Lateral flow assays for viruses diagnosis: Up-to-date technology and future prospects

One-step, rapid, nanoparticle-based biosensor platform for the simultaneous identification of hepatitis B virus and hepatitis C virus in clinical applications

OBJECTIVES

Viral hepatitis caused by hepatitis B virus (HBV) and hepatitis C virus (HCV) infections remain a major global public health challenge, particularly in low- and middle-income countries. It is crucial to utilize a pointof-care (POC) testing platform that is sensitive, specific, rapid, and user-friendly for screening and diagnosis of the two infections. Here, a novel molecular diagnostic assay, integrating multiplex loop-mediated isothermal amplification with a gold nanoparticle-based lateral flow biosensor (mLAMP-AuNPs-LFB) was developed and applied for one-step, visual, rapid, sensitive, and specific identification of HBV and HCV.

METHODS

The AuNPs-based LFB was devised and constructed for the simultaneous detection of HBV and HCV. The HBV-LAMP and HCV-LAMP primers were designed against the S and 5'-untranslated region (5'-UTR) genes from the major HBV genotypes (B, C, D, B/C recombinant, and C/D recombinant) and HCV subtypes (1b, 2a, 3a, 3b, and 6a) in China, respectively. Our assay conditions, both multiplex-LAMP amplification temperature and time were optimized. The sensitivity and specificity of our assay were tested, and the feasibility of our assay was verified through clinical samples.

RESULTS

The AuNPs-based LFB used here was successfully manufactured according to our devise manual. The two unique independent primer pairs were successfully designed based on the S and 5'-UTR genes, respectively. The optimal mLAMP-AuNPs-LFB detection process, involving rapid nucleic acid isolation (10 min), mLAMP (63 °C for 35 min), and visual AuNPs-LFB interpretation (less than 2 min), could be completed within 50 min. The HBV&HCV-mLAMP-AuNPs-LFB assay can detect the target genes (HBV-S and HCV-5'-UTR) with as low as 20 copies of plasmid template per test, and the specificity was 100% for the experimental pathogens.

CONCLUSIONS

The preliminary results manifested that our mLAMP-AuNPs-LFB assay is a valuable tool and has tremendous potential as a POC testing approach for HBV and HCV identification, especially in undeveloped regions.

Performance of rapid antigen tests to detect SARS-CoV-2 variant diversity and correlation with viral culture positivity: implication for diagnostic development and future public health strategies

Antigen-based rapid diagnostic tests (Ag-RDTs) provide timely results, are simple to use, and are less expensive than molecular assays. Recent studies suggest that antigen-based testing aligns with virus culture-based results (a proxy of contagiousness at the peak viral phase of illness); however, the performance of Ag-RDTs for newer SARS-CoV-2 variants is unclear. In this study, we (i) assessed the performance of Ag-RDTs and diagnostic antibodies to detect a range of SARS-CoV-2 variants and (ii) determined whether Ag-RDT results correlated with culture positivity. We noted only minor differences in the limit of detection by variant for all assays, and we demonstrated consistent antibody affinity to the N protein among the different variants. We observed moderate to high sensitivity (46.8%-83.9%) for Ag-RDTs when compared to PCR positivity (100%), and all variants were assessed on each assay. Ag-RDT sensitivity and PCR Ct showed an inverse correlation with the detection of viable virus. Collectively, our results demonstrate that commercially available Ag-RDTs offer variable sensitivity compared to PCR, show similar diagnostic validity across variants, and may predict the risk of transmissibility. These findings may be used to support more tailored SARS-CoV-2 isolation strategies, particularly if other studies clarify the direct association between Ag-RDT positivity and transmission risk. The apparent trade-off between sensitivity in the detection of any PCR-positive infection and concordance with infectious virus positivity may also inform new RDT diagnostic development strategies for SARS-CoV-2 and other epidemic respiratory pathogens.

IMPORTANCE

Despite the availability of vaccines, COVID-19 continues to be a major health concern, and antigen-based rapid diagnostic tests (Ag-RDTs) are commonly used as point-of-care or at-home diagnostic tests. In this study, we evaluated the performance of two commercially available Ag-RDTs and a research Ag-RDT to detect multiple SARS-CoV-2 variants using upper respiratory tract swab samples from clinical COVID-19 cases. Furthermore, we determined whether Ag-RDT results correlated with culture positivity, a potential proxy of viral transmissibility. Our results have important implications to inform future testing and response strategies during periods of high COVID-19 transmission with new variants.

Smartphone-driven centrifugal microfluidics for diagnostics in resource limited settings

The broad availability of smartphones has provided new opportunities to develop less expensive, portable, and integrated point-of-care (POC) platforms. Here, a platform that consists of three main components is introduced: a portable housing, a centrifugal microfluidic disc, and a mobile phone. The mobile phone supplies the electrical power and serves as an analysing system. The low-cost housing made from cardboard serves as a platform to conduct tests. The electrical energy stored in mobile phones was demonstrated to be adequate for spinning a centrifugal disc up to 3000 revolutions per minute (RPM), a rotation speed suitable for majority of centrifugal microfluidics-based assays. For controlling the rotational speed, a combination of magnetic and acoustic tachometry using embedded sensors of the mobile phone was used. Experimentally, the smartphone-based tachometry was proven to be comparable with a standard laser-based tachometer. As a proof of concept, two applications were demonstrated using the portable platform: a colorimetric sandwich immunoassay to detect interleukin-2 (IL-2) having a limit of detection (LOD) of 65.17 ng/mL and a fully automated measurement of hematocrit level integrating blood-plasma separation, imaging, and image analysis that takes less than 5 mins to complete. The low-cost platform weighing less than 150 g and operated by a mobile phone has the potential to meet the REASSURED criteria for advanced diagnostics in resource limited settings.

Development of gold nanoparticle-based lateral-flow strips for NGAL protein detection in urine samples

This study focuses on enhancing the sensitivity of lateral-flow strips (LFSs) based on gold nanoparticles (AuNPs) for the detection of Neutrophil Gelatinase-Associated Lipocalin (NGAL) protein in urine samples. Several sizes of AuNP-based LFS biosensors were tested to optimize colorimetric signals for NGAL detection based on improved conjugation conditions. AuNPs of 39.8 nm diameter at pH 8 were the most sensitive for the detection of NGAL. Through systematic enhancements to the AuNP-based LFS, the study significantly improves the sensitivity, enabling the reliable detection of NGAL protein in urine samples at a level as low as 12.5 ng mL-1. These advances contribute to the refinement of diagnostic tools for the early detection of kidney injury, specifically in cases associated with the presence of NGAL protein, offering a more precise and effective screening approach.

