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

A critical review on metal organic frameworks (MOFs)-based sensors for foodborne pathogenic bacteria detection

The pervasive threat of foodborne pathogenic bacteria necessitates advancements in rapid and reliable detection methods. Traditional approaches suffer from significant limitations including prolonged processing times, limited sensitivity and specificity. This review comprehensively examines the integration of metal organic frameworks (MOFs) with sensor technologies for the enhanced detection of foodborne pathogens. MOFs, with their unique properties such as high porosity, tunable pore sizes, and ease of functionalization, offer new avenues for sensor enhancement. This paper provides a comprehensive analysis of recent developments in MOFs-based sensors, particularly focusing on electrochemical, fluorescence, colorimetric, and surface-enhanced Raman spectroscopy sensors. We have provided a detailed introduction for the operational principles of these sensors, highlighting the role of MOFs play in enhancing their performance. Comparative analyses demonstrate MOFs' superior capabilities in enhancing signal response, reducing response time, and expanding detection limits. This review culminates in presenting MOFs as transformative materials in the detection of foodborne pathogens, paving the way for their broader application in ensuring food safety.

Applications of Metal-Organic Frameworks (MOFs) in Drug Delivery, Biosensing, and Therapy: A Comprehensive Review

The porous materials known as metal-organic frameworks (MOFs) stand out for their enormous surface area, adaptable pore size and shape, and structural variety. These characteristics make them well-suited for various applications, especially in healthcare. This review thoroughly summarizes recent studies on the use of MOFs in drug delivery, biosensing, and therapeutics. MOFs may encapsulate medications, target certain cells or tissues, and regulate their release over time. Additionally, MOFs have the potential to be used in biosensing applications, allowing for the selective detection of chemical and biological substances. MOFs' optical or electrical characteristics may be modified to make biosensors that track physiological data. MOFs show potential for targeted drug delivery and the regulated release of therapeutic substances in cancer treatment. In addition, they may work as potent antibacterial agents, providing a less dangerous option than traditional antibiotics that increase antibiotic resistance. For practical applications, further research is required as well as more consideration for the problems with toxicity and biocompatibility. In addition to addressing the difficulties and promising possibilities in this area, this study intends to provide insights into the potential of MOFs in healthcare for drug delivery, biosensing, and treatment. Despite several essential reviews in this area, it was necessary to look into the most recent research on drug delivery, biosensing, and therapy as a combined concept.

Functionalized metal-organic frameworks with biomolecules for sensing and detection applications of food contaminants

The increasing demand for toxin-free food, driven by the rise in fast food consumption and changing dietary habits, necessitates advanced and efficient detection methods to address the potential risks associated with contaminated food. Nanomaterial-based detection methods have shown significant promise, particularly using metal-organic frameworks (MOFs) combined with biomolecules. This review article provides an overview of recent advancements in using functionalized metal-organic frameworks (FMOFs) with biomolecules to detect various food contaminants, including heavy metals, antibiotics, pesticides, bacteria, mycotoxins and other chemical contaminants. We discuss the fundamental principles of detecting food contaminants, evaluate existing analytical techniques, and explore the development of biomacromolecule-functionalized MOF-based sensors encompassing colorimetric, optical, electrochemical, and portable variants. The review also examines sensing mechanisms, uses FMOFs as signal probes and carriers for capture probes, and assesses sensitivity. Additionally, we explore the opportunities and challenges in producing FMOFs with biomacromolecules for food contaminant assessment. Future directions include improving sensor sensitivity and specificity, developing more cost-effective production methods, and integrating these technologies into real-world food safety monitoring systems. This work aims to pave the way for innovative and reliable solutions to ensure the safety of our food supply.

Electroanalytical Platform for Rapid E. coli O157:H7 Detection in Water Samples

There is a pressing need to enhance early detection methods of E. coli O157:H7 to mitigate the occurrence and consequences of pathogenic contamination and associated outbreaks. This study highlights the efficacy of a portable electrochemical sensing platform that operates without faradaic processes towards detecting and quantifying E. coli O157:H7. It is specifically tailored for quick identification in potable water. The assay processing time is approximately 5 min, addressing the need for swift and efficient pathogen detection. The sensing platform was constructed utilizing specific, monoclonal E. coli antibodies, based on single-capture, non-faradaic, electrochemical immunoassay principles. The E. coli sensor assay underwent testing over a wide concentration range, spanning from 10 to 105 CFU/mL, and a limit of detection (LoD) of 1 CFU/mL was demonstrated. Significantly, the sensor's performance remained consistent across studies, with both inter- and intra-study coefficients of variation consistently below 20%. To evaluate real-world feasibility, a comparative examination was performed between laboratory-based benchtop data and data obtained from the portable device. The proposed sensing platform exhibited remarkable sensitivity and selectivity, enabling the detection of minimal E. coli concentrations in potable water. This successful advancement positions it as a promising solution for prompt on-site detection, characterized by its portability and user-friendly operation. This study presents electrochemical-based sensors as significant contributors to ensuring food safety and public health. They play a crucial role in preventing the occurrence of epidemics and enhancing the supervision of water quality.

