Highly selective and sensitive sandwich immunosensor platform modified with MUA-capped GNPs for detection of spike Receptor Binding Domain protein: A precious marker of COVID 19 infection

Chitosan-enhanced sensitivity of mercaptoundecanoic acid (MUA)- capped gold nanorod based localized surface plasmon resonance (LSPR) biosensor for detection of alpha-synuclein oligomer biomarker in parkinson's disease

Alpha-synuclein oligomers play a crucial role in the early diagnosis of Parkinson's disease (PD). In this study, a mercaptoundecanoic acid (MUA)-capped gold nanorod (GNR)-coated and chitosan (CH)-immobilized fiber optic probe has shown considerable sensitivity of its detection. The proposed U-shaped fiber optic biosensor based on localized surface plasmon resonance (LSPR) was applied to detect α-syn oligomer (OA) biomarker. By analyzing OA concentrations, the biosensor achieved a limit of detection of (LOD) 11 pM within the concentration range of 10-100 pM and the sensitivity value was found as 502.69 Δλ/RIU. Upon analysis of the CV% (coefficient of variation) and accuracy/recovery values, it is revealed that the sensor successfully fulfilled the criteria for success, displaying accuracy/recovery values within the range of 80%-120% and CV% values below 20%. This sensor presents significant advantages, including high sensitivity, specificity, and ability to detect very low concentrations of OA. In conclusion, the suggested U-shaped fiber optic biosensor has the potential to be valuable in the early detection of PD from a clinical perspective.

Paper electrochemical immunosensor for the rapid screening of Galectin-3 patients with heart failure

A paper electrochemical immunosensor for the combined binding and quantification of the heart failure (HF) biomarker Galectin-3 has been developed. The simple design of the new sensor is comprised of paper material that is decorated with gold nanostructures, to maximize its electroactive surface area, and functionalized with target-specific recognition molecules to selectively bind the protein from aqueous solutions. The binding of the protein caused the blockage of the electron flow to the sensor electroactive surface, thus causing its oxidation potential to shift and the corresponding current to reduce quantitatively with the increase in the protein concentration within the working range of 0.5ng/mL-8ng/mL (LOQ-0.5 ng/mL). This novel sensor was able to quantify Galectin-3 concentration in saliva samples from HF patients and healthy controls within 20 min with good reproducibility (RSD = 3.64%), without the need for complex sample processing steps. The electrochemical measurements of the patient samples were cross validated by ELISA where the percent agreement between the two methods was found to be 92.7% (RSD = 7.20%). Therefore, the new paper immunosensor sensor has a strong potential for rapid and cost-effective screening of the Galectin 3 biomarker at points of care, thus supporting the timely diagnosis of heart failure.

Carboxyethylsilanetriol-Coated Magnetic Nanoparticles as an Ultrasensitive Immunoplatform for Electrochemical Magnetosensing of Cotinine

In the present study, an innovative and simple electrochemical magneto biosensor based on carboxyethylsilanetriol-modified iron oxide (Fe3O4) magnetic nanoparticles was designed for ultrasensitive and specific analysis of cotinine, an important marker of smoking. Anticotinine antibodies were covalently immobilized on carboxylic acid-modified magnetic nanoparticles, and the cotinine-specific magnetic nanoparticles created a specific surface on the working electrode surface. The use of magnetic nanoparticles as an immobilization platform for antibodies provided a large surface area for antibody attachment and increased sensitivity. In addition, the advantages of the new immobilization platform were reusing the working electrode numerous times, recording repeatable and reproducible signals, and reducing the necessary volume of biomolecules. The specific interaction between cotinine and cotinine-specific antibody-attached magnetic nanoparticles restricted the electron transfer of the redox probe and changed the impedimetric response of the electrode correlated to the concentration of cotinine. The magneto biosensor had a wide detection range (2-300 pg/mL), a low LOD (606 fg/mL), and an acceptable recovery (97.24-105.31%) in real samples. In addition, the current biosensor's measurement results were in good agreement with those found by the standard liquid chromatography (HPLC) and enzyme-linked immunosorbent assay (ELISA) methods. These results showed that a simple impedimetric immunosensing platform was generated for the cotinine analysis.

