A novel solid phase extraction – Ultra high performance liquid chromatography–tandem mass spectrometry method for the quantification of ochratoxin A in red wines

An Extremely Highly Sensitive ELISA in pg mL-1 Level Based on a Newly Produced Monoclonal Antibody for the Detection of Ochratoxin A in Food Samples

In this study, an extremely highly sensitive enzyme-linked immunosorbent assay (ELISA) based on a newly produced monoclonal antibody (mAb) for the detection of ochratoxin A (OTA) in food samples was developed. OTA-Bovine serum albumin (BSA) conjugate was prepared and used as the immunogen for the production of the mAb. Among four hybridoma clones (8B10, 5C2, 9B7, and 5E11), the antibody from 8B10 displayed the highest affinity recognition for OTA. Based on the mAb (8B10), the IC50 and LOD of the ELISA for OTA were 34.8 pg mL-1 and 1.5 pg mL-1, respectively, which was 1.53~147 times lower than those in published ELISAs, indicating the ultra-sensitivity of our assay. There was no cross-reactivity of the mAb with the other four mycotoxins (AFB1, ZEN, DON, and T-2). Due to the high similarity in molecular structures among OTA, ochratoxin B (OTB), and ochratoxin C (OTC), the CR values of the mAb with OTB and OTC were 96.67% and 22.02%, respectively. Taking this advantage, the ELISA may be able to evaluate total ochratoxin levels in food samples. The recoveries of the ELISA for OTA in spiked samples (corn, wheat, and feed) were 96.5-110.8%, 89.5-94.4%, and 91.8-113.3%; and the RSDs were 5.2-13.6%, 8.2-13.0%, and 7.7-13.7% (n = 3), respectively. The spiked food samples (corn) were measured by ELISA and HPLC-FLD simultaneously. A good correlation between ELISA (x) and HPLC-FLD (y) with the linear regression equation of y = 0.918x - 0.034 (R2 = 0.985, n = 5) was obtained. These results demonstrated that the newly produced mAb-based ELISA was a feasible and ultra-sensitive analytical method for the detection of OTA in food samples.

Quantitative and qualitative analysis of ochratoxin-A using fluorescent CQDs@DNA-based nanoarchitecture assembly to monitor food safety and quality

Ochratoxin A (OTA), a mycotoxin formed by various fungi, such as Aspergillus and Penicillium species, is dangerous to human health. Thus, to circumvent the risk of OTA ingestion, the recognition and quantification of OTA levels are of great significance. A perusal of the literature has revealed that the integration of DNA/Carbon Quantum Dot (CQD)-based hybrid systems may exhibit the unique electronic and optical properties of nanomaterials/nanoarchitecture and consequent recognition properties. Herein, we developed the CQDs@DNA-based hybrid nanoarchitecture system for the selective detection of OTA, which exhibits modulation in the emission spectrum after interaction with OTA, with a significant binding constant (K_a = 3.5 × 10⁵ M^-1), a limit of detection of 14 nM, limit of quantification of 47 nM and working range of 1-10 μM. The mechanism for sensing the OTA has been corroborated using fluorescence, UV-visible absorption spectroscopy, and FTIR techniques, demonstrating the binding mode of CQD@DNA hybrid nano-architecture assembly with OTA. Further, we demonstrated the sensing ability of developed CQDs@DNA-based nanoarchitecture assembly towards the quantification of OTA in real food monitoring analysis for real-time applications, which makes this developed nanoarchitecture assembly the potential candidate to conveniently monitor food safety and quality for human health.

Synthesis and evaluation of a Zn-Al layered double hydroxide for the removal of ochratoxin A. Greenness assessment

The retention behavior of a dangerous toxin, ochratoxin A (OTA), present in food samples and derivatives was evaluated using Layered Double Hydroxides (LDHs). This nanomaterial composed mostly of zinc and aluminum was synthesized by the co-precipitation method and the obtained solid was characterized by different techniques, such as XRD, FTIR, TGA, SEM, and N₂ adsorption-desorption isotherms. Experimental conditions were optimized by chemometric tools. Ochratoxin A determination was performed using an ultra-high-performance liquid chromatography (UHPLC) system coupled to tandem mass spectrometry. From the findings, quantitative removal of the mycotoxin was achieved. Thus, a novel, nanostructured, innocuous, low-cost, easily synthesized material, such as the Zn-Al layered double hydroxide, is proposed for ochratoxin A removal. This might represent an effective and sustainable approach with potential applications to different types of food and feed samples.

