A simple and sensitive electrochemiluminescence aptasensor for determination of ochratoxin A based on a nicking endonuclease-powered DNA walking machine

Application of Biosensors for the Detection of Mycotoxins for the Improvement of Food Safety

Mycotoxins, secondary metabolites synthesized by various filamentous fungi genera such as Aspergillus, Penicillium, Fusarium, Claviceps, and Alternaria, are potent toxic compounds. Their production is contingent upon specific environmental conditions during fungal growth. Arising as byproducts of fungal metabolic processes, mycotoxins exhibit significant toxicity, posing risks of acute or chronic health complications. Recognized as highly hazardous food contaminants, mycotoxins present a pervasive threat throughout the agricultural and food processing continuum, from plant cultivation to post-harvest stages. The imperative to adhere to principles of good agricultural and industrial practice is underscored to mitigate the risk of mycotoxin contamination in food production. In the domain of food safety, the rapid and efficient detection of mycotoxins holds paramount significance. This paper delineates conventional and commercial methodologies for mycotoxin detection in ensuring food safety, encompassing techniques like liquid chromatography, immunoassays, and test strips, with a significant emphasis on the role of electrochemiluminescence (ECL) biosensors, which are known for their high sensitivity and specificity. These are categorized into antibody-, and aptamer-based, as well as molecular imprinting methods. This paper examines the latest advancements in biosensors for mycotoxin testing, with a particular focus on their amplification strategies and operating mechanisms.

Application of DNA-fueled molecular machines in food safety testing

Food is consumed by humans, which is indispensable to human life. Therefore, considerable attention of the whole society has been paid to food safety. Over the last few years, dramatic social development has brought new challenges to food safety, making developing new and quick methods for on-site food safety testing an important necessity. As a result, DNA-fueled molecular machines, characterized by high efficiency, accuracy, and sensitivity in testing, have come into the spotlight, based on which sensors can be constructed to detect toxic and harmful substances in food products. This study reviewed recent research on several DNA-fueled molecular machines, including DNA tweezers, DNA walkers, and DNA origami, for rapidly detecting toxic and harmful substances. Based on the above studies, the sensitivity and timeliness of several DNA molecular machines were summarized and compared, and the development prospect of DNA fuel molecular machines in the field of food safety detection was prospected.

Label-free dual-mode sensing platform based on target-regulated CRISPR-Cas12a activity for ochratoxin A in Morinda officinalis

Many traditional Chinese herbs are susceptible to ochratoxin A (OTA), a potent mycotoxin, which causes serious effects on the quality of the herb and on people's health. The development of methods to detect OTA is extremely important. Most methods for detecting OTA are based on a single-signal output mode, which might be easily influenced by complex environmental conditions. In this research, by taking advantage of the cleavage of DNA by target-induced CRISPR-Cas12a activity and the difference in electrostatic force of DNA to different charge electrochemiluminescent (ECL) and electrochemical (EC) probes, a biosensor is developed for the detection of OTA. First, the CRISPR-Cas12a system consists of a well-designed crRNA, its complementary strand (also as an aptamer for OTA), and Cas12a. Without the target, this CRISPR-Cas12a system is in the "activated stage", which digests hairpin DNA on the electrode, resulting in a weak ECL signal and strong current response. With the introduction of OTA bound with the aptamer, CRISPR-Cas12a activity is inhibited ("locked stage"). Thus, hairpin DNA remained intact on the electrode, resulting in recovery of the ECL signal and attenuation of the current intensity. As a result, this label-free dual-mode sensing platform realizes an assay for OTA in Morinda officinalis. This target-regulated CRISPR-Cas12a activity-sensing platform with dual-mode output not only provides high sensitivity (due to the CRISPR-Cas12a system), but also has good anti-interference ability against complex substrates (due to dual-mode output), and exhibits a broad range of prospects for application.

