SARS-CoV-2 detection methods: A comprehensive review

Rapid detection of SARS-CoV-2 RNA using a one-step fast multiplex RT-PCR coupled to lateral flow immunoassay

BACKGROUND

The COVID-19 has put emphasis on pivotal needs for diagnosis and surveillance worldwide, with the subsequent shortage of diagnostic reagents and kits. Therefore, it has become strategic for the countries to access diagnostics, expand testing capacity, and develop their own diagnostic capabilities and alternative rapid accurate nucleic acid diagnostics that are at lower costs. Here, we propose a visual SARS-CoV-2 detection using a one-step fast multiplex reverse transcription-PCR (RT-PCR) amplification coupled to lateral flow immunoassay detection on a PCRD device (Abingdon Health, UK).

METHODS

We developed various simplex fast-PCRs for screening sets of primer pairs newly designed or selected from literature or from validated WHO diagnostics, targeting S, N, E, RdRp or ORF1ab genes. We retained primers showing specific and stable amplification to assess for their suitability for detection on PCRD. Thus, fast RT-PCR amplifications were performed using the retained primers. They were doubly labeled with Fam and Biotin or Dig and Biotin to allow visual detection of the labeled amplicons on the lateral flow immunoassay PCR Detection (PCRD) device, looking at lack of interaction of the labeled primers (or primer dimers) with the test-lines in negative or no RNA controls. We set up all the assays using RNAs isolated from patients' nasopharyngeal swabs. We used two simplex assays, targeting two different viral genomic regions (N and E) and showing specific detection on PCRD, to set up a one-step fast multiplex RT-PCR assay (where both differently labeled primer pairs were engaged) coupled to amplicons' detection on a PCRD device. We evaluated this novel assay on 50 SARS-CoV-2 positive and 50 SARS-CoV-2 negative samples and compared its performance to the results of the quantitative RT-PCR (RT-qPCR) assays used for diagnosing the patients, here considered as the standard tests.

RESULTS

The new assay achieved a sensitivity of 88% (44/50) and a specificity of 98% (49/50). All patients who presented Ct values lower than 33 were positive for our assay. Except for one patient, those with Ct values above 33 returned negative results.

CONCLUSION

Our results have brought proof of principle on the usefulness of the one-step fast multiplex RT- PCR assay coupled to PCRD as a new assay for specific, sensitive, and rapid detection of SARS-CoV-2 without requiring costly laboratory equipment, and thus, at reduced costs in a format prone to be deployed when resources are limited. This assay offers a viable alternative for COVID-19 diagnosis or screening at points of need.

Expression, purification and immunogenicity analyses of receptor binding domain protein of severe acute respiratory syndrome coronavirus 2 from delta variant

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is responsible for the COVID-19 pandemic. The receptor binding domain (RBD), located at the spike protein of SARS-CoV-2, contains most of the neutralizing epitopes during viral infection and is an ideal antigen for vaccine development. In this study, bioinformatic analysis of the amino acid sequence data of SARS-CoV-2 RBD protein for the better understanding of molecular characteristics was performed. The SARS-CoV-2 RBD gene was inserted into pET-28a vector, and efficiently expressed in E. coli system. Then, the recombinant proteins (RBD monomer and RBD dimer protein) were purified as antigen for animal immunization. Furthermore, the results showed that the recombinant proteins (RBD monomer and RBD dimer protein) had adequate immunogenicity to stimulate specific antibodies against the corresponding protein in immunized mice. Taken together, the results of this study revealed that RBD protein had a high immuno-genicity. This study might have implications for future development of SARS-CoV-2 detection.

Current Updates on Variants of SARS-CoV- 2: Systematic Review

Background

Coronavirus disease 2019 is caused by the severe acute respiratory syndrome coronavirus 2, which has become a pandemic. Severe acute respiratory syndrome coronavirus 2 is an enveloped, unsegmented, positive-sense, single-stranded RNA virus that belongs to the family Coronaviridae.

Aim

The objective of this review is to conduct a qualitative analysis of the current updates on epidemiology, evolution, and vaccine variants for SARS-CoV-2.

Method

The search strategy was done from the database based on the PRISMA criteria for qualitative analysis of this review. Literature on variants of severe acute respiratory syndrome coronavirus 2, published in English in the last 5 years (2019-2023), were included. From 179 a total of 105 articles were reviewed, searched, and retrieved from the electronic databases PubMed. The search was done using keywords like COVID-19, SARS-CoV-2, variants, mutations, and vaccines, and articles were managed using EndNote X8 software. The scope of view for this review was the course of the pandemic by emerging variants and how man is struggling to overcome this sudden pandemic through vaccines. The narrative skeleton was constructed based on the article's scope of view.

Result

From the parent severe acute respiratory syndrome coronavirus 2, many variants emerged during the course of this pandemic. They are mainly categorized into two variants: variants of interest and variants of concern based on the impact on public health. The World Health Organization leveled five variants: Alpha (strain B.1.1.7), Beta (strain B.1.351), Gamma (strain P.1), Delta (strain B.1.617.2), and Omicron (B.1.1.529).

Conclusions

It is crucial to stay informed about the latest developments in the understanding of SARS-CoV-2 variants, as new variants can emerge and impact the course of the pandemic. Health authorities and researchers continuously have to monitor and study these variants to assess their characteristics, transmissibility, severity, and the effectiveness of vaccines against them. One has to always refer to the latest information from reputable health journals or organizations for the most up-to-date and accurate details on COVID-19 variants.