Ultrasensitive Rapid Antigen Test by Geometric Lateral Flow Assays and Highly Doped Upconversion Nanoparticles

The paper-based lateral flow assay (LFA) testing strips are currently the most widely used for point-of-care testing (POCT), valued for their rapid result turnaround times in a few minutes. However, their sensitivity has been limited. Upconversion nanoparticles (UCNPs), especially highly doped ones, have emerged as promising luminescent reporters to enhance the LFA sensitivity. These UCNPs exhibit a nonlinear enhancement in luminescence with excitation power density, necessitating higher power densities for higher brightness. In this study, we utilized a geometric paper strip design to minimize the immune reaction area and maximize the excitation power density, enabling ultrasensitive detection of the SARS-CoV-2 nucleoprotein antigen. This design also slowed the antigen flow on the paper strip, extending the reaction time between antigen and antibody, thereby enhancing the efficiency of the immune reaction. Through this design, our approach achieved over a 100-fold enhancement in the limit of detection (LOD) compared with the widely used LFAs, based on gold colloidal nanoparticles and europium nanoparticles. This innovation expands the scope of LFA applications that require a low LOD.

Reviewing advances in nanophotonic biosensors

Biosensing, a promising branch of exploiting nanophotonic devices, enables meticulous detection of subwavelength light, which helps to analyze and manipulate light-matter interaction. The improved sensitivity of recent high-quality nanophotonic biosensors has enabled enhanced bioanalytical precision in detection. Considering the potential of nanophotonics in biosensing, this article summarizes recent advances in fabricating nanophotonic and optical biosensors, focusing on their sensing function and capacity. We typically classify these types of biosensors into five categories: phase-driven, resonant dielectric nanostructures, plasmonic nanostructures, surface-enhanced spectroscopies, and evanescent-field, and review the importance of enhancing sensor performance and efficacy by addressing some major concerns in nanophotonic biosensing, such as overcoming the difficulties in controlling biological specimens and lowering their costs for ease of access. We also address the possibility of updating these technologies for immediate implementation and their impact on enhancing safety and health.

Palladium/Platinum/Ruthenium Trimetallic Dendritic Nanozymes Exhibiting Enhanced Peroxidase-like Activity for Signal Amplification of Lateral Flow Immunoassays

Developing ultrasensitive lateral flow immunoassays (LFIAs) has garnered significant attention in the field of point-of-care testing. In this study, a trimetallic dendritic nanozyme (Pd@Pt-Ru) was synthesized through Ru deposition on a Pd@Pt core and utilized to enhancing the sensitivity of LFIAs. Pd@Pt-Ru exhibited a Km value of 5.23 mM for detecting H2O2, which indicates an H2O2 affinity comparable with that of horseradish peroxidase. The Ru surface layer reduces the activation energy barrier, which increases the maximum reaction rate. As a proof of concept, the proposed Pd@Pt-Ru nanozyme was incorporated into LFIAs (A-Pd@Pt-Ru-LFIAs) for detecting human chorionic gonadotropin (hCG). Compared with conventional gold nanoparticle (AuNP)-LFIAs, A-Pd@Pt-Ru-LFIAs demonstrated 250-fold increased sensitivity, thereby enabling a visible detection limit as low as 0.1 IU/L. True positive and negative rates both reached 100%, which renders the proposed Pd@Pt-Ru nanozyme suitable for detecting hCG in clinical samples.

A Label-free Optical Biosensor-Based Point-of-Care Test for the Rapid Detection of Monkeypox Virus

Diagnostic approaches that combine the high sensitivity and specificity of laboratory-based digital detection with the ease of use and affordability of point-of-care (POC) technologies could revolutionize disease diagnostics. This is especially true in infectious disease diagnostics, where rapid and accurate pathogen detection is critical to curbing the spread of disease. We have pioneered an innovative label-free digital detection platform that utilizes Interferometric Reflectance Imaging Sensor (IRIS) technology. IRIS leverages light interference from an optically transparent thin film, eliminating the need for complex optical resonances to enhance the signal by harnessing light interference and the power of signal averaging in shot-noise-limited operation to achieve virtually unlimited sensitivity. In our latest work, we have further improved our previous 'Single-Particle' IRIS (SP-IRIS) technology by allowing the construction of the optical signature of target nanoparticles (whole virus) from a single image. This new platform, 'Pixel-Diversity' IRIS (PD-IRIS), eliminated the need for z-scan acquisition, required in SP-IRIS, a time-consuming and expensive process, and made our technology more applicable to POC settings. Using PD-IRIS, we quantitatively detected the Monkeypox virus (MPXV), the etiological agent for Monkeypox (Mpox) infection. MPXV was captured by anti-A29 monoclonal antibody (mAb 69-126-3) on Protein G spots on the sensor chips and were detected at a limit-of-detection (LOD) - of 200 PFU/ml (~3.3 attomolar). PD-IRIS was superior to the laboratory-based ELISA (LOD - 1800 PFU/mL) used as a comparator. The specificity of PD-IRIS in MPXV detection was demonstrated using Herpes simplex virus, type 1 (HSV-1), and Cowpox virus (CPXV). This work establishes the effectiveness of PD-IRIS and opens possibilities for its advancement in clinical diagnostics of Mpox at POC. Moreover, PD-IRIS is a modular technology that can be adapted for the multiplex detection of pathogens for which high-affinity ligands are available that can bind their surface antigens to capture them on the sensor surface.

Electrochemical Lateral Flow Immunoassay with Built-In Electrodes for Ultrasensitive and Wireless Detection of Inflammatory Biomarkers

Paper-based lateral flow immunoassays (LFIAs) are cost-effective, portable, and simple methods for detection of diverse analytes, which however only provide qualitative or semiquantitative results and lack sufficient sensitivity. A combination of LFIA and electrochemical detection, namely, electrochemical lateral flow immunoassay (eLFIA), enables quantitative detection of analytes with high sensitivity, but the integration of external electrodes makes the system relatively expensive and unstable. Herein, the working, counter, and reference electrodes were prepared directly on the nitrocellulose membrane using screen printing, which remarkably simplified the structure of eLFIA and decreased the cost. Moreover, a horseradish peroxidase (HRP)-based electrochemical signal amplification strategy was used for further increasing the analytical sensitivity. HRP captured on the working electrode can catalyze the oxidation of tetramethylbenzidine (TMB) to form the TMB-TMBox precipitate on the electrode surface, which as an electrochemically active product can output an amplified current for quantification. We demonstrated that the eLFIA could detect low-abundant inflammatory biomarkers in human plasma samples with limits of detection of 0.17 and 0.54 pg mL-1 for interleukin-6 and C-reactive protein, respectively. Finally, a fully portable system was fabricated by integrating eLFIA with a flexible and wireless electrochemical workstation, realizing the point-of-care detection of interleukin-6.

