Magnetism-Resolved Separation and Fluorescence Quantification for Near-Simultaneous Detection of Multiple Pathogens

Highly sensitive detection of Salmonella typhimurium via gold and magnetic nanoparticle-mediated sandwich hybridization coupled with ICP-MS

Foodborne pathogens including Salmonella typhimurium (S. typhimurium) are responsible for over 600 million global incidences of illness annually, posing a significant threat to public health. Inductively coupled plasma mass spectrometry (ICP-MS), coupled with element labeling strategies, has emerged as a promising platform for multivariate and accurate pathogen detection. However, achieving high specificity and sensitivity remains a critical challenge. Herein, we synthesize clustered magnetic nanoparticles (MNPs) and popcorn-shaped gold nanoparticles (AuNPs) to conjugate capture and report DNA probes for S. typhimurium, respectively. These engineered nanoparticles facilitate the identification of S. typhimurium DNA through a sandwich hybridization technique. ICP-MS quantification of Au within the sandwich-structure complexes allows for precise S. typhimurium detection. The unique morphology of the AuNPs and MNPs increases the available sites for probe attachment, enhancing the efficiency of S. typhimurium DNA capture, broadening the detection range to 101-1010 copies mL-1, and achieving a low detection limit of 1 copy mL-1, and the overall assay time is 70 min. The high specificity of this method is verified by anti-interference assays against ten other pathogens. The recovery was 96.8-102.8% for detecting S. typhimurium DNA in biological samples. As these specially designed nanoparticles may facilitate the attachment of various proteins and nucleic acid probes, they may become an effective platform for detecting multiple pathogens.

Improving synthesis and binding affinities of nucleic acid aptamers and their therapeutics and diagnostic applications

Nucleic acid aptamers have captivated the attention of analytical and medicinal scientists globally due to their several advantages as recognition molecules over conventional antibodies because of their small size, simple and inexpensive synthesis, broad target range, and high stability in varied environmental conditions. These recognition molecules can be chemically modified to make them resistant to nuclease action in blood serum, reduce rapid renel clearance, improve the target affinity and selectivity, and make them amenable to chemically conjugate with a support system that facilitates their selective applications. This review focuses on the development of efficient aptamer candidates and their application in clinical diagnosis and therapeutic applications. Significant advances have been made in aptamer-based diagnosis of infectious and non-infectious diseases. Collaterally, the progress made in therapeutic applications of aptamers is encouraging, as evident from their use in diagnosing cancer, neurodegenerative diseases, microbial infection, and in imaging. This review also updates the progress on clinical trials of many aptamer-based products of commercial interests. The key development and critical issues on the subject have been summarized in the concluding remarks.

Magnetic-encoded fluorescent nanospheres-based competitive immunoassay for near-simultaneous detection of four mycotoxins in wheat

Simultaneous detection of mycotoxins is important for food safety. In this study, a magnetic-encoded fluorescent nanosphere-based competitive immunosensor (cFMEIS) with 2×2 array was first developed for simultaneous detection of aflatoxin B1 (AFB1), ochratoxin (OTA), deoxynivalenol (DON), and zearalenone (ZEN) in wheat. Specifically, magnetic nanoparticles with strong and weak responses were conjugated with mycotoxin antigens as capture probes. Fluorescent nanoparticles doped with europium ion (Eu3+) and terbium ion (Tb3+) with red and green emission were coupled with mycotoxin antibodies as signal probes. Using a magnetic field, immune complexes were sequentially separated in a complex system and fluorescently detected. The detection limits of AFB1, DON, OTA, and ZEN were 0.032, 0.141, 0.097, and 0.376 μg/kg, respectively. The recoveries in the certified reference material of wheat flour ranged from 81.6 to 120.0 %. Owing to its high accuracy, selectivity, and sensitivity, the cFMEIS shows great promise as an efficient and sensitive multitarget sensor for mycotoxins.

