In situ electrochemical generation of gold nanostructured screen-printed carbon electrodes. Application to the detection of lead underpotential deposition

Article abstract of DOI:10.1016/j.electacta.2009.03.085

In the present work, an electrochemical method for the reproducible and stable generation of gold nanostructures on the surface of screen-printed carbon electrodes was developed. This technique is based on the application of a constant current over an app

Full text of DOI:10.1016/j.electacta.2009.03.085

Electrochimica Acta 54 (2009) 4801–4808
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journal homepage: www.elsevier.com/locate/electacta
In situ electrochemical generation of gold nanostructured screen-printed carbon
electrodes. Application to the detection of lead underpotential deposition
Graciela Martínez-Paredes, María Begon˜a González-García, Agustín Costa-García∗,1
Departamento de Química Física y Analítica, Facultad de Química, Universidad de Oviedo, 33006 Oviedo, Asturias, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
In the present work, an electrochemical method for the reproducible and stable generation of gold nanos-
tructures on the surface of screen-printed carbon electrodes was developed. This technique is based on
the application of a constant current over an appropriate time interval. Gold nanostructured screen-
printed carbon electrodes were characterized using both SEM and electrochemical methods. The mean
diameter and the dispersion of gold nanoparticles that were generated electrochemically depended on
the gold concentration, the time deposition and the current intensity. Smaller diameters and better dis-
tribution of nanoparticles were obtained when a shift of potential to −0.70 V occurred during the gold
electrodeposition process. Moreover, the underpotential deposition (UPD) of lead on these nanostruc-
tured surfaces was studied, as was their behavior as array electrodes. The best results, using UPD combined
with square wave stripping voltammetry, were obtained for gold nanostructured surfaces with a mean
diameter of 78 24 nm and a density of 4.4 × 107 nanoparticles/mm2. These gold nanostructured screen-
printed carbon electrodes were obtained by applying a current intensity of −100 ␮A for 300 s using a gold
concentration of 0.5 mM. The reproducibility and limit of detection obtained using these nanostructured
electrodic surfaces were 2.4% (in terms of RSD) and 0.8 ng/mL, respectively.
Received 15 December 2008
Received in revised form 27 March 2009
Accepted 28 March 2009
Available online 7 April 2009
Keywords:
Gold nanoparticles
Nanostructured electrodic surfaces
Screen-printed carbon electrodes
Electrodeposition method
Lead sensor
Array electrodes
© 2009 Elsevier Ltd. All rights reserved.
1. Introduction
chemical deposition is a convenient and fast method for the
preparation of gold nanoparticles on large areas of conductive sub-
Nanosized particles of noble metals, especially gold nanopar-
ticles, have received interest due to their attractive electronic,
optical and thermal properties as well as their catalytic proper-
ties and potential applications in the fields of physics, chemistry,
biology, medicine and material science as well as their inter-
disciplinary fields [1,2]. For the electroanalytical chemist, more
attention has been paid to gold nanoparticles because of their
good biocompatibility, excellent conducting capability and high
surface-to-volume ratio. The introduction of gold nanoparticles
onto electrochemical interfaces has infused new vigor into electro-
chemistry [3–11]. There are numerous approaches to the fabrication
of gold nanostructures on electrode surfaces, including the use
of gold nanoparticle-modified composite materials [12–16], the
adsorption or electro-adsorption of gold nanoparticles onto elec-
trode surfaces [17–19], covalent binding using organic molecules
(such as thiols and polymers) between the electrode and gold
nanoparticles [20–22], attachment via a polymer film [23], sol–gel
techniques [24] and electrochemical deposition [25-34]. Electro-
strates because the mechanism of electrodeposition is very similar
to crystallisation and allows for the electrodeposition of crystals
with nanometer scale dimensions under an adequate deposition
time. The fundamental principles and simulations for the growth of
gold nanoparticles on graphite electrode surfaces have been inves-
tigated in detail [35–39].
Although different kind of electrodes have been used as sub-
strates for the fabrication of gold nanostructures, it is necessary
to develop cost-effective, disposable and reproducible devices.
