Enhanced red emission of upconversion nanoparticles via Li and Tm codoping and active core-shell construction for sensitive detection of miRNAs.

The overexpression of microRNA-222 (miRNA-222) is closely related to many human diseases, so the development of biosensors to detect this biomarker will contribute to the diagnosis of related diseases. Here, a simple, sensitive and specific fluorescence assay for the detection of miRNA-222 was developed using red-emitting upconversion nanoparticle (UCNP) as the donor and a DNA hairpin with black hole quencher-2 (BHQ-2) as the acceptor. Li and Tm-doped UCNP with a strong emission peak at 654 nm was obtained by changing the doped ion ratio and constructing core-shell structures. Under optimal conditions, the linear range for detecting miRNA-222 is 0.5-2.5 nM and the limit of detection is as low as 0.077 nM without any complicated amplification strategy. Finally, the proposed assay was applied for the detection of miRNA-222 in serum samples. The results obtained were similar to those of the standard method, and the spiked recoveries were in the range of 97.62%-102.14 %, suggesting that the proposed method has practical value in a complex biological sample matrix.