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

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

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

A spatial-potential resolved bipolar electrode electrochemiluminescence biosensor based on polarity conversion for dual-mode detection of miRNA-122 and CEA

In this work, a spatial-potential resolved bipolar electrode electrochemiluminescence (BPE-ECL) biosensor based on polarity conversion strategy and CuHCF electrocatalyst was constructed for dual-mode detection of miRNA-122 and carcinoembryonic antigen (CEA). ECL technology was firstly used to systematically study the polarity conversion of BPE. It was found that changing the polarity of the driving voltage would cause the polarity change of BPE, and led to the change of the luminescent position of Ru(bpy)32+. As a "proof-of-concept application", we developed a shielded dual-channel BPE-ECL biosensor for dual-mode detection of miRNA-122 and CEA. In order to further improve the detection sensitivity, a non-precious metal electrocatalyst CuHCF with outstanding electrocatalytic reduction activity of H2O2 was firstly introduced to the BPE-ECL biosensor for signal amplification, which could generate high faradaic current under the excitation of negative potential. Based on the charge neutrality principle of BPE, the enhancement of the faradaic current resulted in the ECL signal amplification of Ru(bpy)32+. The targets in the sensing grooves caused the introduction or fall off of CuHCF, which led to the ECL signal change of Ru(bpy)32+ in the signal grooves, and realized the dual-mode detection of miRNA-122 and CEA. This work provided a deeper understanding of the polarity change of BPE. Furthermore, the introduction of non-precious metal electrocatalyst had broadened the application range of BPE-ECL sensors.

Signal amplification strategy of DNA self-assembled biosensor and typical applications in pathogenic microorganism detection

Biosensors have emerged as ideal analytical devices for various bio-applications owing to their low cost, convenience, and portability, which offer great potential for improving global healthcare. DNA self-assembly techniques have been enriched with the development of innovative amplification strategies, such as dispersion-to-localization of catalytic hairpin assembly, and dumbbell hybridization chain reaction, which hold great significance for building biosensors capable of realizing sensitive, rapid and multiplexed detection of pathogenic microorganisms. Here, focusing primarily on the signal amplification strategies based on DNA self-assembly, we concisely summarized the strengths and weaknesses of diverse isothermal nucleic acid amplification techniques. Subsequently, both single-layer and cascade amplification strategies based on traditional catalytic hairpin assembly and hybridization chain reaction were critically explored. Furthermore, a comprehensive overview of the recent advances in DNA self-assembled biosensors for the detection of pathogenic microorganisms is presented to summarize methods for biorecognition and signal amplification. Finally, a brief discussion is provided about the current challenges and future directions of DNA self-assembled biosensors.

On-The-Spot Sampling and Detection of Viral Particles on Solid Surfaces Using a Sponge Virus Sensor Incorporated with Finger-Press Fluid Release

This paper presents a sponge-based electrochemical sensor for rapid, on-site collection and analysis of infectious viruses on solid surfaces. The device utilizes a conducting porous sponge modified with graphene, graphene oxide, and specific antibodies. The sponge serves as a hydrophilic porous electrode capable of liquid collection and electrochemical measurements. The device operation involves spraying an aqueous solution on a target surface, swiping the misted surface using the sponge, discharging an electrolyte solution with a simple finger press, and performing in situ incubation and electrochemical measurements. By leveraging the water-absorbing ability of the biofunctionalized conducting sponge, the sensor can effectively collect and quantify virus particles from the surface. The portability of the device is enhanced by introducing a push-release feature that dispenses the liquid electrolyte from a miniature reservoir onto the sensor surface. This reservoir has sharp edges to rupture a liquid sealing film with a finger press. The ability of the device to sample and quantify viral particles is demonstrated by using influenza A virus as the model. The sensor provided a calculated limit of detection of 0.4 TCID50/mL for H1N1 virus, along with a practical concentration range from 1-106 TCID50/mL. Additionally, it achieves a 15% collection efficiency from single-run swiping on a tabletop surface. This versatile device allows for convenient on-site virus detection within minutes, eliminating the need for sample pretreatment and simplifying the entire sample collecting and measuring process. This device presents significant potential for rapid virus detection on solid surfaces.

A nanogap-enhanced SERS nanotag-based lateral flow assay for ultrasensitive and simultaneous monitoring of SARS-CoV-2 S and NP antigens

A lateral flow assay (LFA) strip based on dual 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB)-encoded satellite Fe3O4@Au (Mag@Au) SERS tags with nanogap is reported for  ultrasensitive and simultaneous diagnosis of two SARS-CoV-2 functional proteins. Composed of Fe3O4 core, satellite gold shell with nanogaps, and double-layer DTNB, the Mag@Au nanoparticles with an average size of 238 nm were designed as multifunctional tags to efficiently enrich the target SARS-CoV-2 protein from complex samples, significantly enhancing the SERS signal of the LFA strip and provide quantitative SERS detection of analyte on test lines. The developed dual DTNB-encoded satellite Mag@Au-based LFA allowed simultaneous quantification of spike (S) protein and nucleocapsid (NP) protein with detection limits of 23 pg mL-1 and 2 pg mL-1, respectively, lower than commercial ELISA kits and reported SERS-LFA detection system-based Au NPs and Fe3O4@3 nm Au MNPs. This magnetic SERS-LFA also showed high performance of multi-variant strain detection and further distinguished clinical samples of Omicron variant infection, demonstrating the potential of in situ detection of respiratory virus diseases.

Duplex Electrochemical Microfluidic Sensor for COVID-19 Antibody Detection: Natural versus Vaccine-Induced Humoral Response

The rapid transmission and resilience of coronavirus disease 2019 (COVID-19) have led to urgent demands in monitoring humoral response for effective vaccine development, thus a multiplex co-detection platform to discriminate infection-induced from vaccine-induced antibodies is needed. Here a duplex electrochemical immunosensor for co-detection of anti-nucleocapsid IgG (N-IgG) and anti-spike IgG (S-IgG) is developed by using a two-working electrode system, via an indirect immunoassay, with antibody quantification obtained by differential pulse voltammetry. The screen-printed electrodes (SPEs) are modified by carbon black and electrodeposited gold nanoflowers for maximized surface areas, enabling the construction of an immunological chain for S-IgG and N-IgG electrochemical detection with enhanced performance. Using an optimized immunoassay protocol, a wide linear range between 30-750 and 20-1000 ng mL-1 , and a limit of detection of 28 and 15 ng mL-1 are achieved to detect N-IgG and S-IgG simultaneously in serum samples. This duplex immunosensor is then integrated in a microfluidic device to obtain significantly reduced detection time (≤ 7 min) while maintaining its analytical performance. The duplex microfluidic immunosensor can be easily expanded into multiplex format to achieve high throughput screening for the sero-surveillance of COVID-19  and other infectious diseases.

