Phage-based capacitive biosensor for Salmonella detection

An overview of signal amplification strategies and construction methods on phage-based biosensors

Phages are a class of viruses that specifically infect host bacteria. Compared to other recognition elements, phages offer several advantages such as high specificity, easy to obtain and good environmental tolerance, etc. These advantages underscore the potential of phages as recognition elements in the construction of biosensors. Therefore, the phage-based biosensors are currently garnering widespread attention for detecting pathogens in recent years. However, the test performance such as detection limit, sensitivity and stability of exicting phage-based biosensors require enhancement. In the design of sensors, the selection of various materials and construction methods significantly influences the test performance of the sensor, and employing appropriate signal amplification strategies and construction methods to devise biosensors based on different principles is an effective strategy to enhance sensor performance. The manuscript primarily focuses on the signal amplification strategies and construction methods employed in phage-based biosensors recent ten years, and summarizes the advantages and disadvantages of different signal amplification strategies and construction methods. Meanwhile, the manuscript discusses the relationship between sensor performance and various materials and construction methods, and reviews the application progress of phage-based electrochemical biosensors in the detection of foodborne bacteria. Furthermore, the manuscript points out the present limitations and the future research direction for the field of phage-based biosensors, so as to provide the reference for developing high-performance phage-based biosensors.

Revolutionizing food safety with electrochemical biosensors for rapid and portable pathogen detection

Foodborne diseases remain a worldwide concern, despite the advances made in sanitation, pathogen surveillance and food safety management systems. The methods routinely applied for detecting pathogens in foods are time consuming, labor intensive and usually require trained and qualified individuals. The objective of this review was to highlight the use of biosensors, with a focus on the electrochemical devices, as promising alternatives for detecting foodborne pathogens. These biosensors present high speed for obtaining results, with the possibility of evaluating foods in real time, at low cost, ease of use, in addition to being compact and portable. These aspects are considered advantageous and suitable for use in food safety management systems. This work also shows some limitations for the application of biosensors, and we present perspectives with the development and use of nanomaterials.

MoO3/MIL-125-NH2 with boosted peroxidase-like activity for electrochemical staphylococcus aureus sensing via specific recognition of bacteriophages

Herein, novel nanozyme mimics MoO3/MIL-125-NH2 were reported and conjugated with bacteriophages as a new electrochemical probe for high sensitivity and specific electrochemical detection of staphylococcus aureus. The excellent peroxidase-like activity of MoO3/MIL-125-NH2 composites was attributed to the integration of MIL-125-NH2 with MoO3, which can boost the generation of superoxide radicals (O• 2-) and thus promote the oxidation of TMB in the presence of H2O2. In this work, two bacteriophages named SapYZU04 and SapYZU10 were isolated from sewage samples by using staphylococcus aureus YZUsa12 as the host. In comparison, MoO3/MIL-125-NH2@SapYZU04 was selected as a recognition agent. The DPV current declined linearly with staphylococcus aureus YZUsa12 concentration in the range of 101-108 CFU mL-1, with a low detection limit of 16 CFU mL-1 (S/N = 3). 20 strains including 13 host strains and 7 non-host strains were used to evaluate the selectivity of the proposed sensor. Regardless of the differences in the degrees of lytic performance for phage SapYZU04, all selected host strains can be screened with merely the same DPV current. Host spectrum-oriented bacteriophage sensing is of great importance for the practical application of bacteriophage-based biosensors in the future.

Double phage displayed peptides co-targeting-based biosensor with signal enhancement activity for colorimetric detection of Staphylococcus aureus

The development of simple, fast, sensitive, and specific strategies for the detection of foodborne pathogenic bacteria is crucial for ensuring food safety and promoting human health. Currently, detection methods for Staphylococcus aureus still suffer from issues such as low specificity and low sensitivity. To address this problem, we proposed a sensitivity enhancement strategy based on double phage-displayed peptides (PDPs) co-targeting. Firstly, we screened two PDPs and analyzed their binding mechanisms through fluorescent localization, pull-down assay, and molecular docking. The two PDPs target S. aureus by binding to specific proteins on its outer membrane. Based on this phenomenon, a convenient and sensitive double PDPs colorimetric biosensor was developed. Double thiol-modified phage-displayed peptides (PDP-SH) enhance the aggregation of gold nanoparticles (AuNPs), whereas the specific interaction between the double PDPs and bacteria inhibits the aggregation of AuNPs, resulting in an increased visible color change before and after the addition of bacteria. This one-step colorimetric approach displayed a high sensitivity of 2.35 CFU/mL and a wide detection range from 10-2 × 108 CFU/mL. The combination with smartphone-based image analysis improved the portability of this method. This strategy achieves the straightforward, highly sensitive and portable detection of pathogenic bacteria.