A Critical Review on Detection of Foodborne Pathogens Using Electrochemical Biosensors

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

Azo Reductase Activated Magnetic Resonance Tuning Probe with "Switch-On" Property for Specific and Sensitive Tumor Imaging in Vivo

Cancer remains a threat to human health. However, if tumors can be detected in the early stage, then the effectiveness of cancer treatment could be significantly improved. Therefore, it is worthwhile to develop more sensitive and accurate cancer diagnostic methods. Herein, we demonstrated an azo reductase (AzoR)-activated magnetic resonance tuning (MRET) probe with a "switch-on" property for specific and sensitive tumor imaging in vivo. Specifically, Gd-labeled DNA1 (DNA1-Gd) and cyclodextrin-coated magnetic nanoparticles (MNP-CD) were employed as enhancer and quencher of MRET, respectively, while DNA2, an azobenzene (Azo) group-modified aptamer (AS1411), served as a linker between enhancer and quencher to construct the MRET probe of MNP@DNA(1-2)-Gd. In tumor tissues with high-level AzoR, the T1-weighted magnetic resonance signal of the MRET probe could be restored by intelligently regulating the switch from "OFF" to "ON" after activation with AzoR, thus accurately indicating the location of the tumor accurately. Moreover, the tumor with a 4 times smaller size than that of the normal tumor model could be imaged based on the proposed MRET probe. The as-proposed MRET-based magnetic resonance imaging strategy not only achieves tumor imaging accurately but also shows promise for early diagnosis of tumors, which might improve patients' survival rates and provide an opportunity for image-guided biomedical applications in the future.

Recent Advances in Fluorescent Nanoprobes for Food Safety Detection

Fluorescent nanoprobes show similar fluorescence properties to traditional organic dyes, but the addition of nanotechnology accurately controls the size, shape, chemical composition, and surface chemistry of the nanoprobes with unique characteristics and properties, such as bright luminescence, high photostability, and strong biocompatibility. For example, modifying aptamers or antibodies on a fluorescent nanoprobe provides high selectivity and specificity for different objects to be tested. Fluorescence intensity, life, and other parameters of targets can be changed by different sensing mechanisms based on the unique structural and optical characteristics of fluorescent nanoprobes. What's more, the detection of fluorescent nanoprobes is cost-saving, simple, and offers great advantages in rapid food detection. Sensing mechanisms of fluorescent nanoprobes were introduced in this paper, focusing on the application progress in pesticide residues, veterinary drug residues, heavy metals, microbes, mycotoxins, and other substances in food safety detection in recent years. A brief outlook for future development was provided as well.

Toward waterborne protozoa detection using sensing technologies

Drought and limited sufficient water resources will be the main challenges for humankind during the coming years. The lack of water resources for washing, bathing, and drinking increases the use of contaminated water and the risk of waterborne diseases. A considerable number of waterborne outbreaks are due to protozoan parasites that may remain active/alive in harsh environmental conditions. Therefore, a regular monitoring program of water resources using sensitive techniques is needed to decrease the risk of waterborne outbreaks. Wellorganized point-of-care (POC) systems with enough sensitivity and specificity is the holy grail of research for monitoring platforms. In this review, we comprehensively gathered and discussed rapid, selective, and easy-to-use biosensor and nanobiosensor technologies, developed for the early detection of common waterborne protozoa.

Nanomaterial-Based Fluorescent Biosensor for Food Safety Analysis

Food safety issues have become a major threat to public health and have garnered considerable attention. Rapid and effective detection methods are crucial for ensuring food safety. Recently, nanostructured fluorescent materials have shown considerable potential for monitoring the quality and safety of food because of their fascinating optical characteristics at the nanoscale. In this review, we first introduce biomaterials and nanomaterials for food safety analysis. Subsequently, we perform a comprehensive analysis of food safety using fluorescent biosensors based on nanomaterials, including mycotoxins, heavy metals, antibiotics, pesticide residues, foodborne pathogens, and illegal additives. Finally, we provide new insights and discuss future approaches for the development of food safety detection, with the aim of improving fluorescence detection methods for the practical application of nanomaterials to ensure food safety and protect human health.

