A colorimetric immunoassay for determination of Escherichia coli O157:H7 based on oxidase-like activity of cobalt-based zeolitic imidazolate framework

Development of a nanobody-based immunoassay for the detection of Escherichia coli O157:H7 in food samples

Rapid and accurate detection of foodborne pathogens is crucial for food safety. E. coli O157:H7, a major foodborne pathogen, can cause severe illness even at low concentration, highlighting the necessity for effective detection methods. This study focuses on developing nanobodies specific to E. coli O157:H7, aiming to provide a more efficient, cost-effective, and stable analytical reagents which can be available internationally. An alpaca was immunized and a phage-displayed nanobody library was constructed. Following panning, nanobodies were expressed and characterized for their affinity and specificity. A nanobody-based immunoassay was developed, with a limit of detection of 8.7 × 103 cfu/mL. The matrix effect was evaluated, and the assay successfully detected E. coli O157:H7 in various food samples (with 5 cfu spiked), including ground beef, orange juice, and milk. The study developed a nanobody-based immunoassay for E. coli O157:H7 detection, underscoring the practical applicability of nanobodies for testing food safety monitoring.

Recent advances in metallic and metal oxide nanoparticle-assisted molecular methods for the detection of Escherichia coli

The detection of E. coli is of irreplaceable importance for the maintenance of public health and food safety. In the field of molecular detection, metal and metal oxide nanoparticles have demonstrated significant advantages due to their unique physicochemical properties, and their application in E. coli detection has become a cutting-edge focus of scientific research. This review systematically introduces the innovative applications of these nanoparticles in E. coli detection, including the use of magnetic nanoparticles for efficient enrichment of bacteria and precise purification of nucleic acids, as well as a variety of nanoparticle-assisted immunoassays such as enzyme-linked immunosorbent assays, lateral flow immunoassays, colorimetric methods, and fluorescence strategies. In addition, this paper addresses the application of nanoparticles used in nucleic acid tests, including amplification-free and amplification-based assays. Furthermore, the application of nanoparticles used in electrochemical and optical biosensors in E. coli detection is described, as well as other innovative assays. The advantages and challenges of the aforementioned technologies are subjected to rigorous analysis, and a prospective outlook on the future direction of development is presented. In conclusion, this review not only illustrates the practical utility and extensive potential of metal and metal oxide nanoparticles in E. coli detection, but also serves as a scientific and comprehensive reference for molecular diagnostics in food safety and public health.

A critical review on metal organic frameworks (MOFs)-based sensors for foodborne pathogenic bacteria detection

The pervasive threat of foodborne pathogenic bacteria necessitates advancements in rapid and reliable detection methods. Traditional approaches suffer from significant limitations including prolonged processing times, limited sensitivity and specificity. This review comprehensively examines the integration of metal organic frameworks (MOFs) with sensor technologies for the enhanced detection of foodborne pathogens. MOFs, with their unique properties such as high porosity, tunable pore sizes, and ease of functionalization, offer new avenues for sensor enhancement. This paper provides a comprehensive analysis of recent developments in MOFs-based sensors, particularly focusing on electrochemical, fluorescence, colorimetric, and surface-enhanced Raman spectroscopy sensors. We have provided a detailed introduction for the operational principles of these sensors, highlighting the role of MOFs play in enhancing their performance. Comparative analyses demonstrate MOFs' superior capabilities in enhancing signal response, reducing response time, and expanding detection limits. This review culminates in presenting MOFs as transformative materials in the detection of foodborne pathogens, paving the way for their broader application in ensuring food safety.

A colorimetric biosensor with infrared sterilization based on CuSe nanoparticles for the detection of E. coli O157:H7 in food samples

It is critical to develop quick, accurate, and efficient sterilization for detecting Escherichia coli O157:H7 in order to prevent infections and outbreaks of foodborne illnesses. Herein, we established a colorimetric biosensor with sterilizing properties using copper selenide nanoparticles to detect E. coli O157:H7. The sample was mixed with magnetic nanoprobes and nanozyme probes to form a sandwich structure, and then the unbound nanozyme probes were collected by magnetic separation. Finally, the 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate)-hydrogen peroxide (H2O2) reporting system was added for signal amplification. The change from colorless to green can be seen with the naked eye. Under the optimal conditions, the detection range of E. coli O157:H7 was 102-106 CFU/mL, and the detection limit was 0.35 × 102 CFU/mL. The total detection time was 80 minutes, which can be successfully applied to milk and mineral water. In addition, the colorimetric sensor can kill the target bacteria by irradiating it under a 980-nm laser for 5 minutes. In conclusion, this sensor is a promising tool for rapidly detecting foodborne pathogens and promptly eliminating bacteria.

