To confirm that the GFET signal was responsible for the CRP captured on GFETsig, fluorescence images were taken after electrical measurements. Figure and (e) are typical examples of images of GFETsig and GFETref, respectively. In the GFETsig device, the fluorescence of labeled CRP was observed on both graphene and SiO2 surface, although the fluorescence on the graphene was partially quenched. As the anti-CRP mAb was immobilized via physisorption, they were present on graphene as well as SiO2. Therefore, the antigen-antibody reaction occurred on both the graphene and SiO2 surface. In contrast, the GFETref device displayed no observable fluorescence on either the graphene or SiO2 surface; that is, CRP was not adsorbed. The results indicate that CRP was specifically adsorbed on GFETsig, but not on GFETref, supporting the conclusion that the FET response in Fig. ) and (c) arose from CRP.