The Biomedical Applications of Biomolecule Integrated Biosensors for Cell Monitoring

Cell monitoring is essential for understanding the physiological conditions and cell abnormalities induced by various stimuli, such as stress factors, microbial invasion, and diseases. Currently, various techniques for detecting cell abnormalities and metabolites originating from specific cells are employed to obtain information on cells in terms of human health. Although the states of cells have traditionally been accessed using instrument-based analysis, this has been replaced by various sensor systems equipped with new materials and technologies. Various sensor systems have been developed for monitoring cells by recognizing biological markers such as proteins on cell surfaces, components on plasma membranes, secreted metabolites, and DNA sequences. Sensor systems are classified into subclasses, such as chemical sensors and biosensors, based on the components used to recognize the targets. In this review, we aim to outline the fundamental principles of sensor systems used for monitoring cells, encompassing both biosensors and chemical sensors. Specifically, we focus on biosensing systems in terms of the types of sensing and signal-transducing elements and introduce recent advancements and applications of biosensors. Finally, we address the present challenges in biosensor systems and the prospects that should be considered to enhance biosensor performance. Although this review covers the application of biosensors for monitoring cells, we believe that it can provide valuable insights for researchers and general readers interested in the advancements of biosensing and its further applications in biomedical fields.

Nucleic acid strand displacement for indirect determination of foodborne bacteria by capillary electrophoresis and its application in antagonism and bacteriostasis studies

Foodborne bacteria threaten human's health. Capillary electrophoresis (CE) is a powerful separation means for the determination of bacteria. Direct separation of bacteria suffers from the shortages of low resolution, channel adsorption, and bacterial aggregation. In this work, a method of nucleic acid strand displacement was developed to indirect separate the bacteria by CE. DNA complexes, consisting of probes and aptamers, were mixed with the three bacteria Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. The aptamers could specifically bond with bacteria and release the probes. Through the separation of the probes, the bacteria could be indirectly determined by CE. This method avoided the shortages of direct separation of bacteria. Under the optimized conditions, the three probes for the bacteria could be separated and detected within 2.5 min by high-speed CE with laser-induced fluorescence detection. The limits of detection for the bacteria were in the range 4.20 × 106 to 1.75 × 107  CFU/mL. Finally, the developed method was applied on the study of antagonism of the coexistent bacteria to reveal the relationship between them. Furthermore, the efficiency of bacteriostasis of three traditional Chinese medicines, Coptis chinensis, Schisandra chinensis, and honeysuckle, was also studied by this method.

Electrochromic Sensor Augmented with Machine Learning for Enzyme-Free Analysis of Antioxidants

Our study presents an electrochromic sensor that operates without the need for enzymes or multiple oxidant reagents. This sensor is augmented with machine learning algorithms, enabling the identification, classification, and prediction of six different antioxidants with high accuracy. We utilized polyaniline (PANI), Prussian blue (PB), and copper-Prussian blue analogues (Cu-PBA) at their respective oxidation states as electrochromic materials (ECMs). By designing three readout channels with these materials, we were able to achieve visual detection of antioxidants without relying on traditional "lock and key" specific interactions. Our sensing approach is based on the direct electrochemical reactions between oxidized electrochromic materials (ECMsox) as electron acceptors and various antioxidants, which act as electron donors. This interaction generates unique fingerprint patterns by switching the ECMsox to reduced electrochromic materials (ECMsred), causing their colors to change. Through the application of density functional theory (DFT), we demonstrated the molecular-level basis for the distinct multicolor patterns. Additionally, machine learning algorithms were employed to correlate the optical patterns with RGB data, enabling complex data analysis and the prediction of unknown samples. To demonstrate the practical applications of our design, we successfully used the EC sensor to diagnose antioxidants in serum samples, indicating its potential for the on-site monitoring of antioxidant-related diseases. This advancement holds promise for various applications, including the real-time monitoring of antioxidant levels in biological samples, the early diagnosis of antioxidant-related diseases, and personalized medicine. Furthermore, the success of our electrochromic sensor design highlights the potential for exploring similar strategies in the development of sensors for diverse analytes, showcasing the versatility and adaptability of this approach.

Discriminating macromolecular interactions based on an impedimetric fingerprint supported by multivariate data analysis for rapid and label-free Escherichia coli recognition in human urine

This manuscript presents a novel approach to address the challenges of electrode fouling and highly complex electrode nanoarchitecture, which are primary concerns for biosensors operating in real environments. The proposed approach utilizes multiparametric impedance discriminant analysis (MIDA) to obtain a fingerprint of the macromolecular interactions on flat glassy carbon surfaces, achieved through self-organized, drop-cast, receptor-functionalized Au nanocube (AuNC) patterns. Real-time monitoring is combined with singular value decomposition and partial least squares discriminant analysis, which enables selective identification of the analyte from raw impedance data, without the use of electric equivalent circuits. As a proof-of-concept, the authors demonstrate the ability to detect Escherichia coli in real human urine using an aptamer-based biosensor that targets RNA polymerase. This is significant, as uropathogenic E. coli is a difficult-to-treat pathogen that is responsible for the majority of hospital-acquired urinary tract infection cases. The proposed approach offers a limit of detection of 11.3 CFU/mL for the uropathogenic E. coli strain No. 57, an analytical range in all studied concentrations (up to 105 CFU/mL), without the use of antifouling strategies, yet not being specific vs other E.coli strain studied (BL21(DE3)). The MIDA approach allowed to identify negative overpotentials (-0.35 to -0.10 V vs Ag/AgCl) as most suitable for the analysis, offering over 80% sensitivity and accuracy, and the measurement was carried out in just 2 min. Moreover, this approach is scalable and can be applied to other biosensor platforms.

