Novel fluorescent ELISA for the sensitive detection of zearalenone based on H2O2-sensitive quantum dots for signal transduction

Development of a Sensitive Enzyme Immunoassay Using Phage-Displayed Antigen-Binding Fragments for Zearalenone Detection in Cereal Samples

Zearalenone (ZEN), a non-steroidal estrogenic mycotoxin, contaminates animal feed and grain crops, thereby entering the food chain and posing a significant threat to human health. Consequently, there is an urgent need for a sensitive and rapid method for detecting trace levels of ZEN. In this study, we developed a phage-displayed antigen-binding fragment (Fab-phage) and established a Fab-phage-based enzyme-linked immunosorbent assay (Fab-pELISA) for ZEN detection. Under optimal conditions, this method exhibits a half-maximal inhibitory concentration of 0.36 ng/mL, with a linear range from 0.07 to 3.89 ng/mL and a detection limit of 0.03 ng/mL. The method demonstrates high selectivity towards ZEN and good recovery rates of 97.35-122.66% with relative standard deviations not exceeding 3.5%. Furthermore, the detection results obtained using Fab-pELISA on real cereal samples are consistent with those from high-performance liquid chromatography, meeting practical application requirements. Therefore, the Fab-phage serves as a valuable biochemical reagent, and the established Fab-pELISA represents a promising analytical strategy for detecting ZEN and other trace toxic contaminants in cereals.

A nanopore-based label-free CRISPR/Cas12a system for portable and ultrasensitive detection of zearalenone

BACKGROUND

Food safety has become a serious global concern. Therefore, there is a need for effective detection technologies in this field. Currently, the development of effective on-site detection techniques is extremely important for food safety. However, the traditional on-site detection methods currently lack effective signal amplification. Herein, the aim of this study was to construct a nanopore-based label-free CRISPR/Cas12a system for the detection of Zearalenone (ZEN). The method is expected to be highly sensitive for portable detection of ZEN in food.

RESULTS

The proposed strategy was mainly involved three steps, including the displacement of the target DNA, the triggering of the cleavage of hairpin DNA probes (probes 1) by the trans-cleavage of CRISPR/Cas12a, and the generation of a measurable nanopore current signal. The probes 1 and DNA after the cleavage of probes 1 (probes 2) produce different characteristic nanopore signals as they pass through the nanopore. The established method achieved a low limit of detection (LOD) of 6.52 fM for ZEN and a wide liner range under optimized conditions. Furthermore, the practical applicability of this method was verified in real maize samples and showed good recoveries (90.68-101.98 %) and low relative standard deviations (RSD) (9.21-9.72 %). Therefore, this method is a promising option for rapid and ultrasensitive detection of ZEN.

SIGNIFICANCE AND NOVELTY

The study presented a portable nanopore-based CRISPR/Cas12a signal amplification detection system for the detection of ZEN in food, which had a low LOD and the advantages of rapid, portability, and on-site detection potential. In conclusion, the method presented a promising prospect and universal platform for the detection of ZEN and other mycotoxins, offering a novel insight into on-site food safety detection.

A novel highly sensitive inner filter effect-based fluorescence immunoassay with quantum dots for bioanalysis of zolbetuximab, a monoclonal antibody used for immunotherapy of gastric and gastroesophageal junction adenocarcinoma

Zolbetuximab (ZOL) is a groundbreaking monoclonal antibody targeting CLDN 18.2, a cancer cell surface protein. It is a first-in-class therapy for gastric and gastroesophageal junction adenocarcinoma. However, there is currently any immunoassay available for bioanalysis of ZOL, hindering its pharmacokinetic studies, therapeutic monitoring, and safety profile refinement. To address this gap, this study presents the development and validation of a novel highly sensitive inner filter effect-based fluorescence immunoassay (IFE-FIA) with quantum dots (QDs) as a probe. This assay enables the quantitative determination of ZOL in plasma samples. The assay involved non-competitive capturing of ZOL from the samples using a specific antigen (CLDN 18.2 protein) immobilized on assay plate microwells. A horseradish peroxidase (HRP)-labelled anti-human IgG was used to measure the immune complex. The assay's detection system relies on the formation of a light-absorbing colored product through an HRP-catalyzed oxidative reaction with the substrate 3,3',5,5'-tetramethylbenzidine. This light absorption efficiently quenched the fluorescence of QDs via the IFE. The measured fluorescence signals corresponded to the concentrations of ZOL in the samples. The conditions of the IFE-FIA and its detection system were refined, and the optimum procedures were established. Following the guidelines of immunoassay validation for bioanalysis, the assay was validated, and all the validation criteria were acceptable. The assay demonstrates high sensitivity, accurately quantifying ZOL at concentrations as low as 10 ng/mL in plasma samples, with acceptable precision. Importantly, it avoids interferences from endogenous substances and plasma matrix. The recoveries in spiked human plasma ranged from 96.8 % to 104.5 %, with relative standard deviations of 4.1 %-6.5 %. The proposed IFE-FIA represents a valuable tool for quantifying ZOL in clinical settings, enabling assessment of its pharmacokinetics, therapeutic drug monitoring, and safety profile refinement.

