Engineering, 2012, 5, 159-162
doi:10.4236/eng.2012.410B041 Published Online October 2012 (http://www.SciRP.org/journal/eng)
An Amperometric Sensor for Sunset Yellow FCF Detection
Based on Molecularly Imprinted Polypyrrole
Jinfeng X u, Yi Zhang, Hao Zhou, Ming wei Wa ng, Peidong Xu, Juankun Zhang*
Key Laboratory of Industrial Fermentation Microbiology, Ministry of Education, College of Biotechnology,
Tianjin Key Lab of Industrial Microbiology, College of Biotechnology，Tia njin Uni vers ity of Science an d Technology,
Tianjin 300457 , People’s Republic of China
Received 2012
ABSTRACT
An electrochemical method for fast detecting the concentration of sunset yellow FCF in wine samples was developed in this study.
The sensor based on imprinted films which fabricated by electropolymerization of pyrrole on a glassy carbon electrode in the pres-
ence of sunset yellow FCF as the template. Comparing to the polypyrrole non-imprinted modified (NIP) electrode, the polypyrrole
molecularly imprinted polymer (MIP) electrode improved the electrochemical performance of the sensor significantly. The peak
current at about 0.26 V was linear with the concentration of sunset yellow FCF from 0.4 to 2 μM and from 2 to 8 μM. It can be used
for more than 10 times to maintain a stable response result. The sensor had the good selectivity on sunset yellow FCF, amaranth and
tartrazine, which the selection factors were 1.00, 0.80 and 0.85，respectively.
Keywords: E lectrochemical Sensor; Polypyrrole ; Sunset Yellow FCF; Molecularly Imprinted Polymers
1. Introduction
Sunset yellow FCF is a synthetic azo dye, which has been
widely added into foods and drinks for its high stability to light,
oxygen and pH and low production cost [1]. However, studies
have shown that sunset yellow FCF can cause many adverse
health effects such as high genotoxicity and cytostaticity [ 2] . In
Chin a, sunset yellow FCF is permitted and the value of accept-
able d aily intake (ADI) is between 0 and 2.5 mg·kg-1 according
to the hygienic standards for uses of food additive (GB
2760-1996). Until now, several methods have been applied for
the detection of sunset yellow FCF, such as spectrophotometry
[3] , HLPC [4,5] and LC/MS [6]. However, the detecting
process of these methods was too complicated to proceed, can't
meet the d aily food scen e fast d etectio n requ ir ements. Recen tl y,
numerous electrochemistry methods are applied to sunset yel-
low FCF detection via modified working electrode such as
multi-walled carbon nanotubes film-modified electrode [1,7]
and Platinum wire–coated electrode [8], which have high sen si-
tivity but lower selectivity. A sensor based on MIPs as th e me-
rits of high sensitivity and label free evoked much attention.
Nevertheless, a sensor based on MIPs for sunset yellow FCF
detection has not been reported. Herein, an amperometric sen-
sor for sunset yellow FCF measuring was developed in this
paper.
2. Experimental
2.1. Chemicals and Apparatus
Pyrrole (98%), sunset yellow FCF, amaranth, tartrazine were
purchased from Sangon Biotech (Shanghai) Co.,Ltd. All rea-
gents were an alytical grade an d were used as received, without
further purification. The wine was bought on the market.
All experiments were performed t hrough an electrochemical
analyzer LK2005A (Tianjin, China) connecting to a computer
and carrying out with a conventional three-electrode cell with
glassy carb on (GC) electro de(ø = 4mm) which was covered b y
non-MIP or MIP polypyrrole film as the working electrode,
while an Ag/AgCl/satu rated KCl electrod e and a platinu m wire
served as the reference electrode and the auxiliary electrode
respecti vely.
2.2. Preparation of Electrodes Based on MIP and NIP
Films
A GC electrode was polished carefully with aqueous alumina
slurry (0.5μm) and repeatedly rinsed with distilled water. The
electrolyte solution was prepared with PBS(pH7.0) containing
0.02 M sunset yellow FCF, 0.05 M pyrrole and 0.1 M KCl. The
electropolymerization was performed through cyclic voltam-
metry of +0.4 V to -1.0 V, with a scan rate of 50 mV·s-1 and 10
consecutive scans. Then , the embedded sunset yellow FCF
molecules were removed from the PPy film by overoxidized
process at +1.3 V in the 0.1 M NaOH solution for 600 s. And,
the molecularly imprinted fi lm electrode was activated to ob-
tained MIP film electrodes in 0.2 M PBS (pH6.0) containing
0.1 M KCl by cyclic potential scan . As a control, the
non-imprinted PPy-GC electrode was prepared and treated in
exactly the same way except that the template molecules were
omitted from the electropolymerization stage.
2.3. Electroanalytical Measurements
There are t wice current measurements before and after incuba-
tion of sunset yellow FCF , which were performed using square
wave voltammetry(SWV) in 0.2 M PBS(pH7.0) solution con-
*Corresponding author.

