1. Sensors and Actuators B 191 (2014) 643–649
Contents lists available at ScienceDirect
Sensors and Actuators B: Chemical
journal homepage: www.elsevier.com/locate/snb
Bio-inspired sensor for insect pheromone analysis based on
polyaniline functionalized AFM cantilever sensor
Clarice Steffensa,b,∗
, Alexandra Manzolia
, Juliano E. Oliveirac
, Fabio L. Leited
,
Daniel S. Correaa,b
, Paulo Sergio P. Herrmanna,b,e,∗
a
National Nanotechnology Laboratory for Agribusiness (LNNA), Embrapa Instrumentation, P.O. Box 741, 13560-970 São Carlos, SP, Brazil
b
Federal University of São Carlos (UFSCar), Campus São Carlos, 18052-780 São Carlos, SP, Brazil
c
Federal University of Paraiba (UFPB), Campus João Pessoa, 58051-900 João Pessoa, PB, Brazil
d
Federal University of São Carlos (UFSCar), Campus Sorocaba, 18052-780 Sorocaba, SP, Brazil
e
Embrapa Labex Europe – Germany, Forschungszentrum Jülich, Institute of Bio-Geoscience 2, 52428 Jülich, NWF, Germany
a r t i c l e i n f o
Article history:
Received 3 July 2013
Received in revised form 7 September 2013
Accepted 13 October 2013
Available online xxx
Keywords:
Sensor
Pheromone
Functionalization of cantilever
Conductive polymer
Polyaniline
a b s t r a c t
Bio-inspired materials designed for mimicking nature has gained attention in the last years, owing to
their appealing properties, such as adhesive and self-cleaning properties. However, studies reporting
bio-inspired sensors able to detect minimal amounts of pheromones are still scarce. Here we report on
the functionalization of AFM cantilever with polyaniline (PANI), which was used as a sensor to detect
pheromone 2-heptanone. This hormone is very significant for honey bees, which release it as a repellent
scent marking to avoid enemies and other bees. The functionalization of the sensor was achieved by
depositing a thin film of PANI in the emeraldine state on the cantilever through spin-coating. Infrared
spectroscopy showed that the 2-heptanone was adsorbed by PANI film deposited on cantilever surface.
The linear response of the coated cantilever sensor regarding 2-heptanone concentration for distinct tem-
peratures was evaluated, as well as its mechanical behavior, hysteresis and storage time. The approach
proposed here to functionalize AFM cantilever with PANI film to detect 2-heptanone showed a poten-
tial methodology for designing sensors able to detect minimal amounts of pheromones and natural
compounds.
© 2013 Elsevier B.V. All rights reserved.
1. Introduction
The development of insect colonies is dependent on the com-
munication system established between them, and in some cases
the pheromones released by insects display an important role.
Specifically for honeybees, pheromone 2-heptanone, secreted from
mandibular glands, plays the role of repellent scent marking and
alarm compound to avoid enemies and other robber bees [1,2].
2-Heptanone is not an exclusive hormone used by bees, but it is
also known as an aroma constituent in some types of food, such as
Roquefort cheese, coffee fruits and others [3–5]. Given the signif-
icance of the pheromone 2-heptanone, new strategies to develop
chemical sensors, able to mimic biological receptors that can detect
minimal amounts of different types of pheromones, are of great
importance.
∗ Corresponding authors at: National Nanotechnology Laboratory for Agribusi-
ness (LNNA), Embrapa Instrumentation, P.O. Box 741, 13560-970 São Carlos, SP,
Brazil. Tel.: +55 5435209000; fax: +55 5435209090.
E-mail addresses: clarices@uricer.edu.br, claristeffens@yahoo.com (C. Steffens).
Furthermore, the study of insect pheromones (semiochemi-
cals) for controlled release and environmental monitoring are very
important, since they can provide alternatives to reduce the use of
insecticides and to control insect populations. Among the devices
used for monitoring pheromones, the use of electroantennogram
(EAG) (sensors developed with insect antennae) technique is
promising [6]. The EAG technique employs the insect antenna as a
biosensor for the identification of electroactive molecules, and con-
sists in placing the insect antenna between two electrodes through
a conductive gel. Through a chemical stimulus caused by ions dif-
fusion across the neuronal membrane, changes in the electrical
potential between the antennas can be recorded. Such method-
ology has proven to be of high resolution for analyzing complex
mixtures extracted from plants or insects. However, this approach
presents some drawbacks, since it requires a continuous humidified
air flow to avoid dehydration of the antenna. Moreover, the time for
testing is about 20 min, which is long considering the short lifetime
of the device, and it is very difficult to remove and fix the antenna
to the equipment [7].