Temporal changes to adult case fatality risk of COVID-19 after vaccination in England between May 2020 and February 2022: a national surveillance study

OBJECTIVES

Risk of death after severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has fallen during the pandemic, largely due to immunity from vaccination. In England, the timing and extent of this reduction varied due to staggered eligibility during the primary vaccination campaign, based on age and clinical risk group. Duration of protection is less well understood. Our objective was to estimate the case fatality risk (CFR) by vaccination status and time since last dose during a period of widespread community testing, to better understand the impact of coronavirus disease 2019 (COVID-19) vaccination and duration of protection.

DESIGN

SARS-CoV-2 cases diagnosed between May 2020 and February 2022 were linked to vaccine records from the National Immunisation Management System. CFR was calculated as the proportion of cases that died of COVID-19 per the death certificate, aggregated by week of specimen and stratified by 10-year age band and vaccination status.

SETTING

England, UK.

PARTICIPANTS

A total of 10,616,148 SARS-CoV-2 cases, aged ≥18 years, recorded by England's laboratory reporting system.

MAIN OUTCOME MEASURES

Case fatality risk of COVID-19, stratified by age band and vaccination status.

RESULTS

Overall, a reduction in CFR was observed for all age bands, with a clear temporal link to when the age group became eligible for primary vaccination and then the first booster. CFR increased with age (0.3% 50-59 years; 1.2% 60-69; 4.7% 70-79; 16.3% 80+) and was highest in the unvaccinated - albeit a reduction was observed over time. The highest CFR was seen in the unvaccinated 80+ group prior to vaccination rollout (30.6%). CFR was consistently lowest in vaccinated populations within 6 months of last dose, yet increased after over 6 months elapsed since last dose, across all age bands.

CONCLUSIONS

COVID-19 CFR reduced after vaccination, with the lowest CFR seen across all age bands when vaccinated up to 6 months prior to specimen date. This provides some evidence for continued booster doses in older age groups.

Characterizing a visual lateral flow device for rapid SARS-CoV-2 virus protein detection: pre-clinical and system assessment

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infections have affected more than 769 million individuals worldwide over the last few years. Although the pandemic is transitioning into an endemic, the COVID-19 outbreak is still a global concern. A rapid screening platform is needed for effective preventive and control measures. Herein, a visual rapid lateral flow platform for SARS-CoV-2 nucleocapsid protein detection is developed. Under optimal conditions, the system demonstrated good detection sensitivity and selectivity against tested respiratory viruses. The system provides direct visual detection with a limit of 0.7 ng of the nucleocapsid protein per mL of a sample (0.7 ng mL-1) within 15 minutes. Further, a correlation between direct visual detection and semi-quantitative analysis using a reader showed a similar detection limit (R2 = 0.9571). The repeatability and reproducibility studies highlighted the potential of the system for the rapid screening of SARS-CoV-2 infection, with variations within 5% and 10% at high and low protein concentrations, respectively. Subsequent pre-clinical validation to correlate the performance with the standard molecular approach (RT-PCR) using 170 nasopharyngeal swabs demonstrated 98% estimated sensitivity (95% CI, 89.35-99.95%) and 100% specificity (95% CI, 96.38-100%). The positive and negative predictive values were reported to be 100% and 99%, respectively, with an accuracy of 99.3%. With high viral load samples (Ct value ≤25, n = 47), the system demonstrated 100% detection sensitivity and specificity. The proposed technique provides a valuable platform for potential use in rapid screening, particularly during pandemics, where diagnostic capacity and mass screening are crucial.

Palladium nanoballs coupled with smartphone-thermal reader for photothermal lateral flow immunoassay of Aβ 1-40

Amyloid beta 1-40 (Aβ 1-40) is one of the most abundant substances in the body with the capacity to form insoluble aggregates and is a universal biomarker for the prediction of Alzheimer's disease. Here, a palladium nanoball (PNB)-strip was developed and coupled with a smartphone-thermal reader as an ultrasensitive and cost-effective platform for Aβ 1-40 detection. In this study, PNB was synthesized and introduced into lateral flow strips as an alternative signal source to gold nanoparticles to improve sensitivity because the PNB has a better heat generation ability. Quantitative analysis was performed using a self-developed smartphone-thermal reader, which is portable and cost-effective. The detection limit of the system was determined to be 20 pg mL-1, which fulfils the need for clinical diagnosis at the point-of-care. This work highlights a PNB-strip coupled smartphone-thermal reader for ultrasensitive and cost-effective Aβ 1-40 detection.

Development of a lateral flow assay for rapid and accurate detection of chicken anemia virus

Significant challenges to poultry health are posed by chicken anemia virus (CAV), which induces immunosuppression and causes increased susceptibility to secondary infections. The effective management and containment of CAV within poultry stocks require precise and prompt diagnosis. However, a deficiency persists in the availability of low-cost, rapid, and portable CAV detection devices. In this study, an immunochromatographic lateral-flow test strip-based assay was developed for CAV detection using in-house generated monoclonal antibodies (MABs) against CAV viral protein 1 (VP1). The recombinant truncated VP1 protein (Δ60VP1), with amino acid residues 1 to 60 of the native protein deleted, was produced via a prokaryotic expression system and utilized for immunizing BALB/c mice. Subsequently, high-affinity MABs against Δ60VP1 were generated and screened using conventional hybridoma technology combined with serial dilution assays. Two MABs, MAB1, and MAB3, both binding to distinct epitopes of Δ60VP1, were selected for the development of a lateral-flow assay. Sensitivity analysis demonstrated that the Δ60VP1 antigen could be detected by our homemade lateral-flow assay at concentrations as low as 625 ng/mL, and this sensitivity was maintained for at least 6 mo. The assay exhibited high specificity, as evidenced by its lack of reactivity with surrogate recombinant proteins and the absence of cross-reactivity with other chicken viruses and viral antigens. Comparative analysis with quantitative PCR data demonstrated substantial agreement, with a Kappa coefficient of 0.66, utilizing a sample set comprising 305 clinical chicken serum samples. In conclusion, the first lateral-flow assay for CAV detection was developed in this study, utilizing 2 specific anti-VP1 MABs. It is characterized by simplicity, rapidity, sensitivity, and specificity.