Photoelectrochemical Sensors with Near-Infrared-Responsive Reduced Graphene Oxide and MoS2 for Quantification of Escherichia Coli O157:H7

The photoelectric response is crucial for photocatalysis, having applications in solar cells and photoelectrochemical (PEC) sensors. In this study, we demonstrate improvements in the near-infrared (NIR)-light-driven PEC response via synergism between reduced graphene oxide (rGO) and MoS₂. Intriguingly, rGO modulates the morphology of MoS₂, facilitating carrier generation and migration, improving the PEC performance of the resultant rGO-MoS₂ sheets (GMS), and yielding an approximately 8-fold increase in the photocurrent compared to that of the pure MoS₂. Based on these findings, a NIR-responsive PEC immunosensing platform for the "turn-on" analysis of Escherichia coli O157:H7 on 980 nm light irradiation is reported. Specifically, the device is a three-dimensional magnetic screen-printed paper-based electrode assembled on a home-made PEC cell, and it enables integrated separation and detection. Using a sandwich-type immunocomplex bridged by E. coli O157:H7 and a GMS PEC probe, the immunosensing platform detected E. coli O157:H7 between 5.0 and 5.0 × 10⁶ CFU mL^-1, having an extremely low detection limit of 2.0 CFU mL^-1. Further, the assay enables the direct analysis of E. coli O157:H7 in milk without the need for pretreatment. Our findings suggest directions for the development of NIR-responsive paper-based PEC materials for portable biomolecule sensing.

Recent Advances in Electrochemical Biosensors for the Detection of Salmonellosis: Current Prospective and Challenges

Salmonellosis is a major cause of foodborne infections, caused by Salmonella, posing a major health risk. It possesses the ability to infiltrate the food supply chain at any point throughout the manufacturing, distribution, processing or quality control process. Salmonella infection has increased severely and requires effective and efficient methods for early monitoring and detection. Traditional methods, such as real-time polymerase chain reaction and culture plate, consume a lot of time and are labor-intensive. Therefore, new quick detection methods for on-field applications are urgently needed. Biosensors provide consumer-friendly approaches for quick on-field diagnoses. In the last few years, there has been a surge in research into the creation of reliable and advanced electrochemical sensors for the detection of Salmonella strains in food samples. Electrochemical sensors provide extensive accuracy and reproducible results. Herein, we present a comprehensive overview of electrochemical sensors for the detection of Salmonella by focusing on various mechanisms of electrochemical transducer. Further, we explain new-generation biosensors (microfluidics, CRISPR- and IOT-based) for point-of care applications. This review also highlights the limitations of developing biosensors in Salmonella detection and future possibilities.

Fluorescence Biosensor for One-Step Simultaneous Detection of Mycobacterium tuberculosis Multidrug-Resistant Genes Using nanoCoTPyP and Double Quantum Dots

The diagnosis of multidrug-resistant tuberculosis (MDR-TB) is crucial for the subsequent drug guidance to improve therapy and control the spread of this infectious disease. Herein, we developed a novel florescence biosensor for simultaneous detection of Mycobacterium tuberculosis (Mtb) multidrug-resistant genes (rpoB531 for rifampicin and katG315 for isoniazid) by using our synthesized nanocobalt 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphine (nanoCoTPyP) and double quantum dots (QDs). Several nanoCoTPyPs with different charges and morphology were successfully prepared via the surfactant-assisted method and their quenching ability and restoring efficiency for DNA detection were systematically analyzed. It was found that spherical nanoCoTPyP with positive charge exhibited excellent quenching effect and sensing performance for the two DNAs' detection due to its affinity differences towards single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA). ssDNA attached on QDs (QDs-ssDNA) was specifically hybridized with targets to form QDs-dsDNA, resulting in fluorescence recovery due to the disruption of the interactions between nanoCoTPyP and ssDNA. Two drug-resistant genes could be simultaneously quantified in a single run and relatively low limits of detection (LODs) were obtained (24 pM for T1 and 20 pM for T2). Furthermore, the accuracy and reliability of our method were verified by testing clinical samples. This simple and low-cost approach had great potential to be applied in clinical diagnosis of MDR-TB.

