Antibiotic and mammal IgG based lateral flow assay for simple and sensitive detection of Staphylococcus aureus

Characterisation of a SapYZU11@ZnFe2O4 biosensor reveals its mechanism for the rapid and sensitive colourimetric detection of viable Staphylococcus aureus in food matrices

Although bacteriophage-based biosensors hold promise for detecting Staphylococcus aureus in food products in a timely, simple, and sensitive manner, the associated targeting mechanism of the biosensors remains unclear. Herein, a colourimetric biosensor SapYZU11@ZnFe2O4, based on a broad-spectrum S. aureus lytic phage SapYZU11 and a ZnFe2O4 nanozyme, was constructed, and its capacity to detect viable S. aureus in food was evaluated. Characterisation of SapYZU11@ZnFe2O4 revealed its effective immobilisation, outstanding biological activity, and peroxidase-like capability. The peroxidase activity of SapYZU11@ZnFe2O4 significantly decreased after the addition of S. aureus, potentially due to blockage of the nanozyme active sites. Moreover, SapYZU11@ZnFe2O4 can detect S. aureus from various sources and S. aureus isolates that phage SapYZU11 could not lyse. This may be facilitated by the adsorption of the special receptor-binding proteins on the phage tail fibre and wall teichoic acid receptors of S. aureus. Besides, SapYZU11@ZnFe2O4 exhibited remarkable sensitivity and specificity when employing colourimetric techniques to rapidly determine viable S. aureus counts in food samples, with a detection limit of 0.87 × 102 CFU/mL. Thus, SapYZU11@ZnFe2O4 has broad application prospects for the detection of viable S. aureus cells on food substrates.

Polydopamine modified colloidal gold nanotag-based lateral flow immunoassay platform for highly sensitive detection of pathogenic bacteria and fast evaluation of antibacterial agents

Bacterial infection is a great threat to human health. Lateral flow immunoassays (LFIAs) with the merits of low cost, quick screening, and on-site detection are competitive technologies for bacteria detection, but their detection limits depend on the optical performance of the adopted nanotags. Herein, we presented a LFIA platform for bacteria detection using polydopamine (PDA) functionalized Au nanoparticles (denoted as Au@PDA) as the nanotag. The introduction of PDA could provide enhanced light absorption of Au, as well as numerous functional groups for conjugation. Small recognition molecules i.e. vancomycin (Van) and p-mercaptophenylboronic acid (PMBA) were covalently anchored to Au@PDA, and selected as the specific probes towards Gram-positive (G+) and Gram-negative (G-) bacteria, respectively. Taken Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) as the representative targets of G+ and G- bacteria, two LFA strips were successfully constructed based on the immuno-sandwich principle. They could quantitatively detect S. aureus and E. coli both down to 102 cfu/mL, a very competitive detection limit in comparison with other colorimetric or luminescent probes-based LFIAs. Furthermore, the proposed two strips were applied for the quantitative, accurate, and rapid detection of S. aureus and E. coli in food and human urine samples with good analytical results obtained. In addition, they were integrated as a screening platform for quick evaluation of diverse antibacterial agents within 3 h, which is remarkably shortened compared with that of the two traditional methods i.e. bacterial culture and plate-counting.

Double-Enhanced Photothermal Lateral Flow Biosensor Based on Dual Gold Nanoparticle Conjugates

Bacterial toxins emerge as the primary triggers of foodborne illnesses, posing a significant threat to human health. To ensure food safety, it is imperative to implement point-of-care testing methods. Lateral flow biosensors (LFBs) based on gold nanoparticles (GNPs) have been commonly used for rapid detection, but their applicationis limited by low sensitivity. Based on the localized surface plasmon resonance and photothermal effect of dual gold nanoparticle conjugates (DGNPs), we developed a smartphone-integrated photothermal LFB (PLFB) with double-enhanced colorimetric and photothermal sensitivity. Through numerical simulations, we verified that DGNPs have significantly enhanced photothermal performance compared to single 15 nm GNPs (SGNPs), and applied DGNPs in PLFB for the detection of staphylococcus enterotoxin A (SEA). The colorimetric and photothermal limits of detection of DGNPs-based PLFB for SEA were 0.091 and 0.0038 ng mL-1, respectively. Compared with the colorimetric detection of the SGNPs-based LFB, the colorimetric detection sensitivity of the DGNPs-based PLFB was increased by 10.7 times, and the photothermal detection sensitivity was further improved by 255.3 times. Moreover, the PLFB exhibits robust reproducibility and exceptional specificity and is applicable for detecting SEA in milk samples. This smartphone-integrated PLFB based on DGNPs allows users to detect toxins simply, conveniently, and quickly and has huge application potential in the field of food safety.

