Novel strategies to enhance lateral flow immunoassay sensitivity for detecting foodborne pathogens

DNA sensing based on aggregation of Janus particles using dynamic light scattering

BACKGROUND

The aggregation of isotropic particles through interparticle reactions poses a challenge in control due to the ability of all surfaces to bind to each other, rendering the quantitative detection of such interparticle reactions based on particle size difficult. Here, we proposed a novel detection scheme for DNA utilizing an assembly of Janus particles (JPs) employing dynamic light scattering (DLS). DNA molecules are tethered on one hemisphere of the JP, while the other hemisphere retains its hydrophobic properties.

RESULTS

Aggregation of JPs was induced by the sandwich hybridization of target DNA between them. The assembly of JPs was effectively monitored by the changes in hydrodynamic diameter detected by DLS, revealing that aggregation peaks at 2-3 particles and further reaction was hindered due to the inability of one hemisphere of the JP to interact with another JP. The target DNA demonstrated detectability at concentrations as low as several tens of pM to several nM using a digital sensing method. The two types of target DNA, such as simple (14 base pairs) and HIV-2 specific sequences (20 base pairs) were detectable at nM and pM levels, respectively. Moreover, we substantiated the robustness of our detection scheme through stoichiometric calculations based on an equilibrium model. The present detection mechanism was well explained based on the binding affinity of DNA hybridization.

SIGNIFICANCE

This detection method harnesses the anisotropic nature of JPs and represents the first detection approach based on aggregation. By altering the modification molecules on JPs to match target molecules, such as proteins and organic compounds, a wide range of versatile molecules can be detected using this scheme with high sensitivity. This underscores the broad applicability of the present method.

Orientation of Antibody Modified and Reacted on Carboxy-Functionalized Polystyrene Particle Revealed by Zeta Potential Measurement

The comprehensive understanding of the orientation of antibodies on a solid surface is crucial for affinity-based sensing mechanisms. In this study, we demonstrated that the orientation of primary antibodies modified on carboxy-functionalized polystyrene (PS) particles can be analyzed using zeta potential behavior at different pH based on the combined Gouy-Chapman-Stern model and the acid dissociation of carboxy groups and antibodies. We observed that at low surface concentrations of the primary antibody, a side-on orientation was predominant. However, at higher concentrations (approximately 30000 antibodies per PS particle), the orientation shifted to an end-on type due to steric hindrance. Furthermore, the reaction mechanism of the secondary antibody exhibited pH-dependent behavior. At pH > 7, the zeta potential changes were attributed to the antibody-antibody reaction, whereas at pH < 7, adsorption of secondary antibody onto the PS particle was observed, leading to a change in the orientation of the primary antibody modified on the PS particle to an end-on type. The change in zeta potential due to secondary antibody binding indicated a detection limit of 37000 antibodies per PS particle. As a result, we revealed that the analysis of zeta potential behavior enables the evaluation of antibody orientation and the detection of zeptomole order antibodies. This study represents the first demonstration of this capability. We anticipate that the present concept and results will broaden the quantitative application of zeta potential measurements and have significant implications for research areas, including physical chemistry and analytical chemistry.

Surface Acoustic Wave-Driven Enhancement of Enzyme-Linked Immunosorbent Assays: ELISAW

Enzyme-linked immunosorbent assays (ELISAs) are widely used in biology and clinical diagnosis. Relying on antigen-antibody interaction through diffusion, the standard ELISA protocol can be time-consuming, preventing its use in rapid diagnostics. We present a time-saving and more sensitive ELISA without changing the standard setup and protocol, using surface acoustic waves (SAWs) to enhance performance. Each step of the assay, from the initial antibody binding onto the walls of the well plate to the target analyte molecules' binding for detection─except, notably, for the blocking step─is improved principally via acoustic streaming-driven advection. Using SAWs, the time required for one step of an example ELISA is reduced from 60 to 15 min to achieve the same binding amount. By extending the duration of SAW exposure to 20 min, the sensitivity can be significantly improved over the 60 min, 35 °C ELISA without SAWs. It is also possible to confer beneficial improvements to bead-based ELISA by combining it with SAWs to further reduce the time required for binding to 2 min. By significantly increasing the speed of ELISA, its utility may be improved for a wide range of point-of-care diagnostics applications.

Size-selective sampler combined with an immunochromatographic assay for the rapid detection of airborne Legionella pneumophila

Airborne biological aerosols (also called bioaerosols) are found in various environmental and occupational settings. Among these, pathogenic bioaerosols can cause diseases such as legionellosis, influenza, measles, and tuberculosis. To prevent or minimize people's exposure to these pathogenic bioaerosols in the field, a rapid detection method is required. In this study, a size-selective bioaerosol (SSB) sampler was combined with the immunochromatographic assay (ICA). The SSB sampler can collect bioaerosols on the sampling swab and the lateral flow test kit used in ICA can rapidly detect the pathogens in bioaerosols collected on the swab. Before testing the combined method, the lower limit of detection (LOD) of the lateral flow test kit was determined. Legionella pneumophila (L. pneumophila) was used as a target pathogen. The results show that at least 1.3 × 103L. pneumophila cells are required to be detected by the lateral flow test kit. To test the developed method, L. pneumophila suspension was aerosolized in the sampling chamber and collected using two SSB samplers with different sampling times (10 and 20 min). The developed method could detect aerosolized L. pneumophila and also estimate the concentrations from the lower LOD, sampling time, and formation of a positive line on a test strip. When positive results were obtained from sampling for 10 min and 20 min, concentrations of respirable L. pneumophila were estimated ≥5.2 × 104 CFUresp/m3 and ≥2.6 × 104 CFUresp/m3, respectively. The conventional sampler Andersen impactor with colony counting was also used for comparison. In all cases, the estimated concentrations obtained by the developed method were higher than those obtained by the conventional method. These findings confirm that the developed method can overcome the limitations of conventional methods and eventually benefit environmental and occupational health by providing a better method for risk assessment.