Multimycotoxin Analysis in Oat, Rice, Almond and Soy Beverages by Liquid Chromatography-Tandem Mass Spectrometry

This study developed and validated an analytical methodology for the determination of aflatoxins, enniatins, beauvericin, zearalenone, ochratoxin-A, alternariols, HT-2 and T-2 toxin in soy, oat, rice and almond beverages, based on solid phase extraction columns (SPE) and analyzed by liquid chromatography coupled to mass spectrometry in tandem. C18 SPE was successfully applied, obtaining recoveries that range from 72 ± 12% (ochratoxin-A) to 99 ± 4% (ENA1) at high level (L1) and 65 ± 8% (T-2) to 128 ± 9% (alternariol monomethyl ether) at low levels (L3). The methodology was validated according to Commission Decision 2002/657/EC, with limits of quantification ranging from 0.3 (AFs in oat beverages) to 18 ng/mL (HT-2 in rice beverage). The analysis of 56 beverage samples purchased from Valencia (Spain) showed at least one mycotoxin occurring in 95% of samples, including carcinogenic aflatoxins, and oat beverage was the most contaminated. This is a newest validated methodology for the quantification of sixty mycotoxins in oat, rice, almond and soy beverages.

Application of new N- and S-doped amorphous carbon in D-μSPE and its combination with deep eutectic solvent-based DLLME for the extraction of some mycotoxins from soymilk

A new amorphous carbon-based dispersive micro solid-phase extraction method was developed for the extraction and preconcentration of several mycotoxins from soymilk samples. The extracted analytes were concentrated by a deep eutectic solvent-based dispersive liquid-liquid microextraction method, and then, quantified by a high-performance liquid chromatography-fluorescence detector. The sorbent was prepared from β-cyclodextrin and methionine under mild conditions. The sorbent was doped by N and S, which improved its physicochemical properties. The optimization and validation of the method were performed using the "one-variable-at-a-time" method and International Council Harmonization guideline, respectively. Under the optimal conditions, low limits of detection and quantifications in the ranges of 0.08-0.56 and 0.27-1.9 ng L^-1 were obtained, respectively. Also, intra- (n = 6) and inter-day (n = 6) precisions showed an acceptable repeatability of the present work as they were in the ranges of 3.9-6.2 and 4.6-8.9% at a concentration of 3 ng L^-1 of each analyte, respectively. Finally, the proposed method was performed on different soymilk samples marketed in Tabriz city, and aflatoxin B₁ was found in all samples. One soymilk was contaminated by ochratoxin A.

Recent progress in determination of ochratoxin a in foods by chromatographic and mass spectrometry methods

Ochratoxin A is a highly toxic mycotoxin and has posed great threat to human health. Due to its serious toxicity and wide contamination, great efforts have been made to develop reliable determination methods. In this review, analytical methods are comprehensively summarized in terms of sample preparation strategy and instrumental analysis. Detailed method is described according to the food commodities in the order of cereal, wine, coffee, beer, cocoa, dried fruit and spice. This review mainly focuses on the recent advances, especially reported in the last decade. At last, challenges and perspectives are also discussed to achieve better advancement and promote practical application in this field.

Advances in biosensors for the detection of ochratoxin A: Bio-receptors, nanomaterials, and their applications

Ochratoxin A (OTA) is a class of mycotoxin mainly produced by the genera Aspergillus and Penicillium. OTA can cause various forms of kidney, liver and brain diseases in both humans and animals although trace amount of OTA is normally present in food. Therefore, development of fast and sensitive detection technique is essential for accurate diagnosis of OTA. Currently, the most commonly used detection methods are enzyme-linked immune sorbent assays (ELISA) and chromatographic techniques. These techniques are sensitive but time consuming, and require expensive equipment, highly trained operators, as well as extensive preparation steps. These drawbacks limit their wide application in OTA detection. On the contrary, biosensors hold a great potential for OTA detection at for both research and industry because they are less expensive, rapid, sensitive, specific, simple and portable. This paper aims to provide an extensive overview on biosensors for OTA detection by highlighting the main biosensing recognition elements for OTA, the most commonly used nanomaterials for fabricating the sensing interface, and their applications in different read-out types of biosensors. Current challenges and future perspectives are discussed as well.

