Semiconductor Device-Based Sensors for Gas, Chemical, and Biomedical Applications

Bioaffinity Sensors Based on MOS Field-Effect Transistors 255

© 2011 by Taylor & Francis Group, LLC

− ⋅ = − +( ) ( )ε φ

Si B

q p n N

p n E E V

i F r GS t

= + − −exp(( ) / )φ φ

n n E E V

i F r GS t

= − + − −exp( ( ) / )φ φ (6.38)

Here, V

GS

is the potential applied between the NW source and a reference electrode immersed in

bulk electrolyte, and ∆E

r

accounts for the reference electrode potential in solution and work func-

tion and electron afnity terms. The latter term was used for the ISFET, but for NWs it is common

to use no reference electrode in solution, or sometimes just a metal electrode made of Pt or Au (not

polarized) is used to control the solution potential.

In the electrolyte without biomolecules, the Poisson–Boltzmann (PB) equation ...