanobiosensor research on detecting previous infectious diseases, from influenza to SARS-CoV and MERS-CoV. This unprecedented publishing pace also implies the significance of SARS-CoV-2 and the present pandemic. In this review, 158 studies reporting nanobiosensors for detecting SARS-CoV-2 antigens are collected to discuss the current challenges of nanobiosensors using the criteria of point-of-care (POC) diagnostics along with COVID-specific issues. These advances and lessons during the pandemic pave the way for preparing for the post-COVID era and potential upcoming infectious diseases.

On-site airborne pathogen detection for infection risk mitigation

Human-infecting pathogens that transmit through the air pose a significant threat to public health. As a prominent instance, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that caused the COVID-19 pandemic has affected the world in an unprecedented manner over the past few years. Despite the dissipating pandemic gloom, the lessons we have learned in dealing with pathogen-laden aerosols should be thoroughly reviewed because the airborne transmission risk may have been grossly underestimated. From a bioanalytical chemistry perspective, on-site airborne pathogen detection can be an effective non-pharmaceutic intervention (NPI) strategy, with on-site airborne pathogen detection and early-stage infection risk evaluation reducing the spread of disease and enabling life-saving decisions to be made. In light of this, we summarize the recent advances in highly efficient pathogen-laden aerosol sampling approaches, bioanalytical sensing technologies, and the prospects for airborne pathogen exposure measurement and evidence-based transmission interventions. We also discuss open challenges facing general bioaerosols detection, such as handling complex aerosol samples, improving sensitivity for airborne pathogen quantification, and establishing a risk assessment system with high spatiotemporal resolution for mitigating airborne transmission risks. This review provides a multidisciplinary outlook for future opportunities to improve the on-site airborne pathogen detection techniques, thereby enhancing the preparedness for more on-site bioaerosols measurement scenarios, such as monitoring high-risk pathogens on airplanes, weaponized pathogen aerosols, influenza variants at the workplace, and pollutant correlated with sick building syndromes.

C-MEMS-derived glassy carbon electrochemical biosensors for rapid detection of SARS-CoV-2 spike protein

According to a World Health Organization (WHO) report, the world has experienced more than 766 million cases of positive SARS-CoV-2 infection and more than 6.9 million deaths due to COVID through May 2023. The WHO declared a pandemic due to the rapid spread of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus, and the fight against this pandemic is not over yet. Important reasons for virus spread include the lack of detection kits, appropriate detection techniques, delay in detection, asymptomatic cases and failure in mass screening. In the last 3 years, several researchers and medical companies have introduced successful test kits to detect the infection of symptomatic patients in real time, which was necessary to monitor the spread. However, it is also important to have information on asymptomatic cases, which can be obtained by antibody testing for the SARS-CoV-2 virus. In this work, we developed a simple, advantageous immobilization procedure for rapidly detecting the SARS-CoV-2 spike protein. Carbon-MEMS-derived glassy carbon (GC) is used as the sensor electrode, and the detection is based on covalently linking the SARS-CoV-2 antibody to the GC surface. Glutaraldehyde was used as a cross-linker between the antibody and glassy carbon electrode (GCE). The binding was investigated using Fourier transform infrared spectroscopy (FTIR) characterization and cyclic voltammetric (CV) analysis. Electrochemical impedance spectroscopy (EIS) was utilized to measure the change in total impedance before and after incubation of the SARS-CoV-2 antibody with various concentrations of SARS-CoV-2 spike protein. The developed sensor can sense 1 fg/ml to 1 µg/ml SARS-CoV-2 spike protein. This detection is label-free, and the chances of false positives are minimal. The calculated LOD was ~31 copies of viral RNA/mL. The coefficient of variation (CV) number is calculated from EIS data at 100 Hz, which is found to be 0.398%. The developed sensor may be used for mass screening because it is cost-effective. A schematic representation of the SARS-CoV-2 spike protein sensing using surface functionalized glassy carbon electrode.

The Application of Graphene Field-Effect Transistor Biosensors in COVID-19 Detection Technology: A Review

Coronavirus disease 2019 (COVID-19) is a disease caused by the infectious agent of severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2). The primary method of diagnosing SARS-CoV-2 is nucleic acid detection, but this method requires specialized equipment and is time consuming. Therefore, a sensitive, simple, rapid, and low-cost diagnostic test is needed. Graphene field-effect transistor (GFET) biosensors have become the most promising diagnostic technology for detecting SARS-CoV-2 due to their advantages of high sensitivity, fast-detection speed, label-free operation, and low detection limit. This review mainly focus on three types of GFET biosensors to detect SARS-CoV-2. GFET biosensors can quickly identify SARS-CoV-2 within ultra-low detection limits. Finally, we will outline the pros and cons of the diagnostic approaches as well as future directions.