Redefining serological diagnostics with immunoaffinity proteomics

Serological diagnostics is generally defined as the detection of specific human immunoglobulins developed against viral, bacterial, or parasitic diseases. Serological tests facilitate the detection of past infections, evaluate immune status, and provide prognostic information. Serological assays were traditionally implemented as indirect immunoassays, and their design has not changed for decades. The advantages of straightforward setup and manufacturing, analytical sensitivity and specificity, affordability, and high-throughput measurements were accompanied by limitations such as semi-quantitative measurements, lack of universal reference standards, potential cross-reactivity, and challenges with multiplexing the complete panel of human immunoglobulin isotypes and subclasses. Redesign of conventional serological tests to include multiplex quantification of immunoglobulin isotypes and subclasses, utilize universal reference standards, and minimize cross-reactivity and non-specific binding will facilitate the development of assays with higher diagnostic specificity. Improved serological assays with higher diagnostic specificity will enable screenings of asymptomatic populations and may provide earlier detection of infectious diseases, autoimmune disorders, and cancer. In this review, we present the major clinical needs for serological diagnostics, overview conventional immunoassay detection techniques, present the emerging immunoassay detection technologies, and discuss in detail the advantages and limitations of mass spectrometry and immunoaffinity proteomics for serological diagnostics. Finally, we explore the design of novel immunoaffinity-proteomic assays to evaluate cell-mediated immunity and advance the sequencing of clinically relevant immunoglobulins.

Development and Analytical Evaluation of a Point-of-Care Electrochemical Biosensor for Rapid and Accurate SARS-CoV-2 Detection

The COVID-19 pandemic has underscored the critical need for rapid and accurate screening and diagnostic methods for potential respiratory viruses. Existing COVID-19 diagnostic approaches face limitations either in terms of turnaround time or accuracy. In this study, we present an electrochemical biosensor that offers nearly instantaneous and precise SARS-CoV-2 detection, suitable for point-of-care and environmental monitoring applications. The biosensor employs a stapled hACE-2 N-terminal alpha helix peptide to functionalize an in situ grown polypyrrole conductive polymer on a nitrocellulose membrane backbone through a chemical process. We assessed the biosensor's analytical performance using heat-inactivated omicron and delta variants of the SARS-CoV-2 virus in artificial saliva (AS) and nasal swab (NS) samples diluted in a strong ionic solution, as well as clinical specimens with known Ct values. Virus identification was achieved through electrochemical impedance spectroscopy (EIS) and frequency analyses. The assay demonstrated a limit of detection (LoD) of 40 TCID50/mL, with 95% sensitivity and 100% specificity. Notably, the biosensor exhibited no cross-reactivity when tested against the influenza virus. The entire testing process using the biosensor takes less than a minute. In summary, our biosensor exhibits promising potential in the battle against pandemic respiratory viruses, offering a platform for the development of rapid, compact, portable, and point-of-care devices capable of multiplexing various viruses. The biosensor has the capacity to significantly bolster our readiness and response to future viral outbreaks.

Metallic nanoplatforms for COVID-19 diagnostics: versatile applications in the pandemic and post-pandemic era

The COVID-19 pandemic, which originated in Hubei, China, in December 2019, has had a profound impact on global public health. With the elucidation of the SARS-CoV-2 virus structure, genome type, and routes of infection, a variety of diagnostic methods have been developed for COVID-19 detection and surveillance. Although the pandemic has been declared over, we are still significantly affected by it in our daily lives in the post-pandemic era. Among the various diagnostic methods, nanomaterials, especially metallic nanomaterials, have shown great potential in the field of bioanalysis due to their unique physical and chemical properties. This review highlights the important role of metallic nanosensors in achieving accurate and efficient detection of COVID-19 during the pandemic outbreak and spread. The sensing mechanisms of each diagnostic device capable of analyzing a range of targets, including viral nucleic acids and various proteins, are described. Since SARS-CoV-2 is constantly mutating, strategies for dealing with new variants are also suggested. In addition, we discuss the analytical tools needed to detect SARS-CoV-2 variants in the current post-pandemic era, with a focus on achieving rapid and accurate detection. Finally, we address the challenges and future directions of metallic nanomaterial-based COVID-19 detection, which may inspire researchers to develop advanced biosensors for COVID-19 monitoring and rapid response to other virus-induced pandemics based on our current achievements.

Nanoplasmonic amplification in microfluidics enables accelerated colorimetric quantification of nucleic acid biomarkers from pathogens

Deployment of nucleic acid amplification assays for diagnosing pathogens in point-of-care settings is a challenge due to lengthy preparatory steps. We present a molecular diagnostic platform that integrates a fabless plasmonic nano-surface into an autonomous microfluidic cartridge. The plasmonic 'hot' electron injection in confined space yields a ninefold kinetic acceleration of RNA/DNA amplification at single nucleotide resolution by one-step isothermal loop-mediated and rolling circle amplification reactions. Sequential flow actuation with nanoplasmonic accelerated microfluidic colorimetry and in conjugation with machine learning-assisted analysis (using our 'QolorEX' device) offers an automated diagnostic platform for multiplexed amplification. The versatility of QolorEX is demonstrated by detecting respiratory viruses: SARS-CoV-2 and its variants at the single nucleotide polymorphism level, H1N1 influenza A, and bacteria. For COVID-19 saliva samples, with an accuracy of 95% on par with quantitative polymerase chain reaction and a sample-to-answer time of 13 minutes, QolorEX is expected to advance the monitoring and rapid diagnosis of pathogens.

Smart Sensors and Microtechnologies in the Precision Medicine Approach against Lung Cancer

BACKGROUND AND RATIONALE

The therapeutic interventions against lung cancer are currently based on a fully personalized approach to the disease with considerable improvement of patients' outcome. Alongside continuous scientific progresses and research investments, massive technologic efforts, innovative challenges, and consolidated achievements together with research investments are at the bases of the engineering and manufacturing revolution that allows a significant gain in clinical setting.

AIM AND METHODS

The scope of this review is thus to focus, rather than on the biologic traits, on the analysis of the precision sensors and novel generation materials, as semiconductors, which are below the clinical development of personalized diagnosis and treatment. In this perspective, a careful revision and analysis of the state of the art of the literature and experimental knowledge is presented.

RESULTS

Novel materials are being used in the development of personalized diagnosis and treatment for lung cancer. Among them, semiconductors are used to analyze volatile cancer compounds and allow early disease diagnosis. Moreover, they can be used to generate MEMS which have found an application in advanced imaging techniques as well as in drug delivery devices.

