Novel electrochemical nanoswitch biosensor based on self-assembled pH-sensitive continuous circular DNA

Nucleic acid nanoswitches have a status that cannot be ignored in the field of biosensing due to the excellent biocompatibility and flexibility of design. In our current research, we have constructed a new electrochemical platform based on self-assembled pH-sensitive continuous circular DNA nanoswitch for miRNA-21 detection. We elaborately designed an inside ring probe (IRP) which could form a circle when complemented with an outside ring probe (ORP). Under the weakly acidic condition, IRPs and ORPs are self-assembled into continuous annular DNA, meanwhile, the nanoswitch is activated. However, if it is not a weakly acidic environment with a pH equal to 6, these circles are separated and the nanoswitch cannot be triggered. Therefore, the biosensor doesn't work. Only when the pH is 6, can the nanoswitch be activated. Consequently, a large number of RuHex will accumulate on the continuous annular DNA, which leads to highly sensitive detection of miRNA-21, with concentration ranged from 10 ^–15 to 10 ^-8 M and limit of detection down to 0.84 fM. More importantly, this nanoswitch-based biosensor can directly detect the target microRNA in human serum without pretreatment. Therefore, the proposed novel electrochemical DNA nanoswitch will have broad application prospects in biomarker detection and clinical diagnosis.