Quantitative determination of four mycotoxins in cereal by fluorescent microsphere based immunochromatographic assay

BACKGROUND

Mycotoxins are secondary metabolites produced by fungi, which have serious effects on humans and animals. In this study, we selected the monodispersed polystyrene fluorescent microspheres with good luminescence performance and strong stability as markers to conjugate with four mycotoxins antibodies for preparing fluorescent probes. We have developed a fluorescent microsphere based immunochromatographic assay (FMICA) to detect sensitively and quickly zearalenone (ZEN), aflatoxin B₁ (AFB₁ ), fumonisin B₁ (FB₁ ), and ochratoxin A (OTA) in cereal.

RESULTS

Under optimal experimental conditions, the procedure of this method can be completed within 10 min. The limit of detection (LOD) of FMICA for ZEN, AFB₁ , FB₁ , and OTA is 0.072, 0.093, 0.32, and 0.19 μg L^-1 , respectively. And FMICA has good specificity and no cross-reactivity with other mycotoxins. Four mycotoxins in naturally contaminated cereal samples (corn, rice, and oat) are detected by this method, and the results are highly consistent with that of ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS).

CONCLUSION

The developed FMICA has good accuracy, high sensitivity, simplicity, convenience, rapidity, and low cost, and it could be employed for sensitive and quantitative detecting of mycotoxins in cereal on-site. © 2022 Society of Chemical Industry.

Surface Plasmon Resonance (SPR) biosensor for detection of mycotoxins: A review

Mycotoxin is one of the most important natural pollutants, which poses a global threat to food safety. However, the pollution of mold in food production is inevitable. The detection technology of mycotoxins in food production is an important means to prevent the damage of mycotoxins, so rapid detection and screening to avoid pollution diffusion is essential. The focus of this review is to update the literature on the detection of mycotoxins by surface plasmon resonance (SPR) technology, rather than just traditional chromatographic methods. As a relatively novel and simple analytical method, SPR has been proved to be fast, sensitive and label-free, and has been widely used in real-time qualitative and quantitative analysis of various pollutants. This paper aims to give a broad overview of the sensors for detection and analysis of several common mycotoxins.

Establishment of an Immunological Method for Detection of Bluetongue Virus by Fluorescence-Linked Immunosorbent Assay

Bluetongue (BT) is a severe noncontagious infectious disease that occurs in sheep and wild ruminants but occasionally also in cattle and camels. The worldwide BT pandemic has had a significant impact on global livestock production. Rapid detection helps prevent outbreaks of bluetongue disease. Fluorescence-linked immunosorbent assay (FLISA) labeled with quantum dots (QDs) is typically used for detection due to its high sensitivity. There has been no reported detection of BT virus (BTV) using QD-based fluorescence immunoassays. In this study, monoclonal antibodies (MAbs) against BT were prepared by immunizing BALB/c mice with recombinant VP7 protein. Two MAbs with high sensitivity and specificity were selected as the detection antibody (2F11) and capture antibody (11B7). Then, the detection antibody was coupled with QDs to prepare QD-MAb fluorescence probes. Fluorescence-linked immunosorbent assay is highly specific, detecting only VP7 protein/BTV, and did not show any nonspecific reactions with other reoviruses. The detection limit of VP7 protein was 3.91 ng/mL using fluorescence-linked immunosorbent assay, with a coefficient of variation (CV) of less than 15%. The establishment of rapid, sensitive direct FLISA has potential for bluetongue virus detection and control of BT vaccine quality. IMPORTANCE Bluetongue virus causes the severe infectious disease BT. BTV has many serotypes, and there is no cross-protection among different serotypes. BT is listed as a notifiable animal infectious disease by the World Organisation for Animal Health (OIE) and occurs throughout the world, causing significant economic losses. The establishment of a fast and effective detection method is the key to controlling and preventing this disease. Current methods for detecting BTV mainly include reverse transcription-PCR (RT-PCR), enzyme-linked immunosorbent assays (ELISA), and immunochromatographic strips that are based on antigen-antibody recognition. Immunoassays are most commonly used because of their low cost, high specificity, and fast analysis, making them particularly useful for routine monitoring. These conventional detection strategies for BTV have some drawbacks. Recently, FLISA has been drawing attention due to its sensitivity, which is higher than traditional immunoassays. Fluorescence-linked immunosorbent assays (FLISA) using fluorescent materials as labels overcome ELISA's disadvantage of being time-consuming.

Ultrasensitive Hypoxia Sensing at the Single-Molecule Level via Super-Resolution Quantum Dot-Linked Immunosandwich Assay

Activated hypoxia-inducible factor-1alpha (HIF-1α) plays an important role in the adaptive response of tumor cells to oxygen changes through the transcriptional activation of genes that regulate important biological processes required for tumor survival and progression. In this study, we developed an ultrasensitive hypoxia sensor based on read-out with quantum dots on a gold nanodisc (quantum dot-linked immunosandwich assay, QLISA) with excellent selectivity for HIF-1α. The immunoassay platform was established by comparing the immune response results using Qdot525 as a detection nanoprobe instead of a fluorescent dye (Alexa488) (fluorescent-linked immunosandwich assay, FLISA). In addition, using three-dimensional total internal reflection fluorescence microscopy, the platform was optically sectioned along the z-axis at 10 nm intervals to compare the height difference between the nanodisc and the nanoprobe following the QLISA and FLISA procedures and to localize the target location. Here, the super-resolution QLISA (srQLISA)-based hypoxia sensor exhibited high accuracy and precision for the detection of HIF-1α-extracted samples in cancer spheroids compared with the super-resolution FLISA (srFLISA) method. The developed nanobiosensor method demonstrated a wide dynamic linear detection range of 32.2 zM-8.0 pM with a limit of detection of 16 zM under optimal experimental conditions for HIF-1α, an approximate 10⁶-fold enhanced detection sensitivity compared with the conventional enzyme-linked immunosorbent assay method based on absorbance. The detection of HIF-1α using the newly developed srQLISA sensor allows for independently predicting tumor progression and early cancer onset increases in the microvasculature density of tumor lesions.

