Joint-detection of Salmonella typhimurium and Escherichia coli O157:H7 by an immersible amplification dip-stick immunoassay

A dual-mode biosensing platform based on polydopamine-modified FeCoMOF/Co3O4 nanoenzyme for sensitive detection of Escherichia coli O157:H7

The sensitive and specific detection of Escherichia coli O157:H7 (E. coli O157:H7) plays a crucial role for human health in the food field. Here, polydopamine (PDA)-based FeCoMOF/Co3O4 nanoenzymes (FeCoMOF/Co3O4@PDA) were successfully synthesized with three enzyme-like activities of catalase-like, superoxide dismutase-like and peroxidase-like. The PDA layer not only provided an adhesion surface for protein immobilization, but also significantly increased peroxidase-like activity of FeCoMOF/Co3O4@PDA. FeCoMOF/Co3O4@PDA could be directly coupled with antibody as probe for the E. coli O157:H7 detection. Accordingly, the improved Enzyme-Linked Immunosorbent Assay (ELISA) with a dual detection platform of colorimetric-intelligent sensing was developed. Its detection range was as wide as 101-108 CFU mL-1, and the detection limit was as low as 2 CFU mL-1. In addition, FeCoMOF/Co3O4@PDA-ELISA was further used for E. coli O157:H7 detection in actual samples. Thus, this work demonstrated that the proposed FeCoMOF/Co3O4@PDA-ELISA showed excellent potential for analytical testing of E. coli O157:H7.

Polyphenol-modified 3D Nanoassemblies: A novel antibacterial immunoglobulins loading platform for rapid detection of Salmonella typhimurium

Within the realm of lateral flow assay (LFIA), the conjugation efficiency between signal tracers and antibody constitutes a pivotal determinant for the sensitivity of the detection system. In this study, three-dimensional (3D) complex flower-like MoS2 self-assembled from 2D MoS2, and natural plant polyphenols "Tannic acid" were introduced for surface modification. This composite material exhibits distinct colorimetric signals, excellent monoclonal antibody coupling efficiency, and commendable photothermal properties.Finally, it was used as a signal tracer to establish a 12-min colorimetric/photothermal dual-mode LFIA platform (MoS2/TA-LFIA) for Salmonella Typhimurium detection. Compared to the AuNPs-based LFIA, the dual-mode detection platform limits are decreased by 20-fold (to 5 × 103 cfu/mL) and 100-fold (to 103 cfu/mL), respectively. Furthermore, the MoS2/TA-LFIA exhibits satisfactory recovery and stability when applied to milk and orange juice samples. Thus, this study provides a novel, efficient and reliable antibody loading strategy for LFIA detection of foodborne pathogens.

Magnetic graphene-enhanced exonuclease III assisted amplification strategy driven carbon nanozyme for tri-mode detection of Escherichia coli O157:H7

Ultra-precision point-of-care detection of Escherichia coli O157:H7 in foods is an important issue. Here, the detection sensitivity was improved by a signal cascade amplification strategy synergised by exonuclease III assisted isothermal amplification and reverse magnetic strategy. The double-stranded DNA formed by the aptamer and the target DNA as a sensing switch, avoiding the complex process of specific nucleic acid extraction. Further, the signal display element is a green nanozyme synthesized by co-doping Cu and Cl elements with lignin as precursor, which has excellent peroxidase activity and fluorescence properties. The detection limits of fluorescence, colorimetric, and photothermal modes were 6.1, 8.4, and 9.7 cfu/mL, respectively. In order to enhance the precision of cascade signal amplification and the portability of quantitative detection, we built a neural network BP model installed in a smartphone by measuring multi-component data, which provides flexible and selectable application scenarios for the on-site detection of foodborne pathogens.

