Triple-helix molecular switch photoelectrochemical biosensor for ultrasensitive microRNA detection based on position-controllable CdS//CdTe signal enhancing and switching

Here, a triple-helix molecular switch photoelectrochemical (PEC) biosensor based on position-controllable CdS//CdTe signal enhancing and switching is developed for ultrasensitive and selective detection of microRNA. A hairpin DNA capture probe modified with CdS nanocrystals (NCs) labeled with Rhodamine B (RhB-DNA1-CdS) at each end is introduced to this PEC system through the host-guest interaction between β-CD and RhB. Afterward, a single-strand DNA modified with two CdTe quantum dots (CdTe-DNA2) at each end hybridizes with RhB-DNA1-CdS to form a triple-helix switch conformation, which achieves a cathodic signal enhancing. Subsequently, the relative position between CdS and CdTe is adjusted with the help of intermediate DNAs from 3D DNA walking transformational machine as a super approach for target amplification, leading to the high-efficiency photocurrent-direction switch from cathodic to anodic photocurrents. Based on the significant signal amplification of 3D DNA walking machine, sensitive triple-helix molecular switch and position-controllable signal enhancing and switching strategy, the PEC biosensor exhibits outstanding analytical performance for microRNA-141 detection with a wide linear range from 5 aM to 100 fM and a low detection limit of 1.3 aM. Such a signal enhancing and switching strategy not only avoids the false positive or negative results but also increases the detection sensitivity, which may have promising applications in biomedical and clinical diagnosis.