Advances in aptamers, and application of mycotoxins detection: A review

Mycotoxin contamination in food products can easily cause serious health hazards and economic losses to human beings. How to accurately detect and effectively control mycotoxin contamination has become a global concern. Mycotoxins conventional detection techniques e.g; ELISA, HPLC, have limitations like, low sensitivity, high cost and time-consuming. Aptamer-based biosensing technology has the advantages of high sensitivity, high specificity, wide linear range, high feasibility, and non-destructiveness, which overcomes the shortcomings of conventional analysis techniques. This review summarizes the sequences of mycotoxin aptamers that have been reported so far. Based on the application of four classic POST-SELEX strategies, it also discusses the bioinformatics-assisted POST-SELEX technology in obtaining optimal aptamers. Furthermore, trends in the study of aptamer sequences and their binding mechanisms to targets is also discussed. The latest examples of aptasensor detection of mycotoxins are classified and summarized in detail. Newly developed dual-signal detection, dual-channel detection, multi-target detection and some types of single-signal detection combined with unique strategies or novel materials in recent years are focused. Finally, the challenges and prospects of aptamer sensors in the detection of mycotoxins are discussed. The development of aptamer biosensing technology provides a new approach with multiple advantages for on-site detection of mycotoxins. Although aptamer biosensing shows great development potential, still some challenges and difficulties are there in practical applications. Future research need high focus on the practical applications of aptasensors and the development of convenient and highly automated aptamers. This may lead to the transition of aptamer biosensing technology from laboratory to commercialization.

Recent Advances in Electrochemiluminescence Biosensors for Mycotoxin Assay

Rapid and efficient detection of mycotoxins is of great significance in the field of food safety. In this review, several traditional and commercial detection methods are introduced, such as high-performance liquid chromatography (HPLC), liquid chromatography/mass spectrometry (LC/MS), enzyme-linked immunosorbent assay (ELISA), test strips, etc. Electrochemiluminescence (ECL) biosensors have the advantages of high sensitivity and specificity. The use of ECL biosensors for mycotoxins detection has attracted great attention. According to the recognition mechanisms, ECL biosensors are mainly divided into antibody-based, aptamer-based, and molecular imprinting techniques. In this review, we focus on the recent effects towards the designation of diverse ECL biosensors in mycotoxins assay, mainly including their amplification strategies and working mechanism.

Ultrasensitive electrochemical aptasensor with Nafion-stabilized f-MWCNTs as signal enhancers for OTA detection

In this study, an ultrasensitive electrochemical (EC) aptasensor with Nafion-stabilized functionalized multi-walled carbon nanotubes (f-MWCNTs) as signal enhancers was established for ochratoxin A (OTA) determination. Herein, f-MWCNTs were prepared through functionalization with nitric acid. The incorporation of Nafion promoted a good dispersion of f-MWCNTs and prevented their leaching on the electrode, making a robust stability of the aptasensor. The Nafion-f-MWCNTs composites were used as the sensing substrates to largely enhance the electroactive surface area and the conductivity of the electrode, realizing a significant signal amplification. Carboxyl groups on the surface of f-MWCNTs readily exposed from Nafion membrane to couple with streptavidin, facilitating the immobilization of biotinylated aptamers to achieve selective recognition towards OTA. When OTA existed, aptamers preferentially combined with it, causing a noticeable decline in the current response. Under optimum conditions, a good linear relationship between the current changes and the logarithm of OTA concentration was observed from 0.005 ng/mL to 10 ng/mL, with a limit of detection low to 1 pg/mL for OTA. The specific, sensitive, and reproducible aptasensor succeeded in application in malt samples, confirming a great promise for more contaminants and providing a universal platform in complex matrices by simply replacing the corresponding aptamers.

An accurate and ultrasensitive ratiometric electrochemical aptasensor for determination of Ochratoxin A based on catalytic hairpin assembly

Ochratoxin A (OTA) pollution in agricultural products has raised the pressing to develop sensitive, accurate and convenient detection methods. Herein, an accurate and ultrasensitive ratiometric electrochemical aptasensor was proposed based on catalytic hairpin assembly (CHA) for OTA detection. In this strategy, the target recognition and CHA reaction were both accomplished in the same system, which avoided tedious multi-steps operation and extra reagents, providing the advantage of convenience with only a one-step reaction and without enzyme. The labeled Fc and MB were used as the signal-switching molecules, avoiding various interferences and greatly improving the reproducibility (RSD: 3.197%). This aptasensor achieved trace-level detection for OTA with LOD of 81 fg/mL in the linear range of lower concentration (100 fg/mL-50 ng/mL). Moreover, this strategy was successfully applied to OTA detection in cereals with comparable results of HPLC-MS. This aptasensor provided a viable platform for accurate, ultrasensitive, and one-step detection of OTA in food.