Recent advances in electrochemical aptasensors and genosensors for the detection of pathogens

In recent years, pathogenic microorganisms have caused significant mortality rates and antibiotic resistance and triggered exorbitant healthcare costs. These pathogens often have high transmission rates within human populations. Rapid diagnosis is crucial in controlling and reducing the spread of pathogenic infections. The diagnostic methods currently used against individuals infected with these pathogens include relying on outward symptoms, immunological-based and, some biomolecular ones, which mainly have limitations such as diagnostic errors, time-consuming processes, and high-cost platforms. Electrochemical aptasensors and genosensors have emerged as promising diagnostic tools for rapid, accurate, and cost-effective pathogen detection. These bio-electrochemical platforms have been optimized for diagnostic purposes by incorporating advanced materials (mainly nanomaterials), biomolecular technologies, and innovative designs. This review classifies electrochemical aptasensors and genosensors developed between 2021 and 2023 based on their use of different nanomaterials, such as gold-based, carbon-based, and others that employed other innovative assemblies without the use of nanomaterials. Inspecting the diagnostic features of various sensing platforms against pathogenic analytes can identify research gaps and open new avenues for exploration.

Morphology Control of Self-Assembled Copper Coordination Polymers for Glucose Assays

Low-cost analytical assays enable accessible detection of clinically and environmentally important analytes; however, common enzyme-based assays suffer from high production and storage costs. Catalytically active synthetic materials serve as replacements for natural enzymes, but development of cost-effective, highly efficient synthetic strategies remains a challenge. Here, we utilized a facile synthesis for copper bipyridine coordination polymers (CuBpyCPs) and investigated structure-function relationships to achieve optimal catalytic properties for a glucose assay. We demonstrated the manipulation of CuBpyCP morphology, resulting in nanoscale petal-like structures and microscale high-index faceted structures, and identified three pure crystal morphologies exhibiting a comparable catalytic activity (Km = 0.3-0.5 mM) to horseradish peroxidase.

Aptamer-based diagnostic and therapeutic approaches for animal viruses: A review

Animal diseases often have significant consequences due to the unclear and time-consuming diagnosis process. Furthermore, the emergence of new viral infections and drug-resistant pathogens has further complicated the diagnosis and treatment of viral diseases. Aptamers, which are obtained through systematic evolution of ligands by exponential enrichment (SELEX) technology, provide a promising solution as they enable specific identification and binding to targets, facilitating pathogen detection and the development of novel therapeutics. This review presented an overview of aptasensors for animal virus detection, discussed the antiviral activity and mechanisms of aptamers, and highlighted advancements in aptamer-based antiviral research following the COVID-19 pandemic. Additionally, the challenges and prospects of aptamer-based virus diagnosis and treatment research were explored. Although this review was not exhaustive, it offered valuable insights into the progress of aptamer-based antiviral drug research, target mechanisms, as well as the development of novel antiviral drugs and biosensors.

Key steps for improving bacterial SERS signals in complex samples: Separation, recognition, detection, and analysis

Rapid and reliable detection of pathogenic bacteria is absolutely essential for research in environmental science, food quality, and medical diagnostics. Surface-enhanced Raman spectroscopy (SERS), as an emerging spectroscopic technique, has the advantages of high sensitivity, good selectivity, rapid detection speed, and portable operation, which has been broadly used in the detection of pathogenic bacteria in different kinds of complex samples. However, the SERS detection method is also challenging in dealing with the detection difficulties of bacterial samples in complex matrices, such as interference from complex matrices, confusion of similar bacteria, and complexity of data processing. Therefore, researchers have developed some technologies to assist in SERS detection of bacteria, including both the front-end process of obtaining bacterial sample data and the back-end data processing process. The review summarizes the key steps for improving bacterial SERS signals in complex samples: separation, recognition, detection, and analysis, highlighting the principles of each step and the key roles for SERS pathogenic bacteria analysis, and the interconnectivity between each step. In addition, the current challenges in the practical application of SERS technology and the development trends are discussed. The purpose of this review is to deepen researchers' understanding of the various stages of using SERS technology to detect bacteria in complex sample matrices, and help them find new breakthroughs in different stages to facilitate the detection and control of bacteria in complex samples.

Low-Cost Biosensor Technologies for Rapid Detection of COVID-19 and Future Pandemics

Many systems have been designed for the detection of SARS-CoV-2, which is the virus that causes COVID-19. SARS-CoV-2 is readily transmitted, resulting in the rapid spread of disease in human populations. Frequent testing at the point of care (POC) is a key aspect for controlling outbreaks caused by SARS-CoV-2 and other emerging pathogens, as the early identification of infected individuals can then be followed by appropriate measures of isolation or treatment, maximizing the chances of recovery and preventing infectious spread. Diagnostic tools used for high-frequency testing should be inexpensive, provide a rapid diagnostic response without sophisticated equipment, and be amenable to manufacturing on a large scale. The application of these devices should enable large-scale data collection, help control viral transmission, and prevent disease propagation. Here we review functional nanomaterial-based optical and electrochemical biosensors for accessible POC testing for COVID-19. These biosensors incorporate nanomaterials coupled with paper-based analytical devices and other inexpensive substrates, traditional lateral flow technology (antigen and antibody immunoassays), and innovative biosensing methods. We critically discuss the advantages and disadvantages of nanobiosensor-based approaches compared to widely used technologies such as PCR, ELISA, and LAMP. Moreover, we delineate the main technological, (bio)chemical, translational, and regulatory challenges associated with developing functional and reliable biosensors, which have prevented their translation into the clinic. Finally, we highlight how nanobiosensors, given their unique advantages over existing diagnostic tests, may help in future pandemics.

Lateral flow immunoassay (LFIA) for dengue diagnosis: Recent progress and prospect

Dengue is one of the most widespread and fatal arboviral infections in the world. Early detection of dengue virus (DENV) is essential to prevent the spread of the disease and provide an immediate response. The lateral flow immunoassay (LFIA) systems are low-cost, rapid, sensitive, targeted, and straightforward detection, which is an ideal early detection candidate for point-of-care testing (POCT) in dengue-affected areas. However, current commercial LFIA kits cannot fully satisfy the sensitivity, specificity, serotype differentiation, and multiplex detection requirements. Therefore, various strategies have been applied to optimize the LFIA for DENV detection, including label material improvement, optical enhancement and novel structure design. In this review, we comprehensively presented the snapshot of dengue, the principle of LFIA, and recent progress in the LFIA optimization for dengue diagnoses. Furthermore, this review also discusses insights into the prospect of LFIA dengue diagnostic methods, such as microfluidics, multiplex design, nucleic acid-typed probes and smartphone-assisted result analysis.

