Aptamer-Based Biosensor for Detection of Mycotoxins

Peanuts (Arachis hypogaea L.) and Mycotoxins: Analytical Approaches, Prevalence, and Innovative Detoxification

Mycotoxins are secondary metabolites originating from several species of fungi that have proven to demonstrate high toxicity. In addition, potential contamination sources can promote increased human exposure to the adverse effects of these toxins. For this reason, it was necessary to develop several analytical methods that allow detection with the highest possible sensitivity for these toxic metabolites. Furthermore, since these methods involve high cost, are lengthy, and have sensitivity requirements, the development of multi-analyte detection methods is indispensable. The increasing consumption of groundnuts (legumes) as well as nuts (such as almonds, walnuts, and pistachios) and dried fruit (raisins and dried figs) has increased the risk of poisoning and the harmful effects of mycotoxins, which has encouraged studies for the creation of these methods. This review addresses the most representative methods applied to analyze and quantify mycotoxins in groundnuts (peanuts) together with decontamination techniques. The methodologies presented in this review are primarily based on analytical techniques for nuts and dried fruits. However, each of these methodologies can also be applied to peanut analysis for comparison and use. It is also relevant to highlight the importance of the development of multi-analyte methods in order to identify multiple mycotoxins using a single method, saving time, costs, and resources.

A CRISPR/Cas12a-based competitive aptasensor for ochratoxin A detection

The serious contamination of ochratoxin A (OTA) in agricultural products has promoted the development of rapid, sensitive, and selective analytical methods for OTA monitoring. We demonstrated a competitive aptasensor for OTA detection using CRISPR/Cas12a as an effective signal amplifier. OTA competes with complementary DNA of the aptamer on the microplate to bind to the aptamer. Streptavidin bridges the biotinylated aptamer and biotinylated activator to convert the OTA input into Cas12a activation, which cleaves fluorescent DNA reporters. Under optimized experimental conditions, the aptasensor was demonstrated to work well for sensitive detection of OTA, with a linear range from 0.5 nM to 62.5 nM and a detection limit of 0.5 nM. Moreover, our method not only exhibits high selectivity, but also has satisfactory anti-interference ability against complex sample matrices. Taken together, the CRISPR/Cas12a-based competitive aptasensor offers a simple and sensitive platform for OTA detection, and it holds great promise for food security monitoring.

Core-Satellite Gold Nanoparticle@Silver Nanocluster Nanohybrids for Milk Allergen β-Lactoglobulin Detection Using the Electrochemical Aptasensor

Detecting β-lactoglobulin (β-Lg) with high sensitivity and selectivity is an urgent requirement due to nearly 80% of milk anaphylaxis, such as respiratory tract, skin urticaria, and gastrointestinal disorders, being caused by β-Lg. An ultrasensitive β-Lg electrochemical aptasensor utilizing core-satellite gold nanoparticle@silver nanocluster (AuNPs@AgNCs) nanohybrids as electrocatalysts was developed. First, β-Lg aptamer was anchored on gold electrodes and AuNPs to obtain high selectivity. Aptamer-cDNA-AuNPs conjugation was attached to the functionalized electrode with β-Lg as a "bridge" through the target-ligand interaction. Second, DNA-templated AgNCs were introduced via the hybridization of DNA templates oligonucleotide with cDNA anchored on AuNPs. The formed AuNPs@AgNCs nanohybrids showed enhanced catalytic performance toward the silver deposition reaction. This strategy is demonstrated by determining the oxidation current of produced silver nanoparticles (AgNPs) surrounding AuNPs by β-Lg. A detection limit of 0.87 fg/mL and a linear range of 0.001-1000 pg/mL were obtained. Finally, β-Lg content in food products was analyzed successfully, and RSD of 2.44-8.33% was obtained. The recovery of 87.54-113.70% and RSD of 0.95-9.29% was obtained for standard addition experiments. This proposed aptasensor exhibits excellent sensitivity, selectivity, reproducibility, and stability and has good practical application capability for complex food matrices.

Single-Walled Carbon Nanotubes as Optical Transducers for Nanobiosensors In Vivo

Semiconducting single-walled carbon nanotubes (SWCNTs) may serve as signal transducers for nanobiosensors. Recent studies have developed innovative methods of engineering molecularly specific sensors, while others have devised methods of deploying such sensors within live animals and plants. These advances may potentiate the use of implantable, noninvasive biosensors for continuous drug, disease, and contaminant monitoring based on the optical properties of single-walled carbon nanotubes (SWCNTs). Such tools have substantial potential to improve disease diagnostics, prognosis, drug safety, therapeutic response, and patient compliance. Outside of clinical applications, such sensors also have substantial potential in environmental monitoring or as research tools in the lab. However, substantial work remains to be done to realize these goals through further advances in materials science and engineering. Here, we review the current landscape of quantitative SWCNT-based optical biosensors that have been deployed in living plants and animals. Specifically, we focused this review on methods that have been developed to deploy SWCNT-based sensors in vivo as well as analytes that have been detected by SWCNTs in vivo. Finally, we evaluated potential future directions to take advantage of the promise outlined here toward field-deployable or implantable use in patients.

Detection of zearalenone in miscellaneous beans by functionalized SERS sensor based on sea urchin aptamer

In this work, a sea urchin gold nanoparticles-zearalenone aptamer- tetramethylrhodamine sensor was constructed. Sea urchin gold nanoparticles, prepared using the seed-mediated growth method, were used as Raman substrates. Nucleic acid aptamers were mainly used as specific recognition molecules. Zearalenone detection in miscellaneous beans was accomplished using the principle of conformational change in aptamer. In addition, we evaluated the linear range, sensitivity, and selectivity of our sensor. We observed that at the displacement of 814 cm-1, for Zearalenone concentrations of 0.01-60 ng/mL, the Raman signal intensity linearly correlated with the zearalenone concentration, with a limit of detection of 0.01 ng/mL, and recoveries of 91.7% to 108.3%. The optimum detection time was 30 min. Thus, our sensor exhibited great potential in zearalenone detection in food products.