Screen-printing technology has the strong advantage of creating
a large number of near-identical electrodes that can be used in a
single shot context at a low cost. The establishment of a simple
and quick method for fabricating gold nanoparticles onto a screen-
printed electrode surface would contribute to the generation of a
new transducer for biosensor applications. In this work, an elec-
trochemical method based on the application of a constant current
for the fabrication of stable and reproducible gold nanostructured
screen-printed carbon electrodes (SPCnAuEs) has been developed.
SEM was used to characterize the gold-modified electrodes.
Additionally, these gold nanostructured electrodes were used
as transducers for the detection of lead based on the lead underpo-
tential deposition (UPD) process. Metal UPD on different substrates
has been extensively studied in recent years and offers advantages
∗
Corresponding author. Tel.: +34 985 103 488 fax: +34 985 103 125.
E-mail address: costa@fq.uniovi.es (A. Costa-García).
1
ISE member.
0013-4686/$ – see front matter © 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.electacta.2009.03.085

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G. Martínez-Paredes et al. / Electrochimica Acta 54 (2009) 4801–4808
over the use of bulk metal deposition [40], including better sensi-
tivity and good repeatability of the analytical response. Lead UPD
has been extensively investigated on gold electrodes [41-45] and
very different UPD processes have been observed, depending upon
the nature of the substrate (poly or single-crystalline gold surface
structure). Here, the lead UPD on these gold nanostructured screen-
printed carbon electrodes exhibits two pairs of peaks, as it also
occurs on polycrystalline gold electrodes [43].
SPCEs, an aliquot of 40 ␮L of 0.1 M HCl was dropped onto the elec-
trode and the oxidation of gold was carried out by holding the
electrode at a potential of +0.85 V, recording the current intensity
vs. time. Three electrodes were measured for each gold concentra-
tion, current intensity and deposition time assayed. The area under
the curve (charge) was used to calculate the mass of gold involved
in the process using the Faraday equation.
2.3.3. Anodic stripping voltammetry of lead on SPCnAuEs and
SPGEs
2. Experimental
An aliquot of 40 ␮L of a solution of Pb(NO3)2 in 0.1 M HCl was
dropped onto the different SPCnAuEs and SPGEs, and a potential of
−0.5 V was applied for 90 s. Then, a square wave anodic stripping
was carried out from the electrodeposition potential to +0.1 V, using
a square wave amplitude of 25 mV, a frequency of 50 Hz and a step
potential of 2 mV. Calibration plots of lead were obtained for SPGEs
and different SPCnAuEs.
2.1. Reagents
Standard gold (III) tetrachloro complex (1.000 0.0001 g of
tetrachloroaurate (III) in 500 mL of 1 M HCl), Pb(NO3)2 and
hydrochloric acid (37%) were purchased from Merck. Dilutions from
the standard gold solution and Pb(NO3)2 solutions were prepared
in 0.1 M HCl.
Water was obtained from an ultrapure Millipore Milli-Q water
system.
3. Results and discussion
3.1. Gold nanostructured screen-printed carbon electrodes
(SPCnAuEs)
2.2. Apparatus and electrodes
Voltammetric measurements were performed with an ECO
CHEMIE ␮Autolab Type II potentiostat/galvanostat coupled with a
computer and controlled by Autolab GPES software version 4.9 for
Windows. All measurements were carried out at room temperature.
Screen-printed carbon electrodes (SPCEs) and screen-printed
gold electrodes (SPGEs), together with an edge connector, were pur-
chased from DropSens (Oviedo, Spain). The DropSens electrodes
incorporate a conventional three-electrode configuration, printed
on ceramic substrates (3.4 cm × 1.0 cm). In the case of screen-
printed carbon electrodes (SPCEs), both the working (disk-shaped
4 mm diameter) and counter electrodes are made of carbon inks,
whereas the pseudo-reference electrode and electric contacts are
made of silver. In the case of screen-printed gold electrodes, the
working and counter electrodes are made of gold ink. An insulating
layer was printed over the electrode system, leaving uncovered the
electric contacts and a working area, which constitutes the reservoir
of the electrochemical cell, with a volume of 50 ␮L.
