Application of a biomimetic sensor based on iron phthalocyanine chloride: 4-methylbenzylidene-camphor detection

Article abstract of DOI:10.1590/S0103-50532010000700025

The construction and application of a biomimetic sensor for determination of 4-methylbenzylidene camphor (4-MBC), an ultraviolet (UV) radiation protector, are described. The sensor was prepared by modifying a carbon paste electrode with iron(III) phthalocyanine chloride (FePcCl). Amperometric measurements carried out with the sensor under an applied potential of 0.0 V vs. Ag|AgCl in a mixture of tetrahydrofuran and 0.1 mol L^-1 H₂SO ₄ solution (30:70 volume ratio) showed a linear response range from 1.8×10^-4 to 9.0×10^-4 mol L^-1. A detailed selectivity investigation for other nine UV filters was also performed. A sensor response mechanism was proposed and the results for 4-MBC quantification in commercial sunscreens and in water from swimming pools and rivers are presented.

Full text of DOI:10.1590/S0103-50532010000700025

J. Braz. Chem. Soc., Vol. 21, No. 7, 1377-1383, 2010.
Printed in Brazil - ©2010 Sociedade Brasileira de Química
0103 - 5053 $6.00+0.00
Application of a Biomimetic Sensor Based on Iron Phthalocyanine Chloride:
4-Methylbenzylidene-Camphor Detection#
Ana Carolina Boni,a Maria D. P. T. Sotomayor,a Marcos R. V. Lanza,b
Sônia Maria C. N. Tanakac and Auro A. Tanaka*,c,d
aDepartamento de Química Analítica, Instituto de Química, Universidade Estadual Paulista,
14801-970 Araraquara-SP, Brazil
bDepartamento de Química e Física Molecular, Instituto de Química de São Carlos,
Universidade de São Paulo, 13560-970 São Carlos-SP, Brazil
cDepartamento de Química - CCET - Universidade Federal do Maranhão,
65085-580 São Luís-MA, Brazil
dInstituto Nacional de Ciência e Tecnologia de Bioanalítica, 13083-970 Campinas-SP, Brazil
A construção e a aplicação de um sensor biomimético para a determinação de 4-metilbenzilideno
cânfora (4-MBC), um protetor de radiação ultravioleta (UV), são descritas. O sensor foi preparado
pela modificação de um eletrodo de pasta de carbono com um complexo de cloreto de ferro(III)
com ftalocianina, FePcCl.As medidas amperométricas conduzidas com o sensor, sob um potencial
aplicado de 0,0 V vs. Ag|AgCl em uma mistura de tetraidrofurano e 0,1 mol L-1 H2SO4 (30:70
em volume), mostraram uma resposta linear no intervalo de 1,8×10-4 to 9,0×10-4 mol L-1. Uma
investigação detalhada da seletividade da resposta frente a outros nove filtros UV também foi
realizada. Um mecanismo de resposta do sensor foi proposto e os resultados para a quantificação
de 4-MBC em protetores solares comerciais e em águas de piscinas e de rios são apresentados.
Theconstructionandapplicationofabiomimeticsensorfordeterminationof4-methylbenzylidene
camphor (4-MBC), an ultraviolet (UV) radiation protector, are described. The sensor was
prepared by modifying a carbon paste electrode with iron(III) phthalocyanine chloride (FePcCl).
Amperometric measurements carried out with the sensor under an applied potential of 0.0 V vs.
Ag|AgCl in a mixture of tetrahydrofuran and 0.1 mol L-1 H2SO4 solution (30:70 volume ratio)
showed a linear response range from 1.8×10-4 to 9.0×10-4 mol L-1.A detailed selectivity investigation
for other nine UV filters was also performed. A sensor response mechanism was proposed and the
results for 4-MBC quantification in commercial sunscreens and in water from swimming pools
and rivers are presented.
