Lateral flow assays: Principles, designs and labels

Multimodal triple-mode probe with colorimetric-fluorescence-SERS (CFSERS) for sensitive and quantitative detection of C-reactive protein in clinical diagnostics

Chronic inflammation remains a major global health concern, necessitating the development of advanced tools for continuous, precise monitoring. This study introduces a novel, clinically impactful triple-mode probe that integrates colorimetric, fluorescence, and surface-enhanced Raman scattering (SERS) signals, offering unparalleled multimodal detection capabilities. The probe's design leverages europium chelate-doped polystyrene nanoparticles (ECNPs), ensuring minimal signal cross-interference through a long Stokes shift. A key innovation is the development of a multimodal mapping algorithm that seamlessly integrates these optical signals, providing a sensitive and robust platform for biomarker detection with broad dynamic ranges. The probe's clinical relevance is demonstrated by its application in lateral flow assays (LFAs) for detecting C-reactive protein (CRP) levels, achieving a detection limit of 6.31 ng/mL and dynamic ranges from 23.13 to 2000 ng/mL, significantly outperforming single-mode detection methods. In clinical validation using urine samples from 31 patients, the triple-mode LFA showed excellent correlation (0.9377) and agreement (93.55 %) with gold standard enzyme-linked immunosorbent assay (ELISA) results. This demonstrates that the proposed multimodal platform offers a highly sensitive, cost-effective, and versatile tool for monitoring inflammation and other disease biomarkers, with substantial potential for clinical applications in diagnostics and disease management.

Rapid and sensitive detection of wood smoke exposure biomarkers using europium fluorescent nanoparticle label/lateral flow immunoassay

Exposure to wood smoke is associated with various adverse health problems. Biomonitoring of smoke exposure-associated biomarkers provides accurate measurements of personally absorbed doses. As a specific metabolite of benzene, the quantitative measurement of S-phenylmercapturic acid (S-PMA) plays a vital role in evaluating human exposure to wood smoke. In this study, we developed an efficient lateral flow immunoassay (LFIA) approach for accurately and rapidly measuring S-PMA levels. Europium chelate nanoparticles (EuNPs) conjugated with purified polyclonal sheep anti-S-PMA antibodies were employed as the fluorescent detection probe. This work is based on a competitive immunoassay, where the target S-PMA competes with the immobilized antigen on the test lines for the limited antigen-binding sites on EuNP-conjugated antibodies. Due to this competition, the fluorescent intensity of the EuNPs is inversely proportional to the concentration of the target S-PMA in the sample, enabling quantitative measurement. Owing to the large Stokes shift, superior fluorescent brightness, and saturation of the EuNPs, S-PMA levels can be measured with a limit of detection of 0.32 ng/mL, a detectable range of 0.10-30 ng/mL, and a linear detection range of 0.25-30 ng/mL under optimized conditions. Stability testing revealed that the LFIA strips can be stored at room temperature for up to one year while maintaining excellent detection performance for S-PMA. These results demonstrate that the EuNP-based LFIA is a promising tool for accurate preclinical and point-of-care evaluation of wood smoke exposure. A major advantage of this approach is its ability to accurately analyze smoke biomarkers at anticipated low concentrations. The sensor system allows low-cost, rapid, and on-site data collection and quantification of wood smoke exposure.

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.

A comprehensive review of competitive lateral flow assays over the past decade

Competitive lateral flow assays (LFAs) provide a versatile and cost-effective platform for detecting a wide range of molecular targets across fields such as healthcare, food safety, and environmental monitoring, particularly for small analytes or single epitopes that lack suitable bioreceptor pairs. However, the interpretation of competitive LFAs can be challenging due to their counterintuitive output, where the absence of a test line signifies the presence of the target. In this review, we present a comprehensive overview of the fundamental strategies underlying competitive LFAs, explore the mathematical models that quantify assay performance, and outline the critical parameters involved in their design and optimization. We further highlight notable applications and discuss methods to enhance the user experience through improved result interpretation and user-centric design. By consolidating current knowledge and best practices, this work will serve as a valuable reference for researchers and developers seeking to refine the usability, reliability, and effectiveness of competitive LFAs.

Chemical Sensors and Biosensors for Point-of-Care Testing of Pets: Opportunities for Individualized Diagnostics of Companion Animals

Point-of-care testing (POCT) is recognized as one of the most disruptive medical technologies for rapid and decentralized diagnostics. Successful commercial examples include portable glucose meters, pregnancy tests, and COVID-19 self-tests. However, compared to advancements in human healthcare, POCT technologies for companion animals (pets) remain significantly underdeveloped. This Review explores the latest advancements in pet POCT and examines the challenges and opportunities in the field for individualized diagnostics of cats and dogs. The most frequent diseases and their respective biomarkers in blood, urine, and saliva are discussed. We examine key strategies for developing the next-generation POCT devices by harnessing the potential of selective (bio)receptors and high-performing transducers such as lateral flow tests and electrochemical (bio)sensors. We also present the most recent research initiatives and the successful commercial pet POCT technologies. We discuss future trends in the field, such the role of biomarker discovery and development of wearable, implantable, and breath sensors. We believe that advancing pet POCT technologies benefits not only animals but also humans and the environment, supporting the One Health approach.

A template-free one-step synthesis of trimetallic nano-triangular structures significantly enhances the sensitivity of lateral flow immunoassays for acetamiprid detection

BACKGROUND

Acetamiprid (ACE), a commonly used insecticide, is widely applied in agricultural practices to control pests. However, its potential to leave residues in crops has raised significant concerns due to the associated risks to human health through food consumption. This has made the rapid, accurate, and on-site detection of ACE residues a pressing issue in the realm of global food safety. In the present study, we developed an innovative Platinum-Copper-Nickel Alloy Nano-Triangular Structure (PCNATS) to facilitate the rapid detection of ACE using a competitive assay. The PCNATS, featuring a high specific surface area and a complex three-dimensional structure, were conjugated with anti-ACE monoclonal antibodies to create advanced nanoprobes. ELISA results demonstrated that the PCNATS significantly improved the utilization efficiency of monoclonal antibodies, leading to enhanced sensing performance.

RESULTS

The PCNATS-based lateral flow immunoassay (PCNATS-LFIA) system displayed high sensitivity and accuracy, capable of quantitatively detecting ACE within 10 min. This method exhibited a limit of detection (LOD) of 3.6 ng/kg and a broad detection range from 0.05 pg/mL to 4 μg/mL. Compared to traditional gold nanoparticle-based lateral flow immunoassays (AuNPs-LFIA), the PCNATS-LFIA demonstrated a 1000-fold improvement in sensitivity. Furthermore, the assay showed strong correlation with the fitted standard curve when applied to real celery and papaya samples, achieving a satisfactory recovery rate ranging from 92.9 % to 109.9 % and 101.04 % to 115.76 %, with relative standard deviations (RSD) between 1.68 % to 7.73 % and 1.37 % to 3.02 %.

SIGNIFICANCE

Therefore, the PCNATS-LFIA system offers a portable, efficient, and cost-effective solution for the rapid, on-site detection of ACE residues in agricultural products.