The miniaturization of chemical sensors is a target that has been
pursued by scientists in the last years, since they find applications
in quality food control industry, forensic investigation, biosensors
0925-4005/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.snb.2013.10.053

2. 644 C. Steffens et al. / Sensors and Actuators B 191 (2014) 643–649
for medical diagnosis, portable devices for water and air quality
control, among others [8–16]. Depending on the materials compo-
sition, miniaturization of sensors can enhance their functionality
and properties. Among several types of materials employed as the
“sensing component” of chemical sensors, conductive polymers,
which possess a pi-extended bonding system, are an interesting
choice, owing to their properties such as high sensitivity on the sur-
rounding medium, wide range of synthesis routes, thermal stability
[17,18]. Polyaniline (PANI), for instance, in its several oxidation
states, has found applications as antistatic agent, anticorrosive
coatings, taste sensors, vapor sensor, electroactive membranes, and
electrochromic displays [15,19–23]. One potential approach that
can help the task of miniaturizing sensors is through the func-
tionalization of atomic force microscopy (AFM) cantilevers [24],
although combined efforts are also necessary to reduce the size
of laser sources coupled to commercial AFM equipment. By coating
the cantilever with a layer of active material such as a conductive
polymer, and exposing it to the analyte under investigation, it is
possible to transduce a chemical reaction into a mechanical stim-
ulus, such as changes in surface stress, mechanical deformation, or
mass change [25–27]. This approach is able to detect very small
amounts of the analyte under investigation, with a high degree of
accuracy.
The sensor presented in this work is based on the function-
alization of AFM cantilever with spin-coated film of PANI in the
emeraldine oxidation state, through surface polymerization. The
functionalization was evaluated by Fourier transform infrared
(FTIR) spectroscopy and the response of the sensor was evalu-
ated by measuring the AFM cantilever deflection in the presence
of the pheromone 2-heptanone, at several concentrations and dis-
tinct temperatures. The cyclic mechanical behavior of the coated
cantilever was also studied, in addition to its storage time, sensitiv-
ity, reversibility, repeatability and hysteresis, which parameters are
fundamental for designing reliable and accurate sensor for detec-
ting pheromones.
2. Experimental
2.1. Materials
The PANI interfacial polymerization synthesis in emeraldine
oxidation state was employed due to its ease of synthesis and also to
obtain nanofibers. This synthesis occurs at the interface, between
two immiscible and liquid phases, each containing a reagent, as
described by Huang et al. [10]. For the interfacial synthesis, aniline
(monomer) was dissolved in an organic solvent (dichloroethane)
with the oxidant agent (ammonium persulfate) in hydrochloric
acid (HCl) (1 mol/L). All the reagents used had analytical grade
P.A and were used without any further purification. We employed
ultrapure water presenting resistivity of 18 M cm−1 (Milli-Q sys-
tem Millipore Inc.). Then, the oxidant solution was slowly added
to the monomer solution in order to avoid mixing of the phases.
The reaction was performed in a sealed chemical glass bottle for
2 h, and subsequently filtered (filter paper Milipore 25 ␮m) and
washed with methanol and Mili-Q water. The filtrate was dedoped
in ammonium hydroxide (0.1 M NH4OH) 0.1 mol/L by stirring and
dried for 12 h in a desiccator under vacuum, which yielded the PANI
(salt) in its emeraldine oxidation state. The PANI (salt) was sol-
ubilized in N-methyl pyrrolidinone (NMP) solvent, because PANI
in emeraldine base (dedoped) is completely soluble NMP second
Angelopolous et al. [28]. This dedoped solution was used to func-
tionalize the AFM cantilever surface.