Keywords: iron phthalocyanine, amperometric sensor, methylbenzylidene camphor
Introduction
and in tanning parlours; moreover, they have color
protective abilities and therefore may prevent premature
fading of hair color and damage to hair cuticle. On the
other hand, it has been recently reported that commonly
used chemical UV filters may cause endocrine disrupting
effects in both aquatic and terrestrial animals, as well
as in human skin cells.1-4 In addition, five of the most
commonly UV filters used in cosmetic formulations, i.e.,
oxybenzone, octyl methoxycinnamate (OMC), homosalate,
p-aminobenzoic acid (PABA), octyldimethyl-PABA
(ODP), and 4-methylbenzylidene camphor (4-MBC),
exhibited oestrogenic effects in MCF-7 (Michigan
Chemical ultraviolet (UV) filters have been introduced
in 1889, when an acidified quinine sulfate solution was
used to block UV radiation,1 and thereafter sunscreen has
become an everyday cosmetic with continuously increasing
use.
The positive effect exerted by UV filters is to block
the UV light radiation damage from sunlight, sunlamps
*e-mail: tanaka@ufma.br
# Dedicated to the memory of our friend Professor Ícaro Sousa Moreira,
DQOI-UFC, Brazil

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Application of a Biomimetic Sensor Based on Iron Phthalocyanine Chloride
J. Braz. Chem. Soc.
Cancer Foundation-7) breast cancer cells. Furthermore,
oxybenzone, 4-MBC and OMC were confirmed to be
oestrogenic by classical in vivo uterotrophic assays with
rats dosed in the feed. For the most potent oestrogenic
UV filter 4-MBC, the effect could be even replicated by
application on rat skin, resembling human exposures with
sunscreen cream. In vitro studies have shown other hormone
disruption responses (anti-oestrogenic, androgenic, anti-
androgenic and progestogenic activities) for almost all
the chemical UV filters used in sunscreen formulations.5,6
Recent publication1 has shown that, in Denmark,
urban water is the primary recipient of six UV filters,
including oxybenzone, avobenzone, 4-MBC, octyl
methoxycinnamate, ODP and homosalate, with estimated
8.5-65 tonnes and 7.1-51 tonnes in wastewater and surface
water, respectively. In North of China, it has been observed
that the levels of benzophenone-3 (BNP), 4-MBC, OMC
and octocrylene (OC) in different units of wastewater plants
were in the concentration range 2.13-34.0 ng L-1, with high
concentrations in hot seasons.7
p-aminobenzoic acid (PABA), octyldimethyl-PABA
(ODP), 4-methylbenzylidene camphor (4-MBC),
[3-(4-methylbenzylidene)bornan-2-one], isoamyl
p-methoxycinnamate (IMC) and 2-phenyl-5-
benzimidazolesulfonic acid (PBS) were acquired from
Aldrich. Benzophenone-3 (BNP); octylmethoxycinamate
(OMC); menthyl anthranilate (MA); octyl salicylate (OSA)
and avobenzone (AVB) were purchased from Fluka.
Tetrahydrofuran (thf), acetonitrile (MeCN) and sulfuric
acid were obtained from Synth, Brazil.
The 4-MBC standard solutions were prepared in thf
for the electroanalytical experiments and in the respective
mobile phase for the HPLC experiments.
Sensor construction
In order to obtain homogeneously modified carbon
pastes, the sensor was prepared by mixing an adequate
amount of FePcCl with graphite powder and 1.0 mL of
0.1 mol L-1 phosphate buffer solution (pH 7.0).After drying
at room temperature, 50 μL of mineral oil were added and
mixed to obtain a homogeneous paste, which was placed
into the cavity of a glass tube (4 mm internal diameter and
1 mm depth) with a platinum slide inserted for electrical
contact with the paste. The effect of the FePcCl content
on the sensor response was evaluated by preparing five
different pastes with the macrocycle weight percentage
varying from 5 to 15%.
Since the use of UV filters in countries like Brazil
is expected to continuously increase, and the disposal
of such compounds in aquatic environments is still not
regulated by any government agency, it seems worthwhile
to apply the knowledge in biomimetic sensors based on
metalophthalocyanines and metaloporphyrins for detection
of UV filters, more specifically 4-MBC, which is commonly
used in sunscreens for children.
