Controlled electrostatic gating of carbon nanotube FET devices.

Carbon nanotube transistors are a promising platform for the next generation of nonoptical biosensors. However, the exact nature of the biomolecule interactions with nanotubes in these devices remains unknown, creating one of the major obstacles to their practical use. We assembled alternating layers of oppositely charged polyelectrolytes on the carbon nanotube transistors to mimic gating of these devices by charged molecules. The devices showed reproducible oscillations of the transistor threshold voltage depending on the polarity of the outer polymer layer in the multilayer film. This behavior shows excellent agreement with the predictions of a simple electrostatic model. Finally, we demonstrate that complex interactions of adsorbed species with the device substrate and the surrounding electrolyte can produce significant and sometimes unexpected effects on the device characteristics.