SERS-Based Lateral Flow Strip Biosensor for Simultaneous Detection of Listeria monocytogenes and Salmonella enterica Serotype Enteritidis

Nucleic acid-mediated SERS Biosensors: Signal enhancement strategies and applications

Surface Enhanced Raman Spectroscopy (SERS) is a powerful spectroscopic analysis technique applied in various fields due to its high selectivity, ultra-high sensitivity, and non-destructiveness. As natural biological macromolecules, nucleic acids perform a significant role in SERS biosensing. In this review, we first summarize how nucleic acids mediate the signal enhancement of SERS biosensors from three aspects: substrate self-assembly, analyte biorecognition, and molecular amplification. Among them, SERS substrates can be self-assembled by both DNA modification and coordination or electrostatic interactions. In the field of biorecognition, analyte biorecognition based on three nucleic acid recognition elements can enhance SERS signals by regulating the distance of analytes or Raman reporter molecules to the SERS substrate. In addition, nucleic acid-based enzyme and enzyme-free amplification can enhance SERS signals by enlarging the quantity of analytes or its nucleic acid intermediates. Subsequently, multidimensional applications of nucleic acid-mediated SERS signal enhancement in biomedicine, food safety, and environmental monitoring are listed. Finally, the current challenges and future exploration of nucleic acid-mediated SERS signal enhancement are discussed.

In vitro diagnosis based on SERS-LFIA: research hotspots, increase sensitivities, combined detection, multimodal detection and related patents

In recent years, the SERS-LFIA platform has gained significant traction in in vitro diagnostics. However, a comprehensive review of its advancements and applications is still lacking. This review first employing a bibliometric approach to analyze research trends. It then outlines strategies to enhance sensitivity, focusing on Raman reporter molecules, SERS tags, coupling methods, detection instruments. Additionally, the review explores the use of SERS-LFIA for diagnosing multiple disease biomarkers, highlighting its potential to improve diagnostic accuracy. The review also synthesizes the application of multimodal SERS-LFIA technology, integrating signals such as colorimetric, magnetic, photothermal, fluorescent, and catalytic modalities. This approach enhances detection versatility and broadens diagnostic capabilities. Furthermore, it examines the current patent landscape, providing insights into the technology's commercial and technological progress. Lastly, the review discusses ongoing challenges, including stability and reproducibility and quantitative detection, while suggesting directions for future research. In summary, this review consolidates the latest advancements in SERS-LFIA technology for in vitro diagnostics over the past decade. Anticipated to furnish a robust scientific foundation and theoretical underpinning for the advancement of SERS-LFIA technology, this endeavor aims to enhance its efficacy in clinical diagnostics.

Core-shell Au@Ag NPs-based SERS-LFIA for the simultaneous quantitation of PEDV and PoRVA on site

Porcine epidemic diarrhea virus (PEDV) and porcine group A rotavirus (PoRVA) are predominant pathogens responsible for infectious diarrhea in porcine. Co-infections of PEDV and PoRVA have become a common situation in porcine farms in recent years, which increases the severity of the diarrhea disease and makes the accurate diagnosis more difficult. Rapid quantitation of PEDV and PoRVA is of great significance for the guarantee of disease control. In this study, a 4-mercaptobenzoic acid (MBA) modified core-shell Au@Ag nanoparticles (Au@MBA@Ag NPs) based lateral flow immunochromatography (LFIA) with dual-signal modes of visual observation and surface-enhanced Raman scattering (SERS) signal analysis was developed for the rapid and sensitive detection of PEDV and PoRVA. The established SERS-LFIA was capable of simultaneous quantitation of PEDV and PoRVA in porcine fecal samples within 20 min, with visual limits of detection (LODs) of 6.25 × 102 TCID50/mL and 7.42 × 102 copies/μL for PEDV and PoRVA, respectively. The LODs based on Raman signals were as low as 8.01 × 101 TCID50/mL and 3.19 × 102 copies/μL for PEDV and PoRVA, respectively, which were more than two orders of magnitude lower than the conventional colloidal gold (AuNPs) based colorimetric immunochromatography. Additionally, the SERS-LFIA exhibited no cross-reactivity with other prevalent pathogens and was highly repeatability, with a coefficient of variation (CV) of less than 15 %. When detecting clinical samples, the overall compliance of the SERS-LFIA with RT-PCR results was 93.3 %. Thus, the developed SERS-LFIA showed great potential for field applications on the rapid diagnosis of PEDV and PoRVA infection.

Development and optimization of an antibody-free nucleic acid lateral flow assay (AF-NALFA) as part of a molecular toolkit for visual readout of amplified Listeria monocytogenes DNA

Listeria monocytogenes is a Gram-positive foodborne pathogen responsible for listeriosis, a severe disease with high mortality in immunocompromised individuals. Rapid and accurate detection in food samples is essential for food safety. In this study, we developed and optimized an Antibody-Free Nucleic Acid Lateral Flow Assay (AF-NALFA) as part of a molecular detection toolkit for the visual readout of amplified L. monocytogenes hlyA gene, in combination with ultra-fast asymmetric PCR (aPCR) and oligonucleotide probe hybridization. Three critical parameters were optimized: oligonucleotide probe concentration on test and control lines, gold nanoparticle-probe conjugation ratio, and running buffer composition. In pure bacterial cultures, the limit of detection (LOD) of AF-NALFA was 12.62 copies for L. monocytogenes ATCC 7644, 8.68 copies for ATCC 19117, and 4.83 copies for ATCC 13932. These values were quantitatively assessed using qPCR, confirming the assay's consistency in detecting low DNA copy numbers. The prototype demonstrated 100% specificity against 13 other bacterial species. Furthermore, it was successfully tested in artificially contaminated UHT milk after 1 year of storage at room temperature, detecting L. monocytogenes at 1-30 CFU/mL without DNA purification or selective enrichment. The AF-NALFA enabled visual detection of target ssDNA hybridization within 20 min, offering a rapid, cost-effective alternative to DNA detection methods requiring expensive equipment, specialized expertise, and time-consuming procedures. These findings highlight AF-NALFA's potential as a complementary tool for L. monocytogenes surveillance, providing a practical solution for rapid screening in food safety laboratories and epidemiological monitoring.

