Electrochemiluminescence Detection of Escherichia coli O157:H7 Based on a Novel Polydopamine Surface Imprinted Polymer Biosensor

Molecular imprinting technology for sensing foodborne pathogenic bacteria

Foodborne diseases caused by bacterial pathogens pose a widespread and growing threat to public health in the world. Rapid detection of pathogenic bacteria is of great importance to prevent foodborne diseases and ensure food safety. However, traditional detection methods are time-consuming, labour intensive and expensive. In recent years, many attempts have been made to develop alternative methods for bacterial detection. Biosensors integrated with molecular imprinted polymers (MIPs) and various transducer platforms are among the most promising candidates for the detection of pathogenic bacteria in a highly sensitive, selective and ultra-rapid manner. In this review, we summarize the most recent advances in molecular imprinting for bacterial detection, introduce the underlying recognition mechanisms and highlight the applications of MIP-based biosensors. In addition, the challenges and future perspectives are discussed with the aim of accelerating the development of MIP-based biosensors and extending their applications.

Rapid, sensitive and label-free detection of pathogenic bacteria using a bacteria-imprinted conducting polymer film-based electrochemical sensor

The rapid and sensitive detection of pathogenic bacteria is very important for timely prevention and treatment of foodborne disease. Here, a bacteria-imprinted conductive poly(3-thiopheneacetic acid) (BICP) film-based impedimetric sensor was developed for the rapid, sensitive and label-free detection of staphylococcus aureus (S. aureus). The BICP film preparation was very convenient and eco-friendly, which was in situ deposited on gold electrode surface without the use of toxic organic solvents and cross-linkers. The process of imprinting and recognition were characterized by electrochemical technique and scanning electron microscope. The BICP had a novel structure without cocci-shaped cavities formed in the poly(3-thiopheneacetic acid) (PTAA) matrices. To obtain the optimal sensing performance, a set of factors affecting the imprinting and recognition were investigated. Under the optimized conditions, an extremely rapid recognition within 10 min, a very low limit of detection (LOD) of 2 CFU/mL, and wide linear range from 10 to 10⁸ CFU/mL were achieved by the BICP film-based impedimetric sensor. The sensor also demonstrated high selectivity, and good universality and repeatability. Furthermore, the feasibility of its application has also been demonstrated in the analysis of real milk samples. This sensor offered a simple and universal method for rapid, sensitive, and selective detection of pathogenic bacteria, which could hold great potentials in fields like food safety.

Competitive Lateral Flow Immunoassay Relying on Au-SiO2 Janus Nanoparticles with an Asymmetric Structure and Function for Furazolidone Residue Monitoring

Gold nanoparticles (AuNPs) are the most commonly used signal materials in lateral flow immunoassay (LFIA). However, the assay sensitivity of traditional AuNP-based LFIA is usually limited by the incomplete competition between free target analytes and immobilized antigens for the binding of AuNP-labeled antibodies. To unfreeze this limitation, here, asymmetric Au-SiO₂ Janus NPs (about 66 nm) were designed and synthesized. Au-SiO₂ Janus NPs can assemble into snowman-like anisotropic structures and combine two different physicochemical properties at their opposite sides, where the AuNP side mainly possesses the antibody conjugating and signal providing functions and the SiO₂ side primarily offers the stable function. In virtue of the unique asymmetric nanostructure, only the AuNP side can interact with target analytes by specific antigen-antibody interactions, which could significantly improve the efficiency of competition. Selecting furazolidone as a model analyte, the immunoassay biosensor showed a limit of detection as low as 0.08 ng/mL, 10-fold decreased than that of the AuNPs-LFIA. Moreover, the Au-SiO₂ Janus NP lateral flow immunoassay was well applied in chicken, pork, honey, and beef food samples with visual detection limits of 0.8 ng/g, 0.16 ng/g, 0.4 ng/mL, and 0.16 ng/g, respectively. The Au-SiO₂ Janus NPs possess the advantages of both materials, which will broaden their applications as a potential alternative in the rapid and sensitive detection of antibiotic residues.

Conducting Polymers in the Design of Biosensors and Biofuel Cells

Fast and sensitive determination of biologically active compounds is very important in biomedical diagnostics, the food and beverage industry, and environmental analysis. In this review, the most promising directions in analytical application of conducting polymers (CPs) are outlined. Up to now polyaniline, polypyrrole, polythiophene, and poly(3,4-ethylenedioxythiophene) are the most frequently used CPs in the design of sensors and biosensors; therefore, in this review, main attention is paid to these conducting polymers. The most popular polymerization methods applied for the formation of conducting polymer layers are discussed. The applicability of polypyrrole-based functional layers in the design of electrochemical biosensors and biofuel cells is highlighted. Some signal transduction mechanisms in CP-based sensors and biosensors are discussed. Biocompatibility-related aspects of some conducting polymers are overviewed and some insights into the application of CP-based coatings for the design of implantable sensors and biofuel cells are addressed. New trends and perspectives in the development of sensors based on CPs and their composites with other materials are discussed.

