QCM immunosensor detection of Escherichia coli O157:H7 based on beacon immunomagnetic nanoparticles and catalytic growth of colloidal gold

A review on nanomaterial-based SERS substrates for sustainable agriculture

The agricultural sector plays a pivotal role in driving the economy of many developing countries. Any dent in this economical structure may have a severe impact on a country's population. With rising climate change and increasing pollution, the agricultural sector is experiencing significant damage. Over time this cumulative damage will affect the integrity of food crops and create food security issues around the world. Therefore, an early warning system is needed to detect possible stress on food crops. Here we present a review of the recent developments in nanomaterial-based Surface Enhanced Raman Spectroscopy (SERS) substrates which could be utilized to monitor agricultural crop responses to natural and anthropogenic stress. Initially, our review delves into diverse and cost-effective strategies for fabricating SERS substrates, emphasizing their intelligent utilization across various agricultural scenarios. In the second phase of our review, we spotlight the specific application of SERS in addressing critical food security issues. By detecting nutrients, hormones, and effector molecules in plants, SERS provides valuable insights into plant health. Furthermore, our exploration extends to the detection of contaminants, chemicals, and foodborne pathogens within plants, showcasing the versatility of SERS in ensuring food safety. The cumulative knowledge derived from these discussions illustrates the transformative potential of SERS in bolstering the agricultural economy. By enhancing precision in nutrient management, monitoring plant health, and enabling rapid detection of harmful substances, SERS emerges as a pivotal tool in promoting sustainable and secure agricultural practices. Its integration into agricultural processes not only augments productivity but also establishes a robust defence against potential threats to crop yield and food quality. As SERS continues to evolve, its role in shaping the future of agriculture becomes increasingly pronounced, promising a paradigm shift in how we approach and address challenges in food production and safety.

Emerging trends and future challenges of advanced 2D nanomaterials for combating bacterial resistance

The number of multi-drug-resistant bacteria has increased over the last few decades, which has caused a detrimental impact on public health worldwide. In resolving antibiotic resistance development among different bacterial communities, new antimicrobial agents and nanoparticle-based strategies need to be designed foreseeing the slow discovery of new functioning antibiotics. Advanced research studies have revealed the significant disinfection potential of two-dimensional nanomaterials (2D NMs) to be severed as effective antibacterial agents due to their unique physicochemical properties. This review covers the current research progress of 2D NMs-based antibacterial strategies based on an inclusive explanation of 2D NMs' impact as antibacterial agents, including a detailed introduction to each possible well-known antibacterial mechanism. The impact of the physicochemical properties of 2D NMs on their antibacterial activities has been deliberated while explaining the toxic effects of 2D NMs and discussing their biomedical significance, dysbiosis, and cellular nanotoxicity. Adding to the challenges, we also discussed the major issues regarding the current quality and availability of nanotoxicity data. However, smart advancements are required to fabricate biocompatible 2D antibacterial NMs and exploit their potential to combat bacterial resistance clinically.

High-throughput, highly sensitive and rapid SERS detection of Escherichia coli O157:H7 using aptamer-modified Au@macroporous silica magnetic photonic microsphere array

The aim of this research was to develop a simple, rapid, sensitive, high-throughput detection method for foodborne Escherichia coli (E. coli) O157:H7 based on the aptamer-modified gold nanoparticles@macroporous magnetic silica photonic microsphere (Au@MMSPM). Such Au@MMSPM array system for E. coli O157:H7 not only integrated sample pretreatment with rapid detection, but also showed highly enhanced effect to develop a highly sensitive SERS assay. The established SERS assay platform gave a wide linear detection range (10-10⁶ CFU/mL) and low limit of detection (2.20 CFU/mL) for E. coli O157:H7. The whole analysis time including sample pretreatment and detection was 110 min. This SERS-based assay platform provided a new high-throughput, highly sensitive and fast detection technology for monitoring E. coli O157:H7 in real samples from the fields of food industry, medicine and environment.

Real-Time Biosensing Bacteria and Virus with Quartz Crystal Microbalance: Recent Advances, Opportunities, and Challenges

Continuous monitoring of pathogens finds applications in environmental, medical, and food industry settings. Quartz crystal microbalance (QCM) is one of the promising methods for real-time detection of bacteria and viruses. QCM is a technology that utilizes piezoelectric principles to measure mass and is commonly used in detecting the mass of chemicals adhering to a surface. Due to its high sensitivity and rapid detection times, QCM biosensors have attracted considerable attention as a potential method for detecting infections early and tracking the course of diseases, making it a promising tool for global public health professionals in the fight against infectious diseases. This review first provides an overview of the QCM biosensing method, including its principle of operation, various recognition elements used in biosensor creation, and its limitations and then summarizes notable examples of QCM biosensors for pathogens, focusing on microfluidic magnetic separation techniques as a promising tool in the pretreatment of samples. The review explores the use of QCM sensors in detecting pathogens in various samples, such as food, wastewater, and biological samples. The review also discusses the use of magnetic nanoparticles for sample preparation in QCM biosensors and their integration into microfluidic devices for automated detection of pathogens and highlights the importance of accurate and sensitive detection methods for early diagnosis of infections and the need for point-of-care approaches to simplify and reduce the cost of operation.