Review of Detection Limits for Various Techniques for Bacterial Detection in Food Samples

Foodborne illnesses can be infectious and dangerous, and most of them are caused by bacteria. Some common food-related bacteria species exist widely in nature and pose a serious threat to both humans and animals; they can cause poisoning, diseases, disabilities and even death. Rapid, reliable and cost-effective methods for bacterial detection are of paramount importance in food safety and environmental monitoring. Polymerase chain reaction (PCR), lateral flow immunochromatographic assay (LFIA) and electrochemical methods have been widely used in food safety and environmental monitoring. In this paper, the recent developments (2013-2023) covering PCR, LFIA and electrochemical methods for various bacterial species (Salmonella, Listeria, Campylobacter, Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli)), considering different food sample types, analytical performances and the reported limit of detection (LOD), are discussed. It was found that the bacteria species and food sample type contributed significantly to the analytical performance and LOD. Detection via LFIA has a higher average LOD (24 CFU/mL) than detection via electrochemical methods (12 CFU/mL) and PCR (6 CFU/mL). Salmonella and E. coli in the Pseudomonadota domain usually have low LODs. LODs are usually lower for detection in fish and eggs. Gold and iron nanoparticles were the most studied in the reported articles for LFIA, and average LODs were 26 CFU/mL and 12 CFU/mL, respectively. The electrochemical method revealed that the average LOD was highest for cyclic voltammetry (CV) at 18 CFU/mL, followed by electrochemical impedance spectroscopy (EIS) at 12 CFU/mL and differential pulse voltammetry (DPV) at 8 CFU/mL. LOD usually decreases when the sample number increases until it remains unchanged. Exponential relations (R2 > 0.95) between LODs of Listeria in milk via LFIA and via the electrochemical method with sample numbers have been obtained. Finally, the review discusses challenges and future perspectives (including the role of nanomaterials/advanced materials) to improve analytical performance for bacterial detection.

Rapid and ultra-sensitive lateral flow assay for pathogens based on multivalent aptamer and magnetic nanozyme

Ultra-sensitive LFA methods for pathogen detection commonly depended on tedious and time-consuming nucleic acid amplification. Here, a high affinity multivalent aptamer (multi-Apt) for S. aureus was obtained through exquisite engineering design. The scaffold and conformation of the multi-Apt were found to be key factors in the detection signal of aptsensors. After optimization, the binding affinity of the multi-Apt to S. aureus was improved by more than 8-fold from 135.9 nM to 16.77 nM. By the joint use of the multi-Apt and a multifunctional nanozyme Fe3O4@MOF@PtPd, a fast and ultra-sensitive LFA for S. aureus was developed (termed MA-MN LFA). In this method, a Fe3O4@MOF@PtPd nanozyme was modified with vancomycin and could efficiently capture and separate S. aureus. Moreover, the multi-Apt worked together with the nanozyme to bind with S. aureus to form a ternary complex at the same time, which simply the fabrication of LFA strip. The developed MA-MN LFA could detect S. aureus as low as 2 CFU/mL within 30 min and a wide linear range of 10-1 × 108 CFU/mL was obtained. The detection is easily operated, fast (can be completed within 30 min) and versatile for Gram-positive pathogens, thus has great potential as a powerful tool in pathogen detection.

Biosensors based on core-shell nanoparticles for detecting mycotoxins in food: A review

Mycotoxins are toxic metabolites produced by fungi in the process of infecting agricultural products, posing serious threat to the health of human and animals. Thus, sensitive and reliable analytical techniques for mycotoxin detection are needed. Biosensors equipped with antibodies or aptamers as recognition elements and core-shell nanoparticles (NPs) for the pre-treatment and detection of mycotoxins have been extensively studied. By comparison with monocomponent NPs, core-shell nanostructures exhibit unique optical, electric, magnetic, plasmonic, and catalytic properties due to the combination of functionalities and synergistic effects, resulting in significant improvement of sensing capacities in various platforms, such as surface-enhanced Raman spectroscopy, fluorescence, lateral flow immunoassay and electrochemical sensors. This review focused on the development of core-shell NPs based biosensors for the sensitive and accurate detection of mycotoxins in food samples. Recent developments were categorised and summarised, along with detailed discussion of advantages and shortcomings. The future potential of utilising core-shell NPs in food safety testing was also highlighted.

Advanced diagnostic methods for identification of bacterial foodborne pathogens: contemporary and upcoming challenges

It is a public health imperative to have safe food and water across the population. Foodborne infections are one of the primary causes of sickness and mortality in both developed and developing countries. An estimated 100 million foodborne diseases and 120 000 foodborne illness-related fatalities occur each year in India. Several factors affect foodborne illness, such as improper farming methods, poor sanitary and hygienic conditions at all levels of the food supply chain, the lack of preventative measures in the food processing industry, the misuse of food additives, as well as improper storage and handling. In addition, chemical and microbiological combinations also play a key role in disease development. But recent disease outbreaks indicated that microbial pathogens played a major role in the development of foodborne diseases. Therefore, prompt, rapid, and accurate detection of high-risk food pathogens is extremely vital to warrant the safety of the food items. Conventional approaches for identifying foodborne pathogens are labor-intensive and cumbersome. As a result, a range of technologies for the rapid detection of foodborne bacterial pathogens have been developed. Presently, many methods are available for the instantaneous detection, identification, and monitoring of foodborne pathogens, such as nucleic acid-based methods, biosensor-based methods, and immunological-based methods. The goal of this review is to provide a complete evaluation of several existing and emerging strategies for detecting food-borne pathogens. Furthermore, this review outlines innovative methodologies and their uses in food testing, along with their existing limits and future possibilities in the detection of live pathogens in food.

Bacteria-imprinted impedimetric sensor based on doping-induced nanostructured polypyrrole for determination of Escherichia coli

A simple and label-free bacteria-imprinted impedimetric (BIP) sensor for the sensitive measurement of Escherichia coli has been developed. The BIP sensor is fabricated by one-step electropolymerization of pyrrole (functional monomer), copper phthalocyanine-3, 4', 4'', 4'''-tetrasulfonic acid tetrasodium salt (CuPcTs, dopant), and target bacteria (E. coli O157:H7) on a glassy carbon electrode. After the removal of the bacterial template, the established imprinted sites on the CuPcTs-doped polypyrrole film (PPy/CuPcTs) enable the highly selective rebinding of target bacteria and the resulting impedance change of the sensing interface is used to detect the target bacteria. We found that during the electropolymerization process, CuPcTs induced pyrrole to form granular-like nanostructured PPy/CuPcTs with excellent conductivity compared with the PPy film, substantially improving the sensitivity of the proposed sensor. The sensor presented a wide detection range (102 ~ 107 CFU⋅mL-1, RSD 1.1% ~ 3.5%) with a limit of detection of 21 CFU⋅mL-1. Furthermore, the proposed sensor effectively distinguished E. coli O157:H7 from other non-target bacteria and exhibited good practicality with recoveries from 91 to 103% in spiked real samples, indicating the potential utility of the sensor in food safety and environmental monitoring.

