Page 371 - Organic Electronics in Sensors and Biotechnology

348 Chapter Nine

and a blue shift of the emission maximum to 560 nm upon binding to
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insulin amyloid fibrils. The spectrum for PONT mixed with native
monomeric native insulin shows a weaker intensity with a maximum
at 600 nm and resembles the spectrum for PONT free in solution,
indicating that the interaction between PONT and native insulin is
absent. In contrast to PTAA, the spectral observations indicate that
the interaction with amyloid fibrils is leading to a twisted polymer
backbone and separation of adjacent PONT chain, whereas the PONT
chains are planar and aggregated when mixed with native insulin.
The kinetics of the amyloid fibrillation was also followed by plotting
the ratio of the intensity of the emitted light at 560 and 600 nm. Simi-
lar to the observations with PTAA, the characteristic three different
phases of amyloid fibril formation are seen (Fig. 9.8b).
Another advantage of PONT, compared to the previously described
PTAA, is that this LCP is stable under the acidic conditions used for
fibrillation of insulin. Hence, PONT can be present during the fibrilla-
tion event, allowing the formation of a self-assembled hybrid material
comprised of a natural nanostructure, the amyloid fibril, and an incor-
porated semiconductor, the LCP. Such electroactive luminescent self-
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assembled nanowires were recently reported by Herland et al. This
study showed that it was possible to incorporate the LCP in the amy-
loid fibrils, and luminescent nanowires with different widths and
lengths could be obtained (Fig. 9.8c and d). Hence, stable structurally
defined amyloid fibrils can be used as a template for making well-
defined nanowires on which conjugated polymers can be symmetri-
cally aligned. As amyloid fibrils have a high aspect ratio, unusual sta-
bility, and are rather symmetric, these findings might open up a wide
range of tantalizing possibilities within the research field of bioelec-
tronics and become an attractive avenue for functional nanodevices.
The lack of control over the alignment of the materials appears to be a
factor affecting the performance of electronic devices based on conju-
gated polymers, and the use of amyloid fibrils as a nano-structural
motif might provides a solution to this problem. However, more work
is needed to better characterize and understand the operating mecha-
nism and the device architecture of such hybrid devices, as a complex
set of processes is affecting the performance of electronic devices based
on conjugated polymers. Furthermore, LCPs showing a high conduc-
tivity need to be developed to be used in electronic devices. Such LCPs
will also provide the opportunity of making biosensors for electronic
detection of amyloid fibrils.

9.4.2 Histological Staining of Amyloid Deposits
in Tissue Samples
As described earlier, the LCPs are excellent tools for studying the
amyloid fibril formation in vitro. However, those in vitro systems
only contain the desired molecules. So the question remains: Can the