Replacement of antibodies with bacteriophages in lateral flow assay of Salmonella Enteritidis

Single-tube detection of a foodborne bacterial pathogen using user-friendly portable device

Timely and reliable detection of foodborne bacterial pathogen is crucial for reducing disease burden in low- and middle-income countries. However, laboratory-based methods are often inaccessibility in resource-limited settings. Here, we developed a single-tube assay and a low-cost palm-sized device for on-site detection of the representative foodborne bacterial pathogen, Salmonella Enteritidis. Our assay incorporates the advantages of protein-nucleic acid signal transduction, EXPonential Amplification Reaction (EXPAR), and clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated 12a (Cas12a). After systematically investigating the compatibility of these components, we developed a "three-in-one" integration reaction, termed ST-EXPAR-CRISPR assay. This assay requires only one tube, one controlled temperature (39 °C) and simple operation, eliminating the need for bacterial isolation, nucleic acid extraction, or washing steps. ST-EXPAR-CRISPR assay is capable of detecting as few as 37 CFU/mL of target bacterium. Using our kit and portable device, untrained volunteers successfully detected contamination in food samples outdoors. The simplicity of the detection process and minimal hardware requirements make our assay highly promising for application in point-of-care and on-site scenarios. Moreover, the ST-EXPAR-CRISPR assay can be easily modified to detect other targets by changing the nucleic acid sequence with low research and development cost, potentially reducing the global disease burden.

Phage probe on RAFT polymer surface for rapid enumeration of E. coli K12

This study presents a simple, fast, and sensitive label-free sensing assay for the precise enumeration of modeled pathogenic Escherichia coli K12 (E. coli K12) bacteria for the first time. The method employs the covalent binding bacteriophage technique on the surface of a reversible addition-fragmentation chain transfer (RAFT) polymer film. The Nyquist plots obtained from electrochemical impedance spectroscopy (EIS) identified the charge transfer resistance Rct was calculated from a suitable electrochemical circuit model through an evaluation of the relevant parameter after the immobilization of the bacteriophage and the binding of specific E. coli K12. The impedimetric biosensor reveals specific and reproducible detection with sensitivity in the linear working range of 104.2-107.0 CFU/mL, a limit of detection (LOD) of 101.3 CFU/mL, and a short response time of 15 min. The SERS response validates the surface roughness and interaction of the SERS-tag with E. coli K12-modified electrodes. Furthermore, the covalently immobilized active phage selectivity was proved against various non-targeting bacterial strains in the presence of targeted E.coli K12 with a result of 94 % specificity and 98 % sensitivity. Therefore, the developed phage-based electrode surface can be used as a disposable, label-free impedimetric biosensor for rapid and real-time monitoring of serum samples.

Efficiency of Bacteriophage-Based Detection Methods for Non-Typhoidal Salmonella in Foods: A Systematic Review

Food contamination with non-typhoidal Salmonella (NTS) presents a significant public health risk, underscoring the critical need for rigorous food safety measures throughout the production, distribution, preparation, and consumption stages. Conventional diagnostic strategies are time-consuming and labor-intensive and are thus sub-optimal for throughput NTS detection. Bacteriophages (phages) are highly specialized bacterial viruses and exhibit extreme specificity for their hosts. This organic phage/bacterial interaction provides an invaluable tool that can potentially replace or complement existing S. enterica detection methods. Here, we explored work in this area and reviewed data from PubMed/MEDLINE, Embase, and ScienceDirect up to 4 November 2024. Thirty-five studies were selected from 607 retrieved articles using the JBI Critical Appraisal Checklist to ensure quality. Salmonella enrichment, rapid detection, and effective recovery in diverse food sources for various NTS serovars were targeted. Utilizing phages as bio-probes alongside lateral flow immunoassays, surface-enhanced Raman spectroscopy, fluorescence, and electrochemistry assays enabled rapid and highly sensitive detection of NTS, achieving limits as low as 7 to 8 CFU/mL within 30 min. Balancing detection sensitivity with rapid analysis time is essential. Further research and development will be pivotal to overcoming challenges and maximizing the efficiency of NTS phage-based detection to ensure optimal food safety.