A functionalized Sup35NM nanofibril-assisted oriented antibody capture in lateral flow immunoassay for sensitive detection of dengue type II NS1

Rapid and sensitive dengue non-structural protein 1 (NS1) detection assay is essential for the treatment of disease and currently releases high medical cost burdens. To address the limitations of conventional LFIA strips, we have developed an improved Sup35NM-Z-based LFIA that immobilizes antibodies on cellulose membranes in an orientated manner to increase the sensitivity of LFIA strips. A dual-functional Sup35NM nanofibril was fabricated by fusion with the antibody binding domain; resultant nanofibril from the amyloid Sup35NM was sprayed on the T-line to orientate the capture antibody and produces fluorescence signals. Antibody binding analysis showed that self-assembly of the Sup35NM monomer does not affect the binding activity of the Z-domain with the antibody. The NS1 for DENV-2 infection was chosen as a model target antigen to assess the feasibility of the Sup35NM-Z-domain-based LFIA platform. Under optimal conditions, the Sup35NM-Z-domain-based LFIA detected NS1 within 15 min with a detection limit of 1.29 ng/ml, while the detection limit of traditional LFIA with the same concentration of anti-NS1-Ab1 on the T-line by conventional physical adsorption was 2.20 ng/ml, 1.7 times higher than that of Sup35NM-Z-domain-based LFIA. As compared to traditional LFIAs, the Sup35NM-Z-based LFIA had a wide detection range of 1.29-625 ng/mL. The LFIA's clinical performance in identifying NS1 was also assessed using 15 clinical samples. The LFIA accurately recognized positive and negative samples, equal to 86.7% accuracy. The developed Sup35NM-Z-domain-based LFIA in this study offers great potential for the identification of target markers because of its greatly improved sensitivity and wider detection range.

Highly-Specific Single-Stranded Oligonucleotides and Functional Nanoprobes for Clinical Determination of Chlamydia Trachomatis and Neisseria Gonorrhoeae Infections

Early detection of Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (NG) is the key to controlling the spread of these bacterial infections. An important step in developing biosensors involves identifying reliable sensing probes against specific genetic targets for CT and NG. Here, the authors have designed single-stranded oligonucleotides (ssDNAs) targeting mutually conserved genetic regions of cryptic plasmid and chromosomal DNA of both CT and NG. The 5'- and 3'- ends of these ssDNAs are differentially functionalized with thiol groups and coupled with gold nanoparticles (AuNP) to develop absorbance-based assay. The AuNPs agglomerate selectively in the presence of its target DNA sequence and demonstrate a change in their surface plasmon resonance. The optimized assay is then used to detect both CT and NG DNA extracted from 60 anonymized clinical samples with a clinical sensitivity of ∼100%. The limit of detection of the assays are found to be 7 and 5 copies/µL for CT and NG respectively. Furthermore, it can successfully detect the DNA levels of these two bacteria without the need for DNA extraction and via a lateral flow-based platform. These assays thus hold the potential to be employed in clinics for rapid and efficient monitoring of sexually transmitted infections.

Point-of-Care Testing for Hepatitis Viruses: A Growing Need

Viral hepatitis, caused by hepatitis A virus (HAV), hepatitis B virus (HBV), hepatitis C virus (HCV), hepatitis D virus (HDV), or hepatitis E virus (HEV), is a major global public health problem. These viruses cause millions of infections each year, and chronic infections with HBV, HCV, or HDV can lead to severe liver complications; however, they are underdiagnosed. Achieving the World Health Organization's viral hepatitis elimination goals by 2030 will require access to simpler, faster, and less expensive diagnostics. The development and implementation of point-of-care (POC) testing methods that can be performed outside of a laboratory for the diagnosis of viral hepatitis infections is a promising approach to facilitate and expedite WHO's elimination targets. While a few markers of viral hepatitis are already available in POC formats, tests for additional markers or using novel technologies need to be developed and validated for clinical use. Potential methods and uses for the POC testing of antibodies, antigens, and nucleic acids that relate to the diagnosis, monitoring, or surveillance of viral hepatitis infections are discussed here. Unmet needs and areas where additional research is needed are also described.

Decorated DNA-Based Scaffolds as Lateral Flow Biosensors

Here we develop Lateral Flow Assays (LFAs) that employ as functional elements DNA-based structures decorated with reporter tags and recognition elements. We have rationally re-engineered tile-based DNA tubular structures that can act as scaffolds and can be decorated with recognition elements of different nature (i.e. antigens, aptamers or proteins) and with orthogonal fluorescent dyes. As a proof-of-principle we have developed sandwich and competitive multiplex lateral flow platforms for the detection of several targets, ranging from small molecules (digoxigenin, Dig and dinitrophenol, DNP), to antibodies (Anti-Dig, Anti-DNP and Anti-MUC1/EGFR bispecific antibodies) and proteins (thrombin). Coupling the advantages of functional DNA-based scaffolds together with the simplicity of LFAs, our approach offers the opportunity to detect a wide range of targets with nanomolar sensitivity and high specificity.

Chemical Trends in Sample Preparation for Nucleic Acid Amplification Testing (NAAT): A Review

Nucleic acid amplification testing facilitates the detection of disease through specific genomic sequences and is attractive for point-of-need testing (PONT); in particular, the early detection of microorganisms can alert early response systems to protect the public and ecosystems from widespread outbreaks of biological threats, including infectious diseases. Prior to nucleic acid amplification and detection, extensive sample preparation techniques are required to free nucleic acids and extract them from the sample matrix. Sample preparation is critical to maximize the sensitivity and reliability of testing. As the enzymatic amplification reactions can be sensitive to inhibitors from the sample, as well as from chemicals used for lysis and extraction, avoiding inhibition is a significant challenge, particularly when minimising liquid handling steps is also desirable for the translation of the assay to a portable format for PONT. The reagents used in sample preparation for nucleic acid testing, covering lysis and NA extraction (binding, washing, and elution), are reviewed with a focus on their suitability for use in PONT.

CRISPR/Cas and Argonaute-Based Biosensors for Pathogen Detection

Over the past few decades, pathogens have posed a threat to human security, and rapid identification of pathogens should be one of the ideal methods to prevent major public health security outbreaks. Therefore, there is an urgent need for highly sensitive and specific approaches to identify and quantify pathogens. Clustered Regularly Interspaced Short Palindromic Repeats CRISPR/Cas systems and Argonaute (Ago) belong to the Microbial Defense Systems (MDS). The guided, programmable, and targeted activation of nucleases by both of them is leading the way to a new generation of pathogens detection. We compare these two nucleases in terms of similarities and differences. In addition, we discuss future challenges and prospects for the development of the CRISPR/Cas systems and Argonaute (Ago) biosensors, especially electrochemical biosensors. This review is expected to afford researchers entering this multidisciplinary field useful guidance and to provide inspiration for the development of more innovative electrochemical biosensors for pathogens detection.