Lateral flow assay of pathogenic viruses and bacteria in healthcare

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

Oxygen Sensor-Based Respirometry and the Landscape of Microbial Testing Methods as Applicable to Food and Beverage Matrices

The current status of microbiological testing methods for the determination of viable bacteria in complex sample matrices, such as food samples, is the focus of this review. Established methods for the enumeration of microorganisms, particularly, the 'gold standard' agar plating method for the determination of total aerobic viable counts (TVC), bioluminescent detection of total ATP, selective molecular methods (immunoassays, DNA/RNA amplification, sequencing) and instrumental methods (flow cytometry, Raman spectroscopy, mass spectrometry, calorimetry), are analyzed and compared with emerging oxygen sensor-based respirometry techniques. The basic principles of optical O₂ sensing and respirometry and the primary materials, detection modes and assay formats employed are described. The existing platforms for bacterial cell respirometry are then described, and examples of particular assays are provided, including the use of rapid TVC tests of food samples and swabs, the toxicological screening and profiling of cells and antimicrobial sterility testing. Overall, O₂ sensor-based respirometry and TVC assays have high application potential in the food industry and related areas. They detect viable bacteria via their growth and respiration; the assay is fast (time to result is 2-8 h and dependent on TVC load), operates with complex samples (crude homogenates of food samples) in a simple mix-and-measure format, has low set-up and instrumentation costs and is inexpensive and portable.

Self-corrected dual-optical immunosensors using carbon dots@SiO2@MnO2 improving diethyl phthalate detection accuracy

The traditional immunoassay is widely used for pollutant detection and bioanalysis, but there are still some challenges in ensuring its sensitivity and reliable accuracy. Dual-optical measurement can prove mutual evidence to effectively improve the accuracy of the method by self-correction, which will overcome this problem. In this study, we developed a "visualization and sensing" dual-modal immunoassay based on blue carbon dots@SiO₂@MnO₂ (B-CDs@SiO₂@MnO₂) as "color and fluorescence" immunosensors. Here, MnO₂ nanosheets have the activity of simulating oxidase. 3,3', 5,5'-Tetramethylbenzidine (TMB) can be oxidized to TMB²⁺ under acidic conditions and the color of the solution from colorless to yellow. On the other hand, the MnO₂ nanosheets can quench the fluorescence of B-CDs@SiO₂. After adding ascorbic acid (AA), MnO₂ nanosheets were reduced to Mn²⁺, thereby the fluorescence of B-CDs@SiO₂ was restored. Under the optimum conditions, as the concentration of target substance (diethyl phthalate) increased from 0.05 to 100 ng/mL, the method showed a good linear relationship. The fluorescence measurement signal and the color change signal of the solution visualization support each other and give the information of the corresponding material content. The results of the dual-optical immunoassay maintain good consistency, which proves the accuracy of the developed dual-optical immunoassay for detection of diethyl phthalate is reliable. Additionally, it is demonstrated that the dual-modal method exhibits high accuracy and stability in the assays, pointing to a broad range of application prospects in pollutant analysis.

Machine Learning-Based Analytical Systems: Food Forensics

Despite a large amount of money being spent on both food analyses and control measures, various food-borne illnesses associated with pathogens, toxins, pesticides, adulterants, colorants, and other contaminants pose a serious threat to human health, and thus food safety draws considerable attention in the modern pace of the world. The presence of various biogenic amines in processed food have been frequently considered as the primary quality parameter in order to check food freshness and spoilage of protein-rich food. Various conventional detection methods for detecting hazardous analytes including microscopy, nucleic acid, and immunoassay-based techniques have been employed; however, recently, array-based sensing strategies are becoming popular for the development of a highly accurate and precise analytical method. Array-based sensing is majorly facilitated by the advancements in multivariate analytical techniques as well as machine learning-based approaches. These techniques allow one to solve the typical problem associated with the interpretation of the complex response patterns generated in array-based strategies. Consequently, the machine learning-based neural networks enable the fast, robust, and accurate detection of analytes using sensor arrays. Thus, for commercial applications, most of the focus has shifted toward the development of analytical methods based on electrical and chemical sensor arrays. Therefore, herein, we briefly highlight and review the recently reported array-based sensor systems supported by machine learning and multivariate analytics to monitor food safety and quality in the field of food forensics.

Tetrodotoxin and Its Analogues in Food: Recent Updates on Sample Preparation and Analytical Methods Since 2012

Tetrodotoxin (TTX), found in various organisms including pufferfish, is an extremely potent marine toxin responsible for numerous food poisoning accidents. Due to its serious toxicity and public health threat, detecting TTX and its analogues in diverse food matrices with a simple, fast, efficient method has become a worldwide concern. This review summarizes the advances in sample preparation and analytical methods for the determination of TTX and its analogues, focusing on the latest development over the past five years. Current state-of-the-art technologies, such as solid-phase microextraction, online technology, novel injection technology, two-dimensional liquid chromatography, high-resolution mass spectrometry, newly developed lateral flow immunochromatographic strips, immunosensors, dual-mode aptasensors, and nanomaterials-based approaches, are thoroughly discussed. The advantages and limitations of different techniques, critical comments, and future perspectives are also proposed. This review is expected to provide rewarding insights to the future development and broad application of pretreatment and detection methods for TTX and its analogues.

Activated Carbon-Based Immunochromatographic Strip Test for the Rapid Qualitative Analysis of Swertiamarin and Sweroside

Background

Swertia japonica (S. japonica) is a medicinal plant that belongs to the Gentianaceae family. Several reports confirm the biological effects of the S. japonica extract. This plant is used mainly as a digestive stimulant, appetite stimulant, and gastrointestinal disease remedy in Japan. Secoiridoid glycosides are a group of compounds related to the beneficial effects of this plant.