One-step selective layer assemble: A versatile approach for the development of a SARS-CoV-2 electrochemical immunosensor

The appearance of new viruses and diseases has made the development of rapid and reliable diagnostic tests crucial. In light of it, we proposed a new method for assembling an electrochemical immunosensor, based on a one-step approach for selective layer formation. For this purpose, a mixture containing the immobilizing agent (polyxydroxybutyrate, PHB) and the recognition element (antibodies against SARS-CoV-2 nucleocapsid protein) was prepared and used to modify a screen-printed carbon electrode with electrodeposited graphene oxide, for the detection of SARS-CoV-2 nucleocapsid protein (N-protein). Under optimum conditions, N-protein was successfully detected in three different matrixes - saliva, serum, and nasal swab, with the lowest detectable values of 50 pg mL-1, 1.0 ng mL-1, and 50 pg mL-1, respectively. Selectivity was assessed against SARS-CoV-2 receptor-binding domain protein (RBD) and antibodies against yellow fever (YF), and no significant response was observed in presence of interferents, reinforcing the suitability of the proposed one-step approach for selective layer formation. The proposed biosensor was stable for up to 14 days, and the mixture was suitable for immunosensor preparation even after 60 days of preparation. The proposed assembly strategy reduces the cost, analysis time, and waste generation. This reduction is achieved through miniaturization, which results in the decreased use of reagents and sample volumes. Additionally, this approach enables healthcare diagnostics to be conducted in developing regions with limited resources. Therefore, the proposed one-step approach for selective layer formation is a suitable, simpler, and a reliable alternative for electrochemical immunosensing.

Graphene Field Effect Biosensor for Concurrent and Specific Detection of SARS-CoV-2 and Influenza

The SARS-CoV-2 pandemic has highlighted the need for devices capable of carrying out rapid differential detection of viruses that may manifest similar physiological symptoms yet demand tailored treatment plans. Seasonal influenza may be exacerbated by COVID-19 infections, increasing the burden on healthcare systems. In this work, we demonstrate a technology based on liquid-gated graphene field-effect transistors (GFETs), for rapid and ultraprecise sensing and differentiation of influenza and SARS-CoV-2 surface protein. Most distinctively, the device consists of 4 onboard GFETs arranged in a quadruple architecture, where each quarter is functionalized individually (with either antibodies or chemically passivated control) but measured jointly. The sensor platform was tested against a range of concentrations of viral surface proteins from both viruses with the lowest tested and detected concentration at ∼50 ag/mL, or 88 zM for COVID-19 and 227 zM for Flu, which is 5-fold lower than the values reported previously on a similar platform. Unlike the classic real-time polymerase chain reaction test, which has a turnaround time of a few hours, the graphene technology presents an ultrafast response time of ∼10 s even in complex and clinically relevant media such as saliva. Thus, we have developed a multianalyte, highly sensitive, and fault-tolerant technology for rapid diagnostic of contemporary, emerging, and future pandemics.

μPADs on Centrifugal Microfluidic Discs for Rapid Sample-to-Answer Salivary Diagnostics

A fully integrated device for salivary detection with a sample-in-answer-out fashion is critical for noninvasive point-of-care testing (POCT), especially for the screening of contagious disease infection. Microfluidic paper-based analytical devices (μPADs) have demonstrated their huge potential in POCT due to their low cost and easy adaptation with other components. This study developed a generic POCT platform by integrating a centrifugal microfluidic disc with μPADs to realize sample-to-answer salivary diagnostics. Specifically, a custom centrifugal microfluidic disc integrated with μPADs is fabricated, which demonstrated a high efficiency in saliva treatment. To demonstrate the capability of the integrated device for salivary analysis, the SARS-CoV-2 Nucleocapsid (N) protein, a reliable biomarker for SARS-CoV-2 acute infection, is used as the model analyte. By the chemical treatment of the μPAD surface, and by optimizing the protein immobilization conditions, the on-disc μPADs were able to detect the SARS-CoV-2 N protein down to 10 pg mL-1 with a dynamic range of 10-1000 pg mL-1 and an assay time of 8 min. The integrated device was successfully used for the quantification of the N protein of pseudovirus in saliva with high specificity and demonstrated a comparable performance to the commercial paper lateral flow assay test strips.

Development of Rapid Aptamer-Based Screening Assay for the Detection of Covid-19 Variants

The development of a colorimetric severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) detection assay with the WHO published ASSURED criteria is reported, in which the biosensor should have the following characteristics of (i) being affordable for low-income communities, (ii) sensitive, (iii) specific, (iv) user-friendly to be used by non-skilled personnel, (v) rapid and robust, (vi) equipment-free, and (vii) delivered to the end-users as a simple and easy to use point-of-care tool. Early viral infection detection prevents virus spread and controls the epidemic. We herein report the development of a colorimetric assay in which SARS-COV-2 variants can be detected by colorimetric observation of color on the sensing cotton swab surface. Using the developed biosensor assay, it is possible to discriminate between the various SARS-CoV-2 variants with a LOD of 100 ng/mL within 4 min including sample preconcentration and incubation step. The results illustrated the development of a SARS-CoV-2 colorimetric biosensor that can be mass produced, with low-reagent cost, and can be read-out visually in the field by nonskilled personnel.

