In this paper we report a combined theoretical and experimental approach for analyzing Self Assembled Monolayers (SAMs) modified electrodes. Three different SAMs were compared, consisting in a mixed SAMs of amides and carboxylic groups (Deactivated SAMs), a SAM functionalized with an antibody (Anti-IgG SAMs), and SAM functionalized with two different proteins, Anti-IgG and Bovine Serum Albumin (BSA). Each of these samples is used to describe a different component of a SAMs modified gold electrode implemented in an Electrolyte Gated – Organic Field Effect Transistor Biosensor, where the presence of a diffuse hydrogen bonding between SAMs chains plays a key role for reaching the performance of this device, able to reach the single molecule limit of detection.