ammonia gas sensor based on electrosynthesized polypyrrole films

Talanta 78 (2009) 199–206
Contents lists available at ScienceDirect
Talanta
journal homepage: www.elsevier.com/locate/talanta
Ammonia gas sensor based on electrosynthesized polypyrrole films
Stéphanie Carquigny
a,b
, Jean-Baptiste Sanchez
a
, Franck Berger
a
,
Boris Lakard
b,∗
, Fabrice Lallemand
b
a
LCPR-AC, UMR CEA E4, Université de Franche-Comté, Bâtiment Propédeutique, 16 route de Gray, 25030 Besanc¸ on Cedex, France
b
Institut UTINAM, UMR CNRS 6213, Université de Franche-Comté, Bâtiment Propédeutique, 16 route de Gray, 25030 Besanc¸ on Cedex, France
article info
Article history:
Received 28 July 2008
Received in revised form 24 October 2008
Accepted 31 October 2008
Available online 11 November 2008
Keywords:
Gas sensor
Ammonia
Polypyrrole
Electrochemistry

abstract
In this work, design and fabrication of micro-gas-sensors, polymerization and deposition of poly(pyrrole)
thin films as sensitive layer for the micro-gas-sensors by electrochemical processing, and characterization
of the polymer films by FTIR, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy
(SEM), are reported. The change in conductance of thin polymer layers is used as a sensor signal. The
behaviours, including sensitivity, reproducibility and reversibility, to various ammonia gas concentrations
ranging from 8 ppm to 1000 ppm are investigated. The influence of the temperature on the electrical
response of the sensors is also studied. The experimental results show that these ammonia gas sensors
are efficient since they are sensitive to ammonia, reversible and reproducible at room temperature.
© 2008 Elsevier B.V. All rights reserved.
1. Introduction
Polypyrrole (PPy) has attracted considerable attention because
of the possibility to use redox reactions for transforming it into
states of strongly differing electrical conductivity [1] and because
PPy has a good stability in air and aqueous media. PPy and other
conductive polymers have, therefore, also been classified as organic
metals. There exists a wide range of applications to use organic
metals, such as: cell culture substrates [2,3], field effect transistors
[4–6], light-emitting diodes [7], solar cells [8–10], electrochromic
devices [11,12], electronic circuits [13,14], elastic textile composites
[15], supercapacitors for energy storage and secondary batteries
[16], protection of metals [17,18], ion exchange membranes that
respond to external stimulations [19,20], sensors and biosensors
[21–27]. More, in recent years, attention has also been given to the
use of conducting polymers as active layers in chemical gas sen-
sors, and it has been proved that adsorbed gas molecules (ammonia,
NO
2
,CO
2

) and organic vapors (alcohols, ethers, halocarbons) cause
a change of electrical conductivity in the polymer matrix of organic
metals [28–33]. In comparison with most of thecommercially avail-
able sensors, based usually on metal oxides and operating at high
temperatures, the sensors made of conducting polymers have many
improved characteristics. They have high sensitivities and short
response time; especially, these feathers are ensured at room tem-
perature.
∗
Corresponding author. Tel.: +33 3 63 08 25 78.
E-mail address: (B. Lakard).
Thus, in this paper, an original ammonia gas sensor based on
micropatterned microelectrodes functionalized by electropolymer-
ization of polypyrrole films is studied. Electrochemical deposition
has been chosen since it is the most convenient method to deposit
conducting polymer films [34–36]. Indeed, the thickness of the film
can be controlled by the total charge passed through the elec-
trochemical cell during the film growing process. More, such a
deposition also allows the preparation of films at a well-defined
redox potential in the presence of a given counter-ion, which then
also defines the level and characteristics of the doping reaction
[37]. Thus, electropolymerization is used in this study to fabricate
a gas sensor consisting in PPy films deposited on microstructured
electrode arrays and also across the insulating gap separating the
microstructured electrodes of the sensor. Indeed, if the insulat-
ing gap between the neighboring electrodes is close enough (a
few micrometers), the growing film can cover the insulated gap
and connect electrodes [38,39]. This is important in fabricating
chemiresistors for gas sensing. A microstructured interdigitated
electrode array was chosen since it represents the most suit-