Quantitative measurement of CA 15-3 cancer biomarker using an electrochemical aptasensor based on the electrodeposition of Au thin film on cauliflower-like rGO-MoS2 nanocomposite

The present research was conducted to design and construct an electrochemical aptasensor for evaluating carbohydrate antigen 15-3 (CA15-3) as a biomarker for breast cancer. The aptasensor has been fabricated by a gold thin film (AuTF) electrodeposited on a cauliflower-like reduced graphene oxide-molybdenum sulfide nanocomposite (rGO-MoS2). The modified electrode's surface was used to immobilize the thiolated aptamer, which was subsequently treated with CA 15-3 antigen. The aptasensor fabrication process was assessed using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). This research also applied EIS to the quantitative measurement of CA 15-3 antigen by the proposed aptasensor. The interfacial charge transfer resistance (Rct) alteration before and after incubation of CA 15-3 by the immobilized aptamer was considered a signal for the quantitative measurement of CA 15-3. A linear concentration ranging from 5.0 to 200.0 U mL-1 with a detection limit of 3.0 × 10-1 U mL-1 was obtained for CA 15-3 using the EIS method. This designed aptasensor indicates satisfactory repeatability and stability, good selectivity, and high sensitivity. Moreover, clinical samples were assayed by the prepared aptasensor and compared with the ELISA method, yielding acceptable results. The recovery and relative standard deviation (RSD) of CA 15-3 in human serum samples were in the range 95.0 to 107.0% and 3.5 to 7.5%, respectively.

Aptamer-modified metal organic frameworks for measurement of food contaminants: a review

The measurement of food contaminants faces a great challenge owing to the increasing demand for safe food, increasing consumption of fast food, and rapidly changing patterns of human consumption. As different types of contaminants in food products can pose different levels of threat to human health, it is desirable to develop specific and rapid methods for their identification and quantification. During the past few years, metal-organic framework (MOF)-based materials have been extensively explored in the development of food safety sensors. MOFs are porous crystalline materials with tunable composition, dynamic porosity, and facile surface functionalization. The construction of high-performance biosensors for a range of applications (e.g., food safety, environmental monitoring, and biochemical diagnostics) can thus be promoted through the synergistic combination of MOFs with aptamers. Accordingly, this review article delineates recent innovations achieved for the aptamer-functionalized MOFs toward the detection of food contaminants. First, we describe the basic concepts involved in the detection of food contaminants in terms of the advantages and disadvantages of the commonly used analytical methods (e.g., DNA-based methods (PCR/real-time PCR/multiplex PCR/digital PCR) and protein-based methods (enzyme-linked immunosorbent assay/immunochromatography assay/immunosensor/mass spectrometry). Afterward, the progress in aptamer-functionalized MOF biosensors is discussed with respect to the sensing mechanisms (e.g., the role of MOFs as signal probes and carriers for loading signal probes) along with their performance evaluation (e.g., in terms of sensitivity). We finally discuss challenges and opportunities associated with the development of aptamer-functionalized MOFs for the measurement of food contaminants.

Conjugated Polymers for Aptasensing Applications

Rapid and specific assaying of molecules that report on a pathophysiological condition, environmental pollution, or drug concentration is pivotal for establishing efficient and accurate diagnostic systems. One of the main components required for the construction of these systems is the recognition element (receptor) that can identify target analytes. Oligonucleotide switching structures, or aptamers, have been widely studied as selective receptors that can precisely identify targets in different analyzed matrices with minimal interference from other components in an antibody-like recognition process. These aptasensors, especially when integrated into sensing platforms, enable a multitude of sensors that can outperform antibody-based sensors in terms of flexibility of the sensing strategy and ease of deployment to areas with limited resources. Research into compounds that efficiently enhance signal transduction and provide a suitable platform for conjugating aptamers has gained huge momentum over the past decade. The multifaceted nature of conjugated polymers (CPs), notably their versatile electrical and optical properties, endows them with a broad range of potential applications in optical, electrical, and electrochemical signal transduction. Despite the substantial body of research demonstrating the enhanced performance of sensing devices using doped or nanostructure-embedded CPs, few reviews are available that specifically describe the use of conjugated polymers in aptasensing. The purpose of this review is to bridge this gap and provide a comprehensive description of a variety of CPs, from a historical viewpoint, underpinning their specific characteristics and demonstrating the advances in biosensors associated with the use of these conjugated polymers.

A sensitive enzyme-free electrochemical sensor based on a rod-shaped bimetallic MOF anchored on graphene oxide nanosheets for determination of glucose in huangshui

In this work, we propose a bimetallic Ni-Co based MOF attached to graphene oxide (GO) by a one-step hydrothermal approach which may be employed as an electrochemical enzyme-free glucose sensor. Due to the obvious synergistic catalysis of Ni and Co, as well as the combination of NiCo-MOF and GO, NiCo-MOF/GO not only enhances energy transfer and electrocatalytic performance but also provides a larger surface area and more active sites. Electrochemical studies show that NiCo-MOF/GO exhibits outstanding electrochemical activity, with a sensitivity of 11 177 μA mM^-1 cm^-2 and 4492 μA mM^-1 cm^-2 in the linear ranges of 1-497 μM and 597-3997 μM, a detection limit of 0.23 μM, and a response time of 2 seconds. More importantly, the newly fabricated sensor is successfully applied for glucose determination in huangshui. This method provides a novel strategy for the controlled fermentation process and product quality of Chinese baijiu.

A dual-mode ratiometric aptasensor for accurate detection of pathogenic bacteria based on recycling of DNAzyme activation

Pathogenic bacteria have a significant impact on food safety. Herein, an innovative dual-mode ratiometric aptasensor was constructed for ultrasensitive and accurate detection of Staphylococcus aureus (S. aureus) based on recycling of DNAzyme activation on gold nanoparticles-functionalized MXene nanomaterials (MXene@Au NPs). Electrochemiluminescent (ECL) emitter-labeled probe DNA (probe 2-Ru) containing the blocked DNAzyme was partly hybridized with aptamer and then captured by electrochemical (EC) indicator-labeled probe DNA (probe 1-MB) on electrode surface. When S. aureus presented, the conformation vibration of probe 2-Ru activated the blocked DNAzymes, leading to recycling cleavage of probe 1-MB and ECL tag close to electrode surface. Based on the reverse change tendencies of ECL and EC signals, aptasensor achieved S. aureus quantification from 5 to 10⁸ CFU/mL. Moreover, the self-calibration characteristic of the aptasensor with dual-mode ratiometric readout ensured the reliable measurement of S. aureus in real samples. This work showed useful insight into sensing foodborne pathogenic bacteria.