First organic fluorescence immunoassay for the detection of Enterobacter cloacae in food matrixes

For the first time, a novel fluorescent moiety, 2-amino-4-(7-formyl-1,8-dihydropyren-2-yl)-7-hydroxy-4H-chromene-3-carbonitrile (ACC), was synthesized by an ultrasonication method. The synthesis of this moiety was confirmed via structural elucidation using FTIR and NMR spectroscopy techniques. Further, photophysical properties of the fluorescent moiety were tested using UV-visible and emission spectroscopy techniques. In this case, the moiety was tagged with an antibody of Enterobacter cloacae via 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide (EDC/NHS) coupling and applied as a sensing element for the detection of Enterobacter cloacae (E. cloacae) by UV-visible and emission spectroscopy techniques. The developed fluorescent sensor detected E. cloacae via a FRET mechanism. Under optimized conditions, ACC-anti-E. cloacae detected E. cloacae in the linear range from 101 to 1010 CFU mL-1 with a limit of detection (LOD) of 10.55 CFU mL-1. The developed sensor was applied for the detection of E. cloacae in food samples such as orange, pomegranate, milk, rice, tomato, potato and onion.

High-efficient separation of deoxyribonucleic acid from pathogenic bacteria by hedgehog-inspired magnetic nanoparticles microextraction

Efficient separation of deoxyribonucleic acid (DNA) through magnetic nanoparticles (MN) is a widely used biotechnology. Hedgehog-inspired MNs (HMN) possess a high-surface-area due to the distinct burr-like structure of hedgehog, but there is no report about the usage of HMN for DNA extraction. Herein, to improve the selection of MN and illustrate the performance of HMN for DNA separation, HMN and silica-coated Fe3O4 nanoparticles (Fe3O4@SiO2) were fabricated and compared for the high-efficient separation of pathogenic bacteria of DNA. Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) are typical Gram-negative and Gram-positive bacteria and are selected as model pathogenic bacteria. To enhance the extraction efficiency of two kinds of MNs, various parameters, including pretreatment, lysis, binding and elution conditions, have been optimized in detail. In most separation experiments, the DNA yield of HMN was higher than that of Fe3O4@SiO2. Therefore, a HMN-based magnetic solid-phase microextraction (MSPE) and quantitative real-time PCR (qPCR) were integrated and used to detect pathogenic bacteria in real samples. Interestingly, the HMN-based MSPE combined qPCR strategy exhibited high sensitivity with a limit of detection of 2.0 × 101 CFU mL-1 for E. coli and 4.0 × 101 CFU mL-1 for S. aureus in orange juice, and 2.8 × 102 CFU mL-1 for E. coli and 1.1 × 102 CFU mL-1 for S. aureus in milk, respectively. The performance of the proposed strategy was significantly better than that of commercial kit. This work could prove that the novel HMN could be applicable for the efficient separation of DNA from complex biological samples.

Hollow versatile Ag@Pt alloy nanoparticles with nanozyme activity for detection and photothermal sterilization of Helicobacter pylori

In view of a large number of people infected with Helicobacter pylori (H. pylori) with great harm followed, there is an urgent need to develop a non-invasive, easy-to-operate, and rapid detection method, and to identify effective sterilization strategies. In this study, highly specific nanoprobes with nanozyme activity, Ag@Pt nanoparticles (NPs) with the antibody, were utilized as a novel lateral flow immunoassay (LFIA). The optical label (Ag@Pt NPs) was enhanced by the introduction of the chromogenic substrate 3,3',5,5'-tetramethylbenzidine (TMB) and compared with a gold nanoparticles (Au NPs) optical label. Under the optimal condition, Ag@Pt-LFIA and TMB-enhanced Ag@Pt-LFIA for H. pylori were successfully established, two of which were over twofold and 100-fold more sensitive than conventional visual Au NP-based LFIA, respectively. Furthermore, Ag@Pt NPs with the antibody irradiated with NIR laser (808 nm) at a power intensity of 550 mW/cm2 for 5 min exhibited a remarkable antibacterial effect. The nanoprobes could close to bacteria through effective interactions between antibodies and bacteria, thereby benefiting photothermal sterilization. Overall, Ag@Pt NPs provide promising applications in pathogen detection and therapeutic applications.