Non-enzymatic electrochemiluminescence biosensor for ultrasensitive detection of ochratoxin A based on efficient DNA walker

Ochratoxin A (OTA) with high toxicity represents a serious threat to the agriculture and food chain, consequently to human health. Herein, a simple electrochemiluminescence (ECL) biosensor was constructed for ultrasensitive detection of OTA based on mercaptopropionic acid templated Au nanoclusters (Au NCs) as intensive signal probe and a non-enzymatic 2D DNA walking machine as the effective amplification strategy. Specifically, the target related bipedal DNA walker efficiently moved along 2D DNA tracks through toehold-mediated DNA strand displacement, which triggered abundant signal probes for combining to the DNA tracks. Moreover, the Au NCs could exhibit strong ECL emission due to fast electron transfer from massive Au-S electronic pathways under the electrochemical excitation. Thus, the biosensor possessed significant ECL response for achieving ultrasensitive detection toward OTA with low detection limit of 3.19 fg/mL. Impressively, the sensing platform was also applied to detect OTA from edible oils, exhibiting great application potential in food analysis.

A Colorimetric Aptasensor for Ochratoxin A Detection Based on Tetramethylrhodamine Charge Effect-Assisted Silver Enhancement

A novel colorimetric aptasensor based on charge effect-assisted silver enhancement was developed to detect ochratoxin A (OTA). To achieve this objective, gold nanoparticles (AuNPs), which can catalyze silver reduction and deposition, were used as the carrier of the aptamers tagged with a positively charged tetramethylrhodamine (TAMRA). Due to the mutual attraction of positive and negative charges, the TAMRA attracted and retained the silver lactate around the AuNPs. Thus, the chance of AuNP-catalyzed silver reduction was increased. The charge effect-assisted silver enhancement was verified by tagging different base pair length aptamers with TAMRA. Under optimized conditions, the as-prepared OTA aptasensor had a working range of 1 × 10²-1 × 10⁶ pg mL^-1. The detection limit was as low as 28.18 pg mL^-1. Moreover, the proposed aptasensor has been successfully applied to determine OTA in actual samples with satisfactory results.

A Novel Electrochemiluminescence Immunosensor Based on Resonance Energy Transfer between g-CN and NU-1000(Zr) for Ultrasensitive Detection of Ochratoxin A in Coffee

In this study, an electrochemiluminescence (ECL) immunosensor based on nanobody heptamer and resonance energy transfer (RET) between g-C₃N₄ (g-CN) and NU-1000(Zr) was proposed for ultrasensitive ochratoxin A (OTA) detection. First, OTA heptamer fusion protein was prepared by fusing OTA-specific nanometric (Nb28) with a c-terminal fragment of C4 binding protein (C4bpα) (Nb28-C4bpα). Then, Nb28-C4bpα heptamer with the high affinity used as a molecular recognition probe, of which plenty of binding sites were provided for OTA-Apt-NU-1000(Zr) nanocomposites, thereby improving the immunosensors' sensitivity. In addition, the quantitative analysis of OTA can be achieved by using the signal quenching effect of NU-1000(Zr) on g-CN. As the concentration of OTA increases, the amount of OTA-Apt-NU-1000(Zr) fixed on the electrode surface decreases. RET between g-CN and NU-1000(Zr) is weakened leading to the increase of ECL signal. Thus, OTA content is indirectly proportional to ECL intensity. Based on the above principle, an ultra-sensitive and specific ECL immunosensor for OTA detection was constructed by using heptamer technology and RET between two nanomaterials, with a range from 0.1 pg/mL to 500 ng/mL, and the detection limit of only 33 fg/mL. The prepared ECL-RET immunosensor showed good performance and can be successfully used for the determination of OTA content in real coffee samples, suggesting that the nanobody polymerization strategy and the RET effect between NU-1000(Zr) and g-CN can provide an alternative for improving the sensitivity of important mycotoxin detection.

Nanomaterials-Based Electrochemiluminescence Biosensors for Food Analysis: Recent Developments and Future Directions

Developing robust and sensitive food safety detection methods is important for human health. Electrochemiluminescence (ECL) is a powerful analytical technique for complete separation of input source (electricity) and output signal (light), thereby significantly reducing background ECL signal. ECL biosensors have attracted considerable attention owing to their high sensitivity and wide dynamic range in food safety detection. In this review, we introduce the principles of ECL biosensors and common ECL luminophores, as well as the latest applications of ECL biosensors in food analysis. Further, novel nanomaterial assembly strategies have been progressively incorporated into the design of ECL biosensors, and by demonstrating some representative works, we summarize the development status of ECL biosensors in detection of mycotoxins, heavy metal ions, antibiotics, pesticide residues, foodborne pathogens, and other illegal additives. Finally, the current challenges faced by ECL biosensors are outlined and the future directions for advancing ECL research are presented.