Bacterial surface informatics reliant on multi-mechanism simultaneous detection for Salmonella typhimurium and Staphylococcus aureus

Fully excavating and utilizing the rich information presented on bacterial surfaces can open innovative solutions for the multi-mechanism detection of food-borne pathogens. In this work, a colorimetric-fluorescence dual-signal lateral flow immunoassay was used to establish a simultaneous detection strategy integrating five physical, chemical, and biometric combining mechanisms for Salmonella typhimurium (S. typhimurium) and Staphylococcus aureus (S. aureus). To improve sensitivity, a layer-by-layer design of aggregation-induced emission nanosphere@ polydopamine@ platinum (AIENS@PDA@Pt) nanostructure with excellent colorimetric-fluorescence signal, abundant recognition sites, and rough surface was employed as a signal tag. Under optimal conditions, the colorimetric detection limit of the multi-mechanism reliant simultaneous detection LFIA (multi-MRSD LFIA) for S. typhimurium and S. aureus is 2 × 104 and 5 × 104 cfu·mL-1, respectively, and the fluorescence detection limit is 500 cfu·mL-1 for both target bacteria. This study introduces a novel approach for multi-target, multi-mechanism, and multi-signal output detection of bacteria, providing a significant direction for pathogen research.

Electron Transfer-Driven Nanozymes Boost Biosensor Sensitivity via a Synergistic Signal Amplification Strategy

The conventional gold nanoparticles (AuNPs) with insufficient brightness face substantial challenges in developing a sensitive lateral flow immunoassay (LFIA). Herein, multibranched manganese-gold (Mn-Au) nanoparticles (MnAuNPs) with a Au core-Mn shell nanostructure were synthesized by a one-pot method. The Mn shell of valence-rich and Au core of high electron transfer efficiency endowed MnAuNPs with oxidase-like activity, which oxidized 3,3',5,5'-tetramethylbenzidine (TMB) only by electron transfer. Ox-TMB, which was the oxidation product of TMB, is an excellent photothermal agent. Furthermore, the synergistic photothermal effect of ox-TMB and MnAuNPs significantly enhanced the photothermal conversion efficiency. The synergistic photothermal effect of multibranched MnAuNPs and ox-TMB has enabled highly sensitive quantitative detection. The LFIA based on MnAuNPs (cascade LFIA) has achieved sensitive detection of Escherichia coli O157:H7. The entire detection process was completed in 25 min. The limit of detection of cascade LFIA was 239 CFU mL-1, which was 37.21-fold lower than that of AuNPs-LFIA (8892 CFU mL-1). The recoveries of cascade LFIA were 82.63-111.67%, with coefficients of variation of 4.28-14.19%. Overall, this work suggests the potential of MnAuNPs and ox-TMB in the development of sensitive LFIA and broadens the biosensing strategies for point-of-care testing.

A press-actuated slidable microfluidic colorimetric biosensor for Salmonella detection utilizing nickel mesh sheet and MIL-88@Pd/Pt nanoparticles

A press-actuated slidable microfluidic colorimetric biosensor was designed for rapid, sensitive and multi-channel detection of Salmonella. The nickel mesh sheet (NMS) modified with capture antibodies was employed for capturing target bacteria, and metal organic frameworks decorated with palladium (Pd) and platinum (Pt) nanoparticles (MIL-88@Pd/Pt NPs) modified with detection antibodies were used for amplifying colorimetric signals. The capture efficiency of the immune NMS reached 83 %, and the detection limit of this colorimetric biosensor was 35 CFU/mL in 20 min. The average recoveries for Salmonella in spiked chicken meats ranged from 92.2 % to 102.5 % with a variation from 3.7 % to 7.2 %. The press-actuated slidable microfluidic chip was elaboratively developed with multiple functions, including mixing, separation, washing, catalysis and detection.

Enhanced immunochromatographic assay using multifunctional gold@iridium nanoflower with colorimetric photothermal catalytic activity for the detection of staphylococcal enterotoxin B

The development of a rapid, sensitive, and accurate screening method for staphylococcal enterotoxin B (SEB) in food is urgently needed because trace amounts of SEB can pose a serious threat to human health. Here, we developed a ultrasensitive triple-modal immunochromatographic assay (ICA) for SEB detection. The AuNFs@Ir nanoflowers exhibited enhanced colorimetric, photothermal, and catalytic performance by modulating the sharp branching structure of the gold nanoflowers and depositing high-density Ir atoms. Subsequently, the combination of AuNFs@Ir and ICA promoted colorimetric, catalytic amplified colorimetric, and photothermal-assisted quantitative detection. The results showed detection limits of 0.175, 0.0188, and 0.043 ng mL-1 in the colorimetric/photothermal/catalytic mode, which increased the sensitivity by 16.5-fold, 153.7-fold, and 67.2-fold, respectively, compared with the AuNPs-ICA. Furthermore, the proposed strategy was verified in milk, milk powder, pork, and beef successfully. This strategy improves significantly the sensitivity, accuracy, flexibility and offers an effective insight for foodborne bacterial toxin monitoring.