Metalophthalocyanines and metaloporphyrins have
been widely employed in sensor construction with different
transducer systems, such as optical,8-13 chemoresistive,14-18
impedimetric,19 piezoelectric20,21 and mainly
electrochemical,22-30 since they present high electrocatalytic
activities for many redox reactions. In addition, enzymeless
sensors31,32 using these macrocycles33-38 as biomimetic
active sites of redox enzymes, as peroxidase,34,37 dopamine
monooxigenase38 andP45035,36 havebeendescribed, offering
a real and an alternative tool to official analytical methods.
Furthermore, it is well known that established methods for
identifying pollutants usually require preparative steps and
expensive equipments, such as high performance liquid
chromatography (HPLC) and mass spectrometry (MS),
and the development of alternative methods for selective,
sensitive, quicker and cheaper analyses would be welcome.
Electrochemical measurements
The electrochemical experiments were conducted, at
room temperature, in solutions containing a 70:30 volume
ratio of 0.1 mol L-1 H2SO4 and thf, respectively, and using
a conventional three-electrode cell with the modified
carbon paste electrode as working electrode, Ag|AgCl
electrode and platinum wire as reference and counter
electrodes, respectively. All experiments were carried out
in air-equilibrated solutions, since preliminary experiments
have shown that dissolved oxygen did not interfere in the
sensor response. The data acquisition was performed with a
PalmSens potentiostat (Palm Instruments BV, Netherlands)
interfaced with a microcomputer.
The amperometric measurements were carried out at a
previously optimized potential of 0.0 mV vs.Ag|AgCl, and
the current was continuously monitored and registered until
a steady state was reached (approximately 3 s). Right after,
50 mL of 2.5×10-2 mol L-1 UV filter standard solution was
added to the electrolytic solution and stirred for 10 s for
solution homogenization. Then the current was monitored
in the quiescent solution for 10 s. Thus, successive additions
Experimental
Chemicals and solutions
All chemicals used were of analytical or HPLC
grade. Iron(III) phthalocyanine chloride (FePcCl),

Vol. 21, No. 7, 2010
Boni et al.
1379
of the UV filter standard solutions were performed, in order
to obtain the analytical curve.
hand, the sensor based on carbon paste modified with the
iron(III) complex showed an increase in the reduction
current for potentials less positive than 0.12 V, with a
maximum at around 0.0 V vs. Ag|AgCl. In addition, in
absence of the analyte in the electrolyte, it was possible
to observe a peak at approximately 0.1 V, which can be
associated to the Fe3+/Fe2+ redox couple and recognized as
the catalytic site for the sensor response.
HPLC analyses
The chromatographic analyses were performed in a
Shimadzu® model 20A liquid chromatograph coupled with
SPD-20A UV/Vis detector, SIL-20A auto sampler and a
DGU-20A5 degasser, and monitored by a microcomputer.
The column used was a C18 (250 4.6 mm, Shim-Pack
CLC-ODS) fixed inside a Shimadzu® CTO-10AS oven to
keep the temperature constant.
Due to the lack of an official analytical procedure
for 4-MBC quantification, the procedure reported in the
literature39 was adapted and optimized by preparing the
mobile phase with a mixture of acetonitrile and water in
a volume ratio of 93:7. The flow rate was 1.0 mL min-1
and the injection sample volume was 30 mL. The column
o
temperature was maintained at 30 C. The measurement
wavelength was 321 nm and the analysis time was 15 min
for each standard and sample.
Sunscreen analyses
Figure 1. Voltammetric profiles for unmodified (a and b) and modified
carbon paste electrodes with FePcCl (c and d) in 0.1 mol L-1 H2SO4/thf
70:30 (v:v) solutions in presence (solid line) and absence (dashed line)
of 1.0×10-4 mol L-1 4-MBC. Potential scan rate: 20 mV s-1.
Child commercial sunscreens and a Lanette anionic
gel-cream sample were analyzed. Before each analysis,
the sample was pre-treated according to the procedure
established by the Brazilian sanitary surveillance agency
(ANVISA - Agência Nacional de Vigilancia Sanitária).40
For this, 2.0 g of the sunscreen was mixed with 4.0 mL of
methanol and 250.0 μL of 1.0 mmol L-1 H2SO4, heated at
40 oC for 10 min and finally sonicated for 3 min. After this
pre-treatment, the solution was filtered and injected in the
chromatograph or introduced in the electrochemical cell
for the measurements.
