Multiplex flow-through immunoassay formats for screening of mycotoxins in a variety of food matrices

Magnetic beads-assisted fluorescence aptasensing approach based on dual DNA tweezers for detection of ochratoxin A and fumonisin B1 in wine and corn

A magnetic beads (MBs)-assisted fluorescence aptasensing approach based on dual DNA tweezers and magnetic separation was established for the detection of ochratoxin A (OTA) and fumonisin B₁ (FB₁). A dual DNA tweezers structure with four ends linked with fluorophores (FAM, ROX) and quenchers (BHQ₁, BHQ₂) was designed, and produced the high initial fluorescence signals because of the long spatial distance between FAM and BHQ₁, ROX, and BHQ₂. Bio-aptamer/anti-aptamer of OTA and bio-aptamer/anti-aptamer of FB₁ were respectively annealed to form dsDNA, and immobilized to MBs coated with streptavidin (SA). With the existence of OTA and FB₁, OTA and FB₁ preferentially bound with their respective bio-aptamers, which made anti-aptamers dissociate from dsDNA coupled on MBs. After magnetic separation, the dissociated anti-aptamers reacted with dual DNA tweezers, respectively, which made DNA tweezers close and the fluorescence was quenched. The linear ranges of approach for OTA and FB₁ detection were 0.05-20 ng/mL and 0.1-40 ng/mL, respectively. The limit of detection for OTA and FB₁ was 0.029 ng/mL and 0.061 ng/mL. The prepared MBs-assisted fluorescence aptasensing approach was applied to detect OTA and FB₁ in spiked red wine and corn samples, which showed good recoveries between 92 and 106%.

Development of a Lateral Flow Immunoassay (LFIA) to Screen for the Release of the Endocrine Disruptor Bisphenol A from Polymer Materials and Products

One of the most important chemicals used in the production of polymer plastics and coatings is bisphenol A. However, despite the large number of studies on the toxicity and hormonal activity of BPA, there are still open questions and thus considerable media attention regarding BPA toxicity. Hence, it is necessary to develop a sensitive, simple, cost-efficient, specific, portable, and rapid method for monitoring bisphenol A and for high sample throughput and on-site screening analysis. Lateral flow immunoassays have potential as rapid tests for on-site screening. To meet sensitivity criteria, they must be carefully optimized. A latex microparticle-based LFIA for detection of BPA was developed. The sensitivity of the assay was improved by non-contact printing of spot grids as the control and test lines with careful parameter optimization. Results of the test could be visually evaluated within 10 min with a visual cut-off of 10 µg/L (vLOD). Alternatively, photographs were taken, and image analysis performed to set up a calibration, which allowed for a calculated limit of detection (cLOD) of 0.14 µg/L. The method was validated for thermal paper samples against ELISA and LC-MS/MS as reference methods, showing good agreement with both methods.

Recent progress in visual methods for aflatoxin detection

Aflatoxins (AFs) contamination in food and agricultural products poses a significant threat to human health. Sensitive and accurate detection of AFs provides a strong guarantee for ensuring food safety. Conventional chromatographic-based or mass spectrum methods, which rely on bulky instrument and skilled personnel, are not suitable for on-site surveillance. By contrast, visual detections which possess the merits of rapidity and sophisticated instrument-free present an excellent potential for the on-site detection of AFs. This review intends to summarize the latest development of visual methods for AFs detection, including paper-based tests, chromogenic reactions, and luminescent methods. Emerging technologies, like nanotechnology, DNAzymes, and aptamers combined with these visual methods are introduced. The basic principles, features, and application advantages of each type of visual methods are discussed. The biggest challenges and perspectives on their future trends are also addressed.

Immunochemical approaches for detection of aflatoxin B1 in herbal medicines

INTRODUCTION

Aflatoxin B1 (AFB1) is a toxic low-molecular-weight secondary metabolite of Aspergillus flavus and A. parasiticus. AFB1 was classified as a Group I carcinogen by the World Health Organisation for Research on Cancer in 1993. AFB1 is an unavoidable natural contaminant of some herbal medicine, able to cause serious health issues for humans consuming the related medicine.

