Development of a portable MIP-based electrochemical sensor for detection of SARS-CoV-2 antigen

A polyaniline functionalized NiFeP nanosheet array-based electrochemical immunosensor using Au/Cu2O nanocubes as a signal amplifier for the detection of SARS-CoV-2 nucleocapsid protein

Coronavirus disease 2019 (COVID-19) is an infectious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which emerged as a novel pathogen in 2019. The virus is responsible for a severe acute respiratory syndrome outbreak, affecting the respiratory system of infected individuals. COVID-19 is a super amplifier of basic diseases, and the disease with basic diseases is often more serious. Controlling the spread of the COVID-19 pandemic relies heavily on the timely and accurate detection of the virus. To resolve the problem, a polyaniline functionalized NiFeP nanosheet array-based electrochemical immunosensor using Au/Cu₂O nanocubes as a signal amplifier is fabricated for the detection of SARS-CoV-2 nucleocapsid protein (SARS-CoV-2 NP). Polyaniline (PANI) functionalized NiFeP nanosheet arrays are synthesized as an ideal sensing platform for the first time. PANI is coated on the surface of NiFeP by electropolymerization to enhance biocompatibility, beneficial for the efficient loading of the capture antibody (Ab₁). Significantly, Au/Cu₂O nanocubes possess excellent peroxidase-like activity and exhibit outstanding catalytic activity for the reduction of H₂O₂. Therefore, Au/Cu₂O nanocubes combine with a labeled antibody (Ab₂) through the Au-N bond to form labeled probes, which can effectively amplify current signals. Under optimal conditions, the immunosensor for the detection of SARS-CoV-2 NP shows a wide linear range of 10 fg mL^-1-20 ng mL^-1 and a low detection limit of 1.12 fg mL^-1 (S/N = 3). It also exhibits desirable selectivity, repeatability, and stability. Meanwhile, the excellent analytical performance in human serum samples confirms the practicality of the PANI functionalized NiFeP nanosheet array-based immunosensor. The electrochemical immunosensor based on the Au/Cu₂O nanocubes as a signal amplifier demonstrates great potential for application in the personalized point-of-care (POC) clinical diagnosis.

Label-Free Electrochemical Methods for Disease Detection

Label-free electrochemical biosensing leverages the advantages of label-free techniques, low cost, and fewer user steps, with the sensitivity and portability of electrochemical analysis. In this review, we identify four label-free electrochemical biosensing mechanisms: (a) blocking the electrode surface, (b) allowing greater access to the electrode surface, (c) changing the intercalation or electrostatic affinity of a redox probe to a biorecognition unit, and (d) modulating ion or electron transport properties due to conformational and surface charge changes. Each mechanism is described, recent advancements are summarized, and relative advantages and disadvantages of the techniques are discussed. Furthermore, two avenues for gaining further diagnostic information from label-free electrochemical biosensors, through multiplex analysis and incorporating machine learning, are examined.

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.

Molecularly Imprinted Polymer-Based Electrochemical Sensors for the Diagnosis of Infectious Diseases

The appearance of biological molecules, so-called biomarkers in body fluids at abnormal concentrations, is considered a good tool for detecting disease. Biomarkers are usually looked for in the most common body fluids, such as blood, nasopharyngeal fluids, urine, tears, sweat, etc. Even with significant advances in diagnostic technology, many patients with suspected infections receive empiric antimicrobial therapy rather than appropriate treatment, which is driven by rapid identification of the infectious agent, leading to increased antimicrobial resistance. To positively impact healthcare, new tests are needed that are pathogen-specific, easy to use, and produce results quickly. Molecularly imprinted polymer (MIP)-based biosensors can achieve these general goals and have enormous potential for disease detection. This article aimed to overview recent articles dedicated to electrochemical sensors modified with MIP to detect protein-based biomarkers of certain infectious diseases in human beings, particularly the biomarkers of infectious diseases, such as HIV-1, COVID-19, Dengue virus, and others. Some biomarkers, such as C-reactive protein (CRP) found in blood tests, are not specific for a particular disease but are used to identify any inflammation process in the body and are also under consideration in this review. Other biomarkers are specific to a particular disease, e.g., SARS-CoV-2-S spike glycoprotein. This article analyzes the development of electrochemical sensors using molecular imprinting technology and the used materials' influence. The research methods, the application of different electrodes, the influence of the polymers, and the established detection limits are reviewed and compared.

Development of core-shell magnetic molecularly imprinted polymer-based electrochemical sensor for sensitive and selective detection of ezetimibe

A sensitive electrochemical molecularly imprinted polymer (MIP) sensor was fabricated for detection of ezetimibe (Eze) as an effective cholesterol absorption inhibitor on the surface of a screen-printed carbon electrode based on a magnetic nanoparticle decorated with MIP (Fe₃O₄@MIP). Placing the magnetic nanoparticle inside the MIP increases the biocompatibility, surface-to-volume ratio, and sensitivity of the sensor. Methacrylic acid (MAA) was used as a monomer, ethylene glycol dimethacrylate (EGDMA) as a cross-linker, and Eze as a template. The fabricated Fe₃O₄@MIP was characterized using Fourier-transform infrared spectroscopy (FTIR), Transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Detection of Eze was achieved by differential pulse voltammetry. Using this sensor, Eze can be sensitively detected in the range of 1.0 nM-10 μM and detection limit of 0.7 nM. In addition, we have shown that the proposed sensor successfully detects different concentrations of Eze in human serum samples and thus proves its practical application.

Highly Selective Aptamer-Molecularly Imprinted Polymer Hybrids for Recognition of SARS-CoV-2 Spike Protein Variants

Virus recognition has been driven to the forefront of molecular recognition research due to the COVID-19 pandemic. Development of highly sensitive recognition elements, both natural and synthetic is critical to facing such a global issue. However, as viruses mutate, it is possible for their recognition to wane through changes in the target substrate, which can lead to detection avoidance and increased false negatives. Likewise, the ability to detect specific variants is of great interest for clinical analysis of all viruses. Here, a hybrid aptamer-molecularly imprinted polymer (aptaMIP), that maintains selective recognition for the spike protein template across various mutations, while improving performance over individual aptamer or MIP components (which themselves demonstrate excellent performance). The aptaMIP exhibits an equilibrium dissociation constant of 1.61 nM toward its template which matches or exceeds published examples of imprinting of the spike protein. The work here demonstrates that "fixing" the aptamer within a polymeric scaffold increases its capability to selectivity recognize its original target and points toward a methodology that will allow variant selective molecular recognition with exceptional affinity.

