Optical Reporting by Conjugated Polymers via Conformational Changes - Advanced Fluorescence Reporters in Chemistry and Biology - page 401

a

a b c d e

b

0.5

a

c

b

0.4

d
e

0.3

0.2

A

0.1

0.0
300 400 500 600 700

λ /nm

10 5 M, on a monomer unit
basis) (b) a) polymer b) polymer/DNA probe c) polymer/DNA probe/complementary DNA
sequence d) polymer/DNA probe/1 base mismatched DNA sequence e) polymer/DNA probe/
2 base mismatched DNA sequence after 5 min mixing at 55 C in 0.1 M NaCl/H 2 O. B) UV-vis
spectra of the above corresponding samples [ 19 ]

Fig. 10 (a) Photos of colorimetric changes in solutions of (7.9

the backbone, shortening of effective conjugation lengths, resulting in a spectral
shift back toward blue (Fig. 10c ).
Ho et al. were able to verify the -helical shape of the polymer by circular

dichroism (CD) spectra. No structural elements were observed until the formation
of the double helical DNA at which point they observed a right-handed

a

-helix in
the polythiophene backbone. Their work demonstrates the power of fluorometric
detection as they noted a seven order of magnitude increase in detection sensitivity
(20 fM in 200

a

l) simply through the use of fluorometric detection as opposed to
UV-vis absorption. The polymer in solution has a high fluorescence yield with a
maximum at 530 nm (Fig. 11a ). Upon formation of the “duplex” the fluorescence is
significantly quenched (Fig. 11b ), while with the addition of the complementary
DNA and “triplex” formation, the fluorescence intensity is enhanced by a factor of 5
(Fig. 11c ). The inherent sensitivity of the spectral shift even allowed distinction
between DNA with only one and two mismatched bases (Fig. 10 Bd, e).
In addition this seminal work, other groups have utilized - and improved upon -
such fluorometric polymer-based detection schemes. Using a slightly modified
system, Dor ` et al. were able to improve the detection sensitivity down to

m