Development of a perchlorate sensor based on Co-phthalocyanine derivative by impedance spectroscopy measurements

Article abstract of DOI:10.1016/j.orgel.2014.10.048

In this work, we have prepared a perchlorate sensor based on cobalt phthalocyanine derivative molecules. The membrane was deposited onto gold substrates using dip-coating method. Adhesion and morphological properties have been studied using contact angle measurements. Then, the sensitivity, the detection range and the detection limit were determined using electrochemical impedance spectroscopy (EIS) measurements. The sensor was also studied specificity towards interfering ions nitrate (NO3-), carbonate (CO32-) and sulfate (SO42-) to show the specificity of the membrane. The impedance behavior of the perchlorate sensor (gold/membrane) has been modeled by an equivalent electrical circuit using a modified Randles model for better understanding the phenomena present at the interface membrane/electrolyte.

Full text of DOI:10.1016/j.orgel.2014.10.048

Organic Electronics 16 (2015) 77–86
Contents lists available at ScienceDirect
Organic Electronics
journal homepage: www.elsevier.com/locate/orgel
Development of a perchlorate sensor based on
Co-phthalocyanine derivative by impedance spectroscopy
measurements
M. Braik a,b, C. Dridi a,b, , A. Ali c, M.N. Abbas c, M. Ben Ali a, A. Errachid d
⇑
a Université de Sousse, ISSAT de Sousse, Cité Ettafala, 4003 Ibn Khaldoun Sousse, Tunisia
b Université de Monastir, LIMA, Faculté des Sciences de Monastir, 5019 Monastir, Tunisia
c Analytical Laboratory, Department of Applied Organic Chemistry, National Research Centre, Cairo, Egypt
d Université de Lyon, Lyon1, Institut des Sciences Analytiques (ISA), UMR 5280, 5 Rue de la Doua, 69100 Villeurbanne Cedex, France
a r t i c l e i n f o
a b s t r a c t
Article history:
In this work, we have prepared a perchlorate sensor based on cobalt phthalocyanine deriv-
ative molecules. The membrane was deposited onto gold substrates using dip-coating
method. Adhesion and morphological properties have been studied using contact angle
measurements. Then, the sensitivity, the detection range and the detection limit were
determined using electrochemical impedance spectroscopy (EIS) measurements. The sen-
sor was also studied specificity towards interfering ions nitrate ðNOꢀ3 Þ, carbonate ðCO32ꢀÞ
and sulfate ðSO24ꢀÞ to show the specificity of the membrane. The impedance behavior of
the perchlorate sensor (gold/membrane) has been modeled by an equivalent electrical cir-
cuit using a modified Randles model for better understanding the phenomena present at
the interface membrane/electrolyte.
Received 18 September 2014
Received in revised form 21 October 2014
Accepted 29 October 2014
Available online 11 November 2014
Keywords:
Chemical sensor
Cobalt(II) phthalocyanine derivative
Perchlorate
Gold electrodes
Ó 2014 Elsevier B.V. All rights reserved.
Electrochemical impedance spectroscopy
(EIS)
1. Introduction
thyroid gland and it is, therefore, associated with the dis-
ruption of its function. The perchlorate and iodide ions
Bio/chemical sensors are bio-analytical tools at the
boundaries of biotechnology and analytical chemistry.
They have proved to be valuable alternatives to classical
analytical techniques and research methods. Biosensors
have found applications in various areas, such as medicine,
environment, food, and pharmaceutical industry. They
potentially combine ease of use, fast analysis, and low cost.
Cobalt-Phthalocyanine (Co(II)Pc) derivatives have already
found applications in the design of chemical sensors based
on the use of an electrochemical transducer.
have a similar size and it can be taken up in place of the
iodide ion through the mammalian thyroid gland and
affect the hormones production [1–3]. In this way, perchlo-
rate causes abnormalities in child development and the
development of thyroid cancer. As a result, it is a frequent
task of many analytical laboratories to determine the per-
chlorate anion in product formulations for quality control,
in waste waters for environmental control, and in food
products for contamination control.
The determination of perchlorate ions has been carried
out directly or indirectly by a variety of classical and
instrumental methods, including volumetric titrations [4],
gravimetry [5], spectrophotometry [6,7], atomic absorp-
tion spectrometry [8], potentiometry [1,9,10], surface-
enhanced Raman spectroscopy [11], ion chromatography
(IC) with conductivity detection [12], ion chromatogra-
phy–mass spectrometry [13], and fluorescence [14].