Exploring the diagnostic landscape: Portable aptasensors in point-of-care testing

Aptamers, discovered in the 1990s, have marked a significant milestone in the fields of therapeutics and diagnostics. This review provides a comprehensive survey of aptamers, focusing on their diagnostic applications. It especially encapsulates a decade of aptamer, encompassing research, patents, and market trends. The unique properties and inherent stability of aptamers are discussed, highlighting their potential for various clinical applications. It goes on to introduce biosensor design, emphasizing the advantages of aptamers over antibodies as conventional molecular recognition interface. The operation and design of aptasensors are examined, with a focus on single- and dual-site binding configurations and their respective recognition modes. Paper-based sensors are highlighted as cost-effective, user-friendly alternatives that are gaining widespread adoption, particularly in point-of-care platforms.

Nanozymes-Mediated Lateral Flow Assays for the Detection of Pathogenic Microorganisms and Toxins: A Review from Synthesis to Application

In today's context, there is an increasing awareness among individuals regarding the importance of healthy and safe food consumption. Consequently, there is a growing demand for food products that are safeguarded against the detrimental effects of pathogens and harmful microbial metabolites. Actually, these organisms and their associated toxins pose a significant risk to food safety and are recognized as a critical threat to human health because of their capacity to induce foodborne infections and intoxications. Consequently, in order to address such challenges, it is imperative to enhance recognizing systems comprising bio/nanosensors for detections, which are trustworthy, quick, beneficial and economical. The advent of digital color imaging technology has led to the gradual establishment of lateral flow assays (LFAs) as one of the most significant sensors for point-of-care applications. Unlike colloidal gold nanoparticles (AuNPs), nanozymes offer enhanced color intensity through target-induced precise enrichment of nanozymes at the test line. Additionally, they amplify the color signal by facilitating the catalytic oxidation of colorless substrates into colored products. This dual functionality presents significant potential for the development of well-organized LFAs. In light of this, significant attempts are dedicated to the development of nanozyme-based LFAs. This review aims to outline recent advancements in the synthesis and design of nanozymes with varying compositions that exhibit distinct activities, as well as the structure and employment of nanozyme-based LFAs for the detection of pathogenic microorganisms and their associated toxins. Furthermore, the existing challenges and prospective development directions are outlined to assist readers in advancing the nanozyme-based LFAs performance.

Stacking paper sheets into multi-purpose quick response sensing code with built-in nitrocellulose-membrane-free lateral flow assay for detecting tetracycline in food samples

Lateral flow assays (LFAs) have found extensive applications in food safety and quality monitoring. Now, smartphone technology is redefining how tests are conducted at the point of use. At the same time, quick response (QR) codes enhance digital connectivity for information transmission, data collection, and response linkage. Here, we present a versatile QR code conversion strategy for LFAs that streamlines detection and response workflows, ensuring high user-friendliness and minimal operational requirements for on-site food safety detection. It combines visual cues from test and control zones with QR code generation into a multifunctional smartphone-based scanning and detection system. The proposed QR-coded LFA utilizes low-cost filter paper instead of nitrocellulose membrane and exhibits its applicability and flexibility in sandwich/competitive/multiplexed formats and various scenarios. As a demonstration, the QR-coded LFA, coupled with a companion mobile application, was applied to simultaneously determine tetracycline in food samples and perform the QR code functions.

New Frontiers for the Early Diagnosis of Cancer: Screening miRNAs Through the Lateral Flow Assay Method

MicroRNAs (miRNAs), which circulate in the serum and plasma, play a role in several biological processes, and their levels in body fluids are associated with the pathogenesis of various diseases, including different types of cancer. For this reason, miRNAs are considered promising candidates as biomarkers for diagnostic purposes, enabling the early detection of pathological onset and monitoring drug responses during therapy. However, current methods for miRNA quantification, such as northern blotting, isothermal amplification, RT-PCR, microarrays, and next-generation sequencing, are limited by their reliance on centralized laboratories, high costs, and the need for specialized personnel. Consequently, the development of sensitive, simple, and one-step analytical techniques for miRNA detection is highly desirable, particularly given the importance of early diagnosis and prompt treatment in cases of cancer. Lateral flow assays (LFAs) are among the most attractive point-of-care (POC) devices for healthcare applications. These systems allow for the rapid and straightforward detection of analytes using low-cost setups that are accessible to a wide audience. This review focuses on LFA-based methods for detecting and quantifying miRNAs associated with the diagnosis of various cancers, with particular emphasis on sensitivity enhancements achieved through the application of different labels and detection systems. Early, non-invasive detection of these diseases through the quantification of tailored biomarkers can significantly reduce mortality, improve survival rates, and lower treatment costs.

A New Chemiluminescence-Based Rapid Diagnostic Testing Platform with Sequential Dual-Flow Strips for Cardiac Troponin I (cTnI)

Although the most commonly used method for enhancing a limit of detection (LoD) in immunoassay is adopting chemiluminescence (CL), the liquid form of CL substrates has hindered its use for rapid diagnostic testing (RDT). In order to use the CL-based immunoassay in RDT with minimal user intervention, the liquid CL substrate should be converted to a dry form. In addition, a new RDT platform that is able to perform two sequential flows needs to be developed for the sequential flow control of the CL substrate. In this work, we have successfully developed a new dry form of CL substrate on the strip using a lyophilization process, as well as new lateral flow strips using an additional membrane pad for a time delay to achieve the desired sequential dual flows. Thus, on the dual-flow RDT strips, first the detection antibody conjugated with an enzyme flows over the test and control lines, and then the reconstituted CL substrate flows later. A hydrophilic PVDF membrane was selected as a pad material for the time delay to achieve the sequential dual flows through two flow paths, and flow introduction timing was functionally controlled to secure the time delay of approximately 5 minutes desired between the two flows. A CL-based cardiac troponin I (cTnI) assay was successfully performed on the new dual-flow RDT platform with a sample volume of 120 μL, achieving a LoD of 100 pg/mL. The achieved LoD is better than those possible with most of the currently available RDTs on the market. The new CL-based RDT platform with the capability of dual flows developed in this work can be used for numerous other immunodiagnostic platforms which need further high-sensitivity detection, envisaging a new RDT platform for point-of-care testing with further quantitative analysis.

Plasmonics-Enhanced Dual-Modal Colorimetric and Photothermal Lateral Flow Immunoassay Using Gold Nanocages

Lateral flow immunoassays (LFIA) are widely recognized as cost-effective point-of-care diagnostic tools (POCT) for infectious disease diagnosis. Despite their widespread use, traditional colorimetric LFIAs, which rely on gold nanospheres (GNP), are constrained by a limited sensitivity. To overcome this challenge, we have engineered gold nanocages (GNCs) with optimized core-to-shell morphologies, achieving significant amplification of both colorimetric and photothermal LFIA readout signals. The distinctive morphology of GNCs, featuring adjustable core-to-shell gap thicknesses, enables fine-tuning of the localized surface plasmon resonance (LSPR) peak across a broad spectral range from 600 to 1200 nm. Among the GNC morphologies evaluated, the optimized GNC (GNC-4), characterized by its larger size and maximal core-to-shell gap thickness, exhibited superior color brightness and enhanced photothermal efficiency compared to other GNC morphologies and traditional GNP. The enhanced performance of GNC-4 enabled the detection of influenza A (H1N1), used as the model analyte, achieving a limit of detection (LOD) of 1.8 ng/mL via colorimetric analysis and 1.51 pg/mL using photothermal LFIA. Compared to traditional GNP-based colorimetric LFIA detection, the colorimetric sensitivity of the GNC-4-based LFIA was enhanced by 7-fold, while the photothermal detection sensitivity showed an improvement of over 8000-fold. By incorporating a portable smartphone-based photothermal LFIA platform, our dual-modal LFIA exhibits high sensitivity, practicality in detecting H1N1 in spiked saliva samples, and long-term stability over five months, making it a promising tool for infectious disease detection and a potential model for diagnosing other pathogens.