CONCLUSIONS

Overall, these issues represent critical issues only partially known and generally underestimated by the clinical community. These novel micro-technology-based biosensing devices, based on the use of molecules at atomic concentrations, are crucial for clinical innovation since they have allowed the recent significant advances in cancer biology deciphering as well as in disease detection and therapy. There is an urgent need to create a stronger dialogue between technologists, basic researchers, and clinicians to address all scientific and manufacturing efforts towards a real improvement in patients' outcome. Here, great attention is focused on their application against lung cancer, from their exploitations in translational research to their application in diagnosis and treatment development, to ensure early diagnosis and better clinical outcomes.

Electronic Tongue for Direct Assessment of SARS-CoV-2-Free and Infected Human Saliva-A Feasibility Study

An electronic tongue is a powerful analytical instrument based on an array of non-selective chemical sensors with a partial specificity for data gathering and advanced pattern recognition methods for data analysis. Connecting electronic tongues with electrochemical techniques for data collection has led to various applications, mostly within sensing for food quality and environmental monitoring, but also in biomedical research for the analyses of different bioanalytes in human physiological fluids. In this paper, an electronic tongue consisting of six electrodes (viz., gold, platinum, palladium, titanium, iridium, and glassy carbon) was designed and tested in authentic (undiluted, unpretreated) human saliva samples from eight volunteers, collected before and during the COVID-19 pandemic. Investigations of 11 samples using differential pulse voltammetry and a principal component analysis allowed us to distinguish between SARS-CoV-2-free and infected authentic human saliva. This work, as a proof-of-principle demonstration, provides a new perspective for the use of electronic tongues in the field of enzyme-free electrochemical biosensing, highlighting their potential for future applications in non-invasive biomedical analyses.

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.

CRISPR-Cas13a-powered electrochemical biosensor for the detection of the L452R mutation in clinical samples of SARS-CoV-2 variants

Since the end of 2019, a highly contagious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has deprived numerous lives worldwide, called COVID-19. Up to date, omicron is the latest variant of concern, and BA.5 is replacing the BA.2 variant to become the main subtype rampaging worldwide. These subtypes harbor an L452R mutation, which increases their transmissibility among vaccinated people. Current methods for identifying SARS-CoV-2 variants are mainly based on polymerase chain reaction (PCR) followed by gene sequencing, making time-consuming processes and expensive instrumentation indispensable. In this study, we developed a rapid and ultrasensitive electrochemical biosensor to achieve the goals of high sensitivity, the ability of distinguishing the variants, and the direct detection of RNAs from viruses simultaneously. We used electrodes made of MXene-AuNP (gold nanoparticle) composites for improved sensitivity and the CRISPR/Cas13a system for high specificity in detecting the single-base L452R mutation in RNAs and clinical samples. Our biosensor will be an excellent supplement to the RT-qPCR method enabling the early diagnosis and quick distinguishment of SARS-CoV-2 Omicron BA.5 and BA.2 variants and more potential variants that might arise in the future.

Development of nucleocapsid-specific monoclonal antibodies for SARS-CoV-2 and their ELISA diagnostics on an automatic microfluidic device

Coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has threatened public health globally, and the emergence of viral variants has exacerbated an already precarious situation. To prevent further spread of the virus and determine government action required for virus control, accurate and rapid immunoassays for SARS-CoV-2 diagnosis are urgently needed. In this study, we generated monoclonal antibodies (mAbs) against the SARS-CoV-2 nucleocapsid protein (NP), compared their reactivity using an enzyme-linked immunosorbent assay (ELISA), and selected four mAbs designated 1G6, 3E10, 3F10, and 5B6 which have higher reactivity to NP and viral lysates of SARS-CoV-2 than other mAbs. Using an epitope mapping assay, we identified that 1G6 detected the C-terminal domain of SARS-CoV-2 NP (residues 248-364), while 3E10 and 3F10 bound to the N-terminal domain (residues 47-174) and 3F10 detected the N-arm region (residues 1-46) of SARS-CoV-2 NP. Based on the epitope study and sandwich ELISA, we selected the 1G6 and 3E10 Abs as an optimal Ab pair and applied them for a microfluidics-based point-of-care (POC) ELISA assay to detect the NPs of SARS-CoV-2 and its variants. The integrated and automatic microfluidic system could operate the serial injection of the sample, the washing solution, the HRP-conjugate antibody, and the TMB substrate solution simply by controlling air purge via a single syringe. The proposed Ab pair-equipped microsystem effectively detected the NPs of SARS-CoV-2 variants as well as in clinical samples. Collectively, our proposed platform provides an advanced protein-based diagnostic tool for detecting SARS-CoV-2.

Biosensing strategies for the detection of SARS-CoV-2 nucleic acids

The COVID-19 pandemic had devastating effects throughout the world, producing a severe crisis in the health systems and in the economy of a long list of countries, even developed ones. Therefore, highly sensitive and selective analytical bioplatforms that allow the descentralized and fast detection of the severe acute respiratory síndrome coronavirus 2 (SARS-CoV-2), are extremely necessary. Since 2020, several reviews have been published, most of them focused on the different strategies to detect the SARS-CoV-2, either from RNA, viral proteins or host antibodies produced due to the presence of the virus. In this review, the most relevant biosensors for the detection of SARS-CoV-2 RNA are particularly addressed, with special emphasis on the discussion of the biorecognition layers and the different schemes for transducing the hybridization event.

Highly Sensitive Poly-N-isopropylacrylamide Microgel-based Electrochemical Biosensor for the Detection of SARS-COV-2 Spike Protein

Objective

Late 2019 witnessed the outbreak and widespread transmission of coronavirus disease 2019 (COVID-19), a new, highly contagious disease caused by novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Consequently, considerable attention has been paid to the development of new diagnostic tools for the early detection of SARS-CoV-2.

Methods

In this study, a new poly-N-isopropylacrylamide microgel-based electrochemical sensor was explored to detect the SARS-CoV-2 spike protein (S protein) in human saliva. The microgel was composed of a copolymer of N-isopropylacrylamide and acrylic acid, and gold nanoparticles were encapsulated within the microgel through facile and economical fabrication. The electrochemical performance of the sensor was evaluated through differential pulse voltammetry.

Results

Under optimal experimental conditions, the linear range of the sensor was 10 -13-10 -9 mg/mL, whereas the detection limit was 9.55 fg/mL. Furthermore, the S protein was instilled in artificial saliva as the infected human saliva model, and the sensing platform showed satisfactory detection capability.

Conclusion

The sensing platform exhibited excellent specificity and sensitivity in detecting spike protein, indicating its potential application for the time-saving and inexpensive detection of SARS-CoV-2.

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.

