Biomedical Engineering Reference
In-Depth Information
10.1.4.4
Poly(Styrene -
co
- Acrylic Acid) Coating
Fluorescent magnetic nanospheres have been prepared by encapsulating a
fl uorescent dye and magnetite nanoparticles (10-12 nm) in a hydrophobic
poly(styrene-
co
-acrylic acid) shell [77]. This encapsulation was achieved using
a three-step miniemulsion process. For this, the magnetite nanoparticles
synthesized via the coprecipitation method were fi rst coated with oleic acid
and dispersed in octane, and a solution of sodium lauryl sulfate in water
then added to form a miniemulsion. A second miniemulsion was formed
by mixing styrene, hexadecane, the fl uorescent dye,
N
- (2,6 - diisopropylphenyl) -
perylene - 3,4 - dicarbonacidimide and an initiator, 2,2' - azobis(2 - methylbutyroni-
trile), with sodium lauryl sulfate in water. The miniemulsions of magnetite
and styrene were mixed at a ratio of magnetite powder to monomer of 1 : 1.
The polymerization was conducted at 72 °C under mechanical stirring. After
6 h, acrylic acid (0-15 wt% compared to styrene) was added and the polymerization
continued overnight. The copolymerization of styrene with the hydrophilic
acrylic acid introduced carboxyl groups onto the nanoparticle surface. The
amount of magnetite encapsulated by this process was
30 - 40% (w/w) and
the
M
s
was 35 - 40 emu g
− 1
magnetite compared to 80 emu g
− 1
magnetite for uncoated
magnetite nanoparticles. An increase in carboxylic surface groups led to a
signifi cant increase in the uptake behavior by the four types of cell investi-
gated - HeLa, MSCs, Jurkat cells and KG1a cells - as shown by confocal laser
scanning microscopy. However, a quantitative determination of the iron content
of the cells was unsuccessful. In order to increase the uptake of the nanospheres,
lysine was covalently coupled to the carboxyl groups of the nanospheres using
1 - ethyl - 3 - (3 - dimethylaminopropyl)carbodiimide hydrochloride ( EDC ) and sulfo -
NHS. With the lysine-functionalized nanospheres, the amount of iron uptake was
11 pg per cell, a value signifi cantly higher than was obtained with nanospheres
where poly-
L
-lysine was physically adsorbed onto the surface. Subsequent TEM
studies showed these nanoparticles to be localized in the cell endosomal
compartments.
∼
10.4.2
Nanospheres with Targeting and Recognition Capability
In the previous section, the use of MNPs encapsulated in polymer matrices
for passive imaging of biological systems has been described. While passive
targeting has a number of potential applications, progress and future develop-
ments in the use of MNPs in the imaging of cancers can only be realized
through active targeting against specifi c biomolecules, to enable early and
accurate diagnoses to be performed at a time when the disease would be still
treatable. There is, however, one major hurdle for active targeting: namely, that
of accumulating adequate levels of MNPs at the tumor site so as to allow enhanced
contrast and sensitivity for detection. Hence, in the following sections attention
is focused on polymer-MNP nanospheres with immobilized cancer-targeting
ligands.
