Applications of pH sensor using a covalent bond indicator based on containing functional group copolymer

Article abstract of DOI:10.1080/15421400500366779

The purpose of this study was to immobilize copolymer that is able to covalent bonding with pH indicator. The pH sensitive polymers were synthesized with copolymers that are consisted of acryloylamino acid and chloroalkyl acrylate with MMA to get the optical fiber matrix. Fluoresceinamine indicator, containing amino group was immobilized covalently on prepared copolymers. The prepared pH sensing copolymers were measured sensitivity by UV-Visible spectroscopy. The pH-dependent value of copolymers was examined in the pH range of 2.00 ~ 12.00 HCl/NaOH solution at room temperature. As the length side chain and MMA molar ratio of the copolymers increases, the intensity decreases. Compared with imine group of copolymer-dye derivatives, amide group derivatives have a bathochromic shift on the UV-Visible spectrum.

Full text of DOI:10.1080/15421400500366779

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Applications of pH sensor Using
a Covalent Bond Indicator
Based on Containing Functional
Group Copolymer
Eun-Hee Kang a , Jin-Kyoung Ham a , Jong-Min Shim a
, Jin-Kook Lee a & Mi-Ra Kim b
a Department of Polymer Science and Engineering ,
Pusan National University , Busan, Korea
b Department of Polymer Science and Engineering
and Center for Plastic Information System , Pusan
National University , Busan, Korea
Published online: 23 Aug 2006.
To cite this article: Eun-Hee Kang , Jin-Kyoung Ham , Jong-Min Shim , Jin-Kook Lee &
Mi-Ra Kim (2006) Applications of pH sensor Using a Covalent Bond Indicator Based on
Containing Functional Group Copolymer, Molecular Crystals and Liquid Crystals, 445:1,
285/[575]-290/[580], DOI: 10.1080/15421400500366779
To link to this article: http://dx.doi.org/10.1080/15421400500366779
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Mol. Cryst. Liq. Cryst., Vol. 445, pp. 285=[575]–290=[580], 2006
Copyright # Taylor & Francis LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400500366779
Applications of pH sensor Using a Covalent Bond
Indicator Based on Containing Functional Group
Copolymer
Eun-Hee Kang
Jin-Kyoung Ham
Jong-Min Shim
Jin-Kook Lee
Department of Polymer Science and Engineering, Pusan National
University, Busan, Korea
Mi-Ra Kim
Department of Polymer Science and Engineering and Center
for Plastic Information System, Pusan National University,
Busan, Korea
The purpose of this study was to immobilize copolymer that is able to covalent
bonding with pH indicator. The pH sensitive polymers were synthesized with copo-
lymers that are consisted of acryloylamino acid and chloroalkyl acrylate with
MMA to get the optical fiber matrix. Fluoresceinamine indicator, containing
amino group was immobilized covalently on prepared copolymers. The prepared
pH sensing copolymers were measured sensitivity by UV-Visible spectroscopy.
The pH-dependent value of copolymers was examined in the pH range of
2.00 ꢀ 12.00 HCl=NaOH solution at room temperature. As the length side chain
and MMA molar ratio of the copolymers increases, the intensity decreases. Com-
pared with imine group of copolymer-dye derivatives, amide group derivatives
have a bathochromic shift on the UV-Visible spectrum.
Keywords: MMA copolymer; pH sensor; pH-sensitivity dye; physiological pH range
The authors of this paper would like to thank Brain Korea 21 project and Pusan
National University Research Grant for financial support of this research.
Address correspondence to Jin-Kook Lee, Department of Polymer Science and Engin-
eering, Pusan National University, Busan 609-735, Korea. E-mail: leejk@pusan.ac.kr
285=[575]

