3.6 Quantum Dots
Among various nanomaterials developed, quantum dots (QDs) represent one of the
most successful new biological probes. Compared to conventional organic
fluorophores, QDs have advantageous properties that include tunable emission,
photostability, and high brightness [177, 178]. These unique properties make QDs
highly desirable for certain biological applications and bring new possibilities for
biological imaging [179]. These applications range from solar cells, light-emitting
diodes, laser technologies, and chemical sensing to bioimaging. This has been
motivated by a desire to reach a fundamental understanding of several of their
unique properties and by the wealth of potential applications involving the use of
these materials, ranging from electronic devices to in vivo cellular imaging.
The functionalization of nanoparticles is very important for improving their
application. To date, most of the QDs are prepared in the organic phase and their
surfaces are functionalized with hydrophobic moieties such as tri-n-octyl phosphine
oxide (TOPO) and fatty acids. These hydrophobic QDs are not dispersible in
aqueous or biological fluids [180]. Thus, surface modification of biocompatible
water-dispersible QDs has received tremendous attention in the last decade [181].
Various approaches to the preparation of QDs (Table 13) have been reported.
3.7 Nanocomposites
Polymer nanocomposites are composites with a polymer matrix and filler with at
least one dimension of less than 100 nm. Organic–inorganic nanocomposites are
generally organic polymer composites with inorganic nanoscale building blocks.
They combine the advantages of the inorganic material (e.g., rigidity, thermal
stability) and those of the organic polymer (e.g., flexibility, dielectric properties,
ductility, and processability) [192]. Moreover, they usually also contain special
properties due to the nanofillers, which leads to materials with improved properties.
A defining feature of polymer nanocomposites is that the small size of the fillers
leads to a dramatic increase in interfacial area as compared with traditional
composites. Even at low loadings, this interfacial area creates a significant volume
fraction of interfacial polymer with properties different from the bulk polymer [193,
194]. Organic–inorganic nanocomposite systems can be prepared by various synthesis routes, reflecting the various methods available to introduce each phase. The
organic component can be introduced as: (a) a precursor (monomer or oligomer),
(b) a preformed linear polymer (in molten, solution, or emulsion states), or (c) a
polymer network that is physically (e.g., semicrystalline linear polymer) or chemically (e.g., thermosets, elastomers) crosslinked. The inorganic part can be
introduced as a precursor (e.g., TEOS) or as preformed nanoparticles. Organic or
inorganic polymerization generally becomes necessary if at least one of the starting
moieties is a precursor. There are various types of nanostructural materials, i.e.,
30
P. Dutta et al.
Among various nanomaterials developed, quantum dots (QDs) represent one of the
most successful new biological probes. Compared to conventional organic
fluorophores, QDs have advantageous properties that include tunable emission,
photostability, and high brightness [177, 178]. These unique properties make QDs
highly desirable for certain biological applications and bring new possibilities for
biological imaging [179]. These applications range from solar cells, light-emitting
diodes, laser technologies, and chemical sensing to bioimaging. This has been
motivated by a desire to reach a fundamental understanding of several of their
unique properties and by the wealth of potential applications involving the use of
these materials, ranging from electronic devices to in vivo cellular imaging.
The functionalization of nanoparticles is very important for improving their
application. To date, most of the QDs are prepared in the organic phase and their
surfaces are functionalized with hydrophobic moieties such as tri-n-octyl phosphine
oxide (TOPO) and fatty acids. These hydrophobic QDs are not dispersible in
aqueous or biological fluids [180]. Thus, surface modification of biocompatible
water-dispersible QDs has received tremendous attention in the last decade [181].
Various approaches to the preparation of QDs (Table 13) have been reported.
3.7 Nanocomposites
Polymer nanocomposites are composites with a polymer matrix and filler with at
least one dimension of less than 100 nm. Organic–inorganic nanocomposites are
generally organic polymer composites with inorganic nanoscale building blocks.
They combine the advantages of the inorganic material (e.g., rigidity, thermal
stability) and those of the organic polymer (e.g., flexibility, dielectric properties,
ductility, and processability) [192]. Moreover, they usually also contain special
properties due to the nanofillers, which leads to materials with improved properties.
A defining feature of polymer nanocomposites is that the small size of the fillers
leads to a dramatic increase in interfacial area as compared with traditional
composites. Even at low loadings, this interfacial area creates a significant volume
fraction of interfacial polymer with properties different from the bulk polymer [193,
194]. Organic–inorganic nanocomposite systems can be prepared by various synthesis routes, reflecting the various methods available to introduce each phase. The
organic component can be introduced as: (a) a precursor (monomer or oligomer),
(b) a preformed linear polymer (in molten, solution, or emulsion states), or (c) a
polymer network that is physically (e.g., semicrystalline linear polymer) or chemically (e.g., thermosets, elastomers) crosslinked. The inorganic part can be
introduced as a precursor (e.g., TEOS) or as preformed nanoparticles. Organic or
inorganic polymerization generally becomes necessary if at least one of the starting
moieties is a precursor. There are various types of nanostructural materials, i.e.,
30
P. Dutta et al.