Conjugation of Carboxylated Graphene Quantum Dots with Cecropin P1 for Bacterial Biosensing Applications

Biosensors that can accurately and rapidly detect bacterial concentrations in solution are important for potential applications such as assessing drinking water safety. Meanwhile, quantum dots have proven to be strong candidates for biosensing applications in recent years because of their strong light emission properties and their ability to be modified with a variety of functional groups for the detection of different analytes. Here, we investigate the use of conjugated carboxylated graphene quantum dots (CGQDs) for the detection of Escherichia coli using a biosensing assay that focuses on measuring changes in fluorescence intensity. We have further developed this assay into a novel, compact, field-deployable biosensor focused on rapidly measuring changes in absorbance to determine E. coli concentrations. Our CGQDs were conjugated with cecropin P1, a naturally produced antibacterial peptide that facilitates the attachment of CGQDs to E. coli cells; to our knowledge, this is the first instance of cecropin P1 being used as a biorecognition element for quantum dot biosensors. As such, we confirm the structural modification of these conjugated CGQDs in addition to analyzing their optical characteristics. Our findings have the potential to be used in situations where rapid, reliable detection of bacteria in liquids, such as drinking water, is required, especially given the low range of E. coli concentrations (103 to 106 CFU/mL) within which our two biosensing assays have collectively been shown to function.

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 and challenges on the bioassay of pathogenic bacteria

The present review (containing 242 references) illustrates the importance and application of optical and electrochemical methods as well as their performance improvement using various methods for the detection of pathogenic bacteria. The application of advanced nanomaterials including hyper branched nanopolymers, carbon-based materials and silver, gold and so on. nanoparticles for biosensing of pathogenic bacteria was also investigated. In addition, a summary of the applications of nanoparticle-based electrochemical biosensors for the identification of pathogenic bacteria has been provided and their advantages, detriments and future development capabilities was argued. Therefore, the main focus in the present review is to investigate the role of nanomaterials in the development of biosensors for the detection of pathogenic bacteria. In addition, type of nanoparticles, analytes, methods of detection and injection, sensitivity, matrix and method of tagging are also argued in detail. As a result, we have collected electrochemical and optical biosensors designed to detect pathogenic bacteria, and argued outstanding features, research opportunities, potential and prospects for their development, according to recently published research articles.

Molecularly Imprinted Synthetic Antibodies: From Chemical Design to Biomedical Applications

Billions of dollars are invested into the monoclonal antibody market every year to meet the increasing demand in clinical diagnosis and therapy. However, natural antibodies still suffer from poor stability and high cost, as well as ethical issues in animal experiments. Thus, developing antibody substitutes or mimics is a long-term goal for scientists. The molecular imprinting technique presents one of the most promising strategies for antibody mimicking. The molecularly imprinted polymers (MIPs) are also called "molecularly imprinted synthetic antibodies" (MISAs). The breakthroughs of key technologies and innovations in chemistry and material science in the last decades have led to the rapid development of MISAs, and their molecular affinity has become comparable to that of natural antibodies. Currently, MISAs are undergoing a revolutionary transformation of their applications, from initial adsorption and separation to the rising fields of biomedicine. Herein, the fundamental chemical design of MISAs is examined, and then current progress in biomedical applications is the focus. Meanwhile, the potential of MISAs as qualified substitutes or even to transcend the performance of natural antibodies is discussed from the perspective of frontier needs in biomedicines, to facilitate the rapid development of synthetic artificial antibodies.

Functional Polymers Structures for (Bio)Sensing Application-A Review

In this review we present polymeric materials for (bio)sensor technology development. We focused on conductive polymers (conjugated microporous polymer, polymer gels), composites, molecularly imprinted polymers and their influence on the design and fabrication of bio(sensors), which in the future could act as lab-on-a-chip (LOC) devices. LOC instruments enable us to perform a wide range of analysis away from the stationary laboratory. Characterized polymeric species represent promising candidates in biosensor or sensor technology for LOC development, not only for manufacturing these devices, but also as a surface for biologically active materials' immobilization. The presence of biological compounds can improve the sensitivity and selectivity of analytical tools, which in the case of medical diagnostics is extremely important. The described materials are biocompatible, cost-effective, flexible and are an excellent platform for the anchoring of specific compounds.

