A novel method for sensitive detection of Escherichia coli O157:H7 based on an aptamer and hybridization chain reaction

Graphene-based biosensors in milk analysis: A review of recent developments

Cow's milk, an excellent source of fat, protein, amino acids, vitamins and minerals, is currently one of the most consumed products worldwide. Contaminations originating from diverse sources, such as biological, chemical, and physical, cause dairy product quality problems and thus dairy-related disorders, raising public health issues. For this reason, legal authorities have deemed it necessary to classify certain contaminations in commercial milk and keep them within particular limitations; therefore, it is urgent to develop next-generation detection systems that can accurately identify just the contaminants of concern to human health. This review presents a detailed investigation of biosensors based on graphene and its derivatives, which offer superior sensitivity and selectivity, by classifying the contaminants under the headings biological, chemical, and physical, in cow's milk according to their sources. We reviewed the current status of graphene-based biosensor (GBs) technology for milk or dairy analysis, highlighting its strengths and weaknesses with the help of comparative studies, tables, and charts, and we put forward a novel perspective to handle future challenges.

A functional nucleic acid-based fluorescence sensing platform based on DNA supersandwich nanowires and cation exchange reaction

Accurate and sensitive analysis of p53 DNA is important for early diagnosis of cancer. In this work, a fluorescence sensing system based on DNA supersandwich nanowires and cation exchange (CX)-triggered multiplex signal amplification was constructed for the detection of p53 DNA. In the presence of p53 DNA, the DNA self-assembles to form a DNA supersandwich nanowire that generates long double-stranded DNA. Subsequently, the cation exchange (CX) reaction between ZnS and Ag+ was utilized to release free Zn2+. With the participation of Zn2+, DNAzyme catalyzes the hydrolysis of numerous catalytic molecular beacons, resulting in a greatly enhanced fluorescence signal due to the cycling of DNAzyme. The fluorescence values increased in proportion to the concentrations of p53 DNA in the range of 10 pM to 200 nM, and a detection limit (LOD) of 2.34 pM (S/N = 3) was obtained. This method provides an effective strategy for the quantitative detection of p53 DNA.

Development of Recombinase Aided Amplification (RAA)-Exo-Probe Assay for the Rapid Detection of Shiga Toxin-Producing Escherichia coli

BACKGROUND

Shiga toxin-producing Escherichia coli (STEC) is a significant cause of foodborne illness causing various gastrointestinal diseases including hemolytic uremic syndrome (HUS), the most severe form, which can lead to kidney failure or even death.

OBJECTIVE

Here, we report the development of recombinase aided amplification (RAA)-exo-probe assays targeting the stx1 and stx2 genes for the rapid detection of STEC in food samples.

METHODS

Primers and exo-probes were designed and optimized for the detection of stx1 and stx2 using RAA technology. The optimal STEC RAA-exo-probe assays were then tested for specificity and sensitivity, and validated in both spiked and real food samples.

RESULTS

These assays were found to be 100% specific to STEC strains and were also highly sensitive with a detection limit of 1.6 × 103 CFU/mL or 32 copies/reaction. Importantly, the assays were able to successfully detect STEC in spiked and real food samples (beef, mutton, and pork), with a detection limit as low as 0.35 CFU/25g in beef samples after an overnight enrichment step.

CONCLUSIONS

Overall, the RAA assay reactions completed within ∼20 min and were less dependent on expensive equipment, suggesting they can be easily adopted for in-field testing requiring only a fluorescent reader.

HIGHLIGHTS

As such, we have developed two rapid, sensitive, and specific assays that can be used for the routine monitoring of STEC contamination in food samples, particularly in the field or in poorly equipped labs.

