Performance of the cocaine E-AB sensor is strongly affected by the thickness of the SAM layer used to passivate the electrode, with thicker SAMs leading to greater gain but lower affinity and poorer signaling current. Shown are binding curves for sensors fabricated using six-, three- and two-carbon alkane thiol SAMs (all at a probe density of 1.6 × 1012 molecules/cm2). The solid lines represent a hyperbolic binding curve fit to the data with dissociation constants (Kd) of 95 ± 15, 86 ± 5, and 18 ± 5 μM for the six-, three- and two-carbon SAMs respectively.