A Honeycomb Film Template-Based Method for High-Throughput Preparation of Anti-Salmonella typhimurium 14,028 Phage Microgels

Developing efficient anti-microbials for thoroughly addressing Salmonella contamination is essential for the improvement of food safety. Phage-built materials have shown great potential for biocontrol in environments. Due to challenges in delivery and stability, their widespread use has remained unattainable. Here, we have developed a honeycomb film template-based method for the high-throughput preparation of phage microgels. The honeycomb film template can be simply fabricated in a humid chamber based on a well-established breath figure method. The bacteriophage microgels can be further manufactured by dropping a pre-gelation solution containing bacteriophages into a honeycomb film template. This method can produce over 210,000 phage microgels in every square centimeter template with each microgel containing 1.04 × 107 phages. They can kill 99.90% of the contaminated S. typhimurium 14,028 on chicken samples. This simple, heat-free, and solvent-free method can maintain the strong anti-bacterial efficiency of phages, which can expand the wide application of phage-built microgels for food decontamination.

Principles, Methods, and Real-Time Applications of Bacteriophage-Based Pathogen Detection

Bacterial pathogens in water, food, and the environment are spreading diseases around the world. According to a World Health Organization (WHO) report, waterborne pathogens pose the most significant global health risks to living organisms, including humans and animals. Conventional bacterial detection approaches such as colony counting, microscopic analysis, biochemical analysis, and molecular analysis are expensive, time-consuming, less sensitive, and require a pre-enrichment step. However, the bacteriophage-based detection of pathogenic bacteria is a robust approach that utilizes bacteriophages, which are viruses that specifically target and infect bacteria, for rapid and accurate detection of targets. This review shed light on cutting-edge technologies about the novel structure of phages and the immobilization process on the surface of electrodes to detect targeted bacterial cells. Similarly, the purpose of this study was to provide a comprehensive assessment of bacteriophage-based biosensors utilized for pathogen detection, as well as their trends, outcomes, and problems. This review article summaries current phage-based pathogen detection strategies for the development of low-cost lab-on-chip (LOC) and point-of-care (POC) devices using electrochemical and optical methods such as surface-enhanced Raman spectroscopy (SERS).

A Comprehensive Review on Phage Therapy and Phage-Based Drug Development

Phage therapy, the use of bacteriophages (phages) to treat bacterial infections, is regaining momentum as a promising weapon against the rising threat of multidrug-resistant (MDR) bacteria. This comprehensive review explores the historical context, the modern resurgence of phage therapy, and phage-facilitated advancements in medical and technological fields. It details the mechanisms of action and applications of phages in treating MDR bacterial infections, particularly those associated with biofilms and intracellular pathogens. The review further highlights innovative uses of phages in vaccine development, cancer therapy, and as gene delivery vectors. Despite its targeted and efficient approach, phage therapy faces challenges related to phage stability, immune response, and regulatory approval. By examining these areas in detail, this review underscores the immense potential and remaining hurdles in integrating phage-based therapies into modern medical practices.

Advanced Vibrational Spectroscopy and Bacteriophages Team Up: Dynamic Synergy for Medical and Environmental Applications

Bacteriophages are emerging as a promising alternative in combating antibiotic-resistant bacteria amidst the escalating global antimicrobial resistance crisis. Recently, there has been a notable resurgence of interest in phages, prompting extensive research into their therapeutic potential. Beyond conventional microbiology and virology techniques, such as genomics and proteomics, novel phenotypic and chemical characterization methods are being explored. Among these, there is a growing interest in vibrational spectroscopy, especially in advanced modalities such as surface-enhanced Raman spectroscopy (SERS), tip-enhanced Raman spectroscopy (TERS), and atomic force microscopy-infrared spectroscopy (AFM-IR), which offer improved sensitivity and spatial resolution. This review explores the spectrum of uses of vibrational spectroscopy for bacteriophages, including its role in diagnostics, biosensing, phage detection, assistance in phage-based therapy, and advancing basic research.