A synergistic approach to enhance the photoelectrochemical performance of carbon dots for molecular imprinting sensors

Nanoscale carbon dots (CDs) have drawn increasing attention in photoelectrochemical (PEC) sensors for biotoxin detection owing to their many merits including excellent optical, electric and photoelectric properties. In this work, a novel strategy is proposed to improve the photoelectrical response performance of CDs by taking advantage of the synergistic effect of nitrogen and sulfur co-doping and copper phthalocyanine non-covalent functionalization approaches, which rightly adjusts the energy level of CDs, optimization of intimate interfacial contact, extension of the light absorption range, and enhancement of charge-transfer efficiency. This work demonstrates that heteroatom doping and chemical functionalization can endow CDs with various new and improved physicochemical, optical, and structural performances. This synergy contributes enormously to the molecular imprinting photoelectrochemical (MIP-PEC) sensor for toxin detection, and the work typically provided a wide linear range of 0.01 to 1000 ng mL-1 with a detection limit of 0.51 pg mL-1 for ochratoxin A (OTA).

Preparation and evaluation of highly hydrophilic aptamer-based hybrid affinity monolith for on-column specific discrimination of ochratoxin A

Nonspecific adsorption is a challenge of specific recognition on aptamer-based affinity monoliths. Here, a novel highly hydrophilic polyhedral oligomeric silsesquioxane (POSS)-containing aptamer-based hybrid-silica affinity monolith with a good recognition nature was prepared and used for specific discrimination of ochratoxin A (OTA). A homogeneous polymerization mixture consisted of POSS chemicals, hydrophilic monomers and aptamer solution was directly polymerized via the "one-pot" method. Preparation and characterization of the resultant affinity monolith were studied in detail. A highly hydrophilic nature was obtained and the typical hydrophilic interaction liquid chromatography (HILIC) was observed when acetonitrile (ACN) content in mobile phase was 25%, which reached the highest hydrophilicity of POSS-based hybrid monoliths. By using OTA as model analyte, the nonspecific adsorption was effectively suppressed. The recovery of the analogue ochratoxin B (OTB) was only about 0.1% even if the content of OTB was 50 times more than OTA, which was much better than other POSS-containing monoliths and polar siloxane-based hybrid monoliths. Applied to beer samples, the adsorption of background materials was drastically resisted, and efficient recognition of OTA was obtained with the recoveries of 94.9-99.8%. Much less disturbance was observed than that occurred in hydrophobic POSS-based affinity monolith. It lights an attractive implement with high hydrophilicity and specificity for online selective recognition of OTA.

Three-dimensional hollow porous raspberry-like hierarchical Co/Ni@carbon microspheres for magnetic solid-phase extraction of pyrethroids

A three-dimensional magnetic hollow porous raspberry-like hierarchical Co/Ni@carbon microspheres (3D Co/Ni@carbon) were synthesized by using a bimetal-organic framework (Co/Ni-MOF) as a precursor and subsequent calcination under nitrogen. The 3D Co/Ni@carbon is a novel solid phase extractant that displays outstanding extraction capability and separation efficiency for the pyrethroid pesticides ethofenprox and bifenthrin. This is ascribed to the beneficial effects of facile analyte transport (due to the presence of free pores), the abundant number of adsorption sites (which warrant efficient extraction), and the excellent structural stability of the material. The 3D Co/Ni@carbon was applied to dispersive magnetic solid-phase extraction (d-MSPE), and the two pyrethroids were quantified by HPLC (UV detection wavelength: 220 nm). The method has a high preconcentration factor (937-1012) and give recoveries that range between 85.6-106.9%, with RSDs (for n = 5) of <6% in case of real samples. Graphical abstract The hierarchical porous Co/Ni@carbon microsphere as adsorbent was fabricated, and it showed high extraction efficiency for two pyrethroids.

