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Lo e wa e senso s based on gold nanopa icle-modified polypy ole and
hei p ope ies o ammonia and e hylene
M. Še ka
a
, F.A. Bahos
b
, D. Ma a agui
b
, M. Po oček
a
, Z. K al
d
, J. D bohla o á
a
, I. G àcia
c
,
S. Vallejos
a,c,
*
a
CEITEC - Cen al Eu opean Ins i u e o Technology, B no Uni e si y o Technology, 61200, B no, Czech Republic
b
Ins i u o de Ciencias Aplicadas y Tecnología (ICAT), Uni e sidad Nacional Au ónoma de México, Ciudad Uni e si a ia, Ciudad de México, 04510, Mexico
c
Ins i u o de Mic oelec ónica de Ba celona (IMB-CNM, CSIC), Campus UAB, 08193, Bella e a, Spain
d
The mo Fishe Scien ific, Analy ical Ins umen s - Ma e ials and S uc u al Analysis, Hillsbo o, OR 97123, USA
ARTICLE INFO
Keywo ds:
Gas senso s
SAW senso s
Polypy ole
ABSTRACT
This wo k p esen s he ab ica ion and gas sensing p ope ies o Lo e wa e senso s based on non-modified and
gold nanopa icle-modified polypy ole. Resul s demons a e he in eg a ion o uni o m polypy ole laye s wi h
smoo h g anula su ace and he inco po a ion o dispe sed c ys alline gold nanopa icles wi hin he modified
laye s. Gas sensing es s o he senso s in d y condi ions show enhanced sensing pe o mance o e hylene and
ammonia o he modified sys ems as compa ed o hose wi hou modifica ion and hose epo ed in he li -
e a u e. The effec o humidi y p o es significan in bo h sys ems wi h he esul s showing a dec ease o sen-
si i i y in humid condi ions. Despi e his weakness, he ela i ely acile and scalable ab ica ion o hese senso s,
as well as hei sensing esponse a oom empe a u e may be a ac i e in gas de ec ion sys ems, in which high
humidi y le els can be es ic ed by he use o fil e o p econdi ioning elemen s.
1. In oduc ion
O e he las decades, piezoelec ic acous ic de ices ha e gained
eno mous in e es o senso applica ions, including gas senso s, be-
cause o hei ope a ion a oom empe a u e (RT), high sensi i i y, low
limi s o de ec ion (LOD), ela i ely easy ab ica ion and low cos .
Agains a hos o compe ing echnologies o piezoelec ic acous ic
senso s, su ace acous ic wa e (SAW) based gas senso s ha e gained
mo e in e es han hei bulk acous ic wa e (BAW) coun e pa s, gen-
e ally due o hei highe ope a ing equency and in u n highe sen-
si i i y [1].
In SAW senso s, he p opaga ion o acous ic wa e (ei he Rayleigh,
Shea Ho izon al SAW, Lo e, Leaky, S oneley, o Lamb wa es) is lim-
i ed o he su ace and uned in pa by he cu o he piezoelec ic
c ys al [[2]]. In pa icula , Lo e SAW (L-SAW) based senso s allow
effec i e guidance o he wa e close o he sensing su ace by confining
he wa e ene gy in a hin guiding laye . This slows he eloci y o he
wa e wi h espec o he piezoelec ic subs a e and make he su ace
highly sensi i e o small pe u ba ion [3]. To his end, elas ic laye s
such as SiO
2
a e commonly used on he op o piezoelec ic subs a es as
guiding laye s (pa icula ly due o hei low acous ic loss), bu hey
canno achie e a e y high sensi i i y due o shea s iffness. Howe e ,
o he ma e ials, such as polyme s, wi h slowe ans e se wa e eloci y
and lowe densi y han SiO
2
(due o hei iscoelas ic p ope ies) can
also se e as guiding laye s, p o iding u he ad an ages in e ms o
sensi i i y, al hough wi h g ea e p opaga ion loss han SiO
2
. In his
con ex , a mul iguiding laye concep , in which elas ic and iscoelas ic
p ope ies o SiO
2
and polyme a e balanced is gene ally mo e ad-
an ageous [4]. The Lo e wa e p opaga ion and he a enua ion a e
s ongly dependen on he p ope ies o he guiding laye , including he
hickness and s iffness, hus wi h he op imal hickness o he mul i-
guiding laye s is possible o achie ed he high sensi i e L-SAW senso s
wi h app op ia e a enua ion o he wa e [3,5]. Addi ionally, he spe-
cific use o gas sensi i e polyme s in he mul iguiding laye , which
in e ac physically/chemically wi h he analy es, can also p o ide u -
he enhancemen in e ms o sensi i i y and selec i i y ia polyme
modifica ion o unc ionaliza ion [1b,2b].