A Surface-Enhanced Raman Spectroscopy-Based Aptasensor for the Detection of Deoxynivalenol and T-2 Mycotoxins

The quality of food is one of the emergent points worldwide. Many microorganisms produce toxins that are harmful for human and animal health. In particular, mycotoxins from Fusarium fungi are strictly controlled in cereals. Simple and robust biosensors are necessary for 'in field' control of the crops and processed products. Nucleic acid-based sensors (aptasensors) offer a new era of point-of-care devices with excellent stability and limits of detection for a variety of analytes. Here we report the development of a surface-enhanced Raman spectroscopy (SERS)-based aptasensor for the detection of T-2 and deoxynivalenol in wheat grains. The aptasensor was able to detect as low as 0.17% of pathogen fungi in the wheat grains. The portable devices, inexpensive SERS substrate, and short analysis time encourage further implementation of the aptasensors outside of highly equipped laboratories.

Recent progress on field-effect transistor-based biosensors: device perspective

Over the last few decades, field-effect transistor (FET)-based biosensors have demonstrated great potential across various industries, including medical, food, agriculture, environmental, and military sectors. These biosensors leverage the electrical properties of transistors to detect a wide range of biomolecules, such as proteins, DNA, and antibodies. This article presents a comprehensive review of advancements in the architectures of FET-based biosensors aiming to enhance device performance in terms of sensitivity, detection time, and selectivity. The review encompasses an overview of emerging FET-based biosensors and useful guidelines to reach the best device dimensions, favorable design, and realization of FET-based biosensors. Consequently, it furnishes researchers with a detailed perspective on design considerations and applications for future generations of FET-based biosensors. Finally, this article proposes intriguing avenues for further research on the topology of FET-based biosensors.

Construction of UCNPs-aptamer-AuNPs luminescence energy transfer probe for ratio detection of Staphylococcus aureus

A ratio luminescence probe was developed for detecting Staphylococcus aureus (S. aureus) based on luminescence energy transfer (LET) using double-wavelength emission (550 nm and 812 nm) upconversion nanoparticles (UCNPs) as donor, gold nanoparticles (AuNPs) as acceptor and the aptamer for S. aureus as the specific recognition and link unit. The LET process could cause luminescence quenching because of the spectral overlap between the acceptor and the donor at 550 nm. In the presence of S. aureus, S. aureus selectively combined with the aptamer, and the AuNPs left the surface of UCNPs, which weakened the quenching effect and restored the luminescence of UCNPs. Based on this, the ratio detection was realized by monitoring the change of the luminescence signal of the probe at 550 nm and taking the luminescence signal at 812 nm as the reference signal. Crucially, the probe has a fast reaction speed, with a reaction time of 25 min, and the detection of S. aureus is realized in the concentration range of 5.0 × 103-3.0 × 105 CFU/ml, with the detection limit of 106 CFU/ml. Therefore, the ratio probe has great potential for detecting of S. aureus in food because of its high sensitivity, fast speed and good selectivity.

Colorimetric detection of the potent carcinogen aflatoxin B1 based on the aggregation of L-lysine-functionalized gold nanoparticles in the presence of copper ions

L-lysine functionalized gold nanoparticles (AuNPs-Lys) have been widely used for the detection of worldwide interest analytes. In this work, a colorimetric assay for the detection of the carcinogen aflatoxin B1 (AFB1) based on the aggregation of AuNPs-Lys in the presence of copper ions was developed. For this purpose, AuNPs were synthesized in citrate aqueous solution, functionalized, and further characterized by UV-Vis, fluorescence, Fourier transform infrared spectroscopy (FTIR), nanoparticle tracking analysis (NTA), dynamic light scattering (DLS), and transmission electron microscopy (TEM). In general, AuNPS-Lys (~2.73 × 1011 particles) offered a clear colorimetric response in the presence of AFB1 and Cu2+ ions showing linearity in the range of 6.25 to 200 ng AFB1/mL, with a detection limit of 4.18 ng AFB1/mL via photometric inspection. Moreover, the performance of the proposed methodology was tested using the 991.31 AOAC official procedure based on monoclonal antibodies in maize samples artificially contaminated with AFB1. There was a good agreement between the measured AFB1 concentrations in both assays, the average recoveries for the colorimetric and immunoaffinity assays were between 91.2-98.4% and 96.0-99.2%, respectively. These results indicated that the colorimetric assay could be used as a rapid, eco-friendly, and cost-effective platform for the quantification of AFB1 in maize-based products.

Progress on Electrochemical Biomimetic Nanosensors for the Detection and Monitoring of Mycotoxins and Pesticides

Monitoring agricultural toxins such as mycotoxins is crucial for a healthy society. High concentrations of these toxins lead to the cause of several chronic diseases; therefore, developing analytical systems for detecting/monitoring agricultural toxins is essential. These toxins are found in crops such as vegetables, fruits, food, and beverage products. Currently, screening of these toxins is mostly performed with sophisticated instrumentation such as chromatography and spectroscopy techniques. However, these techniques are very expensive and require extensive maintenance, and their availability is limited to metro cities only. Alternatively, electrochemical biomimetic sensing methodologies have progressed hugely during the last decade due to their unique advantages like point-of-care sensing, miniaturized instrumentations, and mobile/personalized monitoring systems. Specifically, affinity-based sensing strategies including immunosensors, aptasensors, and molecular imprinted polymers offer tremendous sensitivity, selectivity, and stability to the sensing system. The current review discusses the principal mechanisms and the recent developments in affinity-based sensing methodologies for the detection and continuous monitoring of mycotoxins and pesticides. The core discussion has mainly focused on the fabrication protocols, advantages, and disadvantages of affinity-based sensing systems and different exploited electrochemical transduction techniques.

Virtual screening and site-directed mutagenesis-derived aptamers for precise Salmonella typhimurium prediction: emphasizing OmpD targeting and G-quadruplex stability

The efficient detection of the foodborne pathogen Salmonella typhimurium has historically been hampered by the constraints of traditional methods, characterized by protracted culture periods and intricate DNA extraction processes for PCR. To address this, our research innovatively focuses on the crucial and relatively uncharted virulence factor, the Outer Membrane Protein D (OmpD) in Salmonella typhimurium. By harmoniously integrating the power of virtual screening and site-directed mutagenesis, we unveiled aptamers exhibiting marked specificity for OmpD. Among these, aptamer 7ZQS stands out with its heightened binding affinity. Capitalizing on this foundation, we further engineered a repertoire of mutant aptamers, wherein APT6 distinguished itself, reflecting unmatched stability and specificity. Our rigorous validation, underpinned by cutting-edge bioinformatics tools, amplifies the prowess of APT6 in discerning and binding OmpD across an array of Salmonella typhimurium strains. This study illuminates a transformative approach to the prompt and accurate detection of Salmonella typhimurium, potentially redefining boundaries in applied analytical chemistry and bolstering diagnostic precision across diverse research and clinical domains.

