Chemistry Reference
In-Depth Information
As demonstrated by Mistlberger et al. [
19
] spray-drying is a very promising
method for the production of MOSePs in the micrometer range. The obtained
polymeric beads have a nano-porous structure and show excellent linearity from 0
to 100% oxygen saturation, a very rare phenomenon regarding optical sensors.
Smaller MOSePs in the nanometer range can be produced using precipitation
technique [
17
]. A completely different concept was proposed by Kreft et al.
[
123
]. They synthesized mobile pH-sensitive microbeads that consisted of a
seminaphthorhodafluor-dextrane conjugate incorporated in the magnetic poly-
electrolyte shell. In these microbeads, the magnetic nanoparticles were incor-
porated by a layer-by-layer deposition together with positive and negative
polyelectrolytes. Internalization of the beads by endocytosis into breast cancer
cells was achieved, and the change in pH from the alkaline medium outside the
cells to the acidic pH in the endo-/lysosome was followed in real time by fluo-
rescence microscopy.
5.6 Dye-Doped Beads for Other Applications
As was demonstrated above, dye-doped polymeric particles are mostly designed
for sensing and imaging. However, the range of potential applications is much
broader. For example, Kopelman and co-workers demonstrated that ultra-fine
polyacrylamide nanoparticles (
Ø
m) stained with meta-tetra(hydroxy-
phenyl)chlorine can be successfully used for PDT [
124
]. Both dye aggregation
within the water-dispersible nanoparticles and dye leaching were minimized. The
nanobeads were shown to be as efficient in killing cancer cells as free photosensi-
tizer molecules. The same group also showed the photodynamic effect for the
5,10,15,20-tetrakis(4-
N
-methylpyridinio) porphyrin-doped polyacrylamide beads
under 2-photon excitation [
125
]. Rat C6 glioma cells incubated with the nano-
particles and irradiated with 780 nm pulsed light (1 min, 100 mW cm
2
) started to
die 30 min after the exposure and were dead after 120 min. On the other hand, in
the absence of nanoparticles all the cells were found to be still alive after 120 min.
It was demonstrated that polymeric beads doped with phthalocyanines can also be
used for PDT [
126
].
2-3
m
6 Concluding Remarks
As can be summarized from this survey dye-doped beads represent very versatile
analytical tools which are applied in various fields of science and technology. The
size of the particles is of the utmost importance here. The smallest beads are mostly
designed for intracellular monitoring of analytes and much larger beads are often
used in composite materials and sensor arrays. Sensing schemes for optical che-
mosensors are established and are similarly realized on nano- and microscale.
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