Lateral Flow Assays in Infectious Disease Diagnosis

Evaluation of an Innovative Rapid Diagnostic Test for Human Strongyloidiasis to Detect Specific IgG Antibody in Whole-Blood Samples

Human strongyloidiasis is an important intestinal parasitic disease that affects public health globally and is transmitted through contact with infective larvae on contaminated soil. Immunocompromised hosts can experience hyperinfection, which can lead to fatal systemic strongyloidiasis. Here, an innovative point-of-care (POC) test kit, the strongyloidiasis immunochromatographic blood test (the NIE-SsIR whole-blood ICT) kit is described. The kit was used to detect anti-Strongyloides IgG antibody in whole-blood samples (WBSs) instead of serum to diagnose strongyloidiasis. The kit is based on a mixture of two recombinant Strongyloides stercoralis protein antigens (NIE and SsIR) and colloidal-gold-labeled conjugates of anti-human IgG antibody to evaluate diagnostic values with simulated and fresh anticoagulated WBSs. The NIE-SsIR whole-blood ICT kit showed potentially high diagnostic values with simulated WBSs, obtained by spiking patients' sera with red blood cells. The sensitivity, specificity, and positive and negative predictive values were 93.0%, 93.7%, 88.6%, and 96.2%, respectively, at the prevalence of disease simulated under the laboratory conditions of 34.5%. In addition, 18 of 20 fresh anticoagulated WBSs from strongyloidiasis cases were positive, and all 15 WBSs from healthy volunteers were negative. The NIE-SsIR whole-blood ICT kit is a simple and convenient POC testing tool and can possibly be used with fingerstick blood samples, thereby not requiring the drawing of venous blood and separation of the serum. The NIE-SsIR whole-blood ICT kit can assist clinical diagnosis in remote areas and field settings without sophisticated equipment.

Back to Basics: Unraveling the Fundamentals of Lateral Flow Assays

BACKGROUND

Lateral flow assay (LFA) is a rapid analytical technique that has been implemented as a point-of-care approach for analyte detection. Given the rapid expansion of the use of LFA as a point-of-care testing strategy, LFA development has been subjected to extensive research, which has resulted in upgraded designs and technologies, improving levels of specificity and costs associated with manufacturing. This has allowed LFA to become an important option in rapid testing while maintaining appropriate limits of detection for accurate diagnoses.

CONTENT

This review focuses on the theoretical basis of LFA, its components, formats, multiparametric possibilities, labels, and applications. Also, challenges associated with the technique and possible solutions are explored.

SUMMARY

We explore LFA as a detection technique, its benefits, opportunities for improvement, and applications, and how challenges to its design can be approached.

Dual-mode and multiplex lateral flow immunoassay: A powerful technique for simultaneous screening of respiratory viruses

Respiratory viral infectious usually exhibit similar clinical symptoms, making a great challenge for their accurate diagnostic in early stages. Herein, we developed a dual-mode and multiplex lateral flow immunoassay (LFIA), in which near-infrared (NIR)-responsive Janus Aushell-Fe3O4 nanoparticles (NPs) were synthesized as new reporters for highly sensitive colorimetric/photothermal detection of H3N2 influenza and SARS-CoV-2 viruses in a single assay. The Janus Aushell-Fe3O4 well combined the NIR responsiveness and high molar absorption coefficient of Aushell and magnetic properties of Fe3O4. In the detection, two test (T) lines were arranged on the strip, which could capture corresponding virus antigen-Aushell-Fe3O4 complexes, forming color bands. Hence, according to the position of color bands and their photothermal signals, the type and amount of virus could be quickly determined. The naked-eye limits of detection (LODs) for H3N2 and SARS-CoV-2 were both 50 ng/mL. The photothermal quantitative ranges were from 10 to 106 pg/mL with LODs of 2 pg/mL (H3N2) and 7 pg/mL (SARS-CoV-2), which were nearly 10000 times lower than naked-eye detection. Moreover, this multiplex LFIA showed good specificity and anti-interference ability, which was applied to complex samples with satisfactory results. Thus, this Aushell-Fe3O4 LFIA showed great application potential in rapid virus screening and early detection.

Single-Reservoir Electrophoresis to Facilitate Layer-by-Layer Assembly of Gold Nanoparticles in Lateral Flow Immunoassay

Electrophoretically facilitated layer-by-layer assembly of gold nanoparticles (GNPs) in lateral flow immunoassays (LFIAs) significantly enhances the signal-to-background ratio and, consequently, the diagnostic sensitivity of these tests. However, conventional two-reservoir electrophoresis on paper is limited by counterflow induced by capillary action, which disrupts the electrophoretic migration of GNPs toward the anode. This counterflow necessitates manual intervention to facilitate the movement of GNP-labeled immunocomplexes from the membrane to the absorption pad, complicating the assay workflow. To address this challenge, we propose a nonconventional single-reservoir electrophoresis system on paper, which inherently eliminates counterflow. In this configuration, the loading side of the paper strip and the cathode reside within the buffer reservoir, while the anode is directly affixed to the opposite end of the paper strip. We demonstrate the efficacy of this single-reservoir system in driving layer-by-layer assembly, while presenting favorable spatial temperature profiles as a side benefit. By eliminating the need for manual steps, this design streamlines the electrophoresis process and enhances the usability of electrophoretically facilitated LFIA assays.

Accuracy of diagnostic tests for feline sporotrichosis: a systematic review and meta-analysis

BACKGROUND

Feline sporotrichosis is a subcutaneous infection caused by fungi of the Sporothrix genus, particularly concerning in endemic regions of South America, where cats are important vectors. Traditional diagnosis through fungal culture is time-consuming, which can delay the start of treatment.

OBJECTIVE

Our goal was to synthesize the evidence on the accuracy of alternative diagnostic methods for feline sporotrichosis.

METHODS

A systematic review was conducted following the Cochrane Collaboration recommendations and the PRISMA-DTA checklist (CRD42023456520). Searches for observational studies were performed in PubMed, Embase, and Web of Science. Using a random-effects model, bivariate meta-analysis was employed to estimate combined sensitivity, specificity, and diagnostic odds ratio (DOR) with 95% confidence intervals. The results were presented in forest plots and Summary Receiver Operating Characteristic (SROC) curves; heterogeneity was assessed using Tau² and I² statistics (R-software).

RESULTS

Eight studies, totaling 1,920 cats, evaluated five diagnostic methods. PCR tests had the highest accuracy (90% sensitivity, 94% specificity, area under the curve 0.950), while cytological methods demonstrated moderate diagnostic accuracy (89%, 22% and 0.879, respectively). The findings highlight the need for faster, more accurate, and cost-effective diagnostic alternatives, especially in resource-limited regions, and underscore the importance of advancing techniques to improve early detection and treatment of sporotrichosis.