Multifunctional magnetic tags with photocatalytic and enzyme-mimicking properties for constructing a sensitive dual-readout ELISA

ELISA has become the gold standard for detecting harmful substances due to its specific antibody recognition and sensitive enzyme-catalyzed reactions. In this study, multifunctional magnetic Prussian blue nanolabels (MPBNs) were synthesized using a simple gentle two-step method to achieve a dual-readout mode. The MPBNs provide a sensitive colorimetric signal by efficiently catalyzing the oxidation of TMB and exhibit prominent photocatalytic degradation activity towards Rhodamine B (RhB). Supplemented by the quenching effect of oxTMB, the fluorescence was enabled to serve as a sensitive second signal. The magnetic property of the labels facilitates the separation and enrichment of the target, thereby improving sensitivity. Utilizing the versatile MPBNs, the visual limit of detection (vLOD) for Staphylococcus aureus is as low as 100 CFU/mL, with a quantitative analysis range of 102-108 CFU/mL. The introduction of photocatalytic reactions into immunoassay has opened up a new signal response system with strong momentum for development and application.

Colorimetry/fluorescence dual-mode detection of Salmonella typhimurium based on a "three-in-one" nanohybrid with high oxidase-like activity for AIEgen

A colorimetry/fluorescence dual-mode assay based on the aptamer-functionalized magnetic covalent organic framework-supported CuO and Au NPs (MCOF-CuO/Au@apt) was developed for Salmonella typhimurium (S. typhimurium) biosensing. The nanohybrid combined three functions in one: good magnetic separation characteristic, excellent oxidase-mimic activity for tetrap-aminophenylethylene (TPE-4A), and target recognition capability. The attachment of MCOF-CuO/Au@apt onto the surface of S. typhimurium resulted in a significant reduction in the oxidase-mimicking activity of the nanohybrid, which could generate dual-signal of colorimetry and fluorescence through the catalytic oxidation of TPE-4A. Based on this, S. typhimurium could be specifically detected in the linear ranges of 102- 106 CFU·mL-1 and 101- 106 CFU·mL-1, with LODs of 7.6 and 2.1 CFU·mL-1, respectively in colorimetry/fluorescence modes. Moreover, the smartphone and linear discrimination analysis-based system could be used for on-site and portable testing. In addition, this platform showed applicability in detecting S. typhimurium in milk, egg liquid and chicken samples.

An ultrasensitive smartphone-assisted bicolor-ratiometric fluorescence sensing platform based on a "noise purifier" for point-of-care testing of pathogenic bacteria in food

Non-specific binding in fluorescence resonance energy transfer (FRET) remains a challenge in foodborne pathogen detection, resulting in interference of high background signals. Herein, we innovatively reported a dual-mode FRET sensor based on a "noise purifier" for the ultrasensitive quantification of Escherichia coli O157:H7 in food. An efficient FRET system was constructed with polymyxin B-modified nitrogen-sulfur co-doped graphene quantum dots (N, S-GQDs@PMB) as donors and aptamer-modified yellow carbon dots (Y-CDs@Apt) as acceptors. Magnetic multi-walled carbon nanotubes (Fe@MWCNTs) were employed as a "noise purifier" to reduce the interference of the fluorescence background. Under the background purification mode, the sensitivity of the dual-mode signals of the FRET sensor has increased by an order of magnitude. Additionally, smartphone-assisted colorimetric analysis enabled point-of-care detection of E. coli O157:H7 in real samples. The developed sensing platform based on a "noise purifier" provides a promising method for ultrasensitive on-site testing of trace pathogenic bacteria in various foodstuffs.