Metal and metal oxide nanoparticle-assisted molecular assays for the detection of Salmonella

This paper provides a comprehensive overview of the diverse applications and innovations of nanoparticles in the detection of Salmonella. It encompasses a comprehensive range of novel methods, including efficient enrichment, nucleic acid extraction, immunoassays, nucleic acid tests, biosensors, and emerging strategies with the potential for future applications. The surface modification of specific antibodies or ligands enables nanoparticles to achieve highly selective capture of Salmonella, while optimizing the nucleic acid extraction process and improving detection efficiency. The employment of nanoparticles in immunological and nucleic acid tests markedly enhances the specificity and sensitivity of the reaction, thereby optimizing the determination of detection results. Moreover, the distinctive physicochemical properties of nanoparticles enhance the sensitivity, selectivity, and stability of biosensors, thereby facilitating the rapid advancement of bio-detection technologies. It is particularly noteworthy that there has been significant advancement in the application and innovative research of nanozymes in molecular assays. This progress has not only resulted in enhanced detection efficiency but has also facilitated innovation and improvement in detection technologies. As nanotechnologies continue to advance, the use of metal and metal oxide nanoparticles in Salmonella detection is likely to become a more promising and reliable strategy for ensuring food safety and public health.

Advances in Virus Detection Techniques Based on Recombinant Polymerase Amplification

Recombinase polymerase amplification (RPA) has emerged as a rapid, efficient, and highly sensitive method for nucleic acid amplification, thus becoming a focal point of research in the field of virus detection. This paper provides an overview of RPA, emphasizing its unique double-stranded DNA synthesis mechanism, rapid amplification efficiency, and capability to operate at room temperature, among other advantages. In addition, strategies and case studies of RPA in combination with other technologies are detailed to explore the advantages and potential of these integrated approaches for virus detection. Finally, the development prospect of RPA technology is prospected.

Colorimetric sensing for translational applications: from colorants to mechanisms

Colorimetric sensing offers instant reporting via visible signals. Versus labor-intensive and instrument-dependent detection methods, colorimetric sensors present advantages including short acquisition time, high throughput screening, low cost, portability, and a user-friendly approach. These advantages have driven substantial growth in colorimetric sensors, particularly in point-of-care (POC) diagnostics. Rapid progress in nanotechnology, materials science, microfluidics technology, biomarker discovery, digital technology, and signal pattern analysis has led to a variety of colorimetric reagents and detection mechanisms, which are fundamental to advance colorimetric sensing applications. This review first summarizes the basic components (e.g., color reagents, recognition interactions, and sampling procedures) in the design of a colorimetric sensing system. It then presents the rationale design and typical examples of POC devices, e.g., lateral flow devices, microfluidic paper-based analytical devices, and wearable sensing devices. Two highlighted colorimetric formats are discussed: combinational and activatable systems based on the sensor-array and lock-and-key mechanisms, respectively. Case discussions in colorimetric assays are organized by the analyte identities. Finally, the review presents challenges and perspectives for the design and development of colorimetric detection schemes as well as applications. The goal of this review is to provide a foundational resource for developing colorimetric systems and underscoring the colorants and mechanisms that facilitate the continuing evolution of POC sensors.

Towards a Wearable Feminine Hygiene Platform for Detection of Invasive Fungal Pathogens via Gold Nanoparticle Aggregation

Candida albicans is an opportunistic fungus that becomes pathogenic and problematic under certain biological conditions. C. albicans may cause painful and uncomfortable symptoms, as well as deaths in immunocompromised patients. Therefore, early detection of C. albicans is essential. However, conventional detection methods are costly, slow, and inaccessible to women in remote or developing areas. To address these concerns, we have developed a wearable and discrete naked-eye detectable colorimetric platform for C. albicans detection. With some modification, this platform is designed to be directly adhered to existing feminine hygiene pads. Our platform is rapid, inexpensive, user-friendly, and disposable and only requires three steps: (i) the addition of vaginal fluid onto sample pads; (ii) the addition of gold nanoparticle gel and running buffer, and (iii) naked eye detection. Our platform is underpinned by selective thiolated aptamer-based recognition of 1,3-β-D glucan molecules-a hallmark of C. albicans cell walls. In the absence of C. albicans, wearable sample pads turn bright pink. In the presence of C. albicans, the wearable pads turn dark blue due to significant nanoparticle target-induced aggregation. We demonstrate naked-eye colorimetric detection of 4.4 × 106C. albicans cells per ml and nanoparticle stability over a pH range of 3.0-8.0. We believe that this proof-of-concept platform has the potential to have a significant impact on women's health globally.

Flexible microfluidic co-recognition coupled with magnetic enrichment and silent SERS sensing for simultaneous analysis of bacteria in food

Food safety represents a critical global public health issue, with safety challenges posed by foodborne pathogens garnering extensive attention. Therefore, we introduce a co-recognition, enrichment and sensing (CES) all-in-one strategy for analysis of bacteria with low background and high specificity. This method employs antimicrobial peptide (AMP) functionalized magnetic nanoparticles (MNPs) to enrich bacteria and uses aptamer@Au@PBA (KxMFe(CN)6 (M = Pb and Ni)) NPs as silent SERS tags. When both S. aureus and E. coli O157:H7 are present, the silent SERS probes could specifically label the target bacteria, forming a sandwich-like structure. This binding induces silent Raman shifts (2139 cm-1 and 2197 cm-1), enabling quantification of two bacteria. Coupling with the modular flexible microfluidics and magnetic control slider device, this platform facilitates rapid switching between magnetic loading and elution. The CES SERS method demonstrated linear relationships for both S. aureus and E. coli O157:H7 at 50-1600 cfu mL-1, with detection limits of 14 and 18 cfu mL-1, respectively. The method achieved recovery rates of 85.6-112% and relative standard deviations of 1.5-8.6%. Validation using the ELISA method revealed relative errors between -7.5 and 4.3%. The CES approach has potential applications in food safety, environmental monitoring, and biomedical diagnosis.