Multidimensional Applications and Challenges of Riboswitches in Biosensing and Biotherapy

Riboswitches have received significant attention over the last two decades for their multiple functionalities and great potential for applications in various fields. This article highlights and reviews the recent advances in biosensing and biotherapy. These fields involve a wide range of applications, such as food safety detection, environmental monitoring, metabolic engineering, live cell imaging, wearable biosensors, antibacterial drug targets, and gene therapy. The discovery, origin, and optimization of riboswitches are summarized to help readers better understand their multidimensional applications. Finally, this review discusses the multidimensional challenges and development of riboswitches in order to further expand their potential for novel applications.

Microfluidic advances in food safety control

Food contamination is a global concern, particularly in developing countries. Two main types of food contaminants-chemical and biological-are common problems that threaten human health. Therefore, rapid and accurate detection methods are required to address the threat of food contamination. Conventional methods employed to detect these two types of food contaminants have several limitations, including high costs and long analysis time. Alternatively, microfluidic technology, which allows for simple, rapid, and on-site testing, can enable us to control food safety in a timely, cost-effective, simple, and accurate manner. This review summarizes advances in microfluidic approaches to detect contaminants in food. Different detection methods have been applied to microfluidic platforms to identify two main types of contaminants: chemical and biological. For chemical contaminant control, the application of microfluidic approaches for detecting heavy metals, pesticides, antibiotic residues, and other contaminants in food samples is reviewed. Different methods including enzymatic, chemical-based, immunoassay-based, molecular-based, and electrochemical methods for chemical contaminant detection are discussed based on their working principle, the integration in microfluidic platforms, advantages, and limitations. Microfluidic approaches for foodborne pathogen detection, from sample preparation to final detection, are reviewed to identify foodborne pathogens. Common methods for foodborne pathogens screening, namely immunoassay, nucleic acid amplification methods, and other methods are listed and discussed; highlighted examples of recent studies are also reviewed. Challenges and future trends that could be employed in microfluidic design and fabrication process to address the existing limitations for food safety control are also covered. Microfluidic technology is a promising tool for food safety control with high efficiency and applicability. Miniaturization, portability, low cost, and samples and reagents saving make microfluidic devices an ideal choice for on-site detection, especially in low-resource areas. Despite many advantages of microfluidic technology, the wide manufacturing of microfluidic devices still demands intensive studies to be conducted for user-friendly and accurate food safety control. Introduction of recent advances of microfluidic devices will build a comprehensive understanding of the technology and offer comparative analysis for future studies and on-site application.

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.

Current Trends in Mycotoxin Detection with Various Types of Biosensors

One of the most important tasks in food safety is to properly manage the investigation of mycotoxin contamination in agricultural products and foods made from them, as well as to prevent its occurrence. Monitoring requires a wide range of analytical methods, from expensive analytical procedures with high-tech instrumentation to significantly cheaper biosensor developments or even single-use assays suitable for on-site monitoring. This review provides a summary of the development directions over approximately a decade and a half, grouped according to the biologically sensitive components used. We provide an overview of the use of antibodies, molecularly imprinted polymers, and aptamers, as well as the diversity of biosensors and their applications within the food industry. We also mention the possibility of determining multiple toxins side by side, which would significantly reduce the time required for the analyses.

Aptamer-based technology for detecting Bacillus subtilis in soil

The uncertainty associated with the impact of a bioinoculant on soil microbial community and, as a consequence, on soil quality, as well as the need to define its persistence, has prompted the demand for an accurate detection and tracking of the presence and the quantification of a target microbial inoculant in soil. Although DNA or RNA-based molecular detection are well established and commonly applied in this regard, alternative ligands such as DNA-aptamers have several advantages over them, such as low cost, ease of modification, ease of immobilisation on lab-on-chip or nanosensors, high stability and not thermolability. In this study, we used a toggle-cell SELEX method to isolate, select and characterise ssDNA (single-strand DNA) aptamers to detect a Bacillus subtilis strain which is being tested as a plant growth promoting rhizobacteria (PGPR) formulation. Two ssDNA aptamers (patenting application n.102022000022590) showed strong affinity and specificity for B. subtilis strains, with values of the kinetic parameters Kd (dissociation constant) in the nanomolar range and Bmax (maximum intensity of binding) around 1. Validation of the suitability of the aptamers was validated on three inoculated soils characterised by different chemical-physical features and in soil from a field trial with the formulated B. subtilis PCM/B 00105 strain. These are considered significant features to monitor B. subtilis strains in soil, practical to optimise bioinoculant application methods, support regulatory processes and foster the shift of agricultural production toward more sustainable cropping systems. KEY POINTS: • First DNA aptamers binding a B. subtilis strain included in a bioinoculum formulation. • First DNA aptamer binding B. subtilis in soil. • Aptamer may be a method for microbial inoculant detection in soil.

Cytoplasm Hydrogelation-Mediated Cardiomyocyte Sponge Alleviated Coxsackievirus B3 Infection

Viral myocarditis (VMC), commonly caused by coxsackievirus B3 (CVB3) infection, lacks specific treatments and leads to serious heart conditions. Current treatments, such as IFNα and ribavirin, show limited effectiveness. Herein, rather than inhibiting virus replication, this study introduces a novel cardiomyocyte sponge, intracellular gelated cardiomyocytes (GCs), to trap and neutralize CVB3 via a receptor-ligand interaction, such as CAR and CD55. By maintaining cellular morphology, GCs serve as sponges for CVB3, inhibiting infection. In vitro results revealed that GCs could inhibit CVB3 infection on HeLa cells. In vivo, GCs exhibited a strong immune escape ability and effectively inhibited CVB3-induced viral myocarditis with a high safety profile. The most significant implication of this study is to develop a universal antivirus infection strategy via intracellular gelation of the host cell, which can be employed not only for treating defined pathogenic viruses but also for a rapid response to infection outbreaks caused by mutable and unknown viruses.