Fluorescent aptasensor for highly sensitive detection of Staphylococcus aureus based on dual-amplification strategy by integrating DNA walking and hybridization chain reaction

Food-borne diseases caused by bacteria threaten human health. Herein, we presented a new fluorescent aptasensor by coupling DNA walking and hybridization chain reaction (HCR) for convenient and sensitive quantification of bacteria. Staphylococcus aureus (S. aureus) was selected as target. When there was target in the system, the binding of S. aureus with its aptamer caused the disintegration of aptamer/DNA walker on the surface of AuNPs and released DNA walker. With the help of Nt.BsmAI, DNA walker moved along the surface of AuNPs and trigger probe was detached from AuNPs. The trigger probe could initiate hybridization chain reaction (HCR) and opened the stems of H1@AuNPs probe and H2@AuNPs probe. After the addition of nicking endonuclease, the adjacent upconversion nanoparticles (UCNPs, NaYF4:Yb3+, Er3+) were further away from the quenchers (AuNPs) of H1 and H2. Therefore, the fluorescence intensity of UCNPs could be restored via fluorescence resonance energy transfer (FRET). Bacteria were thus detected by recording the fluorescence intensity of UCNPs. This method is simple, rapid and sensitive. It can directly detect bacteria in a low background signal. The limit of detection (LOD) was 10 CFU/mL, detection time was less than 3 h. Recovery rates in simulated milk, honey and human serum samples ranged from 93.6 % to 105.8 %. The strategy opens up new paths for early diagnosis of diseases and food monitoring.

Applying a sandwich-like strategy for dual 'light up' capture and eradication of Staphylococcus aureus using magnetically functionalized materials

In this study, we proposed an innovative application of porcine immunoglobulin G (IgG)-functionalized Fe3O4 (IgG-Fe3O4) specifically designed to target and capture Staphylococcus aureus (S. aureus). In addition, aminophenylboronic acid-modified tetraphenylethylene nanoparticles (APBA-TPE NPs) were utilized, establishing a sandwich-type dual recognition system via interactions with the bacteria's extracellular glycolipids. This approach enables highly sensitive and precise detection of bacterial presence, with a limit of detection (LOD) reaching down to 5.0 CFU/mL. Specifically, the prepared APBA-TPE NPs achieved 99.99% bacterial inactivation within 60 min at a concentration of 200 µg/mL. The results showed that APBA-TPE NPs possess a remarkable capacity for reactive oxygen species (ROS) production, which could attack the bacterial cell membrane, leading to bacterial lysis and content leakage, and ultimately to bacterial death. Furthermore, the material still showed good recoveries ranging from 88.5% to 93.5% in actual water samples, as well as a favorable sterilizing effect of killing all microorganisms for 60 min. This research provides new strategies and insights into the construction of methods for the specific capture, detection, and inactivation of S. aureus.

Nanotechnology-based analytical techniques for the detection of contaminants in aquatic products

Food safety of aquatic products has attracted considerable attention worldwide. Although a series of conventional bioassays and instrumental methods have been developed for the detection of pathogenic bacteria, heavy metal residues, marine toxins, and biogenic amines during the production and storage of fish, shrimp, crabs et al., the nanotechnology-based analyses still have their advantages and are promising since they are cost-efficient, highly sensitive and selective, easy to conduct, facial design, often require no sophisticated instruments but with excellent detection performance. This review aims to summarize the advances of various biosensing strategies for bacteria, metal ions, and small molecule contaminants in aquatic products during the last five years, The review highlights the development in nanotechnologies applied for biorecognition process, signal transduction and amplification methods in each novel approach, the nuclease-mediated DNA amplification, nanomaterials (noble metal nanoparticle, metal-organic frameworks, carbon dots), lateral flow-based biosensor, surface-enhanced Raman scattering, microfluidic chip, and molecular imprinting technologies were especially emphasized. Moreover, this study provides a view of current accomplishments, challenges, and future development directions of nanotechnology in aquatic product safety evaluation.

