Detection of aflatoxin B1 with a new label-free fluorescent aptasensor based on exonuclease I and SYBR Gold

Rapid and specific detection of thiabendazole: enzymatic digestion-enabled fluorescent aptasensor

Thiabendazole, a widely used broad-spectrum fungicide in agriculture, poses risks to human health. To monitor its presence in water, we propose a fluorescent aptasensor utilizing Escherichia coli exonuclease I (Exo I). The findings demonstrate a linear correlation between thiabendazole concentrations and digestion percentage, with a detection limit (LOD) exceeding 1 µM and a determination coefficient (R2) of 0.959. This aptamer-based fluorescence spectroscopy detection system holds promise for a rapid, specific, and sensitive analysis of thiabendazole in environmental waters and food matrices.

A Label-Free Aptasensor for Turn-On Fluorescent Detection of Aflatoxin B1 Based on an Aggregation-Induced-Emission-Active Probe and Single-Walled Carbon Nanohorns

The determination of the aflatoxin B1 (AFB1) content has received widespread attention in the context of food safety, which is a global public health issue. Accordingly, a label-free and turn-on fluorescent AFB1 determination method is developed herein with an ss-DNA aptamer as the recognition element, 4, 4-(1E,1E)-2, 2-(anthracene-9, 10-diyl) bis(ethene-2, 1-diyl) bis(N, N, N-trimethylbenzenaminium iodide) (DSAI) as the aggregation-induced emission (AIE) fluorescent probe, and single-walled carbon nanohorns (SWCNHs) as the selective part with a fluorescence quenching effect. In the presence of AFB1, the AFB1-specific aptamer undergoes a structural transformation and switches from being a random helix to a folded structure. DSAI's fluorescence is protected as a result of the resistance of the transformed aptamer adsorbed on the SWCNHs' surface. Because DSAI's fluorescence is not quenchable, the fluorescence intensity is calculated as a function of the AFB1 concentration. By simply mixing DSAI, aptamer, AFB1 samples, and SWCNHs, the method can be carried out in 2 h, with a limit of detection (LOD) of 1.83 ng/mL. It has a high selectivity in the presence of other mycotoxins, and its performance is confirmed in soybean sauce with a known concentration of AFB1. The LOD was 1.92 ng/mL in the soy sauce samples and the recovery ranged from 95 to 106%, implying that the presented aptasensor has great potential for food analysis.

Recent progress in optical and electrochemical aptasensor technologies for detection of aflatoxin B1

AFB1 (Aflatoxin B1) contamination is becoming a global concern issue due to its extraordinary occurrence, severe toxicity, as well as the great influence on the economic losses, food safety and environment. Therefore, it is desirable to develop novel analytical techniques for simple, rapid, accurate, and even point-of-care testing of AFB1. Fortunately, aptamer, considered as a new generation bioreceptor and even superior to classic antibody and enzyme, has been emerged remarkable application in food hazards detection. Correspondingly, aptasensors have been well-established toward AFB1 determination with outstanding performance. In this article, we first discuss and summarize the recent progress in optical and electrochemical aptasensors to monitor AFB1 over the past three years. In particular, the embedding of advanced nanomaterials for their improved analytical performance is highlighted. Furthermore, the critical analysis on various signal transduction strategies for aptasensors construction is discussed. Finally, we reveal the challenges and provide our opinion in future opportunities for aptasensor development.

Glyphosate-Exonuclease Interactions: Reduced Enzymatic Activity as a Route to Glyphosate Biosensing

N-phosphonomethyle-glycine (glyphosate) is the most widely used pesticide worldwide due to its effectiveness in killing weeds at a moderate cost, bringing significant economic benefits. However, owing to its massive use, glyphosate and its residues contaminate surface waters. On site, fast monitoring of contamination is therefore urgently needed to alert local authorities and raise population awareness. Here the hindrance of the activity of two enzymes, the exonuclease I (Exo I) and the T5 exonuclease (T5 Exo) by glyphosate, is reported. These two enzymes digest oligonucleotides into shorter sequences, down to single nucleotides. The presence of glyphosate in the reaction medium hampers the activity of both enzymes, slowing down enzymatic digestion. It is shown by fluorescence spectroscopy that the inhibition of ExoI enzymatic activity is specific to glyphosate, paving the way for the development of a biosensor to detect this pollutant in drinking water at suitable detection limits, i.e., 0.6 nm.