In the constant current electrolytic process, gold (III) was
reduced and deposited onto the surface of SPCEs. Moreover, by
applying a constant current, the amount of charge that passed
through the electrode surface was kept constant during the elec-
trodeposition process. The amount of gold deposited onto the
electrode surface was calculated for different gold concentra-
tions, current intensities and deposition times, using the procedure
explained in Section 2.3.2 and Faraday’s Law. Although some
authors assert that the complete reoxidation of the electrode-
posited gold is not possible because it is a chemically irreversible
process [36], when a second chronoamperometry measurement
was carried out in the same electrode with a fresh drop of 0.1 M
HCl, no reoxidation of gold was observed.
Fig. 1 shows the variation of the amount of gold deposited on
the electrode surface with current intensity for 120 s of deposi-
tion time (Fig. 1A) and with deposition time for −5 and −50 ␮A
of current intensity (Fig. 1B). For small negative current intensities,
the amount of gold deposited on the electrode surface increased
when a more negative current intensity was applied, reaching a
plateau for all the gold concentrations assayed. The amount of gold
deposited on the electrode surface was higher as the gold con-
centration became higher. The value of current intensity at the
plateau was −1, −10 and −25 ␮A for 0.1, 0.5 and 1 mM gold, respec-
tively. Moreover, the amount of gold deposited on the electrode
surface increased with deposition time (Fig. 1B) for the same cur-
rent intensity. For a gold concentration of 0.1 mM, the increase of
the gold amount deposited on the electrode surface obtained for
−5 and −50 ␮A was similar for deposition times between 60 and
200 s. However, for longer deposition times, the amount of gold
deposited on the electrode surface was higher at −5 ␮A than was
obtained at −50 ␮A. This behavior could be due to the different
potential changes observed during the electrodeposition process
at these current intensities for this gold concentration, because for
−50 ␮A, the potential shifted rapidly towards −0.70 V, whilst for
−5 ␮A, the potential remained at 0.0 V for the first 200 s and then
shifted towards −0.7 V.
SEM images of the working electrode surfaces were obtained
with a JEOL JSM-6100 scanning electron microscope (20 kV, Japan).
Leica QWIN software was used to digitally process the SEM
images.
2.3. Analytical procedures
2.3.1. Electrochemical generation of gold nanostructures on the
electrode surface
To obtain the gold nanoparticles on the electrode surface, an
−
aliquot of 40 ␮L of a solution of 0.1, 0.5 or 1.0 mM AuCl4 in 0.1 M
HCl was dropped onto the SPCEs and a constant current was applied
for a fixed time. Different current intensities and deposition times
were tested. A chronopotentiogram was recorded during the elec-
trodeposition of gold in all cases. After the electrodeposition of gold,
the SPCnAuEs were generously rinsed with water.
2.3.2. Characterization of the gold nanostructured SPCEs
(SPCnAuEs)
Gold nanostructures were characterized via SEM and chronoam-
perometry. For each gold nanostructuration procedure, SEM images
were obtained for three electrodes and the mean diameter of the
gold nanoparticles was measured. Chronoamperometry measure-
ments were performed to determine the amount of gold deposited
over the SPCEs. After the generation of the gold nanostructured
To study the morphology of the gold deposited on the electrode
surfaces, SEM images were obtained for each gold concentration
and for different current intensities and deposition times. Fig. 2
shows some of these SEM micrographs. In all cases, the forma-
tion of gold nanoparticles on the electrode surface with different
mean diameters and distributions can be observed. Additionally,

G. Martínez-Paredes et al. / Electrochimica Acta 54 (2009) 4801–4808
4803
−
Fig. 1. Effect of current intensity (A) and deposition time (B) on the amount of gold deposited on the electrode surface for (ꢀ) 0.1 mM, (ꢁ) 0.5 mM and (᭹) 1.0 mM of AuCl4
.
In (A), deposition time: 120 s; in (B), −5 ␮A (dotted lines) and −50 ␮A (dashed lines). The small graphic beside (B) is the amplification of the graphic corresponding to the
data for 0.1 mM of gold concentration.
Fig. 2. SEM images of the surfaces of gold nanostructured screen-printed carbon electrodes obtained for different experimental conditions. aꢀ and bꢀ are amplified SEM images
of a and b SEM images.

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G. Martínez-Paredes et al. / Electrochimica Acta 54 (2009) 4801–4808
Table 1
Mean diameter and standard deviation of the gold nanoparticles obtained for different gold concentrations, current intensities and deposition times.
