Sensitivity enhancement in lateral flow assays: a systems perspective

Dual lateral flow assay using quantum nanobeads for quantitative detection of BDNF and TNF-α in tears

Glaucoma is a group of neurodegenerative eye diseases characterized by progressive damage to the optic nerve which is typically asymptomatic until irreversible vision loss has occurred. Early screening is essential for timely treatment to prevent visual impairment. However, existing detection methods struggle to achieve a balance between accuracy, time efficiency, and portability. The lateral flow assay (LFA) is a well-established immunoanalytical tool for point-of-care (POC) analysis. Here, we have developed a unique dual-testing, quantum nanobeads-based fluorescence LFA, allowing for the simultaneous and quantitative detection of two glaucoma biomarkers: tumor necrosis factor-α (TNF-α) and brain-derived neurotrophic factor (BDNF). By coating quantum dots on the surface of a SiO2 core, the fluorescent intensity of the quantum nanobeads was enhanced enabling an accurate, efficient, and high-throughput bioanalytical performance, with low detection limits of 3.39 pg mL-1 for TNF-α and 4.13 pg mL-1 for BDNF. The LFA also demonstrated superior selectivity, reproducibility, and stability to the standard enzyme-linked immunosorbent assay (ELISA). Using a 3D-printed readout box, the analysis of the LFA requires only a readily accessible smartphone and image processing software, making it an ideal POC detection tool. This ultrasensitive, economical, and user-friendly LFA demonstrates significant potential as an alternative for glaucoma screening.

Tyramide signal amplification for a highly sensitive multiplex immunoassay based on encoded hydrogel microparticles

Proteins play a crucial role as mediators of immune regulation, homeostasis, and metabolism, making their quantification essential for understanding disease mechanisms in biomedical research and clinical diagnostics. However, conventional methods when used to detect proteins in clinical samples exhibit difficulty in terms of sensitivity, dynamic range, and multiplex capacity. In this study, we developed a highly sensitive multiplex immunoassay based on encoded hydrogel microparticles (MPs) utilizing tyramide signal amplification (TSA). The combination of the large multiplexing capacity of encoded hydrogel microparticles and the signal amplification of tyramide enables a highly sensitive multiplex immunoassay. By employing TSA, we are able to achieve larger detection signals with higher specificity. We effectively decreased the non-specific binding in the hydrogel network by blocking the unreacted acrylate double bonds remaining after the capture antibody-conjugation step and acquired a 3-fold increase in the signal-to-noise ratio. Also, we optimized three parameters mainly affecting the assay sensitivity: the detection antibody concentration, the biotinyl tyramide concentration, and the TSA reaction time. This approach leads to a significant improvement in assay sensitivity, achieving a limit of detection as low as 58 fg mL-1. Compared to the previous method, the assay sensitivity is enhanced 10-fold. In addition, the multiplex capability of the assay is validated by detecting cytokines IL-4, IL-5, IL-6, IL-9, and IL-17, with no observed cross-reactivity. Finally, with enhanced sensitivity, we demonstrate the clinical applicability of our platform by successfully multiplexing these cytokines at concentrations down to several hundreds of fg mL-1 within human serum, which could not be detected using previous methods.

Biosynthetic small molecule antigens mimics medicated lateral flow immunoassay for mycotoxin Fumonisin B1 using nanobody fusion proteins

Lateral flow immunoassays (LFAs) are widely used in point-of-care testing (POCT) for detecting small molecules. However, their application is often hindered by the complex synthesis of traditional chemically synthesized antigens. Nanobody-based coating antigen mimics have shown excellent analytical performance in various immunoassay platforms, but their application in LFAs still faces challenges. Here, we demonstrate the use of nanobody fusion proteins as antigen mimics in the construction of LFAs for detecting small molecules. Anti-idiotypic nanobody (B26) specific to Fumonisin B1 (FB1) was selected as a case study, and the maltose binding protein (MBP)-fused B26 showed optimal performance. Adsorption studies revealed that MBP-B26 showed an approximately 8-fold enhancement in maximum equilibrium adsorption capacity compared to unmodified B26 on nitrocellulose filter (NC) membranes in LFAs, and nearly 1.5-fold increase compared to chemically synthesized antigens. Molecular dynamics simulations also indicated a 28.7 % increase in non-bonding interaction energies. The MBP-B26-based LFAs detection method for FB1 demonstrated high sensitivity (1.76 μg/kg) and more environmentally friendly compared to chemically synthesized antigens. This study establishes a theoretical framework and provides models for the use of nanobody fusion proteins-based LFAs, facilitating broader application in detecting small molecules in POCT.

DNA origami signal amplification in lateral flow immunoassays

Lateral flow immunoassays (LFIAs) enable a rapid detection of analytes in a simple, paper-based test format. Despite their multiple advantages, such as low cost and ease of use, their low sensitivity compared to laboratory-based testing limits their use in e.g. many critical point-of-care applications. Here, we present a DNA origami-based signal amplification technology for LFIAs. DNA origami is used as a molecularly precise adapter to connect detection antibodies to tailored numbers of signal-generating labels. As a proof of concept, we apply the DNA origami signal amplification in a sandwich-based LFIA for the detection of cardiac troponin I (cTnI) in human serum. We show a 55-fold improvement of the assay sensitivity with 40-nm gold nanoparticle labels and an adjustable signal amplification of up to 125-fold with fluorescent dyes. The technology is compatible with a wide range of existing analytes, labels, and sample matrices, and presents a modular approach for improving the sensitivity and reliability of lateral flow testing.

Biosensors and lateral flow immunoassays: Current state and future prospects

The advent of paper-based biosensors represents a novel paradigm in point-of-care (POC) diagnostics, emerging as versatile tools. However, the broad term "biosensors" can be misleading, encompassing a range of techniques such as dipstick assays, electrochemical, microfluidics and immunoassay-based biosensors (including lateral flow (LFA), vertical flow and nucleic acid-based immunoassays). This narrative review aims to consolidate the vast and dispersed information on biosensors into a systematically organized resource addressing both practical and theoretical aspects for researchers developing paper-based biosensors. It offers a comprehensive classification of biorecognition elements and labels, insights into various conjugation techniques, and characterization methods for both labels and conjugates. Following the development and optimization of biological reactions, this review emphasizes the careful selection of membranes and reagents to effectively reproduce molecular reactions on paper. Membranes are critical to biosensor efficacy, with fluid dynamics influenced by factors such as pore size, protein holding capacity and wicking rate. While POC diagnostics have traditionally provided binary (yes/no) results, advancements now allow for semi-quantitative and quantitative results. Technologies such as in-text, printers, various software's and smartphone can be used as colour analysis utilizing colour models beyond RGB like XYZ, grey intensity, CMY, CMYK, HSV and HSL that can analyse and process the colour intensity. AI integration further simplifies result analysis through image analysis, interpretation, predictive modelling, clinical decision support, enhancing detection, data integration and management. This review also emphasizes validation and stability studies in accordance with regulatory guidelines, ensuring the reliability of biosensors. The review ultimately covers: (i) A foundational understanding of various biosensor techniques, focusing on the self-sufficient LFA technique. (ii) Strategies to enhance sensitivity through pre- and post-assay modifications. (iii) A comprehensive troubleshooting section addressing common challenges in bioassay and fabrication. (iv) Multiplexing approaches enabling the simultaneous detection of multiple analytes for enhanced biomarker confirmation. By amalgamating knowledge from these approaches, this review offers the potential to elevate a basic traditional LFA strip into a highly sensitive diagnostic tool. It serves not only as a repository of knowledge but also as a roadmap for researchers and practitioners navigating the burgeoning field of paper-based biosensors.