PAM-free cascaded strand displacement coupled with CRISPR-Cas12a for amplified electrochemical detection of SARS-CoV-2 RNA

The early diagnosis of coronavirus disease 2019 (COVID-19) is dependent on the specific and sensitive detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA. Herein, we develop a highly sensitive and specific electrochemical biosensor for SARS-CoV-2 target RNA detection based on the integration of protospacer adjacent motif (PAM)-free cascaded toehold-mediated strand displacement reaction (TSDR) and CRISPR-Cas12a (PfTSDR-CRISPR). In this study, each target is transformed into multiple DNA substrates with bubble structure in the seed region by the cascaded TSDR, which can directly hybridize with guide RNA (gRNA) without PAM requirement and then activate CRISPR-Cas12a's trans-cleavage activity. Subsequently, the hairpin DNA modified with methylene blue (MB-HP) is cleaved by activated CRISPR-Cas12a. Therefore, as MB leaves the electrode surface, a decreased current signal is obtained. With the involvement of PAM-free cascaded TSDRs and CRISPR-Cas12a amplification strategy, the PfTSDR-CRISPR-based electrochemical biosensor achieves the detection of target RNA as low as 40 aM. The biosensor has high sequence specificity, reliability and robustness. Thanks to the PAM-free cascaded TSDR, the biosensor can achieve universal detection of different target RNA without redesigning gRNA sequence of CRISPR-Cas12a. In addition, this biosensor successfully detects SARS-CoV-2 target RNA in complex samples, which highlights its potential for diagnosing COVID-19.

Label-Free Electrochemical Biosensor Platforms for Cancer Diagnosis: Recent Achievements and Challenges

With its fatal effects, cancer is still one of the most important diseases of today's world. The underlying fact behind this scenario is most probably due to its late diagnosis. That is why the necessity for the detection of different cancer types is obvious. Cancer studies including cancer diagnosis and therapy have been one of the most laborious tasks. Since its early detection significantly affects the following therapy steps, cancer diagnosis is very important. Despite researchers' best efforts, the accurate and rapid diagnosis of cancer is still challenging and difficult to investigate. It is known that electrochemical techniques have been successfully adapted into the cancer diagnosis field. Electrochemical sensor platforms that are brought together with the excellent selectivity of biosensing elements, such as nucleic acids, aptamers or antibodies, have put forth very successful outputs. One of the remarkable achievements of these biomolecule-attached sensors is their lack of need for additional labeling steps, which bring extra burdens such as interference effects or demanding modification protocols. In this review, we aim to outline label-free cancer diagnosis platforms that use electrochemical methods to acquire signals. The classification of the sensing platforms is generally presented according to their recognition element, and the most recent achievements by using these attractive sensing substrates are described in detail. In addition, the current challenges are discussed.

Common framework mutations impact antibody interfacial dynamics and flexibility

Introduction

With the flood of engineered antibodies, there is a heightened need to elucidate the structural features of antibodies that contribute to specificity, stability, and breadth. While antibody flexibility and interface angle have begun to be explored, design rules have yet to emerge, as their impact on the metrics above remains unclear. Furthermore, the purpose of framework mutations in mature antibodies is highly convoluted.

Methods

To this end, a case study utilizing molecular dynamics simulations was undertaken to determine the impact framework mutations have on the VH-VL interface. We further sought to elucidate the governing mechanisms by which changes in the VH-VL interface angle impact structural elements of mature antibodies by looking at root mean squared deviations, root mean squared fluctuations, and solvent accessible surface area.

Results and discussion

Overall, our results suggest framework mutations can significantly shift the distribution of VH-VL interface angles, which leads to local changes in antibody flexibility through local changes in the solvent accessible surface area. The data presented herein highlights the need to reject the dogma of static antibody crystal structures and exemplifies the dynamic nature of these proteins in solution. Findings from this work further demonstrate the importance of framework mutations on antibody structure and lay the foundation for establishing design principles to create antibodies with increased specificity, stability, and breadth.

Sandwich-like electrochemical aptasensing of heat shock protein 70 kDa (HSP70): Application in diagnosis/prognosis of coronavirus disease 2019 (COVID-19)

In this research, by using aptamer-conjugated gold nanoparticles (aptamer-AuNPs) and a modified glassy carbon electrode (GCE) with reduced graphene oxide (rGO) and Acropora-like gold (ALG) nanostructure, a sandwich-like system provided for sensitive detection of heat shock protein 70 kDa (HSP70), which applied as a functional biomarker in diagnosis/prognosis of COVID-19. Initially, the surface of the GCE was improved with rGO and ALG nanostructures, respectively. Then, an aptamer sequence as the first part of the bioreceptor was covalently bound on the surface of the GCE/rGO/ALG nanostructures. After adding the analyte, the second part of the bioreceptor (aptamer-AuNPs) was immobilized on the electrode surface to improve the diagnostic performance. The designed aptasensor detected HSP70 in a wide linear range, from 5 pg mL^-1 to 75 ng mL^-1, with a limit of detection (LOD) of ∼2 pg mL^-1. The aptasensor was stable for 3 weeks and applicable in detecting 40 real plasma samples of COVID-19 patients. The diagnostic sensitivity and specificity were 90% and 85%, respectively, compared with the reverse transcription-polymerase chain reaction (RT-PCR) method.

Electrokinetic Extraction of Doxorubicin from Biological Fluids by Polymer Inclusion Membrane Sampling Probe

A polymer inclusion membrane (PIM) based sampling probe was developed for electrokinetic extraction of drugs from biological fluids. The probe was fabricated by dip-coating a nonconductive glass capillary tube in a homogeneous PIM solution for three cycles. The PIM solution comprised cellulose triacetate (CTA), 2-nitrophenyl octyl ether (NPOE), and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [EMIM][NTf₂] in a ratio of 5:4:2. The developed probe electrokinetically extracted doxorubicin from human plasma, human serum, and dried blood spot (DBS). The practicability and reliability of the electrokinetic extraction were evaluated by LC-MS/MS to quantify the desorption of extracted doxorubicin. Under the optimized conditions, a quantification limit of 0.2-2 ng/mL was achieved for the three biological samples. The probe was further integrated into a portable battery-powered device for safe low-voltage (36 V) electrokinetic extraction. The developed technique is envisioned to provide a more efficient analytical workflow in the laboratory.

Proteolytic Biosensors with Functional Nanomaterials: Current Approaches and Future Challenges

Proteolytic enzymes are one of the important biomarkers that enable the early diagnosis of several diseases, such as cancers. A specific proteolytic enzyme selectively degrades a certain sequence of a polypeptide. Therefore, a particular proteolytic enzyme can be selectively quantified by changing detectable signals causing degradation of the peptide chain. In addition, by combining polypeptides with various functional nanomaterials, proteolytic enzymes can be measured more sensitively and rapidly. In this paper, proteolytic enzymes that can be measured using a polypeptide degradation method are reviewed and recently studied functional nanomaterials-based proteolytic biosensors are discussed. We anticipate that the proteolytic nanobiosensors addressed in this review will provide valuable information on physiological changes from a cellular level for individual and early diagnosis.