Truncation-Enhanced Aptamer Binding Affinity and Its Potential as a Sensor for Macrobrachium rosenbergii Nodavirus Detection

White tail disease in Macrobrachium rosenbergii is caused by M. rosenbergii nodavirus (MrNV) infection, resulting in up to 100% mortality in larvae and post-larvae stages, severely impacting aquaculture production. Existing genome-based detection methods for MrNV are costly and time-consuming, highlighting the need for rapid and cost-effective diagnostic tests. This study evaluated the effects of truncating selected aptamer on its binding affinity to the MrNV capsid protein. The previously isolated and identified aptamer through magnetic-capture SELEX and Next Generation Sequencing demonstrated high binding affinity to the MrNV capsid protein. Truncation at the primer overhang was found to improve binding affinity, reducing the dissociation constant from 347 nM to 30.1 nM. The calculated limit of detection for the truncated aptamer decreased from 5.64 nM to 1.7 nM, while the limit of quantification decreased from 17.1 nM to 5.16 nM. These reductions indicate that the truncated aptamer has higher sensitivity compared to the full-length aptamer. In tests with MrNV-infected M. rosenbergii samples, both the enzyme-linked aptamer assay and the gold nanoparticle aptasensor assay showed consistent results when 0.5 μg of total protein lysate was used. This indicates that the prawn protein concentration interferes with the detection of the viral protein. These findings suggest the potential application of the truncated aptamer as a sensor in the development of a practical aptamer-based diagnostic kit. For instance, an aptamer-based lateral flow assay test kit could provide a user-friendly, cost-effective solution that eliminates the need for sophisticated instrumentation for diagnosis or data interpretation, making it ideal for detecting MrNV infection in M. rosenbergii aquaculture.

Overview of point-of-care diagnostic options for detection of chlamydia trachomatis: current technology and implementation considerations

INTRODUCTION

Chlamydia trachomatis continues to be the most common bacterial infection worldwide and rates continue to increase despite long-standing control efforts. Point of care (POC) testing options may offer improvements in case finding that lead to improved control of this sexually transmitted infection (STI).

AREAS COVERED

This review will provide information on the three tests that have US Food and Drug Administration (FDA) clearance and describe assays in the developmental pipeline. The review will also provide implementation evaluations of the existing tests and offer suggestions about factors to consider prior to adoption of these or newer tests as they become available.

EXPERT OPINION

Technology is developing rapidly and may soon offer many choices of rapid diagnostic tools which can be used in clinical settings to detect chlamydial infections, particularly in underserved populations. The key to successful deployment of new tests will rest on data generated by implementation research to identify the features that create barriers or facilitate adoption of a new clinical paradigm.

Recent advances in rapid detection of Helicobacter pylori by lateral flow assay

Infection with H. pylori (Helicobacter pylori) is the most prevalent human infection worldwide and is strongly associated with many gastrointestinal disorders, including gastric cancer. Endoscopy is mainly used to diagnose H. pylori infection in gastric biopsies. However, this approach is invasive, time-consuming and expensive. On the other hand, serology-based methods can be considered as a non-invasive approach to detecting H. pylori infection. The LFA (lateral flow assay) serves as a rapid point-of-care diagnostic tool. This paper-based platform facilitates the detection and quantification of analytes within human fluids such as blood, serum and urine. Due to ease of production, rapid results, and low costs, LFAs have a wide application in clinical laboratories and hospitals. In this comprehensive review, we examined LFA-based approaches for detection of H. pylori infection from human fluids and compare them with other high-sensitivity methods like ELISA (Enzyme-linked immunosorbent assay). Furthermore, we reviewed methods to elevate LFA sensitivity during H. pylori infection including, CRISPR/Cas system and isothermal amplification approaches. The development and optimization of novel labeling agents such as nanozyme to enhance the performance of LFA devices in detecting H. pylori were reviewed. These innovations aim to improve signal amplification and stability, thereby increasing the diagnostic accuracy of LFA devices. A combination of advances in LFA technology and molecular insight could significantly improve diagnostic accuracy, resulting in a significant improvement in clinical and remote diagnostic accuracy.

Immunochromatographic Lateral Flow Assays to Detect Filovirus Nucleoproteins

The recent large outbreaks of Ebola virus disease in West Africa and the Democratic Republic of the Congo have highlighted the need for rapid diagnostic tests to control this disease. In this chapter, the development of immunochromatographic lateral flow assays to detect filovirus nucleoproteins is described as an example of designing rapid diagnostic tests.

Automation for lateral flow rapid tests: Protocol for an open-source fluid handler and applications to dengue and African swine fever tests

Lateral flow rapid diagnostic tests (RDTs, RTs) are cost-effective with low infrastructure requirements for limited-resource settings, and in any setting can represent a bridge between early disease monitoring at outbreak onset and fully-scaled molecular testing for human or animal diseases. However, the potential of RTs to handle higher throughput testing is hampered by the need for manual processing. Here we review dengue virus and African swine fever virus rapid tests, and present a novel protocol that employs an open-source fluid handler to automate the execution of up to 42 RTs per run. A publicly accessible website, rtWIZARD.lji.org, provides printouts for correctly spacing cassettes, worksheets for sample organization, and test-specific fluid handler protocols to accurately deliver samples from a 48-tube rack to each cassette's sample and running buffer wells. An optional QR-coded sheet allows for de-identified sample-to-result traceability by producing a unique printable label for each cassette, enabling results to be entered via a scanner. This work describes a highly cost-effective model for increasing outbreak diagnostic efficiency and of increasing RT throughput for other applications including workplace testing, food safety, environmental testing, and defense applications.

Application of recombinase polymerase amplification with lateral flow assay to pathogen point-of-care diagnosis

Since the outbreak of the new coronavirus, point-of-care diagnostics based on nucleic acid testing have become a requirement for the development of pathogen diagnostics, which require the ability to accurately, rapidly, and conveniently detect pathogens. Conventional nucleic acid amplification techniques no longer meet the requirements for pathogen detection in low-resource, low-skill environments because they require specialist equipment, complex operations, and long detection times. Therefore, recombinant polymerase amplification (RPA) is becoming an increasingly important method in today's nucleic acid detection technology because it can amplify nucleic acids in 20-30 minutes at a constant temperature, greatly reducing the dependence on specialist equipment and technicians. RPA products are primarily detected through methods such as real-time fluorescence, gel electrophoresis, lateral flow assays (LFAs), and other techniques. Among these, LFAs allow for the rapid detection of amplification products within minutes through the visualization of results, offering convenient operation and low cost. Therefore, the combination of RPA with LFA technology has significant advantages and holds broad application prospects in point-of-care (POC) diagnostics, particularly in low-resource settings. Here, we focus on the principles of RPA combined with LFAs, their application to pathogen diagnosis, their main advantages and limitations, and some improvements in the methods.

