Os(VI)bipy-based electrochemical assay for detection of specific microRNAs as potential cancer biomarkers

• Determination of specific microRNA sequences associated with cancer development.
• Modification of ribose at the 3’-end of microRNA by electroactive Os(VI)bipy.
• Sensitive electrocatalytic signals obtained at mercury-based electrodes.
• Capture of target microRNA from a mixture of other noncomplementary microRNAs.

Recently, altered expression levels of microRNAs (miRNAs) – short noncoding RNA molecules which bind to mRNAs and thus regulate gene expression – were observed in many cancer cells. miRNA expression profiling is therefore of great interest, but current standard methods are still considered relatively laborious and expensive. Electrochemistry has a potential to become quick and inexpensive alternative. Here, we describe modification of miRNA with an electroactive complex composed of six-valent osmium and 2,2′-bipyridine, Os(VI)bipy, specifically binding to the 3′-end of the ribose, which is detectable at hanging mercury drop electrode at femtomole level due to an electrocatalytic nature of a resulting signal. By combining miRNA labeling step with magnetic beads-based hybridization assay, detection of specific miRNA sequence from a mixture of other noncomplementary miRNAs was possible.