The Evaluation of a Lateral Flow Strip Based on the Covalently Fixed "End-On" Orientation of an Antibody for Listeria monocytogenes Detection

In this study, the covalently fixed "end-on" orientation of a monoclonal Listeria monocytogenes antibody (mAb-Lis) to amino terminated oligo (ethylene glycol)-capped gold nanoparticles (NH2-TEG-AuNPs) was used to fabricate an in-house lateral flow strip (LFS), namely, the fixed "end-on" Lis-mAb-NH-TEG-AuNPs LFS. The aim was to evaluate the performance of the fixed "end-on" Lis-mAb-NH-TEG-AuNPs LFS in detecting L. monocytogenes. The proposed LFS enabled the sensitive detection of L. monocytogenes in 15 min with a visual limit of detection of 102 CFU/mL. Quantitative analysis indicated an LOD at 10 CFU/mL. The fixed "end-on" Lis-mAb-NH-TEG-AuNPs LFS showed no cross-reactivity with other pathogenic bacteria and practical performance across different food matrices, including human blood, milk, and mushroom samples. Furthermore, the clinical performance of the fixed "end-on" Lis-mAb-NH-TEG-AuNPs LFS for detecting L. monocytogenes was evaluated by using 12 clinical samples validated by the hemoculture method. It demonstrated excellent concordance with the reference methods, with no false-positive or false-negative results observed. Therefore, the fixed "end-on" Lis-mAb-NH-TEG-AuNPs LFS serves as a promising candidate for a point-of-care test (POCT), enabling the rapid, precise, and highly sensitive detection of L. monocytogenes in clinical samples and contaminated food.

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.

A cheaper substitute for HRP: ultra-small Cu-Au bimetallic enzyme mimics with infinitesimal steric hindrance to promote catalytic lateral flow immunodetection of clenbuterol

A highly sensitive lateral flow immunoassay (LFIA) is developed for the enzyme-catalyzed and double-reading determination of clenbuterol (CLE), in which a new type of probe was adopted through the direct electrostatic adsorption of ultra-small copper-gold bimetallic enzyme mimics (USCGs) and monoclonal antibodies. In the assay, based on the peroxidase activity of USCG, the chromogenic substrate TMB-H2O2 was introduced to trigger its color development, and the results were compared with those before catalysis. The detection sensitivity after catalysis is 0.03 ng mL-1 under optimal circumstances, which is 6-fold better than that of the traditional Au NPs-based LFIA and 2-fold greater than that before catalysis. This approach was successfully applied to the detection of CLE in milk, pork and mutton samples with an optimum assay time of 7 min and best catalytic time of 80 s, after which satisfactory recoveries of 98.53-117.79% were obtained. Cu-Au nanoparticles as a signal tag and the use of their nanozyme properties are the first applications in the field of LFIA. This work can be a promising exhibition for the application of a cheaper substitute for HRP, ultra-small bimetallic enzyme mimics, in LFIAs.

A Lateral Flow Assay Based on Streptavidin-biotin Amplification System with Recombinase Polymerase Amplification for Rapid and Quantitative Detection of Salmonella enteritidis

Salmonella constitutes a prevalent alimentary pathogen, instigating zoonotic afflictions. Consequently, the prompt discernment of Salmonella in sustenance is of cardinal significance. Lateral flow assays utilizing colorimetric methodologies adequately fulfill the prerequisites of point-of-care diagnostics, however, their detection threshold remains elevated, generally permitting only qualitative discernment, an impediment to the preliminary screening of nascent pathogens. In response to this conundrum, we propose a lateral flow diagnostic predicated upon a streptavidin-biotin amplification system with recombinase polymerase amplification engineered for the expeditious and quantitative discernment of Salmonella enteritidis. Trace nucleic acids within a sample undergo exponential amplification via recombinase polymerase amplification to a level discernable, constituting the initial signal amplification. Subsequently, along the test line (T-line) of the lateral flow strip, the chromatic signal undergoes augmentation by securing a greater quantity of AuNPs through the magnification capacity of the streptavidin-biotin mechanism, affecting the second signal amplification. Quantitative results are procured via smartphone capture and transferred to computer software for precise calculation of the targeted quantity. The lateral flow strip exhibits a LOD at 19.41 CFU/mL for cultured S. enteritidis. The RSD of three varying concentrations were respectively 3.74 %, 5.96 %, and 4.25 %.

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.

Recombinase Polymerase Amplification-Based Biosensors for Rapid Zoonoses Screening

Recent, outbreaks of new emergency zoonotic diseases have prompted an urgent need to develop fast, accurate, and portable screening assays for pathogen infections. Recombinase polymerase amplification (RPA) is sensitive and specific and can be conducted at a constant low temperature with a short response time, making it especially suitable for on-site screening and making it a powerful tool for preventing or controlling the spread of zoonoses. This review summarizes the design principles of RPA-based biosensors as well as various signal output or readout technologies involved in fluorescence detection, lateral flow assays, enzymatic catalytic reactions, spectroscopic techniques, electrochemical techniques, chemiluminescence, nanopore sequencing technologies, microfluidic digital RPA, and clustered regularly interspaced short palindromic repeats/CRISPR-associated systems. The current status and prospects of the application of RPA-based biosensors in zoonoses screening are highlighted. RPA-based biosensors demonstrate the advantages of rapid response, easy-to-read result output, and easy implementation for on-site detection, enabling development toward greater portability, automation, and miniaturization. Although there are still problems such as high cost with unstable signal output, RPA-based biosensors are increasingly becoming one of the most important means of on-site pathogen screening in complex samples involving environmental, water, food, animal, and human samples for controlling the spread of zoonotic diseases.