Bimetallic Nanozyme: A Credible Tag for In Situ-Catalyzed Reporter Deposition in the Lateral Flow Immunoassay for Ultrasensitive Cancer Diagnosis

The lateral flow immunoassay (LFIA) is a sought-after point-of-care testing platform, yet the insufficient sensitivity of the LFIA limits its application in the detection of tumor biomarkers. Here, a colorimetric signal amplification method, bimetallic nanozyme-mediated in situ-catalyzed reporter deposition (BN-ISCRD), was designed for ultrasensitive cancer diagnosis. The bimetallic nanozyme used, palladium@iridium core-shell nanoparticles (Pd@Ir NPs), had ultrahigh enzyme-like activity, which was further explained by the electron transfer of Pd@Ir NPs and the change in the Gibbs free energy during catalysis through density functional theory calculations. With gastric cancer biomarkers pepsinogen I and pepsinogen II as model targets, this assay could achieve a cutoff value of 10 pg/mL, which was 200-fold lower than that without signal enhancement. The assay was applied to correctly identify 8 positive and 28 negative clinical samples. Overall, this BN-ISCRD-based LFIA showed great merits and potential in the application of ultrasensitive disease diagnosis.

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

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

Introduction of a multilayered fluorescent nanofilm into lateral flow immunoassay for ultrasensitive detection of Salmonella typhimurium in food samples

Fast and sensitive identification of foodborne bacteria in complex samples is the key to the prevention and control of microbial infections. Herein, an ultrasensitive lateral flow assay (LFIA) based on multilayered fluorescent nanofilm (GO/DQD)-guided signal amplification was developed for the rapid and quantitative determination of Salmonella typhimurium (S. typhi). The film-like GO/DQD was prepared through the electrostatic mediated layer-by-layer assembly of numerous carboxylated CdSe/ZnS quantum dots (QDs) onto an ultrathin graphene oxide (GO) nanosheet, which possessed advantages including higher QD loading, larger surface areas, superior luminescence, and better stability, than traditional spherical nanomaterials. The antibody-modified GO/DQD can effectively attach onto a target bacterial cell to form a GO/DQD-bacteria immunocomplex containing almost ten thousand QDs, thus greatly improving the detection sensitivity of LFIA. The constructed GO/DQD-LFIA biosensor achieved the rapid and sensitive detection of S. typhi in 14 min with detection limits of as low as 9 cells/mL. Moreover, compared with traditional LFIA techniques for bacteria detection, the proposed assay exhibited excellent stability and accuracy in real food samples and enormously improved sensitivity (2-3 orders of magnitude), demonstrating its great potential in the field of rapid diagnosis.

"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.

Ultrasensitive hairpin mediated upconversion fluorescence biosensor for Staphylococcus aureus detection in foods and waters exploiting g-C3N4-assisted catalysis

A novel g-C₃N₄ nanosheets (g-C₃N₄ NSs)-assisted upconversion fluorescent aptasensor was proposed for Staphylococcus aureus (S. aureus) detection by adopting hybridization chain reaction (HCR) as a sensitizer. Two hairpin (H1 and H2) structured DNA probes were engineered predicated on the partial complementary sequence (cDNA) of S. aureus aptamer and modified on the exterior of the upconversion nanoparticles (UCNPs), respectively. The presence of S. aureus initiated the HCR system and activated H1 and H2 probes to form a double-helix away from the g-C₃N₄ NSs vicinity. This led to the decrease in peroxidase-like activity (PA) of the g-C₃N₄ NSs and corresponding fluorescence recovery proportional to the concentration of S. aureus (10-10⁶ cfu mL^-1). The method was applied to real food samples with acceptable recoveries (91.1-101.6%) and further validated by traditional plate counting method (p > 0.05).