Hierarchical Nanobiosensors at the End of the SARS-CoV-2 Pandemic

Nanostructures have played a key role in the development of different techniques to attack severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Some applications include masks, vaccines, and biosensors. The latter are of great interest for detecting diseases since some of their features allowed us to find specific markers in secretion samples such as saliva, blood, and even tears. Herein, we highlight how hierarchical nanoparticles integrated into two or more low-dimensional materials present outstanding advantages that are attractive for photonic biosensing using their nanoscale functions. The potential of nanohybrids with their superlative mechanical characteristics together with their optical and optoelectronic properties is discussed. The progress in the scientific research focused on using nanoparticles for biosensing a variety of viruses has become a medical milestone in recent years, and has laid the groundwork for future disease treatments. This perspective analyzes the crucial information about the use of hierarchical nanostructures in biosensing for the prevention, treatment, and mitigation of SARS-CoV-2 effects.

Expanding the application of graphene vertical devices to dual femtomolar detection of SARS-CoV-2 receptor binding domain in serum and saliva

The emergence of the graphene-based hybrid electrical-electrochemical vertical device (EEVD) has introduced a promising nanostructured biosensor tailored for point-of-care applications. In this study, we present an innovative EEVD capable of simultaneously detecting the receptor binding domain (RBD) of the SARS-CoV-2 spike protein in both serum and saliva. The foundation of the EEVD lies in a poly-neutral red-graphene heterojunction, which has been enhanced with a bioconjugate of gold nanoparticles and antibodies. The biodevice demonstrates a remarkable limit of detection, registering at the femtomolar scale (2.86 fmol L-1 or 0.1 pg mL-1). Its sensitivity is characterized by a 6.1 mV/decade response, and its operational range spans 10-12 to 10-7 g mL-1 in both serum and saliva samples. With a 20.0 μL of biological samples and a rapid processing time of under 10 min, the EEVD achieves the feat of dual antigen detection. The tests achieved 100.0% specificity, accuracy, and sensitivity in saliva, and 100.0% specificity, 88.9% accuracy, and 80.0% sensitivity in serum. This study highlights the EEVD as a low-cost solution of rapid viral detection during the crucial initial phases of COVID-19 infections.

A new ITO-based Aβ42 biosensor for early detection of Alzheimer's disease

In this study, a novel label-free impedimetric immunosensor was fabricated for rapid, selective, and sensitive quantitative analysis of Aβ₄₂ protein for use in the diagnosis of Alzheimer's disease. The immunosensor was fabricated using inexpensive and disposable indium tin oxide polyethylene terephthalate (ITO-PET) electrodes. After the electrodes were modified with 3-glycidoxypropyldimethoxymethylsilane (GPDMMS), the antibody specific to the Aβ₄₂ protein (anti-Aβ₄₂) was immobilized. The affinity interaction between anti-Aβ₄₂ and Aβ₄₂ in the immobilization steps in immunosensor fabrication and in the quantitation of Aβ₄₂ were analyzed using Electrochemical Impedance Spectroscopy (EIS) and Cyclic Voltammetry (CV) techniques. Additionally, the morphological changes occurring on the electrode surface during each immobilization step were imaged using scanning electron microscopy (SEM). The linear detection range of the immunosensor was determined as 1-100 pg/mL with the limit of detection value of 0.37 pg/mL. Analytical properties of the biosensor, including reproducibility, repeatability, storage stability, selectivity, and regeneration were investigated. The kinetic behavior of antibody-antigen complex formation was determined for the first time using single frequency impedance (SFI) analysis on an Aβ₄₂ biosensor. The potential for use of the immunosensor in clinical studies was demonstrated by analysis of Aβ₄₂ in commercially purchased human serum.