Metal-organic frameworks for pharmaceutical and biomedical applications

Metal-organic framework (MOF) materials provide unprecedented opportunities for evaluating valuable compounds for various medical applications. MOFs merged with biomolecules, used as novel biomaterials, have become particularly useful in biological environments. Bio-MOFs can be promising materials in the global to avoid utilization above toxicological substances. Bio-MOFs with crystallin and porosity nature offer flexible structure via bio-linker and metal node variation, which improves their wide applicability in medical science.

Potentiometric aptasensing of Escherichia coli based on electrogenerated chemiluminescence as a highly sensitive readout

We introduce here a versatile approach to read out potentiometric aptasensors by electrogenerated chemiluminescence (ECL), which can amplify the small potential changes induced by the bacterial concentrations via ECL signals. In the present system, the electrode modified with single-walled carbon nanotubes (SWCNTs) and aptamer molecules acts as the reference electrode and is placed in the sample solution for sensing the bacterial concentration changes, while the Ru(bpy)₃²⁺ modified gold electrode serves as the working electrode for generating ECL signals and is placed in the detection solution containing tripropylamine (TPA) spatially separated from the sample solution by a salt bridge. Ru(bpy)₃²⁺ is immobilized on the gold electrode's surface for enhancement of luminous efficiency and reduction of reagent consumption. A moving-part-free fluid flowing system is introduced to promote the mass transport of TPA from the detection solution to the surface of the ECL generating electrode. When a constant potential is imposed between the working and reference electrodes, the potential changes at the SWCNTs-aptamer modified electrode induced by the bacterial concentrations can modulate the potentials at the Ru(bpy)₃²⁺ modified electrode, thus generating the ECL signals. The developed sensing strategy shows a highly sensitive response to E. coli O157: H7 in the linear range of 5-1000 CFU mL^-1 with a low detection limit of 2 CFU mL^-1. We believe that the proposed approach is promising to develop aptasensors for sensitive detection of bacterial cells.

Metal-Organic Frameworks-Based Sensors for Food Safety

Food contains a variety of poisonous and harmful substances that have an impact on human health. Therefore, food safety is a worldwide public concern. Food detection approaches must ensure the safety of food at every step of the food supply chain by monitoring and evaluating all hazards from every single step of food production. Therefore, early detection and determination of trace-level contaminants in food are one of the most crucial measures for ensuring food safety and safeguarding consumers' health. In recent years, various methods have been introduced for food safety analysis, including classical methods and biomolecules-based sensing methods. However, most of these methods are laboratory-dependent, time-consuming, costly, and require well-trained technicians. To overcome such problems, developing rapid, simple, accurate, low-cost, and portable food sensing techniques is essential. Metal-organic frameworks (MOFs), a type of porous materials that present high porosity, abundant functional groups, and tunable physical and chemical properties, demonstrates promise in large-number applications. In this regard, MOF-based sensing techniques provide a novel approach in rapid and efficient sensing of pathogenic bacteria, heavy metals, food illegal additives, toxins, persistent organic pollutants (POPs), veterinary drugs, and pesticide residues. This review focused on the rapid screening of MOF-based sensors for food safety analysis. Challenges and future perspectives of MOF-based sensors were discussed. MOF-based sensing techniques would be useful tools for food safety evaluation owing to their portability, affordability, reliability, sensibility, and stability. The present review focused on research published up to 7 years ago. We believe that this work will help readers understand the effects of food hazard exposure, the effects on humans, and the use of MOFs in the detection and sensing of food hazards.

Metal-organic frameworks based hybrid nanocomposites as state-of-the-art analytical tools for electrochemical sensing applications

Metal-organic frameworks (MOFs) are remarkably porous materials that have sparked a lot of interest in recent years because of their fascinating architectures and variety of potential applications. This paper systematically summarizes recent breakthroughs in MOFs and their derivatives with different materials such as, carbon nanotubes, graphene oxides, carbon fibers, enzymes, antibodies and aptamers etc. for enhanced electrochemical sensing applications. Furthermore, an overview part is highlighted, which provides some insights into the future prospects and directions of MOFs and their derivatives in electrochemical sensing, with the goal of overcoming present limitations by pursuing more inventive ways. This overview can perhaps provide some creative ideas for future research on MOF-based materials in this rapidly expanding field.

Novel Biorecognition Elements against Pathogens in the Design of State-of-the-Art Diagnostics

Infectious agents, especially bacteria and viruses, account for a vast number of hospitalisations and mortality worldwide. Providing effective and timely diagnostics for the multiplicity of infectious diseases is challenging. Conventional diagnostic solutions, although technologically advanced, are highly complex and often inaccessible in resource-limited settings. An alternative strategy involves convenient rapid diagnostics which can be easily administered at the point-of-care (POC) and at low cost without sacrificing reliability. Biosensors and other rapid POC diagnostic tools which require biorecognition elements to precisely identify the causative pathogen are being developed. The effectiveness of these devices is highly dependent on their biorecognition capabilities. Naturally occurring biorecognition elements include antibodies, bacteriophages and enzymes. Recently, modified molecules such as DNAzymes, peptide nucleic acids and molecules which suffer a selective screening like aptamers and peptides are gaining interest for their biorecognition capabilities and other advantages over purely natural ones, such as robustness and lower production costs. Antimicrobials with a broad-spectrum activity against pathogens, such as antibiotics, are also used in dual diagnostic and therapeutic strategies. Other successful pathogen identification strategies use chemical ligands, molecularly imprinted polymers and Clustered Regularly Interspaced Short Palindromic Repeats-associated nuclease. Herein, the latest developments regarding biorecognition elements and strategies to use them in the design of new biosensors for pathogens detection are reviewed.