Enhancing lateral flow immunoassay performance for cardiac troponin I detection with pore-size tailored silica nanoparticles and smartphone-based "AdaptiScan" analysis

The accurate and rapid detection of cardiac troponin I (cTnI) at the point of care is crucial for the timely diagnosis of myocardial infarction (MI). This study introduces an advanced lateral flow immunoassay (LFIA) platform for cTnI detection. We employed small-sized, large-pore dendritic mesoporous silica nanoparticles (DMSN-2) to encapsulate quantum dots (QDs), achieving an enhanced QD loading capacity of 1.427 g QD/g silica, compared to 0.881 g QD/g silica for smaller pore counterparts (DMSN-1). This nano-LFIA was further integrated with "AdaptiScan", a smartphone-based detection system that uses adaptive detection algorithms to automatically extract and analyze fluorescence signals from LFIA strips. This integration of pore-size tailored DMSNs and "AdaptiScan" resulted in a limit of detection for cTnI of 42.6 ng/L, which meets clinical diagnostic requirements. The platform offers a sensitive, cost-effective, and portable solution for rapid detection of MI, potentially transforming point-of-care testing in resource-limited settings.

Lateral flow analysis test strips based on aggregation-induced emission technique: Principle, design, and application

This review examines the potential of aggregation-induced luminescence (AIE) materials in lateral flow assays (LFA) to enhance the sensitivity and specificity of a range of assay applications. LFA is a straightforward and effective paper-based platform for the rapid detection of target analytes in mixtures. Its simple design, low cost, and ease of operation are among the most attractive advantages of LFA. The signal reporting label, which constitutes the core component of LFA detection, is of paramount importance for enhancing the sensitivity of the detection process. The sensitivity of traditional LFA signal labels is insufficient for the detection of biomarkers at low concentrations. To address this issue, AIE materials have been developed in recent years. These materials can significantly enhance the luminescence intensity at high concentrations or in aggregated states, exhibiting excellent photostability and a high signal-to-noise ratio. They possess the advantages of high quantum yields, good photostability, and strong fluorescence, rendering them suitable for a variety of applications, including medical diagnostics, food safety, and environmental monitoring. This review therefore provides an overview of the operational principles of AIE and LFA, details the selection of AIE materials, the design of the platform and their applications, and reviews the latest research. Notable examples include the detection of viral pathogens, bacterial and mycotoxin contamination, antibiotic residues, and pesticide residues. The integration of AIE materials in LFA technology has demonstrated the potential for rapid, accurate, and cost-effective diagnostics. However, challenges remain in large-scale synthesis and multiplexed assays. The paper concludes with a discussion of current limitations and future directions for the technology.

Advances in molecular epidemiology and detection methods of pseudorabies virus

Pseudorabies (PR), a highly contagious disease caused by the pseudorabies virus (PRV), represents a significant threat to the global swine industry. Despite the success of developed countries in controlling the PRV epidemic through swine pseudorabies eradication programs, wild boars, as a potential source of infection, still require sustained attention and effective control measures. Concurrently, there has been considerable global attention directed towards cases of PRV infection in humans. In consideration of the aforementioned factors, this paper presents a comprehensive review of recent developments in the PRV genome, epidemiology, vaccine research, and molecular detection methods. The epidemiology section presents an analysis of the transmission routes, susceptible animal groups, and geographic distribution of PRV, as well as an examination of the trend of the epidemic in recent years. In the field of vaccine research, the current development of genetically engineered vaccines is emphasized, and the immunogenicity and safety of vaccines are discussed. Moreover, the molecular detection techniques utilized to identify PRV, including immunological methods, nucleic acid detection methods, biosensors, and so forth, are presented in a systematic manner. Finally, this paper presents a comprehensive discussion of the current status of PRV-related research and offers insights into future directions, with the aim of providing a foundation for the scientific prevention and control of PRV.

Development of highly sensitive lateral flow immunoassay using PdNPs for detection of Plasmodium species

A lateral flow immunoassay (LFIA) employing palladium nanoparticles (PdNPs) labelled with antibodies has been innovatively designed for the precise detection of Plasmodium falciparum pLDH and HRPII antigen. This study focuses on development of LFIA based on PdNPs detection system to substantially enhance the visual detectability (vLOD), achieving an impressive 12 parasites/microliter (p/µl) vLOD in comparison with conventional system represented 50 p/µl vLOD. The research introduces a novel amplification system that not only heightens the sensitivity of LFIA but also maintains intense coloration. This novel system relies on direct detection of the malaria pLDH and HRPII antigen. In this innovative assay, HRPII antigen interacts with PdNP-conjugated Anti-HRPII detector antibodies, forming an immune complex with Anti-HRPII capture antibodies. The detection limit for HRPII antigen was found to be 8 times higher than that of conventional systems. Moreover, the novel approach for synthesis of PdNPs and their conjugation with antibodies makes this system robust and universally applicable and also extends its potential use to detect various other compounds, including antigens or antibodies from different diseases. This sensitive LFIA detection system presents itself as an efficient screening tool for medical monitoring and point-of-care (POC) settings, offering promising prospects for enhancing disease diagnosis and surveillance.

Development of point-of-care tests for urinary bladder cancer - an historic review and view to future prospectives

Urine is an attractive biospecimen for noninvasive tests to facilitate bladder tumor diagnostics. Three different point-of-care (POC) tests based on lateral flow immunoassays (LFAs) are currently commercially available: UBC® Rapid Test, BTA stat®, and NMP22TM BladderChek. The present review discusses these different tests based on their performance, clinical utility and the nature of the respective analytes. The level of sensitivities of UBC Rapid Test® and BTA stat® for detection of high-grade nonmuscle invasive bladder cancer using urine is in the order of 80%. Estimations of performance are highly dependent on patient selection criteria. UBC® Rapid Test shows a sensitivity of approximately 85% in patients presenting with macrohematuria which is the most common initial clinical symptom. Estimations of specificity are complicated by differences in how control groups are selected in different studies and are therefore more difficult to compare between published reports. Different POC tests differ with regard to the source of the analytes that are measured. The BTA Stat® test is based on detection of plasma proteins (Factor H/Factor H-related proteins), potentially leading to a lack of specificity during conditions of renal dysfunction. A large number of analytes to be used for urine-based bladder cancer tests have been described in the literature, including cytokines and proteases implicated in tumor invasion. These proteins, although biologically relevant, are often present at very low levels in urine that may be unsuitable for development of LFAs. Release of abundant intracellular structural proteins from cells such as cytokeratins (UBC® Rapid Test) and nuclear matrix proteins (NMP22TM) may therefore be advantageous. We conclude that available data support the use of urine-based POC tests as adjuncts during the clinical work up of suspected bladder cancer.