COVID-19 impedimetric biosensor based on polypyrrole nanotubes, nickel hydroxide and VHH antibody fragment: specific, sensitive, and rapid viral detection in saliva samples

SARS-CoV-2 rapid spread required urgent, accurate, and prompt diagnosis to control the virus dissemination and pandemic management. Several sensors were developed using different biorecognition elements to obtain high specificity and sensitivity. However, the task to achieve these parameters in combination with fast detection, simplicity, and portability to identify the biorecognition element even in low concentration remains a challenge. Therefore, we developed an electrochemical biosensor based on polypyrrole nanotubes coupled via Ni(OH)₂ ligation to an engineered antigen-binding fragment of heavy chain-only antibodies (VHH) termed Sb#15. Herein we report Sb#15-His6 expression, purification, and characterization of its interaction with the receptor-binding domain (RBD) of SARS-CoV-2 in addition to the construction and validation of a biosensor. The recombinant Sb#15 is correctly folded and interacts with the RBD with a dissociation constant (K_D) of 27.1 ± 6.4 nmol/L. The biosensing platform was developed using polypyrrole nanotubes and Ni(OH)₂, which can properly orientate the immobilization of Sb#15-His6 at the electrode surface through His-tag interaction for the sensitive SARS-CoV-2 antigen detection. The quantification limit was determined as 0.01 pg/mL using recombinant RBD, which was expressively lower than commercial monoclonal antibodies. In pre-characterized saliva, both Omicron and Delta SARS-CoV-2 were accurately detected only in positive samples, meeting all the requirements recommended by the World Health Organization for in vitro diagnostics. A low sample volume of saliva is needed to perform the detection, providing results within 15 min without further sample preparations. In summary, a new perspective allying recombinant VHHs with biosensor development and real sample detection was explored, addressing the need for accurate, rapid, and sensitive biosensors.

Point-of-care testing: a disposable label-free electrochemical CA125 and HE4 immunosensors for early detection of ovarian cancer

Cancer antigen 125 (CA125) and human epididymal secretory protein 4 (HE4) are critical biomarkers for ovarian cancer diagnosis and progression monitoring; therefore, sensitive determination of their levels in body fluids is crucial. In recent study, label-free CA125 and HE4 immunosensors were prepared using disposable screen-printed carbon electrodes modified with reduced graphene oxide, polythionine, and gold nanoparticles for the sensitive, fast, and practical determination of CA125 and HE4. Differential pulse voltammetry, square wave voltammetry, and electrochemical impedance spectroscopy methods were used for the electrochemical determination of antigens in four different linear ranges (1-100 pg mL^- 1, 0.01-10 ng mL^- 1, 10-50 ng mL^- 1, and 50-500 ng mL^- 1). High sensitivity, low limit of detection, and limit of quantification were obtained for each linear range with a correlation coefficient above 0.99. The application stability of CA125 and HE4 immunosensors was determined as 60 days, and the storage stability was determined as 16 weeks. Immunosensors showed high selectivity in nine different antigen mixtures. The reusability of the immunosensors has been tested up to 9 cycles. The Risk of Ovarian Malignancy Algorithm score% values were calculated using the concentration of CA125 and HE4 in the blood serum and evaluated in terms of ovarian cancer risk. For the point-of-care testing, CA125 and HE4 levels at pg mL^- 1 concentration were measured in blood serum samples using the developed immunosensors and a hand-held electrochemical reader in approximately 20-30 s, and high recoveries were obtained. These disposable label-free immunosensors are user-friendly and can be used in point-of-care tests for rapid and practical detection of CA125 and HE4 with high selectivity, sensitivity, and repeatability.

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.

A versatile 3D printed multi-electrode cell for determination of three COVID-19 biomarkers

3D-printing has shown an outstanding performance for the production of versatile electrochemical devices. However, there is a lack of studies in the field of 3D-printed miniaturized settings for multiplex biosensing. In this work, we propose a fully 3D-printed micro-volume cell containing six working electrodes (WEs) that operates with 250 μL of sample. A polylactic acid/carbon black conductive filament (PLA/CB) was used to print the WEs and subsequently modified with graphene oxide (GO), to support protein binding. Cyclic voltammetry was employed to investigate the electrochemical behaviour of the novel multi-electrode cell. In the presence of K₃[Fe(CN)₆], PLA/CB/GO showed adequate peak resolution for subsequent label-free immunosensing. The innovative 3D-printed cell was applied for multiplex voltammetric detection of three COVID-19 biomarkers as a proof-of-concept. The multiple sensors showed a wide linear range with detection limits of 5, 1 and 1 pg mL^-1 for N-protein, S_RBD-protein, and anti-S_RBD, respectively. The sensor performance enabled the selective sequential detection of N protein, S_RBD protein, and anti-S_RBD at biological levels in saliva and serum. In summary, the miniaturized six-electrode cell presents an alternative for the low-cost and fast production of customizable devices for multi-target sensing with promising application in the development of point-of-care sensors.