Recent advances in the highly sensitive determination of zearalenone residues in water and environmental resources with electrochemical biosensors

Zearalenone (ZEN), a significant class of mycotoxin which is considered as a xenoestrogen, permits, similar to natural estrogens, it's binding to the receptors of estrogen resulting in various reproductive diseases especially, hormonal misbalance. ZEN has toxic effects on human and animal health as a result of its teratogenicity, carcinogenicity, mutagenicity, nephrotoxicity, genotoxicity, and immunotoxicity. To ensure water and environmental resources safety, precise, rapid, sensitive, and reliable analytical and conventional methods can be progressed for the determination of toxins such as ZEN. Different selective nanomaterial-based compounds are used in conjunction with different analytical detection approaches to achieve this goal. The current review demonstrates the state-of-the-art advances of nanomaterial-based electrochemical sensing assays including various sensing, apta-sensing and, immunosensing studies to the highly sensitive determination of various ZEN families. At first, a concise study of the occurrence, structure, toxicity, legislations, and distribution of ZEN in monitoring has been performed. Then, different conventional and clinical techniques and procedures to sensitive and selective sensing techniques have been reviewed and the efficient comparison of them has been thoroughly discussed. This study has also summarized the salient features and the requirements for applying various sensing and biosensing platforms and diverse immobilization techniques in ZEN detection. Finally, we have defined the performance of several electrochemical sensors applying diverse recognition elements couples with nanomaterials fabricated using various recognition elements coupled with nanomaterials (metal NPs, metal oxide nanoparticles (NPs), graphene, and CNT) the issues limiting development, and the forthcoming tasks in successful construction with the applied nanomaterials.

Copper Oxide Nanoparticle-Based Immunosensor for Zearalenone Analysis by Combining Automated Sample Pre-Processing and High-Throughput Terminal Detection

A rapid and high-throughput fluorescence detection method for zearalenone (ZEN) based on a CuO nanoparticle (NP)-assisted signal amplification immunosensor was developed using an automated sample pretreatment and signal conversion system. CuO NPs with high stability and biocompatibility were used as carriers to immobilize anti-ZEN antibodies. The obtained CuO NP-anti-ZEN can maintain the ability to recognize target toxins and act as both a signal source and carrier to achieve signal conversion using automated equipment. In this process, target toxin detection is indirectly transformed to Cu²⁺ detection because of the large number of Cu²⁺ ions released from CuO NPs under acidic conditions. Finally, a simple and high-throughput fluorescence assay based on a fluorescent tripeptide molecule was employed to detect Cu²⁺, using a multifunctional microporous plate detector. A good linear relationship was observed between the fluorescence signal and the logarithm of ZEN concentration in the range of 16.0–1600.0 μg/kg. Additionally, excellent accuracy with a high recovery yield of 99.2–104.9% was obtained, which was concordant with the results obtained from LC-MS/MS of naturally contaminated samples. The CuO NP-based assay is a powerful and efficient screening tool for ZEN detection and can easily be modified to detect other mycotoxins.

Ultrasensitive monitoring strategy of PCR-like levels for zearalenone contamination based DNA barcode

BACKGROUND

The ultrasensitive monitoring strategy of zearalenone (ZEN) is essential and desirable for food safety and human health. In the present study, a coupling of gold nanoparticles-DNA barcode and direct competitive immunoassay-based real-time polymerase chain reaction signal amplification (RT-IPCR) for ZEN close to the sensitivity of PCR-like levels is described and evaluated.

RESULTS

The RT-IPCR benefited from the use of a DNA barcode and RT-PCR detection strategy, thus resulting in ultrasensitive and simple detection for ZEN. Under the optimal RT-IPCR, the linear range of detection was from 0.5 to 1000 pg mL^-1 and the limit of detection was 0.5 pg mL^-1 , which was 400-fold lower than the enzyme-linked immunosorbent assay. The detection procedure was simplified and the detection time was shortened. The specificity, accuracy and precision of the RT-IPCR confirmed a high performance. ZEN-positive contamination levels were from 0.056 to 152.12 ng g^-1 by the RT-IPCR, which was demonstrated to be highly reliable by liquid chromatography-tandem mass spectrometry.

CONCLUSION

The proposed RT-IPCR could be used as an alternative for detecting ZEN with satisfactory ultrasensitivity, simplicity, low cost and high-throughput. The present study could provide a strategy for the ultrasensitive detection of the small molecule with a simple and practical approach, which has significant appeal and application prospects.

