Analytical methods for determination of mycotoxins: a review

Sensitive enzyme-biosensor based on screen-printed electrodes for Ochratoxin A

Horseradish peroxidase has been successfully immobilized in a polypyrrole matrix onto disposable screen-printed carbon electrodes for the selective detection of Ochratoxin A. The chronoamperometric determination of this mycotoxin has been optimized by experimental design methodology, which implied the join evaluation of pH of the buffer solution, applied potential and concentration of H(2)O(2). The slopes of the calibration curves built under the optimum conditions of the experimental variables have been used to estimate the reproducibility and the repeatability of the developed biosensor for Ochratoxin A. Relative standard deviation values of 1.9% (n=5 and alpha=0.05) and 7.1% (n=4 and alpha=0.05) were obtained for reproducibility and repeatability, respectively. The capability of detection for this method was 0.1 ng mL(-1) (alpha=0.05 and beta<0.05). The viability of the developed biosensor in the determination of Ochratoxin A in spiked beer and in roasted coffee has been shown, yielding average recoveries of 103% and 99%, in that order, with relative standard deviation values less than 5% (n=3 and alpha=0.05) in both cases.

Surface plasmon resonance biosensor for the detection of ochratoxin A in cereals and beverages

Ochratoxins are a group of mycotoxins produced as secondary metabolites by fungi which contaminate a large variety of food and feed commodities. Due to their teratogenic and carcinogenic properties, ochratoxins present a serious hazard to human and animal health. There is an increasing need to establish a simple sensitive method to detect these toxins. Here we report a rapid and highly sensitive surface plasmon resonance (SPR) assay of ochratoxin A (OTA) using Au nanoparticles for signal enhancement on a mixed self-assembled monolayer (mSAM) surface. A competitive immunoassay format was used for the development of the OTA immunoassay, which is based on the immobilization of target OTA through its ovalbumin (OVA) conjugate with a polyethylene glycol (PEG) linker. The new OTA conjugate (OTA-PEG-OVA) showed remarkably enhanced performance characteristics compared with those based on the immobilization of a commercial bovine serum albumin BSA-OTA conjugate without a PEG linker. Although OTA concentrations as low as 1.5 ng mL(-1) could be directly detected on this surface, the limit of detection (LOD) can be dramatically improved to 0.042 ng mL(-1) for OTA by applying large gold nanoparticles (40 nm) for signal enhancement. Various chemical conditions to minimize the influence of the food matrix on assay performance were also investigated. Grain samples were simply extracted with 50% methanol and liquid samples treated with poly(vinylpyrrolidone) (PVP) (3 or 5%), without any sample clean-up or pre-concentration step prior to analysis. The LODs for OTA in oats and corn were 0.3 and 0.5 ng g(-1), respectively, while in wine and other beverages, LODs ranged from 0.058 to 0.4 ng mL(-1). No cross-reactivity was observed with three other common mycotoxins. In addition, the mSAM/OTA-PEG-OVA surface exhibited high stability with over 600 binding/regeneration cycles. This approach with simple sample preparation provides a powerful tool for the rapid and sensitive quantitative determination of OTA in food matrices.

Magnetic nanogold microspheres-based lateral-flow immunodipstick for rapid detection of aflatoxin B2 in food

A novel membrane-based lateral-flow immunodipstick assay was developed for the fast screening of aflatoxin B(2) (AFB(2)) as a model compound in food samples. The detector reagent consisted of magnetic nanogold microspheres (MnGMs) with nano-Fe(2)O(3) particles as core and gold nanoparticles as shell, and bio-functionalized with monoclonal anti-AFB(2) antibodies. Manually spotted AFB(2)-bovine serum albumin conjugates (AFB(2)-BSA) and goat anti-mouse IgG on nitrocellulose membrane were used as test and control lines, respectively. As the major advantage, experimental results indicated that the visual detection limit (cutoff value) of the MnGM-based dipstick immunoassay with 0.9 ng/ml AFB(2) was about threefold lower compared to a conventional immunodipstick test using gold nanoparticles as detection reagent. Qualitative results (yes/no) could be obtained within 15 min without expensive equipment. The assay was evaluated with AFB(2) spiked or naturally contaminated samples (n=8), including peanuts, hazelnuts, pistacia and almonds, receiving excellent correspondance with results from high performance liquid chromatography (HPLC). Most importantly, the assay gave no false negative results. By controlling the target antibody this assay can be easily extended for use with other food relevant toxins and thus represents a versatile detection method.

Biosensors for mycotoxin analysis: recent developments and future prospects

The toxicity and prevalence of mycotoxins in commodities and foods has necessitated the development of rapid methods in order to ensure the protection of human food and animal feed supplies. Testing for mycotoxins can be accomplished by many techniques that range from determinative tests in which the presence of the toxin is confirmed, to presumptive tests in which the presence of the toxin is inferred from the presence of markers. This review focuses on tests that fall into a third category, namely indirect assays, where the presence of the toxin is established by it's interaction with an intermediary. Such intermediaries include biological materials that bind mycotoxins, such as antibodies, as well as synthetic materials such as polymers and man-made peptides. The diversity of assays within this category is extraordinary and includes assays based upon traditional microwell formats, microbeads, membranes, electrodes, wave-guides, and solution-phase assays. The microbead format includes platforms as diverse as flow injection immunoassays, tandem column immunoassays, and immunoaffinity columns. The membrane-based formats include flow-through as well as lateral-flow assays. The electrode-based formats incorporate miniaturised immunoassays with electrochemical endpoints. The wave-guide-based devices include formats such as surface plasmon resonance, and fluorescence array biosensors, and the solution phase formats include homogeneous assays such as fluorescence polarisation immunoassay. The breadth of technologies brought to bear upon solving the need for rapid, accurate, detection of mycotoxins is impressive and includes technologies currently available commercially and those which appear poised to enter the marketplace.