Perchlorate ions present an environmental health risk
to humans as it interferes with iodine uptake by the
⇑
Corresponding author at: Centre for Research on Microelectronics and
Nanotechnology of Sousse, Technopole of Sousse B.P. 334, Sahloul, 4034
Sousse, Tunisia. Tel.: +216 98 940 256; fax: +216 73 822 300.
E-mail address: dridi2@yahoo.fr (C. Dridi).
http://dx.doi.org/10.1016/j.orgel.2014.10.048
1566-1199/Ó 2014 Elsevier B.V. All rights reserved.

78
M. Braik et al. / Organic Electronics 16 (2015) 77–86
Despite their good sensitivity, most of these methods
require expensive and sophisticated instruments and also
well-controlled experimental conditions, for e.g. tedious
sample preparation.
The electrochemical impedance spectroscopy (EIS)
technique has recently received attention in the field of
analytical sciences and it has become of compulsory use
to describe and investigate kinetics of the electrochemical
interface for any electrode system [15,16].
ran (THF), lithium perchlorate (LiClO4), and piranha solu-
tion (1:3 hydrogen peroxide (H2O2):sulfuric acid (H2SO4))
were purchased from Sigma Aldrich.
The CoPcAP molecules (Fig. 1) were used in this work.
These were synthesized and purified according to the fol-
lowing synthesis route shown in Fig. 2.
The synthesis of the mono derivatives of phthalocya-
nine is always a challenge. The cobalt monnitro phthalocy-
anine (II) was prepared using 4-nitrophthalic anhydride
and phthalic anhydride in a 1:7 ratio according to example
15 in the procedure previously reported by Baumann et al.
[22]. Our approach is also a modification of the one used
for the preparation of the monocaboxylated phthalocya-
nines [23]. Here, we have chosen not to carry out purifica-
tion after the condensation reaction (Fig. 2) but after the
reduction reaction. The reduction of the mononitro cobalt
phthalocyanine (CoMNPc) to the monoamino derivative
(CoMAPc) (III) was carried out using sodium sulfide as
described in [24]. The CoMAPc dark green solid product
was collected by filtration and washed with methanol,
0.1 M of HCl, 0.1 M of NaOH, and DI water. The product
was purified by passing it through a silica gel column,
using a 1:1 THF:DCM mixture as the eluting solvent. Cobalt
monoaminophthalocyanine-Acrylate polymer (I) was
prepared by amidation [25] of the carboxylic group in the
carboxyethyl-n-butyl Acrylate polymer (IV) with the
CoMAPc using CDI in CH2Cl2.
In our group, we have used a large variety of organic
sensing ionophores and polymeric compounds as sensitive
membranes for ion detection [15–21].
In this work, we present the development of a chemical
sensor based on Co(II)MAPc-Acrylate polymer (CoPcAP)
functionalized onto gold (Au) transducers for the detection
of perchlorate anions. In the first step, we have character-
ized the pre-cleaned electrode surface by contact angle
measurements (CAM) and we have optimized the fabrica-
tion parameters of the Au/CoPcAP sensor (i.e. solution
and conditions). Afterwards, we have studied the sensor
by EIS technique. This technique allows the investigation
of both resistive and capacitive properties. Moreover, to
analyze the phenomena that is occurring at the interface.
For EIS analysis, we have optimized the different measure-
ments parameters (frequency range, polarization, etc.).
After optimization of the measurement conditions, the fab-
ricated sensor was characterized by EIS technique. The
impedance behavior of the structures Au/membrane has
been modeled by an equivalent circuit for improved
understanding of the phenomena present at the interface
membrane/electrolyte. The study of the sensors response
in function to perchlorate and the determination of the
metrological parameters are discussed. Finally, we have
studied the specificity of our chemical sensor by EIS mea-
surements by observing the response for other interfering
anions when compared with perchlorate.
Phosphate-buffered saline (PBS) solution (0.01 M, pH 7)
was prepared using appropriate amounts of K2HPO4 and
KH2PO4 dissolved in DI water.
