Biomedical Engineering Reference
In-Depth Information
Fig. 4.29
Comparison of time-dependent luminescence intensities for DAP and DTTP each at two
ratios
x
.
Broken lines
correspond to mono-exponential fits
To test whether PL quenching dynamics depend on the type of dye molecule
we have performed similar titration experiments with DAP (see the dye structure in
Fig.
4.3
). The results are shown for two DAP concentrations in Fig.
4.29
.
A comparison with data for DTPP (presented also in Fig.
4.29
) reveals that
the quenching dynamics for DAP are by about a factor of 2-3 faster than those
for DTPP, while the final degree of quenching is somewhat larger for DTPP
as compared to DAP. We have recently reported [
74
] that DAP (without any
functional pyridyl group) is also able to cause QD PL quenching (see Fig.
4.11
)
since it intercalates into the ligand shell probably in an upright position of the
long molecular axis with respect to the QD surface. On the other hand, DTPP is
oriented perpendicular to the previous orientation (see scheme in Fig.
4.12
). To
realize such an orientation more ligands will have to be replaced in case of DTPP
as compared to DAP, which will take a longer time as can be seen in the experiment
and as is summarized in Table
4.4
. However, FRET will be stronger for DTPP
since the Foerster-related FRET efficiency is larger for a parallel as compared to
a perpendicular orientation [
74
,
94
,
162
] as is also seen in the experiment.
It follows from data presented in Table
4.3
that on average about 42% of
the QD PL quenching in “CdSe/ZnS QD-DTPP” nanoassemblies in TEHOS can
be assigned to FRET. This is much more as compared to the same kind of
nanoassemblies in toluene for which the observed FRET efficiency is less than
10% [
74
,
162
]. It should be noted that FRET experiments in TEHOS on single
nanoassemblies of the same composition resulted also in a large FRET efficiency of
