Rapid detection of Escherichia coli O157:H7 and Salmonella Typhimurium in foods using an electrochemical immunosensor based on screen-printed interdigitated microelectrode and immunomagnetic separation

A novel fluorometric aptasensor based on carbon nanocomposite for sensitive detection of Escherichia coli O157:H7 in milk

Escherichia coli O157:H7 is an extremely serious foodborne pathogen accounting for a vast number of hospitalizations. In this system, a simple, rapid, and safe compound method was developed based on carbonyl iron powder (CIP) and multiwalled carbon nanotubes (MWCNT). Then, the CIP@MWCNT-based aptasensor was constructed by strong π-stacking between nanocomposite and aptamer, single-strand DNA, causing fluorescent quenching of the dye-labeled aptamer. The restoration of dye fluorescence could be achieved when aptamer came off the surface of the CIP@MWCNT nanocomposite due to the presence of target bacteria. To the best of our knowledge, this fabrication of magnetic carbon nanotubes without irritating and corrosive reagents is described for the first time. The sensing platform was also an improvement on the conventional formation of the aptasensor between carbon materials and DNA aptamer. The nanocomposite was verified by diverse characterization of zeta potential, Fourier-transform infrared spectroscopy, transmission electron microscopy, and energy dispersive x-ray analysis. The CIP@MWCNT-based aptasensor was an effective nanoplatform for quantitative detection of E. coli O157:H7, and was measured to have high specificity, good reproducibility, and strong stability. The aptasensor's capacity to quantify E. coli O157:H7 was as low as 7.15 × 10³ cfu/mL in pure culture. The detection limit of E. coli O157:H7 was 3.15 × 10² cfu/mL in contaminated milk after 1 h of pre-incubation. Hence, the developed assay is a new possibility for effective synthesis of nanocomposites and sensitive tests of foodborne pathogens in the dairy industry.

Recent Progress on the Electrochemical Biosensing of Escherichia coli O157:H7: Material and Methods Overview

Escherichia coli O157:H7 (E. coli O157:H7) is a pathogenic strain of Escherichia coli which has issued as a public health threat because of fatal contamination of food and water. Therefore, accurate detection of pathogenic E. coli is important in environmental and food quality monitoring. In spite of their advantages and high acceptance, culture-based methods, enzyme-linked immunosorbent assays (ELISAs), polymerase chain reaction (PCR), flow cytometry, ATP bioluminescence, and solid-phase cytometry have various drawbacks, including being time-consuming, requiring trained technicians and/or specific equipment, and producing biological waste. Therefore, there is necessity for affordable, rapid, and simple approaches. Electrochemical biosensors have shown great promise for rapid food- and water-borne pathogen detection. Over the last decade, various attempts have been made to develop techniques for the rapid quantification of E. coli O157:H7. This review covers the importance of E. coli O157:H7 and recent progress (from 2015 to 2020) in the development of the sensitivity and selectivity of electrochemical sensors developed for E. coli O157:H7 using different nanomaterials, labels, and electrochemical transducers.

DNA aptamer-based non-faradaic impedance biosensor for detecting E. coli

Developing a real-time, portable, and inexpensive sensor for pathogenic bacteria is crucial since the conventional detection approaches such as enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR) assays are high cost, time-consuming, and require an expert operator. Here we present a portable, inexpensive, and convenient impedance-based biosensor using Interdigitated Electrode (IDE) arrays to detect Escherichia coli (E. coli) as a model to demonstrate the feasibility of an impedance-based biosensor. We manipulated the affinity of the IDE array towards E. coli (E. coli BL21 series) by functionalizing the IDEs' surface with an E. coli outer membrane protein (OMP) Ag1 Aptamer. To determine the dominant factors affecting the sensitivity and the performance of the biosensor in detecting E. coli, we investigated the roles of the substrate material used in the fabrication of the IDE, the concentration of the aptamer, and the composition of the carboxy aliphatic thiol mixture used in the pre-treatment of the IDE surface. In the sensing experiments we used an E. coli concentration range of 25-1000 cfu mL-1 and confirmed the binding of the OMP Ag1 Aptamer to the outer membrane protein of the E. coli by Field Emission Scanning Electron Microscopy (FESEM), Optical Microscopy, and Atomic Force Microscopy (AFM). By tuning the surface chemistry, the IDEs' substrate material, and the concentration of the OMP Ag1 Aptamer, our sensor could detect E. coli with the analytical sensitivity of approximately 1.8 Ohm/cfu and limit of detection of 9 cfu mL-1. We found that the molecular composition of the self-assembled monolayer (SAM) formed on the top of the IDEs before the attachment of the OMP Ag1 Aptamer significantly impacted the sensitivity of the sensor. Notably, with straightforward changes to the molecular recognition elements, this platform device can be used to detect a wide range of other microorganisms and chemicals relevant for environmental monitoring and public health.

