Lateral flow assays for COVID-19

Rapid tests are essential tools for monitoring and containing the COVID-19 pandemic. Lateral flow assays (LFAs) have been introduced for the point-of-care COVID-19 diagnosis, using paper-based devices, and widely used for detecting antigen or antibody related to COVID-19. This book chapter includes a brief overview of the LFAs for rapid test of COVID-19, with focus on nanomaterials for bioconjugation, material selection, human sampling, antibody and antigen tests, viral nucleic acid detection, advantages, limitations, and future perspective. © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023. All rights reserved.

Thematic analysis of national online narratives on regular asymptomatic testing for Covid-19 in schools in England.

OBJECTIVE: To understand the public perceptions of the schools Covid-19 testing programme in England. DESIGN: Qualitative social media analysis. SETTING: Online users of parenting forums (Mumsnet and Netmums), Facebook newspaper pages and Daily Mail online readers, who responded to posts or articles about the schools testing programme in England, between 1 and 31 March, 2021. RESULTS: Overall, seven main themes were identified, these were divided into barriers and facilitators to engaging in testing for Covid-19. Barriers were: uncertainty around testing in the absence of symptoms; concerns about testing; implications about testing positive; mistrust in the Government. Facilitators were: desire to protect others; desire to return to normality; and hearing others' positive experiences. CONCLUSIONS: Our analysis highlighted that alongside well-established barriers to engaging in asymptomatic testing, parents were having to negotiate additional complex decisions around balancing their child's anxiety over testing alongside acknowledgement of the implications of regular testing, such as return to normality and protecting others. Parents and children would benefit from additional practical and social support to facilitate engagement with the schools testing programme.

SARS-Cov-2 Spike-S1 Antigen Test Strip with High Sensitivity Endowed by High-Affinity Antibodies and Brightly Fluorescent QDs/Silica Nanospheres.

The extensive research into developing novel strategies for detecting respiratory syndrome coronavirus 2 (SARS-CoV-2) antigens in clinical specimens, especially the sensitive point-of-care testing method, is still urgently needed to reach rapid screening of viral infections. Herein, a new lateral flow immunoassay (LFIA) platform was reported for the detection of SARS-CoV-2 spike-S1 protein antigens, in which four sensitive and specific SARS-CoV-2 mouse monoclonal antibodies (MmAbs) were tailored by using quantum dot (QD)-loaded dendritic mesoporous silica nanoparticles modified further for achieving the -COOH group surface coating (named Q/S-COOH nanospheres). Importantly, compact QD adsorption was achieved in mesoporous channels of silica nanoparticles on account of highly accessible central-radial pores and electrostatic interactions, leading to significant signal amplification. As such, a limit of detection for SARS-CoV-2 spike-S1 testing was found to be 0.03 ng/mL, which is lower compared with those of AuNPs-LFIA (traditional colloidal gold nanoparticles, Au NPs) and enzyme-linked immunosorbent assay methods. These results show that optimizing the affinity of antibody and the intensity of fluorescent nanospheres simultaneously is of great significance to improve the sensitivity of LFIA.

Multiplexed Reverse Transcription Loop-Mediated Isothermal Amplification Coupled with a Nucleic Acid-Based Lateral Flow Dipstick as a Rapid Diagnostic Method to Detect SARS-CoV-2.

Due to the high reproduction rate of COVID-19, it is important to identify and isolate infected patients at the early stages of infection. The limitations of current diagnostic methods are speed, cost, and accuracy. Furthermore, new viral variants have emerged with higher rates of infectivity and mortality, many with mutations at various primer binding sites, which may evade detection via conventional PCR kits. Therefore, a rapid method that is sensitive, specific, and cost-effective is needed for a point-of-care molecular test. Accordingly, we developed a rapid molecular SARS-CoV-2 detection kit with high specificity and sensitivity, RT-PCR, taking advantage of the loop-mediated isothermal amplification (LAMP) technique. Four sets of six primers were designed based on conserved regions of the SARS-CoV-2 genome: two outer, two inner and two loop primers. Using the optimized protocol, SARS-CoV-2 genes were detected as quickly as 10 min but were most sensitive at 30 min, detecting as little as 100 copies of template DNA. We then coupled the RT-LAMP with a lateral flow dipstick (LFD) for multiplex detection. The LFD could detect two genic amplifications on a single strip, making it suitable for multiplexed detection. The development of a multiplexed RT-LAMP-LFD reaction on crude VTM samples would be suitable for the point-of-care diagnosis of COVID-19 in diagnostic laboratories as well as in private homes.