Recent advances in metal/covalent organic framework-based electrochemical aptasensors for biosensing applications

The booming development of novel porous materials, metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs) has been attracting a lot of attention due to their designabilities, diversities, and extensive applications. MOFs and COFs provide a new potential opportunity and platform to fabricate electrochemical aptasensors for biosensing applications. Compared to other traditional materials, MOF/COF-based electrochemical biosensors can appreciably amplify the electrochemical response signals to improve the sensing performance. Herein, we provide a comprehensive overview of MOF/COF-based electrochemical aptasensors for monitoring different ultra-trace analytes (e.g. antibiotics, pesticides, and cancer markers). This review systematically discusses the classification of electrochemical aptasensors based on various functional materials, including pure MOFs, MOF/conductive composites, metal nanoparticle/MOF composites, pure COFs, COFs/conductive composites, and other hybrid materials. Furthermore, some typical MOF/COF-based electrochemical aptasensors in the recognition of specific targets are described in detail to improve and guide further research for biosensing applications.

Metal-organic frameworks for diagnosis and therapy of infectious diseases

Infectious diseases are one of the leading cause of mortality and morbidity worldwide. Metal-Organic Frameworks (MOFs), which are porous coordination materials composed of bridging organic ligands and metallic ions or clusters, exhibits great potential to be used against several pathogens, such as bacteria, viruses, fungi and protozoa. MOFs can show sustained release capability, high surface area, adjustable pore size and structural flexibility, which makes them good candidates for new therapeutic systems. This review provides a detailed summary of the biological application of MOFs, focussing on diagnosis and treatment of infectious diseases. MOFs have been reported for usage as antimicrobial agents, drug delivery systems, therapeutic composites, nanozymes and phototherapies. Furthermore, different MOF-based biosensors have also been developed to detect specific pathogens by electrochemical, fluorometric and colorimetric assays. Finally, we present limitations and perspectives in this field.

Electrochemical aptasensor for Escherichia coli O157:H7 bacteria detection using a nanocomposite of reduced graphene oxide, gold nanoparticles and polyvinyl alcohol

In recent years, public attention has drawn to food safety due to the constant outbreaks of foodborne diseases; subsequently, to control and prevent this group of diseases, early screening of foodborne pathogens has become significant. In this study, a new aptamer-based electrochemical sensor was proposed to detect Escherichia coli O157:H7 (E. coli), one of the most threatening bacterial pathogens, using nanoparticles-modified glassy carbon electrode. Firstly, the electrode was coated with a reduced graphene oxide-poly(vinyl alcohol) and gold nanoparticles nanocomposite (AuNPs/rGO-PVA/GCE) to increase the electrode surface area and consequently raise the sensor sensitivity. Afterwards, to enhance the selectivity of the modified electrode, aptamers were attached to the surface of the prepared electrode. The prepared electrode was characterized using energy-dispersive spectroscopy, field-emission scanning electron microscopy, atomic force microscopy, Fourier-transform infrared spectroscopy, and electrochemical impedance spectroscopy. The relationship of the E. coli concentration and the peak current in the range from 9.2 CFU mL^-1 to 9.2 × 10⁸ CFU mL^-1 was linear, and the limit of detection was calculated as 9.34 CFU mL^-1. The suitability of the proposed sensor for real sample measurements was investigated by recovery studies in tap water, milk, and meat samples. The results showed that the biosensor and traditional culture counting methods are equally sensitive for detecting E. coli.

On-site detection of food and waterborne bacteria - current technologies, challenges, and future directions

With the rise in outbreaks of pathogenic bacteria in both food and water resulting in an increased instance of infection, there is a growing public health problem in both developed and developing countries. In this increasing threat the most effective method for control and prevention is rapid and cost-effective detection. Research has shifted in recent years towards the development of rapid and on-site assays for the detection of these kinds of bacteria. However, there are still some limitations in the implementation of these assays in the field. This article discusses the current on-site detection methods. Current scope of advancements and limitations in the development or use of these on-site technologies for food and waterborne bacterial detection is evaluated in this study. With the continued development of these technologies, on-site detection will continue to impact many areas of public health. As these methods continue to improve and diversify further, on-site detection could become more widely implemented in food and water analysis.

Biosensors Coupled with Signal Amplification Technology for the Detection of Pathogenic Bacteria: A Review

Foodborne disease caused by foodborne pathogens is a very important issue in food safety. Therefore, the rapid screening and sensitive detection of foodborne pathogens is of great significance for ensuring food safety. At present, many research works have reported the application of biosensors and signal amplification technologies to achieve the rapid and sensitive detection of pathogenic bacteria. Thus, this review summarized the use of biosensors coupled with signal amplification technology for the detection of pathogenic bacteria, including (1) the development, concept, and principle of biosensors; (2) types of biosensors, such as electrochemical biosensors, optical biosensors, microfluidic biosensors, and so on; and (3) different kinds of signal amplification technologies applied in biosensors, such as enzyme catalysis, nucleic acid chain reaction, biotin-streptavidin, click chemistry, cascade reaction, nanomaterials, and so on. In addition, the challenges and future trends for pathogenic bacteria based on biosensor and signal amplification technology were also discussed and summarized.