Polypy ole (PPy) is a conduc i e polyme ha has p o ed sensi-
i i y o a ious gases and o ganic apou s, including ammonia,
e hanol, and ace one [6]. In gene al, PPy was in eg a ed in chemi -
esis i e senso s, and so a , only ew examples o he use o PPy in SAW
senso s we e epo ed in he li e a u e. These examples include SAW
senso s based on Rayleigh wa es o de ec ammonia [[7]], ace one[7c],
NO
2
[8] and H
2
S[8], o shea ho izon al SAW (e.g., Leaky) o de ec
h ps://doi.o g/10.1016/j.snb.2019.127337
Recei ed 9 July 2019; Recei ed in e ised o m 19 Oc obe 2019; Accep ed 23 Oc obe 2019
⁎
Co esponding au ho a : CEITEC - Cen al Eu opean Ins i u e o Technology, B no Uni e si y o Technology, 61200, B no, Czech Republic.
E-mail add esses: [email p o ec ed],[email p o ec ed] (S. Vallejos).
Senso s & Ac ua o s: B. Chemical 304 (2020) 127337
A ailable online 30 Oc obe 2019
0925-4005/ © 2019 The Au ho (s). Published by Else ie B.V. This is an open access a icle unde he CC BY-NC-ND license
(h p://c ea i ecommons.o g/licenses/BY-NC-ND/4.0/).
T
hyd ogen [9]. Acco ding o published esea ch, we ound ha he u i-
liza ion o PPy in L-SAW senso s is less common. Howe e , ou ecen
p elimina y esul s [10] showed he po en ial o PPy-based L-SAW
senso s o de ec low concen a ions o ammonia.
Ce ainly, he syn hesis ou e o PPy defines i gas sensing p ope -
ies, and al hough he e a e a ious a ailable elec ochemical o che-
mical ou es o he syn hesis o nanoscaled PPy, he in eg a ion o PPy
wi h SAW pla o ms using chemical ou es is ye mo e scalable and
ela i ely easie . Fu he mo e, chemical ou es also acili a e he
unc ionaliza ion o PPy wi h di e se nanosized ma e ials, including
noble me als, ca bon-based ma e ials o me al oxides.
The po en ial applica ion o L-SAW senso s in ea ly disease diag-
nosis may be p omising due o hei high sensi i i y and low LOD [1b],
which a e in he ppb ange as hose o specific gas bioma ke s con-
ained in human b ea h [11]. Fo ins ance, e hylene and ammonia ha e
ound o be ele an bioma ke s o oxida i e s ess (OS), a condi ion
ha damages he cells in human body and can lead e en ually o
ch onic diseases such as a he oscle osis, cance , diabe es, ca dio as-
cula , neu odegene a i e and o he degene a i e diseases in humans
[12]. This condi ion is gene ally caused by he p esence o eac i e
oxygen species (ROS) in he body [13], which cause oxida i e de-
g ada ion (lipid pe oxida ion) o polyunsa u a ed a y acids and hus
elease o e hylene in human b ea h [14]. The inc emen o ROS,
mo eo e , has ecen ly ound o be also connec ed o he accumula ion
o u emic oxins caused by kidney dys unc ions and in u n o he e-
lease o ammonia gas in exhaled b ea h [15].