286=[576]
E.-H. Kang et al.
INTRODUCTION
The pH intensity in tissue and blood vessels of human is desirable in a
wide variety of clinical diagnostic studies. Despite the important para-
meter of pH measurement, the development of micro-pH electrode has
the disadvantage of being rigid, no-disposable, and requires a refer-
ence electrode and electrical connection. On the other hand, fiber-optic
chemical sensors (FOCS) using optical properties can offer several
advantages over traditional sensors. The measurement can be per-
formed directly in the sample without electromagnetic interference.
They can also be miniaturized and the multiplexed signal can be
transmitted over the long distances without significant loss to realize
the remote area detection [1,2]. The One challenge in developing
FOCS is to immobilize pH sensing agent in optical fibers, which mea-
sures the hydrogen ion activity. The pH sensor have been designed
and developed which are available for tissue and blood pH measure-
ments in the physiological range of pH 6.8 ꢀ 7.4 [3].
In the device of a typical fiber optic pH sensor, a reagent phase must
be on the end of a fiber optic [4]. Mere attachment of the reagent phase
to the surface of an optical fiber results in no detectable signal due to
the limited area available. Interaction with analyte leads to a change
in the optical properties of the reagent phase, which is probed and
detected through the fiber optic. The reagent phase is polymer matrix
or other supports on which a pH sensor based on an immobilized dye
whose optical properties vary with pH [5,6]. The dye must be cova-
lently attached to the polymer matrix or other supports with a spacer.
Covalent binding of the sensing agent can minimize leaking out prob-
lem leading life-time improvement.
The function of the spacer is to keep the dye molecule at a sufficient
distance from the polymer surface so that it measures a true pH
response with the fast response and does not measure it the laminar
sublayer close to the surface. The spacer ideally should be hydrophilic
so that it would not coil towards the surface [7].
The purpose of this study is to immobilize copolymer which is able to
covalent bonding with pH indicator, with an emphasis on the control of
the spacer length between the dye molecule and polymer surface by using
the different molecular, and to examine a difference of sensitivity func-
tional group which is formed between the dye molecule and the polymer.
EXPERIMENTAL
Fluoresceinamine, aminoacids, chloroalkylalcohol and acryloyl
chloride was used as received from Sigma-Aldrich without further

Acrylate Copolymer Derivatives with pH sensor
287=[577]
SCHEME 1 Synthesis of the copolymer for acryloylamino acid and MMA.
DMAP: 4-Dimethylaminopyridine; DCC: 1,3-Dicyclohexylcarbodiimide.
purification. Methylmethacrylate (MMA) was obtained from Acros
Chem. and used after purification with NaOH(aq) (10%, w=v) and dis-
tillation under reduced pressure.
FT-IR spectra was used to JASCO 460 Plus spectrometer using a
KBr pellet, and 1H-NMR spectra were recorded on a Varian
300 MHz. UV-Visible spectra of intensity were taken on a UVIKON
860 spectrophotometer. ACCMET model 10 pH meter was used to
monitor pH in the tested solution.
Acrylate derivates were synthesized as shown in Scheme 1 and
Scheme 2. Radical copolymerization by MMA was carried out in 1,4-
dioxane at 70ꢁC with BPO as a thermal initiator. The copolymers were
purified by precipitation from filtered methanol, and dried under
vacuum at room temperature.
A wide range of solution covering pH from 2.6–11.8 was prepared
with de-ionized water using of hydrochloric acid (0.1 M) and sodium
SCHEME 2 Synthesis of the copolymer for chloroalkyl acrylate and MMA.