Combining impedance biosensor with immunomagnetic separation for rapid screening of Salmonella in poultry supply chains

Salmonella screening is a key to ensure food safety in poultry supply chains. Currently available Salmonella detection methods including culture, polymerase chain reaction and enzyme-linked immuno-sorbent assay could not achieve rapid, sensitive, and in-field detection. In this study, different strategies for separation and detection of Salmonella were proposed, compared, and improved based on our previous studies on immunomagnetic separation and impedance biosensor. First, the coaxial capillary for immunomagnetic separation of target bacteria was improved with less contamination, and 3 strategies based on the improved capillary and immunomagnetic nanoparticles were compared to separate the target bacteria from sample and form the magnetic bacteria. The experimental results showed that the strategy of capture in tube and separation in capillary was the most suitable with separation efficiency of approximately 88%. Then, the immune gold nanoparticles coated with urease were used to label the magnetic bacteria, resulting in the formation of enzymatic bacteria, which were injected into the capillary. After the urea was catalyzed by the urease on the enzymatic bacteria in the capillary, different electrodes were compared to measure the impedance of the catalysate and the screen-printed electrode with higher sensitivity and better stability was the most suitable. This impedance biosensor-based bacterial detection strategy was able to detect Salmonella as low as 102 CFU/mL in 2 h without complex operations. Compared to the gold standard culture method for practical screening of Salmonella in poultry supply chains, this proposed strategy had an accuracy of approximately 90% for 75 real poultry samples.

Advances in Using Nanotechnology Structuring Approaches for Improving Food Packaging

Recent advances in food packaging materials largely rely on nanotechnology structuring. Owing to several unique properties of nanostructures that are lacking in their bulk forms, the incorporation of nanostructures into packaging materials has greatly improved the performance and enriched the functionalities of these materials. This review focuses on the functions and applications of widely studied nanostructures for developing novel food packaging materials. Nanostructures that offer antimicrobial activity, enhance mechanical and barrier properties, and monitor food product freshness are discussed and compared. Furthermore, the safety and potential toxicity of nanostructures in food products are evaluated by summarizing the migration activity of nanostructures to different food systems and discussing the metabolism of nanostructures at the cellular level and in animal models.

Biological Biosensors for Monitoring and Diagnosis

Quantification and detection of various contaminants in the ecosystem have become critically important in the past few decades due to their exhaustive use in soil and aquatic ecosystems. The contamination by both organic and inorganic contaminants in the ecosystem has drawn attention due to their persistence, biological accumulation, and toxicity. Organic contaminants reach the air, water, food, soil, and other systems through drift mechanism and have detrimental effect on various life systems after entering the food chain, thus interfering the normal biological process of the ecosystem. Inorganic contaminants have less solubility, primarily get adsorbed, and accumulate on lower sediments. The sources of both organic and inorganic contaminants include anthropogenic activities which dispose industrial and sewage effluent directly into water bodies. Most of the contaminants are very much toxic and have tumorigenic, carcinogenic, and mutagenic effect on various life-forms. Biosensors have various prospective and existing applications in the detection of these compounds in the environment by transducing a signal. It also has immense applications in the detection of different contaminants in the food industry, environmental monitoring, disease diagnosis, etc. where reliable and precise analyses are required. This chapter points out a comprehensive glimpse on different biosensors and their characteristics, operating principles, and their designs, based on transduction types and biological components. Efforts have been made to summarize various applications of biosensors in food industry, environmental monitoring, drug delivery systems, and clinical diagnostics etc.

Point-of-Care Strategies for Detection of Waterborne Pathogens

Waterborne diseases that originated due to pathogen microorganisms are emerging as a serious global health concern. Therefore, rapid, accurate, and specific detection of these microorganisms (i.e., bacteria, viruses, protozoa, and parasitic pathogens) in water resources has become a requirement of water quality assessment. Significant research has been conducted to develop rapid, efficient, scalable, and affordable sensing techniques to detect biological contaminants. State-of-the-art technology-assisted smart sensors have improved features (high sensitivity and very low detection limit) and can perform in a real-time manner. However, there is still a need to promote this area of research, keeping global aspects and demand in mind. Keeping this view, this article was designed carefully and critically to explore sensing technologies developed for the detection of biological contaminants. Advancements using paper-based assays, microfluidic platforms, and lateral flow devices are discussed in this report. The emerging recent trends, mainly point-of-care (POC) technologies, of water safety analysis are also discussed here, along with challenges and future prospective applications of these smart sensing technologies for water health diagnostics.