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.

Design of immunoassay based biosensor platforms for SARS-CoV-2 detection using highly specific monoclonal antibodies

The global expand of SARS-CoV-2 has highlighted the importance of early and rapid detection to control the spread of a pandemic. In this study, specific and high-affinity monoclonal antibodies (mAbs) were developed against the conserved nucleocapsid protein of the virus among variants. Appropriate antibody pairs were selected to develop a lateral flow immunoassay (LFIA) and an unconventional application of an amperometric biosensor using unmodified screen-printed electrodes and external magnetic bead preparation. In the study, the LFIA we developed detected the SARS-CoV-2 virus at 104 PFU/mL, while the amperometric biosensor enabled sensitive detection of inactivated SARS-CoV-2 with an LOD of 5.5 PFU/mL. After validating the developed systems, it is considered that the mAbs we have obtained will enable the sensitive and selective detection of SARS-CoV-2 in LFIA and amperometric immunosensor platforms for clinical diagnosis.

Aspergillus Mycotoxins: The Major Food Contaminants

Mycotoxins, a category of fungal secondary metabolites, frequently contaminate food products and pose a severe threat to human health. Aspergillus, a genus of fungi, is capable of producing mycotoxins, with aflatoxins (AFs) and ochratoxins being its principal types. Aspergillus mycotoxins can contaminate a wide range of crops and their derivatives, such as maize, wheat, rice, minor cereals, and peanuts, thereby threatening food and feed safety. In the paper, the related biosynthesis genes and multifaceted biosynthesis pathways of these mycotoxins are first discussed in detail, and elucidated several global regulators, including growth conditions, oxidative stress, and cell signal. Furthermore, how global shifts in temperature and water availability, driven by climate change (including rising temperatures, increased heavy rainfall frequency, prolonged droughts, and elevated carbon dioxide levels), are key determinants of Aspergillus proliferation and mycotoxin production are explored. Finally, to safeguard animal and human health from the detrimental impacts of Aspergillus mycotoxins, the effective and convenient analytical techniques and management strategies for the detection and prevention of contamination are analyzed. Overall, this review provides effective detection techniques and promising solutions to the global contamination of food with Aspergillus mycotoxins, which is of great significance to ensuring food security and protecting people's lives and health.

Nanolabels for biosensors based on lateral flow immunoassays

The COVID-19 outbreak was an important turning point in the development of a new generation of biosensing technologies. The synergistic combination of an immunochromatographic test (lateral flow immunoassays, LFIA) and signal transducers provides enhanced sensitivity and the ability to quantify in the rapid tests. This is possible due to the variety of nanoparticles that can be used as reporter labels. In this review, we first present an overview on the principles of a LFIA and its different formats. We analyze cutting-edge work on these platforms based on different types of nanoparticles used as labels and on the highly sensitive transducers to which they can be coupled. The works discussed herein have a beneficial impact on the fields of clinical analysis, food safety or environmental control, thus highlighting the relevance of the biosensors. Last, we provide insights into the barriers that need to be overcome when designing laboratory prototypes accessible to the society.

Metal Ion-Based Chemical Coordination Amplification: A Chromophore In Situ Deposition Strategy for Visual Sensitivity-Enhanced Lateral Flow Immunochromatography Assays

Traditional lateral flow immunochromatography assays (LFIAs) have faced low sensitivity for trace detection due to the lack of colorimetric brightness. The current strategies to improve sensitivity commonly have the disadvantages of an uncontrollable enhancement process or high background interference, leading to huge obstacles for signal readout. Herein, an in situ metal ion-based chemical coordination amplification (MICCA) strategy has been reported. Metal ion clusters on metal-organic frameworks could coordinate with chromophores to produce colored complexes for visual signal enhancement. A Zr-based metal AIEgen framework (MAF) loaded with Prussian blue was chosen as the dual-mode signal tag for colorimetric and fluorescent readout. MAF could be employed as a grafting substrate to in situ deposit chromophores through the coordination with Zr4+ clusters and arsenazo III. The process of MICCA was in situ, controllable, and free of background interference. For target cancer biomarker alpha-fetoprotein (AFP), the limit of detection (LOD) by the naked eye was 25 ng/mL, and the LODs of MICCA and fluorescence were 5 ng/mL, which was 5-fold decreased. Significantly, MICCA-LFIA could effectively differentiate between AFP-positive and AFP-negative clinical serum samples. The quantitative results were highly consistent with clinical results (R2 = 0.9927). This work explored the application of metal ion-based chemical coordination reactions in signal amplification strategies and provided ideas for high-sensitivity LFIA development.

Recent advances in SERS assays for detection of multiple extracellular vesicles biomarkers for cancer diagnosis

As the prevalence of cancer is escalating, there is an increased demand for early and sensitive diagnostic tools. A major challenge in early detection is the lack of specific biomarkers, and a readily accessible, sensitive and rapid detection method. To meet these challenges, cancer-derived small extracellular vesicles (sEVs) have been discovered as a new promising cancer biomarker due to the high abundance of sEVs in body fluids and their extensive cargo of biomarkers. Additionally, surface-enhanced Raman scattering (SERS) presents a sensitive, multiplexed, and rapid method that has gained attraction with recent studies showing promising results from patient samples for the multiplex detection of cancer sEVs. Various label-based SERS multiplex assays have been developed in the field of SERS including bead assays, lateral flow immunoassays, microfluidic devices, and artificial intelligence (AI)-based label-free SERS chips, targeting multiple surface proteins to ensure comprehensive multiplex diagnostics. These assays hold promise for enabling early detection, quantification, and subtyping of cancer-derived sEVs for cancer diagnostic applications. This review aims to provide a summary of the recent advances in the field of SERS multiplex assays for detection, quantification, and subtyping of sEVs to facilitate cancer diagnosis. This review further provides unique insights into the use of sEVs as a biomarker and aims to address the issues surrounding their translation from laboratories to clinics.