Multifunctional Smart ZnSe-Nanostructure-Based Fluorescent Aptasensor for the Detection of Ochratoxin A

Herein, we present a comprehensive investigation of rationally designed zinc selenide (ZnSe) nanostructures to achieve highly negatively charged ZnSe nanostructures. A Microwave-assisted hydrothermal synthesis method was used to synthesize three types of ZnSe nanostructures, i.e., nanorods, µ-spheres and nanoclusters, as characterized by a zeta potential analyzer, X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy and BET, which were labeled as type A, B and C. Three different solvents were used for the synthesis of type A, B and C ZnSe nanostructures, keeping other synthesis conditions such as temperature, pressure and precursors ratio constant. Based on two heating time intervals, 6 and 9 h, types A, B and C were further divided into types A6, A9, B6, B9, C6 and C9. ZnSe nanostructures were further evaluated based on their fluorescent quenching efficiency. The maximum fluorescence quenching effect was exhibited by the ZnSe-B6 type, which can be attributed to its highly negative surface charge that favored its strong interaction with cationic dye Rhodamine B (Rh-B). Further, the optimized ZnSe-B6 was used to fabricate an aptasensor for the detection of a food-based toxin, ochratoxin-A (OTA). The developed aptasensor exhibited a limit of detection of 0.07 ng/L with a wide linear range of 0.1 to 200 ng/L.

Strategies for Enhancing the Sensitivity of Electrochemiluminescence Biosensors

Electrochemiluminescence (ECL) has received considerable attention as a powerful analytical technique for the sensitive and accurate detection of biological analytes owing to its high sensitivity and selectivity and wide dynamic range. To satisfy the growing demand for ultrasensitive analysis techniques with high efficiency and accuracy in complex real sample matrices, considerable efforts have been dedicated to developing ECL strategies to improve the sensitivity of bioanalysis. As one of the most effective approaches, diverse signal amplification strategies have been integrated with ECL biosensors to achieve desirable analytical performance. This review summarizes the recent advances in ECL biosensing based on various signal amplification strategies, including DNA-assisted amplification strategies, efficient ECL luminophores, surface-enhanced electrochemiluminescence, and ratiometric strategies. Sensitivity-enhancing strategies and bio-related applications are discussed in detail. Moreover, the future trends and challenges of ECL biosensors are discussed.

The combination of highly efficient resonance energy transfer in one nanocomposite and ferrocene-quenching for ultrasensitive electrochemiluminescence bioanalysis

Sensitive and accurate detection of prostate-specific antigen (PSA) is of great significance since it is regarded as a biomarker for prostate diseases. Herein, a facile strategy for the design of highly efficient electrochemiluminescence (ECL) sensor was proposed for PSA assay. Carboxylated graphitic carbon nitride (g-C₃N₄) nanosheet (CCN) and tris (2, 2'-Bipyridyl) ruthenium (II) (Ru(bpy)₃²⁺) encapsulated in silica nanospheres (RuSi NPs) were employed as the donor and acceptor, respectively. CCN and RuSi NPs were covalently bound within one nanocomposite (CCN@RuSi) through the amide bond, which greatly shortened the electron-transfer path. Thus, the resonance energy transfer (RET) efficiency was remarkably increased, providing a high initial ECL intensity for the ECL assay. After the successive introducing of aptamer, PSA, and ferroceneboronic acid (FcBA) on the surface of CCN@RuSi modified electrode, the ECL signal remarkably decreased, which was caused by the steric hindrance of PSA and electron transfer quenching between Fc⁺ and excited-state Ru(bpy)₃²⁺*. Therefore, a highly efficient ECL platform was constructed, which achieved the ultrasensitive detection of PSA with a linear range and a limit of detection of 100 fg/mL - 50 ng/mL and 1.2 fg/mL, respectively. Furthermore, the dual-affinity of the aptamer and FcBA to PSA endowed the sensor with a high selectivity for the determination of PSA in human serum samples. The present work provides an important reference for the integration of RET and quenching strategy in the ECL study with rapid, ultrasensitive, and highly selective detection performances.