Impedimetric transducers based on interdigitated electrode arrays for bacterial detection - A review

Application of the impedance spectroscopy technique to detection of bacteria has advanced considerably over the last decade. This is reflected by the large amount of publications focused on basic research and applications of impedance biosensors. Employment of modern technologies to significantly reduce dimension of impedimetric devices enable on-chip integration of interdigitated electrode arrays for low-cost and easy-to-use sensors. This review is focused on publications dealing with interdigitated electrodes as a transducer unit and different bacteria detection systems using these devices. The first part of the review deals with the impedance technique principles, paying special attention to the use of interdigitated electrodes, while the main part of this work is focused on applications ranging from bacterial growth monitoring to label-free specific bacteria detection.

Advanced Diagnostic Approaches for Necrotrophic Fungal Pathogens of Temperate Legumes With a Focus on Botrytis spp

Plant pathogens reduce global crop productivity by up to 40% per annum, causing enormous economic loss and potential environmental effects from chemical management practices. Thus, early diagnosis and quantitation of the causal pathogen species for accurate and timely disease control is crucial. Botrytis Gray Mold (BGM), caused by Botrytis cinerea and B. fabae, can seriously impact production of temperate grain legumes separately or within a complex. Accordingly, several immunogenic and molecular probe-type protocols have been developed for their diagnosis, but these have varying levels of species-specificity, sensitivity and consequent usefulness within the paddock. To substantially improve speed, accuracy and sensitivity, advanced nanoparticle-based biosensor approaches have been developed. These novel methods have made enormous impact toward disease diagnosis in the medical sciences and offer potential for transformational change within the field of plant pathology and disease management, with early and accurate diagnosis at the point-of-care in the field. Here we review several recently developed diagnostic tools that build on traditional approaches and are available for pathogen diagnosis, specifically for Botrytis spp. diagnostic applications. We then identify the specific gaps in knowledge and current limitations to these existing tools.

Detection of Escherichia coli O157:H7 and Salmonella enterica serotype Typhimurium based on cell elongation induced by beta-lactam antibiotics

Pathogenic bacteria such as Shiga toxigenic Escherichia coli and Salmonella can cause severe food-borne diseases. Rapid and sensitive detection of these foodborne pathogens is essential to ensure food safety. In this study, a novel method based on cell elongation induced by beta-lactam antibiotics for direct microscopic counting of Gram-negative bacteria was established. Combined with the sample preparation steps of membrane filtration and magnetic separation, the detection of E. coli O157:H7 and Salmonella enterica serotype Typhimurium was achieved by direct optical microscopic counting of the number of elongated bacteria. The limit of detection of E. coli O157:H7 and S. typhimurium could reach 20 CFU mL^-1. The recovery tests for E. coli O157:H7 and S. typhimurium in water and milk samples showed acceptable recovery values between 93.6% and 106.2%. This method is sensitive, cost effective, and rapid (<2 h) and shows great potential for the detection of Gram-negative pathogens in various environmental and food samples.

Aptamer-based fluorometric determination of Salmonella Typhimurium using Fe3O4 magnetic separation and CdTe quantum dots

Based on the high sensitivity and stable fluorescence of CdTe quantum dots (QDs) in conjunction with a specific DNA aptamer, the authors describe an aptamer-based fluorescence assay for the determination of Salmonella Typhimurium. The fluorescence detection and quantification of S. Typhimurium is based on a magnetic separation system, a combination of aptamer-coated Fe₃O₄ magnetic particles (Apt-MNPs) and QD-labeled ssDNA2 (complementary strand of the aptamer). Apt-MNPs are employed for the specific capture of S. Typhimurium. CdTe QD-labeled ssDNA2 was used as a signaling probe. Simply, the as-prepared CdTe QD-labeled ssDNA2 was first incubated with the Apt-MNPs to form the aptamer-ssDNA2 duplex. After the addition of S. Typhimurium, they could specifically bind the DNA aptamer, leading to cleavage of the aptamer-ssDNA2 duplex, accompanied by the release of CdTe QD-labeled DNA. Thus, an increased fluorescence signal can be achieved after magnetic removal of the Apt-MNPs. The fluorescence of CdTe QDs (λexc/em = 327/612 nm) increases linearly in the concentration range of 10 to 10¹⁰ cfu•mL^-1, and the limit of detection is determined to be 1 cfu•mL^-1. The detection process can be performed within 2 h and is successfully applied to the analysis of spiked food samples with good recoveries from 90% to 105%.

