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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.

Schematic presentation of a novel assembled G-wire-induced pyrene excimer switching probe for the amplified detection of microRNA based on exonuclease III-assisted target recycling and Fe 3 O 4 @PDA nanoparticles. This work proposes a promising method for G-wire-based biosensing in disease-related biomarkers detection. [Display omitted] • A new fluorescence method for amplified detection of microRNA was developed. • The method used a novel assembled G-wire-induced pyrene excimer switching probe. • The probe was based on Exo III-assisted target recycling and Fe 3 O 4 @PDA NPs. • The approach shows high sensitivity and specificity. • The approach was successfully applied in cancer cell lysates and serum samples. We reported a novel assembled G-wire-induced pyrene excimer switching probe for microRNA (miRNA) amplified detection on the basis of exonuclease III (Exo III)-assisted target recycling and Fe 3 O 4 @PDA nanoparticles. The multifunctional hairpin (HP) probe recognized and effectively bound to target miRNA, which formed a 3′-blunt terminal for Exo-III digestion and miRNA regeneration to initiate another Exo III-mediated cycling cleavage. After digestion, numerous HP-caged c-myc sequences were released, which were positively related to target miRNA and folded to the parallel G-quadruplex with K+. Additionally, Fe 3 O 4 polydopamine nanoparticles (Fe 3 O 4 @PDA NPs)-based magnet separation was conducted to reduce background fluorescence signal, and parallel G-quadruplexes self-asembled into filamentous G-wires with Mg2+. G-wires generated from 5′-terminal pyrene-labeled c-myc sequences made close distance between two labeled pyrene molecules, and induced the "turn-on" fluorescence signal of pyrene excimer switching. Moreover, gamma-cyclodextrin (γ-CD) was added, which promoted pyrene moiety, causing signal amplification in pyrene excimer fluorescence. Therefore, miRNA was efficiently measured within the homogeneous solution. This method detected miRNA within the dynamic range of 1 pM to 5 nM, with the miR-141 limit of detection (LOD) being 99 fM. It distinguished perfect-matched and mismatched target miRNAs, and showed an accurate detection of miRNA levels in different cell lines and favorable reproducibility when analyzing miRNAs within spiked serum samples. We propose a promising method for G-wire-based biosensing in disease-related biomarkers detection. [ABSTRACT FROM AUTHOR]

This paper describes a novel approach utilizing nano-graphite–aptamer hybrid and DNase I for the amplified detection of ochratoxin A (OTA) for the first time. Nano-graphite can effectively quench the fluorescence of carboxyfluorescein (FAM) labeled OTA specific aptamer due to their strong π – π ; stacking interactions; while upon OTA addition, it will bind with aptamer to fold into an OTA–aptamerG-quadruplex structure, which does not adsorb on the surface of nano-graphite and thus retains the dye fluorescence. Meanwhile, the G-quadruplex structure can be cleaved by DNase I, and in such case OTA is delivered from the complex. The released OTA then binds other FAM-labeled aptamers on the nano-graphite surface, and touches off another target recycling, resulting in the successive release of dye-labeled aptamers from the nano-graphite, which leads to significant amplification of the signal. Under the optimized conditions, the present amplified sensing system exhibits high sensitivity toward OTA with a limit of detection of 20 nM (practical measurement), which is about 100-fold higher than that of traditional unamplified homogeneous assay. Our developed method also showed high selectivity against other interference molecules and can be applied for the detection of OTA in real red wine samples. The proposed assay is simple, cost-effective, and might open a door for the development of new assays for other biomolecules. This aptasensor is of great practical importance in food safety and could be widely extended to the detection of other toxins by replacing the sequence of the recognition aptamer. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes a novel approach utilizing nano-graphite-DNA hybrid and DNase I for the amplified detection of silver(I) ion in aqueous solutions for the first time. Nano-graphite can effectively quench the fluorescence of dye-labeled cytosine-rich single-stranded DNA due to its strong π–π stacking interactions; however, in the presence of Ag+, C–Ag+–C coordination induces the probe to fold into a hairpin structure, which does not adsorb on the surface of nano-graphite and thus retains the dye fluorescence. Meanwhile, the hairpin structure can be cleaved by DNase I, and in such case Ag+ is delivered from the complex. The released Ag+ then binds other dye-labeled single-stranded DNA on the nano-graphite surface, and touches off another target recycling, resulting in the successive release of dye-labeled single-stranded DNA from the nano-graphite, which leads to significant amplification of the signal. The present magnification sensing system exhibits high sensitivity toward Ag+ with a limit of detection of 0.3nM (S/N=3), which is much lower than the standard for Ag+ in drinking water recommended by the Environmental Protection Agency (EPA). The selectivity of the sensor for Ag+ against other biologically and environmentally related metal ions is outstanding due to the high specificity of C–Ag+–C formation. Moreover, the sensing system is used for the determination of Ag+ in river water samples with satisfying results. The proposed assay is simple, cost-effective, and might open the door for the development of new assays for other metal ions or biomolecules. [Copyright &y& Elsevier]

Abstract: For early diagnosis of diseases, the need of ultralow detection limit is an ongoing quest. In this work, by taking the uniqueness of Exonuclease III and DNA metallization, we demonstrate a facile turn-on fluorescent method for amplified detection of biothiols at picomolar concentration. This method relies on the amplification process achieved by the recycling of biothiols retrieved target DNA from silver depositions and the specific interactions between quadruplex and NMM. This method is simple in design, economic in operation and exhibits ultralow detection limit and excellent selectivity toward thiol-containing biomolecules among amino acids found in proteins and in serum samples. More importantly, the detection and discrimination process can be seen by the naked eye with the aid of an UV transilluminator. Therefore, this new concept may offer a potential approach for practical applications as an efficient biosensor for early detection of diseases. [Copyright &y& Elsevier]