Colored Cellulose Nanoparticles with High Stability and Easily Modified Surface for Accurate and Sensitive Multiplex Lateral Flow Assay

Decentralized testing using multiplex lateral flow assays (mLFAs) to simultaneously detect multiple analytes can significantly enhance detection efficiency, reduce cost and time, and improve analytic accuracy. However, the challenges, including the monochromatic color of probe particles, interference between different test lines, and reduced specificity and sensitivity, severely hinder mLFAs from wide use. In this study, we prepared polydopamine (PDA)-coated dyed cellulose nanoparticles (dCNPs@P) with tunable colors as the probe for mLFAs. Cellulose nanoparticles (CNPs) were synthesized with uniform spheric shapes and tunable sizes. Dye molecules were loaded on CNPs via a mature industrial dyeing method. The PDA shell provided a reactive surface for facile receptor conjugation and protected the dye from leaking. dCNPs@P displayed a higher signal intensity than gold nanoparticles. They also had higher stability to tolerate salt and varied pH. The dCNP@P-based mLFAs were successfully applied to detect multiple mycotoxins in cereals and determine the levels of inflammatory biomarkers to differentiate between viral and bacterial infections. The tests represented high specificity and accuracy and were more sensitive than the tests using gold nanoparticles. The quantified detection was accessible by measuring the intensities of the colorimetric or photothermal signals. Overall, this study provides a practical system solution for mLFAs based on colored dCNPs@P.

Fluorescent microsphere-based strip for sensitive and quantitative detection of etomidate and metomidate

In this research, we fabricated a sensitive monoclonal antibody (mAb) 2C3 that targeted etomidate (ET) and metomidate (MT) to establish a lateral-flow immunoassay (LFIA) that incorporated fluorescent microsphere sensors, enabling both the qualitative and quantitative detection of ET and MT within 10 min. Analysis indicated that the visual colorimetric values for ET and MT in water samples were 0.3 μg kg-1, respectively, with quantitative detection ranges of 0.08 to 1.31 μg kg-1 and 0.08 to 2.21 μg kg-1, respectively. The visual colorimetric values for ET and MT in urine samples were 0.3 and 1 μg kg-1, respectively, with quantitative detection ranges of 0.12 to 3.13 μg kg-1 and 0.09 to 2.98, respectively, while for ET and MT in serum samples were 3 μg kg-1, with quantitative detection ranges of 0.15 to 21.2 μg kg-1 and 0.08 to 13.8 μg kg-1, respectively. Recovery tests and detection were conducted in water, urine and serum samples, validating the reliability of this method in clinical samples, consistent with those obtained from LC-MS/MS. Collectively, our novel LFIA provides a promising option for rapid on-site detection of ET and MT.

Advancing foodborne pathogen detection: a review of traditional and innovative optical and electrochemical biosensing approaches

Foodborne diseases are a significant cause of morbidity (600 million cases) and mortality (420,000 deaths) worldwide every year and are mainly associated with pathogens. Besides the direct effects on human health, they have relevant concerns related to financial, logistics, and infrastructure for the food and medical industries. The standard pathogen identification techniques usually require a sample enrichment step, plating, isolation, and biochemical tests. This process involves specific facilities, a long-time analysis procedures, and skilled personnel. Conversely, biosensors are an emerging innovative approach to detecting pathogens in real time due to their portability, specificity, sensitivity, and low fabrication costs. These advantages can be achieved from the synergistic work between nanotechnology, materials science, and biotechnology for coupling biomolecules in nano-matrices to enhance biosensing performance. This review highlights recent advancements in electrochemical and optical biosensing techniques for detecting bacteria and viruses. Key properties, such as detection limits, are examined, as they depend on factors like the design of the biorecognition molecule, the type of transducer, the target's characteristics, and matrix interferences. Sensitivity levels reported range from 1 to 1 × 10⁸ CFU/mL, with detection times spanning 10 min to 8 h. Additionally, the review explores innovative approaches, including biosensors capable of distinguishing between live and dead bacteria, multimodal sensing, and the simultaneous detection of multiple foodborne pathogens - emerging trends in biosensor development.

Aptamer and DNAzyme Based Colorimetric Biosensors for Pathogen Detection

The detection of pathogens is critical for preventing and controlling health hazards across clinical, environmental, and food safety sectors. Functional nucleic acids (FNAs), such as aptamers and DNAzymes, have emerged as versatile molecular tools for pathogen detection due to their high specificity and affinity. This review focuses on the in vitro selection of FNAs for pathogens, with emphasis on the selection of aptamers for specific biomarkers and intact pathogens, including bacteria and viruses. Additionally, the selection of DNAzymes for bacterial detection is discussed. The integration of these FNAs into colorimetric biosensors has enabled the development of simple, cost-effective diagnostic platforms. Both non-catalytic and catalytic colorimetric biosensors are explored, including those based on gold nanoparticles, polydiacetylenes, protein enzymes, G-quadruplexes, and nanozymes. These biosensors offer visible detection through color changes, making them ideal for point-of-care diagnostics. The review concludes by highlighting current challenges and future perspectives for advancing FNA-based colorimetric biosensing technologies for pathogen detection.

Quantitative determination of leptin hormone using gold nanoparticle-based lateral flow assay

A lateral flow assay (LFA) has been developed that can be used in point-of-care (PoC) use for the sensitive determination of leptin hormone. The limit of detection value was 0.158 ng/mL and the limit of quantification value was 0.479 ng/mL for leptin hormone. The stability studies showed that the assay response was equal to the initial value even after 6 months. LFA accuracy tests performed in commercial artificial serum samples were compared with the enzyme-linked immunosorbent assay (ELISA). The obtained recovery values between 95 and 110% show that the developed LFA can be used for quantitative determination of leptin hormone. As the result of the study, a fast and disposable assay was developed for the determination of leptin hormone, which can be performed with a small amount of sample in less than 15 min without the need for long-term analysis stages, qualified personnel, expensive equipment and devices.

Novel lateral flow assay to detect H2O2 by utilizing self-biotinylation of G-quadruplex

We herein describe a novel lateral flow assay (LFA) to detect H2O2 by utilizing self-biotinylation of G-quadruplex (G4). In this strategy, the G4 strand promotes the self-biotinylation of G4 itself in the presence of H2O2, which is then allowed to bind to the FAM-labeled complementary detector probe. The resulting biotin-labeled G4/FAM-detector probe complex is captured on the test line, producing a red-colored band during lateral flow readout. Based on this unique approach, we achieved the naked-eye detection of target H2O2 at concentrations as low as 1 μM, with reliable quantification down to 0.388 μM. This method also demonstrated exceptional specificity in distinguishing H2O2 from other non-target molecules. We further verified its versatile applicability by reliably identifying another biomolecule, choline, by coupling with choline oxidase, which generates H₂O₂ during oxidation. This novel LFA strategy holds great promise as a powerful point-of-care testing (POCT) platform for detecting a large spectrum of target biomolecules by employing their corresponding oxidases.

Ultrasensitive Electrochemical Vertical Flow Immunoassay for Rapid and Simultaneous Detection of Interleukin-6 and Procalcitonin

Rapid and multiplexed detection of biomarkers plays an indispensable role in disease diagnosis. Although paper-based lateral flow immunoassays have been widely used in this field, the speediness and throughput are still challenging issues. Herein, an electrochemical vertical flow immunoassay device (eVFID) is fabricated for rapid, ultrasensitive, and multiplexed detection of inflammatory biomarkers. Working electrodes with excellent electrochemical performance and permeability properties were directly fabricated on the nitrocellulose membrane to enable both the vertical flow of the sample solution and electrochemical detection. This vertical configuration can remarkably improve the speediness of the immunoassay and effectively inhibit the cross-talk reactions among immunomolecules, thus allowing rapid and simultaneous detection of multiplexed biomarkers. Furthermore, a signal amplification strategy based on horseradish peroxidase and tetramethylbenzidine was integrated into the eVFID to substantially increase the sensitivity of the electrochemical detection. A low limit of detection of 0.1 and 0.22 pg mL-1 was obtained for two low-abundance inflammatory biomarkers, interleukin-6 (IL-6) and procalcitonin (PCT), respectively. Finally, using a two-channel eVFID, simultaneous detection of IL-6 and PCT in human plasma samples was successfully realized within 5 min. We believe that the eVFID holds great promise for speedy and high-throughput biomarker detection at the point of care.

