Charge transfer from adsorbed proteins

We have used transistor devices with carbon nanotubes as the conducting channel to explore the interaction between the nanotube surface and streptavidin, both in dry and in buffer environments. We find charge transfer between the protein and the nanotubes in both cases. Comparison with simpler molecules allows the estimation of the transferred charge. We argue that this effect can be understood as being due to the interaction between the -NH2 groups of the protein and the aromatic surface.