The Use of Aptamers and Molecularly Imprinted Polymers in Biosensors for Environmental Monitoring: A Tale of Two Receptors

Effective molecular recognition remains a major challenge in the development of robust receptors for biosensing applications. Over the last three decades, aptamers and molecularly imprinted polymers (MIPs) have emerged as the receptors of choice for use in biosensors as viable alternatives to natural antibodies, due to their superior stability, comparable binding performance, and lower costs. Although both of these technologies have been developed in parallel, they both suffer from their own unique problems. In this review, we will compare and contrast both types of receptor, with a focus on the area of environmental monitoring. Firstly, we will discuss the strategies and challenges involved in their development. We will also discuss the challenges that are involved in interfacing them with the biosensors. We will then compare and contrast their performance with a focus on their use in the detection of environmental contaminants, namely, antibiotics, pesticides, heavy metals, and pathogens detection. Finally, we will discuss the future direction of these two technologies.

Electrochemical sensors for rapid diagnosis of pathogens in real time

Microbial infections remain the principal cause for high morbidity and mortality rates. While approximately 1400 human pathogens have been recognized, the majority of healthcare-associated infectious diseases are caused by only a few opportunistic pathogens (e.g., Pseudomonas aeruginosa, Staphylococcus aureus, Escherichia coli), which are associated with increased antibiotic and antimicrobial resistance. Rapid detection, reliable identification and real-time monitoring of these pathogens remain not only a scientific problem but also a practical challenge of vast importance, especially in tailoring effective treatment strategies. Although the development of vaccinations and antibacterial drug treatments are the leading research, progress, and implementation of early warning, quantitative systems indicative of confirming pathogen presence are necessary. Over the years, various approaches, such as conventional culturing, straining, molecular methods (e.g., polymerase chain reaction and immunological assays), microscopy-based and mass spectrometry techniques, have been employed to identify and quantify pathogenic agents. While being sensitive in some cases, these procedures are costly, time-consuming, mostly qualitative, and are indirect detection methods. A great challenge is therefore to develop rapid, highly sensitive, specific devices with adequate figures of merit to corroborate the presence of microbes and enable dynamic real-time measurements of metabolism. As an alternative, electrochemical sensor platforms have been developed as powerful quantitative tools for label-free detection of infection-related biomarkers with high sensitivity. This minireview is focused on the latest electrochemical-based approaches for pathogen sensing, putting them into the context of standard sensing methods, such as cell culturing, mass spectrometry, and fluorescent-based approaches. Description of the latest, impactful electrochemical sensors for pathogen detection will be presented. Recent breakthroughs will be highlighted, including the use of micro- and nano-electrode arrays for real-time detection of bacteria in polymicrobial infections and microfluidic devices for pathogen separation analysis. We will conclude with perspectives and outlooks to understand shortcomings in designing future sensing schemes. The need for high sensitivity and selectivity, low-cost implementation, fast detection, and screening increases provides an impetus for further development in electrochemical detectors for microorganisms and biologically relevant targets.

Applications of Graphene Quantum Dots in Biomedical Sensors

Due to the proliferative cancer rates, cardiovascular diseases, neurodegenerative disorders, autoimmune diseases and a plethora of infections across the globe, it is essential to introduce strategies that can rapidly and specifically detect the ultralow concentrations of relevant biomarkers, pathogens, toxins and pharmaceuticals in biological matrices. Considering these pathophysiologies, various research works have become necessary to fabricate biosensors for their early diagnosis and treatment, using nanomaterials like quantum dots (QDs). These nanomaterials effectively ameliorate the sensor performance with respect to their reproducibility, selectivity as well as sensitivity. In particular, graphene quantum dots (GQDs), which are ideally graphene fragments of nanometer size, constitute discrete features such as acting as attractive fluorophores and excellent electro-catalysts owing to their photo-stability, water-solubility, biocompatibility, non-toxicity and lucrativeness that make them favorable candidates for a wide range of novel biomedical applications. Herein, we reviewed about 300 biomedical studies reported over the last five years which entail the state of art as well as some pioneering ideas with respect to the prominent role of GQDs, especially in the development of optical, electrochemical and photoelectrochemical biosensors. Additionally, we outline the ideal properties of GQDs, their eclectic methods of synthesis, and the general principle behind several biosensing techniques.