Electrochemical biosensors for pathogenic microorganisms detection based on recognition elements

The worldwide spread of pathogenic microorganisms poses a significant risk to human health. Electrochemical biosensors have emerged as dependable analytical tools for the point-of-care detection of pathogens and can effectively compensate for the limitations of conventional techniques. Real-time analysis, high throughput, portability, and rapidity make them pioneering tools for on-site detection of pathogens. Herein, this work comprehensively reviews the recent advances in electrochemical biosensors for pathogen detection, focusing on those based on the classification of recognition elements, and summarizes their principles, current challenges, and prospects. This review was conducted by a systematic search of PubMed and Web of Science databases to obtain relevant literature and construct a basic framework. A total of 171 publications were included after online screening and data extraction to obtain information of the research advances in electrochemical biosensors for pathogen detection. According to the findings, the research of electrochemical biosensors in pathogen detection has been increasing yearly in the past 3 years, which has a broad development prospect, but most of the biosensors have performance or economic limitations and are still in the primary stage. Therefore, significant research and funding are required to fuel the rapid development of electrochemical biosensors. The overview comprehensively evaluates the recent advances in different types of electrochemical biosensors utilized in pathogen detection, with a view to providing insights into future research directions in biosensors.

Capacitive biosensors for label-free and ultrasensitive detection of biomarkers

Capacitive biosensors are label-free capacitors that can detect biomarkers with the outstanding advantages of simplicity, low cost, and ultrahigh sensitivity. A typical capacitive biosensor consists of a bioreceptor and a transducer, where the bioreceptor captures the biomarker to form a bioreceptor/biomarker conjugate and the transducer generates a detectable signal. In general, antibodies, aptamers, or proteins are exploited as the bioreceptor, while various electrodes including carbon electrodes (CEs), gold electrodes (AuEs), or interdigitated electrodes (IDEs) may serve as the transducer. Because the formation of bioreceptor/biomarker conjugates often leads to a change in capacitance, the capacitive signal is then employed for biomarker detection. This review summarizes recent advances in capacitive biosensors for the detection of biomarkers over the last five years. With a focus on the three common types of bioreceptors, i.e., antibodies, aptamers, and proteins, capacitive biosensors using CEs, AuEs, and IDEs as the transducers are discussed in detail. The immobilization of bioreceptors and signal amplification strategies are described to provide a robust overview of capacitive biosensors for biomarker detection. In addition, analytical methods and future prospects are given to support the application of capacitive biosensors.

A Critical Review on Detection of Foodborne Pathogens Using Electrochemical Biosensors

An outbreak of foodborne pathogens would cause severe consequences. Detecting and diagnosing foodborne diseases is crucial for food safety, and it is increasingly important to develop fast, sensitive, and cost-effective methods for detecting foodborne pathogens. In contrast to traditional methods, such as medium-based culture, nucleic acid amplification test, and enzyme-linked immunosorbent assay, electrochemical biosensors possess the advantages of simplicity, rapidity, high sensitivity, miniaturization, and low cost, making them ideal for developing pathogen-sensing devices. The biorecognition layer, consisting of recognition elements, such as aptamers, antibodies and bacteriophages, and other biomolecules or polymers, is the most critical component to determine the selectivity, specificity, reproducibility, and lifetime of a biosensor when detecting pathogens in a biosample. Furthermore, nanomaterials have been frequently used to improve electrochemical biosensors for sensitively detecting foodborne pathogens due to their high conductivity, surface-to-volume ratio, and electrocatalytic activity. In this review, we survey the characteristics of biorecognition elements and nanomaterials in constructing electrochemical biosensors applicable for detecting foodborne pathogens during the past five years. As well as the challenges and opportunities of electrochemical biosensors in the application of foodborne pathogen detection are discussed.

Bacteriophage-based biosensors for detection of pathogenic microbes in wastewater

Wastewater is discarded from several sources, including industry, livestock, fertilizer application, and municipal waste. If the disposed of wastewater has not been treated and processed before discharge to the environment, pathogenic microorganisms and toxic chemicals are accumulated in the disposal area and transported into the surface waters. The presence of harmful microbes is responsible for thousands of human deaths related to water-born contamination every year. To be able to take the necessary step and quick action against the possible presence of harmful microorganisms and substances, there is a need to improve the effective speed of identification and treatment of these problems. Biosensors are such devices that can give quantitative information within a short period of time. There have been several biosensors developed to measure certain parameters and microorganisms. The discovered biosensors can be utilized for the detection of axenic and mixed microbial strains from the wastewaters. Biosensors can further be developed for specific conditions and environments with an in-depth understanding of microbial organization and interaction within that community. In this regard, bacteriophage-based biosensors have become a possibility to identify specific live bacteria in an infected environment. This paper has investigated the current scenario of microbial community analysis and biosensor development in identifying the presence of pathogenic microorganisms.

