MAKARA, SAINS. VOL. XX, NO. XX, BULAN XX TAHUN XX: XXX-XXX
MODIFICATION OF GOLD NANOPARTICLES AT CARBON
ELECTRODES AND THE APPLICATIONS FOR ARSENIC (III)
DETECTIONS
Ivandini Tribidasari Anggraningrum1*), Lany Wijaya1, Jarnuzi Gunlazuardi1, and Yasuaki Einaga2
1. Department of Chemistry, Faculty of Mathematics and Science, University of Indonesia, Depok 16424, Indonesia
2. Department of Chemistry, Faculty of Science and Technology, Keio University,
Hiyoshi 3-14-1 Hiyoshi, Yokohama 223-8522, Japan
*)
E-mail: ivandini.tri@ui.ac.id
Abstract
Modification of carbon, including boron-doped diamond (BDD) and glassy carbon (GC), using gold nanoparticle
(AuNP) was developed by self-assembly technique. This technique is based on the affinity of AuNP to interact with
amine terminal groups after surface modification of BDD and GC. The fabricated materials, AuNP-BDD and AuNPGC, were then utilized as electrodes for As3+ detection using anodic stripping voltammetry (ASV) technique. Anodic
stripping voltammograms of both AuNP-BDD and AuNP-GC electrodes showed similar peak potentials of As 0
oxidation at ~0.21 V (vs. Ag/AgCl) in optimum conditions of -500 mV, 180 s, and 100 mV/s for deposition potential,
deposition time, and scan rate, respectively. AuNP-BDD shows better performances in the case of wide linear
concentration range (0-20 mM) and low limit of detection (0.39 M or 4.64 ppb), whereas those of AuNP-GC were
linear in the concentration range of 0-10mM with a detection limit of 0.14 M (13.12 ppb). Excellent reproducibility
was shown with RSDs (n=20) of 2.93% and 4.54% at AuNP-BDD and AuNP-GC, respectively. Although, decreasing
of current responses in 6-concecutive days was found more at AuNP-BDD (~20.1%) than that at AuNP-GC (~2.8%).
Abstrak
Mohon tuliskan Judul dalam bahasa Indonesia. Modifikasi elektroda karbon, glassy carbon (GC) dan boron-doped
diamond (BDD), menggunakan nanopartikel emas (AuNP) dilakukan dengan menggunakan teknik self-assembly.
Teknik ini dipilih berdasarkan afinitas AuNP yang lebih tinggi terhadap gugus amina yang dimodifikasikan pada BDD
dan GC. Material yang diperoleh, AuNP-GC dan AuNP-BDD, kemudian digunakan sebagai elektroda pendeteksi As3+
menggunakan teknik anodic stripping voltammetry (ASV). Anodic stripping voltammograms dari kedua elektroda
menunjukkan puncak potensial oksidasi As0 pada ~0.21 V (vs. Ag/AgCl) pada kondisi optimum potensial deposisi -500
mV, waktu deposisi 180 s, dan scan rate 100 mV/s. AuNP-BDD memiliki daerah pengukuran yang lebih luas (0-20
mM) dan limit deteksi yang lebih rendah (0.39 M atau 4.64 ppb), sedangkan AuNP-GC linier pada daerah konsentrasi
0-10 mM dengan limit deteksi 0.14 M (13.12 ppb). Keberulangan yang baik ditunjukkan dengan RSDs (n=20) 2.93%
pada AuNP-BDD dan 4.54% pada AUNP-BDD. Meskipun penurunan yang lebih banyak pada pengukuran 6 hari
berturut-turut ditemukan pada AuNP-BDD (~20.1%) daripada pada AuNP-GC (~2.8%).
Keywords: anodic stripping voltammetry, arsenic, boron-doped diamond, glassy carbo, gold nanoparticles
Maximum contamination level allowed based on World
Health Organization (WHO) and U.S. Environtmental
Protection Agency guide line is about 50-10 mg/mL [34].