The silicon microcantilevers were purchased from NT-MDT
company, with resonance frequency of 12 (±2) kHz, spring con-
stant of 0.03–0.13 N m−1 and dimensions (rectangular shape) of
350.0 ␮m-length; 30.0 ␮m-width and 0.5–1.5 ␮m thickness. The
microcantilevers surfaces were cleaned by employing plasma
“sputtering” in high vacuum. The argon gas pressure was lower
than 0.1 mbar and the background pressure was 0.1 mbar. As exper-
imental variables, we employed a radio frequency of 40 kHz, power
of 150 W and treatment temperature of 130 ◦C. Subsequently the
microcantilevers were dried in an oven at 50 ◦C for 10 h and stored
in vacuum desiccator.
The pheromone 2-heptanone (MM = 114.18 g/mol, den-
sity = 0.82 g/cm3 (20 ◦C) and boiling point: 150–152 ◦C) was
purchased from Aldrich and used without further purification.
2.2. Polyaniline-modified cantilever
The AFM cantilever used to detect 2-heptanone pheromone was
functionalized with PANI in salt emeraldine oxidation state, doped
with HCl, thin film by the spin-coating method. For that purpose,
3 ␮L of the dedoped PANI solution was added to the AFM can-
tilever surface, which was placed in the spin coater, which was
operated using a rotation of 500 rpm for 8 s, increased to 1000 rpm
for 15 s, and finally maintained at 3000 rpm for 60 s. Subsequently,
cantilevers sensors were dried in a desiccator under vacuum for
12 h at room temperature and finally doped with HCl (1 mol/L).
Silicon wafers (antimony doped type) were purchased com-
mercially (NT-MDT) and coated with PANI films using the same
experimental parameters used to functionalize the AFM cantilever,
aiming at verifying the influence of the spin-coated PANI on its sur-
face roughness. To detect and distinguish the characteristic peaks
of PANI and 2-heptanone through FTIR measurements (Nicolet 470
Nexus FTIR spectrometer) silicon wafer coated with doped PANI
films was prepared using the same experimental conditions used
to functionalize the AFM cantilever. In addition, we also collected
the FTIR spectra of PANI films on silicon wafers in atmosphere con-
taining the pheromone 2-heptanone.
The morphology and roughness of PANI films deposited on
the microcantilevers surfaces were analyzed with a Dimension V
(Veeco) AFM, using a silicon nitride tip attached to a cantilever
with a spring constant of 42 N m−1 and resonance frequency of
285 kHz. All images were obtained in tappingTM mode at a scan
rate of 0.001 kHz. The images and RMS (root-mean-square aver-
age) roughness were processed with the aid of the Gwydion© 2.1
data analysis software. RMS can be described by [29]:
RMS =
1
N
N
i=1
Z2
i
1/2
(1)
being N the number of data points and Z the distance from the mean
surface level.
The coated and uncoated microcantilever surfaces were char-
acterized with a field emission scanning electron microscope
(FE-SEM) (JEOL, JSM-6701F), operating at 5 kV for determining the
size, shape and distribution of the PANI films.
2.3. Sensor performance measurements
The performance of the sensor was evaluated by measuring the
deflection of the coated and uncoated (reference) cantilever in an
AFM. The deflections were measured in voltage, with resolution
of millivolts (mV), through monitoring the laser beam position,
which is focused at the endpoint of the cantilever and reflected
to a four-quadrant photodiode. This signal value was converted
in nanometers after obtaining the system sensitivity. All measure-
ments of deflection were performed in triplicate at static mode of
operation.

3. C. Steffens et al. / Sensors and Actuators B 191 (2014) 643–649 645
Fig. 1. AFM images (2D) of (a) pure silicon wafers (uncoated) and (b) silicon wafers modified with spin-coated films of PANI.
The functionalization was done in just one side of the microcan-
tilever sensor. The cantilever displacement, caused by 2-heptanone
adsorption, is monitored by using a laser apparatus where the bend-
ing is induced by an increase in surface stress on the functionalized
side of the cantilever. Although the oscillating mode in dynamic
AFM can also be used as a sensing plataform for monitoring liq-
uid samples, as reported by [30], in this work we used the static
mode for analyzing volatiles in an atmosphere with very low con-
tent of pheromone concentration, which results have proven that
the AFM functionalized microcantilever provided high sensitivity
to pheromone.
The deflection of the functionalized cantilever as a function of
the pheromone concentration at 10, 20 and 30 ◦C was measured by
inserting with a syringe defined amounts (in ppmv, calculated by
using the ideal gas equation) of 2-heptanone in the AFM chamber,
with sequential measurements of the AFM cantilever deflection.