Conjugation of visual enhancers in lateral flow immunoassay for rapid forensic analysis: A critical review

During crime scene investigations, numerous traces are secured and may be used as evidence for the evaluation of source and/or activity level propositions. The rapid chemical analysis of a biological trace enables the identification of body fluids and can provide significant donor profiling information, including age, sex, drug abuse, and lifestyle. Such information can be used to provide new leads, exclude from, or restrict the list of possible suspects during the investigative phase. This paper reviews the state-of-the-art labelling techniques to identify the most suitable visual enhancer to be implemented in a lateral flow immunoassay setup for the purpose of trace identification and/or donor profiling. Upon comparison, and with reference to the strengths and limitations of each label, the simplistic one-step analysis of noncompetitive lateral flow immunoassay (LFA) together with the implementation of carbon nanoparticles (CNPs) as visual enhancers is proposed for a sensitive, accurate, and reproducible in situ trace analysis. This approach is versatile and stable over different environmental conditions and external stimuli. The findings of the present comparative analysis may have important implications for future forensic practice. The selection of an appropriate enhancer is crucial for a well-designed LFA that can be implemented at the crime scene for a time- and cost-efficient investigation.

Smartphone-based lateral flow immunoassay for sensitive determination of lactate dehydrogenase at the point of care

Lactate dehydrogenase (LDH), a prevalent enzyme involved in anaerobic glycolysis, is released into body fluids following cell damage and has long been a general marker of tissue injury. However, due to its lack of selectivity and the advent of more accurate biomarkers, the clinical utility of LDH has been largely limited to confirming hemolysis. LDH has been recognized as a valuable prognostic biomarker for various cancers, making its monitoring crucial during cancer management. Traditional LDH methods include spectrophotometric analysis of NADH at 340 nm, native electrophoresis, or enzyme-linked immunosorbent assay. This study presents the first lateral flow immunoassay (LFIA) for the smartphone-based quantification of serum LDH levels at the point of care. Highly-affinity and specific antibodies have been produced, with 5 nM equilibrium dissociation constant and no cross-reactivity with human serum albumin and human immunoglobulin G. Utilizing carbon nanoparticles as signal transducers significantly enhanced the quantification limit 55-fold, compared to the conventional gold nanoparticles-based LFIA, achieving a quantification limit of 1.5 ng mL-1. The developed assay demonstrated a mean recovery rate of 115 ± 21 % when evaluating LDH-spiked serum samples. This method can be an interesting home-testing tool for monitoring cancer progression or therapy effectiveness.

Lateral Flow Immunosensing of Salmonella Typhimurium Cells in Milk: Comparing Three Sequences of Interactions

To ensure the safety of foodstuffs, widespread non-laboratory monitoring for pathogenic contaminants is in demand. A suitable technique for this purpose is lateral flow immunoassay (LFIA) which combines simplicity, rapidity, and productivity with specific immune detection. This study considered three developed formats of LFIA for Salmonella Typhimurium, a priority pathogenic contaminant of milk. Common sandwich LFIA with all immunoreagents pre-applied to the test strip (format A) was compared with incubation of the sample and (gold nanoparticle-antibody) conjugate, preceding the lateral flow processes (format B), and sequential passages of the sample and the conjugate along the test strip (format C). Under the chosen conditions, the detection limits and the assay times were 3 × 104, 1 × 105, and 3 × 105 cells/mL, 10, 15, and 20 min for formats A, B, and C, respectively. The selected format A of LFIA was successfully applied to test milk samples. The sample's dilution to a fat content of 1.0% causes pathogen detection, with 70-110% revealing and 1.5-8.5% accuracy. The obtained results demonstrate that the developed LFIA allows the detection of lower concentrations of Salmonella cells and, in this way, accelerates decision-making in food safety control.

Application of Monoclonal Anti-Mycolate Antibodies in Serological Diagnosis of Tuberculosis

Patient loss to follow-up caused by centralised and expensive diagnostics that are reliant on sputum is a major obstacle in the fight to end tuberculosis. An affordable, non-sputum biomarker-based, point-of-care deployable test is needed to address this. Serum antibodies binding the mycobacterial cell wall lipids, mycolic acids, have shown promise as biomarkers for active tuberculosis. However, anti-lipid antibodies are of low affinity, making them difficult to detect in a lateral flow immunoassay-a technology widely deployed at the point-of-care. Previously, recombinant monoclonal anti-mycolate antibodies were developed and applied to characterise the antigenicity of mycolic acid. We now demonstrate that these anti-mycolate antibodies specifically detect hexane extracts of mycobacteria. Secondary antibody-mediated detection was applied to detect the displacement of the monoclonal mycolate antibodies by the anti-mycolic acid antibodies present in tuberculosis-positive guinea pig and human serum samples. These data establish proof-of-concept for a novel lateral flow immunoassay for tuberculosis provisionally named MALIA-mycolate antibody lateral flow immunoassay.

Sliding Microneedle - Lateral flow immunoassay strip device for highly sensitive biomarker detection in interstitial fluid

Diabetes is a chronic disease with significant complications, necessitating regular treatment and checkups, which can be costly and time-consuming for patients. To address this, we developed the Sliding Microneedle (MN)-Lateral flow immunoassay strip (LFIAs) device that combines the advantages of MNs and LFIAs to detect IL-6, an independent biomarker for diabetes complications. This device offers rapid and highly sensitive detection of IL-6 by extracting interstitial fluid (ISF) through MNs and transferring it to LFIAs. The stainless MN, embedded in the 3D-printed Sliding MN-LFIAs device, was inserted into the skin at a 20° angle, minimizing blood contamination risk. With a filter paper attached to the MN surface, the device collected 4.65 ± 0.05 μL of ISF containing IL-6 within 90 s. The ISF was then transferred to the LFIAs using a running buffer. After a 15-min reaction, silver enhancement (SE) treatment was applied, allowing for the highly sensitive and specific detection of IL-6 at 102 pg/mL concentrations. The Sliding MN-LFIAs device successfully distinguished between normal and diabetic rat models, demonstrating its potential as an effective tool for detecting diabetes complications quickly and affordably.

Lateral flow assay sensitivity and signal enhancement via laser µ-machined constrains in nitrocellulose membrane

Lateral flow assay (LFA) is a handful diagnostic technology that can identify severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and other common respiratory viruses in one strip, which can be tested at the point-of-care without the need for equipment or skilled personnel outside the laboratory. Although its simplicity and practicality make it an appealing solution, it remains a grand challenge to substantially enhance the colorimetric LFA sensitivity. In this work, we present a straightforward approach to enhance the sensitivity of LFA by imposing the flow constraints in nitrocellulose (NC) membranes via a number of vertical femtosecond laser micromachined microchannels which is important for prolonged specific binding interactions. Porous NC membrane surfaces were structured with different widths and densities µ-channels employing a second harmonic of the Yb:KGW femtosecond laser and sample XYZ translation over a microscope objective-focused laser beam. The influence of the microchannel parameters on the vertical wicking speed was evaluated from the video recordings. The obtained results indicated that µ-channel length, width, and density in NC membranes controllably increased the immunological reaction time between the analyte and the labeled antibody by 950%. Image analysis of the colorimetric indicators confirmed that the flow rate delaying strategy enhanced the signal sensitives by 40% compared with pristine NC LFA.

