Dual-Modal Immunosensor Made with the Multifunction Nanobody for Fluorescent/Colorimetric Sensitive Detection of Aflatoxin B1 in Maize

Nanobodies-based colloidal gold immunochromatographic assay for specific detection of parathion

Parathion is one of organophosphorus pesticide, which has been prohibited in agricultural products due to its high toxicity to human beings. However, there are still abuse cases for profit in agricultural production. Hence, we established nanobodies-based colloidal gold immunochromatographic assay (GICA) in which nanobodies (Nbs) as an excellent recognition element, greatly improving the stability and sensitivity of ICA. Under the optimal conditions, the developed Nbs-based GICA showed a cut-off value of 50 ng/mL for visual judgment and a half-inhibitory concentration (IC50) of 2.39 ng/mL for quantitative detection. The limit of detection (LOD) was as low as 0.15 ng/mL which was significantly 50-fold higher sensitivity than the commercial mAb-ICA. Additionally, this method exhibited good recoveries for the detection of cabbage, cucumber, and orange samples and excellent correlation with the UPLC-MS/MS method. The results showed that this method developed in this work based on nanobody can be used in practical detection of parathion in foods and nanobody is novel prospective antibody resource for immunoassays of chemical contaminants.

Highly sensitive and label free on-site monitoring immunosensor for detection of Aflatoxin B1 from real samples

Aflatoxin B1 (AF-B1) are toxins secreted by secondary metabolites of molds that have adverse effects on humans and animals resulting in huge economic losses. Here we report on field useable, cost effective and direct electrochemical sensor based on conducting polymer composite electrode, Poly (3,4-ethylenedioxythiophene): polystyrene sulphonic acid (PEDOT-PSS) for label-free detection of AF-B1. Structural and morphological characterization of composite electrodes were carried out using XRD and SEM. We compared two different electroanalytical techniques namely, transient capacitance and differential pulse voltammetry, to select the most prominent technique for analyzing the mycotoxin easily. For direct detection of AF-B1, transient capacitance measurement at 77 and 1000 Hz was employed wherein sensor showed linearity in 18.18-300.0 ng mL-1 range at 77 Hz for AF-B1. Best limit of detection (LOD) for AF-B1 was 55.41 ng mL-1 (369 pM) at 77 Hz with very good repeatability. DPV showed linearity in the range 18.18-342.85 ng mL-1 with LOD 435 pM. For demonstration of application of this sensor directly using minimum sample preparation, AF-B1 sensing has been confirmed successfully using white button mushrooms and okra stored at ambient conditions. Sensor response with real samples suggest usefulness of sensor to monitor stored farm products easily.

Ionic liquid-functionalized mesoporous multipod silica for simultaneously effective extraction of aflatoxin B1 and its two precursors from grain

BACKGROUND

Aflatoxin B1 (AFB1) and its precursors contaminate food and agricultural products, posing a significant risk to food safety and human health, but simultaneous and effective extraction and determination of AFB1 and its precursors with varied structures is still a challenging task.

RESULTS

In this study, a bisimidazolium-type ionic liquid functionalized mesoporous multipod silica (SiO2@mPMO-IL(im)2) was fabricated to extract AFB1 and its two precursors, i.e., averantin and sterigmatocystin. The SiO2@mPMO-IL(im)2 could simultaneously extract three targets with varied structures based on the multipods, mesopores, and multifunctional groups. The density functional theory calculations further verified the multiple interactions between SiO2@mPMO-IL(im)2 and targets. The fabricated SiO2@mPMO-IL(im)2 could effectively extract and determine three targets in grains by combing with dispersive solid-phase extraction and high-performance liquid chromatography. Good linearity (r2 > 0.9978), low LODs (0.9-1.5 μg kg-1) and LOQs (3.0-4.5 μg kg-1), satisfactory spiked recoveries (92.5%-106.8%) and high precisions (RSD<6.4%) were observed.

SIGNIFICANCE AND NOVELTY

This work demonstrates the feasibility of SiO2@mPMO-IL(im)2 for simultaneous and effective extraction of toxins with varied structures and provides a promising sample preparation for the analysis of AFB1 and its precursors in grain samples.