Applications of the phage display technology in molecular biology, biotechnology and medicine

The phage display technology is based on the presentation of peptide sequences on the surface of virions of bacteriophages. Its development led to creation of sophisticated systems based on the possibility of the presentation of a huge variability of peptides, attached to one of proteins of bacteriophage capsids. The use of such systems allowed for achieving enormous advantages in the processes of selection of bioactive molecules. In fact, the phage display technology has been employed in numerous fields of biotechnology, as diverse as immunological and biomedical applications (in both diagnostics and therapy), the formation of novel materials, and many others. In this paper, contrary to many other review articles which were focussed on either specific display systems or the use of phage display in selected fields, we present a comprehensive overview of various possibilities of applications of this technology. We discuss an usefulness of the phage display technology in various fields of science, medicine and the broad sense of biotechnology. This overview indicates the spread and importance of applications of microbial systems (exemplified by the phage display technology), pointing to the possibility of developing such sophisticated tools when advanced molecular methods are used in microbiological studies, accompanied with understanding of details of structures and functions of microbial entities (bacteriophages in this case).

Synthetic biology-inspired cell engineering in diagnosis, treatment, and drug development

The fast-developing synthetic biology (SB) has provided many genetic tools to reprogram and engineer cells for improved performance, novel functions, and diverse applications. Such cell engineering resources can play a critical role in the research and development of novel therapeutics. However, there are certain limitations and challenges in applying genetically engineered cells in clinical practice. This literature review updates the recent advances in biomedical applications, including diagnosis, treatment, and drug development, of SB-inspired cell engineering. It describes technologies and relevant examples in a clinical and experimental setup that may significantly impact the biomedicine field. At last, this review concludes the results with future directions to optimize the performances of synthetic gene circuits to regulate the therapeutic activities of cell-based tools in specific diseases.

A caprylate esterase-activated fluorescent probe for sensitive and selective detection of Salmonella enteritidis

Salmonella enteritidis is one of the most common foodborne pathogens. Many methods have been developed to detect Salmonella, but most of them are expensive, time-consuming, and complex in experimental procedures. Developing a rapid, specific, cost-effective, and sensitive detection method is still demanded. In this work, a practical detection method is presented using salicylaldazine caprylate as the fluorescent probe, which could be hydrolyzed by caprylate esterase liberated from Salmonella lysed by phage, to form strong fluorescent salicylaldazine. The Salmonella could be detected accurately with a low limit of detection of 6 CFU/mL and a broad concentration range of 10-10⁶ CFU/mL. Moreover, this method was successfully used for the rapid detection of Salmonella in milk within 2 h through pre-enrichment by ampicillin-conjugated magnetic beads. The novel combination of fluorescent turn-on probe salicylaldazine caprylate and phage ensures this method has excellent sensitivity and selectivity.

Colorimetric platform based on synergistic effect between bacteriophage and AuPt nanozyme for determination of Yersinia pseudotuberculosis

The development of a novel colorimetric method is reported, using vB_YepM_ZN18 phages along with AuPt nanozyme for the sensitive detection of Y. pseudotuberculosis. The phage used in this work has been extracted from hospital sewer water and is highly specific toward Y. pseudotuberculosis. The synthesized AuPt NPs possess peroxidase-like activity, which is suitable in the development of nanozyme based detection system. Furthermore, phages@MB and AuPt@phages are added into the bacterial samples for co-incubation, forming an intercalated complex. The magnetic separation and absorbance analysis of enzymatic reaction are carried out for the detection of targeted bacteria. The proposed method has a limit of detection of 14 CFU/mL, a wide linear range from 2.50 × 10¹ ~ 2.50 × 10⁷ CFU/mL and the assay completion time is 40 min. Benefitting from the outperformance of this sensor, we have successfully employed the developed sensing platform for the detection of Y. pseudotuberculosis in food industry and hospital specimens.

Biophysical Properties of Bifunctional Phage-Biosensor

Biosensor research is a swiftly growing field for developing rapid and precise analytical devices for biomedical, pharmaceutical, and industrial use and beyond. Herein, we propose a phage-based biosensor method to develop a sensitive and specific system for biomedical detection. Our method is based on in vitro selected phages and their interaction with the targeted analytes as well as on optical properties that change according to the concentration of the model analyte. The green fluorescent protein (GFP) was chosen as our model analyte as it has its own well-known optical properties. Brilliant green was used as a reporter component for the sensor. Its presence enables a color intensity (absorbance) change when the analyte is present in the solution. Furthermore, the reporter dye functioned as a quencher for an additional lanthanide label in our assay. It mediated the specific phage-derived interference in the signal measured with the time-resolved luminescence. Most importantly, our results confirmed that the presented bifunctional phage with its liquid crystal properties enabled the measurement of GFP in a concentration-dependent, quantitative manner with a limit of detection of 0.24 µg/mL. In the future, our novel method to develop phage-based biosensors may provide highly sensitive and specific biosensors for biomedical or otherwise-relevant targets.