Gold Nanoparticles-Based Colorimetric Assays for Environmental Monitoring and Food Safety Evaluation

Recent years have witnessed an exponential increase in the research on gold nanoparticles (AuNPs)-based colorimetric sensors to revolutionize point-of-use sensing devices. Hence, this review is compiled focused on current progress in the design and performance parameters of AuNPs-based sensors. The review begins with the characteristics of AuNPs, followed by a brief explanation of synthesis and functionalization methods. Then, the mechanisms of AuNPs-based sensors are comprehensively explained in two broad categories based on the surface plasmon resonance (SPR) characteristics of AuNPs and their peroxidase-like catalytic properties (nanozyme). SPR-based colorimetric sensors further categorize into aggregation, anti-aggregation, etching, growth-mediated, and accumulation-based methods depending on their sensing mechanisms. On the other hand, peroxidase activity-based colorimetric sensors are divided into two methods based on the expression or inhibition of peroxidase-like activity. Next, the analytes in environmental and food samples are classified as inorganic, organic, and biological pollutants, and recent progress in detection of these analytes are reviewed in detail. Finally, conclusions are provided, and future directions are highlighted. Improving the sensitivity, reproducibility, multiplexing capabilities, and cost-effectiveness for colorimetric detection of various analytes in environment and food matrices will have significant impact on fast testing of hazardous substances, hence reducing the pollution load in environment as well as rendering food contamination to ensure food safety.

Development of an on-site lateral flow immune assay based on mango leaf derived colloidal silver nanoparticles for rapid detection of Staphylococcus aureus in milk

In order to ensure food safety, screening food samples for the presence of pathogens has been categorised as a legal testing item throughout the globe. One of the most prevalent zoonotic bacteria transmitted through dairy milk is Staphylococcus aureus. Given the limitations of the conventional detection methods, in the current study we desigined a competitive lateral flow immune assay (LFIA) using colloidal silver nanoparticles derived from mango leaves for the detection of Staphylococcus aureus in cow milk. SpA, a recombinant protein of Staphylococcus aureus, was used to raised hyperimmune sera used for developing the assay followed by conjugation with the synthesized nanoparticles. To increase the specificity of the assay, the milk samples were prenriched with selective agar exclusively require for Staphyloccocus aureus. The assay was found to be completed within 7-8 h by observing test and control lines in LFIA strips. The developed assay was found to specifically detect the bacteria as low as 1000 cfu/ml of milk samples. With a total 230 number of raw and clinical mastitis milk samples, the assay was validated and achieved relative accuracy, specificity, and sensitivity values of 97.39, 98.03, and 96.1%, respectively. The developed LFIA, which uses economically feasible and stable silver nanoparticles derived from mango leaves, has the potential for routine screening of milk samples for the presence of Staphylococcus aureus, especially in low-resource settings, allowing for early diagnosis, which facilitates effective treatment for the dairy animals and prevents the transmission of the disease in consumers.

Recent Progress in the Diagnosis of Staphylococcus in Clinical Settings

Staphylococci are mainly found on the skin or in the nose. These bacteria are typically friendly, causing no harm to healthy individuals or resulting in only minor issues that can go away on their own. However, under certain circumstances, staphylococcal bacteria could invade the bloodstream, affect the entire body, and lead to life-threatening problems like septic shock. In addition, antibiotic-resistant Staphylococcus is another issue because of its difficulty in the treatment of infections, such as the notorious methicillin-resistant Staphylococcus aureus (MRSA) which is resistant to most of the currently known antibiotics. Therefore, rapid and accurate diagnosis of Staphylococcus and characterization of the antibiotic resistance profiles are essential in clinical settings for efficient prevention, control, and treatment of the bacteria. This chapter highlights recent advances in the diagnosis of Staphylococci in clinical settings with a focus on the advanced technique of surface-enhanced Raman spectroscopy (SERS), which will provide a framework for the real-world applications of novel diagnostic techniques in medical laboratories via bench-top instruments and at the bedside through point-of-care devices.

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.