Ultra-sensitive detection of SARS-CoV-2 S1 protein by coupling rolling circle amplification with poly(N-isopropylacrylamide)-based sandwich-type assay

In the past few years, the COVID-19 pandemic, caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) seriously threatens global public health security due to its high contagiousness. It remains of vital importance to develop a rapid and sensitive assay for SARS-CoV-2. In this work, we proposed a sandwich-type assay based on poly(N-isopropylacrylamide) (PNIPAM), allowing efficient detection of the SARS-CoV-2 S1 protein in the homogeneous solution. Firstly, a direct sandwich-type assay was established with a linear range of 0.2-2 μg/mL and a limit of detection (LOD) of 0.11 μg/mL, which could realize rapid detection in about 1 h. Furthermore, the sandwich-type assay coupled with rolling circle amplification (RCA) obtained an increase in sensitivity of 5.9 × 104 folds with a wide linear range of 0.01 - 100 ng/mL and a LOD of 1.88 pg/mL. The average recoveries in unpretreated saliva were 90 %-113.0 %, indicating the potential of the developed method for application in practical samples. Given the high selectivity and sensitivity of the developed method, it has a significant potential for rapid and early detection of SARS-CoV-2.

Poor nutrition doubles post-COVID-19 syndrome risk in cancer patients: insights from a Chinese multicentre study

Background

Since 2019, approximately 760 million SARS-CoV-2 cases have been reported globally, with post-COVID-19 syndrome posing significant challenges for cancer patients due to their immunosuppressed status and poor nutritional conditions. The role of nutritional status in influencing their infection risk and post-COVID-19 outcomes remains unclear, underscoring the need for targeted research and strategies.

Objective

To investigate the impact of baseline nutritional status on SARS-CoV-2 infection and the risk of post-COVID-19 syndrome in cancer patients.

Methods

A multicenter cross-sectional study was conducted from December 2022 to June 2023 in four tertiary hospitals across China. Cancer inpatients aged 18 years and older were enrolled and classified into two groups based on their Nutritional Risk Screening (NRS) scores. The correlation between SARS-CoV-2 infection, post-COVID-19 syndrome and nutritional status were analyzed using multivariable logistic regression.

Results

Among 834 eligible cancer patients, 10.8% were in the high nutritional risk group (NRS ≥ 3). The prevalence of SARS-CoV-2 infection was 58.8% (95% confidence interval, CI: 56.8-60.8%), and post-COVID-19 syndrome was 21.0% (95% CI: 10.4-14.4%). After adjusting for confounding factors, the high nutritional risk group had a significantly higher prevalence of post-COVID-19 syndrome compared to the low nutritional risk group (32.7% vs. 19.5%, AOR: 2.37, 95% CI: 1.23-4.54, p = 0.010). However, no significant difference in SARS-CoV-2 infection rates was found between the two groups (61.1% vs. 58.5%, AOR: 1.12, 95% CI: 0.70-1.80; p = 0.634).

Interpretation

Poor baseline nutritional status in cancer patients is associated with a higher prevalence of post-COVID-19 syndrome, providing preliminary information on post-COVID-19 syndrome in this population. These findings underscore the importance of adequate nutritional management in cancer patients, particularly during pandemic recurrences.

Optimization of Reverse Transcription Loop-Mediated Isothermal Amplification for In Situ Detection of SARS-CoV-2 in a Micro-Air-Filtration Device Format

The Coronavirus disease 2019 (COVID-19) pandemic has supercharged innovation in the field of molecular diagnostics and led to the exploration of systems that permit the autonomous identification of airborne infectious agents. Airborne virus detection is an emerging approach for determining exposure risk, although current methods limit intervention timeliness. Here, we explore reverse transcription loop-mediated isothermal amplification (RT-LAMP) assays for one-pot detection of Severe acute respiratory syndrome Coronavirus 2 (SARS-CoV-2) (SCV2) run on membrane filters suitable for micro-air-filtration of airborne viruses. We use a design of experiments statistical framework to establish the optimal additive composition for running RT-LAMP on membrane filters. Using SCV2 liquid spike-in experiments and fluorescence detection, we show that single-pot RT-LAMP on glass fiber filters reliably detected 0.10 50% tissue culture infectious dose (TCID50) SCV2 per reaction (3600 E-gene copies) and is an order of magnitude more sensitive than conventional RT-LAMP.

Ultra-sensitive colorimetric detection of SARS-CoV-2 by novel gold nanoparticle (AuNP)-assisted loop-mediated isothermal amplification (LAMP) and freezing methods

Loop-mediated isothermal amplification (LAMP) is a molecular diagnosis technology with the advantages of isothermal reaction conditions and high sensitivity. However, the LAMP reactions are prone to producing false-positive results and thus are usually less reliable. This study demonstrates a gold nanoparticle (AuNP)-assisted colorimetric LAMP technique for diagnosing SARS-CoV-2, which aims to overcome the false-positive results. The AuNPs were functionalized with E gene probes, specifically tailored to bind to the amplified E-gene LAMP product, using the freezing method. Varied salt concentration and AuNP/probe combinations were tested for the highest visual performance. The experiments were conducted on synthetic SARS-CoV-2 RNA (Omicron variant), as well as on clinical samples. The assay showed an exceptional sensitivity of 8.05 fg of LAMP amplicon mixture (0.537 fg/µL). The average reaction time was ~ 30 min. In conclusion, AuNP-assisted LAMP detection will not identify any potential unspecific amplification, which helps to improve the efficiency and reliability of LAMP assays in point-of-care applications. The freezing method to functionalize the AuNPs with probes simplifies the assay, which can be utilized in further diagnostic studies.