288=[578]
E.-H. Kang et al.
hydroxide (0.1 M). The dye-copolymers were made into concentration
of 10À1 M in DMF solution. As the pH of the solution varies, optical
absorption peak was taken measurements with UV-Visible spectro-
photometer.
RESULTS AND DISCUSSION
The structure of monomers, copolymers and copolymer-dye derivatives
1
were characterized by various instrumental methods such as H-NMR,
FT-IR, and UV-Visible spectroscopy. In the first place, the FT-IR
spectrum of monomers were able to find the strong carbonyl bond at
1649 cmÀ1 in amide group and the carbonyl stretching vibration at
1731 cmÀ1 in ester group, disappearing of ÀOH peak at 3400 cmÀ1. The
copolymers were found from the result that a peak of vinyl group
2
(C C, sp streching) disappeared from 3100 cmÀ1 in the FT-IR and
=
1
5 ꢀ 6 ppm in the H-NMR spectrum. The FT-IR spectrum copolymer
indicators were found out the bending of aromatic ring at 1630 cmÀ1and
and 1447 cmÀ1and ÀOH peak of alcohol at 3442 cmÀ1.
The pH responses obtained for the fluoresceinamine dye immobi-
lized in the copolymers in solution are shown in Figure 1. Chloroalkyl
acrylate copolymer derivatives indicator have been a maximum
absorption band at 491 nm that is associated with the deprotonated
form of the dye. Contrary to theirs, acryloylamino acid copolymer
derivatives indicator were found at 530 nm. The reason why acryloyla-
mino acid copolymer indicator derivatives have got bathochromic
shift is that between polymer and dye indicator have influence on
FIGURE 1 Absorption spectra of the sensor dye immobilized in copolymer for
several pH values: (a) poly(MMA-co-acryloylaminobutylate) fluoresceinamine;
(b) poly(MMA-co-2-chloroethyl acrylate) fluoresceinamine.

Acrylate Copolymer Derivatives with pH sensor
289=[579]
delocalization of electron by increasing of conjugation. Additionally,
when the solution pH increases, the increase of responded absorption
at 491 nm and 530 nm was observed individually. It is occurred when
the dye makes the deprotonated form. Also it is shown that the absor-
bance of the sensor dye immobilized in a short chain is higher than
that of the sensor dye immobilized in a long chain (Fig. 2). Based on
this result, we can predict that as the chain length of the copolymer
is longer, the absorbance intensity is weaker. To put it more con-
cretely, as increasing side chain length seems to be decrease reactivity
about MMA.
We varied the molar ratio of the MMA and acrylate monomers in
the copolymerization from 9:1 to 1:9 (MMA: chloroalkyl acrylate,
MMA: acryloylamino acid). The response curve of the absorbance is
shown in Figure 2. As the molar ratio of MMA increases, the
absorbance intensity decreases as expected. It clearly shows that the
sensing dye is the attached fluoresceinamine and the quantity of
the sensing dye affects the intensity.
The pKa of the immobilized copolymer derivatives indicator were
calculated by the change of absorbance at 491 nm and 530 nm with
pH respectively. In case of chloroalkyl acrylate copolymer derivatives
indicator, the absorbance changes gradually in pH region of 2.5–5.0. In
pH region of 5.0–8.0, the absorbance changes rapidly with the pH.
From this calibration curve, we can conclude that the immobilized
fluoresceinamine has an average pKa of 6.7 that is in the physiological
pH range. The absorbance change is observed from 2.0 to 12. Because
of large change by absorbance in pH region of 5.0–8.0, it is possible to
measure blood pH with chloroalkyl acrylate copolymer derivatives
FIGURE 2 There is UV-Visible absorption spectrum; (a) as the chain length
of the copolymer in the feed molar ratio MMA:chloroalkyl acrylate, 9:1; (b) as
the feed molar ratio MMA and 4-Chlorobutyl acrylate.

290=[580]
E.-H. Kang et al.
indicator. On the contrary, acryloylamino acid copolymer derivatives
indicator have an average pKa of 8.9. It is presumed that bulky
volume of molecule and limited reactivity with MMA has an effect
on the reaction.
CONCLUSIONS
The pH sensing materials had been prepared by a combination of
acrylate monomers and fluoresceinamine. We investigated the effect
of alkyl length in copolymers-indicator. As the length of side group
increases, the absorbance decreased. As the alkyl chain and MMA
molar ratio of the copolymer increases, the intensity decreases.
Compared with imine group of copolymer-dye derivatives, amide
group derivatives have a bathochromic shift on the UV-Visible
spectrum.
These results led us to the conclusion that we can control the inten-
sity of the sensing dye. This study will be to provide measurements for
pH sensor matrix in devices in the future.
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