OBJECTIVE

Therefore, this study aimed to develop an efficient fluorescence polarisation immunoassay (FPIA) and a rapid, low-cost, and easy-to-use membrane-based flow-through immunoassay (MBA) for determination of AFB1 in herbal medicine Origanum vulgare L., Rubus idaeus L., Urtica dioica L. and Sorbus aucuparia L.

RESULTS

A cut-off level of the developed MBA was 0.8 ppb. Validation of the developed test was performed with blank and spiked samples. Using three naturally contaminated or three artificially spiked samples. The FPIA showed a linear working range of 8.6 to 64 ppb, and a half maximal inhibitory concentration (IC₅₀ ) of 24 ppb.

CONCLUSION

The results were in good correlation with the enzymelinked immunosorbent assay (ELISA) results (the IC₅₀ 0.1 ppb). Both the sample preparation and analysis are simple, cost-effective and easy to perform on-site in non-laboratory environments. Liquid chromatography with tandem mass spectrometry (LC-MS/MS) was used as a confirmatory technique.

Detection of aflatoxin B1 with a new label-free fluorescent aptasensor based on exonuclease I and SYBR Gold

This paper describes a new label-free fluorescent aptasensor for the detection of aflatoxin B1 (AFB1) based upon exonuclease I (Exo I) and SYBR Gold, in which SYBR Gold, aptamer, AFB1, and Exo I were used. Specific combinations of aptamer and AFB1 occurred in the presence of AFB1 and consequently altered the spatial structure of the aptamer, thereby preventing its digestion by Exo I. When SYBR Gold was added, intense fluorescence was observed. Additionally, a good linear relationship was observed under optimized conditions between the fluorescence intensities and the AFB1 concentrations (R2 = 0.993). The established aptamer sensor was highly sensitive and exhibited a low limit of detection of 1.82 ng mL-1, with superior specificity for AFB1. It was also used in the quantification of AFB1 levels in soybean sauce samples and demonstrated satisfactory recoveries in the scope of 94.8-108.9%. The proposed sensor is highly sensitive, low cost, and capable of rapid detection and can thus be used to determine mycotoxin levels in a wide range of feeds and food products in a high-throughput and quantitative means.

Current trends in rapid tests for mycotoxins

There are an ample number of commercial testing kits available for mycotoxin analysis on the market today, including enzyme-linked immunosorbent assays, membrane-based immunoassays, fluorescence polarisation immunoassays and fluorometric assays. It can be observed from the literature that not only are developments and improvements ongoing for these assays but there are also novel assays being developed using biosensor technology. This review focuses on both the currently available methods and recent innovative methods for mycotoxin testing. Furthermore, it highlights trends that are influencing assay developments such as multiplexing capabilities and rapid on-site analysis, indicating the possible detection methods that will shape the future market.

Microarray-Based Immunoassay for Parallel Quantification of Multiple Mycotoxins in Oat

Because multianalyte methods are highly desirable in order to keep analysis time and costs low, the biosensor development increasingly focuses on parallel analysis of several mycotoxins. Here, we describe an indirect competitive immunoassay on regenerable, reusable glass microchips for the parallel determination of aflatoxins, ochratoxin A, deoxynivalenol, and fumonisin B1 in oat extracts, using a fully automated flow-through device with chemiluminescence readout.

