H7 Detection Research Articles

Flow-Through Electrochemical Biosensor for the Detection of Listeria monocytogenes Using Oligonucleotides.

Consumption of food contaminated by Listeria monocytogenes can result in Listeriosis, an illness with hospitalization rates of 94% and mortality rates up to 30%. As a result, U.S. regulatory agencies governing food safety retain zero-tolerance policies for L. monocytogenes. However, detection at such low concentrations often requires strategies such as increasing sample size or culture enrichment. A novel flow-through immunoelectrochemical biosensor has been developed for Escherichia coli O157:H7 detection in 1 L volumes without enrichment. The current work further augments this biosensor’s capabilities to (1) include detection of L. monocytogenes and (2) accommodate genetic detection to help overcome limitations based upon antibody availability and address specificity errors in phenotypic assays. Herein, the conjugation scheme for oligo attachment and the conditions necessary for genetic detection are laid forth while results of the present study demonstrate the sensor’s ability to distinguish L. monocytogenes DNA from L. innocua with a limit of detection of ~2 × 104 cells/mL, which agrees with prior studies. Total time for this assay can be constrained to <2.5 h because a timely culture enrichment period is not necessary. Furthermore, the electrochemical detection assay can be performed with hand-held electronics, allowing this platform to be adopted for near-line monitoring systems.

Assembly of polyoxometalates/polydopamine nanozymes as a multifunctional platform for glutathione and Escherichia coli O157:H7 detection

A new P2W18Fe4/PDA (P2W18Fe4 = K10P2W18Fe4(H2O)2O68 and PDA = polydopamine) nanocomposite has been synthesized with peroxidase activity for glutathione (GSH) and Escherichia coli O157:H7 (E. coliO157:H7) detection. The size of P2W18Fe4/PDA is about 104 ± 16 nm, which is the smallest among the reported polyoxometalates (POMs)/PDA composites. The polydopamine functionalization not only provides an adhesive surface for the immobilization of biomolecules onto P2W18Fe4, but also, significantly increases the peroxidase-like activity of P2W18Fe4, probably due to its enhanced affinity to organic substrates. P2W18Fe4/PDA can catalyze the oxidation of o-phenylenediamine (OPD) to form yellow 2, 3-diaminophenazine (DAB) in the presence of H2O2 through hydroxyl radical. The GSH can efficiently react with the hydroxyl radicals from H2O2 catalyzed by P2W18Fe4/PDA to inhibit the production of DAB. Thus, we can determination the concentration of GSH with the decreasing spectrometric signal of the DAB. The limit of colorimetric detection was 0.18 mM with the linear range from 2 to 8 mM. The limit of fluorescent detection was 4.02 μM with the linear range from 15.63 to 250 μM. The assay was successfully applied to the detection of GSH in SH-SY5Y cells lysate samples with higher sensitivity and specificity. The detection of E. coli O157:H7 was achieved by the sandwich immunoassay with the P2W18Fe4/PDA nanozymes as labeling markers. A linear correlation was established between absorbance intensity and E. coli O157:H7 from 103 to 106 CFU / mL with a detection limit of 4.2 × 102 CFU/mL. These primary results enlarge the POMs’ analytic application field.

Evaluation and comparison of recombinase polymerase amplification coupled with lateral-flow bioassay for Escherichia coli O157:H7 detection using different genes