Molecular characterization of SARS-CoV-2 nucleocapsid protein

Corona Virus Disease 2019 (COVID-19) is a highly prevalent and potent infectious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Until now, the world is still endeavoring to develop new ways to diagnose and treat COVID-19. At present, the clinical prevention and treatment of COVID-19 mainly targets the spike protein on the surface of SRAS-CoV-2. However, with the continuous emergence of SARS-CoV-2 Variants of concern (VOC), targeting the spike protein therapy shows a high degree of limitation. The Nucleocapsid Protein (N protein) of SARS-CoV-2 is highly conserved in virus evolution and is involved in the key process of viral infection and assembly. It is the most expressed viral structural protein after SARS-CoV-2 infection in humans and has high immunogenicity. Therefore, N protein as the key factor of virus infection and replication in basic research and clinical application has great potential research value. This article reviews the research progress on the structure and biological function of SARS-CoV-2 N protein, the diagnosis and drug research of targeting N protein, in order to promote researchers' further understanding of SARS-CoV-2 N protein, and lay a theoretical foundation for the possible outbreak of new and sudden coronavirus infectious diseases in the future.

SARS-CoV-2 wastewater surveillance in the Czech Republic: Spatial and temporal differences in SARS-CoV-2 RNA concentrations and relationship to clinical data and wastewater parameters

This study presents the results of systematic wastewater monitoring of SARS-CoV-2 RNA and basic wastewater parameters from four different wastewater treatment plants (WWTPs) in the Czech Republic over the 2020-2022 epidemic. Two-step reverse-transcription quantitative PCR targeting genes encoding the N and Nsp12 proteins was employed to detect SARS-CoV-2 RNA loading in 420 wastewater samples. The results obtained were used to evaluate the potential of wastewater analysis for describing the epidemiological situation in cities of different sizes and determining temporal differences based on the prevailing SARS-CoV-2 variant. Strong correlations between the number of active and hospitalised COVID-19 cases in each WWTP catchment area and the concentration of SARS-CoV-2 RNA detected in the wastewater clearly demonstrated the suitability of this wastewater-based epidemiological approach for WWTPs of different sizes and characteristics, despite differences in SARS-CoV-2 variant waves, with some WWTPs showing high predictive potential. This study demonstrated on the data from the Czech Republic that targeted systematic monitoring of wastewater provides sufficiently robust data for surveillance of viral loads in sample populations, and thus contributes to preventing the spread of infection and subsequent introduction of appropriate measures.

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

BACKGROUND

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

RESULTS

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

SIGNIFICANCE

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

Rapid identification of SARS-CoV-2 strains via isothermal enzymatic recombinase amplification and nanopore sequencing

Surveillance of the SARS-CoV-2 genome has become a crucial technique in the management of COVID-19, aiding the pandemic response and supporting effective public health interventions. Typically, whole-genomic sequencing is used along with PCR-based target enrichment techniques to identify SARS-CoV-2 variants, which is a complicated and time-consuming process that requires central laboratory facilities. Thus, there is an urgent need to develop rapid and cost-effective tools for precise on-site detection and identification of SARS-CoV-2 strains. In this study, we demonstrate the rapid diagnosis of COVID-19 and identification of SARS-CoV-2 variants by amplification and sequencing of the entire SARS-CoV-2 S gene using isothermal enzymatic recombinase amplification combined with the advanced Oxford nanopore sequencing technique. The entire procedure, from sampling to sequencing, takes less than 8 hours and can be performed with limited resources. The newly developed method has noteworthy implications for examining the transmission dynamics of the virus, detecting novel genetic variants, and assessing the effect of mutations on diagnostic approaches, antiviral treatments, and vaccines.

A semi-quantitative visual lateral flow immunoassay for SARS-CoV-2 antibody detection for the follow-up of immune response to vaccination or recovery

The lateral flow immunoassay (LFIA) technique is largely employed for the point-of-care detection of antibodies especially for revealing the immune response in serum. Visual LFIAs usually provide the qualitative yes/no detection of antibodies, while quantification requires some equipment, making the assay more expensive and complicated. To achieve visual semi-quantification, the alignment of several lines (made of the same antigen) along a LFIA strip has been proposed. The numbering of the reacting lines has been used to correlate with the quantity of some biomarkers in serum. Here, we designed the first semiquantitative LFIA for detecting antibodies and applied it to classify the immune response to SARS-CoV-2 raised by vaccination or natural infection. We used a recombinant spike receptor-binding domain (RBD) as the specific capture reagent to draw two test lines. The detection reagent was selected among three possible ligands that are able to bind to anti-spike human antibodies: the same RBD, staphylococcal protein A, and anti-human immunoglobulin G antibodies. The most convenient detector, adsorbed on gold nanoparticles, was chosen based on the highest correlation with an antibody titre of 171 human sera, measured by a reference serological method, and was the RBD (Spearman's rho = 0.84). Incorporated into the semiquantitative LFIA, it confirmed the ability to discriminate high- and low-titre samples and to classify them into two classes (Dunn's test, P < 0.05). The proposed approach enabled the semiquantification of the immune response to SARS-CoV-2 by the unaided eye observation, thus overcoming the requirement of costly and complicated equipment, and represents a general strategy for the development of semiquantitative serological LFIAs.

