  We describe two different modes for electronically detecting an adsorbed
molecule using a nanoscale transistor. The attachment of an ionic molecular
target shifts the threshold voltage through modulation of the depletion layer
electrostatics. A stronger bonding between the molecule and the channel,
involving actual overlap of their quantum mechanical wavefunctions, leads to
scattering by the molecular traps that creates characteristic fingerprints when
scanned with a backgate. We describe a theoretical approach to model these
transport characteristics.
