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Tannic acid mediated hollow biocatalytic zeolitic imidazolate frameworks as a “three-in-one” label for enhancing the sensitivity of fluorescence immunosensor
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•Glucose oxidase @hollow ZIF-8@MPN (GHZM) was designed based on enzyme immobilization.•GHZM exhibited cascade catalysis with the “snowball effect”.•The abundant catechol groups of GHZM improved the coupling efficiency of antibodies.•The novel immunosensor was developed based on GHZM for the detection E. coli O157:H7.•LOD of the proposed immunosensor was 12.51-fold lower than that of traditional ELISA.
Benefiting from the special structure feature, zeolitic imidazolate frameworks (ZIFs) have emerged as a carrier for enzyme immobilization. However, the sensitivity of the immunosensor with ZIFs needs further enhancement. Herein, a “three-in-one” label mediated by tannic acid (TA) was designed, demonstrating high enzyme activity, cascade signal amplification capability, and high coupling effectivity with antibodies. The acid property of TA was used as an etchant to etch ZIFs in situ for the generation of hollow ZIFs, which retained the conformational freedom of glucose oxidase for preserving their excellent catalytic activity. The TA on the surface of ZIFs coordinated Fe3+ ions through its phenol groups, forming metal polyphenol network films, which possessed peroxidase-like activity for cascade signal amplification. Meanwhile, the large amount of catechol groups of TA improved the coupling efficiency of antibodies. Based on the proposed “three-in-one” label, a novel fluorescence immunosensor was developed for the sensitive detection of Escherichia coli O157:H7. The limit of detection of the fluorescence immunosensor was 1.35 × 103 CFU mL−1 and 12.51-fold lower than that of traditional immunoassay. This proposed strategy provides a convenient method for preparing hollow ZIFs, facilitating the applications of ZIFs in the fields of biosensors.