Shiga toxin-producing Escherichia coli serotype O157:H7 is a food and waterborne zoonotic pathogen causing gastroenteritis in humans. Rapid and simple detection in water and food is imperative to control its spread. However, traditional microbial detection approaches are time-consuming, expensive and complex to operate at the point-of-care without professional training. We present a rapid, simple, sensitive, specific and portable method for detection of E. coli O157:H7 in drinking water, apple juice and milk. We evaluated the effect of gene selection in detecting E. coli O157:H7 using recombinase polymerase amplification coupled with a lateral flow assay using rfbE, fliC and stx gene targets. As low as 100 ag and 1 fg DNA, 4–5 CFU/mL and 101 CFU/mL of E. coli O157:H7 was detected using the stx and rfbE gene targets respectively with 100% specificity, whilst the detection limit was 10 fg DNA and 102 CFU/mL for the fliC gene target, with 72.8% specificity. The RPA-LFA can be completed within 8 min at temperatures between 37 and 42 °C with reduced handling and simple equipment requirements. The test threshold amplification of the target was achieved in 5–30 min of incubation. In conclusion, RPA-LFA represents a potential rapid and effective alternative to conventional methods for the monitoring of E. coli O157:H7 in food and water.

Review of recent advances in improved lateral flow immunoassay for the detection of pathogenic Escherichia coli O157:H7 in foods

AbstractThe incidence of foodborne diseases has continuingly increased over the years and resulted in public health problem globally. EnterohemorrhagicEscherichia coliO157:H7 (E. coliO157:H7) is a human pathogen that causes diarrhea and hemorrhagic colitis.E. coliO157:H7 can be found in various foods. It is important to detect this foodborne pathogen to provide safe food supply. A lot of methods, for example, culture and PCR‐based test, used to detect foodborne pathogens are laborious and time consuming. Hence, a variety of methods have been developed for rapid, simple and reliable detection ofE. coliO157:H7 as it is required in many food analyses. Lateral flow immunoassay (LFIA) are advantageous over conventional detection methods in terms of their rapidity and simplicity for end user, especially the LFIA can be developed as the strip test for on‐site point‐of‐care test (POCT) products. Gold nanoparticles (AuNPs; colloid gold) are the most commonly used labels in the LFIA for the visual analysis, however, there are still several limitations that restrict their applications of traditional LFIA. Therefore, recent reports on improved LFIA forE. coliO157:H7 detection in foods are continuously reported. This review intends to provide these recent advances in improved LFIA methods for the detection ofE. coliO157:H7 in foods.

A rapid detection of Escherichia coli O157:H7 by competition visual antigen macroarray

AbstractPathogenic bacterial contamination is a serious problem for the food industry and in public health. Rapid, accurate and affordable testing for pathogenic bacterial strains is desirable. In this study, a competition visual antigen macroarray (CVAM) for rapid detection of Escherichia coli O157:H7 (E. coli O157:H7) has been developed. This array was able to utilize an HRP‐labeled anti‐E. coli O157:H7 MAb at a concentration of 1:20000 while having a similar sensitivity of 10 5 CFU/ml for E. coli O157:H7 detection as double antibody sandwich array and conventional ELISA. The detection time of CVAM was short as 2 h and can be examined directly by the naked eye. Moreover, there was no cross‐reactivity in the detection of tested in this study. Application of CVAM for the detection of E. coli O157:H7 artificially contaminated milk samples was feasible that showed the antigen array could be applied in the detection of food pathogen infections.

Rapid, Quantitative, High-Sensitive Detection of Escherichia coli O157:H7 by Gold-Shell Silica-Core Nanospheres-Based Surface-Enhanced Raman Scattering Lateral Flow Immunoassay.

Escherichia coli O157:H7 is regarded as one of the most harmful pathogenic microorganisms related to foodborne diseases. This paper proposes a rapid-detection biosensor for the sensitive and quantitative analysis of E. coli O157:H7 in biological samples by surface-enhanced Raman scattering (SERS)-based lateral flow immunoassay (LFIA). A novel gold-shell silica-core (SiO2/Au) nanosphere (NP) with monodispersity, good stability, and excellent SERS activity was utilized to prepare high-performance tags for the SERS-based LFIA system. The SiO2/Au SERS tags, which were modified with two layers of Raman reporter molecules and monoclonal antibodies, effectively bind with E. coli O157:H7 and form sandwich immune complexes on the test lines. E. coli O157:H7 was quantitatively detected easily by detecting the Raman intensity of the test lines. Under optimal conditions, the limit of detection (LOD) of the SiO2/Au-based SERS-LIFA strips for the target bacteria was 50 cells/mL in PBS solution, indicating these strips are 2,000 times more sensitive than colloidal Au-based LFIA strips. Moreover, the proposed assay demonstrated high applicability in E. coli O157:H7 detection in biological samples, including tap water, milk, human urine, lettuce extract and beef, with a low LOD of 100 cells/mL. Results indicate that the proposed SERS-based LFIA strip is applicable for the sensitive and quantitative determination of E. coli O157:H7.