Multiple fluorescence immunoassay for the simultaneous detection of Zearalenone and Ochratoxin A

A sensitive and accurate multiple fluorescence immunoassay for the simultaneous quantitative detection of Zearalenone (ZEN) and Ochratoxin A (OTA) in single spot based on multicolor quantum dots (QDs) labeling was developed for the first time. Two kinds of ZnCdSe/ZnS (core/shell) QDs with maximum emission wavelengths at 520 nm (green) and 610 nm (orange-red) were selected as marking materials, respectively. The anti-ZEN-mAb-QDs and anti-OTA-mAb-QDs were designed as the immune fluorescent probes. Fluorescence was measured at the same excitation wavelength and two different emission wavelengths to determine each target. The procedure for QDs-based multiple fluorescence labeled immunosorbent assay (M-FLISA) was developed. The 50% inhibition concentrations (IC₅₀) of ZEN and OTA were 0.034 and 1.175 ng/mL. Moreover, the limits of detection (LOD) for the simultaneous determination were 0.0239 and 2.339 ng/g for ZEN and OTA in maize, respectively. In addition, the recoveries ranged from 93.15 to 101.90% for ZEN and from 95.29 to 102.43% for OTA, with the coefficient variation (CV) of 2.70-8.86% and 3.51-6.22% respectively. There was good consistency between the M-FLISA and high performance liquid chromatography (HPLC) results, which confirmed that the M-FLISA was suitable for the simultaneous quantitative detection of various mycotoxins.

Direct and Competitive Optical Grating Immunosensors for Determination of Fusarium Mycotoxin Zearalenone

Novel optical waveguide lightmode spectroscopy (OWLS)-based immunosensor formats were developed for label-free detection of Fusarium mycotoxin zearalenone (ZON). To achieve low limits of detection (LODs), both immobilised antibody-based (direct) and immobilised antigen-based (competitive) assay setups were applied. Immunoreagents were immobilised on epoxy-, amino-, and carboxyl-functionalised sensor surfaces, and by optimising the immobilisation methods, standard sigmoid curves were obtained in both sensor formats. An outstanding LOD of 0.002 pg/mL was obtained for ZON in the competitive immunosensor setup with a dynamic detection range between 0.01 and 1 pg/mL ZON concentrations, depending on the covalent immobilisation method applied. This corresponds to a five orders of magnitude improvement in detectability of ZON relative to the previously developed enzyme-linked immonosorbent assay (ELISA) method. The selectivity of the immunosensor for ZON was demonstrated with structural analogues (α-zearalenol, α-zearalanol, and β-zearalanol) and structurally unrelated mycotoxins. The method was found to be applicable in maize extract using acetonitrile as the organic solvent, upon a dilution rate of 1:10,000 in buffer. Thus, the OWLS immunosensor method developed appears to be suitable for the quantitative determination of ZON in aqueous medium. The new technique can widen the range of sensoric detection methods of ZON for surveys in food and environmental safety assessment.

A mix-and-detect method based on colloidal gold immunochromatographic assay for on-site detection of zearalenone in edible oils

The common methods to detect zearalenone (ZEN) in edible oils need organic solvents to extract ZEN and then some sample purification process before detection, so, it is not convenient for on-site use. Here a simple method without organic solvents and a sample purification process was developed for the determination of ZEN in edible oils. The detection process only needs mixing oil with a surfactant solution in the indicated ratio and then loading the mixture onto a colloidal gold immunochromatographic (CGI) strip for detection. The optimized surfactant was AEO15 among the seven surfactants studied in this paper. The ZEN residue in edible oil could be quantitatively determined with a detection limit of 44.3 ng g-1, and the working range of the standard curve was from 50 to 800 ng g-1. This method has been successfully applied to the detection of ZEN in plant oils with recoveries ranging from 81 ± 7% to 129 ± 9% for spiked samples. The detection results for the ZEN residue in oil samples from a local market by this method were in good agreement with those obtained by the national standard method.

A bio-bar-code photothermal probe triggered multi-signal readout sensing system for nontoxic detection of mycotoxins

Herein, a photothermal triggered multi-signal readout (MSR) system was innovatively established with great convenience for low-cost and sensitive point-of-care testing (POCT). In this sensing system, an intelligent multi-signal readout interface (MSRI) with multidimensional response-ability to thermal stimulus was developed and utilized as a sensing element. A bio-bar-code photothermal probe peptides@H₂N-HCNTs acted as a target associated photothermal agent anchored on MSRI via competitive reaction. The multi-signal assay of target was realized under the driven of 808 nm laser, photo-to-thermal conversion effect of photothermal probe caused dramatically thermal energy increase on MSRI. As a result, the competitive recognition events were translated into several detectable signals on MSRI, including a local temperature elevation, a visual color change from blue to green as well as weight loss on MSRI, all of these signals were proportional to the target concentration. This assay has been successfully applied in field work for detecting zearalenone (ZEN), a common mycotoxin in grain food, with linear ranger from 10^-7 ng/mL to 10^-1 ng/mL and detection limits of 1.06 × 10^-7 ng/mL. Combination of the different signal principles was expected to result in more reliable and precise results. Accordingly, this creatively designed MSR-system not only provided a platform for sensitive monitor of mycotoxin but also offered new method for reliable and affordable personal assays in daily life and low-resource setting.