Molecularly Imprinted Polymers and Surface Imprinted Polymers Based Electrochemical Biosensor for Infectious Diseases

Owing to their merits of simple, fast, sensitive, and low cost, electrochemical biosensors have been widely used for the diagnosis of infectious diseases. As a critical element, the receptor determines the selectivity, stability, and accuracy of the electrochemical biosensors. Molecularly imprinted polymers (MIPs) and surface imprinted polymers (SIPs) have great potential to be robust artificial receptors. Therefore, extensive studies have been reported to develop MIPs/SIPs for the detection of infectious diseases with high selectivity and reliability. In this review, we discuss mechanisms of recognition events between imprinted polymers with different biomarkers, such as signaling molecules, microbial toxins, viruses, and bacterial and fungal cells. Then, various preparation methods of MIPs/SIPs for electrochemical biosensors are summarized. Especially, the methods of electropolymerization and micro-contact imprinting are emphasized. Furthermore, applications of MIPs/SIPs based electrochemical biosensors for infectious disease detection are highlighted. At last, challenges and perspectives are discussed.

Sensitive detection of a bacterial pathogen using allosteric probe-initiated catalysis and CRISPR-Cas13a amplification reaction

The ability to detect low numbers of microbial cells in food and clinical samples is highly valuable but remains a challenge. Here we present a detection system (called ‘APC-Cas’) that can detect very low numbers of a bacterial pathogen without isolation, using a three-stage amplification to generate powerful fluorescence signals. APC-Cas involves a combination of nucleic acid-based allosteric probes and CRISPR-Cas13a components. It can selectively and sensitively quantify Salmonella Enteritidis cells (from 1 to 10⁵ CFU) in various types of samples such as milk, showing similar or higher sensitivity and accuracy compared with conventional real-time PCR. Furthermore, APC-Cas can identify low numbers of S. Enteritidis cells in mouse serum, distinguishing mice with early- and late-stage infection from uninfected mice. Our method may have potential clinical applications for early diagnosis of pathogens.

The detection of pathogens in food and clinical samples remains a challenge. Here, Shen et al. present a detection system, involving a combination of nucleic acid-based allosteric probes and CRISPR-Cas13a components, that can detect very low numbers of a bacterial pathogen in milk and serum samples without isolation.

A smartphone-integrated paper sensing system for fluorescent and colorimetric dual-channel detection of foodborne pathogenic bacteria

Infections caused by foodborne microorganisms are a great threat to the global environment and public healthcare today. Thus, rapid, portable and sensitive assays that can realize the identification of foodborne bacteria are highly desired. In this study, a smart fluorescent and colorimetric dual-readout sensing system has been established for simple and rapid E. coli determination by utilizing the Cu²⁺-triggered oxidation of o-phenylenediamine (OPD). Initially, Cu²⁺ can oxidize OPD to OPDox, resulting in an orange-yellow fluorescence and visible pale-yellow color. However, E. coli can effectively reduce Cu²⁺ into Cu⁺, inhibiting the Cu²⁺-triggered oxidation of OPD to OPDox. Consequently, the introduction of E. coli can turn off both the fluorescence and the UV-vis absorbance signals of the OPD-Cu²⁺ system, illustrating an original mechanism for fluorescent and colorimetric dual-channel detection of E. coli. Moreover, a filter paper-based visual sensor was built and coupled with OPD-Cu²⁺ solution under the assistance of a UV lamp. The as-prepared sensor can detect E. coli quantitatively with the help of a typical smartphone color-scanning application (APP). Thus, this study offers a valid dual-mode assay for sensitive and on-site visible detection of E. coli, guaranteeing the reliability of the results and is more attractive for practical use. Graphical Abstract Schematic illustration of the smartphone-integrated sensing system for fluorescent and colorimetric dual-channel detection of E. coli based on the Cu²⁺-OPD system.

Rapid and accurate detection of Escherichia coli O157:H7 in beef using microfluidic wax-printed paper-based ELISA

Escherichia coli O157:H7 is a severe foodborne pathogen. Paper-based ELISA can rapidly and accurately detect E.coli O157:H7 in beef. The method has good sensitivity, specificity and repeatability. It is suitable for point-of-care testing and offers new ideas for the detection of other foodborne pathogens.

Graphene Quantum Dot-Based Electrochemical Immunosensors for Biomedical Applications

In the area of biomedicine, research for designing electrochemical sensors has evolved over the past decade, since it is crucial to selectively quantify biomarkers or pathogens in clinical samples for the efficacious diagnosis and/or treatment of various diseases. To fulfil the demand of rapid, specific, economic, and easy detection of such biomolecules in ultralow amounts, numerous nanomaterials have been explored to effectively enhance the sensitivity, selectivity, and reproducibility of immunosensors. Graphene quantum dots (GQDs) have garnered tremendous attention in immunosensor development, owing to their special attributes such as large surface area, excellent biocompatibility, quantum confinement, edge effects, and abundant sites for chemical modification. Besides these distinct features, GQDs acquire peroxidase (POD)-mimicking electro-catalytic activity, and hence, they can replace horseradish peroxidase (HRP)-based systems to conduct facile, quick, and inexpensive label-free immunoassays. The chief motive of this review article is to summarize and focus on the recent advances in GQD-based electrochemical immunosensors for the early and rapid detection of cancer, cardiovascular disorders, and pathogenic diseases. Moreover, the underlying principles of electrochemical immunosensing techniques are also highlighted. These GQD immunosensors are ubiquitous in biomedical diagnosis and conducive for miniaturization, encouraging low-cost disease diagnostics in developing nations using point-of-care testing (POCT) and similar allusive techniques.

