Field-effect transistor with recombinant potassium channels: fast and slow response by electrical and chemical interactions

Electrical interfacing of semiconductor devices with ion channels is the basis for a development of neuroelectronic systems and of cell-based biospecific electronic sensors. To elucidate the mechanism of cell-chip coupling, we studied the voltage-gated potassium channel Kv1.3 in HEK 293 cells on field-effect transistors in silicon with a metal-free gate of silicon dioxide. Upon intracellular depolarization there is a positive change of the effective extracellular voltage on the transistor with an amplitude that correlates with the gating of Kv1.3 channels, but with a dynamics that is far slower than channel gating. After repolarization there is a fast negative change of the transistor signal followed by a slow relaxation dynamics without any membrane current. To rationalize the involved transistor response, we propose a concept that combines the electrodiffusion of ions in the cell-chip junction with selective ion binding in the electrical double layer of silicon dioxide. The model implies (i) an electrical charging and discharging of the cell-chip capacitance within a microsecond, (ii) a changing K+ concentration in the cell-chip junction within a millisecond and (iii) a changing adsorption of K+ and Na+ ions within tens of milliseconds. The total transistor signal is a superposition of the changed electrical potential in the extracellular space between cell and chip and of the changed surface potential at the chip surface.