Advances, applications, and limitations of portable and rapid detection technologies for routinely encountered foodborne pathogens

Traditional foodborne pathogen detection methods are highly dependent on pre-treatment of samples and selective microbiological plating to reliably screen target microorganisms. Inherent limitations of conventional methods include longer turnaround time and high costs, use of bulky equipment, and the need for trained staff in centralized laboratory settings. Researchers have developed stable, reliable, sensitive, and selective, rapid foodborne pathogens detection assays to work around these limitations. Recent advances in rapid diagnostic technologies have shifted to on-site testing, which offers flexibility and ease-of-use, a significant improvement from traditional methods' rigid and cumbersome steps. This comprehensive review aims to thoroughly discuss the recent advances, applications, and limitations of portable and rapid biosensors for routinely encountered foodborne pathogens. It discusses the major differences between biosensing systems based on the molecular interactions of target analytes and biorecognition agents. Though detection limits and costs still need further improvement, reviewed technologies have high potential to assist the food industry in the on-site detection of biological hazards such as foodborne pathogens and toxins to maintain safe and healthy foods. Finally, this review offers targeted recommendations for future development and commercialization of diagnostic technologies specifically for emerging and re-emerging foodborne pathogens.

Aptamers: A prospective tool for infectious diseases diagnosis

It is well known that people's health is seriously threatened by various pathogens (such as Mycobacterium tuberculosis, Treponema pallidum, Novel coronavirus, HIV, Mucor, etc.), which leads to heavy socioeconomic burdens. Therefore, early and accurate pathogen diagnosis is essential for timely and effective therapies. Up to now, diagnosing human contagious diseases at molecule and nano levels is remarkably difficult owing to insufficient valid probes when it comes to determining the biological markers of pathogens. Aptamers are a set of high‐specificity and high‐sensitivity plastic oligonucleotides screened in vitro via the selective expansion of ligands by exponential enrichment (SELEX). With the advent of aptamer‐based technologies, their merits have aroused mounting academic interest. In recent years, as new detection and treatment tools, nucleic acid aptamers have been extensively utilized in the field of biomedicine, such as pathogen detection, new drug development, clinical diagnosis, nanotechnology, etc. However, the traditional SELEX method is cumbersome and has a long screening cycle, and it takes several months to screen out aptamers with high specificity. With the persistent development of SELEX‐based aptamer screening technologies, the application scenarios of aptamers have become more and more extensive. The present research briefly reviews the research progress of nucleic acid aptamers in the field of biomedicine, especially in the diagnosis of contagious diseases.

Bulk and Surface Acoustic Wave Biosensors for Milk Analysis

Milk and dairy products are common foods and, therefore, are subject to regular controls. Such controls cover both the identification and quantification of specific components and the determination of physical parameters. Components include the usual milk ingredients, mainly carbohydrates, proteins, and fat, and any impurities that may be present. The latter range from small molecules, such as drug residues, to large molecules, e.g., protein-based toxins, to pathogenic microorganisms. Physical parameters of interest include viscosity as an indicator of milk gelation. Bulk and surface acoustic wave sensors, such as quartz crystal microbalance (QCM) and surface acoustic wave (SAW) devices, can principally be used for both types of analysis, with the actual application mainly depending on the device coating and the test format. This review summarizes the achievements of acoustic sensor devices used for milk analysis applications, including the determination of physical liquid parameters and the detection of low- and high-molecular-weight analytes and microorganisms. It is shown how the various requirements resulting from the respective analytes and the complex sample matrix are addressed, and to what extent the analytical demands, e.g., with regard to legal limits, are met.

The revolution of PDMS microfluidics in cellular biology

Microfluidics is revolutionizing the way research on cellular biology has been traditionally conducted. The ability to control the cell physicochemical environment by adjusting flow conditions, while performing cellular analysis at single-cell resolution and high-throughput, has made microfluidics the ideal choice to replace traditional in vitro models. However, such a revolution only truly started with the advent of polydimethylsiloxane (PDMS) as a microfluidic structural material and soft-lithography as a rapid manufacturing technology. Indeed, before the "PDMS age," microfluidic technologies were: costly, time-consuming and, more importantly, accessible only to specialized laboratories and users. The simplicity of molding PDMS in various shapes along with its inherent properties (transparency, biocompatibility, and gas permeability) has spread the applications of innovative microfluidic devices to diverse and important biological fields and clinical studies. This review highlights how PDMS-based microfluidic systems are innovating pre-clinical biological research on cells and organs. These devices were able to cultivate different cell lines, enhance the sensitivity and diagnostic effectiveness of numerous cell-based assays by maintaining consistent chemical gradients, utilizing and detecting the smallest number of analytes while being high-throughput. This review will also assist in identifying the pitfalls in current PDMS-based microfluidic systems to facilitate breakthroughs and advancements in healthcare research.

Preparation of Notch-4 Receptor Containing Quartz Crystal Microbalance Biosensor for MDA MB 231 Cancer Cell Detection

Quartz crystal microbalance (QCM) is a highly sensitive system that is used as a biosensor for biomolecules and cells. Detection and characterization of cancer cells in circulation or biopsy samples is of crucial importance for cancer diagnosis. Here, we introduce approaches for breast cancer cell detection via their surface molecules. The sensor system is based on preliminary coating of QCM chip with polymeric nanoparticles to increase the surface area and allow for the attachment of proteins to the chip surface. This is followed by the attachment of a specific protein in order to functionalize the chip. Breast cancer cells and fibroblast cells as control are cultured and applied to this chip. The functionalized QCM system can detect breast cancer cells with high affinity and selectivity. Here, we present the preparation methods of QCM-based sensors for selective detection of MDA MB 231 cancer cells. Selectivity of QCM-based sensor is carried out in the presence of L929 mouse fibroblast cells.