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

To identify and evaluate the application of two novel monoclonal antibody (mAb) 2G12 against outer membrane protein (Omp) C and mAb 12B1 targeting the O chain of the lipopolysaccharides (LPS) of Escherichia coli O157:H7 (ECO157). The sensitivity and specificity of these two antibodies were evaluated with eight ECO157 strains and 68 untargeted strains. mAb 2G12 and 12B1 had no detectable binding with any of the non-O157 strains at 6·0 log10 CFU per ml, while its high specificity and affinity remained with all ECO157 strains. When a higher level (8·0 log10 CFU per ml) was tested, 2G12 and 12B1 did not react with 82·35 and 97·06% of the non-O157 strains respectively. Based on the pair of two antibodies, the sandwich enzyme-linked immunosorbent assay detected 100% (8/8) of ECO157 strains and none of the non-ECO157 strains. The detection limit of ECO157 strains in pure culture were 4·2±0·2 log10 CFU per ml. When the developed test was applied to artificially inoculated beef samples, the detection limit was 6·0 log10 CFU per gram without enrichment and 1·0 log10 CFU per gram after 12h of enrichment. The two novel antibodies identified in this study served as great candidates for the recovery, and detection of ECO157 from different environmental and food samples. ECO157-specific detection was improved by a combination of the novel OmpC mAb and LPS mAb with defined target antigen and good specificity.

Naked-eye based point-of-care detection of E.coli O157: H7 by a signal-amplified microfluidic aptasensor

Fast and sensitive detection of E.coli O157: H7 is significantly essential for clinical management as well as for transmission prevention during disease outbreaks. Though many types of detection strategies have been implemented for measuring E.coli O157: H7, most of them still rely on complex instruments or tedious/laborious setups, which restrict their applications in resource-limited scenarios. Herein, we introduce an eye-based microfluidic aptasensor (EA-Sensor) for fast detection of E.coli O157: H7 without the assist of any instruments. We demonstrate the perfect coupling of aptamer sensing, hybridization chain reaction (HCR)-amplification and a distance-based visualized readout to quantitatively determine the pathogen concentration. We first used gel-electrophoresis assay to evaluate the system and the results proved that E.coli O157: H7 was well recognized by the aptamer and HCR could increase the signal by about 100 folds. In addition, the Aptamer specificity and signal-amplification ability were verified on the EA-Sensor for sensing E.coli O157: H7 by naked eyes. Furthermore, we demonstrated that E.coli O157: H7 in milk could be accurately and conveniently measured with good performance. With the benefits of operation integration and strategy integration, our EA-Sensor shows advantages of high specificity, easy operation, efficient amplification and visualized readout, which offers a favorable point-of-care tool for E.coli O157: H7 or other pathogen detection in resource-constrained settings.

Development of a combined immunochromatographic lateral flow assay for accurate and rapid Escherichia coli O157:H7 detection.

Escherichia coli O157:H7 is an important pathogenic Bacterium that threatens human health. A convenient, sensitive and specific method for the E. coli O157:H7 detection is necessary. We developed two pairs of monoclonal antibodies through traditional hybridoma technology, one specifically against E. coli O157 antigen and the other specifically against E. coli H7 antigen. Using these two pairs of antibodies, we developed two rapid test kits to specifically detect E. coli O157 antigen and E. coli H7 antigen, respectively. The detection sensitivity for O157 positive E. coli is 1×103 CFU per ml and for H7 positive E. coli is 1×104 CFU per ml. Combining these two pairs of antibodies together, we developed a combo test strip that can specifically detect O157: H7, with a detection sensitivity of 1×104 CFU per ml, when two detection lines are visible to the naked eye. This is currently the only rapid detection reagent that specifically detects O157: H7 by simultaneously detecting O157 antigen and H7 antigens of E. coli. Our product has advantages of simplicity and precision, and can be a very useful on-site inspection tool for accurate and rapid detection of E. coli O157:H7 infection.