Isothermal nucleic acid amplification for monitoring hand-foot-and-mouth disease: current status and future implications

With the global prevalence of the hand-foot-and-mouth disease (HFMD) epidemic, the development of reliable point-of-care testing (POCT) is crucial for the timely identification and prevention of outbreaks. Isothermal nucleic acid amplification techniques (INAATs) have attracted much attention because of their high efficiency for rapid diagnosis. In this work, we systematically summarize the current status of INAATs for HFMD and discuss advantages and drawbacks of various INAATs for HFMD. The INAATs for HFMD detection mainly include loop-mediated isothermal amplification (LAMP), simultaneous amplification and testing (SAT), and recombinase polymerase amplification (RPA). Among them, LAMP has excelled in several diagnostic metrics and has made significant progress in the field of POCT. SAT has been effective in overcoming the problem of RNA degradation. RPA is suited for on-site testing due to its rapid amplification rate and low reaction temperature. In addition, this study explores the potential of INAATs in lateral flow strips (LFS) test and microfluidic devices for HFMD. LFS is typically used for qualitative analysis and supports multiple detection. Microfluidics can integrate necessary processes of sample pre-processing, amplification, and signal output, enabling high-throughput qualitative or quantitative detection and demonstrating the potential of monitoring HFMD. We hope the current work will provide insights into INAATs for monitoring HFMD and serve as a reference for the implementation of on-site EV detection for public health.

Screening Methods for Antimicrobial Residues in the Dairy Chain-The Past and the Present

The presence of residues of antimicrobial substances in milk has been an important hygienic and technological parameter of raw milk quality since the 1960s. The presented review focuses on screening methods (microbiological inhibition methods and rapid specific tests) that are used in the control of antimicrobial residues in milk in the context of their historical development up to the present. We briefly explain the principles of the methods and discuss their pros and cons. The aim was to provide both the historical perspective on this topic and provide useful information on screening methods that are currently routinely used for the detection of residues of antimicrobials at farms, in the dairy industry, and in milk quality control laboratories.

Validation of Recombinase Polymerase Amplification with In-House Lateral Flow Assay for mcr-1 Gene Detection of Colistin Resistant Escherichia coli Isolates

BACKGROUND/OBJECTIVES

The emergence of the mobilized colistin resistance 1 (mcr-1) gene, which causes colistin resistance, is a serious concern in animal husbandry, particularly in pigs. Although antibiotic regulations in many countries have prohibited the use of colistin in livestock, the persistence and dissemination of this plasmid-mediated gene require effective and rapid monitoring. Therefore, a rapid, sensitive, and specific method combining recombinase polymerase amplification (RPA) with an in-house lateral flow assay (LFA) for the mcr-1 gene detection was developed.

METHODS

The colistin agar test and broth microdilution were employed to screen 152 E. coli isolates from pig fecal samples of five antibiotic-used farms. The established RPA-in-house LFA was validated with PCR for mcr-1 gene detection.

RESULTS

The RPA-in-house LFA was completed within 35 min (20 min of amplification and 5-15 min on LFA detection) at 37 °C. The sensitivity, specificity, and accuracy were entirely 100% in concordance with PCR results. No cross-reactivity was detected with seven common pathogenic bacteria or other mcr gene variants.

CONCLUSIONS

Therefore, the in-house RPA-LFA serves as a point-of-care testing tool that is rapid, simple, and portable, facilitating effective surveillance of colistin resistance in both veterinary and clinical settings, thereby enhancing health outcomes.

Perspectives in Aptasensor-Based Portable Detection for Biotoxins

Biotoxins are pervasive in food and the environment, posing significant risk to human health. The most effective strategy to mitigate the risk arising from biotoxin exposure is through their specific and sensitive detection. Aptasensors have emerged as pivotal tools, leveraging aptamers as biorecognition elements to transduce the specificity of aptamer-target interactions into quantifiable signals for analytical applications, thereby facilitating the meticulous detection of biotoxins. When integrated with readily portable devices such as lateral flow assays (LFAs), personal glucose meters (PGMs), smartphones, and various meters measuring parameters like pH and pressure, aptasensors have significantly advanced the field of biotoxin monitoring. These commercially available devices enable precise, in situ, and real-time analysis, offering great potential for portable biotoxin detection in food and environmental matrices. This review highlights the recent progress in biotoxin monitoring using portable aptasensors, discussing both their potential applications and the challenges encountered. By addressing these impediments, we anticipate that a portable aptasensor-based detection system will open new avenues in biotoxin monitoring in the future.

Point-of-care testing for early-stage liver cancer diagnosis and personalized medicine: Biomarkers, current technologies and perspectives

Liver cancer is a highly prevalent and lethal form of cancer worldwide. In the absence of early diagnosis, treatment options for this disease are severely restricted. Recent advancements in genomics and bioinformatics have facilitated the discovery of a multitude of novel biomarkers that accurately depict an individual's disease diagnosis, progression, and treatment response. Leveraging these breakthroughs, personalized medicine employs an individual's biomarker profile to enable early detection of liver cancer and inform decisions regarding treatment selection, dosage determination, and prognosis assessment. The current lack of readily applicable, timely, and economically viable tools for biomarker analysis has hindered the incorporation of personalized medicine into regular clinical procedures. Over the past decade, significant advancements have been achieved in the field of molecular point-of-care testing (POCT) and amplification techniques, leading to substantial improvements in the diagnosis of liver cancer and the implementation of precision medicine. Instrument-free PCR technology or plasma PCR technology can shorten the complex procedure of in vitro detection of nucleic acid-based biomarkers. Also, compared to traditional ELISA, various nanomaterials modified with monoclonal antibodies to target proteins for recognition, capture, and detection have improved the efficiency of protein-based biomarker detection. These advances have reduced the time and cost of clinical detection of early-stage hepatocellular carcinoma and improved the efficiency of timely diagnosis and survival of suspected patients while reducing unnecessary testing costs and procedures. This review aims to provide a comprehensive overview of the current and emerging biomarkers employed in the early detection of liver cancer, as well as the advancements in point-of-care molecular testing technology and platforms. The primary objective is to assess their potential in facilitating the implementation of personalized medicine. This review ultimately revealed that the diagnosis of early-stage hepatocellular carcinoma not only requires sensitive biomarkers, but its various modifications and changes during the progression of cirrhosis to early-stage hepatocellular carcinoma will be a greater focus of our attention in the future. The rapid development of POCT has facilitated the opportunity to readily detect liver cancer in the general population in the future, and the integration of multi-pathway multiplexing and intelligent algorithms has improved the sensitivity and accuracy of early liver cancer biomarker detection. It is expected that the integration of point-of-care technology will be instrumental in the widespread adoption of personalized medicine in the foreseeable future.

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.