1. Introduction
Arsenic exists in four oxidation levels, including -3, 0,
+3, and +5. As(III) is more toxic than As(V) or
organoarsenic compounds. Long term exposure to
arsenite increases health risks aranging from
conjuctivitis, skin, and internal cancer to diabetes, and
vascular, reproductive, neurological effects [1-2].
Many methods have been developed to detect As (III),
including graphite furnace atomic absorption
spectrometry [5], inductively coupled plasma mass
1
2
MAKARA, SAINS. VOL. XX, NO. XX, BULAN XX TAHUN XX: XXX-XXX
spectrometry (ICPMS) [6], and high performance liquid
chromatography coupled by ICPMS [7]. However, those
techniques have some disadvantages, such as time
consuming analysis, expensive instrument requirement,
and impractible application for in situ analysis [5-7]. On
the other hand, electrochemical methods, especially
anodic stripping voltammetry (ASV), can provide high
accuracy for very low concentration detection of metal
ions (in ppb) with fast, inexpensive, simple and easily
modified measurements [8-16].
Preparation of BDD electrodes. BDD electrodes were
deposited on Si (100) wafers in a microwave plasmaassisted chemical vapor deposition (MPCVD) system
(ASTeX Corp.) with a plasma power of 3000 W. The
deposition time was fixed at 6 hours. Detail of the
preparation has been described elsewhere [21-22]. A
mixture of acetone and methanol in a ratio of 9:1 (v/v)
was used as the carbon source. B2O3, used as boron
source, was dissolved in the acetone-methanol solution
at a concentration of 104 ppm (B/C).
Carbon electrode is generally used in electroanalysis
since it is inexpensive, easy to get, inert as well as high
conductivity and stability. Moreover, carbon has good
biocompatibility [17]. However, carbon is less sensitive
to arsen oxidation or reduction [18]. Surface
modification, such as metal modification, is generaly
required to overcome the problem. Modification of
carbon surface with metal nanoparticles provides some
advantages in electrochemical sensor as it facilitates
electron transfer between electrode surface and analyte
[18]. Moreover, nano dimension of the modifying
metals can theoretically enhance the surface area, which
means increasing of catalytic activity. Some methods to
modify carbon with metal nano particles have been
developed, such as vacuum vapour deposition,
electrochemical deposition and sputtering method [1416,19]. However, the methods have some
disadvantages, especially in low stability of the
deposited metal due to the lack of chemical interaction
between metal and carbon [18-19]. Since ASV
technique involves 2 steps, including pre-concentration
step or deposition of analyte at electrode surface and
stripping oxidation step, stable deposited metal particle
on the surface is higly required.
Preparation of colloidal gold nanoparticles. Colloidal
gold nanoparticles were prepared by adding 0.5 mL of
0.01 M HAuCl4 solution into 18.5 mL of water and
stirred for 5 min in room temperature. Into that
solution, 0.5 mL of 0.1 M sodium citrate was added and
stirred for 5 min. Then, 0.5 mL of 0.1 M freshly
prepared NaBH4 solution was added. Characterization
was handled by UV-visible spectroscopy at an
adsorption band of ~519 nm. TEM was utilized to
investigate the nanoparticle dimension.
In this work, carbon electrodes were modified by -NH2
functional groups in order to increase the affinity to
gold nanoparticles. This technique is known as selfassembly technique since the functional groups can
direct the nanoparticle to be placed at the functional
group site at carbon surface [20]. Furthermore, high
affinity of carbon surface to metal nanoparticle was
expected to improve the stability of the deposited
nanoparticles [20]. The composite material produced
was then utilized as electrodes for As 3+ detection.
Electrochemical
measurements.