In his con ex , he p esen s udy epo s he ab ica ion o
mul iguiding L-SAW senso s based on SiO
2
and gas sensi i e PPy na-
nopa icles (NPs) unc ionalized wi h gold NPs. The wo k deepens in o
he p ope ies o he second guiding laye and he influence o wo
diffe en gold loadings on he sensing unc ionali y owa ds low con-
cen a ions o ammonia and e hylene as po en ial gaseous bioma ke s.
2. Expe imen al
2.1. Syn hesis o PPy and Au/PPy NPs
PPy NPs we e ob ained ia oxida i e chemical polyme iza ion o
py ole monome , as desc ibed p e iously [16]. In he fi s s ep, poly-
inyl alcohol (PVA, 7.5 g) was dissol ed in 92.5 ml o deionize wa e ,
Fig. 1. (a) (b) Schema ic iew o he L-SAW sensing elemen . SEM-image o he
PPy guiding/sensi i e laye modified wi h Au NPs a e spin coa ing; no ice he
diffe ence in b igh ness/con as o he PPy g ains and he Au NPs.
Fig. 2. UV– is analysis o (a) PPy NPs, (b) Au NPs, (c) Au/PPy NPs (1:10, black
colo ) and Au/PPy NPs (10:1, g een colo ). (Fo in e p e a ion o he e e ences
o colou in his figu e legend, he eade is e e ed o he web e sion o his
a icle).
M. Še ka, e al. Senso s & Ac ua o s: B. Chemical 304 (2020) 127337
2
whe eupon 3.73 g o i on ca ions (III) o FeCl
3
we e added in he so-
lu ion and s i ed o 10 min. In second s ep, py ole (0.01 mol) was
added o his aqueous solu ion and s i ed o 5 h a RT. As soon as
py ole was mixed wi h he oxidan (FeCl
3
), a apid polyme iza ion
eac ion occu ed, which u ned he solu ion in o a cha ac e is ic black
colo indica ing he o ma ion o PPy.
Colloid Au NPs we e syn hesized acco ding o Tu ke ich me hod
[17], i.e., in a we chemical syn hesis, ia he educ ion o gold sal by
sodium ci a e. B iefly, 20 mL o 0.001 M o gold (III) chlo ide ihy-
d a e (HAuCl
4
·3H
2
O) was added o a flask and placed on a s i ing
ho pla e a 150 °C. As soon as he solu ion each i s boiling poin , 2 mL
o 1% sodium ci a e dihyd a e (Na
3
C
6
H
5
O
7
*2H
2
O) was added and
empe a u e was dec eased o 100 °C. The eac ion was un un il he
solu ion became eddish. A e wa ds he solu ion was emo ed om he
ho pla e and cool down.
Au/PPy NPs we e p epa ed by mixing Au and PPy NPs solu ions
wi h wo diffe en a ios, 1:10 and 1:2. The Au/PPy NPs solu ion was
sonica ed in ul asonic ba h o 10 min and used immedia ely, ei he o
i s cha ac e iza ion o o spin coa ing on he L-SAW subs a es o
sensing es .
2.2. Ma e ial cha ac e iza ion
The abso p ion spec a o PPy, Au and Au/PPy NPs we e measu ed
a oom empe a u e using UV– is-NIR spec opho ome e (Ca y 5000)
in he ange o 200–800 nm. The NPs solu ions we e measu ed in 1 cm
op ical pa h qua z cu e e. The mo phology and size dis ibu ion o he
PPy, Au and Au/PPy NPs we e examined using High Resolu ion
T ansmission Elec on Mic oscope (HR-TEM, FEI TITAN Themis
60–300 kV wi h Cs image co ec o ) a accele a ing ol ages o 60 kV
o PPy and Au/PPy NPs and 300kV o Au NPs. The samples o HR-
TEM analysis we e p epa ed by placing a d op o he co esponding NPs
solu ion on o TEM holey ca bon holey g ids.