Point-of-Care Devices for Viral Detection: COVID-19 Pandemic and Beyond

The pandemic of COVID-19 and its widespread transmission have made us realize the importance of early, quick diagnostic tests for facilitating effective cure and management. The primary obstacles encountered were accurately distinguishing COVID-19 from other illnesses including the flu, common cold, etc. While the polymerase chain reaction technique is a robust technique for the determination of SARS-CoV-2 in patients of COVID-19, there arises a high demand for affordable, quick, user-friendly, and precise point-of-care (POC) diagnostic in therapeutic settings. The necessity for available tests with rapid outcomes spurred the advancement of POC tests that are characterized by speed, automation, and high precision and accuracy. Paper-based POC devices have gained increasing interest in recent years because of rapid, low-cost detection without requiring external instruments. At present, microfluidic paper-based analysis devices have garnered public attention and accelerated the development of such POCT for efficient multistep assays. In the current review, our focus will be on the fabrication of detection modules for SARS-CoV-2. Here, we have included a discussion on various strategies for the detection of viral moieties. The compilation of these strategies would offer comprehensive insight into the detection of the causative agent preparedness for future pandemics. We also provide a descriptive outline for paper-based diagnostic platforms, involving the determination mechanisms, as well as a commercial kit for COVID-19 as well as their outlook.

COVID severity test (CoST sensor)-An electrochemical immunosensing approach to stratify disease severity

With the evolution of the COVID-19 pandemic, there is now a need for point-of-care devices for the quantification of disease biomarkers toward disease severity assessment. Disease progression has been determined as a multifactor phenomenon and can be treated based on the host immune response within each individual. CoST is an electrochemical immunosensor point-of-care device that can determine disease severity through multiplex measurement and quantification of spike protein, nucleocapsid protein, D-dimer, and IL-2R from 100 μL of plasma samples within a few minutes. The limit of detection was found to be 3 ng/mL and 21 ng/mL for S and N proteins whereas for D-dimer and IL-2R it was 0.0006 ng/mL and 0.242 ng/mL, respectively. Cross-reactivity of all the biomarkers was studied and it was found to be <20%. Inter and intra-assay variability of the CoST sensor was less than <15% confirming its ability to detect the target biomarker in body fluids. In addition, this platform has also been tested to quantify all four biomarkers in 40 patient samples and to predict the severity index. A significant difference was observed between healthy and COVID-19 samples with a p-value of 0.0002 for D-dimer and <0.0001 for other proteins confirming the ability of the COST sensor to be used as a point of care device to assess disease severity at clinical sites. This device platform can be modified to impact a wide range of disease indications where prognostic monitoring of the host response can be critical in modulating therapy.

Sensitive detection of SARS-CoV-2 spike protein based on electrochemical impedance spectroscopy of Fe3O4@SiO2–Au/GCE biosensor

Highly contagious COVID-19 disease is caused by a novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which poses a serious threat to global public health. Therefore, the development of a fast and reliable method for the detection of SARS-CoV-2 is an urgent research need. The Fe3O4@SiO2–Au is enriched with a variety of functional groups, which can be used to fabricate a sensitive electrochemical biosensor by biofunctionalization with angiotensin-converting enzyme 2 (ACE2). Accordingly, we developed a novel electrochemical sensor by chemically modifying a glassy carbon electrode (GCE) with Fe3O4@SiO2–Au nanocomposites (hereafter Fe3O4@SiO2–Au/GCE) for the rapid detection of S-protein spiked SARS-CoV-2 by electrochemical impedance spectroscopy (EIS). The new electrochemical sensor has a low limit detection (viz., 4.78 pg/mL) and a wide linear dynamic range (viz., 0.1 ng/mL to 10 μg/mL) for detecting the EIS response signal of S-protein. The robust Fe3O4@SiO2–Au/GCE biosensor has high selectivity, stability, and reproducibility for the detection of S-protein with good recovery of saliva samples.