Impedance-Based Neutralizing Antibody Detection Biosensor with Application in SARS-CoV-2 Infection

Although safe and efficacious coronavirus disease-2019 (COVID-19) vaccines are available, real protective immunity is revealed by the serum COVID-19 neutralizing antibody (NAb) concentration. NAbs deactivate the virus by attaching to the viral receptor-binding domain (RBD), which interacts with angiotensin-converting enzyme 2 (ACE2) on the human cell. This paper introduces inexpensive, rapid, sensitive, and quantifiable impedance-based immunosensors to evaluate the NAb. The sensor limit of detection is experimentally determined in different buffer dilutions using bovine IgG-anti-bovine IgG interaction. The dominance of AC electrokinetic transport and molecular diffusion in the sensor is investigated using scaling analysis and numerical simulations. The results demonstrated that the sensor detection mechanism is mainly based on the diffusion of the biomolecules onto the electrode surface. After evaluating the sensor working principles, viral RBD buffers, including different NAb concentrations, are applied to the sensor, immobilized with the human ACE2 (hACE2). Results demonstrate that the sensor is capable of NAb detection in the analytical measuring interval between 45 ng/mL and 185 ng/mL. Since the present sensor provides fast test results with lower costs, it can be used to assess the NAb in people's blood serum before receiving further COVID vaccine doses.

Electrochemical Immunosensors Based on Zinc Oxide Nanorods for Detection of Antibodies Against SARS-CoV-2 Spike Protein in Convalescent and Vaccinated Individuals

Even after over 2 years of the COVID-19 pandemic, research on rapid, inexpensive, and accurate tests remains essential for controlling and avoiding the global spread of SARS-CoV-2 across the planet during a potential reappearance in future global waves or regional outbreaks. Assessment of serological responses for COVID-19 can be beneficial for population-level surveillance purposes, supporting the development of novel vaccines and evaluating the efficacy of different immunization programs. This can be especially relevant for broadly used inactivated whole virus vaccines, such as CoronaVac, which produced lower titers of neutralizing antibodies. and showed lower efficacy for specific groups such as the elderly and immunocompromised. We developed an impedimetric biosensor based on the immobilization of SARS-CoV-2 recombinant trimeric spike protein (S protein) on zinc oxide nanorod (ZnONR)-modified fluorine-doped tin oxide substrates for COVID-19 serology testing. Due to electrostatic interactions, the negatively charged S protein was immobilized via physical adsorption. The electrochemical response of the immunosensor was measured at each modification step and characterized by scanning electron microscopy and electrochemical techniques. We successfully evaluated the applicability of the modified ZnONR electrodes using serum samples from COVID-19 convalescent individuals, CoronaVac-vaccinated with or without positive results for SARS-CoV-2 infection, and pre-pandemic samples from healthy volunteers as controls. ELISA for IgG anti-SARS-CoV-2 spike protein was performed for comparison, and ELISA for IgG anti-RBDs of seasonal coronavirus (HCoVs) was used to test the specificity of immunosensor detection. No cross-reactivity with HCoVs was detected using the ZnONR immunosensor, and more interestingly, the sensor presented higher sensitivity when compared to negative ELISA results. The results demonstrate that the ZnONRs/spike-modified electrode displayed sensitive results for convalescents and vaccinated samples and shows excellent potential as a tool for the population's assessment and monitoring of seroconversion and seroprevalence.

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.

A loop-mediated isothermal amplification-enabled analytical assay for the detection of SARS-CoV-2: A review

The number of words: 4645, the number of figures: 4, the number of tables: 1The outbreak of COVID-19 in December 2019 caused a global pandemic of acute respiratory disease, and with the increasing virulence of mutant strains and the number of confirmed cases, this has resulted in a tremendous threat to global public health. Therefore, an accurate diagnosis of COVID-19 is urgently needed for rapid control of SARS-CoV-2 transmission. As a new molecular biology technology, loop-mediated isothermal amplification (LAMP) has the advantages of convenient operation, speed, low cost and high sensitivity and specificity. In the past two years, rampant COVID-19 and the continuous variation in the virus strains have demanded higher requirements for the rapid detection of pathogens. Compared with conventional RT-PCR and real-time RT-PCR methods, genotyping RT-LAMP method and LAMP plus peptide nucleic acid (PNA) probe detection methods have been developed to correctly identified SARS-CoV-2 variants, which is also why LAMP technology has attracted much attention. LAMP detection technology combined with lateral flow assay, microfluidic technology and other sensing technologies can effectively enhance signals by nucleic acid amplification and help to give the resulting output in a faster, more convenient and user-friendly way. At present, LAMP plays an important role in the detection of SARS-CoV-2.

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

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

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.

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.

Enhanced Enzymatically Amplified Metallization on Nanostructured Surfaces for Multiplexed Point-of-Care Electrical Detection of COVID-19 Biomarkers

Inexpensive yet sensitive and specific biomarker detection is a critical bottleneck in diagnostics, monitoring, and surveillance of infectious diseases such as COVID-19. Multiplexed detection of several biomarkers can achieve wider diagnostic applicability, accuracy, and ease-of-use, while reducing cost. Current biomarker detection methods often use enzyme-linked immunosorbent assays (ELISA) with optical detection which offers high sensitivity and specificity. However, this is complex, expensive, and limited to detecting only a single analyte at a time. Here, it is found that biomarker-bound enzyme-labeled probes act synergistically with nanostructured catalytic surfaces and can be used to selectively reduce a soluble silver substrate to generate highly dense and conductive, localized surface silver metallization on microelectrode arrays. This enables a sensitive and quantitative, simple, direct electronic readout of biomarker binding without the use of any intermediate optics. Furthermore, the localized and dry-phase stable nature of the metallization enables multiplexed electronic measurement of several biomarkers from a single drop (<10 µL) of sample on a microchip.This method is applied for the multiplexed point-of-care (POC) quantitative detection of multiple COVID-19 antigen-specific antibodies. Combining a simple microchip and an inexpensive, cellphone-interfaced, portable reader, the detection and discrimination of biomarkers of prior infection versus vaccination is demonstrated.

