Small regulatory RNAs, such as microRNAs (miRNAs), are a family of 21-25 nucleotide non-coding RNAs that regulate gene expression at the post-transcriptional level. Interaction between the miRNA and its mRNA target often results in inhibition of protein synthesis. To date, more than 1,000 miRNAs have been identified in animals and plants according to the miRNA registry. Growing evidence suggests that miRNAs are important regulators of cell division and differentiation as well as human cancer genes. Recently, the discovery of regulatory effects on gene expression has led to numerous studies on the characterization of miRNA function in molecular processes and as possible tools in drug discovery.
Interest in small regulatory RNAs, such as miRNAs, has created demand for novel tools to study expression. Presently, Northern blot is the standard technique for small RNA expression analysis. The main advantage of Northern blotting is that it does not require an amplification step that may artificially generate false positives. However, a major drawback of Northern blots is poor sensitivity, especially when monitoring expression of short nucleotide sequences such as miRNAs. In addition, a large amount of total RNA is often required for Northern blots. Despite improvements in detection such as using locked nucleic acid probes, the procedures for Northern blot assay remain labor intensive and time-consuming.