Test Article for automation purposes

Digital recombinase polymerase amplification (dRPA) aims to quantify the initial amount of nucleic acid by dividing nucleic acid and all reagents required for the RPA reaction evenly into numerous individual reaction units, such as chambers or droplets. dRPA turns out to be a prominent technique for quantifying the absolute quantity of target nucleic acid because of its advantages including low equipment requirements, short time consumption, as well as high sensitivity and specificity. dRPA combined with microfluidics are recognized as simple, various, and high-throughput nucleic acid quantization systems. This paper classifies the microfluidic dRPA systems over the last decade. We analyze and summarize the vital technologies of various microfluidic dRPA systems (e.g., chip preparation process, segmentation principle, microfluidic control, and statistical analysis methods), and major efforts to address limitations (e.g., prevention of evaporation and contamination, accurate initiation, and reduction of manual operation). In addition, this paper summarizes key factors and potential constraints to the success of the microfluidic dRPA to help more researchers, and possible strategies to overcome the mentioned challenges. Lastly, actual suggestions and strategies are proposed for the subsequent development of microfluidic dRPA.

Dual-channel biosensor for simultaneous detection of S. typhimurium and L. monocytogenes using nanotags of gold nanoparticles loaded metal-organic frameworks

Simultaneous detection of multiple foodborne pathogens is of great importance for ensuring food safety. Herein, we present a sensitive dual-channel electrochemical biosensor based on copper metal organic frameworks (CuMOF) and lead metal organic framework (PbMOF) for simultaneous detection of Salmonella typhimurium (S. typhimurium) and Listeria monocytogenes (L. monocytogenes). The MOF-based nanotags were prepared by functionalizing gold nanoparticles loaded CuMOF (Au@CuMOF) and PbMOF (Au@PbMOF) with signal DNA sequences 1 (sDNA1) and sDNA2, respectively. By selecting invA of S. typhimurium and inlA gene of L. monocytogenes as targe sequences, a sandwich-typed dual-channel biosensor was developed on glassy carbon electrodes (GCE) through hybridization reactions. The sensitive detection of S. typhimurium and L. monocytogenes was achieved by the direct differential pulse voltametric (DPV) signals of Cu2+ and Pb2+. Under optimal conditions, channel 1 of the biosensor showed linear range for invA gene of S. typhimurium in 1 × 10-14-1 × 10-8 M with low detection limit (LOD) of 3.42 × 10-16 M (S/N = 3), and channel 2 of the biosensor showed linear range for inlA gene of L. monocytogenes in 1 × 10-13-1 × 10-8 M with LOD of 6.11 × 10-15 M (S/N = 3). The dual-channel biosensor showed good selectivity which were used to detect S. typhimurium with linear range of 5-1.0 × 104 CFU mL-1 (LOD of 2.33 CFU mL-1), and L. monocytogenes with linear range of 10 - 1.0 × 104 CFU mL-1 (LOD of 6.61 CFU mL-1).

Recent advances in surface enhanced Raman spectroscopy for bacterial pathogen identifications

BACKGROUND

The rapid and reliable detection of pathogenic bacteria at an early stage is a highly significant research field for public health. However, most traditional approaches for pathogen identification are time-consuming and labour-intensive, which may cause physicians making inappropriate treatment decisions based on an incomplete diagnosis of patients with unknown infections, leading to increased morbidity and mortality. Therefore, novel methods are constantly required to face the emerging challenges of bacterial detection and identification. In particular, Raman spectroscopy (RS) is becoming an attractive method for rapid and accurate detection of bacterial pathogens in recent years, among which the newly developed surface-enhanced Raman spectroscopy (SERS) shows the most promising potential.

AIM OF REVIEW

Recent advances in pathogen detection and diagnosis of bacterial infections were discussed with focuses on the development of the SERS approaches and its applications in complex clinical settings.

KEY SCIENTIFIC CONCEPTS OF REVIEW

The current review describes bacterial classification using surface enhanced Raman spectroscopy (SERS) for developing a rapid and more accurate method for the identification of bacterial pathogens in clinical diagnosis. The initial part of this review gives a brief overview of the mechanism of SERS technology and development of the SERS approach to detect bacterial pathogens in complex samples. The development of the label-based and label-free SERS strategies and several novel SERS-compatible technologies in clinical applications, as well as the analytical procedures and examples of chemometric methods for SERS, are introduced. The computational challenges of pre-processing spectra and the highlights of the limitations and perspectives of the SERS technique are also discussed.Taken together, this systematic review provides an overall summary of the SERS technique and its application potential for direct bacterial diagnosis in clinical samples such as blood, urine and sputum, etc.

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

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

Europium Nanoparticle-Based Lateral Flow Strip Biosensors Combined with Recombinase Polymerase Amplification for Simultaneous Detection of Five Zoonotic Foodborne Pathogens

The five recognized zoonotic foodborne pathogens, namely, Listeria monocytogenes, Staphylococcus aureus, Streptococcus suis, Salmonella enterica and Escherichia coli O157:H7, pose a major threat to global health and social-economic development. These pathogenic bacteria can cause human and animal diseases through foodborne transmission and environmental contamination. Rapid and sensitive detection for pathogens is particularly important for the effective prevention of zoonotic infections. In this study, rapid and visual europium nanoparticle (EuNP)-based lateral flow strip biosensors (LFSBs) combined with recombinase polymerase amplification (RPA) were developed for the simultaneous quantitative detection of five foodborne pathogenic bacteria. Multiple T lines were designed in a single test strip for increasing the detection throughput. After optimizing the key parameters, the single-tube amplified reaction was completed within 15 min at 37 °C. The fluorescent strip reader recorded the intensity signals from the lateral flow strip and converted the data into a T/C value for quantification measurement. The sensitivity of the quintuple RPA-EuNP-LFSBs reached a level of 10¹ CFU/mL. It also exhibited good specificity and there was no cross-reaction with 20 non-target pathogens. In artificial contamination experiments, the recovery rate of the quintuple RPA-EuNP-LFSBs was 90.6-101.6%, and the results were consistent with those of the culture method. In summary, the ultrasensitive bacterial LFSBs described in this study have the potential for widespread application in resource-poor areas. The study also provides insights in respect to multiple detection in the field.

