Biomedical Engineering Reference
In-Depth Information
self-assemble, but rather those that used SWCNT surface as a template to
form a stable coating.
As an alternative, Schmidt and Pasquali used a new strategy to obtain
suspensions of highly luminescent SWCNTs by using a combination of
surfactant (SDBS) and a biocompatible polymer (polyvinylpyrrolidone,
PVP) or by polymerising
in situ
its monomer vinyl pyrrolidone (ISPVP).
131
PVP or VP adsorbed strongly to the external surface of the SDBS micelle
due to charge transfer between the sulphate group of SDBS and the
nitrogen of PVP and/or VP (Fig. 9.21). At neutral pH values, the PVP slightly
disrupted the SDBS micelle and affected the tubes' luminescence, while the
monomer did not. In acidic conditions, conformational changes of PVP and
VP polymerisation determined eficient wrapping of the SDBS-SWCNTs,
providing additional protection against the surrounding environment.
Therefore, stable suspensions in a wide range of pH were obtained, while
avoiding photoluminescence changes or locculation of the samples. The
results showed incredible stability of the ISPVP-SDBS-SWCNT complex
even after extended dialysis and after lyophilisation and resuspension in
deionised water. Moreover, using NIR photoluminescence microscopy, it was
demonstrated that ISPVP-SDBS-SWCNT suspensions were stable and strongly
luminescent in living cell cultures, where they interacted eficiently on cell
membranes and did not display any sign of aggregation.
pH
=
7
n
O
p
H
= 7
N
pH = 2
po lym er
PVP
O
N
SD BS
monomer
VP
O- Na+
O
O
S
(C H
2
)
10
Figure 9.21
Scheme of (Left) SDBS-SWCNT at pH 7. (Centre-up and right) PVP-SDBS-
SWCNT at pH 7 and 2. (Centre-below and right) VP-SDBS-SWCNT at pH 7 and 2 for
which cationic polymerisation occurred. Figure modiied from Duque
et al
.
131
with
permission. See also Colour Insert.
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