As shown in Fig. 1(b), the average of FET responses for prion adsorbed on the surface prior to any chemical modification(Vg= −25 mV) was much lower than the detection of modified prion. Whereas the FET biosensors exhibit 3–4 folds higher signal of Vg for prion after the chemical modification using EDC/NHS(Vg= −84 mV) and further conjugation reaction with ethylenediamine (Vg= −109 mV).