The lack of decoration with positively charged compounds resulted negative charges on both CRP and the GFET surface, leading to a repulsive force that decreased the efficiency of the antigenantibody reaction. Consequently, the low value of S in Fig. ) is attributed to the strong nonlinear electrolytic screening and low antigen-antibody reaction efficiency. These results further emphasize the significance of surface-charge modulation of GFETs for biosensing applications.