Sensing of Biomolecules - Bionanoelectronics: Bioinquiring and Bioinspired Devices - page 80

Δ G (ns)

dsRNA

2

dsDNA

1

poly(A)

poly(C)

poly(U)

0.1 V (V)

0.6

Fig. 2.22 Schematized electronic signatures for dsRNA and the homopolymers A, C, and U

of probe-hybridized miRNA from cellular RNA was recently reported ( Wanunu
et al. 2010 ). Practically, a target miRNA is hybridized to a probe and then enriched
with the p19 protein. The miRNA is further detected using a nanopore, the method
having the ability to detect miRNA at picogram levels.
Graphene is the last discovery in the area of nanopore sensing. The hole in
graphene is fabricated using the FIB technique ( Schneider et al. 2010 ). Despite the
fact that graphene is a one-atom-thick material, it is a remarkable ionic isolator
( Garaj et al. 2010 ), and its small thickness makes it the ideal nanopore for the
electronic DNA base sequence detection.

2.3 MEMS/NEMS Biodetection

MEMS (microelectromechanical systems) and NEMS (nanoelectromechanical sys-
tems) are devices in which the mechanical and electrical properties are simulta-
neously exploited in a series of applications such as sensing, imaging, or even
computing. MEMS have at least one dimension at the micrometer scale (1-100m),
while in the case of NEMS, one dimension is in the nanometer (10 9 m) range.
The most widespread MEMS or NEMS device is the cantilever, which is
schematically represented in Fig. 2.23 . The cantilever can be integrated with
electronic and/or optoelectronic devices able to process the information or to control
its mechanical movement. The cantilever is, in principle, a mechanical resonator that
bends due to a thermal, electric, magnetic, or optical force. The typical actuation of
a cantilever involves electrical forces, case in which the cantilever is often ended
with a nanoscale metallic tip. The cantilever bends toward the substrate due to the
attractive electrical force exerted by the voltage V applied between the substrate
electrode and the cantilever.