Recent Advances and a Roadmap to Aptamer-Based Sensors for Bloodstream Infections

The present review is intended to describe bloodstream infections (BSIs), the major pathogens responsible for BSIs, conventional tests and their limitations, commercially available methods used, and the aptamer and nanomaterials-based approaches developed so far for the detection of BSIs. The advantages associated with aptamers and the aptamer-based sensors, the comparison between the aptamers and the antibodies, and the various types of aptasensors developed so far for the detection of bloodstream infections have been described in detail in the present review. Also, the future outlook and roadmap toward aptamer-based sensors and the challenges associated with the aptamer development have also been concluded in this review.

An electrochemical biosensor based on methylene blue-loaded nanocomposites as signal-amplifying tags to detect pathogenic bacteria

A sandwich-type electrochemical biosensor was successfully constructed for the sensitive detection of pathogenic bacteria. In this biosensor platform, methylene blue (MB) organic-inorganic nanocomposites (MB@MI) were synthesized from magainin I (MI, antimicrobial peptide specific to Escherichia coli O157:H7), Cu3(PO4)2 and MB via a one-pot method, and were explored as a novel electrochemical signal label of biosensors generating amplified electrochemical signals by differential pulse voltammetry (DPV). E. coli O157:H7 specifically sandwich bound to the aptamers on the electrode surface and MB@MI nanocomposites, and the changes in the current signal generated on the electrode surface were used for the quantitative determination of E. coli O157:H7. Under optimum conditions, the proposed biosensor showed excellent performance with a wide linear range of 102-107 CFU mL-1 and a low detection limit of 32 CFU mL-1, featuring favorable selectivity, repeatability and stability. According to the experiments conducted on real samples, the proposed approach is capable of detecting pathogenic bacteria in clinical diagnostics.

Highly Sensitive and Cost-Effective Portable Sensor for Early Gastric Carcinoma Diagnosis

Facile and efficient early detection of cancer is a major challenge in healthcare. Herein we developed a novel sensor made from a polycarbonate (PC) membrane with nanopores, followed by sequence-specific Oligo RNA modification for early gastric carcinoma diagnosis. In this design, the gastric cancer antigen CA72-4 is specifically conjugated to the Oligo RNA, thereby inhibiting the electrical current through the PC membrane in a concentration-dependent manner. The device can determine the concentration of cancer antigen CA72-4 in the range from 4 to 14 U/mL, possessing a sensitivity of 7.029 µAU^-1mLcm^-2 with a linear regression (R²) of 0.965 and a lower detection limit of 4 U/mL. This device has integrated advantages including high specificity and sensitivity and being simple, portable, and cost effective, which collectively enables a giant leap for cancer screening technologies towards clinical use. This is the first report to use RNA aptamers to detect CA72-4 for gastric carcinoma diagnosis.

A stepwise recognition strategy for the detection of telomerase activity via direct electrochemical analysis of metal-organic frameworks

The detection of telomerase is of great significance for monitoring cell canceration. The conventional methods depend on the extension of telomerase towards its primer to conduct signal transduction. Herein, a specific and reliable detection strategy based on stepwise recognition was developed for tandem detection of metal ions and enzymes. We first synthesized an electrically active metal-organic framework (MIL-101(Fe)), which can act directly as a signal reporter in phosphate buffered saline after being modified with capture DNA (cDNA). When the zinc ion is added as a coenzyme factor, the modified hairpin DNA on the electrode is cleaved by DNAzyme to yield the activated primer. After the addition of telomerase, the cleaved DNA strand would be extended, and the resulting sequence will be hybridized with the signal label of MIL-101(Fe)-cDNA. Therefore, a signal-on strategy for the detection of telomerase was achieved based on the direct electrochemical analysis of MIL-101(Fe). Moreover, this electrochemical biosensor can discriminate telomerase activity among different cell lines. The stepwise recognition ensured the advantages of an electrochemical biosensor such as high sensitivity and specificity during the detection process, providing a novel method for monitoring and diagnosis of diseases.

Aptamer-functionalized metal-organic frameworks (MOFs) for biosensing

As a class of crystalline porous materials, metal-organic frameworks (MOFs) have attracted increasing attention. Due to the nanoscale framework structure, adjustable pore size, large specific surface area, and good chemical stability, MOFs have been applied widely in many fields such as biosensors, biomedicine, electrocatalysis, energy storage and conversions. Especially when they are combined with aptamer functionalization, MOFs can be utilized to construct high-performance biosensors for numerous applications ranging from medical diagnostics and food safety inspection, to environmental surveillance. Herein, this article reviews recent innovations of aptamer-functionalized MOFs-based biosensors and their bio-applications. We first briefly introduce different functionalization methods of MOFs with aptamers, which provide a foundation for the construction of MOFs-based aptasensors. Then, we comprehensively summarize different types of MOFs-based aptasensors and their applications, in which MOFs serve as either signal probes or signal probe carriers for optical, electrochemical, and photoelectrochemical detection, with an emphasis on the former. Given recent substantial research interests in stimuli-responsive materials and the microfluidic lab-on-a-chip technology, we also present the stimuli-responsive aptamer-functionalized MOFs for sensing, followed by a brief overview on the integration of MOFs on microfluidic devices. Current limitations and prospective trends of MOFs-based biosensors are discussed at the end.