J. F. XU ET AL.
160
taining 4mM Fe(CN)63-/4-, between 0.6V and 0.0V. After the
first current measurement, the imprinted or non-imprinted
PPy-GC electrode was dipped into a 0.2 M PBS(pH6.0) con-
taining prepared concentration of sunset yellow FCF to adsorp
for 10 min, then was washed with distilled water carefully to
remove the possible adsorptive substance on the electrode sur-
face, and then was transferred to the first detection electro-
chemical cell using the same measurements (SWV). All mea-
surement s were performed at ro om temperatu re.
2.4. Analysis of Real Sa mples
50.00 mL samples of wine were boiled to eliminate CO2 and
ethanol, adjusted pH to 6.0 using 2.5 M NaOH after cooling,
and then the wine was transferred to a 50mL flask to volume
with distilled water. Standard curve regression method was
used to determine the content of the sunset yellow FCF. The
treated wine samples were then spiked with appropriate amount
of suns et yellow FCF for recovery experiments.
2.5. The Structure of Three Analogue
To investigate the selectivity of the MIP and NIP electrode in
this research, three same concentration of analogue were de-
tected to evaluate the detection response. The structure of sun-
set yellow FCF, amaranth and tartrazine were shown in the
Figure 1.
3. Results and Discussion
3.1. Electropolymerization of MIP a n d NIP
Polypyrrole
The thickness of polymer film can easily be adjusted by con-
trolling the scan rates and the number of cycles during electro-
polymerization process [9]. We developed series of experi-
ments in which electro des were fab ricated with d ifferent cycle s
of 5, 10 and 15 to optimize the number of CV cycles to use to
form the ‘sensing’ layer of the electrode. The results shown that
the highest current response of the MIP electrodes to sunset
yellow FCF was obtained by applying 10 cycles. Figure 2
showed that one cathodic peak was observed at -0.77 V at the
first negative scan, and the current decreased si gnificantly with
the increase of cyclic scan times and were stabile after 8-cycle
scans. The other cathodic peak was observed at -0.07 V. After
the first negative scan and was constant. The reductive peak
appeared at 0.06 V and peak current was constant also. As
shown in the inset of Figure 2, there was no t a cath o di c peak at
-0.77 V, which could correspond to the reduction of sunset
yellow FCF molecules. The result s indicat ed that the fo rmation
of PPy films on the surface of GC electrode hindered the
monomer further accessing to the GC electrode surface, which
was the same as Xie’s [ 10] study and the sunset yellow FCF
and the PPy backbone could unified together stabliy. It was
because t hat th e posi tive ch aracte ri sti c of th e Pp y backbo ne an d
the negative charge of sunset yellow FCF molecules were
strongly absorbed onto the electrode surface through hydrogen
bonding and electrostatic interactions.
3.2. Electrochemical Behavior of Sunset Yellow FCF
on the Imprinted PPy-GC Electrode
The electro chemical behavio r of sunset yello w FCF was inves-
tigated by MIP and NIP electrode. The catalytic effect of the
MIP elect rode to different concentrations of sunset yellow FCF
were investigated in pH 7.0 PBS by SWV. Sunset yellow FCF
gave an oxidation peak response at about 0.250V at the NIP
electrod e, while an anod ic peak appeared at about 0.275V with
the use of MIP electrode and the peak current decreased with
the increased concentration of sunset yellow FCF. The en-
hanced peak current response and a shift in the oxidation poten-
tial of sunset yellow FCF at about 0.025V in the anodic direc-
tion were the clear evidences of the catalytic effect of the MIP
electrode towards the oxidation of sunset yellow FCF.
The calibration curve for the SWV peak current versus sun-
set yellow FCF was observed at MIP electrode under optimum
experimental conditions. There were two linear regions in the
curve which were 0.002mM to 0.008mM with the correlation
coefficient of 0.987 and 0.0004 mM to 0.002mM with the cor-
relation coefficient of 0.993.
3.3. Optimization of Experimental Parameters
1) Concentration Selection of Pyrrole and Sunset Yellow
FCF
The concen trations of monomer (pyrrole) an d template (sun-
set yello w FCF) du ring po lymerizatio n det ermine the an alytical
behavior of the sensor. The monomer concentration should be
proportional to the thickness of the deposit and amount of im-
printed molecule (t empl ate) in th e p ol ymeric matri x [9]. So it is
necessary to select the proper concentration of sunset yellow
FCF a nd pyrrole to both make the response of sunset yellow
FCF highest and obtain not a signal for pyrrole. The electro-
chemical p erformances of several i mprin ted PP y-GC electr odes
which were produced in different solutions of sunset yellow
FCF and pyrrole, were investigated in 0.2M PBS pH 7.0 con-
taining 1.7×10-5M sunset yellow FCF at the MIP electrode.
