Recent Advances for the Detection of Ochratoxin A

Abstract

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.

Keywords: amplified detection; aptamers; mycotoxins; ochratoxin A.

Figure 1

Chemical structures of ochratoxin A (a) and ochratoxin B (b).

Figure 2

Working principle of the DNA hydrogel encapsulating AuNPs for visual detection of Ochratoxin A (OTA). The formation of OTA-aptamer complex collapses the backbone of the hydrogel network and the preloaded AuNPs in the hydrogel are released, leading to a change of the supernatant from colorless to red, which could be observed by the naked eye (Adapted from Ref. [80], Copyright 2015, American Chemical Society).

Figure 3

A schematic cartoon depicts a design of a hemin-conjugated DNA hairpin, and its structural change upon recognition of OTA, which forms an active G-quadruplex; the red, blue, and black dashed lines in the left denote EAD2, the OTA aptamer, and a spacer region, respectively. (Adapted from Ref. [85], Copyright 2014, Royal Society of Chemistry).

Figure 4

A schematic illustration shows the principle of Tb³⁺-sensitized OTA detection. In response to OTA, small complementary strands are released from magnetic nanoparticle (MNP)-aptamer nanohybrids to solution phase, which substantially enhances luminescence of Tb³⁺ ion by base coordination under exposure of UV light. (Refer to Ref. [93] for details.).

Figure 5

A schematic illustration of principle of OTA detection based on combining magnetic separation of aptamer-functionalized magnetic nanoparticles (MNPs) and upconversion nanoparticles (UCNPs) as luminescent labeling. (Adapted from Ref. [100], Copyright 2011, Royal Society of Chemistry).

Figure 6

A schematic illustration of an alkaline phosphatase (ALP)-tagged OTA-binding DNA aptamer that was immobilized on a gold surface through hybridization, which undergoes a conformation switch upon OTA binding that triggers the enzyme inhibition. The enzyme activity can easily regenerated by simply applying a short potential pulse. (Adapted from Ref. [107], Copyright 2014, American Chemical Society).

Figure 7

A schematic illustration of signal amplified strategy based on target-induced strand release coupling cleavage of nicking endonuclease and its application to OTA detection. In response to the formation of aptamer-OTA complex, the released DNA2 strands from magnetic beads are first hybridized with DNA3, which play a role of PCR template to produce DNA4. Since the PCR template could be recycled by the nicking enzyme, the amount of DN4 was several ten times as much as DNA2 and eventually quantitated with chemiluminescence. (Refer to Ref. [57] for details.)

Figure 8

A schematic illustration shows the principle of electrochemical detection of OTA, employing exonuclease for target recycling. The complementary strands of OTA aptamer are tagged with ferrocene and form a hairpin structure, upon OTA-aptamer binding and releasing from the electrode. OTA is recycled with exonuclease dismantling the OTA aptamer. (Refer to Ref. [118] for details.)

Figure 9

A schematic cartoon showing OTA-induced hybridization chain reaction (HCR) process and the detection mechanism. (Refer to Ref. [121] for details.) Conceptual structure of the oligonucleotide H1 and H2 (a), and the subsequent chain elongation mechanism (b).

Figure 10

A schematic representation showing a label-free, direct, and noncompetitive homogeneous Förster resonance energy transfer (FRET) immunoassay system for detection of quantitative analysis of OTA, based on the intrinsic fluorescence properties of the anti-OTA and OTA complex (Adapted from Ref. [123], Copyright 2011, Royal Society of Chemistry).

Figure 11

A schematic cartoon showing steps in the construction of the OTB based biosensing glass bead material and the displacement reaction upon incubation with OTA. (Refer to Ref. [137] for details.)