Ratiometric fluorescent detection of miRNA-21 via pH-regulated adsorption of DNA on polymer dots and exonuclease III-assisted amplification

Abstract

This work proposed a simple and sensitive method for ratiometric fluorescent detection of nucleic acids via pH-dependent adsorption of dye-labeled DNA on polymer dots. The polymer dots (Pdots) could be conveniently prepared with nanoprecipitation in water. The mixture of dye-labeled DNA and Pdots at neutral pH showed the fluorescence of Pdots, while the adsorption of dye-labeled DNA on Pdots at acidic pH led to fluorescence resonance energy transfer from the Pdots to dye, and thus the fluorescence of dye. As a result, a signal switch could be designed for the detection of nucleic acids complementary to the DNA after combining with exonuclease III-assisted digestion of DNA. Using miRNA-21 as a target model and Cy3-labeled DNA as the probe, the hybridization of DNA with miRNA-21 provided active sites for EXO III, which released the hybridized miRNA-21 for cyclic digestion of DNA, and thus decreased the adsorption of Cy3-labeled DNA on Pdots and the fluorescence of Cy3. The ratio of fluorescent intensity of Pdots to Cy3 showed linear increase upon increasing miRNA-21 concentration ranging from 0.01 to 2.5 nM. The limit of detection at 3σ was 4.0 pM. The excellent performance and good extendability of the proposed strategy demonstrated its promising application in bioanalysis.