In this work, we explore the use of electrochemical methods (i.e., impedance) along with the arsenic-specific aptamer (ArsSApt) to fabricate and study the interfacial properties of an arsenic (As(III)) sensor. The ArsSApt layer was self-assembled on a gold substrate, and upon binding of As(III), a detectable change in the impedimetric signal was recorded because of conformational changes at the interfacial layer. These interfacial changes are linearly correlated with the concentration of arsenic present in the system. This target-induced signal was utilized for the selective detection of As(III) with a linear dynamic range of 0.05-10 ppm and minimum detectable concentrations of ca. 0.8 μM. The proposed system proved to be successful mainly because of the combination of a highly sensitive electrochemical platform and the recognized specificity of the ArsSApt toward its target molecule. Also, the interaction between the ArsSApt and the target molecule (i.e., arsenic) was explored in depth. The obtained results in this work are aimed at proving the development of a simple and environmentally benign sensor for the detection of As(III) as well as in elucidating the possible interactions between the ArsSApt and arsenic molecules.