Electro-oxidation nitrite based on copper calcined layered double hydroxide and gold nanoparticles modified glassy carbon electrode

Article abstract of DOI:10.1016/j.electacta.2011.08.026

In this paper, a novel nitrite sensor was constructed based on electrodeposition of gold nanoparticles (AuNPs) on a copper calcined layered double hydroxide (Cu-CLDH) modified glassy carbon electrode. Electrochemical experiments showed that AuNPs/CLDH com

Full text of DOI:10.1016/j.electacta.2011.08.026

Electrochimica Acta 56 (2011) 9769–9774
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Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
Electro-oxidation nitrite based on copper calcined layered double hydroxide and
gold nanoparticles modified glassy carbon electrode
∗
Lin Cui, Xiaomeng Meng, Minrong Xu, Kun Shang, Shiyun Ai , Yinping Liu
College of Chemistry and Material Science, Shandong Agricultural University, Taian 271018, Shandong, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 23 June 2011
Received in revised form 4 August 2011
Accepted 8 August 2011
Available online 31 August 2011
In this paper, a novel nitrite sensor was constructed based on electrodeposition of gold nanoparticles
(AuNPs) on a copper calcined layered double hydroxide (Cu-CLDH) modified glassy carbon electrode. Elec-
trochemical experiments showed that AuNPs/CLDH composite film exhibited excellent electrocatalytic
oxidation activity with nitrite due to the synergistic effect of the Cu-CLDH with AuNPs. The fabricated
sensor exhibited excellent performance for nitrite detection within a wide concentration interval of
1
–191 ␮M and with a detection limit of 0.5 ␮M. The superior electrocatalytic response to nitrite was
Keywords:
Calcined layered double hydroxides
mainly attributed to the large surface area, minimized diffusion resistance, and enhanced electron trans-
fer of the Cu-CLDH and AuNPs composition film. This platform offers a novel route for nitrite sensing with
wide analytical applications and will supply the practical applications for a variety of simple, robust, and
easy-to-manufacture analytical approaches in the future.
(
CLDHs)
Gold nanoparticles (AuNPs)
Nitrite
Non-enzymatic
© 2011 Elsevier Ltd. All rights reserved.
1
. Introduction
incorporation of DNA and Cyt c for the electrochemical oxidation
of nitrite [14], and both of the biosensors showed a fast response
−
Nitrite (NO2 ) is a typical inorganic pollutant and its anthro-
to nitrite. Although the enzymatic biosensors had good selectivity
and high sensitivity, their stability was limited due to easy denat-
uration by environmental changes because their catalytic activity
originated from the intrinsic nature of enzymes [15], and due to
leakage of the enzymes during their storage and the immobiliza-
tion procedure. Moreover, the preparation and purification of the
enzymes was usually time-consuming and expensive. Therefore,
many efforts have been made to develop non-enzymatic sensors to
solve these problems.
It is becoming more and more significant in analytical chemistry
to take advantages of various inorganic nanomaterials, because of
the following intrinsic advantages: regular structures, chemical and
thermal stabilities, high surface reaction activity, high catalytic effi-
ciency, large surface-to-volume ratio, and strong adsorption ability
[16]. There are many such kinds of inorganic nanomaterials, such as
clay [17,18], macroporous active carbon [19], zeolite [20], sol–gel
matrix [21], metallic carbon nanotubes [22–24], transition metal
disulfide [25], transition metal oxides [26–31], and conducting
polymers [32]. Each of these materials has been used in the con-
struction of non-enzymatic electrochemical sensors because of its
unique and particular properties.
pogenic sources include wastes from fertilizers, preservative, and
adulterants in food [1]. Nitrite promotes the irreversible oxidiza-
tion of hemoglobin and reduces the capability of the blood to
transport oxygen [2]. In addition, it can react with amines to form N-
nitrosamines, many of which are known carcinogens [3,4]. Hence,
selective and sensitive methods for nitrite detection have become
important. There are many analytical technologies for nitrite detec-
tion, and these technologies mainly utilize spectrophotometry,
chromatography, capillary electrophoresis chemiluminescence, or
electrochemistry. Electrochemical techniques have been proven to
be among the most advantageous methods for the determination
of nitrite, and nitrite sensors that are based on electrochemical
methods [5,6], especially biosensors [7–11], are most favorable.