able geometry to serve as a transducer in chemical gas sensors,
based on conductivity changes. Following their deposition, theelec-
tropolymerized polypyrrole layers are characterized by infrared
spectroscopy (IR), X-ray photoelectron spectroscopy (XPS) and
scanning electron microscopy (SEM). Then,polymerfilms are tested
as ammonia gas sensors. In particular, their response, in terms of
conductance changes when exposed to different ammonia concen-
tration, was studied. The reproducibility and the reversibility of the
signal exhibited by the PPy films to ammonia exposure but also the
influence of temperature on this response are also studied.
0039-9140/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.talanta.2008.10.056
200 S. Carquigny et al. / Talanta 78 (2009) 199–206
Fig. 1. (a) Experimental set-up used for the analysis of NH
3
vapors and (b) schematic drawing of the ammonia gas sensor.
2. Experimental
2.1. Fabrication of gas sensors
The gas sensors were fabricated using microsystem technolo-
gies, and in particular using lift-off process that consists in a
photolithography followed by a sputtering of platinum on a SiO
2
wafer. The first step of the photolithography process consisted in
drawing the required pattern (see Fig. 1) with commercial mask
design software Cadence. Then a Cr/Glass mask, on which the shape
of the pattern has been drawn, was made with an electromask
optical pattern generator. The process started with a 100-oriented
standard 3

silicon wafer, which was thermally wet-oxidized, at

1200
◦
C in water vapor, in order to produce a 1.3 ␮m thickness SiO
2
layer. Next, a 1.4-␮m thickness layer of negative photoresist (AZ
5214, from Clariant), suitable for lift-off, was deposited by spin
coating. Then, the wafer was first exposed with the mask to a 36-
mJ/cm
2
UV radiation flux delivered by an EVG 620 apparatus, and
then without any mask to a 210-mJ/cm
2
UV radiation flux. Thus,
the pattern was transferred to the resist, which was then devel-
oped, using AZ 726 developer, to dissolve the resist where the metal
was deposited. Then, a magnetron sputtering (Alcatel SCM 441
apparatus) was used to coat microsystems with titanium (30 nm,
used to improve platinum layer), then platinum (150 nm). The fab-
rication parameters for Pt and Ti films were the following ones:
base pressure: 4.6 × 10
−7
mbar, pressure (Ar) during sputtering:
5 × 10
−3
mbar, power: 150 W, target material purity: 99.99%, film
thickness: 150 nm for Pt films and 30 nm for Ti films. The remaining
resist layer was then dissolved using acetone. After the gas sensors
have been fabricated, thepattern and the dimensions are controlled
using an optical microscope. More details about the microsystem
fabrication can be found in a previous paper [27]. A microstruc-

tured interdigitated electrode array was chosen since it represents
the most suitable geometry to serve as a transducer in chemical gas
sensors, based on conductivity changes. Thewidth and length of the
100 bands (50 bands on each microelectrode array) were 10 0 ␮m
and 9996 ␮m, respectively (Fig. 1). The width of the gap between
the two microelectrode array was 4 ␮m to allow the coating of the
gap by the polypyrrole film.
2.2. Electrochemistry
Pyrrole (Py) and LiClO
4
were obtained from Sigma–Aldrich (ana-
lytical grade). Pyrrole was use d at the concentration of 0.05 M in
an aqueous solution of 0.1 M LiClO
4
. The electrochemical appara-
tus was a classical three-electrode set-up using a Tacussel PGZ301,
from Radiometer, potentiostat–galvanostat. The microsystem was
used as working electrode. The reference electrode was a saturated
calomel electrode (SCE) and the counter-electrode was a platinum
wire. All electrochemical experiments were carried out at room
temperature (293 K). Cyclic voltammetry experiments were car-
ried out with a sweep rate of 100 mV s
−1
between −0.3 V/SCE and
+1.5 V/SCE. Each solution was purged by ultrahigh purity argon.
Chronoamperometry experiments were carried out at a potential
of +1.3 V/SCE.
2.3. Characterization of the polymer films
2.3.1. XPS
The polymer surface was characterized by X-ray photoelectron

spectroscopy (XPS, SSX-100 spectrometer). XPS was used to control
the elemental composition and to determine the oxidation state of
elements. All recorded spectra were recorded at a 35
◦
take-off angle
relative to the substrate with a spectrometer using the monochro-
matized Al K␣ radiation (1486.6 eV). The binding energies of the
core-levels were calibrated against the C
1s
binding energy set at
285.0 eV, an energy characteristic of alkyl moieties. The peaks were
analyzed using mixed Gaussian–Lorentzian curves (80% ofGaussian
character).
2.3.2. SEM
Examinations of polymer morphologies were performed using
a high-resolution scanning electron microscope. Once synthesize d
and dried, polymer samples were examined in a LEO microscope
(SEM LEO stereoscan 440, manufactured by Zeiss–Leica, Köln, Ger-
many) with an electron beam energy of 15 keV.
2.3.3. IRTF-ATR
All spectra were recorded using a Shimadzu spectrometer
(IR-Prestige 21) in ATR reflexion mode. The specific accessory
used for these analyses is the ATR Miracle Diamond/KRS5 which
allowed us to record spectra between 4000 cm
−1
and 700 cm
−1
.
Resolution was fixed at 4 cm
−1