Recent progress in optical and electrochemical aptasensor technologies for detection of aflatoxin B1

AFB1 (Aflatoxin B1) contamination is becoming a global concern issue due to its extraordinary occurrence, severe toxicity, as well as the great influence on the economic losses, food safety and environment. Therefore, it is desirable to develop novel analytical techniques for simple, rapid, accurate, and even point-of-care testing of AFB1. Fortunately, aptamer, considered as a new generation bioreceptor and even superior to classic antibody and enzyme, has been emerged remarkable application in food hazards detection. Correspondingly, aptasensors have been well-established toward AFB1 determination with outstanding performance. In this article, we first discuss and summarize the recent progress in optical and electrochemical aptasensors to monitor AFB1 over the past three years. In particular, the embedding of advanced nanomaterials for their improved analytical performance is highlighted. Furthermore, the critical analysis on various signal transduction strategies for aptasensors construction is discussed. Finally, we reveal the challenges and provide our opinion in future opportunities for aptasensor development.

Applications and Tuning Strategies for Transcription Factor-Based Metabolite Biosensors

Transcription factor (TF)-based biosensors are widely used for the detection of metabolites and the regulation of cellular pathways in response to metabolites. Several challenges hinder the direct application of TF-based sensors to new hosts or metabolic pathways, which often requires extensive tuning to achieve the optimal performance. These tuning strategies can involve transcriptional or translational control depending on the parameter of interest. In this review, we highlight recent strategies for engineering TF-based biosensors to obtain the desired performance and discuss additional design considerations that may influence a biosensor's performance. We also examine applications of these sensors and suggest important areas for further work to continue the advancement of small-molecule biosensors.

Advanced biosensors for mycotoxin detection incorporating miniaturized meters

Advanced biosensors, considered as emerging technologies, are capable of accurate, quantitative and real-time analysis for point-of-care testing (POCT) applications. Moreover, the integrating of miniaturized meters into these advanced biosensors makes them ideally appropriate for portable, sensitive and selective detection of biomolecules. Miniaturized meters including PGMs (personal glucose meters), thermometer, pressuremeter, pH meter, etc. are the most accurate devices and wide availability in the market, exhibiting a promising potential towards detection of small molecule mycotoxins. In this article, we introduce and analyze the recent advancements for sensing of mycotoxins measured by handheld meters since the first report in 2012. Furthermore, limitations and challenges for versatile meters application against mycotoxins in food matrix are highlighted. By overcoming the bottleneck problems, we believe the miniaturized meters-based biosensor platform will provide great possibilities for mycotoxins analysis and launch them to the market.

Aptamer-based rapid diagnosis for point-of-care application

Aptasensors have attracted considerable interest and widespread application in point-of-care testing worldwide. One of the biggest challenges of a point-of-care (POC) is the reduction of treatment time compared to central facilities that diagnose and monitor the applications. Over the past decades, biosensors have been introduced that offer more reliable, cost-effective, and accurate detection methods. Aptamer-based biosensors have unprecedented advantages over biosensors that use natural receptors such as antibodies and enzymes. In the current epidemic, point-of-care testing (POCT) is advantageous because it is easy to use, more accessible, faster to detect, and has high accuracy and sensitivity, reducing the burden of testing on healthcare systems. POCT is beneficial for daily epidemic control as well as early detection and treatment. This review provides detailed information on the various design strategies and virus detection methods using aptamer-based sensors. In addition, we discussed the importance of different aptamers and their detection principles. Aptasensors with higher sensitivity, specificity, and flexibility are critically discussed to establish simple, cost-effective, and rapid detection methods. POC-based aptasensors' diagnostic applications are classified and summarised based on infectious and infectious diseases. Finally, the design factors to be considered are outlined to meet the future of rapid POC-based sensors.

A Novel and Label-Free Chemiluminescence Detection of Zearalenone Based on a Truncated Aptamer Conjugated with a G-Quadruplex DNAzyme

Zearalenone (ZEN), one of the most frequently occurring mycotoxin contaminants in foods and feeds, poses considerable threat to human and animal health, owing to its acute and chronic toxicities. Thus, rapid and accurate detection of ZEN has attracted broad research interest. In this work, a novel and label-free chemiluminescence aptasensor based on a ZEN aptamer and a G-quadruplex DNAzyme was constructed. It was established on a competitive assay between ZEN and an auxiliary DNA for the aptamer, leading to activation of the G-quadruplex/hemin DNAzyme and subsequent signal amplification by chemiluminescence generation after substrate addition. To maximize the detection sensitivity, numerous key parameters including truncated aptamers were optimized with molecular docking analysis. Upon optimization, our aptasensor exhibited a perfect linear relationship (R² = 0.9996) for ZEN detection in a concentration range of 1-100 ng/mL (3.14-314.10 nM) within 40 min, achieving a detection limit of 2.85 ng/mL (8.95 nM), which was a 6.7-fold improvement over that before optimization. Most importantly, the aptasensor obtained a satisfactory recovery rate of 92.84-137.27% and 84.90-124.24% for ZEN-spiked wheat and maize samples, respectively. Overall, our label-free chemiluminescence aptasensor displayed simplicity, sensitivity, specificity and practicality in real samples, indicating high application prospects in the food supply chain for rapid detection of ZEN.

Synthetic receptors in medicine

Cellular signaling is controlled by ligand receptor interaction and subsequent biochemical changes inside the cell. Manipulating receptors as per need that can be a strategy to alter the disease pathologies in various conditions. With recent advances in synthetic biology, now it is possible to engineer the artificial receptor "synthetic receptors." Synthetic receptors are the engineering receptors that have potential to alter the disease pathology by altering/manipulating the cellular signaling. Several synthetic receptors are being engineered that have shown positive regulation in several disease conditions. Thus, synthetic receptor-based strategy opens a new avenue in the medical field to cope up with various health issues. The current chapter summarizes updated information about the synthetic receptors and their applications in the medical field.