Contamination of Zearalenone from China in 2019 by a Visual and Digitized Immunochromatographic Assay

Zearalenone (ZEN) is a prevalent mycotoxin that needs intensive monitoring. A semi-quantitative and quantitative immunochromatographic assay (ICA) was assembled for investigating ZEN contamination in 187 samples of cereal and their products from China in 2019. The semi-quantitative detection model had a limit of detection (LOD) of 0.50 ng/mL with visual judgment and could be completely inhibited within 5 min at 3.0 ng/mL ZEN. The quantitative detection model had a lower LOD of 0.25 ng/mL, and ZEN could be accurately and digitally detected from 0.25-4.0 ng/mL. The ICA method had a high sensitivity, specificity, and accuracy for on-site ZEN detection. For investigation of the authentic samples, the ZEN-positive rate was 62.6%, and the ZEN-positive levels ranged from 2.7 to 867.0 ng/g, with an average ZEN-positive level being 85.0 ng/g. Of the ZEN-positive samples, 6.0% exceeded the values of the limit levels. The ZEN-positive samples were confirmed to be highly correlated using LC-MS/MS (R² = 0.9794). This study could provide an efficiency and accuracy approach for ZEN in order to achieve visual and digitized on-site investigation. This significant information about the ZEN contamination levels might contribute to monitoring mycotoxin occurrence and for ensuring food safety.

Sensor Based on Molecularly Imprinted Polymer Membranes and Smartphone for Detection of Fusarium Contamination in Cereals

The combination of the generic mobile technology and inherent stability, versatility and cost-effectiveness of the synthetic receptors allows producing optical sensors for potentially any analyte of interest, and, therefore, to qualify as a platform technology for a fast routine analysis of a large number of contaminated samples. To support this statement, we present here a novel miniature sensor based on a combination of molecularly imprinted polymer (MIP) membranes and a smartphone, which could be used for the point-of-care detection of an important food contaminant, oestrogen-like toxin zearalenone associated with Fusarium contamination of cereals. The detection is based on registration of natural fluorescence of zearalenone using a digital smartphone camera after it binds to the sensor recognition element. The recorded image is further processed using a mobile application. It shows here a first example of the zearalenone-specific MIP membranes synthesised in situ using "dummy template"-based approach with cyclododecyl 2, 4-dihydroxybenzoate as the template and 1-allylpiperazine as a functional monomer. The novel smartphone sensor system based on optimized MIP membranes provides zearalenone detection in cereal samples within the range of 1-10 µg mL^-1 demonstrating a detection limit of 1 µg mL^-1 in a direct sensing mode. In order to reach the level of sensitivity required for practical application, a competitive sensing mode is also developed. It is based on application of a highly-fluorescent structural analogue of zearalenone (2-[(pyrene-l-carbonyl) amino]ethyl 2,4-dihydroxybenzoate) which is capable to compete with the target mycotoxin for the binding to zearalenone-selective sites in the membrane's structure. The competitive mode increases 100 times the sensor's sensitivity and allows detecting zearalenone at 10 ng mL^-1. The linear dynamic range in this case comprised 10-100 ng mL^-1. The sensor system is tested and found effective for zearalenone detection in maize, wheat and rye flour samples both spiked and naturally contaminated. The developed MIP membrane-based smartphone sensor system is an example of a novel, inexpensive tool for food quality analysis, which is portable and can be used for the "field" measurements and easily translated into the practice.

A simple mesoporous silica nanoparticle-based fluorescence aptasensor for the detection of zearalenone in grain and cereal products

Zearalenone (ZEN) is a type of estrogenic mycotoxin commonly occurring in cereals. The aim of this study was to design a simple, rapid, inexpensive and ultrasensitive fluorescence assay for the determination of ZEN. Here, amino-modified mesoporous silica nanoparticles (MSNs-NH₂) were synthesized to be the positive charge-rich reactor. A 6-carboxy-fluorescein-labeled aptamer (aptamer-FAM) was designed as the signal probe, ZEN-capture probe and negative charge reactor. In the absence of ZEN, the negatively charged aptamer-FAM combined with the positively charged MSNs-NH₂ in an electrostatic manner. In the presence of ZEN, the fluorescence intensity in the supernatant increased significantly because the aptamer-FAM could bind to ZEN instead of MSNs-NH₂. Under the optimal experimental conditions, this assay exhibited excellent specificity, repeatability and a wide linearity range of 0.005-150 ng/mL, with a detection limit of 0.012 ng/mL. Additionally, it showed high recovery (83.3-101.5%) for the spiked samples. There was no statistically significant difference in the ZEN concentrations detected by the proposed assay and HPLC in naturally contaminated samples. Overall, this design provides a new strategy for the rapid, inexpensive and sensitive detection of ZEN, and it could be applied to develop fluorometric assays for different targets by the selection of appropriate aptamers. Graphical abstract.

A fluorescence microplate assay based on molecularly imprinted silica coated quantum dot optosensing materials for the separation and detection of okadaic acid in shellfish

Molecularly imprinted polymers (MIPs) are attracting substantial interest as artificial plastic antibodies because of their biometric capability for targeting small molecules. In this study, molecularly imprinted silica material-coated quantum dots (MIS-QDs) with selective recognition capability to okadaic acid (OA) were developed and characterized. The synthesized MIS-QDs with specific imprinting cavities exhibited excellent recognition capability similar to those of biological antibodies and high fluorescence (FL) quenching selectivity for OA. Furthermore, the MIS-QDs with unsaturated bonds were immobilized onto the surface of 96-well microplates by cold plasma-induced grafting. A novel direct competitive microplate assay strategy was then proposed. The FL quenching properties of the developed microplate assay showed an excellent linear relationship with OA in the range of 10.0-100.0 μg/kg with a correlation coefficient of 0.9961. The limit of detection for OA was 0.25 μg/kg in the shellfish samples. The mean quantitative recoveries were 92.5%-101.0% and 92.9%-101.3%, with relative standard deviations of <7.7% and 7.6% for pure solvents and purified shellfish samples, respectively. The established microplate assay strategy can be used as a rapid and high-throughput method for analyzing OA marine toxins in biological samples.

