Detection of a thousand copies of miRNA without enrichment or modification

We report direct quantitative analysis of multiple miRNAs with a detection limit of 1000 copies without miRNA enrichment or modification. A 300-fold improvement over the previously published detection limit was achieved by combining capillary electrophoresis with confocal time-resolved fluorescence detection through an embedded capillary interface. The method was used to determine levels of three miRNA biomarkers of breast cancer (miRNA 21, 125b, 145) in a human breast cancer cell line (MCF-7). A 30 pL volume of the cell lysate with approximately a material content of a single cell was sampled for the analysis. MiRNA 21, which is up-regulated in breast cancer, was detected at a level of approximately 12 thousand copies per cells. MiRNAs 125b and 145, which are down-regulated in breast cancer, were below the 1000-copy detection limit. This sensitive method may facilitate the analysis of miRNA in fine-needle-biopsy samples and even in single cells without enrichment or modification of miRNA. Advantageously, the instrumental setup developed here can be reproduced by others as it requires no sophisticated custom-made parts.