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

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

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

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

CRISPR-Cas12a-Mediated Hue-Recognition Lateral Flow Assay for Point-of-Need Detection of Salmonella

Nucleic acid detection of pathogens in a point-of-need (PON) manner is of great significance yet remains challenging for sensitive and accurate visual discrimination. Here, we report a CRISPR-Cas12a-mediated lateral flow assay for PON detection of Salmonella typhimurium (S.ty) that is a prevailing pathogen disseminated through tainted food. The variation of the fluorescence color of the test line is exploited to interpret the results, enabling the discrimination between positive and negative samples on the basis of a hue-recognition mechanism. By leveraging the cleavage activity of Cas12a and hue-recognition readout, the assay facilitated by recombinase polymerase amplification can yield a visual detection limit of 1 copy μL-1 for S.ty genomic DNA within 1 h. The assay also displays a high specificity toward S.ty in fresh chicken samples, as well as a sensitivity 10-fold better than that of the commercial test strip. Moreover, a semiquantitative detection of S.ty ranging from 0 to 4 × 103 CFU/mL by the naked eye is made possible, thanks to the easily discernible color change of the test line. This approach provides an easy, rapid, accurate, and user-friendly solution for the PON detection of Salmonella and other pathogens.

Living virus-based nanohybrids for biomedical applications

Living viruses characterized by distinctive biological functions including specific targeting, gene invasion, immune modulation, and so forth have been receiving intensive attention from researchers worldwide owing to their promising potential for producing numerous theranostic modalities against diverse pathological conditions. Nevertheless, concerns during applications, such as rapid immune clearance, altering immune activation modes, insufficient gene transduction efficiency, and so forth, highlight the crucial issues of excessive therapeutic doses and the associated biosafety risks. To address these concerns, synthetic nanomaterials featuring unique physical/chemical properties are frequently exploited as efficient drug delivery vehicles or treatments in biomedical domains. By constant endeavor, researchers nowadays can create adaptable living virus-based nanohybrids (LVN) that not only overcome the limitations of virotherapy, but also combine the benefits of natural substances and nanotechnology to produce novel and promising therapeutic and diagnostic agents. In this review, we discuss the fundamental physiochemical properties of the viruses, and briefly outline the basic construction methodologies of LVN. We then emphasize their distinct diagnostic and therapeutic performances for various diseases. Furthermore, we survey the foreseeable challenges and future perspectives in this interdisciplinary area to offer insights. This article is categorized under: Biology-Inspired Nanomaterials > Protein and Virus-Based Structures Therapeutic Approaches and Drug Discovery > Emerging Technologies.

Evaluation of long- and short-term storage conditions and efficiency of a novel microencapsulated Salmonella phage cocktail for controlling Salmonella in chicken meat

This study aims to assess the stability and activity of using a lyophilization, formulation design and to evaluate their efficiency for controlling Salmonella in chicken meat. The phage-loaded 0.3 M sucrose gelatin mixture at 4 and 25 °C displayed significantly less phage titer loss (p < 0.05) than the other excipients and liquid phage cocktail in 12 months. The results showed that there were significant reductions of Salmonella at the end of the storage in chicken meat for newly prepared phage powder (1.86 log CFU/cm2 and 2.18 log CFU/cm2), lyophilized phage powders stored at 4 °C (1.08 log CFU/cm2 and 1.26 log CFU/cm2) and stored at 25 °C (0.66 log CFU/cm2 and 1.00 log CFU/cm2) for 10 months at MOI 100 and 1000, respectively. The results demonstrated that lyophilized phages in a simple food grade formulation can be successfully stored and might be used in biocontrol of Salmonella in meat.

