Fluorescent DNA-poly(phenylenevinylene) hybrid hydrogels for monitoring drug release

Article abstract of DOI:10.1039/b817788k

A new class of fluorescent DNA-poly(phenylenevinylene) hybrid hydrogels (DNA/SP-PPV) have been prepared by in situ polymerization of monomer with salmon DNA as template, which are used for monitoring drug release driven by media pH. The Royal Society of Chemistry 2009.

Full text of DOI:10.1039/b817788k

Chemical Communications
www.rsc.org/chemcomm
Number 6 | 14 February 2009 | Pages 605–712
ISSN 1359-7345
COMMUNICATION
Shu Wang et al.
FEATURE ARTICLE
Fluorescent DNA–
J. Justin Gooding et al.
poly(phenylenevinylene) hybrid
hydrogels for monitoring drug
release
The importance of surface chemistry
in mesoporous materials: lessons
from porous silicon biosensors

COMMUNICATION
www.rsc.org/chemcomm | ChemComm
Fluorescent DNA–poly(phenylenevinylene) hybrid hydrogels for
monitoring drug releasew
Hongwei Tang, Xinrui Duan, Xuli Feng, Libing Liu, Shu Wang,* Yuliang Li and Daoben Zhu
Received (in Cambridge, UK) 9th October 2008, Accepted 12th November 2008
First published as an Advance Article on the web 1st December 2008
DOI: 10.1039/b817788k
A new class of fluorescent DNA–poly(phenylenevinylene) hybrid
hydrogels (DNA/SP–PPV) have been prepared by in situ poly-
merization of monomer with salmon DNA as template, which
are used for monitoring drug release driven by media pH.
positively charged sulfonium precursor of PPV (SP–PPV)18
that can cross-link DNA by electrostatic interactions. As
shown in Scheme 1, we synthesized the monomer by reaction
of 2-(20,50-bis(chloromethyl)-40-methoxyphenoxy)acetic acid
with tetrahydrothiophene in methanol with 33% yield, and
then the monomer was polymerized in the presence of salmon
DNA in mixed DMSO/alkaline water solution to yield
fluorescent DNA/SP–PPV composite hydrogel by in situ poly-
merization and self-assembly processes. Using four different
feed molar ratios of monomer to DNA base pair (bp)
(0.5, 0.75, 1.0 and 1.25), the DNA/SP–PPV hydrogels were
obtained and denoted as Gel 1, Gel 2, Gel 3 and Gel 4,
respectively. The polymerizations were performed homo-
geneously at 25 1C for 40 minutes following by precipitating
the reaction solution into acetone to afford the hydrogels.
Fig. 1(a) and (b) show the dried Gel 2 and wet Gel 2 swollen in
water for 12 h, respectively. The dried hydrogel could absorb
water more than three hundred times by weight. Scanning
electron microscopy (SEM) (Fig. 1(c)) showed the surface
morphology of wet Gel 2, where an intense gel structure
was observed. A fluorescent microscope image (Fig. 1(d))
confirmed its fluorescent characteristics.
Recently, DNA or DNA-inspired hydrogels have attracted
much attention because of their wide applications in drug
delivery, tissue engineering, gene therapy and biosensors.1–5