Design and Preparation of Sensing Surfaces for Capacitive Biodetection

Despite their high sensitivity and their suitability for miniaturization, biosensors are still limited for clinical applications due to the lack of reproducibility and specificity of their detection performance. The design and preparation of sensing surfaces are suspected to be a cause of these limitations. Here, we first present an updated overview of the current state of use of capacitive biosensors in a medical context. Then, we summarize the encountered strategies for the fabrication of capacitive biosensing surfaces. Finally, we describe the characteristics which govern the performance of the sensing surfaces, along with recent developments that were suggested to overcome their main current limitations.

Detection of Salmonella Typhimurium with Gold Nanoparticles Using Quartz Crystal Microbalance Biosensor

Demonstration of the Salmonella Typhimurium detection system was shown utilizing a quartz crystal microbalance (QCM) biosensor and signal enhancement by gold nanoparticles. In this study, a benchtop system of a QCM biosensor was utilized for the detection of Salmonella Typhimurium. It was designed with a peristaltic pump system to achieve immobilization of antibodies, detection of Salmonella, and the addition of gold nanoparticles to the sensor. As a series of biochemical solutions were introduced to the surface, the proposed system was able to track the changes in the resonant frequency which were proportional to the variations of mass on the sensor. For antibody immobilization, polyclonal antibodies were immobilized via self-assembled monolayers to detect Salmonella O-antigen. Subsequently, Salmonella Typhimurium was detected by antibodies and the average frequency before and after detecting Salmonella was compared. The highest frequency shifts were −26.91 Hz for 109 CFU/mL while the smallest frequency shift was −3.65 Hz corresponding to 103 CFU/mL. For the specificity tests, non-Salmonella samples such as E. coli, Listeria, and Staphylococcus resulted in low cross-reactivity. For signal amplification, biotinylated antibodies reacted to Salmonella followed by streptavidin—100 nm AuNPs through biotin-avidin interaction. The frequency shifts of 103 CFU/mL showed −28.04 Hz, and consequently improved the limit of detection.

A rapid colorimetric lateral flow test strip for detection of live Salmonella Enteritidis using whole phage as a specific binder

Specific antibodies are essential components of immunoassay, which can be applied for the detection of pathogens. However, producing an antibody specific to live bacterial pathogens by the classical method of immunizing animals with live pathogens can be impractical. Phage display technology is an effective alternative method to obtain antibodies with the desired specificity against selected antigenic molecules. In this study, we demonstrated the power of a microarray-based technique for obtaining specific phage-derived antibody fragments against Salmonella, an important foodborne pathogen. The selected phage-displayed antibody fragments were subsequently employed to develop a lateral flow test strip assay for the detection of live Salmonella. The test strips showed specificity to Salmonella Enteritidis without cross-reactivity to eight serovars of Salmonella or other bacteria strains. The test strip assay requires 15 min, whereas the conventional biochemical and serological confirmation test requires at least 24 h. The microarray screening technique for specific phage-based binders and the test strip method can be further applied to other foodborne pathogens.

Properties of a Novel Salmonella Phage L66 and Its Application Based on Electrochemical Sensor-Combined AuNPs to Detect Salmonella

Salmonella is widespread in nature and poses a significant threat to human health and safety. Phage is considered as a new tool for the control of food-borne pathogens. In this study, Salmonella phage L66 (phage L66) was isolated from sewage by using Salmonella Typhimurium ATCC 14028 as the host bacterium, and its basic properties were obtained by biological and bioinformatics analysis. Phage L66 had a broad host spectrum, with an optimal infection complex of 0.1 and an optimal adsorption rate of 90.06%. It also exhibited thermal stability between 30 °C~60 °C and pH stability pH from 3 to 12, and the average lysis amount was 46 PFU/cell. The genome sequence analysis showed that the genome length of phage L66 was 157,675 bp and the average GC content was 46.13%. It was predicted to contain 209 genes, 97 of which were annotated with known functions based on the evolutionary analysis, and phage L66 was attributed to the Kuttervirus genus. Subsequently, an electrochemical sensor using phage L66 as a recognition factor was developed and the working electrode GDE-AuNPs-MPA-Phage L66 was prepared by layer-by-layer assembly for the detection of Salmonella. The slope of the impedance was 0.9985 within the scope from 20 to 2 × 10⁷ CFU/mL of bacterial concentration. The minimum detection limit of the method was 13 CFU/mL, and the average spiked recovery rate was 102.3% with a relative standard deviation of 5.16%. The specificity and stability of this sensor were excellent, and it can be applied for the rapid detection of Salmonella in various foods. It provides a phage-based electrochemical biosensor for the detection of pathogenic bacteria.