2.2. Instrumentation
2.2.1. Electrochemical impedance spectroscopy
All electrochemical experiments were conducted inside
a Faraday cage at 25 3 °C. EIS measurements were carried
out in an electrochemical cell with a volume of 25 mL and
consisted of three electrodes: (1) the working electrode
SiO2/Si/SiO2/Ti/Au (0.3 cm2); (2) a platinum auxiliary elec-
trode (0.5 cm2); and (3) a saturated calomel electrode
(SCE) as a reference. The measurements were recorded
with PBS solution (0.01 M at pH 7) as an electrolyte, a fre-
quency range between 100 kHz and 100 mHz at a potential
2. Materials and methods
2.1. Materials
All the chemicals used were of analytical reagent grade.
Deionized (DI) water was used throughout. Tetrahydrofu-
H3C
n
m
CH3
O
O
O
O
O
N
H
CH3
N
N
N
N
Fe
Co
N
N
N
N
Fig. 1. Cobalt phthalocyanine-C-mono amido-butyl Acrylate carboxyl acid.

M. Braik et al. / Organic Electronics 16 (2015) 77–86
79
Fig. 2. Synthesis routes for the production of cobalt phthalocyanine-C-mono amido-butyl Acrylate carboxyl acid.
of ꢀ300 mV and with an amplitude of 10 mV sinusoidal
3. Results and discussion
modulation. An Autolab PGSTAT30 potentiostat/galvano-
stat was connected to a computer and controlled by the
frequency response analyzer (FRA) software. The software
was used for the acquisition and analysis of the impedance
data.
3.1. Contact angle measurements
To investigate the gold surface quality a wettability
study was performed. Before and after thin film deposition
was analyzed with water as the liquid probe. Fig. 3 shows
the evolution of the contact angle as a function of the treat-
ments performed on the gold surface. In the first step, the
gold surface was cleaned with acetone and the contact
angle was measured at 77.8°. This value shows the hydro-
philic properties of the surface. In the second step, the sur-
face was activated with piranha solution for 3 min. Here,
the contact angle value decreased to 53.0°, which shows
2.2.2. Contact angle measurement
Wettability measurements were performed with
Digidrop apparatus GBX (France) in order to characterize
the quality of the deposited film. Firstly, 5 L of DI water
a
l
was deposited onto the thin film surface. Afterwards, the
water droplet behavior obtained on the surface was
acquired with a digital camera.
2.3. Membrane preparation and sensor construction
For construction of the sensor, in the first step, we have
used gold electrodes as the transducer with a surface area
of ꢁ0.3 cm2. These electrodes were cleaned with piranha
solution for 2 min in order to activate the surface [26].
The electrodes were then rinsed with ultra-pure water to
remove adsorbed species and, after that; the surfaces were
dried under nitrogen flow. For the second step, 4 mg of
CoPcAP was dissolved in 1 mL of THF and deposited onto
the gold electrodes by dip coating method. Finally, the thin
films were dried at room temperature for 24 h.
Fig. 3. Contact angle histogram of the gold surface.

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M. Braik et al. / Organic Electronics 16 (2015) 77–86
the improvement of the hydrophilic character on the sur-
face. From this, we can note that the adhesion of the mem-
brane on the gold surface is easiest and most important. In
the final step, the contact angle after the deposition of the
ionophore was measured and an increase of the contact
angle value was observed from 53.0° to 87.6°. This clearly
demonstrates that the surface has been functionalized,
and it indicates that the surface has decreased in its hydro-
philic properties.
3.0x104
2.5x104
2.0x104
1.5x104
1.0x104
Gold
Gold/Co(II)MAPc-Acrylate Polymer
5.0x103
0.0
3.2. EIS measurements
3.2.1. Optimization of the measurement conditions
0
1x104 2x104 3x104 4x104 5x104 6x104 7x104 8x104 9x104
Zreal (Ohm.cm-2)
From the electrochemical point of view, the solid elec-
trolyte interface behaves as the equivalent circuit, widely
described by the Randles circuit [27]. In such a model,
the diffusion or Warburg impedance ZW is in series with
the charge transfer resistance Rct and both are generally
in parallel with the double layer capacitance Cdl. A resis-
tance in series, Rs represents the resistance of the electro-
lyte solution. Several studies using different receptors
deposited on gold electrodes have shown the reliability
of this model [28,29].
