Chemistry Reference
In-Depth Information
Fig. 5 PL spectra from
solutions containing
14/ssDNA
8
-Fl (a,
circles
),
14/dsDNA
8
-Fl (a,
squares
),
1/ssDNA
8
-Fl (b,
circles
), and
1Br/dsDNA
8
-Fl (b,
squares
)
in 25 mM phosphate buffer.
Excitation wavelength is
352 nm for 14 and 385 nm for
1: [ssDNA
8
-Fl or dsDNA
8
-
Fl]
¼
2.0
10
8
M,
[FU]
¼
1.2
10
6
M. The
emission spectrum of
dsDNA
8
-F1 upon direct
excitation of Fl at 490 nm in
the absence of the donor is
shown in black
25
a
20
15
10
5
0
b
12
8
4
0
400
450
500
550
600
650
Wavelength (nm)
10
8
Mat
dsDNA
8
-F1 and ssDNA
8
-F1 at [ssDNA
8
-Fl or dsDNA
8
-Fl]
¼
2.0
10
6
M. The integrated Fl emission from 14/
dsDNA-Fl is over twofold more intense than that from 14/ssDNA
1
-Fl, and there
is no significant difference observed between 1Br/ssDNA
1
-F1 and 1Br/dsDNA-F1.
These results indicate that 14 has improved selectivity between dsDNA and ssDNA
as compared to 1Br. The improvement in the signal amplification for 13 and 14
should arise from the fact that they have multiple-transition dipole moment orienta-
tions relative to the linear counterpart polymer 1Br.
To match the biosensors using different acceptor chromophores, the emission
spectra of CCPs were turned to improve the spectral overlap (
J
(
[Fluorene Unit] ([FU])
¼
1.2
)). Previous reports
have shown that interchain FRET within CPs is more efficient than intrachain
FRET due to stronger electronic coupling and increased transfer dimensionality
for interchain relative to intrachain interactions [
77
]. Complex formation between
the polymer and oppositely charged DNA molecules induces polymer aggregation
and increases the local concentration of 2,1,3-benzothiadiazole (BT) units, leading
to enhanced interchain contacts and improved electronic coupling between optical
partners. The fundamental information inspired the design of CCPs with donor-
acceptor architecture for improved spectral overlap with dye-labeled nucleic acid
[
78
]. A cationic poly(fluorene-
alt
-1,4-phenylene) derivative containing 5 mol% BT
units (15) was synthesized. In dilute solutions, the polymer emits blue with an
emission maximum at 380 nm. Upon addition of ssDNA, green emission ranging
from 500 to 650 nm dominates the solution fluorescence because of the enhanced
l
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