Consecutively, the probe is incubated in a SAM to make the surface of the probe that is unoccupied unreactive to target or further aptamer binding. The optimized SAM thickness is thick enough for the surface to be passivated against target binding and thin enough to transfer electrons from the redox reporter to the electrode. SAM thickness can be measured as length. It has been reported that cocaine E-AB sensors generate more signal when the SAM is thinner and therefore more conductive. However, reducing the SAM from 6 carbons to 2 carbons decreases signal, and peak current is generated using a 6-carbon SAM.