Objective

We developed an immunochromatographic strip test for major secoiridoid glycosides, such as swertiamarin (SM) and sweroside (SS) detection.

Methods

We fabricated an immunoprobe using activated carbon as a reporter molecule and a monoclonal antibody against SM and SS (MAb D2) as a detection molecule. The test and control zones of the strip test contained SM-cBSA and Goat pAb anti-mouse IgM HRP conjugate, respectively. The immunoprobe reacted competitively with free SM and/or SS and immobilized SM-cBSA. The results were read and interpreted by the black spot intensity in the test zone.

Results

We succeeded in developing a strip test system with a detection limit (LOD) of 12.5 µg/mL. The selectivity and reliability evaluation revealed that the strip test is suitable for detecting SM and SS in S. japonica. The result was ready to be read in 30 min.

Conclusions

This method can be a useful tool for the screening of biologically active S. japonica samples for further preparation of traditional medicine.

Highlights

To the best of our knowledge, this is the first immunochromatographic strip test developed for the detection of SM and SS in S. japonica samples.

Highly Sensitive Electrochemical Immunoassay Using Signal Amplification of the Coagulation Cascade

Here, we report a highly sensitive immunoassay for human immunoglobulin G (IgG) that uses signal amplification of the coagulation cascade. Z-Phe-Pro-Lys-p-nitroaniline (FPK-pNA) was used as a substrate for thrombin activation in the last step of the coagulation cascade. During the coagulation cascade, pNA is liberated from FPK-pNA and can be detected electrochemically. Using square wave voltammetry with a glassy carbon electrode, we demonstrated that pNA can be quantified in a solution modeling the coagulation cascade prepared by mixing FPK-pNA and pNA. Characterization of the reactivity of thrombin toward FPK-pNA revealed that thrombin efficiently reacted with FPK-pNA. Subsequent characterization of factor XIa activity of factor XIa-labeled antibody revealed that factor XIa was not inactivated during labeling. Finally, a coagulation cascade-based immunoassay for human IgG was performed using a factor XIa-labeled antibody on magnetic beads. The limit of detection for human IgG was 5.0 pg/mL (33 fM) indicating that the coagulation cascade can amplify the immunoassay sensitivity compared to immunoassay using a thrombin-labeled antibody as a condition without a coagulation cascade. Coagulation cascade-based immunoassay was also highly selective. In the near future, we will report a highly sensitive immunoassay for the simultaneous detection of multiple analytes using a coagulation cascade-based immunoassay and Limulus amebocyte lysate reaction-based immunoassay we previously reported.

Paper-Based Fluidic Sensing Platforms for β-Adrenergic Agonist Residue Point-of-Care Testing

The illegal use of β-adrenergic agonists during livestock growth poses a threat to public health; the long-term intake of this medication can cause serious physiological side effects and even death. Therefore, rapid detection methods for β-adrenergic agonist residues on-site are required. Traditional detection methods such as liquid chromatography have limitations in terms of expensive instruments and complex operations. In contrast, paper methods are low cost, ubiquitous, and portable, which has led to them becoming the preferred detection method in recent years. Various paper-based fluidic devices have been developed to detect β-adrenergic agonist residues, including lateral flow immunoassays (LFAs) and microfluidic paper-based analytical devices (μPADs). In this review, the application of LFAs for the detection of β-agonists is summarized comprehensively, focusing on the latest advances in novel labeling and detection strategies. The use of μPADs as an analytical platform has attracted interest over the past decade due to their unique advantages and application for detecting β-adrenergic agonists, which are introduced here. Vertical flow immunoassays are also discussed for their shorter assay time and stronger multiplexing capabilities compared with LFAs. Furthermore, the development direction and prospects for the commercialization of paper-based devices are considered, shedding light on the development of point-of-care testing devices for β-adrenergic agonist residue detection.

Simultaneous Detection of Five Foodborne Pathogens Using a Mini Automatic Nucleic Acid Extractor Combined with Recombinase Polymerase Amplification and Lateral Flow Immunoassay

In recent years, foodborne disease outbreaks have caused huge losses to the economy and have had severe impacts on public health. The accuracy and variety of detection techniques is crucial to controlling the outbreak and spread of foodborne diseases. The need for instruments increases the difficulty of field detection, while manually-handled samples are subject to user error and subjective interpretation. Here, we use a mini automatic nucleic acid extractor combined with recombinant polymerase amplification (RPA) and lateral flow immunoassay (LFIA) for simultaneous quantitative detection of five major foodborne pathogens. The pre-treatment device using the magnetic bead method allows for nucleic acid extraction of the reagent tank without manual operation, which is highly efficient and stable for preventing aerosol contamination. The nuc gene of Staphylococcus aureus, the toxR gene of Vibrio parahaemolyticus, the rfbE gene of Escherichia coli O157:H7, the hlyA gene of Listeria monocytogenes, and the fimY gene of Salmonella enterica were used as target fragments. The labeled antibody concentration is optimized on the LFIA to find the equilibrium point for the binding capacity of the five chemical markers and to efficiently and accurately visualize the bands. The RPA assay shows an optimal performance at 37 °C for 15 min. The optimized RPA-LFIA detection limit can reach 10¹ CFU/mL. There was no cross-reactivity among forty-eight strains. Furthermore, the average recoveries in spiked food samples were 90.5–104.5%. In summary, the RPA-LFIA established in this study can detect five pathogenic bacteria simultaneously with little dependence on laboratory equipment, and it has promising prospects for screening in low-resource areas.