Risks to human and animal health related to the presence of deoxynivalenol and its acetylated and modified forms in food and feed

Deoxynivalenol (DON) is a mycotoxin primarily produced by Fusarium fungi, occurring predominantly in cereal grains. Following the request of the European Commission, the CONTAM Panel assessed the risk to animal and human health related to DON, 3-acetyl-DON (3-Ac-DON), 15-acetyl-DON (15-Ac-DON) and DON-3-glucoside in food and feed. A total of 27,537, 13,892, 7,270 and 2,266 analytical data for DON, 3-Ac-DON, 15-Ac-DON and DON-3-glucoside, respectively, in food, feed and unprocessed grains collected from 2007 to 2014 were used. For human exposure, grains and grain-based products were main sources, whereas in farm and companion animals, cereal grains, cereal by-products and forage maize contributed most. DON is rapidly absorbed, distributed, and excreted. Since 3-Ac-DON and 15-Ac-DON are largely deacetylated and DON-3-glucoside cleaved in the intestines the same toxic effects as DON can be expected. The TDI of 1 μg/kg bw per day, that was established for DON based on reduced body weight gain in mice, was therefore used as a group-TDI for the sum of DON, 3-Ac-DON, 15-Ac-DON and DON-3-glucoside. In order to assess acute human health risk, epidemiological data from mycotoxicoses were assessed and a group-ARfD of 8 μg/kg bw per eating occasion was calculated. Estimates of acute dietary exposures were below this dose and did not raise a health concern in humans. The estimated mean chronic dietary exposure was above the group-TDI in infants, toddlers and other children, and at high exposure also in adolescents and adults, indicating a potential health concern. Based on estimated mean dietary concentrations in ruminants, poultry, rabbits, dogs and cats, most farmed fish species and horses, adverse effects are not expected. At the high dietary concentrations, there is a potential risk for chronic adverse effects in pigs and fish and for acute adverse effects in cats and farmed mink.

Sensitive Flow-through Immunoassay for Rapid Multiplex Determination of Cereal-borne Mycotoxins in Feed and Feed Ingredients

An easy-to-operate membrane-based flow-through test for multiplex screening of four mycotoxins (zearalenone, deoxynivalenol, aflatoxin B₁, and ochratoxin A) in a variety of cereal-based feed ingredients and compound feeds, such as wheat, barley, soybean, wheat bran, rice, rice bran, maize, rapeseed meal, and sunflower meal, and various types of complete feed (duckling feed, swine feed, broiler feed, piglet feed) was developed and validated. First, the antibodies were evaluated by enzyme-linked immunosorbent assay and then employed in the membrane rapid test. The cutoff levels for zearalenone, deoxynivalenol, aflatoxin B₁, and ochratoxin A were 50, 200, 1, and 10 μg/kg, respectively, based on European regulations and consumers' requirements. As sample pretreatment, consecutive steps of extraction, dilution, solid-phase extraction by addition of C18 sorbent, and final filtration of supernatant were followed. Both the sample preparation and the analysis procedure were simple, cost-effective, and easy to perform on-site in a nonlaboratory environment. The impact of sample processing on the result of the experiment was investigated supported by experimental design. The validation procedure was performed on the basis of Commission Regulation 2006/401/EC. The numbers of false-positive and false-negative outcomes were <5%, going along with the Commission Decision 2002/657/EC. Liquid chromatography-tandem mass spectrometry was performed as a confirmatory technique.

Analytical methods for determination of mycotoxins: An update (2009-2014)

Mycotoxins are a problematic and toxic group of small organic molecules that are produced as secondary metabolites by several fungal species that colonise crops. They lead to contamination at both the field and postharvest stages of food production with a considerable range of foodstuffs affected, from coffee and cereals, to dried fruit and spices. With wide ranging structural diversity of mycotoxins, severe toxic effects caused by these molecules and their high chemical stability the requirement for robust and effective detection methods is clear. This paper builds on our previous review and summarises the most recent advances in this field, in the years 2009-2014 inclusive. This review summarises traditional methods such as chromatographic and immunochemical techniques, as well as newer approaches such as biosensors, and optical techniques which are becoming more prevalent. A section on sampling and sample treatment has been prepared to highlight the importance of this step in the analytical methods. We close with a look at emerging technologies that will bring effective and rapid analysis out of the laboratory and into the field.