Endotoxin in Sepsis: Methods for LPS Detection and the Use of Omics Techniques

Lipopolysaccharide (LPS) or endotoxin, the major cell wall component of Gram-negative bacteria, plays a pivotal role in the pathogenesis of sepsis. It is able to activate the host defense system through interaction with Toll-like receptor 4, thus triggering pro-inflammatory mechanisms. A large amount of LPS induces inappropriate activation of the immune system, triggering an exaggerated inflammatory response and consequent extensive organ injury, providing the basis of sepsis damage. In this review, we will briefly describe endotoxin's molecular structure and its main pathogenetic action during sepsis. In addition, we will summarize the main different available methods for endotoxin detection with a special focus on the wider spectrum offered by omics technologies (genomics, transcriptomics, proteomics, and metabolomics) and promising applications of these in the identification of specific biomarkers for sepsis.

An electrochemical biosensor for the detection of aflatoxin B1 based on the specific aptamer and HCR biological magnification

Aflatoxin B1 (AFB1) is a highly toxic mycotoxin, which causes severe acute or cumulative poisoning. Therefore, it is important to develop sensitive and selective detection methods for AFB1 for the safety of food and medicinal herbs. Herein, we have developed a "signal-on" electrochemical aptasensor based on the high specificity of the aptamer and hybridization chain reaction (HCR) biological amplification for AFB1 detection. In this work, thiol-modified complementary DNA (cDNA) immobilized on the surface of a gold electrode (GE) served as an initiator DNA. When AFB1 was present, it competed with the cDNA for binding to the aptamers, which resulted in the detaching of aptamers from the cDNA-aptamer duplexes. Then, the single-stranded cDNA acted as an initiator to trigger the HCR signal amplification. Therefore, long double-stranded DNA (dsDNA) products were produced, which could load large amounts of methylene blue (MB) molecules to generate a distinct electrochemical signal. Under the optimized conditions, the proposed electrochemical aptasensor achieved the ultrasensitive detection of AFB1 with a linear detection range of 0.01-100 pg mL^-1, and a limit of detection (LOD) down to 2.84 fg mL^-1. Furthermore, the electrochemical aptasensor was successfully applied for detecting AFB1 in corn and two kinds of traditional Chinese medicine samples, indicating the potential value for AFB1 detection in practical samples.

Advancement and Challenges of Biosensing Using Field Effect Transistors

Field-effect transistors (FETs) have become eminent electronic devices for biosensing applications owing to their high sensitivity, faster response and availability of advanced fabrication techniques for their production. The device physics of this sensor is now well understood due to the emergence of several numerical modelling and simulation papers over the years. The pace of advancement along with the knowhow of theoretical concepts proved to be highly effective in detecting deadly pathogens, especially the SARS-CoV-2 spike protein of the coronavirus with the onset of the (coronavirus disease of 2019) COVID-19 pandemic. However, the advancement in the sensing system is also accompanied by various hurdles that degrade the performance. In this review, we have explored all these challenges and how these are tackled with innovative approaches, techniques and device modifications that have also raised the detection sensitivity and specificity. The functional materials of the device are also structurally modified towards improving the surface area and minimizing power dissipation for developing miniaturized microarrays applicable in ultra large scale integration (ULSI) technology. Several theoretical models and simulations have also been carried out in this domain which have given a deeper insight on the electron transport mechanism in these devices and provided the direction for optimizing performance.

Nuclease Triggered "Signal-On" and Amplified Fluorescent Sensing of Fumonisin B1 Incorporating Graphene Oxide and Specific Aptamer

Remarkable advancements have been achieved in the development of rapid analytic techniques toward fumonisin B₁ (FB₁) monitoring and even trace levels for food safety in recent years. However, the point-of-care testing for quantitative and accurate FB₁ determination is still challenging. Herein, an innovative aptasensor was established to monitor FB₁ by utilizing graphene oxide (GO) and nuclease-triggered signal enhancement. GO can be utilized as a fluorescence quenching agent toward a fluorophore-modified aptamer, and even as a protectant of the aptamer from nuclease cleavage for subsequent target cycling and signal amplification detection. This proposed sensing strategy exhibited a good linearity for FB₁ determination in the dynamic range from 0.5 to 20 ng mL⁻¹ with a good correlation of R² = 0.995. Its limit of detection was established at 0.15 ng mL⁻¹ (S/N = 3), which was significantly lower than the legal requirements by three orders of magnitude. The interferent study demonstrated that the introduced aptasensor possessed high selectivity for FB₁. Moreover, the aptasensor was successfully applied to the detection of wheat flour samples, and the results were consistent with the classical ELISA method. The rapid response, sensitive and selective analysis, and reliable results of this sensing platform offer a promising opportunity for food mycotoxin control in point-of-care testing.

Combating small molecule environmental contaminants: detection and sequestration using functional nucleic acids

Small molecule contaminants pose a significant threat to the environment and human health. While regulations are in place for allowed limits in many countries, detection and remediation of contaminants in more resource-limited settings and everyday environmental sources remains a challenge. Functional nucleic acids, including aptamers and DNA enzymes, have emerged as powerful options for addressing this challenge due to their ability to non-covalently interact with small molecule targets. The goal of this perspective is to outline recent efforts toward the selection of aptamers for small molecules and describe their subsequent implementation for environmental applications. Finally, we provide an outlook that addresses barriers that hinder these technologies from being widely adopted in field friendly settings and propose a path forward toward addressing these challenges.

Design of a Quencher-Free Fluorescent Aptasensor for Ochratoxin A Detection in Red Wine Based on the Guanine-Quenching Ability

This study describes a quencher-free fluorescent aptasensor for ochratoxin A (OTA) detection using the specific quenching ability of guanine for fluorescein (FAM) molecules based on photo-induced electron transfer (PIET). In this strategy, OTA is detected by monitoring the fluorescence change induced by the conformational change of the aptamer after target binding. A new shorter OTA aptamer compromising three guanine bases at the 5' end was used in this study. This new aptamer, named G3-OTAapt1-FAM (F1), was labeled with FAM on the 3' end as a fluorophore. In order to increase the binding affinity of the aptamer and OTA, G3-OTAapt2-FAM (F2) was designed; this added a pair of complementary bases at the end compared with F1. To prevent the strong self-quenching of F2, a complementary chain, A13, was added. Although the F1 aptasensor was simpler to implement, the sensitivity of the F2 aptasensor with A13 was better than that of F1. The proposed F1 and F2 sensors can detect OTA with a concentration as low as 0.69 nmol/L and 0.36 nmol/L, respectively.