Nanomaterial-based aptamer biosensors for ochratoxin A detection: a review

Ochratoxin A (OTA) is a widely distributed mycotoxin that often contaminates food, grains and animal feed. It poses a serious threat to human health because of its high toxicity and persistence. Therefore, the development of an inexpensive, highly sensitive, accurate and rapid method for OTA detection is imperative. In recent years, various nanomaterials used in the establishment of aptasensors have attracted great attention due to their large surface-to-volume ratio, good stability and facile preparation. This review summarizes the development of nanomaterial-based aptasensors for OTA determination and sample treatment over the past 5 years. The nanomaterials used in OTA aptasensors include metal, carbon, luminescent, magnetic and other nanomaterials. Finally, the limitations and future challenges in the development of nanomaterial-based OTA aptasensors are reviewed and discussed.

Target-Activated, Light-Actuated Three-Dimensional DNA Walker Nanomachine for Amplified miRNA Detection

Accurate analysis of microRNA (miRNA) is promising for elucidation of cancer processes and therapeutic effects. In this study, we reported a new target-activated, light-actuated three-dimensional (3D) DNA walker on gold nanoparticles for sensitive detection of miRNA using pyrene-incorporated DNAzyme analogues. In this design, the target miRNA activated the 3D DNA walker system to releases the walking arm. Then, under ultraviolet light irradiation, the pyrene DNAzyme on the walking arm would consecutively cleave the disulfide bonds of substrate strands and recover the fluorescence signal, thus achieving the amplified miRNA detection. The sophisticated design of the light-actuated 3D DNA walker was systematically investigated. Furthermore, this strategy could also be employed for miRNA analysis in serum samples with satisfactory reproducibility. Notably, the proposed light-actuated 3D DNA walker-based technique eliminated the need of enzymes, cofactors, and RNA backbones, thereby significantly improving the stability and efficiency. Overall, the light-actuated 3D DNA walker-based strategy enabled facile, sensitive, and specific detection of miRNA and provided new perspectives in diagnostics.

Signal enhancing strategies in aptasensors for the detection of small molecular contaminants by nanomaterials and nucleic acid amplification

Small molecular contaminants (such as mycotoxins, antibiotics, pesticide residues, etc.) in food and environment have given rise to many biological and ecological toxicities, which has attracted worldwide attention in recent years. Meanwhile, due to the advantages of aptamers such as high specificity and stability, easy synthesis and modification, as well as low cost and immunogenicity, various aptasensors for the detection of small molecular contaminants have been flourishing. An aptasensor as a whole is composed of an aptamer-based target recognizer and a signal transducer, which are fields of concentrated research. In the practical detection applications, in order to achieve the quantitative detection of small molecular contaminants at low abundance in real samples, a large number of signal enhancing strategies have been utilized in the development of aptasensors. Recent years is a vintage period for efficient signal enhancing strategies of aptasensors by the aid of nanomaterials and nucleic acid amplification that are applied in the elements for target recognition and signal conversion. Therefore, this paper meticulously reviews the signal enhancing strategies based on nanomaterials (including the (quasi-)zero-dimensional, one-dimensional, two-dimensional and three-dimensional nanomaterials) and nucleic acid amplification (including enzyme-assisted nucleic acid amplification and enzyme-free nucleic acid amplification). Furthermore, the challenges and future trends of the abovementioned signal enhancing strategies for application are also discussed in order to inspire the practitioners in the research and development of aptasensors for small molecular contaminants.

Novel electrochemiluminescent assay for the aptamer-based detection of testosterone

This work presents a proof-of-concept assay for the detection and quantification of small molecules based on aptamer recognition and electrochemiluminescence (ECL) readout. The testosterone-binding (TESS.1) aptamer was used to demonstrate the novel methodology. Upon binding of the target, the TESS.1 aptamer is released from its complementary capture probe - previously immobilized at the surface of the electrode - producing a decrease in the ECL signal after a washing step removing the released (labeled) TESS.1 aptamer. The analytical capability of the ECL assay towards testosterone detection was investigated displaying a linear range from 0.39 to 1.56 μM with a limit of detection of 0.29 μM. The selectivity of the proposed assay was assessed by performing two different negative control experiments; i) detection of testosterone with a randomized ssDNA sequence and ii) detection of two other steroids, i.e. deoxycholic acid and hydrocortisone with the TESS.1 aptamer. In parallel, complementary analytical techniques were employed to confirm the suggested mechanism: i) native nano-electrospray ionization mass spectrometry (native nESI-MS) was used to determine the stoichiometry of the binding, and to characterize aptamer-target interactions; and, ii) isothermal titration calorimetry (ITC) was carried out to elucidate the dissociation constant (K_d) of the complex of testosterone and the TESS.1 aptamer. The combination of these techniques provided a complete understanding of the aptamer performance, the binding mechanism, affinity and selectivity. Furthermore, this important characterization carried out in parallel validates the real functionality of the aptamer (TESS.1) ensuring its use towards selective testosterone binding in further biosensors. This research will pave the way for the development of new aptamer-based assays coupled with ECL sensing for the detection of relevant small molecules.