Ultrasensitive nano-gold labelled, duplex lateral flow immunochromatographic assay for early detection of sugarcane mosaic viruses

Sugarcane is one of the important food and bioenergy crops, cultivated all over the world except European continent. Like many other crops, sugarcane production and quality are hampered by various plant pathogens, among them viruses that infect systemically and cause severe impact to cane growth. The viruses are efficiently managed by their elimination through tissue culture combined with molecular diagnostics, which could detect virus titre often low at 10^-12 g mL^-1. To harmonize the virus diagnostics by molecular methods, we established a nanocatalysis-based high sensitive lateral flow immunochromatographic assay (LFIA) simultaneously to detect two major sugarcane viruses associated with mosaic disease in sugarcane. LFIA is known for poor sensitivity and stability with its signalling conjugates. However, we synthesized positively charged Cysteamine-gold nanoparticles and used them to prepare highly stable to sensitive immunoconjugates and as a colourimetric detection label. Further nanogold signal enhancement was performed on LFIA to obtain a high detection sensitivity, which is higher than the conventional immunoassays. The linear detection range of the nano-LIFA was 10^-6 to 10^-9 g mL^-1, and with the signal enhancement, the LOD reached up to 10^-12 g ml^-1. This research paper provides relative merits and advancement on nano-LFIA for specific detection of sugarcane viruses in sugarcane for the first time.

The Emerging Roles of Silver Nanoparticles to Target Viral Life Cycle and Detect Viral Pathogens

Along the line of recent vaccine advancements, new antiviral therapeutics are compelling to combat viral infection-related public health crises. Several properties of silver nanoparticles (AgNPs) such as low level of cytotoxicity, ease of tunability of the AgNPs in the ultra-small nanoscale size and shape through different convenient bottom-up chemistry approaches, high penetration of the composite with drug formulations into host cells has made AgNPs, a promising candidate for developing antivirals. In this review, we have highlighted the recent advancements in the AgNPs based nano-formulations to target cellular mechanisms of viral propagation, immune modulation of the host, and the ability to synergistically enhance the activity of existing antiviral drugs. On the other hand, we have discussed the recent advancements on AgNPs based detection of viral pathogens from clinical samples using inherent physicochemical properties. This article will provide an overview of our current knowledge on AgNPs based formulations that has promising potential for developing a counteractive strategy against emerging and existing viruses.

A monoclonal antibody-based time-resolved fluorescence microsphere lateral flow immunoassay for paclobutrazol detection

Paclobutrazol (PBZ) is a plant growth inhibitor and fungicide, but it is also carcinogenic and teratogenic, and has potential harm to human health. In this study, two PBZ haptens (PBZ-1, PBZ-2) were synthesized and conjugated with carrier proteins to get artificial antigens. A highly specific monoclonal antibody (mAb) against PBZ was prepared. The antibody subtype was IgG₁ and the concentration was 11.03 mg/mL. A sensitive and rapid time-resolved fluorescence microsphere lateral flow immunoassay (TRFMs-LFIA) was established based on the mAb. The activated pH, the mAbs diluents, the mAb reacting concentration and the probe amount were optimized. The visual limit of detection (vLOD) and quantitative limit of detection (qLOD) of the TRFMs-LFIA for PBZ were 50 and 1.72 ng/mL respectively, and the 50% inhibiting concentration (IC₅₀) was 9.38 ng/mL. The pretreatment procedures are simple and rapid, and the detection time of TRFMs-LFIA strip is 6 min. Qualitative and quantitative analysis of PBZ could be achieved under a UV light or with a portable fluorescence immunoassay analyzer. The average recovery rates ranged from 96.2% to 111.9% and the corresponding coefficients of variation (CV) were 4.0%–11.2% in spiked wheat and rice samples. Twenty real wheat and rice samples were measured by the TRFMs-LFIA and compared with Ultra-performance liquid chromatography/tandem mass spectrometry (UPLC-MS/MS). The measured values showed a good accordance. These results indicated that the proposed assay will provide a novel effective strategy for on-site detection of PBZ.

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A new immunogen was prepared using thyroglobulin as carrier protein coupled with hapten.

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A high-sensitivity mAb was prepared using a heterologous coating antigen.

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Based on anti-PBZ mAb, TRAMs-LFIA was developed for the detection of paclobutrazol residue for the first time.

•

The proposed LFIA was rapid, easy to operate and highly accurate.

Lateral Flow Immunoassay Coupled with Copper Enhancement for Rapid and Sensitive SARS-CoV-2 Nucleocapsid Protein Detection

The coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory coronavirus 2 (SARS-CoV-2) is still raging all over the world. Hence, the rapid and sensitive screening of the suspected population is in high demand. The nucleocapsid protein (NP) of SARS-CoV-2 has been selected as an ideal marker for viral antigen detection. This study describes a lateral flow immunoassay (LFIA) based on colloidal gold nanoparticles for rapid NP antigen detection, in which sensitivity was improved through copper deposition-induced signal amplification. The detection sensitivity of the developed LFIA for NP antigen detection (using certified reference materials) under the optimized parameters was 0.01 μg/mL and was promoted by three orders of magnitude to 10 pg/mL after copper deposition signal amplification. The LFIA coupled with the copper enhancement technique has many merits such as low cost, high efficiency, and high sensitivity. It provides an effective approach to the rapid screening, diagnosis, and monitoring of the suspected population in the COVID-19 outbreak.

High-Throughput Flow-Through Direct Immunoassays for Targeted Bacteria Detection

Regulatory authorities require analytical methods for bacteria detection to analyze large sample volumes (typically 100 mL). Currently only the Membrane Filtration and the Most Probable Number assays analyze such large volumes, while other assays for bacteria detection (ELISA, lateral flow assays, etc.) typically analyze volumes 1000 times smaller. This study describes flow-through direct immunoassays (FTDI), a new methodology for the targeted detection of bacteria in liquid samples of theoretically any volume. Flow-through direct immunoassays are performed in fluid-permeable microwells (e.g., wells of a filter well plate) that have a membrane on their bottom where the bacteria are trapped before their detection using a direct immunoassay. Two versions of FTDI assays for the detection of E. coli in 10 mL of sample were developed. A rapid FTDI assay that can be completed in less than 2.5 h can detect E. coli bacteria in levels down to 17 CFU/mL, and an ultrasensitive FTDI assay that employs an additional bacteria culturing step to boost the sensitivity can detect E. coli bacteria in levels lower than 1 CFU/mL in less than 5.5 h. All the steps of the assays, including the immunoassay steps, the culturing step, and the analytical signal measurement step are performed inside the well plate to decrease the chance of contamination and ensure a safe, easy process for the user. The assays were assessed and validated in tap water, river water, and apple juice samples, and the results suggests that the assays are robust, precise, and accurate. When the assays are performed in 96-well filter plates, a filter well plate vacuum manifold and a multichannel peristaltic pump are also used, so multiple samples can be analyzed in parallel to allow high-throughput analysis of samples.