A Critical Review on Detection of Foodborne Pathogens Using Electrochemical Biosensors

An outbreak of foodborne pathogens would cause severe consequences. Detecting and diagnosing foodborne diseases is crucial for food safety, and it is increasingly important to develop fast, sensitive, and cost-effective methods for detecting foodborne pathogens. In contrast to traditional methods, such as medium-based culture, nucleic acid amplification test, and enzyme-linked immunosorbent assay, electrochemical biosensors possess the advantages of simplicity, rapidity, high sensitivity, miniaturization, and low cost, making them ideal for developing pathogen-sensing devices. The biorecognition layer, consisting of recognition elements, such as aptamers, antibodies and bacteriophages, and other biomolecules or polymers, is the most critical component to determine the selectivity, specificity, reproducibility, and lifetime of a biosensor when detecting pathogens in a biosample. Furthermore, nanomaterials have been frequently used to improve electrochemical biosensors for sensitively detecting foodborne pathogens due to their high conductivity, surface-to-volume ratio, and electrocatalytic activity. In this review, we survey the characteristics of biorecognition elements and nanomaterials in constructing electrochemical biosensors applicable for detecting foodborne pathogens during the past five years. As well as the challenges and opportunities of electrochemical biosensors in the application of foodborne pathogen detection are discussed.

Recent Developments in Lateral Flow Assays for Salmonella Detection in Food Products: A Review

Salmonellosis is a disease transmitted by contaminated food and is one of the leading causes of infections worldwide, making the early detection of Salmonella of crucial importance for public health. However, current detection methods are laborious and time-consuming, thus impacting the entire food supply chain and leading to production losses and economic sanctions. To mitigate these issues, a number of different biosensors have been developed, including lateral flow assays (LFAs), which have emerged as valuable tools in pathogen detection due to their portability, ease of use, time efficiency, and cost effectiveness. The performance of LFAs has been considerably enhanced by the development of new nanomaterials over the years. In this review, we address the principles and formats of the assay and discuss future prospects and challenges with an emphasis on LFAs developed for the detection of different Salmonella serovars in food.

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

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

Nanobody-based immunomagnetic separation platform for rapid isolation and detection of Salmonella enteritidis in food samples

Rapid separation and identification of Salmonella enteritidis (S. enteritidis) in food is of great importance to prevent outbreaks of foodborne diseases. Herein, by using O and H antigens as targets, an epitope-based bio-panning strategy was applied to isolate specific nanobodies towards S. enteritidis. This method constitutes an efficient way to obtain specific antibody fragments and test pairwise nanobodies. On this basis, a double nanobody-based sandwich enzyme-linked immunosorbent assay (ELISA) coupled with immunomagnetic separation (IMS) was developed to rapid enrich and detect S. enteritidis in food. The detection limit of the IMS-ELISA was 3.2 × 10³ CFU/mL. In addition, 1 CFU of S. enteritidis in food samples can be detected after 4-h cultivation, which was shortened by 2 h after IMS. The IMS-ELISA strategy could avoid matrix interference and shorten the enrichment culture time, which has great potential for application in monitoring bacterial contamination in food.

"Lock-and-key" recognizer-encoded lateral flow assays toward foodborne pathogen detection: An overview of their fundamentals and recent advances

In light of severe health risks of foodborne pathogenic bacterial diseases, the potential utility of point-of-care (POC) sensors is recognized for pathogens detection. In this regard, lateral flow assay (LFA) is a promising and user-friendly option for such application among various technological approaches. This article presents a comprehensive review of "lock-and-key" recognizer-encoded LFAs with respect to their working principles and detection performance against foodborne pathogenic bacteria. For this purpose, we describe various strategies for bacteria recognition including the antibody-based antigen-antibody interactions, nucleic acid aptamer-based recognition, and phage-mediated targeting of bacterial cells. In addition, we also outline the technological challenges along with the prospects for the future development of LFA in food analysis. The LFA devices built based upon many recognition strategies are found to have great potential for rapid, convenient, and effective POC detection of pathogens in complex food matrixes. Future developments in this field should emphasize the development of high-quality bio-probes, multiplex sensors, and intelligent portable readers.