Fluorescence-based aptasensors for small molecular food contaminants: From energy transfer to optical polarization

Small molecular food contaminants, such as mycotoxins, pesticide residues and antibiotics, are highly probable to be passively introduced in food at all stages of its processing, including planting, harvest, production, transportation and storage. Owing to the high risks caused by the unknowing intake and accumulation in human, there is an urgent need to develop rapid, sensitive and efficient methods to monitor them. Fluorescence-based aptasensors provide a promising platform for this area owing to its simple operation, high sensitivity, wide application range and economical practicability. In this paper, the common sorts of small molecular contaminants in foods, namely mycotoxins, pesticides, antibiotics, etc, are briefly introduced. Then, we make a comprehensive review, from fluorescence resonance energy transfer (in turn-on, turn-off, and ratiometric mode, as well as energy upconversion) to fluorescence polarization, of the fluorescence-based aptasensors for the determination of these food contaminants reported in the last five years. The principle of signal generation, the advances of each sort of fluorescent aptasensors, as well as their applications are introduced in detail. Additionally, we also discussed the challenges and perspectives of the fluorescent aptasensors for small molecular food contaminants. This work will offer systematic overview and inspiration for amateurs, researchers and developers of fluorescence-based aptasensors for the detection of small molecules.

Detection of aflatoxin B1 with a new label-free fluorescence aptasensor based on PVP-coated single-walled carbon nanohorns and SYBR Gold

This paper describes a novel fluorescence label-free aptasensor to detect aflatoxin B₁ (AFB₁) by utilizing SYBR Gold, aptamer, and single-walled carbon nanohorns (SWCNHs). In the presence of AFB₁, the conformation of AFB₁-specific aptamer went through and the spatial structure of this specific aptamer was transformed accordingly. Due to the resistance of the transformed aptamer when adsorbed on the surface of SWCNHs, the protection of the fluorescence of SYBR Gold was accomplished. Consequently, concentrations of AFB₁ showed a strong association with fluorescence intensity. The detection limit (LOD) of AFB₁ was 1.89 ng/mL, while the linear range was 5-200 ng/mL and fluorescence intensity satisfactorily correlated (R² = 0.9919) with the logarithm of AFB₁ concentration.

Recent progress in fluorescent aptasensors for the detection of aflatoxin B1 in food

Aflatoxin B1 pollution is one of the most critical issues of food safety and has been categorized as a group I carcinogen by the International Agency for Research on Cancer. Aflatoxin B1 exists in various foods and feedstuff products and can be produced and contaminate food products in all processes, including growth, harvest, storage, or processing. Therefore, it is of great value for detecting and on-site monitoring aflatoxin B1. Aptamers are short single-stranded DNA or RNA obtained from the nucleic acid molecular library through SELEX. With advantages of high specificity, large affinity, and easy modification, aptasensors have become popular in a wide range of promising applications. This review focuses on recent advances on fluorescent aptamer sensors for the detection of aflatoxin B1, including their design strategies, working mechanisms, and applications to on-site detection. Finally, the current challenges and prospects are discussed.

Highly sensitive magnetic relaxation sensing method for aflatoxin B1 detection based on Au NP-assisted triple self-assembly cascade signal amplification

Highly sensitive detection of aflatoxin B₁ (AFB₁) is of great significance because of its high toxicity and carcinogenesis. We propose a magnetic relaxation sensing method based on gold nanoparticles (Au NPs)-assisted triple self-assembly cascade signal amplification for highly sensitive detection of AFB₁. Both AFB₁ antibody and initiator DNA (iDNA) are labeled on Au NPs to form Ab-Au-iDNA probe. iDNA is enriched by Au NPs to achieve first signal amplification. Different amounts of Ab-Au-iDNA were bound with AFB₁ antigen by indirect competitive immunoassay, and then hybridization chain reaction event was initiated by iDNA to produce long hybridization chain reaction products to enrich more horseradish peroxidase-streptavidin for the second signal amplification. Dopamine could be rapidly converted to polydopamine by HRP catalysis, which is used as the third signal amplification. The Fe³⁺ solution, providing paramagnetic ions with a strong magnetic signal, could be adsorbed by the polydopamine due to the formation of coordination bonds of phenolic hydroxyl groups with Fe³⁺. This effective interaction between polydopamine and Fe³⁺ significantly changes the transverse relaxation time signal of Fe³⁺ supernatant solution, which can be used as a magnetic probe for highly sensitive detection of AFB₁. The sensor exhibited high specificity and sensitivity with a detection limit of 0.453 pg/mL owing to the Au NP-assisted triple self-assembly cascade signal amplification strategy. It has been successfully employed for AFB₁ detection in animal feed samples with consistent results of enzyme linked immune sorbent assay and high-performance liquid chromatography.