Ultrasensitive and fast detection of SARS-CoV-2 using RT-LAMP without pH-dependent dye

This study investigates the performance of reverse transcription loop-mediated isothermal amplification (RT-LAMP) assay for the colorimetric detection of SARS-CoV-2 using fluorometric dye, namely, calcein. The detection limit (LoD) with the N-ID1 primer set resulted in superior performance, corresponding to ~ 2 copies/reaction or ~ 0.1 copies/μL of the RNA sample. The color development can be observed by the naked eye, using an ultraviolet (UV) transilluminator or a hand-UV light without the requirement of expensive devices. The average time-to-reaction (TTR) value was 26.2 min in high-copy number samples, while it was about 50 min in rRT-PCR. A mobile application was proposed to quantify the positive and negative results based on the three-color spaces (RGB, Lab, and HSB). Compared to rRT-PCR (n = 67), this assay allows fast and sensitive visual detection of SARS-CoV-2, with high sensitivity (90.9%), selectivity (100%), and accuracy (94.03%). Besides, the assay was sensitive regardless of variants. Since this assay uses a fluorescent dye for visual observation, it can be easily adapted in RT-LAMP assays with high sensitivity. Thus, it can be utilized in low-source centers and field testing such as conferences, sports meetings, refugee camps, companies, and schools.

CRISPR-Cas system: A promising tool for rapid detection of SARS-CoV-2 variants

COVID-19, caused by SARS-CoV-2, remains a global health crisis. The emergence of multiple variants with enhanced characteristics necessitates their detection and monitoring. Genome sequencing, the gold standard, faces implementation challenges due to complexity, cost, and limited throughput. The CRISPR-Cas system offers promising potential for rapid variant detection, with advantages such as speed, sensitivity, specificity, and programmability. This review provides an in-depth examination of the applications of CRISPR-Cas in mutation detection specifically for SARS-CoV-2. It begins by introducing SARS-CoV-2 and existing variant detection platforms. The principles of the CRISPR-Cas system are then clarified, followed by an exploration of three CRISPR-Cas-based mutation detection platforms, which are evaluated from different perspectives. The review discusses strategies for mutation site selection and the utilization of CRISPR-Cas, offering valuable insights for the development of mutation detection methods. Furthermore, a critical analysis of the clinical applications, advantages, disadvantages, challenges, and prospects of the CRISPR-Cas system is provided.

A novel assay based on DNA melting temperature for multiplexed identification of SARS-CoV-2 and influenza A/B viruses

Introduction

The severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) and influenza viruses can cause respiratory illnesses with similar clinical symptoms, making their differential diagnoses challenging. Additionally, in critically ill SARS-CoV-2-infected patients, co-infections with other respiratory pathogens can lead to severe cytokine storm and serious complications. Therefore, a method for simultaneous detection of SARS-CoV-2 and influenza A and B viruses will be clinically beneficial.

Methods

We designed an assay to detect five gene targets simultaneously via asymmetric PCR-mediated melting curve analysis in a single tube. We used specific probes that hybridize to corresponding single-stranded amplicons at low temperature and dissociate at high temperature, creating different detection peaks representing the targets. The entire reaction was conducted in a closed tube, which minimizes the risk of contamination. The limit of detection, specificity, precision, and accuracy were determined.

Results

The assay exhibited a limit of detection of <20 copies/μL for SARS-CoV-2 and influenza A and <30 copies/μL for influenza B, with high reliability as demonstrated by a coefficient of variation for melting temperature of <1.16% across three virus concentrations. The performance of our developed assay and the pre-determined assay showed excellent agreement for clinical samples, with kappa coefficients ranging from 0.98 (for influenza A) to 1.00 (for SARS-CoV-2 and influenza B). No false-positive, and no cross-reactivity was observed with six common non-influenza respiratory viruses.

Conclusion

The newly developed assay offers a straightforward, cost-effective and nucleic acid contamination-free approach for simultaneous detection of the SARS-CoV-2, influenza A, and influenza B viruses. The method offers high analytical sensitivity, reliability, specificity, and accuracy. Its use will streamline testing for co-infections, increase testing throughput, and improve laboratory efficacy.