[AuCl4−] (mM)
Deposition time (s)
Current intensity (␮A)
Potential changes
−5
−10
−50
−100
120
77 8 nm
85 19 nm
105 12 nm
80 20 nm
−5 ␮A, +0.40 to +0.00 V and it
remains at this potential for
200 s. Then, the potential shifts
to −0.70 V
0.1
41 13 nm
68 10 nma
120 15 nm
−10 ␮A, +0.40 to −0.1 V an
maintained at this potential for
80 s. Then the potential shifts
to −0.70 V
70 13 nm
76 17 nm
73 20 nm
300
72 15 nma
−50 and −100 ␮A, the
potential shifts to −0.70 V
638 9 nm
231 28 nm
164 35 nm
−5 ␮A, the potential remains at
70 20 nm
78 24 nm
120
300
+0.40 V
0.5
75 14 nma
123 41 nma
72 22 nma
−10 ␮A, +0.40 to +0.00 V for
50 s and then the potential
remains at this potential
−50 ␮A, +0.40 to −0.30 V and it
remains at this potential for
50 s. Then the potential shifts
to −0.70 V
890 66 nm
202 79 nm
84 26 nm
78 25 nma
89 14 nma
770 90
−100 ␮A, the potential shifts to
−0.70 V
799 90 nm
200 29 nm
−5 and −10 ␮A, the potential
73 22 nm
120
300
remains at +0.40 V
1.0
129 41 nm
1108 206
74 24 nm
536 98 nm
78 22 nm
201 58 nm
−50 and −100 ␮A, the
130 48 nm
potential shifts to −0.70 V
234 40 nma
192 55 nma
97 21 nma
The value of mean diameter written with bold letters corresponds to the group with greater number of nanoparticles.
a
In these cases, the electrode surface was covered with two groups of gold nanoparticles with two mean diameters.
the mean and standard deviation of the diameters of gold nanopar-
ticles formed on the working electrode of SPCEs were obtained
from SEM images. Their values are listed in Table 1. Moreover, in
the last column of Table 1, changes in the potential observed dur-
ing the electrodeposition of gold at constant current are shown.
In most cases, two groups of nanoparticles with two mean diame-
ters covered the electrode surfaces. It can be observed from Fig. 2
and the data given in Table 1 that when a more negative con-
stant current intensity was applied during gold electrodeposition
for the same gold concentration and the same deposition time,
the mean diameters of the nanoparticles decreased or remained
constant. Moreover, the quantity of larger nanoparticles decreased
whereas the number of the smaller nanoparticles increased to cre-
ate a situation where monodisperse nanoparticles were obtained in
all cases with a mean diameter around 75 nm (except for the case of
a gold concentration of 1 mM and 300 s of deposition time). This was
noted when a shift towards more negative potentials (−0.70 V) was
recorded during the gold electrodeposition. This shift in potential
occurred at different values of current intensities, depending on the
gold concentration and deposition time. For example, in Fig. 3, it can
be observed that for a gold concentration of 0.1 mM, the potential
observed during the gold electrodeposition for −5 ␮A (thick black
chronopotentiogram) changed from +0.40 to 0.00 V, remained at
this potential for the first 200 s, and then shifted towards −0.70 V.
However, when the current intensity applied was −100 ␮A (thin
black chronopotentiogram), the potential shifted rapidly towards
−0.70 V and remained at this value during 300 s. For a 1.0 mM
gold concentration and a current intensity of −5 ␮A, the potential
recorded remained constant at +0.40 V during the gold electrode-
position process (grey chronopotentiogram). In the acid medium,
the generation of hydrogen occurred at this potential (−0.70 V); this
improved the nucleation of gold on the electrode surface in a detri-
ment of growth of nanoparticles. Therefore, more gold nuclei were
formed. Moreover, the rate of growth was similar for each individual
metal nanoparticle and strongly favored narrowing of the distri-
bution. When the potential remained at positive values (or small
negative potentials), the generation of hydrogen did not occur and
the individual metal nanoparticles grew independently from each
other and the particle size dispersion produced via nucleation in
two groups of nanoparticles was preserved during particle growth.