After the deflection measurements, nitrogen was inserted into the
chamber to clean it up, in which procedure was repeated for every
set of measurements.
The flux of the gas inside the chamber was 10 mL/min, which
was obtained using a commercial flowmeter (Aalborg). For exper-
iments at temperatures of 10, 20 and 30 ◦C, a heated water-bath
(Nova Ética, Model 521/2D) was used to maintain the chamber
temperature constant. The temperature and humidity inside of
the chamber (9 mL) was monitored with a commercial sensor
(SensiriumTM).
The cantilever sensing performance for 2-heptanone in the pres-
ence of other pheromones, such as linalool and orange oil (vegetal
based pheromones), was evaluated by inserting 5 wt% of the two
other pheromones in the AFM chamber, after it was stabilized with
1000 ppmv of 2-heptanone in an atmosphere at 20 ◦C (controlled
temperature). The choice of linalool and orange oil to be investi-
gated together with 2-heptanone in the sensor performance was
made based on the fact that they are all floral odorants [31–34]. In
this sense, linalool and orange oil they are “interferents” for playing
the same biological effect of 2-heptanone (pheromone) for bees, but
as we could observed in our results, they do not interfere greatly
on the sensor performance for 2-heptanone.
The pheromone content was varied from 0 to 1000 ppmv (cal-
culated by the ideal gas equation) by insertion and removal of
2-heptanone from the AFM chamber. The sensor response as a func-
tion of storage time, for periods of 0, 15, 30, 45 and 60 days, was
evaluated by measuring the deflection of the functionalized can-
tilever in the presence of 2-heptanone as a function of time (from 0
to 1000 min). Cantilevers sensors were stored in a vacuum desicca-
tor and before each analysis were doped with HCl 1 M. Before all the
measurements with the cantilevers sensors, the AFM equipment
was stabilized for 2 h to reach a stable baseline.
3. Results and discussion
3.1. Characterization of PANI film and pheromone
The deposition of PANI films by spin-coating on the surface of
the AFM cantilever can alter considerably its surface roughness,
which was corroborated by the RMS values when comparing the
coated and uncoated surface. Uncoated Silicon surface presented a
roughness of 0.002 (±0.0003) ␮m, while the modified silicon sur-
face with PANI film presented a roughness of 0.079 (±0.007) ␮m,
considering a superficial area of 100.0 ␮m2. The increase in rough-
ness shown in Fig. 1(b) is caused by the presence of spin-coated
film of PANI over the substrate, which provides chemical sensing
properties to the AFM cantilever. The PANI-coated microcantilever
(Fig. 1(b)) displays a uniform layer formed with the presence of
polymeric aggregates, which plays an important role on the sensor
sensitivity.
SEM images of uncoated and PANI-coated microcantilever (see
procedure in Section 2) are displayed in Fig. 2(a)–(c), in which
functionalization followed the same procedure of the silicon sub-
strates. Fig. 2(b) and (c) shows in detail the morphology of PANI
films deposited on the microcantilever tip surface, which displays
nanofibers-like structures, with diameters lower than 100 nm.
Such increase in surface area, due to the nanofibers presence, is
highly desirable for designing sensitive layer in sensors, once it
provides a more efficient interaction with the analyte, increas-
ing the sensor sensitivity for detecting small changes in analytes
[21,35].
To verify the interaction of 2-heptanone with PANI films, we
obtained the FTIR spectra of pure PANI film deposited on silicon
wafer, and that in an atmosphere containing 2-heptanona. Both
spectra are displayed in Fig. 3. The bands located at 1100, 3240
and 3400 cm−1 are typical of doped PANI, and indicate that the
doping state was not change by the presence of the pheromone.
Although the two spectra are similar, the interaction of pheromone
with the PANI film deposited on the cantilever shows peak inten-
sities at 1640 and 2930 cm−1. The peak at 2930 cm−1 is typical of
C-H stretching, while the peak at 1640 cm−1 is related to carbonyl
groups and saturated aliphatic ketone [36,37]. In a previous work,
Moore [38], isolated and characterized by FTIR the pheromone
released by termites, and found high intensity peaks located at
3070 and 1640 cm−1, which are close to the ones found here for
2-heptanone. This hormone presents a weak physical interaction
with PANI, leading to its adsorption on the PANI functionalized
microcantilever surface. Such interaction do not change the oxi-
dation levels of conducting polymers, but alter the properties of
the sensing materials, which makes this volatile detectable by the
sensor.