Advances in electrochemical immunosensors

Immunosensors are compact tools on which antibody and antigen interactions are formed. The specific interaction between antibody and antigen is detected by using a transducer and an electrical signal is measured. This specific interaction between these molecules makes immunosensor very attractive for several applications in different fields. Electrochemical immunosensors are successful devices in selective and sensitive detection of several analytes. Electrochemical transducing methods such as voltammetric, potentiometric, conductometric or impedimetric have been utilized in different applications due to their excellent properties such as being low-cost, sensitivity and simplicity. In this chapter, the fundamentals of electrochemical immunosensors are summarized and different applications in food, environmental and clinical analyses are investigated and discussed.

Magnetic nanoparticles for smart electrochemical immunoassays: a review on recent developments

This review (with 129 refs) summarizes the progress in electrochemical immunoassays combined with magnetic particles that was made in the past 5 years. The specifity of antibodies linked to electrochemical transduction (by amperometry, voltammetry, impedimetry or electrochemiluminescence) gains further attractive features by introducing magnetic nanoparticles (MNPs). This enables fairly easy preconcentration of analytes, minimizes matrix effects, and introduces an appropriate label. Following an introduction into the fundamentals of electrochemical immunoassays and on nanomaterials for respective uses, a large chapter addresses method for magnetic capture and preconcentration of analytes. A next chapter discusses commonly used labels such as dots, enzymes, metal and metal oxide nanoparticles and combined clusters. The large field of hybrid nanomaterials for use in such immunoassays is discussed next, with a focus on MNPs composites with various kinds of graphene variants, polydopamine, noble metal nanoparticles or nanotubes. Typical applications address clinical markers (mainly blood and urine parameters), diagnosis of cancer (markers and cells), detection of pathogens (with subsections on viruses and bacteria), and environmental and food contaminants as toxic agents and pesticides. A concluding section summarizes the present status, current challenges, and highlights future trends. Graphical abstract Magnetic nanoparticles (MNP) with antibodies (Ab) capture and preconcentrate analyte from sample (a) and afterwards become magnetically (b) or immunospecifically (c) bound at an electrode. Signal either increases due to the presence of alabel (b) or decreases as the redox probe is blocked (c).

Aptamer surface functionalization of microfluidic devices using dendrimers as multi-handled templates and its application in sensitive detections of foodborne pathogenic bacteria

A microfluidic system that incorporates both dendrimers and aptamers to detect E. coli O157:H7 is developed. To achieve this, generation 7-polyamidoamine dendrimers were immobilized onto the detection surfaces of PDMS microfluidic channels; subsequently aptamers against E. coli O157:H7 were conjugated onto the microchannel surfaces via the immobilized dendrimers as templates. Surface modifications were characterized by FTIR, XPS, water contact angles, fluorescence microscopy and AFM to confirm the success of each surface modification steps. The efficacy of this simple microchannel in detection was investigated using E. coli O157:H7 spiked samples. Our results showed that this interesting approach significantly increased the amount of aptamers available on the microfluidic channel surfaces to capture E. coli O157:H7 cells to allow sensitive detection, which in turn resulted in detections of E. coli O157:H7 cells at a low limit of detection of 10² cells mL^-1. The results also demonstrated that in comparison with the generation 4-polyamidoamine dendrimers (G4) modified microchannels, those modified with G7 showed enhanced detection signals, improved target capturing efficiencies, and at higher throughput. This simple whole cell detection design has not been reported in the literature and it is an interesting and effective approach to developing a sensitive and rapid detection platform for foodborne pathogenic bacteria.

Determining meat freshness using electrochemistry: Are we ready for the fast and furious?

Electrochemistry is providing a variety of sensors at an extremely rapid pace. Many of these sensors offer powerful attributes like a multitude of platforms like voltammetry, impedimetry, amperometry and conductometry, as well as sensor-related gains like high sensitivity, selectivity and low cost. It is natural that their applications to food, especially meat freshness determination, are also increasing. Novel methods for rapidly assessing meat freshness are vital for meeting the increasing worldwide demand for meat products. Therefore, we present a short and succinct review of the most promising electrochemical sensor types, including those based on conductive polymers, nanocomposites and metal nanoparticles. From the wide range of sensors that have been designed to detect microbial pathogens and chemical degradation, we have covered a basic snapshot to yield an impression of recent gains in the research genre of meat freshness.