Differential detection of SARS-CoV-2 variants and influenza A viruses utilizing a dual lateral flow strip based on colloidal gold-labeled monoclonal antibodies

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and the seasonal influenza virus are spreading among humans concurrently, especially with the ongoing replacement of mutant strains. It is challenging to differentiate between symptoms for therapy due to the comparable symptoms following infection with the SARS-CoV-2 variants and influenza viruses. Meanwhile, in order to achieve rapid point-of-care testing (POCT) to manage the spread of the disease, we developed a dual lateral flow strip based on colloidal gold-labeled monoclonal antibodies that can perform differential detection of SARS-CoV-2 variants and influenza A viruses (IAV) in this study. High-affinity monoclonal antibodies (mAbs) targeting SARS-CoV-2 and IAV were prepared to capture antigens and labeled with colloidal gold nanoparticles (AuNPs). Based on high-affinity mAbs, two targets were immobilized on one nitrocellulose (NC) membrane to establish the lateral flow strip (LFS) for differential diagnosis of SARS-CoV-2 and IAV. With no reactivity to other viruses, this LFS is extremely specific and can only identify SARS-CoV-2 and IAV. The LFS showed a limit of detection (LOD) of 4.88 ng/mL for the Omicron BA.2 RBD protein and 2.44 ng/mL for the nucleoprotein (NP) protein of H1N1. When analyzing 16 SARS-CoV-2 positive clinical samples, eight IAV positive clinical samples, and six negative samples that had already been pre-confirmed by commercial kits, its clinical application is effectively and accurately proven. These results demonstrated that the LFS integrated with AuNPs has great potential to facilitate quick, easy, and reliable POCT diagnosis for promoting the control of infectious diseases.

Acoustic pipette and biofunctional elastomeric microparticle system for rapid picomolar-level biomolecule detection in whole blood

Most biosensing techniques require complex processing steps that generate prolonged workflows and introduce potential points of error. Here, we report an acoustic pipette to purify and label biomarkers in 70 minutes. A key aspect of this technology is the use of functional negative acoustic contrast particles (fNACPs), which display biorecognition motifs for the specific capture of biomarkers from whole blood. Because of their large size and compressibility, the fNACPs robustly trap along the pressure antinodes of a standing wave and separate from blood components in under 60 seconds with >99% efficiency. fNACPs are subsequently fluorescently labeled in the pipette and are analyzed by both a custom, portable fluorimeter and flow cytometer. We demonstrate the detection of anti-ovalbumin antibodies from blood at picomolar levels (35 to 60 pM) with integrated controls showing minimal nonspecific adsorption. Overall, this system offers a simple and versatile approach for the rapid, sensitive, and specific capture of biomolecules.

Immunodetection of Poorly Soluble Substances: Limitations and Their Overcoming

Immunoassays based on the specific antigen-antibody interactions are efficient tools to detect various compounds and estimate their content. Usually, these assays are implemented in water-saline media with composition close to physiological conditions. However, many substances are insoluble or cannot be molecularly dispersed in such media, which objectively creates problems when interacting in aquatic environments. Thus, obtaining immunoreactants and implementing immunoassays of these substances need special methodological solutions. Hydrophobicity of antigens as well as their limited ability to functionalization and conjugation are often overlooked when developing immunoassays for these compounds. The main key finding is the possibility to influence the behavior of hydrophobic compounds for immunoassays, which requires specific approaches summarized in the review. Using the examples of two groups of compounds-surfactants (alkyl- and bisphenols) and fullerenes, we systematized the existing knowledge and experience in the development of immunoassays. This review addresses the challenges of immunodetection of poorly soluble substances and proposes solutions such as the use of hydrotropes, other solubilization techniques, and alternative receptors (aptamers and molecularly imprinted polymers).

Lateral flow assays: Progress and evolution of recent trends in point-of-care applications

Paper based point-of-care (PoC) detection platforms applying lateral flow assays (LFAs) have gained paramount approval in the diagnostic domain as well as in environmental applications owing to their ease of utility, low cost, and rapid signal readout. It has centralized the aspect of self-evaluation exhibiting promising potential in the last global pandemic era of Covid-19 implementing rapid management of public health in remote areas. In this perspective, the present review is focused towards landscaping the current framework of LFAs along with integration of components and characteristics for improving the assay by pushing the detection limits. The review highlights the synergistic aspects of assay designing, sample enrichment strategies, novel nanomaterials-based signal transducers, and high-end analytical techniques that contribute significantly towards sensitivity and specificity enhancement. Various recent studies are discussed supporting the innovations in LFA systems that focus upon the accuracy and reliability of rapid PoC testing. The review also provides a comprehensive overview of all the possible difficulties in commercialization of LFAs subjecting its applicability to pathogen surveillance, water and food testing, disease diagnostics, as well as to agriculture and environmental issues.

An Fe3O4-Au heterodimer nanoparticle-based lateral flow assay for rapid and simultaneous detection of multiple influenza virus nucleic acids

Sensitive, convenient and rapid detection and subtyping of influenza viruses are crucial for timely treatment and management of infected people. Compared with antigen detection, nucleic acid detection has higher specificity and can shorten the detection window. Hence, in this work, we improved the lateral flow assay (LFA, one of the most promising user-friendly and on-site methods) to achieve detection and subtyping of H1N1, H3N2 and H9N2 influenza virus nucleic acids. Firstly, the antigen-antibody recognition mode was transformed into a nucleic acid hybridization reaction. Secondly, Fe3O4-Au heterodimer nanoparticles were prepared to replace frequently used Au nanoparticles to obtain better coloration. Thirdly, four lines were arranged on the LFA strip, which were three test (T) lines and one control (C) line. Three T lines were respectively sprayed by the DNA sequences complementary to one end of H1N1, H3N2 and H9N2 influenza virus nucleic acids, while Fe3O4-Au nanoparticles were respectively coupled with the DNA sequences complementary to the other end of H1N1, H3N2 and H9N2 nucleic acids to construct three kinds of probes. The C line was sprayed by the complementary sequences to the DNAs on all three kinds of probes. In the detection, by hybridization reaction, the probes were combined with their target nucleic acids which were captured by the corresponding T lines to form color bands. Finally, according to the position of the color bands and their grey intensity, simultaneous qualitative and semi-quantitative detection of the three influenza virus nucleic acids was realized. The detection results showed that this multi-channel LFA had good specificity, and there was no significant cross reactivity among the three subtypes of influenza viruses. The simultaneous detection achieved comparable detection limits with individual detections. Therefore, this multi-channel LFA had good application potential for sensitive and rapid detection and subtyping of influenza viruses.