and 60 scans were realized to
acquire each spectrum. All samples were constituted with PPy
powder.
S. Carquigny et al. / Talanta 78 (2009) 199–206 201
Fig. 2. Electrochemical synthesis of polypyrrole films by oxidation of an aqueous solution of pyrrole and LiClO
4
by cyclic voltammetry (a) or chronoamperometry (b).
2.4. Gas measurements
An initial ammonia concentration equal to 1000 ppm in nitro-
gen was used for the experiment. All the studies were carried
out in nitrogen atmosphere. The sensor’s electrical responses were
obtained by monitoring the variations in the sensor’s instantaneous
conductance versus acquisition time, for a constant temperature of
the sensitive layer. The conductance measurements lasted about
3 h for each acquisition. The protocol used for the conductance
experiments was the same for each sensor. Each sensor’s electri-
cal response was obtained under a constant gas flow (N
2
or NH
3
diluted in N
2
)rateof50mLmin
−1
. Specially designed equipment
was developed for this study. Mass flowmeters were used to obtain
different NH
3
concentrations. This experimental set-up allowed
PPy-based gas sensors to be exposed to the different ammonia

concentrations.
The effect of gases on the sensor’s electrical properties was
recorded using a basic divisor voltage bridge (Fig. 1). With these
experimental conditions, the relationship between the variation
of the sensor’s conductance and the variation of the voltage U
R
is
defined as:
G
C
=
1
R((E/U
R
) − 1)
Any decrease (or increase) of the sensor’s conductance was
recorded as a decrease (or increase) of the electrical signal.
Each new sensor was exposed to a constant nitrogen flow for
12 h before conducing each experiment. This process allowed for
the desorption of pollutant chemical compounds adsorbed onto
the sensitive layer during the storage.
3. Results and discussion
3.1. Electrochemical synthesis of polymer films
Electrochemical synthesis of polypyrrole was performed by
cyclic voltammetry, from an aqueous solution containing 0.1 M pyr-
role and 0.1 MLiClO
4
, on the platinum microelectrodes of the sensor
using a potential sweep rate of 0.1 V s
−1

between −0.3 V/SCE and
+1.5 V/SCE (Fig. 2a). For this aqueous solution of pyrrole, the first
scan showed the oxidation of pyrrole at +1.25 V/SCE. Following
scans showed the oxidation peak of polypyrrole at +0.5 V/SCE and
the reduction peak of polypyrrole at about +0.2V/SCE. Moreover,
the polymer film is a conductive one since the current remains
constant during all the potential scans.
PPy films can also be formed at a constant potential. As in the
case of polymer formation by potential scans, the films are homo-
geneous and very adherent to the substrate. From Fig. 2a, we chose
to carry out the potentiostatic depositions at +1.3 V/SCE. Fig. 2b
shows the I–t curves obtained for a fixed potential of +1.3 V/SCE
and for a deposition time of 60 s. This chronoamperometric curve
shows that, after an increase corresponding to the formation of
pyrrole cation radicals, the current decreases following a linear rela-
tionship with t
−1/2
. This behaviour indicates a diffusion-controlled
process. This current response is due to the nucleation and growth
of the polymer. At longer times, after the nucleation transient, the
chronoamperometry shows a constant I–t response for PPy.
3.2. XPS characterization of the polypyrrole films
Fig. 3a shows the XPS of the films obtained from the oxidation of
an aqueous solution containing pyrrole and LiClO
4
since this tech-
nique is widely used to control the elemental composition of a solid
film. The XPS analyses confirm the presence of PPy, incorporating
ClO
4

−
doping agents, on the platinum surfaces. Indeed, XPS spec-
tra of polymer samples reveal the presence of C, N, O, Cl, Pt for
all polymers. Thus, C
1s
signal (Fig. 3b) can be fitted by five differ-
ent carbon species at 284.0, 284.8, 286.1, 287.8 and 289.8 eV. The
two components at the lowest binding energy relevant to ␤ and
␣ carbon atoms, respectively, revealed the first interesting finding.
In fact, the comparison of these two carbon atoms areas showed
that, following overoxidation, the ␤ carbons in the film were less
abundant than the ␣ ones. This indicates, that the ␤ positions were
the ones involved in the polymer functionalization. The third peak
at 286.1 eV is attributed to carbons of the polymer C
NorC N
+
;
the fourth one at 287.8 eV to C
N
+
carbons and the peak much
weaker at 289.8 eV to carbonyl C
O groups. The appearance of a
C
O component may be associated with the overoxidation of PPy
at the ␤ carbon site in the pyrrole rings. The N
1s
spectra (Fig. 3c)
indicate the presence of four peaks in the case of PPy. It contains a
main signal at 399.6eV which is characteristic of pyrrolylium nitro-