Biosensing platform on ferrite magnetic nanoparticles: Synthesis, functionalization, mechanism and applications

Ferrite magnetic nanoparticles (FMNPs) are gaining popularity to design biosensors for high-performance clinical diagnosis. The fusion of information shows that FMNPs based biosensors require well-tuned FMNPs as detection probes to produce large and specific biological signals with minimal non-specific binding. Nevertheless, there is a noticeable lacuna of information to solve the issues related to suitable synthesis route, particle size reduction, functionalization, sensitivity towards targeted intercellular biological tiny particles, and lower signal-to-noise ratio. Therefore it allows exploring unique characteristics of FMNPs to design a suitable sensing device for intracellular measurements and diseases detection. This review focuses on the extensively used synthesis routes, their advantages and limitations, crystalline structure, functionalization, along with recent applications of FMNPs in biosensors, taking into consideration their analytical figures of merit and range of linearity. This work also addresses the current progress, key factors for sensitivity, selectivity and productivity improvement along with the challenges, future trends and perspectives of FMNPs based biosensors.

Nano-Al2O3 can mediate transduction-like transformation of antibiotic resistance genes in water

The prevalence of various antibiotic resistance genes (ARGs) and resistant bacteria has caused global public health risks. The carrier transport mediated by phages or membrane vesicles is an important way for horizontal transfer of ARGs. Nano metal oxide particles (NMOPs), which can enter cell through the cell membrane, may be used as the carriers of genes. However, whether they can be used as transmembrane delivery vectors for the horizontal ARG transfer remains unknown. Here, we set up a model of MONPs-mediated transfer of ARGs, and demonstrate that NMOPs, especially for nano-Al₂O₃, can act as carriers mediating the transduction-like ARG transformation in water. The highest transfer rate mediated by nano-Al₂O₃ is 4.53 × 10⁴ cfu/mmol, and it is 10⁴ times higher than that of control. Nano-Al₂O₃ can combine with plasmid coding for ARGs to form high-density package and prevent ARGs from degradation by endonuclease. The results of superresolution fluorescence microscopy and transmission electron microscopy show that nano-Al₂O₃ can carry ARGs for transmembrane transport. Genome-wide transcription microarray and qPCR indicate that SOS response was closely related to transduction-like ARG transformation mediated by nano-Al₂O₃. This study is the first to demonstrate that as a new transmembrane carrier, nano-Al₂O₃ can also cause ARGs diffusion in water.

Biosensors for rapid detection of Salmonella in food: A review

Salmonella is one of the main causes of foodborne infectious diseases, posing a serious threat to public health. It can enter the food supply chain at various stages of production, processing, distribution, and marketing. High prevalence of Salmonella necessitates efficient and effective approaches for its identification, detection, and monitoring at an early stage. Because conventional methods based on plate counting and real-time polymerase chain reaction are time-consuming and laborious, novel rapid detection methods are urgently needed for in-field and on-line applications. Biosensors provide many advantages over conventional laboratory assays in terms of sensitivity, specificity, and accuracy, and show superiority in rapid response and potential portability. They are now recognized as promising alternative tools and one of the most on-site applicable and end user-accessible methods for rapid detection. In recent years, we have witnessed a flourishing of studies in the development of robust and elaborate biosensors for detection of Salmonella in food. This review aims to provide a comprehensive overview on Salmonella biosensors by highlighting different signal-transducing mechanisms (optical, electrochemical, piezoelectric, etc.) and critically analyzing its recent trends, particularly in combination with nanomaterials, microfluidics, portable instruments, and smartphones. Furthermore, current challenges are emphasized and future perspectives are discussed.

A sandwich-type bacteriophage-based amperometric biosensor for the detection of Shiga toxin-producing Escherichia coli serogroups in complex matrices

Immuno-based biosensors are a popular tool designed for pathogen screening and detection. The current antibody-based biosensors employ direct, indirect, or sandwich detection approaches; however, instability, cross-reactivity, and high-cost render them unreliable and impractical. To circumvent these drawbacks, here we report a portable sandwich-type bacteriophage-based amperometric biosensor, which is highly-specific to various Shiga toxin-producing Escherichia coli (STEC) serogroups. Environmentally isolated and biotinylated bacteriophages were directly immobilized onto a streptavidin-coated screen-printed carbon electrode (SPCE), which recognized and captured viable target cells. Samples (50 μL) were transferred to these bacteriophage-functionalized SPCEs (12 min, room temp) before sequentially adding a bacteriophage-gold nanoparticle solution (20 μL), H2O2 (40 mM), and 1,1'-ferrocenedicarboxylic acid for amperometric tests (100 mV s-1) and analysis (ANOVA and LSD, P < 0.05). The optimum biotin concentration (10 mM) retained 94.47% bacteriophage viability. Non-target bacteria (Listeria monocytogenes and Salmonella Typhimurium) had delta currents below the threshold of a positive detection. With less than 1 h turn-around time, the amperometric biosensor had a detection limit of 10-102 CFU mL-1 for STEC O157, O26, and O179 strains and R 2 values of 0.97, 0.99, and 0.87, respectively, and a similar detection limit was observed in complex matrices, 10-102 CFU g-1 or mL-1 with R 2 values of 0.98, 0.95, and 0.76, respectively. The newly developed portable amperometric biosensor was able to rapidly detect viable target cells at low inoculum levels, thus providing an inexpensive and improved alternative to the current immuno- and laboratory-based STEC screening methods.

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.

