RNA samples are separated through gel electrophoresis and transferred onto a membrane. Expression of a specific miRNA is detected with a biotin-labeled probe. This regular Northern blot assay is suitable for most moderate to high expressors of miRNA. The Highly Sensitive Northern Blot (NB-1001 and HP-XXXX) is needed to analyze low expressors of miRNA. The biotin-labeled probes contain two moieties: complementary sequence of the miRNA and a tag sequence. The tag sequence is then detected by an amplifier enriched with biotin molecules.