Advances in paper based isothermal nucleic acid amplification tests for water-related infectious diseases

Water-associated or water-related infectious disease outbreaks are caused by pathogens such as bacteria, viruses, and protozoa, which can be transmitted through contaminated water sources, poor sanitation practices, or insect vectors. Low- and middle-income countries bear the major burden of these infections due to inadequate hygiene and subpar laboratory facilities, making it challenging to monitor and detect infections in a timely manner. However, even developed countries are not immune to these diseases, as inadequate wastewater management and contaminated drinking water supplies can also contribute to disease outbreaks. Nucleic acid amplification tests have proven to be effective for early disease intervention and surveillance of both new and existing diseases. In recent years, paper-based diagnostic devices have made significant progress and become an essential tool in detecting and managing water-associated diseases. In this review, we highlight the importance of paper and its variants as a diagnostic tool and discuss the properties, design modifications, and various paper-based device formats developed and used for detecting water-associated pathogens.

Recent Trends in SERS-Based Plasmonic Sensors for Disease Diagnostics, Biomolecules Detection, and Machine Learning Techniques

Surface-enhanced Raman spectroscopy/scattering (SERS) has evolved into a popular tool for applications in biology and medicine owing to its ease-of-use, non-destructive, and label-free approach. Advances in plasmonics and instrumentation have enabled the realization of SERS's full potential for the trace detection of biomolecules, disease diagnostics, and monitoring. We provide a brief review on the recent developments in the SERS technique for biosensing applications, with a particular focus on machine learning techniques used for the same. Initially, the article discusses the need for plasmonic sensors in biology and the advantage of SERS over existing techniques. In the later sections, the applications are organized as SERS-based biosensing for disease diagnosis focusing on cancer identification and respiratory diseases, including the recent SARS-CoV-2 detection. We then discuss progress in sensing microorganisms, such as bacteria, with a particular focus on plasmonic sensors for detecting biohazardous materials in view of homeland security. At the end of the article, we focus on machine learning techniques for the (a) identification, (b) classification, and (c) quantification in SERS for biology applications. The review covers the work from 2010 onwards, and the language is simplified to suit the needs of the interdisciplinary audience.

Paper-based sensors for bacteria detection

The detection of pathogenic bacteria is essential to prevent and treat infections and to provide food security. Current gold-standard detection techniques, such as culture-based assays and polymerase chain reaction, are time-consuming and require centralized laboratories. Therefore, efforts have focused on developing point-of-care devices that are fast, cheap, portable and do not require specialized training. Paper-based analytical devices meet these criteria and are particularly suitable to deployment in low-resource settings. In this Review, we highlight paper-based analytical devices with substantial point-of-care applicability for bacteria detection and discuss challenges and opportunities for future development.

Combined antibodies against internalins A and B proteins have potential application in immunoassay for detection of Listeria monocytogenes

Listeria monocytogenes is a food-borne bacterium that causes listeriosis upon the ingestion of contaminated food. Traditional methods to detect L. monocytogenes require pre-enrichment broths to increase its concentration. To improve the screening of contaminated food and prevent listeriosis outbreaks, rapid, specific and sensitive assays are needed to detect L. monocytogenes. This study developed a prototype lateral flow immunochromatographic assay (LFIA) employing antibodies against L. monocytogenes Internalin A (InlA) and Internalin B (InlB) proteins, that are involved in non-phagocytic cell invasion. The following antibodies were used to capture L. monocytogenes antigenic targets: mouse anti-Internalin A monoclonal antibody (MAb-2D12) conjugated to colloidal gold nanoparticles and a mouse anti-Internalin B polyclonal antibody. This test was able to detect pure L. monocytogenes from culture with a limit of detection (LOD) ranging from 5.9 × 103 to 1.5 × 104 CFU/mL. In milk artificially contaminated with L. monocytogenes, the LOD was 1 × 105 CFU/mL. This prototype test discriminated L. monocytogenes from other bacterial species (Listeria innocua, Enterobacter cloacae, Bacillus cereus). Results indicate that this LFIA developed using antibodies against L. monocytogenes InlA and InlB proteins is a sensitive and specific tool that can be potentially useful to rapidly detect L. monocytogenes in contaminated food.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-022-05597-9.

Rapid detection of beer spoilage bacteria based on label-free SERS technology

Beer spoilage bacteria have been a headache for major breweries. In order to rapidly identify spoilage bacteria and improve the sensitivity and signal-to-noise ratio of bacterial SERS detection, the label-free SERS technique was used as a starting point, and we found eight bacteria species that led to beer spoilage. The impact of AgNP concentration and AgNP and bacterial binding time on the final results were thoroughly investigated. To maximize the increase in the SERS signal, an aluminized chip was created. We merged the t-SNE reduced dimensional analysis algorithm, and SVM, KNN, and LDA machine learning algorithms to further investigate the effect of the approach on the final identification rate. The results demonstrate that SERS spectra had an increased intensity and signal-to-noise ratio. The machine learning classification accuracy rates were all above 90%, indicating that the bacteria were correctly classified and identified.

