See discussions, stats, and author profiles for this publication at: https://www.researchgate.

net/publication/362866082

Portable Breathalyzer for Exhaled Volatile Organic Compounds Monitoring in

Lung Diseases

Conference Paper · June 2022

DOI: 10.1109/MeMeA54994.2022.9856480

CITATIONS READS
2 233

7 authors, including:

Alec Chevrot Justina Venckute Larsson

Swiss Federal Institute of Technology in Lausanne KTH Royal Institute of Technology
1 PUBLICATION 2 CITATIONS 4 PUBLICATIONS 27 CITATIONS

SEE PROFILE SEE PROFILE

Sarah Cuesta Ata Golparvar

Swiss Federal Institute of Technology in Lausanne Delft University of Technology
1 PUBLICATION 2 CITATIONS 44 PUBLICATIONS 633 CITATIONS

SEE PROFILE SEE PROFILE

All content following this page was uploaded by Ata Golparvar on 31 August 2022.

The user has requested enhancement of the downloaded file.

 Portable Breathalyzer for Exhaled Volatile Organic
Compounds Monitoring in Lung Diseases
Alec Chevrot, Justina Venckute, Sarah Cuesta, Ata Golparvar, Amar Kapic, Gian Luca Barbruni* , Sandro Carrara
Integrated Circuit Laboratory (ICLAB), École Polytechnique Fédérale de Lausanne (EPFL), Neuchâtel, Switzerland
*Correspondence Author (gianluca.barbruni@epfl.ch)