Lab in a Tube: Point-of-Care Detection of Escherichia coli.

Significant levels of infectious diseases caused by pathogenic bacteria are nowadays a worldwide matter, carrying considerable public health care challenges and huge economic concerns. Because of the rapid transmission of these biothreat agents and the outbreak of diseases, a rapid detection of pathogens in early stages is crucial, particularly in low-resources settings. To this aim, we developed for the first time a new sensing approach carried out in a single step for Escherichia coli O157:H7 detection. The detection principle is based on Förster resonance energy transfer using gold nanoclusters as a signal reporter and gold nanoparticles conjugated with antibodies as a quencher. The sensing platform includes an ultraviolet-light-emitting diode to provide the proper excitation and consists of a microtube containing two pieces of fiber glass; one of them is embedded with label-free gold nanoclusters and the other one with gold nanoparticles conjugated with antibodies. Upon the addition of the sample containing bacteria, the florescence of gold nanoclusters is recovered. The assay was evaluated by the naked eye (on/off) and quantitatively with use of a smartphone camera. The biosensor proved to be highly specific and sensitive, achieving a limit of detection as low as 4.0 cfu mL-1. Additionally, recoveries of 110% and 95% were obtained when the platforms in spiked river and tap water, respectively, were evaluated.

Antibacterial effect of silver nanoparticles on antibiotic resistant E. coli O157:H7 isolated from some dairy products

Food safety is a worldwide health goal so foodborne diseases are a main health concern. A total 150 of dairy products samples (locally made yoghurt, ice cream and Talaga cheese) (50 for each type) were examined for E.coli O157:H7 detection and PCR confirmation using fliCH7 gene. E. coli O157:H7 was detected at 18%, 4%, 8% respectively, in samples. The isolates showed broad antibiotic resistance against vancomycin (84.6%), penicillin G (76.9%), cloxacillin (69.2%) and tetracycline (61.5%). Because of increasing number of microorganisms that are resistant to multiple antibiotics causing continuing economic losses in dairy manufacturing, there is an urgent need for development of alternative, cost-effective, and efficient antimicrobial agents to overcome antimicrobial resistance. Here, silver nanoparticle (AgNPs) solution was prepared, identified by transmission electron microscopy (TEM) with an average size 26.5 nm and examined for bactericidal activity against E. coli O157:H7 by using well diffusion assay. The mean inhibition zones of 25 and 50 µg/ml concentrations of Ag-NPs were 15.0±1.2 and 20.9±1.4 mm, respectively. In addition, the statistical analysis showed highly significant differences in the bactericidal effect of different Ag-NPs concentrations on E. coli O157:H7 strains. Bacterial sensitivity to nanoparticles is a key factor in manufacture, so nanoparticles were considered suitable for long life application in food packaging and food safety.

Development of support based on chitosan and cellulose nanocrystals for the immobilization of anti-Shiga toxin 2B antibody

This work describes the development of membrane based on chitosan (CHI), cellulose nanocrystals (CNCs), and glycerol (GLY), and optimization of the formulation for immobilization of monoclonal anti-Shiga toxin 2B antibody (mAnti-stx2B-Ab) for E. coli O157:H7 detection. The effect of CHI deacetylation degree & viscosity, CNCs and GLY concentrations on Anti-stx2B-Ab immobilization efficiency was evaluated. Fractional factorial and Box-Behnken designs were applied to screen the effects of compounds interactions and optimize their concentrations for detection of Anti-stx2B-Ab. The results demonstrated that the use of 0.6 % (w/v) CNCs improved significantly the Anti-stx2B-Ab immobilization and the level of signal detection. The detection limit of Escherichia coli O157:H7 by developed optimized membrane is 1 log CFU/mL. The time needed for detection of E. coli O157:H7 was only 4 h of enrichment compared to 24 h with conventional methods. The developed immobilization support has potential for future pathogen detection in food and biomedical samples.