Localized surface plasmon resonance biosensor chip surface modification and signal amplifications toward rapid and sensitive detection of COVID-19 infections

We developed a multi-pronged approach to enhance the detection sensitivity of localized surface plasmon resonance (LSPR) sensor chips to detect SARS-CoV-2. To this end, poly(amidoamine) dendrimers were immobilized onto the surface of LSPR sensor chips to serve as templates to further conjugate aptamers specific for SARS-CoV-2. The immobilized dendrimers were shown to reduce surface nonspecific adsorptions and increase capturing ligand density on the sensor chips, thereby improving detection sensitivity. To characterize the detection sensitivity of the surface-modified sensor chips, SARS-CoV-2 spike protein receptor-binding domain was detected using LSPR sensor chips with different surface modifications. The results showed that the dendrimer-aptamer modified LSPR sensor chip exhibited a limit of detection (LOD) of 21.9 pM, a sensitivity that was 9 times and 152 times more sensitive than the traditional aptamer- or antibody-based LSPR sensor chips, respectively. In addition, detection sensitivity was further improved by combining rolling circle amplification product and gold nanoparticles to further amplify the detection signals by increasing both the target mass and plasmonic coupling effects. Using pseudo SARS-CoV-2 viral particles as detection targets, we demonstrated that this combined signal intensification approach further enhanced the detection sensitivity by 10 folds with a remarkable LOD of 148 vp/mL, making it one of the most sensitive SARS-CoV-2 detection assays reported to date. These results highlight the potential of a novel LSPR-based detection platform for sensitive and rapid detection of COVID-19 infections, as well as other viral infections and point-of-care applications.

Utilization of a Glucometer Test Strip and Enzymatic Reactions to Quantify Anti-SARS-CoV-2 Spike RBD IgG Antibody and SARS-CoV-2 Virus in Saliva and Serum

A sensor capable of quantifying both anti-SARS-CoV-2 spike receptor-binding domain (RBD) antibody levels and the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus in saliva and serum was developed. This was accomplished by exploiting the enzymatic reaction of maltose and orthophosphate (PO43-) in the presence of maltose phosphorylase to generate an equivalent amount of glucose that was detected using a commercial glucometer test strip and a potentiostat. Important for this approach is the ability to generate PO43- in an amount that is directly related to the concentration of the analytes. RBD-modified magnetic microparticles were used to capture anti-SARS-CoV-2 spike RBD antibodies, while particles modified with anti-SARS-CoV-2 nucleocapsid antibodies were used to capture SARS-CoV-2 nucleocapsid protein from inactivated virus samples. A magnet was used to isolate and purify the magnetic microparticles (with analyte attached), and alkaline phosphatase-conjugated secondary antibodies were bound to the analytes attached to the respective magnetic microparticles. Finally, through enzymatic reactions, specific amounts of PO43- (and subsequently glucose) were generated in proportion to the analyte concentration, which was then quantified using a commercial glucometer test strip. Utilizing glucose test strips makes the sensor relatively inexpensive, with a cost per test of ∼US $7 and ∼US $12 for quantifying anti-SARS-CoV-2 spike RBD antibody and SARS-CoV-2, respectively. Our sensor exhibited a limit of detection of 0.42 ng/mL for anti-SARS-CoV-2 spike RBD antibody, which is sensitive enough to quantify typical concentrations of antibodies in COVID-19-infected or vaccinated individuals (>1 μg/mL). The limit of detection for the SARS-CoV-2 virus is 300 pfu/mL (5.4 × 106 RNA copies/mL), which exceeds the performance recommended by the WHO (500 pfu/mL). In addition, the sensor exhibited good selectivity when challenged with competing analytes and could be used to quantify analytes in saliva and serum matrices with an accuracy of >94% compared to RT-qPCR.

Facile and Unplugged Surface Plasmon Resonance Biosensor with NIR-Emitting Perovskite Nanocomposites for Fast Detection of SARS-CoV-2

The emergence of the coronavirus disease 2019 (COVID-19) pandemic prompted researchers to develop portable biosensing platforms, anticipating to detect the analyte in a label-free, direct, and simple manner, for deploying on site to prevent the spread of the infectious disease. Herein, we developed a facile wavelength-based SPR sensor built with the aid of a 3D printing technology and synthesized air-stable NIR-emitting perovskite nanocomposites as the light source. The simple synthesis processes for the perovskite quantum dots enabled low-cost and large-area production and good emission stability. The integration of the two technologies enabled the proposed SPR sensor to exhibit the characteristics of lightweight, compactness, and being without a plug, just fitting the requirements of on-site detection. Experimentally, the detection limit of the proposed NIR SPR biosensor for refractive index change reached the 10-6 RIU level, comparable with that of state-of-the-art portable SPR sensors. In addition, the bio-applicability of the platform was validated by incorporating a homemade high-affinity polyclonal antibody toward the SARS-CoV-2 spike protein. The results demonstrated that the proposed system was capable of discriminating between clinical swab samples collected from COVID-19 patients and healthy subjects because the used polyclonal antibody exhibited high specificity against SARS-CoV-2. Most importantly, the whole measurement process not only took less than 15 min but also needed no complex procedures or multiple reagents. We believe that the findings disclosed in this work can open an avenue in the field of on-site detection for highly pathogenic viruses.

Bifunctional Au@Pt/Au nanoparticles as electrochemiluminescence signaling probes for SARS-CoV-2 detection

A novel immunosensor based on electrochemiluminescence resonance energy transfer (ECL-RET) for the sensitive determination of N protein of the SARS-CoV-2 coronavirus is described. For this purpose, bifunctional core@shell nanoparticles composed of a Pt-coated Au core and finally decorated with small Au inlays (Au@Pt/Au NPs) have been synthesized to act as ECL acceptor, using [Ru (bpy)₃]²⁺ as ECL donor. These nanoparticles are efficient signaling probes in the immunosensor developed. The proposed ECL-RET immunosensor has a wide linear response to the concentration of N protein of the SARS-CoV-2 coronavirus with a detection limit of 1.27 pg/mL. Moreover, it has a high stability and shows no response to other proteins related to different virus. The immunosensor has achieved the quantification of N protein of the SARS-CoV-2 coronavirus in saliva samples. Results are consistent with those provided by a commercial colorimetric ELISA kit. Therefore, the developed immunosensor provides a feasible and reliable tool for early and effective detection of the virus to protect the population.

