Fluorescence and colorimetric detection of ATP based on a strategy of self-promoting aggregation of a water-soluble polythiophene derivative

Article abstract of DOI:10.1039/c5cc01713k

A sensitive fluorescent and colorimetric dual-modal probe for the detection of ATP has been developed based on a strategy of self-promoting aggregation of a cationic polythiophene derivative bearing anthracene groups in the side chain with a detection limit as low as 10^-9 M. This journal is

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Sensitive fluorescent and colorimetric detection of ATP
based on a strategy of self-promoting aggregation of a
water-soluble polythiophene derivative
Cite this: DOI: 10.1039/x0xx00000x
Dandan Cheng,a Yandong Li,b Jing Wang,a Yujiao Sun,a Lu Jin,a Chenxi Lib and Yan Lu*a
Received
Accepted
DOI: 10.1039/x0xx00000x
www.rsc.org/
A sensitive fluorescent and colorimetric dual-modal probe for
the detection of ATP have been developed based on a strategy
of self-promoting aggregation of a cationic polythiophene
derivative bearing anthracene groups in the side chain with a
detection limit as low as 10-9 M range.
colorimetric dual-modal probe for the detection of ATP by
taking advantage of a strategy of self-promoting aggregation of
a cationic copolymer CPT bearing anthracene groups in the
side chain. The overall strategy is illustrated in Scheme 1. Upon
mixing, electrostatic interactions bring together the optical
probe CPT and ATP. The spatial constraints with in CPT/ATP
aggregates force the CPT adopt a more planar conformation,
subsequently resulting in a aggregation mode of PT backbones.
During this process, anthracene groups with large aromatic
plane in the side chain of CPT will promote the polymer
The detection of adenosine triphosphate (ATP) has drawn
considerable attention in recent years,1 because ATP plays
important roles in cell biology.2-4 Visible detection and imaging
of ATP can facilely offer useful information about the
production and consumption of ATP in real time.5 Accordingly,
a number of fluorescent or colorimetric sensors for ATP have
been designed and reported.6 However, It remains a challenge
to find new approaches that could improve the simplicity,
selectivity, and sensitivity of ATP detection.
aggregation through interchain
π-π stacking interaction to
provide more sensitive sensing for ATP compared with the
cationic PT1 system (Scheme 1). Attempts have also been made
to open a new and general way for improving the sensitivity of
PT-based probes for small molecules as well as to understand
the copolymer CPT/ATP supracomplex formation by the use of
different techniques and through fine-tuning experimental
conditions.
Recently, a new sensory material based on water-soluble
polythiophene (PT) derivatives have received extensive
attention because of their sensitive chain conformation to
external stimuli,7-12 providing an unique potential for
colorimetric and fluorometric dual-output. Up to date, several
kinds of cationic PT derivatives have been synthesized and
applied to be colorimetric and fluorescent probes for the
detection of DNA and proteins,12e,13 monitoring the helicity and
conformational transition in polysaccharides,14 and sensing
small bioanions such as nucleotides,6i,7a folic acid and so on.15-
17
It is easy to find that various biomacromolecules, such as
DNA and protein, can bind strongly with PT chains, providing
efficient colorimetric and fluorescent signal outputs, whereas
small analytes with simple structures cannot induce distinct
conformational changes and aggregation of PT-based probes
due to the relative weak interactions between analytes and PT
chains, resulting in the weak optical outputs. To improve the
sensitivity for sensing some small anions with PT-based probe
system, a strategy based on the premodification of analytes to
increase the interactions between analytes and probe has been
developed.16-18 Herein, we develop a sensitive fluorescent and
Scheme 1 Schematic illustration of the detection of ATP based on a self-
accelerating aggregation of CPT.
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VJieowuArrtnicalelONnlainme e
DOI: 10.1039/C5CC01713K
Copolymer probe CPT was synthesized by the chemical
oxidative polymerization with FeCl3 in chloroform of 3-(4-
Methyl-3’-thienyloxy)propyltrimethyl-ammonium
with
4-[9-anthrylcarboxy(N-methylamino)]thiophene,14a,19
Synthetic details are presented in the ESI.
bromide
Fig. 3 Absorption spectra of CPT (100
ꢀ
M) in water in the absence of anionic
guest and (a) in the presence of an equimolar amount of ATP, ADP, or AMP, or
(b) in the presence of an equimolar amount of ATP, UTP, or phosphate.
To address the molecular mechanism beyond this
observation, the influence of the nucleotides those bear
different numbers of phosphate groups (negative charges) and
different nucleobase moieties on the polymer aggregation was
examined. The changes in the absorption spectra of CPT in
water upon addition of biologically important anions such as
ADP, AMP, UTP, UMP, as well as chloride and various
phosphate ions (as sodium salts) were shown in Fig. 2 and Fig.
3. As shown in Fig. 2, after addition of an equimolar amount of
these anions to aqueous solutions of CPT, most of the solutions
Fig. 1 UV-vis titration spectra of CPT (100
increasing amounts of ATP. [ATP] = 0, 4, 8, 12, 16, 20, 24, 28, 32, 36, 44, 52, 60,