Simultaneous Detection of SARS-CoV-2 Nucleoprotein and Receptor Binding Domain by a Multi-Area Reflectance Spectroscopy Sensor

The COVID-19 pandemic has emphasized the urgent need for point-of-care methods suitable for the rapid and reliable diagnosis of viral infections. To address this demand, we report the rapid, label-free simultaneous determination of two SARS-CoV-2 proteins, namely, the nucleoprotein and the receptor binding domain peptide of S1 protein, by implementing a bioanalytical device based on Multi Area Reflectance Spectroscopy. Simultaneous detection of these two proteins is achieved by using silicon chips with adjacent areas of different silicon dioxide thickness on top, each of which is modified with an antibody specific to either the nucleoprotein or the receptor binding domain of SARS-CoV-2. Both areas were illuminated by a single probe that also collected the reflected light, directing it to a spectrometer. The online conversion of the combined reflection spectra from the two silicon dioxide areas into the respective adlayer thickness enabled real-time monitoring of immunoreactions taking place on the two areas. Several antibodies have been tested to define the pair, providing the higher specific signal following a non-competitive immunoassay format. Biotinylated secondary antibodies and streptavidin were used to enhance the specific signal. Both proteins were detected in less than 12 min, with detection limits of 1.0 ng/mL. The assays demonstrated high repeatability with intra- and inter-assay coefficients of variation lower than 10%. Moreover, the recovery of both proteins from spiked samples prepared in extraction buffer from a commercial self-test kit for SARS-CoV-2 collection from nasopharyngeal swabs ranged from 90.0 to 110%. The short assay duration in combination with the excellent analytical performance and the compact instrument size render the proposed device and assay suitable for point-of-care applications.

Fe3O4@SiO2@NiAl-LDH microspheres implication in separation, kinetic and structural properties of phenylalanine dehydrogenase

Fe3O4@SiO2@NiAl-LDH three-components microsphere contains a Fe3O4@SiO2 magnetic core and a layered double hydroxide with nickel cation provide the binding ability to (His)-tagged-protein and exhibits high performance in protein separation and purification. The morphology and chemistry of the synthesized Fe3O4@SiO2@NiAl-LDH microspheres were characterized by energy-dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR), vibrating sample magnetometer (VSM), Dynamic light scattering (DLS). Purified enzyme was assesed with SDS-PAGE (sodium dodecyl sulfate-polyacrylamide gel electrophoresis and intrinsic fluorescence spectroscopy. In this study, the separation of phenylalanine dehydrogenase (PheDH) by Fe3O4@SiO2@NiAl -LDH was performed and the effect of microsphere was investigated on the kinetic and structural properties of PheDH. After purification, kinetic parameters such as Km, Vmax, Kcat, kcat/Km, optimum temperature, thermal stability, and and activation energy were evaluated and compared according to the mentioned methods. The interaction between the enzyme and the microsphere displayed a high performance in protein binding capacity. The results also revealed that the kinetic parameters of the enzyme changed in a dose-dependent manner in the presence of a microsphere. Moreover, the results of intrinsic fluorescence and Circular Dichroism (CD) confirmed the structural changes of the protein in the interaction with the microsphere.

Microchip gas chromatography column using magnetic beads coated with polydimethylsiloxane and metal organic frameworks

Micro gas chromatography (μGC) using microfabricated silicon columns has been developed in response to the requirement for portable on-site gas analysis. Although different stationary phases have been developed, repeatable and reliable surface coatings in these rather small microcolumns remains a challenge. Herein, a new stationary phase coating strategy using magnetic beads (MBs) as carriers for micro column is presented. MBs modified with organopolysiloxane (MBs@OV-1) and a metal organic framework (MBs@HKUST-1) are deposited in on-chip microcolumns assisted with a magnetic field with an optimized modification process. MBs@OV-1 column showed a minimum HETP of 0.074 cm (1351 plates/m) of 62 cm/s. Mixtures of volatile organic compounds are successfully separated using MBs carried stationary phase which demonstrates that this technique has good chromatographic column efficiency. This method not only provides a novel coating process, washing and characterization of the stationary phases but also establishes a straightforward strategy for testing new absorbent materials for μGC systems.

Double-antibody-based nano-biosensing system for the onsite monitoring of SARS-CoV-2 variants

The fast and reliable diagnosis of COVID-19 is the foremost priority for promoting public health interventions. Therefore, double-antibody-based immunobiosensor chips were designed, constructed, and exploited for clinical diagnosis. Gold nanoparticles/tungsten oxide/carbon nanotubes (AuNPs/WO3/CNTs) were used as the active working sensor surface to support the chemical immobilization of a mixture of SARS-CoV-2 antibodies (anti-RBD-S and anti-RBD-S-anti-Llama monoclonal antibodies). The morphology and chemical functionalization of the fabricated disposable immunochips was characterized using scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). After full assay optimization, the immunobiosensor showed a high sensitivity to detect SARS-CoV-2-S protein with limits of detection and quantification of 1.8 and 5.6 pg/mL, respectively. On the other hand, for the SARS-CoV-2 whole virus particle analysis, the detection and quantification limits were determined to be 5.7 and 17 pg/mL, respectively. The biosensor showed a highly selective response toward SARS-CoV-2, even in the presence of influenza, nontargeting human coronaviruses, and Middle East respiratory syndrome coronavirus (MERS-CoV). The immunochips exhibited distinct responses toward the variants of concern: B.1>C.36.3>Omicron> Delta> Alpha coronavirus variants. For biosensor validation, twenty-nine clinical specimens were analyzed, and the impedimetric responses were positively detected for two Delta samples, eighteen Omicron samples, and six B.1-type samples in addition to three negative samples. Eventually, the immunobiosensor was fabricated in the form of ready-to-use chips capable of sensitive detection of virus variants, especially variants of concern (VOC) and interest, in a specimen within 15 min. The chips provided instantaneous detection with the direct application of clinical samples and are considered a point-of-care device that could be used in public places and hot spots.