Abstract—Measurement of exhaled volatile organic compounds

(VOC) in breath, also called exhaled volatilomes, has long been
claimed to be a potential source of rapid, cost-effective, and non-
invasive clinically applicable biomarkers. However, the current
preclinical exploratory studies remain stagnant and questioned
due to the lack of standardization collection, profiling, and robust
data analysis. Thus, this study proposes a new portable device
concept as instrumentation to address the measurement and
profiling issue in analyzing VOC concentration from exhaled
Fig. 1. The overall scheme of the proposed portable breathalyzer includes
breath. In particular, the propanol concentration measurement the exchangeable nozzle to enable sanitary operation by multiple users, an
is proposed here to monitor various lung diseases as a case study. interchangeable sensor compartment for quick adjustment to enable different
The proposed device is based on a selective aptamer-based bio- biomarker detection, and a segment display to ensure low-power operation
nano-chip coupled with an agarose gel integrated seamlessly into when displaying the readings.
custom-designed instrumentation as a new breathalyzer to enable
a single handheld operation. The device includes an exchangeable
chip compartment to allow a rapid bio-nano interface modi-
disease (COPD) [4]. There have been several VOC identified
fication to detect various VOC for different applications. We
ideated, designed, and simulated the working principle of the in breath linked to lung cancer. The most prevalent established
proposed portable breathalyzer to demonstrate the possibility in several studies were propanol, acetone, isoprene, pentane,
for measuring VOC dealing with lung diseases. We anticipate benzene hexanal, ethylbenzene, and toluene [5] [6].
the contributions here creates a framework and guide the future The state-of-art in highly accurate VOC detection includes
promotion of VOC analysis from preclinical lab investigations to
clinical trials settings.
proton transfer reaction-, gas chromatography-, and selected
ion flow tube-mass spectrometry [7]. Although these methods
Index Terms—agarose gel, aptamer, bio-nano-chip, biosensors, are highly successful in VOC identification, they all come with
breath analysis, finite element analysis (FEM), lung cancer, requirements of dedicated instrumentation and trained person-
mobile health (mHealth), personalized medicine, point-of-care nel to operate. Therefore, they are inadequate for realizing
(POC), portable devices.
portable devices, and novel technologies are actively sought
to develop point-of-care units to be used outside clinics to
I. I NTRODUCTION detect VOC [8].
According to the World Health Organisation, lung cancer Electrochemical sensors have been extensively investigated
is one of the deadliest cancers ever, with mortality of 1.8 over the last decades due to their advantages, such as low
million in 2020 [1]. Early detection and monitoring of its detection limit, high accuracy, and broad detection range [9].
different stages are key factors in decreasing mortality and [10]. It has been shown that VOC bind to aptamers by diffusion
morbidity [1]. Therefore, an easy-to-use, non-invasive, and into agarose gel [11]. Additionally, field-effect transistor-based
portable device is required to detect and monitor lung-linked biosensor (bio-FET) containing carbon nanotubes (CNT) and
complications. aptamers have also been applied for VOC detection [12].
Exhaled breath is a readily available human specimen for Aptamers are short ribonucleic acid (RNA) or single-stranded
measuring biomarkers related to several diseases, including deoxyribonucleic acid (ssDNA) sequences that form complex
lung disorders [2]. Therefore, measurement of the breath par- secondary and tertiary structures. They can bind to different
ticles opens a vast range of possibilities in remote and mobile target molecules selectively and specifically [10]. Aptamers
health tracking as well as clinical diagnosis and therapeutic are obtained by systematic evolution of ligands by exponential
monitoring. Various molecules are found floating in exhaled enrichment (SELEX) method, in which a random aptamer
breath, such as metabolites and volatile organic compounds library and mutation over several cycles are done to find a
(VOC) [3]. The latter are small organic molecules with low high-affinity target [13]. In the sensor, the aptamers can be
molecular weight which are generated from internal organs and bound to the CNT by CDI-Tween with the blocking agents
could be targeted for medical diagnosis of lung diseases such such as Lipa-DEA [14]. CNT are advantageous in lowering the
as lung cancer, asthma, and chronic obstructive pulmonary external potential and the limit of detection (LOD) [15] [16].
 A. Breathalyzer Design and Simulations
To analyze the impact of the geometry, a numerical model
simulation was performed, which provides inputs to design
the bio-nano interference as well as readout electronics by
providing the expected concentration of a given VOC (e.g.,
propanol) at the interface. The model is implemented in
COMSOL Multiphysics® 5.6 (v5.6.0.341) and a finite element
Fig. 2. The overall structure of the handheld breathalyzer during a typical analysis (FEA) is performed. The fluid flow analysis is a