A Label-Free Aptasensor for Ochratoxin a Detection Based on the Structure Switch of Aptamer

A label-free sensing platform is developed based on switching the structure of aptamer for highly sensitive and selective fluorescence detection of ochratoxin A (OTA). OTA induces the structure of aptamer, transforms into G-quadruplex and produces strong fluorescence in the presence of zinc(II)-protoporphyrin IX probe due to the specific bind to G-quadruplex. The simple method exhibits high sensitivity towards OTA with a detection limit of 0.03 nM and excellent selectivity over other mycotoxins. In addition, the successful detection of OTA in real samples represents a promising application in food safety.

Solid phase extraction as sample treatment for the determination of Ochratoxin A in foods: A review

Ochratoxin A (OTA) is a mycotoxin produced by two main types of fungi, Aspergillus and Penicillium species. OTA is a natural contaminant found in a large number of different matrices and is considered as a possible carcinogen for humans. Hence, low maximum permitted levels in foods have been established by competent authorities around the world, making essential the use of very sensitive analytical methods for OTA detection. Sample treatment is a crucial step of analytical methodology to get clean and concentrated extracts, and therefore low limits of quantification. Solid phase extraction (SPE) is a useful technique for rapid and selective sample preparation. This sample treatment enables the concentration and purification of analytes from the sample solution or extract by sorption on a solid sorbent. This review is focused on sample treatment procedures based on SPE prior to the determination of OTA in food matrices, published from 2010.

T-2 Toxin/HT-2 Toxin and Ochratoxin A ELISAs Development and In-House Validation in Food in Accordance with the Commission Regulation (EU) No 519/2014

T-2 toxin/HT-2 toxin (T-2/HT-2) and ochratoxin A (OTA) are mycotoxins that can contaminate a variety of agricultural commodities. To protect consumers' health, indicative limits for T-2/HT-2 and maximum limits for OTA have been set by the European Commission, requiring food business operators and controlling agencies to conduct routine checks for the presence of these harmful contaminants. Screening methods are increasingly used for monitoring purposes. Due to the demand for new and improved screening tools, two individual detection methods, T-2/HT-2 and OTA enzyme-linked immunosorbent assays (ELISAs), were developed in this study. The T-2/HT-2 ELISA was based on a T-2 monoclonal antibody with an IC50 (50% inhibitory concentration) of 0.28 ng/mL and 125% cross-reactivity with HT-2. As regards the OTA ELISA, a new sensitive monoclonal antibody specific to OTA with an IC50 of 0.13 ng/mL was produced. Both developed ELISA tests were then validated in agricultural commodities in accordance with the new performance criteria guidelines for the validation of screening methods for mycotoxins included in Commission Regulation (EU) No 519/2014. The T-2/HT-2 ELISA was demonstrated to be suitable for the detection of T-2/HT-2 in cereals and baby food at and above the screening target concentration (STC) of 12.5 μg/kg and 7.5 μg/kg, respectively. The OTA ELISA was shown to be applicable for the detection of OTA in cereals, coffee, cocoa and wine at and above the STC of 2 μg/kg, 2.5 μg/kg, 2.5 μg/kg and 0.4 ng/mL, respectively. The accuracy of both ELISAs was further confirmed by analysing proficiency test and reference samples. The developed methods can be used for sensitive and high-throughput screening for the presence of T-2/HT-2 and OTA in agricultural commodities.

High-Throughput Low-Background G-Quadruplex Aptamer Chemiluminescence Assay for Ochratoxin A Using a Single Photonic Crystal Microsphere

We reported a novel hemin-G-quadruplex aptamer chemiluminescence assay platform for ochratoxin A (OTA) using the single silica photonic crystal microsphere (SPCM). The oligonucleotide A sequence containing aptamer sequences of hemin and OTA is immobilized on the surface of SPCM. The other oligonucleotide B sequence containing a partially complementary sequence with one part OTA aptamer and one part hemin aptamer is used as a blocking chain. The hybridization between chain A and chain B will be influenced by the presence or absence of OTA in the system, which will affect the bioactivity of DNAzyme. Thus, the chemiluminescence signal depends on the concentration of OTA in the samples. In the single particle assay platform, the signal/noise is remarkably enhanced, and the background signal can be ignored by separating hemin from the surface of SPCM. The limit of detection of the new method reaches to the pg/mL scale, and the linear detection range is 4 orders of magnitude for OTA. The new assay platform can provide a sensitive, cost-efficient, simple, and high-throughput screening for OTA.