Recent trends and advancements in electrochemiluminescence biosensors for human virus detection

Researchers are constantly looking to find new techniques of virus detection that are sensitive, cost-effective, and accurate. Additionally, they can be used as a point-of-care (POC) tool due to the fact that the populace is growing at a quick tempo, and epidemics are materializing greater often than ever. Electrochemiluminescence-based (ECL) biosensors for the detection of viruses have become one of the most quickly developing sensors in this field. Thus, we here focus on recent trends and developments of these sensors with regard to virus detection. Also, quantitative analysis of various viruses (e.g., Influenza virus, SARS-CoV-2, HIV, HPV, Hepatitis virus, and Zika virus) with a specific interest in Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) was introduced from the perspective of the biomarker and the biological receptor immobilized on the ECL-based sensors, such as nucleic acids-based, immunosensors, and other affinity ECL biosensors.

The evolving epidemiology of monkeypox virus

Monkeypox, caused by the monkeypox virus (MPXV), is a zoonotic disease endemic mainly in West and Central Africa. As of 27 September 2022, human monkeypox has occurred in more than 100 countries (mostly in non-endemic regions) and caused over 66,000 confirmed cases, which differs from previous epidemics that mainly affected African countries. Due to the increasing number of confirmed cases worldwide, the World Health Organization (WHO) has declared the monkeypox outbreak as a Public Health Emergency of International Concern on July 23, 2022. The international outbreak of human monkeypox represents a novel route of transmission for MPXV, with genital lesions as the primary infection, and the emergence of monkeypox in the current outbreak is also new, as novel variants emerge. Clinical physicians and scientists should be aware of this emerging situation, which presents a different scenario from previous outbreaks. In this review, we will discuss the molecular virology, evasion of antiviral immunity, epidemiology, evolution, and detection of MPXV, as well as prophylaxis and treatment strategies for monkeypox. This review also emphasizes the integration of relevant epidemiological data with genomic surveillance data to obtain real-time data, which could formulate prevention and control measures to curb this outbreak.

Emerging Multiplex Nucleic Acid Diagnostic Tests for Combating COVID-19

The COVID-19 pandemic caused by SARS-CoV-2 has drawn attention to the need for fast and accurate diagnostic testing. Concerns from emerging SARS-CoV-2 variants and other circulating respiratory viral pathogens further underscore the importance of expanding diagnostic testing to multiplex detection, as single-plex diagnostic testing may fail to detect emerging variants and other viruses, while sequencing can be too slow and too expensive as a diagnostic tool. As a result, there have been significant advances in multiplex nucleic-acid-based virus diagnostic testing, creating a need for a timely review. This review first introduces frequent nucleic acid targets for multiplex virus diagnostic tests, then proceeds to a comprehensive and up-to-date overview of multiplex assays that incorporate various detection reactions and readout modalities. The performances, advantages, and disadvantages of these assays are discussed, followed by highlights of platforms that are amenable for point-of-care use. Finally, this review points out the remaining technical challenges and shares perspectives on future research and development. By examining the state of the art and synthesizing existing development in multiplex nucleic acid diagnostic tests, this review can provide a useful resource for facilitating future research and ultimately combating COVID-19.

Nonlinear dielectric spectroscopy biosensor for SARS-CoV-2 detection

The coronavirus disease caused by the SARS-CoV-2 virus has affected people worldwide for more than two years. Here we present a new diagnostic method based on nonlinear dielectric spectroscopy to detect the presence of the SARS-CoV-2 virus in swab samples. A known current is injected into the virus sample suspension, and the biomarker is the third harmonic detected in the power spectrum of the recorded signal. Computational modeling of harmonic production supports the hypothesis of ion channels (the E-protein) with nonlinear current-voltage characteristics being present on the virus envelope as a possible origin of harmonics. The developed system is able to distinguish between positive and negative samples with 5-10 dBc (decibels relative to the carrier) higher third harmonic ratios in positive samples, in agreement with the computational estimation. Our early results demonstrate that this method can detect the virus in solution. This is the first time harmonic signatures are used to detect SARS-CoV-2 in swab samples.

Design and finite element modeling of two-dimensional nanomechanical biosensors for SARS-CoV-2 detection

SARS-CoV-2 is the causative agent of COVID-19 disease. The development of different variants has increased the prevalence, pathogenicity, and mortality of the SARS-CoV-2. Prompt diagnosis and timely initiation of therapy can undoubtedly minimize the damage caused by this virus. In this study, a wide range of emerging single layer two-dimensional materials (SL2DMs), including graphene, grapheme oxide (GO), reduced graphene oxide (rGO), hexagonal boron nitride (h-BN), Ti3C2Tx MXene, and MoS2that can be used to fabricate highly sensitive biosensors, are analyzed using the finite element method based on antigen-antibody interaction. Important design parameters including sensor size, sensor aspect ratio, number of viruses, and applying in-plane strain on sensor performance are analyzed using frequency shift technique. In the following, an analytical relationship that can predict the limit of detection (LOD) according to the above parameters is proposed. The results show that all the above materials have a good performance in detecting viruses in the sample range of 10-100 viruses. This range can be reduced significantly by applying strains of less than 0.1. Also, applying strain increases shift frequency index by 2 to 3 times, which is a significant result. The maximum and minimum sensor performance are obtained for GO and Ti3C2Tx, respectively. The results of this paper can be used to build a new generation of two-dimensional biosensors for rapid detection of COVID-19 and other viruses.

An electrochemical membrane-based aptasensor for detection of severe acute respiratory syndrome coronavirus-2 receptor-binding domain

Herein, we report an electrochemical membrane-based aptasensor for the determination of the SARS-CoV-2 receptor-binding domain (SARS-CoV-2-RBD). For this purpose, the nanoporous anodic aluminium oxide membrane (NPAOM) was first fabricated electrochemically. The NPAOM was then functionalized with 3-mercaptopropyl trimethoxysilane (NPAOM-Si-SH). After that, the NPAOM-Si-SH was decorated with gold nanoparticles by using gold ion and sodium borohydride. The NPAOM-Si-S-Au_nano was then attached to the surface of the working electrode of a laser-engraved graphene electrode (LEGE). Subsequently, the LEGE/NPAOM-Si-S-Au_nano was fixed inside a flow cell that was made by using a three-dimensional (3D) printer, and then thiolated aptamer was transferred into the flow cell using a pump. The electrochemical behavior of the LEGE/NPAOM-Si-S-Au_nano-Aptamer was studied using square wave voltammetry (SWV) in the presence of potassium ferrocyanide as a redox probe. The response of the LEGE/NPAOM-Si-S-Au_nano-Aptamer to the different concentrations of the SARS-CoV-2-RBD in human saliva sample was investigated in the concentration range of 2.5-40.0 ng/mL. The limit of the detection was found to be 0.8 ng/mL. The LEGE/NPAOM-Si-S-Au_nano-Aptamer showed good selectivity to 5.0 ng/mL of SARS-CoV-2-RBD in the presence of five times of the interfering agents like hemagglutinin and neuraminidase as the influenza A virus major surface glycoproteins.