In general, gold monodispersed nanostructured surfaces were
formed at a current intensity of −100 ␮A. For values of current
intensity less negative than −100 ␮A, the general trend was toward
the formation of two groups of nanoparticles, though this trend
depends on the gold concentration and deposition time. At this
current intensity value (−100 ␮A), the density of nanoparticles
increased with the gold concentration and deposition time, except
when the mean diameter of gold nanoparticles increased (Table 1,
Fig. 3. Chronopotentiograms obtained during the gold electrodeposition for a gold
concentration of 0.1 mM and current intensities of −5 ␮A (thick black curve) and
−100 ␮A (thin black curve) and for a gold concentration of 1.0 mM and a current
intensity of −5 ␮A (grey curve).

G. Martínez-Paredes et al. / Electrochimica Acta 54 (2009) 4801–4808
4805
1 mM gold concentration and 300 s of deposition time). Although
the selection of the appropriate gold nanostructured electrode sur-
face will depend on the application, better reproducibility and
distribution of the gold nanostructured surfaces is obtained by
applying a current intensity of −100 ␮A during 300 s for gold con-
centrations of 0.1 or 0.5 mM.
3.2. Electrochemical behavior of lead on SPCnAuEs
Fig. 4 shows three cyclic voltammograms for a lead concentra-
tion of 200 ␮g/mL, obtained using a SPCE (A), a SPGE (B) and a
gold nanostructured SPCE (C), characterized by SEM in the previ-
ous section. A cathodic process (C1) was observed at a potential of
−0.625 V, corresponding to the bulk deposition of lead on SPCE as
well as the anodic stripping of lead (A1) at a potential of −0.37 V.
In the cases of SPGE and SPCnAuE, small peaks were observed at
potentials more positive than the bulk lead deposition and strip-
ping processes. With SPGE, a single cathodic process was observed
at −0.324 V(Cn)and ananodicprocesswas observedat −0.43 V (A3).
In the case of SPCnAuE, two cathodic peaks were observed at −0.26
and −0.45 V (C2 and C3 in Fig. 4C); an anodic stripping peak was
also observed at −0.13 V (A2). These two cathodic peaks, observed
in the presence of gold on the electrode surface, correspond to the
formation of a lead monolayer on the gold substrate at potentials
more positive than the reversible Nernst potential for bulk metal
formation, referred to as underpotential deposition (UPD) [40–45].
The processes observed here are consistent with previous reports
of lead UPD on a polycrystalline gold rotating ring-disk electrode,
where two pairs of peaks were observed [41,43]. The process labeled
Cn in Fig. 4B corresponds to the two peaks of lead UPD that over-
lapped in a single process, whereas on the SPCnAuE, these peaks
were observed to be separate. However, the anodic stripping pro-
cess corresponding to the second lead UPD (A3) was not observed
on SPCnAuE because it was overlapped by the anodic stripping peak
of the lead bulk deposition (A1).
Fig. 5A displays four cyclic voltammograms obtained for a lead
concentration of 500 ng/mL on SPCE (a), SPGE (b) and two SPCnAuEs
(c and d). Lead was previously deposited at −0.8 V over 90 s on the
electrode surface and then an anodic stripping scan was carried
out. Whereas on the SPCE lead bulk deposition was observed, in
the cases of gold electrodes only the first lead UPD was observed
under these experimental conditions. In accord with the results
of other studies [43], the second UPD peak did not appear until
the first UPD had reached its maximal charge. Moreover, lead bulk
deposition only appeared when the first and second peaks of lead
UPD reached their maximal charge. This behavior can be seen in
Fig. 5B, where lead was deposited during different deposition times
at −0.8 V on a SPCnAuE. The first peak of lead UPD increased with
the deposition time reaching a plateau at 300 s, where the second
peak of lead UPD appeared. This behavior was also observed when
lead concentration was increased (data not shown). In the case of
SPGE, the saturation of the first UPD occurred at higher deposition
times and lead concentrations due to the greater electrode area.
Both the cathodic and corresponding anodic stripping peaks of the
first lead UPD were linear with scan rate, according to the following
equations:
Fig. 4. Cyclic voltammograms obtained for a lead concentration of 200 ␮g/mL using
a SPCE (A), a SPGE (B) and a SPCnAuE (C). Potential scans were carried out from 0.00
to −1.2 V (A), −0.7 V (B) and −0.9 V (C) at 100 mV/s. SPCnAuE was obtained by gold
electrodeposition at −100 ␮A for 300 s; gold concentration: 1.0 mM.