Ultrasensitive biosensing pathogenic bacteria by combining aptamer-induced catalysed hairpin assembly circle amplification with microchip electrophoresis

Because foodborne pathogenic bacteria are in a great variety and may cause many infectious diseases even at low concentrations, a highly sensitive and selective method has long-been desired for bacteria detection. In this study, a microchip electrophoretic method for biosensing E. coli O157:H7 was developed by using E. coli O157:H7 aptamer (apt-E) for specific bacteria recognition together with aptamer-induced catalysed hairpin assembly (CHA) for significantly improving the sensitivity of bacteria detection. Briefly, three nucleic acid strands (apt-E, hairpin H1, and H2) were used in the CHA amplification. Because different quantities of H1/H2 complexes were formed due to the circle amplification induced with different amounts of apt-E and the correlation between the concentrations of apt-E and E. coli O157:H7, E. coli O157:H7 thus could be quantified by the detection of H1/H2 complexes with microchip electrophoresis (MCE). Under the optimal conditions, the limit of detection was 75 CFU mL−1. This method was also applied to detect E. coli O157:H7 in defatted milk with a satisfying recovery rate. The proposed strategy for E. coli O157:H7 detection is label-free, enzyme-free, ultra-sensitive, and cost-effective. It is also practical and could be applied to detect other bacteria in food samples.

Multiple RT-PCR Detection of H5, H7, and H9 Subtype Avian Influenza Viruses and Newcastle Disease Virus

Objective: This paper focuses on the multiple detection RT-PCR technology of H5, H7, AND H9 subtype avian influenza viruses and Newcastle disease virus, and points out the specific detection methods and detection procedures of avian influenza and Newcastle disease virus. Methods: The genes of Newcastle disease virus carrying out the HA gene sequence of H5, H7 and H9 subtype AIV in GenBank were used to establish a strategy for simultaneous detection of three subtypes of avian influenza virus and Newcastle disease virus. Results: The results showed that the program can detect and distinguish H5, H7 and H9 subtype avian influenza viruses and Newcastle disease virus at one time. Conclusion: Multiple RT-PCR detection method has high detection sensitivity and can detect and determine different subtypes of avian influenza virus and Newcastle disease virus quickly and accurately, therefore, it has a crucial role in the detection and control of avian influenza H5, H7 and H9 subtypes and Newcastle disease.

Surface stress-induced membrane biosensor based on double-layer stable gold nanostructures for E. coli detection.

The surface stress-based biosensor has been applied in fast and sensitive identification of Escherichia coli (E. coli)with significance for public health, food, and water safety. However, the stable sensitive element of flexible biosensor based on surface stress is still crucial and challengeable. Here, the authors reported surface stress-induced biosensors based on double-layer stable gold nanostructures (D-AuNS-SSMB) for E. coli O157:H7 detection. Bacterial detection demonstrates the high stability of the biosensor. The resistance change of biosensor is linear to the logarithmic value of the E. coli O157:H7 concentrations ranging from 103 to 107 CFU/mL with a limit of detection (LOD) of 43 CFU/mL. The captured signals of D-AuNS-SSMB comes from surface stress generated by antigen-antibody binding. In addition, the biosensor exhibits good stability, reproducibility and specificity in detection of E. coli O157:H7 as well. This study provides a new preparation method of stable sensitive element for the E. coli detection.

