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

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

A sensitive MnO2 nanosheet sensing platform based on a fluorescence aptamer sensor for the detection of zearalenone

An aptamer sensor based on manganese dioxide (MnO₂) nanosheets was developed for the detection of zearalenone (ZEN). The ZEN aptamer was modified at the 5'-end by a 6-carboxyfluorescein (6-FAM) fluorophore with self-assembly on MnO₂ nanosheets. Interaction of the 6-FAM fluorophore at the 5'-end of the ZEN aptamer with the MnO₂ nanosheet lowered fluorescence (FL) intensity due to fluorescence resonance energy transfer (FRET). The introduction of ZEN into the sensing system resulted in hybridization with the ZEN aptamer, forming a stable G-quadruplex/ZEN, which exhibited a low affinity for the MnO₂ nanosheet surface. The distance between the 6-FAM fluorophore and MnO₂ nanosheet hampered FRET, with a consequent strong FL signal. Under the optimal experimental conditions, the FL intensity of the sensing system showed a good linear correlation with ZEN concentration in the range of 1.5-10.0 ng mL^-1, and a detection limit (S/N = 3) of 0.68 ng mL^-1. The sensing system delivered enhanced specificity for the detection of ZEN, and can find wide application in the detection of other toxins by replacing the sequence of the recognition aptamer.

Parameter Optimization of Support Vector Machine to Improve the Predictive Performance for Determination of Aflatoxin B1 in Peanuts by Olfactory Visualization Technique

This study proposes a novel method for detection of aflatoxin B₁ (AFB₁) in peanuts using olfactory visualization technique. First, 12 kinds of chemical dyes were selected to prepare a colorimetric sensor to assemble olfactory visualization system, which was used to collect the odor characteristic information of peanut samples. Then, genetic algorithm (GA) with back propagation neural network (BPNN) as the regressor was used to optimize the color component of the preprocessed sensor feature image. Support vector regression (SVR) quantitative analysis model was constructed by using the optimized combination of characteristic color components to achieve determination of the AFB₁ in peanuts. In this process, the optimization performance of grid search (GS) algorithm and sparrow search algorithm (SSA) on SVR parameter was compared. Compared with GS-SVR model, the model performance of SSA-SVR was better. The results showed that the SSA-SVR model with the combination of seven characteristic color components obtained the best prediction effect. Its correlation coefficients of prediction (R_P) reached 0.91. The root mean square error of prediction (RMSEP) was 5.7 μg·kg^-1, and ratio performance deviation (RPD) value was 2.4. The results indicate that it is reliable to use the colorimetric sensor array with strong specificity for the determination of the AFB₁ in peanuts. In addition, it is necessary to properly optimize the parameters of the prediction model, which can obviously improve the generalization performance of the multivariable model.

Organic Cation Receptor for Colorimetric Lateral Flow Device: Detection of Zearalenone in Food Samples

As per the WHO reports, it has been estimated that almost 25% of food crops contain mycotoxins as the major contaminant. In this work, we developed a paper-based colorimetric lateral flow device (CLFD) impregnated with an organic cation receptor (OCR) for sensitive and selective detection of zearalenone (ZEN). Various techniques such as ultraviolet (UV)-visible absorption, cyclic voltammetry, and fluorescence spectroscopy were used for the detection of mycotoxins, and it was observed that OCR shows sensitivity and selectivity toward zearalenone (ZEN) only, irrespective of any other analytes. Furthermore, the colorimetric test revealed that the developed OCR shows a change in color with the addition of ZEN from greenish-gray to blue that is visible to the naked eye. The quantification of ZEN was also achieved using RGB analysis and compared with UV-visible spectroscopy data. Further, for the on-site detection of ZEN, a paper-based CLFD was also developed and used to evaluate the spiked corn sample containing ZEN, and it provided significant results with a limit of detection (LOD) of 0.31 nM (3σ method), good linearity (R² = 0.9702), good reproducibility (SD = ±6%, triplicate), and good recovery of ZEN of 95-102% with a variation coefficient (VC) varying from 1.56 to 4.62%. Therefore, the device has the potential to check the mycotoxin toxicity in food products and is helpful in remote and developing areas.