2.3. Lo e-wa e senso s ab ica ion
L-SAW delay line pla o ms consis ing o a piezoelec ic subs a e
(ST-90°X qua z, 9 mm × 4 mm × 0.5 mm) wi h wo (inpu /ou pu )
aluminium in e digi a ed ansducing (IDTs, 200 nm hick) po s, see
Fig. 1. The double finge pai IDTs ha e ou s ips pe pe iod
(λ=28μm) and his s uc u e is epea ed 75 imes o each po . The
IDTs ape u e and dis ance be ween IDTs po s (delay line) a e 2.1 mm.
The fi s guiding SiO
2
laye (3 μm hick) was deposi ed on he op o
subs a e. Addi ionally, SiO
2
laye se ed as an isola ing laye be ween
IDTs and second guiding laye . The whole ab ica ion p ocess consis ed
o a ious mic o ab ica ion s eps, including me alliza ion, oxide de-
posi ion and li hog aphy; u he de ails o he ab ica ion p ocess we e
epo ed p e iously [18].
The second guiding/sensi i e laye (350 ± 50 nm hick) was spin-
coa ed o e he fi s (SiO
2
) guiding laye a a speed o 4000 pm and
accele a ion o 4000 pm/s o 1 min. To con ol he ep oducibili y o
he spin coa ing, he L-SAW subs a es we e placed in o a cus omized
holde buil o keep he subs a es in a fix posi ion and alignmen
du ing he coa ing. Mo eo e , shadow masks we e used o co e he
elec ode con ac s placed in he ou side co ne s. Subsequen ly, he
delay line and IDTs po s a ea was co e ed wi h 60 μl o he co e-
sponding solu ion (i.e., PPy, Au/PPy (1:10) o (1:2)) and spin coa ed.
The edge effec (s udy by p ofilome y) nea o he elec ode con ac
and hei possible wa e eflec ion was con olled by applying a hin
film o silicon (d ied a 60 ºC o 1 h) a he ou side co ne s.
To ab ica e he L-SAW de ice wi h app op ia e wa e a enua ion
and p e en high noise in he oscilla o sys em, he hickness o fi s and
second guiding/sensi i e laye we e uned expe imen ally. Resul s o
a ious sys ems, including SiO
2
laye s wi h 1.6, 2.5, 3, and 3.8μm and
PPy o AuPPy spin coa ed a a ious pm ( om 2000 o 4000), showed
a good comp omise in e ms o losses (∼20 dB) o he L-SAW senso s
comp ising a 3 μm SiO
2
laye . The e o e, hese sys ems we e employed
o u he ma e ial and gas sensing es s.
2.4. Lo e-wa e senso s cha ac e iza ion
The mo phology o he second guiding laye (PPy, Au/PPy (1:10)
and (1:2)) a e hei in eg a ion wi h he L-SAW subs a es we e
cha ac e ized using FIB/SEM Mic oscope (Helios G4 NanoLab
DualBeam™) and Scanning P obe Mic oscope (B uke Dimension Icon,
wo king in ScanAsys -Ai Type mode). The L-SAW senso s we e elec-
ically cha ac e ized be o e and a e he in eg a ion o PPy o Au/PPy
NPs using RF ansmission pa ame e S
21
(360B Au oma ic Ne wo k
Fig. 3. HR-TEM images o he (a) PPy NPs and (b) Au/PPy NPs wi h (c) close iew on he Au NPs. Size dis ibu ion o he (d) PPy NPs and (e) Au NPs es ima ed o a
popula ion o 100 and 45 pa icles, espec i ely.
M. Še ka, e al. Senso s & Ac ua o s: B. Chemical 304 (2020) 127337
3
Analyze , Wil on) o analyse he inse ion loss o each sample. All
es ed L-SAW senso s we e analysed by Time-o -Fligh Seconda y Ion
Mass Spec ome y (ToF-SIMS) using TOF.SIMS5 (Ion-To ). ToF-SIMS
combined wi h spu e dep h p ofiling is used o p o ide he in o ma-
ion o he su ace chemical composi ion, whe e laye -by-laye spu -
e ing allows econs uc ing elemen al and molecula dis ibu ion by
sample dep h [19]. A c a e wi h a ea o 300 × 300 μm
2
was spu e ed
by Cs
+
beam (1 keV). Elec on flood gun was used o educe cha ging o
he sample. The pulsed Bi
+
wi h accele a ion ol age o 30 keV was
used as he p ima y ion in o de o collec he seconda y ion mass
spec a.The seconda y ions emi ed om he su ace o he c a e
bo om we e de ec ed in nega i e ion mode by he TOF mass spec o-
me e . The analyses we e ob ained om a eas o 100 × 100 μm
2
. The
ins umen was uned o a mass esolu ion g ea e han 4000 a m/z =
29
Si.
