Target-induced site-specific cleavage of phosphorothioate-modified hairpin DNA for amplified and label-free sensitive electrochemical myeloperoxidase assay

Abstract

Abnormal myeloperoxidase (MPO) expression is associated with inflammation and neurodegenerative diseases. By using a new phosphorothioate (PT)-modified DNA hairpin probe, we fabricate a label-free and highly sensitive electrochemical sensor for monitoring MPO via integration of DNAzyme-assisted cleavage recycling with DNA polymerization reaction catalyzed by terminal deoxynucleotidyl transferase (TdT). The target MPO mediates the specific cleavage of PT-modified hairpin probes with assistance of hydrogen peroxide and chloride ion to initiate DNAzyme-based cyclic cleavage of substrate hairpin probes for the release of numerous trigger strands. Subsequent hybridizations of the trigger strands with the thiolated-hairpin probes on the electrode surface expose the 3′-OH termini of hairpin probes for triggering TdT–catalyzed in situ DNA polymerization formation of long ssDNAs containing multiple G-quadruplex repeats. Hemin is confined on the electrode surface via the formation of G-quadruplex/hemin complexes to produce highly enhanced current signals for the determination of MPO in a sensitive and label-free way. The proposed sensor exhibits a linear range of 0.1–100 ng mL−1 and achieves a low detection limit of 0.046 ng mL−1 for MPO. Such sensor also shows high selectivity against other interferents and shows the capability to detect MPO in diluted human serum samples.