application scenario. VOC are directly exhaled into the device. The flow is key aspect of the device design. In this regard, two different
directed onto the exchangeable sensor compartment composed of agarose gel configurations are investigated: i) a vertical flow aiming at
to collect VOC and an aptamer-based bio-nano interface to selectively detect
the particular VOC of interest. hitting the sensing part directly and then exiting below and
ii) an horizontal flow proposition. The fluid flow comparison
between the two initial geometry propositions enables us to
Still, the current problem with these sensors is that they cannot decide which configuration is optimum. The vertical design
be readily used directly to detect floating VOC in the breath implies higher flow resistance, leading to difficulties in exhal-
consisting of long chains, resulting in extended response time. ing. Therefore, the horizontal flow configuration was preferred.
Furthermore, although some diseases are reported to have only During the simulations given a mach number extremely in-
a single biomarker, in many disorders such as cancer, several ferior to 0.3, the air is considered an incompressible fluid. Due
molecules concentrations are required for accurate monitoring to the geometry and the edges present in the domain, the model
[17]. has been performed considering a turbulent flow. The diffusion
In this work, we propose novel instrumentation as a portable is simulated using the transport of diluted species equations.
breathalyzer unit based on electrochemical detection to moni- The fluid properties considered during the studies are the
tor and rapidly quantify the presence of several molecules (Fig. following: atmospheric pressure of 1.013 [hP a], constant tem-
1). As a proof-of-concept study, this work focuses on detecting perature of 305 [K], constant air density of 1.225 [kg/m3 ],
propanol, which is known to be one of the most attractive and constant kinematic viscosity of 1.7894 · 10−5 [kg/ms].
molecules to be monitored in lung cancer analysis. The Modeling the diffusion inside the gel is one of the main parts
proposed system can be highly versatile, capable of analyzing of the simulation. Here, the focused particle is propanol, and
different VOC concentrations simultaneously and providing the chosen gel is a 2% agarose gel. In a continuum media, the
rapid data processing for real-time breath monitoring. The diffusivity Do of a solute of hydrodynamic radius rs is given
proposed portable system will contribute to developing future by (1):
research directions and pave the way to enable portable VOC kB · T
Do = (1)
breathalyzers to provide critical inputs and daily follow-up in 6 · π · η · rs
monitoring various lung diseases and their remission process. where kB is the Boltzmann constant, T the absolute temper-
ature and η the dynamic viscosity of the liquid. In a gel,
II. S YSTEM P ROPOSAL diffusivity can be altered by polymer chains. These chains
Fig. 2 illustrates the working principle of the proposed form a network with open spaces between the chains. The
device for rapid VOC detection. The system is inspired by open spaces are characterized by their mesh size, which can
a typical alcohol breathalyzer where a person holds the device be micro or nanoscopic and are filled by aqueous solutions
with a single hand and blows into the nozzle for a few [19]. Two ways of diffusion are offered, either via free volume
seconds. The system’s heart houses a selective electrochemical or alongside aqueous solution through the mesh of size ζ. As
detection part combined with dedicated readout circuitry. First, it is not possible to diffuse via both ways at the same time,
the nano- or micro-sized VOC in the sensor compartment are the effective ratio diffusion over Do can be expressed as the
captured with a 2% agarose gel [11]. Then, they are targeted sum of the probabilities of diffusing [19], leading to (2):
on the selective, aptamer-based bio-nano interface, which later D rF V rs 3 ϕp
allows electrochemical detection of the specific VOC. Agarose = [erf ( )exp(−( ) ( ))
Do rs rF V W ϕb − 1
gel constitutes a compatible interface between the sensing rF V rs + rf 2 (2)
section and air and has shown useful to trap exhaled VOC, +erf c( )exp(−π( ) )]
rs ζ + 2rf
and therefore it enables VOC capture and directs them toward
the bio-nano interface based on selective aptamers [11, 18]. Where erf and erf c stand for the error function and com-
Finally, a dedicated CMOS readout circuitry converts the plementary error function, respectively. The two addends re-
biochemical activity at the bio-CMOS interface into electrical spectively corresponds to the diffusion across free volume
signals, which are then processed, analyzed, and displayed. and the second way of diffusing derived from Fick’s law
Particular attention was put into developing a unit to be able [20]. The parameters are: rf = 3.5 [nm] the polymer chain
to measure different specific particles by easily replacing the radius [21], rs = 0.2575 [nm] the particle hydrodynamic
sensor compartment. radius [22], ϕp = 0.0195 the polymer volume fraction (fiber
Fig. 3. The binding and reaction in the proposed nano-bio interface for
detecting exhaled propanol using a costume-designed breathalyzer.

