Patent ID: 8383396

Claim:
An analytical apparatus comprising: a field effect transistor having a conductive electrode that is in contact with a sample solution, said conductive electrode having a probe immobilized on a surface thereof, said field effect transistor having a source, a drain and a gate, said conductive electrode being connected to the gate of said field effect transistor via a conductive wire; a reference electrode that is in contact with said sample solution but not with said field effect transistor; an AC power supply directly connected to the reference electrode for applying an alternating current voltage of a constant frequency with a direct current voltage superimposed thereon between said conductive electrode and the reference electrode; and a DC power supply directly connected to the source of the field effect transistor for applying direct current between the source and the drain, and wherein changes in electrical characteristics of the field effect transistor are detected when the AC power supply supplies current to the reference electrode and the DC power supply supplies DC current to the source of the field effect transistor.