2.5. E hylene and ammonia es s
The gas sensing p ope ies o he L-SAW senso s we e es ed a RT
(24 °C) in a con inuous gas flow es chambe . The es s consis ed in
moni o ing he equency changes o he senso s owa d a ious e hy-
lene (P axai ) and ammonia (P axai ) concen a ions (2, 5 and 10 ppm)
Fig. 4. (a) Top iew SEM image and (b) 3D AFM image o he second guiding/
sensi i e laye based on Au/PPy NPs a e spin coa ing. (c) Roughness p ofile o
he laye analysed om he AFM images.
Fig. 5. (a) Nega i e SIMS spec um o Au
-
ion in he dep h p ofile o PPy and
Au/PPy (1:10 and 1:2) guiding/sensi i e laye s. (b) Co ela ion o Au NPs
loadings and in ensi y o seconda y Au
-
ions in PPy and Au/PPy (1:10 and 1:2)
guiding/sensi i e laye s.
Fig. 6. Elec ical esponse egis e ed o he e e ence sample (uncoa ed, wi h
only SiO
2
guiding laye ) and he L-SAW senso s con aining he second guiding/
sensi i e PPy laye .
M. Še ka, e al. Senso s & Ac ua o s: B. Chemical 304 (2020) 127337
4
using syn he ic d y ai as dilu ing and ca ie gas. Fu he es s o he
senso s in humid ambien we e pe o med a 10 and 30 % RH as hese
a e he humidi y le els eached in ‘ac ual’b ea h samples a e p e-
condi ioning and fil e ing mois u e [20]. Bo h, empe a u e and hu-
midi y we e moni o inside he es chambe using a humidi y/ em-
pe a u e senso (SHT71, ope a ing anges om 0 o 100 % ela i e
humidi y (RH), accu acy o ± 3 % RH).
Each L-SAW senso wo ks in an oscilla o ci cui , which includes an
amplifie and a di ec ional couple . The e o e, he oscilla ing equency
o he senso is shi ed o any pe u ba ion. In addi ion, he amplifi-
ca ion s age o he oscilla o is con olled by a heos a de ice, which
op imizes he gain o he oscilla o o each senso , o p e en ha he
inse ion losses exceed he amplifie gain du ing he gas expe imen .
The measu emen s o he equency o a pe iod o wo minu es gen-
e ally displayed good s abili y wi h he noise do no exceeding 10 Hz. A
he e odyne configu a ion was used o signal acquisi ion, mixing he
signal o he oscilla o coupled o a e e ence L-SAW senso (wi h only
SiO
2
guiding laye ) and he signal o he oscilla o coupled o he PPy
based L-SAW senso . The equencies ob ained om he mixe we e
acqui ed by a equency coun e . The senso s we e placed in a con-
inuous flow es chambe (100 mL/min) equipped wi h mass-flow
con olle s. The exposu e ime o he senso s o each analy e con-
cen a ion was se o 2 min, wi h a subsequen pu ging using syn he ic
d y ai o 30 min. The e e ence L-SAW senso was used in he gas
sensing a ay, o compensa e he mal and o he en i onmen al depen-
den d i s on he piezoelec ic subs a es. Du ing he gas es , he e-
e ence elemen was no exposed o a ge gas analy es, and he final
ou pu signal o he L-SAW senso s was sub ac ed om he e e ence
sample. The e o e, he senso esponse was defined as he equency
shi , which is he di e gence o senso s equency ead offdu ing he
exposu e o syn he ic ai and gas.
