Label-free impedimetric aptasensor based on epoxy-graphite electrode for the recognition of cytochrome c

In this work, we present a label -free impedimetric aptasensor for the recognition of cytochrome c (Cyt c) at a pM concentration level based on an epoxy-graphite composite electrode. The technique employed for the detection of the protein Cyt c is electrochemical impedance spectroscopy (EIS). Detection occurs when the protein interacts with the immobilized aptamer on the aptasensor. The aptamer immobilization technique is based on its wet physical adsorption onto the electrode surface, which assures a simple, ready-to-use preparation of the biosensing platform. The work first optimizes concentration of immobilized aptamer, followed by blocking agent to avoid non specific interactions, and finally performs the label-free detection of Cyt c. The amount of protein is quantified by the observed increase of the electron-transfer resistance, determined employing EIS and the [Fe(CN)6]3−,4− redox marker. Results demonstrate that the aptasensor has a good detection range for Cyt c between 50 pM and 50 nM, as well as a high sensitivity with a low detection limit of 63.2 pM, well below levels of this protein in serum. Cross response of the developed aptamer biosensor versus potential interfering proteins also present in human serum has been fully characterized.