Structural Insights into the Mechanism of High-Affinity Binding of Ochratoxin A by a DNA Aptamer

A 36-mer guanine (G)-rich DNA aptamer (OBA36) is able to distinguish one atomic difference between ochratoxin analogues A (OTA) and B (OTB), showing prominent recognition specificity and affinity among hundreds of aptamers for small molecules. Why OBA36 has >100-fold higher binding affinity to OTA than OTB remains a long-standing question due to the lack of high-resolution structure. Here we report the solution NMR structure of the aptamer-OTA complex. It was found that OTA binding induces the aptamer to fold into a well-defined unique duplex-quadruplex structural scaffold stabilized by Mg²⁺ and Na⁺ ions. OTA does not directly interact with the G-quadruplex, but specifically binds at the junction between the double helix and G-quadruplex through π-π stacking, halogen bonding (X-bond), and hydrophobic interaction. OTB has the same binding site as OTA but lacks the X-bond. The strong X-bond formed between the chlorine atom of OTA and the aromatic ring of C5 is the key to discriminating the strong binding toward OTA. The present research contributes to a deeper insight of aptamer molecular recognition, reveals structural basis of the high-affinity binding of aptamers, and provides a foundation for further aptamer engineering and applications.

A fluorescent aptasensor for the detection of Aflatoxin B1 by graphene oxide mediated quenching and release of fluorescence

Aflatoxin B1 contamination in food and agro commodities has been major concern of global food safety and trade industry. There is an urgent need to develop sensitive and on-site detection methods for aflatoxins mainly, AFB1 monitoring. In the present study, a fluorophore (Alexa Fluor 488) based aptamer biosensor was devised in combination with graphene oxide (GO) for the detection of Aflatoxin B1 (AFB1). The optimized diagnostic procedure consisted of a fluorescent modified aptamer (Ax-AFLA5) as detection probe and GO mediated quenching of the same; to the quenched system AFB1 was added resulting in subsequent release of fluorescence. The principle of GO based adsorption of ssDNA and successive desorption in the presence of target mycotoxin was utilised in development of the bioassay. In presence of target mycotoxin, the GO adsorbed ssDNA attained a structural conformation resulting in desorption and subsequent release of fluorescence. Assay parameters such as concentration of fluorescent probe, GO and incubation time were evaluated and optimized. The optical signal thus generated could determine presence of AFB1 in the given sample. Selectivity of the method with other mycotoxins was evaluated. The linear range of AFB1 from 0.2-200 ppb was assessed. Visible green fluorescence release was observed at 20 ppb under UV transilluminator and the detection limit of the developed assay was interpreted as 20 ppb of AFB1. The suitability of the assay for AFB1 quantification in groundnut and natural samples was also evaluated. Thus, the developed assay can be a field deployable, reliable and rapid alternative tool for onsite screening method of aflatoxins and other mycotoxins at field level.

Advances in Design Strategies of Multiplex Electrochemical Aptasensors

In recent years, the need for simple, fast, and economical detection of food and environmental contaminants, and the necessity to monitor biomarkers of different diseases have considerably accelerated the development of biosensor technology. However, designing biosensors capable of simultaneous determination of two or more analytes in a single measurement, for example on a single working electrode in single solution, is still a great challenge. On the other hand, such analysis offers many advantages compared to single analyte tests, such as cost per test, labor, throughput, and convenience. Because of the high sensitivity and scalability of the electrochemical detection systems on the one hand and the specificity of aptamers on the other, the electrochemical aptasensors are considered to be highly effective devices for simultaneous detection of multiple-target analytes. In this review, we describe and evaluate multi-label approaches based on (1) metal quantum dots and metal ions, (2) redox labels, and (3) enzyme labels. We focus on recently developed strategies for multiplex sensing using electrochemical aptasensors. Furthermore, we emphasize the use of different nanomaterials in the construction of these aptasensors. Based on examples from the existing literature, we highlight recent applications of multiplexed detection platforms in clinical diagnostics, food control, and environmental monitoring. Finally, we discuss the advantages and disadvantages of the aptasensors developed so far, and debate possible challenges and prospects.

Real-time detection of ochratoxin A in wine through insight of aptamer conformation in conjunction with graphene field-effect transistor

Mycotoxins comprise a frequent type of toxins present in food and feed. The problem of mycotoxin contamination has been recently aggravated due to the increased complexity of the farm-to-fork chains, resulting in negative effects on human and animal health and, consequently, economics. The easy-to-use, on-site, on-demand, and rapid monitoring of mycotoxins in food/feed is highly desired. In this work, we report on an advanced mycotoxin biosensor based on an array of graphene field-effect transistors integrated on a single silicon chip. A specifically designed aptamer against ochratoxin A (OTA) was used as a recognition element, where it was covalently attached to graphene surface via pyrenebutanoic acid, succinimidyl ester (PBASE) chemistry. Namely, an electric field stimulation was used to promote more efficient π-π stacking of PBASE to graphene. The specific G-rich aptamer strand suggest its π-π stacking on graphene in free-standing regime and reconfiguration in G-quadruplex during binding an OTA molecule. This realistic behavior of the aptamer is sensitive to the ionic strength of the analyte solution, demonstrating a 10-fold increase in sensitivity at low ionic strengths. The graphene-aptamer sensors reported here demonstrate fast assay with the lowest detection limit of 1.4 pM for OTA within a response time as low as 10 s, which is more than 30 times faster compared to any other reported aptamer-based methods for mycotoxin detection. The sensors hold comparable performance when operated in real-time within a complex matrix of wine without additional time-consuming pre-treatment.

A novel approach to design electrochemical aptamer-based biosensor for ultrasensitive detecting of zearalenone as a prevalent estrogenic mycotoxin

BACKGROUND

Zearalenone is a well-known estrogenic mycotoxin produced by Fusarium species, a serious threat to the agricultural and food industries worldwide. Zearalenone, with its known metabolites, are biomarkers of exposure to certain fungi, primarily through food. It has considerable toxic effects on biological systems due to its carcinogenicity, mutagenicity, renal toxicity, teratogenicity, and immunotoxicity.