A Highly Sensitive Impedimetric DNA Biosensor Based on Hollow Silica Microspheres for Label-Free Determination of E. coli

A novel label-free electrochemical DNA biosensor was constructed for the determination of Escherichia coli bacteria in environmental water samples. The aminated DNA probe was immobilized onto hollow silica microspheres (HSMs) functionalized with 3-aminopropyltriethoxysilane and deposited onto a screen-printed electrode (SPE) carbon paste with supported gold nanoparticles (AuNPs). The biosensor was optimized for higher specificity and sensitivity. The label-free E. coli DNA biosensor exhibited a dynamic linear response range of 1 × 10-10 µM to 1 × 10-5 µM (R2 = 0.982), with a limit of detection at 1.95 × 10-15 µM, without a redox mediator. The sensitivity of the developed DNA biosensor was comparable to the non-complementary and single-base mismatched DNA. The DNA biosensor demonstrated a stable response up to 21 days of storage at 4 ℃ and pH 7. The DNA biosensor response was regenerable over three successive regeneration and rehybridization cycles.

Power of Scanning Electron Microscopy and Energy Dispersive X-Ray Analysis in Rapid Microbial Detection and Identification at the Single Cell Level

The demand for rapid, consistent and easy-to-use techniques for detecting and identifying pathogens in various areas, such as clinical diagnosis, the pharmaceutical industry, environmental science and food inspection, is very important. In this study, the reference strains of six food-borne pathogens, namely, Escherichia coli 0157: H7 ATCC 43890, Cronobacter sakazakii ATCC 29004, Salmonella Typhimurium ATCC 43971, Staphylococcus aureus KCCM 40050, Bacillus subtilis ATCC 14579, and Listeria monocytogenes ATCC 19115, were chosen for scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis. In our study, the time-consuming sample preparation step for the microbial analysis under SEM was avoided, which makes this detection process notably rapid. Samples were loaded onto a 0.01-µm-thick silver (Ag) foil surface to avoid any charging effect. Two different excitation voltages, 10 kV and 5 kV, were used to determine the elemental information. Information obtained from SEM-EDX can distinguish individual single cells and detect viable and nonviable microorganisms. This work demonstrates that the combination of morphological and elemental information obtained from SEM-EDX analysis with the help of principal component analysis (PCA) enables the rapid identification of single microbial cells without following time-consuming microbiological cultivation methods.

PC software-based portable cyclic voltammetry system with PB-MCNT-GNPs-modified electrodes for E. coli detection

PC software-based portable cyclic voltammetry (PCV) systems have the advantages of portability, high performance, and real-time detection. In this paper, the PCV system used cyclic voltammetry (CV) as the main detection and analysis method and contained the following components: a three-electrode unit, a portable potentiostat, and PC software. The PC software was used as the system control and display, and a dynamic peak position adjustment (DPPA) algorithm for E. coli measurements based on thick biofilm modification on electrodes was designed especially for this system to realize the real-time correspondence between the measured results and the modified electrodes. The performance test results obtained by setting different detection parameters in the PCV system were compared with those of commercial electrochemical workstations. The difference was less than 4.99%, with a relative standard deviation less than 0.20%. An electrochemical biosensor based on a Prussian blue-multiwalled carbon nanotube-gold nanoparticle composite was developed for E. coli detection. After constructing an antibody-BSA-E. coli electrode modification on the sensor, experimental data processed by the DPPA algorithm showed that the logarithm (lg Df_E.coli) of the E. coli dilution factor and the peak current response had a linear relationship. The PCV system could quickly and accurately detect E. coli concentrations with dynamic adjustment algorithms for biofilm-modified electrodes. Furthermore, the system could detect the electrochemical activities of various high-sensitivity biomolecules, showing great detection potential for on-site monitoring and meeting the requirements of real-time and portable detection in various food safety fields.

Universal and reusable hapten/antibody-mediated portable optofluidic immunosensing platform for rapid on-site detection of pathogens

A universal and reusable hapten-antibody-mediated portable optofluidic immunosensing platform (OIP) was developed for rapid on-site detection of pathogens. By using Escherichia coli O157:H7 (E. coli O157:H7) and bisphenol A-Bovine serum albumin (BPA-BSA)/anti-BPA antibody as a model pathogen and a mediated hapten-antibody, respectively, a novel immunoassay mechanism was proposed to detect pathogens. The BPA-BSA-modified immunosensor and E. coli O157:H7 were initially saturated with anti-BPA antibodies (mouse IgG) and anti-E. coli O157:H7 antibodies (mouse IgG), respectively. Then, the fluorescence-labeled secondary antibodies (goat anti-mouse IgG antibody) were incubated with E. coli O157:H7 with their antibodies. Next, the mixture was introduced into the immunosensor surface bound to the anti-BPA antibodies. A high concentration of E. coli O157:H7 in the sample reduced the number of fluorescence-labeled secondary antibodies bound to the immunosensor surface, thus resulting in the detection of low fluorescence signals. Under optimized conditions, the hapten-antibody-mediated OIP system exhibited a detection limit of 8 cfu/mL E. coli O157:H7 after concentrating 100 times by using centrifugation, and a test cycle, including prereaction, detection, and regeneration, was less than 1 h. The robustness of the hapten-carrier protein-modified immunosensor surface allowed multiple pathogen immunoassays. The proposed strategy demonstrated good recovery, precision, and accuracy through the evaluation of the spiked water samples. We expect that the new platform can be readily used for the detection of other pathogens in a variety of application fields ranging from environmental monitoring and food safety to medical diagnosis.