Overview of Rapid Detection Methods for Salmonella in Foods: Progress and Challenges

Salmonella contamination in food production and processing is a serious threat to consumer health. More and more rapid detection methods have been proposed to compensate for the inefficiency of traditional bacterial cultures to suppress the high prevalence of Salmonella more efficiently. The contamination of Salmonella in foods can be identified by recognition elements and screened using rapid detection methods with different measurable signals (optical, electrical, etc.). Therefore, the different signal transduction mechanisms and Salmonella recognition elements are the key of the sensitivity, accuracy and specificity for the rapid detection methods. In this review, the bioreceptors for Salmonella were firstly summarized and described, then the current promising Salmonella rapid detection methods in foodstuffs with different signal transduction were objectively summarized and evaluated. Moreover, the challenges faced by these methods in practical monitoring and the development prospect were also emphasized to shed light on a new perspective for the Salmonella rapid detection methods applications.

Upconverting phosphor technology-based lateral flow assay for the rapid and sensitive detection of anti-Trichinella spiralis IgG antibodies in pig serum

Background

Trichinella spiralis is a zoonotic food-borne parasite. A disease caused by infection with T. spiralis is called trichinellosis in humans. It is important to investigate the epidemic situation and the surveillance of herds and then prevent infection in humans. Therefore, this study is to develop a rapid and sensitive diagnostic method for on-site test in domestic and wild animals.

Methods

Upconverting phosphor nanoparticles (UCNPs), an excellent optical label, were conjugated with the excretory-secretory (ES) antigens from T. spiralis muscle larvae (ML) or goat anti-rabbit IgG, and a lateral flow (LF) assay based on these probes (UCNPs-ES/goat anti-rabbit IgG) was developed for the rapid and sensitive detection of anti-T. spiralis IgG antibodies in pig serum. The assay is named the UPT-LF-ES assay. In addition, the probes were characterized, and the assay was optimized. A cut-off threshold of the assay was also identified by using 169 known negative pig samples. Performance of the assay to T. spiralis with different infective numbers, cross-reactivity with other parasitic infections, the single-blinded experiment, and coincidence were evaluated with the assay.

Results

The UPT-LF-ES assay was successfully constructed and optimized based on the probes of UCNPs-ES/goat anti-rabbit IgG. In the pigs infected with 100, 1000, and 10,000 ML, positive results were first presented at 35 days post-infection (dpi), 30 dpi, and 25 dpi, respectively. The assay had no cross-reaction with other parasitic infections. A single-blinded experiment indicated that the sensitivity and specificity of the UPT-LF-ES assay were 100% and 100%, respectively, the area under the receiver operating characteristic (ROC) curve was 1.000. In addition, the value detected by the UPT-LF-ES assay was significantly different between positive and negative samples. Moreover, compared with the “gold standard” magnetic stirrer method, the coincidence rate of the UPT-LF-ES assay was 87.27%, and the kappa (K) coefficient was 0.7454, showing a substantial agreement.

Conclusions

The UPT-LF-ES assay is a useful point-of-care test (POCT) with T. spiralis in the detection of pig, which contributes to preventing human trichinellosis.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-04949-2.

Universal fluorescence nanoprobes to enhance the sensitivity of immunochromatographic assay for detection of 17β-estradiol in milk

The pollution caused by estrogens in the environment and food has received increasing attention. It is still challenging for on-site immunochromatographic assay (ICA) detection of estrogens. The performance of the prepared probes plays a decisive role in the sensitivity and stability of the ICA system. The published probes usually directly couple the detection antibody to the label, ignoring the influence of the label on the activity of the antibody. In this study, 17β-estradiol (E₂) was used as a model analyte for the ICA system. Two universal probes were constructed based on quantum dot nanobeads (QBs), recombinant protein A (SPA, from Staphylococcus aureus), and rabbit anti-mouse immunoglobulin G antibody (anti-IgG). The probes were prepared by coupling QBs with SPA, releasing anti-E₂ monoclonal antibody (mAb), and maintaining its activity. The prepared universal probes can orient recognize the Fc region of mAb and fully expose its Fab region, improving the detection sensitivity of the ICA system. The free anti-E₂ mAb and the universal probe (QBs@SPA or QBs@SPA@anti-IgG) were used as the detection antibodies and signal donors, respectively. The results show that the proposed ICA based on QBs@SPA and QBs@SPA@anti-IgG probes could detect E₂ with IC₅₀ of 8.83 and 0.93 ng/mL, respectively, within 15 min under optimal conditions. The recovery results of ICA based on QBs@SPA and QBs@SPA@anti-IgG probes showed good agreement with the findings of the high-performance liquid chromatography (HPLC) analysis for spiked samples. The developed ICA system based on universal probes was superior in terms of sensitivity, rapidity, and applicability, and held great promise for its implementation in detecting environmental and food small-molecule pollutants.

Advances in differentiation and identification of foodborne bacteria using near infrared spectroscopy

Rapid and sensitive detection of foodborne bacteria is a growing concern for ensuring safe food supply and preventing human foodborne infections. It is difficult for conventional methods to meet these detection requirements because they are often tedious and time-consuming. In the recent years, near infrared (NIR) spectroscopy has been found to be a promising method for all sorts of analyses in microbiology due to its highly specific absorption signature and non-destructive measurements. In this review, we first briefly introduce the fundamental and basic operational procedure of NIR spectroscopy for foodborne bacteria detection. Then we summarize the main advances and contributions of this technique in the study of foodborne bacteria. Finally, we conclude that much work still remains to be done before NIR spectroscopy really becomes a viable alternative in the field of microbiological characterization.