Assessment of ochratoxin A occurrence in Argentine red wines using a novel sensitive quechers-solid phase extraction approach prior to ultra high performance liquid chromatography-tandem mass spectrometry methodology

BACKGROUND

The assessment of ochratoxin A (OTA) in wine is relevant for food safety and its continuous control allows to reduce the risk of intake. Thus, a novel sensitive QuEChERS-SPE (Quick, Easy, Cheap, Effective, Rugged and Safe - Solid Phase Extraction) pretreatment prior to liquid chromatography coupled to tandem mass spectrometry was developed for the determination of OTA in red wine samples from different grape-growing regions in Argentine.

RESULTS

A sensitive methodology was achieved and thus the limits of detection and quantification were 0.02 and 0.05 µg L^-1 , respectively. Recoveries ranged from 89.0% to 105.3%. The method was applied to 136 red wine samples (Argentina's flagship varieties: Malbec and Cabernet Sauvignon) from ten grape-growing regions, during vintages 2013-2015. Although all of the samples investigated were contaminated with OTA (concentrations ranged from 0.02 to 0.98 µg L^-1 ), the levels detected were lower than the maximum allowable concentration limit of 2.0 µg L^-1 established by international regulations.

CONCLUSION

The methodology proposed is suitable for reliable OTA analysis in red wines. Similarly, the values obtained from the samples analyzed were in accordance with the current regulations and, as a consequence, preventive actions to reduce this mycotoxin incidence can be undertaken. © 2016 Society of Chemical Industry.

Highly Sensitive Colorimetric Detection of Ochratoxin A by a Label-Free Aptamer and Gold Nanoparticles

A label-free aptamer-based assay for the highly sensitive and specific detection of Ochratoxin A (OTA) was developed using a cationic polymer and gold nanoparticles (AuNPs). The OTA aptamer was used as a recognition element for the colorimetric detection of OTA based on the aggregation of AuNPs by the cationic polymer. By spectroscopic quantitative analysis, the colorimetric assay could detect OTA down to 0.009 ng/mL with high selectivity in the presence of other interfering toxins. This study offers a new alternative in visual detection methods that is rapid and sensitive for OTA detection.

Identification of a high-affinity monoclonal antibody against ochratoxin A and its application in enzyme-linked immunosorbent assay

Ochratoxin A (OTA) is one of the most commonly occurring mycotoxins produced by some species of Aspergillus and can contaminate cereal and cereal products. A high-affinity anti-OTA monoclonal antibody (mAb) was generated from a hybridoma cell line 2D8 using splenocytes from a BALB/c mouse immunized with synthesized OTA-bovine serum albumin conjugate. The mAb 2D8 is specific with high affinity (3.75 × 10(9) L/M). An indirect competitive ELISA (ic-ELISA) was then developed using this mAb for quantitative determination of OTA in corn and feed samples. Using the optimized conditions, there was good linearity between OTA concentration and competitive inhibition (y = -0.6076x + 0.2441, R(2) = 0.9923) with the working range from 2.4 to 23.6 μg/kg, IC50 at 7.6 μg/kg and lower limit of detection at 1.4 μg/kg. The recovery rates in spiked samples were 91.2-110.3%. Of the 56 corn and feed samples, this ic-ELISA and a commercial kit both found the same 13 samples positive for OTA with good linear correlation between the two methods in OTA quantification (R(2) = 0.9706). We conclude that this ic-ELISA can be used for rapid and quantitative screening of corn and feed samples for the presence of OTA.

Label-Free Luminescent Switch-On Probe for Ochratoxin A Detection Using a G-Quadruplex-Selective Iridium(III) Complex

A library of six luminescent Ir(III) complexes were synthesized and studied for their capacity to function as probes for G-quadruplex DNA. The novel Ir(III) complex 1 was discovered to be selective for G-quadruplex structures and was subsequently used for the construction of a label-free G-quadruplex-based ochratoxin A (OTA) sensing platform in aqueous solution. The assay exhibited linearity for OTA in the range of 0 to 60 nM (R2=0.9933), and the limit of detection for OTA was 5 nM. Furthermore, this assay was highly selective for OTA over its structurally related analogues.