Molecularly Imprinted Polymers for Cell Recognition

Since their conception 50 years ago, molecularly imprinted polymers (MIPs) have seen extensive development both in terms of synthetic routes and applications. Cells are perhaps the most challenging target for molecular imprinting. Although early work was based almost entirely around microprinting methods, recent developments have shifted towards epitope imprinting to generate MIP nanoparticles (NPs). Simultaneously, the development of techniques such as solid phase MIP synthesis has solved many historic issues of MIP production. This review briefly describes various approaches used in cell imprinting with a focus on applications of the created materials in imaging, drug delivery, diagnostics, and tissue engineering.

Recent Advances in Electrochemiluminescence Sensors for Pathogenic Bacteria Detection

Pathogenic bacterial contamination greatly threats human health and safety. Rapidly biosensing pathogens in the early stage of infection would be helpful to choose the correct drug treatment, prevent transmission of pathogens, as well as decrease mortality and economic losses. Traditional techniques, such as polymerase chain reaction and enzyme-linked immunosorbent assay, are accurate and effective, but are greatly limited because they are complex and time-consuming. Electrochemiluminescence (ECL) biosensors combine the advantages of both electrochemical and photoluminescence analysis and are suitable for high sensitivity and simple pathogenic bacteria detection. In this review, we summarize recent advances in ECL sensors for pathogenic bacteria detection and highlight the development of paper-based ECL platforms in point of care diagnosis of pathogens.

Highly sensitive bioaffinity electrochemiluminescence sensors: Recent advances and future directions

Electrogenerated chemiluminescence (also called electrochemiluminescence and abbreviated ECL) has attracted much attention in various fields of analysis due to the potential remarkably high sensitivity, extremely wide dynamic range and excellent controllability. Electrochemiluminescence biosensor, by taking the advantage of the selectivity of the biological recognition elements and the high sensitivity of ECL technique was applied as a powerful analytical device for ultrasensitive detection of biomolecule. In this review, we summarize the latest sensing applications of ECL bioanalysis in the field of bio affinity ECL sensors including aptasensors, immunoassays and DNA analysis, cytosensor, molecularly imprinted sensors, ECL resonance energy transfer and ratiometric biosensors and give future perspectives for new developments in ECL analytical technology. Furthermore, the results herein discussed would demonstrate that the use of nanomaterials with unique chemical and physical properties in the ECL biosensing systems is one of the most interesting research lines for the development of ultrasensitive electrochemiluminescence biosensors. In addition, ECL based sensing assays for clinical samples analysis and medical diagnostics and developing of immunosensors, aptasensors and cytosensor for this purpose is also highlighted.

Molecularly Imprinted Polymer-Based Hybrid Materials for the Development of Optical Sensors

We report on the development of new optical sensors using molecularly imprinted polymers (MIPs) combined with different materials and explore the novel strategies followed in order to overcome some of the limitations found during the last decade in terms of performance. This review pretends to offer a general overview, mainly focused on the last 3 years, on how the new fabrication procedures enable the synthesis of hybrid materials enhancing not only the recognition ability of the polymer but the optical signal. Introduction describes MIPs as biomimetic recognition elements, their properties and applications, emphasizing on each step of the fabrication/recognition procedure. The state of the art is presented and the change in the publication trend between electrochemical and optical sensor devices is thoroughly discussed according to the new fabrication and micro/nano-structuring techniques paving the way for a new generation of MIP-based optical sensors. We want to offer the reader a different perspective based on the materials science in contrast to other overviews. Different substrates for anchoring MIPs are considered and distributed in different sections according to the dimensionality and the nature of the composite, highlighting the synergetic effect obtained as a result of merging both materials to achieve the final goal.