A label-free dual immunosensor for the simultaneous electrochemical determination of CA125 and HE4 biomarkers for the early diagnosis of ovarian cancer

The blood levels of cancer antigen 125 (CA125) and human epididymal secretory protein 4 (HE4) are measured in the diagnosis and progression monitoring of ovarian cancer (OC), and the Risk of Ovarian Malignancy Algorithm (ROMA) score% values are calculated for cancer risk assessment. For the first time, disposable dual screen-printed carbon electrodes modified with reduced graphene oxide, polythionine, and gold nanoparticles were used to fabricate label-free electrochemical dual CA125-HE4 immunosensors for the sensitive, fast, and practical simultaneous determination of CA125 and HE4. DPV and SWV methods were used to simultaneously determine antigens in two different linear ranges (1-100 pg mL^-1 and 1-50 ng mL^-1). High sensitivity, low LOD, and LOQ were obtained for two linear ranges with a correlation coefficient above 0.99. The application stability of the dual CA125-HE4 immunosensors was determined as 60 days, and the storage stability was determined as 16 weeks. The dual immunosensors exhibited high selectivity in eight different antigen mixtures. The reusability of the dual immunosensors has been tested up to 9 cycles. ROMA score% values for pre-menopausal and post-menopausal status were calculated using the concentration of CA125 and HE4 in the blood serum and assessing OC risk. The disposable dual immunosensors can be used in point-of-care tests for rapid and practical simultaneous determination of CA125 and HE4 with high selectivity, sensitivity, and repeatability.

Flexible Label-Free Platinum and Bio-PET-Based Immunosensor for the Detection of SARS-CoV-2

The demand for new devices that enable the detection of severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) at a relatively low cost and that are fast and feasible to be used as point-of-care is required overtime on a large scale. In this sense, the use of sustainable materials, for example, the bio-based poly (ethylene terephthalate) (Bio-PET) can be an alternative to current standard diagnostics. In this work, we present a flexible disposable printed electrode based on a platinum thin film on Bio-PET as a substrate for the development of a sensor and immunosensor for the monitoring of COVID-19 biomarkers, by the detection of L-cysteine and the SARS-CoV-2 spike protein, respectively. The electrode was applied in conjunction with 3D printing technology to generate a portable and easy-to-analyze device with a low sample volume. For the L-cysteine determination, chronoamperometry was used, which achieved two linear dynamic ranges (LDR) of 3.98-39.0 μmol L-1 and 39.0-145 μmol L-1, and a limit of detection (LOD) of 0.70 μmol L-1. The detection of the SARS-CoV-2 spike protein was achieved by both square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS) by a label-free immunosensor, using potassium ferro-ferricyanide solution as the electrochemical probe. An LDR of 0.70-7.0 and 1.0-30 pmol L-1, with an LOD of 0.70 and 1.0 pmol L-1 were obtained by SWV and EIS, respectively. As a proof of concept, the immunosensor was successfully applied for the detection of the SARS-CoV-2 spike protein in enriched synthetic saliva samples, which demonstrates the potential of using the proposed sensor as an alternative platform for the diagnosis of COVID-19 in the future.