Imaging Diffractometric Biosensors for Label-Free, Multi-Molecular Interaction Analysis

Biosensors are used for the specific and sensitive detection of biomolecules. In conventional approaches, the suspected target molecules are bound to selected capture molecules and successful binding is indicated by additional labelling to enable optical readout. This labelling requires additional processing steps tailored to the application. While numerous label-free interaction assays exist, they often compromise on detection characteristics. In this context, we introduce a novel diffractometric biosensor, comprising a diffractive biosensor chip and an associated optical reader assembly. This innovative system can capture an entire assay, detecting various types of molecules in a label-free manner and present the results within in a single, comprehensive image. The applicability of the biosensor is assessed for the detection of viral DNA as well as proteins directly in human plasma, investigating different antigens. In our experiments, we achieve a detection limit of 4.2 pg/mm², which is comparable to other label-free optical biosensors. The simplicity and robustness of the method make it a compelling option for advancing biosensing technologies. This work contributes to the development of an imaging diffractometric biosensor with the potential for multiple applications in molecular interaction analysis.

Sensitive Colorimetric Lateral Flow Assays Enabled by Platinum-Group Metal Nanoparticles with Peroxidase-Like Activities

The last several decades have witnessed the success and popularity of colorimetric lateral flow assay (CLFA) in point-of-care testing. Driven by increasing demand, great efforts have been directed toward enhancing the detection sensitivity of CLFA. Recently, platinum-group metal nanoparticles (PGM NPs) with peroxidase-like activities have emerged as a type of promising colorimetric labels for enhancing the sensitivity of CLFA. By incorporating a simple and rapid post-treatment process, the PGM NP-based CLFAs are orders of magnitude more sensitive than conventional gold nanoparticle-based CLFAs. In this perspective, the study begins with introducing the design, synthesis, and characterization of PGM NPs with peroxidase-like activities. The current techniques for surface modification of PGM NPs are then discussed, followed by operation and optimization of PGM NP-based CLFAs. Afterward, opinions are provided on the social impact of PGM NP-based CLFAs. Lastly, this perspective is concluded with an outlook of future research directions in this emerging field, where the challenges and opportunities are discussed.

Au Nanoshell-Based Lateral Flow Immunoassay for Colorimetric and Photothermal Dual-Mode Detection of Interleukin-6

Interleukin-6 (IL-6) detection and monitoring are of great significance for evaluating the progression of many diseases and their therapeutic efficacy. Lateral flow immunoassay (LFIA) is one of the most promising point-of-care testing (POCT) methods, yet suffers from low sensitivity and poor quantitative ability, which greatly limits its application in IL-6 detection. Hence, in this work, we integrated Aushell nanoparticles (NPs) as new LFIA reporters and achieved the colorimetric and photothermal dual-mode detection of IL-6. Aushell NPs were conveniently prepared using a galvanic exchange process. By controlling the shell thickness, their localized surface plasmon resonance (LSPR) peak was easily tuned to near-infrared (NIR) range, which matched well with the NIR irradiation light. Thus, the Aushell NPs were endowed with good photothermal effect. Aushell NPs were then modified with IL-6 detection antibody to construct Aushell probes. In the LFIA detection, the Aushell probes were combined with IL-6, which were further captured by the capture IL-6 antibody on the test line of the strip, forming a colored band. By observation with naked eyes, the colorimetric qualitative detection of IL-6 was achieved with limit of 5 ng/mL. By measuring the temperature rise of the test line with a portable infrared thermal camera, the photothermal quantitative detection of IL-6 was performed from 1~1000 ng/mL. The photothermal detection limit reached 0.3 ng/mL, which was reduced by nearly 20 times compared with naked-eye detection. Therefore, this Aushell-based LFIA efficiently improved the sensitivity and quantitative ability of commercial colloidal gold LFIA. Furthermore, this method showed good specificity, and kept the advantages of convenience, speed, cost-effectiveness, and portability. Therefore, this Aushell-based LFIA exhibits practical application potential in IL-6 POCT detection.

A nanoparticle-assisted signal-enhancement technique for lateral flow immunoassays

Lateral flow immunoassay (LFIA), an affordable and rapid paper-based detection technology, is employed extensively in clinical diagnosis, environmental monitoring, and food safety analysis. The COVID-19 pandemic underscored the validity and adoption of LFIA in performing large-scale clinical and public health testing. The unprecedented demand for prompt diagnostic responses and advances in nanotechnology have fueled the rise of next-generation LFIA technologies. The utilization of nanoparticles to amplify signals represents an innovative approach aimed at augmenting LFIA sensitivity. This review probes the nanoparticle-assisted amplification strategies in LFIA applications to secure low detection limits and expedited response rates. Emphasis is placed on comprehending the correlation between the physicochemical properties of nanoparticles and LFIA performance. Lastly, we shed light on the challenges and opportunities in this prolific field.

Study of Highly Efficient Au/Pt Nanoparticles for Rapid Screening of Clostridium difficile

This study synthesized core/shell gold-platinum nanoparticles and characterized their colorimetric properties; ultraviolet-visible spectroscopy revealed that the synthesized nanoparticles exhibited distinct colors from conventional gold nanoparticles. Furthermore, the nanoparticles were subjected to lateral flow assays using Protein A, and the results revealed that they outperformed conventional spherical gold nanoparticles in terms of color development. This improvement can be attributed to the distinct core/shell structures of our nanoparticles. Further evaluation revealed that these nanoparticles could facilitate the detection of Clostridium difficile Toxin B visually at an extremely low concentration (1 ng/mL) without the requirement for advanced instrumentation. This substantial improvement in sensitivity can be attributed to the meticulous design and nanoscale engineering of the structure of the nanoparticles.