A review of advances in aptamer-based cell detection technology

Since cells are the basic structural and functional units of organisms, the detection or quantitation of cells is one of the most common basic problems in life science research. The established cell detection techniques mainly include fluorescent dye labeling, colorimetric assay, and lateral flow assay, all of which employ antibodies as cell recognition elements. However, the widespread application of the established methods generally dependent on antibodies is limited, because the preparation of antibodies is complicated and time-consuming, and unrecoverable denaturation is prone to occur with antibodies. By contrast, aptamers that are generally selected through the systematic evolution of ligands by exponential enrichment can avoid the disadvantages of antibodies due to their controllable synthesis, thermostability, and long shelf life, etc. Accordingly, aptamers may serve as novel molecular recognition elements like antibodies in combination with various techniques for cell detection. This paper reviews the developed aptamer-based cell detection methods, mainly including aptamer-fluorescent labeling, aptamer-isothermal amplification assay, electrochemical aptamer sensor, aptamer-based lateral flow analysis, and aptamer-colorimetric assay. The principles, advantages, progress of application in cell detection and future development trend of these methods were specially discussed. Overall, different assays are suitable for different detection purposes, and the development of more accurate, economical, efficient, and rapid aptamer-based cell detection methods is always on the road in the future. This review is expected to provide a reference for achieving efficient and accurate detection of cells as well as improving the usefulness of aptamers in the field of analytical applications.

Bridge-DNA synthesis triggered by an allosteric aptamer for the colorimetric detection of pathogenic bacteria

Rapid and sensitive quantification of pathogenic bacteria is highly desired for environmental health supervision and food safety control. Yet, the amplification and detection of bacteria with a concentration lower than 10² cfu mL^-1 remains a great challenge. Here, we combined an allosteric aptamer (AAP) with a gold nanoparticle (AuNP) for assembling a bridge-DNA synthesis system (named as AuNP-BDS) to amplify the bacterial signals. The AAP and its paired primer (PP) were covalently linked to two different AuNPs, respectively: one named as AAP-AuNP and the other PP-AuNP. Upon recognition of the antigen from the pathogenic bacteria, AAP alters its conformation to initiate DNA synthesis on the AuNP surface. The DNA products from AAP-AuNP and PP-AuNP form bridges to each other through base pairing, resulting in the aggregation and colorimetric response of the AuNPs. By using E. coli O157:H7 as an example, the AuNP-BDS could quantify pathogenic bacteria in water with a concentration as low as 10 cfu mL^-1 within 60 min and without any enrichment. The colorimetric response values of AuNP-BDS were found to be linearly related to the bacterial concentrations in the range of 10 to 10³ cfu mL^-1. Good practicability of the AuNP-BDS in quantifying E. coli O157:H7 from tap water, juices, and milks was demonstrated. The AuNP-BDS could be exploited to facilitate the rapid and sensitive quantification of pathogenic bacteria for food safety control.

LAMP-Based Point-of-Care Biosensors for Rapid Pathogen Detection

Seeking optimized infectious pathogen detection tools is of primary importance to lessen the spread of infections, allowing prompt medical attention for the infected. Among nucleic-acid-based sensing techniques, loop-mediated isothermal amplification is a promising method, as it provides rapid, sensitive, and specific detection of microbial and viral pathogens and has enormous potential to transform current point-of-care molecular diagnostics. In this review, the advances in LAMP-based point-of-care diagnostics assays developed during the past few years for rapid and sensitive detection of infectious pathogens are outlined. The numerous detection methods of LAMP-based biosensors are discussed in an end-point and real-time manner with ideal examples. We also summarize the trends in LAMP-on-a-chip modalities, such as classical microfluidic, paper-based, and digital LAMP, with their merits and limitations. Finally, we provide our opinion on the future improvement of on-chip LAMP methods. This review serves as an overview of recent breakthroughs in the LAMP approach and their potential for use in the diagnosis of existing and emerging diseases.

Colorimetric nano-beacon and magnetic separation-based rapid and visual assay for gram-negative bacteria

Food-borne diseases caused by pathogenic bacteria are one of the serious factors affecting human health. However, the most commonly used detection methods for pathogenic bacteria not only require expensive instruments, but also take a long time due to the complicated and cumbersome detection process. Therefore, the development of a fast, simple, and low-cost detection method for pathogenic bacteria is crucial for food safety and human health. In this work, based on the high binding ability of antimicrobial peptide (AMP) and polymyxin B (PMB) to bacteria, combined with magnetic separation technology, a new enzyme-free colorimetric strategy was constructed to achieve visual detection of Gram-negative bacteria in complex samples. The sensor system was divided into the following two parts: a colorimetric signal amplification nanoprobe, which was modified with AMP to enable effective binding of the colorimetric probe to the surface of bacteria, and a PMB-modified magnetic nanobead (MNB), which was used as the capture and enrichment unit of Gram-negative bacteria, as a result of which PMB could effectively distinguish Gram-negative bacteria from Gram-positive bacteria. Under optimized conditions, the detection limit of the method for Gram-negative bacteria (e.g. E. coli (G^-)) was as low as 10 CFU/mL, and it was successfully applied to complex real samples. In addition, the developed colorimetric sensor offered advantages, such as fast response, less time consumption, high sensitivity, and low cost. It can be expected to become a new diagnostic tool for on-site detection of pathogenic bacteria in remote areas.

