Calcium ion assisted fluorescence determination of microRNA-167 using carbon dots-labeled probe DNA and polydopamine-coated Fe3O4 nanoparticles.

A selective and sensitive fluorescence biosensor is described for determination of microRNA-167 using fluorescent resonant energy transfer (FRET) strategy. The FRET system comprises carbon dots (CDs, donor) labeled with probe DNA (pDNA) and polydopamine (PDA)-coated Fe3O4 nanoparticles (Fe3O4@PDA NPs, acceptor). The CDs-pDNA can be absorbed onto the surface of Fe3O4@PDA NPs because of the strong π interaction between pDNA and PDA. With the enhanced adsorption ability of Fe3O4@PDA NPs by Ca2+, the fluorescence intensity of CDs at 445 nm (excitation at 360 nm) is quenched. In presence of microRNA-167, the hybridized complex of CDs-pDNA-microRNA-167 will be released from the surface of Fe3O4@PDA NPs due to the weak π interaction of the complex and PDA. This results in the fluorescence recovery of CDs. By application of twice-magnetic separation, the biosensor shows a wide linear range of 0.5-100 nM to microRNA-167 with a 76 pM detection limit. The method was applied to the determination of microRNA-167 in samples of total microRNA extractions from A. thaliana seedlings, and the recoveries ranged from 96.4 to 98.3%.