New extraction sorbent based on aptamers for the determination of ochratoxin A in red wine

Novel oligonucleotide-based sorbent for the selective extraction of cadmium from serum samples

The objective was to develop a sorbent functionalized with aptamers for the selective extraction of cadmium from biological samples. Two oligonucleotide sequences reported in literature as specific to cadmium were covalently grafted on activated Sepharose, with grafting yields of 45%. Once the supports packed in cartridges, a thorough study of the percolation conditions favoring Cd(II) retention was performed, demonstrating the importance of the nature of this medium. A high selectivity was reached when applying the optimal conditions as a recovery of 85% was obtained using the sorbent functionalized with one of the specific aptamers and only 1% on the control sorbent grafted with a scramble sequence. A high specificity was also obtained as recoveries for most of other ions were lower than 15%. The capacity of this oligosorbent estimated to 180 ng of Cd(II) for 30 mg of support was perfectly adapted to the trace analysis of Cd(II). The extraction procedure was then applied to a serum sample which was first subjected to acid precipitation. The initial concentration of cadmium in the serum was estimated to 1.83 µg/L using standard addition method and an extraction yield of 75 ± 1.6% was measured. Comparison of these results with those obtained without oligoextraction (recovery of 57%) showed a significant reduction of matrix effects in ICP-MS thanks to the use of the oligosorbent, underlining its interest for a more reliable quantification of Cd(II). This result was confirmed by performing the oligoextraction protocol on a certified serum.

Aptamer loaded superparamagnetic beads for selective capturing and gentle release of activated protein C

Activated protein C (APC) is a serine protease with anticoagulant and cytoprotective activities which make it an attractive target for diagnostic and therapeutic applications. In this work, we present one-step activation of APC from a commercial source of protein C (PC, Ceprotin) followed by rapid and efficient purification using an APC-specific aptamer, HS02-52G, loaded on MyOne superparamagnetic beads. Due to the Ca²⁺-dependent binding of APC to HS02-52G, an efficient capturing of APC was applied in the presence of Ca²⁺ ions, while a gentle release of captured APC was achieved in the elution buffer containing low EDTA concentration (5 mM). The captured and eluted APC showed more than 95% purity according to SDS-PAGE gel analysis and an enzyme-linked fluorescent assay (VIDAS Protein C). The purification yield of 45% was calculated when 4.2 µg APC was used, however this yield reduced to 21% if the starting amount of APC increased to 28.5 µg. Altogether, this method is recommended for rapid and efficient PC activation and APC purification. The purified APC can be used directly for downstream processes where high concentration of pure and active APC is needed.

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.

Immunoaffinity Extraction and Alternative Approaches for the Analysis of Toxins in Environmental, Food or Biological Matrices

The evolution of instrumentation in terms of separation and detection allowed a real improvement of the sensitivity and analysis time. However, the analysis of ultra-traces of toxins in complex samples requires often a step of purification and even preconcentration before their chromatographic analysis. Therefore, immunoaffinity sorbents based on specific antibodies thus providing a molecular recognition mechanism appear as powerful tools for the selective extraction of a target molecule and its structural analogs to obtain more reliable and sensitive quantitative analysis in environmental, food or biological matrices. This review focuses on immunosorbents that have proven their efficiency in selectively extracting various types of toxins of various sizes (from small mycotoxins to large proteins) and physicochemical properties. Immunosorbents are now commercially available, and their use has been validated for numerous applications. The wide variety of samples to be analyzed, as well as extraction conditions and their impact on extraction yields, is discussed. In addition, their potential for purification and thus suppression of matrix effects, responsible for quantification problems especially in mass spectrometry, is presented. Due to their similar properties, molecularly imprinted polymers and aptamer-based sorbents that appear to be an interesting alternative to antibodies are also briefly addressed by comparing their potential with that of immunosorbents.

A label-free, direct solid-phase fluorimetric analysis of ochratoxin A in agricultural products with monoclonal antibody-immobilized monolith

We established a method for directly measuring mycotoxin ochratoxin A (OTA) in foods by solid-phase fluorescence of monolith-immobilized antibodies. The antibody was introduced onto only one side of an 8 mm-diameter, 3 mm-thick monolith via covalently immobilized protein G. 4 μg (2.7 × 10^-11 mol) of antibody was immobilized per one monolith. A maximum of 10 μg (2.4 × 10^-11 mol) OTA adsorbed to the activated side of each monolith. The amount of OTA adsorbed and the fluorescence intensity showed good linearity in the range of 0.5-3 ng OTA. Loading the sample solution onto the non-antibody side on the monolith blocked the hydrophobic fluorescent matrices from reaching the immobilized surface of the antibody. The proposed method was able to detect 1 ng OTA/g in solid samples with complex matrices. Mean recoveries obtained at spiked concentration of 3 ng g^-1 OTA/g were 78-90% with relative standard deviations of <7.9%.

