An ultrasensitive electrochemical biosensor for detection of microRNA-21 based on redox reaction of ascorbic acid/iodine and duplex-specific nuclease assisted target recycling.

A novel electrochemical biosensor was developed based on multiwall carbon nanotubes/graphene oxide nanoribbons (MWCNTs/GONRs) for sensitive analysis of microRNA-21. Signal-amplified strategy was achieved by duplex-specific nuclease assisted target recycling and alkaline phosphatase-induced redox reactions. At the fabrication process of the sensor, ssDNA capture probes were immobilized on the surface of the MWCNTs@GONRs/AuNPs modified electrode through the Au-S bond, and the streptavidin-conjugated alkaline phosphatase (SA-ALP) was attached to the end of the probe. In the absence of miRNA-21, SA-ALP catalysed the conversion of ascorbic acid 2-phosphate (AAP) into ascorbic acid (AA), triggered a redox reaction under iodine, producing a marked electrochemical response. When miRNA-21 was hybridized to the capture probe, the duplex would be cleaved by the duplex-specific nuclease (DSN), causing the electrochemical signals being significantly decreased as a result of SA-ALP detached from the electrode surface. Under the optimized conditions, our biosensor showed satisfactory sensitivity (detection limit, 0.034 fM), excellent selectivity and good accuracy (recoveries, 77.4-120.2%; RSD, 5.2-7.3%) after systematic evaluations. The proposed approach was applied to detect miRNA-21 from human serum samples, which indicated that it was reliable and could be widely used as an effective tool for rapid detection of the target in serums.