A
singlecompartment cell were used for electrochemical
measurements. An Ag/AgCl (saturated KCl) and Pt wire
electrode were used as the reference and counter
electrodes, respectively. The planar working electrode
was mounted on the bottom of the cell by using of a
Vitton O-ring. The geometric area of the working
electrode was estimated to be 0.26 cm2. The supporting
electrolyte was 0.1 M HCl. All measurements were
made at room temperature (23+2 C) in stirring
condition. Stripping voltammograms were recorded
using a potentiostat (Hokuto-Denko, Hz-1000).
2. Experiment
Materials. Hydrochloric acid, potassium chloride, 1propanol, ammonium hydroxide and sodium citrate
analytical grade were all purchased from Merck.
HAuCl4 and NaBH4 were supplied by Aldrich. Sodium
(meta)-arsenit and α-alumina 0.5 were obtained from
Wako. All chemicals were used without further
purification. Double distilled water used throughout this
study.
Modification of GC and BDD electrodes. Glassy
carbon (GC) electrode was polished well by aqueous
slurries of α-alumina (0.5 μm), whereas no pretreatment
was required for the BDD. Both materials were then
ultrasonicated in 1-propanol and water, each for 10 min,
before drying in room temperature. The materials were
then immersed in concentrated NH4OH solution and
irradiated under UV source (λ = 254 nm) for about 6 h.
After cleaning and drying process, both materials were
immersed in colloidal gold nanoparticles for 20 min
followed by drying in 60 C. The materials were then
electrochemically characterized and used as working
electrodes.
3. Results and Discussion
HAuCl4 solution changed from yellow to red ruby after
reduction reaction with NaBH4 and sodium citric,
indicating
the
formation
of
AuNPs
[12].
Characterization of colloidal AuNPs by UV–visible
spectrophotometer shows maximum absorption at ~519
nm (Figure 1). Stability of AuNP swas also examined.
MAKARA, SAINS. VOL. XX, NO. XX, BULAN XX TAHUN XX: XXX-XXX
The spectra of the first minute to the 7th day showed that
the adsorption peak was not significantly changed,
indicating good stability of the AuNPs colloid. The
stability could be achieved due to the presence of
sodium citric as the capping agent. Furthermore, TEM
characterization (Figure 2) shows that the AuNPs
formed groups or clusters with an average size of 30
nm.
GC and BDD surface generally provide oxygen
termination as the result of oxidation process in air
[21,23]. Some reports shows that although AuNPs can
be deposited at original BDD or GC surface, the
stability was very low, especially at BDD [8,19]. The
surface of oxygen termination is known to have
negative charge due to significant difference in the
electronegativity of oxygen and carbon on the surface.
This creates an electrostatic barrier to binding of
negatively charged AuNPs, because in the present work,
negatively charged citrate ions are used to stabilize the
3
AuNPs colloid [22]. As the result, the deposited AuNPs
could be easily removed from the electrode surface
during the measurement or in the cleaning process [21].
On the other hand, nitrogen termination can provide
positive charged since H+ adsorbed on the amino groups
attached to the BDD surface and facilited adsorption of
negatively charged AuNPs [20]. Therefore, in this work
GC and BDD surface was modified to provide nitrogen
termination.
Modification
was conducted by
photochemistry to exchange oxygen to be amina (-NH2)
functional group at the surface. The presence of -NH2
functional group was expected to drive the deposition of
AuNPs at the surface. Tian et al. proposed a covalent
bond between AuNPs and -NH2 could be formed in selfassembly process [20], which was expected to stabilize
the position of AuNPs at the carbon surface. The AuNPmodified GC and BDD electrodes were then named as
Au-NP-GC and AuNP-BDD.
Characterization of AuNP-GC and AuNP-BDD was
conducted by stripping voltammetry of solution of As 3+
in 0.1 M HCl. Non modified GC and BDD were also
examined as control. Theoretically, during deposition
process in ASV method, As3+ is reduced to As0 at the
surface of gold nanoparticles to form intermetallic AuAs. As0 is then reoxidized to As3+ in stripping process.