The CoPcAP/Au/Ti/SiO2/Si/SiO2 structure was used to
determine the optimal experimental conditions, in terms
of voltage and frequency for the considered sensor. The
effect of polarization is significant at low frequencies. By
polarizing the electrode, we can substantially decrease
the values of the ZW. By polarizing the CoPcAP/Au/Ti/
SiO2/Si/SiO2 structure at ꢀ300 mV, as represented in
Fig. 4, the value of Rct was strongly decreased and
Fig. 5. Nyquist plots obtained for the gold electrode before and after
functionalization with Co(II)MAPc-Acrylate polymer. Frequency range:
100 kHz–100 mHz, an amplitude of 10 mV sinusoidal modulation, and
polarization potential of ꢀ300 mV in 0.01 M PBS (pH7).
9x104
8x104
7x104
6x104
5x104
4x104
3x104
2x104
100 10-3 Hz
841 10-3 Hz
Gold
Gold/Co(II)MAPc-Acrylate polymer
3000
Hz
100 10-3 Hz
1x104
0
3.0x106
0 mV
0,0
0,2
0,4
0,6
0,8
)
1,0
1,2
1,4
-100 mV
2.5x106
ω-1/2 (s-1/2
-200 mV
-250 mV
-300 mV
2.0x106
Fig. 6. Determination of the coverage rate of the gold electrode:
Zreal = f(xꢀ1/2).
1.5x106
1.0x106
consequently the ZW was minimized (Table 1). Therefore,
it was possible to improve the recognition process of CoP-
CPA membranes especially at low frequencies of
excitation.
5.0x105
0.0
3.2.2. Coverage rate determination of the gold electrode
Applying the same experimental conditions for EIS
measurements of the gold electrode (ꢀ300 mV of polariza-
tion, a frequency range between100 kHz and 100 mHz, and
with an amplitude of 10 mV), we have determined the
impedance behavior before and after functionalization
with CoPcAP (Fig. 5). To determine the coverage rate (h)
of the gold surface we have plotted the real impedance part
for before and after functionalization, this was made as a
function of the inverse of the square root of the sinusoidal
excitation pulsation (xꢀ1/2) (Fig. 6). In the low-frequency,
the linear range intercept is at xꢀ1/2 ? 0 with the real
impedance axis (ordinate axis) on ionic charge transfer
resistance (Rct) [30].
0.0
5.0x105
1.0x106
1.5x106
2.0x106
2.5x106
Zreal (Ohm.cm-2)
Fig. 4. Impedance spectra (in Nyquist presentation) of Co(II)MAPc-
Acrylate polymer/Au/Ti/SiO2/Si/SiO2 structure for different polarizations
vs saturated calomel reference electrode (SCE) (frequency range:
100 kHz–100 mHz and an amplitude of 10 mV sinusoidal modulation in
0.01 M PBS (pH7)).
Table 1
Warburg impedance variation as a function of the polarization potential.
Polarization (mV)
W (K O)
ꢀ100
ꢀ200
ꢀ250
ꢀ300
1196.10
155.40
75.78
From this, the coverage rate of the gold electrode was
obtained by Eq. (1) [31–34] and we have obtained a value
of 78.82%.
1.74

M. Braik et al. / Organic Electronics 16 (2015) 77–86
81
0.08
0.06
0.04
0.02
0.00
-0.02
-0.04
of 5 mM K3Fe(CN)6 in PBS (pH 7) solution. Fig. 7 shows the
cyclic voltammetry measurement of the Au/CoPcAP struc-
ture with a scan rate of 100 mV/s. We can observe redox
peaks due to Fe(CN)36ꢀ/4ꢀ (ꢁ100 mV) for the gold electrode
and the redox couple due to CoIII/CoII was observed at
ꢁ800 mV. The behavior of the cyclic voltammetry for
gold/CoPcAP was also noticed in the literature [35,36].
CoII/CoIII
Fe(CN)63-/4-
3.3.2. Impedance analysis of the functionalized gold electrode
In the presence of perchlorate ions, we noticed that at a
low frequency the impedance of the electrochemical sys-
tem decreases significantly with increasing concentrations
of ClOꢀ4 ions. In the Nyquist diagram (Fig. 8), the approxi-
mate form is a combination of two interfaces (semicircles).