Most nitrite biosensors are dependent on protein catalysis for
a reductive reaction by nitrite. However, these kinds of biosen-
sors are complicated and the products are complex [10–12]. Thus,
the electrochemical oxidation of nitrite with enzymatic and non-
enzymatic nitrite sensors has been studied in recent years. We
have constructed two types of nitrite biosensors that are based on
the immobilization of Cytochrome c (Cyt c) on multi-walled car-
bon nanotubes (MWCNT)–poly(amidoamine) (PAMAM)–chitosan
Calcination products of layered double hydroxides (LDHs),
known as calcined layered double hydroxides (CLDHs), owe their
popularity to their numerous attributes such as their larger sur-
face areas, higher metal dispersion, smaller crystallite size, greater
stability against sintering, and lower diffusion resistance than
LDHs [33]. Moreover, CLDHs have the advantages of having porous
(
Chit) nanocomposites [13]. This nanocomposite, with the
∗ Corresponding author. Tel.: +86 538 8247660; fax: +86 538 8242251.
E-mail addresses: ashy@sdau.edu.cn, chemashy@yahoo.com.cn (S. Ai).
0
013-4686/$ – see front matter © 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.electacta.2011.08.026

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L. Cui et al. / Electrochimica Acta 56 (2011) 9769–9774
structures and both of abundant acidic and basic sites [34], which
can bind to an enzyme. The synthesis of sheets of CLDHs that con-
tain transition metal ions is of particular interest because of the
strongly enhanced activity of the oxidation properties of these met-
als in mixed oxides. CLDHs, especially those containing Cu, were
investigated for the ability to selectively hydrogenate cinnamalde-
hyde [35] and for good catalytic properties in the catalytic oxidation
of phenol [36–38]. In previous work, we had also used Cu-CLDH
as a mimic of peroxidase to detect the hydrogen peroxide [39].
Following this work, we demonstrated the construction of a new
amperometric sensor for electro-oxidation of nitrites based on Cu-
CLDH and AuNPs.
The AuNPs/CLDH composite film was fabricated and electro-
chemically characterized to explore its catalytic activity for nitrite
oxidation. This material exhibited excellent performance for nitrite
electro-oxidation, such as a high electrocatalytic activity, a low
detection limit, and good selectivity. The AuNPs/CLDH modified
electrode opens up new opportunities for fast, simple, and sensitive
analyses of nitrite. With its enhanced stability, ease of prepara-
tion, and special properties, AuNPs, coupled with CLDH composite,
can be used as a new material for use in a wide range of poten-
tial applications in sensors, biotechnology, and environmental
chemistry.