Raman spectroscopy: Principles and recent applications in food safety

Food contaminant is a significant issue because of the adverse effects on human health and economy. Traditional detection methods such as liquid chromatography-mass spectroscopy for detecting food contaminants are expensive and time-consuming, and require highly-trained personnel and complicated sample pretreatment. Raman spectroscopy is an advanced analytical technique in a manner of non-destructive, rapid, cost-effective, and ultrasensitive sensing various hazards in agri-foods. In this chapter, we summarized the principle of Raman spectroscopy and surface enhanced Raman spectroscopy, the methods to process Raman spectra, the recent applications of Raman/SERS (surface-enhanced Raman spectroscopy) in detecting chemical contaminants (e.g., pesticides, antibiotics, mycotoxins, heavy metals, and food adulterants) and microbiological hazards (e.g., Salmonella, Campylobacter, Shiga toxigenic E. coli, Listeria, and Staphylococcus aureus) in foods.

Nanosheet antibody mimics based label-free and dual-readout lateral flow immunoassay for Salmonella enteritidis rapid detection

Portable devices for on-site foodborne pathogens detection are urgently desirable. Lateral flow immunoassay (LFIA) provides an efficient strategy for pathogens detection, however, antibody labeling independence and detection reliability, are still challenging. Here, we report the development of a label-free LFIA with dual-readout using glucan-functionalized two-dimensional (2D) transition metal dichalcogenides (TMDs) tungsten disulfide (WS₂) as detection probes for sensitive detection of Salmonella enteritidis (S. enteritidis). In particular, glucan-functionalized WS₂, synthesized via liquid exfoliation, are reliable detection antibody candidates which served as antibody mimics for bacteria capturing. This LFIA has not only eliminated the intricate antibody labeling process and screening of paired antibodies in conventional LFIAs, but also promised dual-readout (colorimetric/Raman) for flexible detection. Under optimized conditions, this LFIA achieves selective detection of S. enteritidis with a low visual detection limit of 10³ CFU/mL and a broad linear range of 10³-10⁸ CFU/mL. Additionally, the LFIA could be successfully applied in drinking water and milk with recoveries of 85%-109%. This work is desirable to expand the application of 2D TMDs in biosensors and offers a brand-new alternative protocol of detection antibodies in foodborne pathogens detection.

Advances in surface-enhanced Raman spectroscopy technology for detection of foodborne pathogens

Rapid control and prevention of diseases caused by foodborne pathogens is one of the existing food safety regulatory issues faced by various countries and has received wide attention from all sectors of society. The development of rapid and reliable detection methods for foodborne pathogens remains a hot research area for food safety and public health because of the limitations of complex steps, time-consuming, low sensitivity, or poor selectivity of commonly used methods. Surface-enhanced Raman spectroscopy (SERS), as a novel spectroscopic technique, has the advantages of high sensitivity, selectivity, rapid and nondestructive detection and has exhibited broad application prospects in the determination of pathogenic bacteria. In this study, the enhancement mechanisms of SERS are briefly introduced, then the characteristics and properties of liquid-phase, rigid solid-phase, and flexible solid-phase are categorized. Furthermore, a comprehensive review of the advances in label-free or label-based SERS strategies and SERS-compatible techniques for the detection of foodborne pathogens is provided, and the advantages and disadvantages of these methods are reviewed. Finally, the current challenges of SERS technology applied in practical applications are listed, and the possible development trends of SERS in the field of foodborne pathogens detection in the future are discussed.