Comparison of DNA extraction methods for COVID-19 host genetics studies

The coronavirus disease 2019 (COVID-19) pandemic has resulted in global shortages in supplies for diagnostic tests, especially in the developing world. Risk factors for COVID-19 severity include pre-existing comorbidities, older age and male sex, but other variables are likely play a role in disease outcome. There is indeed increasing evidence that supports the role of host genetics in the predisposition to COVID-19 outcomes. The identification of genetic factors associated with the course of SARS-CoV-2 infections relies on DNA extraction methods. This study compared three DNA extraction methods (Chelex®100 resin, phenol-chloroform and the QIAamp DNA extraction kit) for COVID-19 host genetic studies using nasopharyngeal samples from patients. The methods were compared regarding number of required steps for execution, sample handling time, quality and quantity of the extracted material and application in genetic studies. The Chelex®100 method was found to be cheapest (33 and 13 times cheaper than the commercial kit and phenol-chloroform, respectively), give the highest DNA yield (306 and 69 times higher than the commercial kit and phenol-chloroform, respectively), with the least handling steps while providing adequate DNA quality for downstream applications. Together, our results show that the Chelex®100 resin is an inexpensive, safe, simple, fast, and suitable method for DNA extraction of nasopharyngeal samples from COVID-19 patients for genetics studies. This is particularly relevant in developing countries where cost and handling are critical steps in material processing.

Rapid and sensitive one-tube detection of mpox virus using RPA-coupled CRISPR-Cas12 assay

Mpox is caused by a zoonotic virus belonging to the Orthopoxvirus genus and the Poxviridae family. In this study, we develop a recombinase polymerase amplification (RPA)-coupled CRISPR-Cas12a detection assay for the mpox virus. We design and test a series of CRISPR-derived RNAs(crRNAs) targeting the conserved D6R and E9L genes for orthopoxvirus and the unique N3R and N4R genes for mpox viruses. D6R crRNA-1 exhibits the most robust activity in detecting orthopoxviruses, and N4R crRNA-2 is able to distinguish the mpox virus from other orthopoxviruses. The Cas12a/crRNA assay alone presents a detection limit of 108 copies of viral DNA, whereas coupling RPA increases the detection limit to 1-10 copies. The one-tube RPA-Cas12a assay can, therefore, detect viral DNA as low as 1 copy within 30 min and holds the promise of providing point-of-care detection for mpox viral infection.

Designing of rapid assay for the detection of RdRp/Orf1ab specific to SARS-CoV-2

SARS-CoV-2 is still threat and mostly used detection method is real time reverse transcriptase polymerase chain reaction (rRT-PCR) for the open reading frame (Orf1ab), RNA-dependent RNA polymerase (RdRp), nucleocapsid (N) and envelope (E) genes of virus. However, rRT-PCR may have false negative rate for the nucleic acid detection. Since the RdRp/Orf1ab has high sensitivity for the molecular detection, two sandwich models, Model 1A-Model 1B, based on hybridization on lateral flow assay (LFA) were designed here and applied with the synthetic and clinical samples of RdRp/Orf1ab. In this purpose colloidal gold nanoparticles (AuNPs) were used as label. Membranes having different flow rate, three oligonucleotide probe concentrations and running buffers were used. Although synthetic target sequence was recognized by all the LFAs, PCR products obtained from either the synthetic plasmid DNA or oro/nasopharyngeal swabs were detected by Model 1 A using W12 membrane. Designed strip assays detected the RdRp/Orf1ab of the clinical samples as 100% sensitivity and specifity. It means that they might be used for the detection of virus and can be modified for the recognition of mutant genes of virus. These findings also demonstrated the importance of membranes, sandwich models, probe concentrations and sample contents for developing LFAs for viral detection.

Immunochromatographic enhancement strategy for SARS-CoV-2 detection based on nanotechnology

The global outbreak of coronavirus disease 2019 (COVID-19) has been catastrophic to both human health and social development. Therefore, developing highly reliable and sensitive point-of-care testing (POCT) for detecting severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has become a priority. Among all available POCTs, the lateral flow immunoassay (LFIA, also known as immunochromatography) has proved to be effective due to its accuracy, portability, convenience, and speed. In areas with a scarcity of laboratory resources and medical personnel, the LFIA provides an affordable option for the diagnosis of COVID-19. This review offers a comprehensive overview of methods for improving the sensitivity of SARS-CoV-2 detection using immunochromatography based on nanotechnology, sorted according to the different detection targets (antigens, antibodies, and nucleic acids). It also looks into the performance and properties of the various sensitivity enhancement strategies, before delving into the remaining challenges in COVID-19 diagnosis through LFIA. Ultimately, it seeks to provide helpful guidance in selecting an appropriate strategy for SARS-CoV-2 immunochromatographic detection based on nanotechnology.

Neutralizing Activity of SARS-CoV-2 Antibodies in Patients with COVID-19 and Vaccinated Individuals

BACKGROUND

Serological diagnosis of COVID-19 is complex due to the emergence of different SARS-CoV-2 variants.

METHODS

164 serum samples from (I) patients who recovered from COVID-19 (n = 62) as well as (II) vaccinated individuals (n = 52) and (III) vaccinated individuals who were infected with different SARS-CoV-2 variants after vaccination (n = 50) were included. All samples were tested using EIA (binding antibodies) and a virus neutralization test (VNT) using the Wuhan strain (NT antibodies). Group III was further tested with a VNT using the Alpha/Delta/Omicron strains.