Functionalized AuMBA@Ag Nanoparticles as an Optical and SERS Dual Probe in a Lateral Flow Strip for the Quantitative Detection of Escherichia coli O157:H7

A method combining surface-enhanced Raman scattering (SERS) with a lateral flow strip (LFS) was developed for the quantitative and sensitive analysis of Escherichia coli O157:H7. AuMBA @Ag nanoparticles were prepared as SERS probes, and 4-methylthiobenzoic acid (MBA) as a Raman reporter was inserted into the interior gap of the Au@Ag core-shell nanoparticles, which replaced the Au nanoparticles that serve as SERS nanotags in traditional LFS. Using this developed SERS-LFS, the presence of the target bacteria could be tested through the appearance of a red band on the test line. Furthermore, quantitative analysis of E. coli O157:H7 was achieved by measuring the specific Raman intensity of MBA on the test line. The sensitivity of this SERS-LFS biosensor is 5 × 104 CFU/mL of E. coli O157:H7, which is 10-fold higher than that of a naked eye-based colorimetric LFS. This quantitative detection of E. coli O157:H7 ( = 1993.86 - 6812.17, R2 = 0.9947) was obtained with a wide linear range (5 × 104 to 5 × 108 ) due to the signal enhancement of the SERS nanotags. In addition, the SERS-LFS could differentiate E. coli O157:H7 from closely related bacterial species or nontarget contaminants, suggesting high specificity of this assay. The applicability of SERS-LFS to the analysis of E. coli O157:H7 in milk, chicken breast, and beef was also validated, indicating that the sensitivity was not disturbed by the food matrix. In summary, the SERS-LFS developed in this study could be a powerful tool for the quantitative and sensitive screening of E. coli O157:H7 in a food matrix. PRACTICAL APPLICATION: This study demonstrates that a surface-enhanced Raman scattering (SERS)-based lateral flow strip (LFS) could be used as a rapid and sensitive method for Escherichia coli O157:H7 detection. Furthermore, this SERS-based LFS could achieve quantitative detection of the target, eliminating the defect of the traditional colloidal gold LFS, which is not quantifiable.

Ultrasensitive SERS determination of avian influenza A H7N9 virus via exonuclease III-assisted cycling amplification

The avian influenza A H7N9 virus is known as one of the newly discovered highly pathogenic avian influenzas with serious threat to public health and the poultry industry. In this work, an ultrasensitive surface-enhanced Raman scattering (SERS) determination of H7N9 virus via exonuclease III-assisted cycling amplification was proposed to meet the needs of rapid, sensitive and accurate detection of H7N9-related genes. The SERS strategy aims to simultaneously determine the characteristic gene fragments of H7 and N9 by specially designing Capture, Replace, and Probe single-strand DNAs to realize exonuclease III-assisted cycling amplifications, and then integrating the cyclic amplification with SERS-active Ag nanorods array substrate to achieve an ultrasensitive SERS determination of H7N9. After characterizing the effectiveness of the sensing mechanism and further investigating the surface blocking and the dosage of exonuclease III, the optimal surface blocking was achieved by using 10 μM and 100 μM mercaptohexanol for H7 and N9 detection respectively, and the optimal Exo III concentrations for sensing H7 and N9 were 0.10 U μL−1 and 0.30 U μL−1 respectively. Under the optimal conditions, dual and specific detections of H7 and N9 gene fragments were obtained with detection linear interval from 1 fM to 100 pM and limit of detections low to 31 aM of H7 and 44 aM of N9, as well as recovery in the range of 93.8–106.2% with relative standard deviation less than 6.12%. The proposed ultrasensitive SERS strategy can provide a powerful tool for determining H7N9 virus and other avian influenza viruses.

