Dual-Modal Biosensor for the Determination of Femtomolar miRNA-126 Based on Electrochemical Impedance Spectroscopy and Electrochemiluminescence with Hybridization Chain Reaction Amplification

In this study, a novel dual-modal electrochemical impedance spectroscopy (EIS) and electrochemiluminescence (ECL) biosensor for sensitive detection of femtomolar miRNA-126 was developed based on hybridization chain reaction (HCR). The capture unit was Fe 3 O 4 @SiO 2 @AuNPs-cDNA, being Fe 3 O 4 @SiO 2 @AuNPs nanoparticles coated by hairpin cDNA which could capture miRNA-126 specifically. The signal unit was HCR-Ru(phen) 3 2+ , which was a long double-stranded DNA obtained through HCR with a great number of ECL signal labels Ru(phen) 3 2+ embedded. In presence of target miRNA-126, stem-loop structure of cDNA in the capture unit was opened and a partial dsDNA was formed, the residue bases of which hybridized with the signal unit to form a capture unit/miRNA-126/signal unit complex on the electrode surface. In this case, dual-modal biosensor was prepared easily by the help of magnet, and EIS and ECL detection was both acquired. In addition, a miRNA-126 molecule corresponded to a long double-stranded DNA and a large amount of Ru(phen) 3 2+ ions embedded, so the electrochemical impedance and the ECL intensity were greatly increased, with a limit of detection (LOD) of 2 fM. And, EIS and ECL results could be checked mutually, improving the detection accuracy and reliability. It offers a simple, fast, sensitive, selective and accurate approach for versatile analysis of microRNAs.