New quasi-Co/Cu-MOF nanozyme coupled with entropy-driven DNA amplification cascades for highly sensitive electrochemical aptamer growth differentiation factor 15 assay.

Background: The monitoring of concentration variation of the newly developed growth differentiation factor 15 (GDF15) biomarker in human serum is of great significance for diagnosing cardiovascular diseases. Current methods for the detection of the GDF15 protein mainly are based on antibody-assisted immunoassays, which encounter the limitations in terms of sensitivity, complexity and costs. The development of simple and sensitive biosensors for GDF15 can therefore facilitate the diagnosis of cardiovascular diseases.

Results: A new bimetallic quasi-Cu/Co-MOF nanozyme with high catalytic performance for electrochemical reduction of HO is synthesized via simple one-step precipitation and low-temperature calcination method. Such nanozymes are further employed as amplification tags and coupled with cyclic entropy-driven DNA signal enhancement strategies to construct ultrasensitive aptamer-based biosensor for detecting GDF15 in human serums. GDF15 molecules associate with two aptamers and release the ssDNA trigger sequences via target-binding induced displacement reaction. These ssDNAs subsequently initiate cyclic DNA-fueled strand displacement and catalytic hairpin assembly (CHA) reaction cascades for confining many quasi-Cu/Co-MOF nanozymes on sensor electrode, which yield drastically amplified HO reduction current for detecting GDF15 down to 0.12 pg mL with a dynamic range of 0.5 pg mL to 20 ng mL. The electrochemical aptasensor also presents good reproducibility and selectivity and exhibits the capability to detect GDF15 in diluent serums.

Significance: Our aptamer-based GDF15 protein electrochemical assay clearly outperforms current existing antibody-based methods and the quasi-Cu/Co-MOF nanozyme/entropy-driven cascaded signal amplification means can be used as a universal strategy for sensitive monitoring of different biomolecular markers for diverse applications.