Carbon-based biosensors: Next-generation diagnostic tool for target-specific detection of SARS-CoV-2 (COVID-19)

Severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) was declared a global pandemic in 2020. Having rapidly spread around the globe, with the emergence of new variants, there is a crucial need to develop diagnostic kits for its rapid detection. Since it validated accuracy and reliability, the reverse transcription polymerase chain reaction (RT-PCR) test has been declared the gold standard for disease detection. However, despite its reliability, the requirement of specialized facilities, reagents, and duration of a PCR run limits its usage for rapid detection. There is thus a continuous increase in the design and development of rapid, point-of-care (PoC), and cost-effective diagnostic kits. In this review, we discuss the potential of carbon-based biosensors for target-specific detection of coronavirus disease 19 (COVID-19) and present an overview of investigation within the timeframe of the last four years (2019-2022), which have developed novel platforms using carbon nanomaterial-based approaches for viral detection. The approaches discussed offer rapid, accurate, and cost-effective strategies for COVID-19 detection for healthcare personnel and research workers.

Using low-cost disposable immunosensor based on flexible PET screen-printed electrode modified with carbon black and gold nanoparticles for sensitive detection of SARS-CoV-2

To help meet the global demand for reliable and inexpensive COVID-19 testing and environmental analysis of SARS-CoV-2, the present work reports the development and application of a highly efficient disposable electrochemical immunosensor for the detection of SARS-CoV-2 in clinical and environmental matrices. The sensor developed is composed of a screen-printed electrode (SPE) array which was constructed using conductive carbon ink printed on polyethylene terephthalate (PET) substrate made from disposable soft drink bottles. The recognition site (Spike S1 Antibody (anti-SP Ab)) was covalently immobilized on the working electrode surface, which was effectively modified with carbon black (CB) and gold nanoparticles (AuNPs). The immunosensing material was subjected to a multi-technique characterization analysis using X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) with elemental analysis via energy dispersive spectroscopy (EDS). The electrochemical characterization of the electrode surface and analytical measurements were performed using cyclic voltammetry (CV) and square-wave voltammetry (SWV). The immunosensor was easily applied for the conduct of rapid diagnoses or accurate quantitative environmental analyses by setting the incubation period to 10 min or 120 min. Under optimized conditions, the biosensor presented limits of detection (LODs) of 101 fg mL^-1 and 46.2 fg mL^-1 for 10 min and 120 min incubation periods, respectively; in addition, the sensor was successfully applied for SARS-CoV-2 detection and quantification in clinical and environmental samples. Considering the costs of all the raw materials required for manufacturing 200 units of the AuNP-CB/PET-SPE immunosensor, the production cost per unit is 0.29 USD.

An ultrasensitive ELISA to assay femtomolar level SARS-CoV-2 antigen based on specific peptide and tyramine signal amplification

The SARS-CoV-2 spreading rapidly has aroused catastrophic public healthcare issues and economy crisis worldwide. It plays predominant role to rapidly and accurately diagnose the virus for effective prevention and treatment. As an abundant transmembrane protein, spike protein (SP) is one of the most valuable antigenic biomarkers for diagnosis of COVID-19. Herein a phage expression of WNLDLSQWLPPM peptide specific to SARS-CoV-2 SP was screened. Molecular docking revealed that the isolated peptide binds to major antigenic epitope locating at S2 subunit with hydrogen bonding. Taking the specific peptide as antigen sensing probe and tyramine signal amplification (TSA), an ultrasensitive "peptide-antigen-antibody" ELISA (p-ELISA) was explored, by which the limit of detection (LOD) was 14 fM and 2.8 fM SARS-CoV-2 SP antigen for first TSA and secondary TSA, respectively. Compared with the LOD by the p-ELISA by direct mode, the sensitivity with 2nd TSA enhanced 100 times. Further, the proposed p-ELISA method can detect SARS-CoV-2 pseudoviruses down to 10 and 3 TCID₅₀/mL spiked in healthy nasal swab sample with 1st TSA and 2nd TSA, separately. Thus, the proposed p-ELISA method with TSA is expected to be a promising ultrasensitive tool for rapidly detecting SARS-CoV-2 antigen to help control the infectious disease.