Dual-template molecularly imprinted electrochemical biosensor for IgG-IgM combined assay based on a dual-signal strategy

Detection of immunoglobulins (Igs) is of clinical significance for early diagnosis and timely treatment of diseases. Herein, a dual-template molecularly imprinted (DTMI) electrochemical biosensor was developed for IgG-IgM combined assay. In this DTMI electrochemical biosensor, Prussian blue (PB) and thionine (TH) decorated on graphene oxide (GO) and multi-walled carbon nanotubes (MWCNTs), respectively, were utilized as the dual-signal probes, and Au nanoparticles (AuNPs) were used for Igs anchoring and signal amplification. Polypyrrole (PPy) was electrodeposited on the biosensor surface and acted as the molecularly imprinted polymers (MIPs). After the removal of the IgG and IgM templates, the resultant DTMI electrochemical biosensor was used for IgG-IgM combined assay, and the concentrations of IgG and IgM could be indicated by the changes in the peak currents of PB (ΔI_PB) and TH (ΔI_TH), respectively. The DTMI electrochemical biosensor displayed a wide linear range and a low limit of detection (LOD) for both IgG (28.80 pg mL^-1) and IgM (0.58 pg mL^-1). Finally, the developed DTMI biosensor was used for IgG-IgM combined assay in clinical serum samples, and the results were comparable to those obtained by conventional immunoturbidimetry, implying its great potential in clinical diagnosis.

FRET-based hACE2 receptor mimic peptide conjugated nanoprobe for simple detection of SARS-CoV-2

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has led to a pandemic of acute respiratory disease, namely coronavirus disease (COVID-19). This disease threatens human health and public safety. Early diagnosis, isolation, and prevention are important to suppress the outbreak of COVID 19 given the lack of specific antiviral drugs to treat this disease and the emergence of various variants of the virus that cause breakthrough infections even after vaccine administration. Simple and prompt testing is paramount to preventing further spread of the virus. However, current testing methods, namely RT-PCR, is time-consuming. Binding of the SARS-CoV-2 spike (S) glycoprotein to human angiotensin-converting enzyme 2 (hACE2) receptor plays a pivotal role in host cell entry. In the present study, we developed a hACE2 mimic peptide beacon (COVID19-PEB) for simple detection of SARS-CoV-2 using a fluorescence resonance energy transfer system. COVID19-PEB exhibits minimal fluorescence in its ''closed'' hairpin structure; however, in the presence of SARS-CoV-2, the specific recognition of the S protein receptor-binding domain by COVID19-PEB causes the beacon to assume an ''open'' structure that emits strong fluorescence. COVID19-PEB can detect SARS-CoV-2 within 3 h or even 50 min and exhibits strong fluorescence even at low viral concentrations, with a detection limit of 4 × 10³ plaque-forming unit/test. Furthermore, in SARS-CoV-2-infected patient samples confirmed using polymerase chain reaction, COVID19-PEB accurately detected the virus. COVID19-PEB could be developed as a rapid and accurate diagnostic tool for COVID-19.

State-of-the-Art Smart and Intelligent Nanobiosensors for SARS-CoV-2 Diagnosis

The novel coronavirus appeared to be a milder infection initially, but the unexpected outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), commonly called COVID-19, was transmitted all over the world in late 2019 and caused a pandemic. Human health has been disastrously affected by SARS-CoV-2, which is still evolving and causing more serious concerns, leading to the innumerable loss of lives. Thus, this review provides an outline of SARS-CoV-2, of the traditional tools to diagnose SARS-CoV-2, and of the role of emerging nanomaterials with unique properties for fabricating biosensor devices to diagnose SARS-CoV-2. Smart and intelligent nanomaterial-enabled biosensors (nanobiosensors) have already proven their utility for the diagnosis of several viral infections, as various detection strategies based on nanobiosensor devices are already present, and several other methods are also being investigated by researchers for the determination of SARS-CoV-2 disease; however, considerably more is undetermined and yet to be explored. Hence, this review highlights the utility of various nanobiosensor devices for SARS-CoV-2 determination. Further, it also emphasizes the future outlook of nanobiosensing technologies for SARS-CoV-2 diagnosis.

Screen-printed electrode-based biosensors modified with functional nucleic acid probes and their applications in this pandemic age: a review

Electrochemical methodology has probably been the most used sensing platform in the past few years as they provide superior advantages. In particular, screen-printed electrode (SPE)-based sensing applications stand out as they provide extraordinary miniaturized but robust and user-friendly detection system. In this context, we are focusing on the modification of SPE with functional nucleic acid probes and nanostructures to improve the electrochemical detection performance in versatile sensing applications, particularly in the fight against the COVID-19 pandemic. Aptamers are immobilized on the electrode surface to detect non-nucleic acid targets and complementary probes to recognize and capture nucleic acid targets. In a step further, SPE-based biosensors with the modification of self-assembled DNA nanostructures are emphasized as they offer great potential for the interface engineering of the electrode surface and promote the excellent performance of various interface reactions. By equipping with a portable potentiostat and a smartphone monitoring device, the realization of this SPE-based miniaturized diagnostic system for the further requirement of fast and POC detection is revealed. Finally, more novel and excellent works are previewed and future perspectives in this field are mentioned.

Ultrabright nanoparticle-labeled lateral flow immunoassay for detection of anti-SARS-CoV-2 neutralizing antibodies in human serum

The level of anti-SARS-CoV-2 neutralizing antibodies (NAb) is an indispensable reference for evaluating the acquired protective immunity against SARS-CoV-2. Here, we established an ultrabright nanoparticles-based lateral flow immunoassay (LFIA) for one-step rapid semi-quantitative detection of anti-SARS-CoV-2 NAb in vaccinee's serum. Once embedded in polystyrene (PS) nanoparticles, the aggregation-induced emission (AIE) luminogen, AIE₄₉₀, exhibited ultrabright fluorescence due to the rigidity of PS and severe inhibition of intramolecular motions. The ultrabright AIE₄₉₀-PS nanoparticle was used as a fluorescent marker of LFIA. Upon optimized conditions including incubation time, concentrations of coated proteins and conjugated nanoparticles, amounts of antigens modified on the surface of nanoparticles, dilution rate of serum samples, and so on, the ultrabright nanoparticles-based LFIA could accurately identify 70 negative samples and 63 positive samples from human serum (p < 0.0001). The intra- and inter-assay precisions of the established method are above 13% and 16%, respectively. The established LFIA has tremendous practical value of generalization as a rapid semi-quantitative detection method of anti-SARS-CoV-2 NAb. Meanwhile, the AIE₄₉₀-PS nanoparticle is also promising to detect many other analytes by altering the protein on the surface.

