Biomedical Engineering Reference
In-Depth Information
Fig. 5.6 Sensor responses to mouse IgA and mouse IgG for ( a ) goat anti-mouse IgG-
functionalized nanowire and ( b ) goat anti-mouse IgA-functionalized nanowire (Copyright 2007
Nature Publishing Group)
In the early days of silicon nanowire biosensor research, “bottom-up” nanowires
were widely used. However, in terms of integration, alternative “top-down” fabri-
cation methods are becoming more attractive. The use of “top-down” method has
also been demonstrated in a sensor application [ 29 ]. The sensor response is shown
in Fig. 5.6 .
Up to this point, we have summarized electrical detection-based biosensors and
dielectric-based biosensors. To utilize both types of sensor technology, a dielectric-
modulated field-effect transistor (DMFET) has been suggested. The DMFET has
many advantages, such as label-free detection, easy integration of readout systems,
compatibility with low-cost CMOS technology, and high applicability for detecting
various types of biomolecules, including those that are electrically neutral. The
details of DMFET will be explained below.
Dielectric-Modulated Field-Effect Transistor (DMFET)
Basic Structure and Theory
The DMFET structure can be obtained via the modification of a conventional FET
(Fig. 5.7 a) [ 30 - 32 ]. The gate is suspended above the gate oxide, and a nanogap is
formed by a carving process between the gate and the gate oxide, as shown in
Fig. 5.7 b. Biomolecules can be introduced and bound within the nanogap using
nanofluidics [ 33 ]. To create biosensors, a DMFET can be functionalized with recep-
tors (Fig. 5.7 c) that capture specific analytes (Fig. 5.7 d) in the sample solution. The
electrical characteristics of DMFETs are subsequently affected by the properties
of the biomolecules introduced into the nanogap; in particular, the charge density
and the dielectric constant of the biomolecules alter the electrical properties of the
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