A novel signal‐on fluorescent aptasensor for ochratoxin A detection based on RecJ f exonuclease‐induced signal amplification

Exonuclease-based aptasensors: Promising for food safety and diagnostic aims

As of today's requirement, developing cost-effective smart sensing tools with ultrahigh sensitivity for food safety insurance is of special importance. For this purpose, aptamer-based biosensors (aptasensors) powered by the superiorities of the recycling signal amplification strategies have been expanded especially. Target recycling supported by enzymes is an appealing approach for implementing signal amplification. As the supreme biocatalyst enzymes, exonucleases can inaugurate signal improvement by involving a single target in a process would result in appreciable repeating cycles of the cleavage of the phosphodiester bonds between the building blocks of the nucleic acid strands, and also, their terminals. Although there are diverse substances for catalyzing amplification strategies, including nanoparticles, carbon-based nanocomposites, and quantum dots (QDs), exonucleases are of superiority over them by simplifying the amplification process with no need for the complicated pre-treatment processes. The outstanding selectivity and great sensitivity of the aptasensors tuned by amplification potency of exonucleases nominate them as the promising sensing tools for label-free, ease-of-use, cost-effective, and real-time diagnosis of diverse targets. Here, we summarize the achievements and perspectives in the scientific branch of aptasensor design for the qualitative monitoring of diverse targets by cooperation of exonucleases with the conspicuous potential for the signal amplification. Finally, some results are expressed to provide a comprehensive viewpoint for developing novel nuclease-based aptasensors in the future.

Development of a Novel Magnetic-Bead-Based Automated Strategy for Efficient and Low-Cost Sample Preparation for Ochratoxin A Detection Using Mycotoxin–Albumin Interaction

The mycotoxin ochratoxin A (OTA) is toxic to humans and frequently contaminates wine and beer. Antibodies are essential recognition probes for the detection of OTA. However, they have several drawbacks, such as high costs and difficulty in preparation. In this study, a novel magnetic-bead-based automated strategy for efficient and low-cost OTA sample preparation was developed. Human serum albumin, which is an economical and stable receptor based on the mycotoxin–albumin interaction, was adapted and validated to replace conventional antibodies to capture OTA in the sample. Ultra-performance liquid chromatography–fluorescence detection was used in combination with this preparation method for efficient detection. The effects of different conditions on this method were investigated. The recovery of OTA samples spiked at three different concentrations ranged from 91.2% to 102.1%, and the relative standard deviations (RSDs) were 1.2%–8.2% in wine and beer. For red wine and beer samples, the LODs were 0.37 and 0.15 µg/L, respectively. This reliable method overcomes the drawbacks of conventional methods and offers significant application prospects.

A signal-enhancement fluorescent aptasensor based on the stable dual cross DNA nanostructure for simultaneous detection of OTA and AFB1

The simultaneous detection of multiple mycotoxins is of great significance for food safety and human health. Herein, a simple, convenient and accurate fluorescent aptasensor was designed based on the dual cross DNA nanostructure for the simultaneous detection of ochratoxin A (OTA) and aflatoxin B₁ (AFB₁), in which the stable dual cross DNA nanostructure provided an assay platform using the fluorescent dye-labeled aptamers as a sensing element. Owing to the higher affinity of aptamers for their target, the aptamer probes were released from the assay platform in the presence of OTA and AFB₁, resulting in an enhanced fluorescence at 570 nm and 670 nm. This "signal-on" fluorescent aptasensor assay system can effectively avoid background signals and minimize false positive. Furthermore, the designed method can realize the simultaneous detection of OTA and AFB₁ during the whole experiment. The limits of detection (LOD) were as low as 0.0058 ng/mL for OTA, ranging from 0.01 to 50 ng/mL and 0.046 ng/mL for AFB₁, ranging from 0.05 to 100 ng/mL. The proposed fluorescent aptasensor exhibits excellent performance in practical application and provides a novel approach for the simultaneous detection of multiple mycotoxins by simply changing the aptamers. A "signal-on" fluorescent aptasensor assay system based on the stable dual cross DNA nanostructure was successfully developed for simultaneous detection of OTA and AFB₁ with lower detection limits in wider linear ranges.

Versatile Integration of Liquid-Phase Microextraction and Fluorescent Aptamer Beacons: A Synergistic Effect for Bioanalysis

Fluorescent aptamer beacons (FABs) are a major category of biosensors widely used in environmental analysis. However, due to their low compatibility, it is difficult to use the common FABs for biological samples. To overcome this challenge, construction of FABs with complex structures to adapt the nature of biological samples is currently in progress in this field. Unlike previous works, we moved our range of vision from the FAB itself to the biological sample. Inspired by this idea, in this work, flat membrane-based liquid-phase microextraction (FM-LPME) with sufficient sample cleanup and preconcentration capacities was integrated with FABs. With the merits of both FM-LPME and FABs, the integrated LPME-FAB system displayed a clear synergistic enhancement for target analysis. Specifically, LPME in the LPME-FAB system provided purified and enriched Hg²⁺ for the FAB recognition, while the FAB recognition event promoted the extraction efficiency of LPME. Due to superior performances, the LPME-FAB system achieved highly sensitive analysis of Hg²⁺ in urine samples with a detection limit of 27 nM and accuracies in the range of 98-113%. To the best of our knowledge, this is the first time that an integrated LPME-FAB system was constructed for target analysis in biological samples. We believe that this study will provide a new insight into the next generation of biosensors, where the integration of sample preparation with detection probes is as important as the design of complex probes in the field of bioanalysis.