4. 646 C. Steffens et al. / Sensors and Actuators B 191 (2014) 643–649
Fig. 2. Scanning electron microscopy (SEM) images (scale bars are displayed in each image) of the uncoated and coated microcantilever with PANI: (a) non-functionalized
microcantilever, (b) functionalized with PANI and (c) a close view of the structure formed by the spin-coated film of PANI deposited on the cantilever, showing the nanofiber
like-structure.
Fig. 3. FTIR spectra of PANI film and PANI film in an atmosphere containing 2-
heptanone. The inset shows the chemical structure of 2-heptanone pheromone.
4. Sensor performance
The deflection of the coated microcantilever in the presence of
1000 ppmv of 2-heptanone pheromone as a function of time is dis-
played in Fig. 4. The solid line is a guide to the eye to evidence
the response time of the sensor, given by the experimental data
of deflection (solid squares) as a function of time. The error bars
represent the standard deviation obtained by the triplicate mea-
surements. The coated cantilever keeps a deflection of 600 nm in an
Fig. 4. Deflection of the coated cantilever with PANI as a function of time in the
presence of 1000 ppm of 2-heptanone pheromone. The solid line is a guide to the
eye to evidence the sensor response time.
atmosphere free of 2-heptanone (from 0 up to 175 s). After insertion
of 1000 ppmv of 2-heptanone (though an orifice which was 1.5 cm
far from microcantilever, in controlled atmospheric pressure), and
diffusion into the AFM chamber, the cantilever deflection starts to
drop off, reaching nearly zero after 250 s. Such behavior evidences
the interaction between the pheromone adsorbed and the PANI film
deposited on the AFM cantilever tip. The pheromone 2-heptanone
may have weak physical interactions with the sensing coating,
involving absorbing or swelling the polymer. Thus, a change occurs
in the polymer matrix, causing a swelling of the sensitive coat-
ing (on one side of the functionalized cantilever), and therefore
leading to a surface stress during the adsorption of pheromone
molecules. Such adsorption causes the static bending responsible
for the deflection.
The cyclic mechanical deflection of cantilever as a function of
time was also studied and is displayed in Fig. 5. The cyclic deflection
of the AFM cantilever, achieved by inserting 500 and 1000 ppmv of
2-heptanone into the AFM chamber and subsequent cleaning with
N2 gas (baseline for a 100 nm deflection), shows an amplitude of
nearly 300 nm and 600 nm, respectively, and presents virtually the
same deflection behavior up to 4000 s, indicating high repeatability.
This is a desirable aspect for designing sensor devices. The recovery
and response time for the functionalized cantilever is nearly 120 s.
It was also possible to observe that the coated cantilever sensor
has good reversibility of 94 ± 4% during the successive cycles. The
response difference in distinct cycles may be due to saturation on
the polymer-based-sensor response of (caused by a doping inter-
action). Such saturation may cause a delay in the sensor response
Fig. 5. Mechanical behavior of the coated cantilever with PANI in the presence
of 1000 ppm and 500 ppm of 2-heptanone pheromone, for cyclic deflection as a
function of time.

5. C. Steffens et al. / Sensors and Actuators B 191 (2014) 643–649 647
Fig. 6. Bio-inspired sensor properties for the pheromone 2-heptanone, which shows
the cantilever deflection as a function of pheromone concentration, measured in
three distinct temperatures.
when it is exposed to sequential gas insertion cycles. However, it is
observed high baseline stability after successive cycles.
Giving the importance of characterizing the sensor response
regarding the analyte concentration, we measured the AFM func-
tionalized cantilever deflection as a function of 2-heptanone
concentration, at three different temperatures: 10, 20 and 30 ◦C.
The results obtained, in the concentration range from 10 up to
1000 ppmv (Fig. 6), which shows a linear behavior between deflec-
tion and pheromone concentration for fixed temperatures. This
linear dependence was observed for 10, 20 and 30 ◦C, and such
behavior is very helpful for sensing applications, once it allows
to predict, for a given temperature, the amount of pheromone in
the environment, through deflection measurements of the coated
cantilever. In addition, an increase of pheromone sensitivity as a
function of temperature can also be observed.
