Chemistry Reference
In-Depth Information
preparing multifunctional particles using phospholipids is based on the
ability to encapsulate more than one particle at a time, which is usually
considered an unwanted occurrence. Park
et al.
have incorporated near-
IR-emitting QDs and magnetic iron oxide nanoparticles in a phospholipid
micelle.
262
It is noteworthy that the QDs and iron oxide were encapsulated
together, and the ratio of QDs to metal oxide particles could be altered
controllably. An anticancer drug, doxorubicin, was also included in the
heterostructure, and a peptide known to target nucleolin in endothelial cells
was conjugated to the particle surface. The targeted structures were then
used to image mice
in vivo
with MDA-MB-435 tumours. A
d
n
1
y
4
n
g
|
6
er harvesting the
tumours, examinations by both MRI and optical microscopy con
rmed the
presence of the nanostructures, although signi
cant levels of particles were
also found in the liver. An interesting related method of preparing multi-
functional materials is the inclusion of iron oxide and QDs in the lipid cores
of lipoprotein micelles,
263
giving what was termed
with hydro-
dynamic diameters of 250 nm. These materials were functionalised with
apolipoprotein and lipoprotein lipase and used in examining liver cells
in vivo
using both MRI and optical imaging. An similar interesting example is
the incorporation of CdSe/ZnS QDs into glyconanospheres with a diameter of
ca.
190 nm.
264
The QDs were initially phase-transferred using mercapto-
succinic acid, and linked electrostatically with polylysine inside the sphere.
The spheres were inherently unstable and dissociated a
'
nanosomes
'
er
ca.
10 hours,
although this was addressed by coupling the particles to avidin. The nano-
spheres used dextran molecules on the surface to examine interactions with
carbohydrate-binding proteins.
A similar method of encapsulation has been widely adopted, using an
engineered amphiphilic polymer with pendant side chains that resulted in
interdigitation with the nanoparticle capping group. The usual polymer
chosen was PAA modi
.
ed with 40% OA.
265
Phase transfer was achieved in the
same manner as phospholipid phase transfer; CdSe/ZnS QDs were dissolved
in chloroform along with the polymer, and le
to evaporate, and the resulting
solid was redispersed in water. The polymer could be further cross-linked by
EDC-mediated cross-coupling to lysine, and then further conjugated to
proteins or antibodies as needed. In a nice example, the negatively charged
polymer has also been used to electrostatically coordinate to a cationic dye,
which then formed J-aggregates.
266
In most applications, however, cross-
linking by lysine was not necessary as most applications only needed phase
transfer. A detailed study by Anderson
267
highlighted that 40% modi
cation
appeared to be the optimum degree of modi
cation, although ODA appeared
to be a better side chain for e
c example,
particle diameter measured by dynamic light scattering was found to
increase from 9.7 to 17.2 nm upon addition of the polymer. Interestingly, the
size of the
cient phase transfer. In a speci
nal particle/polymer conjugate appeared to be approximately the
same regardless of the size of the initial particle. The emission of encapsu-
lated QDs appeared to drop initially a
er transfer, although the lumines-
cence was found to recover to some degree on standing for several days.
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