Selection and applications of functional nucleic acids for infectious disease detection and prevention

Infectious diseases caused by pathogenic microorganisms such as viruses and bacteria pose a great threat to human health. Although a significant progress has been obtained in the diagnosis and prevention of infectious diseases, it still remains challenging to develop rapid and cost-effective detection approaches and overcome the side effects of therapeutic agents and pathogen resistance. Functional nucleic acids (FNAs), especially the most widely used aptamers and DNAzymes, hold the advantages of high stability and flexible design, which make them ideal molecular recognition tools for bacteria and viruses, as well as potential therapeutic drugs for infectious diseases. This review summarizes important advances in the selection and detection of bacterial- and virus-associated FNAs, along with their potential prevention ability of infectious disease in recent years. Finally, the challenges and future development directions are concluded.

Pathogen detection with electrochemical biosensors: Advantages, challenges and future perspectives

Detection of pathogens, e.g., bacteria and viruses, is still a big challenge in analytical medicine due to their vast number and variety. Developing strategies for rapid, inexpensive, specific, and sensitive detection of the pathogens using nanomaterials, integrating with microfluidics devices, amplification methods, or even combining these strategies have received significant attention. Especially, after the health-threatening COVID-19 outbreak, rapid and sensitive detection of pathogens became very critical. Detection of pathogens could be realized with electrochemical, optical, mass sensitive, or thermal methods. Among them, electrochemical methods are very promising by bringing different advantages, i.e., they exhibit more versatile detection schemes and real-time quantification as well as label-free measurements, which provides a broader application perspective. In this review, we discuss the recent advances for the detection of bacteria and viruses using electrochemical biosensors. Moreover, electrochemical biosensors for pathogen detection were broadly reviewed in terms of analyte, bio-recognition and transduction elements. Different fabrication techniques, detection principles, and applications of various pathogens with the electrochemical biosensors were also discussed.

Sensitive impedimetric detection of troponin I with metal-organic framework composite electrode

Metal-organic frameworks (MOFs) are promising materials for biosensing applications due to their large surface to volume ratio, easy assembly as thin films, and better biocompatibility than other nanomaterials. Their application in electrochemical biosensing devices can be realized by integrating them with other conducting materials, like polyaniline (PANI). In the present research, a composite of a copper-MOF (i.e., Cu3(BTC)2) with PANI has been explored to develop an impedimetric sensor for cardiac marker troponin I (cTnI). The solvothermally synthesized Cu3(BTC)2/PANI composite has been coated as a thin layer on the screen-printed carbon electrodes (SPE). This electroconductive thin film was conjugated with anti-cTnI antibodies. The above formed immunosensor has allowed the impedimetric detection of cTnI antigen over a clinically important concentration range of 1-400 ng mL-1. The whole process of antigen analysis could be completed within 5 min. The detection method was specific to cTnI even in the co-presence of other possibly interfering proteins.

Advances in nanomaterial-based electrochemical biosensors for the detection of microbial toxins, pathogenic bacteria in food matrices

There is a growing demand to protect food products against the hazard of microbes and their toxins. To satisfy such goals, it is important to develop highly sensitive, reliable, sophisticated, rapid, and cost-effective sensing techniques such as electrochemical sensors/biosensors. Although diverse forms of nanomaterials (NMs)-based electrochemical sensing methods have been introduced in markets, the reliability of commercial products is yet insufficient to meet the practical goal. In this review, we focused on: 1) sources of pathogenic microbes and their toxins; 2) possible routes of their entrainment in food, and 3) current development of NM-based biosensors to realize real-time detection of the target analytes. At last, future prospects and challenges in this research field are discussed.

Electrochemical Aptasensors Based on Hybrid Metal-Organic Frameworks

Metal-organic frameworks (MOFs) offer a unique variety of properties and morphology of the structure that make it possible to extend the performance of existing and design new electrochemical biosensors. High porosity, variable size and morphology, compatibility with common components of electrochemical sensors, and easy combination with bioreceptors make MOFs very attractive for application in the assembly of electrochemical aptasensors. In this review, the progress in the synthesis and application of the MOFs in electrochemical aptasensors are considered with an emphasis on the role of the MOF materials in aptamer immobilization and signal generation. The literature information of the use of MOFs in electrochemical aptasensors is classified in accordance with the nature and role of MOFs and a signal mode. In conclusion, future trends in the application of MOFs in electrochemical aptasensors are briefly discussed.

Dual-Modular Aptasensor for Detection of Cardiac Troponin I Based on Mesoporous Silica Films by Electrochemiluminescence/Electrochemical Impedance Spectroscopy

A simple, dual-modular aptasensor for accurate determination of cardiac troponin I (cTnI), a sensitive biomarker of acute myocardial infarction, is reported. It has the parallel output of electrochemiluminescence (ECL) and electrochemical impedance spectroscopy (EIS) based on target-gated transportation of signal probes (luminol/H₂O₂ or Fe(CN)₆^3-/4-). The sensing capacity is originated from the amino-functionalized mouth margin of the nanochannels in a vertically oriented mesoporous silica film, which was in situ-grown on indium tin oxide-coated glass. With the linkage of glutaraldehyde to couple the aptamer as a trapper, it brings in the high specific target-gated response toward cTnI as decreased ECL or increased EIS. The concentration of cTnI is measurable by the ECL response within a wide linear range from 0.05 pg mL^-1 to 10 ng mL^-1, as well as the EIS response for a linear range between 0.05 pg mL^-1 and 1 ng mL^-1. Significantly, the self-verification of these two data from ECL and EIS validated each other with a satisfactory linear correlation (R² = 0.999), thereby realizing the more reliable and accurate quantification to avoid false results. The designed strategy is an effective method for detection of cTnI, which is of great potential to apply in clinical detection.