3D Film-Like Nanozyme with a Synergistic Amplification Effect for the Ultrasensitive Immunochromatographic Detection of Respiratory Viruses

Greatly improving the sensitivity and detection range of lateral flow immunoassays (LFAs) by at least 100 times without using additional instruments remains challenging. Herein, we develop a three-dimensional (3D) film-like nanozyme (GO-Pt30-AuPt5) by ordered assembly of one layer of 30 nm Pt nanoparticles (NPs) and one layer of small Au@Pt satellites (5 nm) onto a two-dimensional (2D) graphene oxide (GO) nanofilm, in which GO greatly increased the interface area and stability of the nanozyme whereas Pt and Au@Pt NPs synergistically enhanced colorimetric/catalytic activities. The grafting of outer Au@Pt satellites converted the 2D nanofilm into a 3D flexible nanozyme with numerous catalytic sites for enzymatic deposition signal amplification and binding sites for target capture. The introduction of GO-Pt30-AuPt5 into multiplex LFA achieved the ultrasensitive and simultaneous detection of two important respiratory viruses with sensitivity of 1 pg/mL level, which was about 100 times higher than that without signal enrichment and at least 20 and 1900 times higher than those of traditional enzyme-linked immunosorbent assay and AuNP-based LFA, respectively. The clinical utility of the proposed assay was validated through the diagnosis of 49 real clinical respiratory tract specimens. Our proposed LFA shows great potential for the ultrasensitive screening of pathogens in the field.

Analysis of urine cell-free DNA in bladder cancer diagnosis by emerging bioactive technologies and materials

Urinary cell-free DNA (UcfDNA) is gaining recognition as an important biomarker for diagnosing bladder cancer. UcfDNA contains tumor derived DNA sequences, making it a viable candidate for non-invasive early detection, diagnosis, and surveillance of bladder cancer. The quantification and qualification of UcfDNA have demonstrated high sensitivity and specificity in the molecular characterization of bladder cancer. However, precise analysis of UcfDNA for clinical bladder cancer diagnosis remains challenging. This review summarizes the history of UcfDNA discovery, its biological properties, and the quantitative and qualitative evaluations of UcfDNA for its clinical significance and utility in bladder cancer patients, emphasizing the critical role of UcfDNA in bladder cancer diagnosis. Emerging bioactive technologies and materials currently offer promising tools for multiple UcfDNA analysis, aiming to achieve more precise and efficient capture of UcfDNA, thereby significantly enhancing diagnostic accuracy. This review also highlights breakthroughs in detection technologies and substrates with the potential to revolutionize bladder cancer diagnosis in clinic.

Enhancing antibody detection sensitivity in lateral flow immunoassays using endospores of Bacillus subtilis as signal amplifiers

Antibody detection is the critical first step for tracking the spread of many diseases including COVID-19. Lateral flow immunoassay (LFIA) is the most commonly used method for rapid antibody detection because it is easy-to-use and inexpensive. However, LFIA has limited sensitivity when gold nanoparticles (AuNPs) are used as the signals. In this study, the endospores of Bacillus subtilis were used in combination with AuNP in a LFIA to detect antibodies. The endospores serve as a signal amplifier. The detection limit was about 10-8 M for anti-beta galactosidase antibody detection whereas the detection limit of conventional LFIA is about 10-6 M. Furthermore, the proposed methods have no additional user steps compared with the traditional LFIA. This method, therefore, improved the sensitivity 100-fold without compromising any advantages of LFIA. We believe that the proposed method will be useful for detection of antibodies against HIV, Zika virus, SARS-CoV-2, and so on.

Nanomaterials in the treatment and diagnosis of rheumatoid arthritis: Advanced approaches

Rheumatoid arthritis (RA), a chronic inflammatory condition that affects persons between the ages of 20 and 40, causes synovium inflammation, cartilage loss, and joint discomfort as some of its symptoms. Diagnostic techniques for RA have traditionally been split into two main categories: imaging and serological tests. However, significant issues are associated with both of these methods. Imaging methods are costly and only helpful in people with obvious symptoms, while serological assays are time-consuming and require specialist knowledge. The drawbacks of these traditional techniques have led to the development of novel diagnostic approaches. The unique properties of nanomaterials make them well-suited as biosensors. Their compact dimensions are frequently cited for their outstanding performance, and their positive impact on the signal-to-noise ratio accounts for their capacity to detect biomarkers at low detection limits, with excellent repeatability and a robust dynamic range. In this review, we discuss the use of nanomaterials in RA theranostics. Scientists have recently synthesized, characterized, and modified nanomaterials and biomarkers commonly used to enhance RA diagnosis and therapy capabilities. We hope to provide scientists with the promising potential that nanomaterials hold for future theranostics and offer suggestions on further improving nanomaterials as biosensors, particularly for detecting autoimmune disorders.

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.

Enhancing Sensitivity in SARS-CoV-2 Rapid Antigen Testing through Integration of a Water-Soluble Polymer Wall

Lateral flow immunoassays (LFIAs) are recognized for their practicality in homecare and point-of-care testing, owing to their simplicity, cost-efficiency, and rapid visual readouts. Despite these advantages, LFIAs typically fall short in sensitivity, particularly in detecting viruses such as SARS-CoV-2, thus limiting their broader application. In response to this challenge, we have innovated an approach to substantially enhance LFIA sensitivity. This involves the integration of a water-soluble dextran-methacrylate polymer wall with a 15% grafting degree positioned between the test and control lines on the LFIA strip. This novel modification significantly improved the sensitivity of the assay, achieving detection limits as low as 50 pg mL-1 and enhancing the sensitivity by 5-20-fold relative to existing LFIA kits available on the market. Furthermore, our developed LFIA kit (WSPW-LFIA) demonstrated exceptional specificity for SARS-CoV-2. Coupled with a straightforward fabrication process and robust stability, the WSPW-LFIA represents a promising advancement for real-time in vitro diagnosis across a spectrum of diseases.

Development and evaluation of a Lateral flow immunoassay (LFIA) prototype for the detection of IgG anti-SARS-CoV-2 antibodies

Lateral flow immunoassays (LFIA) for antibody detection represent cost-effective and user-friendly tools for serology assessment. This study evaluated a new LFIA prototype developed with a recombinant chimeric antigen from the spike/S and nucleocapsid/N proteins to detect anti-SARS-CoV-2 IgG antibodies. The evaluation of LFIA sensitivity and specificity used 811 serum samples from 349 hospitalized, SARS-CoV-2 RT-qPCR positive COVID-19 patients, collected at different time points and 193 serum samples from healthy controls. The agreement between ELISA results with the S/N chimeric antigen and LFIA results was calculated. The LFIA prototype for SARS-CoV-2 using the chimeric S/N protein demonstrated 85 % sensitivity on the first week post symptoms onset, reaching 94 % in samples collected at the fourth week of disease. The agreement between LFIA and ELISA with the same antigen was 92.7 %, 0.827 kappa Cohen value (95 % CI [0.765-0.889]). Further improvements are needed to standardize the prototype for whole blood use. The inclusion of the novel chimeric S + N antigen in the COVID-19 IgG antibody LFIA demonstrated optimal agreement with results from a comparable ELISA, highlighting the prototype's potential for accurate large-scale serologic assessments in the field in a rapid and user-friendly format.

