Chemistry Reference
In-Depth Information
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Figure 6.7
Surface modi
cation of nanoparticles and the resulting phase transfer.
Reprinted with permission from I. Potapova, R. Mruk, S. Prehl, R.
Zentel, T. Basche and A. Mews,
J. Am. Chem. Soc.
, 2003,
125
, 320.
Copyright 2003 American Chemical Society.
a mixture of octadecylamine (ODA) and aliphatic phosphonium salts, giving
a positive charge to link to QDs with a negatively charged functional group.
Mixing an aqueous solution of the nanoparticles with a chloroform solution
of polymer resulted in the coordination of the positively charged groups,
leaving the long alkyl chain to induce solubility in non-polar solvents, hence
inducing another phase transfer back to an organic solution. It was noted
that the phase transfer would only work with 30
-
50% of charged side chains;
.
fewer charged side chains resulted in insu
cient linking with the dots
whereas too many resulted in a polymer that was insoluble in chloroform.
Another polymeric capping agent designed speci
cally to address solu-
bility problems with thiolated monomeric species has been described by Liu
et al.
235
The polymer was engineered and prepared by reversible addition
-
fragmentation chain-transfer mediated polymerisation to yield a material
with three distinct subunits
an imidazole group for linking to QDs, a PEG
group to induce water solubility, and a primary amine/biotin group for bio-
functionalisation. The exchange of hydrophobic ligands on CdSe/ZnCdS with
the multifunctional polymer was easily achieved by simple dissolution and
precipitation, followed by dialysis. Phase exchange of CdSe/CdS particles
(prepared by the successive ion layer adsorption and reaction (SILAR) route
described in Chapter 5) was achieved and was notable for the material
—
s high
quantum yield in water (65%). The hydrodynamic diameter was equivalent to
DHLA
'
PEG functionalised QDs (
ca.
11 nm), but exhibited superior colloidal
stability of at least 2 months. The multifunctional polymer could then be
further functionalised with dyes such as 5-carboxy-X-rhodamine, and Forster
resonance energy transfer (FRET) experiments were undertaken. Further
experiments with QDs capped with the multifunctional polymer showed
almost no non-speci
-
c binding in labelling experiments, and conjugation to
streptavidin for targeted imaging was simply achieved by coupling chemistry.
It is worth noting at this point that aminopolymers with dyes attached have
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