Electrochemical immunosensor nanoarchitectonics with the Ag-rGO nanocomposites for the detection of receptor-binding domain of SARS-CoV-2 spike protein

As the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) poses a grave threat to human life and health, it is essential to develop an efficient and sensitive detection method to identify infected individuals. This study described an electrode platform immunosensor to detect SARS-CoV-2-specific spike receptor-binding domain (RBD) protein based on a bare gold electrode modified with Ag-rGO nanocomposites and the biotin-streptavidin interaction system. The Ag-rGO nanocomposites was obtained by chemical synthesis and characterized by electrochemistry and scanning electron microscope (SEM). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to record the electrochemical signals in the electrode modification. The differential pulse voltammetry (DPV) results showed that the limit of detection (LOD) of the immunosensor was 7.2 fg mL^-1 and the linear dynamic detection range was 0.015 ~ 158.5 pg mL^-1. Furthermore, this sensitive immunosensor accurately detected RBD in artificial saliva with favorable stability, specificity, and reproducibility, indicating that it has the potential to be used as a practical method for the detection of SARS-CoV-2.

Methylene Blue functionalized carbon nanodots combined with different shape gold nanostructures for sensitive and selective SARS-CoV-2 sensing

The development of DNA-sensing platforms based on new synthetized Methylene Blue functionalized carbon nanodots combined with different shape gold nanostructures (AuNs), as a new pathway to develop a selective and sensitive methodology for SARS-CoV-2 detection is presented. A mixture of gold nanoparticles and gold nanotriangles have been synthetized to modify disposable electrodes that act as an enhanced nanostructured electrochemical surface for DNA probe immobilization. On the other hand, modified carbon nanodots prepared a la carte to contain Methylene Blue (MB-CDs) are used as electrochemical indicators of the hybridization event. These MB-CDs, due to their structure, are able to interact differently with double and single-stranded DNA molecules. Based on this strategy, target sequences of the SARS-CoV-2 virus have been detected in a straightforward way and rapidly with a detection limit of 2.00 aM. Moreover, this platform allows the detection of the SARS-CoV-2 sequence in the presence of other viruses, and also a single nucleotide polymorphism (SNPs). The developed approach has been tested directly on RNA obtained from nasopharyngeal samples from COVID-19 patients, avoiding any amplification process. The results agree well with those obtained by RT-qPCR or reverse transcription quantitative polymerase chain reaction technique.

A Short Review Comparing Carbon-Based Electrochemical Platforms With Other Materials For Biosensing SARS-Cov-2

Due to the 2019 SARS-CoV-2 outbreak, low-cost, fast, and user-friendly diagnostic kits for biosensing SARS-CoV-2 in real samples employing multiple working electrodes are in high demand. Choosing SARS-CoV-2 detecting electrodes is difficult because each has advantages and limitations. Carbon-based electrochemical sensing applications have attracted attention from the electrochemical sensing community because carbon and carbon-based materials have been a godsend for testing utilizing an electrochemical platform. Carbon working electrode electrochemical platforms are cost-effective and fast. Covid-sensors use carbon-based materials because they can be easily changed (with inorganic and organic functionalities), have quick response kinetics, and are chemically resistant. Covid-19 sensing materials include graphene and graphite. This review explains how carbon materials have been employed in N and S protein electrochemical detection. Here, we discussed a carbon-based technology for SARS-CoV-2 biosensing. We've compared carbon-based electrochemical sensing to different electrodes.

Development of sandwich electrochemiluminescence immunosensor for COVID-19 diagnosis by SARS-CoV-2 spike protein detection based on Au@BSA-luminol nanocomposites

Coronavirus disease (COVID-19) is a new and highly contagious disease posing a threat to global public health and wreaking havoc around the world. It's caused by the Coronavirus that causes severe acute respiratory syndrome (SARS-CoV-2). In the current pandemic situation, rapid and accurate SARS-CoV-2 diagnosis on a large scale is critical for early-stage diagnosis. Early detection and monitoring of viral infections can aid in controlling and preventing infection in large groups of people. Accordingly, we developed a sensitive and high-throughput sandwich electrochemiluminescence immunosensor based on antigen detection for COVID-19 diagnosis (the spike protein of SARS-CoV-2). For the spike protein of SARS-CoV-2, the ECL biosensor had a linear range of 10 ng mL-1 to 10 µg mL-1 with a limit of detection of 1.93 ng mL-1. The sandwich ECL immunosensor could be used in early clinical diagnosis due to its excellent recovery in detecting SARS-CoV-2, rapid analysis (90 min), and ease of use.