The dependence of the sweep rate-normalized current
density (DIp n-1/2) with the potential sweep rate (n) is shown
in Figure 2. The plot shape is characteristic of a typical
electrocatalytical reduction process,35,36,41 indicating that
the sensor response is carried out first by a chemical
reaction between the analyte and the iron complex (catalyst)
and further by an electrochemical process involving the
Aquatic sample analyses
Two water samples from swimming pools and five
samples collected from rivers near to the city ofAraraquara,
in São Paulo state, were enriched with 4-MBC and analyzed
with the proposed sensor, in order to evaluate the matrix
effects.
Results and Discussion
The electrochemical behaviors of the 4-MBC on the
carbon paste electrode unmodified or modified with FePcCl
are illustrated in Figure 1. The response of the unmodified
paste electrode did not present any difference before and
after addition of 4-MBC to the electrolyte. On the other
-1/2
Figure 2. Plot of the sweep rate-normalized current density (DIp n
)
versus the sweep rate (n). [4-MBC]= 2.0×10-4 mol L-1 in 0.1 mol L-1
H2SO4/thf 70:30 (v:v) solution.

1380
Application of a Biomimetic Sensor Based on Iron Phthalocyanine Chloride
J. Braz. Chem. Soc.
catalytic site regeneration (Fe3+/Fe2+ redox process), with
the current being proportional to the 4-MBC concentration
and associated with the reduction of ferric to ferrous ions.
On the other hand, when the response profile was
investigated beyond the sensor linear range, the curve
presented a hyperbolic shape (data not shown), as expected
for enzymatic biosensors and biomimetic sensors that
follow a Michaelis-Menten kinetic relationship.31,36 Thus, in
order to evaluate the apparent Michaelis–Menten constant
sensitivities are obtained with a,b-unsaturated ketones,
and as the unsaturation in the ketone group diminishes the
sensitivity also decreases.
app
(K ) for the 4-MBC sensor, the Lineweaver-Burk graph
MM
app
MM
was constructed (Figure 3). The obtained K value was
of 3.1×10-4 mol L-1, which is appropriate for enzymatic and
biomimetic catalysts with high analyte affinity.31
Figure 5. Relative response (%) obtained with the FePcCl-based sensor
for ten different UV filters. The parameter was calculated considering the
sensor response for 4-MBC as 100%.
O
OH
O
O
4-MBC
BNP
O
Figure 3. Lineweaver-Burk plot for the 4-MBC reduction catalyzed by
O
the FePcCl-based sensor.
O
NH2
O
Therefore the experimental data suggests that the
FePcCl complex acts as a biomimetic catalyst according to
the mechanism presented in Figure 4. In this mechanism,
the reduction of the 4-MBC ketone group to alcohol41 via
one electron in acid media promotes the oxidation of Fe2+
to Fe3+, and is followed by the regeneration of Fe2+ on
the electrode surface. The mechanism also suggests that
the substrate (4-MBC) reduction is favored if the ketone
is a a,b-unsaturated group, as demonstrated with the 10
(ten) UV filters (Figure 5) investigated in the selectivity
experiments (Figure 6). It was observed that higher
MA
OMC
O
O
O
N
O
OH
IMC
OSA
O
O
HO3S
N
N
H
O
PBS
AVB
O
N
NH2
OH
O
O
ODP
PABA
Figure 6. Chemical structures of ten UV filters evaluated in the selectivity
studies. 4-MBC: 4-methylbenzylidene camphor; BNP: benzophenone-3;
OMC: octyl-methoxycinnamate; OSA: octyl salicylate; MA: menthyl
anthranilate; IMC: isoamyl p-methoxycinnamate; AVB: avobenzone;
ODP: octyldimethyl-PABA; PBS: 2-phenyl-5-benzimidazolesulfonic acid
and PABA: 4-aminobenzoic acid.
Figure 4. Mechanism proposed for the 4-MBC sensor.

Vol. 21, No. 7, 2010
Boni et al.