Rapid and sensitive detection of mycotoxins by advanced and emerging analytical methods: A review

Quantification of mycotoxins in foodstuffs is extremely difficult as a limited amount of toxins are known to be presented in the food samples. Mycotoxins are secondary toxic metabolites, made primarily by fungal species, contaminating feeds and foods. Due to the presence in globally used grains, it is an unpreventable problem that causes various acute and chronic impacts on human and animal health. Over the previous few years, however, progress has been made in mycotoxin analysis studies. Easier techniques of sample cleanup and advanced chromatographic approaches have been developed, primarily high-performance liquid chromatography. Few extremely sophisticated and adaptable tools such as high-resolution mass spectrometry and gas chromatography-tandem MS/MS have become more important. In addition, Immunoassay, Advanced quantitative techniques are now globally accepted for mycotoxin analysis. Thus, this review summarizes these traditional and highly advance methods and their characteristics for evaluating mycotoxins.

An aptamer affinity column for purification and enrichment of aflatoxin B1 and aflatoxin B2 in agro-products

We have developed an aptamer affinity column (AAC) for the purification and enrichment of trace aflatoxin B₁ (AFB₁) and aflatoxin B₂ (AFB₂) in genuine agro-products through the covalent conjugation of amino modified aptamer and NHS-activated Sepharose. The coupling and working conditions found to be suitable for this AFB-AAC were examined in regard to coupling time (2 min), loading volume (30 mL), and the methanol concentration (< 10%) used in the loading step. The performance of AFB-AAC was then further evaluated in terms of capacity (329.1 ± 13.7 ng for AFB₁ and 162.5 ± 8.9 ng for AFB₂), selectivity (excellent), reusability (twenty-three times for AFB₁ and twelve times for AFB₂), and repeatability (92.7% ± 2.9% for AFB₁ and 71.5% ± 3.4% for AFB₂). Furthermore, the AAC clean-up combined with HPLC-FLD demonstrated excellent linearity over a wide range, good sensitivity with an LOD of 50 pg mL^-1 for AFB₁ and 15 pg mL^-1 for AFB₂, and acceptable recovery with different spiking levels in different matrices. Finally, the AAC was successfully applied to analyte AFB₁ and AFB₂ in four types of agro-products as well as a maize flour reference material, and the results were found to be in accordance with those of commercial IACs. This study provides a reference for the analysis of other trace analytes by merely changing the corresponding aptamer and represents a strong contender for immune affinity columns. Graphical abstract An aptamer affinity column for purification and enrichment of aflatoxin B₁ and aflatoxin B₂ in agro-products with the aid of HPLC-FLD and a post-column photochemical derivatization reactor.

Highly hydrophilic polyhedral oligomeric silsesquioxane (POSS)-containing aptamer-modified affinity hybrid monolith for efficient on-column discrimination with low nonspecific adsorption

A highly hydrophilic aptamer-modified POSS-containing hybrid affinity monolith is presented for efficient on-column discrimination with low non-specific adsorption.

A facile AuNPs@aptamer-modified mercaptosiloxane-based hybrid affinity monolith with an unusually high coverage density of aptamer for on-column selective extraction of ochratoxin A

A convenient and high-performance AuNPs@aptamer-modified mercaptosiloxane-based hybrid affinity monolithic column with an unusually high coverage density of aptamers was facilely prepared and used for on-column selective recognition of ochratoxin A (OTA). Due to the high surface-to-volume ratio of AuNPs, the robust conjugation of Au-SH and large specific surface area of hybrid-silica monolith, high coverage density of 5'-SH-aptamers up to 3494 pmol μL-1 was achieved, which was 2.5-10 folds higher than that of other previously reported affinity monoliths modified with AuNPs@Apt. Using OTA as the model analyte, the highly selective recognition of OTA was carried out via online coupling with HPLC, and the cross-reactivity towards analogues, such as OTB and aflatoxin B1, was weak. High recovery yields of OTA were achieved at more than 92% (n = 3) even when OTB was added at a high concentration level up to 50 ng mL-1. For sample analysis, efficient discrimination of OTA was successfully obtained with a sensitive detection limit of 25 pg mL-1. The recoveries of OTA with different fortified levels were achieved at 88.6%-94.1% and 88.2%-94.3% for beer and wine samples, respectively. This protocol provides a facile approach for fabricating a desirable affinity monolith modified with abundant aptamers for highly selective and sensitive on-column extraction of target analyte OTA.

