Simple, colorimetric detection of microRNA based on target amplification and DNAzyme.

Considering the crucial role played by microRNAs (miRNAs) in biological processes, we developed a novel strategy for simple and colorimetric detection of miRNA by combining target amplification with DNAzyme. Throughout the work, a 22-nt oligonucleotide sequence was used as a model analyte. A label-free hairpin probe (HP) was used as a simple platform for sensing the target. In the presence of the target, the HP was opened, and then the isothermal circular strand-displacement process occurred with the help of a primer, deoxynucleotide solution mixture (dNTPs), Klenow fragment exo(-) polymerase, and Nb.BbvCI nicking enzyme. As a result, the target was recycled and multicopies of target analogues were generated that function in the same manner as the target, accompanied by the accumulation of signal elements. In this work, as low as 0.5 fM nucleic acid target was detected by horseradish peroxidase-mimicking DNAzyme catalyzing the oxidation of ABTS(2-) to colored ABTS(•-).