Internet-of-medical-things integrated point-of-care biosensing devices for infectious diseases: Toward better preparedness for futuristic pandemics

Microbial pathogens have threatened the world due to their pathogenicity and ability to spread in communities. The conventional laboratory-based diagnostics of microbes such as bacteria and viruses need bulky expensive experimental instruments and skilled personnel which limits their usage in resource-limited settings. The biosensors-based point-of-care (POC) diagnostics have shown huge potential to detect microbial pathogens in a faster, cost-effective, and user-friendly manner. The use of various transducers such as electrochemical and optical along with microfluidic integrated biosensors further enhances the sensitivity and selectivity of detection. Additionally, microfluidic-based biosensors offer the advantages of multiplexed detection of analyte and the ability to deal with nanoliters volume of fluid in an integrated portable platform. In the present review, we discussed the design and fabrication of POCT devices for the detection of microbial pathogens which include bacteria, viruses, fungi, and parasites. The electrochemical techniques and current advances in this field in terms of integrated electrochemical platforms that include mainly microfluidic- based approaches and smartphone and Internet-of-things (IoT) and Internet-of-Medical-Things (IoMT) integrated systems have been highlighted. Further, the availability of commercial biosensors for the detection of microbial pathogens will be briefed. In the end, the challenges while fabrication of POC biosensors and expected future advances in the field of biosensing have been discussed. The integrated biosensor-based platforms with the IoT/IoMT usually collect the data to track the community spread of infectious diseases which would be beneficial in terms of better preparedness for current and futuristic pandemics and is expected to prevent social and economic losses.

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.

Pre-polymerization process simulation, synthesis and investigation the properties of dipicolinic acid molecularly imprinted polymers

Molecularly imprinted polymers (MIPs) have attracted much attention in recent years due to their structure predictability, recognition specificity, and universal application, as well as robustness, simplicity, and cheapness. In this study, firstly, the pre-polymerization process of molecularly imprinted polymer of dipicolinic acid (DPA) was simulated by molecular dynamics. Then, the appropriate functional monomer molecule for printing was selected and its intermolecular bond with the DPA molecule was evaluated. The monomers 2-vinyl pyridine, acrylic acid (AA), and methacrylic acid (MAA) were selected with potential energies of 3.93 kcal/mol, 3.15 kcal/mol, and 2.78 kcal/mol, respectively. Finally, the ability of functional groups to form hydrogen bonds was estimated, and molecularly imprinted polymers (MIPs) and non-imprinted polymers (NIPs) were synthesized by bulk polymerization. MAA and AA were used as functional monomers to identify DPA molecules. The morphology of MIP and NIP was investigated using a scanning electron microscope (SEM). Their performance was evaluated in the absorption of DPA molecules and picolinic acid (PA) molecules and the printing factor of synthesis polymers. The results showed that fabricated MIPs can be used in the structure of sensors, and the synthesis process is a key factor that significantly affects the polymer properties. The MIP based on the AA monomer showed a higher adsorption rate/capacity and maximum printing factor than MAA monomer-based MIP.

Single-Molecule Evaluation of the SARS-CoV-2 Nucleocapsid Protein Using Gold Particle-in-a-Frame Nanostructures Enhanced Fluorescent Assay

Ultrasensitive evaluation of low-abundance analytes, particularly with limits approaching a single molecule, is a key challenge in the design of an assay for profiling severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antigen. Herein, we report an aptamer claw strategy for directly evaluating the SARS-CoV-2 antigen based on gold particle-in-a-frame nanostructures (Au PIAFs). Au PIAF was used as a metal-enhanced fluorescence material. The assay integrated with a microplate reader achieved a sensitivity of 44 fg·mL-1 in under 3 min and accurately detected the SARS-CoV-2 nucleocapsid protein (N protein) in human saliva samples. When our assay is combined with a single-molecule counting platform, the limit of detection can be as low as 0.84 ag·mL-1. This rapid and ultrasensitive assay holds promise as a tool for screening SARS-CoV-2 and other contagious viruses.

A Comprehensive Overview of Sensors Applications for the Diagnosis of SARS-CoV-2 and of Drugs Used in its Treatment

During the COVID-19 process, determination-based analytical chemistry studies have had a major place at every stage. Many analytical techniques have been used in both diagnostic studies and drug analysis. Among these, electrochemical sensors are frequently preferred due to their high sensitivity, selectivity, short analysis time, reliability, ease of sample preparation, and low use of organic solvents. For the determination of drugs used in the SARS-CoV-2, such as favipiravir, molnupiravir, ribavirin, etc., electrochemical (nano)sensors are widely used in both pharmaceutical and biological samples. Diagnosis is the most critical step in the management of the disease, and electrochemical sensor tools are widely preferred for this purpose. Diagnostic electrochemical sensor tools can be biosensor-, nano biosensor-, or MIP-based sensors and utilize a wide variety of analytes such as viral proteins, viral RNA, antibodies, etc. This review overviews the sensor applications in SARS-CoV-2 in terms of diagnosis and determination of drugs by evaluating the most recent studies in the literature. In this way, it is aimed to compile the developments so far by shedding light on the most recent studies and giving ideas to researchers for future studies.

Electrochemical and Bioelectrochemical Sensing Platforms for Diagnostics of COVID-19

Rapid transmission and high mortality rates caused by the SARS-CoV-2 virus showed that the best way to fight against the pandemic was through rapid, accurate diagnosis in parallel with vaccination. In this context, several research groups around the world have endeavored to develop new diagnostic methods due to the disadvantages of the gold standard method, reverse transcriptase polymerase chain reaction (RT-PCR), in terms of cost and time consumption. Electrochemical and bioelectrochemical platforms have been important tools for overcoming the limitations of conventional diagnostic platforms, including accuracy, accessibility, portability, and response time. In this review, we report on several electrochemical sensors and biosensors developed for SARS-CoV-2 detection, presenting the concepts, fabrication, advantages, and disadvantages of the different approaches. The focus is devoted to highlighting the recent progress of electrochemical devices developed as next-generation field-deployable analytical tools as well as guiding future researchers in the manufacture of devices for disease diagnosis.