Magnetic Fluorescent Quantum Dots Nanocomposites in Food Contaminants Analysis: Current Challenges and Opportunities

The presence of food contaminants can cause foodborne illnesses, posing a severe threat to human health. Therefore, a rapid, sensitive, and convenient method for monitoring food contaminants is eagerly needed. The complex matrix interferences of food samples and poor performance of existing sensing probes bring significant challenges to improving detection performances. Nanocomposites with multifunctional features provide a solution to these problems. The combination of the superior characteristics of magnetic nanoparticles (MNPs) and quantum dots (QDs) to fabricate magnetic fluorescent quantum dots (MNPs@QDs) nanocomposites are regarded as an ideal multifunctional probe for food contaminants analysis. The high-efficiency pretreatment and rapid fluorescence detection are concurrently integrated into one sensing platform using MNPs@QDs nanocomposites. In this review, the contemporary synthetic strategies to fabricate MNPs@QDs, including hetero-crystalline growth, template embedding, layer-by-layer assembly, microemulsion technique, and one-pot method, are described in detail, and their advantages and limitations are discussed. The recent advances of MNPs@QDs nanocomposites in detecting metal ions, foodborne pathogens, toxins, pesticides, antibiotics, and illegal additives are comprehensively introduced from the perspectives of modes and detection performances. The review ends with current challenges and opportunities in practical applications and prospects in food contaminants analysis, aiming to promote the enthusiasm for multifunctional sensing platform research.

Theranostic applications of stimulus-responsive systems based on Fe2O3

According to the interaction of nanoparticles with biological systems, enthusiasm for nanotechnology in biomedical applications has been developed in the past decades. Fe2O3 nanoparticles, as the most stable iron oxide, have special merits that make them useful widely for detecting diseases, therapy, drug delivery, and monitoring the therapeutic process. This review presents the fabrication methods of Fe2O3-based materials and their photocatalytic and magnetic properties. Then, we highlight the application of Fe2O3-based nanoparticles in diagnosis and imaging, different therapy methods, and finally, stimulus-responsive systems, such as pH-responsive, magnetic-responsive, redox-responsive, and enzyme-responsive, with an emphasis on cancer treatment. In addition, the potential of Fe2O3 to combine diagnosis and therapy within a single particle called theranostic agent will be discussed.

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.

Quantum dot biosensor combined with antibody and aptamer for tracing food-borne pathogens

Due to the increasing number of food-borne diseases, more attention is being paid to food safety. Food-borne pathogens are the main cause of food-borne diseases, which seriously endanger human health, so it is necessary to detect and control them. Traditional detection methods cannot meet the requirements of rapid detection of food due to many shortcomings, such as being time-consuming, laborious or requiring expensive instrumentation. Quantum dots have become a promising nanotechnology in pathogens tracking and detection because of their excellent optical properties. New biosensor detection methods based on quantum dots are have been gradually developed due to their high sensitivity and high specificity. In this review, we summarize the different characteristics of quantum dots synthesized by carbon, heavy metals and composite materials firstly. Then, attention is paid to the principles, advantages and limitations of the quantum dots biosensor with antibodies and aptamers as recognition elements for recognition and capture of food-borne pathogens. Finally, the great potential of quantum dots in pathogen detection is summarized.

Recent advancement in nano-optical strategies for detection of pathogenic bacteria and their metabolites in food safety

Pathogenic bacteria and their metabolites are the leading risk factor in food safety and are one of the major threats to human health because of the capability of triggering diseases with high morbidity and mortality. Nano-optical sensors for bacteria sensing have been greatly explored with the emergence of nanotechnology and artificial intelligence. In addition, with the rapid development of cross fusion technology, other technologies integrated nano-optical sensors show great potential in bacterial and their metabolites sensing. This review focus on nano-optical strategies for bacteria and their metabolites sensing in the field of food safety; based on surface-enhanced Raman scattering (SERS), fluorescence, and colorimetric biosensors, and their integration with the microfluidic platform, electrochemical platform, and nucleic acid amplification platform in the recent three years. Compared with the traditional techniques, nano optical-based sensors have greatly improved the sensitivity with reduced detection time and cost. However, challenges remain for the simple fabrication of biosensors and their practical application in complex matrices. Thus, bringing out improvements or novelty in the pretreatment methods will be a trend in the upcoming future.