Enhancing the sensitivity of rapid antigen detection test (RADT) of different SARS-CoV-2 variants and lineages using fluorescence-labeled antibodies and a fluorescent meter.

RT-qPCR is considered the gold standard for diagnosis of COVID-19; however, it is laborious, time-consuming, and expensive. RADTs have evolved recently as relatively inexpensive methods to address these shortcomings, but their performance for detecting different SARS-COV-2 variants remains limited. RADT test performance could be enhanced using different antibody labeling and signal detection techniques. Here, we aimed to evaluate the performance of two antigen RADTs for detecting different SARS-CoV-2 variants: (i) the conventional colorimetric RADT (Ab-conjugated with gold beads); and (ii) the new Finecare™ RADT (Ab-coated fluorescent beads). Finecare™ is a meter used for the detection of a fluorescent signal. 187 frozen nasopharyngeal swabs collected in Universal transport (UTM) that are RT-qPCR positive for different SARS-CoV-2 variants were selected, including Alpha (n = 60), Delta (n = 59), and Omicron variants (n = 108). Sixty flu and 60 RSV-positive samples were included as negative controls (total sample number = 347). The conventional RADT showed sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of 62.4% (95%CI: 54-70), 100% (95%CI: 97-100), 100% (95%CI: 100-100), and 58% (95%CI: 49-67), respectively. These measurements were enhanced using the Finecare™ RADT: sensitivity, specificity, PPV, and NPV were 92.6% (95%CI: 89.08-92.3), 96% (95%CI: 96-99.61), 98% (95%CI: 89-92.3), and 85% (95%CI: 96-99.6) respectively. The sensitivity of both RADTs could be greatly underestimated because nasopharyngeal swab samples collected UTM and stored at -80 °C were used. Despite that, our results indicate that the Finecare™ RADT is appropriate for clinical laboratory and community-based surveillance due to its high sensitivity and specificity.

Recent Trends in Lateral Flow Immunoassays with Optical Nanoparticles.

Rapid, accurate, and convenient diagnosis is essential for effective disease management. Various detection methods, such as enzyme-linked immunosorbent assay, have been extensively used, with lateral flow immunoassay (LFIA) recently emerging as a major diagnostic tool. Nanoparticles (NPs) with characteristic optical properties are used as probes for LFIA, and researchers have presented various types of optical NPs with modified optical properties. Herein, we review the literature on LFIA with optical NPs for the detection of specific targets in the context of diagnostics.

Updates on the Biofunctionalization of Gold Nanoparticles for the Rapid and Sensitive Multiplatform Diagnosis of SARS-CoV-2 Virus and Its Proteins: From Computational Models to Validation in Human Samples.

Since the outbreak of the pandemic respiratory virus SARS-CoV-2 (COVID-19), academic communities and governments/private companies have used several detection techniques based on gold nanoparticles (AuNPs). In this emergency context, colloidal AuNPs are highly valuable easy-to-synthesize biocompatible materials that can be used for different functionalization strategies and rapid viral immunodiagnosis. In this review, the latest multidisciplinary developments in the bioconjugation of AuNPs for the detection of SARS-CoV-2 virus and its proteins in (spiked) real samples are discussed for the first time, with reference to the optimal parameters provided by three approaches: one theoretical, via computational prediction, and two experimental, using dry and wet chemistry based on single/multistep protocols. Overall, to achieve high specificity and low detection limits for the target viral biomolecules, optimal running buffers for bioreagent dilutions and nanostructure washes should be validated before conducting optical, electrochemical, and acoustic biosensing investigations. Indeed, there is plenty of room for improvement in using gold nanomaterials as stable platforms for ultrasensitive and simultaneous "in vitro" detection by the untrained public of the whole SARS-CoV-2 virus, its proteins, and specific developed IgA/IgM/IgG antibodies (Ab) in bodily fluids. Hence, the lateral flow assay (LFA) approach is a quick and judicious solution to combating the pandemic. In this context, the author classifies LFAs according to four generations to guide readers in the future development of multifunctional biosensing platforms. Undoubtedly, the LFA kit market will continue to improve, adapting researchers' multidetection platforms for smartphones with easy-to-analyze results, and establishing user-friendly tools for more effective preventive and medical treatments.

Lateral flow immunoassays for antigens, antibodies and haptens detection.