Advances in nucleic acid aptamer-based detection of respiratory virus and bacteria: a mini review

Respiratory pathogens infecting the human respiratory system are characterized by their diversity, high infectivity, rapid transmission, and acute onset. Traditional detection methods are time-consuming, have low sensitivity, and lack specificity, failing to meet the needs of rapid clinical diagnosis. Nucleic acid aptamers, as an emerging and innovative detection technology, offer novel solutions with high specificity, affinity, and broad target applicability, making them particularly promising for respiratory pathogen detection. This review highlights the progress in the research and application of nucleic acid aptamers for detecting respiratory pathogens, discussing their selection, application, potential in clinical diagnosis, and future development. Notably, these aptamers can significantly enhance the sensitivity and specificity of detection when combined with detection techniques such as fluorescence, colorimetry and electrochemistry. This review offers new insights into how aptamers can address the limitations of traditional diagnostic methods and advance clinical diagnostics. It also highlights key challenges and future research directions for the clinical application of nucleic acid aptamers.

A review: early detection of oral cancer biomarkers using microfluidic colorimetric point-of-care devices

Oral squamous cell carcinoma (OSCC) is the most common type of head and neck cancers. OSCC constitutes 90% of the head and neck malignancies. The delayed identification of oral cancer is the primary cause of ineffective medical treatment. To address this issue, low-cost, reliable point-of-care devices that can be utilized for large-scale screening, even in low-resource settings, including rural areas and primary healthcare centers, are of great interest. Herein, a comprehensive analysis of numerous salivary biomarkers that exhibit significant variations in concentration between individuals with oral cancer and those without is given. Furthermore, the article explores several point-of-care devices that exhibit potential in the realm of oral cancer detection. The biomarkers are discussed with a focus on their structural characteristics and role in oral cancer progression. The devices based on colorimetry and microfluidics are discussed in detail, considering their compliance with the 'REASSURED' criteria given by the World Health Organization (WHO) and suitability for mass screening in low-resource settings. Finally, the discourse revolves around the fundamental aspects pertaining to the advancement of multiplex, cost-effective point-of-care devices designed for widespread screening purposes.

Integrating loop-mediated isothermal amplification with lateral flow assay to achieve a highly sensitive method for detecting Streptococcus suis Genome in raw pork

Streptococcus suis (S.suis), a zoonotic foodborne pathogen prevalent in Southeast Asia, poses a substantial threat to human and animal health because of its ability to cause severe and life-threatening illnesses. To address this challenge, a rapid and highly sensitive detection platform for S. suis in raw pork was developed by integrating loop-mediated isothermal amplification (LAMP) and a lateral flow assay (LFA), S. suis LAMP-LFA. LAMP reactions targeting the S. suis glutamate dehydrogenase (gdh) gene were optimized for specific detection of S. suis within 45 min at an isothermal temperature of 65 °C. The assay exhibited marked sensitivity, with a detection limit of 100 fg for genomic DNA extracted from S. suis cultures. Notably, this method showed no cross-reactivity with other bacterial contaminants commonly found in raw pork. The resulting LAMP amplicons were effectively detected using LFA, with a test limit of 101 CFU per 25 g of raw pork. S. suis LAMP-LFA proved to be highly specific and reliable, with no false-positives detected in spiked pork samples or pork samples containing other bacterial contaminants. Due to its high sensitivity, specificity, and rapid turnaround time, the proposed technique has immense potential as a field-deployable screening test for S. suis detection in raw pork, contributing to enhanced food safety and public health protection.

Plug-and-play protein biosensors using aptamer-regulated in vitro transcription

Molecular biosensors that accurately measure protein concentrations without external equipment are critical for solving numerous problems in diagnostics and therapeutics. Modularly transducing the binding of protein antibodies, protein switches or aptamers into a useful output remains challenging. Here, we develop a biosensing platform based on aptamer-regulated transcription in which aptamers integrated into transcription templates serve as inputs to molecular circuits that can be programmed to a produce a variety of responses. We modularly design molecular biosensors using this platform by swapping aptamer domains for specific proteins and downstream domains that encode different RNA transcripts. By coupling aptamer-regulated transcription with diverse transduction circuits, we rapidly construct analog protein biosensors and digital protein biosensors with detection ranges that can be tuned over two orders of magnitude and can exceed the binding affinity of the aptamer. Aptamer-regulated transcription is a straightforward and inexpensive approach for constructing programmable protein biosensors that could have diverse applications in research and biotechnology.

From Lab to Home: Ultrasensitive Rapid Detection of SARS-CoV-2 with a Cascade CRISPR/Cas13a-Cas12a System Based Lateral Flow Assay

Currently, CRISPR/Cas-based molecular diagnostic techniques usually rely on the introduction of nucleic acid amplification to improve their sensitivity, which is usually more time-consuming, susceptible to aerosol contamination, and therefore not suitable for at-home molecular testing. In this research, we developed an advanced CRISPR/Cas13a-Cas12a-based lateral flow assay that facilitated the ultrasensitive and rapid detection of SARS-CoV-2 RNA directly from samples, without the need for nucleic acid amplification. This method was called CRISPR LFA enabling at-home RNA testing (CLEAR). CLEAR used a novel cascade mechanism with specially designed probes that fold into hairpin structures, enabling visual detection of SARS-CoV-2 sequences down to 1 aM sensitivity levels. More importantly, CLEAR had a positive coincidence rate of 100% and a negative coincidence rate of 100% for clinical nasopharyngeal swabs from 16 patients. CLEAR was particularly suitable for at-home molecular testing, providing a low-cost, user-friendly solution that can efficiently distinguish between different SARS-CoV-2 variants. CLEAR overcame the common limitations of high sensitivity and potential contamination associated with traditional PCR-based systems, making it a promising tool for widespread public health application, especially in environments with limited access to laboratory resources.

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.

The Evaluation of Clinical Applications for the Detection of the Alzheimer's Disease Biomarker GFAP

One of the most prevalent neurodegenerative diseases is Alzheimer's disease (AD). The hallmarks of AD include the accumulation of amyloid plaques and neurofibrillary tangles, which cause related secondary diseases, progressive neurodegeneration, and ultimately death. The most prevalent cell type in the human central nervous system, astrocytes, are crucial for controlling neuronal function. Glial fibrillary acidic protein (GFAP) is released from tissue into the bloodstream due to astrocyte breakdown in neurological diseases. Increased levels of GFAP in the serum can function as blood markers and be an effective prognostic indicator to help diagnose neurological conditions early on, from stroke to neurodegenerative diseases. The human central nervous system (CNS) is greatly affected by diseases associated with blood GFAP levels. These include multiple sclerosis, intracerebral hemorrhage, glioblastoma multiforme, traumatic brain injuries, and neuromyelitis optica. GFAP demonstrates a strong diagnostic capacity for projecting outcomes following an injury. Furthermore, the increased ability to identify GFAP protein fragments helps facilitate treatment, as it allows continuous screening of CNS injuries and early identification of potential recurrences. GFAP has recently gained attention due to data showing that the plasma biomarker is effective in identifying AD pathology. AD accounts for 60-70% of the approximately 50 million people with dementia worldwide. It is critical to develop molecular markers for AD, whose number is expected to increase to about 3 times and affect humans by 2050, and to investigate possible targets to confirm their effectiveness in the early diagnosis of AD. In addition, most diagnostic methods currently used are image-based and do not detect early disease, i.e. before symptoms appear; thus, treatment options and outcomes are limited. Therefore, recently developed methods such as point-of-care (POC), on-site applications, and enzyme-linked immunosorbent assay-polymerase chain reaction (ELISA-PCR) that provide both faster and more accurate results are gaining importance. This systematic review summarizes published studies with different approaches such as immunosensor, lateral flow, POC, ELISA-PCR, and molecularly imprinted polymer using GFAP, a potential blood biomarker to detect neurological disorders. Here, we also provide an overview of current approaches, analysis methods, and different future detection strategies for GFAP, the most popular biosensing field.

