Fluorescence Reporting Based on FRET Between Conjugated Polyelectrolyte and Organic Dye for Biosensor Applications - Advanced Fluorescence Reporters in Chemistry and Biology - page 435

Fig. 7 Normalized PL spectra in water of (a) 15/PNA 1 -Cy5, (b) 15/ss-DNA 1 /PNA 1 -Cy5, and (c)
15/ss-DNA 2 /PNA 1 -Cy5: (PNA 1 -Cy5) 10 8 M, [RU] 10 7 M; excitation at ¼ 2.0 ¼ 1.6

380 nm [ 77 ]

intermolecular FRET from the fluorene backbone to the end-cappers. As a conse-
quence, the aggregates of 16 have a better spectral overlap with the acceptor
absorption as compared to its uncapped counterpart 17. Thus, the polymer-sensitized
dye emission of ssDNA 8 -F1 for 16 is five fold stronger than that for 17,which
ultimately results in better fluorescence contrast between complementary and non-
complementary DNA for 16 relative to that for 17.
In addition to the modulation of the backbone structure of CCPs for improved
FRET, we find that the side chains also have an impact on the donor and acceptor
self-quenching upon complexation. The effect of CCP charge density on polymer-
sensitized dye emission was investigated using three cationic PF derivatives (17, 18
and 19)[ 80 ]. The facile functionality at fluorene C-9 position enables to vary the
side chains of cationic PFs without substantially changing their optoelectronic
properties (energy levels). On the basis of previous studies, ssDNA 8 -TR was chosen
as the signaling probe to minimize the interference of PET process and to facilitate
the study of charge density effect. The absorption and emission spectra of 17, 18
and 19 in water are similar because of the same electronic backbone structure. The
emission maxima for 17, 18, and 19 are 426, 421 and 426 nm, respectively.
Thereby, similar overlap between the polymer emission and TR absorption is
present. Polymers 17, 18, and 19 also have similar quantum yields in water,
which were measured to be 0.46, 0.50, and 0.50, respectively. Energy transfer
studies between these polymers and ssDNA 8 -TR were conducted in water at fixed
[ssDNA 8 -TR] 10 8 M (based on strands) with is the ratio of polymer

positive charges relative to ssDNA negative charges) ranging from 0 to 1.05. The
largest difference in TR emission intensity for 19/ssDNA 8 -TR relative to 17/ssDNA 8 -
TR and 18/ssDNA 8 -TR is observed at

¼ 2 ' ( '

10 7 M. The

' ¼ 1.05 where [RU] ¼ 2.1