Direct immobilization of antibodies on Zn-doped Fe 3 O 4 nanoclusters for detection of pathogenic bacteria

Advances in detection methods for viable Salmonella spp.: current applications and challenges

Salmonella is a common intestinal pathogen that can cause food poisoning and intestinal disease. The high prevalence of Salmonella necessitates efficient and sensitive methods for its identification, detection, and monitoring, especially of viable Salmonella. Conventional culture methods need to be more laborious and time-consuming. And they are relatively limited in their ability to detect Salmonella in the viable but non-culturable status if present in the sample to be tested. As a result, there is an increasing need for rapid and accurate techniques to detect viable Salmonella spp. This paper reviewed the status and progress of various methods reported in recent years that can be used to detect viable Salmonella, such as culture-based methods, molecular methods targeting RNAs and DNAs, phage-based methods, biosensors, and some techniques that have the potential for future application. This review can provide researchers with a reference for additional method options and help facilitate the development of rapid and accurate assays. In the future, viable Salmonella detection approaches will become more stable, sensitive, and fast and are expected to play a more significant role in food safety and public health.

Array-based microbial identification upon extracellular aminoglycoside residue sensing

Sensitive and rapid identification of pathogenic microorganisms is of great importance for clinical diagnosis and treatment. In this study, we developed an ultrasensitive colorimetric sensor array (CSA) based on the interactions between aminoglycoside antibiotics (AMGs) and Ag nanoparticles decorated with β-cyclodextrin (AgNPs@β-CD) to discriminate microorganisms quickly and accurately. Microorganisms can absorb different amounts of AMGs after incubation. Upon the addition of AgNPs@β-CD, the corresponding extracellular AMG residues will bind to AgNPs@β-CD, leading to color changes due to the modifications in localized surface plasmon resonance. The array was developed using 4 AMGs as sensing elements and AgNPs@β-CD as the colorimetric probe to generate a unique colorimetric response pattern for each microorganism. Standard chemometric methods indicated excellent discrimination among 20 microorganisms at low concentrations of 2 × 10⁶ CFU/mL. Therefore, this ultrasensitive CSA can be used for microbial discrimination portably and efficiently. Importantly, the concentration of microbial discrimination by our array is much lower than that of prior CSAs. This method of extracellular residue sensing also provided a new strategy to improve the sensitivity of conventional CSA in the discrimination of microorganisms, to measure the amount of intercellular uptake of AMGs by microorganisms, and to screen drugs that can easily be accumulated by the pathogenic microorganisms.

Detection of Escherichia coli using luminometer with pyruvate kinase

Portable and quantitative detection of Escherichia coli (E. coli) has the potential to reform clinical diagnostics, food safety, and environmental monitoring. At present, most commercial devices used for pathogen detection have disadvantages such as expensive, highly complex operations, or limited detection specificity. Using the common luminometer and the properties of pyruvate kinase utilizing phosphoenolpyruvate to generate adenosine triphosphate (ATP), we have developed a method that could specifically quantify E. coli. The system is based on a sandwich hybridization procedure wherein both oligonucleotide probes recognize each end of the target of pathogenic 16S rRNAs segment. The detection probe DNA-conjugated pyruvate kinase can link ATP production to the detection of pathogenic nucleic acid in the samples. The luminometer-based system is capable of detecting E. coli with single bacteria resolution. The platform should be easily used to the detection of many other toxic analytes through the application of suitable functional-DNA recognition elements.

Recent advances in dual recognition based surface enhanced Raman scattering for pathogenic bacteria detection: A review

Rapid and reliable detection of pathogenic bacteria at the early stage represents a highly topical research area for food safety and public health. Although culture based method is the gold standard method for bacteria detection, recent techniques have promoted the development of alternative methods, such as surface enhanced Raman scattering (SERS). SERS provides additional advantages of high speed, simultaneous detection and characterization, multiplex analysis, and comparatively low cost. However, conventional SERS methods for bacteria detection are facing limitations of low sensitivity, susceptible to matrix interference, and poor accuracy. In recent years, specific detection of pathogenic bacteria with dual recognition based SERS methods has attracted increasing attentions. These methods include two steps recognition of target bacteria, and integrate the functions of target separation and detection. Considering their merits of excellent specificity, ultrahigh sensitivity, multiplex detection capability, and potential for on-site applications, these methods are promising alternatives for rapid and reliable detection of pathogenic bacteria. Herein, this review aims to summarize the recent advances in dual recognition based SERS methods for specific detection of pathogenic bacteria. Their advantages and limitations are discussed, and further perspectives are tentatively given. This review provides new insights into the application of SERS as a reliable tool for pathogenic bacteria detection.