1381
Table 1. Dependence of the sensor response on the amount of FePcCl
in the carbon paste. Measurements carried out in 0.1 mol L-1 H2SO4/thf
solutions with 70:30 volume ratio. Applied potential: 0.0 V vs. Ag|AgCl
Typical chronoamperometric signals and the
corresponding analytical curve for 4-MBC are shown
in Figure 7. The applied potential of 0.0 V vs. Ag|AgCl
was prior optimized in the potential range from -0.1 up
to +0.1 V vs. Ag|AgCl at intervals of 0.025 V (data not
shown). The higher sensitivity obtained at 0.0 V is in
agreement with the voltammetric profile (Figure 2), in
which the higher current variation was observed at 0.0 V
vs. Ag|AgCl. It is important to emphasize that, for sensor
construction, potentials close to this value are preferred
in order to minimize possible interferences from other
electrochemically active compounds.
FeClPc amount (%)
Sensitivity (μA L mol-1)
3.5 × 103
5.0
7.5
8.4 × 103
10.0
12.5
15.0
6.3 × 104
7.6 × 104
2.6 × 104
analytical curves in the corresponding linear range of
the sensor. In this case, the repeatability was defined
in terms of the relative standard deviation (RSD) from
seven sensitivities. The reproducibility of the sensor was
estimated in terms of the RSD for sensitivities calculated
for five sensors prepared and used on different days by two
experimentalists in different laboratories.
Table 2.Analytical parameters for 4-MBC determination on the proposed
sensors based on carbon paste modified with FePcCl
Parameter
Response
1.8 to 9.0×10-4
76308 2505
0.9984
14
Linear range (mol L-1)
Sensitivity (mA L mol-1)
Correlation coefficient
Detection limit (mmol L-1)
Quantification limit (mol L-1)
Response time (s)
0.5×10-4
0.5
Figure 7. Typical analytical curve profile of the FePcCl sensor for 4-MBC
under optimized conditions. Inset: chronoamperometric measurement for
successive additions of the analyte.
Measurement repeatability (%) (RSD, n = 7)
Sensor reproducibility (%) (RSD, n = 5)
1.9
1.8
The electrolyte solution consisted of a mixture of
0.1 mol L-1 H2SO4 and tetrahydrofuran (thf) with a 70:30
optimized volume ratio. The experiments showed that, for
7.00 mL of this electrolyte, at least ten successive additions
of 500 mL of the standard UV filter solution (solubilized
in thf) could be carried out without phase separation.
In addition, when other acid or buffer solutions were
tested no satisfactory responses were obtained, indicating
the important role of H+ ions in the sensor response, as
suggested in the proposed mechanism (see Figure 4).
The influence of the FePcCl content in the carbon paste
was also evaluated for the analytical sensor response and
the results (Table 1) showed that 12.5% gives the highest
sensitivity for 4-MBC detection.
The proposed sensor was tested for UV filter
quantification in three commercial sunscreen formulations
(denoted as 1, 2 and 3) used by children in Brazil. The
concentrations were determined by the sensor using the
external calibration method and compared with those
obtained with the chromatographic method (Table 3). One
can see that that the results are not significantly different at
a confidence level of 95%, and it is possible to emphasize
that both methods offer similar relative standard deviation
values. Such data suggest an excellent sensor precision and
the methodology as an efficient and rapid alternative for
sunscreen analyses.
After optimization of the parameters involved in the
sensor preparation and chronoamperometric measurements,
the analytical parameters for 4-MBC quantification were
evaluated and are summarized in Table 2. The detection
and quantification limits were calculated as suggested by
the IUPAC recommendations.43 The repeatability of the
measurements was estimated by plotting seven successive
In order to verify if the sensor could be applied to
aquatic environments, water samples from two private
swimming pools (samplesA and B) and five rivers close to
Araraquara city (SP, Brazil) were analyzed after enrichment
with 4-MBC. The good recovery results (Table 4), with
values close to 100% for the swimming pool samples and
lower values but still acceptable for the river samples,

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Application of a Biomimetic Sensor Based on Iron Phthalocyanine Chloride
J. Braz. Chem. Soc.
Table 3. Determination of 4-MBC in sunscreen samples using the sensor based on FePcCl modified carbon paste; the chromatographic method was
employed as reference
Sample
UV filter concentration in % (m/m)
Error / %
Label value
Comparative method (HPLC)
Proposed sensor
Sunscreen 1a
Sunscreen 2b
Sunscreen 3c
6.0
6.0
8.0
7.8
6.9
8.5
8.1
7.1
8.9
3.8
2.9
4.7
Validities: aJune 2010, bDecember 2009, cFebruary 2009.
