▎ 摘　　要

Electrochemical nanobiosensors have revolutionized the field of medical diagnosis owing to the unique prop-erties of the utilized nanomaterial that can boost the sensitivity of these devices. The higher sensitivity is especially critical when a small sample containing little quantity of the biomarker, miRNAs for instance, should be quantified for medical diagnosis. Here, a novel sensitive electrochemical nanobiosensor for miR-155, an early breast cancer detection biomarker, is introduced. A combination of reduced graphene oxide modified with nickel-iron (Fe-Ni@rGO), silver-conjugated graphene quantum dots (GQD-Ag), and gold nanostars (GNS) were used. This novel and advanced nanocomposite expanded the surface area and conductivity of the electrode surface to remarkably enhance the sensitivity of the nanobiosensor. A series of systematic characterization, both electrochemical and microscopic, were employed to assess the nanocomposite features using SEM, EDS, TEM, AFM, CV, and EIS. Thiolated single-stranded capture probes were immobilized on the GNS to selectively capture the target miR-155, and hematoxylin was the electrochemical label. The results showed high sensitivity with a low detection limit of 20.2 aM and a wide dynamic range of 0.05 fM-50.0 pM, which is superior to most of the previously reported miRNA nanobiosensors. The specificity was suitable towards the miR-155 compared to its one-and three-base mismatched oligos, a non-complementary and a mixture of the target with all the other non -complementary. Finally, the results of the real sample study in the serum environment revealed a very low interference in measurements which, along with the high sensitivity and selectivity, raises the possibility of using these nanobiosensors as promising candidates for breast cancer detection/screening applications in the future.