One-Step Modification of Electrode Surface for Ultrasensitive and Highly Selective Detection of Nucleic Acids with Practical Applications.

Electrochemistry-based nucleic acid sensors have long been plagued by the limited accessibility of target molecules to the capture probes immobilized on heterogeneous surfaces, which largely hinders their practical application. In this work, we find that dual-thiolated hairpin DNA immobilized on an electrode surface as the capture probe cannot only efficiently bind with target molecule as well as the signal probe but also process impressive protein-repelling ability, which allows us to directly detect as few as attomolar targets (∼300 copies in 100 μL sample) with single-base discrimination ability. Meanwhile, the preparation of functional electrode surface becomes simple (one step), fast (30 min), and homogeneous (just one probe modified surface without small molecules coassembled). These advantages are attributed to the unique probe design, where the stem of the capture probe can act as rigid scaffold to keep it upright, and the loop of the capture probe may provide an enclosed platform for target and signal probe binding. More importantly, through tuning the distance between enzyme and the electrode surface (from 8.5 to 13.6 nm), we find that the performance of the sensor can be favorably controlled. Furthermore, taking advantage of this new binding model, different complex samples including polymerase chain reaction (PCR) product, mRNA, and micro RNA can be conveniently analyzed, which may hold great potential for real application.