Integrating molecular imprinting into flexible covalent organic frameworks for selective recognition and efficient extraction of aflatoxins

Covalent organic frameworks (COFs) are promising adsorbents for extraction, but their selectivity for molecular recognition remains a challenging issue due to the very limited structural design with rigid structure. Herein, we report an elegant strategy for the design and synthesis of molecularly imprinted flexible COFs (MI-FCOFs) via one-pot reaction between the flexible building block of 2,4,6-tris(4-formylphenoxy)- 1,3,5-triazine and linear 4-phenylenediamine for selective extraction of aflatoxins. The flexible chain structure enabled the developed MI-FCOF to adjust the shape and conformation of frameworks to suit the template molecule, giving high selectivity for aflatoxins recognition. Moreover, MI-FCOF with abundant imprinted sites and function groups exhibited an exceptional adsorption capacity of 258.4 mg g-1 for dummy template which is 3 times that of no-imprinted FCOF (NI-FCOF). Coupling MI-FCOF based solid-phase extraction with high-performance liquid chromatography gave low detection limits of 0.003-0.09 ng mL-1 and good precision with relative standard deviations ≤ 6.7% for the determination of aflatoxins. Recoveries for the spiked rice, corn, wheat and peanut samples were in the range of 85.4%- 105.4%. The high selectivity of the developed MI-FCOF allows matrix-free determination of AFTs in food samples. This work offers a new way to the design of MI-FCOF for selective molecular recognition.

UiOL@AIEgens-assisted lateral flow immunosensor for the ultrasensitive dual-modal point-of-care detection of aflatoxin B1

Aflatoxin B1 (AFB1) contamination in food has attracted worldwide attention. The sensitive detection of AFB1 is vital for ensuring food quality and safety. This study developed an ultrasensitive signal-enhanced lateral flow immunosensor (LFIS) based on the functionalized zirconium metal-organic framework (MOF) of a UiO linker enriched with abundant aggregation-induced emission luminogen (UiOL@AIEgens) probes for the rapid dual-modal point-of-care (POC) determination of AFB1. Using UiO MOFs with numerous active sites as the carrier facilitated abundant AIEgens enrichment on the surface. After coupling with enough anti-AFB1 monoclonal antibodies (mAbs), the green-emissive UiOL@AIEgens-mAbs probes with high specificity and remarkably-enhanced fluorescence responses were obtained to competitively capture target AFB1 in the standard or sample solution and AFB1 antigen immobilized on the test (T) line of the POC LFIS. Under optimum conditions, the LFIS was capable of visual qualitative and smartphone-assisted dual-modal determination of target AFB1 within 7 min. Detection occurred in a range of 0.01-5 ng/mL at an ultra-low detection limit of 0.003 ng/mL, which was 300- and 600-fold lower than traditional immunoassays and the maximum limit set by the European Union, respectively. Moreover, the feasibility and robustness of the LFIS platform were assessed by detecting AFB1 in maize and lotus seed samples with average recoveries of 94.3-109.0%. The developed UiOL@AIEgens-based POC LFIS can be used for ultrasensitive, reliable, on-site detection in food. This study provides a new method for the real-time monitoring of AFB1 and other harmful contaminants in food and more complex matrices.

Nafion-Immobilized Functionalized MWCNT-based Electrochemical Immunosensor for Aflatoxin B1 Detection

The ubiquitous aflatoxin B1 (AFB1) contamination in foods and other complex matrices has brought great challenges for onsite monitoring. In this study, an ultrasensitive Nafion-immobilized functionalized multiwalled carbon nanotube (MWCNT)-based electrochemical (EC) immunosensor was developed for trace AFB1 detection. The introduced Nafion film could steadily stabilize functionalized MWCNTs with uniform distribution and tiling on the surface of a Au electrode. Functionalized MWCNTs with a large specific surface area, numerous active sites to couple with abundant anti-AFB1 monoclonal antibodies (mAbs), and high conductivity served as the signal amplifier for remarkably enhancing the sensing performance of the immunosensor. In the presence of AFB1, it was specifically captured by mAbs to reduce the amplified current signals, which were recorded by differential pulse voltammetry for the accurate quantitation of AFB1. Because of the synergistic effects of Nafion on the stabilization of functionalized MWCNTs as signal enhancers, the developed EC immunosensor exhibited an extremely high selectivity, excellent sensitivity with a limit of detection as low as 0.021 ng/mL, and a wide dynamic range of 0.05-100 ng/mL, besides fascinating merits of easy construction, low cost, good stability in 7 days, and good reusability. The anti-interference ability of the immunosensor was verified against three other mycotoxins, and the practicability and accuracy were confirmed by measuring AFB1 in fortified malt, lotus seed, and hirudo samples with a satisfactory recovery of 92.08-104.62%. This novel immunosensing platform could be extended to detect more mycotoxins in complex matrices to ensure food safety.