RESULTS

The highest antibody index (AI) was observed in vaccinated individuals infected with COVID-19 (median AI = 50, IQR = 27-71) and the lowest in vaccinated individuals (median AI = 19, IQR = 8-48). Similarly, NT antibody titer was highest in vaccinated individuals infected with COVID-19 (median 128; IQR = 32-256) compared to vaccinated individuals (median 32, IQR = 4-128) and patients with COVID-19 (median 32, IQR = 8-64). The correlation between AI and NT titer was strongly positive in vaccinated individuals and moderately positive in patients with COVID-19. No significant correlation was observed in vaccinated individuals infected with COVID-19. In patients infected with Alpha and Delta, the lowest VNT positivity rate was for the Omicron variant (85.0%/83.3%). Patients infected with the Alpha variant showed the lowest NT titer for the Omicron variant (median titer 32) compared to the Wuhan/Delta variants (64/128). Patients infected with the Delta variant had the lowest NT titer to the Omicron variant (median 32), compared to the Wuhan/Alpha variants (64/128). Patients infected with the Omicron variant showed similar titers to the Delta/Wuhan variants (128) and higher to the Alpha variant (256).

CONCLUSIONS

The cross-immunity to SARS-CoV-2 is lowest for the Omicron variant compared to the Alpha/Delta variants.

Reviewing methods of deep learning for diagnosing COVID-19, its variants and synergistic medicine combinations

The COVID-19 pandemic has necessitated the development of reliable diagnostic methods for accurately detecting the novel coronavirus and its variants. Deep learning (DL) techniques have shown promising potential as screening tools for COVID-19 detection. In this study, we explore the realistic development of DL-driven COVID-19 detection methods and focus on the fully automatic framework using available resources, which can effectively investigate various coronavirus variants through modalities. We conducted an exploration and comparison of several diagnostic techniques that are widely used and globally validated for the detection of COVID-19. Furthermore, we explore review-based studies that provide detailed information on synergistic medicine combinations for the treatment of COVID-19. We recommend DL methods that effectively reduce time, cost, and complexity, providing valuable guidance for utilizing available synergistic combinations in clinical and research settings. This study also highlights the implication of innovative diagnostic technical and instrumental strategies, exploring public datasets, and investigating synergistic medicines using optimised DL rules. By summarizing these findings, we aim to assist future researchers in their endeavours by providing a comprehensive overview of the implication of DL techniques in COVID-19 detection and treatment. Integrating DL methods with various diagnostic approaches holds great promise in improving the accuracy and efficiency of COVID-19 diagnostics, thus contributing to effective control and management of the ongoing pandemic.

Recent Advances in Quantum Dot-Based Lateral Flow Immunoassays for the Rapid, Point-of-Care Diagnosis of COVID-19

The COVID-19 pandemic has spurred demand for efficient and rapid diagnostic tools that can be deployed at point of care to quickly identify infected individuals. Existing detection methods are time consuming and they lack sensitivity. Point-of-care testing (POCT) has emerged as a promising alternative due to its user-friendliness, rapidity, and high specificity and sensitivity. Such tests can be conveniently conducted at the patient's bedside. Immunodiagnostic methods that offer the rapid identification of positive cases are urgently required. Quantum dots (QDs), known for their multimodal properties, have shown potential in terms of combating or inhibiting the COVID-19 virus. When coupled with specific antibodies, QDs enable the highly sensitive detection of viral antigens in patient samples. Conventional lateral flow immunoassays (LFAs) have been widely used for diagnostic testing due to their simplicity, low cost, and portability. However, they often lack the sensitivity required to accurately detect low viral loads. Quantum dot (QD)-based lateral flow immunoassays have emerged as a promising alternative, offering significant advancements in sensitivity and specificity. Moreover, the lateral flow immunoassay (LFIA) method, which fulfils POCT standards, has gained popularity in diagnosing COVID-19. This review focuses on recent advancements in QD-based LFIA for rapid POCT COVID-19 diagnosis. Strategies to enhance sensitivity using QDs are explored, and the underlying principles of LFIA are elucidated. The benefits of using the QD-based LFIA as a POCT method are highlighted, and its published performance in COVID-19 diagnostics is examined. Overall, the integration of quantum dots with LFIA holds immense promise in terms of revolutionizing COVID-19 detection, treatment, and prevention, offering a convenient and effective approach to combat the pandemic.

Droplet digital PCR versus real-time PCR for in-house validation of porcine detection and quantification protocol: An artificial recombinant plasmid approach

Authenticity and traceability are essential for modern food and medicine inspection, and reliable techniques are important for the trade of halal foods, which reach more than 20 percent of the world market. A sensitive and accurate porcine detection method is required to develop a conformity assessment system that includes laboratory testing for porcine-free certification. This study proposes a procedure that could be incorporated into the development of a standardized control and protocol for real-time PCR (qPCR) methods and their traceability using droplet digital PCR (ddPCR). The design used a recombinant pUC57 plasmid as an amplification target to carry the 97 bp fragment of the porcine ATCB gene. The absolute quantification and linearity assessment showed high precision with R2 values of 0.9971 and 0.9998 for qPCR and ddPCR, respectively. In general, both methods showed comparable results in terms of linearity and detection limit. However, both limit of detection assessments showed high sensitivity, although ddPCR showed a slightly higher sensitivity than that of qPCR, especially at low DNA concentrations. Multiple-sample and inter-participatory testing evaluations revealed a high sensitivity, broad applicability, and robustness of the qPCR method. Therefore, we conclude that based on a recombinant plasmid analysis with a low quantity (less than five copy number), the digital PCR method produced more reliable results. These results could provide scientific information for regulatory authorities, especially those in Indonesia, to consider the development and formulation of a well-established qPCR protocol for porcine detection using expected DNA concentrations.