A self-enhanced electrochemiluminescent ratiometric zearalenone immunoassay based on the use of helical carbon nanotubes

A self-enhanced electrochemiluminescent ratiometric immunoassay for zearalenone is described. A system composed of N-aminobutyl-N-ethylisoluminol (ABEI) and glutathione (GSH) produces a strong electrochemiluminescence (ECL) at an applied potential of 0.8 V, probably because of short electron transfer distance and reduced energy loss. The method also uses octahedral anatase mesocrystals (OAM) with a large specific surface facilitating immobilization of ABEI and GSH. Helical carbon nanotubes, possessing a large specific surface, superior mechanical stability, and excellent electrical conductivity which serve as a solid support, greatly enhanced the loading capacity for g-C₃N₄ nanosheets and horseradish peroxidase-labeled anti-antibody. The peroxidase accelerates the decomposition of H₂O₂ to produce reactive oxygen species (ROSs), amplifying the blue ECL of ABEI and the green ECL of g-C₃N₄. The ratiometric sandwich immunoassay (performed by the ratio of ECL intensity at - 1.3 V and 0.8 V) allows for sensitive and reliable determination of ZEN in a wide linear range from 1.0 × 10^-4 ng/mL to 10 ng/mL. The method was successfully applied to the analysis of corn hazelnut samples for ZEN. Graphical abstract Schematic presentation of a self-enhanced electrochemiluminescent ratiometric immunosensor based on octahedral anatase mesocrystals (OAM) supported ABEI-glutathione (GSH) and g-C₃N₄ functionalized helical carbon nanotubes (HCNT) for zearalenone (ZEN) determination.

Fluorescent enzyme-linked immunoassay based on silane-doped carbon dots for sensitive detection of microcystin-LR in water and crucian samples

In this work, a fluorescent nanoparticles labeling-free fluorescence enzyme-linked immunoassay (FELISA) has been established for the ultrasensitive detection of microcystin-LR (MC-LR) in water and fish samples. Polyclonal antibody against MC-LR was labeled with horseradish peroxidase (HRP) and used as signal probe for binding with analyte in sample or for coating antigen. After washing of the unbound antibody, the substrate system (2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate) (ABTS)/H₂O₂) was added. The oxidation product of ABTS (ox-ABTS) catalyzed by HRP effectively caused the fluorescence quenching of subsequently added silane-doped carbon dots (Si-CDs), and the change in fluorescence intensity of Si-CDs was used to realize the quantitative detection of MC-LR. Under the optimum conditions, the Si-CDs based FELISA method showed a good linear relationship from 0.001 to 3.20 μg L^-1 (R² = 0.994) and provided a low detection limit of 0.6 ng L^-1, which was approximately 30-fold lower than that of traditional indirect competitive ELISA. Average recovery values from 79.9% to 109.2% was obtained from spiked water and crucian samples, suggesting its potential application on the monitoring of MR-LR at a trace level.

Detection of zearalenone in an aptamer assay using attenuated internal reflection ellipsometry and it's cereal sample applications

Mycotoxins are toxic compounds produced by the metabolism of certain fungi that threaten the food and agricultural industry. Over hundreds of mycotoxins, one of the most common toxins, zearalenone (ZEN), has toxic effects on human and animal health due to its mutagenicity, treatogenicity, carcinogenicity, nephrotoxicity, immunotoxicity, and genotoxicity. In this work, attenuated internal reflection spectroscopic ellipsometry (AIR-SE) combined with the signal amplification via surface plasmon resonance conditions that were proved to be a highly sensitive analytical tool in bio-sensing was developed for the sensitive and selective ZEN detection in cereal products such as corn, wheat, rice, and oat. Combined with the oligonucleotide aptamer for ZEN recognition, our proposed method showed good performance with yielding 0.08 ng/mL LOD and 0.01-1000 ng/mL detection range. A mini-review was also introduced in, to compare various methods for ZEN detection.

Electrochemiluminescent competitive immunoassay for zearalenone based on the use of a mimotope peptide, Ru(II)(bpy)3-loaded NiFe2O4 nanotubes and TiO2 mesocrystals

An ultrasensitive competitive-type electrochemiluminescence immunoassay for the mycotoxin zearalenone is described. The method is based on the use of (a) a mimotope peptide that was selected from a phage displayed peptide library and used to substitute ZEN for designing the competitive assay; (b) NiFe₂O₄ nanotubes with large specific surface area loaded with the ECL probe Ru(bpy)₃²⁺; and (c) poly(vinylpyrrolidone) (PVP)-assisted synthesis of TiO₂ mesocrystals that acts as the sensing platform and support for antibody immobilization. Under the optimized conditions and at an ECL working potential of 1.1 V, a linear response is found for ZEN in the 0.1 to 1.0 × 10^-5 ng·mL^-1 concentration range with a detection limit as low as 3.3 fg·mL^-1. Graphical abstract An ultrasensitive competitive-type electrochemiluminescence (ECL) immunosensor based on mimotope peptide was constructed for the detection of Zearalenone.

