Ultrasensitive electrochemical sensing platform for microRNA based on tungsten oxide-graphene composites coupling with catalyzed hairpin assembly target recycling and enzyme signal amplification

An ultrasensitive electrochemical biosensor for microRNA (miRNA) is developed based on tungsten oxide-graphene composites coupling with catalyzed hairpin assembly target recycling and enzyme signal amplification . WO 3 -Gr is prepared by a simple hydrothermal method and then coupled with gold nanoparticles to act as a sensing platform. The thiol-terminated capture probe H1 is immobilized on electrode through Au–S interaction. In the presence of target miRNA, H1 opens its hairpin structure by hybridization with target miRNA. This hybridization can be displaced from the structure by another stable biotinylated hairpin DNA (H2), and target miRNA is released back to the sample solution for next cycle. Thus, a large amount of H1-H2 duplex is produced after the cyclic process. At this point, a lot of signal indicators streptavidin-conjugated alkaline phosphatase (SA-ALP) are immobilized on the electrode by the specific binding of avidin-biotin. Then, thousands of ascorbic acid , which is the enzymatic product of ALP, induces the electrochemical-chemical-chemical redox cycling to produce a strongly electrochemical response in the presence of ferrocene methanol and tris (2-carboxyethyl) phosphine. Under the optimal experimental conditions, the established biosensor can detect target miRNA down to 0.05   fM (S/N=3) with a linear range from 0.1   fM to 100   pM, and discriminate target miRNA from mismatched miRNA with a high selectivity .