Microfabrication of engineered Lactococcus lactis biocarriers with genetically programmed immunorecognition probes for sensitive lateral flow immunoassay of antibiotic in milk and lake water

Micro/nanomaterials display considerable potential for increasing the sensitivity of lateral flow immunoassay (LFIA) by acting as 3D carriers for both antibodies and signals. The key to achieving high detection sensitivity depends on the probe's orientation on the material surface and its multivalent biomolecular interactions with targets. Here, we engineer Lactococcus lactis as the bacterial microcarrier (BMC) for a multivalent immunorecognition probe that was genetically programmed to display multifunctional components including a phage-screened single-chain variable fragment (scFv), an enhanced green fluorescent protein (eGFP), and a C-terminal peptidoglycan-binding domain (AcmA) anchored on BMC through the cell wall peptidoglycan. The innovative design of this biocarrier system, which incorporates a lab-on-a-chip microfluidic device, allows for the rapid and non-destructive self-assembly of the multivalent scFv-eGFP-AcmA@BMC probe, in which the 3D structure of BMC with a large peptidoglycan surface area facilitates the precisely orientated attachment and immobilization of scFv-eGFP-AcmA. This leads to a remarkable fluorescence aggregation amplification effect in LFIA, outperforming a monovalent 2D scFv-eGFP-AcmA probe for florfenicol detection. By designing a portable sensing device, we achieved an exceptionally low detection limit of 0.28 pg/mL and 0.21 pg/mL for florfenicol in lake water and milk sample, respectively. The successful microfabrication of this biocarrier holds potential to inspire innovative biohybrid designs for environment and food safety biosensing applications.

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.

NFC-enabled potentiostat and nitrocellulose-based metal electrodes for electrochemical lateral flow assay

Rapid detection of pathogens at the point-of-need is crucial for preventing the spread of human, animal and plant diseases which can have devastating consequences both on the lives and livelihood of billions of people. Colorimetric, lateral flow assays consisting of a nitrocellulose membrane, are the preferred format today for low-cost on-site detection of pathogens. This assay format has, however, historically suffered from poor analytical performance and is not compatible with digital technologies. In this work, we report the development of a new class of digital diagnostics platform for precision point-of-need testing. This new versatile platform consists of two important innovations: i) A wireless and batteryless, microcontroller-based, low-cost Near Field Communication (NFC)-enabled potentiostat that brings high performance electroanalytical techniques (cyclic voltammetry, chronoamperometry, square wave voltammetry) to the field. The NFC-potentiostat can be operated with a mobile app by minimally trained users; ii) A new approach for producing nitrocellulose membranes with integrated electrodes that facilitate high performance electrochemical detection at the point-of-need. We produced an integrated system housed in a 3D-printed phone case and demonstrated its use for the detection of Maize Mosaic Virus (MMV), a plant pathogen, as a proof-of-concept application.

2D Film-Like Magnetic SERS Tag with Enhanced Capture and Detection Abilities for Immunochromatographic Diagnosis of Multiple Bacteria

Here, a multiplex surface-enhanced Raman scattering (SERS)-immunochromatography (ICA) platform is presented using a graphene oxide (GO)-based film-like magnetic tag (GFe-DAu-D/M) that effectively captures and detects multiple bacteria in complex specimens. The 2D GFe-DAu-D/M tag with universal bacterial capture ability is fabricated through the layer-by-layer assembly of one layer of small Fe3O4 nanoparticles (NPs) and two layers of 30 nm AuNPs with a 0.5 nm built-in nanogap on monolayer GO nanosheets followed by co-modification with 4-mercaptophenylboronic acid (MPBA) and 5,5'-dithiobis-(2-nitrobenzoic acid).The GFe-DAu-D/M enabled the rapid enrichment of multiple bacteria by MPBA and quantitative analysis of target bacteria on test lines by specific antibodies, thus achieving multiple signal amplification of magnetic enrichment effect and multilayer dense hotspots and eliminating matrix interference in real-world applications. The developed technology can directly and simultaneously diagnose three major pathogens (Staphylococcus aureus, Pseudomonas aeruginosa, and Salmonella typhimurium) with detection limits down to the level of 10 cells mL-1. The good performance of the proposed method in the detection of real urinary tract infection specimens is also demonstrated, suggesting the great potential of the GFe-DAu-D/M-ICA platform for the highly sensitive monitoring of bacterial infections or contamination.

Rapid, visual, label-based biosensor platform for identification of hepatitis C virus in clinical applications

OBJECTIVES

In the current study, for the first time, we reported a novel HCV molecular diagnostic approach termed reverse transcription loop-mediated isothermal amplification integrated with a gold nanoparticles-based lateral flow biosensor (RT-LAMP-AuNPs-LFB), which we developed for rapid, sensitive, specific, simple, and visual identification of HCV.

METHODS

A set of LAMP primer was designed according to 5'untranslated region (5'UTR) gene from the major HCV genotypes 1b, 2a, 3b, 6a, and 3a, which are prevalent in China. The HCV-RT-LAMP-AuNPs-LFB assay conditions, including HCV-RT-LAMP reaction temperature and time were optimized. The sensitivity, specificity, and selectivity of our assay were evaluated in the current study. The feasibility of HCV-RT-LAMP-AuNPs-LFB was confirmed through clinical serum samples from patients with suspected HCV infections.

RESULTS

An unique set of HCV-RT-LAMP primers were successfully designed targeting on the 5'UTR gene. The optimal detection process, including crude nucleic acid extraction (approximately 5 min), RT-LAMP reaction (67℃, 30 min), and visual interpretation of AuNPs-LFB results (~ 2 min), could be performed within 40 min without specific instruments. The limit of detection was determined to be 20 copies per test. The HCV-RT-LAMP-AuNPs-LFB assay exhibited high specificity and anti-interference.

CONCLUSIONS

These preliminary results confirmed that the HCV-RT-LAMP-AuNPs-LFB assay is a sensitive, specific, rapid, visual, and cost-saving assay for identification of HCV. This diagnostic approach has great potential value for point-of-care (POC) diagnostic of HCV, especially in resource-challenged regions.

