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

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 reso-nance 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 hybridi-zation 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 con-centration ranging from 0.01 to 2.5 nM. The limit of detection at 3 sigma was 4.0 pM. The excellent performance and good extendability of the proposed strategy demonstrated its promising application in bioanalysis.