Label-free and sensitive strategy for microRNAs detection based on the formation of boronate ester bonds and the dual-amplification of gold nanoparticles.

MicroRNAs (miRNAs), regulating gene expression by translational repression or degradation of messenger RNAs, are believed to be important for cancer diagnosis and prognosis serving as reliable molecular biomarkers. Simple, sensitive, and cost-effective assays for miRNAs are therefore in urgent demand. The main difference in the structure of RNA versus DNA is the presence of a hydroxyl group at the 2' position of the ribose sugar in RNA, which makes the RNA molecule contain cis-diol at the end of the chain. Hydrophilic boronic acids are well known to form covalent bonds with cis-diols. In this work, we reported a label-free and sensitive method for the detection of miRNAs based on the formation of boronate ester covalent bonds and the dual-amplification of gold nanoparticles (AuNPs). Specifically, miRNAs were captured by the pre-immobilized DNA probes at the gold electrode, and derivatized with 4-mercaptophenylboronic acid (MBA)-capped AuNPs (MBA-AuNPs) through the formation of tight covalent bonds between the boronic acids of MBA-AuNPs and diols of miRNAs. Electrochemically active dopamine (DA)-capped AuNPs (DA-AuNPs) were then attached by the anchored MBA-AuNPs via the interaction of boronic acids and DA tags, which facilities the amplified voltammetric detection of miRNAs. Analytical merits (e.g., sensitivity, reproducibility, storage stability, dynamic range, and selectivity) were addressed. We believe that the results will be valuable for the development of biosensor for the detection of miRNAs in a biological matrix.