Proof-of-Concept: Smartphone- and Cloud-Based Artificial Intelligence Quantitative Analysis System (SCAISY) for SARS-CoV-2-Specific IgG Antibody Lateral Flow Assays

Smartphone-based point-of-care testing (POCT) is rapidly emerging as an alternative to traditional screening and laboratory testing, particularly in resource-limited settings. In this proof-of-concept study, we present a smartphone- and cloud-based artificial intelligence quantitative analysis system (SCAISY) for relative quantification of SARS-CoV-2-specific IgG antibody lateral flow assays that enables rapid evaluation (<60 s) of test strips. By capturing an image with a smartphone camera, SCAISY quantitatively analyzes antibody levels and provides results to the user. We analyzed changes in antibody levels over time in more than 248 individuals, including vaccine type, number of doses, and infection status, with a standard deviation of less than 10%. We also tracked antibody levels in six participants before and after SARS-CoV-2 infection. Finally, we examined the effects of lighting conditions, camera angle, and smartphone type to ensure consistency and reproducibility. We found that images acquired between 45° and 90° provided accurate results with a small standard deviation and that all illumination conditions provided essentially identical results within the standard deviation. A statistically significant correlation was observed (Spearman correlation coefficient: 0.59, p = 0.008; Pearson correlation coefficient: 0.56, p = 0.012) between the OD450 values of the enzyme-linked immunosorbent assay and the antibody levels obtained by SCAISY. This study suggests that SCAISY is a simple and powerful tool for real-time public health surveillance, enabling the acceleration of quantifying SARS-CoV-2-specific antibodies generated by either vaccination or infection and tracking of personal immunity levels.

Rapid Detection of SARS-CoV-2 RNA Using Reverse Transcription Recombinase Polymerase Amplification (RT-RPA) with Lateral Flow for N-Protein Gene and Variant-Specific Deletion-Insertion Mutation in S-Protein Gene

Rapid molecular testing for severe acute respiratory coronavirus 2 (SARS-CoV-2) variants may contribute to the development of public health measures, particularly in resource-limited areas. Reverse transcription recombinase polymerase amplification using a lateral flow assay (RT-RPA-LF) allows rapid RNA detection without thermal cyclers. In this study, we developed two assays to detect SARS-CoV-2 nucleocapsid (N) gene and Omicron BA.1 spike (S) gene-specific deletion-insertion mutations (del211/ins214). Both tests had a detection limit of 10 copies/µL in vitro and the detection time was approximately 35 min from incubation to detection. The sensitivities of SARS-CoV-2 (N) RT-RPA-LF by viral load categories were 100% for clinical samples with high (>9015.7 copies/µL, cycle quantification (Cq): < 25) and moderate (385.5-9015.7 copies/µL, Cq: 25-29.9) viral load, 83.3% for low (16.5-385.5 copies/µL, Cq: 30-34.9), and 14.3% for very low (<16.5 copies/µL, Cq: 35-40). The sensitivities of the Omicron BA.1 (S) RT-RPA-LF were 94.9%, 78%, 23.8%, and 0%, respectively, and the specificity against non-BA.1 SARS-CoV-2-positive samples was 96%. The assays seemed more sensitive than rapid antigen detection in moderate viral load samples. Although implementation in resource-limited settings requires additional improvements, deletion-insertion mutations were successfully detected by the RT-RPA-LF technique.

Validation of a MALDI-TOF MS Method for SARS-CoV-2 Detection on the Bruker Biotyper and Nasopharyngeal Swabs: A Brazil-UK Collaborative Study

We developed a MALDI-TOF mass spectrometry method for the detection of the SARS-CoV-2 virus in saliva-gargle samples using Shimadzu MALDI-TOF mass spectrometers in the UK. This was validated in the USA to CLIA-LDT standards for asymptomatic infection detection remotely via sharing protocols, shipping key reagents, video conferencing, and data exchange. In Brazil, more so than in the UK and USA, there is a need to develop non-PCR-dependent, rapid, and affordable SARS-CoV-2 infection screening tests that also identify variant SARS-CoV-2 and other virus infections. In addition, travel restrictions necessitated remote collaboration with validation on the available clinical MALDI-TOF-the Bruker Biotyper (microflex^® LT/SH)-and on nasopharyngeal swab samples, as salivary gargle samples were not available. The Bruker Biotyper was shown to be almost log10³ more sensitive at the detection of high molecular weight spike proteins. A protocol for saline swab soaks out was developed, and duplicate swab samples collected in Brazil were analyzed by MALDI-TOF MS. The swab collected sample spectra that varied from that of saliva-gargle in three additional mass peaks in the mass region expected for IgG heavy chains and human serum albumin. A subset of clinical samples with additional high mass, probably spike-related proteins, were also found. Further, spectral data comparisons and analysis, subjected to machine learning algorithms in order to resolve RT-qPCR positive from RT-qPCR negative swab samples, showed 56-62% sensitivity, 87-91% specificity, and a 78% agreement with RT-qPCR scoring for SARS-CoV-2 infection.