Vancomycin-modified poly-l-lysine magnetic separation combined with multiplex polymerase chain reaction assay for efficient detection of Bacillus cereus in milk

In this study, a new vancomycin (Van)-modified poly-l-lysine (PLL) magnetic bead (MB) technique was developed for isolation of gram-positive bacteria. The method combines magnetic separation with a multiplex PCR (mPCR) assay and gel electrophoresis for easy and rapid detection of Bacillus cereus. Vancomycin was used as a molecular ligand between the MB and the d-alanyl-d-alanine moieties on the cell wall surface of B. cereus. The PLL served as a flexible molecular tether between the MB and Van that reduced steric hindrance maintaining the biological activity of Van. The MB-PLL-Van capture nanoprobes exhibited excellent capture and isolation efficiency for B. cereus in spiked milk matrix samples without interference from the complex food matrix. The subsequent mPCR assay showed high specificity for the 4 target genes in B. cereus, the entFM, cesB, cer, and 16S rRNA genes, that were used to achieve efficient genotyping and detection. Under optimum conditions, the limit of detection reached 10³ cfu/mL, with a dynamic range of detection at 10³ to 10⁷ cfu/mL in pure culture. Application of the MB-PLL-Van mediated mPCR assay for B. cereus in milk matrix samples achieved results similar to those of the pure culture. In addition, with a 6-h pre-enrichment of B. cereus that was spiked in milk matrix samples, the limit of detection reached 10¹ cfu/mL. The MB-PLL-Van mediated mPCR assay developed in this study could be used as a universal technology platform for the efficient enrichment and genotyping of gram-positive bacteria.

Point-of-Need Diagnostics for Foodborne Pathogen Screening

Foodborne illness is a major public health issue that results in millions of global infections annually. The burden of such illness sits mostly with developing countries, as access to advanced laboratory equipment and skilled lab technicians, as well as consistent power sources, is limited and expensive. Current gold standards in foodborne pathogen screening involve labor-intensive sample enrichment steps, pathogen isolation and purification, and costly readout machinery. Overall, time to detection can take multiple days, excluding the time it takes to ship samples to off-site laboratories. Efforts have been made to simplify the workflow of such tests by integrating multiple steps of foodborne pathogen screening procedures into a singular device, as well as implementing more point-of-need readout methods. In this review, we explore recent advancements in developing point-of-need devices for foodborne pathogen screening. We discuss the detection of surface markers, nucleic acids, and metabolic products using both paper-based and microfluidic devices, focusing primarily on developments that have been made between 2015 and mid-2020.

Biosensor surface functionalization by a simple photochemical immobilization of antibodies: experimental characterization by mass spectrometry and surface enhanced Raman spectroscopy

Surface functionalization is a key step in biosensing since it is the basis of an effective analyte recognition. Among all the bioreceptors, antibodies (Abs) play a key role thanks to their superior specificity, although the available immobilization strategies suffer from several drawbacks. When gold is the interacting surface, the recently introduced Photochemical Immobilization Technique (PIT) has been shown to be a quick, easy-to-use and very effective method to tether Abs oriented upright by means of thiols produced via tryptophan mediated disulphide bridge reduction. Although the molecular mechanism of this process is quite well identified, the detailed morphology of the immobilized antibodies is still elusive due to inherent difficulties related to the microscopy imaging of Abs. The combination of Mass Spectrometry, Surface-Enhanced Raman Spectroscopy and Ellman's assay demonstrates that Abs irradiated under the conditions in which PIT is realized show only two effective disulphide bridges available for binding. They are located in the constant region of the immunoglobulin light chain so that the most likely position Ab assumes is side-on, i.e. with one Fab (i.e. the antigen binding portion of the antibody) exposed to the solution. This is not a limitation of the recognition efficiency in view of the intrinsic flexibility of the Ab structure, which makes the free Fab able to sway in the solution, a feature of great importance in many biosensing applications.

Emerging Point-of-care Technologies for Food Safety Analysis

Food safety issues have recently attracted public concern. The deleterious effects of compromised food safety on health have rendered food safety analysis an approach of paramount importance. While conventional techniques such as high-performance liquid chromatography and mass spectrometry have traditionally been utilized for the detection of food contaminants, they are relatively expensive, time-consuming and labor intensive, impeding their use for point-of-care (POC) applications. In addition, accessibility of these tests is limited in developing countries where food-related illnesses are prevalent. There is, therefore, an urgent need to develop simple and robust diagnostic POC devices. POC devices, including paper- and chip-based devices, are typically rapid, cost-effective and user-friendly, offering a tremendous potential for rapid food safety analysis at POC settings. Herein, we discuss the most recent advances in the development of emerging POC devices for food safety analysis. We first provide an overview of common food safety issues and the existing techniques for detecting food contaminants such as foodborne pathogens, chemicals, allergens, and toxins. The importance of rapid food safety analysis along with the beneficial use of miniaturized POC devices are subsequently reviewed. Finally, the existing challenges and future perspectives of developing the miniaturized POC devices for food safety monitoring are briefly discussed.

