Indirect and sensitive determination of microRNAs by magnetic field-assisted capillary sieving electrophoresis combined with catalytic hairpin assembly

To determine multiple microRNAs (miRNAs) from cells simultaneously is essential for understanding biological functions. Capillary electrophoresis (CE) can simultaneously determine multiple miRNAs by separation. Nevertheless, similar lengths and low concentrations in cells make miRNAs hard to separate and detect. In this study, CE with laser-induced fluorescence detection was combined with catalytic hairpin assembly (CHA) to determine three miRNAs, miR-21, miR-31, and miR-122. The amplification products of CHA, which were DNA duplexes, were designed to have different lengths for different miRNAs. This allowed for easy separation of the duplexes of different miRNAs by CE. The indirect determination of miRNAs was then achieved by separating and detecting these duplexes. A magnetic field was first applied on the capillary sieving electrophoresis to assist in the separation of the duplexes. Under the optimal conditions, the three duplexes could be completely separated within 2.5 min with the detection limits of miRNAs in the range 1.12–4.05 × 10⁻¹⁵ M. MiR-21 and miR-31 were successfully determined from Hela cells, while miR-122 was determined from chicken livers by this method. The recoveries ranged from 97.5% to 118%. The developed method was sensitive and reliable for miRNA determination.