Aptamer-based polyhedral oligomeric silsesquioxane (POSS)-containing hybrid affinity monolith prepared via a "one-pot" process for selective extraction of ochratoxin A

A novel aptamer-based polyhedral oligomeric silsesquioxane (POSS)-containing hybrid affinity monolith has been prepared with a facile "one-pot" process simultaneously via "free radical polymerization" and "thiol-ene" click reaction, and used for on-line selective extraction and practical analysis to trace ochratoxin A (OTA). By using the ternary porogenic mixture composed of water/DMF/PEG, a homogeneous polymerization mixture with POSS chemicals, acrylate-based monomers and aptamer aqueous solution was obtained, and the copolymerization of POSS chemicals, polymer monomers and aptamer aqueous solution was systematically studied. Characterizations such as the morphology, FT-IR and fluorescence spectra, mechanical stability, dynamic binding capacity, cross-reactivity and selectivity of the resultant affinity monolith were also evaluated. Attributed to the porous monolithic structure and aptamer-based affinity interaction, acceptable selective recognition and recovery yields towards trace OTA were obtained. With a 5-fold volume enrichment, the limit of detection (LOD) and limit of quantitation (LOQ) of OTA in fortified beer samples were gained at 0.025 ng/mL (S/N = 3) and 0.045 ng/mL (S/N = 10), respectively. It could be competent for the sensitive measure of actual OTA residues in real beer samples. In comparison with the previously reported strategies containing common "sol-gel" chemistry, the proposed protocol to fabricating aptamer-modified POSS-containing hybrid affinity monolith showed a simpler preparation with acceptable selectivity and higher recovery to trace OTA.

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.

Selective tools for the solid-phase extraction of Ochratoxin A from various complex samples: immunosorbents, oligosorbents, and molecularly imprinted polymers

The evolution of instrumentation in terms of separation and detection has allowed a real improvement of the sensitivity and the analysis time. However, the analysis of ultra-traces of toxins such as ochratoxin A (OTA) from complex samples (foodstuffs, biological fluids…) still requires a step of purification and of preconcentration before chromatographic determination. In this context, extraction sorbents leading to a molecular recognition mechanism appear as powerful tools for the selective extraction of OTA and of its structural analogs in order to obtain more reliable and sensitive quantitative analyses of these compounds in complex media. Indeed, immunosorbents and oligosorbents that are based on the use of immobilized antibodies and of aptamers, respectively, and that are specific to OTA allow its selective clean-up from complex samples with high enrichment factors. Similar molecular recognition mechanisms can also be obtained by developing molecularly imprinted polymers, the synthesis of which leads to the formation of cavities that are specific to OTA, thus mimicking the recognition site of the biomolecules. Therefore, the principle, the advantages, the limits of these different types of extraction tools, and their complementary behaviors will be presented. The introduction of these selective tools in miniaturized devices will also be discussed.

Temperature-responsive Solid-phase Extraction Column for Biological Sample Pretreatment

We have developed a novel solid-phase extraction (SPE) system utilizing a temperature-responsive polymer hydrogel-modified stationary phase. Aminopropyl silica beads (average diameter, 40 - 64 μm) were coated with poly(N-isopropylacrylamide) (PNIPAAm)-based thermo-responsive hydrogels. Butyl methacrylate (BMA) and N,N-dimethylaminopropyl acrylamide (DMAPAAm) were used as the hydrophobic and cationic monomers, respectively, and copolymerized with NIPAAm. To evaluate the use of this SPE cartridge for the analysis of drugs and proteins in biological fluids, we studied the separation of phenytoin and theophylline from human serum albumin (HSA) as a model system. The retention of the analytes in an exclusively aqueous eluent could be modulated by changing the temperature and salt content. These results indicated that this temperature-responsive SPE system can be applied to the pretreatment of biological samples for the measurement of serum drug levels.