Table 1 shows that the pheromone evaporation rate increased
with temperature raise, which was probed by the PANI-
functionalized microcantilever, while the uncoated microcan-
tilever (reference) was not sensitive to the hormone at the set of
temperatures tested (Fig. 6). Such results are a proof that the func-
tionalization of the microcantilever with PANI is responsible for
providing sensitivity regarding 2-heptanone hormone. We can also
infer that there is a linear relation between the sensor responses
for distinct sets of temperature, which is important for practical
applications. The curves presented in Fig. 6 yielded limit of detec-
tion (ppmv) of 31 (10 and 20 ◦C) and 56 (30 ◦C), and sensitivity
(nm/ppmv) of 0.2 ± 0.01 (10 ◦C), 0.7 ± 0.04 (20 ◦C) and 0.7 ± 0.03
(30 ◦C). The uncoated microcantilever did not present response for
the investigated pheromone. Marfaing et al. [39] studied the effect
of concentration and nature of pheromones in bees by EAG, obtain-
ing limit of detection values of tenths of ppm, which are similar to
the ones determined for the PANI-modified cantilever.
The cantilever sensor response in the presence of other
pheromones than heptanone was also studied and can be seen
in Fig. 7. For that purpose, we injected into the AFM chamber
1000 ppmv of 2-heptanone, and after 250 s and 370 s, we injected
Table 1
Sensor properties for 2-heptanone, which shows the cantilever deflection as a func-
tion of pheromone concentration, measured in three distinct temperatures.
Temperature (◦
C) R2
Sensitivity (nm/ppmv) Detection limit
(ppmv)
10 0.99 0.19 ± 0.01 31
20 0.99 0.67 ± 0.04 31
30 0.99 0.69 ± 0.03 56
Reference (20 ◦
C) 0.99 0.008 ± 0.001 0
Fig. 7. Functionalized cantilever sensor response for 2-heptanone in the presence
of linalool and orange oil (both are other pheromones) as a function of time.
5 wt% of linalool and orange oil, respectively, which are two flo-
ral volatiles routinely present in beekeeping environments. We
observe that for an empty chamber the maximum deflection of
the functionalized microcantilever reaches 45 nm. After insertion
of 2-heptanone, the deflection was drastically increased to nearly
500 nm (increase of more than 1000%), indicating the high sensi-
tivity of the functionalized microcantilever to 2-heptanone. After
insertion of linalool, the deflection reached nearly 530 nm (increase
of 6% compared to heptanone). Subsequently, we added orange
oil, and the total deflection reached 560 nm (the two volatiles
increased the deflection in 12% when compared to 2-heptanone).
The results show that the functionalized cantilever sensor response
for 2-heptanone, in terms of deflection, is not heavily affected by
the presence of 5% (weight/weight) concentration of the other two
volatiles, indicating the sensing robustness of the functionalized
cantilever.We measured the deflection of the functionalized can-
tilever in the presence of 2-heptanone as a function of time for 0, 15,
30, 45 and 60 days. The results obtained displayed in Table 2, point
out that the sensor deflection, for the same time range (1000 min),
decreases gradually as the storage days increase, i.e., the sensor
sensitivity decreases with time (Fig. 8). Usually, the electrical con-
ductivity of polyaniline not is stable for long time due to leaching
of the dopant, where the dopant molecules HCl can dissolve in the
residual water and subsequently be lost by evaporation [40]. This
fact can be related to the slight reduction of the sensors sensitiv-
ity with the time. According to Bai et al. [41] the performances of
sensors based on conducting polymers are expected to decrease
when they are stored in air for a relatively long time. This phe-
nomenon can be explained as de-doping of conducting polymers.
In our case the cantilevers sensors were stored in a vacuum des-
iccator and before each analysis were doped with HCl 1 M, which
helped to keep the good electrical properties of the sensors for 60
days. However, even after 60 storage days, the sensor still presents
a reasonable sensitivity of 0.53 ± 0.01 nm/ppmv, but in a lower
level compared to 0, 15, 30, days (see Table 2).Comparing the can-
tilevers sensors with EAG, it can be observed a large increase in the
Table 2
Storage time, detection limit and sensitivity of functionalized cantilever deflection
as a function of time, measured for 0, 15, 30, 45 and 60 days.