Visual Detection of COVID-19 from Materials Aspect

ABSTRACT

In the recent COVID-19 pandemic, World Health Organization emphasized that early detection is an effective strategy to reduce the spread of SARS-CoV-2 viruses. Several diagnostic methods, such as reverse transcription-polymerase chain reaction (RT-PCR) and lateral flow immunoassay (LFIA), have been applied based on the mechanism of specific recognition and binding of the probes to viruses or viral antigens. Although the remarkable progress, these methods still suffer from inadequate cellular materials or errors in the detection and sampling procedure of nasopharyngeal/oropharyngeal swab collection. Therefore, developing accurate, ultrafast, and visualized detection calls for more advanced materials and technology urgently to fight against the epidemic. In this review, we first summarize the current methodologies for SARS-CoV-2 diagnosis. Then, recent representative examples are introduced based on various output signals (e.g., colorimetric, fluorometric, electronic, acoustic). Finally, we discuss the limitations of the methods and provide our perspectives on priorities for future test development.

Performance of electrochemical immunoassays for clinical diagnostics of SARS-CoV-2 based on selective nucleocapsid N protein detection: Boron-doped diamond, gold and glassy carbon evaluation

The 21st century has already brought us a plethora of new threats related to viruses that emerge in humans after zoonotic transmission or drastically change their geographic distribution or prevalence. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was first spotted at the end of 2019 to rapidly spread in southwest Asia and later cause a global pandemic, which paralyzes the world since then. We have designed novel immunosensors targeting conserved protein sequences of the N protein of SARS-CoV-2 based on lab-produced and purified anti-SARS-CoV-2 nucleocapsid antibodies that are densely grafted onto various surfaces (diamond/gold/glassy carbon). Titration of antibodies shows very strong reactions up to 1:72 900 dilution. Next, we showed the mechanism of interactions of our immunoassay with nucleocapsid N protein revealing molecular recognition by impedimetric measurements supported by hybrid modeling results with both density functional theory and molecular dynamics methods. Biosensors allowed for a fast (in less than 10 min) detection of SARS-CoV-2 virus with a limit of detection from 0.227 ng/ml through 0.334 ng/ml to 0.362 ng/ml for glassy carbon, boron-doped diamond, and gold surfaces, respectively. For all tested surfaces, we obtained a wide linear range of concentrations from 4.4 ng/ml to 4.4 pg/ml. Furthermore, our sensor leads to a highly specific response to SARS-CoV-2 clinical samples versus other upper respiratory tract viruses such as influenza, respiratory syncytial virus, or Epstein-Barr virus. All clinical samples were tested simultaneously on biosensors and real-time polymerase chain reactions.

Recent advances in airborne pathogen detection using optical and electrochemical biosensors

The world is currently facing an adverse condition due to the pandemic of airborne pathogen SARS-CoV-2. Prevention is better than cure; thus, the rapid detection of airborne pathogens is necessary because it can reduce outbreaks and save many lives. Considering the immense role of diverse detection techniques for airborne pathogens, proper summarization of these techniques would be beneficial for humans. Hence, this review explores and summarizes emerging techniques, such as optical and electrochemical biosensors used for detecting airborne bacteria (Bacillus anthracis, Mycobacterium tuberculosis, Staphylococcus aureus, and Streptococcus pneumoniae) and viruses (Influenza A, Avian influenza, Norovirus, and SARS-CoV-2). Significantly, the first section briefly focuses on various diagnostic modalities applied toward airborne pathogen detection. Next, the fabricated optical biosensors using various transducer materials involved in colorimetric and fluorescence strategies for infectious pathogen detection are extensively discussed. The third section is well documented based on electrochemical biosensors for airborne pathogen detection by differential pulse voltammetry, cyclic voltammetry, square-wave voltammetry, amperometry, and impedance spectroscopy. The unique pros and cons of these modalities and their future perspectives are addressed in the fourth and fifth sections. Overall, this review inspected 171 research articles published in the last decade and persuaded the importance of optical and electrochemical biosensors for airborne pathogen detection.

A Low-Cost Handheld Impedimetric Biosensing System for Rapid Diagnostics of SARS-CoV-2 Infections

Current laboratory diagnostic approaches for virus detection give reliable results, but they require a lengthy procedure, trained personnel, and expensive equipment and reagents; hence, they are not a suitable choice for home monitoring purposes. This paper addresses this challenge by developing a portable impedimetric biosensing system for the identification of COVID-19 patients. This sensing system has two main parts: a throwaway two-working electrode (2-WE) strip and a novel read-out circuit, specifically designed for simultaneous signal acquisition from both working electrodes. Highly reliable electrochemical signal tracking from multiplex immunosensors provides a potential for flexible and portable multi-biomarker detection. The electrodes' surfaces were functionalized with SARS-CoV-2 Nucleocapsid Antibody enabling the selective detection of Nucleocapsid protein (N-protein) along with self-validation in the clinical nasopharyngeal swab specimens. The proposed programmable highly sensitive impedance read-out system allows for a wide dynamic detection range, which makes the sensor capable of detecting N-protein concentrations between 0.116 and 10,000 pg/mL. This lightweight and economical read-out arrangement is an ideal prospect for being mass-produced, especially during urgent pandemic situations. Also, such an impedimetric sensing platform has the potential to be redesigned for targeting not only other infectious diseases but also other critical disorders.

Smart Immunosensors for Point-of-Care Serological Tests Aimed at Assessing Natural or Vaccine-Induced SARS-CoV-2 Immunity

Innovative and highly performing smart voltammetric immunosensors for rapid and effective serological tests aimed at the determination of SARS-CoV-2 antibodies were developed and validated in human serum matrix. Two immunosensors were developed for the determination of immunoglobulins directed against either the nucleocapsid or the spike viral antigen proteins. The immunosensors were realized using disposable screen-printed electrodes modified with nanostructured materials for the immobilization of the antigens. Fast quantitative detection was achieved, with analysis duration being around 1 h. Signal readout was carried out through a smart, compact and battery-powered potentiostat, based on a Wi-Fi protocol and devised for the Internet of Things (IoT) paradigm. This device is used for the acquisition, storage and sharing of clinical data. Outstanding immunosensors' sensitivity, specificity and accuracy (100%) were assessed, according to the diagnostic guidelines for epidemiological data. The overall performance of the sensing devices, combined with the portability of the IoT-based device, enables their suitability as a high-throughput diagnostic tool. Both of the immunosensors were validated using clinical human serum specimens from SARS-CoV-2 infected patients, provided by IRCCS Ospedale San Raffaele.