Lateral flow immunoassay (LFIA) is widely used as a rapid point-of-care testing (POCT) technique in food safety, veterinary and clinical detection on account of the accessible, fast and low-cost characteristics. After the outbreak of the coronavirus disease 2019 (COVID-19), different types of LFIAs have attracted considerable interest because of their ability of providing immediate diagnosis directly to users, thereby effectively controlling the outbreak. Based on the introduction of the principles and key components of LFIAs, this review focuses on the major detection formats of LFIAs for antigens, antibodies and haptens. With the rapid innovation of detection technologies, new trends of novel labels, multiplex and digital assays are increasingly integrated with LFIAs. Therefore, this review will also introduce the development of new trends of LFIAs as well as its future perspectives.

Advancements in portable instruments based on affinity-capture-migration and affinity-capture-separation for use in clinical testing and life science applications.

The shift from testing at centralized diagnostic laboratories to remote locations is being driven by the development of point-of-care (POC) instruments and represents a transformative moment in medicine. POC instruments address the need for rapid results that can inform faster therapeutic decisions and interventions. These instruments are especially valuable in the field, such as in an ambulance, or in remote and rural locations. The development of telehealth, enabled by advancements in digital technologies like smartphones and cloud computing, is also aiding in this evolution, allowing medical professionals to provide care remotely, potentially reducing healthcare costs and improving patient longevity. One notable POC device is the lateral flow immunoassay (LFIA), which played a major role in addressing the COVID-19 pandemic due to its ease of use, rapid analysis time, and low cost. However, LFIA tests exhibit relatively low analytical sensitivity and provide semi-quantitative information, indicating either a positive, negative, or inconclusive result, which can be attributed to its one-dimensional format. Immunoaffinity capillary electrophoresis (IACE), on the other hand, offers a two-dimensional format that includes an affinity-capture step of one or more matrix constituents followed by release and electrophoretic separation. The method provides greater analytical sensitivity, and quantitative information, thereby reducing the rate of false positives, false negatives, and inconclusive results. Combining LFIA and IACE technologies can thus provide an effective and economical solution for screening, confirming results, and monitoring patient progress, representing a key strategy in advancing diagnostics in healthcare.

Research progress in methods for detecting neutralizing antibodies against SARS-CoV-2.

The emergence of SARS-CoV-2 has seriously affected the lives of people worldwide. Clarifying the attenuation rule of SARS-CoV-2 neutralizing antibody (NAb) in vivo is the key to prevent reinfection and recurrence of virus. Currently, the commonly used methods for detecting NAb include virus neutralization tests, pseudovirus neutralization assays, lateral flow immunochromatography and enzyme-linked immunosorbent assays. The detection of NAb not only can be used to evaluate the level of immunity after vaccination or infection but also can provide important theoretical support for virus reinfection, recurrence and vaccine iteration. In this research, the related technologies of SARS-CoV-2 NAb detection were reviewed, aiming to provide better research ideas for SARS-CoV-2 epidemic prevention and control.

Toward rapid and sensitive point‐of‐care diagnosis with surface‐enhanced Raman scattering‐based optofluidic systems

With the recent global outbreaks of infectious diseases such as coronavirus disease 2019, developing a detection system capable of quickly and accurately diagnosing diseases on‐site has become a pressing need. The ability to diagnose patients in the field is crucial for the prompt isolation and treatment of infected individuals and the prevention of the spread of the disease. Our research group has recently developed a surface‐enhanced Raman scattering optofluidic system that enables rapid and accurate point‐of‐care diagnostics. This account will introduce the principle and configuration of the fluidic devices, such as lateral flow assay strips or microfluidic channels, and the portable Raman spectrometer. We will also highlight the challenges that must be addressed for using this system in clinical settings. Rapid and accurate diagnosis is critical for effective disease management and control, and developing this system can significantly improve our ability to respond to outbreaks of infectious diseases. [ FROM AUTHOR] Copyright of Bulletin of the Korean Chemical Society is the property of John Wiley & Sons, Inc. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full . (Copyright applies to all s.)

