Abstract
According to the miRBase (v 22.1), released on October 2018, there are more than 1900 identified human microRNA mature sequences. MicroRNAs (aka miRNAs or miRs) are a class of short non-coding RNA sequences, which have been detected within the cells or in body fluids. They act as gene expression regulators and intervene in numerous physiologic and development processes. They posttranscriptionally/ translationally regulate expression of some proteins by forming miRNA-induced silencing complex (mRISC) by binding to 3’-UTR regions of the target messenger RNA to inhibit the protein synthesis. It has been noted that up- and down-regulation of miRs are associated with the pathogenesis of several types of human cancers since their target proteins are tumor-suppressive or oncogenic ones. This chapter will present a general summary of miRNA biogenesis, their link to cancer, and biological methods for their detection. Thanks to their ease of use and high sensitivity, electrochemical and optical techniques were used to detect miRNAs with or without the assistance of amplification methods. We will review the state-of-the-art electrochemical and optical methods for their detection, emphasizing the progress achieved in the last five years (2015-2020). Finally, we will present the main advantages, challenges, and future prospects for future research on detecting miRNAs for clinical diagnosis or prognosis in cancers.