Fe-N-C single-atom nanozyme for ultrasensitive, on-site and multiplex detection of mycotoxins using lateral flow immunoassay.

Sensitive, on-site and multiple detection of mycotoxins is a vital early-warning tool to minimize food losses and protect human health and the environment. Although paper-based lateral flow immunoassay (LFIA) has been extensively applied in mycotoxins monitoring, low-cost, portable, ultrasensitive and quantitative detection is still a formidable challenge. Herein, a series of Fe-N-C single-atom nanozymes (SAzymes) were synthesized and systematic characterized. The optimal Fe-N-C SAzyme with highly efficient catalytic performance was successfully used as both label and catalyst in lateral flow immunoassays for mycotoxin detection. By taking advantage of the catalytic amplified system, the qualitative and quantitative detection can be easily and flexibly done via observing the test lines by naked eyes or a smartphone, with the limit of detections (LODs) of 2.8 and 13.9 pg mL-1 for AFB1 and FB1, which were respectively over 700- and 71,000-fold lower than the maximum limit set by the European Union. Besides, underlying catalytic mechanisms and the active sites of the Fe-N-C SAzyme are also investigated by DFT simulation. This work not only provides a promising detection strategy for the application of advanced SAzymes but also offers experimental and theoretical guidelines to understand the active centers of Fe-N-C SAzymes and the catalytic process.

A versatile nanozyme integrated colorimetric and photothermal lateral flow immunoassay for highly sensitive and reliable Aspergillus flavus detection.

Visual lateral flow immunoassays (LFA) have been recognized as the attractive point-of-care testing (POCT) for bioanalysis; however, they have been constrained by insufficient sensitivity and limited reliability. Herein, combining the catalytic sites of Cu nanoparticles with an inherent photothermal polydopamine (PDA) scaffold via a one-step process, a compact Cu-anchored PDA (PCu) was engineered as the efficient signal element for the multimodal LFA (mLFA). The robust PCu with peroxidase-mimics and photothermal properties, could simultaneously provide triple signal readouts for colorimetric, amplified colorimetric and photothermal detection toward Aspergillus flavus (A. flavus). Attractively, the multiple guaranteed detection of PCu-based mLFA enabled the accurate and sensitive detection of A. flavus mycelium biomass, down to 0.45 and 0.22 ng mL-1, which was 19- and 40-fold improvements compared to traditional colorimetry. Besides, mLFA was successfully applied to actual samples with satisfactory recoveries from 89.9 to 109%, indicating the highly reliable analytical performance. This work paved a prospective way for the construction of efficient peroxidase-mimics and superior photothermal multifunctional nanomaterials, providing a potential versatile visual POCT platform for analytical events.

Nanozyme-strip based on MnO2 nanosheets as a catalytic label for multi-scale detection of aflatoxin B1 with an ultrabroad working range.

Lateral flow immunoassay (LFIA) is the most effective real-time detection method for aflatoxin B1 (AFB1). Here, we constructed a nanozyme-strip based on MnO2 nanosheets (MnO2 NSs) as a catalytic label for detection of AFB1. By taking advantage of the MnO2-TMB catalytic amplified system, the new test achieves rapid detection with high sensitivity and ultrawide range. The limit of detection of the assay was 15 pg mL-1, which was over 100-fold lower than the maximum limit set by the European Union (EU) of AFB1 in foods. In addition, the strip test could offer 7 dynamic detection ranges, spanning 4 orders of magnitude, which could cater to the varieties of limits on AFB1 residues in foods and feeds set by different countries. The estimated recoveries were in the range of 85.67%-106.38% with coefficients of variations (CVs) less than 9.68%. Overall, the developed approach is a rapid, reliable, sensitive and widely available tool for on-site detection of AFB1.

A direct competitive nanozyme-linked immunosorbent assay based on MnO2 nanosheets as a catalytic label for the determination of fumonisin B1.

A direct competitive nanozyme-linked immunosorbent assay (dcNLISA) based on MnO2 nanosheets (MnO2 NSs) as a nanozyme label was developed for the highly sensitive determination of fumonisin B1 (FB1). MnO2 NS-labeled fumonisin B1-bovine serum albumin was easily synthesized as a competing antigen for the dcNLISA. And color changes derived from the MnO2-3,3',5,5'-tetramethylbenzidine (TMB) system were exploited as the output signals of the dcNLISA. Several experimental parameters including the concentrations of the coating antibody, pH values, ionic strength and methanol concentration were optimized. Under the optimal conditions, the proposed method demonstrated a linear range (1.17-20.74 ng mL-1) with a reliable correlation coefficient (R2 = 0.9989), a satisfactory limit of detection (0.63 ng mL-1) and high selectivity for the detection of FB1. The recoveries of FB1 in spiked corn and wheat samples were in the range of 85.31-108.16% with coefficients of variation (CVs) ranging from 6.14% to 9.23%. Meanwhile, the testing results showed good consistency (R2 = 0.9892) between the developed dcNLISA and the reference method, liquid chromatography/mass spectrometry/mass spectrometry (LC-MS/MS) method. The proposed method was proven to be simple, sensitive, cost-effective and reliable for the screening of FB1 in cereals.

Adsorptive removal of aflatoxin B1 from vegetable oils via novel adsorbents derived from a metal-organic framework.

Vegetable oils are essential daily diet, but they are simply contaminated with aflatoxin B1 (AFB1), a serious toxic compound to human health. Adsorption method due to the easy operation, high efficiency and low costing is set to become a main detoxification technique for AFB1. Unfortunately, previous reported adsorbents were rarely used for detoxification in food industry since they cannot meet the criteria of large-scale production of edible oils. Metal-organic frameworks (MOFs) with unique textural properties could be favorable precursors for synthesis of advanced materials. In this research, three kinds of Cu-BTC MOF-derived porous materials were prepared by different carbonization temperature and characterized by XRD, SEM, FT-IR, and nitrogen adsorption-desorption techniques. Isotherm and kinetic studies on the adsorption behaviour of AFB1 onto the three porous carbonaceous materials have been systematically conducted. The results revealed that the porous carbonaceous materials could act as the excellent adsorbents that were of enough adsorption sites for AFB1, mainly due to the hierarchical porous structure and large surface areas for the enhancement of adsorption capacity. Notably, the porous carbonaceous materials could not only remove more than 90% of AFB1 from real vegetable oils within 30 min, but also remain the treated oils at low cytotoxicity. Meanwhile, the detoxification process could little affect the quality of oils. Thus, the Cu-BTC MOF-derived porous carbonaceous materials with high efficiency, safe, practical and economic characteristics could be novel potential adsorbents used in the application of AFB1 removal from contaminated vegetable oils.