volume fraction) [21], rF V = 170 [nm] the free volume

void radius [21], ζ = 2 [nm] the average mesh size, and
rF V W = 0.269 [nm] the free volume void radius for water
[19]. This leads to a diffusion constant of 9.1 · 10−10 [m2 /s]
which is comparable to the values found for the same particle
hydrodynamic radius [21]. Fig. 4. Finite element analysis shows the propanol concentration inside
the device flow chamber and the gel after 600 seconds. Flow inlet, outlet,
The numerical model study is decomposed into two phases and the final position of the agarose gel-based sensing compartment facing
to both simplify the procedure and reduce time consumption. outlet alongwith the first and second vortexes. First vortex creates a suction
In the first phase, the inlet amplitude is set to a velocity like deteriorative effect while the second one is contributive if the sensing
compartment is placed facing the output.
of 1 [m/s]. The peak respiratory flow (PEF) and the inlet
dimensions leading to an input area of 2 [cm2 ] ensure that this
flow is feasible to maintain for 10 s. A time-dependent function selectivity [14]. The propanol-specific probe (i.e., previously
is used to model the inlet for the first study. It is a piecewise engineered aptamers by SELEX) are added using CDI-Tween
function with an intensity of 1 from 0 to 10 [s] and 0 from 10 as an intermediate linker between the CNT and the aptamer.
to 15 [s]. The same function is applied to the concentration Finally, the MB redox probe is attached at the end of the
inlet. The concentration amplitude is 2.93 · 10−5 [mol/m3 ] aptamer. On top of the catalyst, two gold electrodes are
and has been derived from the values in ppb [6]. The outlet fabricated to collect the charges, which are the products of the
reference pressure value of 1 [atm] is applied to the pressure. electrochemical reaction. In particular, the propanol-aptamer
All the other boundaries are considered walls, except the gel link produces a redox reaction that releases current at the CNT
boundaries for the transport of diluted species. The initial surface. This current is proportional to the concentration of
conditions are set at zero velocity and zero concentration. the analyte and it can be easily measured at the bio-CMOS
The first phase results are taken as initial conditions for the interface with an integrated readout circuity.
second phase. The latter is inlet-free, and a 10 [min] diffusion
is considered. The final mesh has been iteratively optimized III. R ESULTS AND D ISCUSSION
using a mapped model, and it consists of 15000 elements with Fig. 4 presents the results of the FEM analysis. The FEM
an average quality of 1.0. has been performed in two steps. The first step corresponds
to the phase during which a user would blow for 10 seconds
B. Bio-Nano-CMOS Interface Design into the device. The second step simulates the devices at rest
The selectivity of the electrochemical detection is based on for 600 seconds. It shows, via the concentration gradients, the
aptamer-probes, developed explicitly for propanol detection. presence and the influence of vortexes created by the geometry.
The electrochemical detection principle is depicted in Fig. 3. In addition, FEM analysis shows the propanol concentration
A methylene blue (MB) redox probe is attached at the end inside the device flow chamber and the gel after 600 seconds.
of the aptamer. Whenever the aptamer binds to the analyte At the final state, the concentration is higher in two areas.
(i.e., propanol), a conformational change occurs, and the MB These areas correspond to the two vortexes initiated by the
is moved closer to the surface of the carbon nanotubes. This geometry and the flow. The first one is located between the
will lead to an electron transfer that will increase the faradaic inlet and the gel, and the second is distal to the gel. Initially,
current. The latter can be detected by chronoamperometry the gel was placed on the opposite side compared to the gel
or amperometry [23]. The proposed chip is designed starting (i.e., it was placed on the white part shown in Fig 4). However,
from a Si substrate insulated with a thin layer of SiO2 (i.e., due to geometry, a vortex created in the first top corner of
obtained by thermal oxidation). A Fe catalyst is patterned into the device between the inlet and the gel and suction effect
the substrate to fabricate CNT by chemical vapor deposition is observed. Therefore after the 10 [min] of diffusion in the
to improve the sensitivity of the bio-CMOS interfaces.Then, second phase, the concentration in the gel remains low, below
Lipa-DEA blockers are added to avoid or minimize any side 106 mol/m3 . Contrary to the first vortex, the second vortex
reactions from other components that compromise the system appearing in the second part of the design is beneficial if
Fig. 5. The concentration inside the gel after 600 seconds. At a depth of Fig. 6. Recorded redox current as a function of breath exhale propanol
0.5 [mm] inside the gel, the concentration amplitude is 10−5 [mol/m3 ]. concentration. C1 and C2 represent the minimum and maximum values of
propanol concentration for smokers, respectively.