68, 80 M from top to down.
ꢀM) in tris-HCl buffer solution with
ꢀ
Titration of CPT with ATP in tris-HCl buffer solution (2
mM, pH 7.4) at 23 C was monitored by absorption
spectroscopy. As shown in Fig. 1, the absorption maximum of
CPT appears at around 450 nm ( = 7.08
103 M-1 cm-1),
which is associated to the * transition of random-coiled
polymer chains. Upon adding increasing amounts of ATP, the
absorption maximum is gradually red-shifted from 450 to 588
nm together with solution color change from yellow to deep
violet. The remarkable red-shift (by 138 nm) and the
appearance of characteristic vibronic bands at 540 and 588 nm
were related to the changes in the conformation from
nonplanar-to-planar and aggregation mode of PT backbones as
demonstrated by dynamic light scattering (DLS) (Fig. S1, ESI).
remained yellow with λmax
< 450 nm except for those that
°
contained ADP and UTP, which gave amber color solutions
with shifts of the absorption maximum to about 580 and 500
nm associated with vibronic bands, respectively. The most
remarkable effect was noted, however, upon addition of ATP,
which gave a deep violet solution (Fig. 2). The dramatic color
change of CPT upon addition of ATP provides a very simple
means for naked-eye discrimination of ATP from various
nucleotides in aqueous solution. From Fig. 3a, the largest
absorbance response of aqueous CPT solution was observed
upon the addition of an equimolar amount of ATP, whereas
unconspicuous changes occurred upon blending with adenosine
monophosphate (AMP), suggesting that the amount of negative
charge on the analyte plays a crucial role in the polymer
aggregation. However, only the presence of inorganic
polyphosphate ion does not induce a distinct change in the color
of the solution of CPT and no supramolecular aggregate is
formed in the mixture (Fig. 3b). Thus, it is very important to
consider the effect of different nucleotides on the aggregation
of CPT. As shown in Fig. 3b, relatively smaller spectral
changes were observed upon exposure of CPT to uridine
triphosphate (UTP) and various inorganic phosphates,
indicating that the nucleobase adenine with a larger aromatic
plane facilitated the polymer aggregation through hydrophobic
effects.
ε
×
π-π
It was noted that titration reached saturation at [ATP] = 80 ꢀM
(0.8 equiv), which is far below that in the PT1 system (5 equiv)
in water,6i signifying that aggregation of CPT chains were
facilitated upon noncovalent binding with ATP which is
probably related to the interchain
π-π stacking interaction
between anthracene groups (Scheme 1). Benesi-Hildebrand
analysis of the absorption changes (Fig. S2, ESI) showed a near
1:1 stoichiometry for the complex formed between CPT and
ATP with a binding constant of Kassoc = 7400 M-1 in buffer
solution.20
We then examined the circular dichroism (CD) spectral
changes of CPT in water with a variety of nucleotides (Fig. S6,
ESI). CPT itself is optically inactive, and no CD pattern in the
π-π* transition region was detected, which indicates that CPT
adopts an achiral random-coiled conformation in water. Upon
binding with ATP, an intense split-type induced CD (ICD) in
Fig. 2 Changes in the color of solutions of CPT (100 ꢀM) in water induced by the
addition of an equimolar amount of various anions.
the
π-π* transition region was observed, suggesting the
formation of chiral superstructures between CPT and ATP.12b
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DOI: 10.1039/C5CC01713K
In addition, the ICDs intensities increase gradually with side-chain steric/electrostatic repulsive and interchain attractive
increasing the concentrations of ATP (Fig. S7, ESI).
interactions of PTs. This strategy is expected to be applied to
other conjugated polyelectrolyte (CPE)-based sensing system.
This work was sponsored by NSFC (51373122 and
21074093) and NCET-12-1066.
Notes and references
a
School of Materials Science & Engineering, Tianjin University of
Technology, Tianjin, 300384, China. E-mail: luyan@tjut.edu.cn
b
Key Laboratory of Functional Polymer Materials, Institute of Polymer
Chemistry, College of Chemistry, Nankai University, Tianjin, 300071,
China.
Electronic Supplementary Information (ESI) available: Experimental
details and characterization data. See DOI: 10.1039/c000000x/
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Fig. 4 Fluorescent titration spectra of CPT (100
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fluorescence was detected upon addition of an equimolar
amount of ADP and AMP, respectively (Fig. S8, ESI). These
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more effective in the presence of ATP than with the use of
other nucleotides such as ADP, AMP, UTP and UMP.
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use of the Stern–Volmer equation (Fig. S12, ESI). The Stern–
Volmer constant, KSV, determined from the linear portion of a
plot of F0/Fi versus [ATP] is of 4.46
The detection limit, based on fluorescence quenching, for ATP
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10-9 M.21
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and fluorescent dual-response probe for the detection of ATP at
physiological pH conditions based on a strategy of self-
promoting aggregation of a PT derivative. Although further
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