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

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

Electrochemical biosensor detection on respiratory and flaviviruses

Viruses have spread throughout the world and cause acute illness or death among millions of people. There is a growing concern about methods to control and combat early-stage viral infections to prevent the significant public health problem. However, conventional detection methods like polymerase chain reaction (PCR) requires sample purification and are time-consuming for further clinical diagnosis. Hence, establishing a portable device for rapid detection with enhanced sensitivity and selectivity for the specific virus to prevent further spread becomes an urgent need. Many research groups are focusing on the potential of the electrochemical sensor to become a key for developing point-of-care (POC) technologies for clinical analysis because it can solve most of the limitations of conventional diagnostic methods. Herein, this review discusses the current development of electrochemical sensors for the detection of respiratory virus infections and flaviviruses over the past 10 years. Trends in future perspectives in rapid clinical detection sensors on viruses are also discussed. KEY POINTS: • Respiratory related viruses and Flavivirus are being concerned for past decades. • Important to differentiate the cross-reactivity between the virus in same family. • Electrochemical biosensor as a suitable device to detect viruses with high performance.

Emerging Landscape of SARS-CoV-2 Variants and Detection Technologies

In 2019, a new coronavirus was identified that has caused significant morbidity and mortality worldwide. Like all RNA viruses, severe acute respiratory syndrome coronavirus 2 (SARS-Cov-2) evolves over time through random mutation resulting in genetic variations in the population. Although the currently approved coronavirus disease 2019 vaccines can be given to those over 5 years of age and older in most countries, strikingly, the number of people diagnosed positive for SARS-Cov-2 is still increasing. Therefore, to prevent and control this epidemic, early diagnosis of infected individuals is of great importance. The current detection of SARS-Cov-2 coronavirus variants are mainly based on reverse transcription-polymerase chain reaction. Although the sensitivity of reverse transcription-polymerase chain reaction is high, it has some disadvantages, for example, multiple temperature changes, long detection time, complicated operation, expensive instruments, and the need for professional personnel, which brings considerable inconvenience to the early diagnosis of this virus. This review comprehensively summarizes the development and application of various current detection technologies for novel coronaviruses, including isothermal amplification, CRISPR-Cas detection, serological detection, biosensor, ensemble, and microfluidic technology, along with next-generation sequencing. Those findings offer us a great potential to replace or combine with reverse transcription-polymerase chain reaction detection to achieve the purpose of allowing predictive diagnostics and targeted prevention of SARS-Cov-2 in the future.

Detection of COVID-19-related biomarkers by electrochemical biosensors and potential for diagnosis, prognosis, and prediction of the course of the disease in the context of personalized medicine

As a more efficient and effective way to address disease diagnosis and intervention, cutting-edge technologies, devices, therapeutic approaches, and practices have emerged within the personalized medicine concept depending on the particular patient's biology and the molecular basis of the disease. Personalized medicine is expected to play a pivotal role in assessing disease risk or predicting response to treatment, understanding a person's health status, and, therefore, health care decision-making. This work discusses electrochemical biosensors for monitoring multiparametric biomarkers at different molecular levels and their potential to elucidate the health status of an individual in a personalized manner. In particular, and as an illustration, we discuss several aspects of the infection produced by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) as a current health care concern worldwide. This includes SARS-CoV-2 structure, mechanism of infection, biomarkers, and electrochemical biosensors most commonly explored for diagnostics, prognostics, and potentially assessing the risk of complications in patients in the context of personalized medicine. Finally, some concluding remarks and perspectives hint at the use of electrochemical biosensors in the frame of other cutting-edge converging/emerging technologies toward the inauguration of a new paradigm of personalized medicine.

An ultrasensitive aptasensor of SARS-CoV-2 N protein based on ion current rectification with nanopipettes

Since the outbreak of COVID-19 in the world, it has spread rapidly all over the world. Rapid and effective detection methods have been a focus of research. The SARS-CoV-2 N protein (NP) detection methods currently in use focus on specific recognition of antibodies, but the reagents are expensive and difficult to be produced. Here, aptamer-functionalized nanopipettes utilize the unique ion current rectification (ICR) of nanopipette to achieve rapid and highly sensitive detection of trace NP, and can significantly reduce the cost of NP detection. In the presence of NP, the surface charge at the tip of the nanopipette changes, which affects ion transport and changes the degree of rectification. Quantitative detection of NP is achieved through quantitative analysis. Relying on the high sensitivity of nanopipettes to charge fluctuations, this sensor platform achieves excellent sensing performance. The sensor platform exhibited a dynamic working range from 10²-10⁶ pg/mL with a detection limit of 73.204 pg/mL, which showed great potential as a tool for rapidly detecting SARS-CoV-2. As parallel and serial testing are widely used in the clinic to avoid missed diagnosis or misdiagnosis, we hope this platform can play a role in controlling the spread and prevention of COVID-19.

Biomimetic Material for Quantification of Methotrexate Using Sensor Based on Molecularly Imprinted Polypyrrole Film and MWCNT/GCE

This study investigates biomimetic sensors for the detection of methotrexate contaminants in environmental samples. Sensors inspired by biological systems are the focus of this biomimetic strategy. Methotrexate is an antimetabolite that is widely used for the treatment of cancer and autoimmune diseases. Due to the widespread use of methotrexate and its rampant disposal into the environment, the residues of this drug are regarded as an emerging contaminant of huge concern, considering that exposure to the contaminant has been found to lead to the inhibition of some essential metabolic processes, posing serious risks to humans and other living beings. In this context, this work aims to quantify methotrexate through the application of a highly efficient biomimetic electrochemical sensor constructed using polypyrrole-based molecularly imprinted polymer (MIP) electrodeposited by cyclic voltammetry on a glassy carbon electrode (GCE) modified with multi-walled carbon nanotubes (MWCNT). The electrodeposited polymeric films were characterized by infrared spectrometry (FTIR), scanning electron microscopy (SEM), and cyclic voltammetry (CV). The analyses conducted using differential pulse voltammetry (DPV) yielded a detection limit of 2.7 × 10^-9 mol L^-1 for methotrexate, a linear range of 0.01-125 μmol L^-1, and a sensitivity of 0.152 μA L mol^-1. The results obtained from the analysis of the selectivity of the proposed sensor through the incorporation of interferents in the standard solution pointed to an electrochemical signal decay of only 15.4%. The findings of this study show that the proposed sensor is highly promising and suitable for use in the quantification of methotrexate in environmental samples.

