For some applications, the discovery of signal changes within similar peptide sequences may be a more efficient way of characterization rather than complete ex-Novo sequencing . The addition of AAs to a peptide increases the complexity of the charge distribution as the electro-affinity of residues and terminals are modified by each bond making difficult to predict the surface potential or the total capacitance. The problem of modeling the final behavior is indeed complex as it involves other interactions including hydrogen, van-der-Waals and electrostatic forces, which are all highly correlated. Here, we propose a phenomenological way to distinguish variations in short polypeptides (addition, substitution or mutation) which is based on the detection of charges present on the reactive sites of the polypeptides using the site-binding method as discussed in the methodology section. We propose here to study the DYK sequence because it can be recognized by flag monoclonal antibodies . We consider the peptide immobilized by the carboxylicterminal of the first AA, and thus only the amine-terminal of the last AA and the sidechains of the AAs contribute to different proton affinities. The values of pK in this system could also be resolved phenomenologically. To discover new signatures, we use the same approach until now of considering the nominal pK values of the AAs in liquid. However, the phenomenological constants can be expected to provide more resolution than the nominal ones, as the complex interactions All in all, the behaviour of Ψo, δΨo 2 /δpH 2 , and CT from these peptides can be explained based on the properties of the proton affinity of their radicals and their length (as we have avoided AA with sulphur), and although they have a richer behaviour than single AAs that may require more complex analysis, still, their fingerprints can be retrieved from their analysis. As the length of the peptides is below the screening length, we expect to be able to measure these peptides' characteristics. Nevertheless, optimizing the ionic strength in these analyses may be crucial because while decreasing it may have a positive effect to decrease the Debye length to probe longer peptides, it can also have a negative impact on the manifestation of the fingerprints by increasing the linearity of the Ψo observed. Measuring polypeptides instead of single AAs can help in multiplexing several FET sensors to detect possible variations in a polypeptide or protein-peptide interactions even with different samples. Thus, irrespective of the complexity of the polypeptides, using a reaction like Edman's degradation to remove N-peptides, with a detailed analysis of surface potential and capacitance including the signal transduction from FET can bring out the precise tool for peptide sequencing.