Figure 3 shows plots of the stripping process in ASV.
There is no oxidation peak was found at non modified
GC and BDD electrodes, whereas well-defined peaks
a
Figure 1. UV-vis Spectra of Gold Nanoparticles in
Various Time from the 1st Min to the 7th Day
after Synthesis
b
Figure 2. TEM Image of Golf Nanoparticles in 40.000
Times of Magnification
Figure 3. Stripping Voltammograms of 6 M As3+ in 0.1
M HCl Solution at (i) Non Modified and (ii)
AuNP-modified (a) BDD and (b) GC Electrodes.
Potential Deposition, Time Deposition, and Scan
Rate of -500 mV, 180 s, and 100 mV/s were
Applied, Respectively
4
MAKARA, SAINS. VOL. XX, NO. XX, BULAN XX TAHUN XX: XXX-XXX
were observed at the potential of ~0.21 V (vs. Ag/AgCl)
at AuNP-GC and AuNP-BDD electrodes, indicated that
both electrodes have succesfully been modified.
The measurement condition was optimized for
deposition potential and time. Deposition potential is the
given potential to reduce As3+ in the solution to be As0
at the electrode surface. The higher the potential, the
higher energy supplied to reduce As3+. Figure 4 shows
influence of deposition potentials at the oxidation peak
currents. Similar trends were observed at both
electrodes. The figure shows that peak current increased
with the increasing of negative potential and achieved
the highest current at the potential of -500 mV. The
peak current then decreased significantly at more
negative potential due to competition between reduction
of As3+ and reduction of H+ [21]. Consequently, -500
mV was then fixed as the optimum potential deposition.
Influence of deposition time to the peak currents was
shown in Figure 5. The longer the deposition time the
higher the peak current. However, the peak currents
start to be stable at the deposition time of 180 s,
indicating that all of As3+ was compeletely reduced to
be As0 in 180 s. Therefore, 180 s was fixed for optimum
deposition time.
In the case of measurements using cyclic or linear
sweep voltammetry, current responses produced at GC
electrode is generally higher than that at BDD electrode
[21]. Sp2 configuration of GC causes adsorption
controlled mechanism at GC surface, whereas diffussion
controlled ocurs at BDD surface with sp3 configuration
[17,21,24]. Adsorption controlled mehanism generally
can accumulate more analyte at the surface, resulting in
higher current responses [21]. However, it is interesting
to see that peak currents of stripping voltammetry at
AuNP-BDD is always higher than that at AuNP-GC
(Figure 3). The smaller current at AUNP-GC is
probably due to the strong adsorption at GC that caused
the stripping step was more difficult. Although the
active site of both electrodes is AuNPs, the deposition
of As0 at the AuNP-GC surface might also block the
surface of GC, resulting in slower stripping process. The
broad peaks at AuNP-GC (Figure 3a) confirmed the
evidence. Possibility that more amount of AuNP at
BDD than that at GC could be negligible since the
photochemical reaction of NH2 formation should be
more effective at sp2 than at sp3. However,
characterization using XPS is required to prove.
Analytical performances of the electrodes were also
investigated at the optimum measurement conditions. at
AuNP-BDD the current responses is liniear in the
concentration range of 0-20 mM with a detection limit
of 0.14 M (4.64 ppb) (Figure 6.b), whereas at AuNPGC, linear calibration curve (Figure 6.a) can be
achieved in a concentration range of 0–10 M with a
limit detection of 0.39 M (13.12 ppb), whereas. Better
performance of AuNP-BDD caused by its very low
background current, resulting in very low limit of
detection and wide range of concentration. It is known
that BDD has superior low background current among
other solid electrodes [21].