Development and characteristics of polymer monoliths for advanced LC bioscreening applications: A review

Biomedical research advances over the past two decades in bioseparation science and engineering have led to the development of new adsorbent systems called monoliths, mostly as stationary supports for liquid chromatography (LC) applications. They are acknowledged to offer better mass transfer hydrodynamics than their particulate counterparts. Also, their architectural and morphological traits can be tailored in situ to meet the hydrodynamic size of molecules which include proteins, pDNA, cells and viral targets. This has enabled their development for a plethora of enhanced bioscreening applications including biosensing, biomolecular purification, concentration and separation, achieved through the introduction of specific functional moieties or ligands (such as triethylamine, N,N-dimethyl-N-dodecylamine, antibodies, enzymes and aptamers) into the molecular architecture of monoliths. Notwithstanding, the application of monoliths presents major material and bioprocess challenges. The relationship between in-process polymerisation characteristics and the physicochemical properties of monolith is critical to optimise chromatographic performance. There is also a need to develop theoretical models for non-invasive analyses and predictions. This review article therefore discusses in-process analytical conditions, functionalisation chemistries and ligands relevant to establish the characteristics of monoliths in order to facilitate a wide range of enhanced bioscreening applications. It gives emphasis to the development of functional polymethacrylate monoliths for microfluidic and preparative scale bio-applications.

Recent Advances for the Detection of Ochratoxin A

Ochratoxin A (OTA) is one of the mycotoxins secreted by Aspersillus and Penicillium that can easily colonize various grains like coffee, peanut, rice, and maize. Since OTA is a chemically stable compound that can endure the physicochemical conditions of modern food processing, additional research efforts have been devoted to develop sensitive and cost-effective surveillance solutions. Although traditional chromatographic and immunoassays appear to be mature enough to attain sensitivity up to the regulation levels, alternative detection schemes are still being enthusiastically pursued in an attempt to meet the requirements of rapid and cost-effective detections. Herein, this review presents recent progresses in OTA detections with minimal instrumental usage, which have been facilitated by the development of OTA aptamers and by the innovations in functional nanomaterials. In addition to the introduction of aptamer-based OTA detection techniques, OTA-specific detection principles are also presented, which exclusively take advantage of the unique chemical structure and related physicochemical characteristics.

Man-Made Synthetic Receptors for Capture and Analysis of Ochratoxin A

Contemporary analytical methods have the sensitivity required for Ochratoxin A detection and quantification, but direct application of these methods on real samples can be rarely performed because of matrix complexity. Thus, efficient sample pre-treatment methods are needed. Recent years have seen the increasing use of artificial recognition systems as a viable alternative to natural receptors, because these materials seem to be particularly suitable for applications where selectivity for Ochratoxin A is essential. In this review, molecularly imprinted polymers, aptamers and tailor-made peptides for Ochratoxin A capture and analysis with particular attention to solid phase extraction applications will be discussed.

Deploying aptameric sensing technology for rapid pandemic monitoring

The genome of virulent strains may possess the ability to mutate by means of antigenic shift and/or antigenic drift as well as being resistant to antibiotics with time. The outbreak and spread of these virulent diseases including avian influenza (H1N1), severe acute respiratory syndrome (SARS-Corona virus), cholera (Vibrio cholera), tuberculosis (Mycobacterium tuberculosis), Ebola hemorrhagic fever (Ebola Virus) and AIDS (HIV-1) necessitate urgent attention to develop diagnostic protocols and assays for rapid detection and screening. Rapid and accurate detection of first cases with certainty will contribute significantly in preventing disease transmission and escalation to pandemic levels. As a result, there is a need to develop technologies that can meet the heavy demand of an all-embedded, inexpensive, specific and fast biosensing for the detection and screening of pathogens in active or latent forms to offer quick diagnosis and early treatments in order to avoid disease aggravation and unnecessary late treatment costs. Nucleic acid aptamers are short, single-stranded RNA or DNA sequences that can selectively bind to specific cellular and biomolecular targets. Aptamers, as new-age bioaffinity probes, have the necessary biophysical characteristics for improved pathogen detection. This article seeks to review global pandemic situations in relation to advances in pathogen detection systems. It particularly discusses aptameric biosensing and establishes application opportunities for effective pandemic monitoring. Insights into the application of continuous polymeric supports as the synthetic base for aptamer coupling to provide the needed convective mass transport for rapid screening is also presented.