The fluorescent probe-based recombinase-aided amplification for rapid detection of Escherichia coli O157:H7

Escherichia coli O157:H7 (E. coli O157:H7) is a common foodborne morbigenous microorganism, which can spread through fecal-oral transmission. Humans can be infected by ingesting foods and water contaminated with E. coli O157:H7, which can cause various symptoms. In present study, we have successfully developed a quick and hypersensitive fluorescent probe-based Recombinase-aided amplification (RAA) method and applied in E. coli O157:H7 detection at 39 °C in 20 min. The sensitivity of the assay in pure E. coli O157:H7 suspension was 5.6 × 10⁰ CFU/mL. The fluorescent probe-based RAA assay was further applied in three samples, and the limit of detection (LOD) in skimmed milk, lettuces and lake water was 5.4 × 10¹ CFU/mL, 7.9 × 10¹ CFU/mL and 5.2 × 10¹ CFU/mL, separately. This method showed a high sensitivity and short detection time, which has the feasible application in on-site test in real samples.

A disposable gold foil paper-based aptasensor for detection of enteropathogenic Escherichia coli with SERS analysis and magnetic separation technology

Rapid and sensitive detection of enteropathogenic Escherichia coli (EPEC) in fluids with complex background is an important task for safety quality control in the field of medicine, environment, and food. In this study, a gold foil paper-based aptasensor was developed for the detection of enteropathogenic EPEC O26:K60 with surface-enhanced Raman spectroscopy (SERS) and magnetic separation technology mediated by Fe₃O₄@Au composite. The gold foil paper was firstly modified with thiolated capture probe and SERS tag. The thiolated aptamer probe for EPEC was immobilized onto a Fe₃O₄@Au composite. In the presence of EPEC, highly specific recognition between the aptamer probe and EPEC made the Fe₃O₄@Au composite partially dissociated from the gold foil paper. This led to a decreased Raman intensity response, which showed an obvious negative linear correlation with increasing concentration of EPEC over a wide concentration range from 10 to 10⁷ CFU/mL under an excitation wavelength of 633 nm. The detection limit was about 2.86 CFU/mL in a buffer solution and a licorice extractum and the detection time was only 2.5 h. The results demonstrate that the gold foil paper-based aptasensor can be an excellent biosensing platform that offers a reliable, rapid, and sensitive alternative for EPEC detection.

Aptamer-based diagnostic and therapeutic approaches in animals: Current potential and challenges

Fast and precise diagnosis of infectious and non-infectious animal diseases and their targeted treatments are of utmost importance for their clinical management. The existing biochemical, serological and molecular methods of disease diagnosis need improvement in their specificity, sensitivity and cost and, are generally not amenable for being used as points-of-care (POC) device. Further, with dramatic changes in environment and farm management practices, one should also arm ourselves and prepare for emerging and re-emerging animal diseases such as cancer, prion diseases, COVID-19, influenza etc. Aptamer – oligonucleotide or short peptides that can specifically bind to target molecules – have increasingly become popular in developing biosensors for sensitive detection of analytes, pathogens (bacteria, virus, fungus, prions), drug residues, toxins and, cancerous cells. They have also been proven successful in the cellular delivery of drugs and targeted therapy of infectious diseases and physiological disorders. However, the in vivo application of aptamer-mediated biosensing and therapy in animals has been limited. This paper reviews the existing reports on the application of aptamer-based biosensors and targeted therapy in animals. It also dissects the various modifications to aptamers that were found to be successful in in vivo application of the aptamers in diagnostics and therapeutics. Finally, it also highlights major challenges and future directions in the application of aptamers in the field of veterinary medicine.