An enzyme-free biosensor for sensitive detection of Salmonella using curcumin as signal reporter and click chemistry for signal amplification

In this study, an enzyme-free biosensor was developed for sensitive and specific detection of Salmonella typhimurium (S. typhimurium) using curcumin (CUR) as signal reporter and 1,2,4,5-tetrazine (Tz)-trans-cyclooctene (TCO) click chemistry for signal amplification.

Methods: Nanoparticles composed of CUR and bovine serum albumin (BSA) were formulated and reacted with Tz and TCO to form Tz-TCO-CUR conjugates through Tz-TCO click chemistry. Then, the Tz-TCO-CUR conjugates were functionalized with polyclonal antibodies (pAbs) against S. typhimurium to form CUR-TCO-Tz-pAb conjugates. Magnetic nanoparticles (MNPs) conjugated with monoclonal antibodies (mAbs) against S. typhimurium through streptavidin-biotin binding were used to specifically and efficiently separate S. typhimurium from the background by magnetic separation. CUR-TCO-Tz-pAb conjugates were reacted with the magnetic bacteria to form CUR-Tz-TCO bacteria. Finally, CUR was released quickly from the CUR-Tz-TCO bacteria in the presence of NaOH, and the color change was measured at the characteristic wavelength of 468 nm for bacteria quantification.

Results: A linear relationship between absorbance at 468 nm and concentration of S. typhimurium from 102 to 106 CFU/mL was found. The lower detection limit was calculated to be as low as 50 CFU/mL and the mean recovery was 107.47% for S. typhimurium in spiked chicken samples.

Conclusion: This biosensor has the potential for practical applications in the detection of foodborne pathogens.

An impedance biosensor for simultaneous detection of low concentration of Salmonella serogroups in poultry and fresh produce samples

This paper reports the design, fabrication and testing of a microfluidic based impedance biosensor for rapid and simultaneous detection of three Salmonella serogroups. The microfluidic device consists of three microchannels, each one includes a region for focusing the Salmonella cells into the centerline of the microchannel and direct them toward the sensing region to obtain highly concentrated samples using positive dielectrophoresis force. A region for bacteria sensing consists of interdigitated electrode (IDE) array with 10 pairs of fingers. Three types of Salmonella antibodies (type B, D and E) were mixed separately with the cross-linker (Sulfo-LC-SPDP) to enhance the immobalization of the antibodies to the detection electrodes. The electrode surfaces was then functionalized with the three mixtures, one for each channel. As target antigen binds to the antibody, it results in impedance change. The Salmonella samples were spiked with Salmonella type B, introduced into the biosensor via the sample inlet into the focusing region, and then toward the sensing region where they bind to the immobilized antibody, causing a change in the impedance. The performance of the devices was tested using single Salmonella serotype B and two Salmonella serotypes B, and D, with a limit of detection of 7 cells/ml. The biosensor was also able to differentiate live from dead bacteria eliminating the false positive results. Finally, the device was also able to detect Salmonella selectively when other type of pathogen was present.

Electrical detection of pathogenic bacteria in food samples using information visualization methods with a sensor based on magnetic nanoparticles functionalized with antimicrobial peptides

Outbreaks of foodborne diseases demand simple, rapid techniques for detecting pathogenic bacteria beyond the standard methods that are not applicable to routine analysis in the food industry and in the points of food consumption. In this work, we developed a sensitive, rapid and low-cost assay for detecting Escherichia coli (E. coli), Staphylococcus aureus (S. aureus) and Salmonella typhimurium (S. typhi) in potable water and apple juice. The assay is based on electrical impedance spectroscopy measurements with screen-printed interdigitated electrodes coupled with magnetite nanoparticles functionalized with the antimicrobial peptide melittin (MLT). The data were analyzed with the information visualization methods Sammon's Mapping and Interactive Document Map to distinguish samples at two levels of contamination from food suitable for consumption. With this approach it has been possible to detect E. coli concentration down to 1 CFU mL^-1 in potable water and 3.5 CFU mL^-1 in apple juice without sample preparation, within only 25 min. This approach may serve as a low-cost, quick screening procedure to detect bacteria-related food poisoning, especially if the impedance data of several sensing units are combined.