gens (
NH-structure) and a high BE tail (BE = 400.4 and 402.0 eV)
attributable to the positively charged nitrogen (
NH
+
(polaron) and
NH
+
(bipolaron). The spectra also show a small contribution at
397.0 eV that we associate with
N-structure. Fig. 3d represents
the Cl
2p
core-level XPS spectrum at 207.5 eV binding energy due
to the perchlorate anions present in the film as a doping agent.
Consequently, these XPS spectra confirm that polypyrrole films
incorporating ClO
4
−
doping agents are obtained from the oxidation
of pyrrole in various solvents.
202 S. Carquigny et al. / Talanta 78 (2009) 199–206
Fig. 3. Survey-scan XPS of polypyrrole films electrosynthesized by oxidation of an aqueous solution of pyrrole and LiClO
4
(a). (b) C 1s (c) N 1s (d) Cl 2p XPS spectra of the
same polypyrrole film.
3.3. Morphological characterization
Scanning electron microscopy was used to determine the sur-
face morphology of the polypyrrole films on the microstructured
electrode arrays but also to check that PPy films were deposited

across the insulating gap on the microstructured electrode arrays.
Thus, Fig. 4 shows that the whole surface of the platinum micro-
electrodes is coated by a homogeneous and very compact film of
polypyrrole composed of many nodules (1–2 ␮m long). The mean
Fig. 4. SEM image of PPy film grown on the sensor surface.
film thickness of this polypyrrole film (x) was estimated to 2.25 ␮m
from the electrical charge (q), associated with pyrrole oxidation by
application of Faraday’s law and assuming 100% current efficiency
for polypyrrole formation: x = qM/AzF, where M is the molar mass
of the polymer, F is the Faraday constant,  is the density of the
polymer and z is the number of electrons involved. The nominal
density of the polypyrrole films ()wastakenas1.5gcm
−3
and an
electron loss z of 2.25 was considered.
More, Fig. 4 shows that nodules of PPy are also present in the
insulating gap between the microelectrodes indicating that the
growing film covers the insulated gap and connect microelectrodes.
This point is important since the PPy layer must connect each pair
of interdigitated electrodes in order to obtain the sensitive layer of
the gas sensor.
3.4. Evaluation of the sensor’s electrical signal under NH
3
flow
Firstly, the sensor was exposed to a NH
3
flow at a concentration
equal to 500 ppm with a temperature of the sensitive layer near to
room temperature. The signal’s electrical variation was recorded
versus time. Fig. 5a represents the evolution of the PPy’s conduc-

tance in presence of ammonia and nitrogen. The curve shows the
evolution of the electrical signal when the sensor is first stabilised
under N
2
flow (until 300 s.), second exposed to NH
3
flow (from 300 s
to 6000 s) and then to nitrogen flow (from 600 s to 14,000 s). This
acquisition protocol was used for all the experiments described in
this paper.
In presence of pollutant in the gas chamber (NH
3
), we clearly
notice a decrease in sensor’s sensitive layer conductance. Ammo-
nia reacts with the PPy and induces a modification of the sensor’s
sensitive layer electrical properties. After ammonia exposition, the
S. Carquigny et al. / Talanta 78 (2009) 199–206 203
Fig. 5. Sensor’s electrical response under NH
3
(500 ppm) and N
2
flow.
sensor is submitted to a nitrogen flow (after 6000 s). Fig. 5a indi-
cates an increase of the sensor’s conductance. This modification of
conductance can be attributed to the desorption of ammonia from
sensitive layer. Among to this electrical variation under NH
3
flow,
it is possible to obtain one supplementary information. Looking at
the beginning of the exposition to pollutant flow, the conductance

variation is linear with time. In this way, the calculation of the slope
value gives us information about the sensitivity of the gas sensor.
For a concentration of ammonia equal to 500 ppm the value of the
slope equals to 63.20 nS s
−1
.
In order to evaluate a possible reproductibility of the gas sensor
under ammonia flow at room temperature, we studied two succes-
sive electrical responses of the same gas sensor under pollutant.
The purpose was to compare thesensor’s conductance between two
successive acquisitions. In Fig. 5b is represented the first electrical
response obtained under a constant NH
3
flow and nitrogen flow.
The second curve shows the successive response under NH
3
flow
and N
2
flow after a nitrogen flow exposition of the sensitive layer
during 12 h at room temperature. As shown in Fig. 5b, we notice
a superposition of the signal under ammonia flow during the first
minutes of acquisition. If we consider that the sensor’s electrical
response is measured by referring to experimental point obtained
at the beginning of the exposition of the sensor, one can say that the
electrical signal is reproductible with the same sensor at room tem-
perature. The values of the slope are nearly the same (63.20 nS s
−1
and 65.42 nS s
−1