A Novel and Highly Efficient Microextraction Method for the Determination of Aflatoxin Precursor Averantin in Fatty Grain Samples

Averantin (AVN) is an important aflatoxin biosynthetic precursor and has been listed in the screening range of mycotoxins. Herein, a novel ionic liquid-based one-, two-, and three-phase transition microextraction (IL-OTTPTME) method was combined with high-performance liquid chromatography for the extraction and determination of AVN in fatty grain samples. The formation of a homogeneous solution and three-phase system during the IL-OTTPTME process allowed both efficient extraction and coextracted lipid cleanup. Density functional theory calculations and distribution coefficient determination results demonstrated that AVN extraction by IL mainly occurred through hydrogen-bond and π-π interactions. Under optimized conditions, the LOD and LOQ of the proposed method were 0.5 and 1.5 ng/g, respectively. Finally, the method was used to determine AVN in several grains with different fat contents, achieving satisfactory relative recoveries (86.0-107.8%) and RSDs (1.2-6.2%, n = 3).

Magnetic nanoparticle-based immunosensors and aptasensors for mycotoxin detection in foodstuffs: An update

Mycotoxin contamination of food crops is a global challenge due to their unpredictable occurrence and severe adverse health effects on humans. Therefore, it is of great importance to develop effective tools to prevent the accumulation of mycotoxins through the food chain. The use of magnetic nanoparticle (MNP)-assisted biosensors for detecting mycotoxin in complex foodstuffs has garnered great interest due to the significantly enhanced sensitivity and accuracy. Within such a context, this review includes the fundamentals and recent advances (2020-2023) in the area of mycotoxin monitoring in food matrices using MNP-based aptasensors and immunosensors. In this review, we start by providing a comprehensive introduction to the design of immunosensors (natural antibody or nanobody, random or site-oriented immobilization) and aptasensors (techniques for aptamer selection, characterization, and truncation). Meanwhile, special attention is paid to the multifunctionalities of MNPs (recoverable adsorbent, versatile carrier, and signal indicator) in preparing mycotoxin-specific biosensors. Further, the contribution of MNPs to the multiplexing determination of various mycotoxins is summarized. Finally, challenges and future perspectives for the practical applications of MNP-assisted biosensors are also discussed. The progress and updates of MNP-based biosensors shown in this review are expected to offer readers valuable insights about the design of MNP-based tools for the effective detection of mycotoxins in practical applications.

Improvement of the sensitivity of lateral flow systems for detecting mycotoxins: Up-to-date strategies and future perspectives

Mycotoxins are dangerous human and animal health-threatening secondary fungal metabolites that can be found in various food and agricultural products. Several countries have established regulations to restrict their presence in food and agricultural products destined for human and animal consumption. Consequently, the need to develop highly sensitive and smart detection systems was recognized worldwide. Lateral flow assay possesses the advantages of easy operation, rapidity, stability, accuracy, and specificity, and it plays an important role in the detection of mycotoxins. Nevertheless, strategies to comprehensively improve the sensitivity of lateral flow assay to mycotoxins in food have rarely been highlighted and discussed. In this article, a comprehensive overview was presented on the application of lateral flow assay in mycotoxin detection in food samples by highlighting the principle of lateral flow assay, presenting a detailed discussion on various analytical performance-improvement strategies, such as the development of high-affinity recognition reagents, immunogen immobilization methods, and signal amplification. Additionally, a detailed discussion on the various signal analyzers and interpretation approaches was provided. Finally, current hurdles and future perspectives on the application of lateral flow assay in the detection of mycotoxins were discussed.