Hybrid nanoflower-based electrochemical lateral flow immunoassay for Escherichia coli O157 detection

An electrochemical biosensor has been developed for detection of Escherichia coli O157 by integrating lateral flow with screen-printed electrodes. The screen-printed electrodes were attached under the lateral flow detection line, and organic-inorganic nanoflowers prepared from E. coli O157-specific antibodies as an organic component were attached to the lateral flow detection line. In the presence of E. coli O157, an organic-inorganic nanoflower-E. coli O157-antimicrobial peptide-labelled ferrocene sandwich structure is formed on the lateral flow detection line. Differential pulse voltammetry is applied using a smartphone-based device to monitor ferrocene on the detection line. The resulting electrochemical biosensor could specifically detect E. coli O157 with a limit of detection of 25 colony-forming units mL-1. Through substitution of antibodies of organic components in organic-inorganic nanoflowers, biosensors have great potential for the detection of other pathogens in biomedical research and clinical diagnosis.

A portable CRISPR-Cas12a triggered photothermal biosensor for sensitive and visual detection of Staphylococcus aureus and Listeria monocytogenes

The detection of foodborne pathogens is crucial for ensuring the maintenance of food safety. In the present study, a portable CRISPR-Cas12a triggered photothermal biosensor integrating branch hybrid chain reaction (bHCR) and DNA metallization strategy for sensitive and visual detection of foodborne pathogens was proposed. The sheared probes were utilized to block the locker probes, which enabled preventing the assembly of bHCR in the absence of target bacteria, while target bacteria can activate the cleavage of sheared probes through CRISPR-Cas12a. Therefore, the locker probes functioned as initiating chains, triggering the formation of the branching double-stranded DNA consisting of H1, H2, and H3. The silver particles, which were in situ deposited on the DNA structure, functioned as a signal factor for conducting photothermal detection. Staphylococcus aureus and Listeria monocytogenes were selected as the foodborne pathogens to verify the analytical performance of this CRISPR-Cas12a triggered photothermal sensor platform. The sensor exhibited a sensitive detection with a low detection limit of 1 CFU/mL, while the concentration ranged from 100 to 108 CFU/mL. Furthermore, this method could efficiently detect target bacteria in multiple food samples. The findings demonstrate that this strategy can serve as a valuable reference for the development of a portable platform enabling quantitative analysis, visualization, and highly sensitive detection of foodborne bacteria.

Trifunctional Nanocomposites with Colorimetric Magnetic Catalytic Activities Labels in Sandwich Immunochromatographic Detection of Escherichia coli O157:H7

The emergence of nanoenzymes has catalyzed the robust advancement of the lateral flow immunoassay (LFIA) in recent years. Among them, multifunctional nanocomposite enzymes with core-shell architectures are considered preferable for promoting the sensing ability due to their good biocompatibility, precise control over size, and surface properties etc. Herein, we developed a dual-channel ensured lateral flow immunoassay (DFLIA) platform utilizing a magnetic, colorimetric, and catalytic multifunctional nanocomposite enzyme (Fe3O4@TCPP@Pd) [TCPP, Tetrakis (4-carboxyphenyl) porphyrin] for the ultrasensitive and highly accurate rapid detection of Escherichia coli O157:H7 (E. coli O157:H7). Fe3O4@TCPP@Pd-mAb exhibits superior performance compared to traditional AuNPs, including enhanced sensitivity and an extended linear detection range, benefiting from its high brightness signal, strong magnetic separation ability, and high peroxidase activity (Vmax = 2.32 μM S1-). Moreover, the Fe3O4@TCPP@Pd-labeled mAb probe exhibited exceptional stability and high affinity toward E. coli O157:H7 (with an affinity constant of approximately 1.723 × 109 M-1), indicating its potential for the efficient capture of the pathogen. Impressively, the developed Fe3O4@TCPP@Pd-DFLIA achieved ultrasensitive detection for E. coli O157:H7 with pre- and postcatalytic naked-eye detection sensitivities of 255 cfu/mL and 77 cfu/mL, respectively, representing an approximately 41-fold improvement over the conventional AuNP-based LFIA and also possessed good specificity and reproducibility [relative standard deviation (RSD) < 10%]. Additionally, the established DFLIA exhibited satisfactory recoveries in detecting pork and milk samples, further validating the reliability of this platform for immunoassays and demonstrating its potential for utilization in bioassays and clinical diagnostics.