The main ways to create DNA hydrogel structures include
enzyme-catalyzed assembly of branched DNA1 and chemical
cross-linking of DNA.5 Very recently, the interactions between
negatively charged DNA and positively charged surfactants
have been used to form DNA gel particles by interfacial
diffusion.6 Up to date, although many DNA or DNA-inspired
hydrogel have been constructed,1–5 no fluorescent DNA
hydrogel has been developed except for the ones stained with
DNA-specific fluorescent dyes.1
Conjugated polymers (CPs) are characterized by a delocalized
electronic structure. These materials have established themselves
as useful components in optoelectronic devices such as
light-emitting diodes (LEDs),7 field effect transistors (FETs)8
and photovoltaic devices.9 Recently, conjugated polymers are
widely used as platforms to sensitively detect chemicals and
biological molecules (such as saccharide, protein, DNA and
RNA) due to amplification by a collective system response
in comparison with small molecule based sensors.10–17 Here
we attempted to combine the biofunction of DNA with
optical properties of conjugated polymers to fabricate novel
DNA-conjugated polymer composite hydrogel and to explore
their unprecedented levels of structural organization and novel
properties. It bridges two non-overlapping research areas: con-
jugated polymers and DNA hydrogel. These DNA-conjugated
polymer hydrogels are a new class of materials that could
be exploited in the monitoring of drug release. In these new
materials, the DNA retains biocompatible aspects and con-
jugated polymers retain their optical properties in the gel state.
For the conjugated polymer in the hydrogel, PPV derivative
was chosen owing to two reasons. First, the cationic monomer
of PPV has good compatibility to water media that is a
prerequisite for interrogating biological macromolecules.
Second, the monomer is easily polymerized by Wessling reac-
tion in alkaline aqueous solution at room temperature to yield
To get better performance of DNA/SP–PPV hydrogels,
their swelling behaviors19 and optical properties were studied
Beijing National Laboratory for Molecular Science, Key Laboratory
of Organic Solids, Institute of Chemistry, Chinese Academy of
Sciences, Beijing, 100190, PR China. E-mail: wangshu@iccas.ac.cn;
Fax: +86 10 6263 6680; Tel: +86 10 6263 6680
w Electronic supplementary information (ESI) available: Details
for the preparation and characterization of G1–G4. See DOI:
10.1039/b817788k
Scheme 1 Synthetic reaction of PPV derivative from monomer
and preparation of DNA/SP–PPV hydrogels. Four DNA/SP–PPV
hydrogels using feed molar ratios of monomer to DNA bp of 0.5, 0.75,
1.0 and 1.25 were obtained as noted as Gel 1, Gel 2, Gel 3 and Gel 4,
respectively.
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Chem. Commun., 2009, 641–643 | 641

