Fundamentals on Bionanotechnologies - Bionanoelectronics: Bioinquiring and Bioinspired Devices - page 28

a b

CdS (semiconductor nanoparticles) Pt metal nanoparticles

dithiol

gold substrate dithiol

Fig. 1.25 Tridimensional assemblies of ( a ) metal nanoparticles-semiconductor nanoparticles and
( b ) metal nanoparticles-metal nanoparticles

Metal particles covered with organic molecules such as thiols are able to self-
organize in 1D, 2D, and 3D arrays ( Rao et al. 2000 ). In particular, 2D nanoparticle
arrays are fabricated by mixing a hydrosol incorporating metal nanoparticles (Pd,
Au) with a toluene solution of alkali thiol. Subsequently, the mixture of 3-4-nm
metal nanoparticles and thiol is deposited on a surface and form a large and regular
2D array in which the nanoparticles are equally spaced in the x and y directions by
about 5-6 nm ( Rao et al. 2000 ). This 2D array is in fact an array of quantum dots in
which the Coulomb blockade phenomenon manifests in electrical measurements.
Three-dimensional assemblies are fabricated via producing solutions of dithiol
molecules and metal particles and then dipping a substrate into these solutions,
followed by washing with toluene solution, and drying. Metal nanoparticle-
semiconductor nanoparticle or metal nanoparticle-metal nanoparticle assemblies
can be fabricated using this method (see Fig. 1.25 a, b, respectively).
Nanoparticles are not only metallic but also semiconducting, such as silicon
nanoparticles, elemental II-VI semiconductor quantum dots, and III-V nanoclus-
ters. A review of fabrication of various types of nanoparticles is Adair et al. ( 1998 ).
Nanoparticles play a central role in many areas of bionanoelectronics, especially
in the area of controlled drug delivery and cancer therapies based on nanomaterials
( Biswas et al. 2010 ). Also, core/shell nanoparticles are extremely used in biosensing,
drug delivery, or cell labeling. The core/shell nanoparticles are of several types: (1)
inorganic core/shell nanoparticles such as silver/silica or CdSe/CdTe nanoparticles,
(2) organic/inorganic core/shell nanoparticles, in particular polymer/metal nanopar-
ticles, such as CuS/PVA or TiO 2 =celuloze, and (3) polymeric nanoparticles such as
PMMA/PVC ( Sounderya and Zhang 2008 ).
Also, many applications involve nanoparticles from group IV such as carbon
nanoparticles. Because carbon is the key element of any known form of life, and
in the human body carbon is the most encountered element after oxygen ( Fan
and Chu 2010 ), carbon nanoparticles such as diamond and graphite nanoparti-
cles display important applications in the area of bioimaging and drug delivery
nanosystems.
Similar to nanoparticles, nanowires are metallic, semiconducting, superconduct-
ing, or magnetic and are widespread used in many bionanoelectronic applications.
The physical properties of nanowires, such as the quantized conductance behavior