Aptamers: An Emerging Tool for Diagnosis and Therapeutics in Tuberculosis

Tuberculosis (TB) has been plaguing human civilization for centuries, and currently around one-third of the global population is affected with TB. Development of novel intervention tools for early diagnosis and therapeutics against Mycobacterium tuberculosis (M.tb) is the main thrust area in today's scenario. In this direction global efforts were made to use aptamers, the chemical antibodies as tool for TB diagnostics and therapeutics. This review describes the various aptamers introduced for targeting M.tb and highlights the need for development of novel aptamers to selectively target virulent proteins of M.tb for vaccine and anti-TB drugs. The objective of this review is to highlight the diagnostic and therapeutic application of aptamers used for tuberculosis. The discovery of aptamers, SELEX technology, different types of SELEX development processes, DNA and RNA aptamers reported for diseases and pathogenic agents as well have also been described in detail. But the emphasis of this review is on the development of aptamers which can block the function of virulent mycobacterial components for developing newer TB vaccine candidates and/or drug targets. Aptamers designed to target M.tb cell wall proteins, virulent factors, secretory proteins, or combination could orchestrate advanced diagnosis and therapeutic measures for tuberculosis.

Size-dependent optical extinction of MoS2 nanosheets and their aptamer-induced dispersion behavior for the label-free detection of Escherichia coli O157:H7

For aptamer-modified nanomaterial biosensors label-free detection methods are desirable due to them being simple and low in cost. Among these methods, nanomaterial aggregation for signal conversion is common, using materials such as gold nanoparticles. However, for MoS2 nanosheets (MoS2-NSs), signal conversion of its aggregation is difficult, resulting in the limited development of its label-free sensing applications. Herein, for the first time, the extinction spectrum has been employed to quickly transform the signal of MoS2-NS aggregation and reveal the size-dependent extinction response of MoS2-NS aggregation. Moreover, the size-dependent optical extinction behavior of MoS2-NSs, using aptamers to induce the dispersion of the MoS2-NSs and greatly improve their ability to identify targets, is studied. Importantly, this method has been employed to achieve the label-free detection of Escherichia coli O157:H7. The present investigation shows the promising use of MoS2-NSs for the development of label-free detection.

Size-Resolved Single Entity Collision Biosensing for Dual Quantification of MicroRNAs in a Single Run

Limited to the accuracy of size resolution, single entity collision biosensing (SECBS) for multiplex immunoassays remains challenging, because it is difficult to get the true value of nanoparticle (NP) sizes based on the current intensity due to the complex movement of NPs on the electrode surface. Considering that the size-dependent movement of NPs meanwhile will generate a characteristic current shape, in this work, the huge difference in the current rise time of 5 and 15 nm Pt NPs colliding on an Au ultramicroelectrode (d = 30 μm) was originally used to develop a size-resolved SECBS for multiplex immunoassays of miRNAs. The limit concentration that can be detected was 0.5 fM. Compared with conventional electrochemical biosensors for multiplex immunoassays, for the size-resolved SECBS, one does not need to worry about potential overlapping. Therefore, the proposed method demonstrates a promising potential for the application of SECBS in multiplex immunoassays.