2.3. Preparation of the different modified electrodes
Prior to modification, the glassy carbon electrode (GCE) was
carefully polished with 0.3 ␮m and 0.03 ␮m ␣-alumina powders
in sequence. It was then sonicated in anhydrous ethanol for 3 min
and then in double distilled deionized water for 3 min. Next, it
−
1
was dried with nitrogen. A Cu-CLDH (2 mg mL ) solution was
first prepared with redistilled deionized water, followed by ultra-
sonication for 2 h. With a microinjector, 10 ␮L of the Cu-CLDH
solution was deposited onto the electrode surface. After the sol-
vent had evaporated, the electrode surface was thoroughly rinsed
with redistilled deionized water and dried in air, this electrode
was denoted as CLDH/GCE. Next, CLDH/GCE was immersed into a
3.0 mM HAuCl4 solution containing 0.2 M Na SO . Electrodeposi-
2
4
tion of Au nanoparticles was carried out at −0.2 V for 45 s, followed
by gentle washing in double distilled deionized water and dry-
ing by nitrogen blowing. This modified electrode was denoted as
AuNPs/CLDH/GCE. Both of the modified electrodes were stored at
◦
4 C in a refrigerator before use.
2.4. Analytical application
In order to investigate the applicability of the proposed anal-
ysis method, different ham samples were analyzed to determine
nitrite concentration. The pretreatment was performed according
to a previous report [41]. In brief, 5 g of crushed sample was mixed
with 12.5 mL of saturated borax solution. Next, redistilled deion-
ized water was added, and the mixture was heated until boiling
for 15 min. To precipitate the proteins, 2.5 mL of 30% ZnSO4 was
introduced, and after cooling to room temperature, the resulting
mixture was diluted to 50 mL with redistilled deionized water and
2
. Experimental
2.1. Reagents and apparatus
Mg(NO ) ·6H O, Al(NO ) ·9H O, Cu(NO ) ·3H O, and other
3
2
2
3 3
2
3 2
2
chemicals that were obtained from the Chemical Reagent Company
of Shanghai (China) were of pure analytical grade and used without
further purification. Hydrogen tetrachloroaurate (HAuCl ·4H O)
◦
then filtered. The resulting sample solution was stored at 4 C until
it was mixed with 0.1 M PBS (pH 7.0) for nitrite determination using
the proposed procedure.
4
2
was obtained from Sigma. Phosphate buffer solution (PBS) was
prepared by mixing a stock solution of 0.1 M NaH PO4 and 0.1 M
2
Na HPO4 and adjusting the pH either with 0.1 M H PO4 or 0.1 M
3. Results and discussion
2
3
NaOH. All of the chemicals were of analytical reagent grade,
and all of the solutions were prepared with redistilled deionized
water.
3.1. Characterization of Cu-CLDH
Electrochemical experiments were performed with CHI660C
electrochemical workstation (Shanghai Chenhua Co., China) with
a conventional three-electrode cell. A bare glassy carbon elec-
trode (d = 3 mm) or a modified glassy carbon electrode was used
as the working electrode. A saturated calomel electrode (SCE) and
a platinum wire were used as the reference electrode and auxiliary
electrode, respectively. Scanning electron microscopy (SEM) was
performed on a Hitachi S-3000N instrument (Japan), and powder
X-ray diffraction (XRD) patterns were carried out with a Rigaku
D/MAX 2200PC X-ray diffractometer (Japan) with Cu K␣ radia-
tion (ꢀ = 0.154178 nm, graphite monochromator, 28 kV and 20 mA).
The typical XRD pattern of Cu-CLDH is shown in Fig. 1A. The
◦
◦
sample was scanned for 2ꢁ, ranging from 10 to 80 , and the XRD
analysis revealed that Cu-CLDH was composed of CuO (JCPDS-ICDD
80-1916), which has a high crystallinity. The calcination of LDH
◦
at 500 C destroyed its layered structure completely and resulted
in the formation of spinel phases, which was accompanied by a
tenorite phase (CuO). Fig. 1B displays a typical SEM image of the
Cu-CLDH and shows that many pores on the surface of Cu-CLDH
◦
can be observed. After being calcinated at 500 C, sample sinter-
ing occurred, LDH started to break into smaller pieces and pores
appeared due to the loss of water and anions. Therefore, a Cu-
CLDH film could give a larger specific surface area, a high surface
reaction activity, and an efficient transmission channel for the ana-
lyzed molecules to reach the active sites, which will all help to
improve the stability and sensitivity of the modified electrode. After
electrodeposition of AuNPs onto the CLDH/GCE, the AuNPs were
inserted into the porous structure of the CLDH (see supporting
information, Fig. 1S).