Cathodic peak : ip (␮A) = 0.031v (mV/s) + 3.33, r2 = 0.9979
Anodic stripping peak :
On the other hand, the cathodic and anodic peak currents of
the lead UPD, when SPCnAuEs were used as working electrodes,
were higher when the mean diameter of gold nanoparticles formed
on the electrode surface increased (compare cyclic voltammogram
c with d in Fig. 5A and see Table 1). According to other authors
[33], this occurs because the gold nanoparticles (electrochemically
generated on the electrode surface) have more active surface gold
ip (␮A) = 0.049v (mV/s) + 4.24, r2 = 0.9951
This behavior allowed for the conclusion that the UPD process
on the SPCnAuE is an adsorption-controlled process. A simi-
lar behavior was obtained on SPGE and other gold electrodes
[43,45].

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G. Martínez-Paredes et al. / Electrochimica Acta 54 (2009) 4801–4808
Fig. 6. Square wave voltammogram obtained for a concentration of lead of 50 ng/mL,
using a SPCnAuE fabricated as in Fig. 5A. Amplitude: 25 mV; frequency: 50 Hz; step
potential: 2 mV. Lead potential deposition: −0.50 V; lead deposition time: 90 s.
layers of each individual nanoparticle do not overlap. Thus, the ratio
between the faradaic and capacitive currents is higher.
Using this lead UPD process combined with anodic stripping
square wave voltammetry, calibration plots for lead using differ-
ent gold nanostructured screen-printed carbon electrodes were
obtained. A calibration plot for lead using screen-printed gold
electrodes was also obtained. Fig. 6 shows a square wave voltam-
mogram for 50 ng/mL of lead obtained for SPCnAuE, which was
fabricated by electrodepositing gold from a solution of 0.1 mM of
−
AuCl4 in 0.1 M HCl at −100 ␮A for 300 s. Lead was previously
deposited at −0.5 V for 90 s. An anodic stripping peak for lead was
observed at −0.25 V. In Table 2, nanoparticle densities, slopes and
linear ranges of the calibration plots obtained as well as limits
of detection and interelectrodic reproducibilities are listed. Wider
linear ranges and more sensitive calibration plots were obtained
for SPCnAuEs that are covered with monodisperse nanoparticles
due to higher surface-to-volume ratios. For these monodispersed
nanostructured surfaces, the best limit of detection and interelec-
trodic reproducibility were obtained with SPCnAuEs with a higher
nanoparticles density (4.4 × 107 nanoparticles/mm2) because of a
higher mass transport rate. This density value was obtained by
applying a current intensity of −100 ␮A during 300 s for a gold con-
centration of 0.5 mM. Moreover the sensitivity (in terms of slope of
calibration plot) obtained with SPGEs was less than or equal to those
obtained with SPCnAuEs, and the interelectrodic reproducibility
obtained for screen-printed gold electrodes was worse than those
obtained for SPCnAuEs. Comparing the results to those obtained
in other works where different gold modified screen-printed elec-
trodes were used, the limits of detection obtained here are similar
to those obtained in other works, although the linear ranges are
Fig. 5. (A) Cyclic voltammograms obtained for a lead concentration of 500 ng/mL
using a SPCE (a), a SPGE (b) and two SPCnAuEs (c and d). Lead was deposited onto
the electrode at −0.8 V for 90 s, then, a potential scans were carried out from −0.8 V
to +0. 3 V at 0.5 V/s. SPCnAuEs was obtained by gold electrodeposition at −100 ␮A
for 300 s; gold concentration: 0.1 mM (c) and 1.0 mM (d). (B) Cyclic voltammograms
obtained for the same lead concentration at different deposition times: (a) 45 s, (b)
60 s, (c) 90 s, (d) 180 s, (e) 300 s and (f) 600 s using a SPCnAuE fabricated as in Fig. 4.
atoms, which results in a higher reduction current than that of the
bulk gold. Moreover, it was observed that peak separations (ꢀEp)
of the redox signals at the SPCE, SPGE and SPCnAuEs were 330, 130,
and 10 mV, respectively. This significant improvement in the elec-
trochemical performance is attributed to the metal modification of
the electrode surface. Moreover, according to other authors [46], the
gold nanostructured screen-printed carbon electrode can be con-
sidered as a nanodisc array-type electrode, at which the diffusion
layers of individual metal nanoparticles overlap with each other to
form a linearly expanding diffusion region, whereas the capacitive
Table 2
Lead calibration plots obtained with different gold nanostructured screen-printed carbon electrodes and screen-printed gold electrodes.
