Construction of an ultrasensitive electrochemical sensing platform for microRNA-21 based on interface impedance spectroscopy.

A hybridization chain reaction (HCR) amplification-based electrochemical impedimetric biosensor is fabricated for the quick, sensitive, and specific detection of miRNA-21 (miR-21) via monitoring of electrode interfacial property changes in real-time. Two sequences of H1 and H2 are adopted to trigger HCR amplification. A large amount of linear DNA concatemer are formed which could change the interfacial properties of the electrode. Interfacial charge transfer resistance difference (Rct) is probed via electrochemical impedance spectroscopy (EIS) and Randles equivalent circuit. After amplifying via HCR, oligonucleotides with negatively charged repelling [Fe(CN)6]3-/4- ions can form a spatial blockage. HCR amplification strategy markedly enhanced the electrochemical signal with a limit of detection (LOD) down to 4.63 fM (S/N = 3). This strategy exhibited excellent selectivity for three different miRNAs: miR-199a, miR-141, and miR-155. Moreover, results show that the proposed method can be applied to miR-21 detection in the total RNA extracted from five cells. This work presents an enzyme-free and label-free EIS nucleic acid sensor for sensitively and selectively detecting miR-21, offering a promising approach in early diseases diagnosis.