◦
◦
Additionally, a 2ꢁ range (from 10 to 80 ) was investigated at a
◦
−1
.
scanning speed of 10 min
2.2. Preparation of Cu-CLDH
The Cu-LDH was prepared as in a previous report [40]. Briefly,
a 20 mL solution containing 1.208 g Cu(NO ) , 3.846 g Mg(NO )
3
2
3 2
and 3.751 g Al(NO ) , was titrated with a 20 mL mixture solution of
3.2. Electrochemical impedance spectroscopy characterization
3
3
2
.40 g NaOH and 5.30 g Na CO under vigorous stirring. During syn-
2 3
◦
thesis, the temperature was maintained at 25 C, and the resulting
suspension was subsequently kept at 65 C for 1 h with stirring. The
Electrochemical impedance spectroscopy (EIS) was carried out
to investigate the changes in electron transfer resistance (Ret) that
were detected by surface-modified sensors. Fig. 2 shows Nyquist
plots for bare GCE (a), CLDH/GCE (b), and AuNPs/CLDH/GCE (c) in
5.0 × 10 M [Fe(CN)6]
be seen, curve b presents a larger semicircle domain compared
◦
resulting product was filtered and washed thoroughly with deion-
ized water until a neutral pH was obtained and then dried at 60 C
◦
−
3
3−/4−
solution containing 0.1 M KCl. As can
for two days in air. The Cu-CLDH was obtained by heating Cu-LDH
◦
in a muffle furnace at 500 C for 7 h.

L. Cui et al. / Electrochimica Acta 56 (2011) 9769–9774
9771
Fig. 1. XRD (A) and SEM (B) images of the Cu-CLDH.
to curve a, implying a very large Ret on the CLDH nanostructures
modified electrode. This increase was attributed to the non-
conductive properties of CLDH. After the AuNPs were deposited
onto the CLDH/GCE, the AuNPs/CLDH/GCE showed a lower interfa-
cial electron-transfer resistance, as seen in curve c, indicating that
good conductivity by the AuNPs could hold high electron-transfer
efficiency. It also suggested that CLDH was successfully immobi-
lized on the GCE surface.
shown in Fig. 4B, the cathodic and anodic peak currents increased
linearly with the increase of the square root of the scan rates,
−
1
from 20 to 200 mV s , showing a diffusion-controlled process.
This result might be attributed to a slow electron hopping across
the matrix of the composite membrane. At higher sweep rates
−
1
(300–1000 mV s ), the peak currents became proportional to the
scan rate (inset in Fig. 4C), which indicated that the reaction was a
surface-controlled process.
As shown in Fig. 4D, a graph of Ep = f(log v) yields two straight
lines with slopes of −2.3 RT/˛nF and 2.3 RT/(1 − ˛)nF for the
cathodic peak and anodic peak, respectively. Thus, the value of ˛
can be estimated to be 0.52 from the slopes of the straight lines
based on the following equation [42]:
3
.3. Electrochemical property of AuNPs/CLDH/GCE
Electrochemical behaviors of the differently modified electrodes
in 0.1 M PBS (pH 7.0) were investigated using cyclic voltammetry.
As can be seen in Fig. 3, no redox peaks for the bare GCE (curve
a) or AuNPs modified GCE is observed (curve b). However, the
AuNPs/CLDH modified electrode exhibited a pair of well-defined
peaks at +117 mV and +191 mV (curve c), which were attributed to
the redox of Cu /Cu in the AuNPs/CLDH conjugate. Moreover, from
the inset in Fig. 3, it is evident that the redox peaks current of the
Cu-CLDH/GCE was much smaller than that of the AuNPs/CLDH/GCE;
meanwhile, a peak separation (ꢂEp) was much larger. This indi-
cated that the AuNPs played an important role in facilitating the
electron exchange between the Cu-CLDH and glassy carbon elec-
trode surface.
v
v
a
˛
log
= log
(1)
c
1 − ˛
In order to calculate the value of the apparent heterogeneous
II
I
electron transfer rate constant (k ), the following Laviron equation
s
was used [42]:
RT ˛(1 − ˛)nFꢂEp
log ks = ˛ log(1−˛)+(1−˛) log ˛− log
−
(2)
nFv
2.3RT
where ˛ is the electron transfer coefficient, n is the number of elec-
trons, ꢂEp is the separation of the redox peaks, and v is the scan
rate. ks can therefore be calculated to be 1.05 ± 0.2 s−
1
.
