The aflatoxin B 1 (AFB 1 ) early warning technique based on precursors is an effective strategy for the prevention of AFB 1 contamination risk. The determination of precursors is imperative to ensure the efficiency of the early warning technique. Herein, a controllable magnetic adsorbent Fe 3 O 4 /ZIFs was first introduced for the effective extraction and determination of averantin (AVN) and sterigmatocystin (ST) precursors in cereal by combining magnetic solid-phase extraction (MSPE) and high-performance liquid chromatography (HPLC). Benefiting from the abundant adsorption sites and multifunctional groups matching the analytes , Fe 3 O 4 /ZIFs effectively and simultaneously extracted AVN and ST with great differences in polarity and structure via multiple interactions. AVN was extracted by Fe 3 O 4 /ZIFs mainly through π–π and hydrophobic interactions, while ST was extracted predominantly by electrostatic interactions and surface complexation. The limits of detection were 0.08 μg kg −1 (AVN) and 0.36 μg kg −1 (ST). The developed method exhibited satisfactory spiked recoveries (79.1%–105.4%) in the determination of AVN and ST in rice. This work provides a novel analytical strategy for further studying AFB 1 early warning technique and the formation and transformation of aflatoxins .
Escherichia coli ( E. coli ) is often used as a host to produce a variety of recombinant proteins. However, the direct production of soluble and active protein containing disulfide bonds in E. coli remains a major challenge. In this study, we established a new, innovative soluble protein expression system based on the synergistic action of elastin-like polypeptide (ELP) and intein. Kinds of proteins including nanobodies, hIL-3 (Human Interleukin-3) analogue and AVN (the N terminal of A. ventricosus MiSp) with amino acid sequences that are normally express as insoluble form or difficult to express could be successfully expressed in soluble form in E. coli with this system. The soluble expression of the target proteins in the cytoplasm was achieved by the fusion of the solubility enhancer ELP, and the fusion of intein allowed the target proteins to be directly separated from the solubility enhancers in a mild enzyme-free environment. Through a one or two-step operation, nanobodies with high affinity activity, IL-3 analogue with bioactivity and soluble AVN were easily purified. This simple and efficient soluble expression system could thus be widely applied to facilitate the expression of difficult-to-express proteins.
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