a
a
b
b
Figure 4. Effect of Deposition Potentials at Oxidation
Peak Currents of Stripping Voltammograms of
20 μM As3+ in HCl 0.1 M Solution at (a) AuNPBDD and (b) AuNP-GC electrodes. Deposition
Time and Scan Rate of 180 s and 100 mV/s were
Applied, Respectively
Figure 5. Effect of Time Deposition at Oxidation Peaks of
Stripping Voltammograms of 20 μM As3+ in HCl
0.1 M Solution at (a) AuNP-BDD and (b) AuNPGC Electrodes. Potential Deposition and Scan
Rate of -500 mV and 100 mV/s were Applied,
Respectively
MAKARA, SAINS. VOL. XX, NO. XX, BULAN XX TAHUN XX: XXX-XXX
a
b
Figure 6. Stripping
Voltammograms
of
Various
Concentrations of As3+ in 0.1 M HCl Solutions
at (a) AuNP-BDD and (b) AuNP-GC Electrodes.
Applied Condition was Similar to that of Figure
3. Insets: Plots of Current Responses vs.
Concentrations
5
electrodes, especially AuNP-BDD was shown by RSDs
of 2.93% and 4.56% at AuNP-BDD and AuNP-GC,
respectively. AuNP-BDD is considered to be more
stable than AuNP-GC due to less adsorptive behavior of
BDD than GC as the AuNP-BDD electrode surface
remains clean after every measurement, whereas
impurity was adsorbed at AuNP-GC surface. In the case
of gold nanoparticles, adsorption behavior of the gold
particles is minimized due to small dimensions of the
particles.
Stability of the electrodes was also examined. Figure 8
shows stripping voltammograms of 10 mM As3+ in 0.1
M HCl solution at both electrodes for a 6-succesive
days. Higher decreasing of current observed at AuNPBDD (~20%) was due to leaching of the gold
nanoparticles from electrode surface during storage time
between measurements. Leaching at AuNP-BDD could
be higher due to the adsorption weakness of BDD
surface, indicating that only physical adsorption, in
terms of positive negative interaction, occurred between
amina functional groups and gold nanoparticles. In the
case of GC, although chemical bonds were also not
formed, high adsorption behavior caused advantages to
keep AuNPs at the electrde surface as shown by lower
current decreasing than AuNP-BDD (~2.8%)
a
a
b
Figure 7. Stripping Voltammograms of 10 μM As3+ in 0.1
M HCl Solution at (a) AuNP-BDD and (b)
AuNP-BGC in 20 Consecutive Measurements.
Applied Condition was Similar to that of Figure
3
Reproducibility of current responses of AuNP-GC and
AuNP-BDD was investigated. Figure 7 shows stripping
voltammograms of 10 M As3+ in 0.1 M HCl in 20consecutive measurements. Excellent stability of the
Figure 8. Stripping Voltammograms of 10 μM As3+ in 0.1
M HCl Solution at (a) AuNP-BDD and (b)
AuNP-GC in 6- Succesive Days. Applied
Condition was Similar to that of Figure 3.
Insets: Plots of Oxidation Current Peaks vs.
Time
6
MAKARA, SAINS. VOL. XX, NO. XX, BULAN XX TAHUN XX: XXX-XXX
4. Conclusion
Fabrication of AuNP-BDD and AuNP-GC was
successfully conducted using self-assembly technique
after surface modification of -NH2 functional groups.
The composite material was utilized as electrodes for
As(III) detection using anodic stripping voltammetry
(ASV) with optimum condition of -500 mV, 180 s and
100 mV/s as deposition potential, deposition time and
scan rate, respectively. AuNP-BDD shows better
analytical performance than AuNP-GC in terms of
current responses, detectable concentration range, low
limit of detection, and reproducibility of current
responses due to very low adsorption properties of
BDD. However, stability of AuNP-BDD electrode is
lower than AuNP-GC.
Ackowlegdement
This research is partly funded by Hibah Riset Unggulan
Universitas Indonesia under contract number
240AP/DRPM-UI/N1.4/2008.
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