For the test of selective chemical modification only occurred to the prion proteins, we examined the FET response after addition of the chemical reagents (EDC and NHS) to the thiamine-immobilized surface with and without the presence of prion proteins. The introduction of chemical reagent to the sample with the presence of prion on the surface produced noticeable FET responses, indicating that the chemical modification occurred and affected the prion protein’s charge on the surface. By contrast, the sample of thiamine-immobilized surface without the existence of prion pro-teins showed small change in the FET response after the addition of chemical reagents.