INTRODUCTION

This study aims to design a simple, quick, precise, and cost-effective method on a biosensor platform to evaluate the low levels of this toxin in foodstuffs and agricultural products.

METHODS

An aptamer-based electrochemical biosensor was introduced that utilizes screen-printed gold electrodes instead of conventional electrodes. The electrode position process was employed to develop a gold nanoparticle-modified surface to enhance the electroactive surface area. Thiolated aptamers were immobilized on the surface of gold nanoparticles, and subsequently, the blocker and analyte were added to the modified surface. In the presence of a redox probe, electrochemical characterization of differential pulse voltammetry, cyclic voltammetry, and electrochemical impedance spectroscopy were used to investigate the various stages of aptasensor fabrication.

RESULTS

The proposed aptasensor for zearalenone concentration had a wide linear dynamic range covering the 0.5 pg/mL to 100 ng/mL with a 0.14 pg/mL detection limit. Moreover, this aptasensor had high specificity so that a non-specific analyte cannot negatively affect the selectivity of the aptasensor.

CONCLUSION

Overall, due to its simple design, high sensitivity, and fast performance, this aptasensor showed a high potential for assessing zearalenone in real samples, providing a clear perspective for designing a portable and cost-effective device.

Nanowired dual-electrodes surface to monitor cerebral ischemia by current-volt measurements

The level of clotting protein 'factor IX' (FIX) is highly associated with cerebral ischemia, and this research work has developed a sensitive detection of FIX on dielectrode sensor by current-volt measurement. Sensing area was grown with zinc oxide nanowire to attach more probe for FIX interaction. Aptamer was utilized as the detection probe and attached on the sensing electrode surface through amine-aldehyde chemical linkage. In addition, biotin-streptavidin interaction was utilized to attach the higher number aptamers on the electrode surface connected with dual-probe station. FIX detection limit was found as 10 fM in the phosphate buffer saline spiked samples and 1:320 dilution of human serum. The linear ranges were as 10 fM to 100 pM and 1:320 to 1:80, respectively. With a good determination co-efficient [y = 2.6813x - 3.8467; R 2 = 0.9479] this biosensing strategy helps to quantify FIX and monitor the condition of cerebral ischemia.

An Aptamer-Array-Based Sample-to-Answer Biosensor for Ochratoxin A Detection via Fluorescence Resonance Energy Transfer

Food toxins are a hidden threat that can cause cancer and tremendously impact human health. Therefore, the detection of food toxins in a timely manner with high sensitivity is of paramount importance for public health and food safety. However, the current detection methods are relatively time-consuming and not practical for field tests. In the present work, we developed a novel aptamer-chip-based sample-to-answer biosensor (ACSB) for ochratoxin A (OTA) detection via fluorescence resonance energy transfer (FRET). In this system, a cyanine 3 (Cy3)-labeled OTA-specific biotinylated aptamer was immobilized on an epoxy-coated chip via streptavidin-biotin binding. A complementary DNA strand to OTA aptamer at the 3′-end was labeled with a black hole quencher 2 (BHQ2) to quench Cy3 fluorescence when in proximity. In the presence of OTA, the Cy3-labeled OTA aptamer bound specifically to OTA and led to the physical separation of Cy3 and BHQ2, which resulted in an increase of fluorescence signal. The limit of detection (LOD) of this ACSB for OTA was 0.005 ng/mL with a linearity range of 0.01–10 ng/mL. The cross-reactivity of ACSB against other mycotoxins, ochratoxin B (OTB), aflatoxin B1 (AFB1), zearalenone (ZEA), or deoxynilvalenol (DON), was less than 0.01%. In addition, this system could accurately detect OTA in rice samples spiked with OTA, and the mean recovery rate of the spiked-in OTA reached 91%, with a coefficient of variation (CV) of 8.57–9.89%. Collectively, the ACSB may represent a rapid, accurate, and easy-to-use platform for OTA detection with high sensitivity and specificity.

Shortened and multivalent aptamers for ultrasensitive and rapid detection of alternariol in wheat using optical waveguide sensors

Alternariol (AOH) is one of the common mycotoxins existing in a variety of foods at low level. Aptamers hold great promise for the development of sensitive and rapid aptasensors, but suffer from the excessive length and the difficulty in identification of critical binding domains (CBDs). In this study, the 5 nt CBD of the original 59-nt AOH aptamer (AOH-59, K_D = 423 nM) was identified to be a 'C' bulge in between two A-T base pairs. AOH-59 was successfully shortened to a 23 nt aptamer (AOH 6C, K_D = 701 nM). A 30 nt bivalent aptamer B-2-3 (K_D = 445 nM) and a 39 nt trivalent aptamer T-2-3 (K_D = 274 nM) were obtained by simply incorporating one or two CBDs into AOH 6C. The AOH 6C-, B-2-3-, and T-2-3-based optical waveguide aptasensors possessed the unprecedented detection of limits (LODs, S/N = 3) of 42 ± 3, 6 ± 1 and 2 ± 1 fM, respectively. Using the AOH 6C-based sensor as an example, we further demonstrated the detection of AOH spiked in wheat powder with a LOD of 37 pg/g, 20-230-fold lower than those achieved by ELISAs. The sensor was capable for 35 times 2-min regeneration and the assay time including the extraction of AOH from wheat was only about 1 h. We not only devised the first aptasensors for AOH detection, but also provided a simple strategy to design multivalent aptamers for small molecule targets.

Recent advances in immunoassays and biosensors for mycotoxins detection in feedstuffs and foods

Mycotoxins are secondary metabolites produced by fungus. Many mycotoxin species are highly toxic and are frequently found in cereals and feedstuffs. So, powerful detection methods are vital and effective ways to prevent feed contamination. Traditional detection methods can no longer meet the needs of massive, real-time, simple, and fast mycotoxin monitoring. Rapid detection methods based on advanced material and sensor technology are the future trend. In this review, we highlight recent progress of mycotoxin rapid detection strategies in feedstuffs and foods, especially for simultaneous multiplex mycotoxin determination. Immunoassays, biosensors, and the prominent roles of nanomaterials are introduced. The principles of different types of recognition and signal transduction are explained, and the merits and pitfalls of these methods are compared. Furthermore, limitations and challenges of existing rapid sensing strategies and perspectives of future research are discussed.