Nucleic Acid Amplification Techniques in Immunoassay: An Integrated Approach with Hybrid Performance

An immunoassay is mostly employed for the direct detection of food contaminants, and a molecular assay for targeting nucleic acids employs amplification techniques for distinguishing genes. The integration of an immunoassay with nucleic acid amplification techniques inherits the direct and rapid performance of an immunoassay and the ultrasensitive merit of a molecular assay. Enthusiastic attention has been attracted in recent years on the utilization of isothermal amplification techniques in an immunoassay, as well as the employment of a lateral flow immunoassay in a molecular assay. Thus, this Review discussed these kinds of approaches from two categories: immuno-nucleic acid amplification (I-NAA) and nucleic acid amplification-immunoassay (NAA-I). The advantages, drawbacks, and future developments were discussed for a comprehensive understanding.

Antibody- and nucleic acid-based lateral flow immunoassay for Listeria monocytogenes detection

Listeria monocytogenes is an invasive opportunistic foodborne pathogen and its routine surveillance is critical for protecting the food supply and public health. The traditional detection methods are time-consuming and require trained personnel. Lateral flow immunoassay (LFIA), on the other hand, is an easy-to-perform, rapid point-of-care test and has been widely used as an inexpensive surveillance tool. In recent times, nucleic acid-based lateral flow immunoassays (NALFIA) are also developed to improve sensitivity and specificity. A significant improvement in lateral flow-based assays has been reported in recent years, especially the ligands (antibodies, nucleic acids, aptamers, bacteriophage), labeling molecules, and overall assay configurations to improve detection sensitivity, specificity, and automated interpretation of results. In most commercial applications, LFIA has been used with enriched food/environmental samples to ensure detection of live cells thus prolonging the assay time to 24-48 h; however, with the recent improvement in LFIA sensitivity, results can be obtained in less than 8 h with shortened and improved enrichment practices. Incorporation of surface-enhanced Raman spectroscopy and/or immunomagnetic separation could significantly improve LFIA sensitivity for near-real-time point-of-care detection of L. monocytogenes for food safety and public health applications.

Gold nanoparticle-based immunochromatographic assay for detection Pseudomonas aeruginosa in water and food samples

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An ICA was developed for P. aeruginosa detection.

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The ICA strip showed a limit of detection of 2.41 × 10⁴ CFU/mL.

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The ICA could be applied to detect P. aeruginosa in water and food samples.

Pseudomonas aeruginosa (P. aeruginosa) is the common infection-causing bacterial pathogen. Conventional methods for the detection of P. aeruginosa are time-consuming, and therefore, a more rapid analytical method is required. Here, monoclonal antibodies (Mabs) against P. aeruginosa (CICC 10419) were prepared and based on paired Mabs, an immunochromatographic assay (ICA) was developed. The ICA strip showed a limit of detection of 2.41 × 10⁴ CFU/mL and the linear range of detection was 3.13 × 10⁴-1.0 × 10⁶ CFU/mL. No cross-reactivity was observed when other common Gram-negative and Gram-positive bacteria were used. The analytical performance of the ICA strip indicated that the developed ICA had good specificity and stability. Moreover, the feasibility of the ICA strip was verified by detecting P. aeruginosa (CICC 10419) in spiked water and food samples. The ICA strip could detect samples contaminated with a low-level of P. aeruginosa (CICC 10419) after 8 h enrichment.

Monoclonal Antibodies Application in Lateral Flow Immunochromatographic Assays for Drugs of Abuse Detection

Lateral flow assays (lateral flow immunoassays and nucleic acid lateral flow assays) have experienced a great boom in a wide variety of early diagnostic and screening applications. As opposed to conventional examinations (High Performance Liquid Chromatography, Polymerase Chain Reaction, Gas chromatography-Mass Spectrometry, etc.), they obtain the results of a sample's analysis within a short period. In resource-limited areas, these tests must be simple, reliable, and inexpensive. In this review, we outline the production process of antibodies against drugs of abuse (such as heroin, amphetamine, benzodiazepines, cannabis, etc.), used in lateral flow immunoassays as revelation or detection molecules, with a focus on the components, the principles, the formats, and the mechanisms of reaction of these assays. Further, we report the monoclonal antibody advantages over the polyclonal ones used against drugs of abuse. The perspective on aptamer use for lateral flow assay development was also discussed as a possible alternative to antibodies in view of improving the limit of detection, sensitivity, and specificity of lateral flow assays.

The universal dual-mode aptasensor for simultaneous determination of different bacteria based on naked eyes and microfluidic-chip together with magnetic DNA encoded probes

It was critically important to develop some sensitive, convenient and on-site methods for simultaneous assay of different pathogenic bacteria in foods. In this work, a dual-mode aptasensor was established for fulfilling above aims combing colorimetry with microfluidic chip. This as-prepared dual-mode aptasensor not only realized rapid screening by naked eye on-site, but also the simultaneous quantification of multiple bacteria. Namely, the presence of pathogenic bacteria was firstly judged by naked eyes with Salmonella typhimurium (S.T) and Vibrio parahaemolyticus (V.P) as models. And then, S.T and V.P in positive samples were simultaneously quantified by microfluidic chip. In order to obtain the multiple signals, a series of magnetic DNA encoded-probes (MDEs) was fabricated containing rolling cycle amplified long DNA chain (RCA-DNA) rich in G-quadruplex sequences. They can combine with hemin as DNAzyme to catalyze 3,3'-5,5'-Tetramethyl benzidine (TMB)-H₂O₂ system for color development and be cleaved by EcoRV endonuclease to produce DNA fragments with different lengths. The microfluidic chip was employed to separate and quantify the fragments for quantifying S.T and V.P simultaneously. For this protocol, 100 CFU·mL^-1 of V.P or S.T could be observed by the naked eye and as low as 32 S.T and 30 CFU·mL^-1 V.P could be detected by the chip within 3 min. The dual-mode aptasensor could quickly screen positive samples, and simultaneously perform quantitative detection of the bacteria in positive samples. Our protocol demonstrated its potential in on-site qualification & simultaneous quantification of foodborne bacteria in foods.