Development of an Immunofluorescence Assay Module for Determination of the Mycotoxin Zearalenone in Water

Project Aquafluosense is designed to develop prototypes for a fluorescence-based instrumentation setup for in situ measurements of several characteristic parameters of water quality. In the scope of the project an enzyme-linked fluorescent immunoassay (ELFIA) method has been developed for the detection of several environmental xenobiotics, including mycotoxin zearalenone (ZON). ZON, produced by several plant pathogenic Fusarium species, has recently been identified as an emerging pollutant in surface water, presenting a hazard to aquatic ecosystems. Due to its physico-chemical properties, detection of ZON at low concentrations in surface water is a challenging task. The 96-well microplate-based fluorescence instrument is capable of detecting ZON in the concentration range of 0.09-400 ng/mL. The sensitivity and accuracy of the analytical method has been demonstrated by a comparative assessment with detection by high-performance liquid chromatography and by total internal reflection ellipsometry. The limit of detection of the method, 0.09 ng/mL, falls in the low range compared to the other reported immunoassays, but the main advantage of this ELFIA method is its efficacy in combined in situ applications for determination of various important water quality parameters detectable by induced fluorimerty-e.g., total organic carbon content, algal density or the level of other organic micropollutants detectable by immunofluorimetry. In addition, the immunofluorescence module can readily be expanded to other target analytes if proper antibodies are available for detection.

Cyclodextrins Can Entrap Zearalenone-14-Glucoside: Interaction of the Masked Mycotoxin with Cyclodextrins and Cyclodextrin Bead Polymer

Zearalenone (ZEN) is a Fusarium-derived xenoestrogenic mycotoxin. In plants, zearalenone-14-O-β-d-glucoside (Z14G) is the major conjugated metabolite of ZEN, and is a masked mycotoxin. Masked mycotoxins are plant-modified derivatives, which are not routinely screened in food and feed samples. Cyclodextrins (CDs) are cyclic oligosaccharides built up from D-glucopyranose units. CDs can form stable host-guest type complexes with lipophilic molecules (e.g., with some mycotoxins). In this study, the interaction of Z14G with native and chemically modified β- and γ-CDs was examined employing fluorescence spectroscopy and molecular modeling. Furthermore, the removal of Z14G from aqueous solution by insoluble β-CD bead polymer (BBP) was also tested. Our results demonstrate that Z14G forms the most stable complexes with γ-CDs under acidic and neutral conditions (K ≈ 103 L/mol). Among the CDs tested, randomly methylated γ-CD induced the highest increase in the fluorescence of Z14G (7.1-fold) and formed the most stable complexes with the mycotoxin (K = 2 × 103 L/mol). Furthermore, BBP considerably reduced the Z14G content of aqueous solution. Based on these observations, CD technology seems a promising tool to improve the fluorescence analytical detection of Z14G and to discover new mycotoxin binders which can also remove masked mycotoxins (e.g., Z14G).

A novel HPLC flow cell integrated UV light emitting diode induced fluorescence detector as alternative for sensitive determination of aflatoxins

A novel UV light emitting diode induced fluorescence detector (LED-IF) with HPLC flow cell was designed and evaluated for determination of aflatoxins. Ray tracing method was employed to optimize the design of the optical components (such as reshaping thin lens for light source and fluorescence collection), and optical structure, and the geometry of flow cell. An ordinary UV LED with wavelength of 370 nm and radiant power of 5 mW was used as excitation light source. A photoelectric amplifier AccuOpt2000 with light sensitivity of 10^-5∼10^-4lx was utilized for fluorescence detection, instead of a photo multiplier tube (PMT). The lowest detection limit (LOD) of the LED-IF was 0.077 ppb for aflatoxin B₁ by HPLC method without derivatization. The LED-IF was then coupled with a homemade iodine derivatization device, which was connected to the HPLC column outlet for determination of aflatoxins in edible oil and peanut samples. It was found that the edible oil sample contained aflatoxin B₁ and B₂ at average level of 7.14 (n = 3) and 0.30 ng/g (n = 3), respectively; while the peanut sample contained aflatoxin B₁ and B₂ at average level of 9.22 (n = 3) and 1.36 ng/g (n = 3), respectively. The overall power consumption of the LED-IF was 1 W/12 V. The sensitivity of the LED-IF was similar to commercial fluorescence detectors, which utilized a pulse Xe lamp as excitation light source and a PMT for detection, with power consumption of 150 W.