A review on immobilised aptamers for high throughput biomolecular detection and screening

The discovery of Systematic Evolution of Ligands by Exponential Enrichment (SELEX) assay has led to the generation of aptamers from libraries of nucleic acids. Concomitantly, aptamer-target recognition and its potential biomedical applications have become a major research endeavour. Aptamers possess unique properties that make them superior biological receptors to antibodies with a plethora of target molecules. Some specific areas of opportunities explored for aptamer-target interactions include biochemical analysis, cell signalling and targeting, biomolecular purification processes, pathogen detection and, clinical diagnosis and therapy. Most of these potential applications rely on the effective immobilisation of aptamers on support systems to probe target species. Hence, recent research focus is geared towards immobilising aptamers as oligosorbents for biodetection and bioscreening. This article seeks to review advances in immobilised aptameric binding with associated successful milestones and respective limitations. A proposal for high throughput bioscreening using continuous polymeric adsorbents is also presented.

Miniaturized DNA aptamer-based monolithic sorbent for selective extraction of a target analyte coupled on-line to nanoLC

A complete characterization of a novel target-specific DNA aptamer-based miniaturized solid phase extraction (SPE)-sorbent coupled on-line to nanoLC is presented. A miniaturized oligosorbent (mOS) was prepared via the in situ sol-gel synthesis of a hybrid organic-inorganic monolith in 100 μm i.d. capillary columns using tetraethoxysilane and 3-aminopropyltriethoxysilane as precursors, followed by covalent binding of a 5'-amino-modified DNA aptamer with a C12 spacer arm specific for a molecule of small molecular weight. Ochratoxin A (OTA), one of the most abundant naturally occurring mycotoxins, was chosen as model analyte to demonstrate the principle of such an approach. The mOS was coupled on-line to RP-nanoLC-LIF. Selective extraction of OTA on several mOSs was demonstrated with an average extraction recovery above 80 % when percolating spiked binding buffer and a low recovery on control monoliths grafted with a non-specific aptamer. Reproducibility of mOSs preparation was highlighted by comparing extraction yields. Otherwise, the mOSs demonstrated no cross-reactivity towards an OTA structural analogue, i.e., ochratoxin B. Due to the high specific surface area of the hybrid silica-based monolith, the coverage density of DNA aptamers covalently immobilized in the capillaries was very high and reached 6.27 nmol μL(-1), thus leading to a capacity above 5 ng of OTA. This miniaturized device was then applied to the selective extraction of OTA from beer samples. It revealed to be effective in isolating OTA from this complex matrix, thus improving the reliability of its analysis at the trace level.

Aptamer-based-sorbents for sample treatment--a review

To improve selectivity during sample pretreatment, various selective tools inducing a molecular recognition mechanism during the extraction procedure have been developed, such as sorbents constituted of immobilized antibodies, i.e., immunosorbents, or molecularly imprinted polymers. More recently, as an alternative to both previous approaches, aptamers immobilized onto a solid support, i.e., oligosorbents, were proposed. Thanks to the high affinity and high selectivity of the interaction that some aptamers offer toward some target analytes, they also provide powerful techniques that make selective extraction and the concentration of a target analyte from liquid matrices in one step or sample purification of extracts from solid matrices possible. This review describes the development and the properties of these oligosorbents developed for different types of targets-pharmaceuticals, mycotoxins, proteins, cells, etc. After describing the immobilization procedures, we discuss different parameters characterizing the potential of aptamer-based supports as extraction sorbents. Close relations exist between extraction recoveries and the affinity and amounts of aptamers immobilized on the extraction device. In addition, analyte-aptamer interactions may be affected by matrix components and by additives in the samples. This may also lower extraction recoveries and affect the stability and the possible reusability of the aptamer-based sorbent. All these points are discussed and illustrated. Numerous examples of applications of these sorbents to the treatment of complex samples such as food samples, environmental samples, and biological fluids are also reported. Their association with analytical devices, from conventional to miniaturized analytical systems, is also discussed.

Aptamer-affinity column clean-up coupled with ultra high performance liquid chromatography and fluorescence detection for the rapid determination of ochratoxin A in ginger powder

Aptamers are single-stranded oligonucleotides with high affinity and specificity and are widely used in targets separation and enrichment. Here, an aptamer-affinity column (AAC) was firstly prepared in-house through a covalent immobilization strategy. Then, ochratoxin A (OTA) in ginger powder was absorbed and enriched using the new aptamer-based clean-up technology for the first time, and was further analyzed by ultra high performance liquid chromatography with fluorescence detection. After optimization, the average recoveries for blank samples spiked with OTA at 5, 15, and 45 μg/kg ranged from 85.36 to 96.83%. Furthermore, the AAC exhibited a similar accuracy as an immunoaffinity column to clean up OTA in ginger powder. Above all, it exhibited better reusability, twice that of the immunoaffinity column, had lower toxicity and cost, and took less time. Of 25 contaminated ginger powder samples, OTA contamination levels ranged from 1.51 to 4.31 μg/kg, which were lower than the European Union (EU) regulatory limits. All the positive samples were further confirmed by ultra-fast LC with MS/MS. In conclusion, the method of clean-up based on the AAC coupled to ultra-HPLC with fluorescence detection was rapid, specific, and sensitive for the quantitative analysis of OTA in a complex matrix.