Storage time Detection limit (ppmv) Sensitivity (nm/ppmv)
0 31 0.67 ± 0.04
15 27 0.69 ± 0.04
30 14 0.54 ± 0.04
45 15 0.51 ± 0.04
60 21 0.53 ± 0.01

6. 648 C. Steffens et al. / Sensors and Actuators B 191 (2014) 643–649
Fig. 8. Functionalized cantilever deflection as a function of time, measured for 0,
15, 30, 45 and 60 days, showing its storage time behavior.
durability of these cantilevers sensors compared with sensors and
biosensors prepared with live parts of the insect for instance, Park
et al. [42,43] reported lifetimes of typical EAG sensors lower than
8 h, which is much shorter than the ones obtained in this work.
5. Conclusions
A sensor based on the functionalization of AFM cantilever with
PANI film was obtained and used to detect and quantify the
pheromone 2-heptanone. Infrared spectroscopy spectra showed
that the pheromone 2-heptanone was adsorbed on the PANI film
deposited on the cantilever tip, indicating a chemical affinity
between both compounds. We observed that the functionalized
cantilever sensor displayed a linear response on the 2-heptanone
concentration for distinct temperatures, with good mechanical
behavior for cyclic mechanical deflection. Besides, the sensing
properties of the functionalized cantilever are not greatly affected
by two other volatile pheromones tested, and only a small hystere-
sis on the mechanical deflection of the cantilever was observed,
confirming its robustness. The sensor storage time, evaluated up
to 60 days, showed that the sensor maintains its sensing capac-
ity, with low loss of properties. The results described here, based
on a methodology to functionalize AFM cantilever with polyaniline
for detecting 2-heptanone, open new opportunities for designing
miniaturized systems used for pheromone analysis and sensing.
Acknowledgments
The authors would like to thank Embrapa Instrumentation,
responsible for the National Nanotechnology Laboratory for
Agribusiness (LNNA) for the infrastructure and facilities, FAPESP
(2009/08244-0) and INCT-NAMITEC (CNPq 573738/2008-4) for the
financial support.
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Biographies
Clarice Steffens received her PhD in biotechnology in 2012 from Federal Univer-
sity of São Carlos, Brazil. She is currently working a full professor at Department
of Food Engineering, URI – Erechim. His research includes conducting polymers,
microcantilever, atomic force microscopy, gas/odor sensing, electronic nose and
nanotechnologies.
Alexandra Manzoli received her PhD in science (analytical chemistry) in 2003 from
Federal University of São Carlos, Brazil. She is currently working as a visiting research
at Embrapa Agricultural Instrumentation (Embrapa/CNPDIA), Brazil. Her field of
interests includes electrochemical quartz crystal nanobalance, semiconductors,
atomic force microscopy, conducting polymer, gas/odor sensing, electronic nose and
biosensor.
Juliano E. Oliveira received his PhD degree in materials science and engineering
from Federal University of Sao Carlos (DEMa-UFSCar), São Carlos, Brazil in 2011.
He is currently Professor at Federal University of Paraiba (DEMat-UFPB), Brazil. His
research interests include polymeric nanostructures and their applications in the
biosystems.
Fabio L. Leite received his MSc and PhD degree in materials science and engineering
from the University of São Paulo (USP – São Carlos), in 2002 and 2006, respectively.
Currently, he is an Adjunct Professor and Researcher in the Federal University of São
Carlos (UFSCar), in Sorocaba-SP, Brazil. His research interests are mainly related to
atomic force microscopy, nanomedicine, nanoneurobiophysics and nervous system
diseases.
Daniel S. Correa received his PhD in materials science and engineering in
2009 from Universidade de São Paulo, São Carlos, Brazil. During 2009–2010,
he worked as a post-doctoral fellow at the Instituto de Física de São Car-
los at Universidade de São Paulo. Currently, he is a researcher at Embrapa
Instrumentac¸ ão. His research interest includes nanostructured chemical sensors,
optical properties of organic materials and laser microfabrication of polymeric
materials.
Paulo Sergio P. Herrmann Júnior received his PhD in science (physical chem-
istry) in 1999 from Institute of Chemistry of São Carlos (IQSC) at University of
São Paulo (USP), Brazil. He is currently a full researcher at Embrapa Instrumenta-
tion Center in Brazil. His field of interests includes scanning probe microscopy and
nanotechnology.