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

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

The role of electrochemical biosensors in SARS-CoV-2 detection: a bibliometrics-based analysis and review

The global pandemic of COVID-19, which began in late 2019, has resulted in extremely high morbidity and severe mortality worldwide, with important implications for human health, international trade, and national politics. Severe acute respiratory syndrome coronavirus (SARS-CoV-2) is the primary pathogen causing COVID-19. Analytical chemistry played an important role in this global epidemic event, and detection of SARS-CoV-2 even became a part of daily life. Analytical chemists have devoted much effort and enthusiasm to this event, and different analytical techniques have shown very rapid development. Electrochemical biosensors are highly efficient, sensitive, and cost-effective and have been used to detect many highly pathogenic viruses long before this event. However, another fact is that electrochemical biosensors are not the technology of choice for most detection applications. This review describes for the first time the role played by electrochemical biosensors in SARS-CoV-2 detection from a bibliometric perspective. This paper analyzed 254 relevant research papers up to June 2022. The contributions of different countries and institutions to this topic were analyzed. Keyword analysis was used to explore different methodological attempts of electrochemical detection techniques. More importantly, we are trying to find an answer to the question: do electrochemical biosensors have the potential to become a genuinely employable detection technology in an outbreak of infectious disease?

Impedimetric Detection of Calreticulin by a Disposable Immunosensor Modified with a Single-Walled Carbon Nanotube-Conducting Polymer Nanocomposite

A label-free impedimetric immunosensing system was constructed for ultrasensitive determination of the calreticulin (CALR) biological marker in human serum samples utilizing an electrochemical impedance spectroscopy analysis technique for the first time. The new biosensor fabrication procedure consisted of electrodeposition of single-walled carbon nanotubes (SWCNTs) incorporating polymerization of an oxiran-2-yl methyl 3-(1H-pyrrol-1-yl) propanoate monomer (Pepx) onto a low-cost and disposable indium tin oxide (ITO) electrode. The SWCNTs-PPepx nanocomposite layer was prepared onto the ITO after the one-step fabrication procedure. The fabrication procedure of the immunosensor and the characteristic biomolecular interactions between the anti-CALR and CALR were characterized by electrochemical analysis and morphological monitoring techniques. Under optimum conditions, the proposed biosensor was responsive to CALR concentrations over the detection ranges of 0.015-60 pg/mL linearly, and it had a very low detection limit (4.6 fg/mL) and a favorable sensitivity (0.43 kΩ pg^-1 mL cm^-2). The reliability of the biosensor system in clinical analysis was investigated by successful quantification of CALR levels in human serum. Moreover, the repeatability and reproducibility results of the biosensor were evaluated by using Dixon, Grubbs, T-test, and F-tests. Consequently, the proposed biosensor was a promising method for scientific, rapid, and successful analysis of CALR in human serum samples.

Analytical performances of different diagnostic methods for SARS-CoV-2 virus - A review

Covid-19 is a dreadful pandemic of the 21st century that has created fear among people, affected the whole world, and taken thousands of lives. It infects the respiratory system and causes flu-type symptoms. According to the WHO reports, 2,082,745 deaths and 96,267,473 confirmed cases were perceived all around the globe till January 22, 2021. The significant roots of transmission are inhalation and direct contact with the infected surface. Its incubation period is 2-14 days and remains asymptomatic in most people. However, no treatment and vaccine are available for the people, so preventive measures like social distancing, wearing personal protective equipment (PPE), and frequent hand-washing are the practical and only options for cure. It has affected every sector of the world, whether it is trade or health all around the world. There is high demand for diagnostic tools as high-scale and expeditious testing is crucial for controlling disease spread; thus, detection methods play an essential role. Like flu, Covid-19 is also detected through RT-PCR, as the World Health Organization (WHO) suggested, but it is time taking and expensive method that many countries cannot afford. A vaccine is a crucial aspect of eradicating disease, and for SARS-CoV-2), plasma therapy and antibiotics therapy are used in the early spreading phase. The later stage involves forming a vaccine based on spike protein, N-protein, and whole-viral antigen that effectively immunizes the population worldwide until herd immunity can be achieved. In this review, we will discuss all possible and developed techniques for identifying SARS-CoV-2 and make a comparison of their specificity, selectivity, and cost; thus, we choose an appropriate method for fast, reliable, and pocket-friendly detection.