Development of a Point-of-Care SPR Sensor for the Diagnosis of Acute Myocardial Infarction

A novel point-of-care surface plasmon resonance (SPR) sensor was developed for the sensitive and real-time detection of cardiac troponin I (cTnI) using epitope-imprinted molecular receptors. The surface coverage of a nano-molecularly imprinted polymer (nanoMIP)-functionalized SPR sensor chip and the size of nanoMIPs (155.7 nm) were characterized using fluorescence microscopy and dynamic light scattering techniques, respectively. Atomic force microscopy, electrochemical impedance spectroscopy, square wave voltammetry and cyclic voltammetry techniques confirmed the successful implementation of each step of the sensor fabrication. The SPR bio-detection assay was initially established by targeting the cTnI peptide template, and the sensor allowed the detection of the peptide in the concentration range of 100-1000 nM with a correlation coefficient (R²) of 0.96 and limit of detection (LOD) of 76.47 nM. The optimum assay conditions for protein recognition were subsequently determined, and the cTnI biomarker could be detected in a wide concentration range (0.78-50 ng mL^-1) with high reproducibility (R² = 0.91) and sensitivity (LOD: 0.52 ng mL^-1). The overall sensor results were subjected to three binding isotherm models, where nanoMIP-cTnI interaction followed the Langmuir binding isotherm with the dissociation constant of 2.99 × 10^-11 M, indicating a very strong affinity between the cTnI biomarker and epitope-imprinted synthetic receptor. Furthermore, the selectivity of the sensor was confirmed through studying with a control nanoMIP that was prepared by imprinting a non-specific peptide template. Based on the cross-reactivity tests with non-specific molecules (i.e., glucose, p53 protein, transferrin and bovine serum albumin), the nanoMIP-SPR sensor is highly specific for the target biomarker. The developed biomimetic sensor, relying on the direct assay strategy, holds great potential not only for the early and point-of-care testing of acute myocardial infarction but also for other life-threatening diseases that can be diagnosed by determining the elevated levels of certain biomarkers.

Label free electrochemical DNA biosensor for COVID-19 diagnosis

The COVID-19 pandemic has significantly increased the development of the development of point-of-care (POC) diagnostic tools because they can serve as useful tools for detecting and controlling spread of the disease. Most current methods require sophisticated laboratory instruments and specialists to provide reliable, cost-effective, specific, and sensitive POC testing for COVID-19 diagnosis. Here, a smartphone-assisted Sensit Smart potentiostat (PalmSens) was integrated with a paper-based electrochemical sensor to detect severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). A disposable paper-based device was fabricated, and the working electrode directly modified with a pyrrolidinyl peptide nucleic acid (acpcPNA) as the biological recognition element to capture the target complementary DNA (cDNA). In the presence of the target cDNA, hybridization with acpcPNA probe blocks the redox conversion of a redox reporter, leading to a decrease in electrochemical response correlating to SARS-CoV-2 concentration. Under optimal conditions, a linear range from 0.1 to 200 nM and a detection limit of 1.0 pM were obtained. The PNA-based electrochemical paper-based analytical device (PNA-based ePAD) offers high specificity toward SARS-CoV-2 N gene because of the highly selective PNA-DNA binding. The developed sensor was used for amplification-free SARS-CoV-2 detection in 10 nasopharyngeal swab samples (7 SARS-CoV-2 positive and 3 SARS-CoV-2 negative), giving a 100% agreement result with RT-PCR.

Advancement in COVID-19 detection using nanomaterial-based biosensors

Coronavirus disease 2019 (COVID-19) pandemic has exemplified how viral growth and transmission are a significant threat to global biosecurity. The early detection and treatment of viral infections is the top priority to prevent fresh waves and control the pandemic. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been identified through several conventional molecular methodologies that are time-consuming and require high-skill labor, apparatus, and biochemical reagents but have a low detection accuracy. These bottlenecks hamper conventional methods from resolving the COVID-19 emergency. However, interdisciplinary advances in nanomaterials and biotechnology, such as nanomaterials-based biosensors, have opened new avenues for rapid and ultrasensitive detection of pathogens in the field of healthcare. Many updated nanomaterials-based biosensors, namely electrochemical, field-effect transistor, plasmonic, and colorimetric biosensors, employ nucleic acid and antigen-antibody interactions for SARS-CoV-2 detection in a highly efficient, reliable, sensitive, and rapid manner. This systematic review summarizes the mechanisms and characteristics of nanomaterials-based biosensors for SARS-CoV-2 detection. Moreover, continuing challenges and emerging trends in biosensor development are also discussed.

Evaluation of the interaction between SARS-CoV-2 spike glycoproteins and the molecularly imprinted polypyrrole

The SARS-CoV-2 spike glycoprotein (SARS-CoV-2-S) was used as a template molecule and polypyrrole (Ppy) was applied as an electro-generated conducting polymer, which was acting as a matrix for the formation of molecular imprints. Two types of Ppy-layers: molecularly imprinted polypyrrole (MIP-Ppy) and non-imprinted polypyrrole (NIP-Ppy) were electrochemically deposited on the working platinum electrode. The performance of electrodes modified by MIP-Ppy and NIP-Ppy layers was evaluated by pulsed amperometric detection (PAD). During the assessment of measurement results registered by PAD, the integrated Cottrell equation (Anson plot) was used to calculate the amount of charge passed through the MIP-Ppy and NIP-Ppy layers. The interaction between SARS-CoV-2 spike glycoproteins and molecularly imprinted polypyrrole (MIP-Ppy) was assessed by the Anson plot based calculations. This assessment reveals that SARS-CoV-2-S glycoproteins are interacting with MIP-Ppy more strongly than with NIP-Ppy.

Molecularly imprinted miniature electrochemical biosensor for SARS-CoV-2 spike protein based on Au nanoparticles and reduced graphene oxide modified acupuncture needle

Accurate detection of SARS-CoV-2 spike (SARS-CoV-2-S) protein is of clinical significance for early diagnosis and timely treatment of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Herein, a surface molecularly imprinted miniature biosensor was fabricated. Au nanoparticles (AuNPs), reduced graphene oxide (rGO), poly(methylene blue)/poly(ionic liquids) and poly(ionic liquids) were successively electrodeposited onto the pinpoint of an acupuncture needle (AN). The molecularly imprinted miniature biosensor was obtained after the template of SARS-CoV-2-S protein was removed, which could be used for sensitive detection of SARS-CoV-2-S protein. The linear range and limit of detection (LOD) were 0.1 ∼ 1000 ng mL^-1 and 38 pg mL^-1, respectively, which were superior to other molecularly imprinted biosensors previously reported. The developed miniature biosensor also exhibited high specificity and stability. The reliability of the biosensor was evaluated by the detection of SARS-CoV-2-S protein in clinical serum samples.