).
By comparing the two acquisitions (Fig. 5b curves 1 and 2),
when the sensor is rinsed with nitrogen flow, the second electrical
response is slightly shifted. This phenomenon is probably due to a
chemical modification of thesensitive surface after a first detection.
This point will be confirmed with infrared analysis.
Various ammonia concentrations from 8 ppm to 1000 ppm were
tested using the same sensor. Fig. 6a shows some of the electri-
cal responses obtained for various ammonia concentrations. Before
each pollutant expositions, the gas sensor is stabilised by nitrogen
flow during 12 h at room temperature.
Fig. 6a shows a decrease of the instantaneous conductance for
each NH
3
concentrations. This decrease depends on the concen-
trations of the pollutant in the gas chamber. In particular, if we
determine the value of theslope of the electrical responses obtained
for each ammonia concentrations, we can plot the variation of
the slope versus ammonia concentrations. Fig. 6b represents the
evolution of the slope versus the ammonia concentration. Above
concentrations of 500 ppm, we noticed a smooth plate which was
due to the saturation of the sensitive layer. For lower concentra-
tions, there is a linear relationship between the value of the slope
and the ammonia’s concentration.
3.5. Influence of the sensitive layer’s temperature on the sensor’s
electrical signal under NH
3
flow
Chemiresistors, based on metallic oxides, generally works at
high temperatures (about 450

◦
C) in order to optimize the elec-
trical response. In order to evaluate the impact of temperatures on
the electrical signal of the PPy-based gas sensor, the sensing layer
was heated at temperatures ranging from 25
◦
Cto100
◦
C(Table 1).
A concentration of ammonia equals to 500 ppm was used for this
experiment. Curves show the evolution of the electrical signal when
Fig. 6. Sensor’s electrical responses to various ammonia concentrations (a). Slope of the gas sensor’s electrical response vs. NH
3
concentrations (b).
204 S. Carquigny et al. / Talanta 78 (2009) 199–206
Fig. 7. Infrared spectra of polypyrrole powder before and after an exposition to ammonia flow for 1 h.
Table 1
Values of the slope under ammonia flow at different temperatures.
PPy’s temperature (
◦
C) Slope (nS s
−1
)
25 116.72
50 72.29
75 74.04
100 78.57
the sensor is first stabilised under N
2
flow (until 400 s), second

exposed to NH
3
flow (from 400 s to 1200 s) and then to nitrogen
flow (from 1200 s to 3500 s).
Looking at Table 1 which represents the values of the slope for
each temperature, we understand that an increase of the PPy’s sen-
sitive layer temperature decreases the sensitivity of the gas sensor.
The best sensitivity was obtained at room temperature. Conse-
quently, in term of power consumption, the PPy-based gas sensor
show very interesting detection properties compared to resistive
sensors which have higher working temperatures (300–500
◦
C).
3.6. Interaction mechanism
In order to understand the interaction mechanism between
ammonia and the gas sensor’s sensitive surface we proceed to
an infrared characterization of PPy powder before and after being
exposed to NH
3
flow.
First we characterized the PPy powder unexposed to NH
3
vapors. The spectrum represented in Fig. 7a shows the presence
of broad absorption bands characteristics of polypyrrole material.
These absorption bands corresponds to: N
H stretching in sec-
ondary amine (3600 cm
−1
), N H deformation in secondary amine
(1600 cm

−1
), C C aromatic stretching (1400 cm
−1
)etC N stretch-
ing (1050cm
−1
).
Then, in order to understand the mechanism of ammonia
adsorption onto PPy surfaces, polypyrrole samples were exposed
during 1 h to NH
3
1000 ppm flow. The spectra obtained for this
sample, compared to PPy under N
2
, is represented in Fig. 7b. Com-
pared to the PPy powder spectrum (Fig. 7a), two broad absorption
bands appeared when PPy was exposed to NH
3
flow. The first
one at 3260 cm
−1
may be attributed to the stretching vibration
of N
H binding in NH
3
+◦
radical group. The second one seems
to be superposed to the C
C aromatic stretching band centered
at 1400 cm