Colorimetric and surface-enhanced Raman scattering dual-mode magnetic immunosensor for ultrasensitive detection of blood phosphorylated tau in Alzheimer's disease

Phosphorylation of tau at Ser 396, 404 (p-tau^396,404) is the earliest phosphorylation event and a promising biomarker for the early diagnosis of Alzheimer's disease (AD). However, the detection of blood p-tau is challenging because of its low abundance, easy degradation, and complex formation with various blood proteins or cells, often leading to the underestimation of p-tau levels in conventional plasma-based assays. Herein, we developed a colorimetric and surface-enhanced Raman scattering (SERS) dual-mode magnetic immunosensor for highly sensitive, specific, and robust detection of p-tau^396,404 in whole blood samples. The detection assay was based on an immunoreaction between p-tau^396,404 proteins, wherein antibody-modified superparamagnetic iron oxide nanoparticles act as recognition elements to capture p-tau^396,404 in blood, and then horseradish peroxidase- and Raman tags label the corresponding paired antibody as a reporter to provide high signal-to-noise ratios for the immunosensor. This dual-mode immunosensor achieved identified as low as 1.5 pg/mL of p-tau^396,404 in the blood in SERS mode and 24 pg/mL in colorimetric mode by the naked eye. More importantly, this immunosensor rapidly and accurately distinguished AD patients from healthy individuals based on blood p-tau^396,404 levels, and also had the potential to distinguish AD patients of different severities. Therefore, the dual-mode immunosensor is promising for rapid clinical diagnosis of AD, especially in large-scale AD screening.

Recent Progress in Nanotechnology-Based Approaches for Food Monitoring

Throughout the food supply chain, including production, storage, and distribution, food can be contaminated by harmful chemicals and microorganisms, resulting in a severe threat to human health. In recent years, the rapid advancement and development of nanotechnology proposed revolutionary solutions to solve several problems in scientific and industrial areas, including food monitoring. Nanotechnology can be incorporated into chemical and biological sensors to improve analytical performance, such as response time, sensitivity, selectivity, reliability, and accuracy. Based on the characteristics of the contaminants and the detection methods, nanotechnology can be applied in different ways in order to improve conventional techniques. Nanomaterials such as nanoparticles, nanorods, nanosheets, nanocomposites, nanotubes, and nanowires provide various functions for the immobilization and labeling of contaminants in electrochemical and optical detection. This review summarizes the recent advances in nanotechnology for detecting chemical and biological contaminations in the food supply chain.

Engineered Core-Shell Multifunctional Nano-Tracer in Raman-Silent Region with Highly Retained Affinity to Enhance Lateral Flow Immunoassays

Stimulated surface-enhanced Raman scattering (SERS) in combination with engineered nano-tracer offers extraordinary potential in lateral flow immunoassays (LFIAs). Nonetheless, the investigation execution of SERS-LFIA is often compromised by the intricacy and overlap of the Raman fingerprint spectrum as well as the affinity-interference of nano-tracer to antibody. To circumvent these critical issues, an engineered core-shell multifunctional nano-tracer (named APNPs) with precise control of the size of nano-core (AuNPs) and coating of the nano-shell (Prussian blue nanomaterials) is prepared for SERS-LFIA via a modified enlarging particle size and coating modification strategy. Importantly, this nano-tracer exhibits enhanced coupling efficiency, highly retained affinity, reinforced colloid stability, and unique SERS signal (2156 cm^-1 ) in the silent region (1800-2800 cm^-1 ) with high signal-to-background ratio simultaneously, all of which are beneficial to the enhancement of the analysis performance. With a proof-of-concept demonstration for detection of ractopamine (RAC), a dual-pattern LFIA that synergizes both the enlarged particle size and coating modification supported colorimetric/biological silence Raman dual-response (coined as the ECCRD assay) is demonstrated by integrating APNPs with the competitive-type immunoreaction. This research may contribute to the rational design of multifunctional nano-tracer, and the ECCRD assay can be expanded for a wide spectrum of applications in environmental monitoring and biomedical diagnosis.