An electrochemical biosensor for SARS-CoV-2 detection via its papain-like cysteine protease and the protease inhibitor screening

The persistent coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is still infecting hundreds of thousands of people every day. Enriching the kits for SARS-CoV-2 detection and developing the drugs for patient treatments are still urgently needed for combating the spreading virus, especially after the emergence of various mutants. Herein, an electrochemical biosensor has been fabricated in this work for the detection of SARS-CoV-2 via its papain-like cysteine protease (PLpro) and the screening of protease inhibitor against SARS-CoV-2 by using our designed chimeric peptide-DNA (pDNA) nanoprobes. Utilizing this biosensor, the sensitive and specific detection of SARS-CoV-2 PLpro can be conducted in complex real environments including blood and saliva. Five positive and five negative patient throat swab samples have also been tested to verify the practical application capability of the biosensor. Moreover, we have obtained a detection limit of 27.18 fM and a linear detection range from 1 pg mL^-1 to 10 μg mL^-1 (I = 1.63 + 4.44 lgC). Meanwhile, rapid inhibitor screening against SARS-CoV-2 PLpro can be also obtained. Therefore, this electrochemical biosensor has the great potential for COVID-19 combating and drug development.

Electrochemical sensor based on a ZnO-doped graphitized carbon for the electrocatalytic detection of the antibiotic hydroxychloroquine. Application: tap water and human urine

Abstract

In December 2019, the world experienced a new coronavirus, SARS-CoV-2, causing coronavirus disease 2019 originating from Wuhan.The virus has crossed national borders and now affects more than 200 countries and territories. Hydroxychloroquine has been considered as a drug capable of treating COVID-19. The objective of this work is to establish a simple platform for electrocatalytic detection of hydroxychloroquine in human urine samples and pharmaceutical samples (tablets) using a ZnO@CPE sensor constructed by simple and inexpensive hydrothermal methods using a square wave voltammetry method. The best results are obtained in a PBS electrolyte with irreversible behavior of the hydroxychloroquine complement and controlled by diffusion coupled with absorption phenomena. The ZnO@CPE shifts the oxidation potential of hydroxychloroquine with the formation of a single very intense peak at the position of Epa = 0.5 V/(vs Ag/AgCl) with a shift is ΔEp = 0.1 V(vs Ag/AgCl) compared to the unmodified electrode. The obtained ZnO@CPE hybrid nanocomposite was characterized by different techniques and showed excellent electrocatalytic activity and higher active surface area compared to the bare carbon paste electrode. Under the optimized experimental conditions, the ZnO@CPE sensor showed good analytical performance for the determination of trace amounts of hydroxychloroquine, a wide linearity range from 10^-3 M to 0.8 × 10^-6 M with a very low detection limit in the range of 1.33 × 10^-7 M, satisfactory selectivity, acceptable repeatability and reproducibility. The calculated recovery and coefficient of variation for the two samples analyzed are very satisfactory, ranging from 97.6 to 102% and 1.2 to 2.3% respectively. The proposed applied method and the fabricated sensor offer the possibility to analyze traces of hydroxychloroquine in real human urine and water samples.

Graphical abstract

Strategy for the electro-oxidation reaction of hydroxychloroquine on the electro-catalytic surface of the ZnO@Carbon graphite electrode and real-time detection of hydroxychloroquine.

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

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

Recent molecularly imprinted polymers applications in bioanalysis

Molecular imprinted polymers (MIPs) as extraordinary compounds with unique features have presented a wide range of applications and benefits to researchers. In particular when used as a sorbent in sample preparation methods for the analysis of biological samples and complex matrices. Its application in the extraction of medicinal species has attracted much attention and a growing interest. This review focus on articles and research that deals with the application of MIPs in the analysis of components such as biomarkers, drugs, hormones, blockers and inhibitors, especially in biological matrices. The studies based on MIP applications in bioanalysis and the deployment of MIPs in high-throughput settings and optimization of extraction methods are presented. A review of more than 200 articles and research works clearly shows that the superiority of MIP techniques lies in high accuracy, reproducibility, sensitivity, speed and cost effectiveness which make them suitable for clinical usage. Furthermore, this review present MIP-based extraction techniques and MIP-biosensors which are categorized on their classes based on common properties of target components. Extraction methods, studied sample matrices, target analytes, analytical techniques and their results for each study are described. Investigations indicate satisfactory results using MIP-based bioanalysis. According to the increasing number of studies on method development over the last decade, the use of MIPs in bioanalysis is growing and will further expand the scope of MIP applications for less studied samples and analytes.

Ultrasensitive electrochemical biosensors based on zinc sulfide/graphene hybrid for rapid detection of SARS-CoV-2

The coronavirus disease 2019 (COVID-19) is a highly contagious and fatal disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). In general, the diagnostic tests for COVID-19 are based on the detection of nucleic acid, antibodies, and protein. Among different analytes, the gold standard of the COVID-19 test is the viral nucleic acid detection performed by the quantitative reverse transcription polymerase chain reaction (qRT-PCR) method. However, the gold standard test is time-consuming and requires expensive instrumentation, as well as trained personnel. Herein, we report an ultrasensitive electrochemical biosensor based on zinc sulfide/graphene (ZnS/graphene) nanocomposite for rapid and direct nucleic acid detection of SARS-CoV-2. We demonstrated a simple one-step route for manufacturing ZnS/graphene by employing an ultrafast (90 s) microwave-based non-equilibrium heating approach. The biosensor assay involves the hybridization of target DNA or RNA samples with probes that are immersed into a redox active electrolyte, which are detectable by electrochemical measurements. In this study, we have performed the tests for synthetic DNA samples and, SARS-CoV-2 standard samples. Experimental results revealed that the proposed biosensor could detect low concentrations of all different SARS-CoV-2 samples, using such as S, ORF 1a, and ORF 1b gene sequences as targets. This microwave-synthesized ZnS/graphene-based biosensor could be reliably used as an on-site, real-time, and rapid diagnostic test for COVID-19.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s42114-023-00630-7.

The SARS-CoV-2 specific IgG antibodies biophotonic sensor

In this paper, we present the design and the principle of operation of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) specific immunoglobulin G (IgG) biophotonic sensor, which is based on the single-mode telecommunication fiber. We fabricated the sensor head at the face of the single mode fiber-28. Due to the process of bio-functionalization, our sensor has the ability to selectively detect the SARS-CoV-2 specific IgG antibodies. The results of preliminary tests allowed us to correctly determine the presence of antibodies in less than 1 min in 5 μl in a volume sample of concentration of 10 μg/ml, which according to studies, corresponds to the concentration of IgG antibodies in human serum. Additionally, the tested sample can be smaller than 5 μl in volume.