A Fluorescent Immunochromatography Test Strip for the Rapid Identification of SVV and FMDV

Seneca Valley virus (SVV) and foot-and-mouth disease virus (FMDV) belong to the Picornaviridae family, which can cause similar symptoms. After infection, pigs will develop fever; loss of appetite; blister lesions on the skin and mucous membrane of the mouth, nose, and hoof; and other similar diseases, and the spread is very fast, causing major economic losses to the pig industry. Therefore, a rapid, accurate, and sensitive diagnostic method is necessary to enable rapid prevention and control measures for preventing the spread of these diseases. Here, a fluorescent immunochromatography test strip, using Eu-doped fluorescence beads and monoclonal antibody, was developed for the simultaneous determination of FMDV and SVV. The test process for the assay could be completed in 12 min, which avoided the time cost of the current methods for FMDV/SVV detection. Under optimized conditions, the limit of detection of SVV is 5 × 104 PFU/mL, and that of FMDV is 5 × 104 PFU/mL under the Fluorescence Immunoassay Analyzer. Our assay results showed a good linear correlation with RT-PCR installed in the clinical laboratory. The species design has a promising application prospect in the surveillance and control of the outbreak of idiopathic blister.

A comprehensive review of aptamer screening and application for lateral flow strip: Current status and future perspectives

The detection of biomarkers is of great significance for medical diagnosis, food safety, environmental monitoring, and agriculture. However, bio-detection technology at present often necessitates complex instruments, expensive reagents, specialized expertise, and prolonged procedures, making it challenging to fulfill the demand for rapid, sensitive, user-friendly, and economical testing. In contrast, lateral flow strip (LFS) technology offers simple, fast, and visually accessible detection modality, allowing real-time analysis of clinical specimens, thus finding widespread utility across various domains. Within the realm of LFS, the application of aptamers as molecular recognition probes presents distinct advantages over antibodies, including cost-effectiveness, smaller size, ease of synthesis, and chemical stability. In recent years, aptamer-based LFS has found extensive application in qualitative, semi-quantitative, and quantitative detection across food safety, environmental surveillance, clinical diagnostics, and other domains. This review provided a concise overview of different aptamer screening methodologies, selection strategies, underlying principles, and procedural, elucidating their respective advantages, limitations, and applications. Additionally, we summarized recent strategies and mechanisms for aptamer-based LFS, such as the sandwich and competitive methods. Furthermore, we classified LFSs constructed based on aptamers, considering the rapid advancements in this area, and discussed their applications in biological and chemical detection. Finally, we delved into the current challenges and future directions in the development of aptamer and aptamer-based LFS. Although this review was not thoroughly, it would serve as a valuable reference for understanding the research progress of aptamer-based LFS and aid in the development of new types of aptasensors.

Upconverting Nanoparticle-based Enhanced Luminescence Lateral-Flow Assay for Urinary Biomarker Monitoring

Development of efficient portable sensors for accurately detecting biomarkers is crucial for early disease diagnosis, yet remains a significant challenge. To address this need, we introduce the enhanced luminescence lateral-flow assay, which leverages highly luminescent upconverting nanoparticles (UCNPs) alongside a portable reader and a smartphone app. The sensor's efficiency and versatility were shown for kidney health monitoring as a proof of concept. We engineered Er3+- and Tm3+-doped UCNPs coated with multiple layers, including an undoped inert matrix shell, a mesoporous silica shell, and an outer layer of gold (UCNP@mSiO2@Au). These coatings synergistically enhance emission by over 40-fold and facilitate biomolecule conjugation, rendering UCNP@mSiO2@Au easy to use and suitable for a broad range of bioapplications. Employing these optimized nanoparticles in lateral-flow assays, we successfully detected two acute kidney injury-related biomarkers─kidney injury molecule-1 (KIM-1) and neutrophil gelatinase-associated lipocalin (NGAL)─in urine samples. Using our sensor platform, KIM-1 and NGAL can be accurately detected and quantified within the range of 0.1 to 20 ng/mL, boasting impressively low limits of detection at 0.28 and 0.23 ng/mL, respectively. Validating our approach, we analyzed clinical urine samples, achieving biomarker concentrations that closely correlated with results obtained via ELISA. Importantly, our system enables biomarker quantification in less than 15 min, underscoring the performance of our novel UCNP-based approach and its potential as reliable, rapid, and user-friendly diagnostics.

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.

Isolation of camel single domain antibodies against Yersinia pestis V270 antigen based on a semi-synthetic single domain antibody library and development of a VHH-based lateral flow assay

BACKGROUND

Antibodies have been proven effective as diagnostic agents for detecting zoonotic diseases. The variable domain of camel heavy chain antibody (VHH), as an antibody derivative, may be used as an alternative for traditional antibodies in existing immunodiagnostic reagents for detecting rapidly spreading infectious diseases.

OBJECTIVES

To expedite the isolation of specific antibodies for diagnostic purposes, we constructed a semi-synthetic camel single domain antibody library based on the phage display technique platform (PDT) and verified the validity of this study.

METHODS

The semi-synthetic single domain antibody sequences consist of two parts: one is the FR1-FR3 region amplified by RT-PCR from healthy camel peripheral blood lymphocytes (PBLs), and the other part is the CDR3-FR4 region synthesised as an oligonucleotide containing CDR3 randomised region. The two parts were fused by overlapping PCR, resulting in the rearranged variable domain of heavy-chain antibodies (VHHs). Y. pestis low-calcium response V protein (LcrV) is an optional biomarker to detect the Y. pestis infection. The semi-synthetic library herein was screened using recombinant (LcrV) as a target antigen.

RESULTS

After four cycles of panning the library, four VHH binders targeting 1-270 aa residues of LcrV were isolated. The four VHH genes with unique sequences were recloned into an expression vector and expressed as VHH-hFc chimeric antibodies. The purified antibodies were identified and used to develop a lateral flow immunoassay (LFA) test strip using latex microspheres (LM) for the rapid and visual detection of Y. pestis infection.

CONCLUSIONS

These data demonstrate the great potential of the semi-synthetic library for use in isolation of antigen-specific nanobodies and the isolated specific VHHs can be used in antigen-capture immunoassays.