Aptasensors for mycotoxins in foods: Recent advances and future trends

Mycotoxin contamination in foods has posed serious threat to public health and raised worldwide concern. The development of simple, rapid, facile, and cost-effective methods for mycotoxin detection is of urgent need. Aptamer-based sensors, abbreviated as aptasensors, with excellent recognition capacity to a wide variety of mycotoxins have attracted ever-increasing interest of researchers because of their simple fabrication, rapid response, high sensitivity, low cost, and easy adaptability for in situ measurement. The past few decades have witnessed the rapid advances of aptasensors for mycotoxin detection in foods. Therefore, this review first summarizes the reported aptamer sequences specific for mycotoxins. Then, the recent 5-year advancements in various newly developed aptasensors, which, according to the signal output mode, are divided into electrochemical, optical and photoelectrochemical categories, for mycotoxin detection are comprehensively discussed. A special attention is taken on their strengths and limitations in real-world application. Finally, the current challenges and future perspectives for developing novel highly reliable aptasensors for mycotoxin detection are highlighted, which is expected to provide powerful references for their thorough research and extended applications. Owing to their unique advantages, aptasensors display a fascinating prospect in food field for safety inspection and risk assessment.

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.

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.

DNA Nanotechnology-Based Biosensors and Therapeutics

Over the past few decades, DNA nanotechnology engenders a vast variety of programmable nanostructures utilizing Watson-Crick base pairing. Due to their precise engineering, unprecedented programmability, and intrinsic biocompatibility, DNA nanostructures cannot only interact with small molecules, nucleic acids, proteins, viruses, and cancer cells, but also can serve as nanocarriers to deliver different therapeutic agents. Such addressability innate to DNA nanostructures enables their use in various fields of biomedical applications such as biosensors and cancer therapy. This review is begun with a brief introduction of the development of DNA nanotechnology, followed by a summary of recent applications of DNA nanostructures in biosensors and therapeutics. Finally, challenges and opportunities for practical applications of DNA nanotechnology are discussed.

Application of the Dimeric G-Quadruplex and toehold-mediated strand displacement reaction for fluorescence biosensing of ochratoxin A

Ochratoxin A (OTA) is one of the most toxic mycotoxins that exists in various agro-products and foods. Here, a non-label and enzyme-free fluorescence biosensor for highly specific detection of OTA has been developed by the combination of toehold-mediated strand displacement reaction (TMSD) and G-quadruplex dimer/ThT (G-dimer/ThT). The DNA duplex (aptamer-IP) is composed of the anti-OTA aptamer and a single stranded initiation probe (IP). In the presence of OTA, the attachment of target to aptamer leads to the liberation of the IP, which activates the cycle TMSD amplifications of two hairpin probes (H1 and H2) accompanied by the production of numerous H1-H2 assemblies. This double-stranded H1-H2 structure results in the proximity between the 5'-end overhang tail of H1 and the 3'-end stem of H2 to liberate the pre-blocked G-dimer sequence for lighting up ThT. In addition, the method displayed a stable fluorescence emission in the high-salt media. It was successfully applied to analyze OTA in real food samples. Hence, the constructed fluorescence biosensing platform might provide a new way for OTA and other toxin analysis detection.