Zearalenone Contamination in Corn, Corn Products, and Swine Feed in China in 2016-2018 as Assessed by Magnetic Bead Immunoassay

In total, 405 samples of corn, corn products, and swine feed from China in 2016-2018 were surveyed for zearalenone (ZEN) contamination using a magnetic bead immunoassay-coupled biotin-streptavidin system (BAS-MBI). The developed BAS-MBI had a limit of detection (LOD) of 0.098 ng mL-1, with half-maximal inhibition concentration (IC50) of 0.71 ng mL-1 in working buffer, and an LOD of 0.98 ng g-1; the detection range was from 0.98 to 51.6 ng g-1 in authentic agricultural samples. The BAS-MBI has been demonstrated to be a powerful method for the rapid, sensitive, specific, and accurate determination of ZEN. The ZEN positivity rate reached the highest level of 40.6% in 133 samples in 2016; ZEN levels ranged from 1.8 to 1100.0 ng g-1, with an average level of 217.9 ng g-1. In 2017, the ZEN positivity rate was the lowest at 24.5% in 143 samples; ZEN levels ranged from 1.1 to 722.6 ng g-1, with an average of 166.7 ng g-1. In 2018, the ZEN positivity rate was 31.8% in 129 samples; ZEN levels ranged from 1.3 to 947.8 ng g-1, with an average of 157.0 ng g-1. About 20% of ZEN-positive samples exceeded maximum limit levels. An alternative method of ZEN detection and a valuable reference for ZEN contamination in corn and its related products in China are provided. This survey suggests the need for prevention of serious ZEN contamination, along with management for food safety and human health.

A Gold Growth-Based Plasmonic ELISA for the Sensitive Detection of Fumonisin B1 in Maize

In this paper, a highly sensitive plasmonic enzyme-linked immunosorbent assay (pELISA) was developed for the naked-eye detection of fumonisin B₁ (FB₁). Glucose oxidase (GOx) was used as an alternative to horseradish peroxidase as the carrier of the competing antigen. GOx catalyzed the oxidation of glucose to produce hydrogen peroxide, which acted as a reducing agent to reduce Au³⁺ to Au on the surface of gold seeds (5 nm), This reaction led to a color change in the solution from colorless to purple, which was observable to the naked eye. Various parameters that could influence the detection performance of pELISA were investigated. The developed method exhibited a considerably high sensitivity for FB₁ qualitative naked-eye detection, with a visible cut-off limit of 1.25 ng/mL. Moreover, the proposed pELISA showed a good linear range of 0.31–10 ng/mL with a half maximal inhibitory concentration (IC₅₀) of 1.86 ng/mL, which was approximately 13-fold lower than that of a horseradish peroxidase- (HRP)-based conventional ELISA. Meanwhile, the proposed method was highly specific and accurate. In summary, the new pELISA exhibited acceptable accuracy and precision for sensitive naked-eye detection of FB₁ in maize samples and can be applied for the detection of other chemical contaminants.

Monitoring zearalenone in corn flour utilizing novel self-enhanced electrochemiluminescence aptasensor based on NGQDs-NH2-Ru@SiO2 luminophore

Accurate and early diagnosis of mycotoxin is particularly significant to the food and agricultural product safety. In the present work, a sensitive and effective monitoring method for zearalenone (ZEN) was exploited based on a novel self-enhanced electrochemiluminescence (ECL) aptasensor. The self-enhanced lumonophore was compounded by electrostatically combining amine-functionalized Ru(bpy)₃²⁺-doped silica nanoparticles (NH₂-Ru@SiO₂ NPs) and nitrogen doped graphene quantum dots (NGQDs) together. Since the emitter and co-reactant simultaneously existed in the same nanoparticle, shortened electron-transfer distance and decreased energy loss was obtained. Therefore, self-enhanced ECL aptasensor based on the novel complex expressed the widest linear range of 10 fg mL^-1-10 ng mL^-1 and the lowest detection limit of 1 fg mL^-1 for ZEN detection. More importantly, ZEN produced during the mildew process of corn flour was monitored by the developed aptasensor, which exhibited superior determination and potential application in real samples.

Voltammetric behavior of mycotoxin zearalenone at a single walled carbon nanotube screen-printed electrode

A voltammetric method at a single walled carbon nanotube screen-printed electrode was applied for the determination of zearalenone in food samples.

A mimotope peptide-based dual-signal readout competitive enzyme-linked immunoassay for non-toxic detection of zearalenone

In this study, a mimotope peptide-based non-toxic photoelectrochemical (PEC) competitive enzyme-linked immunoassay (ELISA) was established for ultrasensitive detection of zearalenone (ZEN) with dual-signal readout.