Net-Shaped DNA Nanostructure-Based Lateral Flow Assays for Rapid and Sensitive SARS-CoV-2 Detection

Lateral flow assay (LFA)-based rapid antigen tests are experiencing extensive global uptake as an expeditious and highly effective modality for the screening of viral infections during the COVID-19 pandemic. While these devices have played a significant role in alleviating the burden on the public healthcare system, their specificity and sensitivity fall short compared with molecular tests. In this study, we endeavor to address both limitations through the utilization of DNA nanotechnology in LFA format, wherein we substitute the target-specific antibody with designer DNA nanostructure-based molecular probes for recognizing the SARS-CoV-2 virus via multivalent, pattern-matching interactions. We meticulously designed a Net-shaped DNA nanostructure and strategically arranged trimeric clusters of aptamers that specifically recognize the spike proteins of SARS-CoV-2. This approach has proven instrumental in bolstering virus-binding affinity on the LFAs. Our findings indicate high LFA sensitivity, enabling the detection of viral loads ranging from 103 to 108 viral copies/mL. This notable sensitivity is maintained across various SARS-CoV-2 viral strains, obviating the need for intricate sample preparation protocols. The significance of this heightened sensitivity lies in the crucial role played by the designer DNA nanostructure, which facilitates the detection of extremely low levels of viral loads. This not only enhances the overall reliability of self-testing but also reduces the likelihood of false-negative results, especially in cases of low viral load within patient samples.

Development of a Paper-based Hematocrit Test and a Lateral Flow Assay to Detect Critical Fibrinogen Concentrations Using a Bottom-Up Pyramid Workflow Approach

Fibrinogen is a coagulation factor in human blood and the first one to reach critical levels in major bleeding. Hypofibrinogenemia (a too low fibrinogen concentration in blood) poses great challenges to first responders, clinicians, and healthcare providers since it represents a risk factor for exsanguination and massive transfusion requirements. Thus, the rapid assessment of the fibrinogen concentration at the point of care has gained considerable importance in preventing and managing major blood loss. However, in whole blood measurements, hematocrit variations affect the amount (volume fraction) of plasma that passes the detection zone. In an attempt to accurately determine realistic critical levels of fibrinogen (<1.5 mg/mL) in patients needing immediate treatment and medical interventions, we have developed novel diagnostic systems capable of estimating hematocrit and critical fibrinogen concentrations. A lateral flow assay (LFA) for the detection of fibrinogen has been developed by establishing a workflow employing rapid characterization methods to streamline LFA development. The integration of two detection lines enables (i) the identification of fibrinogen (first line) present in the sample and (ii) the determination of the clinically critical fibrinogen concentrations below 1.5 mg/mL (second line). Furthermore, the paper-based separation of blood cells from plasma provides a semiquantitative estimate of the hematocrit by analyzing the fractions. Initial validation of the point-of-care (PoC) hematocrit test revealed good comparability to a standard laboratory method. The developed diagnostic systems have the ability to accelerate decision-making in cases with major bleeding.

Serodiagnosis of multiple cancers using an extracellular protein kinase A autoantibody-based lateral flow platform

Extracellular protein kinase A autoantibody (ECPKA-AutoAb) has been suggested as a universal cancer biomarker due to its higher amounts in serum of several types of cancer patients than that of normal individuals. Herein, we first developed a lateral flow immunoassay (LFIA) tool, using a sandwich format, toward ECPKA-AutoAb in human serum. For this format, 3G2 as a capture antibody was identified using hybridoma technique and a series of screenings where it showed superior capacity to recognize Enzo PKA catalytic subunit alpha (Cα), compared to other PKA antibodies and antigens. Using these components, we performed sandwich ELISA toward a mimic and real sample of ECPKA-AutoAb. As per the results, limit of detection (LOD) was found to be 135 ng/mL and ECPKA-AutoAb levels were higher in various cancer patients than in normal individuals like previous studies. Based on these results, we applied this sandwich format into LFIA tool and found that the LOD of the fabricated LFIA tool showed about 3.8 ng/mL using spiked PKA-Ab, which is significantly improved compared to the LOD of sandwich ELISA. Also, the developed LFIA tool demonstrated a remarkable ability to detect significant differences in ECPKA-AutoAb levels between normal and cancer patients within 15 min, showing a potential for point-of-care (PoC) detection. One interesting point is that our LFIA strip contains an additional conjugation pad II, named because of its position behind the conjugation pad, in which PKA Cα is dried, enabling a sandwich format.

Recent advances in SERS-based immunochromatographic assay for pathogenic microorganism diagnosis: A review

Infectious diseases caused by bacteria, viruses, fungi, and other pathogenic microorganisms are among the most harmful public health problems in the world, causing tens of millions of deaths and incalculable economic losses every year. The establishment of rapid, simple, and highly sensitive diagnostic methods for pathogenic microorganisms is important for the prevention and control of infectious diseases, guidance of timely treatment, and the reduction of public safety risks. Lateral flow immunoassay (LFA) based on the colorimetric signal of colloidal gold is the most popular point-of-care testing technology at present, but it is limited by poor sensitivity and low throughput and hardly meets the needs of the highly sensitive screening of pathogenic microorganisms. In recent years, the combination of surface-enhanced Raman scattering (SERS) and LFA technology has developed into a novel analytical platform with high sensitivity and multiple detection capabilities and has shown great advantages in the detection of pathogenic microorganisms and infectious diseases. This review summarizes the working principle, design ideas, and application of the existing SERS-based LFA methods in pathogenic microorganism detection and further introduces the effect of new technologies such as Raman signal encoding, magnetic enrichment, novel membrane nanotags, and integrated Raman reading equipment on the performance of SERS-LFA. Finally, the main challenges and the future direction of development in this field of SERS-LFA are discussed.

Electrokinetic focusing of SARS-CoV-2 spike protein via ion concentration polarization in a paper-based lateral flow assay

The COVID-19 pandemic highlighted the importance of designing sensitive and selective point-of-care (POC) diagnostic sensors for early and rapid detection of infection. Paper-based lateral flow assays (LFAs) are easy to use, inexpensive, and rapid, but they lack sensitivity. Preconcentration techniques can improve the sensitivity of LFAs by increasing the local concentration of the analyte before detection. Here, ion concentration polarization (ICP) is used to focus the analyte, SARS-CoV-2 Spike protein (S-protein), directly over a test line composed of angiotensin converting enzyme 2 (ACE2) capture probes. ICP is the enrichment and depletion of electrolyte ions at opposing ends of an ion-selective membrane under a voltage bias. The ion depleted zone (IDZ) establishes a steep gradient in electric field strength along its boundary. Enrichment of charged species (such as a biomolecule analyte) occurs at an axial location along this electric field gradient in the presence of a fluid flow that counteracts migration of those species - a phenomenon called ICP focusing. In this paper, running buffer composition and pretreatment solutions for ICP focusing in a paper-based LFA are evaluated, and the method of voltage application for ICP-enrichment is optimized. With a power consumption of 1.8 mW, S-protein is concentrated by a factor of 21-fold, leading to a 2.9-fold increase in the signal from the LFA compared to a LFA without ICP-enrichment. The described ICP-enhanced LFA is significant because the preconcentration strategy is amenable to POC applications and can be applied to existing LFAs for improvement in sensitivity.