Electrodeposition immobilized molybdenum disulfide quantum dots and their electrochemiluminescence application in the detection of melamine residues in milk powder

In this paper, one-step hydrothermal and electrodeposition methods were used to prepare a MoS2 quantum dot (QD) solid-phase electrochemiluminescent (ECL) electrode for the detection of melamine residues in milk powder. With the assistance of chitosan, MoS2 QDs fixed by the one-step electrodeposition method show better ECL performance than those by traditional deposition methods due to better dispersibility and stability. Based on the quenching of the MoS2 QDs ECL signal by melamine, quantitative detection of melamine in the sample was performed. The structure and morphology of a MoS2-CHIT/indium tin oxide (ITO) solid-phase ECL electrode were characterized by TEM and XPS, and melamine was detected by the ECL method using a three-electrode system. The proposed sensor exhibited good linearity in the range of 1.00 × 10-11 to 1.00 × 10-7 mol L-1 (ΔI = 12 100.62 + 1009.93 lg c (mol L-1), R2 = 0.997), and the method shows the advantages of simplicity and sensitivity compared to traditional detection methods. The interference of common ions in milk powder on the modified electrode was within 5%, and the recovery rate of real sample detection was within 97-98%. As a result, the proposed method is suitable for detecting melamine residues in milk powder.

Enhanced electrochemiluminescence of CdS quantum dots capped with mercaptopropionic acid activated by EDC for Zika virus detection

Enhanced electrochemiluminescence (ECL) signals of CdS quantum dots capped with 3-mercaptopropionic acid (MPA@CdS QDs) have been observed after using N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide (EDC) to activate the carboxyl groups. The generated ECL signals are strong enough that their images can be captured using a Huawei mobile phone. A possible mechanism for the generation of enhanced ECL signals has been proposed. Then, a sandwich immunosensor platform for detecting Zika virus (ZIKV) was fabricated with silica microspheres as the carrier and MPA@CdS QDs as ECL signal labels. Due to the dual signal amplification of EDC activation and microsphere enrichment, good linearity from 1.0 fg mL-1 to 1.0 ng mL-1 was exhibited by the QD-based ECL immunosensor for ZIKV detection. The detection limit was 0.3 fg mL-1.

DNA walker-assisted aptasensor for highly sensitive determination of Ochratoxin A

Ochratoxin A (OTA), a toxic secondary metabolite produced via various fungus, poses a serious threat to the health of human beings and animals. In this paper, an aptasensor for OTA detection based on gold nanoparticles decorated molybdenum oxide (AuNPs-MoO_x) nanocomposites, hybridization chain reaction (HCR) and a restriction endonuclease (Nb.BbvCI)-aided walker DNA machine was successfully constructed. In this electrochemical platform, the HCR was also used to embed more electrical signal molecules of methylene blue (MB) on silver nanoparticles (AgNPs) to achieve signal amplification. Under the optimum conditions, after adding OTA and Nb.BbvCI in turn and responding adequately under appropriate conditions, aptamer-DNA (6-DNA) carries the OTA away from the electrode surface, and walker DNA was hybridized autonomously with 5-DNA, releasing a large amount of 5'-DNA with the help of Nb.BBVCI. Finally, the electrochemical signal obtained by differential pulse voltammetry (DPV) was weakened. As an artificial and popular signal amplification technique, the DNA walking machine greatly improved the sensitivity. The proposed biosensor exhibited excellent analytical performance in the range of 0.01-10000 pg mL^-1 with a detection limit as low as 3.3 fg mL^-1. Furthermore, direct comparison with ultraperformance liquid chromatography (UPLC) indicates excellent agreement to actual samples such as apple juice, orange juice, red wine and serum.

Aptasensors for mycotoxin detection: A review

Mycotoxins are toxic compounds produced by fungi, which represent a risk to the food and feed supply chain, having an impact on health and economies. A high percentage of feed samples have been reported to be contaminated with more than one type of mycotoxin. Systematic, cost-effective and simple tools for testing are critical to achieve a rapid and accurate screening of food and feed quality. In this review, we describe the various aptamers that have been selected against mycotoxins and their incorporation into optical and electrochemical aptasensors, outlining the strategies exploited, highlighting the advantages and disadvantages of each approach. The review also discusses the different materials used and the immobilization methods employed, with the aim of achieving the highest sensitivity and selectivity.

A novel colorimetric immunoassay for sensitive monitoring of ochratoxin A based on an enzyme-controlled citrate-iron(iii) chelating system

Schematic illustration of an enzyme-controlled citrate-iron(iii) chelating system-based colorimetric immunoassay for sensitive determination of ochratoxin A.