Identification of allosteric nucleotide sites of tetramethylrhodamine-labeled aptamer for noncompetitive aptamer-based fluorescence anisotropy detection of a small molecule, ochratoxin A

Aptamer-based fluorescence anisotropy (FA) assay combines the advantages of affinity aptamers in good stability, easy generation, and facile labeling and the benefits of FA in homogeneous analysis, such as robustness, simplicity, and high reproducibility. By using a fluorophore-labeled aptamer, FA detection of a small molecule is not as easy as detection of protein because the binding of a small molecule cannot cause significant increase of molecular weight of the dye-labeled aptamer. The intramolecular interaction between labeled tetramethylrhodamine (TMR) and DNA aptamer bases dramatically affects the local rotation and FA of TMR. This intramolecular interaction can be altered by aptamer conformation change upon target binding, leading to a significant change of FA of TMR. Taking this unique feature of a TMR-labeled aptamer, we described a noncompetitive aptamer-based fluorescence anisotropy assay for detection of small molecules by using ochratoxin A (OTA) as a model. We successfully identified the specific TMR-labeling sites of aptamers with sensitive FA response to OTA from the 5'-end, 3'-end and the internal thymine (T) bases. The aptamer with a TMR labeled on the 10th T base exhibited a remarkable FA reduction response to OTA (Δr = 0.078), without requiring any proteins or nanomaterials as FA signal enhancers. This FA approach for OTA showed high sensitivity with a detection limit of 3 nM, a dynamic range from 3 nM to 3 μM, and good selectivity over the tested compounds with similar structures to OTA. The new strategy allowed the detection of OTA in diluted red wine and urine samples.

Characterization of oligosorbents and application to the purification of ochratoxin A from wheat extracts

The aim of this work was to optimize the preparation of an anti-ochratoxin A (OTA) oligosorbent (OS), a solid-phase extraction sorbent based on OTA aptamers covalently immobilized on sepharose. Different syntheses were carried out by modifying the side of the oligonucleotide chain bound to the sepharose, the length of the spacer arm between the aptamer and the sepharose and the amount of the aptamers introduced during the covalent grafting. Indeed, the capacity of OSs prepared using 3'- or 5'-amino-modified sequences with a C6 or a C12 was studied. In the best conditions, the concentration of aptamers sequence used during their grafting was increased and a capacity close to 40 nmol g(-1) of OS was reached. The potential of the resulting OSs was also studied in pure media. For this, their selectivity was checked by comparing them to a control sorbent prepared without immobilizing aptamers. Extraction recoveries close to 100% were obtained on all OSs, while no retention was observed on the control sorbent. OS does not demonstrate any cross-reactivity towards OTA metabolites, i.e., ochratoxin B and ochratoxin hydroquinone. The oligosorbent was finally applied to the clean-up of OTA from wheat sample extracts. Extraction recoveries were not affected by matrix interferences and the resulting chromatogram clearly highlights the selectivity of the sorbent that allows the removal of matrix components thus improving the reliability of the quantitation of OTA in real samples.

Aptamers: a promosing tool for ochratoxin A detection in food analysis

The contamination of food and feed by mycotoxins has become an increasingly serious problem. Mycotoxins represent a major risk to human and animal health, as well as economics. Herein, we focus on Ochratoxin A (OTA), which is one of the most common mycotoxins contaminating feed and foodstuffs. OTA is a secondary metabolite produced by various Aspergillus and Penicillium strains. Upon ingestion, OTA has a number of acute and chronic toxic effects. It is nephrotoxic, teratogenic, immunosuppressive, and carcinogenic (group 2B). As a consequence, some regulatory limits have been introduced on the levels of OTA in several commodities. The toxic nature of OTA demands highly sensitive and selective monitoring techniques to protect human and animal health. As alternative to traditional analytical techniques, biochemical methods for OTA analysis have attained great interest in the last few decades. They are mainly based on the integration of antibodies or aptamers as biorecognition elements in sensing platforms. However, aptamers have gained more attention in affinity-based assays because of their high affinity, specificity, stability, and their easy chemical synthesis. In this brief review, we present an overview of aptamer-based assays and their applications in OTA purification and detection, appeared in the literature in the last five years.