Electrode Gold deposition
[AuCl4−] (mM) Current intensity (␮A)b
Density (nanoparticles number/mm2) Linear range (ng/mL) Slope (␮A mL/ng) R2
DL (ng/mL) RSD%a
0.1
0.5
1.0
−10
−100
−10
1.8 × 107
3.0 × 107
4.2 × 106 c
4.4 × 107
1.2 × 106 c
9.1 × 106
2.5–150
2.5–100
1–250
1–1000
2.5–150
2.5–1000
0.056
0.081
0.065
0.089
0.054
0.118
0.9981
0.9995
0.9964
0.9978
0.9976
0.9992
2.0
1.5
0.7
0.8
1.0
2.0
3.6
2.4
2.4
2.4
4.0
4.0
SPCnAuE
−100
−10
−100
SPGE
15–1000
0.050
0.9975
10
13.0
a
Reproducibility obtained for four electrodes.
Deposition time of gold = 300 s.
Total nanoparticles number/mm2 of the two mean diameters.
b
c

G. Martínez-Paredes et al. / Electrochimica Acta 54 (2009) 4801–4808
4807
cles with a mean diameter around 75 nm, and the nanoparticle
density increases with gold concentration and deposition time,
except for the case of 1.0 M gold concentration and 300 s of depo-
sition time, where a larger mean diameter is obtained (130 nm).
This is due to the generation of hydrogen during the deposition
of gold, which facilitates the nucleation of gold on the electrode
surface and, consequently, a better dispersion of the nanoparticles
is obtained. Compared to screen-printed carbon electrodes, these
screen-printed gold electrodes and gold nanostructured screen-
printed carbon electrodes show a lead UPD process at more positive
values than seen for lead bulk deposition. This UPD process, com-
bined with square wave anodic stripping voltammetry, allows one
to obtain higher sensitivity in detecting lead, according to the liter-
ature. However, the gold nanostructuring of the electrode surface
allows one to obtain higher cathodic and anodic stripping peaks.
Therefore, an enhancement of the sensitivity is produced because
these electrodes act as a nanodisc array-type electrode, with a
higher ratio between the faradaic and capacitive currents. The sen-
sitivity in terms of slope of the lead calibration plot is higher for
those gold nanostructured screen-printed carbon electrodes with
higher nanoparticle density due to a higher surface-to-volume ratio
and a higher mass transport rate.
Fig. 7. Stability of the lead sensor for a month. Lead concentration: 25 ng/mL.
wider. Gold-coated carbon screen-printed electrodes obtained by
electrochemically preplating a gold film from a gold solution have
been used to measure lead and the limits of detection obtained in
this case were 0.1 and 0.6 ng/mL for 20 and 4 min of lead deposition
times, respectively [27]. In addition, gold-sputtered [47] and gold-
based screen-printed electrodes [48] have been used as lead sensors
and in these cases the limits of detection were 0.8 and 0.5 ng/mL
for 120 s of lead deposition time.
In comparison to other works, where screen-printed carbon
electrodes modified with calixarenes [49] or -(2-pyridylazo)-2-
naphthol (PAN) [50] were used to detect lead, the limits of detection
were higher (5 ng/mL for 10 min deposition time, and 15 ng/mL for
5 min deposition time, respectively) than those obtained with these
gold nanostructured screen-printed carbon electrodes.
Moreover, the methodology described in this work allows for
reproducible and stable gold nanostructured screen-printed carbon
electrodes that can be excellent platforms for the design of differ-
ent sensors (enzymatic, immuno- or genosensors) because of their
good biological compatibility, excellent conducting capability and
high surface-to-volume ratio.
Acknowledgement
This work has been financially supported by Spanish project
BIO2006-15336-C04-01.
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