Recombinase Polymerase Amplification Combined with Fluorescence Immunochromatography Assay for On-Site and Ultrasensitive Detection of SARS-CoV-2

This study established a portable and ultrasensitive detection method based on recombinase polymerase amplification (RPA) combined with high-sensitivity multilayer quantum dot (MQD)-based immunochromatographic assay (ICA) to detect the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The RPA-MQD-based ICA method is reported for the first time and has the following advantages: (i) RPA is free from the constraints of instruments and can be promoted in point-of-care testing (POCT) scenarios, (ii) fluorescence ICA enhances the portability of detection operation so that the entire operation time is controlled within 1 h, and (iii) compared with common colorimetric-based RPA-ICA, the proposed assay used MQD to provide strong and quantifiable fluorescence signal, thus enhancing the detection sensitivity. With this strategy, the proposed RPA-MQD-based ICA can amplify and detect the SARS-CoV-2 nucleic acid on-site with a sensitivity of 2 copies/reaction, which is comparable to the sensitivity of commercial reverse transcription quantitative polymerase chain reaction (RT-qPCR) kits. Moreover, the designed primers did not cross-react with other common respiratory viruses, including adenovirus, influenza virus A, and influenza virus B, suggesting high specificity. Thus, the established portable method can sensitively detect SARS-CoV-2 nucleic acid without relying on equipment, having good application prospects in SARS-CoV-2 detection scenarios under non-lab conditions.

Colorimetric Approach for Nucleic Acid Salmonella spp. Detection: A Systematic Review

Water- and food-related health issues have received a lot of attention recently because food-poisoning bacteria, in particular, are becoming serious threats to human health. Currently, techniques used to detect these bacteria are time-consuming and laborious. To overcome these challenges, the colorimetric strategy is attractive because it provides simple, rapid and accurate sensing for the detection of Salmonella spp. bacteria. The aim of this study is to review the progress regarding the colorimetric method of nucleic acid for Salmonella detection. A literature search was conducted using three databases (PubMed, Scopus and ScienceDirect). Of the 88 studies identified in our search, 15 were included for further analysis. Salmonella bacteria from different species, such as S. Typhimurium, S. Enteritidis, S. Typhi and S. Paratyphi A, were identified using the colorimetric method. The limit of detection (LoD) was evaluated in two types of concentrations, which were colony-forming unit (CFU) and CFU per mL. The majority of the studies used spiked samples (53%) rather than real samples (33%) to determine the LoDs. More research is needed to assess the sensitivity and specificity of colorimetric nucleic acid in bacterial detection, as well as its potential use in routine diagnosis.

Critical insight into recombinase polymerase amplification technology

INTRODUCTION

Recombinase polymerase amplification (RPA) is a promising and emerging technology for rapidly amplifying target nucleic acid from minimally processed samples and through small portable instruments. RPA is suitable for point-of-care testing (POCT) and on-site field testing, and it is compatible with microfluidic devices. Several detection assays have been developed, but limited research has dug deeper into the chemistry of RPA to understand its kinetics and fix its shortcomings.

AREAS COVERED

This review provides a detailed introduction of RPA molecular mechanism, kits formats, optimization, application, pros, and cons. Moreover, this critical review discusses the nonspecificity issue of RPA, highlights its consequences, and emphasizes the need for more research to resolve it. This review discusses the reaction kinetics of RPA in relation to target length, product quantity, and sensitivity. This critical review also questions the novelty of recombinase-aided amplification (RAA). In short, this review discusses many aspects of RPA technology that have not been discussed previously and provides a deeper insight and new perspectives of the technology.

EXPERT OPINION

RPA is an excellent choice for pathogen detection, especially in low-resource settings. It has a potential to replace PCR for all purposes, provided its shortcomings are fixed and its reagent accessibility is improved.

Emerging Bioanalytical Devices and Platforms for Rapid Detection of Pathogens in Environmental Samples

The development of robust bioanalytical devices and biosensors for infectious pathogens is progressing well with the advent of new materials, concepts, and technology. The progress is also stepping towards developing high throughput screening technologies that can quickly identify, differentiate, and determine the concentration of harmful pathogens, facilitating the decision-making process for their elimination and therapeutic interventions in large-scale operations. Recently, much effort has been focused on upgrading these analytical devices to an intelligent technological platform by integrating them with modern communication systems, such as the internet of things (IoT) and machine learning (ML), to expand their application horizon. This review outlines the recent development and applications of bioanalytical devices and biosensors to detect pathogenic microbes in environmental samples. First, the nature of the recent outbreaks of pathogenic microbes such as foodborne, waterborne, and airborne pathogens and microbial toxins are discussed to understand the severity of the problems. Next, the discussion focuses on the detection systems chronologically, starting with the conventional methods, advanced techniques, and emerging technologies, such as biosensors and other portable devices and detection platforms for pathogens. Finally, the progress on multiplex assays, wearable devices, and integration of smartphone technologies to facilitate pathogen detection systems for wider applications are highlighted.

Biosensors, modern technology for the detection of cancer-associated bacteria

Cancer is undoubtedly one of the major human challenges worldwide. A number of pathogenic bacteria are deemed to be potentially associated with the disease. Accordingly, accurate and specific identification of cancer-associated bacteria can play an important role in cancer control and prevention. A variety of conventional methods such as culture, serology, and molecular-based methods as well as PCR and real-time PCR have been adopted to identify bacteria. However, supply costs, machinery fees, training expenses, consuming time, and the need for advanced equipment are the main problems with the old methods. As a result, advanced and modern techniques are being developed to overcome the disadvantages of conventional methods. Biosensor technology is one of the innovative methods that has been the focus of researchers due to its numerous advantages. The main purpose of this study is to provide an overview of the latest developed biosensors for recognizing the paramount cancer-associated bacteria.

