biological characteristics of GNPs. GNPs of size between 10 and 100 nm are
mainly accumulated in the reticuloendothelial system (RES), and the distribution
homogeneity increases as the particle size decreases [8]. GNPs of size between 15
and 20 nm could pass through the blood–retinal barrier or blood–brain barrier [9].
Small sized GNPs with diameter between 1 and 2 nm have higher toxicity
potential due to the possibility that they irreversibly bind to some important
biopolymers [10].
22.2.1.2 Quantum Dots (QDs)
QDs are semiconductor particles which emit light by stimulation [11]. The color or
wavelength of the light emitted from a QD depends on the crystal’s size. QDs with
smaller size (less than 2 nm in diameter) exhibit blue fluorescence (380 in diameter)
exhibit red fluorescence (605 in diameter) [12]. QDs are made of a metalloid
crystalline core and shell, which protects the core and gives bioavailability [13].
QDs have distinct electronic and optical characteristics, for instance, large
absorption coefficients, and high levels of photostability and brightness. The broad
excitation wavelength range and the narrow and symmetric emission spectra mean
that QDs are appropriate for multiplex imaging using several intensities and colors
by combination of encoded proteins/genes to image tumors [14].
22.2.1.3 Iron Oxide Nanoparticles (IONPs)
IONPs categorized according to size as standard superparamagnetic iron oxide
(SPIO) (60–150 nm), ultra-small superparamagnetic iron oxide (USPIO) (5–
40 nm), or monocrystalline iron oxide (MION)—a part of USPIO (10–30 nm).
Superparamagnetic iron oxide nanoparticles (SPIONPs) have distinctive properties,
for instance, biocompatibility and easy surface modification, making them attractive
as tumor imaging probes. SPIONPs are made of ferric iron and ferrous iron.
SPIONPs can make a T2 relaxation effect, which results in T2-weighted MRI
images signal reduction. This T2 relaxation effect is due to the heterogeneity of the
magnetic field surrounding the NPs, thus results in proton magnetic moments
dephasing [15]. As SPIONPs are dissolved under acidic conditions, SPIONPS are
considered benign in the body [16]. Although some IONPs have toxicity problems,
coated SPIONPs have been investigated and identified as relatively nontoxic [17].
When used for MRI contrast agents, SPIONPs are usually covered with synthetic
polymers, for example, silicone or sugars [18].
414
Y. Kim and D. S. Lee
mainly accumulated in the reticuloendothelial system (RES), and the distribution
homogeneity increases as the particle size decreases [8]. GNPs of size between 15
and 20 nm could pass through the blood–retinal barrier or blood–brain barrier [9].
Small sized GNPs with diameter between 1 and 2 nm have higher toxicity
potential due to the possibility that they irreversibly bind to some important
biopolymers [10].
22.2.1.2 Quantum Dots (QDs)
QDs are semiconductor particles which emit light by stimulation [11]. The color or
wavelength of the light emitted from a QD depends on the crystal’s size. QDs with
smaller size (less than 2 nm in diameter) exhibit blue fluorescence (380 in diameter)
exhibit red fluorescence (605 in diameter) [12]. QDs are made of a metalloid
crystalline core and shell, which protects the core and gives bioavailability [13].
QDs have distinct electronic and optical characteristics, for instance, large
absorption coefficients, and high levels of photostability and brightness. The broad
excitation wavelength range and the narrow and symmetric emission spectra mean
that QDs are appropriate for multiplex imaging using several intensities and colors
by combination of encoded proteins/genes to image tumors [14].
22.2.1.3 Iron Oxide Nanoparticles (IONPs)
IONPs categorized according to size as standard superparamagnetic iron oxide
(SPIO) (60–150 nm), ultra-small superparamagnetic iron oxide (USPIO) (5–
40 nm), or monocrystalline iron oxide (MION)—a part of USPIO (10–30 nm).
Superparamagnetic iron oxide nanoparticles (SPIONPs) have distinctive properties,
for instance, biocompatibility and easy surface modification, making them attractive
as tumor imaging probes. SPIONPs are made of ferric iron and ferrous iron.
SPIONPs can make a T2 relaxation effect, which results in T2-weighted MRI
images signal reduction. This T2 relaxation effect is due to the heterogeneity of the
magnetic field surrounding the NPs, thus results in proton magnetic moments
dephasing [15]. As SPIONPs are dissolved under acidic conditions, SPIONPS are
considered benign in the body [16]. Although some IONPs have toxicity problems,
coated SPIONPs have been investigated and identified as relatively nontoxic [17].
When used for MRI contrast agents, SPIONPs are usually covered with synthetic
polymers, for example, silicone or sugars [18].
414
Y. Kim and D. S. Lee