A multiplex chemiluminescent biosensor for type B-fumonisins and aflatoxin B1 quantitative detection in maize flour

A multiplex chemiluminescence biosensor based on a lateral flow immunoassay was developed for on-site quantitative detection of fumonisins and aflatoxin B1 in maize.

Simultaneous detection of ochratoxin A and fumonisin B1 in cereal samples using an aptamer-photonic crystal encoded suspension array

A simple, new aptamer-photonic crystal encoded suspension array was designed to simultaneously quantify and qualify ochratoxin A(OTA) and fumonisin B1(FB1) in cereal samples. The aptamers of OTA and FB1 were immobilized on the surfaces of photonic crystals by chemical bonding. When the target mycotoxins appear in a sample, the fluorescence-labeled complementary DNA of the aptamer dissociates from their double DNA hybrid and results in an obvious decrease in fluorescence intensity of the microsphere. The difference value of fluorescent intensities for each kind of silica photonic crystal microsphere (SPCM) quantitatively conveys the concentration of mycotoxin, and the structure colors or reflectance peak positions of the SPCMs confirm the kind of mycotoxin detected. The reaction conditions including the immobilization method for aptamers, hybridization, and incubation conditions have been optimized. This developed method displayed a wide linear detection range (0.01-1 ng/mL for OTA and 0.001-1 ng/mL for FB1) and a low limit of detection (0.25 pg/mL for OTA and 0.16 pg/mL for FB1). The recovery rates in the spiked cereal samples ranged from 81.80% to 116.38% for OTA and 76.58%-114.79% for FB1. The positive detection results in the naturally contaminated cereal samples were in agreement with those of classic enzyme-linked immunosorbent assay (ELISA). This simple suspension array scheme displays a great application potential for the high throughput screen assay of mycotoxins.

On-chip sample preparation and analyte quantification using a microfluidic aqueous two-phase extraction coupled with an immunoassay

Immunoassays are fast and sensitive techniques for analyte quantification, and their use in point-of-care devices for medical, environmental, and food safety applications has potential benefits of cost, portability, and multiplexing. However, immunoassays are often affected by matrix interference effects, requiring the use of complex laboratory extraction and concentration procedures in order to achieve the required sensitivity. In this paper we propose an integrated microfluidic device for the simultaneous matrix clean-up, concentration and detection. This device consists of two modules in series, the first performing an aqueous two-phase extraction (ATPE) for matrix extraction and analyte pre-concentration, and the second an immunoassay for quantification. The model analyte was the mycotoxin ochratoxin A (OTA) in a wine matrix. Using this strategy, a limit of detection (LoD) of 0.26 ng mL(-1) was obtained for red wine spiked with OTA, well below the regulatory limit for OTA in wines of 2 ng mL(-1) set by the European Union. Furthermore, the linear response on the logarithmic concentration scale was observed to span 3 orders of magnitude (0.1-100 ng mL(-1)). These results are comparable to those obtained for the quantification of OTA in plain buffer without an integrated ATPE (LoD = 0.15 ng mL(-1)). The proposed method was also found to provide similar results for markedly different matrices, such as red and white wines. This novel approach based on aqueous two-phase systems can help the development of point-of-care devices that can directly deal with real samples in complex matrices without the need for extra extraction processes and equipment.

Development of ultrasensitive direct chemiluminescent enzyme immunoassay for determination of aflatoxin M1 in milk

A direct competitive chemiluminescent enzyme-linked immunosorbent assay (CL-ELISA) for detecting aflatoxin M1 (AFM1) was developed. To improve the sensitivity of the assay, a mixture of 3-(10'-phenothiazinyl)-propane-1-sulfonate (SPTZ) and 4-morpholinopyridine (MORPH) was used to enhance peroxidase-induced CL. The concentrations of the coating anti-AFM1 antibody and the conjugate of AFB1 with horseradish peroxidase the conditions of the chemiluminescent assay were varied to optimise the condition of the chemiluminescent assay. The lower detection limit values and dynamic working range of CL-ELISA of AFM1 were 0.001 ng mL(-1) and 0.002-0.0075 ng mL(-1), respectively. A 20-fold dilution of milk samples prevented a matrix effect of the milk and allowed measurement of AFM1 at concentrations below than the maximum acceptable limit. Values of recovery within and between assays were 81.5-117.6% and 86-110.6%, respectively. The results of using the developed CL-ELISA to analyse samples of six brands of milk that were purchased in Taiwan revealed that AFM1 was absent from all studied samples.