3.4. Influence of scan rate
Cyclic voltammograms (CVs) of the AuNPs/CLDH/GCE in 0.1 M
PBS (pH 7.0) at different scan rates were studied (Fig. 4A). As
Fig. 3. Cyclic voltammograms of bare GCE (a), AuNPs/GCE (b) and AuNPs/CLDH/GCE
−
1
Fig. 2. Nyquist plot of the bare GCE (a), CLDH/GCE (b) and AuNPs/CLDH/GCE (c) in
(c) in a solution of 0.1 M PBS (pH 7.0) at 100 mV s . Inset: the CV of Cu-CLDH/GCE
in 0.1 M PBS (pH 7.0) at 100 mV s
mM [Fe(CN)6]3
−/4−
containing 0.1 M KCl.
−1
.
5

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L. Cui et al. / Electrochimica Acta 56 (2011) 9769–9774
Fig. 4. (A) Cyclic voltammograms of the AuNPs/CLDH/GCE at different scan rates in 0.1 M PBS (pH 7.0). Scan rates from (a) to (q) are as follows: 20, 40, 60, 80, 120, 140, 160,
−1
1
80, 200, 300, 400, 500, 600, 700, 800, 900, and 1000 mV s , respectively. (B) The dependence of current on the square root of the scan rate. (C) Plots of anodic and cathodic
peak currents versus scan rate. (D) Variation of anodic and cathodic peak potentials versus the logarithm of the scan rate.
−
3.5. Electrochemical effective surface area
NO2 at the bare GCE, CLDH/GCE, and AuNPs/CLDH/GCE are shown
−
in the inset of Fig. 5. At the bare GCE, the CV of NO2 demonstrated
Fig. 2S (see supporting information, Fig. 2S) shows the plots of
a wave with an anodic peak potential (Epa) of 1.03 V. The oxida-
tion peak current of NO2 at the CLDH/GCE was greater than at the
1
/2
−
Q–t and Q–t
at the bare GCE and AuNPs/CLDH modified elec-
−4
trodes in 1 × 10 M K [Fe(CN) ] solution containing 1 M KCl. From
bare GCE, and the potential shifted negatively to 0.942 V. This result
might be attributed to the porous structure of CLDH possessing a
larger surface area, which could provide a favorable microenviron-
3
6
1/2
the slope of the plot of Q versus t , the electrochemical effec-
tive surface area for the bare GCE and the AuNPs/CLDH/GCE could
−
4
−
be calculated by chronocoulometry using 1 × 10 M K [Fe(CN) ]
ment for more NO2 oxidation. After the AuNPs were deposited
3
6
as a model complex (the diffusion coefficient D of K [Fe(CN) ] is
onto the CLDH surface, the anodic peak potential shifted nega-
tively to 0.763 V, which was much lower than 0.9 V, as was shown
in our previous work [13]. It also showed about a 2-fold larger peak
current (ipa) signal than for the bare GCE, indicating that AuNPs
3
6
6
2
−1
7
.6 × 10− cm s [43]) and based on Eq. (3) given by Anson [44]:
2
nFAcD1/2t1/2
ꢃ1/2
Q(t) =
+ Qdl + Qads
(3)
−
facilitated faster electron-transfer kinetics of the NO2 oxidation.
where n is the electron transfer number; A is the surface area of
the working electrode; c is the concentration of substrate; D is the
diffusion coefficient; Qdl is the double layer charge which could
be eliminated by background subtraction; and Qads is the Faradaic
charge. Other symbols have their usual meanings. The plots of Q–t
This result might be explained by CLDH composite film provid-
ing abundant active sites and Au nanoparticles improving the
1/2
and Q–t
Q and t
are shown in Fig. 2S. The linear relationship between
1/2
1/2
could be expressed as follows: Q = 2.165 t − 0.1860
1/2
(
for the GCE, ␮C, s1/2, R = 0.9948), Q = 13.63 t − 13.08 (for the
1/2
AuNPs/CLDH/GCE, ␮C, s , R = 0.9919). Using these equations, A
could be calculated to be 0.0721 cm2 and 0.164 cm2 for the GCE
and AuNPs/CLDH/GCE, respectively. These results indicated that
the effective surface area of the electrode increased obviously after
modification of the GCE with AuNPs/CLDH, which would enhance
−
the current response of NO2 on the electrode.
