Non-tandem enzymatic modules-encapsulated metal-organic framework cubes with mutual-validated operation for dual-modal competitive immunoassay of antibiotics

Abstract

Adaptive fusion of nanoscale metal-organic frameworks (nMOFs) and enzyme-based immunoassay is an insightful combination for inspired establishment of antibiotic assay, typically in a competitive format, in which inherent enzymes in nMOFs can serve as generators for amplifying catalytic signals. Albeit important, there is currently a lack of explorations of enzymatic signal outputs with multiple modalities in typical competitive immunoassays, which may face the false signals and lack cross-validation. Herein, non-tandem bi-enzymatic modules such as urease and horseradish peroxidase were co-encapsulated into nMOF cubes and functionalized with antibodies into entities for dual-modal competitive immunoassay of oxytetracycline (OTC), which can convert the bi-enzymatic catalytic signals into fluorogenic and chromogenic reflection and can gain the mutual validation merits. The fluorescence mode can achieve an OTC detection range from 5 ng/mL to 2000 ng/mL, with a detection limit (LOD) of 2.14 ng/mL; complementally, the absorbance mode can achieve a relatively narrow detection range from 1 ng/mL to 200 ng/mL, but a lower LOD of 0.32 ng/mL. The dual-mode sensing parameters of the competitive immunoassay in responding to OTC analysis differed in terms of the linear range and detection limit, which can be integrated to offer reciprocal authentication and expand the detection diversity. Overall, our proposed method may provide a new idea in dual-modal competitive immunoassay of antibiotics, signifying its promising expansion for rational substitution of enzymatic modules and its potential performance in wide applications.