Inpatient Admission Pathway for Patients with Rheumatological Disorders

Background/Aims Rheumatology is a complex specialty covering many conditions of varying severity, from muscle pain through inflammatory arthritis such as Rheumatoid arthritis (RA) and connective tissue diseases. Most of the conditions can be managed in an outpatient/day case setting. However, acutely ill patients require safe and prompt inpatient management including specific intravenous infusions. This need to be done urgently and cannot wait to be accommodated through the Infusion unit at our hospital. Historically Medicine Acute Admission Unit has been the route to bring in these patients. However, operational bed pressures faced challenges leading to instances of delayed treatment with complications including fatality. This led to creating a direct inpatient admission pathway to the specialist ward. Methods Ward Matron designed the following robust pathway for direct patient admission to our specialist Rheumatology ward, Jevington ward. This was implemented in February 2022 after discussion and agreement with Clinical Lead consultant, pharmacist, clinical site managers and other colleagues. Rheumatology team and nurses covered the ward during working hours and by the on-call team out of hours. The overall responsibility remained with the rheumatology team. The referrals accepted only after completing appropriate paperwork. Patients carried out Lateral Flow Test (LFT) at home prior to admission. We ensured negative results and followed the Trust COVID 19 screening protocols. Subsequent screenings were done according to the updated guidelines. The planned assessment and treatments were carried out by the ward team complying with BSR/ EULAR Guidelines, infusion protocols such as standard and continuous Iloprost Infusion Protocols of the Trust. Results We assessed the delay in patient's admission, length of stay, patient outcome and experience after implementing the pathway. The significant change has been in the time to admit;from two weeks in 2018 & 19 to two days this year. This is reflected in the patient feedback. All our acutely ill patients were assessed, treated and discharged promptly on this specialist ward. Conclusion This pathway allowed safe and prompt treatment, prognosis and excellent experience for acutely ill patients with rheumatological disorders. This additionally enabled reduced length of stay supporting financial sustainability of the Trust. (Table Presented).

Modelling the impact of repeat asymptomatic testing policies for staff on SARS-CoV-2 transmission potential.

Repeat asymptomatic testing in order to identify and quarantine infectious individuals has become a widely-used intervention to control SARS-CoV-2 transmission. In some workplaces, and in particular health and social care settings with vulnerable patients, regular asymptomatic testing has been deployed to staff to reduce the likelihood of workplace outbreaks. We have developed a model based on data available in the literature to predict the potential impact of repeat asymptomatic testing on SARS-CoV-2 transmission. The results highlight features that are important to consider when modelling testing interventions, including population heterogeneity of infectiousness and correlation with test-positive probability, as well as adherence behaviours in response to policy. Furthermore, the model based on the reduction in transmission potential presented here can be used to parameterise existing epidemiological models without them having to explicitly simulate the testing process. Overall, we find that even with different model paramterisations, in theory, regular asymptomatic testing is likely to be a highly effective measure to reduce transmission in workplaces, subject to adherence. This manuscript was submitted as part of a theme issue on "Modelling COVID-19 and Preparedness for Future Pandemics".

Self-enhancement lateral flow immunoassay for COVID-19 diagnosis.

Equipment-free colorimetric-based lateral flow immunoassay (LFIA) is the most convenient and popular tool for various applications, including diagnostic tools requiring high sensitivity for the detection of pathogens. Thus, improvements and developments of LFIA are constantly being reported. Herein, we enriched the sensitivity of LFIA using the gold enhancement principle, emphasizing needlessly complicated apparatus, only one step for the strip test operation, and typical time incubation (15 min) process. Self-enhanced LFIA was then executed for subsequent flows by overlapping the additionally enhanced pad composed of gold ions and reducing agent on the conjugate pad and the sample pad. Self-enhanced LFIA was performed to detect SARS-CoV-2 antigens in saliva. The obtained result depicted that the achieved sensitivity was up to tenfold compared with that of conventional LFIA by visual measurements. The detection limits of self-enhanced LFIA detecting nucleocapsid protein antigens in the saliva sample was 0.50 and 0.10 ng/mL employed by naked eye detection and calibration curve-based calculation, respectively. When the proposed device was applied to 207 human saliva samples, the diagnostic performance presented a 96.10 % sensitivity and 99.23 % specificity. This self-enhanced LFIA could be implemented in large-scale production and demonstrates higher sensitivity with effortless use, which meets the requirements for point-of-care testing and on-field mass screening.

A New Software Interface for Registering Rapid Antigen Test Results to Prevent Fraud.

