A photocathode based on BiOI-Bi/CNTs for microRNA detection coupling with target recycling strand displacement amplification

A novel cathode photoelectrochemical (CPEC) biosensor by integrating BiOI-Bi/CNTs photocathode with target recycling strand displacement amplification (TRSDA) was proposed for selective and sensitive detection of microRNA (miRNA). Herein, an innovative strategy of two-site hybridization in a hairpin loop to specifically recognize the target miRNA was designed. Strand displacement amplification (SDA) reaction was triggered by target let-7a miRNA with the assistance of polymerase and nicking enzyme. TRSDA was then realized by using short complementary sequence hidden in the 3 '-terminal region of the hairpin probe stem, which produced large amount of product DNA (pDNA). The as-generated pDNA fragments were collected by capture probe (CP) on BiOI-Bi/CNTs platform. Since K3[Fe(CN)6] could take in photoelectrons from BiOI-Bi/CNTs effectively, the photocurrent was largely decreased because DNA layer on CPEC platform inhibited photoelectron transfer towards electron acceptor. Under optimized conditions, the photocurrent response of biosensor was linear with let7a concentration from 0.2 to 2000 pM, and the detection limit (S/N = 3) was as low as 0.1 pM. The proposed approach opened up new opportunity for developing robust biochemical detection systems.