Light-up RNA aptamer signaling-CRISPR-Cas13a-based mix-and-read assays for profiling viable pathogenic bacteria

Viable pathogenic bacteria cause serious human diseases via systemic infections and food poisoning. Herein, we constructed a light-up RNA aptamer signaling-CRISPR-Cas13a assay enabling mix-and-read detection of viable pathogenic bacteria. Directly targeting pathogen RNAs via CRISPR-Cas13a allows precisely discriminating viable bacteria from dead bacteria. We introduced a light-up RNA aptamer, Broccoli, serving as the substate of activated CRISPR-Cas13a to monitor the presence of pathogen RNAs, eliminating the need to use chemically labeled RNA substrate. Sequentially, the assay allows a reverse transcription-free, nucleic acid amplification-free, and label-free quantification of RNA targets and viable pathogenic bacteria. It could detect as low as 10 CFU of Bacillus cereus and precisely quantify viable bacteria with a content ranging from 0% to 100% in 10⁵ CFU total bacteria. The quantification of viable bacteria allows more accurately estimating the ability of B. cereus to spoil food. The RNA assay promises its use in point-of-use detection of viable pathogens and biosafety control.

Identification of novel monoclonal antibodies targeting the outer membrane protein C and lipopolysaccharides for Escherichia coli O157:H7 detection

AIMS

To identify and evaluate the application of two novel monoclonal antibody (mAb) 2G12 against outer membrane protein (Omp) C and mAb 12B1 targeting the O chain of the lipopolysaccharides (LPS) of Escherichia coli O157:H7 (ECO157).

METHODS AND RESULTS

The sensitivity and specificity of these two antibodies were evaluated with eight ECO157 strains and 68 untargeted strains. mAb 2G12 and 12B1 had no detectable binding with any of the non-O157 strains at 6·0 log₁₀ CFU per ml, while its high specificity and affinity remained with all ECO157 strains. When a higher level (8·0 log₁₀ CFU per ml) was tested, 2G12 and 12B1 did not react with 82·35 and 97·06% of the non-O157 strains respectively. Based on the pair of two antibodies, the sandwich enzyme-linked immunosorbent assay detected 100% (8/8) of ECO157 strains and none of the non-ECO157 strains. The detection limit of ECO157 strains in pure culture were 4·2 ± 0·2 log₁₀ CFU per ml. When the developed test was applied to artificially inoculated beef samples, the detection limit was 6·0 log₁₀ CFU per gram without enrichment and 1·0 log₁₀ CFU per gram after 12 h of enrichment.

CONCLUSIONS

The two novel antibodies identified in this study served as great candidates for the recovery, and detection of ECO157 from different environmental and food samples.

SIGNIFICANCE AND IMPACT OF THE STUDY

ECO157-specific detection was improved by a combination of the novel OmpC mAb and LPS mAb with defined target antigen and good specificity.

Development of rapid gold nanoparticles based lateral flow assays for simultaneous detection of Shigella and Salmonella genera

Salmonella and Shigella genera are common pathogens that contaminate foods and beverages. Lateral flow assays (LFA) are commonly used to detect these pathogens. However, most of the developed LFAs are for single detection. Simultaneous detection of pathogens is required to reduce cost and time. In this work, 40 nm gold nanoparticles (AuNPs) were synthesized using the seeding growth method as labeling agent. The AuNPs were characterized and conjugated with mouse anti-Gram negative endotoxin antibody. The nitrocellulose membrane HF135 was immobilized with anti-mouse IgG antibody as a control line and two separate test lines with either anti-Shigella or anti-Salmonella antibody, respectively. Color intensity of test lines was observed for positive samples. A milk sample was used as proof of concept to mimic actual contamination. The limit of detection of the LFA was 3.0 × 10⁶ CFU/mL for multiplex detection of Shigella flexneri and Salmonella Typhi and for both single detections. The result was comparable with the enzyme-linked immunosorbent assay (ELISA) analysis. The produced LFA could differentiate between Shigella flexneri, Shigella boydii, Salmonella Enteritidis, and Salmonella Typhi. The developed LFA was able to identify Shigella flexneri and Salmonella Typhi with good sensitivity in milk samples, thus, beneficial to ensure the safety of food before entering the market.

An immunochromatographic strip sensor for sildenafil and its analogues

In this study, a new hapten of sildenafil (Sild) was successfully synthesized and a sensitive monoclonal antibody (mAb) against Sild was produced based on this new hapten. The subclass of the mAb was IgG2a, and the half-maximal inhibitory concentration (IC50) of the mAb was 0.53 ng mL-1. Next, an immunochromatographic assay (ICA) was established for detecting Sild and its analogues in functional foods, where the visual detection limit (vLOD) and cut-off values were 0.5 and 20 μg kg-1, respectively. With the aid of a strip scan reader, the ICA can measure Sild with an LOD of 0.7 μg kg-1 and a line range of detection between 1.40 and 13.11 μg kg-1. The whole test process takes only 15 min. Therefore, the ICA provides a useful tool for the on-site detection and rapid initial screening of Sild in functional food samples.

Using bimetallic Au@Pt nanozymes as a visual tag and as an enzyme mimic in enhanced sensitive lateral-flow immunoassays: Application for the detection of streptomycin

Because of the advantages of simplicity, cost-effectiveness and visibility, lateral-flow immunoassays (LFAs) have been widely used in the food safety field. However, the low sensitivity of LFAs needs to be solved. Nanozymes have amazing potential for application in biosensors due to their excellent and abundant enzyme-like characteristics. In this study, an Au@Pt nanozyme synthesized by a one-step method showed the higher affinity with TMB/H₂O₂ and higher catalytic efficiency than that of horseradish peroxidase (HRP). For the detection of streptomycin (STR), a typical aminoglycoside antibiotic, a novel LFA based on Au@Pt as a visual tag and an enhanced LFA based on the enzyme-like activity of Au@Pt by addition of the chromogenic substrate 3-amino-9-ethyl-carbazole (AEC) were established and compared with conventional LFA based on AuNPs. The qualitative limit of detection (LOD) was 1 ng mL^-1 for the LFA based on Au@Pt as the visual tag and 0.1 ng mL^-1 for the enhanced LFA based on the activity of Au@Pt, in comparison to 8 ng mL^-1 for LFA based on AuNPs. Furthermore, the level of streptomycin in milk samples from Zhenjiang City was successfully evaluated by the novel LFA based on Au@Pt nanozyme. These results suggest that LFAs based on nanozymes are a promising and effective tool for food safety.