−1
. This latter band may be attributed to N H bend-
ing vibration. These results confirmed that the interaction between
NH
3
and PPy-induced chemical modifications of the sensitive layer.
These infrared analyses explained the shift observed between two
successive NH
3
detections using PPy-based gas sensors.
According to the infrared results, we propose an interaction
mechanism for the adsorption of ammonia onto polypyrrole thin
films. The different stages of ammonia adsorption onto the PPy
layer which is considered as a p-type semi-conducting material
(positive hole conduction) are the following ones:
S. Carquigny et al. / Talanta 78 (2009) 199–206 205
The first step of this mechanism is the lost of an electron by the
doublet of nitrogen of some nitrogens of the polymer backbone.
This electron transfer between ammonia molecule and the poly-
mer’s positive hole induces a diminution of the sensitive positive
charge density which leads to a decrease in the conductance layer.
After adsorption of NH
3
, the polymer becomes less conducting. In
this mechanism, it is proposed that ammonia is adsorbed onto PPy
surface forming NH
3
+
◦
radical groups according to infra-red spec-

tra. This mechanism is completing the various works realised on the
ammonia detection studies using PPy-based gas sensors [40,41].
3.7. Comparison with other works
Before this study, other authors used conducting polymer
films to develop gas sensors. These polymer films were obtained
using different techniques. The most often used technique was
the chemical deposition by dip-coating [42–45], and the oth-
ers were: spin-coating from soluble conducting polymers [46,47],
thermal evaporation by heating and deposition of the conduct-
ing polymer on a substrate [48], vapor deposition polymerization
[49], drop-coating of a dried polymer solution [50,51], UV-
photopolymerization [52], deposition of Langmuir–Blodgett film
[53] and electrochemical deposition [54,55]. We decide to use this
latter technique since the thickness of the film can be controlled
by the total charge passed through the electrochemical cell dur-
ing film growing process. Moreover, the film can be deposited
on patterned microelectrode arrays [38]. However, if the insulat-
ing gap between the neighboring electrodes is close enough, the
growing film can cover the insulated gap and connect electrodes
[39].
Amongst the various polymer films, polypyrrole is one of the
most studied andinteresting in particularthanks to its high conduc-
tivity. Consequently, many papers have already used this polymer
as active layer of gas sensors. Thus, PPy obtained by chemical oxi-
dation was used for the detection of CO [56],CO
2
[57], xylene
[58], alcohols [43,59,60] or acetone [61]. PPy obtained by vapor
deposition polymerization was also used for the detection of
methanol, ethanol, CCl

4
and benzene [62]. PPy obtained by UV-
photopolymerization was used for the detection of sevoflurane
[52]. It can also be noticed that the surfaces coated by PPy in all
these studies were either gold microelectrode arrays deposited on
aluminia substrates [43,52,56,58,60] or ITO substrates [57,59,62].
Polypyrrole deposited by electrochemical way was also incorpo-
rated in gas sensors for the detection of ethanol gas [54], benzene,
xylene and toluene [55].
Other studies focused on ammonia gas sensors using polypyr-
role as sensitive layer. Thus, an ammonia gas sensor based on
Langmuir–Blodgett PPy film was developed but its lower detectable
limit was of 100 ppm of NH
3
in N
2
[53]. Bai et al. have electrochemi-
cally co-polymerized polypyrrole and sulfonated polyaniline on an
ITO substrate to obtain an ammonia sensor but it was efficient only
for ammonia concentration higher than 20 ppm [63]. Another study
from Brie et al. presents an ammonia sensor using electrosynthe-
sized PPy film, with various doping agents, but this study is limited
to concentrations higher than 10 ppm [32]. Thus, only a study by
Guernion et al. presented an ammonia sensor giving a response
below 10 ppm but in this study PPy is chemically oxidized on a
poly(etheretherketone) surface [64]. Concerning ammonia sensors
using polymer films deposited on microelectrode arrays, an inter-
esting work was carrie d out by Lin et al. [65]. In this work an
electrosynthesized copolymer PPy–poly(vinyl alcohol) was used
and was efficient for ammonia gas concentrations ranging from

50 ppm to 150 ppm. Consequently, the results obtained in our study
are competitive with all these results since the ammonia gas sen-
sors developed in this paper showed a detectable limit of 8ppm
of NH
3
in N
2
. More, the best responses were obtained at room
temperature and were reproductible.
4. Conclusion
The aim of this work was to validate the use of polypyrrole-based
gas sensor for the detection of ammonia at concentrations lower
than 10 ppm. From this study we first electrosynthesized PPy films
doped with small anions ClO
−
4
on metallic electrodes to develop
a chemical resistor gas sensor. A homogeneous polymer deposited
film with a thickness close to the micrometer was obtained. The
various tests conducted under ammonia flow showed an interest-
ing sensitivity (lower than 10 ppm) and a good reproductibility. By
comparison withmost of chemiresistors gas sensors, our PPy-based
sensor presents best sensitivity at room temperature.
References
[1] J. Albuquerque, L. Mattoso, D. Balogh, R. Faria, J. Masters, A.G. MacDiarmid,
Synth. Met. 113 (2000) 19.
[2] H.K. Song, B. Toste, K. Ahmann, D. Hoffman-Kim, G.T.R. Palmore, Biomaterials
27 (2006) 473.
[3] W.R. Stauffer, X.T. Cui, Biomaterials 27 (2006) 2405.
[4] C.D. Dimitrakopoulos, P.R.L. Malenfant, Adv. Mater. 14 (2002) 99.