Rapid, highly sensitive detection of Gram-negative bacteria with lipopolysaccharide based disposable aptasensor

Gram-negative bacteria are one of the most common microorganisms in the environment. Their differential detection and recognition from Gram-positive bacteria has been attracting much attention over the years. Using Escherichia coli (E. coli) as a model, we demonstrated on-site detection of Gram-negative bacteria by an AC electrokinetics-based capacitive sensing method using commercial microelectrodes functionalized with an aptamer specific to lipopolysaccharides. Dielectrophoresis effect was utilized to enrich viable bacteria to the microelectrodes rapidly, achieving a detection limit of 10² cells/mL within a 30 s' response time. The sensor showed a negligible response to Staphylococcus aureus (S. aureus), a Gram-positive species. The developed sensor showed significant advantages in sensitivity, selectivity, cost, operation simplicity, and response time. Therefore, this sensing method has shown great application potential for environmental monitoring, food safety, and real-time diagnosis.

Conductometric Sensor for PAH Detection with Molecularly Imprinted Polymer as Recognition Layer

A conductometric sensor based on screen-printed interdigital gold electrodes on glass substrate coated with molecularly imprinted polyurethane layers was fabricated to detect polycyclic aromatic hydrocarbons (PAHs) in water. The results prove that screen-printed interdigital electrodes are very suitable transducers to fabricate low-cost sensor systems for measuring change in resistance of PAH-imprinted layers while exposing to different PAHs. The sensor showed good selectivity to its templated molecules and high sensitivity with a detection limit of 1.3 nmol/L e.g., for anthracene in water which is lower than WHO’s permissible limit.

An electrochemical immunoassay for Escherichia coli O157:H7 using double functionalized Au@Pt/SiO2 nanocomposites and immune magnetic nanoparticles

A sensitive Point-of-Care Testing (POCT) with Au-Pt bimetallic nanoparticles (Au@Pt) functionalized silica nanoparticle (SiO₂ NPs) and Fe₃O₄ magnetic nanoparticles (Fe₃O₄ NPs) was designed for the quantitative detection of Escherichia coli O157:H7 (E. coli O157:H7). The poly-(4-styrenesulfonic acid-co-maleic acid) (PSSMA) as a negatively charged polyelectrolyte can be easily coated on surface of the amino group modified SiO₂ NPs via electrostatic force. PSSMA is also a good stabilizer for water-soluble bimetallic nanostructures. The PSSMA is first time used as a "bridge" to connect the negative charge Au@Pt NPs to the SiO₂ NPs, forming Au@Pt/SiO₂ NPs. Antibody and invertase conjugated Au@Pt/SiO₂ NPs (denoted as Ab/invertase-Au@Pt/SiO₂ NPs) were used as signal labels. Monoclonal antibody against E. coli O157:H7 (Ab) functionalized magnetic nanoparticles (denoted as Ab-Fe₃O₄@SiO₂ NPs) were used to enrich and capture the E. coli O157:H7 in positive sample. The immunosensing platform also composed of a personal glucometer (PGM) using for signal readout. Based on this sandwich-type immunoassay, the invertase in the final formed sandwich immunocomplex catalyzed the hydrolysis of sucrose to produce a large amount of glucose for quantitative readout by the PGM. Under optimal conditions, a linear relationship between the glucose concentration and the logarithm of E. coli O157:H7 concentration was obtained in the concentration range from 3.5 × 10² to 3.5 × 10⁸ CFU mL^-1 with a detection limit of 1.83 × 10² CFU mL^-1 (3σ). This method was used to detect E. coli O157:H7 in spiked milk samples, indicating its potential practical application. This protocol can be applied in various fields of study.

Label-free impedimetric glycan biosensor for quantitative evaluation interactions between pathogenic bacteria and mannose

In order to understanding the pathogenic mechanism of infectious diseases, it was important to study the selective recognition and interaction between pathogenic bacteria and host cells. In this paper, a novel electrochemical impedance biosensor was proposed, in which the Man/MUA-MH/Au sensing surface (Man: mannose; MUA: 11-mercapto eleven acid; MH: 6-mercapto hexanol) was fabricated and was of good biologically active and stability. The capture capacity of the designed sensing surface for S. typhimurium ATCC14028, E. coli JM109 and E. coli DH5α were characterized by Electrochemical impedance spectroscopy (EIS). According to Randless equivalent circuit and the Frumkin isotherm model, electron transfer impedance (R_et) was obtained and the binding affinity of the three bacteria and Man was calculated. It was shown that the sensing surface had a better binding affinity for S. typhimurium ATCC14028 with K_ADS(S.T.) = 2.16 × 10⁶ CFU/mL. The impedance normalized value NIC _(S.T.-Man) was of a good linear relationship with the logarithm of bacterial concentration (R² = 0.96) in the range of 50-1000 CFU/mL. The detection limit was 50 CFU/mL. Meanwhile, the E. coli JM109 which expresses type 1 fimbriae was also adsorbed on the designed sensing surface with K_ADS(JM109) = 5.84 × 10³ CFU/mL. It was illustrated that the novel electrochemical impedance biosensor could be more rapid and reliable for studying interactions between pathogen and glycan, and it was also perspective for a new point-of-care diagnostic tool for evaluating the pathogenicity bacteria.