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

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

A Rapid Label-Free Disposable Electrochemical Salivary Point-of-Care Sensor for SARS-CoV-2 Detection and Quantification

The coronavirus disease 2019 (COVID-19) pandemic has created an urgent need for accurate early diagnosis and monitoring. A label-free rapid electrochemical point-of-care (POC) biosensor for SARS-CoV-2 detection in human saliva is reported here to help address the shortcomings of traditional nucleic acid amplification methods and give a quantitative assessment of the viral load to track infection status anywhere, using disposable electrochemical sensor chips. A new chemical construct of gold nanoparticles (GNp) and thionine (Th) are immobilized on carboxylic acid functionalized carbon nanotubes (SWCNT-COOH) for high-performance biosensing. The sensor uses saliva with a one-step pretreatment and simple testing procedure as an analytical medium due to the user-friendly and non-invasive nature of its procurement from patients. The sensor has a response time of 5 min with a limit of detection (LOD) reaching 200 and 500 pM for the freely suspended spike (S) protein in phosphate buffer saline (PBS) and human saliva, respectively. The sensor's performance was also proven for detecting a COVID-19 pseudovirus in an electrolyte solution with a LOD of 106 copies/mL. The results demonstrate that the optimized POC sensor developed in this work is a promising device for the label-free electrochemical biosensing detection of SARS-CoV-2 and different species of viruses.

How an ACE2 mimicking epitope-MIP nanofilm recognizes template-related peptides and the receptor binding domain of SARS-CoV-2

Here we aim to gain a mechanistic understanding of the formation of epitope-imprinted polymer nanofilms using a non-terminal peptide sequence, i.e. the peptide GFNCYFP (G485 to P491) of the SARS-CoV-2 receptor binding domain (RBD). This epitope is chemisorbed on the gold surface through the central cysteine 488 followed by the electrosynthesis of a ∼5 nm thick polyscopoletin film around the surface confined templates. The interaction of peptides and the parent RBD and spike protein with the imprinted polyscopoletin nanofilm was followed by electrochemical redox marker gating, surface enhanced infrared absorption spectroscopy and conductive AFM. Because the use of non-terminal epitopes is especially intricate, here we characterize the binding pockets through their interaction with 5 peptides rationally derived from the template sequence, i.e. implementing central single amino acid mismatch as well as elongations and truncations at its C- and N- termini. Already a single amino acid mismatch, i.e. the central Cys488 substituted by a serine, results in ca. 15-fold lower affinity. Further truncation of the peptides to tetrapeptide (EGFN) and hexapeptide (YFPLQS) results also in a significantly lower affinity. We concluded that the affinity towards the different peptides is mainly determined by the four amino acid motif CYFP present in the sequence of the template peptide. A higher affinity than that for the peptides is found for the parent proteins RBD and spike protein, which seems to be due to out of cavity effects caused by their larger footprint on the nanofilm surface.

Rapid Conductometric Detection of SARS-CoV-2 Proteins and Its Variants Using Molecularly Imprinted Polymer Nanoparticles

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) biosensors have captured more attention than the conventional methodologies for SARS-CoV-2 detection due to having cost-effective platforms and fast detection. However, these reported SARS-CoV-2 biosensors suffer from drawbacks including issues in detection sensitivity, degradation of biomaterials on the sensor's surface, and incapability to reuse the biosensors. To overcome these shortcomings, molecularly imprinted polymer nanoparticles (nanoMIPs) incorporated conductometric biosensor for highly accurate, rapid, and selective detection of two model SARS-CoV-2 proteins: (i) receptor binding domain (RBD) of the spike (S) glycoprotein and (ii) full length trimeric spike protein are introduced. In addition, these biosensors successfully responded to several other SARS-CoV-2 RBD spike protein variants including Alpha, Beta, Gamma, and Delta. Our conductometric biosensor selectively detects the two model proteins and SARS-CoV-2 RBD spike protein variant samples in real-time with sensitivity to a detection limit of 7 pg mL-1 within 10 min of sample incubation. A battery-free, wireless near-field communication (NFC) interface is incorporated with the biosensor for fast and contactless detection of SARS-CoV-2 variants. The smartphone enabled real-time detection and on-screen rapid result for SARS-CoV-2 variants can curve the outbreak due to its ability to alert the user to infection in real time.

Label-free electrochemical aptasensor for the detection of SARS-CoV-2 spike protein based on carbon cloth sputtered gold nanoparticles

The proliferation and transmission of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), or the (COVID-19) disease, has become a threat to worldwide biosecurity. Therefore, early diagnosis of COVID-19 is crucial to combat the ongoing infection spread. In this study we propose a flexible aptamer-based electrochemical sensor for the rapid, label-free detection of SARS-CoV-2 spike protein (SP). A platform made of a porous and flexible carbon cloth, coated with gold nanoparticles, to increase the conductivity and electrochemical performance of the material, was assembled with a thiol functionalized DNA aptamer via S-Au bonds, for the selective recognition of the SARS-CoV-2 SP. The various steps for the sensor preparation were followed by using scanning electron microscopy, cyclic voltammetry and differential pulse voltammetry (DPV). The proposed platform displayed good mechanical stability, revealing negligible changes on voltammetric responses to bending at various angles. Quantification of SARS-CoV-2 SP was performed by DPV and chronopotentiometry (CP), exploiting the changes of the electrical signals due the [Fe(CN)₆]^3-/4- redox probe, when SARS-CoV-2 SP binds to the aptamer immobilized on the electrode surface. Current density, in DPV, and square root of the transition time, in CP, varied linearly with the log[ SARS-CoV-2 SP], providing lower limits of detection (LOD) of 0.11 ng/mL and 37.8 ng/mL, respectively. The sensor displayed good selectivity, repeatability, and was tested in diluted human saliva, spiked with different SARS-CoV-2 SP concentrations, providing LODs of 0.167 ng/mL and 46.2 ng/mL for DPV and CP, respectively.