Developments in mycotoxin analysis: an update for 2012-2013

This review highlights developments in mycotoxin analysis and sampling over a period between mid-2012 and mid-2013. It covers the major mycotoxins: aflatoxins, Alternaria toxins, ergot alkaloids, fumonisins, ochratoxins, patulin, trichothecenes and zearalenone. A wide range of analytical methods for mycotoxin determination in food and feed were developed last year, in particular immunochemical methods and liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS)-based methods. After a section on sampling and sample preparation, due to the rapid spread and developments in the field of LC-MS/MS multimycotoxin methods, a separate section has been devoted to this area of research. It is followed by a section on mycotoxins in botanicals and spices, before continuing with the format of previous reviews in this series with dedicated sections on method developments for the individual mycotoxins.

Using commercial immunoassay kits for mycotoxins: ‘joys and sorrows’?

Rapid test methods are widely used for measuring mycotoxins in a variety of matrices. This review presents an overview of the current commercially available immunoassay rapid test formats. Enzyme linked immune-sorbent assay (ELISA), lateral flow tests, flow through immunoassay, fluorescent polarisation immunoassay, and immunoaffinity columns coupled with fluorometric assay are common formats in the current market. The two existing evaluation programs for commercial testing kits by United State Department of Agricultural Grain Inspection, Packers & Stockyards Administration (USDA-GIPSA) and AOAC Research Institute are introduced. The strengths and weaknesses of these test kits are discussed with regard to the application scope, variance, specificity and cross reactivity, accuracy and precision, and measurement range. Generally speaking, the current commercially available testing kits meet research and industrial needs as ‘fit-for-purpose’. Furthermore, quality assurance concerns and future perspectives are elaborated for broader application of commercial test kits in research, industry and regulatory applications. It is expected that new commercial kits based on advanced technologies such as electrochemical affinity biosensors, molecularly imprinted polymers, surface plasmon resonance, fluorescence resonance energy transfer, aptamer-based biosensors and dynamic light scattering might be available to users in the future. Meanwhile, harmonisation of testing kit evaluation, incorporation of more quality assurance into the testing kit utilisation scheme, and a larger variety of kits available at lower cost will expand the usage of testing kits for food safety testing worldwide.

Cross-reactivity of rapid immunochemical methods for mycotoxins detection towards metabolites and masked mycotoxins: the current state of knowledge

The cross-reactivity of antibodies employed within immunochemistry-based analytical methods may lead to overestimation of the results. Under certain conditions, specifically when controlling mycotoxin maximum limits serious problems can be encountered. Not only the structurally related mycotoxins, such as their masked (conjugated) forms, but also the unidentified matrix components are responsible for concentration overestimation of respective target analytes. The cross-reactivity phenomenon may also pose a risk of miss-interpretation of the proficiency tests results, when the assigned value becomes influenced by over-estimated results reported by users of immunochemical tests. In this paper, the current state of the knowledge on trueness problems associated with the rapid screening immunochemical methods have been reviewed. Special attention is focused on discussion of cross-reactivity in the ELISA tests, because this rapid test dominates the routine screening practice. However, the cross-reactions reported in lateral flow test strips, fluorescence polarisation immunoassay, or immunosensors have also been addressed.

Cellulose: from biocompatible to bioactive material

The immobilization of biomolecules onto cellulose paper turns this environmentally friendly material into a platform for diagnostic devices.