Lateral flow assay of pathogenic viruses and bacteria in healthcare

Healthcare-associated pathogenic viruses and bacteria can have a serious impact on human health and have attracted widespread global attention. The lateral flow assay is a unidirectional detection based on the binding of a target analyte and a bioreceptor on the device via lateral flow. With incredible advantages over traditional chromatographic methods, such as rapid detection, ease of manufacture and cost effectiveness, these test strips are increasingly considered the ideal form for point-of-care applications. This review explores lateral flow assays for pathogenic viruses and bacteria, with a particular focus on methodologies, device components, construction methods, and applications. We anticipate that this review could provide exciting opportunities for developing new lateral flow devices for pathogens and advance related healthcare applications.

Multiplexed CRISPR-based Methods for Pathogen Nucleic Acid Detection

Bacterial and viral pathogens are devastating to human health and well-being. In many regions, dozens of pathogen species and variants co-circulate. Thus, it is important to detect many different species and variants of pathogens in a given sample through multiplexed detection methods. CRISPR-based nucleic acid detection has shown to be a promising step towards an easy-to-use sensitive, specific, and high-throughput method to detect nucleic acids from DNA and RNA viruses and bacteria. Here, we review the current state of multiplexed nucleic acid detection methods with a focus on CRISPR-based methods. We also look toward the future of multiplexed point-of-care diagnostics.

A microfluidic biosensor for the diagnosis of chronic wasting disease

Cervids are affected by a neurologic disease that is always fatal to individuals and has population effects. This disease is called chronic wasting disease (CWD) and is caused by a misfolded prion protein. The disease is transmitted via contact with contaminated body fluids and tissue or exposure to the environment, such as drinking water or food. Current CWD diagnosis depends on ELISA screening of cervid lymph nodes and subsequent immunohistochemistry (IHC) confirmation of ELISA-positive results. The disease has proven to be difficult to control in part because of sensitivity and specificity issues with the current test regimen. We have investigated an accurate, rapid, and low-cost microfluidic microelectromechanical system (MEMS) biosensing device for the detection of CWD pathologic prions in retropharyngeal lymph nodes (RLNs), which is the current standard type of CWD diagnostic sample. The device consists of three novel regions for concentrating, trapping, and detecting the prion. The detection region includes an array of electrodes coated with a monoclonal antibody against pathologic prions. The experimental conditions were optimized using an engineered prion control antigen. Testing could be completed in less than 1 hour with high sensitivity and selectivity. The biosensor detected the engineered prion antigen at a 1:24 dilution, while ELISA detected the same antigen at a 1:8 dilution. The relative limit of detection (rLOD) of the biosensor was a 1:1000 dilution of a known strong positive RLN sample, whereas ELISA showed a rLOD of 1:100 dilution. Thus, the biosensor was 10 times more sensitive than ELISA, which is the currently approved CWD diagnostic test. The biosensor's specificity and selectivity were confirmed using known negative RPLN samples, a negative control antibody (monoclonal antibody against bovine coronavirus BCV), and two negative control antigens (bluetongue virus and Epizootic hemorrhagic disease virus). The biosensor's ability to detect pathogenic prions was verified by testing proteinase-digested positive RLN samples.

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.

Comparison of Three Lateral Flow Immunoassay Formats for the Detection of Antibodies against the SARS-CoV-2 Antigen

Reliable detection of specific antibodies against pathogens by lateral flow immunoassay (LFIA) greatly depends on the composition of the detectable complex and the order of its assembly. We compared three LFIA formats for revealing anti-SARS-CoV-2 antibodies in sera with the following detected complexes in the analytical zone of the strip: antigen-antibodies-labeled immunoglobulin-binding protein (Scheme A); antigen-antibodies-labeled antigen (Scheme B); and immunoglobulin-binding protein-antibodies-labeled antigen (Scheme C). The lowest detection limit was observed for Scheme C, and was equal to 10 ng/mL of specific humanized monoclonal antibodies. When working with pooled positive sera, Scheme C had a detection limit 15 times lower than Scheme B and 255 times lower than Scheme A. Due to the high sensitivity of Scheme C, its application for the panel of human sera (n = 22) demonstrated 100% diagnostic specificity and sensitivity. These consistent results be useful for designing the format of LFIA serodiagnosis for other diseases.

Rapid and visual identification of HIV-1 using reverse transcription loop-mediated isothermal amplification integrated with a gold nanoparticle-based lateral flow assay platform

Human immunodeficiency virus type one (HIV-1) infection remains a major public health problem worldwide. Early diagnosis of HIV-1 is crucial to treat and control this infection effectively. Here, for the first time, we reported a novel molecular diagnostic assay called reverse transcription loop-mediated isothermal amplification combined with a visual gold nanoparticle-based lateral flow assay (RT-LAMP-AuNPs-LFA), which we devised for rapid, specific, sensitive, and visual identification of HIV-1. The unique LAMP primers were successfully designed based on the pol gene from the major HIV-1 genotypes CRF01_AE, CRF07_BC, CRF08_BC, and subtype B, which are prevalent in China. The optimal HIV-1-RT-LAMP-AuNPs-LFA reaction conditions were determined to be 68°C for 35 min. The detection procedure, including crude genomic RNA isolation (approximately 5 min), RT-LAMP amplification (35 min), and visual result readout (<2 min), can be completed within 45 min. Our assay has a detection limit of 20 copies per test, and we did not observe any cross-reactivity with any other pathogen in our testing. Hence, our preliminary results indicated that the HIV-1-RT-LAMP-AuNPs-LFA assay can potentially serve as a useful point-of-care diagnostic tool for HIV-1 detection in a clinical setting.

Use of Lateral Flow Assays in Forensics

Already for some decades lateral flow assays (LFAs) are 'common use' devices in our daily life. Also, for forensic use LFAs are developed, such as for the analysis of illicit drugs and DNA, but also for the detection of explosives and body fluid identification. Despite their advantages, including ease-of-use, LFAs are not yet frequently applied at a crime scene. This review describes (academic) developments of LFAs for forensic applications, focusing on biological and chemical applications, whereby the main advantages and disadvantages of LFAs for the different forensic applications are summarized. Additionally, a critical review is provided, discussing why LFAs are not frequently applied within the forensic field and highlighting the steps that are needed to bring LFAs to the forensic market.

