Interfacing Biomolecules, Cells and Tissues with Nanowire-based Electrical Devices - Applications of Electrochemistry and Nanotechnology in Biology and Medicine - page 69

tection, for a wide-range of biological and chemical species from
single molecules up to ultimate level of living cells.
In this manuscript we present representative examples in
which these novel electrical devices have been used for living cells
and tissues. Recording electrical signals from cells and tissues is a
substantial tool for interrogating areas ranging from the fundamen-
tal biophysical studies of function in, for example, the heart and
brain, through medical monitoring and intervention. NW-FET de-
vices have the potential to form strongly coupled interfaces with
cell membranes due to their inherent intrinsic characteristics, thus
they can be used as highly sensitive local probes for extracellular
and intracellular recordings, as recently demonstrated. As basic
research, the direction is most stimulating and fruitful; however, it
is important to realize that these powerful tools, if integrated with
fundamental biology, can provide essential breakthroughs. Pulling
down the barriers between very different sciences and technologies
leads to surprising and new insights. The field is certainly most
inter-disciplinary.
II. NANOWIRE FIELD-EFFECT DEVICES AS SENSORS
Detectors based on semiconductor nanowires are configured as
field-effect-transistors (FETs), which exhibit a conductance
change in response to variations in the electric field or potential at
the surface of the channel region. 7,10a In a standard FET, a semi-
conductor is connected to metal source and drain electrodes,
through which a current is injected and collected, respectively. The
conductance of the semiconductor is switched on and off or modu-
lated by a third gate electrode capacitively coupled through a thin
dielectric layer, 10b Fig. 1A . In the case of a p-Si or other p-type
semiconductor, applying a positive gate voltage depletes carriers
and reduces the conductance, whereas applying a negative gate
voltage leads to an accumulation of carriers and increases the con-
ductance. Conductance modulations are dependent on the thick-
ness of the oxide dielectric layer of the gate. 11 The dependence of
the conductance on gate voltage makes FETs natural candidates
for electrically based sensing, because the electric field resulting
from the binding of a charged species to the gate dielectric is ana-