The response of the MIP electrode to sunset yellow FCF sam-
ples were shown in Table 1. The highest current response was
obtained at 50mM pyrrole and 20mM sunset yellow FCF（serial
number1）,which were chosen as the optimum concentrations.
O
O
N
N
S
NaO
NN
HO
SO
O
NaO
sunset yellow FCF
N=N
HO
NaO-S-
O
O
SONa
O
O
SO
OONa
amaranth
S
OO
ONa
N=N
O
NaO
OH
S
OO
NaO
tartrazine
Figure 1. T he structure of sunset yellow FCF, amaranth and tartrazine.

J. F. XU ET AL.
161
Figure 2. Cyclic voltammograms of the electropolymerization for
imprinted PPy-GC electrode. Inset was cyclic voltammograms of
the electropolymerization process for nonimprinted PPy-GC elec-
trode. Scan rate: 50 mV·s-1, sweep cycle: 10.
Sunset yellow FCF tartrazineamaranth
0
10
20
30
40
50
60
Current (μA)
The substanc e being examined
MIP
NIP
Figure 3. Selectivity of the imprinted and non-imprinted PPy-GC
electrode for sunset yellow FCF, amaranth and tartrazine.
Table 1. The Response of Different MIP Electrodes to Sunset Yel lo w FCF Samp les.
Serial
Number Concentration of pyrrole(mM) Conc e ntra tion of sunse t yellow FCF (mM) Wav e cur ren t valu e bef o re enrichment (μA)a Wave cur rent va lu e after
enrichment (μA) a Wav e c u r re nt va lue of su nse t yellow FCF in the sample a
1 100 10 120.875±10.605 70.4 23±18.592 50.4 51±7.993
2 50 10 128.364±9.498 66.3 63±6.388 62.000±5.820
3 30 10 128.052±1.406 75.9 15±6.685 49.180±4.671
4 20 10 117.126±1.641 52.2 56±4.341 64.870±2.700
5 10 10 144.131±3.868 76.0 57±2.066 68.074±1.802
6 10 20 147.133±6.405 80.081±8.53 67.052±5.600
7 30 20 147.979±7.627 84.0 65±10.680 63.913±3.953
8 50 20 142.711±3.844 66.4 20±7.917 80.679±0.702
a . Average of three measurements ± standard deviation.
2) Selectio n of Incubation Time
To select the proper incubation time, the prep ared Ppy-GC
electrode was incubated in the 0.2 M PBS containing 1.7×
10-5M sunset yellow FCF for different time of 0~20 min. The
results shown that the square wave voltammetric responses
were decreased rapidly with the time increasing in the first 4
min, then maintained constantly after 8 min. Thus, we chosed
10 min to be the the optimum incubation time for the determi-
nation of sunset yellow FCF in all experiments reported.
3) Selectivity of the Impri nted PPy-GC Electrode
The prepared imprinted and non-imprinted PPy-GC electrod e
were incubated into three structure analogues solution of 0.005
mM to study the selectivity of the sensor. The results were
shown in Figure 3, indicated that the imprinted Ppy-GC elec-
trode had higher recognition selectivity to sunset yellow FCF
than to amaranth and tartrazine on the same conditions. The
choose factors of the sensor for sunset yellow FCF, amaranth
and tartrazine were 1.00、0.80 and 0.85 respectively. The resul ts
also indicated that the MIP PPy-GC electrode had a better de-
tection performance than non-MIP PPy-GC electrode. It was
because that the imprinted PP y fi lms for the formation of deli-
cate imprinted sites and the stabilization of imprinted sites
which can significantly increases selectivity of electrochemical
biosensors through their size, shape and functional group dis-
tribution [14]. Therefore, the imprinted Ppy-GC which we had
prepared could apply to the detection of sunset yellow FCF in
wine sample.
4) Analysis of Commercial Samples and Recovery Experi-
ment
Through the research methods above, the content of sunset
yellow FCF in the wine sample was determine. It was found
that t here was 8 .81×1 0-2 mM sunset yellow FCF in treated wine
sample, t he recovery was 24.4% which was very low. The rea-
son might be that the polypyrrole films had th e positive char ge
after activation treatment to absorb charged material in the
sample which competed the binding sites of sunset yellow FCF.
So when detecting the content of sunset yellow FCF, it was
needed to do some special treatments to the wine sample to
shield the interference of el ectron ic material.
4. Conclusion
In this work, the molecularly imprinted PPy films modified
glassy carbon electrode was prepared by electrochemical poly-
merization of pyrrole with the cyclic voltammetry in the pres-
ence of template of sunset yellow FCF molecules. The results
demonstrated that the electrochemical sensor could significant-
ly improve the sensitivity and selectivity of sunset yellow FCF

J. F. XU ET AL.
162
analysis. Therefore, the electrochemical sensor could be poten-
tially exploited for detecting the residual analysis of sunset
yellow FCF in the wine samples.
5. Acknowledgements
The authors thank the Ministry of Science and Technology of
the People’s Republic of China (2009GJA10047) to suppo rt the
work.
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