A signal-on electrochemical aptasensor based on silanized cellulose nanofibers for rapid point-of-use detection of ochratoxin A

An innovative ultrasensitive electrochemical aptamer-based sensor was developed for ochratoxin A (OTA) detection in cold brew coffee through revolutionary combination of nanofibers, electrochemical method, and aptamer technologies. The assembly of the aptasensor was based on the activation of silanized cellulose nanofibrous membranes as a supporting matrix for methylene blue (MB) redox probe-labeled aptamer tethering. Cellulose nanofibrous membranes were regenerated by deacetylating electrospun cellulose acetate nanofibrous membranes with deacetylation efficacy of 97%, followed by silanization of the nanofiber surfaces by using (3-aminopropyl)triethoxysilane (APTES). A replacement of conventionally casted membranes by the nanofibrous membranes increased the active surface area on the working electrode of a screen-printed three-electrode sensor by more than two times, consequently enhancing the fabricated aptasensor performance. The developed aptasensor demonstrated high sensitivity and specificity toward OTA in a range 0.002-2 ng mL^-1, with a detection limit of 0.81 pg mL^-1. Moreover, the assembled aptamer-based sensor successfully detected OTA in cold brew coffee samples without any pretreatment. The aptasensor exhibited good reusability and stability over long storage time. Graphical abstract.

Recent Advances in Ochratoxin A Electrochemical Biosensors: Recognition Elements, Sensitization Technologies, and Their Applications

Ochratoxin A (OTA) is a class of mycotoxin that are mainly produced by Aspergillus and Penicillium and widely found in plant origin food. OTA-contaminated foods can cause serious harm to animals and humans, while high stability of OTA makes it difficult to remove in conventional food processing. Thus, sensitive and rapid detection of OTA undoubtedly plays an important role in OTA prevention and control. In this paper, the conventional and novel methods of OTA at home and abroad are summarized and compared. The latest research progress and related applications of novel OTA electrochemical biosensors are mainly described with a new perspective. We innovatively divided the recognition element into single and combined recognition elements. Specifically, signal amplification technologies applied to the OTA electrochemical aptasensor are proposed. Furthermore, summary of the current limitations and future challenges in OTA analysis is included, which provide reference for the further research and applications.

Multicolor colorimetric detection of ochratoxin A via structure-switching aptamer and enzyme-induced metallization of gold nanorods

Colorimetric aptasensors have been intensively studied for the ochratoxin A (OTA) detection, but they mostly exhibit just one-color change, resulting in poor visual resolution and limited use for semi-quantitative analysis. Thus, we designed a high-resolution colorimetric assay on the basis of aptamer structural switching and enzyme-induced metallization of gold nanorods (AuNRs). DNA-alkaline phosphatase (ALP)-immobilized magnetic beads were prepared. The aptamer bounded to OTA to form G-quadruplexes, releasing ALP-labelled complementary DNA (cDNA-ALP). After magnetic separation, cDNA-ALP catalyzed the decomposition of ascorbic acid 2-phosphate to ascorbic acid that reduced Ag⁺, forming an Ag shell on the surface of AuNRs. This caused a blue-shift of the longitudinal local surface plasmon resonance peak of the AuNRs and a naked eye visible multicolor change. Under optimal conditions, the assay exhibited a 9.0 nM detection limit for OTA, with high specificity. This method is promising for the on-site visual semi-quantitative detection of mycotoxins in foods.

Predominant Mycotoxins, Pathogenesis, Control Measures, and Detection Methods in Fermented Pastes

Fermented pastes are some of the most popular traditional products in China. Many studies reported a strong possibility that fermented pastes promote exposure to mycotoxins, including aflatoxins, ochratoxins, and cereulide, which were proven to be carcinogenic and neurotoxic to humans. The primary mechanism of pathogenicity is by inhibiting protein synthesis and inducing oxidative stress using cytochrome P450 (CYP) enzymes. The level of mycotoxin production is dependent on the pre-harvest or post-harvest stage. It is possible to implement methods to control mycotoxins by using appropriate antagonistic microorganisms, such as Aspergillus niger, Lactobacillus plantarum, and Saccharomyces cerevisiae isolated from ordinary foods. Also, drying products as soon as possible to avoid condensation or moisture absorption in order to reduce the water activity to lower than 0.82 during storage is also effective. Furthermore, organic acid treatment during the soaking process reduces toxins by more than 90%. Some novel detection technologies based on magnetic adsorption, aptamer probes, and molecular-based methods were applied to rapidly and accurately detect mycotoxins in fermented pastes.