Antibody Phage Display Technology for Sensor-Based Virus Detection: Current Status and Future Prospects

Viruses are widespread in the environment, and many of them are major pathogens of serious plant, animal, and human diseases. The risk of pathogenicity, together with the capacity for constant mutation, emphasizes the need for measures to rapidly detect viruses. The need for highly sensitive bioanalytical methods to diagnose and monitor socially significant viral diseases has increased in the past few years. This is due, on the one hand, to the increased incidence of viral diseases in general (including the unprecedented spread of a new coronavirus infection, SARS-CoV-2), and, on the other hand, to the need to overcome the limitations of modern biomedical diagnostic methods. Phage display technology antibodies as nano-bio-engineered macromolecules can be used for sensor-based virus detection. This review analyzes the commonly used virus detection methods and approaches and shows the prospects for the use of antibodies prepared by phage display technology as sensing elements for sensor-based virus detection.

A nitrocellulose/cotton fiber hybrid composite membrane for paper-based biosensor

Nitrocellulose (NC) membrane was fabricated and tested for its potential use in various paper-based biosensors for use in point-of-care testing. However, contemporary technologies are complex, expensive, non-scalable, limited by conditions, and beset with potentially adverse effects on the environment. Herein, we proposed a simple, cost-effective, scalable technology to prepare nitrocellulose/cotton fiber (NC/CF) composite membranes. The NC/CF composite membranes with a diameter of 20 cm were fabricated in 15 min using papermaking technology, which contributes to scalability in the large-scale production of these composites. Compared with existing commercial NC membranes, the NC/CF composite membrane is characterized by small pore size (3.59 ± 0.19 μm), low flow rate (156 ± 55 s/40 mm), high dry strength (up to 4.04 MPa), and wet strength (up to 0.13 MPa), adjustable hydrophilic-hydrophobic (contact angles ranged from 29 ± 4.6 to 82.8 ± 2.4°), the good adsorption capacity of protein (up to 91.92 ± 0.07 μg). After lateral flow assays (LFAs) detection, the limit of detection is 1 nM, which is similar to commercial NC membrane (Sartorius CN 140). We envision the NC/CF composite membrane as a promising material for paper-based biosensors of point-of-care testing applications.

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.

Lateral Flow Immunoassay for Proteins

Protein biomarkers are useful for disease diagnosis. Identification thereof using in vitro diagnostics such as lateral flow immunoassays (LFIAs) has attracted considerable attention due to their low cost and ease of use especially in the point of care setting. Current challenges, however, do remain with respect to material selection for each component in the device and the synergistic integration of these components to display detectable signals. This review explores the principle of LFIA for protein biomarkers, device components including biomaterials and labeling methods. Medical applications and commercial status are examined as well. This review highlights critical methodologies in the development of new LFIAs and their role in advancing healthcare worldwide.

Fluorescent detection of emerging virus based on nanoparticles: From synthesis to application

The spread of COVID-19 has caused huge economic losses and irreversible social impact. Therefore, to successfully prevent the spread of the virus and solve public health problems, it is urgent to develop detection methods with high sensitivity and accuracy. However, existing detection methods are time-consuming, rely on instruments, and require skilled operators, making rapid detection challenging to implement. Biosensors based on fluorescent nanoparticles have attracted interest in the field of detection because of their advantages, such as high sensitivity, low detection limit, and simple result readout. In this review, we systematically describe the synthesis, intrinsic advantages, and applications of organic dye-doped fluorescent nanoparticles, metal nanoclusters, up-conversion particles, quantum dots, carbon dots, and others for virus detection. Furthermore, future research initiatives are highlighted, including green production of fluorescent nanoparticles with high quantum yield, speedy signal reading by integrating with intelligent information, and error reduction by coupling with numerous fluorescent nanoparticles.

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.

Advances on Hormones in Cosmetics: Illegal Addition Status, Sample Preparation, and Detection Technology

Owing to the rapid development of the cosmetic industry, cosmetic safety has become the focus of consumers' attention. However, in order to achieve the desired effects in the short term, the illegal addition of hormones in cosmetics has emerged frequently, which could induce skin problems and even skin cancer after long-term use. Therefore, it is of great significance to master the illegal addition in cosmetics and effectively detect the hormones that may exist in cosmetics. In this review, we analyze the illegally added hormone types, detection values, and cosmetic types, as well as discuss the hormone risks in cosmetics for human beings, according to the data in unqualified cosmetics in China from 2017 to 2022. Results showed that although the frequency of adding hormones in cosmetics has declined, hormones are still the main prohibited substances in illegal cosmetics, especially facial masks. Because of the complex composition and the low concentration of hormones in cosmetics, it is necessary to combine efficient sample preparation technology with instrumental analysis. In order to give the readers a comprehensive overview of hormone analytical technologies in cosmetics, we summarize the advanced sample preparation techniques and commonly used detection techniques of hormones in cosmetics in the last decade (2012-2022). We found that ultrasound-assisted extraction, solid phase extraction, and microextraction coupled with chromatographic analysis are still the most widely used analytical technologies for hormones in cosmetics. Through the investigation of market status, the summary of sample pretreatment and detection technologies, as well as the discussion of their development trends in the future, our purpose is to provide a reference for the supervision of illegal hormone residues in cosmetics.

Lateral flow assays for detection of disease biomarkers

Early diagnosis saves lives in many diseases. In this sense, monitoring of biomarkers is crucial for the diagnosis of diseases. Lateral flow assays (LFAs) have attracted great attention among paper-based point-of-care testing (POCT) due to their low cost, user-friendliness, and time-saving advantages. Developments in the field of health have led to an increase of interest in these rapid tests. LFAs are used in the diagnosis and monitoring of many diseases, thanks to biomarkers that can be observed in body fluids. This review covers the recent advances dealing with the design and strategies for the development of LFA for the detection of biomarkers used in clinical applications in the last 5 years. We focus on various strategies such as choosing the nanoparticle type, single or multiple test approaches, and equipment for signal transducing for the detection of the most common biomarkers in different diseases such as cancer, cardiovascular, infectious, and others including Parkinson's and Alzheimer's diseases. We expect that this study will contribute to the different approaches in LFA and pave the way for other clinical applications.

