We illustrate the signatures with four exemplary AAs: Alanine (Ala or A), Arginine (Arg or R), the exact pK values by the double-layer capacitance and the effect of the interplay between the buffering activity of the AA, which shifts the local pH. A higher value of the sidechain pK shifts the δΨo 2 /δpH 2 curve to higher pH values for AAs with similar behavior, whereas the maxima and minima values are higher for a larger difference in amine-pK and sidechain-pK. Figure (a) shows the absence of an isoelectric point, but the deprotonation of A's amine radical reaches 50% at its pK value and decreases drastically with a further increase in pH due to the higher charge balance effect of counterions with reduced buffer capacity. As compared to A, an extra amine sidechain of R adds up the positive charge in superposition to the amine radical (α-Carbon) resulting in a shift of the maxima to a higher PH. These singularity points at the zero and the maxima and minima shown by δΨo 2 /δpH 2 can constitute the variable to construct unique fingerprints of each AAs.