It is important to note that the semicircles decreased
with increasing concentrations of perchlorate (for. i.e. a
decrease in Rct). It can also be noted that the most signifi-
cant variation of the impedance occurs at low frequencies.
At this frequency region an electrolyte/gold interface is
formed when a significant amount of electrolyte solution
penetrates into the pores existing in the membrane, this
was confirmed by the limited coverage rate at 78.82%.
From an electrochemical point of view, when a metal is
placed in contact with an electrolyte, faradic phenomena
assisted by charge transfer take place at the interface.
Then, when the detected perchlorate anions increase the
interface gold/electrolyte is slowed down due to the spatial
hindrance of perchlorate anions which decrease the charge
transfer resistance.
-1.0
-0.5
0.0
0.5
1.0
1.5
E (mV) vs SCE
(saturated calomel electrode)
Fig. 7. Cyclic voltammetry measurements of gold/CoPcAP structures in
5 mM K3Fe(CN)6 in 0.01 M PBS (pH7) solution, and a scan rate of 100 mV/s.
Â
Ã
h ¼ 1 ꢀ RctðGold electrodeÞ=R0 ðfunctionalized electrodeÞ
ct
ð1Þ
h is the coverage rate, Rct is the ionic charge transfer of the
gold electrode before functionalization, and Rct is the ionic
charge transfer after functionalization.
0
3.3. Electrochemical characterization: sensor response
3.3.1. Cyclic voltammetry characterization
Cyclic voltammetry methods are known to provide an
excellent insight into the redox properties of the film onto
the surface of the gold electrode. The electrochemical char-
acterization of the gold/CoPcAP structure were performed
using the cyclic voltammetry experiments in the presence
The response of Au/CoPcAP membrane sensor for some
anions is believed to be due to the coordination of the ana-
lyte anion as an axial ligand, to the metal center of the car-
rier molecule [37]. Therefore, the sensitivity of the
5x104
10-10
10-9 M
10-8
10-7 M
10-6 M
10-5 M
10-4 M
10-3 M
M
2x103
M
4x104
1x103
3x104
0
3,0x103
6,0x103
9,0x103
Zreal (Ohm.cm -2
)
10-2
Solid line:fit
M
2x104
1x104
0
1x104
2x104
3x104
4x104
Zreal (Ohm.cm-2)
5x104
6x104
7x104
8x104
9x104
0
Fig. 8. Impedance spectra (in Nyquist presentation) of Co(II)MAPc-Acrylate polymer/Au/Ti/SiO2/Si/SiO2 structure for different ClOꢀ4 concentrations,
between 10ꢀ10 M and 10ꢀ2 M. Frequency range: 100 kHz–100 mHz, an amplitude of 10 mV sinusoidal modulation, and polarization potential of ꢀ300 mV in
0.01 M PBS (pH7) solution.

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M. Braik et al. / Organic Electronics 16 (2015) 77–86
1,6
1,5
1,4
1,3
1,2
1,1
1,0
established that the selective interaction of an analyte
anion and a lipophilic ion carrier within the membrane is
essential for the development of anion-selective mem-
branes [1,38]. In the case of organometallic compounds
[39], the anion selectivity is mainly governed by a specific
interaction between the central metals and the anions
rather than the lipophilicity of the anions or a simple oppo-
site charge interaction with anions [40]. The preferential
response of the ionophore used towards ClOꢀ4 is believed
to be associated with the coordination of perchlorate to
the metal center of the carrier molecule with little influ-
ence from anion hydration energy, and it is the relative
affinity of the ClOꢀ4 as a suitable ligand for Co(II) that dic-
tates the observed specificity pattern of the electrodes.
Variation of the coordination affinity towards the various
anions to the central metal of the ionophore strongly influ-
ences the selectivity. It is interesting to note that the
observed specificity pattern for the proposed sensors gov-
erned by the so-called Hofmeister selectivity sequence:
ClOꢀ4 > SCNꢀ > Iꢀ > NO3ꢀ > Brꢀ > Clꢀ > HCOꢀ3 > CH3COOꢀ
> SO24ꢀ > HPO24ꢀ (i.e. selectivity based solely on the lipo-
philicity of anions) [41,42] commonly observed with ion
exchanger based membrane sensors and supporting a neu-
tral or charged carrier sensing mechanism with the present
ionophore.