Development of an Antigen Capture Lateral Flow Immunoassay for the Detection of Burkholderia pseudomallei

Early diagnosis is essential for the successful management of Burkholderia pseudomallei infection, but it cannot be achieved by the current gold standard culture technique. Therefore, this study aimed to develop a lateral flow immunoassay (LFIA) targeting B. pseudomallei capsular polysaccharide. The development was performed by varying nitrocellulose membrane reaction pads and chase buffers. The prototype LFIA is composed of Unisart CN95 and chase buffer containing tris-base, casein, and Surfactant 10G. The assay showed no cross-reactivity with E. coli, S. aureus, P. aeruginosa, and P. acne. The limit of detections (LODs) of the prototype LFIA was 107 and 106 CFU/mL B. pseudomallei in hemoculture medium and artificial urine, respectively. These LODs suggest that this prototype can detect melioidosis from positive hemoculture bottles but not straight from urine. Additionally, these LODs are still inferior compared to Active Melioidosis Detect (AMDTM). Overall, this prototype holds the potential to be used clinically with hemoculture bottles. However, further improvements should be considered, especially for use with urine samples.

Rapid Nucleic Acid Diagnostic Technology for Pandemic Diseases

The recent global pandemic of coronavirus disease 2019 (COVID-19) has enormously promoted the development of diagnostic technology. To control the spread of pandemic diseases and achieve rapid screening of the population, ensuring that patients receive timely treatment, rapid diagnosis has become the top priority in the development of clinical technology. This review article aims to summarize the current rapid nucleic acid diagnostic technologies applied to pandemic disease diagnosis, from rapid extraction and rapid amplification to rapid detection. We also discuss future prospects in the development of rapid nucleic acid diagnostic technologies.

Biosensor-based multiple cross displacement amplification platform for visual and rapid identification of hepatitis C virus

Hepatitis C remains a global health problem, especially in poverty-stricken areas. A rapid and sensitive point-of-care (POC) diagnostic tool is critical for the early detection and timely treatment of hepatitis C virus (HCV) infection. Here, for the first time, we reported a novel molecular diagnostic assay, termed reverse transcription multiple cross displacement amplification integrated with a gold-nanoparticle-based lateral flow biosensor (RT-MCDA-AuNPs-LFB), which was developed for rapid, sensitive, specific, and visual identification of HCV. HCV-RT-MCDA induced rapid isothermal amplification through a specific primer set targeting the 5'untranslated region gene from the major HCV genotypes 1b, 2a, 3b, 6a, and 3a that are prevalent in China. The optimal reaction temperature and time for RT-MCDA-AuNPs-LFB were 68°C and 25 min, respectively. The limit of detection of the assay was 10 copies per test, and the specificity was 100% for the experimental strains. The whole detection procedure, including crude nucleic acid isolation (~5 min), RT-MCDA (68°C, 25 min), and visual AuNPs-LFB result confirmation (less than 2 min), was performed within 35 min. The preliminary results indicated that the HCV-RT-MCDA-AuNPs-LFB assay could be a valuable tool for sensitive, specific, visual, cost-saving, and rapid detection of HCV and has potential as a POC diagnostic platform for field screening and early clinical detection of HCV infection.

Point-Of-Care Ultra-Portable Single-Molecule Bioassays for One-Health

Screening asymptomatic organisms (humans, animals, plants) with a high-diagnostic accuracy using point-of-care-testing (POCT) technologies, though still visionary holds great potential. Convenient surveillance requires easy-to-use, cost-effective, ultra-portable but highly reliable, in-vitro-diagnostic devices that are ready for use wherever they are needed. Currently, there are not yet such devices available on the market, but there are a couple more promising technologies developed at readiness-level 5: the Clustered-Regularly-Interspaced-Short-Palindromic-Repeats (CRISPR) lateral-flow-strip tests and the Single-Molecule-with-a-large-Transistor (SiMoT) bioelectronic palmar devices. They both hold key features delineated by the World-Health-Organization for POCT systems and an occurrence of false-positive and false-negative errors <1-5% resulting in diagnostic-selectivity and sensitivity >95-99%, while limit-of-detections are of few markers. CRISPR-strip is a molecular assay that, can detect down to few copies of DNA/RNA markers in blood while SiMoT immunometric and molecular test can detect down to a single oligonucleotide, protein marker, or pathogens in 0.1mL of blood, saliva, and olive-sap. These technologies can prospectively enable the systematic and reliable surveillance of asymptomatic ones prior to worsening/proliferation of illnesses allowing for timely diagnosis and swift prognosis. This could establish a proactive healthcare ecosystem that results in effective treatments for all living organisms generating diffuse and well-being at efficient costs.

Rapid deep learning-assisted predictive diagnostics for point-of-care testing

Prominent techniques such as real-time polymerase chain reaction (RT-PCR), enzyme-linked immunosorbent assay (ELISA), and rapid kits are currently being explored to both enhance sensitivity and reduce assay time for diagnostic tests. Existing commercial molecular methods typically take several hours, while immunoassays can range from several hours to tens of minutes. Rapid diagnostics are crucial in Point-of-Care Testing (POCT). We propose an approach that integrates a time-series deep learning architecture and AI-based verification, for the enhanced result analysis of lateral flow assays. This approach is applicable to both infectious diseases and non-infectious biomarkers. In blind tests using clinical samples, our method achieved diagnostic times as short as 2 minutes, exceeding the accuracy of human analysis at 15 minutes. Furthermore, our technique significantly reduces assay time to just 1-2 minutes in the POCT setting. This advancement has the potential to greatly enhance POCT diagnostics, enabling both healthcare professionals and non-experts to make rapid, accurate decisions.

Au@Ag Core-Shell Nanoparticles for Colorimetric and Surface-Enhanced Raman-Scattering-Based Multiplex Competitive Lateral Flow Immunoassay for the Simultaneous Detection of Histamine and Parvalbumin in Fish

Foodborne allergies and illnesses represent a major global health concern. In particular, fish can trigger life-threatening food allergic reactions and poisoning effects, mainly caused by the ingestion of parvalbumin toxin. Additionally, preformed histamine in less-than-fresh fish serves as a toxicological alert. Consequently, the analytical assessment of parvalbumin and histamine levels in fish becomes a critical public health safety measure. The multiplex detection of both analytes has emerged as an important issue. The analytical detection of parvalbumin and histamine requires different assays; while the determination of parvalbumin is commonly carried out by enzyme-linked immunosorbent assay, histamine is analyzed by high-performance liquid chromatography. In this study, we present an approach for multiplexing detection and quantification of trace amounts of parvalbumin and histamine in canned fish. This is achieved through a colorimetric and surface-enhanced Raman-scattering-based competitive lateral flow assay (SERS-LFIA) employing plasmonic nanoparticles. Two distinct SERS nanotags tailored for histamine or β-parvalbumin detection were synthesized. Initially, spherical 50 nm Au@Ag core-shell nanoparticles (Au@Ag NPs) were encoded with either rhodamine B isothiocyanate (RBITC) or malachite green isothiocyanate (MGITC). Subsequently, these nanoparticles were bioconjugated with anti-β-parvalbumin and antihistamine, forming the basis for our detection and quantification methodology. Additionally, our approach demonstrates the use of SERS-LFIA for the sensitive and multiplexed detection of parvalbumin and histamine on a single test line, paving the way for on-site detection employing portable Raman instruments.