A microfluidic device and instrument prototypes for the detection of Escherichia coli in water samples using a phage-based bioluminescence assay

Current quantification methods of Escherichia coli (E. coli) contamination in water samples involve long incubation, laboratory equipment and facilities, or complex processes that require specialized training for accurate operation and interpretation. To address these limitations, we have developed a microfluidic device and portable instrument prototypes capable of performing a rapid and highly sensitive bacteriophage-based assay to detect E. coli cells with detection limit comparable to traditional methods in a fraction of the time. The microfluidic device combines membrane filtration and selective enrichment using T7-NanoLuc-CBM, a genetically engineered bacteriophage, to identify 4.1 E. coli CFU in 100 mL of drinking water within 5.5 hours. The microfluidic device was designed and tested to process up to 100 mL of real-world drinking water samples with turbidities below 10 NTU. Prototypes of custom instrumentation, compatible with our valveless microfluidic device and capable of performing all of the assay's units of operation with minimal user intervention, demonstrated similar assay performance to that obtained on the benchtop assay. This research is the first step towards a faster, portable, and semi-automated, phage-based microfluidic platform for improved in-field water quality monitoring in low-resource settings.

AuAg nanocages/graphdiyne for rapid elimination and detection of trace pathogenic bacteria

We prepared a biocompatible AuAg nanocages/graphdiyne @ polyethylene glycol (AuAg/GDY@PEG) composite. The combination of AuAg and GDY to obtain a synergistically enhanced photothermal effect, and the antibacterial effect of GDY and AuAg are used in combined anti-infective therapy. The in vitro antibacterial activity of AuAg/GDY@PEG was investigated, showing an impressive broad-spectrum antibacterial activity with the killing rate > 99.999%. Based on the photothermal conversion ability of AuAg/GDY@PEG, a simple photothermal immunoassay for pathogenic bacteria was successfully established. Sandwich immune response was performed on a microporous plate, the microplate containing the antibody binds specifically to the bacterium being tested, which then binds to the material with the antibody on its surface, and the signal was a change in temperature under 808 nm near-infrared light. The limit of detection (LOD) for S. typhimurium detection is 10³ CFU mL^-1, with a range of 10³-10⁷ CFU mL^-1. This method is accurate, rapid and low-cost, which can be used for on-site detection of pathogenic bacteria in food.

New analytical methods using carbon-based nanomaterials for detection of Salmonella species as a major food poisoning organism in water and soil resources

Salmonella is one of the most prevalent causing agents of food- and water-borne illnesses, posing an ongoing public health threat. These food-poisoning bacteria contaminate the resources at different stages such as production, aggregation, processing, distribution, as well as marketing. According to the high incidence of salmonellosis, effective strategies for early-stage detection are required at the highest priority. Since traditional culture-dependent methods and polymerase chain reaction are labor-intensive and time-taking, identification of early and accurate detection of Salmonella in food and water samples can prevent significant health economic burden and lessen the costs. The immense potentiality of biosensors in diagnosis, such as simplicity in operation, the ability of multiplex analysis, high sensitivity, and specificity, have driven research in the evolution of nanotechnology, innovating newer biosensors. Carbon nanomaterials enhance the detection sensitivity of biosensors while obtaining low levels of detection limits due to their possibility to immobilize huge amounts of bioreceptor units at insignificant volume. Moreover, conjugation and functionalization of carbon nanomaterials with metallic nanoparticles or organic molecules enables surface functional groups. According to these remarkable properties, carbon nanomaterials are widely exploited in the development of novel biosensors. To be specific, carbon nanomaterials such as carbon nanotubes, graphene and fullerenes function as transducers in the analyte recognition process or surface immobilizers for biomolecules. Herein the potential application of carbon nanomaterials in the development of novel Salmonella biosensors platforms is reviewed comprehensively. In addition, the current problems and critical analyses of the future perspectives of Salmonella biosensors are discussed.