Multiple Isothermal Amplification Coupled with CRISPR-Cas14a for the Naked-eye and Colorimetric Detection of Aflatoxin B1

Aflatoxin B1 (AFB1) is highly toxic and challenging to remove, posing significant risks to both human health and economic development. Therefore, there is an urgent need to develop rapid, simple, and sensitive detection technologies. In this study, we introduce a naked-eye and colorimetric method based on multiple isothermal amplifications coupled with CRISPR-Cas14a and investigate its biosensing properties. This technique utilizes composite nanoprobes (MAPs) comprising magnetic nanoparticles and gold nanoparticles. AFB1 is efficiently identified through an aptamer competition process facilitated by magnetic nanoparticles , which triggers multiple isothermal amplification. This converts trace amounts of the toxin into a large quantity of DNA signal. Upon specific activation of the CRISPR-Cas14a complex, the MAPs are cleaved, resulting in significant changes in both color and colorimetric signal. The method demonstrates acceptable sensitivity, with a detection limit of 31.90 pg mL-1 and a wide detection range from 0.05 to 10 ng mL-1. Furthermore, the assay exhibits satisfactory specificity and high accuracy when it is applied to practical samples. Our approach offers a universal sensing platform with potential applications in food safety, environmental monitoring, and clinical diagnostics.

Self-Assembly Multivalent Fluorescence-Nanobody Coupled Multifunctional Nanomaterial with Colorimetric Fluorescence and Photothermal to Enhance Immunochromatographic Assay

The multimodal lateral flow immunoassay (LFIA) has provided accurate and reliable results for fast and immediate detection. Nonetheless, multimodal LFIA remains challenging to develop biosensors with high sensitivity and tolerance to matrix interference in agro-food. In this study, we developed a self-assembled multivalent fluorescence-nanobody (Nb26-EGFP-H6) with 16.5-fold and 30-fold higher affinity and sensitivity than a monovalent nanobody (Nb26). Based on the Nb26-EGFP-H6, we synthesized enhanced immune-probes Zn-CN@Nb26-EGFP-H6 by pyrolyzing and oxidizing an imidazolating zeolite framework-8 (ZIF-8) to obtain photothermal metal-carbon nanomaterials (Zn-CN) for immobilizing Nb26-EGFP-H6. The rough and porous structure of Zn-CN with a large surface area facilitates the enrichment and immobilization of antibodies. A trimodal lateral flow immunoassay (tLFIA) with colorimetric, fluorescent, and photothermal triple signal outputs was constructed for the detection of aflatoxin B1 (AFB1) in maize. Attractively, the Zn-CN-based tLFIA's multiplex guarantees accurate and sensitive detection of AFB1, with triple signal detection limits of 0.0012 ng/mL (colorimetric signals), 0.0094 ng/mL (fluorescent signals), and 0.252 ng/mL (photothermal signals). The sensitivity of the trimode immunosensor was 628-fold and 42-fold higher than that of the original Nb26-based ELISA (IC50) and the unimodal LFIA (LOD). This work provides an idea for constructing a sensitive, tolerant matrix and efficient and accurate analytical platform for rapidly detecting AFB1 in food.

Fluorescent/Colorimetric Dual-Mode Discriminating Gln and Val Enantiomers Based on Carbon Dots

Discrimination and quantification of amino acid (AA) enantiomers are particularly important for diagnosing and treating diseases. Recently, dual-mode probes have gained a lot of research interest because they can catch more detecting information compared with the single-mode probes. Thus, it is of great significance to develop a dual-mode sensor realizing AA enantiomer discrimination conveniently and efficiently. In this work, carbon dot L-TCDs were prepared by N-methyl-1,2-benzenediamine dihydrochloride (OTD) and l-tryptophan. With the assistance of H2O2, L-TCDs show an excellent discrimination performance for enantiomers of glutamine (Gln) and valine (Val) in both fluorescent and colorimetric modes. The fluorescence enantioselectivity of Gln (FD/FL) and Val (FL/FD) is 5.29 and 4.13, respectively, and the colorimetric enantioselectivity of Gln (ID/IL) and Val (IL/ID) is 13.26 and 3.42, individually. The chiral recognition mechanism of L-TCDs was systematically studied. L-TCDs can be etched by H2O2, and the participation of AA enantiomers results in different amounts of the released OTD, which provides fluorescent and colorimetric signals for identifying and quantifying the enantiomers of Gln and Val. This work provides a more convenient and flexible dual-mode sensing strategy for discriminating AA enantiomers, which is expected to be of great value in facile and high-throughput chiral recognition.