Donald O. Besong has already documented that the online registration of unsupervised lateral flow test results poses concerns in the case of a serious pandemic where there are not enough medics to read scans or watch videos of candidates' results [1]. Scanning or videorecording requires a high number of available medics [1] in an adverse pandemic scenario. In the above paper [1], an artificial intelligence (AI) interface with image recognition was suggested as a method to prevent cheating during the online registration of unsupervised test results. The second solution suggested was a method that obscures the meaning of the result the candidate reads from their test device so that a software interface can resolve that from a database [1]. This is an entirely new method.In this paper, the latter (entirely new) method is proposed and described in detail. Precisely, this simple but new method is all about blinding the test strips so that the candidate does not know what the face values signify. The software then connects to a database of unique strip identification numbers to determine the test result when the candidate or patient registers their results. Both strip number and the value of their test must be entered to register results. This method has never been proposed or implemented. The technique will be described in detail.

Evaluation of a new lateral flow assay for the quantitative detection of Anti-SARS- CoV- 2 specific IgG

Background: Antibody testing for COVID-19 may represent an interesting tool to document past SARS-CoV- 2 infections, both in individual patients with suspected COVID-19 symptoms or late-stage complications who had no (conclusive) PCR test. In addition, measuring SARS-CoV- 2 antibodies may offer a prognostic value and convey information on protective immunity in vaccination trials. The objective of the study is the evaluation of a rapid test for the quantitative interpretation of Anti-SARS- CoV- 2 IgG compared with other in-vitro methods. Method(s): The Anti-SARS- CoV- 2 LFA (Lateral Flow Assay) is a rapid test for the quantitative measurement of IgG antibodies to SARS-CoV- 2 in human serum, plasma and whole blood within 20 minutes. The complexes of Anti-SARS- CoV- 2 antibodies from patient's sample and coloured conjugate are retained at the test line by the complete SARS-CoV- 2 Spike Protein. The use of a special scanner system provides the opportunity of quantitative interpretation of the results, by using calibration curve established with "First WHO International Standard for anti-SARS- CoV- 2 immunoglobulin (human)". Result(s): Serum samples were taken from the serum bank at Dr. Fooke Laboratorien GmbH and tested for Anti-SARS- CoV- 2 IgG by the newly developed LFA (Dr. Fooke Laboratorien GmbH). The results were compared with established assay methods like Anti-SARS- CoV- 2 ELISA IgG (Dr. Fooke Laboratorien GmbH and Euroimmun). Good agreements were observed. Sensitivity and specificity between the newly developed LFA and Anti-SARS- CoV- 2 ELISA IgG of Dr. Fooke / Euroimmun were found at 0.95/0.88 and 1.00/0.93, respectively. The calibration curve established with "First WHO International Standard for anti-SARS- CoV- 2 immunoglobulin (human)" shows a reproducibility of > 90%. Conclusion(s): The Anti-SARS- CoV- 2 LFA shows comparable results to the ELISA systems of Dr. Fooke Laboratorien and Euroimmun. By the use of small amounts of serum, plasma or whole blood (10muL) the patients receive a fast and reliable result. A calibration curve, established with "First WHO International Standard for anti-SARS- CoV- 2 immunoglobulin (human)" offers the comparability to quantitative ELISA systems.

SERS/photothermal-based dual-modal lateral flow immunoassays for sensitive and simultaneous antigen detection of respiratory viral infections

Lateral flow immunoassay (LFIA) is one of the most common analytical platforms for point-of-care testing (POCT), which is capable of large-scale primary screening and home self-testing of infectious diseases. However, the sensitivity of conventional AuNPs-based LFIA is relatively low and more prone to false negatives. Herein, we report a novel LFIA based on gold-core-silver-shell bimetallic nanoparticles (Au4-ATP@Ag NPs) emitting Surface-enhanced Raman scatting (SERS) and Photothermal (PT) effect, named SERS/PT-based dual-modal LFIA (SERS/PT-dmLFIA), for the antigen detection of infectious diseases pathogens, which displayed an excellent performance. For influenza A virus (IAV), influenza B virus (IBV), and Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) N protein detection, the limit of detections (LoD) with Raman as signal were 31.25, 93.75, and 31.25 pg mL-1 respectively, and the LoDs with temperature difference (∆T) as signal were as low as 15.63, 187.5, and 15.63 pg mL-1 respectively, which were over 4-fold more sensitive than visual-based LFIA. The proposed SERS/PT-dmLFIA was used for detecting virus antigen in pharyngeal swabs and showed ideal coincidence rate of over 95% compared to the commercialized assays. In addition, we explored the development of multiplex SERS/PT-dmLFIA that can detect IAV, IBV, and SARS-CoV-2 antigens simultaneously without cross reactivity. Overall, the SERS/PT-dmLFIA for antigen detection not only exhibits high sensitivity, accuracy and specificity, but also have characteristics of rapidity and simplicity, which holds high potential for rapid diagnosis of infectious diseases in laboratory testing, mass screening, and home self-testing. © 2023 Elsevier B.V.