A Sensitive Capacitive Biosensor for Protein a Detection Using Human IgG Immobilized on an Electrode Using Layer-by-Layer Applied Gold Nanoparticles

A capacitive biosensor for the detection of protein A was developed. Gold electrodes were fabricated by thermal evaporation and patterned by photoresist photolithography. A layer-by-layer (LbL) assembly of thiourea (TU) and HAuCl4 and chemical reduction was utilized to prepare a probe with a different number of layers of TU and gold nanoparticles (AuNPs). The LbL-modified electrodes were used for the immobilization of human IgG. The binding interaction between human IgG and protein A was detected as a decrease in capacitance signal, and that change was used to investigate the correlation between the height of the LbL probe and the sensitivity of the capacitive measurement. The results showed that the initial increase in length of the LbL probe can enhance the amount of immobilized human IgG, leading to a more sensitive assay. However, with thicker LbL layers, a reduction of the sensitivity of the measurement was registered. The performance of the developed system under optimum set-up showed a linearity in response from 1 × 10-16 to 1 × 10-13 M, with the limit detection of 9.1 × 10-17 M, which could be interesting for the detection of trace amounts of protein A from affinity isolation of therapeutic monoclonal antibodies.

Rapid and sensitive detection of Salmonella in milk based on hybridization chain reaction and graphene oxide fluorescence platform

Salmonella is a foodborne pathogen that has contributed to numerous food safety accidents worldwide, making it necessary to detect contamination at an early stage. A pair of specific primers based on the invA gene of Salmonella was designed for PCR. Target double-stranded DNA (dsDNA) from PCR was purified and denatured at high temperature to obtain target single-stranded DNA (ssDNA). Two carboxyfluorescein-labeled hairpin probes (H1-FAM and H2-FAM) were designed with complementary portions to the ssDNA sequence so that binding could trigger H1-FAM and H2-FAM hybridization chain reaction (HCR) to produce a long dsDNA complex. In this study, graphene oxide (GO) was used in the development of a homogeneous fluorescence detection platform for Salmonella. Using this HCR-GO assay platform, Salmonella detection was completed in 3.5 h. Salmonella was reliably and specifically detected with a limit of detection (LOD) of 4.2 × 10¹ cfu/mL in pure culture. Moreover, this new HCR-GO assay platform was successfully applied to the detection of Salmonella in artificially contaminated milk with a LOD of 4.2 × 10² cfu/mL.

Substrate Materials for Biomolecular Immobilization within Electrochemical Biosensors

Electrochemical biosensors have potential applications for agriculture, food safety, environmental monitoring, sports medicine, biomedicine, and other fields. One of the primary challenges in this field is the immobilization of biomolecular probes atop a solid substrate material with adequate stability, storage lifetime, and reproducibility. This review summarizes the current state of the art for covalent bonding of biomolecules onto solid substrate materials. Early research focused on the use of Au electrodes, with immobilization of biomolecules through ω-functionalized Au-thiol self-assembled monolayers (SAMs), but stability is usually inadequate due to the weak Au-S bond strength. Other noble substrates such as C, Pt, and Si have also been studied. While their nobility has the advantage of ensuring biocompatibility, it also has the disadvantage of making them relatively unreactive towards covalent bond formation. With the exception of Sn-doped In2O3 (indium tin oxide, ITO), most metal oxides are not electrically conductive enough for use within electrochemical biosensors. Recent research has focused on transition metal dichalcogenides (TMDs) such as MoS2 and on electrically conductive polymers such as polyaniline, polypyrrole, and polythiophene. In addition, the deposition of functionalized thin films from aryldiazonium cations has attracted significant attention as a substrate-independent method for biofunctionalization.

Strategies for Surface Immobilization of Whole Bacteriophages: A Review

Bacteriophage immobilization is a key unit operation in emerging biotechnologies, enabling new possibilities for biodetection of pathogenic microbes at low concentration, production of materials with novel antimicrobial properties, and fundamental research on bacteriophages themselves. Wild type bacteriophages exhibit extreme binding specificity for a single species, and often for a particular subspecies, of bacteria. Since their specificity originates in epitope recognition by capsid proteins, which can be altered by chemical or genetic modification, their binding specificity may also be redirected toward arbitrary substrates and/or a variety of analytes in addition to bacteria. The immobilization of bacteriophages on planar and particulate substrates is thus an area of active and increasing scientific interest. This review assembles the knowledge gained so far in the immobilization of whole phage particles, summarizing the main chemistries, and presenting the current state-of-the-art both for an audience well-versed in bioconjugation methods as well as for those who are new to the field.