An intelligent readable and capture-antibody-independent lateral flow immunoassay based on Cu2-xSe nanocrystals for point-of-care detection of Escherichia coli O157:H7

Escherichia coli (E. coli) O157:H7 is a common foodborne pathogen which can cause serious harm. It is particularly important to establish a simple and portable method to achieve on-site pathogen detection. In this study, a capture-antibody-independent lateral flow immunoassay (LFIA) was constructed based on Cu2-xSe nanocrystals (Cu2-xSe NCs) for rapid detection of E. coli O157:H7. Cu2-xSe NCs can not only be regarded as the "nano-antibody" for the recognition of E. coli O157:H7 through electrostatic adsorption, but also as nanozymes that show good peroxidase-like catalytic activity. The formed compound of E. coli O157:H7 and Cu2-xSe NCs would be captured by a detection antibody on the T line due to the specific recognition of the antibody and E. coli O157:H7. Then, Cu2-xSe NCs could catalyze the oxidation of TMB by H2O2 to generate oxTMB, thereby generating blue bands. Meanwhile, we developed a mobile app for rapid data analysis. Under the optimal reaction conditions, E. coli O157:H7 could be detected within 70 min. The detection limit of this method was 2.65 × 105 CFU mL-1 with good specificity and stability. Additionally, it could achieve on-site rapid detection of E. coli O157:H7 in environmental water samples, providing a promising biosensor for portable pathogen detection.

Sensitive Immunochromatographic Determination of Salmonella typhimurium in Food Products Using Au@Pt Nanozyme

In this study, we developed a sensitive immunochromatographic analysis (ICA) of the Salmonella typhimurium bacterial pathogen contaminating food products and causing foodborne illness. The ICA of S. typhimurium was performed using Au@Pt nanozyme as a label ensuring both colorimetric detection and catalytic amplification of the analytical signal due to nanozyme peroxidase-mimic properties. The enhanced ICA enabled the detection of S. typhimurium cells with the visual limit of detection (LOD) of 2 × 102 CFU/mL, which outperformed the LOD in the ICA with traditional gold nanoparticles by two orders of magnitude. The assay duration was 15 min. The specificity of the developed assay was tested using cells from various Salmonella species as well as other foodborne pathogens; it was shown that the test system detected only S. typhimurium. The applicability of ICA for the determination of Salmonella in food was confirmed in several samples of milk with different fat content, as well as chicken meat. For these real samples, simple pretreatment procedures were proposed. Recoveries of Salmonella in foodstuffs were from 74.8 to 94.5%. Due to rapidity and sensitivity, the proposed test system is a promising tool for the point-of-care control of the Salmonella contamination of different food products on the whole farm-to-table chain.

Recent Advances in Nanozyme-Mediated Strategies for Pathogen Detection and Control

Pathogen detection and control have long presented formidable challenges in the domains of medicine and public health. This review paper underscores the potential of nanozymes as emerging bio-mimetic enzymes that hold promise in effectively tackling these challenges. The key features and advantages of nanozymes are introduced, encompassing their comparable catalytic activity to natural enzymes, enhanced stability and reliability, cost effectiveness, and straightforward preparation methods. Subsequently, the paper delves into the detailed utilization of nanozymes for pathogen detection. This includes their application as biosensors, facilitating rapid and sensitive identification of diverse pathogens, including bacteria, viruses, and plasmodium. Furthermore, the paper explores strategies employing nanozymes for pathogen control, such as the regulation of reactive oxygen species (ROS), HOBr/Cl regulation, and clearance of extracellular DNA to impede pathogen growth and transmission. The review underscores the vast potential of nanozymes in pathogen detection and control through numerous specific examples and case studies. The authors highlight the efficiency, rapidity, and specificity of pathogen detection achieved with nanozymes, employing various strategies. They also demonstrate the feasibility of nanozymes in hindering pathogen growth and transmission. These innovative approaches employing nanozymes are projected to provide novel options for early disease diagnoses, treatment, and prevention. Through a comprehensive discourse on the characteristics and advantages of nanozymes, as well as diverse application approaches, this paper serves as a crucial reference and guide for further research and development in nanozyme technology. The expectation is that such advancements will significantly contribute to enhancing disease control measures and improving public health outcomes.