Amplified electrochemical microRNA biosensor using a hemin-G-quadruplex complex as the sensing element

A novel signal amplified electrochemical microRNA (miRNA) biosensor was developed here using hemin-G-quadruplex as signal unit. A hairpin structure DNA probe (43 bases) was immobilized on the gold nanoparticles (AuNPs) modified gold electrode surface with the segment at its 39'-end complementary to miRNA-21 (22 bases) and the segment at its 59'-end complementary to capture DNA (21 bases). Upon hybridization with the target miRNA-21, the hairpin structure was unfolded, which was further hybridized with capture DNA loaded on AuNPs. The AuNP contained two kinds of DNA; one was complementary to the hairpin structure DNA probe, while the other was aptamer for hemin. The electrochemical signal of hemin self-assembled in the center of G-quadruplex structure of the aptamer was measured using chronoamperometry. The miRNA-21 target was analyzed with a detection limit of 3.96 pM. Using isolated total RNA from human gastric carcinoma BGC-823 cells, human breast adenocarcinoma MCF-7 cells, human hepatocarcinoma HepG2 cells and human colon cancer HT-29 cells, the assay detected specifically miRNA-21 and over-expression of oncogene miRNA-21 was demonstrated.