Fundamentals on Bionanotechnologies - Bionanoelectronics: Bioinquiring and Bioinspired Devices - page 46

Fig. 1.46 Nanogap made in a
single-walled CNTs

oxidative plasma

PMMA

SWCNT

Si substrate

2 nm

Si substrate

widths of 10-50 nm obtained by particle lithographic techniques are more than
enough, but when we want to contact electrically only one molecule, the oxidative
plasma is used to cut the electrodes in a precise manner, as in the example presented
in Fig. 1.46 . Nanogaps as small as 2 nm can be obtained in this way. Further, the
CNT can be functionalized with the COOH group, and the device is ready to detect
the hybridization of DNAs via conduction measurements ( Guo et al. 2008 ).
Not only metallic contacts but also nanowires ( Tian et al. 2010 ) and graphene
( He et al. 2010 ) can be used as nanogap electrodes. The biosensing applications of
electric nanogaps are reviewed by Chen et al. ( 2010 ).

1.4 Microfluidics and Nanofluidics

The last section of this chapter is addressed to micro- and nanofluidics. Micro-
and nanofluidics is an area dedicated to the miniaturization of plumbing and the
control of fluidic flows, which enable system integration of various biological
sensors and the development of devices such as lab on a chip, which are analogous
to the electrical integrated circuits. However, some microfluidics applications are
encountered in the daily life: inkjet printing and liquid-crystals displays.
An interesting fact about the scale of electronic and fluidic processes is pointed
out in Squires and Quake ( 2005 ). The success of integration of transistors on a
chip reaching nowadays a density of 2-3 billions/chip is due to the fact that the
downscaling of the geometrical dimensions of electronic devices does not affect
their physical properties (up to gate lengths of 10-30 nm, where short channel
effects strongly perturb the behavior of CMOS transistors). On the contrary,
fluidic systems change strongly their properties depending on the length scales.
Microfluidics deals with channels with dimensions of 100 m, the corresponding
volume of a cube with 100 m sides being 1 nl. Some microchannel shapes are
displayed in Fig. 1.47 .