Development of loop-mediated isothermal amplification (LAMP) assays using five primers reduces the false-positive rate in COVID-19 diagnosis

The reverse-transcription loop-mediated isothermal amplification (RT-LAMP) is a cheaper and faster testing alternative for detecting SARS-CoV-2. However, a high false-positive rate due to misamplification is one of the major limitations. To overcome misamplifications, we developed colorimetric and fluorometric RT-LAMP assays using five LAMP primers, instead of six. The gold-standard RT-PCR technique verified the assays' performance. Compared to other primer sets with six primers (N, S, and RdRp), the E-ID1 primer set, including five primers, performed superbly on both colorimetric and fluorometric assays. The sensitivity of colorimetric and fluorometric assays was 89.5% and 92.2%, respectively, with a limit of detection of 20 copies/µL. The colorimetric RT-LAMP had a specificity of 97.2% and an accuracy of 94.5%, while the fluorometric RT-LAMP obtained 99% and 96.7%, respectively. No misamplification was evident even after 120 min, which is crucial for the success of this technique. These findings are important to support the use of RT-LAMP in the healthcare systems in fighting COVID-19.

The Potential of Nanobodies for COVID-19 Diagnostics and Therapeutics

The infectious severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is the causative agent for coronavirus disease 2019 (COVID-19). Globally, there have been millions of infections and fatalities. Unfortunately, the virus has been persistent and a contributing factor is the emergence of several variants. The urgency to combat COVID-19 led to the identification/development of various diagnosis (polymerase chain reaction and antigen tests) and treatment (repurposed drugs, convalescent plasma, antibodies and vaccines) options. These treatments may treat mild symptoms and decrease the risk of life-threatening disease. Although these options have been fairly beneficial, there are some challenges and limitations, such as cost of tests/drugs, specificity, large treatment dosages, intravenous administration, need for trained personal, lengthy production time, high manufacturing costs, and limited availability. Therefore, the development of more efficient COVID-19 diagnostic and therapeutic options are vital. Nanobodies (Nbs) are novel monomeric antigen-binding fragments derived from camelid antibodies. Advantages of Nbs include low immunogenicity, high specificity, stability and affinity. These characteristics allow for rapid Nb generation, inexpensive large-scale production, effective storage, and transportation, which is essential during pandemics. Additionally, the potential aerosolization and inhalation delivery of Nbs allows for targeted treatment delivery as well as patient self-administration. Therefore, Nbs are a viable option to target SARS-CoV-2 and overcome COVID-19. In this review we discuss (1) COVID-19; (2) SARS-CoV-2; (3) the present conventional COVID-19 diagnostics and therapeutics, including their challenges and limitations; (4) advantages of Nbs; and (5) the numerous Nbs generated against SARS-CoV-2 as well as their diagnostic and therapeutic potential.

The clinical characteristics of pediatric patients infected by SARS-CoV-2 Omicron variant and whole viral genome sequencing analysis

Pediatric population was generally less affected clinically by SARS-CoV-2 infection. Few pediatric cases of COVID-19 have been reported compared to those reported in infected adults. However, a rapid increase in the hospitalization rate of SARS-CoV-2 infected pediatric patients was observed during Omicron variant dominated COVID-19 outbreak. In this study, we analyzed the B.1.1.529 (Omicron) genome sequences collected from pediatric patients by whole viral genome amplicon sequencing using Illumina next generation sequencing platform, followed by phylogenetic analysis. The demographic, epidemiologic and clinical data of these pediatric patients are also reported in this study. Fever, cough, running nose, sore throat and vomiting were the more commonly reported symptoms in children infected by Omicron variant. A novel frameshift mutation was found in the ORF1b region (NSP12) of the genome of Omicron variant. Seven mutations were identified in the target regions of the WHO listed SARS-CoV-2 primers and probes. On protein level, eighty-three amino acid substitutions and fifteen amino acid deletions were identified. Our results indicate that asymptomatic infection and transmission among children infected by Omicron subvariants BA.2.2 and BA.2.10.1 are not common. Omicron may have different pathogenesis in pediatric population.

A prevalence study of COVID-19 among healthcare workers in a pandemic hospital in the Samsun province of Turkey

Among populations globally, many healthcare workers have been disproportionally impacted by the COVID-19 pandemic because of their above average exposure to people infected with SARS-CoV-2. Exposure to asymptomatic or pre-symptomatic individuals is particularly challenging, if those individuals continue to work, not knowing that they are potentially infectious. This study aimed to measure the level of asymptomatic infection in a cohort of workers in a healthcare setting in Turkey during the second major wave of infection in late 2020. Blood samples were collected and tested by electrochemiluminescence immunoassay for SARS-CoV-2 IgM and IgG antibodies. Nasal and throat swabs were performed in a subset of this cohort and RT-qPCR was used to search for the presence of SARS-CoV-2 RNA. The results showed that approximately 23% of the cohort were positive for anti-SARS-CoV-2 IgM antibodies and approximately 22% were positive for anti-SARS-CoV-2 IgG antibodies despite no reported history of COVID-19 symptoms. Just less than 30% of a subset of the group were positive for the presence of SARS-CoV-2 RNA indicating the likelihood of a current or recent infection, again despite a lack of typical COVID-19 associated symptoms. This study indicates a high rate of asymptomatic infection and highlights the need for regular testing of groups such as healthcare workers when community prevalence of disease is high and there is a desire to limit entry of virus into settings where vulnerable people may be present, because symptoms cannot be relied on as indicators of infection or infectiousness.