Label-Free Monitoring of Microorganisms and Their Responses to Antibiotics Based on Self-Powered Microbead Sensors

Rapid detection of bacteria and their susceptibility to specific antibiotics plays a vital role in microbial infection treatments. Antimicrobial susceptibility testing (AST) is a common measure to select effective drugs. However, the conventional practices, such as broth dilution, E-test, and disk diffusion, in clinical applications require a long turnaround time (∼3 days), thereby compromising treatments and increasing mortality. This study presents self-powered sensors for on-site microorganism monitoring and rapid AST based on functionalized microbeads. The microbead sensors are driven by Brownian motion, rendering external power unnecessary. Fluorescent microbeads ( d_p = 2 μm) were coated with vancomycin to capture bacteria. The growth and responses of Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus under antibiotic treatment were evaluated. The method showed stable selective binding despite the presence of some interferential substances, such as proteins and cells. Diffusivity change was strongly related to bacterial concentration. Accordingly, the diffusivity values of microbeads bound with motile and nonmotile bacteria exhibited specific patterns because of extra motility from microbes and increased particle diameter. Only a drop of microbead-bacteria suspension (∼5 μL) was needed in a microchip for each measurement. The microchip provided a steady environment for measurement over a few hours. By distinguishing the slope of the last four data points in the temporal diffusivity curve, bacterial susceptibility or resistance to specific antibiotics could be determined within a time frame of 2 h. The study provides insights into saving more lives by using a fast and robust AST technique in future clinical practice.

Label-free and enzyme-free sensitive fluorescent method for detection of viable Escherichia coli O157:H7

We have developed a label-free, enzyme-free, modification-free and DNA extraction-free fluorescent aptasensing (LEFA) method for detection of E. coli O157:H7 based on G-quadruplex formation using two ingeniously designed hairpin probes (GHP1 and GHP2). In the presence of E. coli O157:H7, it released the single stranded initiation sequence (IS) resulting in the toehold strand displacement between GHP1 and GHP2, which in turn led to the cyclic reuse of the production of DNA assemblies with numerous G-quadruplex structures and initiation sequences. Then these G-quadruplex structures can be recognized quickly by N-methyl mesoporphyrin IX (NMM) resulting in significantly enhanced fluorescence. The LEFA method was successfully implemented for detecting E. coli O157:H7 with a detection limit of 66 CFU/mL in pure culture, 10 CFU/mL and 1 CFU/mL after pre-incubation of the milk and tap water for 4 and 8 h, respectively. Moreover, the strategy could distinguish viable E. coli O157:H7 from dead E. coli O157:H7 and other species of pathogen cells. Furthermore, the whole process of the strategy is accomplished within 100 min. The results indicated that the approach may be used to effectively control potential microbial hazards in human health, food safety, and animal husbandry.

Fiber optic surface plasmon resonance sensor for detection of E. coli O157:H7 based on antimicrobial peptides and AgNPs-rGO

A fiber optic surface plasmon resonance (FOSPR) sensor was developed for detection of Escherichia coli O157:H7 (E. coli O157:H7) in water and juice, based on antimicrobial peptides (AMP), Magainin I, as recognition elements and silver nanoparticles-reduced graphene oxide (AgNPs-rGO) nanocomposites assisted signal amplification. The uniform AgNPs-rGO was fixed on the surface of optical fiber and covered with gold film. Not only was the SPR response greatly enhanced, but also the AgNPs was prevented from being oxidized. The FOSPR showed a sensitivity of about 1.5 times higher than that fabricated only with gold film. In the assay, Magainin I, immobilized on the surface of gold film, could specifically capture E. coli O157:H7, resulting in the wavelength shift of the SPR absorption peak. Under the optimized conditions, the SPR resonance wavelength exhibited a good linear relationship with natural logarithm of the target bacteria concentration in the range of 1.0 × 10³ to 5.0 × 10⁷ cfu/mL with the detection limit of 5.0 × 10² cfu/mL (S/N = 3). The FOSPR sensor showed good specificity for E. coli O157:H7 detection compared to other bacteria similar to the target bacterial species. Furthermore, the FOSPR sensor was successfully applied to the detection of E. coli O157:H7 in water, fruit and vegetable juice with the satisfactory recoveries of 88-110%. This assay for E. coli O157:H7 detection possesses high sensitivity, good selectivity, reproducibility and stability. In addition, the AMP based SPR biosensing methodology could be extended to detect a wide variety of foodborne pathogens. Therefore, the versatile method might become a potential alternative tool in food analysis and early clinical diagnosis.

Ultrasensitive Detection of Escherichia coli O157:H7 by Immunomagnetic Separation and Selective Filtration with Nitroblue Tetrazolium/5-Bromo-4-chloro-3-indolyl Phosphate Signal Amplification

Here, we report an enhanced colorimetric method using enzymatic amplification with nitroblue tetrazolium (NBT)/5-bromo-4-chloro-3-indolyl phosphate (BCIP) precipitation for the ultrasensitive detection of Escherichia coli O157:H7 through immunomagnetic separation-selective filtration. Biotinylated anti- E. coli O157:H7 antibody and streptavidin-alkaline phosphatase were conjugated to the surface of magnetic nanoparticles, and E. coli O157:H7-conjugates complexes remained on the membrane filter surface. The resultant light brown spots on the membrane filter were amplified with NBT/BCIP solution to yield enzyme-catalyzed precipitation, which increased with an increasing E. coli O157:H7 concentration. E. coli O157:H7 was detected in pure samples with limits of detection of 10 and 6.998 colony-forming units (CFU)/mL through visual observation and measurement of optical density, respectively. The proposed method was applied to a lettuce sample inoculated with selective E. coli O157:H7, which was detected within 55 min without cross-reactivity to non-target bacteria. This enhanced colorimetric method has potential for on-site detection of food contaminants and environmental pollutants.