Role of Wearable Sensing Technology to Manage Long COVID

Long COVID consequences have changed the perception towards disease management, and it is moving towards personal healthcare monitoring. In this regard, wearable devices have revolutionized the personal healthcare sector to track and monitor physiological parameters of the human body continuously. This would be largely beneficial for early detection (asymptomatic and pre-symptomatic cases of COVID-19), live patient conditions, and long COVID monitoring (COVID recovered patients and healthy individuals) for better COVID-19 management. There are multitude of wearable devices that can observe various human body parameters for remotely monitoring patients and self-monitoring mode for individuals. Smart watches, smart tattoos, rings, smart facemasks, nano-patches, etc., have emerged as the monitoring devices for key physiological parameters, such as body temperature, respiration rate, heart rate, oxygen level, etc. This review includes long COVID challenges for frequent monitoring of biometrics and its possible solution with wearable device technologies for diagnosis and post-therapy of diseases.

Advances of CRISPR-Cas13 system in COVID-19 diagnosis and treatment

The ongoing global pandemic of coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has resulted in over 570 million infections and 6 million deaths worldwide. Early detection and quarantine are essential to arrest the spread of the highly contagious COVID-19. High-risk groups, such as older adults and individuals with comorbidities, can present severe symptoms, including pyrexia, pertussis, and acute respiratory distress syndrome, on SARS-CoV-2 infection that can prove fatal, demonstrating a clear need for high-throughput and sensitive platforms to detect and eliminate SARS-CoV-2. CRISPR-Cas13, an emerging CRISPR system targeting RNA with high specificity and efficiency, has recently drawn much attention for COVID-19 diagnosis and treatment. Here, we summarized the current research progress on CRISPR-Cas13 in COVID-19 diagnosis and treatment and highlight the challenges and future research directions of CRISPR-Cas13 for effectively counteracting COVID-19.

Recent Advances in Colorimetric Sensors Based on Gold Nanoparticles for Pathogen Detection

Infectious pathogens cause severe threats to public health due to their frightening infectivity and lethal capacity. Rapid and accurate detection of pathogens is of great significance for preventing their infection. Gold nanoparticles have drawn considerable attention in colorimetric biosensing during the past decades due to their unique physicochemical properties. Colorimetric diagnosis platforms based on functionalized AuNPs are emerging as a promising pathogen-analysis technique with the merits of high sensitivity, low-cost, and easy operation. This review summarizes the recent development in this field. We first introduce the significance of detecting pathogens and the characteristics of gold nanoparticles. Four types of colorimetric strategies, including the application of indirect target-mediated aggregation, chromogenic substrate-mediated catalytic activity, point-of-care testing (POCT) devices, and machine learning-assisted colorimetric sensor arrays, are systematically introduced. In particular, three biomolecule-functionalized AuNP-based colorimetric sensors are described in detail. Finally, we conclude by presenting our subjective views on the present challenges and some appropriate suggestions for future research directions of colorimetric sensors.

Lateral Flow Immunoassays for SARS-CoV-2

The continued circulation of SARS-CoV-2 virus in different parts of the world opens up the possibility for more virulent variants to evolve even as the coronavirus disease 2019 transitions from pandemic to endemic. Highly transmissible and virulent variants may seed new disruptive epidemic waves that can easily put the healthcare system under tremendous pressure. Despite various nucleic acid-based diagnostic tests that are now commercially available, the wide applications of these tests are largely hampered by specialized equipment requirements that may not be readily available, accessible and affordable in less developed countries or in low resource settings. Hence, the availability of lateral flow immunoassays (LFIs), which can serve as a diagnostic tool by detecting SARS-CoV-2 antigen or as a serological tool by measuring host immune response, is highly appealing. LFI is rapid, low cost, equipment-free, scalable for mass production and ideal for point-of-care settings. In this review, we first summarize the principle and assay format of these LFIs with emphasis on those that were granted emergency use authorization by the US Food and Drug Administration followed by discussion on the specimen type, marker selection and assay performance. We conclude with an overview of challenges and future perspective of LFI applications.

Introduction of graphene oxide-supported multilayer-quantum dots nanofilm into multiplex lateral flow immunoassay: A rapid and ultrasensitive point-of-care testing technique for multiple respiratory viruses

A lateral flow immunoassay (LFA) biosensor that allows the sensitive and accurate identification of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and other common respiratory viruses remains highly desired in the face of the coronavirus disease 2019 pandemic. Here, we propose a multiplex LFA method for the on-site, rapid, and highly sensitive screening of multiple respiratory viruses, using a multilayered film-like fluorescent tag as the performance enhancement and signal amplification tool. This film-like three-dimensional (3D) tag was prepared through the layer-by-layer assembly of highly photostable CdSe@ZnS-COOH quantum dots (QDs) onto the surfaces of monolayer graphene oxide nanosheets, which can provide larger reaction interfaces and specific active surface areas, higher QD loads, and better luminescence and dispersibility than traditional spherical fluorescent microspheres for LFA applications. The constructed fluorescent LFA biosensor can simultaneously and sensitively quantify SARS-CoV-2, influenza A virus, and human adenovirus with low detection limits (8 pg/mL, 488 copies/mL, and 471 copies/mL), short assay time (15 min), good reproducibility, and high accuracy. Moreover, our proposed assay has great potential for the early diagnosis of respiratory virus infections given its robustness when validated in real saliva samples.

ELECTRONIC SUPPLEMENTARY MATERIAL

Supplementary material (Section S1 Experimental section, Section S2 Calculation of the maximum number of QDs on the GO@TQD nanofilm, Section S3 Optimization of the LFA method, and Figs. S1-S17 mentioned in the main text) is available in the online version of this article at 10.1007/s12274-022-5043-6.

Detection of SARS-CoV-2 Using Reverse Transcription Helicase Dependent Amplification and Reverse Transcription Loop-Mediated Amplification Combined with Lateral Flow Assay

Rapid and accurate detection and identification of pathogens in clinical samples is essential for all infection diseases. However, in the case of epidemics, it plays a key role not only in the implementation of effective therapy but also in limiting the spread of the epidemic. In this study, we present the application of two nucleic acid isothermal amplification methods—reverse transcription helicase dependent amplification (RT-HDA) and reverse transcription loop-mediated amplification (RT-LAMP)—combined with lateral flow assay as the tools for the rapid detection of SARS-CoV-2, the etiological agent of COVID-19, which caused the ongoing global pandemic. In order to optimize the RT-had, the LOD was 3 genome copies per reaction for amplification conducted for 10–20 min, whereas for RT-LAMP, the LOD was 30–300 genome copies per reaction for a reaction conducted for 40 min. No false-positive results were detected for RT-HDA conducted for 10 to 90 min, but false-positive results occurred when RT-LAMP was conducted for longer than 40 min. We concluded that RT-HDA combined with LFA is more sensitive than RT-LAMP, and it is a good alternative for the development of point-of-care tests for SARS-CoV-2 detection as this method is simple, inexpensive, practical, and does not require qualified personnel to perform the test and interpret its results.