Nanoscale Materials Applying for the Detection of Mycotoxins in Foods

Trace amounts of mycotoxins in food matrices have caused a very serious problem of food safety and have attracted widespread attention. Developing accurate, sensitive, rapid mycotoxin detection and control strategies adapted to the complex matrices of food is crucial for in safeguarding public health. With the continuous development of nanotechnology and materials science, various nanoscale materials have been developed for the purification of complex food matrices or for providing response signals to achieve the accurate and rapid detection of various mycotoxins in food products. This article reviews and summarizes recent research (from 2018 to 2023) on new strategies and methods for the accurate or rapid detection of mold toxins in food samples using nanoscale materials. It places particular emphasis on outlining the characteristics of various nanoscale or nanostructural materials and their roles in the process of detecting mycotoxins. The aim of this paper is to promote the in-depth research and application of various nanoscale or structured materials and to provide guidance and reference for the development of strategies for the detection and control of mycotoxin contamination in complex matrices of food.

Magnetic relaxation switching immunoassay based on "limited-magnitude" particles for sensitive quantification of aflatoxin B1

Aflatoxin B₁ (AFB₁) is a highly toxic and carcinogenic chemical substance that endangers food safety and human health. Magnetic relaxation switching (MRS) immunosensors are utilized in a variety of applications in food analysis due to its resistance to matrix interferences, but they often suffer from magnetic separation-based multi-washing steps and low sensitivity. Herein, we propose novel MRS strategy for the sensitive detection of AFB₁ using "Limited-Magnitude" size particles: a single millimeter sized polystyrene spheres (PS_mm) and 150 nm superparamagnetic nanoparticles (MNP₁₅₀). Only a single PS_mm is used as the microreactor to enhance all of the magnetic signal on its surface in high concentration by an immune competitive response, successfully preventing signal dilution, which can be transferred by pipette, simplifying the process of separation and washing. The established single polystyrene sphere magnetic relaxation switch biosensor (SMRS) was able to quantify AFB₁ from 0.02 to 200 ng/mL with a detection limit of 14.3 pg/mL. SMRS biosensor has been successfully used for the detection of AFB₁ in wheat and maize samples, and the results in agreement with high performance liquid chromatography-tandem mass spectrometry (HPLC-MS). Benefiting from high sensitivity and convenient operation, the simple and enzyme-free method is promising in trace small molecules applications.

A self-assembled DNA double-crossover-based fluorescent aptasensor for highly sensitivity and selectivity in the simultaneous detection of aflatoxin M1 and aflatoxin B1

Realizing the simultaneous speedy detection of multiple mycotoxins in contaminated food and feed is of great practical importance in the domain of food manufacturing and security. Herein, a fluorescent aptamer sensor based on self-assembled DNA double-crossover was developed and used for effective simultaneous quantitative detection of aflatoxins M₁ and B₁ by fluorescence resonance energy transfer (FRET). Fluorescent dye-modified aflatoxin M₁ and B₁ aptamers are selected as recognition elements and signal probes, and DNA double crosses are consistently locked by the aflatoxin aptamers, which results in a "turn-off" of the fluorescent signal. In the presence of AFM₁ and AFB₁, the aptamer sequences are more inclined to form Apt-AFM₁ and Apt-AFB₁ complexes, and the fluorescent probes are released from the DNA double-crossing platform, leading to an enhanced fluorescent signal (Cy3: 568 nm; Cy5: 660 nm). Under the optimal conditions, the signal response of the constructed fluorescent aptamer sensor showed good linearity with the logarithm of AFM₁ and AFB₁ concentrations, with detection limits of 6.24 pg/mL and 9.0 pg/mL, and a wide linear range of 0.01-200 ng/mL and 0.01-150 ng/mL, respectively. In addition, the effect of potential interfering substances in real samples was analyzed, and the aptasensor presented a good interference immunity. Moreover, by modifying and designing aptamer probes, the sensor can be applied to high-throughput simultaneous screening of other analytes, providing a new approach for the development of fluorescent aptamer sensors.