Novel Biosensors for the Rapid Detection of Toxicants in Foods

The modern environmental and food analysis requires sensitive, accurate, and rapid methods. The growing field of biosensors represents an answer to this demand. Unfortunately, most biosensor systems have been tested only on distilled water or buffered solutions, although applications to real samples are increasingly appearing in recent years. In this context, biosensors for potential food applications continue to show advances in areas such as genetic modification of enzymes and microorganisms, improvement of recognition element immobilization, and sensor interfaces. This chapter investigates the progress in the development of biosensors for the rapid detection of food toxicants for online applications. Recent progress in nanotechnology has produced affordable, mass-produced devices, and to integrate these into components and systems (including portable ones) for mass market applications for food toxicants monitoring. Sensing includes chemical and microbiological food toxicants, such as toxins, insecticides, pesticides, herbicides, microorganisms, bacteria, viruses and other microorganisms, phenolic compounds, allergens, genetically modified foods, hormones, dioxins, etc. Therefore, the state of the art of recent advances and future targets in the development of biosensors for food monitoring is summarized as follows: biosensors for food analysis will be highly sensitive, selective, rapidly responding, real time, massively parallel, with no or minimum sample preparation, and platform suited to portable and handheld nanosensors for the rapid detection of food toxicants for online uses even by nonskilled personnel.

Whole-bacterium SELEX of DNA aptamers for rapid detection of E.coli O157:H7 using a QCM sensor

The rapid detection of foodborne pathogens is critical to ensure food safety. The objective of this study is to select aptamers specifically bound to Escherichia coli O157:H7 using the whole-bacterium SELEX (Systematic Evolution of Ligands by Exponential Enrichment) and apply the selected aptamer to a QCM (quartz crystal microbalance) sensor for rapid and sensitive detection of target bacteria. A total of 19 rounds of selection against live E. coli O157:H7 and 6 rounds of counter selection against a mixture of Staphylococcus aureus, Listeria monocytogenes, and Salmonella Typhimurium, were performed. The aptamer pool from the last round was cloned and sequenced. One sequence S1 that appeared 16 times was characterized and a dissociation constant (K_d) of 10.30nM was obtained. Subsequently, a QCM aptasensor was developed for the rapid detection of E. coli O157:H7. The limit of detection (LOD) and the detection time of the aptasensor was determined to be 1.46×10³ CFU/ml and 50min, respectively. This study demonstrated that the ssDNA aptamer selected by the whole-bacterium SELEX possessed higher sensitivity than previous work and the potential use of the constructed QCM aptasensor in rapid screening of foodborne pathogens.

Exploiting pH-Regulated Dimer-Tetramer Transformation of Concanavalin A to Develop Colorimetric Biosensing of Bacteria

Gold nanoparticles (AuNPs) aggregation-based colorimetric biosensing remains a challenge for bacteria due to their large size. Here we propose a novel colorimetric biosensor for rapid detection of Escherichia coli O157:H7 (E. coli O157:H7) in milk samples based on pH-regulated transformation of dimer/tetramer of Concanavalin A (Con A) and the Con A-glycosyl recognition. Briefly, antibody-modified magnetic nanoparticles was used to capture and concentrate E. coli O157:H7 and then to label with Con A; pH adjusted to 5 was then applied to dissociate Con A tetramer to release dimer, which was collected and re-formed tetramer at pH of 7 to cause the aggregation of dextran-modified AuNPs. The interesting pH-dependent conformation-transformation behavior of Con A innovated the design of the release from the bacteria surface and then the reconstruction of Con A. Therefore, we realized the sensitive colorimetric biosensing of bacteria, which are much larger than AuNPs that is generally not suitable for this kind of method. The proposed biosensor exhibited a limit of detection down to 41 CFU/mL, short assay time (~95 min) and satisfactory specificity. The biosensor also worked well for the detection in milk sample, and may provide a universal concept for the design of colorimetric biosensors for bacteria and virus.

Development of Engineered Bacteriophages for Escherichia coli Detection and High-Throughput Antibiotic Resistance Determination

T7 bacteriophages (phages) have been genetically engineered to carry the lacZ operon, enabling the overexpression of beta-galactosidase (β-gal) during phage infection and allowing for the enhanced colorimetric detection of Escherichia coli (E. coli). Following the phage infection of E. coli, the enzymatic activity of the released β-gal was monitored using a colorimetric substrate. Compared with a control T7 phage, our T7_lacZ phage generated significantly higher levels of β-gal expression following phage infection, enabling a lower limit of detection for E. coli cells. Using this engineered T7_lacZ phage, we were able to detect E. coli cells at 10 CFU·mL^-1 within 7 h. Furthermore, we demonstrated the potential for phage-based sensing of bacteria antibiotic resistance profiling using our T7_lacZ phage, and subsequent β-gal expression to detect antibiotic resistant profile of E. coli strains.