−
3
.6. Electro-oxidation behavior of NO2 on the AuNPs/CLDH/GCE
Fig. 5 shows typical CVs of the AuNPs/CLDH/GCE in the absence
−
−1
and presence of NO2 at a scan rate of 100 mV s in a 0.1 M PBS
(
−
pH 7.0) solution. Upon addition of NO2 , an obvious anodic peak
was observed, and the peak current increased significantly with
−
increasing NO2 concentrations (see b–d in Fig. 5). Moreover, the
Fig. 5. Cyclic voltammograms for the AuNPs/CLDH/GCE in a 0.1 M PBS (pH 7.0) at
electrocatalytic behaviors of the differently modified electrodes
towards the electrochemical oxidation of NO2 were also investi-
gated by analyzing the CVs. The cyclic voltammograms for 100 ␮M
−
various concentrations of NO2 : (a) 0 ␮M, (b) 25 ␮M, (c) 50 ␮M, (d) 75 ␮M, and (e)
−
−1
−
. Inset: CVs of 100 ␮M NO2 using the bare GCE
100 ␮M, at scan rate of 100 mV s
(e), CLDH/GCE (f) and AuNPs/CLDH/GCE (g) in the same conditions.

L. Cui et al. / Electrochimica Acta 56 (2011) 9769–9774
9773
−
Fig. 6. (A) Cyclic voltammograms at the AuNPs/CLDH/GCE in 0.1 M PBS (pH 7.0) and 100 ␮M NO2 at different scan rates (from a to j: 20, 40, 60, 80, 120, 160, 200, 300, 400,
−1
5
00 mV s , respectively). (B) The linear dependence of the anodic peak current on the square root of the scan rate.
−
electrocatalytic activity for NO2 . The catalytic oxidation mecha-
nism can be explained with the following process:
process [47]. Having a porous structure, Cu-CLDH together with
−
AuNPs could catalyze the oxidation of NO2
.
−
−
NO2 ↔ 2NO + 2e
(4)
(5)
(6)
2
−
3
.7. Amperometric response of the proposed NO2 biosensor
−
2
NO + H O → NO + NO − + 2H+
2
2
3
2
Fig. 7 records the amperometric current–time curves of the
AuNPs/CLDH/GCE at an applied potential of +0.763 V upon the suc-
cessive addition of NO2 to a continuously stirred solution of 0.1 M
PBS (pH 7.0). With the addition of NO2 , a drastic increase in the
−
−
+ 2H+ + 2e−
NO2 + H O → NO
2
3
−
−
First, nitrite loses an electron to form NO [reaction (4)]. Second,
2
this step is followed by a homogeneous disproportionation [reac-
response current was observed (Fig. 7A). The response to the addi-
tion of NO2 was very fast and reached the steady-state value (95%
−
tion (5)] of NO into nitrate and nitrite, which can be written as the
2
total reaction (6) [45,46].
of the maximum current) in less than 3 s. Such a fast response
−
The influence of the Cu-CLDH load, ranging from 0.5 to
implied that the AuNPs/CLDH could promote the oxidation of NO2
.
−
1
−
4
mg mL , on the cyclic voltammetry of 1.0 mM NO2 in a 0.1 M
The faster response was mainly attributed to the synergistic effect
of CLDH and AuNPs providing a necessary conductive pathway to
PBS (pH 7.0) was studied (see supporting information, Fig. 3S).
The current response increased with an increasing loaded amount
of Cu-CLDH until it reached 2 mg mL , but the current response
decreased when the Cu-CLDH load amount increased further. This
could be caused by the active center being blocked and/or by
increasing film thickness. Hence, a Cu-CLDH load of 2 mg mL was
used throughout this work.