Development of a paper printed colorimetric sensor based on Cu-Curcumin nanoparticles for evolving point-of-care clinical diagnosis of sodium

The homeostatic control of Sodium (Na⁺) ion in the human body assumes paramount relevance owing to its physiological importance. Any deviation from the normal level causes serious health problems like hypernatremia, hyponatremia, stroke, kidney problems etc. Therefore, quantification of Na⁺ levels in body fluids has significant diagnostic and prognostic importance. However, interfering ions like Potassium ion (K⁺) is the major hurdle in sodium detection. In this work, we synthesized the clusters of 3-9 nm-sized highly stable and pure Copper nanoparticles surface functionalised with curcumin, through chemical reduction method. Each cluster of particles is encapsulated in a curcumin layer which is clearly visible in TEM images. The results show that these curcumin functionalized Cu NPs (CuC) are highly selective to the colorimetric detection of Na⁺. The ions like K⁺, Mg²⁺ and Zn²⁺ did not interfere with the Na⁺ in this sensing technique. Low-cost paper-based sensor strips are fabricated and calibrated for the sensing of sodium in the physiological range and shade cards were developed as a calorimetric guide for estimation of Na⁺ which makes them ideal point of care diagnostic platform. We demonstrate that the proposed CuC paper strip can be used for detecting Na⁺ concentration within the whole physiological range in both blood serum and urine.

Overview and Future Perspectives of Microfluidic Digital Recombinase Polymerase Amplification (dRPA)

Digital recombinase polymerase amplification (dRPA) aims to quantify the initial amount of nucleic acid by dividing nucleic acid and all reagents required for the RPA reaction evenly into numerous individual reaction units, such as chambers or droplets. dRPA turns out to be a prominent technique for quantifying the absolute quantity of target nucleic acid because of its advantages including low equipment requirements, short time consumption, as well as high sensitivity and specificity. dRPA combined with microfluidics are recognized as simple, various, and high-throughput nucleic acid quantization systems. This paper classifies the microfluidic dRPA systems over the last decade. We analyze and summarize the vital technologies of various microfluidic dRPA systems (e.g., chip preparation process, segmentation principle, microfluidic control, and statistical analysis methods), and major efforts to address limitations (e.g., prevention of evaporation and contamination, accurate initiation, and reduction of manual operation). In addition, this paper summarizes key factors and potential constraints to the success of the microfluidic dRPA to help more researchers, and possible strategies to overcome the mentioned challenges. Lastly, actual suggestions and strategies are proposed for the subsequent development of microfluidic dRPA.

State of the art: Lateral flow assays toward the point-of-care foodborne pathogenic bacteria detection in food samples

Diverse chemicals and some physical phenomena recently introduced in nanotechnology have enabled scientists to develop useful devices in the field of food sciences. Concerning such developments, detecting foodborne pathogenic bacteria is now an important issue. These kinds of bacteria species have demonstrated severe health effects after consuming foods and high mortality related to acute cases. The most leading path of intoxication and infection has been through food matrices. Hence, quick recognition of foodborne bacteria agents at low concentrations has been required in current diagnostics. Lateral flow assays (LFAs) are one of the urgent and prevalently applied quick recognition methods that have been settled for recognizing diverse types of analytes. Thus, the present review has stressed on latest developments in LFAs-based platforms to detect various foodborne pathogenic bacteria such as Salmonella, Listeria, Escherichia coli, Brucella, Shigella, Staphylococcus aureus, Clostridium botulinum, and Vibrio cholera. Proper prominence has been given on exactly how the labels, detection elements, or procedures have affected recent developments in the evaluation of diverse bacteria using LFAs. Additionally, the modifications in assays specificity and sensitivity consistent with applied food processing techniques have been discussed. Finally, a conclusion has been drawn for highlighting the main challenges confronted through this method and offered a view and insight of thoughts for its further development in the future.

Multiplex optical bioassays for food safety analysis: Toward on-site detection

Food safety analysis plays a significant role in controlling food contamination and supervision. In recent years, multiplex optical bioassays (MOBAs) have been widely applied to analyze multiple hazards due to their efficiency and low cost. However, due to the challenges such as multiplexing capacity, poor sensitivity, and bulky instrumentation, the further application of traditional MOBAs in food screening has been limited. In this review, effective strategies regarding food safety MOBAs are summarized, such as spatial-resolution modes performed in multi-T lines/dots strips or arrays of strip/microplate/microfluidic chip/SPR chip and signal-resolution modes employing distinguishable colorimetric/luminescence/fluorescence/surface plasma resonance/surface-enhanced Raman spectrum as signal tags. Following this, new trends on how to design engineered sensor architecture and exploit distinguishable signal reporters, how to improve both multiplexing capacity and sensitivity, and how to integrate these formats into smartphones so as to be mobile are summarized systematically. Typically, in the case of enhancing multiplexing capacity and detection throughput, microfluidic array chips with multichannel architecture would be a favorable approach to overcome the spatial and physical limitations of immunochromatographic assay (ICA) test strips. Moreover, noble metal nanoparticles and single-excitation, multiple-emission luminescence nanomaterials hold great potential in developing ultrasensitive MOBAs. Finally, the exploitation of innovative multiplexing strategy hybridized with powerful and widely available smartphones opens new perspectives to MOBAs. In future, the MOBAs should be more sensitive, have higher multiplexing capacity, and easier instrumentation.