A novel polydopamine electrochemiluminescence organic nanoparticle-based biosensor for parathyroid hormone detection

In this work, polydopamine electrochemiluminescence (ECL)-organic nanoparticles (EONs) based immunosensing strategy was designed for parathyroid hormone (PTH) detection. Dopamine is oxidized and polymerized to form polydopamine organic nanoparticle via self-polymerization process. Unlike the low photoluminescent efficiency and unsatisfactory fluorescence characters of the fluorescent organic nanoparticles (FONs), the polydopamine EONs do not only show unique physicochemical properties and excellent biocompatibility, but also provide ideal electrochemical properties and bright ECL signals, which can be employed as high-quality ECL luminophores. The ECL-related properties and performance of the EONs are further discussed in this paper. The sensing method has a linear response in the range of 0.05-8 ng/mL with a detection limit of 17 pg/mL. The applicability of this method is evaluated through the determination of PTH in human plasma samples with satisfactory results. To our best knowledge, this was the first time about the exploration of polydopamine organic nanoparticles as ECL luminophores in the biosensing application.

Recent Advances in Electrosynthesized Molecularly Imprinted Polymer Sensing Platforms for Bioanalyte Detection

The accurate detection of biological materials has remained at the forefront of scientific research for decades. This includes the detection of molecules, proteins, and bacteria. Biomimetic sensors look to replicate the sensitive and selective mechanisms that are found in biological systems and incorporate these properties into functional sensing platforms. Molecularly imprinted polymers (MIPs) are synthetic receptors that can form high affinity binding sites complementary to the specific analyte of interest. They utilise the shape, size, and functionality to produce sensitive and selective recognition of target analytes. One route of synthesizing MIPs is through electropolymerization, utilising predominantly constant potential methods or cyclic voltammetry. This methodology allows for the formation of a polymer directly onto the surface of a transducer. The thickness, morphology, and topography of the films can be manipulated specifically for each template. Recently, numerous reviews have been published in the production and sensing applications of MIPs; however, there are few reports on the use of electrosynthesized MIPs (eMIPs). The number of publications and citations utilising eMIPs is increasing each year, with a review produced on the topic in 2012. This review will primarily focus on advancements from 2012 in the use of eMIPs in sensing platforms for the detection of biologically relevant materials, including the development of increased polymer layer dimensions for whole bacteria detection and the use of mixed monomer compositions to increase selectivity toward analytes.

Entrapment of uropathogenic E. coli cells into ultra-thin sol-gel matrices on gold thin films: A low cost alternative for impedimetric bacteria sensing

Bacterial infections are causing worldwide morbidity and mortality. One way to limit infectious outbreaks and optimize clinical management of infections is through the development of fast and sensitive sensing of bacteria. Most sensing approaches are currently based on immunological detection principles. We report here on an impedimetric sensor to selectively and sensitive detect uropathogenic E. coli cells (E. coli UTI89) using artificial recognition sites. We show here the possibility to imprint the rod-shape structure of E. coli UTI 89 into ultra-thin inorganic silica coatings on gold electrodes in a reproducible manner. A linear range from to 1 × 100 -1 × 104 cfu mL-1 is obtained. With a detection limit for E. coli UTI89 below 1 cfu mL-1 from five blank signals (95% confidence level) and excellent selective binding capabilities, these bacterial cell imprinted electrodes brings us closer to a low cost specific bacterial recognition surfaces.

Two-dimensional porphyrin-based covalent organic framework: A novel platform for sensitive epidermal growth factor receptor and living cancer cell detection

A porphyrin-based covalent organic framework (denoted as p-COF) was synthesized by a simple oil-bath method and exploited as a novel sensing layer for immobilizing epidermal growth factor receptor (EGFR)-targeting aptamer strands to detect trace EGFR and living michigan cancer foundation-7 (MCF-7) cells for the first time. p-COF presented a nanosheet-like structure, large cavities, rich nitrogen-bearing groups, high electrochemical activity, excellent bioaffinity, low toxicity, and good stability in aqueous solution; the microstructural features of this material enabled strong immobilization of the aptamer strands. Interactions between the aptamer strands and EGFR significantly changed the electrochemical signals of the modified electrode due to the formation of an aptamer-EGFR complex. The p-COF-based aptasensor exhibited an extremely low detection limit (LOD) of 5.64 fg·mL^-1 obtained from differential pulse voltammetry and 7.54 fg·mL^-1 originated from electrochemical impedance spectroscopy with a broad linear detection range of 0.05-100 pg·mL^-1 of the EGFR concentration. When detecting living MCF-7 cells, the p-COF-based aptasensor showed an LOD of 61 cell·mL^-1 with a linear detection range of 500 × 10⁵ cell·mL^-1. The fabricated aptasensor exhibited high selectivity, good stability, reproducibility, acceptable recyclability, and favorable applicability in human serum samples. We believe that the developed p-COF-based aptasensor is a potential candidate for the sensitive detection of target cancer markers or living cells.