Combining Inducible Lectin Expression and Magnetic Glyconanoparticles for the Selective Isolation of Bacteria from Mixed Populations

The selective isolation of bacteria from mixed populations has been investigated in varied applications ranging from differential pathogen identification in medical diagnostics and food safety to the monitoring of microbial stress dynamics in industrial bioreactors. Selective isolation techniques are generally limited to the confinement of small populations in defined locations, may be unable to target specific bacteria, or rely on immunomagnetic separation, which is not universally applicable. In this proof-of-concept work, we describe a novel strategy combining inducible bacterial lectin expression with magnetic glyconanoparticles (MGNPs) as a platform technology to enable selective bacterial isolation from cocultures. An inducible mutant of the type 1 fimbriae, displaying the mannose-specific lectin FimH, was constructed in Escherichia coli allowing for "on-demand" glycan-binding protein presentation following external chemical stimulation. Binding to glycopolymers was only observed upon fimbrial induction and was specific for mannosylated materials. A library of MGNPs was produced via the grafting of well-defined catechol-terminal glycopolymers prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization to magnetic nanoparticles. Thermal analysis revealed high functionalization (≥85% polymer by weight). Delivery of MGNPs to cocultures of fluorescently labeled bacteria followed by magnetic extraction resulted in efficient depletion of type 1 fimbriated target cells from wild-type or afimbriate E. coli. Extraction efficiency was found to be dependent on the molecular weight of the glycopolymers utilized to engineer the nanoparticles, with MGNPs decorated with shorter Dopa-(ManAA)₅₀ mannosylated glycopolymers found to perform better than those assembled from a longer Dopa-(ManAA)₂₀₀ analogue. The extraction efficiency of fimbriated E. coli was also improved when the counterpart strain did not harbor the genetic apparatus for the expression of the type 1 fimbriae. Overall, this work suggests that the modulation of the genetic apparatus encoding bacterial surface-associated lectins coupled with capture through MGNPs could be a versatile tool for the extraction of bacteria from mixed populations.

Recent Advances in Aptamer-Based Biosensors for Global Health Applications

Since aptamers were first reported in the early 2000s, research on their use for the detection of health-relevant analytical targets has exploded. This review article provides a brief overview of the most recent developments in the field of aptamer-based biosensors for global health applications. The review provides a description of general aptasensing principles and follows up with examples of recent reports of diagnostics-related applications. These applications include detection of proteins and small molecules, circulating cancer cells, whole-cell pathogens, extracellular vesicles, and tissue diagnostics. The review also discusses the main challenges that this growing technology faces in the quest of bringing these new devices from the laboratory to the market.

Recent advances on aptamer-based biosensors for detection of pathogenic bacteria

As a significant constituent in biosphere, bacteria have a great influence on human activity. The detection of pathogen bacteria is closely related to the human health. However, the traditional methods for detection of pathogenic bacteria are time-consuming and difficult for quantification, although they are practical and reliable. Therefore, novel strategies for rapid, sensitive, and cost-effective detection are in great demand. Aptamer is a kind of oligonucleotide that selected by repeated screening in vitro or systematic evolution of ligands by exponential enrichment (SELEX) technology. Over the past years, owing to high affinity and specificity of aptamers, a variety of aptamer-based biosensors have been designed and applied for pathogen detection. In this review, we have discussed the recent advances on the applications of aptamer-based biosensors in detection of pathogenic bacteria. In addition, we also point out some problems in current methods and look forward to the further development of aptamer-based biosensors for pathogen detection.

Recent advances in functionalized nanomaterials for the diagnosis and treatment of bacterial infections

The growing problem of resistant infections due to antibiotic misuse is a worldwide concern that poses a grave threat to healthcare systems. Thus, it is necessary to discover new strategies to combat infectious diseases. In this review, we provide a selective overview of recent advances in the use of nanocomposites as alternatives to antibiotics in antimicrobial treatments. Metals and metal oxide nanoparticles (NPs) have been associated with inorganic and organic supports to improve their antibacterial activity and stability as well as other properties. For successful antibiotic treatment, it is critical to achieve a high drug concentration at the infection site. In recent years, the development of stimuli-responsive systems has allowed the vectorization of antibiotics to the site of infection. These nanomaterials can be triggered by various mechanisms (such as changes in pH, light, magnetic fields, and the presence of bacterial enzymes); additionally, they can improve antibacterial efficacy and reduce side effects and microbial resistance. To this end, various types of modified polymers, lipids, and inorganic components (such as metals, silica, and graphene) have been developed. Applications of these nanocomposites in diverse fields ranging from food packaging, environment, and biomedical antimicrobial treatments to diagnosis and theranosis are discussed.