the gel faces the outlet. Therefore, the gel was replaced in
front of the outlet to benefit from the second vortex and avoid the simulation of the diffusion in gel, we found a concentration
the suction effect, as illustrated in Fig. 4. In that case, the of 10−5 [mol/m3 ] for smokers. The diffusion constant is taken
concentration of 105 mol/m3 at 0.5[mm] depth was recorded from the simulation as well (i.e., D = 9.1 · 10−10 [m2 /s1 ]).
(Fig. 5). Therefore, the final geometry of the gel will be given The time interval of the reading is set to a typical value of
with a thickness close to 0.5 mm, which contributes to increase t0 = 10[ms]. Finally, with these parameters, we have a current
the sensitivity of the device. In selecting gel thickness, the total range of 0−17[pA], which is high enough to neglect electrical
height of the sensing part was also considered as well as the noises and the calibration curve is linear below 10−5 [mol/m3 ]
reproducibility of the recordings. Indeed, gels are not perfectly with a sensitivity of 1.7[µA·m3 /mmol] (Fig. 6). The obtained
homogeneous, and the smaller the gel thickness is, the higher theoretical calibration curve of Fig. 6 is capable of clearly
the external environment’s impact will be. It should be noted distinguish propanol concentrations in smokers (i.e, minimum
that the saturation of the gel is not considered here. On the concentration C1 - 5 [nA] and maximum concentration C2 -
other hand, the chosen VOC is a really small particle compared 17 [nA]).
to others exhaled particles. Therefore, adding a filter to the The relationship between the current and analyte concen-
inlet may prevent the bigger particle from reaching the gel tration depends upon the region of transistor operation and,
and avoiding saturation. Nonetheless, proper model validation therefore, calibration is needed. Moreover, the sensor is still
should be conducted experimentally to confirm the results. sensitive to temperature changes and should be calibrated by
Despite this limitation, the model enables some iterations on an additional temperature sensing node.
the device development by giving insights on the geometry
influence and providing inputs for the future readout circuitry
design.
The range of faradaic current is calculated by (3): IV. C ONCLUSION
√ Volatile organic compounds (VOC) functionalized medical
nF A D
∆Iw = √ · ∆CR (3) devices have the potential to enable remote health tracking
π∆t0 and follow-up checkups of complex complications at home
where A is the surface of the graphene surface made of CNT comfort using facile breathalyzing. The possibility of moni-
(e.g., A = 1 [mm2 ]), n is the number of electrons involved toring exhaled breath non-invasively opens many possibilities
in each redox reaction, D is diffusion constant, ∆t0 is time in personalized remote healthcare. This paper reports our
interval, ∆CR is propanol concentration and F is the Faraday first findings in the systematic development for propanol
constant (F = 96485 e−Cmol ). The amount of propanol in measurement in lung diseases.
breath has been considered 54.8 ppb in smoker patients and Here, we studied the best fit geometry to develop the
17.0 ppb in smoker controls [6]. proposed instrumentation as breathalyzer unit by a series
The concentrations of propanol are different from control of finite element analyses and further model and stimulate
patients to test patients, and we want to detect both extremes the concentration intake of the agarose gel in the bio-nano
with a margin large enough. Studies show that propanol interface during the modeled exhaled breath flow. To provide
concentration in smokers was as much as 58 [µmol/l] and as a reasonable substitute to the current breathalyzer studies or
much as 0−4[µmol/l] in non-smokers. Putting these values in improve the current version of the devices, a multi-physical
model and a finite simulation analysis presented here will [8] Kenneth I Ozoemena and Sandro Carrara. “Biomedical elec-
be useful and supplement the somewhat limited number of trochemical sensors for resource-limited countries”. In: Cur-
studies in the literature. Later, we proposed a possible sensitive rent Opinion in Electrochemistry 3.1 (2017), pp. 51–56.
[9] Danielle W Kimmel et al. “Electrochemical sensors and
detection mechanism using the selective aptamer-based bio- biosensors”. In: Analytical chemistry 84.2 (2012), pp. 685–
nano interface and its fabrication process. We subsequently 707.
examined the anticipated theoretical faradaic current genera- [10] DK Anthony, P Supriya, and E Andrew. “Aptamer as thera-