Rolling circle amplification and its application in microfluidic systems for Escherichia coli O157:H7 detections

AbstractRolling circle amplification (RCA) has been widely used to enhance detection signals as its long single‐stranded RCA products can provide multiple binding sites for signal probes for sensitive detections. In the current study, we employ atomic force microscopy (AFM) to monitor the RCA products during the course of the RCA process over time. Subsequently, the results of the RCA obtained from the AFM study are combined with those from the conventional electrophoresis method to optimize RCA reactions for rapid and sensitive detection. We show that there appears to be an inhomogeneous RCA initiation phase in early to mid‐stage of the RCA reaction where some chains grow faster while others grow slower or remain dormant, an observation that has not been reported in the literature. Furthermore, we demonstrate that the RCA can significantly enhance detection signals by up to 100‐fold. We also show that the Escherichia coli O157:H7 detection with the RCA can be carried out in different food matrices with excellent detection sensitivities and specificities. In conclusion, these results suggest that a microfluidic device in combination with RCA signal enhancement is a simple and robust approach to sensitive whole‐cell detection in food samples.Practical applicationsThe current research has exciting potentials for applications in sensitive detections of food samples for food safety inspections.

The Validation of the VereBeef™ Detection Kit.

VereBeef™ Detection Kit, incorporating both multiplex PCR and microarray technologies on a lab-on-chip platform, is intended for qualitative detection and differentiation of Escherichia coli O157:H7, E. coli O26, E. coli O45, E. coli O103, E. coli O111, E. coli O121, E. coli O145, Shiga toxin-producing E. coli (STEC) virulence factors (stx1A, stx2A, eae), and Salmonella species in one test using raw beef trim samples. This product underwent extensive evaluations, including inclusivity-exclusivity, method comparison, robustness, lot-to-lot variability, and stability studies. The inclusivity/exclusivity study demonstrated that VereBeef Detection Kit specifically detects and identifies target analytes without occurrence of false-positive and false-negative detection. In the method comparison study, the performance of the VereBeef Detection Kit was compared with U.S. Department of Agriculture Food Safety and Inspection Service Microbiology Laboratory Guidebook's methods for target organism detection in raw beef trim using E. coli O157:H7 single inoculation and Salmonella and non-O157 STEC dual inoculation. Data demonstrated equivalence in both methods. The robustness study showed that changes in the test parameters do not impact assay performance. Collectively, VereBeef Detection Kit is able to detect target pathogens in raw beef trim with a minimum enrichment time of 8 h for E. coli O157:H7 detection and 10 h for Salmonella and non-O157 STEC detection.

An electrochemical immunobiosensor for ultrasensitive detection of Escherichia coli O157:H7 using CdS quantum dots-encapsulated metal-organic frameworks as signal-amplifying tags

We report here cadmium sulfide quantum dots (CdS QDs)-encapsulated metal-organic frameworks as signal-amplifying tags for ultrasensitive electrochemical detection of Escherichia coli O157:H7 (E. coli O157:H7). CdS QDs were encapsulated in zeolitic imidazolate framework-8 (ZIF-8) to form CdS@ZIF-8 muti-core-shell particles by in situ growth of ZIF-8 in the presence of CdS QDs. To specifically recognize E. coli O157:H7 cells, CdS@ZIF-8 particles were coated with polyethyleneimine to introduce amino groups on their surfaces, followed by surface modification of anti-E. coli O157:H7 antibody. A sandwich-type electrochemical immunobiosensor for the detection of E. coli O157:H7 was fabricated using CdS@ZIF-8 particles as signal tags. Cd(II) ions were released from CdS@ZIF-8 tags by HCl leaching, enabling the detection of E. coli O157:H7 by differential pulse voltammetry. Under the optimized conditions, the linear range of the biosensor is from 10 to 108 colony forming units (CFU) per mL for E. coli O157:H7 detection, with the detection limit of 3 CFU mL−1 (S/N = 3). The sensitivity of the biosensor for E. coli O157:H7 detection using CdS@ZIF-8 particles as signal tags is 16 times that of a biosensor using CdS QDs as signal tags, because the number of CdS QDs labeled to each bacterial cell increases greatly resulting from a great number of CdS QDs encapsulated in each CdS@ZIF-8 label. This method was successfully used to detect E. coli O157:H7 in milk samples.