Biomedical equipments, vaccine and drug in the prevention, diagnosis and treatment of COVID-19

SARS-CoV-2 virus caused an infectious disease, named COVID-19. Biomedical equipments, vaccine and drug have played a crucial role in the prevention, diagnosis and treatment. Nevertheless, up to now, there still has been no literature summarizing the diagnosis, prevention and treatment of this infectious disease from the perspective of biomedical equipments. Thus, this review wants to give an overview on the biomedical equipments, vaccine and drug in the prevention, diagnosis and treatment of this disease, and avoids the overlap with previous research, more emphasis on biomedical equipments, and less emphasis on biomaterials. The existing problems in the current research and application were summarized, and the future research direction was proposed, so as to provide reference to deal with similar viral infections in the future.

Insight of smart biosensors for COVID-19: A review

The review discusses the diagnostic application of biosensors as point-of-care devices in the COVID-19 pandemic. Biosensors are important analytical tools that can be used for the robust and effective detection of infectious diseases in real-time. In this current scenario, the utilization of smart, efficient biosensors for COVID-19 detection is increasing and we have included a few smart biosensors such as smart and intelligent based biosensors, plasmonic biosensors, field effect transistor (FET) biosensors, smart optical biosensors, surface enhanced Raman scattering (SERS) biosensor, screen printed electrode (SPE)-based biosensor, molecular imprinted polymer (MIP)-based biosensor, MXene-based biosensor and metal-organic frame smart sensor. Their significance as well as the benefits and drawbacks of each kind of smart sensor are mentioned in depth. Furthermore, we have compiled a list of various biosensors which have been developed across the globe for COVID-19 and have shown promise as commercial detection devices. Significant challenges in the development of effective diagnostic methods are discussed and recommendations have been made for better diagnostic outcomes to manage the ongoing pandemic effectively.

Electrochemical detection of carmoisine in the presence of tartrazine on the surface of screen printed graphite electrode modified with nickel-cobalt layered double hydroxide ultrathin nanosheets

Toxic effluents containing azo dyes are discharged from various industries and they adversely affect water resoures, soil, aquatic ecosystems. Also, excessive use of food azo dyes can be carcinogenic, toxic, and adversely affect human health. Therefore, the determination of food azo dyes is significant from the perspective of human health and aquatic organisms. In the present work, nickel-cobalt layered double hydroxide nanosheets were prepared and analyzed by various techniques (field emission-scanning electron microscopy, X-ray diffraction, and fourier Transform-Infrared spectroscopy). Then, the screen printed graphite electrode modified with nickel-cobalt layered double hydroxide nanosheets was used for the detection of carmoisine. The nickel-cobalt layered double hydroxide nanosheets/screen printed graphite electrode significantly improved the oxidation of carmoisine by increasing the response current and lowering potentials compared to unmodified screen printed graphite electrode. Based on the findings from differential pulse voltammetry, the nickel-cobalt layered double hydroxide nanosheets/screen printed graphite electrode sensor response towards carmoisine was linear (0.3-125.0 μM) with a detection limit of 0.09 μM. A sensitivity of 0.3088 μA μM^-1 was achieved. Also, the nickel-cobalt layered double hydroxide nanosheets/screen printed graphite electrode was used for voltammetric detection of carmoisine in the presence of tartrazine. Due to the catalytic activity of prepared layered double hydroxide, the prepared sensor exhibited remarkable separation of the peaks when carmoisine and tartrazine coexist. In addition, the prepared sensor showed good stability. Finally, the proposed sensor had promising applicability for analysis of study analytes in powdered juice and lemon juice, with commendable recoveries between 97.3% and 104.8%.

Dual-clamped One-Pot SERS-based Biosensors for Rapid and Sensitive Detection of SARS-CoV-2 Using Portable Raman Spectrometer

Rapid and sensitive diagnostics of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is of utmost importance to control the widespread coronavirus disease 2019 (COVID-19) upsurge. This study demonstrated a novel one-pot surface-enhanced Raman scattering (SERS) based immunoassay to detect SARS-CoV-2, without any washing process using a portable Raman spectrometer. The SERS-immune assay was designed using a regular digital versatile disk (DVD) substrate integrated with Raman reporter labeled silver nanoparticles for double clamping effects. The disks were molded to form nanopillar arrays and coated with silver film to enhance the sensitivity of immunoassay. The SERS platform demonstrated a limit of detection (LoD) up to 50 pg mL^-1 for SARS-CoV-2 spike protein and virus-like-particle (VLP) protein in phosphate buffer saline within a turnaround time of 20 minutes. Moreover, VLP protein spiked in untreated saliva achieved an LoD of 400 pg mL^-1, providing a cycle threshold (Ct) value range of 30-32, closer to reverse transcription-polymerase chain reaction (RT-PCR) results (35-40) and higher than the commercial rapid antigen tests, ranging from 25-28. Therefore, the developed one-pot SERS based biosensor exhibited highly sensitive and rapid detection of SARS-CoV-2, which could be a potential point-of-care platform for early and cost-effective diagnosis of the COVID-19 virus.