Graphene-interfaced electrical biosensor for label-free and sensitive detection of foodborne pathogenic E. coli O157:H7

E. coli O157:H7 is an enterohemorrhagic bacteria responsible for serious foodborne outbreaks that causes diarrhoea, fever and vomiting in humans. Recent foodborne E. coli outbreaks has left a serious concern to public health. Therefore, there is an increasing demand for a simple, rapid and sensitive method for pathogen detection in contaminated foods. In this study, we developed a label-free electrical biosensor interfaced with graphene for sensitive detection of pathogenic bacteria. This biosensor was fabricated by interfacing graphene with interdigitated microelectrodes of capacitors that were biofunctionalized with E. coli O157:H7 specific antibodies for sensitive pathogenic bacteria detection. Here, graphene nanostructures on the sensor surface provided superior chemical properties such as high carrier mobility and biocompatibility with antibodies and bacteria. The sensors transduced the signal based on changes in dielectric properties (capacitance) through (i) polarization of captured cell-surface charges, (ii) cells' internal bioactivity, (iii) cell-wall's electronegativity or dipole moment and their relaxation and (iv) charge carrier mobility of graphene that modulated the electrical properties once the pathogenic E. coli O157:H7 captured on the sensor surface. Sensitive capacitance changes thus observed with graphene based capacitors were specific to E. coli O157:H7 strain with a sensitivity as low as 10-100 cells/ml. The proposed graphene based electrical biosensor provided advantages of speed, sensitivity, specificity and in-situ bacterial detection with no chemical mediators, represents a versatile approach for detection of a wide variety of other pathogens.

A rapid and visual aptasensor for Lipopolysaccharides detection based on the bulb-like triplex turn-on switch coupled with HCR-HRP nanostructures

For previously reported aptasensor, the sensitivity and selectivity of aptamers to targets were often suppressed due to the reporter label of single-stranded molecular beacon or hindrance of the duplex DNA strand displacement. To solve the affinity declining of aptamers showed in traditional way and realize on-site rapid detection of Lipopolysaccharides (LPS), we developed an ingenious structure-switching aptasensor based on the bulb-like triplex turn-on switch (BTTS) as the effective molecular recognition and signal transduction element and streptavidin-horseradish peroxidase modified hybridization chain reaction (HCR-HRP) nanocomposites as the signal amplifier and signal report element. In the presence of LPS, the bulb-like LPS-aptamer (BLA) and LPS formed the LPS/aptamer complex, while the BTTS disassembled and liberated the dissociative bridge probes (BP) to achieve molecular recognition and signal transduction. Immobilized BP, captured by immobilized capture probes (CP), triggered hybridization chain reactions (HCR) to amplify the switching signal, and the HCR products were then modified with streptavidin-horseradish peroxidase (SA-HRP) to form HCR-HRP nanostructures to output colorimetric signals. In less than four hours, the proposed biosensor showed a detection limit of 50pg/mL of LPS quantitatively with the portable spectrophotometer and the observation limit of 20ng/mL semi-quantitatively with the naked eye, opening up new opportunities for LPS detection in future clinical diagnosis, food security and environment monitoring.

A novel method for monitoring troponin T fragment from rabbit skeletal muscle during aging using quartz crystal microbalance

BACKGROUND

Troponin T (TnT) is degraded during aging of meat. The proteolytic fragment of TnT, especially the 30 kDa fragment, is used as one of indices for estimating aging of meat. We have tried to use quartz crystal microbalance (QCM), which is widely used to analyze interaction among macromolecules, to detect proteolytic fragments of TnT during aging of meat.

RESULT

The frequency of the QCM sensor with immobilized anti-TnT antibody in high-salt solution extracts of both myofibrils and whole meat decreased with time of aging. The staining intensity of the bands, including a 30 kDa fragment bound to anti-TnT antibody, also increased with time of aging in western blotting. These results confirm that TnT is degraded during aging and released from thin filaments, and QCM analysis is sufficiently sensitive to detect the TnT fragments.

CONCLUSION

The QCM analysis of muscle and myofibrillar extracts using anti-TnT antibody-immobilized sensor can be used as a convenient tool for monitoring the extent of aging of meat. © 2015 Society of Chemical Industry.

Label-free ITO-based immunosensor for the detection of very low concentrations of pathogenic bacteria

Here we describe the fabrication of a highly sensitive and label-free ITO-based impedimetric immunosensor for the detection of pathogenic bacteria Escherichia coli O157:H7. Anti-E. coli antibodies were immobilized onto ITO electrodes using a simple, robust and direct methodology. First, the covalent attachment of epoxysilane on the ITO surface was demonstrated by Atomic Force Microscopy and cyclic voltammetry. The immobilization of antibody on the epoxysilane layer was quantified by Optical Waveguide Lightmode Spectroscopy, obtaining a mass variation of 12 ng cm(− 2) (0.08 pmol cm(− 2)). Microcontact printing and fluorescence microscopy were used to demonstrate the specific binding of E. coli O157:H7 to the antibody-patterned surface. We achieved a ratio of 1:500 Salmonella typhimurium/E. coli O157:H7, thus confirming the selectivity of the antibodies and efficiency of the functionalization procedure. Finally, the detection capacity of the ITO-based immunosensor was evaluated by Electrochemical Impedance Spectroscopy. A very low limit of detection was obtained (1 CFU mL(− 1)) over a large linear working range (10–10(6) CFU mL(− 1)). The specificity of the impedimetric immunosensor was also examined. Less than 20% of non-specific bacteria (S. typhimurium and E. coli K12) was observed. Our results reveal the applicability of ITO for the development of highly sensitive and selective impedimetric immunosensors.

