Carbon Paste Gold Nanoparticles Sensor for the Selective
Determination of Dopamine in Buffered Solutions
Nada F. Atta,
z
Ahmed Galal, Fekria M. Abu-Attia, and Shereen M. Azab
Department of Chemistry, Faculty of Science, University of Cairo, Giza 12613, Egypt
An effective electrochemical sensor for the selective determination of dopamine DA in the presence of ascorbic acid AA and
uric acid UA in 0.04 mol L
-1
universal buffer solution pH 7.4 is introduced. The sensor is based on a carbon paste CP
electrode modified with gold nanoparticles. In a mixture of DA, AA, and UA, the sensor shows high selective response toward DA
and no response for AA or UA. The effect of various experimental parameters including time of deposition of gold nanoparticles
on the CP electrode, pH, and scan rate on the voltammetric response of DA was investigated. At the optimum conditions, the
concentration of DA was determined using differential pulse voltammetry in a linear range of 1.0 10
-7
to 5.0
10
-6
mol L
-1
and 5.0 10
-6
to 1.3 10
-4
mol L
-1
with correlation coefficients of 0.9995 and 0.9988 and a detection limit
of 5.9 10
-9
and 8.2 10
-8
mol L
-1
, respectively. The modified electrode can be used for the determination of DA spiked into
human serum samples, and excellent recovery results were obtained over a wide concentration range of DA. Moreover, validation
parameters, such as reproducibility, sensitivity, and recovery were evaluated successfully in the determination of DA in diluted
human urine.
© 2010 The Electrochemical Society. DOI: 10.1149/1.3456629 All rights reserved.
Manuscript submitted February 12, 2010; revised manuscript received April 26, 2010. Published July 16, 2010.
Dopamine DA is one of the important neurotransmitters that
are widely distributed in the mammalian central nervous system for
message transfer. It plays a very important role in the functioning of
central nervous, renal, hormonal, and cardiovascular systems.
1
Ab-
normal levels of DA lead to brain disorders such as Parkinson and
schizophrenia diseases.
2-4
Uric acid UA is another important bio-
molecule present in urine and blood. It is a primary end product of
purine metabolism. Its abnormal concentration levels lead to several
diseases such as hyperuricaemia and gout.
5,6
Ascorbic acid AA is a
vital component in human diet and is present in both animal and
plant kingdoms.
7
Usually, AA, DA, and UA coexist in our body
fluids and therefore selective determination of these molecules is
very important from the clinical point of view. At bare electrodes,
the selective determination of AA, DA, and UA is impossible be-
cause their oxidation potentials are very close. Besides, stability and
reproducibility cannot be achieved at bare electrodes due to the sur-
face fouling caused by the adsorption of oxidized products of AA on
electrode surface.
8
Paracetamol or acetaminophen ACOP is a
widely used over-the-counter analgesic pain reliever and anti-
pyretic fever reducer. It is commonly used for the relief of fever,
headaches, and other minor aches and pains and is a major ingredi-
ent in numerous cold and flu remedies. Paracetamol is also used in
the management of more severe pain such as postoperative pain.
9
Carbon paste CP electrode, which is made up of carbon particles
and organic liquid, has been widely applied in the electroanalytical
community due to its low cost, ease of fabrication, high sensitivity
for detection, and renewable surface.
10-14
Electrodeposition of gold nanoparticles onto the surface of the
CP electrode was another strategy to enhance the sensitivity of the
immunosensor. Several research works had been conducted to con-
struct a CP electrode modified with gold nanoparticles to be used as
an immunosensor for the determination of -fetoprotein,
15
carci-
noma antigen,
16
or in streptavidin–biotine interaction,
17
or as en-
zyme biosensors,
18
also in the determination of hypoxanthine,
19
sulfur-containing compounds,
20
and homocysteiene.
21
The elec-
trodeposition of gold nanoparticles onto other surfaces such as
glassy carbon in sensing of allergen–antibody interaction
22
and ace-
tylcholine esterase–choline oxidase
23
were examined. Monitoring of
silver and gold electrodeposition on glassy carbon and silicon,
24
screen-printed,
25
and indium tin oxide surfaces
26-31
were also stud-
ied. Also, gold and gold–platinum alloy nanoparticles were elec-
trodeposited on multiwalled carbon nanotubes for investigation of
direct electron transfer of glucose oxidase
32
and for nitrite
oxidation,
33
respectively. Simultaneous electrochemical determina-
tion of DA, AA, and UA was studied using different modified elec-
trodes such as polyacid chrome blue K modified glassy carbon
electrode,
34
CP electrode modified with tin hexacyanoferrate,
35
nano-Au self-assembled glassy carbon electrode,
36
and recently by
modifying Pt or conducting polymer surfaces by Pd or Pt
nanoparticles.
37-40
In this study, an electrochemical sensor based on gold nanopar-
ticles and graphite was constructed for the selective determination of
DA. The gold nanoparticles on the surface of the electrode amplified
the signal significantly. Moreover, the sensor showed sensitive and
selective determination of DA in the presence of AA and UA.
Experimental
Materials and reagents.— DA, AA, UA and ACOP were pur-
chased from Aldrich and were used as received. Britton–Robinson
B–R 4.0 10
-2
mol L
-1
buffer solution of pH 2–11
CH
3
COOH + H
3
BO
3
+H
3
PO
4
and phosphate buffer saline PBS,
pH 7.4, 137 mmol L
-1
NaCl, 2.7 mmol L
-1
KCl, 87 mmol L
-1
Na
2
HPO
4
, and 14 mmol L
-1
KH
2
PO
4
were used as the supporting
electrolytes. pH was adjusted using 0.2 mol L
-1
NaOH. All solu-
tions were prepared from analytical grade chemicals and sterilized
Milli-Q deionized water.
Construction of gold nanoparticles modified CP electrode.— A CP
electrode with a diameter of 3 mm was fabricated as described
elsewhere
41
then was immersed into a 6 mmol L
-1
hydrogen tetra-
chloroaurate HAuCl
4
solution containing 0.1 mol L
-1
KNO
3
prepared in doubly distilled water and deaerated by bubbling with
nitrogen. A constant potential of -0.4 V vs Ag/AgCl was applied
for 400 s. The surface coverage of gold nanoparticles was 2.05
10
-6
mol cm
-2
. Then, the modified electrode GNMCPE was
washed with doubly distilled water and dried carefully by a paper
without touching the surface and then left to dry in air for 10 min
before being used.
Instrumental and experimental setups.— Electrochemical mea-
surements.— All voltammetric measurements were performed using
a personal computer-controlled AEW2 electrochemistry work sta-
tion and data were analyzed with an EC
prog3
electrochemistry soft-
ware, manufactured by Sycopel Scientific Limited Tyne & Wear,
U.K.. The one compartment cell with the three electrodes was con-
nected to the electrochemical workstation through a C
3
stand from
BAS. A platinum wire from BAS was employed as auxiliary elec-
trode. All the cell potentials were measured with respect to Ag/AgCl
3 mol L
-1
NaCl reference electrode from BAS. One compartment
glass cell 15 mL fitted with a gas bubbler was used for electro-
chemical measurements. Solutions were degassed using pure nitro-
gen before and throughout the electrochemical measurements. A
z
E-mail: Nada_fah1@yahoo.com
Journal of The Electrochemical Society, 157 9 F116-F123 2010
0013-4651/2010/1579/F116/8/$28.00 © The Electrochemical Society
F116