Controllable fabrication of magnetic core–shell nanocomposites with high peroxide mimetic properties for bacterial detection and antibacterial applications

Pathogenic bacterial infection has become a growing threat to public health; therefore, exploration of a sensitive and specific method for the identification of bacteria is very important.

Live E. coli bacteria label-free sensing using a microcavity in-line Mach-Zehnder interferometer

The paper presents the first study to date on selective label-free biosensing with a microcavity in-line Mach-Zehnder interferometer induced in an optical fiber. The sensing structures were fabricated in a single-mode fiber by femtosecond laser micromachining. In contrast to other studies of this sensing scheme, where only the sensitivity to refractive index changes in the cavity was investigated, this research used chemical surface treatment of the sensor to ensure detection specificity. Immobilized MS2 bacteriophages were applied as recognition elements specifically targeting live E. coli C3000 bacteria. It is shown that the sensor allows for real-time monitoring of biological phenomena taking place on the surface of the microcavity. The developed biosensor exhibits ultrahigh refractive index sensitivity of 15,000 nm/RIU and is capable of detecting live E. coli bacteria concentrations as low as 100 colony forming units (CFU)/mL in liquid volume as low as picoliters.

A single-tube approach for in vitro diagnostics using diatomaceous earth and optical sensor

Versatile, simple and efficient sample preparation is desirable for point-of-care testing of emerging diseases such as zoonoses, but current sample preparation assays are insensitive, labour-intensive and time-consuming and require multiple instruments. We developed a single-tube sample preparation approach involving direct pathogen enrichment and extraction from human specimens using diatomaceous earth (DE). Amine-modified DE was used to directly enrich a zoonotic pathogen, Brucella, in a large sample volume. Next, a complex of amine-modified DE and dimethyl suberimidate was used for nucleic acid extraction from the enriched pathogen. Using our single-tube approach, the pathogen can be enriched and extracted within 60min at a level of 1 colony formation unit (CFU) from a 1ml sample volume in the same tube. The performance of this approach is 10-100 times better than that of a commercial kit (102 to 103CFU/ml) but does not require a large centrifuge. Finally, we combined the single-tube approach with a bio-optical sensor for rapid and accurate zoonotic pathogen detection in human urine samples. Using the combination system, Brucella in human urine can be efficiently enriched (~ 8-fold) and the detection limit is enhanced by up to 100 times (1CFU/ml bacteria in urine) compared with the commercial kit. This combined system is fast and highly sensitive and thus represents a promising approach for disease diagnosis in the clinical setting.

Thiol–ene click chemistry towards easy microarraying of half-antibodies

UV light catalyses in a few seconds the thiol–ene coupling reaction between half-antibodies and vinyl functionalized surfaces, providing high performance microarrays.

Highly Chemiluminescent Magnetic Beads for Label-Free Sensing of 2,4,6-Trinitrotoluene

Until now, despite the great success acquired in scientific research and commercial applications, magnetic beads (MBs) have been used for nothing more than a carrier in most cases in bioassays. In this work, highly chemiluminescent magnetic beads containing N-(4-aminobutyl)-N-ethyl isoluminol (ABEI) and Co²⁺ (Co²⁺/ABEI/MBs) were first synthesized via a facile strategy. ABEI and Co²⁺ were grafted onto the surface of carboxylated MBs by virtue of a carboxyl group and electrostatic interaction. The as-prepared Co²⁺/ABEI/MBs exhibited good paramagnetic properties, satisfactory stability, and intense chemiluminescence (CL) emission when reacted with H₂O₂, which was more than 150 times that of ABEI functionalized MBs. Furthermore, it was found that 2,4,6-trinitrotoluene (TNT) aptamer could attach to the surface of Co²⁺/ABEI/MBs via electrostatic interaction and coordination interaction between TNT aptamer and Co²⁺, leading to a decrease in CL intensity due to the catalytic site Co²⁺ being blocked by the aptamer. In the presence of TNT, TNT would bind strongly with TNT aptamer and detach from the surface of Co²⁺/ABEI/MBs, resulting in partial restoration of the CL signal. Accordingly, label-free aptasensor was developed for the determination of TNT in the range of 0.05-25 ng/mL with a detection limit of 17 pg/mL. This work demonstrates that Co²⁺/ABEI/MBs are easily connected with recognition biomolecules, which are not only magnetic carriers but also direct sensing interfaces with excellent CL activity. It provides a novel CL interface with a magnetic property which easily separates analytes from the sample matrix to construct label-free bioassays.