Target-Triggered Formation of Artificial Enzymes on Filamentous Phage for Ultrasensitive Direct Detection of Circulating miRNA Biomarkers in Clinical Samples.

Integrating artificial enzymes onto nanostructures target- and site-specifically is still a challenge. Here we show that target miRNAs trigger the formation of DNAzyme site-specifically at the tip of filamentous phage for detecting miRNA biomarkers. Through an antibody-modified oligonucleotide, the tip of the phage with magnetic nanoparticles on the sidewall captures a target miRNA, inducing the formation of DNAzyme that extends from the phage tip through a hybridization chain reaction. After magnetic separation, the resultant complex catalyzes a colorimetric reaction with the signal correlated to target concentrations, leading to the quantification of miRNAs with a detection limit of 5.0 fM, about 10 folds lower than the phage-free approach. Our approach can differentiate miRNA mutants and quantify miRNA in human plasma, tumor cells, and tissues with high sensitivity, suggesting that the target-triggered integration of enzymes and phages holds promise for searching for new catalysts.