Recent progress in visual methods for aflatoxin detection

Aflatoxins (AFs) contamination in food and agricultural products poses a significant threat to human health. Sensitive and accurate detection of AFs provides a strong guarantee for ensuring food safety. Conventional chromatographic-based or mass spectrum methods, which rely on bulky instrument and skilled personnel, are not suitable for on-site surveillance. By contrast, visual detections which possess the merits of rapidity and sophisticated instrument-free present an excellent potential for the on-site detection of AFs. This review intends to summarize the latest development of visual methods for AFs detection, including paper-based tests, chromogenic reactions, and luminescent methods. Emerging technologies, like nanotechnology, DNAzymes, and aptamers combined with these visual methods are introduced. The basic principles, features, and application advantages of each type of visual methods are discussed. The biggest challenges and perspectives on their future trends are also addressed.

Recent Advances in Aptamer Sensors

Recently, aptamers have attracted attention in the biosensing field as signal recognition elements because of their high binding affinity toward specific targets such as proteins, cells, small molecules, and even metal ions, antibodies for which are difficult to obtain. Aptamers are single oligonucleotides generated by in vitro selection mechanisms via the systematic evolution of ligand exponential enrichment (SELEX) process. In addition to their high binding affinity, aptamers can be easily functionalized and engineered, providing several signaling modes such as colorimetric, fluorometric, and electrochemical, in what are known as aptasensors. In this review, recent advances in aptasensors as powerful biosensor probes that could be used in different fields, including environmental monitoring, clinical diagnosis, and drug monitoring, are described. Advances in aptamer-based colorimetric, fluorometric, and electrochemical aptasensing with their advantages and disadvantages are summarized and critically discussed. Additionally, future prospects are pointed out to facilitate the development of aptasensor technology for different targets.

Hairpin DNA assisted dual-ratiometric electrochemical aptasensor with high reliability and anti-interference ability for simultaneous detection of aflatoxin B1 and ochratoxin A

The simultaneous detection of multiple mycotoxins in grains is significant due to the enhanced toxicity induced by their synergistic effects. In this work, a dual-ratiometric electrochemical aptasensing strategy for the simultaneous detection of aflatoxin B1 (AFB1) and ochratoxin A (OTA) was developed. Here, an anthraquinone-2-carboxylic acid (AQ)-labelled complementary DNA (cDNA) was used to provide separate and specific binding sites to assemble the ferrocene-labelled AFB1 aptamer (Fc-Apt1) and methylene blue-labelled OTA aptamer (MB-Apt2). The target-induced current ratios of I_Fc/I_AQ and I_MB/I_AQ were then used to quantitatively relate to AFB1 and OTA, respectively. Following this principle, two types of aptasensors involving the hairpin DNA (hDNA) and linear single-stranded DNA (ssDNA) as the cDNA were fabricated for performance comparisons. The results revealed that hairpin DNA with a rigid 2D structure can greatly improve the assembly and recognition efficiency of the sensing interface, which makes the hDNA-based aptasensor possess high sensitivity, reliability and anti-interference ability. The hDNA-based aptasensor exhibited a detection range of 10-3000 pg mL^-1 for AFB1 and 30-10000 pg mL^-1 for OTA, respectively, with no observable cross-reactivity. Furthermore, the aptasensor was applied to analyze corn and wheat samples, and the reliability was validated by HPLC-MS/MS. Our work has presented a novel way for fabricating a high-performance aptasensor for simultaneous detection of multiple mycotoxins.