Optical Reporting by Conjugated Polymers via Conformational Changes - Advanced Fluorescence Reporters in Chemistry and Biology - page 402

Fig. 11 Fluorescence spectra in solution (200 nM, on a monomer unit basis): a) polymer, b)
polymer/DNA probe “duplex”, c) polymer/DNA probe/complementary DNA sequence “triplex”,
d) polymer/DNA probe/1 base mismatched DNA sequence “triplex”, and polymer/DNA probe/1
base mismatched DNA sequence “triplex” (100 equivalents mixture), e) polymer/DNA probe/
2 base mismatched DNA sequence “triplex” mixture at 55 C in 10 mM Tris buffer containing
0.1 M NaCl (pH 8) [ 19 ]

zeptomolar concentrations [ 20 ]. Meanwhile, Raymond et al. modified the detection
platform to be used on glass slides and microarrays for the purpose of high-
throughput nucleic acid detection [ 21 ]. Research conducted in the labs of Ingan as

and Bazan have improved solubility and handling as well as detection methods
using fluorescence energy resonance transfer (FRET) for nucleic acid detection
[ 22 , 23 ]. The latter will be discussed in details in the following chapter.

€

4.2 Protein Detection

Ho and Leclerc continued their work on sensing systems by utilizing the established
binding capabilities of artificial nucleic acid aptamers [ 24 ]. Aptamers are known for
their ability to specifically bind to ions, proteins, and other small molecules. In their
study, they synthesized two ss-DNA aptamers: X1, 5 0 -GGTTGGTGTGGTTGG-3 0 ,
specific for binding to thrombin protein and X2, 5 0 -GGTGGTGTTGTGGT-3 0 ,a
known nonbonding sequence. Once more employing a noncovalently-bound com-
bination of probe with polymer transducer, they demonstrated a color change upon
interaction with the ligand of interest. The choice of the X1 aptamer enabled
binding to both potassium ions and the -thrombin protein.

Figure 12 shows the difference in absorption spectra of the polymer's colori-
metric changes upon interaction with the different ions. Note that the absorption
wavelength for the polymer/aptamer complex with potassium is distinct from the
other ions, all of which have a similar shift. Fluorescence spectra of the polymer/
aptamer transducing complex with the

a

a -thrombin ligand (Fig. 13 )indicatesachange