Table 4. Recovery of 4-MBC using the proposed sensor in water samples from swimming pools and rivers
Sample
4-MBC (mol L-1)
Recovery (%)
Added
Found
Swimming pool A
2.00 × 10-4
2.00 × 10-4
2.00 × 10-4
2.00 × 10-4
2.00 × 10-4
2.00 × 10-4
2.00 × 10-4
1.94 × 10-4
1.96 × 10-4
1.86 × 10-4
1.80 × 10-4
1.90 × 10-4
1.82 × 10-4
1.76 × 10-4
97
98
93
90
95
91
88
Swimming pool B
Jacaré Pepira river
Jacaré Guaçú river
Jaú river
Tietê river in the limit with the Igaraçu city
Tietê river under the bridge in Barra Bonita city
indicated that the sensor was successfully applied in the
direct analyses of such water samples.
3. Schmitt, C.; Oetken, M.; Dittberner, O.;Wagner, M.; Oehlmann,
J.; Environ. Pollut. 2008, 152, 322.
4. Maerkel, K.; Durrer, S.; Henseler, M.; Schlumpf, M.;
Lichtensteiger, W.; Toxicol. Appl. Pharmacol. 2007, 218, 152.
5. Ma, R.; Cotton, B.; Lichtensteiger, W.; Schlumpf, M.; Toxicol.
Sci. 2003, 74, 43.
Conclusion
This work described an alternative methodology for
the determination of the chemical UV filter 4-MBC on
a sensitive and selective amperometric sensor based on
a carbon paste modified with FePcCl. The sensor was
satisfactorily applied in sunscreen and water samples from
swimming pools and rivers and it opens up real possibility
for UV filter quantification in other aquatic environments,
such as sewage effluents and wastewater from treatment
plants.
6. Kunz, P. Y., Fent, K.; Aquatic Toxicol. 2006, 79, 305.
7. Li, W.; Ma, Y.; Guo, C.; Hu, W.; Liu, K.; Wang, Y.; Zhu, T.;
Water Res. 2007, 41, 3506.
8. Basova, T.; Plyashkevich,V.; Hassan,A.; Gurek,A. G.; Gumus,
G.; Ahsen, V.; Sens. Actuators, B 2009, 139, 557.
9. Singh, S.; Tripathi, S. K.; Saihi, G. S. S.; Mater. Chem. Phys.
2008, 112, 793.
10. El-Basaty, A. B.; El-Brolossy, T. A; Abdalla, S.; Negm, S.;
Abdella, R. A; Talaat, H.; Surf. Interface Anal. 2008, 40, 1623.
11. Krasnovsky Jr., A. A.; Stremedlovskaya, V. S.; Surf. Interface
Anal. 2008, 12, 1194.
Acknowledgments
The authors gratefully acknowledge financial support
from the Brazilian agencies CNPq, ABN/Banco Real and
FAPESP. A. C. B. is also indebted to ABN Bank/Banco
Real for a fellowship.
12. Gao, Z. X.; Li, H. F.; Liu, J.; Lin, J. M.; Anal. Chim. Acta 2008,
621, 143.
13. Sutarlie, L.; Yang, K. L.; Sens. Actuators, B 2008, 134,
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14. Kilinç, N.; Atilla, D.; Ozturk, S.; Gurek, A. G.; Ozturk, Z. Z.;
Ahsen, V.; Thin Solid Films 2009, 517, 6206.
15. Bohrer, F. I.; Colesniuc, C. N.; Park, J.; Ruidiaz, M. E.; Schuller,
I. K.; Kummel, A. C.; Trogler, W. C.; J. Am. Chem. Soc. 2009,
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