▎ 摘　　要

We describe here an aptasensor for the ultrasensitive detection of Staphylococcus aureus by electrochemical impedance spectroscopy (EIS). Single-stranded DNA was linked to a nanocomposite prepared from reduced graphene oxide (rGO) and gold nanoparticles (AuNP). Thiolated ssDNA was covalently linked to the AuNPs linked to rGO, and probe DNA was immobilized on the surface of an AuNP-modified glassy carbon electrode to capture and concentrate Staph. aureus. The probe DNA of the aptasensor selectively captures the target bacteria in its three-dimensional space, and these results in a dramatic increase in impedance. Scanning electron microscopy, cyclic voltammetry and EIS were used to monitor the single steps of the electrode assembly process. The effect was utilized to quantify the bacteria in the concentration range from 10 to 10(6) cfu mL(-1) and with a detection limit of 10 cfu mL(-1) (S/N = 3). The relative standard deviation of Staphylococcus aureus detection was equal to 4.3 % (10(5) cfu mL(-1), n = 7). In addition to its sensitivity, the biosensor exhibits high selectivity over other pathogens.