Rapid high-throughput analysis of ochratoxin A by the self-assembly of DNAzyme-aptamer conjugates in wine

We report a new label-free colorimetric aptasensor based on DNAzyme-aptamer conjugate for rapid and high-throughput detection of Ochratoxin A (OTA, a possible human carcinogen, group 2B) in wine. Two oligonucleotides were designed for this detection. One is N1 for biorecognition, which includes two adjacent sequences: the OTA-specific aptamer sequence and the horseradish peroxidase (HRP)-mimicking DNAzyme sequence. The other is a blocking DNA (B2), which is partially complementary to a part of the OTA aptamer and partially complementary to a part of the DNAzyme. The existence of OTA reduces the hybridization between N1 and B2. Thus, the activity of the non-hybridized DNAzyme is linearly correlated with the concentration of OTA up to 30 nM with a limit of detection of 4 nM (3σ). Meanwhile, a double liquid-liquid extraction (LLE) method is accordingly developed to purify OTA from wine. Compared with the existing HPLC-FD or immunoassay methods, the proposed strategy presents the most appropriate balance between accuracy and facility, resulting in a considerable improvement of real-time quality control, and thereby, preventing chronic poisoning caused by OTA contained red wine.

Fluorescent sensing ochratoxin A with single fluorophore-labeled aptamer

We explored a fluorescent strategy for sensing ochratoxin A (OTA) by using a single fluorophore-labeled aptamer for detection of OTA. This method relied on the change of the fluorescence intensity of the labeled dye induced by the specific binding of the fluorescent aptamer to OTA. Different fluorescein labeling sites of aptamers were screened, including the internal thymine bases, 3'-end, and 5'-end of the aptamer, and the effect of the labeling on the aptamer affinity was investigated. Some fluorophore-labeled aptamers showed a signal-on or signal-off response. With the fluorescent aptamer switch, simple, rapid, and selective sensing of OTA at nanomolar concentrations was achieved. OTA spiked in diluted red wine could be detected, showing the feasibility of the fluorescent aptamer for a complex matrix. This method shows potential for designing aptamer sensors for other targets.

Determination of ochratoxin A in wine by means of immunoaffinity and aminopropyl solid-phase column cleanup and fluorometric detection

A new analytical method for the determination of ochratoxin A (OTA) in red wine has been developed by using a double-extract cleanup and a fluorometric measurement after spectral deconvolution. Wine samples were diluted with a solution containing 1% polyethylene glycol and 5% sodium hydrogencarbonate, filtered, and purified by immunoaffinity and aminopropyl solid-phase column. OTA contents in the purified extract were determined by a spectrofluorometer (excitation wavelength, 330 nm; emission wavelength, 470 nm) after deconvolution of fluorescence spectra. Average recoveries from wine samples spiked with OTA at levels ranging from 0.5 to 3.0 ng/mL were 94.5-105.4% with relative standard deviations (RSD) of <15% (n = 4). The limit of detection (LOD) was 0.2 ng/mL, and the total time of analysis was 30 min. The developed method was tested on 18 red wine samples (naturally contaminated and spiked with OTA at levels ranging from 0.4 to 3.0 ng/mL) and compared with AOAC Official Method 2001.01, based on immunoaffinity column cleanup and HPLC with fluorescence detector. A good correlation (r(2) = 0.9765) was observed between OTA levels obtained with the two methods, highlighting the reliability of the proposed method, the main advantage of which is the simple OTA determination by a benchtop fluorometer with evident reductions of cost and time of analysis.

Screening interaction between ochratoxin A and aptamers by fluorescence anisotropy approach

By taking advantage of the intrinsic fluorescence of ochratoxin A (OTA), we present a fluorescence anisotropy approach for rapid analysis of the interactions between OTA and aptamers. The specific binding of OTA with a 36-mer aptamer can induce increased fluorescence anisotropy (FA) of OTA as the result of the freedom restriction of OTA and the increase of molecular volume, and the maximum FA change is about 0.160. This FA approach enables an easy way to investigate the effects of buffer compositions like metal ions on the affinity binding. FA analysis shows the interaction between OTA and aptamer is greatly enhanced by the simultaneous presence of Ca(2+) and Na(+), while the binding affinity of aptamer decreases more than 18-fold when only Ca(2+) exists, and the binding is completely lost when Ca(2+) is absent. Crucial region of the aptamer for binding can be mapped through FA analysis and aptamer mutation. The demonstrated FA approach maintains the advantages of FA in simplicity, rapidity, and robustness. This investigation will help the development of aptamer-based assays for OTA detection in optimizing the binding conditions, modification of aptamers, and rational design.