Electrochemical immunosensors - A powerful tool for analytical applications

Immunosensors are biosensors based on interactions between an antibody and antigen on a transducer surface. Either antibody or antigen can be the species immobilized on the transducer to detect antigen or antibody, respectively. Because of the strong binding forces between these biomolecules, immunosensors present high selectivity and very high sensitivity, making them very attractive for many applications in different science fields. Electrochemical immunosensors explore measurements of an electrical signal produced on an electrochemical transductor. This signal can be voltammetric, potentiometric, conductometric or impedimetric. Immunosensors utilizing electrochemical detection have been explored in several analyses since they are specific, simple, portable, and generally disposable and can carry out in situ or automated detection. This review addresses the potential of immunosensors destined for application in food and environmental analysis, and cancer biomarker diagnosis. Emphasis is given to the approaches that have been used for construction of electrochemical immunosensors. Additionally, the fundamentals of immunosensors, technology of transducers and nanomaterials and a general overview of the possible applications of electrochemical immunosensors to the food, environmental and diseases analysis fields are described.

An Electrochemical Aptasensor Using Coaxial Capillary with Magnetic Nanoparticle, Urease Catalysis and PCB Electrode for Rapid and Sensitive Detection of Escherichia coli O157:H7

The continuous outbreaks of foodborne diseases have drawn public attentions to food safety. Early screening of foodborne pathogens is crucial to prevent and control of foodborne diseases. In this study, a novel electrochemical aptasensor was developed for rapid and sensitive detection of E. coli O157:H7 using the coaxial capillary with immune magnetic nanoparticles (MNPs) for specific separation of the target bacteria, the urease with urea for amplification of the impedance signals, and the PCB gold electrode for measurement of the impedance change. The streptavidin modified MNPs were conjugated with the biotinylated polyclonal antibodies (PAbs) to form the immune MNPs, and captured in the coaxial capillary with the line-up high gradient magnetic fields to separate the bacteria from the large volume of sample. Then, the gold nanoparticles (GNPs) were modified with the aptamers against E. coli and the urease, and injected into the capillary to react with the bacteria and form the MNP-PAb-bacteria-aptamer-GNP-urease complexes. Finally, the urease on the complexes was used to catalyze the hydrolysis of urea into ammonium ions and carbonate ions in the capillary, leading to the decrease in the impedance of the catalysate, which was measured by the gold plating PCB electrode. The impedance change of the catalysate and the concentration of the bacteria had a good linear relationship. This aptasensor was able to detect E. coli as low as 10¹ CFU/mL in 3 h, and the mean recovery of E. coli in the spiked pasteurized milk was ~99%. This proposed aptasensor has the potential for practical applications of foodborne pathogen detection due to its short detection time, high sensitivity and low cost.

A sensitive biosensor using double-layer capillary based immunomagnetic separation and invertase-nanocluster based signal amplification for rapid detection of foodborne pathogen

Combining double-layer capillary based high gradient immunomagnetic separation, invertase-nanocluster based signal amplification and glucose meter based signal detection, a novel biosensor was developed for sensitive and rapid detection of E. coli O157:H7 in this study. The streptavidin modified magnetic nanobeads (MNBs) were conjugated with the biotinylated polyclonal antibodies against E. coli O157:H7 to form the immune MNBs, which were captured by the high gradient magnetic field in the double-layer capillary to specifically separate and efficiently concentrate the target bacteria. Calcium chloride was used with the monoclonal antibodies against E. coli O157:H7 and the invertase to form the immune invertase-nanoclusters (INCs), which were used to react with the target bacteria to form the MNB-bacteria-INC complexes in the capillary. The sucrose was then injected into the capillary and catalyzed by the invertase on the complexes into the glucose, which was detected using the glucose meter to obtain the concentration of the glucose for final determination of the E. coli O157:H7 cells in the sample. A linear relationship between the readout of the glucose meter and the concentration of the E. coli O157:H7 cells (from 10² to 10⁷ CFU/mL) was found and the lower detection limit of this biosensor was 79 CFU/mL. This biosensor might be extended for the detection of other foodborne pathogens by changing the antibodies and has shown the potential for the detection of foodborne pathogens in a large volume of sample to further increase the sensitivity.

