To demonstrate the crucial role of the surface charge in GFET biosensing, we carried out a control experiment in which CRP sensing was performed without surface-charge modulation. A schematic of the device configuration is depicted in Fig. . Figure shows the time series of ΔVDP during the blank sample and CRP measurements. In contrast to Fig. ) and (c), the values of ΔVDP and S in Fig. (b) and (c) remained nearly constant. Notably, S did not surpass the noise floor at a concentration of 76 nM, although it was twice as high as that in Fig. . Given that S was lower than the noise floor, it was concluded that the device did not respond to CRP in the absence of surface-charge modulation.