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

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

Picomolar or beyond Limit of Detection Using Molecularly Imprinted Polymer-Based Electrochemical Sensors: A Review

Over the last decades, molecularly imprinted polymers (MIPs) have emerged as selective synthetic receptors that have a selective binding site for specific analytes/target molecules. MIPs are synthetic analogues to the natural biological antigen-antibody system. Owing to the advantages they exhibit, such as high stability, simple synthetic procedure, and cost-effectiveness, MIPs have been widely used as receptors/sensors for the detection and monitoring of a variety of analytes. Moreover, integrating electrochemical sensors with MIPs offers a promising approach and demonstrates greater potential over traditional MIPs. In this review, we have compiled the methods and techniques for the production of MIP-based electrochemical sensors along with the applications of reported MIP sensors for a variety of analytes. A comprehensive in-depth analysis of recent trends reported on picomolar (pM/10^-12 M)) and beyond picomolar concentration LOD (≥pM) achieved using MIPs sensors is reported. Finally, we discuss the challenges faced and put forward future perspectives along with our conclusion.

Discriminative electrochemical biosensing of wildtype and omicron variant of SARS-CoV-2 nucleocapsid protein with single platform

Electrochemical biosensors for determining wildtype and omicron variant of the severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) nucleocapsid antigen in nasopharyngeal swab samples were produced by using functionalised graphene oxide and the wildtype and omicron types of SARS-CoV-2 nucleocapsid antibody modified glassy carbon electrodes. The developed biosensors characterised by cyclic voltammetry, scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy were able to detect 0.76 and 0.24 ag/mL of the wildtype and omicron SARS-CoV-2 nucleocapsid antigen protein in linear ranges varied from 1 ag/mL to 100 fg/mL and from 1 ag/mL to 10 fg/mL, respectively. The performance of both biosensors produced was compared in nasopharyngeal swab samples containing the wildtype and omicron variant of the SARS-CoV-2, and it was evaluated whether they could be used interchangeably.

Ultrasensitive voltammetric detection of SARS-CoV-2 in clinical samples

In every pandemic, it is critical to test as many people as possible and keep track of the number of new cases of infection. Therefore, there is a need for novel, fast and unambiguous testing methods. In this study, we designed a sandwich-type voltammetric immunosensor based on unlabeled- and labeled with a redox probe antibodies against virus spike protein for fast and ultrasensitive detection of SARS-CoV-2. The process of the preparation of the sensor layer included chemisorption of cysteamine layer and covalent anchoring of antibody specific for the S1 subunit of the S protein. The source of the voltametric signal was the antibody labeled with the redox probe, which was introduced onto biosensor surface only after the recognition of the virus. This easy-to-handle immunosensor was characterized by a wide analytical range (2.0·10^-7 to 0.20 mg·L^-1) and low detection limit (8.0·10^-8 mg·L^-1 ≡ 0.08 pg·mL^-1 ≡ 4 virions·μL^-1). The utility of the designed device was also evidenced by the detection of SARS-CoV-2 in the clinical samples. Moreover, the main advantage and a huge novelty of the developed device, compared to those already existing, is the moment of generating the analytical signal of the redox probe that appears only after the virus recognition. Thus, our diagnostic innovation may considerably contribute to controlling the COVID-19 pandemic. The as-developed immunosensor may well offer a novel alternative approach for viral detection that could complement or even replace the existing methods.

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

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

A novel photoelectrochemical immunosensor based on TiO2@Bi2WO6 hollow microspheres and Ag2S for sensitive detection of SARS-COV-2 nucleocapsid protein

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-COV-2) is a cluster of β coronaviruses. The 2019 coronavirus disease (COVID-19) caused by SARS-COV-2 is emerging as a global pandemic. Thus, early diagnosis of SARS-COV-2 is essential to prevent severe outbreaks of the disease. In this experiment, a novel label-free photoelectrochemical (PEC) immunosensor was obtained based on silver sulfide (Ag2S) sensitized titanium dioxide@bismuth tungstate (TiO2@Bi2WO6) nanocomposite for quantitative detection of SARS-COV-2 nucleocapsid protein. The constructed TiO2@Bi2WO6 hollow microspheres had large specific surface area and could produce high photocurrent intensity under visible light illumination. Ag2S was in-situ grown on the surface of thioglycolic acid (TGA) modified TiO2@Bi2WO6. In particular, TiO2@Bi2WO6 and Ag2S formed a good energy level match, which could effectively enhance the photocurrent conversion efficiency and strength the photocurrent response. Ascorbic acid (AA) acted as an effective electron donor to effectively eliminate photogenerated holes. Under optimal experimental conditions, the constructed immunosensor presented a supersensitive response to SARS-COV-2 nucleocapsid protein, with a desirable linear relationship ranged from 0.001 to 50 ng/mL for nucleocapsid protein and a lower detection limit of 0.38 pg/mL. The fabricated sensor exhibited a wide linear range, excellent selectivity, specificity and stability, which provided a valuable referential idea for the detection of SARS-COV-2.

Hosseini I, Lu Y, Yedire SG, Mahshid SS, Tabatabaiefar MA, Liang C, Mahshid S. A Versatile Biomimic Nanotemplating Fluidic Assay for Multiplex Quantitative Monitoring of Viral Respiratory Infections and Immune Responses in Saliva and Blood

The last pandemic exposed critical gaps in monitoring and mitigating the spread of viral respiratory infections at the point-of-need. A cost-effective multiplexed fluidic device (NFluidEX), as a home-test kit analogous to a glucometer, that uses saliva and blood for parallel quantitative detection of viral infection and body's immune response in an automated manner within 11 min is proposed. The technology integrates a versatile biomimetic receptor based on molecularly imprinted polymers in a core-shell structure with nano gold electrodes, a multiplexed fluidic-impedimetric readout, built-in saliva collection/preparation, and smartphone-enabled data acquisition and interpretation. NFluidEX is validated with Influenza A H1N1 and SARS-CoV-2 (original strain and variants of concern), and achieves low detection limit in saliva and blood for the viral proteins and the anti-receptor binding domain (RBD) Immunoglobulin G (IgG) and Immunoglobulin M (IgM), respectively. It is demonstrated that nanoprotrusions of gold electrodes are essential for the fine templating of antibodies and spike proteins during molecular imprinting, and differentiation of IgG and IgM in whole blood. In the clinical setting, NFluidEX achieves 100% sensitivity and 100% specificity by testing 44 COVID-positive and 25 COVID-negative saliva and blood samples on par with the real-time quantitative polymerase chain reaction (p < 0.001, 95% confidence) and the enzyme-linked immunosorbent assay.

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

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