[5] R. Poddar, C. Luo, Solid-State Electron. 50 (2006) 1681.
[6] H.E.A. Huitema, G.H. Gelinck, J.B.P.H. van der Putten, K.E. Kuijk, C.M. Hart, E.
Cantatore, P.T. Herwig, A.J.J.M. van Breemen, D.M. de Leeuw, Nature 414 (2001)
599.
[7] A. Kraft, A.C. Grimsdale, A.B. Holmes (Eds.), Angew. Chem. Int. 37 (1998) 402.
[8] W.U. Huynh, J.J. Dittmer, A.P. Alivisatos, Science 295 (2002) 2425.
[9] B. Sun, E. Marx, N.C. Greenham, Nano Lett. 3 (2003) 961.
[10] G. Yu, J. Gao, J.C. Hummelen, F. Wudl, A.J. Heeger, Science 270 (1995) 1789.
[11] A.A. Argun, A. Cirpan, J.R. Reynolds, Adv. Mater. 15 (2003) 1338.
[12] D. DeLongchamp, P.T. Hammond, Adv. Mater. 13 (2001) 1455.
[13] B. Crone, A. Dodabalapur, Y.Y. Lin, R.W. Filas, Z. Bao, A. LaDuca, R. Sarpeshkar,
H.E. Katz, W. Li, Nature 403 (2000) 521.
[14] C.J. Drury, C.M.J. Mutsaers, C.M. Hart, M. Matters, D.M. de Leeuw, Appl. Phys.
Lett. 73 (1998) 108.
[15] H.K. Kim, M.S. Kim, S.Y. Chun, Y.H. Park, B.S. Jeon, J.Y. Lee, Y.K. Hong, J. Joo, S.H.
Kim, Mol. Cryst. Liq. Cryst. 405 (2003) 161.
[16] M. Hughes, M.S.P. Shaffer, A.C. Renouf, C. Singh, G.Z. Chen, D.J. Fray, A.H. Windle,
Adv. Mater. 14 (2002) 382.
[17] S.U. Rahman, M.A. Abul-Hamayel, B.J. Abdul Aleem, Surf. Coat. Technol. 200
(2006) 2948.
[18] C.M. Li, C.Q. Sun, W. Chen, L. Pan, Surf. Coat. Technol. 198 (2005) 474.
[19] J.W. Gardner, P.N. Bartlett, Sens. Actuators A A51 (1995) 57.
[20] T. Zama, S. Hara, W. Takashima, K. Kaneto, Bull. Chem. Soc., Jpn. 78 (2005) 506.
[21] A. Mazzoldi, A. Della Santa, D.E. De Rossi, Polymer Sensors and Actuators,
Springer-Verlag (Ed.), Heidelberg, 1999, pp. 207–244.
[22] C. Hagleitner, A. Hierlemann, D. Lange, A. Kummer, N. Kerness, O. Brand, H.
Baltes, Nature 414 (2001) 293.
[23] G. Chen, Z. Guan, C.T. Chen, L. Fu, V. Sundaresan, F.H. Arnold, Nat. Biotechnol.
15 (1997) 354.
[24] U. Lange, N.V. Roznyatovskaya, V.M. Mirsky, Anal. Chim. Acta 614 (2008) 1.