Advances in detection of infectious agents by aptamer-based technologies

Infectious diseases still remain one of the biggest challenges for human health. Accurate and early detection of infectious pathogens are crucial for transmission control, clinical diagnosis, and therapy. For a traditional reason, most immunological and microbiological laboratories are equipped with instruments designated for antibody-based assays in detection of infectious pathogens or clinical diagnosis. Emerging aptamer-based technologies have pushed a shift from antibody-based to aptamer-based assays due to equal specificity, even better sensitivity, lower manufacturing cost and more flexibility in amending for chemiluminescent, electrochemical or fluorescent detection in a multifaceted and high throughput fashion in comparison of aptamer-based to antibody-based assays. The nature of aptamer-based technologies is particularly suitable for point-of-care testing in remote areas at warm or hot atmosphere, and mass screening for potential infection in pandemic of emerging infectious agents, such as SARS-CoV or SARS-CoV-2 in an epicentre or other regions. This review intends to summarize currently available aptamer-based technologies in detection of bacterial, viral, and protozoan pathogens for research and clinical application. It is anticipated that potential technologies will be further optimized and validated for clinical translation in meeting increasing demands for prompt, precise, and reliable detection of specific pathogens in various atmospheric conditions.

Biosensors for rapid detection of Salmonella in food: A review

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

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

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

Recent advances on functional nucleic acid-based biosensors for detection of food contaminants

It has seen increasing development of reliable, robust, and flexible biosensors for rapid food-safety analysis in the past few decades. Recently, functional nucleic acid-based biosensors have attracted attention because of their programmability, bottom-up characteristics, and structural switches. However, few systematic reviews devoted to categorizing the potential of DNA nanostructures and devices were found for detecting food contaminants. Hence, the applications of functional nucleic acid-based biosensors were reviewed for analyzing food contaminants, including foodborne pathogen bacteria, biotoxins, heavy metals, and et al. In addition to categorizing the various biosensors, multiple signal readout strategies, such as optical, electrochemical, and mass-based signals were also examined. Finally, the future changes and potential opportunities, as well as practical applications of functional nucleic acid-based biosensors were discussed.

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

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

A transcription aptasensor: amplified, label-free and culture-independent detection of foodborne pathogens via light-up RNA aptamers

We report a transcription aptasensor by using a light-up RNA aptamer. It allows for sensitive, label-free and culture-free detection of intact foodborne pathogens, and no separation, purification or enrichment processes are involved.

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.

Research advances of DNA aptasensors for foodborne pathogen detection

Aptamers, referring to single-stranded DNA or RNA molecules can specifically recognize and bind to their targets. Based on their excellent specificity, sensitivity, high affinity, and simplicity of modification, aptamers offer great potential for pathogen detection and biomolecular screening. This article reviews aptamer screening technologies and aptamer application technologies, including gold-nanoparticle lateral flow assays, fluorescence assays, electrochemical assays, colorimetric assays, and surface-enhanced Raman assays, in the detection of foodborne pathogens. Although notable progress (more rapid, sensitive, and accurate) has been achieved in the field, challenges and drawbacks in their applications still remain to be overcome.

