Electrochemical detection of microRNA based on SA-PPy/AuNPs nanocomposite with the signal amplification through catalytic hairpin assembly reaction and the spontaneous catalytic reaction of Fe3+/Cu2+

MicroRNAs (miRNAs) are becoming biomarkers for the clinical diagnosis of many diseases. However, their intrinsic properties such as low enrichment and short sequence restrict their applications. Here, we designed an ultrasensitive dual signal amplification electrochemical biosensor based on sodium alginate-polypyrrole/Au nanoparticles (SA-PPy/AuNPs) nanocomposite for the detection of miRNAs. Firstly, a planar intercalated copper(II) complex was synthesized to be the signal molecule. Then, catalytic hairpin assembly (CHA) reaction and catalytic reaction between ferric ion and copper ion were combined as a dual signal amplification to improve the sensitivity of the biosensor. In the presence of target miRNAs, multiple double helix structure formed for the CHA reaction was triggered, which immobilized more copper(II) complex on the surface of the working electrode and a strong signal was obtained in the square wave voltammetry (SWV) test. Also, the signal can be re-amplified again in the presence of ferric ion in the electrolyte. Under the optimal conditions, based on these strategies, a sensitive electrochemical biosensor was constructed for the detection of miRNAs in the range of 1 fM to 1 nM and the limit of detection was as low as 0.34 fM. Furthermore, the developed biosensor with excellent selectivity and reproducibility tested on human serum samples shows broad application prospects in the early stage of tumor diagnosis.