Deep Learning-Enabled Multiplexed Point-of-Care Sensor using a Paper-Based Fluorescence Vertical Flow Assay

Multiplexed computational sensing with a point-of-care serodiagnosis assay to simultaneously quantify three biomarkers of acute cardiac injury is demonstrated. This point-of-care sensor includes a paper-based fluorescence vertical flow assay (fxVFA) processed by a low-cost mobile reader, which quantifies the target biomarkers through trained neural networks, all within <15 min of test time using 50 µL of serum sample per patient. This fxVFA platform is validated using human serum samples to quantify three cardiac biomarkers, i.e., myoglobin, creatine kinase-MB, and heart-type fatty acid binding protein, achieving less than 0.52 ng mL-1 limit-of-detection for all three biomarkers with minimal cross-reactivity. Biomarker concentration quantification using the fxVFA that is coupled to neural network-based inference is blindly tested using 46 individually activated cartridges, which shows a high correlation with the ground truth concentrations for all three biomarkers achieving >0.9 linearity and <15% coefficient of variation. The competitive performance of this multiplexed computational fxVFA along with its inexpensive paper-based design and handheld footprint makes it a promising point-of-care sensor platform that can expand access to diagnostics in resource-limited settings.

An Artificial Miniaturized Peroxidase for Signal Amplification in Lateral Flow Immunoassays

Signal amplification strategies are widely used for improving the sensitivity of lateral flow immunoassays (LFiAs). Herein, the artificial miniaturized peroxidase Fe(III)-MimochromeVI*a (FeMC6*a), immobilized on gold nanoparticles (AuNPs), is used as a strategy to obtain catalytic signal amplification in sandwich immunoassays on lateral flow strips. The assay scheme uses AuNPs decorated with the mini-peroxidase FeMC6*a and anti-human-IgG as a detection antibody (dAb), for the detection of human-IgG, as a model analyte. Recognition of the analyte by the capture and detection antibodies is first evidenced by the appearance of a red color in the test line (TL), due to the accumulation of AuNPs. Subsequent addition of 3,3',5,5'-tetramethylbenzidine (TMB) induces an increase of the test line color, due to the TMB being converted into an insoluble colored product, catalyzed by FeMC6*a. This work shows that FeMC6*a acts as an efficient catalyst in paper, increasing the sensitivity of an LFiA up to four times with respect to a conventional LFiA. Furthermore, FeMC6*a achieves lower limits of detection that are found in control experiments where it is replaced with horseradish peroxidase (HRP), its natural counterpart. This study represents a significant proof-of-concept for the development of more sensitive LFiAs, for different analytes, based on properly designed artificial metalloenzymes.

Advancing diagnostic efficacy using a computer vision-assisted lateral flow assay for influenza and SARS-CoV-2 detection

Lateral flow assays (LFAs) have emerged as indispensable tools for point-of-care testing during the pandemic era. However, the interpretation of results through unassisted visual inspection by untrained individuals poses inherent limitations. In our study, we propose a novel approach that combines computer vision (CV) and lightweight machine learning (ML) to overcome these limitations and significantly enhance the performance of LFAs. By incorporating CV-assisted analysis into the LFA assay, we achieved a remarkable three-fold improvement in analytical sensitivity for detecting Influenza A and for SARS-CoV-2 detection. The obtained R2 values reached approximately 0.95, respectively, demonstrating the effectiveness of our approach. Moreover, the integration of CV techniques with LFAs resulted in a substantial amplification of the colorimetric signal specifically for COVID-19 positive patient samples. Our proposed approach, which incorporates a simple machine learning algorithm, provides substantial enhancements in assay sensitivity, improving diagnostic efficacy and accessibility of point-of-care testing without requiring significant additional resources. Moreover, the simplicity of the machine learning algorithm enables its standalone use on a mobile phone, further enhancing its practicality for point-of-care testing.

Enhancing the Sensitivity of Lateral Flow Assay with Europium Nanoparticles for Accurate Human IgG Quantification

Accurate quantification of immunoglobulin G (IgG) levels is vital for understanding immune status and diagnosing various medical conditions. Lateral flow assays (LFAs) offer rapid and convenient diagnostic tools, but their sensitivity has been a limitation. Our research introduces a refined method incorporating europium nanoparticles, enhancing both sensitivity and accuracy of LFAs in human IgG measurement. Utilizing a unique sandwich format, carboxylate-modified polystyrene Eu (III) chelate microparticles (CM-EUs) acted as the primary reporters. The concentrations of both detection and capture antibodies on the strip were optimized to bolster the LFA's quantitative performance. The subsequent calibration curve between the IgG concentration and the measured intensity ratio (VR) established the linearity and analytical sensitivity of our method with a high correlation coefficient (r = 0.99) and an impressively low limit of detection (LoD = 0.04 ng/mL). Our precision assessment, segmented into intra-assay and inter-assay evaluations, showcases the method's consistency and reproducibility. The LFA assay's stability was established by demonstrating its resistance to degradation and affirming its potential for extended storage without a dip in performance. The study's findings underscore the potential of this method to contribute to diagnostic medicine and improve patient care.

PNA-Pdx: Versatile Peptide Nucleic Acid-Based Detection of Nucleic Acids and SNPs

Monitoring diseases caused by pathogens or by mutations in DNA sequences requires accurate, rapid, and sensitive tools to detect specific nucleic acid sequences. Here, we describe a new peptide nucleic acid (PNA)-based nucleic acid detection toolkit, termed PNA-powered diagnostics (PNA-Pdx). PNA-Pdx employs PNA probes that bind specifically to a target and are then detected in lateral flow assays. This can precisely detect a specific pathogen or genotype genomic sequence. PNA probes can also be designed to invade double-stranded DNAs (dsDNAs) to produce single-stranded DNAs for precise CRISPR-Cas12b-based detection of genomic SNPs without requiring the protospacer-adjacent motif (PAM), as Cas12b requires PAM sequences only for dsDNA targets. PNA-Pdx identified target nucleic acid sequences at concentrations as low as 2 copies/μL and precisely detected the SARS-CoV-2 genome in clinical samples in 40 min. Furthermore, the specific dsDNA invasion by the PNA coupled with CRISPR-Cas12b precisely detected genomic SNPs without PAM restriction. Overall, PNA-Pdx provides a novel toolkit for nucleic acid and SNP detection as well as highlights the benefits of engineering PNA probes for detecting nucleic acids.

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.

Post-Assay Chemical Enhancement for Highly Sensitive Lateral Flow Immunoassays: A Critical Review

Lateral flow immunoassay (LFIA) has found a broad application for testing in point-of-care (POC) settings. LFIA is performed using test strips-fully integrated multimembrane assemblies containing all reagents for assay performance. Migration of liquid sample along the test strip initiates the formation of labeled immunocomplexes, which are detected visually or instrumentally. The tradeoff of LFIA's rapidity and user-friendliness is its relatively low sensitivity (high limit of detection), which restricts its applicability for detecting low-abundant targets. An increase in LFIA's sensitivity has attracted many efforts and is often considered one of the primary directions in developing immunochemical POC assays. Post-assay enhancements based on chemical reactions facilitate high sensitivity. In this critical review, we explain the performance of post-assay chemical enhancements, discuss their advantages, limitations, compared limit of detection (LOD) improvements, and required time for the enhancement procedures. We raise concerns about the performance of enhanced LFIA and discuss the bottlenecks in the existing experiments. Finally, we suggest the experimental workflow for step-by-step development and validation of enhanced LFIA. This review summarizes the state-of-art of LFIA with chemical enhancement, offers ways to overcome existing limitations, and discusses future outlooks for highly sensitive testing in POC conditions.