Fig. 3 (a) Circular dichroism of wet DNA/SP–PPV hydrogels Gels
1–4. The spectra are normalized with respect to the intensity of the
band at 275 nm. (b) Gel electrophoresis of DNase I digestion on DNA
and Gel 2.
that native DNA was maintained in its B-DNA form in the
DNA/SP–PPV hydrogels. Noted that the intensity ratio of
the negative CD band at 245 nm to positive one at 275 nm
(I245 nm/I275 nm) decreases gradually with increasing the feed
molar ratio of PPV monomer to DNA in DNA/SP–PPV
hydrogels, which shows that higher cross-linker amount can
produce the entangled DNA assembly efficiently and the
helicity of the DNA is reduced. Considering the optical
properties and swelling degree together, Gel 2 was chosen
for the following experiments.
Fig. 1 Swelling, optical properties and morphologies of DNA/SP–PPV
hydrogels: (a) dried Gel 2, (b) wet Gel 2 swollen in water for 12 h, (c)
SEM image of Gel 2, (d) fluorescent microscope image of wet Gel 2.
by adjusting the feed molar ratios of monomer to DNA bp. As
shown in Fig. 2, the swelling degree (Q) decreases with
increasing feed molar ratios of monomer to DNA and reaches
a plateau after feed molar ratio of 1.0. More specifically, the
Q is 963 for Gel 1 at the lowest feed molar ratios of monomer
to DNA bp; whereas at the highest feed molar ratio, the Q is
only 248 for Gel 4. Both the compatibility of the polymer
chains to water media and the crosslinking density of
the networked structures play a key role in the swelling of
hydrogels. Decreasing the feed molar ratio of monomer
to DNA bp results in the increase of the swelling ability of
DNA/SP–PPV hydrogel. We noted that stable hydrogel
networks cannot form if the feed molar ratio of monomer to
DNA bp is lower than 0.5. As shown in Fig. 2, the best
fluorescence quantum yield is obtained for Gel 2 (4.5%) with
feed molar ratio of 0.75. Fig. 3(a) shows the CD spectra of the
pristine DNA at pH 7.0 and pH 12.6 (the pH of the poly-
merization reaction solution) and four DNA/SP–PPV hydro-
gels Gel 1, Gel 2, Gel 3 and Gel 4. The CD spectra of DNA
itself and hydrogels show characteristic feature of B-form
DNA that consists of a positive band around 275 nm and a
negative signal at 245 nm.20 These findings provide evidence
To investigate the stability of Gel 2, the effects of DNase,
temperature and ultrasound on it were studied. Fig. 3b shows
that pristine DNA could be digested by DNase I, while the
DNA in DNA/SP–PPV hydrogel almost did not digest. This
result indicates that the DNA in hydrogel was protected by
SP–PPV and could not be exposed to the DNase I. Fig. S1a
(ESIw) shows the pictures of Gel 2 at four different tempera-
tures. For native DNA, the melting temperature is about
87 1C. The Gel 2 was stable even at 90 1C, and collapsed
until 98 1C. A higher melting transition was observed in
DNA/SP–PPV hydrogel than native DNA. Fig. S1b (ESIw)
shows the photographs of Gel 2 before and after treatment
under ultrasound for 5 h. It was clear that the DNA/SP–PPV
hydrogel was stable under continuous ultrasonic irradiation.
Due to the synergistic combination of DNA and conjugated
polymer, the hybrid hydrogel was stable to heat, ultrasonic
and DNase digestion to some extent. This significant feature
imparts the DNA/SP–PPV hydrogel to possibly be exploited
in biological applications.
Inspired by these unique advantages of DNA/SP–PPV
hydrogel, we explored it for use as a platform to monitor
controlled drug release. In this study, we first prepared a
porous material by lyophilizing wet Gel 2 where the water
was removed by the process of freeze drying under vacuum.
The DNA/SP–PPV material exhibits strong fluorescence.
Upon loading the drug with fluorescence quenching ability
by diffusion, the fluorescence of DNA/SP–PPV is efficiently
quenched. After the release of the drug, its fluorescence is
recovered. Thus the release of drug can be monitored by
observing emission changes of DNA/SP–PPV hydrogel.
In our experiments, antihypertensive nicardipine hydro-
chloride containing one nitro group was chosen as the drug
that is a highly efficient electron-transfer quencher.21,22 There
is one amino group in the drug which exhibits one positive
Fig. 2 Swelling degrees and fluorescent quantum yields of DNA/SP–PPV
hydrogels as a function of feed molar ratio of monomer to DNA bp.
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642 | Chem. Commun., 2009, 641–643

In summary,
a
novel class of fluorescent DNA–
poly(phenylenevinylene) hybrid hydrogels have been prepared
by in situ polymerization of monomer in the presence of salmon
DNA. These hybrid hydrogels offer the possibility of exploring
unusual physicochemical and/or biological properties owing to
the combination of DNA with conjugated polymers. Fine
tuning of the optical properties and swelling behaviors of these
DNA/SP–PPV hydrogels can be accomplished by adjusting
the feed molar ratios of monomer to DNA. Due to the
synergistic combination of DNA and conjugated polymer,
the hybrid hydrogel was stable to heat, ultrasound and DNase
digestion to some extent. These DNA/SP–PPV hydrogels are a
new class of materials that can be exploited in the biomedical
field, such as monitoring drug loading and release by fluores-
cence technique.
The authors are grateful to the ‘‘100 Talents’’ program of
the Chinese Academy of Sciences, the National Natural
Science Foundation of China (No. 20725308 and 20721061)
and the Major Research Plan of China (No. 2006CB932102).
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Fig. 4 (a) Monitoring the releasing of drug from Gel 2 by observing
changes of emission intensity of Gel 2 after immersing into phosphate
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