In the present research, we have developed a novel label free aptasensor based on screen printed carbon electrode (SPCE) modified with three-dimensional magnetic reduced graphene oxide(3D-MRGO)/ polyaniline(PA)/gold nanoparticle(AuNP) nanocomposite for impedimetric determination of cocaine. To achieve this goal, a specific thiolated cocaine aptamer was immobilized onto the surface of synthesized nanocomposite. The signaling mechanism of the proposed aptasensor was based on increase in the [Fe(CN)6] 3-/4- charge transfer resistance (RCT) as an electrochemical probe in the presence of target an- alyte. In order to collect of 3D-MRGO/PA/AuNP/aptamer on the surface of working electrode easily, a new electrochemical cell was fabricated. The advantages of the new electrochemical cell configuration can be counted as reusing SPCE for several times, obtaining repeatable responses, reducing required volume of electrolyte and probe solution and making proposed method more user-friendly. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR) were used for the characterization of synthesized nanocomposite and modified electrode surface. Under optimized condition, cocaine was determined in a linear con- centration range from 0.09 to 85 nM with a detection limit of 0.029 nM by EIS.
