Double-loop hairpin probe and doxorubicin-loaded gold nanoparticles for the ultrasensitive electrochemical sensing of microRNA

An electrochemical microRNA (miRNA) analysis platform by combining double-loop hairpin probe (DHP) and doxorubicin-loaded gold nanoparticles (AuNPs@Dox) for ultrasensitive miRNA detection is proposed. Firstly, we here report a DHP that is simultaneously engineered to incorporate a miRNA recognition sequence, an output segment and output's complementary fragment. The important aspect of this hairpin probe is that it would not be degraded by duplex specific nuclease (DSN) and circumvents elaborately chemical modification disadvantages encountered by classic molecular beacon. For the DHP-based DSN signal amplification system, DHP hybridizes with target miRNA to form DNA-miRNA heteroduplexes, and the DSN can hydrolyze the DNA in the heteroduplexes structure selectively, while released target miRNA strand can initiate another cycle resulting in a significant signal amplification and the accumulated output segments could be responsible for strand displacement on the electrode directly. Furthermore, a great deal of doxorubicin (Dox) are loaded on the gold nanoparticles (AuNPs) to fabricate the AuNPs@Dox biocomposites that could magnify the electrochemical signal and enable the ultrasensitive analysis of miRNA. As a result, the miRNA was capable of being detected in a limit of 0.17 pM and other kinds of miRNA were discriminated facilely by this method. The described DHP as a toolbox and the nano-biocomposites as a novel signal material would not only promote the design of electrochemical biosensors but also open a good way to promote the establishment of test method in malignant tumors.