3.1. Concept of SCM-GFET Biosensors. Figure (c) illustrates our device, which comprises two configurations of GFETs: one is a sensing GFET (GFETsig), where the surface was decorated with QACs and capture probes, and the other was a reference GFET (GFETref), which was used to record the background as it did not possess capture probes. Due to variations in the fabrication process, the values of VDP,sig and VDP,ref were diverse; thus, we computed their means (μsig and μref) to enhance the measurement reliability. Background changes, such as variations in ionic strength, pH, and temperature of the buffer solution, were eliminated through differential measurements (ΔVDP = μsigμref). The implementation of a positively charged compound to counteract the negative potential of graphene (ζ = -45 mV ) enables the devices to effectively overcome strong nonlinear electrolytic screening. After the initial measurements, the surface charges of the GFETs in Region 1 were modulated by the QACs, whereas those in Region 2 were not. Following the rinse process, electrical measurements were conducted for 40 min. The corresponding plots in Fig. This shift is attributed to the positive charge of the quaternary ammonium group, which induces opposite charges in the graphene channel. In contrast, those in Region 2 remained relatively unchanged despite a slight drift, as shown in Fig. and.