Diagnostics and analysis of SARS-CoV-2: current status, recent advances, challenges and perspectives

The disastrous spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has induced severe public healthcare issues and weakened the global economy significantly. Although SARS-CoV-2 infection is not as fatal as the initial outbreak, many infected victims suffer from long COVID. Therefore, rapid and large-scale testing is critical in managing patients and alleviating its transmission. Herein, we review the recent advances in techniques to detect SARS-CoV-2. The sensing principles are detailed together with their application domains and analytical performances. In addition, the advantages and limits of each method are discussed and analyzed. Besides molecular diagnostics and antigen and antibody tests, we also review neutralizing antibodies and emerging SARS-CoV-2 variants. Further, the characteristics of the mutational locations in the different variants with epidemiological features are summarized. Finally, the challenges and possible strategies are prospected to develop new assays to meet different diagnostic needs. Thus, this comprehensive and systematic review of SARS-CoV-2 detection technologies may provide insightful guidance and direction for developing tools for the diagnosis and analysis of SARS-CoV-2 to support public healthcare and effective long-term pandemic management and control.

Design of a rapid electrochemical biosensor based on MXene/Pt/C nanocomposite and DNA/RNA hybridization for the detection of COVID-19

Since the rapid spread of the SARS-CoV-2 (2019), the need for early diagnostic techniques to control this pandemic has been highlighted. Diagnostic methods based on virus replication, such as RT-PCR, are exceedingly time-consuming and expensive. As a result, a rapid and accurate electrochemical test which is both available and cost-effective was designed in this study. MXene nanosheets (Ti₃C₂Tx) and carbon platinum (Pt/C) were employed to amplify the signal of this biosensor upon hybridization reaction of the DNA probe and the virus's specific oligonucleotide target in the RdRp gene region. By the differential pulse voltammetry (DPV) technique, the calibration curve was obtained for the target with varying concentrations ranging from 1 aM to 100 nM. Due to the increase in the concentration of the oligonucleotide target, the signal of DPV increased with a positive slope and a correlation coefficient of 0.9977. Therefore, at least a limit of detection (LOD) was obtained 0.4 aM. Furthermore, the specificity and sensitivity of the sensors were evaluated with 192 clinical samples with positive and negative RT-PCR tests, which revealed 100% accuracy and sensitivity, 97.87% specificity and limit of quantification (LOQ) of 60 copies/mL. Besides, various matrices such as saliva, nasopharyngeal swabs, and serum were assessed for detecting SARS-CoV-2 infection by the developed biosensor, indicating that this biosensor has the potential to be used for rapid Covid-19 test detection.

Portable microfluidic impedance biosensor for SARS-CoV-2 detection

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

A surface molecularly imprinted electrochemical biosensor for the detection of SARS-CoV-2 spike protein by using Cu7S4-Au as built-in probe

Sensitive detection of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) spike protein (S protein) is of significant clinical importance in the diagnosis of COVID-19 pandemic. In this work, a surface molecularly imprinted (SMI) electrochemical biosensor is fabricated for the detection of SARS-CoV-2 S protein. Cu₇S₄-Au is used as the built-in probe and modified on the surface of a screen-printed carbon electrode (SPCE). 4-Mercaptophenylboric acid (4-MPBA) is anchored to the surface of the Cu₇S₄-Au through Au-SH bonds, which can be used for the immobilization of the SARS-CoV-2 S protein template through boronate ester bonds. After that, 3-aminophenylboronic acid (3-APBA) is electropolymerized on the electrode surface and used as the molecularly imprinted polymers (MIPs). The SMI electrochemical biosensor is obtained after the elution of the SARS-CoV-2 S protein template with an acidic solution by the dissociation of the boronate ester bonds, which can be utilized for sensitive detection of the SARS-CoV-2 S protein. The developed SMI electrochemical biosensor displays high specificity, reproducibility and stability, which might be a potential and promising candidate for the clinical diagnosis of COVID-19.