Multi-mycotoxin analysis of finished grain and nut products using high-performance liquid chromatography-triple-quadrupole mass spectrometry

Mycotoxins in foods have long been recognized as potential health hazards due to their toxic and carcinogenic properties. A simple and rapid method was developed to detect 26 mycotoxins (aflatoxins, ochratoxins, fumonisins, trichothecenes, and ergot alkaloids) in corn, rice, wheat, almond, peanut, and pistachio products using high-performance liquid chromatography-triple-quadrupole mass spectrometry. Test portions of homogenized grain or nut products were extracted with acetonitrile/water (85:15, v/v), followed by high-speed centrifugation and dilution with water. Mean recoveries (± standard deviations) were 84 ± 6, 89 ± 6, 97 ± 9, 87 ± 12, 104 ± 16, and 92 ± 18% from corn, rice, wheat, almond, peanut, and pistachio products, respectively, and the matrix-dependent instrument quantitation limits ranged from 0.2 to 12.8 μg/kg, depending on the mycotoxin. Matrix effects, as measured by the slope ratios of matrix-matched and solvent-only calibration curves, revealed primarily suppression and were more pronounced in nuts than in grains. The measured mycotoxin concentrations in 11 corn and wheat reference materials were not different from the certified concentrations. Nineteen mycotoxins were identified and measured in 35 of 70 commercial grain and nut products, ranging from 0.3 ± 0.1 μg/kg (aflatoxin B1 in peanuts) to 1143 ± 87 μg/kg (fumonisin B1 in corn flour). This rapid and efficient method was shown to be rugged and effective for the multiresidue analysis of mycotoxins in finished grain and nut products.

Automated regenerable microarray-based immunoassay for rapid parallel quantification of mycotoxins in cereals

An automated flow-through multi-mycotoxin immunoassay using the stand-alone Munich Chip Reader 3 platform and reusable biochips was developed and evaluated. This technology combines a unique microarray, prepared by covalent immobilization of target analytes or derivatives on diamino-poly(ethylene glycol) functionalized glass slides, with a dedicated chemiluminescence readout by a CCD camera. In a first stage, we aimed for the parallel detection of aflatoxins, ochratoxin A, deoxynivalenol, and fumonisins in cereal samples in a competitive indirect immunoassay format. The method combines sample extraction with methanol/water (80:20, v/v), extract filtration and dilution, and immunodetection using horseradish peroxidase-labeled anti-mouse IgG antibodies. The total analysis time, including extraction, extract dilution, measurement, and surface regeneration, was 19 min. The prepared microarray chip was reusable for at least 50 times. Oat extract revealed itself as a representative sample matrix for preparation of mycotoxin standards and determination of different types of cereals such as oat, wheat, rye, and maize polenta at relevant concentrations according to the European Commission regulation. The recovery rates of fortified samples in different matrices, with 55-80 and 58-79%, were lower for the better water-soluble fumonisin B1 and deoxynivalenol and with 127-132 and 82-120% higher for the more unpolar aflatoxins and ochratoxin A, respectively. Finally, the results of wheat samples which were naturally contaminated with deoxynivalenol were critically compared in an interlaboratory comparison with data obtained from microtiter plate ELISA, aokinmycontrol® method, and liquid chromatography-mass spectrometry and found to be in good agreement.

Developments in mycotoxin analysis: an update for 2011-2012

This review highlights developments in mycotoxin analysis and sampling over a period between mid-2011 and mid- 2012. It covers the major mycotoxins aflatoxins, Alternaria toxins, ergot alkaloids, fumonisins, ochratoxin, patulin, trichothecenes, and zearalenone. A section on mycotoxins in botanicals and spices is also included. Methods for mycotoxin determination continue to be developed using a wide range of analytical systems ranging from rapid immunochemical-based methods to the latest advances in mass spectrometry. This review follows the format of previous reviews in this series (i.e. sections on individual mycotoxins), but due to the rapid spread and developments in the field of multimycotoxin methods by liquid chromatography-tandem mass spectrometry, a separate section has been devoted to advances in this area of research.