A Portable Impedance Immunosensing System for Rapid Detection of Salmonella Typhimurium

SalmonellaTyphimurium is one of the most dangerous foodborne pathogens and poses a significant threat to human health. The objective of this study was to develop a portable impedance immunosensing system for rapid and sensitive detection of S. Typhimurium in poultry. The developed portable impedance immunosensing system consisted of a gold interdigitated array microelectrode (IDAM), a signal acquisitive interface and a laptop computer with LabVIEW software. The IDAM was first functionalized with 16-Mercaptohexadecanoic acid, and streptavidin was immobilized onto the electrode surface through covalent bonding. Then, biotin-labelled S. Typhimurium-antibody was immobilized onto the IDAM surface. Samples were dropped on the surface of the IDAM and the S. Typhimurium cells in the samples were captured by the antibody on the IDAM. This resulted in impedance changes that were measured and displayed with the LabVIEW software. An equivalent circuit of the immunosensor demonstrated that the largest change in impedance was due to the electron-transfer resistance. The equivalent circuit showed an increase of 35% for the electron-transfer resistance value compared to the negative control. The calibration result indicated that the portable impedance immunosensing system could be used to measure the standard impedance elements, and it had a maximum error of measurement of approximately 13%. For pure culture detection, the system had a linear relationship between the impedance change and the logarithmic value of S. Typhimurium cells ranging from 76 to 7.6 × 10⁶ CFU (colony-forming unit) (50 μL)⁻¹. The immunosensor also had a correlation coefficient of 0.98, and a high specificity for detection of S. Typhimurium cells with a limit of detection (LOD) of 10² CFU (50 μL)⁻¹. The detection time from the moment a sample was introduced to the display of the results was 1 h. To conclude, the portable impedance immunosensing system for detection of S. Typhimurium achieved an LOD that is comparable with commercial electrochemical impedance instruments. The developed impedance immunosensor has advantages in portability, low cost, rapid detection and label-free features showing a great potential for in-field detection of foodborne pathogens.

Electrochemical Biosensors for Rapid Detection of Foodborne Salmonella: A Critical Overview

Salmonella has represented the most common and primary cause of food poisoning in many countries for at least over 100 years. Its detection is still primarily based on traditional microbiological culture methods which are labor-intensive, extremely time consuming, and not suitable for testing a large number of samples. Accordingly, great efforts to develop rapid, sensitive and specific methods, easy to use, and suitable for multi-sample analysis, have been made and continue. Biosensor-based technology has all the potentialities to meet these requirements. In this paper, we review the features of the electrochemical immunosensors, genosensors, aptasensors and phagosensors developed in the last five years for Salmonella detection, focusing on the critical aspects of their application in food analysis.

Electrochemical biosensors for Salmonella: State of the art and challenges in food safety assessment

According to the recent statistics, Salmonella is still an important public health issue in the whole world. Legislated reference methods, based on counting plate methods, are sensitive enough but are inadequate as an effective emergency response tool, and are far from a rapid device, simple to use out of lab. An overview of the commercially available rapid methods for Salmonella detection is provided along with a critical discussion of their limitations, benefits and potential use in a real context. The distinguished potentialities of electrochemical biosensors for the development of rapid devices are highlighted. The state-of-art and the newest technologic approaches in electrochemical biosensors for Salmonella detection are presented and a critical analysis of the literature is made in an attempt to identify the current challenges towards a complete solution for Salmonella detection in microbial food control based on electrochemical biosensors.

Recent Advances in Electrochemical Immunosensors

Immunosensors have experienced a very significant growth in recent years, driven by the need for fast, sensitive, portable and easy-to-use devices to detect biomarkers for clinical diagnosis or to monitor organic pollutants in natural or industrial environments. Advances in the field of signal amplification using enzymatic reactions, nanomaterials such as carbon nanotubes, graphene and graphene derivatives, metallic nanoparticles (gold, silver, various oxides or metal complexes), or magnetic beads show how it is possible to improve collection, binding or transduction performances and reach the requirements for realistic clinical diagnostic or environmental control. This review presents these most recent advances; it focuses first on classical electrode substrates, then moves to carbon-based nanostructured ones including carbon nanotubes, graphene and other carbon materials, metal or metal-oxide nanoparticles, magnetic nanoparticles, dendrimers and, to finish, explore the use of ionic liquids. Analytical performances are systematically covered and compared, depending on the detection principle, but also from a chronological perspective, from 2012 to 2016 and early 2017.