Carbon Quantum Dots Encapsulated Molecularly Imprinted Fluorescence Quenching Particles for Sensitive Detection of Zearalenone in Corn Sample

An eco-friendly and efficient one-step approach for the synthesis of carbon quantum dots (CDs) that encapsulated molecularly imprinted fluorescence quenching particles (MIFQP) and their application for the determination of zearalenone (ZEA) in a cereal sample are described in this study. CDs with high luminescence were first synthesized, and then encapsulated in the silica-based matrix through a non-hydrolytic sol-gel process. The resulting ZEA-imprinted particles exhibited not only an excellent specific molecular recognition of ZEA, but also good photostability and obvious template binding-induced fluorescence quenching. Under the optimized conditions, the fluorescence intensity of MIFQP was inversely proportional to the concentration of ZEA. By validation, the detection range of these fluorescence quenching materials for ZEA was between 0.02 and 1.0 mg L-1, and the detection limit was 0.02 mg L-1 (S/N = 3). Finally, the MIFQP sensor was successfully applied for ZEA determination in corn with recoveries from 78% to 105% and the relative standard deviation (RSD %) was lower than 20%, which suggests its potential in actual applications.

Antibody immobilization strategy for the development of a capacitive immunosensor detecting zearalenone

A highly sensitive flow-injection capacitive immunosensor was developed for detection of the mycotoxin zearalenone (ZEN). Different strategies for immobilization of an anti-ZEN antibody on the surface of a gold electrode, i.e. polytyramine or self-assembled monolayers (SAMs) of 3-mercaptopropionic acid (3-MPA) and lipoic acid (LA), were used and their performances were compared. The LA- and 3-MPA-based systems showed broad linear ranges for ZEN determination, i.e. from 0.010 nM to 10 nM and from 0.020 nM to 10 nM, respectively. Under optimal conditions, the LA-based immunosensor was capable of performing up till 13 regeneration-interaction cycles (with use of glycine HCl, pH 2.4) with a limit of detection (LOD) of 0.0060 nM, equivalent to 1.9 pg mL^-1. It also demonstrated a good inter-assay precision (RSD < 10%). However, the tyramine-based capacitive immunosensor showed a bad repeatability (only 4 regeneration-interaction cycles were possible) and inter-assay precision (RSD > 15%) which did not allow sensitive and precise measurements. The LA-based method was compared with a direct ELISA. These results demonstrated that the label-free developed capacitive immunosensor had a better sensitivity and shorter analysis time in comparison with the direct microwell-plate format.

Novel Colorimetric Aptasensor for Zearalenone Detection Based on Nontarget-Induced Aptamer Walker, Gold Nanoparticles, and Exonuclease-Assisted Recycling Amplification

Zearalenone (ZEN) toxicity is a significant risk for human beings. Thus, it is of high importance to develop sensitive, precise, and inexpensive analytical methods for ZEN detection, especially in human serum. Here, a colorimetric aptasensor is presented for the determination of ZEN based on the nontarget-induced aptamer walker, catalytic reaction of gold nanoparticles (AuNPs), exonuclease III (Exo III) as a signal amplifier, and 4-nitrophenol as a colorimetric agent. Low amount of ZEN requirement and signal amplification are some of the distinct advantages of the proposed aptasensor. In the absence of ZEN, the aptamer (Apt) starts walking on the AuNP surface with the help of Exo III and binds to multiple complementary strands of aptamer, leading to the change of sample color from yellow to colorless. Upon the addition of ZEN, both the Apt and complementary strand exist as single-stranded DNAs on the surface of AuNPs, resulting in less access of 4-nitrophenol to the surface of AuNPs and less catalytic performance of AuNPs. In this situation, the color of the sample remains yellow (the color of 4-nitrophenol). The presented aptasensor was capable to detect ZEN in a wide linear dynamic range, 20-80 000 ng/L, with a detection limit of 10 ng/L. The prepared sensing strategy was successfully used for ZEN determination in the human serum sample.

Fluoroimmunoassays for the detection of zearalenone in maize using CdTe/CdS/ZnS quantum dots

CdTe/CdS/ZnS quantum dots (QDs) were synthesized in aqueous phase and conjugated with a new anti-zearalenone (ZEN) monoclonal antibody. Using this novel fluorescent probe, a fluoroimmunoassay (FLISA) and a rapid immunochromatographic strip (ICTS) were developed for the detection of ZEN in maize. Our proposed FLISA allowed for ZEN determination in the range of 0.038-0.977 ng/mL with an IC₅₀ of 0.162 ng/mL and a limit of detection (LOD) of 0.012 ng/mL occurring in maize. The rapid ICTS had a visual LOD of 1.0 ng/mL in buffer solution and 1.5 ng/mL in maize extract. These two QDs-based immunoassays were all successfully verified by commercial ELISA kits. The results confirmed that: firstly, the FLISA can be used as a robust method for the sensitive detection of ZEN; and secondly, the ICTS is ideally suited for rapidly screening large numbers of samples.

Developments in mycotoxin analysis: an update for 2015-2016

This review summarises developments in the determination of mycotoxins over a period between mid-2015 and mid-2016. Analytical methods to determine aflatoxins, Alternaria toxins, ergot alkaloids, fumonisins, ochratoxins, patulin, trichothecenes and zearalenone are covered in individual sections. Advances in proper sampling strategies are discussed in a dedicated section, as are methods used to analyse botanicals and spices and newly developed liquid chromatography mass spectrometry based multi-mycotoxin methods. This critical review aims to briefly discuss the most important recent developments and trends in mycotoxin determination as well as to address limitations of presented methodologies.