Formulations for Bacteriophage Therapy and the Potential Uses of Immobilization

The emergence of antibiotic-resistant pathogens is becoming increasingly problematic in the treatment of bacterial diseases. This has led to bacteriophages receiving increased attention as an alternative form of treatment. Phages are effective at targeting and killing bacterial strains of interest and have yielded encouraging results when administered as part of a tailored treatment to severely ill patients as a last resort. Despite this, success in clinical trials has not always been as forthcoming, with several high-profile trials failing to demonstrate the efficacy of phage preparations in curing diseases of interest. Whilst this may be in part due to reasons surrounding poor phage selection and a lack of understanding of the underlying disease, there is growing consensus that future success in clinical trials will depend on effective delivery of phage therapeutics to the area of infection. This can be achieved using bacteriophage formulations instead of purely liquid preparations. Several encapsulation-based strategies can be applied to produce phage formulations and encouraging results have been observed with respect to efficacy as well as long term phage stability. Immobilization-based approaches have generally been neglected for the production of phage therapeutics but could also offer a viable alternative.

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.

Electrochemical Immuno- and Aptamer-Based Assays for Bacteria: Pros and Cons over Traditional Detection Schemes

Microbiological safety of the human environment and health needs advanced monitoring tools both for the specific detection of bacteria in complex biological matrices, often in the presence of excessive amounts of other bacterial species, and for bacteria quantification at a single cell level. Here, we discuss the existing electrochemical approaches for bacterial analysis that are based on the biospecific recognition of whole bacterial cells. Perspectives of such assays applications as emergency-use biosensors for quick analysis of trace levels of bacteria by minimally trained personnel are argued.

Recent Progress in the Detection of Bacteria Using Bacteriophages: A Review

Bacteria will likely become our most significant enemies of the 21st century, as we are approaching a post-antibiotic era. Bacteriophages, viruses that infect bacteria, allow us to fight infections caused by drug-resistant bacteria and create specific, cheap, and stable sensors for bacteria detection. Here, we summarize the recent developments in the field of phage-based methods for bacteria detection. We focus on works published after mid-2017. We underline the need for further advancements, especially related to lowering the detection (below 1 CFU/mL; CFU stands for colony forming units) and shortening the time of analysis (below one hour). From the application point of view, portable, cheap, and fast devices are needed, even at the expense of sensitivity.

Laser-Induced Graphene Electrochemical Immunosensors for Rapid and Label-Free Monitoring of Salmonella enterica in Chicken Broth

Food-borne illnesses are a growing concern for the food industry and consumers, with millions of cases reported every year. Consequently, there is a critical need to develop rapid, sensitive, and inexpensive techniques for pathogen detection in order to mitigate this problem. However, current pathogen detection strategies mainly include time-consuming laboratory methods and highly trained personnel. Electrochemical in-field biosensors offer a rapid, low-cost alternative to laboratory techniques, but the electrodes used in these biosensors require expensive nanomaterials to increase their sensitivity, such as noble metals (e.g., platinum, gold) or carbon nanomaterials (e.g., carbon nanotubes, or graphene). Herein, we report the fabrication of a highly sensitive and label-free laser-induced graphene (LIG) electrode that is subsequently functionalized with antibodies to electrochemically quantify the food-borne pathogen Salmonella enterica serovar Typhimurium. The LIG electrodes were produced by laser induction on the polyimide film in ambient conditions and, hence, circumvent the need for high-temperature, vacuum environment, and metal seed catalysts commonly associated with graphene-based electrodes fabricated via chemical vapor deposition processes. After functionalization with Salmonella antibodies, the LIG biosensors were able to detect live Salmonella in chicken broth across a wide linear range (25 to 10⁵ CFU mL^-1) and with a low detection limit (13 ± 7 CFU mL^-1; n = 3, mean ± standard deviation). These results were acquired with an average response time of 22 min without the need for sample preconcentration or redox labeling techniques. Moreover, these LIG immunosensors displayed high selectivity as demonstrated by nonsignificant response to other bacteria strains. These results demonstrate how LIG-based electrodes can be used for electrochemical immunosensing in general and, more specifically, could be used as a viable option for rapid and low-cost pathogen detection in food processing facilities before contaminated foods reach the consumer.

Efficient affinity-tagging of M13 phage capsid protein IX for immobilization of protein III-displayed oligopeptide probes on abiotic platforms

We developed a genetic approach to efficiently add an affinity tag to every copy of protein IX (pIX) of M13 filamentous bacteriophage in a population. Affinity-tagged phages can be immobilized on a surface in a uniform monolayer in order to position the pIII-displayed peptides or proteins for optimal interaction with ligands. The tagging consists of two major steps. First, gene IX (gIX) of M13 phage is mutated in Escherichia coli via genetic recombineering with the gIX::aacCI insertion allele. Second, a plasmid that co-produces the affinity-tagged pIX and native pVIII is transformed into the strain carrying the defective M13 gIX. This genetic complementation allows the formation of infective phage particles that carry a full complement (five copies per virion) of the affinity-tagged pIX. To demonstrate the efficacy of our method, we tagged a M13 derivative phage, M13KE, with Strep-tag II. In order to tag pIX with Strep-tag II, the phage genes for pIX and pVIII were cloned and expressed from pASG-IBA4 which contains the E. coli OmpA signal sequence and Strep-Tag II under control of the tetracycline promoter/operator system. We achieved the maximum phage production of 3 × 10¹¹ pfu/ml when Strep-Tag II-pIX-pVIII fusion was induced with 10 ng/ml of anhydrotetracycline. The complete process of affinity tagging a phage probe takes less than 5 days and can be utilized to tag any M13 or fd pIII-displayed oligopeptide probes to improve their performance.