Universal and ultrasensitive detection of foodborne bacteria on a lateral flow assay strip by using wheat germ agglutinin-modified magnetic SERS nanotags

Rapid, direct and sensitive detection of foodborne bacteria in complex samples is still challenging. Here, we reported a universal surface-enhanced Raman scattering (SERS)-based lateral flow assay (LFA) for highly sensitive detection of foodborne bacteria in food and environmental samples using wheat germ agglutinin (WGA)-modified Fe3O4@Au (Au@MNP-WGA) nanotags. The Au@MNP-WGA tag with numerous intraparticle hotspots was integrated into the LFA system for the first time, which can not only greatly improve the detection sensitivity through the dual amplification effect of magnetic enrichment and SERS enhancement but also achieve the broad-spectrum capture of multiple bacteria. In addition, monoclonal antibodies were separately immobilized onto the test line of different LFA strips to ensure the specific detection of different target pathogens. With this strategy, the proposed assay can achieve the universal and highly sensitive determination of three common foodborne bacteria, namely, Listeria monocytogenes, Campylobacter jejuni, and Staphylococcus aureus, with low detection limit (10 cells mL-1), short testing time (<35 min), and high reproducibility (RSD < 8.14%). Given its good stability and accuracy in complex samples, the Au@MNP-WGA-based SERS-LFA has great potential to be a powerful tool for the universal and on-site detection of different foodborne pathogens.

Toward Next Generation Lateral Flow Assays: Integration of Nanomaterials

Lateral flow assays (LFAs) are currently the most used point-of-care sensors for both diagnostic (e.g., pregnancy test, COVID-19 monitoring) and environmental (e.g., pesticides and bacterial monitoring) applications. Although the core of LFA technology was developed several decades ago, in recent years the integration of novel nanomaterials as signal transducers or receptor immobilization platforms has brought improved analytical capabilities. In this Review, we present how nanomaterial-based LFAs can address the inherent challenges of point-of-care (PoC) diagnostics such as sensitivity enhancement, lowering of detection limits, multiplexing, and quantification of analytes in complex samples. Specifically, we highlight the strategies that can synergistically solve the limitations of current LFAs and that have proven commercial feasibility. Finally, we discuss the barriers toward commercialization and the next generation of LFAs.

Ultrasensitive multichannel immunochromatographic assay for rapid detection of foodborne bacteria based on two-dimensional film-like SERS labels

Rapid and sensitive detection of multiple foodborne bacteria without DNA amplification is still challenging. Here, we proposed an immunochromatographic assay (ICA) with multiplex analysis ability and high sensitivity for direct detection of bacteria in real food samples, based on an improved surface-enhanced Raman scattering (SERS) sensing strategy. Multifunctional Au shell-coated graphene oxide nanosheets (GO@Au) were fabricated and for the first time introduced into the ICA system as a two-dimensional film-like SERS label, which possessed huge surface area, excellent stability, and superior SERS activity. Different from the conventional spherical nanotags, the antibody-conjugated GO@Au nanosheet effectively and rapidly adhered to bacterial cells, improved the dispersibility of bacteria-nanolabel complexes on the ICA strips, and provided numerous stable hotspots for SERS signal enhancement. The combination of GO@Au labels and the ICA system achieved the multiplex and ultrasensitive determination of three major foodborne pathogens, namely, Staphylococcus aureus, Escherichia coli O157:H7, and Salmonella typhimurium, in a single test, with low detection limits (8, 10, and 10 cells/mL) and short detection time (20 min). The proposed biosensor demonstrated high stability and good accuracy in various food samples and is thus a promising tool for the rapid identification of bacteria.