An ultrasensitive fluorescence detection template of pathogenic bacteria based on dual catalytic hairpin DNA Walker@Gold nanoparticles enzyme-free amplification

Integrating the advantages of catalytic hairpin components and multi-foot DNA walker, we designed a 16S rRNA detection probe template for pathogen bacteria, which utilizes DNA ligation quencher and dual catalytic hairpin@DNA walker to induce signal recovery. The dual catalytic hairpin@DNA walker uses the walking position of the target on the AuNP as a foothold to promote the reaction, so that the biosensing of the low-abundance target sequence can induce signal recovery. During the entire experiment, no enzyme is required, which can avoid the limitation of enzyme degradation under unfavorable conditions and the inability to detect the target. Most importantly, the detection template has the advantages of high sensitivity, and its detection limit is significantly better than that of single hairpin DNA walker probe. As the detection system can sensitively and rapidly detect its targeted bacteria and not rely on any enzyme and sophisticated instrumentation, it has great potential for sensitive and specific pathogenic bacteria detection.

An Emerging Fluorescent Carbon Nanobead Label Probe for Lateral Flow Assays and Highly Sensitive Screening of Foodborne Toxins and Pathogenic Bacteria

By virtue of the fascinating merits of low cost, rapid screening, and on-site detection, fluorescence lateral flow assays (FLFAs) have attracted considerable attention. Their detection limits are closely associated with the label probes used. The development of high-performance and robust phosphors remains a great challenge. Herein, we presented a new label probe, i.e., fluorescent carbon nanobeads (FCNBs), for FLFAs. Monodispersive, water-soluble, and highly emissive FCNBs were facilely prepared via a hydrothermal carbonization manner. Their abundant amino groups were beneficial for versatile surface functionalization. After being modified by biomolecules, the fabricated FCNB reporter probes were adopted for the construction of lateral flow test strips toward representative foodborne toxins, i.e., aflatoxin B1 (AFB1), and pathogenic bacteria, i.e., Staphylococcus aureus (S. aureus), respectively. The detection limits (0.01 ng/mL for AFB1 and 10² cfu/mL for S. aureus) were about 1 or 2 orders of magnitude lower than most reported methods. Furthermore, the proposed test strips were successfully applied for the quantitative, accurate, and rapid screening of AFB1 and S. aureus in food samples. This work provided a promising label probe for FLFAs and would open the opportunity to exploit a sensing platform by modifying different ligands onto the FCNBs.

Improving the sensitivity of lateral flow immunoassay for Salmonella typhimurium detection via flow-rate regulation

Application of the traditional immunochromatographic assay (ICGA) has been limited by its poor sensitivity. The objective of this study was to increase the sensitivity of the traditional ICGA. A dual-mode ICGA (D-M ICGA) was developed by combining a nanozyme-assisted signal-amplification strategy with a magnetic-nanoparticle-based flow-speed-control strategy. Salmonella typhimurium can be detected simultaneously based on color and magnetic signals in the detection area of the D-M ICGA strip. The calculated limits of detection of 50 cfu·mL^-1 and 75 cfu·mL^-1 in the color and magnetic modes, respectively, were approximately 1000 times lower than those of the traditional ICGA. The selectivity and practical applicability of the D-M ICGA were also confirmed in this study. The results prove that the D-M ICGA is an assay that could be used for Salmonella typhimurium detection and can be easily adapted to detect other pathogenic bacteria.

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.

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.

A universal SERS-based lateral flow assay was proposed for highly sensitive detection of foodborne bacteria in food and environmental samples using wheat germ agglutinin-modified Fe₃O₄@Au nanotags.

Simultaneous quantitative analysis of Listeria monocytogenes and Staphylococcus aureus based on antibiotic-introduced lateral flow immunoassay

Food poisoning caused by microorganisms has caused widespread concern. Herein, a highly sensitive on-site screening test strip for the detection of different pathogenic microorganisms (Listeria monocytogenes and Staphylococcus aureus) was designed. In this analysis platform, colloidal gold-coupled vancomycin was used as a signal unit to label Gram-positive bacteria, and highly sensitive polyclonal antibodies were used as recognition molecules to capture these specific strains. Compared with the traditional dual-antibody sandwich model, this new type of antibiotic-pathogen-antibody sandwich model is low-cost and can simultaneously detect multiple microorganisms. Under optimal conditions, this strategy showed satisfactory sensitivity and a wide linear range (L. monocy and S. aure could be directly assayed within linear ranges of 5 × 10⁴ to 10⁷ and 5 × 10² to 10⁷ CFU mL^-1, and the visual detection limits were 10⁵ and 10³ CFU mL^-1, respectively). The analytical performance and practicability of this sensor system have been further studied. This developed biosensor was applied to bacteria-contaminated water, milk and broth with satisfactory results. All of these attractive characteristics make the assay possess potential applications in food safety, medical diagnosis and environmental monitoring.