A rapid and facile analytical approach to detecting Salmonella Enteritidis with aptamer-based surface-enhanced Raman spectroscopy

Salmonella should be absence in pharmaceutical preparations and foods according to regulations in many countries. Up to now, rapidly detecting Salmonella at 1 CFU·[10 g (mL) ]^-1 in pharmaceutical preparation or 1 CFU·[25 g (mL) ]^-1 in food samples is still a challenge. Herein, we present an aptamer-based surface-enhanced Raman spectroscopy (SERS) method for rapidly detecting Salmonella Enteritidis by using a handheld Raman instrument. The aptamer could specifically recognize S. Enteritidis, and 4-MBA self-assembled on the surface of Au@Ag NPs was used as a Raman reporter molecule. The method was validated to be high specific with no interference from other five pathogenic bacteria. It could identify S. Enteritidis contaminant at ∼ 1 CFU·(10 g)^-1 spiked level in a real sample (Wenxin granule, a botanical drug) after 6 h of enrichment. The detection time was much shorter than that of the methods (more than 54 ∼ 96 h) in the standards of pharmaceutical preparations and foods. In addition, the method could quantitatively determinate S. Enteritidis with satisfactory results. The SERS peak intensities of 4-MBA at 1072 cm^-1 showed a good linear correlation (R² = 0.9873) with the logarithms of S. Enteritidis concentrations ranging from 4.17 × 10² to 1.39 × 10⁷ CFU·mL^-1. T-test result (P = 0.425) revealed that there was no significant difference between the determination results obtained by the SERS method and the plate counting method. Therefore, the study indicated that the method was practical and reliable, and it could be a promising alternative for the on-site detection of S. Enteritidis.

Naked-eye detection strategies coupled with isothermal nucleic acid amplification techniques for the detection of human pathogens

Nucleic acid amplification-based techniques have gained acceptance by the scientific, and general, community as reference methodologies for many different applications. Since the development of the gold standard of these techniques, polymerase chain reaction (PCR), back in the 1980s many improvements have been made, and alternative techniques emerged reporting improvements over PCR. Among these, isothermal amplification approaches resulted of particular interest as could overcome the need of specialized equipment to accurately control temperature changes, but it was after year 2000 that these techniques have flourished in a huge number of novel alternatives with many different degrees of complexities and requirements. An added value is their possibility to be combined with many different naked-eye detection strategies, simplifying the resources needed, allowing to reduce cost, and serving as the basis for novel developments of lab-on-chip systems, and miniaturized devices, for point-of-care testing. In this review, we will go over different types of naked-eye detection strategies, combined with isothermal amplification. This will provide the readers up-to-date information for them to select the most appropriate strategies depending on the particular needs and resources for their experimental setup.

Towards quantitative point of care detection using SERS lateral flow immunoassays

The rapid detection of biomolecules in a point of care (POC) setting is very important for diagnostic purposes. A platform which can provide this, whilst still being low cost and simple to use, is paper-based lateral flow immunoassays (LFIA). LFIA combine immunology and chromatography to detect a target by forming an immunocomplex with a label which traps them in a test zone. Qualitative analysis can be performed using the naked eye whilst quantitative analysis takes place by measuring the optical signal provided by the label at the test zone. There are numerous detection methods available; however, many suffer from low sensitivity and lack of multiplexing capabilities or are poor at providing POC quantitative analysis. An attractive method to overcome this is to use nanoparticles coated in Raman reporters as the labelled species and to analyse test zones using surface-enhanced Raman scattering (SERS). Due to the wide variety of metal nanoparticles, Raman reporter and laser excitations that are available, SERS-based LFIA have been adapted to identify and quantify multiple targets at once. Large Raman microscopes combined with long mapping times have limited the platform to the lab; however, by transferring the analysis to portable Raman instruments, rapid and quantitative measurements can be taken at the POC without any loss in sensitivity. Portable or handheld SERS-LFIA platforms can therefore be used anywhere, from modern clinics to remote and resource-poor settings. This review will present an overview of SERS-based LFIA platforms and the major recent advancements in multiplexing and portable and handheld detection with an outlook on the future of the platform.

Tailoring noble metal nanoparticle designs to enable sensitive lateral flow immunoassay

Lateral flow immunoassay (LFIA) with gold nanoparticles (AuNPs) as signal reporters is a popular point-of-care diagnostic technique. However, given the weak absorbance of traditional 20-40 nm spherical AuNPs, their sensitivity is low, which greatly limits the wide application of AuNP-based LFIA. With the rapid advances in materials science and nanotechnology, the synthesis of noble metal nanoparticles (NMNPs) has enhanced physicochemical properties such as optical, plasmonic, catalytic, and multifunctional activity by simply engineering their physical parameters, including the size, shape, composition, and external structure. Using these engineered NMNPs as an alternative to traditional AuNPs, the sensitivity of LFIA has been significantly improved, thereby greatly expanding the working range and application scenarios of LFIA, particularly in trace analysis. Therefore, in this review, we will focus on the design of engineered NMNPs and their demonstration in improving LFIA. We highlight the strategies available for tailoring NMNP designs, the effect of NMNP engineering on their performance, and the working principle of each engineering design for enhancing LFIA. Finally, current challenges and future improvements in this field are briefly discussed.

Rapid and sensitive detection of Hg2+ with a SERS-enhanced lateral flow strip

A SERS-LFS strategy was designed and applied for the direct detection of target Hg2+ with greatly improved sensing performance by SERS measurements on the T line of the LFS, which did not change the intrinsic simplicity of the LFS.

An Overview for the Nanoparticles-Based Quantitative Lateral Flow Assay

The development of the lateral flow assay (LFA) has received much attention in both academia and industry because of their broad applications to food safety, environmental monitoring, clinical diagnosis, and so forth. The user friendliness, low cost, and easy operation are the most attractive advantages of the LFA. In recent years, quantitative detection has become another focus of LFA development. Here, the most recent studies of quantitative LFAs are reviewed. First, the principles and corresponding formats of quantitative LFAs are introduced. In the biomaterial and nanomaterial sections, the detection, capture, and signal amplification biomolecules and the optical, fluorescent, luminescent, and magnetic labels used in LFAs are described. The invention of dedicated strip readers has drawn further interest in exploiting the better performance of LFAs. Therefore, next, the development of dedicated reader devices is described and the usefulness and specifications of these devices for LFAs are discussed. Finally, the applications of LFAs in the detection of metal ions, biotoxins, pathogenic microorganisms, veterinary drugs, and pesticides in the fields of food safety and environmental health and the detection of nucleic acids, biomarkers, and viruses in clinical analyses are summarized.