Competitive horseradish peroxidase-linked aptamer assay for sensitive detection of Aflatoxin B1

Aflatoxin B1 (AFB1) is one of highly toxic mycotoxins and a known human carcinogen. The frequent contamination of AFB1 in food products and large health risk of AFB1 have raised global concerns. Sensitive detection of AFB1 is of vital importance and highly demanded. Herein, we reported a competitive horseradish peroxidase (HRP)-linked aptamer assay for AFB1, combining the advantages of aptamer for affinity binding and enzyme label for signal amplification. In this assay, free AFB1 in solution competed with a covalent conjugate of bovine serum albumin-AFB1 (BSA-AFB1) coated on the wells of microplate in binding to the HRP-labeled aptamer probe. HRP attached on BSA-AFB1 in the wells catalyzed the conversion of substrates into products, allowing the final detection of AFB1 through measurement of the generated products. When TMB (3,3',5,5'-tetramethylbenzidine dihydrochloride) was used as substrate, absorbance analysis of the product of enzyme reaction enabled the detection of AFB1 at 0.2nM. We further lowered the detection limit of AFB1 to 0.01nM through chemiluminescence analysis by using chemiluminescence substrate of HRP. This assay enabled the detection of AFB1 in complex sample matrix, such as diluted white wine and maize flour. This assay provides a simple, sensitive and rapid method for AFB1 determination.

Interaction of α- and β-zearalenols with β-cyclodextrins

Zearalenone (ZEN) is a mycotoxin produced by Fusarium fungi. ZEN primarily contaminates different cereals, and exerts a strong xenoestrogenic effect in animals and humans. ZEN is a fluorescent mycotoxin, although molecular interactions and microenvironmental changes significantly modify its spectral properties. During biotransformation, ZEN is converted into α-zearalenol (α-ZOL) and β-zearalenol (β-ZOL), the toxic metabolites of ZEN, which mimick the effect of estrogen. Cyclodextrins (CDs) are host molecules, and have been studied extensively; they can form stable complexes with several mycotoxins, including ZEN. However, information is limited regarding the interactions of CDs with ZOLs. Therefore, we studied the interactions of α- and β-ZOLs with native and six chemically modified β-CDs by fluorescence spectroscopy. Fluorescence enhancement during complex formation, as well as binding constants, were determined. To understand ZOL-CD interactions better, molecular modeling studies were also carried out. Both mycotoxin derivatives formed the most stable complexes with methylated and sulfobutylated CD-derivatives; however, the CD complexes of α-ZOL were significantly stronger than those of β-ZOL. The data presented here indicate which of the chemically modified β-CDs appear more suitable as fluorescence enhancers or as potential mycotoxin binders.

Interference-free analysis of aflatoxin B1and G1in various foodstuffs using trilinear component modeling of excitation–emission matrix fluorescence data enhanced through photochemical derivatization

A novel ‘dilute-and-shoot’ strategy coupling self-weighted alternating normalized residue fitting algorithm with two-dimensional fluorescence detection enhanced by photochemical derivatization was proposed for rapid analysis of aflatoxin B₁and G₁.

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.

Developments in mycotoxin analysis: an update for 2010-2011

This review highlights developments in mycotoxin analysis and sampling over a period between mid-2010 and mid-2011. It covers the major mycotoxins: aflatoxins, Alternaria toxins, ergot alkaloids, fumonisins, ochratoxin, patulin, trichothecenes, and zearalenone. Analytical methods for mycotoxins continue to be developed and published. Despite much interest in immunochemical methods and in the rapid development of LC-MS methodology, more conventional methods, sometimes linked to novel clean-up protocols, have also been the subject of research publications over the above period. Occurrence of mycotoxins falls outside the main focus of this review; however, where relevant to analytical method development, this has been mentioned.