Highly sensitive glutathione assay and intracellular imaging with functionalized semiconductor quantum dots

Glutathione (GSH) plays a vital role in biological systems and is associated with human pathology. The engineering of semiconductor quantum dots (QDs) as fluorescent probes for GSH sensing and bioimaging is a potential yet rarely reported approach. Herein, we report the in situ growth of manganese dioxide nanosheets (MnO2) on silica-coated semiconductor quantum dots (QD@SiO2), to prepare a stable and biocompatible fluorescent nanoprobe (QD@SiO2-MnO2) for the selective and sensitive detection of GSH. The modification of QD@SiO2 with MnO2 significantly quenched the fluorescence of CdSe/ZnS QDs, yet the addition of GSH efficiently recovered the fluorescence of the nanoprobe due to the decomposition of MnO2 by GSH. This nanosensor showed a rapid response to GSH with a low detection limit, and high selectivity towards GSH over potential interferences. Furthermore, the MnO2-engineered QDs had good biocompatibility and cellular uptake ability, and were successfully applied for the real-time imaging of intracellular GSH. We envision that semiconductor QD-based probes will stimulate the study of GSH dynamics and facilitate the understanding of GSH-related pathophysiological events.

Point-of-Care Testing of Pathogenic Bacteria at the Single-Colony Level via Gas Pressure Readout Using Aptamer-Coated Magnetic CuFe2O4 and Vancomycin-Capped Platinum Nanoparticles

Pressure measurements are performed everyday with simple devices, and in the field of analytical chemistry the pressure-based signaling strategy offers two important advantages, signal amplification and particular applicability in point-of-care settings. Herein, by using vancomycin (Van)-functionalized platinum nanoparticles (PtNPs@Van) and aptamer-coated magnetic CuFe₂O₄ nanoprobes dual-recognition units integrated with a catalyzed breakdown of H₂O₂ for O₂ generation, we demonstrated that gas pressure can be used as a readout means for highly sensitive pathogenic bacteria identification and quantification. Using Staphylococcus aureus ( S. aureus) as a test case, integration of the molecular dual-recognition component with the catalyzed gas-generation reaction leads to a significant pressure change (Δ P), and the correlation between the concentration of S. aureus and the Δ P signal was found to be linear from 5.0 to 1.0 × 10⁴ cfu/mL with a detection limit of 1.0 cfu/mL. Other nontarget bacteria show negative results, verifying the high specificity of the present strategy. When employed to assay S. aureus in saliva and milk samples, the approach shows recoveries from 93.3% to 107.1% with relative standard derivation (RSD) less than 8.8%. By the integration of catalyzed gas-generation reaction with the designed molecular recognition event, obviously the pressure-based signaling strategy could facilitate pathogenic bacteria identification and quantification not only in the laboratory but also in point-of-care settings, which could have great potential in the application of food safety and infectious disease diagnosis.

Robust and highly specific fluorescence sensing of Salmonella typhimurium based on dual-functional phi29 DNA polymerase-mediated isothermal circular strand displacement polymerization

A simple and robust fluorescence sensing strategy has been developed for the detection of pathogenic bacteria by the combination of the dual functionality of phi29 DNA polymerase with isothermal circular strand displacement polymerization (ICSDP).

A novel electrochemical aptasensor based on nontarget-induced high accumulation of methylene blue on the surface of electrode for sensing of α-synuclein oligomer

This study describes a novel electrochemical aptasensor for detection of α-synuclein (α-syn) oligomer, an important biomarker related to Parkinson's and Alzheimer's diseases. The sensing platform is based on exonuclease I (Exo I), terminal deoxynucleotidyl transferase (TdT) and methylene blue. The aptasensor exploits the improved sensitivity because of applications of TdT and Exo I and also a label-free aptamer (Apt). Furthermore, direct immobilization of complementary strand of aptamer (CS) instead of Apt on the surface of electrode prohibits Apt self-assembled monolayer aggregation and keeps the function of the Apt. In the absence of α-syn oligomer, TdT enhances lengths of Apt and CS and so, increases accumulation of methylene blue as redox agent on the surface of electrode, leading to a strong current signal. While in the presence of α-syn oligomer, Exo I digests CS on the electrode surface, resulting in less accumulation of methylene blue on the electrode surface and a weak current signal. The relative electrochemical signal of the aptasensor increased linearly with the logarithm of α-syn oligomer concentration in the range from 60 pM to 150 nM. The detection limit was 10 pM. Furthermore, the sensor showed high precision and repeatability for detection of α-syn oligomer in serum samples.