Shape-Encoded Functional Hydrogel Pellets for Multiplexed Detection of Pathogenic Bacteria Using a Gas Pressure Sensor

Gas pressure is a promising signal readout mode in point-of-care testing for its merits such as rapidity, simplicity, affordability, and no need for sophisticated instrumentation. Herein, a gas pressure sensor for multiplexed detection of pathogenic bacteria was developed on a hydrogel platform. Spherical and square hydrogel pellets prepared by cross-linking of sodium alginate were functionalized with nisin and ConA for the capture of Staphylococcus aureus and Escherichia coli O157:H7, respectively. By using the shape-encoded functional hydrogel pellets and aptamer-modified platinum-coated gold nanoparticles (Au@PtNPs), a dual-molecule recognition mode was established for rapid and specific detection of the two pathogenic bacteria. Au@PtNPs were applied as signal probes to efficiently catalyze the decomposition of H₂O₂ for generating abundant O₂, which was converted into an amplified gas pressure signal. In two closed containers, the significant gas pressure signals were monitored with a portable pressure meter to quantitate the two pathogenic bacteria. The sensor was successfully applied to detect the pathogenic bacteria in various environmental, biological, and food samples. Thus, the proof-of-principle work paves a new avenue for multiplexed detection of pathogenic bacteria with shape-encoded hydrogel pellets combined with gas pressure signal readout.

A capillary driven microfluidic chip for SERS based hCG detection

In this study, a capillary driven microfluidic chip-based immunoassay was developed for the determination of Human Chorionic Gonadotropin (hCG) protein, which is prohibited by the World Anti-Doping Agency (WADA). Here, we used antibody modified magnetic metal organic framework nanoparticles (MMOFs) as a capture prob in urine sample. MMOF captured hCG was transferred in a capillary driven microfluidic chip consisting of four chambers, and the interaction of MMOF with gold nanorods labelled with 5,5'-Dithiobis-(2-nitrobenzoic acid) (DTNB) as a Raman label was carried out in the capillary driven microfluidic chip. The movement of MMOF through first chamber to the last chamber was achieved with a simple magnet. In the last chamber of capillary driven microfluidic chip, SERS signals of DTNB molecules from the sandwich complex were recorded using a Raman spectrophotometer. The selectivity of the developed method was demonstrated by applying the same procedure for the detection of Human Luteinizing Hormone (hLH), Human Chorionic Gonadotropin Hormone (hGH) and Immunoglobulin G (IgG) protein. The regression coefficient and limit of detection obtained from the standard addition method were found as 0,9985 and 0,61 IU/L, respectively. Furthermore, the conventional ELISA method confirmed that the results obtained by the presented method were acceptable with the similarity of 97.9% in terms of average recovery value, for the detection of hCG in urine samples. The analysis system developed for target proteins will be an alternative technique such as Western Blot used in routine analysis that is expensive and time consuming.

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.

Ten Years of Lateral Flow Immunoassay Technique Applications: Trends, Challenges and Future Perspectives

The Lateral Flow Immunoassay (LFIA) is by far one of the most successful analytical platforms to perform the on-site detection of target substances. LFIA can be considered as a sort of lab-in-a-hand and, together with other point-of-need tests, has represented a paradigm shift from sample-to-lab to lab-to-sample aiming to improve decision making and turnaround time. The features of LFIAs made them a very attractive tool in clinical diagnostic where they can improve patient care by enabling more prompt diagnosis and treatment decisions. The rapidity, simplicity, relative cost-effectiveness, and the possibility to be used by nonskilled personnel contributed to the wide acceptance of LFIAs. As a consequence, from the detection of molecules, organisms, and (bio)markers for clinical purposes, the LFIA application has been rapidly extended to other fields, including food and feed safety, veterinary medicine, environmental control, and many others. This review aims to provide readers with a 10-years overview of applications, outlining the trends for the main application fields and the relative compounded annual growth rates. Moreover, future perspectives and challenges are discussed.