COMMUNICATION
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A novel cationic conjugated polymer for homogeneous fluorescence-
based DNA detection{
Hui Peng, Christian Soeller and Jadranka Travas-Sejdic*
Received (in Cambridge, UK) 23rd May 2006, Accepted 6th July 2006
First published as an Advance Article on the web 2nd August 2006
DOI: 10.1039/b607293c
A novel water-soluble cationic conjugated polymer, poly({2,5-
bis[3-(N,N-diethylamino)-1-oxapropyl]-para-phenylenevinylene}-
alt-para-phenylenevinylene) dibromide, was synthesized and
used to develop a simple label-free DNA detection essay.
Fig. 1 shows the sequence of reactions to obtain poly({2,5-
bis[3-(N,N-diethylamino)-1-oxapropyl]-para-phenylenevinylene}-alt-
para-phenylenevinylene) (PPVNEt
-oxapropyl)-1,4-diiodobenzene was synthesized according to ref. 19.
). 2,5-Bis(3-[N,N-diethylamino]-
2
1
PPVNEt2 was obtained by a Heck coupling reaction, using a
catalytic system containing palladium acetate, tributylamine and
tri-ortho-tolylphosphine under a nitrogen atmosphere (see ESI{ for
details). The weight-average molecular weight of PPVNEt2,
measured by gel permeation chromatography (GPC) in THF, is
Conjugated polyelectrolytes (CPEs) are versatile new materials
that combine features of conventional conjugated polymers and
polyelectrolytes, resulting in unique electrical and optical properties
that have made them ideally suited for applications in electrooptic
1
2–4
devices, biosensors and drug delivery. Modification of CPEs
with anionic or cationic functional groups yields materials that
possess the properties of conjugated polymers but are also water
soluble which is essential for interfacing with biological substrates
such as proteins and DNA. These water-soluble conjugated
polymers are attractive sensor materials because their electrical,
optical and optoelectric properties can be greatly modified by
9
kDa with a polydispersity of 2.8.
The cationic, water soluble polymer was prepared from neutral
PPVNEt
Fig. 2 presents UV-vis absorption and photoluminescence spectra
of PPVNEt (in chloroform) and PPVNEt Br (in water). Clearly,
a shift in absorption maxima occurred between the neutral and
charged polymers. PPVNEt exhibits maximal absorption at
54 nm while the absorption peak of PPVNEt Br is blue shifted
2
by quaternization with bromoethane, as shown in Fig. 1.
2
2
2
2
5
small perturbations of the local electrochemical environment. The
4
2
2
enormous potential of this approach was first demonstrated by
Chen et al. who developed a sensitive ‘real-time’ biosensor for
detection of aromatics and proteins based on poly(2-methoxy-(5-
by 42 nm to 412 nm. This shift may be due to a solvatochromic
20
effect, also observed in substituted polythiophenes and poly-
21
2
(diacetylene). The photoluminescence spectra of PPVNEt and
6
propyloxy)sulfonate phenylenevinylene).
PPVNEt
while excited at the wavelength of maximal absorption. The
emission peak wavelengths were 517 and 520 nm for PPVNEt
and PPVNEt Br , respectively.
2 2
Br were recorded in chloroform and water, respectively,
Cationic conjugated polymers (CCPs), in particular, have
proven to be very useful for DNA sequence detection based on
electrostatic interaction with the negatively charged phosphate
2
2
2
4
,7–9
backbone.
Previously reported CCPs for DNA detection were
Homogeneous DNA fluorescence analysis has great importance
due to its high sensitivity and simple operation. In general, labeling
of two nucleic acids or dual modification of the same altered
strand are necessary in such methods to achieve sequence
4,10,11
either polythiophene derivatives
7,12–14
lene) derivatives.
or poly(fluorene-co-pheny-
Poly(para-phenylenevinylene) (PPV) is a well-known lumines-
cent conjugated polymer. Recently, considerable research has been
focused on anionic PPV derivatives as substrates for chemo- or
22
specificity. In this work, the synthesized cationic polymer was
used to detect specific hybridization with minimal DNA
6,15–18
bio-sensors.
In these sensors, amplified fluorescence quench-
ing is achieved by electron or energy transfer due to a strong
association between polymers and oppositely charged quenchers
resulting in efficient energy migration and exciton delocalization
6,16
across the polymer.
However, the anionic charge of these PPV
derivatives makes detection of equally charged anionic biomole-
cules, such as DNA, problematic. Here, we report the synthesis of
a novel cationic water-soluble PPV, poly({2,5-bis[3-(N,N-diethyl-
amino)-1-oxapropyl]-para-phenylenevinylene}-alt-para-phenylenevi-
2 2
nylene dibromide (PPVNEt Br ) that overcomes this limitation
as demonstrated by a novel DNA assay and is an addition to
the currently limited number of available CCPs.
Polymer Electronics Research Centre, The University of Auckland,
Private Bag 92019, Auckland, New Zealand.
E-mail: j.travas-sejdic@auckland.ac.nz; Fax: +64 (9) 3737422;
Tel: +64 (9)3737599 ext. 88291
+
2
Fig. 1 Synthesis of PPVNEt
CO
. i, 2-Chlorotriethylamine hydrochloride,
K
2
3
, acetone, 71%; ii, para-divinylbenzene, palladium acetate, tri-ortho-
tolylphosphine, tri-n-butylamine, DMF, 65%; iii, bromoethane, THF,
{ Electronic supplementary information (ESI) available: Synthesis details.
See DOI: 10.1039/b607293c
90%.
This journal is ß The Royal Society of Chemistry 2006
Chem. Commun., 2006, 3735–3737 | 3735