tion with proposal concentration change. peutics”. In: Nat Rev Drug Discov 9 (2010), pp. 537–530.
Additionally, the aptamer-based bio/nano interface’s selec- [11] Satoshi Fujii et al. “Pesticide vapor sensing using an aptamer,
nanopore, and agarose gel on a chip”. In: Lab on a Chip 17.14
tion will depend on the target VOC. Indeed, all particles do not (2017), pp. 2421–2425.
have the same size, so the sensitivity could be different if the [12] Christopher E Kehayias. “Volatile Organic Compound De-
same gel were considered. The interchangeable section of the tection and Disease Diagnostics Using DNA-Functionalized
devices provides the required degree of freedom to enable fur- Carbon Nanotube Sensor Arrays”. PhD thesis. University of
Pennsylvania, 2021.
ther sensing part developments that, by simple modifications, [13] Qingxiu Liu et al. “SELEX tool: a novel and convenient
could aim at detecting other VOCs. The sensing part should gel-based diffusion method for monitoring of aptamer-target
be optimized to have the highest selectivity and sensitivity binding”. In: Journal of biological engineering 14.1 (2020),
in each case. Of course, in future work, the sensitivity and pp. 1–13.
selectivity by further experimentation will be carried out to [14] Inger Vikholm-Lundin and Reetta Piskonen. “Binary mono-
layers of single-stranded oligonucleotides and blocking agent
estimate the device’s limitations by other known gas and then for hybridisation”. In: Sensors and Actuators B: Chemical
determine the target VOC in exhaled breath related to lung 134.1 (2008), pp. 189–192.
disease. Nonetheless, we expect the contributions here will [15] Nguyen Thanh Tung et al. “Peptide aptamer-modified
pave the way for future research in transitioning VOC-based single-walled carbon nanotube-based transistors for high-
point of care devices to clinical trials. performance biosensors”. In: Scientific reports 7.1 (2017),
pp. 1–9.
V. ACKNOWLEDGMENT [16] Sandro Carrara. Bio/CMOS interfaces and co-design. Springer
This work was supported by the École Polytechnique Science & Business Media, 2012.
[17] Sagnik Das and Mrinal Pal. “Non-invasive monitoring of
Fédérale de Lausanne (EPFL) research fund. human health by exhaled breath analysis: A comprehensive
R EFERENCES review”. In: Journal of The Electrochemical Society 167.3
(2020), p. 037562.
[1] J Ferlay et al. Global cancer Observatory: cancer today. Lyon, [18] Emma Tait et al. “Analysis of pathogenic bacteria using
France: international agency for research on cancer. 2018. exogenous volatile organic compound metabolites and optical
[2] Raed A Dweik and Anton Amann. “Exhaled breath analysis: sensor detection”. In: RSC Adv. 5 (2015), pp. 15494–15499.
the new frontier in medical testing”. In: Journal of breath [19] Eneko Axpe et al. “A multiscale model for solute diffusion in
research 2.3 (2008), p. 030301. hydrogels”. In: Macromolecules 52.18 (2019), pp. 6889–6897.
[3] Jose E Belizario, Joel Faintuch, and Miguel Garay Malpartida. [20] Steven R Lustig and Nikolaos A Peppas. “Solute diffusion in
“Breath biopsy and discovery of exclusive volatile organic swollen membranes. IX. Scaling laws for solute diffusion in
compounds for diagnosis of infectious diseases”. In: Frontiers gels”. In: Journal of Applied Polymer Science 36.4 (1988),
in Cellular and Infection Microbiology (2021), p. 783. pp. 735–747.
[4] Ileana Andreea Ratiu et al. “Volatile organic compounds in [21] Alain Pluen et al. “Diffusion of macromolecules in agarose
exhaled breath as fingerprints of lung cancer, asthma and gels: comparison of linear and globular configurations”. In:
COPD”. In: Journal of Clinical Medicine 10.1 (2021), p. 32. Biophysical journal 77.1 (1999), pp. 542–552.
[5] Zhunan Jia et al. “Critical review of volatile organic com- [22] Marcus Yizhak. “The properties of solvents”. In: John Wiley
pound analysis in breath and in vitro cell culture for detection and Sons 4 (1999), p. 239.
of lung cancer”. In: Metabolites 9.3 (2019), p. 52. [23] Yi Xiao, Rebecca Y Lai, and Kevin W Plaxco. “Preparation
[6] Ileana Andreea Ratiu et al. “Volatile organic compounds in of electrode-immobilized, redox-modified oligonucleotides for
exhaled breath as fingerprints of lung cancer, asthma and electrochemical DNA and aptamer-based sensing”. In: Nature
COPD”. In: Journal of Clinical Medicine 10.1 (2021), p. 32. protocols 2.11 (2007), pp. 2875–2880.
[7] Michal Holčapek, Robert Jirásko, and Miroslav Lısa. “Recent
developments in liquid chromatography–mass spectrometry
and related techniques”. In: Journal of Chromatography A
1259 (2012), pp. 3–15.

View publication stats