Upconversion Nanoprobes Based on a Horseradish Peroxidase-Regulated Dual-Mode Strategy for the Ultrasensitive Detection of Staphylococcus aureus in Meat

Staphylococcus aureus (S. aureus) is one of the foodborne pathogens that can cause infectious diseases and food poisoning. Herein, colorimetric and fluorescent dual-mode nanoprobes were developed for ultrasensitive detection of S. aureus to immediately respond to public health emergencies, reduce false positives, and improve measurement accuracy and persuasiveness. The nanoprobe consists of aptamer-labeled magnetic nanoparticles (apt-MNPs) as the capture signal probe and horseradish peroxidase and complementary DNA-functionalized upconversion nanoparticles (HRP-UCNPs-cDNA) as the chromogenic signal probe. In the absence of S. aureus, the probe forms an immune complex through base complementation with an observable signal. When S. aureus is introduced to this system, it preferentially binds to the apt-MNPs, releasing HRP-UCNPs-cDNA from the apt-MNPs and restoring the chromogenic probe signal. Under optimum conditions, an ultrasensitive assay of S. aureus was obtained, with limits of detection of 22 CFU mL^-1 for fluorescence and 20 CFU mL^-1 for colorimetry in a linear range of 56-5.6 × 10⁶ CFU mL^-1. Additionally, the standard plate counting method confirmed the reliability and accuracy of the established nanoprobe with an insignificant difference. Hence, the developed dual-mode platform has extensive application prospects for speedy and specific determination of S. aureus in meat.

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.

Development of Highly Sensitive Immunosensor for Detection of Staphylococcus aureus Based on AuPdPt Trimetallic Nanoparticles Functionalized Nanocomposite

The rapid and sensitive detection of Staphylococcus aureus (S. aureus) is essential to ensure food safety and protect humans from foodborne diseases. In this study, a sensitive and facile electrochemical immunosensor using AuPdPt trimetallic nanoparticles functionalized multi-walled carbon nanotubes (MWCNTs-AuPdPt) as the signal amplification platform was designed for the label-free detection of S. aureus. The nanocomposite of MWCNTs-AuPdPt was prepared by an in situ growth method of loading AuPdPt trimetallic nanoparticles on the surface of MWCNTs. The synthesized MWCNTs-AuPdPt featured good conductivity and superior catalytic performance for hydrogen peroxide. The nanocomposite of MWCNTs-AuPdPt with good biocompatibility and high specific surface area was further functionalized by anti-S. aureus antibodies. The immobilized antibodies could efficiently capture S. aureus to the modified electrode by an immune reaction, which resulted in the change of catalytic current intensity to realize the sensitive detection of S. aureus. The designed immunosensor could detect S. aureus in a linear range from 1.1 × 102 to 1.1 × 107 CFU mL-1 with a low detection limit of 39 CFU mL-1. Additionally, the proposed immunosensor was successfully applied to determine S. aureus in actual samples with acceptable results. This strategy provided a promising platform for highly sensitive determination of S. aureus and other pathogens in food products.

Dual-signal lateral flow assay using vancomycin-modified nanotags for rapid and sensitive detection of Staphylococcus aureus

This paper reports a colorimetric-fluorescent dual-signal lateral flow assay (LFA) based on vancomycin (Van)-modified SiO2-Au-QD tags for sensitive and quantitative detection of Staphylococcus aureus (S. aureus). The combination of high-performance Van-tags and detection antibodies integrated into the LFA system produced assays with high sensitivity and specificity. The visualization limit of the colorimetric signal and the detection limit of the fluorescence signal of the proposed method for S. aureus can reach 104 and 100 cells mL-1, respectively.