Hybrid polymer dot-magnetic nanoparticle based immunoassay for dual-mode multiplexed detection of two mycotoxins

We designed polymer dot-magnetic nanoparticle nanohybrids for signal enhancement in a test strip platform. Besides, the multicolor emissions of the Pdots embed multiplexing ability for this test strip. Two mycotoxins, aflatoxin B1 and zearalenone, were tested with the determined limits of detection of 2.15 ng mL-1 and 4.87 ng mL-1, respectively.

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.

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.

An improved up-conversion nanoparticles-based immunochromatographic assay for rapid detection of zearalenone in cereals

A novel improved up-conversion nanoparticles-based immunochromatographic assay (IUCNPs-ICA) was developed for the detection of zearalenone (ZEN). Lu³⁺-doped UCNPs were synthesized using the solvothermal method, and the UCNPs doped with 30 % Lu³⁺ displayed optimal optical properties. The IUCNPs-ICA was subsequently developed for the detection of ZEN in cereals under optimized conditions. The detection time and limit of detection (LOD) were 10 min and 0.1 μg/L, respectively. Moreover, a good linear relationship was observed from 0 to 100 μg/L ZEN (r² = 0.9946) and high specificity for other mycotoxins. LODs in spiked maize and wheat reached 0.16 μg/kg, and recovery rates were 82.11-100.76 % and 79.64-98.51 %. There was good consistency between the results of IUCNPs-ICA, colloidal gold-ICA, and high-performance liquid chromatography (HPLC) in the detection of natural cereal samples. The collective results support the utility of IUCNPs-ICA as a reliable on-site screening method for ZEN residue analysis in various cereals.

A review of rapid food safety testing: using lateral flow assay platform to detect foodborne pathogens

The detrimental impact of foodborne pathogens on human health makes food safety a major concern at all levels of production. Conventional methods to detect foodborne pathogens, such as live culture, high-performance liquid chromatography, and molecular techniques, are relatively tedious, time-consuming, laborious, and expensive, which hinders their use for on-site applications. Recurrent outbreaks of foodborne illness have heightened the demand for rapid and simple technologies for detection of foodborne pathogens. Recently, Lateral flow assays (LFA) have drawn attention because of their ability to detect pathogens rapidly, cheaply, and on-site. Here, we reviewed the latest developments in LFAs to detect various foodborne pathogens in food samples, giving special attention to how reporters and labels have improved LFA performance. We also discussed different approaches to improve LFA sensitivity and specificity. Most importantly, due to the lack of studies on LFAs for the detection of viral foodborne pathogens in food samples, we summarized our recent research on developing LFAs for the detection of viral foodborne pathogens. Finally, we highlighted the main challenges for further development of LFA platforms. In summary, with continuing improvements, LFAs may soon offer excellent performance at point-of-care that is competitive with laboratory techniques while retaining a rapid format.

Rapid and sensitive detection of E. coli O157:H7 by lateral flow immunoassay and silver enhancement

The aim of this study was to develop a sensitive lateral flow immunoassay (LFIA) for the rapid detection of Escherichia coli (E. coli) O157:H7, a pathogen contributor to diseases and fatalities worldwide. Au nanoparticles with high stability, uniform size, and shape were synthesized and coated with heterobifunctional PEG polymer with carboxyl groups, and they were bioconjugated to be used as label in sandwich-LFIA. Then, a silver enhancement strategy was developed as an accessible, rapid, and cost-effective approach for signal amplification to reduce the limit of detection (LOD). The optimal results were achieved when a solution of silver nitrate and hydroquinone/citrate buffer was added to the strips for 4 min. This led to a decrease in the visual LOD from 2 × 10⁶ (CFU mL^-1) to 2 × 10³ (CFU mL^-1), resulting in a threefold improvement in sensitivity compared to the conventional LFIA system. The specificity of the system was evaluated by using non-target bacteria (E. coli BL21 and E. coli T515) and its reliability was determined by testing commercial food samples (milk, tap water, and orange juice), demonstrating its effectiveness for quickly detecting pathogenic bacteria in food products.

SERS immuno- and apta-assays in biosensing/bio-detection: Performance comparison, clinical applications, challenges

Surface Enhanced Raman Spectroscopy is increasingly used as a sensitive bioanalytical tool for detection of variety of analytes ranging from viruses and bacteria to cancer biomarkers and toxins, etc. This comprehensive review describes principles of operation and compares the performance of immunoassays and aptamer assays with Surface Enhanced Raman scattering (SERS) detection to each other and to some other bioassay methods, including ELISA and fluorescence assays. Both immuno- and aptamer-based assays are categorized into assay on solid substrates, assays with magnetic nanoparticles and assays in laminar flow or/and strip assays. The best performing and recent examples of assays in each category are described in the text and illustrated in the figures. The average performance, particularly, limit of detection (LOD) for each of those methods reflected in 9 tables of the manuscript and average LODs are calculated and compared. We found out that, on average, there is some advantage in terms of LOD for SERS immunoassays (0.5 pM median LOD of 88 papers) vs SERS aptamer-based assays (1.7 pM median LOD of 51 papers). We also tabulated and analyzed the clinical performance of SERS immune and aptamer assays, where selectivity, specificity, and accuracy are reported, we summarized the best examples. We also reviewed challenges to SERS bioassay performance and real-life application, including non-specific protein binding, nanoparticle aggregation, limited nanotag stability, sometimes, relatively long time to results, etc. The proposed solutions to those challenges are also discussed in the review. Overall, this review may be interesting not only to bioanalytical chemist, but to medical and life science researchers who are interested in improvement of bioanalyte detection and diagnostics.

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.

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.

Enhanced Lateral Flow Immunoassay with Double Competition and Two Kinds of Nanoparticles Conjugates for Control of Insecticide Imidacloprid in Honey

Finding optimal conditions for competitive lateral flow immunoassay is a controversial task. The content of specific antibodies labeled by nanoparticles should be simultaneously high to reach intense signals and low to register an influence on the signals for minimal concentrations of the target analyte. We propose to use two kinds of complexes of gold nanoparticles in the assay, with antigen-protein conjugates and with specific antibodies. The first complex interacts both with immobilized antibodies in the test zone and with antibodies on the surface of the second complex. In this assay, the coloration is enhanced by the binding of two-colored preparations in the test zone, whereas the antigen in the sample inhibits both the binding of the first conjugate with the immobilized antibodies and with the second conjugate. This approach is realized for the detection of insecticide imidacloprid (IMD), an important toxic contaminant connected with the recent global death of bees. The proposed technique expands the working range of the assay, that is, in accordance with its theoretical analysis. The reliable change of coloration intensity is achieved for a 2.3-times-lower concentration of the analyte. The limit of IMD detection is 0.13 ng/mL for tested solutions and 1.2 µg/kg for initial honey samples. The combination of two conjugates doubles the coloration in the absence of the analyte. The developed lateral flow immunoassay is applicable for five-fold-diluted honey samples without extraction, does not require additional stages (all reagents are pre-applied to the test strip), and is implemented in 10 min.