IMPORTANCE

Escherichia coli O157:H7 is a major threat to public health. At present, the detection methods for E. coli O157:H7 mainly include traditional bacterial culture, immunology (enzyme-linked immune-sorbent assay) and molecular biology techniques (polymerase chain reaction). These methods have the limitations of professional operation, waste of time and energy, and high cost. Therefore, we have developed a simple, fast, bactericidal colorimetric biosensor to detect E. coli. O157:H7. The entire process was completed in 80 minutes. The method has been successfully applied to milk and mineral water samples with satisfactory results, proving that the method is an effective method for real-time detection and inactivation of bacteria.

Direct, Rapid Detection of Pathogens from Urine Samples

The problem of rapidly detecting pathogens directly from clinical samples poses significant analytical challenges. Addressing this issue in relation to urinary tract infections, we propose an effective protocol and related immunomagnetic test kits enabling versatile screening for the presence of pathogenic bacteria in unprocessed urine samples. To achieve this, the components of a typical immunomagnetic separation protocol were optimized towards the sensitive assessment of the aggregates formed out of immunomagnetically tagged target pathogens collected from clinical samples. Specifically, a dedicated immunomagnetic material was developed via the functionalization of standardized, micron-sized magnetic beads with generic antibodies against gram-specific bacterial constituents with mannan binding lectin. As such, we demonstrate efficient procedures for achieving the enhanced, specific, and pathogen-mediated cluster formation of these tailored affinity-coated magnetic beads in complex samples. We further show how cluster analysis, in conjunction with the use of nonspecific, inexpensive fluorescent dye, allows for a straightforward optical assessment of the bacterial load directly from urine samples. The optimized sensing protocol and related kits provide, in less than 60 min, qualitative (positive/negative) information on the bacterial load with 85% specificity and 96% sensitivity, which is appropriate to empower clinical microscopy with a new analytic dimension. The procedure is prone to automation, can be conveniently used in clinical microbiology laboratories and, since it preserves the viability of the captured bacteria, can be interfaced with downstream analyses and antimicrobial susceptibility testing. Moreover, the study emphasizes a suite of practical validation assays that are useful for bringing the tool-box of immunomagnetic materials outside the academic laboratory and into real-life applications.

Nanobody and Nanozyme-Enabled Immunoassays with Enhanced Specificity and Sensitivity

Immunoassay as a rapid and convenient method for detecting a variety of targets has attracted tremendous interest with its high specificity and sensitivity. Among the commonly used immunoassays, enzyme-linked immunosorbent assay has been widely used as a gold standard method in various fields that consists of two main components including a recognition element and an enzyme label. With the rapid advances in nanotechnology, nanobodies and nanozymes enable immunoassays with enhanced specificity and sensitivity compared with conventional antibodies and natural enzymes. This review is focused on the applications of nanobodies and nanozymes in immunoassays. Nanobodies advantage lies in their small size, high specificity, mass expression, and high stability. Nanozymes with peroxidase, phosphatase, and oxidase activities and their applications in immunoassays are highlighted and discussed in detail. In addition, the challenges and outlooks in terms of the use of nanobodies and the development of novel nanozymes in practical applications are discussed.

One-pot facile synthesis of enzyme-encapsulated Zn/Co-infinite coordination polymer nanospheres as a biocatalytic cascade platform for colorimetric monitoring of bacteria viability

A rapid method for colorimetric monitoring of bacterial viability is described. The colorimetric method was carried out based on glucose oxidase-encapsulated Zn/Co-infinite coordination polymer (Zn/Co-ICP@GOx), which was prepared in aqueous solution free of toxic organic solvents at room temperature. The Zn/Co-ICP@GOx was confirmed to be a robust sphere structure with an average diameter of 147.53 ± 20.40 nm. It integrated the catalytic activity of natural enzyme (GOx) and mimetic peroxidase (Co (П)) all in one, efficiently acting as a biocatalytic cascade platform for glucose catalytic reaction. Exhibiting good multi-enzyme catalytic activity, stability, and selectivity, Zn/Co-ICP@GOx can be used for colorimetric glucose detection. The linear range was 0.01-1.0 mmol/L, and the limit of detection (LOD) was 0.005 mmol/L. As the glucose metabolism is a common expression of bacteria, the remaining glucose can indirectly represent the bacterial viability. Hence, a Zn/Co-ICP@GOx-based colorimetric method was developed for monitoring of bacterial viability. The color was intuitively observed with the naked eye, and the bacterial viability was accurately quantified by measurement of the absorbance at 510 nm. The method was applied to determination of bacterial viability in water and milk samples with recoveries of 99.0-103% and RSD of 0.43-7.5%. The method was rapid (less than 40 min) and applicable to different bacterial species irrespective of Gram-positive and Gram-negative bacteria, providing a universal and promising strategy for real-time monitoring of bacterial viability.