Chemistry Reference
In-Depth Information
tethering of the organic dyes onto the nanoparticles [17]. Wiesner
et
al.
developed the synthesis of highly fluorescent nanoparticles, which
are composed of organic dyes (rhodamine B isothiocyanate (RBITC),
cyanine 5 NHS ester (Cy5-NHS)) loaded core and a protective shell
[18]. The fluorescent cores were obtained by adapting Stöber's
protocol: the hydrolysis-condensation was performed on a mixture
of TEOS and organic dyes conjugated to APTES. In the second step,
the protective shell was obtained by hydrolysis-condensation of a
mixture of TEOS and APTES whose amino group makes possible the
covalent immobilization of neutral poly (ethylene glycol) chains. Such
a post-functionalization favors the renal clearance of nanoparticles
and significantly reduces the liver uptake after the
in vivo
injection
of these highly fluorescent nanoprobes [19].
NH
2
HO
OH
Si
NH
2
NH
2
Si
O
Si
O
O
O
O
O
OH
NH
2
H
2
O
OH
H
2
N
O
OSi O
OSi
O
OH
M
HO
OH
O
O
O
M
Si
NH
2
TEOS
APTES
M
M
M
M
HO
NH
2
O
Si
M
x
O
y
NH
2
Si
M
x
O
y
OH
H
2
N
HO
O
CH
3
CH
3
Si
NH
2
O
O
OH
O
O
HO
NH
2
O
NH
2
H
3
C
OSi O
CH
3
H
3
C
OSi
H
2
N
OH
OH
NH
2
TMOS
CH
3
APTMS
CH
3
Scheme 4.3
Encapsulation of an oxide nanoparticle in an aminated
polysiloxane shell obtained by hydrolysis-condensation of a
mixture of TEOS + APTES or TMOS + APTMS.
The microemulsion technique can also be exploited for the
synthesis of fluorescent silica nanoprobes. The research group of
W. Tan determined the experimental conditions for the production
of fluorescent nanoparticles in water in oil (W/O) microemulsion
(reverse microemulsion). Water droplets (micelles) are dispersed in
oil (cyclohexane) phase and stabilized by a surfactant layer (Triton
X-100) for preventing the coalescence of droplets. The alkaline
hydrolysis-condensation of TEOS and organic dyes conjugated
APTES takes place inside the micelles. This group demonstrated the
versatility of this strategy since various organic and inorganic dyes
can be covalently or noncovalently encapsulated in the amorphous
silica matrix [16, 20]. They succeeded to tune the color of the resulting
nanoprobes and, therefore, to cover the visible spectral domain by
embedding in the same nanoparticles several distinct organic dyes
but with various ratios [21]. Moreover, these nanoparticles can be
post-functionalized. In other words, the surface of these fluorescent
nanoparticles can be derivatized by the covalent immobilization of