New Insights into Aptamers: An Alternative to Antibodies in the Detection of Molecular Biomarkers

Aptamers are short oligonucleotides with single-stranded regions or peptides that recently started to transform the field of diagnostics. Their unique ability to bind to specific target molecules with high affinity and specificity is at least comparable to many traditional biorecognition elements. Aptamers are synthetically produced, with a compact size that facilitates deeper tissue penetration and improved cellular targeting. Furthermore, they can be easily modified with various labels or functional groups, tailoring them for diverse applications. Even more uniquely, aptamers can be regenerated after use, making aptasensors a cost-effective and sustainable alternative compared to disposable biosensors. This review delves into the inherent properties of aptamers that make them advantageous in established diagnostic methods. Furthermore, we will examine some of the limitations of aptamers, such as the need to engage in bioinformatics procedures in order to understand the relationship between the structure of the aptamer and its binding abilities. The objective is to develop a targeted design for specific targets. We analyse the process of aptamer selection and design by exploring the current landscape of aptamer utilisation across various industries. Here, we illuminate the potential advantages and applications of aptamers in a range of diagnostic techniques, with a specific focus on quartz crystal microbalance (QCM) aptasensors and their integration into the well-established ELISA method. This review serves as a comprehensive resource, summarising the latest knowledge and applications of aptamers, particularly highlighting their potential to revolutionise diagnostic approaches.

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.

SERS-based microdevices for use as in vitro diagnostic biosensors

Advances in surface-enhanced Raman scattering (SERS) detection have helped to overcome the limitations of traditional in vitro diagnostic methods, such as fluorescence and chemiluminescence, owing to its high sensitivity and multiplex detection capability. However, for the implementation of SERS detection technology in disease diagnosis, a SERS-based assay platform capable of analyzing clinical samples is essential. Moreover, infectious diseases like COVID-19 require the development of point-of-care (POC) diagnostic technologies that can rapidly and accurately determine infection status. As an effective assay platform, SERS-based bioassays utilize SERS nanotags labeled with protein or DNA receptors on Au or Ag nanoparticles, serving as highly sensitive optical probes. Additionally, a microdevice is necessary as an interface between the target biomolecules and SERS nanotags. This review aims to introduce various microdevices developed for SERS detection, available for POC diagnostics, including LFA strips, microfluidic chips, and microarray chips. Furthermore, the article presents research findings reported in the last 20 years for the SERS-based bioassay of various diseases, such as cancer, cardiovascular diseases, and infectious diseases. Finally, the prospects of SERS bioassays are discussed concerning the integration of SERS-based microdevices and portable Raman readers into POC systems, along with the utilization of artificial intelligence technology.

Development of DNA-Based Lateral Flow Assay for Detection of LDLR Gene Mutation for Familial Hypercholesterolemia

Background

The techniques for detecting single nucleotide polymorphisms (SNP) require lengthy and complex experimental procedures and expensive instruments that may only be available in some laboratories. Thus, a deoxyribonucleic acid (DNA)-based lateral flow assay (LFA) was developed as a point-of-care test (POCT) diagnostic tool for genotyping. In this study, single nucleotide variation (E101K) in the low-density lipoprotein receptor (LDLR) gene leading to familial hypercholesterolemia (FH) was chosen as a model.

Methods

Hypercholesterolemic individuals (n = 103) were selected from the Malaysian Cohort project (UKM Medical Molecular Biology Institute) while the control samples were selected from the Biobank (UKM Medical Molecular Biology Institute). The DNA samples were isolated from whole blood. Polymerase chain reaction (PCR) amplification process was performed using bifunctional labelled primers specifically designed to correspond to the variant that differentiates wild-type and mutant DNA for visual detection on LFA. The variant was confirmed using Sanger sequencing, and the sensitivity and specificity of the LFA detection method were validated using the Agena MassARRAY® technique.

Results

Out of 103 hypercholesterolemic individuals, 5 individuals (4.8%) tested positive for E101K, LDLR mutation and the rest, including healthy control individuals, tested negative. This result was concordant with Sanger sequencing and Agena MassARRAY®. These five individuals could be classified as Definite FH, as the DNA diagnosis was confirmed. The sensitivity and specificity of the variant detection by LFA is 100% compared to results using the genotyping method using Agena MassARRAY®.

Conclusion

The developed LFA can potentially be used in the POC setting for detecting the E101K variant in the LDLR gene. This LFA can also be used to screen family members with E101K variant in the LDLR gene and is applicable for other SNP's detection.

A versatile upconversion-based multimode lateral flow platform for rapid and ultrasensitive detection of microRNA towards health monitoring

MicroRNAs are small single-stranded RNA molecules associated with gene expression and immune response, suggesting their potential as biomarkers for health monitoring. Herein, we designed a novel upconversion-based multimode lateral flow assay (LFA) system to detect microRNAs in body fluids by simultaneously producing three unique signals within a detection strip. The core-shell Au-DTNB@Ag nanoparticles act as both the Raman reporters and acceptors, quenching fluorescence from upconversion nanoparticles (UCNPs, NaYF4: Yb3+, Er3+) via the Förster resonance energy transfer mechanism. Using microRNA-21 as a representative analyte, the LFA system offers remarkable detection range from 2 nM to 1 fM, comparable to outcomes from signal amplification methods, due to the successful single-layer self-assembly of UCNPs on the NC membrane, which greatly enhances both the convenience and sensitivity of the LFA technique. Additionally, our proprietary fluorescence-Raman detection platform simplifies result acquisition by reducing procedural intricacies. The biosensor, when evaluated with diverse bodily fluids, showed remarkable selectivity and sustained stability. Importantly, our LFA biosensor effectively identified periodontitis and lung cancer patients from healthy subjects in genuine samples, indicating significant potential for disease prediction, early diagnosis, and progression tracking. This system holds promise as a multifunctional tool for various biomarker assays.

Realization of qualitative to semi-quantitative trace detection via SERS-ICA based on internal standard method

Surface-enhanced Raman spectroscopy (SERS) can quickly identify molecular fingerprints and has been widely used in the field of rapid detection. However, the non-uniformity inherent in SERS substrate signals, coupled with the finite nature of the detection object, significantly hampers the advancement of SERS. Nowadays, the existing mature immunochromatographic assay (ICA) method is usually combined with SERS technology to address the defects of SERS detection. Nevertheless, the porous structure of the strip will also affect the signal uniformity during detection. Obviously, a method using SERS-ICA is needed to effectively solve signal fluctuations, improve detection accuracy, and has certain versatility. This paper introduces an internal standard method combining deep learning to predict and process Raman data. Based on the signal fluctuation of single-antigen SERS-ICA test strip, the double-antigen SERS-ICA test strip was constructed. The full spectrum Raman data of double-antigen SERS-ICA test strip was normalized by the sum of two characteristic peaks of internal standard molecules, and then processed by deep learning algorithm. The Relative Standard Deviation (RSD) of Raman data of bisphenol A was compared before and after internal standard normalization of double-antigen SERS-ICA test strip. The RSD processed by this method was increased by 3.8 times. After normalization, the prediction accuracy of Root Mean Square Error (RMSE) is improved by 2.66 times, and the prediction accuracy of R-square (R2) is increased from 0.961 to 0.994. The results showed that RMSE and R2 were used to comprehensively predict the collected data of double-antigen SERS-ICA test strip, which could effectively improve the prediction accuracy. The internal standard algorithm can effectively solve the challenges of uneven hot spots and poor signal reproducibility on the test strip to a certain extent, so as to improve the semi-quantitative accuracy.