2
3
4
5
6
7
8
9
10
p [ClO-4]
Fig. 9. Variation of the impedance Z/Z0 vs. p½ClOꢀ4 ꢄ of Co(II) phthalocy-
anine-Acrylate polymer thin film, Z0 is the impedance value without
perchlorate anions in the solution.
1,6
X= ClO-4
X= NO-3
1,5
1,4
X= CO23-
X= SO24-
1,3
1,2
1,1
1,0
3.4. Modelisation of the results
The experimental EIS measurements of the gold elec-
trode functionalized by the CoPcAP are an overlap of two
semi-circles observed as a single semi-circle with a large
diameter (Fig. 11b). This figure reveals that the phase plot
presents two phase angle maxima. Consequently, the
Nyquist plot was analyzed as a combination of two closely
interacting semi-circles (Fig. 11a) which can indicate the
requirement of other components in the equivalent electri-
cal circuit model [43,44]. To understand the physical origin
of the observed response, the data was simulated with the
equivalent electrical circuit formed by a serial association
of three components (Fig. 12).
2
4
6
8
10
p [X]
Fig. 10. Variation of the impedance Z/Z0 vs. p[X] of Co(II) phthalocyanine-
Acrylate polymer thin film.
perchlorate sensor was analyzed at a potential of ꢀ300 mV
and a frequency of 0.5 Hz.
ꢃ The first one at the low-frequency range used to repre-
sent the metal/solution interface, Rct the charge-transfer
resistance and CPE2 is the electrical double layer capac-
itance at the gold/electrolyte interface.
ꢃ The second component at higher frequencies is formed
by a parallel resistance Rm and capacitance CPE1. Rm is
attributed to the membrane resistance and a capaci-
tance, CPE1 is assigned to the electric capacitor consist-
ing of the metal and the electrolyte, with the film as the
dielectric [44,45].
Fig. 9 shows the variation of ꢀLog(Z/Z0), as a function of
perchlorate concentration, where Z0 is the impedance
value without perchlorate anions in the solution. Here, a
linear behavior with a large detection range between
9.1 ꢂ 10ꢀ10 and 10ꢀ3 M was observed. The detection limit
of our perchlorate sensor was ꢁ9.1 ꢂ 10ꢀ10 M which is bet-
ter than the values reported in the literature [1,11].
3.3.3. Specificity
ꢃ The last component is a series resistance of the electro-
The sensing properties and specificities of the CoPcAP
membrane deposited on the gold electrode was investi-
gated towards nitrate ðNOꢀ3 Þ, carbonate ðCO23ꢀÞ, and sulfate
ðSO24ꢀÞ anions. Fig. 10 shows the variation of the impedance
measurements after the addition of different interfering
anion concentrations. The EIS variation of NOꢀ3 , CO32ꢀ and
SO24ꢀ was nearly constant. This was in respect to the varia-
tion for different concentrations of ClOꢀ4 . From Fig. 10, we
noticed that the obtained result highlights the good
specificity of our sensor to perchlorate anions. It is well
lyte solution.
The two constant phase elements CPE1 and CPE2 are
non-ideal capacitances and can be expressed by [44–49]:
n
ZCPE ¼ 1=Qðj
x
Þ
ð2Þ
where Q is a constant, j is the imaginary number,
x
is the
angular frequency, and 0 < n < 1. CPE becomes more capac-
itive, when the value n tends to be 1.

M. Braik et al. / Organic Electronics 16 (2015) 77–86
83
Fig. 11. Plot of EIS experimental measurements and the fit results of Au/Co(II)MAPc-Acrylate polymer, (a) Bode plot and (b) Nyquist plot. Total error value:
v2 ꢁ 10ꢀ3
.
Fig. 12. Equivalent circuit used for fitting of the impedance. Rm: resistance of the thin film, CPE1 and CPE2: constant phase elements, Rct: ionic charge
transfer resistance and Rs: resistance of the solution.
Finally, the experimental EIS measurements were fitted
using the Frequency Response Analysis (FRA) software. The
different fits were made with a total error value of
v2 ꢁ 10ꢀ2 [46,47].