Nanoparticle-Based Bioaffinity Assays: From the Research Laboratory to the Market

Advances in the development of new biorecognition elements, nanoparticle-based labels as well as instrumentation have inspired the design of new bioaffinity assays. This review critically discusses the potential of nanoparticles to replace current enzymatic or molecular labels in immunoassays and other bioaffinity assays. Successful implementations of nanoparticles in commercial assays and the need for rapid tests incorporating nanoparticles in different roles such as capture support, signal generation elements, and signal amplification systems are highlighted. The limited number of nanoparticles applied in current commercial assays can be explained by challenges associated with the analysis of real samples (e.g., blood, urine, or nasal swabs) that are difficult to resolve, particularly if the same performance can be achieved more easily by conventional labels. Lateral flow assays that are based on the visual detection of the red-colored line formed by colloidal gold are a notable exception, exemplified by SARS-CoV-2 rapid antigen tests that have moved from initial laboratory testing to widespread market adaption in less than two years.

High-density Au nanoshells assembled onto Fe3O4 nanoclusters for integrated enrichment and photothermal/colorimetric dual-mode detection of SARS-CoV-2 nucleocapsid protein

Traditional lateral flow immunoassays (LFIA) suffer from insufficient sensitivity, difficulty for quantitation, and susceptibility to complex substrates, limiting their practical application. Herein, we developed a polyethylenimine (PEI)-mediated approach for assembling high-density Au nanoshells onto Fe3O4 nanoclusters (MagAushell) as LFIA labels for integrated enrichment and photothermal/colorimetric dual-mode detection of SARS-CoV-2 nucleocapsid protein (N protein). PEI layer served not only as "binders" to Fe3O4 nanoclusters and Au nanoshells, but also "barriers" to ambient environment. Thus, MagAushell not only combined magnetic and photothermal properties, but also showed good stability. With MagAushell, N protein was first separated and enriched from complex samples, and then loaded to the strip for detection. By observation of the color stripes, qualitative detection was performed with naked eye, and by measuring the temperature change under laser irradiation, quantification was attained free of sophisticated instruments. The introduction of Fe3O4 nanoclusters facilitated target purification and enrichment before LFIA, which greatly improved the anti-interference ability and increased the detection sensitivity by 2 orders compared with those without enrichment. Moreover, the high loading density of Au nanoshells on one Fe3O4 nanocluster enhanced the photothermal signal of the nanoprobe significantly, which could further increase the detection sensitivity. The photothermal detection limit reached 43.64 pg/mL which was 1000 times lower than colloidal gold strips. Moreover, this method was successfully applied to real samples, showing great application potential in practice. We envision that this LFIA could serve not only for SARS-CoV-2 detection but also as a general test platform for other biotargets in clinical samples.

Rapid Point-of-Care Identification of Aspergillus Species in Microbial Keratitis

Importance

Microbial keratitis (MK) is a common cause of unilateral visual impairment, blindness, and eye loss in low-income and middle-income countries. There is an urgent need to develop and implement rapid and simple point-of-care diagnostics for MK to increase the likelihood of good outcomes.

Objective

To evaluate the diagnostic performance of the Aspergillus-specific lateral-flow device (AspLFD) to identify Aspergillus species causing MK in corneal scrape and corneal swab samples of patients presenting with microbial keratitis.

Design, Setting, and Participants

This diagnostic study was conducted between May 2022 and January 2023 at the corneal clinic of Aravind Eye Hospital in Madurai, Tamil Nadu, India. All study participants were recruited during their first presentation to the clinic. Patients aged 15 years or older met the eligibility criteria if they were attending their first appointment, had a corneal ulcer that was suggestive of a bacterial or fungal infection, and were about to undergo diagnostic scrape and culture.

Main Outcomes and Measures

Sensitivity and specificity of the AspLFD with corneal samples collected from patients with MK. During routine diagnostic scraping, a minimally invasive corneal swab and an additional corneal scrape were collected and transferred to aliquots of sample buffer and analyzed by lateral-flow device (LFD) if the patient met the inclusion criteria. Photographs of devices were taken with a smartphone and analyzed using a ratiometric approach, which was developed for this study. The AspLFD results were compared with culture reports.

Results

The 198 participants who met the inclusion criteria had a mean (range) age of 51 (15-85) years and included 126 males (63.6%). Overall, 35 of 198 participants with corneal scrape (17.7%) and 17 of 40 participants with swab samples (42.5%) had positive culture results for Aspergillus species. Ratiometric analysis results for the scrape samples found that the AspLFD achieved high sensitivity (0.89; 95% CI, 0.74-0.95), high negative predictive value (0.97; 95% CI, 0.94-0.99), low negative likelihood ratio (0.12; 95% CI, 0.05-0.30), and an accuracy of 0.94 (95% CI, 0.90-0.97). Ratiometric analysis results for the swab samples showed that the AspLFD had high sensitivity (0.94; 95% CI, 0.73-1.00), high negative predictive value (0.95; 95% CI, 0.76-1.00), low negative likelihood ratio (0.07; 95% CI, 0.01-0.48), and an accuracy of 0.88 (95% CI, 0.73-0.96).

Conclusions and Relevance

Results of this diagnostic study suggest that AspLFD along with the ratiometric analysis of LFDs developed for this study has high diagnostic accuracy in identifying Aspergillus species from corneal scrapes and swabs. This technology is an important step toward the provision of point-of-care diagnostics for MK and could inform the clinical management strategy.

Mobile Efficient Diagnostics of Infectious Diseases via On-Chip RT-qPCR: MEDIC-PCR

The COVID-19 outbreak has caused public and global health crises. However, the lack of on-site fast, reliable, sensitive, and low-cost reverse transcription polymerase chain reaction (RT-PCR) testing limits early detection, timely isolation, and epidemic prevention and control. Here, the authors report a rapid mobile efficient diagnostics of infectious diseases via on-chip -RT-quantitative PCR (RT-qPCR): MEDIC-PCR. First, the authors use a roll-to-roll printing process to accomplish low-cost carbon-black-based disposable PCR chips that enable rapid LED-induced photothermal PCR cycles. The MEDIC-PCR can perform RT (3 min), and PCR (9 min) steps. Further, the cohort of 89 COVID-19 and 103 non-COVID-19 patients testing is completed by the MEDIC-PCR to show excellent diagnostic accuracy of 97%, sensitivity of 94%, and specificity of 98%. This MEDIC-PCR can contribute to the preventive global health in the face of a future pandemic.

