Binding-induced output of catalyst DNA for efficient payload of DNAzyme on magnetic beads by catalyzed hairpin assembly

Abstract The assay of biomarker proteins is of critical importance for disease diagnosis. In this work, we have designed a cascaded strand displacement reaction system for detection of low abundant biomarker protein in serum samples. The proposed binding-induced strand displacement conversion system, first converts a protein recognition event into the output of the DNA (cDNA) catalyst, and then the output cDNA catalytically load the reporter DNAzyme onto magnetic beads based on catalyzed hairpin assembly (CHA) reaction. The high density of the hairpin DNA on a magnetic bead surface results in an over 20-fold improvement in the reaction efficiency of CHA, compared with conventional CHA. In addition, the magnetic beads are able to efficiently separate the serum sample matrix that could remarkably affect the DNAzyme-catalyzed chemiluminescent (CL) reaction. This type of magnetic biosensor allows for the detection of 0.5 pM target protein in serum samples, whereas when using homogenous CHA biosensors, the CL signal for 2 nM PDGF-BB is seriously inhibited by the serum matrix. Since the sensing system integrates the protein recognition, signaling, signal amplification and matrix separation functions, it is promising for the assay of proteins in biological samples.