Specific detection of the cleavage activity of mycobacterial enzymes using a quantum dot based DNA nanosensor

We present a quantum dot based DNA nanosensor specifically targeting the cleavage step in the reaction cycle of the essential DNA-modifying enzyme, mycobacterial topoisomerase I. The design takes advantages of the unique photophysical properties of quantum dots to generate visible fluorescence recovery upon specific cleavage by mycobacterial topoisomerase I. This report, for the first time, demonstrates the possibility to quantify the cleavage activity of the mycobacterial enzyme without the pre-processing sample purification or post-processing signal amplification. The cleavage induced signal response has also proven reliable in biological matrices, such as whole cell extracts prepared from Escherichia coli and human Caco-2 cells. It is expected that the assay may contribute to the clinical diagnostics of bacterial diseases, as well as the evaluation of treatment outcomes.

A Label-Free Impedance Immunosensor Using Screen-Printed Interdigitated Electrodes and Magnetic Nanobeads for the Detection of E. coli O157:H7

Escherichia coli O157:H7 is one of the leading bacterial pathogens causing foodborne illness. In this study, an impedance immunosensor based on the use of magnetic nanobeads and screen-printed interdigitated electrodes was developed for the rapid detection of E. coli O157:H7. Magnetic nanobeads coated with anti-E. coli antibody were mixed with an E. coli sample and used to isolate and concentrate the bacterial cells. The sample was suspended in redox probe solution and placed onto a screen-printed interdigitated electrode. A magnetic field was applied to concentrate the cells on the surface of the electrode and the impedance was measured. The impedance immunosensor could detect E. coli O157:H7 at a concentration of 10^4.45 cfu·mL⁻¹ (~1400 bacterial cells in the applied volume of 25 μL) in less than 1 h without pre-enrichment. A linear relationship between bacteria concentration and impedance value was obtained between 10⁴ cfu·mL⁻¹ and 10⁷ cfu·mL⁻¹. Though impedance measurement was carried out in the presence of a redox probe, analysis of the equivalent circuit model showed that the impedance change was primarily due to two elements: Double layer capacitance and resistance due to electrode surface roughness. The magnetic field and impedance were simulated using COMSOL Multiphysics software.

Sensitive detection of Campylobacter jejuni using nanoparticles enhanced QCM sensor

A quartz crystal microbalance (QCM) sensor platform was used to develop an immunosensor for the detection of food pathogen Campylobacter jejuni. Rabbit polyclonal antibodies and commercially available mouse monoclonal antibodies against C. jejuni were investigated to construct direct, sandwich and gold-nanoparticles (AuNPs) amplified sandwich assays. The performance of the QCM immunosensor developed using sandwich assay by utilising the rabbit polyclonal antibody as the capture antibody and conjugated to AuNPs as the detection antibody gave the highest sensitivity. This sensor achieved a limit of detection (LOD) of 150 colony forming unit (CFU)mL(-1) of C. jejuni in solution. The QCM sensor showed excellent sensitivity and specificity for Campylobacter detection with low cross reactivity for other foodborne pathogens such as Salmonella Typhimurium, (7%) Listeria monocytogenes (3%) and Escherichia coli (0%). The development of this biosensor would help in the sensitive detection of Campylobacter which can result in reducing pre-enrichment steps; hence, reducing assay time. This work demonstrates the potential of this technology for the development of a rapid and sensitive detection method for C. jejuni.

Sensitive detection of Escherichia coli O157:H7 using Pt-Au bimetal nanoparticles with peroxidase-like amplification

Escherichia coli O157:H7 is one of the most notorious foodborne pathogens causing serious disease at low infectious dose. To protect consumers from deadly foodborne E. coli O157:H7 infection, it is vital to develop a simple, reliable, sensitive and rapid method which can detect low level E. coli O157:H7 in foods at real-time. We have successfully developed a novel immunochromatographic assay (ICA) with enhanced sensitivity for the visual and quantitative detection of E. coli O157:H7. Sandwich-type immunoreactions were performed on the ICA, and Pt-Au bimetal nanoparticles (NPs) were accumulated on the test zone. The signal amplification is based on Pt-Au bimetal NPs possessing high peroxidase activity toward 3,3',5,5'-tetramethylbenzidine, which can produce characteristic colored bands and thus, enable visual detection of E. coli O157:H7 without instrumentation. The innovative aspect of this approach lies in the visualization and quantification of target pathogen through the detection of color intensity. Due to the excellent peroxidase activity of Pt-Au NPs, they emit strong visible color intensity in less than 1 min for visual observation even in low concentration range of E. coli O157:H7. Quantification was performed using a commercial assay meter. The sensitivity was improved more than 1000-folds compared to the conventional test strip based on colored gold-colloids. Although the feasibility was demonstrated using E. coli O157:H7 as a model analyte, this approach could be easily developed to be a universal signal amplification technique and applied to detection of a wide variety of foodborne pathogens and protein biomarkers.

Quartz-Crystal Microbalance (QCM) for Public Health: An Overview of Its Applications

Nanobiotechnologies, from the convergence of nanotechnology and molecular biology and postgenomics medicine, play a major role in the field of public health. This overview summarizes the potentiality of piezoelectric sensors, and in particular, of quartz-crystal microbalance (QCM), a physical nanogram-sensitive device. QCM enables the rapid, real time, on-site detection of pathogens with an enormous burden in public health, such as influenza and other respiratory viruses, hepatitis B virus (HBV), and drug-resistant bacteria, among others. Further, it allows to detect food allergens, food-borne pathogens, such as Escherichia coli and Salmonella typhimurium, and food chemical contaminants, as well as water-borne microorganisms and environmental contaminants. Moreover, QCM holds promises in early cancer detection and screening of new antiblastic drugs. Applications for monitoring biohazards, for assuring homeland security, and preventing bioterrorism are also discussed.