3.4.1. Bulk resistance Rm and charge transfer resistance Rct
variations
Fig. 13 and Table 2 show the evolution of the bulk resis-
tance Rm and the ionic charge transfer resistance Rct with

84
M. Braik et al. / Organic Electronics 16 (2015) 77–86
R2=0.982
1.0
0.9
0.8
0.7
0.6
0.5
1.00
0.95
0.90
0.85
0.80
0.75
R2=0.978
Slope = 0.061
Slope = 0.044
1
2
3
4
5
6
7
8
9
10
11
p [ClO-4]
Fig. 13. Variation of bulk resistance and charge transfer resistance of the Co(II)MAPc-Acrylate polymer membrane against ClOꢀ4 concentration.
Table 2
Fitting data for Co(II)Phthalocyanine-Acrylate polymer based impedimetric sensor for different perchlorate concentrations.
Perchlorate concentration (M) Rs (K O)
CPE1 (
l
F)
n
Rm (K O)
CPE2 (
l
F)
n
Rct (K O)
v2
10ꢀ10
10ꢀ9
10ꢀ8
10ꢀ7
10ꢀ6
10ꢀ5
10ꢀ4
10ꢀ3
10ꢀ2
2.643 0.109 0.08392 0.005 0.65 4.250 0.100 1.850 0.043 0.7814 0.005 78.3 0.807 0.035148
2.556 0.106 0.08637 0.006 0.65 4.030 0.099 1.798 0.040 0.7883 0.005 78.2 0.778 0.071805
2.517 0.123 0.09320 0.008 0.65 3.730 0.110 1.876 0.051 0.7789 0.006 74.2 0.889 0.052200
2.319 0.116 0.08855 0.008 0.65 3.600 0.107 1.789 0.044 0.7954 0.005 70.6 0.740 0.054245
2.395 0.123 0.10730 0.012 0.65 3.113 0.115 1.799 0.051 0.7945 0.006 67.7 0.710 0.061359
2.441 0.127 0.11750 0.015 0.65 2.793 0.117 1.797 0.055 0.7962 0.006 62.6 0.768 0.060613
2.479 0.114 0.13510 0.016 0.65 2.708 0.106 1.729 0.057
0.803 0.007 61.4 0.305 0.069149
0.1460 0.020 0.65 2.582 0.113 1.812 0.070 0.7931 0.008 60.0 0.870 0.079202
0.1839 0.023 0.65 2.100 0.086 1.747 0.060 0.8048 0.007 59.6 0.930 0.181540
2.428 0.121
1.926 0.092
the perchlorate concentrations. As illustrated in this figure,
we have observed a decrease of these resistances with
increasing perchlorate concentration. Such behavior can
be attributed to an axial ligation of perchlorate as reported
in the literature for other CoPcAP sensors [50]. In addition,
we noticed that there were two recognition processes: the
first one was at the electrolyte/membrane interface and
the second one was at the electrolyte/gold interface
through the existing pores in the membrane.
equivalent electrical circuit model to understand the phe-
nomena at the interface of the electrolyte/membrane. The
sensitivity was studied according to the variation of the
circuit parameters and with the injection of varying anion
concentrations. The perchlorate sensor based on CoPcAP
has a good specificity and sensitivity for perchlorate.
Finally, we have developed a perchlorate anions sensor
based on Co(II)Pc derivatives with low cost fabrication, a
large linear detection range (9.1 ꢂ 10ꢀ10–10ꢀ3 M), and a
low detection limit (9.1 ꢂ 10ꢀ10 M).
At low concentrations (10ꢀ9 to 10ꢀ4 M) we observed a
linear detection behavior for the two processes with
improved sensitivity for the bulk/electrolyte interface (Rm
evolution). However, at higher concentrations (10ꢀ4 to
10ꢀ2 M) we have observed a saturation of the Rct values.
This can be explained by the decrease of electrolyte/gold
interface due to the incorporation of the perchlorate ions
in the membrane.
Acknowledgements
This work was partially supported by the FP7-PEOPLE-
2012-IRSES No. 318053: SMARTCANCERSENS project and
NATO Science for Peace (SFP) Project CBP.NUKR.SFP
984173.
The authors would like to thank Dr. M. Lee for improv-
ing the english style of the manuscript.
4. Conclusion
We have investigated the sensitivity of a new chemical
sensor based on CoPcAP. Sensitive films dip-coated on gold
electrodes have been characterized by EIS. The analysis of
the impedance spectra was performed on the basis of an
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