Single cell immunodetection of Escherichia coli O157:H7 on an indium-tin-oxide electrode by using an electrochemical label with an organic-inorganic nanostructure

A rapid and highly sensitive method is described for the detection of enterohemorrhagic Escherichia coli O157:H7. An organic-inorganic nanostructure in which numerous gold nanoparticles (AuNPs) are enclosed with polyaniline (PANI) was utilized as an electrochemical label. The nanostructure showed (a) strong light scattering intensity due to the coupling effect of the surface plasmon resonance based on the presence of AuNPs, and (b) high electrochemical response due to the redox activity of PANI. To achieve selectivity, antibody against E. coli O157:H7 was immobilized on the surface of the nanostructure. The method exploits the combination of strong adsorption of bacterial cells onto the indium-tin-oxide (ITO) glass electrode without any special processing and specific binding of the nanostructured label to E. coli O157:H7. This enables the electrochemical detection of a single cell on the ITO electrode. The electrochemical response to E. coli O157:H7 was 30-fold higher than that to other types of bacteria. This procedure can be applied to the determination of E. coli O157:H7 even in the presence of other bacteria. Graphical abstract Schematic of a voltammetric immunoassay for Escherichia coli O157:H7 by using a nanocomposite consisting of gold nanoparticles and polyaniline on an ITO electrode.

A redox cycling-amplified electrochemical immunosensor for α-fetoprotein sensitive detection via polydopamine nanolabels

A sandwich-type electrochemical immunosensor for sensitive detection of a tumor marker, α-fetoprotein (AFP), was fabricated by employing polydopamine-detection antibody nanoparticles (PDANPs-Ab2) as selective redox cycling-based signal amplifiers on an electrodeposited nano-gold electrode. In this research, PDANPs prepared through oxidative polymerization of dopamine were found to amplify the oxidation charge transfer of the electrochemical mediator (1,1'-ferrocene dimethanol, FDM), which was supported by cyclic voltammetry (CV) and X-ray photoelectron spectroscopy (XPS) investigation. Therefore, PDANPs were utilized as label materials of electrochemical immunosensors to enhance sensitivity for the first time. Meanwhile, the nano-gold electrode was used as a platform to accelerate electron transfer and immobilize capture antibody (Ab1). The electrochemical performance of the AFP immunosensor was investigated in PBS containing FDM with CV. Under optimal conditions, the constructed AFP immunosensor exhibited a wide linear range from 1 pg mL-1 to 50 ng mL-1 and a low detection limit of 0.3 pg mL-1, as well as excellent stability, reproducibility and selectivity. Measurements of AFP in human serum gave excellent correlation with the clinical standard Chemiluminescence Microparticle Immuno Assay (CMIA). These results indicated that the developed immunosensor may have promising application in the clinical diagnosis of AFP and other tumor markers.

Electrochemical Methodologies for the Detection of Pathogens

Bacterial infections remain one of the principal causes of morbidity and mortality worldwide. The number of deaths due to infections is declining every year by only 1% with a forecast of 13 million deaths in 2050. Among the 1400 recognized human pathogens, the majority of infectious diseases is caused by just a few, about 20 pathogens only. While the development of vaccinations and novel antibacterial drugs and treatments are at the forefront of research, and strongly financially supported by policy makers, another manner to limit and control infectious outbreaks is targeting the development and implementation of early warning systems, which indicate qualitatively and quantitatively the presence of a pathogen. As toxin contaminated food and drink are a potential threat to human health and consequently have a significant socioeconomic impact worldwide, the detection of pathogenic bacteria remains not only a big scientific challenge but also a practical problem of enormous significance. Numerous analytical methods, including conventional culturing and staining techniques as well as molecular methods based on polymerase chain reaction amplification and immunological assays, have emerged over the years and are used to identify and quantify pathogenic agents. While being highly sensitive in most cases, these approaches are highly time, labor, and cost consuming, requiring trained personnel to perform the frequently complex assays. A great challenge in this field is therefore to develop rapid, sensitive, specific, and if possible miniaturized devices to validate the presence of pathogens in cost and time efficient manners. Electrochemical sensors are well accepted powerful tools for the detection of disease-related biomarkers and environmental and organic hazards. They have also found widespread interest in the last years for the detection of waterborne and foodborne pathogens due to their label free character and high sensitivity. This Review is focused on the current electrochemical-based microorganism recognition approaches and putting them into context of other sensing devices for pathogens such as culturing the microorganism on agar plates and the polymer chain reaction (PCR) method, able to identify the DNA of the microorganism. Recent breakthroughs will be highlighted, including the utilization of microfluidic devices and immunomagnetic separation for multiple pathogen analysis in a single device. We will conclude with some perspectives and outlooks to better understand shortcomings. Indeed, there is currently no adequate solution that allows the selective and sensitive binding to a specific microorganism, that is fast in detection and screening, cheap to implement, and able to be conceptualized for a wide range of biologically relevant targets.