Phage-based Electrochemical Sensors: A Review

Phages based electrochemical sensors have received much attention due to their high specificity, sensitivity and simplicity. Phages or bacteriophages provide natural affinity to their host bacteria cells and can serve as the recognition element for electrochemical sensors. It can also act as a tool for bacteria infection and lysis followed by detection of the released cell contents, such as enzymes and ions. In addition, possible detection of the other desired targets, such as antibodies have been demonstrated with phage display techniques. In this paper, the recent development of phage-based electrochemical sensors has been reviewed in terms of the different immobilization protocols and electrochemical detection techniques.

Research Progress of M13 Bacteriophage-Based Biosensors

Recently, new virus-based sensor systems that operate on M13 bacteriophage infrastructure have attracted considerable attention. These systems can detect a range of chemicals with excellent sensitivity and selectivity. Filaments consistent with M13 bacteriophages can be ordered by highly established forms of self-assembly. This allows M13 bacteriophages to build a homogeneous distribution and infiltrate the network structure of nanostructures under mild conditions. Phage display, involving the genetic engineering of M13 bacteriophages, is another strong feature of the M13 bacteriophage as a functional building block. The numerous genetic modification possibilities of M13 bacteriophages are clearly the key features, and far more applications are envisaged. This paper reviews the recent progress in the application of the M13 bacteriophage self-assembly structures through to sensor systems and discusses future M13 bacteriophage technology.

Understanding and Exploiting Phage-Host Interactions

Initially described a century ago by William Twort and Felix d’Herelle, bacteriophages are bacterial viruses found ubiquitously in nature, located wherever their host cells are present. Translated literally, bacteriophage (phage) means ‘bacteria eater’. Phages interact and infect specific bacteria while not affecting other bacteria or cell lines of other organisms. Due to the specificity of these phage–host interactions, the relationship between phages and their host cells has been the topic of much research. The advances in phage biology research have led to the exploitation of these phage–host interactions and the application of phages in the agricultural and food industry. Phages may provide an alternative to the use of antibiotics, as it is well known that the emergence of antibiotic-resistant bacterial infections has become an epidemic in clinical settings. In agriculture, pre-harvest and/or post-harvest application of phages to crops may prevent the colonisation of bacteria that are detrimental to plant or human health. In addition, the abundance of data generated from genome sequencing has allowed the development of phage-derived bacterial detection systems of foodborne pathogens. This review aims to outline the specific interactions between phages and their host and how these interactions may be exploited and applied in the food industry.

Fluorescence immunoassay through histone-ds-poly(AT)-templated copper nanoparticles as signal transductors for the sensitive detection of Salmonella choleraesuis in milk

The rapid and sensitive detection of foodborne pathogens is one of the most important issues in food safety control. In this work, we developed a novel fluorescence immunoassay method for the sensitive detection of Salmonella choleraesuis. The method uses the fluorescent signals of histone-ds-poly(AT)-templated copper nanoparticles (His-pAT CuNP) as signal transducers and glucose oxidase as an alternative for horseradish peroxidase for the generation of hydrogen peroxide (H₂O₂) through the catalysis of glucose. The H₂O₂ is then further converted into hydroxyl radical (·OH) by Fenton reagents. Owing to the ultrahigh sensitivity of His-pAT CuNP synthesis toward ·OH, the proposed fluorescence immunoassay method exhibited excellent sensitivity for S. choleraesuis, with a limit of detection of 8.04 × 10¹ cfu/mL, which is 3 orders of magnitude lower than that of the tetramethylbenzidine-based traditional immunoassay. The reliability of the proposed method was evaluated by using spiked milk samples with S. choleraesuis concentration ranging from 8.8 × 10¹ to 8.8 × 10⁴ cfu/mL. The average recoveries for the intra- and inter-assay ranged from 73.52 to 96.59% and from 66.99 to 98.24% with a coefficient of variation from 6.85 to 31.26% and 5.46 to 17.99%, respectively. These results indicated that the proposed fluorescence immunoassay possesses a great potential for ultra-sensitive detection of foodborne pathogens in food safety control.