Development of polypyrrole (nano)structures decorated with gold nanoparticles toward immunosensing for COVID-19 serological diagnosis

The rapid and reliable detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) seroconversion in humans is crucial for suitable infection control. In this sense, many studies have focused on increasing the sensibility, lowering the detection limits and minimizing false negative/positive results. Thus, biosensors based on nanoarchitectures of conducting polymers are promising alternatives to more traditional materials since they can hold improved surface area, higher electrical conductivity and electrochemical activity. In this work, we reported the analytical comparison of two different conducting polymers morphologies for the development of an impedimetric biosensor to monitor SARS-CoV-2 seroconversion in humans. Biosensors based on polypyrrole (PPy), synthesized in both globular and nanotubular (NT) morphology, and gold nanoparticles are reported, using a self-assembly monolayer of 3-mercaptopropionic acid and covalently linked SARS-CoV-2 Nucleocapsid protein. First, the novel hybrid materials were characterized by electron microscopy and electrochemical measurements, and the biosensor step-by-step construction was characterized by electrochemical and spectroscopic techniques. As a proof of concept, the biosensor was used for the impedimetric detection of anti-SARS-CoV-2 Nucleocapsid protein monoclonal antibodies. The results showed a linear response for different antibody concentrations, good sensibility and possibility to quantify 7.442 and 0.4 ng/mL of monoclonal antibody for PPy in the globular and NT morphology, respectively. The PPy-NTs biosensor was able to discriminate serum obtained from COVID-19 positive versus negative clinical samples and is a promising tool for COVID-19 immunodiagnostic, which can contribute to further studies concerning rapid, efficient, and reliable detections.

Nanodiamond conjugated SARS-CoV-2 spike protein: electrochemical impedance immunosensing on a gold microelectrode

A promising immunosensing strategy in diagnosing SARS-CoV-2 is proposed using a 10-µm gap-sized gold interdigitated electrode (AuIDE) to target the surface spike protein (SP). The microelectrode surface was modified by (3-glycidyloxypropyl) trimethoxysilane to enforce the epoxy matrix, which facilitates the immobilization of the anti-SP antibody. The immunosensing performance was evaluated by integrating a nanosized (~ 10 nm) diamond-complexed SP as a target. The proposed immunoassay was quantitatively evaluated through electrochemical impedance spectroscopy (EIS) with the swept frequency from 0.1 to 1 MHz using a 100 mV_RMS AC voltage supply. The immunoassay performed without diamond integration showed low sensitivity, with the lowest SP concentration measured at 1 pM at a determination coefficient of R² = 0.9681. In contrast, the nanodiamond-conjugated SP on the immunosensor showed excellent sensitivity with a determination coefficient of R² = 0.986. SP detection with a nanodiamond-conjugated target on AuIDE reached the low limit of detection at 189 fM in a linear detection range from 250 to 8000 fM. The specificity of the developed immunosensor was evaluated by interacting influenza-hemagglutinin and SARS-CoV-2-nucleocapsid protein with anti-SP. In addition, the authentic interaction of SP and anti-SP was validated by enzyme-linked immunosorbent assay.

Clinical Accuracy of Instrument-Read SARS-CoV-2 Antigen Rapid Diagnostic Tests (Ag-IRRDTs)

This systematic review (PROSPERO registration number: CRD42021282476) aims to collect and analyse current evidence on real-world performance based on clinical accuracy of instrument-read rapid antigen diagnostic tests (Ag-IRRDTs) for SARS-CoV-2 identification. We used PRISMA Checklist and searched databases (PubMed, Web of Science Core Collection and FIND) for publications evaluating the accuracy of SARS-CoV-2 Ag-IRRDTs as of 30 September 2021, and included 40 independent clinical studies resulting in 48 Ag-IRRDT datasets with 137,770 samples. Across all datasets, pooled Ag-IRRDT sensitivity was 67.1% (95% CI: 65.9%-68.3%) and specificity was 99.4% with a tight CI. Pooled sensitivity and specificity of SARS-CoV-2 Ag-IRRDTs did not demonstrate a significant superiority over SARS-CoV-2 rapid antigen tests which do not require a reader instrument, even in the case where surveillance and screening datasets were excluded from the analysis. Nevertheless, they provide connectivity advantages and remove operator interface (in results-reading) issues. The lower sensitivity of certain brands of Ag-IRRDTs can be overcome in high prevalence areas with high frequency of testing. New SARS-CoV-2 variants are major concern for current and future diagnostic performance of these tests.