Nucleic acid aptamers against biotoxins: a new paradigm toward the treatment and diagnostic approach

Nucleic acid aptamers are short single-stranded DNA or RNA oligonucleotides that can bind to their targets with very high affinity and specificity, and are generally selected by a process referred to as systematic evolution of ligands by exponential enrichment. Conventional antibody-based therapeutic and diagnostic approach currently employed against biotoxins pose major limitations such as the requirement of a live animal for the in vivo enrichment of the antibody species, decreased stability, high production cost, and side effects. Aptamer technology is a viable alternative that can be used to combat these problems. Fully sequestered in vitro, aptamers eliminate the need for a living host. Furthermore, one of the key advantages of using aptamers instead of antibodies is that they can be selected against very weakly immunogenic and cytotoxic substances. In this review, we focus on nucleic acid aptamers developed against various biotoxins of plant, microorganism, or animal origin and show how these can be used in diagnostics (e.g., biosensors) and therapy.

Analytical performances of a DNA-ligand system using time-resolved fluorescence for the determination of ochratoxin A in wheat

The analytical performances of a novel DNA-ligand system using the time-resolved fluorescence (TRF) response of ochratoxin A (OTA)-terbium-DNA aptamer interaction were tested for the quantitative determination of OTA in wheat. Wheat was extracted with acetonitrile/water (60:40, v/v) followed by clean-up through affinity columns containing a DNA-aptamer-based oligosorbent. Then, OTA was detected by TRF spectroscopy after reaction with a terbium fluorescent solution containing the DNA-aptamer probe. The entire procedure was performed in less than 30 min, including sample preparation, and allowed analysis of several samples simultaneously with a 96-well microplate reader. The average recovery from samples spiked with 2.5-25 μg kg(-1) OTA was 77%, with a relative standard deviation lower than 6% and a quantification limit of 0.5 μg kg(-1). Comparative analyses of 29 naturally contaminated (up to 14 μg kg(-1)) wheat samples using the aptamer-affinity column/TRF method or the immunoaffinity column/high-performance liquid chromatography method showed good correlation (r = 0.985) in the range tested. The trueness of the aptamer-based method was additionally assessed by analysis of two quality control wheat materials for OTA. The DNA-ligand system is innovative, simple and rapid, and can be used to screen large quantities of samples for OTA contamination at levels below the EU regulatory limit with analytical performances satisfying EU criteria for method acceptability.

Aptamer-targeted magnetic nanospheres as a solid-phase extraction sorbent for determination of ochratoxin A in food samples

A sorbent based on the aptamer for ochratoxin A was immobilized onto magnetic nanospheres (MNS) and used to develop a magnetic solid-phase extraction procedure to clean up food samples in conjunction with high-performance liquid chromatography separation and fluorescence detection. Specific retention of ochratoxin A by the sorbent was demonstrated, and the capacity of the MNS-aptamer sorbent was determined. The efficacy of this new approach was successfully evaluated through comparison with solid-phase extraction on commercial C18 cartridge. Several different food samples fortified in the range of with 2.5-50 μg/kg yielded mean recoveries from 67% to 90%, respectively. Finally, this oligosorbent was applied to the selective extraction of ochratoxin A from unfortified food samples.

Single-walled carbon nanotubes based quenching of free FAM-aptamer for selective determination of ochratoxin A

Ochratoxin A, a toxin produced by Aspergillus ochraceus and Penicillium verrucosum, is one of the most abundant food-contaminating mycotoxins in the world. It has been classified by the International Agency for Research on Cancer (IARC) as a possible human carcinogen. In this paper, a sensitive and selective fluorescent aptasensor for ochratoxin A (OTA) detection was constructed, utilizing single-walled carbon nanotubes (SWNTs) as quencher which can quench the fluorescence of free unfolded toxin-specific aptamer attached with FAM (carboxyfluorescein). Without any coating materials as compared to graphene-oxide based sensor, we obtained the detection limit of our sensing platform based on SWNTs to be 24.1 nM with a linear detection range from 25 nM to 200 nM. This technique responded specifically to OTA without interference from other analogues (N-acetyl-L-phenylalanine, warfarin and OTB). It has also been verified for real sample application by testing 1% beer containing buffer solution spiked with a series of concentration of OTA.