Advances in Nanotechnology-Based Biosensing of Immunoregulatory Cytokines

Cytokines are a large group of small proteins secreted by immune and non-immune cells in response to external stimuli. Much attention has been given to the application of cytokines' detection in early disease diagnosis/monitoring and therapeutic response assessment. To date, a wide range of assays are available for cytokines detection. However, in specific applications, multiplexed or continuous measurements of cytokines with wearable biosensing devices are highly desirable. For such efforts, various nanomaterials have been extensively investigated due to their extraordinary properties, such as high surface area and controllable particle size and shape, which leads to their tunable optical emission, electrical, and magnetic properties. Different types of nanomaterials such as noble metal, metal oxide, and carbon nanoparticles have been explored for various biosensing applications. Advances in nanomaterial synthesis and device development have led to significant progress in pushing the limit of cytokine detection. This article reviews currently used methods for cytokines detection and new nanotechnology-based biosensors for ultrasensitive cytokine detection.

Oligonucleotide aptamers for pathogen detection and infectious disease control

During an epidemic or pandemic, the primary task is to rapidly develop precise diagnostic approaches and effective therapeutics. Oligonucleotide aptamer-based pathogen detection assays and control therapeutics are promising, as aptamers that specifically recognize and block pathogens can be quickly developed and produced through simple chemical synthesis. This work reviews common aptamer-based diagnostic techniques for communicable diseases and summarizes currently available aptamers that target various pathogens, including the SARS-CoV-2 virus. Moreover, this review discusses how oligonucleotide aptamers might be leveraged to control pathogen propagation and improve host immune system responses. This review offers a comprehensive data source to the further develop aptamer-based diagnostics and therapeutics specific for infectious diseases.

Aptamers isolated against mosquito-borne pathogens

Mosquito-borne diseases are a major threat to public health. The shortcomings of diagnostic tools, especially those that are antibody-based, have been blamed in part for the rising annual morbidity and mortality caused by these diseases. Antibodies harbor a number of disadvantages that can be clearly addressed by aptamers as the more promising molecular recognition elements. Aptamers are defined as single-stranded DNA or RNA oligonucleotides generated by SELEX that exhibit high binding affinity and specificity against a wide variety of target molecules based on their unique structural conformations. A number of aptamers were developed against mosquito-borne pathogens such as Dengue virus, Zika virus, Chikungunya virus, Plasmodium parasite, Francisella tularensis, Japanese encephalitis virus, Venezuelan equine encephalitis virus, Rift Valley fever virus and Yellow fever virus. Intrigued by these achievements, we carry out a comprehensive overview of the aptamers developed against these mosquito-borne infectious agents. Characteristics of the aptamers and their roles in diagnostic, therapeutic as well as other applications are emphasized.

Upconversion nanoparticles-based FRET system for sensitive detection of Staphylococcus aureus

Staphylococcus aureus (S. aureus) is a pathogenic bacterium that seriously endangers food safety. Herein, a rapid, sensitive and specific aptasensor based on upconversion fluorescence resonance energy transfer (FRET) was developed for S. aureus detection in food. Aptamer-functionalized gold nanoparticles (AuNPs-aptamers) were bonded to cDNA-modified upconversion nanoparticles (UCNPs-cDNA) by complementary pairing, resulting in fluorescence quenching. After adding S. aureus into the system, the aptamers preferentially combined with S. aureus, dissociated UCNPs-cDNA from AuNPs-aptamers, and the fluorescence was recovered. Under optimized conditions, there was a significant linear correlation between fluorescence intensity and S. aureus concentration over the range 47-4.7 × 10⁷ CFU/mL (R² = 0.9904) with a detection limit of 10.7 CFU/mL. Furthermore, the precision and accuracy of the developed biosensor were validated using standard plate count method, yielding no significant differences. The proposed method has potential application for rapid and sensitive quantification of S. aureus in food.

Recent Advances in Conventional Methods and Electrochemical Aptasensors for Mycotoxin Detection

The presence of mycotoxins in foodstuffs and feedstuffs is a serious concern for human health. The detection of mycotoxins is therefore necessary as a preventive action to avoid the harmful contamination of foodstuffs and animal feed. In comparison with the considerable expense of treating contaminated foodstuffs, early detection is a cost-effective way to ensure food safety. The high affinity of bio-recognition molecules to mycotoxins has led to the development of affinity columns for sample pre-treatment and the development of biosensors for the quantitative analysis of mycotoxins. Aptamers are a very attractive class of biological receptors that are currently in great demand for the development of new biosensors. In this review, the improvement in the materials and methodology, and the working principles and performance of both conventional and recently developed methods are discussed. The key features and applications of the fundamental recognition elements, such as antibodies and aptamers are addressed. Recent advances in aptasensors that are based on different electrochemical (EC) transducers are reviewed in detail, especially from the perspective of the diagnostic mechanism; in addition, a brief introduction of some commercially available mycotoxin detection kits is provided.

Aptasensor for Quantification of Leptin Through PCR Amplification of Short DNA-Aptamers

Protein quantification is traditionally performed through enzyme-linked immunosorbent assay (ELISA), which involves long preparation times. To overcome this, new approaches use aptamers as an alternative to antibodies. In this paper, we present a new approach to quantify proteins with short DNA aptamers through polymerase chain reaction (PCR) resulting in shorter protocol times with comparatively improved limits of detection. The proposed method includes a novel way to quantify both the target protein and the corresponding short DNA-aptamers simultaneously, which also allows us to fully characterize the performance of aptasensors. Human leptin is used as a target protein to validate this technique, because it is considered an important biomarker for obesity-related studies. In our experiments, we achieved the lowest limit of detection of 100 pg/mL within less than 2 h, a limit affected by the dissociation constant of the leptin aptamer, which could be improved by selecting a more specific aptamer. Because of the simple and inexpensive approach, this technique can be employed for Lab-On-Chip implementations and for rapid "on-site" quantification of proteins.