Since 1952, when Shockley invented Field-Effect Transistors (FETs); there have been undergoing many significant modifications to cater to the needs of sensing applications. In 1970, Bergveld developed an ion-sensitive Field-Effect Transistor (ISFET) which is used for ion detection in a chemical environment. With further development of technology, novel functionalizations for ISFET devices have been fabricated for protein and DNA detection. Various simulations have been carried out to further deepen the knowledge of the impact of functionalizations on the performance parameters . In this paper, analytical simulations have been carried out to effectively simulate the Gouy-Chapman-Stern model with the Site-Binding model for different amino acid functionalized on various types of gate oxides. Further, we plan on integrating numerical TCAD simulations with this work.