Rapid Detection of Sars Cov-2 Infection in Comparision with Rt-Pcr in Tertiary Care Hospital

Objectives: The goal of the present study was to assess the SARS-CoV-2 antigen detection test's performance features and compare them to the real-time reverse transcription polymerase chain reaction (RT-PCR) test, the gold standard test for the diagnosis of COVID-19 cases. Method(s): From October 2020 to May 2021, patients attending the OPD, including those undergoing surgery, at a Tertiary Care Teaching Hospital in Telangana provided 1000 respiratory samples, primarily nasopharyngeal swabs. A skilled technician had collected two nasopharyngeal swabs from each person in a COVID sample collection room while wearing personal protective equipment and following strict infection control procedures. One swab was used for the rapid antigen test given by the standard Q COVID-19 Ag test kit and placed into the extraction buffer tube. Second swab was kept in the viral transport medium and used for AllplexTM 2019-nCoV Assay (Seegene, Korea), which targets envelope gene (E), and RNA dependent RNA polymerase (RdRp) and nucleocapsid (N) genes of SARS CoV-2, was used for SARS-CoV-2 RNA detection according to the manufacturer's instructions. Result(s): Out of 1000 samples tested for COVID-19, 623 (63.7%) were males and 377 (36.3%) were females. Out of 1000 samples, 347 samples were RT-PCR positive and 653 were RT-PCR negative. Out of 347 RT-PCR samples positive, 341 were Rapid antigen test positive samples and six were negative. Overall sensitivity and specificity are 98.27% and 99.85%, respectively. Conclusion(s): The real-time RT-PCR assay's sensitivity and specificity were comparable to those of the rapid assay for SARS-CoV-2 antigen detection. It can be utilized for contact tracing measures to control the COVID-19 pandemic in places such as border crossings, airports, interregional bus and train stations, and mass testing campaigns needing quick findings. This is especially true in areas with a high prevalence of the disease.Copyright © 2023 The Authors. Published by Innovare Academic Sciences Pvt Ltd.

Design and Development of Nanoscale Aptasensors for Viral Diagnostics

Viral infection may be a serious threat for human beings. Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is a highly transmissible virus causing coronavirus disease 2019 (COVID-19) in humans and creating a universal pandemic outbreak. The current methods for detection of SARS-CoV-2 include real-time reverse transcription-polymerase chain reaction (RT-PCR), enzyme-linked immunosorbent assay (ELISA), and loop-mediated isothermal amplification (LAMP). Though the methods are widely used for the diagnosis of COVID-19, they too have their limitations such as time-consuming process, sophisticated instrumental setup, which requires highly skilled personnel for operation, and prevalence of false positive/negative reports. Therefore, there is a pressing need to develop alternative tools such as point-of-care testing (POCT) devices to detect SARS-CoV-2 rapidly, accurately, and user-friendly. Here, the authors propose a one-step diagnostic method using aptamer-based sensing technology. The intended design of aptamer-based biosensors (also known as aptasensors) utilizes the optical properties of gold nanoparticles (AuNP) conjugated with angiotensin-converting enzyme-2 (ACE-2) aptamers targeting SARS-CoV-2 using lateral flow assay (LFA). This study leads to the development of portable nanoscale aptasensors for viral diagnostics. © 2022 by the authors.

SARS-CoV-2 evolved variants optimize binding to cellular glycocalyx.

Viral variants of concern continue to arise for SARS-CoV-2, potentially impacting both methods for detection and mechanisms of action. Here, we investigate the effect of an evolving spike positive charge in SARS-CoV-2 variants and subsequent interactions with heparan sulfate and the angiotensin converting enzyme 2 (ACE2) in the glycocalyx. We show that the positively charged Omicron variant evolved enhanced binding rates to the negatively charged glycocalyx. Moreover, we discover that while the Omicron spike-ACE2 affinity is comparable to that of the Delta variant, the Omicron spike interactions with heparan sulfate are significantly enhanced, giving rise to a ternary complex of spike-heparan sulfate-ACE2 with a large proportion of double-bound and triple-bound ACE2. Our findings suggest that SARS-CoV-2 variants evolve to be more dependent on heparan sulfate in viral attachment and infection. This discovery enables us to engineer a second-generation lateral-flow test strip that harnesses both heparin and ACE2 to reliably detect all variants of concern, including Omicron.