Highly Sensitive Optical Detection of Escherichia coli Using Terbium-Based Metal-Organic Framework

Metal-organic frameworks (MOFs) are envisaged as highly useful for the development of biosensors. Herein, for the first time, we report the optical detection of Escherichia coli using a water-dispersible terbium MOF (Tb-BTC; BTC, 1,3,5-benzenetricarboxylic acid). The successful synthesis of Tb-BTC is verified using spectroscopic and morphological techniques like UV-vis, fluorescence and FTIR spectroscopy, X-ray diffraction analysis, and electron microscopy. Tb-BTC has been bio-interfaced with anti-E. coli antibodies and then investigated as a biosensor for E. coli. The biosensor displays detection ability in an analyte concentration range of 1.3 × 10² to 1.3 × 10⁸ cfu/mL with a detection limit of 3 cfu/mL, having a response time of 5 min and a total analysis time of about 20-25 min. The results are also found to be reproducible and specific in the presence of some other interfering bacterial species. As demonstrated, the present sensor provides highly sensitive and specific detection of E. coli in fruit juice sample. To the best of our knowledge, this is the first report to showcase the potential of the MOF-based fluorescent biosensor for the detection of E. coli.

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.

Magnetically controlled colorimetric aptasensor for chlorpyrifos based on copper-based metal-organic framework nanoparticles with peroxidase mimetic property

The fabrication of a magnetically controlled colorimetric aptasensor for chlorpyrifos is reported. The aptasensor was fabricated by the attachment of the colorimetric labels onto the magnetic carrier due to the hybridization reaction between the complementary DNA and aptamer. Chlorpyrifos detection was realized by monitoring the color changes of the TMB/H₂O₂ solution before and after incubation of the aptasensor with chlorpyrifos via exposure to external magnetic force. The color change was monitored at 650 nm by UV-Vis spectrophotometer. Under the optimal conditions, this magnetically controlled Cu-MOF-based aptasensor showed a detection limit of 4.4 ng/mL with a linear range of 0-1250 ng/mL. The colorimetric aptasensor displayed high selectivity for chlorpyrifos toward other interfering pesticides. The aptasensor was successfully applied for the spiked test of chlorpyrifos in fruits and vegetable samples with good recovery, which were in agreement with data obtained by GC-MS analysis. This magnetically controlled Cu-MOF-based sensing strategy not only leads to development of efficient and facile phase separation, but also expands the MOF's target scope from H₂O₂ or glucose to pesticides. Graphical abstract.

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.

Recent Progress in the Identification of Aptamers Against Bacterial Origins and Their Diagnostic Applications

Aptamers have gained an increasing role as the molecular recognition element (MRE) in diagnostic assay development, since their first conception thirty years ago. The process to screen for nucleic acid-based binding elements (aptamers) was first described in 1990 by the Gold Laboratory. In the last three decades, many aptamers have been identified for a wide array of targets. In particular, the number of reports on investigating single-stranded DNA (ssDNA) aptamer applications in biosensing and diagnostic platforms have increased significantly in recent years. This review article summarizes the recent (2015 to 2020) progress of ssDNA aptamer research on bacteria, proteins, and lipids of bacterial origins that have implications for human infections. The basic process of aptamer selection, the principles of aptamer-based biosensors, and future perspectives will also be discussed.

Aptamer-Based Biosensors for Environmental Monitoring

Due to their relative synthetic and chemical simplicity compared to antibodies, aptamers afford enhanced stability and functionality for the detection of environmental contaminants and for use in environmental monitoring. Furthermore, nucleic acid aptamers can be selected for toxic targets which may prove difficult for antibody development. Of particular relevance, aptamers have been selected and used to develop biosensors for environmental contaminants such as heavy metals, small-molecule agricultural toxins, and water-borne bacterial pathogens. This review will focus on recent aptamer-based developments for the detection of diverse environmental contaminants. Within this domain, aptamers have been combined with other technologies to develop biosensors with various signal outputs. The goal of much of this work is to develop cost-effective, user-friendly detection methods that can complement or replace traditional environmental monitoring strategies. This review will highlight recent examples in this area. Additionally, with innovative developments such as wearable devices, sentinel materials, and lab-on-a-chip designs, there exists significant potential for the development of multifunctional aptamer-based biosensors for environmental monitoring. Examples of these technologies will also be highlighted. Finally, a critical perspective on the field, and thoughts on future research directions will be offered.

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

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

Metal-Organic Framework Nanoparticles Induce Pyroptosis in Cells Controlled by the Extracellular pH

Ion homeostasis is essential for cellular survival, and elevated concentrations of specific ions are used to start distinct forms of programmed cell death. However, investigating the influence of certain ions on cells in a controlled way has been hampered due to the tight regulation of ion import by cells. Here, it is shown that lipid-coated iron-based metal-organic framework nanoparticles are able to deliver and release high amounts of iron ions into cells. While high concentrations of iron often trigger ferroptosis, here, the released iron induces pyroptosis, a form of cell death involving the immune system. The iron release occurs only in slightly acidic extracellular environments restricting cell death to cells in acidic microenvironments and allowing for external control. The release mechanism is based on endocytosis facilitated by the lipid-coating followed by degradation of the nanoparticle in the lysosome via cysteine-mediated reduction, which is enhanced in slightly acidic extracellular environment. Thus, a new functionality of hybrid nanoparticles is demonstrated, which uses their nanoarchitecture to facilitate controlled ion delivery into cells. Based on the selectivity for acidic microenvironments, the described nanoparticles may also be used for immunotherapy: the nanoparticles may directly affect the primary tumor and the induced pyroptosis activates the immune system.