Selective determination of cadmium and lead ions in different food samples by poly (riboflavin)/carbon black-modified glassy carbon electrode

In this research, a poly (riboflavin)/carbon black-modified glassy carbon electrode (PRF/CB/GCE) is introduced as a novel electrochemical sensor toward Cd²⁺ and Pb²⁺ simultaneous measurement in presence of bismuth ions, applying differential pulse anodic stripping voltammetry (DPASV). Regarding the optimized conditions, the linear ranges were achieved from 0.5 to 600 nM for Cd²⁺ and Pb²⁺. The detection limit (LOD) was found to be 0.16 nM for Cd²⁺ and 0.13 nM for Pb²⁺. In order to perform the technique in real application, the proposed electrode was used to simultaneously detect ions in rice, honey, and vegetable samples with satisfactory recoveries - indicating that the sensor possesses good practicability to determine Cd²⁺ and Pb²⁺. Moreover, an atomic absorption spectrometry (AAS) was used in order to detect the concentration of ions as a reference technique in rice, honey, and vegetable samples.

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

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

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

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

Functional Nanomaterials Enhancing Electrochemical Biosensors as Smart Tools for Detecting Infectious Viral Diseases

Electrochemical biosensors are known as analytical tools, guaranteeing rapid and on-site results in medical diagnostics, food safety, environmental protection, and life sciences research. Current research focuses on developing sensors for specific targets and addresses challenges to be solved before their commercialization. These challenges typically include the lowering of the limit of detection, the widening of the linear concentration range, the analysis of real samples in a real environment and the comparison with a standard validation method. Nowadays, functional nanomaterials are designed and applied in electrochemical biosensing to support all these challenges. This review will address the integration of functional nanomaterials in the development of electrochemical biosensors for the rapid diagnosis of viral infections, such as COVID-19, middle east respiratory syndrome (MERS), influenza, hepatitis, human immunodeficiency virus (HIV), and dengue, among others. The role and relevance of the nanomaterial, the type of biosensor, and the electrochemical technique adopted will be discussed. Finally, the critical issues in applying laboratory research to the analysis of real samples, future perspectives, and commercialization aspects of electrochemical biosensors for virus detection will be analyzed.

Using Nanomaterials for SARS-CoV-2 Sensing via Electrochemical Techniques

Advancing low-cost and user-friendly innovations to benefit public health is an important task of scientific and engineering research. According to the World Health Organization (WHO), electrochemical sensors are being developed for low-cost SARS-CoV-2 diagnosis, particularly in resource-limited settings. Nanostructures with sizes ranging from 10 nm to a few micrometers could deliver optimum electrochemical behavior (e.g., quick response, compact size, sensitivity and selectivity, and portability), providing an excellent alternative to the existing techniques. Therefore, nanostructures, such as metal, 1D, and 2D materials, have been successfully applied in in vitro and in vivo detection of a wide range of infectious diseases, particularly SARS-CoV-2. Electrochemical detection methods reduce the cost of electrodes, provide analytical ability to detect targets with a wide variety of nanomaterials, and are an essential strategy in biomarker sensing as they can rapidly, sensitively, and selectively detect SARS-CoV-2. The current studies in this area provide fundamental knowledge of electrochemical techniques for future applications.

The Applications of Electrochemical Immunosensors in the Detection of Disease Biomarkers: A Review

Disease-related biomarkers may serve as indicators of human disease. The clinical diagnosis of diseases may largely benefit from timely and accurate detection of biomarkers, which has been the subject of extensive investigations. Due to the specificity of antibody and antigen recognition, electrochemical immunosensors can accurately detect multiple disease biomarkers, including proteins, antigens, and enzymes. This review deals with the fundamentals and types of electrochemical immunosensors. The electrochemical immunosensors are developed using three different catalysts: redox couples, typical biological enzymes, and nanomimetic enzymes. This review also focuses on the applications of those immunosensors in the detection of cancer, Alzheimer's disease, novel coronavirus pneumonia and other diseases. Finally, the future trends in electrochemical immunosensors are addressed in terms of achieving lower detection limits, improving electrode modification capabilities and developing composite functional materials.

Magnetic biosensors for identification of SARS-CoV-2, Influenza, HIV, and Ebola viruses: a review

Infectious diseases such as novel coronavirus (SARS-CoV-2), Influenza, HIV, Ebola, etc kill many people around the world every year (SARS-CoV-2 in 2019, Ebola in 2013, HIV in 1980, Influenza in 1918). For example, SARS-CoV-2 has plagued higher than 317 000 000 people around the world from December 2019 to January 13, 2022. Some infectious diseases do not yet have not a proper vaccine, drug, therapeutic, and/or detection method, which makes rapid identification and definitive treatments the main challenges. Different device techniques have been used to detect infectious diseases. However, in recent years, magnetic materials have emerged as active sensors/biosensors for detecting viral, bacterial, and plasmids agents. In this review, the recent applications of magnetic materials in biosensors for infectious viruses detection have been discussed. Also, this work addresses the future trends and perspectives of magnetic biosensors.