[25] B. Lakard, O. Segut, S. Lakard, G. Herlem, T. Gharbi, Sens. Actuators B 122 (2007)
101.
[26] S. Lakard, G. Herlem, N. Valles-Villareal, G.Michel, A. Propper, T. Gharbi, B. Fahys,
Biosens. Bioelectron. 20 (2005) 1946.
[27] O. Segut, B. Lakard, G. Herlem, J.Y. Rauch, J.C. Jeannot, L. Robert, B. Fahys, Anal.
Chim. Acta 597 (2007) 313.
[28] L. Torsi, M. Pezzuto, P. Siciliano, R. Rella, L. Sabbatini, L. Valli, P.G. Zambonin,
Sens. Actuators B 48 (1998) 362.
[29] R. Gangopadhyay, A. De, Sens. Actuators B 77 (2001) 326.
[30] J. Janata, M. Josowicz, Nat. Mater. 2 (2003) 19.
[31] A.C. Partridge, P. Harris, M.K. Andrews, Analyst 121 (1996) 1349.
[32] M. Brie, R. Turcu, C. Neamtu, S. Pruneanu, Sens. Actuators B 37 (1996) 119.
[33] M. Matsuguchi, J. Io, G. Sugiyama, Y. Sakai, Synth. Met. 128 (2002) 15.
[34] J.M. Slater, E.J. Watt, N.J. Freeman, I.P. May, D.J. Weir, Analyst 117 (1992) 1265.
[35] J.W. Gardner, M. Vidic, P. Ingleby, A .C. Pike, J.E. Brignell, P. Scivier, P.N. Bartlett,
A.J. Duke, J.M. Elliott, Sens. Actuators B 48 (1998) 289.
[36] P. Ingleby, J.W. Gardner, P.N. Bartlett, Sens. Actuators B 57 (1999) 17.
[37] M. Gross, D. Müller, H.G. Nothofer, U. Scherf, D. Neher, C. Braüchle, K. Meerholz,
Nature 405 (2000) 661.
[38] G.W. Lu, L.T. Qu, G.Q. Shi, Electrochim. Acta 51 (2005) 340.
[39] J. Reemts, J. Parisi, D. Schlettwein, Thin Solid Films 466 (20 04) 320.
[40] H. Bai, G. Shi, Sensors 7 (2007) 267.
[41] I. Lähdesmäki, W.K. Kubiak, A. Lewenstam, A. Ivaska, Talanta 52 (2000)
269.
[42] S.T. McGovern, G.M. Spinks, G.G. Wallace, Sens. Actuators B 107 (2005) 657.
206 S. Carquigny et al. / Talanta 78 (2009) 199–206
[43] J.H. Cho, J.B. Yu, J.S. Kim, S.O. Sohn, D.D. Lee, J.S. Huh, Sens. Actuators B 108
(2005) 389.
[44] S. Brady, K.T. Lau, W. Megill, G.G. Wallace, D. Diamond, Synth. Met. 154 (2005)
25.

[45] M.S. Silverstein, H.W. Tai, A. Sergienko, Y.L. Lumelsky, S. Pavlovsky, Polymer 46
(2005) 6682.
[46] G.K. Prasad, T.P. Radhakrishnan, D.S. Kumar, M.G. Krishna, Sens. Actuators B 106
(2005) 626.
[47] R. Tongpool, S. Yoriya, Thin Solid Films 477 (2005) 148.
[48] N.E. Agbor, M.C. Petty, A.P. Monkman, Sens. Actuators B 28 (1995) 173.
[49] E. Stussi, S. Cella, G. Serra, G.S. Venier, Mater. Sci. Eng.C4(1996) 27.
[50] L. Ruangchuay, A. Sirivat, J. Schwank, React. Funct. Polym. 61 (2004) 11.
[51] H.G.O. Sandberg, T.G. Backlund, R. Osterbacka, S. Jussila, T. Makela, H. Stubb,
Synth. Met. 155 (2005) 662.
[52] R.J. Wu, Y.C. Huang, M. Chavali, T.H. Lin, S.L. Hung, H.N. Luk, Sens. Actuators B
126 (2007) 387.
[53] M. Penza, E. Milella, M.B. Alba, A. Quirini, L. Vasanelli, Sens. Actuators B 40
(1997) 205.
[54] Q. Fang, D.G. Chetwynd, J.A. Covington, C.S. Toh, J.W. Gardner, Sens. Actuators
B 84 (2002) 66.
[55] J.N. Barisci, G.G. Wallace, M.K. Andrews, A.C. Partridge, P.D. Harris, Sens. Actu-
ators B 84 (2002) 252.
[56] S. Radhakrishnan, S. Paul, Sens. Actuators B 125 (2007) 60.
[57] S.A. Waghuley, S.M. Yenorkar, S.S. Yawale, S.P. Yawale, Sens. Actuators B 128
(2008) 366.
[58] C.W. Lin, Y.L. Liu, R. Thangamuthu, Sens. Actuators B 94 (2003) 36.
[59] J.E.G. de Souza, F.L. dos Santos, B.B. Neto, C.G. dos Santos, M.V.B. dos Santos, C.P.
de Melo, Sens. Actuators B 88 (2003) 246.
[60] H.K. Jun, Y.S. Hoh, B.S. Lee, S.T. Lee, J.O. Lim, D.D. Lee, J.S. Huh, Sens. Actuators B
96 (2003) 576.
[61] J.B. Yu, H.G. Byun, M.S. So, J.S. Huh, Sens. Actuators B 108 (2005) 305.
[62] C.P. de Melo, B.B. Neto, E.G. de Lima, L.F.B. de Lira, J.E.G. de Souza, Sens. Actuators
B 109 (2005) 348.
[63] H. Bai, Q. Chen, C. Li, C. Lu, G. Shi, Polymer 48 (20 07) 4015.

[64] N. Guernion, R.J. Ewen, K. Pihlainen, N.M. R atcliffe, G.C. Teare, Synth. Met. 126
(2002) 301.
[65] C.W. Lin, B.J. Hwang, C.R. Lee, Mater. Chem. Phys. 58 (1999) 114.