New technologies and reagents in lateral flow assay (LFA) designs for enhancing accuracy and sensitivity

Lateral flow assays (LFAs) are a popular method for quick and affordable diagnostic testing because they are easy to use, portable, and user-friendly. However, LFA design has always faced challenges regarding sensitivity, accuracy, and complexity of the operation. By integrating new technologies and reagents, the sensitivity and accuracy of LFAs can be improved while minimizing the complexity and potential for false positives. Surface enhanced Raman spectroscopy (SERS), photoacoustic techniques, fluorescence resonance energy transfer (FRET), and the integration of smartphones and thermal readers can improve LFA accuracy and sensitivity. To ensure reliable and accurate results, careful assay design and validation, appropriate controls, and optimization of assay conditions are necessary. Continued innovation in LFA technology is crucial to improving the reliability and accuracy of rapid diagnostic testing and expanding its applications to various areas, such as food testing, water quality monitoring, and environmental testing.

SALAD: Syringe-based Arduino-operated Low-cost Antibody Dispenser

Lateral Flow Assays (LFA) have been one of the most widely adopted technologies in clinical diagnosis over recent years, especially during the COVID-19 pandemic, due to their feasibility, compactness, and rapid readout. However, the precise dispensing of antibodies-a key part of the fabrication process-requires costly line dispenser equipment, which poses a challenge to researchers with limited budgets. This study aims to resolve this key issue by introducing a Syringe-based Arduino-operated Low-cost Antibody Dispenser (SALAD). By utilizing a microneedle, stepper motor-driven syringe pump, and conveyor belt, SALAD can form micro-droplets to create an even band of antibodies. Our evaluation results showed comparable performance between SALAD and a commercialized model - Claremont ALFRD, with SALAD exceeding in affordability and feasibility. SALAD yielded an even signal, uniform bandwidth, and low background noise, yet optimization in the conveyor belt should be considered to enhance stability. With a low manufacturing cost ($200.61) compared to the commercialized models, our model is expected to provide an affordable approach for LFA researchers.

Quantitative injection strip platform using water-soluble paper and magnet based on a lateral flow assay

Quantitative analysis for lateral flow immunoassay (LFA) strips was conducted continuously. Quantitative analysis means measuring concentration, which represents the number of molecules per unit volume. In this study, we designed a quantitative injection (QI) strip by modifying the structure of general LFA strips to inject the same unit volume. To achieve the injection of the same unit volume, we used water-soluble paper and magnet. In addition, the QI strip was fabricated to enable the physical separation of the gold conjugate pad from the nitrocellulose membrane (NC membrane) at the optimized time after sample injection. The optimized time refers to the time from the point at which the sample started flowing on the NC membrane to the point at which the strip was separated. At the samples of same concentration, the LFA strip increases detection signals as the volume of injected sample increases. In contrast to the LFA strip, the QI strip maintained consistent detection signals even with increasing volume of injected sample. Furthermore, the QI strip demonstrated an 11-fold lower deviation compared to the LFA strip. These results are attributed to the separation function of the QI strip. In conclusion, the QI strip is more suitable for quantitative analysis compared to the LFA strip due to the same unit volume without additional equipment such as a pipette. This study is expected to contribute to the development of user-friendly POCT and strip-based quantitative analysis.

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.

Visualized Lateral Flow Assay for Dual Viral RNA Fragment Detection

In this technical note, we report an easy-to-produce, reverse-transcription-free, and protein-enzyme-free lateral flow assay for detection of viral RNA fragments by taking SARS-CoV-2 ORF1ab and N as target models. Catalytic hairpin assembly is utilized for dual RNA fragment orthogonal reaction to generate copious amounts of opened hairpin duplexes, which bridge DNA-modified gold nanoparticles and capture strands on the strip to induce coloration. The dual RNA fragments are simultaneously visualized during one time of sample flow, and single-base-mismatched nontarget sequences can be differentiated. The test strip can be flexibly adapted to detect evolutional SARS-CoV-2 variants such as Delta and Omicron. It also shows potential in visually detecting long-sequence virus simulants and achieves a sensitivity comparable to that of RT-qPCR by incorporation with upstream sample amplification. The lateral flow assay should offer a convenient and reliable technique for viral nucleic acid detection.

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.

Enabling a universal lateral flow readout for DNA strand displacement via disassembling chemical labels

Herein, we describe a novel strategy that enables lateral flow readout for DNA strand displacement via disassembling chemical labels (DCL). Comparing it to a classic fluorogenic assay, we demonstrate that our DCL-based lateral flow assay is highly sensitive and specific, capable of discriminating single nucleotide variants in buccal swab samples.

Lateral Flow Assay for Hepatitis B Detection: A Review of Current and New Assays

From acute to chronic hepatitis, cirrhosis, and hepatocellular cancer, hepatitis B infection causes a broad spectrum of liver diseases. Molecular and serological tests have been used to diagnose hepatitis B-related illnesses. Due to technology limitations, it is challenging to identify hepatitis B infection cases at an early stage, particularly in a low- and middle-income country with constrained resources. Generally, the gold-standard methods to detect hepatitis B virus (HBV) infection requires dedicated personnel, bulky, expensive equipment and reagents, and long processing times which delay the diagnosis of HBV. Thus, lateral flow assay (LFA), which is inexpensive, straightforward, portable, and operates reliably, has dominated point-of-care diagnostics. LFA consists of four parts: a sample pad where samples are dropped; a conjugate pad where labeled tags and biomarker components are combined; a nitrocellulose membrane with test and control lines for target DNA-probe DNA hybridization or antigen-antibody interaction; and a wicking pad where waste is stored. By modifying the pre-treatment during the sample preparation process or enhancing the signal of the biomarker probes on the membrane pad, the accuracy of the LFA for qualitative and quantitative analysis can be improved. In this review, we assembled the most recent developments in LFA technologies for the progress of hepatitis B infection detection. Prospects for ongoing development in this area are also covered.

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.

