The DNA transistor interface: The interplay between pH, electric field and membrane screening dictates sensitivity

When DNA binds to a transistor, the surface potential (ψ_o) shifts in response to charges located within a Debye length. The native surface charge and screening capacitance are often described by the Gouy-Chapman (GC) double-layer model, which uses the Poisson-Boltzmann (PB) distribution for ions. GC model neglects screening within the DNA layer and is often insufficient to explain experimentally observed Δψ_o (40-80mV). We show that surface buffering capacity, E-field in the underlying oxide and ion screening in the DNA layer strongly influence sensitivity and lead to Δψ_o values larger than the GC model prediction. We present a formulation based on the Born charge dielectric interaction and find that a lowering in permittivity within the DNA lattice leads to ion exclusion and lower screening. We find that sensitivity to DNA charge is highest when the surface is closest to the point of zero charge (PZC).