Aptamer immobilization on amino-functionalized metal-organic frameworks: an ultrasensitive platform for the electrochemical diagnostic of Escherichia coli O157:H7

Herein, we report the development of an electrochemical biosensor for Escherichia coli O157:H7 diagnostic based on amino-functionalized metal-organic frameworks (MOFs) as a new generation of organic-inorganic hybrid nanocomposites. The electrical and morphological properties of MOFs were enhanced by interweaving each isolated MOF crystal with polyaniline (PANI). Subsequent attachment of the amine-modified aptamer to the polyanilinated MOFs was accomplished using glutaraldehyde (GA) as a cross-linking agent. The prepared biocompatible platform was carefully characterized by means of field-emission scanning electron microscopy (FESEM), energy-dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FT-IR), and X-ray powder diffraction (XRD) techniques. The biosensor fabrication and its electrochemical characterizations were monitored by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques. Differential pulse voltammetry (DPV) was applied to monitoring and quantitation of the interaction between the aptamer and E. coli O157:H7 using methylene blue (MB) as an electrochemical indicator. Changes in the reduction peak current of MB in the presence of E. coli O157:H7 was recorded as an analytical signal and indicated a relationship with the logarithm of the E. coli O157:H7 concentration in the range of 2.1 × 10¹ to 2.1 × 10⁷ CFU mL^-1 with a LOQ of 21 CFU mL^-1 and LOD of 2 CFU mL^-1. The electrochemical aptasensor displayed good recovery values for the detection of E. coli O157:H7 in environmental real samples and also could act as a smart device to investigate the effects of antibacterial agents against E. coli O157:H7.

Recent Progress in Biosensors for Environmental Monitoring: A Review

The environmental monitoring has been one of the priorities at the European and global scale due to the close relationship between the environmental pollution and the human health/socioeconomic development. In this field, the biosensors have been widely employed as cost-effective, fast, in situ, and real-time analytical techniques. The need of portable, rapid, and smart biosensing devices explains the recent development of biosensors with new transduction materials, obtained from nanotechnology, and for multiplexed pollutant detection, involving multidisciplinary experts. This review article provides an update on recent progress in biosensors for the monitoring of air, water, and soil pollutants in real conditions such as pesticides, potentially toxic elements, and small organic molecules including toxins and endocrine disrupting chemicals.

AgBr nanoparticles/3D nitrogen-doped graphene hydrogel for fabricating all-solid-state luminol-electrochemiluminescence Escherichia coli aptasensors

It is necessary to develop rapid, simple and accurate detection method for Escherichia coli (E. coli) due to its widely distributed pathogenic bacteria. Herein, we prepared AgBr nanoparticles (NPs) anchored 3D nitrogen-doped graphene hydrogel (3DNGH) nanocomposites with an exceptionally large accessible surface by a simple hydrothermal approach. The as-prepared 3DNGH porous nanocomposite not only showed better conductivity than that of 3D graphene due to introducing nitrogen element into graphene framework, but also provided a high loading volume for immobilizing luminol. Meanwhile the anchored AgBr NPs served as the catalyst can effectively enhance the ECL behavior of luminol. And the resulting luminol/AgBr/3DNGH exhibited more excellent ECL performances, which was about 2, 3, 8 times enhanced respectively, comparing to luminol/AgBr/3DGH, luminol/3DNGH and luminol/AgBr/2DNG. Further, the multifunctional nanoarchitecture was used as the all-solid-state ECL platform for fabricating Escherichia coli aptasensors via glutaraldehyde as crosslinking agent between amine-functionalized E. coli aptamer and luminol/AgBr/3DNGH. Based on the steric hindrance mechanism that E.coli can significantly decrease the ECL intensity, the proposed aptasensor displayed a linear response for E.coli in the range from 0.5 to 500 cfu/mL with an extremely low detection limit of 0.17 cfu/mL (S/N). In addition, this ECL aptasensor possessed great advantages including the simple operation process, low-cost and sensitivity, which provided a promising approach for the E.coli detection in biomedical, food detection and environmental analysis.

Fluorescence detection of cholesterol using a nitrogen-doped graphene quantum dot/chromium picolinate complex-based sensor

A novel N-GQDs/CrPic-based cholesterol sensor with high sensitivity and selectivity has been constructed.