No-cost ballpoint pen dispenser for lateral flow assays

We have developed a no-cost, lightweight, human-powered dispenser using an empty ballpoint pen. Used in lateral flow assays, this dispenser restricts antibody deposition to narrow zones, allowing freehand drawing of test and control lines. The lines can be drawn in widths ranging from 0.15 to 1.00 mm. Naphthol green B, a compatible stain, was used to label antibody solutions and certify handwriting traces. Using human chorionic gonadotropin (HCG) as a model antigen, we demonstrated that the pen dispenser can imprint antibodies on nitrocellulose membranes without affecting their microstructure and chromatographic function. A lateral flow assay using the pen dispenser detected HCG at 0.1 μg/mL, comparable to the sensitivity of standard tests using traditional benchtop dispensers.

Modular Set of Reagents in Lateral Flow Immunoassay: Application for Antibiotic Neomycin Detection in Honey

A scheme of modular competitive immunochromatography with an analyte-independent test strip and changeable specific immunoreactants has been proposed. Native (detected) and biotinylated antigens interact with specific antibodies during their preincubation in solution, that is, without the immobilization of reagents. After this, the detectable complexes on the test strip are formed by the use of streptavidin (which binds biotin with high affinity), anti-species antibodies, and immunoglobulin-binding streptococcal protein G. The technique was successfully applied for the detection of neomycin in honey. The visual and instrumental detection limits were 0.3 and 0.014 mg/kg, respectively, and the degree of neomycin revealed in honey samples varied from 85% to 113%. The efficiency of the modular technique with the use of the same test strip for different analytes was confirmed for streptomycin detection. The proposed approach excludes the necessity of finding the condition of immobilization for each new specific immunoreactant and transferring the assay to other analytes by a simple choice of concentrations for preincubated specific antibodies and the hapten-biotin conjugate.

Fluorophore-encapsulated nanobeads for on-site, rapid, and sensitive lateral flow assay

Since December 2019, the rapid and sensitive detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has become a priority for public health. Although the lateral flow assay (LFA) sensor has emerged as a rapid and on-site SARS-CoV-2 detection technique, the conventional approach of using gold nanoparticles for the signaling probe had limitations in increasing the sensitivity of the sensor. Herein, our newly suggested methodology to improve the performance of the LFA system could amplify the sensor signal with a facile fabrication method by concentrating fluorescent organic molecules. A large Stokes shift fluorophore (single benzene) was encapsulated into polystyrene nanobeads to enhance the fluorescence intensity of the probe for LFA sensor, which was detected on the test line with a longpass filter under ultraviolet light irradiation. This approach provides comparatively high sensitivity with the limit of detection of 1 ng mL^-1 for the SARS-CoV-2 spike protein and a fast detection process, which takes less than 20 min. Furthermore, our sensor showed higher performance than gold nanoparticle-based commercial rapid diagnostics test kits in clinical tests, proving that this approach is more suitable and reliable for the sensitive and rapid detection of viruses, bacteria, and other hazardous materials.

Current Methods for the Detection of Antibodies of Varicella-Zoster Virus: A Review

Infection with the varicella-zoster virus (VZV) causes chickenpox and shingles, which lead to significant morbidity and mortality globally. The detection of serum VZV-specific antibodies is important for the clinical diagnosis and sero-epidemiological research of VZV infection, and for assessing the effect of VZV vaccine immunization. Over recent decades, a variety of methods for VZV antibody detection have been developed. This review summarizes and compares the current methods for detecting VZV antibodies, and discussed future directions for this field.

Handling Detection Limits of Multiplex Lateral Flow Immunoassay by Choosing the Order of Binding Zones

Changes in the limits of detection (LODs) for a multiplex lateral flow immunoassay (LFIA) caused by different locations of the binding zone on the test strips were studied. Due to the non-equilibrium conditions of the immune reactions in LFIAs, their analytical parameters are susceptible to the binding constants of antigen-antibody reactions and assay duration. Consequently, the integration of several tests into one multiplex assay can cause a significant worsening of the sensitivity. In this study, we propose a simple methodology for the determination of the best arrangement of binding zones, which takes into account the binding constants for immunoreagents. LFIAs of four mycotoxins, namely, aflatoxin B1, deoxynivalenol, T-2 toxin, and ochratoxin A, were integrated into a multiplex test strip. An enzyme-linked immunosorbent assay was applied to determine the equilibrium and kinetic constants of the immunoreactants for each analyte. It was found that the arrangement of binding zones with a descending order of the equilibrium association constants was optimal and provided both lower detection limits and a more uniform coloration. The selected position of the binding zones allowed decreasing the LODs down to 2 and 27 times for ochratoxin A and deoxynivalenol, respectively. The proposed approach can be applied to multiplex LFIAs for different analytes.

Real-time, smartphone-based processing of lateral flow assays for early failure detection and rapid testing workflows

Despite their simplicity, lateral flow immunoassays (LFIAs) remain a crucial weapon in the diagnostic arsenal, particularly at the point-of-need. However, methods for analysing LFIAs still rely heavily on sub-optimal human readout and rudimentary end-point analysis. This negatively impacts both testing accuracy and testing times, ultimately lowering diagnostic throughput. Herein, we present an automated computational imaging method for processing and analysing multiple LFIAs in real-time and in parallel. This method relies on the automated detection of signal intensity at the test line, control line, and background, and employs statistical comparison of these values to predictively categorise tests as "positive", "negative", or "failed". We show that such a computational methodology can be transferred to a smartphone and detail how real-time analysis of LFIAs can be leveraged to decrease the time-to-result and increase testing throughput. We compare our method to naked-eye readout and demonstrate a shorter time-to-result across a range of target antigen concentrations and fewer false negatives compared to human subjects at low antigen concentrations.

Capture-SELEX: Selection Strategy, Aptamer Identification, and Biosensing Application

Small-molecule contaminants, such as antibiotics, pesticides, and plasticizers, have emerged as one of the substances most detrimental to human health and the environment. Therefore, it is crucial to develop low-cost, user-friendly, and portable biosensors capable of rapidly detecting these contaminants. Antibodies have traditionally been used as biorecognition elements. However, aptamers have recently been applied as biorecognition elements in aptamer-based biosensors, also known as aptasensors. The systematic evolution of ligands by exponential enrichment (SELEX) is an in vitro technique used to generate aptamers that bind their targets with high affinity and specificity. Over the past decade, a modified SELEX method known as Capture-SELEX has been widely used to generate DNA or RNA aptamers that bind small molecules. In this review, we summarize the recent strategies used for Capture-SELEX, describe the methods commonly used for detecting and characterizing small-molecule-aptamer interactions, and discuss the development of aptamer-based biosensors for various applications. We also discuss the challenges of the Capture-SELEX platform and biosensor development and the possibilities for their future application.