Detection of charged macromolecules by means of fi eld-effect devices (FEDs): possibilities and limitations - Electrochemical Sensors, Biosensors and Their Biomedical Applications - page 192

C i

Gate insulator

C sc

Si

(a)

DNA

Ions

C ML

R ML

C i

Gate insulator

Si C sc

(b)

FIGURE 7.3 Simplifi ed equivalent circuit of an original (unmodifi ed) EIS structure (a) and EIS biosen-
sor functionalized with charged macromolecules (b). C i , C sc and C ML are capacitances of the gate insulator,
the space-charge region in the semiconductor, and the molecular layer, respectively; R ML is the resistance of
the molecular layer.

∆ C

Increasing of negative
charges on an insulator
surface

∆ V fb

EIS

EISDNA

p-Si

Voltage

FIGURE 7.4 Capacitance-voltage ( C-V ) curve for a bare (unmodifi ed) EIS sensor and EIS sensor with
a molecular layer (here, DNA). The presence of the additional molecular layer shifts the C-V curve of the
original EIS structure along both the capacitance (∆ C ) and voltage axis (∆ V fb ).