Amperometric immunosensor developed for sensitive detection of SARS-CoV-2 spike S1 protein in combined with portable device

In this present study, an amperometric immunosensor was developed based on disposable screen-printed carbon electrode (SPCE) for specific and sensitive detection of SARS-CoV-2 S1 protein. Anti-SARS-CoV-2 S1 monoclonal antibody was firstly immobilized onto the electrode surface. Then, the sandwich complex was formed by addition of S1 protein, secondary antibody and HRP-IgG, respectively. Chronoamperometry measurements were done in the presence of TMB mediator and the detection of SARS-CoV-2 S1 protein was performed by using 10 μL sample. The limit of detection (LOD) was found to be 0.19 ng/mL (equals to 24.7 amol in 10 μL sample) in the linear range of 0.5–10 ng/mL obtained in buffer medium. The applicability of this assay was investigated in the linear range of 0.5–3 ng/mL S1 protein in artificial saliva medium with the LOD as 0.13 ng/mL (equals to 16.9 amol in 10 μL sample). The selectivity study was examined in the presence of Hemagglutinin antigen (HA) in both mediums; buffer and artificial saliva while resulting with the successful discrimination between S1 protein and HA. The one of ultimate goals of our study is to present the possible implementation of this assay to point of care (POC) analysis. Under this aim, this assay was performed in combination with a portable device that is the commercial electrochemical analyzer. Amperometric detection of S1 protein in the range of 0.5–5 ng/mL was also successfully performed in artificial saliva medium with a resulting LOD as 0.15 ng/mL (equals to 19.5 amol in 10 μL sample). In addition, a selectivity study was similarly carried out by portable device.

Fabrication of 3D Amino-Functionalized Metal-Organic Framework on Porous Nickel Foam Skeleton to Combinate Follicle Stimulating Hormone Antibody for Specific Recognition of Follicle-Stimulating Hormone

In this study, a superficial and highly efficient hydrothermal synthesis method was developed for the in situ growth of amine-functionalized iron containing metal-organic frameworks (H2N-Fe-MIL-101 MOFs) on porous nickel foam (NicF) skeletons (H2N-Fe-MIL-101/NicF). The uniform decoration of the H2N-Fe-MIL-101 nanosheets thus generated on NicF was immobilized with follicle-stimulating hormone (FSH) antibody (Ab-FSH) to detect FSH antigen. In the present work, the Ab-FSH tagged H2N-Fe-MIL-101/NicF electrode was first applied as an immunosensor for the recognition of FSH, electrochemically. With all of the special characteristics, this material demonstrated superior specific recognition and sensitivity for FSH with an estimated detection limit (LOD) of 11.6 and 11.5 fg/mL for buffered and serum solutions, respectively. The availability of specific functional groups on MOFs makes them an interesting choice for exploring molecular sensing applications utilizing Ab-FSH tagged biomolecules.

Recent Progress in Electrochemical Immunosensors

Biosensors used for medical diagnosis work by analyzing physiological fluids. Antibodies have been frequently used as molecular recognition molecules for the specific binding of target analytes from complex biological solutions. Electrochemistry has been introduced for the measurement of quantitative signals from transducer-bound analytes for many reasons, including good sensitivity. Recently, numerous electrochemical immunosensors have been developed and various strategies have been proposed to detect biomarkers. In this paper, the recent progress in electrochemical immunosensors is reviewed. In particular, we focused on the immobilization methods using antibodies for voltammetric, amperometric, impedimetric, and electrochemiluminescent immunosensors.