Fig. 6A presents cyclic voltammograms of the AuNPs/CLDH/GCE
at different scan rates in PBS (pH 7.0) containing 1.0 mM NaNO2.
The peak current increased linearly with the square root of the
−
transfer electrons of NO2 , which were favorable for nitrite oxi-
−
1
dation. As shown in Fig. 7B, the response was proportional to the
−
concentration of NO2 in the ranges of 1–191 ␮M (R = 0.999), with a
detection limit of 0.5 ␮M, a signal-to-noise ratio of 3 and a high sen-
−
1
−1
sitivity of 382.2 ␮A mM . Although the detection limit was higher
than that of a CuNPs/thiol/Au electrode [10], it was much lower
than that of inorganic material or protein nitrite sensors, such as
the following: a ccNiR/Nf/MV/GCE (60 ␮M) [48], a Hb-meso-Al O -
2
3
PVA/GCE (30 ␮M) [49], a Ferricyanide/CPE (26.3 ␮M) [50], a copper
modified electrode (11 ␮M) [51], a Mb-ZnO/GCE (4 ␮M) [8], a nano-
Au/P3MT/GCE(2.3 ␮M) [6], a catalase/MWNTs/GCE (1.35 ␮M) [52],
and a Hb/nano-Au/TiO2 sol–gel/GCE (1.2 ␮M) [10]. This indicated
−
1
1/2
scan rate in the range of 20–500 mV s ; ipa = −3.629 − 13.92 v
−1/2
(
␮A, mV s
, R = 0.9960) (Fig. 6B). The results suggested that
the kinetics of the overall process were controlled by a diffusion
Fig. 7. (A) Typical current–time curve of the AuNPs/CLDH/GCE upon the successive addition of 1, 10 or 20 ␮M NaNO2 into a gently stirred solution of 0.1 M PBS (pH 7.0) at
0.763 V. (B) The linear relationships between the catalytic current and the NaNO2 concentration.
+

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L. Cui et al. / Electrochimica Acta 56 (2011) 9769–9774
Table 1
Determination of nitrite in three different ham samples.
−
−
Founda (NO2 , ␮M)
−
Sample
Content (NO2 , ␮M)
Added (NO2 , ␮M)
Spectroscopy
R.S.D. (%)
Recovery (%)
1
2
3
1.95 ± 0.21
2.02 ± 0.32
1.89 ± 0.20
2.50
2.50
2.50
4.49 ± 0.25
4.58 ± 0.34
4.28 ± 0.23
4.53 ± 0.31
4.61 ± 0.43
4.32 ± 0.36
3.2
2.8
2.5
100.9
101.33
97.49
a
Mean for five separate measurements.
that this proposed method could potentially be used for sensitively
monitoring the concentration of NaNO2.
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.8. Interference
[
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[
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The potential interference for the detection of nitrite using this
biosensor was also examined by adding the following ions into the
PBS solution (pH 7.0) at the same concentration that was used for
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+
+
2+
2+
−
−
−
2−
2−
,
3
1869.
−
2−
3−
H PO , HPO4 and PO4 . None of the ions caused interference.
2
4
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The fabrication reproducibility of six electrodes, carried out
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−
ing 1.0 mM NO2 with a relative standard deviation (R.S.D.) of 6.8%.
[
[
When not in use, the sensors were suspended in 0.1 M PBS in a
◦
refrigerator at 4 C. The operational and storage stability of the pro-
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−
of 1.0 mM NO2 every 3 days for over 1 month. It was found that
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−
the peak current for NO2 oxidation retained 92% of its initial cur-
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1
-month of storage. These results implied that the modified elec-
6
trode was stable.
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In order to evaluate the performance and feasibility of this
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The AuNPs/CLDH modified electrode was prepared and it offers
−
−
a remarkable decrease in the overvoltage for NO2 oxidation.
This sensor was constructed successfully for NO2 determina-
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cost, convenient preparation and rapid detection. Furthermore, the
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3
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selective sensor for the detection of NO2 in real samples.
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Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
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