3. Resul s and discussion
3.1. Cha ac e iza ion o he PPy and Au/PPy NPs
Fig. 2 displays he UV– is spec a o he syn he ized PPy, Au, and
Au/PPy NPs; he spec um o Au/PPy (10:1) mix u e, i.e., wi h 10 imes
highe olume ic amoun o Au NPs han PPy NPs, is also included in
Fig. 2c o compa a i e pu pose. The UV– is spec um o PPy NPs
(Fig. 2a) shows a b oad abso p ion peak a 461 nm assigned o π–π*
elec on ansi ion om alence band o he conduc ion band due o he
p esence o pola ons [21]. The UV– is spec um o he Au NPs (Fig. 2b)
is consis en wi h he li e a u e showing he maximum o su ace
plasmon esonance abso p ion a 523 nm and indica ing he o ma ion
o NPs wi h diame e s be ween 15 and 20 nm [22]. The analysis o he
Au/PPy NPs wi h diffe en Au loadings (i.e., 1:10 and 1:2) showed si-
mila spec a o ha eco ded on he non-modified PPy NPs (Fig. 2a).
Howe e , he compa ison o he spec a o Au/PPy NPs (1:10, Fig. 2c-
black line) and Au/PPy NPs (10:1, Fig. 2c - g een do line) demons a es
ha he shape and posi ion o he abso p ion maximum depends on he
dominan olume ic quan i y. The e o e, he appa en absence o he
Au plasmon peak a 523 nm in he Au/PPy NPs (1:10 and 1:2) solu ions
is connec ed wi h he low amoun o Au NPs in hese mix u es.
HR-TEM analysis o he PPy NPs (Fig. 3a) showed amo phous
sphe ical pa icles wi h sizes be ween 35 and 55 nm (Fig. 3d). Simila ly,
HR-TEM analysis o he Au/PPy NPs (Fig. 3b) displayed he p esence o
seg ega ed PPy and Au sphe ical pa icles; no ice he b igh ness/con-
as diffe ences, which indica e he p esence o bo h, Au (highe con-
as ) and PPy (low con as ) NPs. The numbe o PPy NPs we e e-
ma kably la ge in compa ison o he Au NPs in he es ed sample,
confi ming he ela i ely low amoun o Au NPs in he Au/PPy mix u e.
The a e age pa icle size analysis indica es ha he mean diame e o
Au NPs is app oxima ely 15 nm o a size dis ibu ion anging be ween
12 and 25 nm (Fig. 3e). HR-TEM o he Au NPs emphasized hei high
c ys allini y showing la ice inge spacing o 0.24 nm (Fig. 3c). This is
consis en wi h he (111) plane o he ace cen ed cubic ( cc) gold
(d= 2.35500 Å, ICCD ca d no. 04-0784).
In summa y, he analysis o he solu ions p epa ed o spin coa ing
o he second guiding/sensi i e laye s demons a e he syn hesis o bo h
PPy and Au NPs. UV– is and HR-TEM poin ed ou o weak chemical
in e ac ions be ween he Au and he PPy NPs in he mixed solu ions.
3.2. Cha ac e iza ion o PPy and Au/PPy NPs in eg a ed wi h Lo e-wa e
pla o ms
SEM (Fig. 4a) and AFM (Fig. 4b) analysis o he second guiding/
sensi i e laye s, a e spin coa ing o he L-SAW ansducing pla o ms,
displayed uni o m films wi h g anula mo phology. The films p o ed
good adhesion o he subs a e and he hickness o he films obse ed
by c oss-sec ional SEM images (see Fig. 1b) was ound o be
350 ± 50 nm. Fo his hickness o he guiding laye (PPy, Au/PPy), L-
SAW senso s showed he app op ia e a enua ion (low inse ion loss).
The PPy and Au/PPy guiding/sensi i e laye s analyzed by scanning
p obe mic oscope (Fig. 4c) in an a ea o 2 μmx2μm showed ela i ely
low RMS ( oo mean squa e) oughness o app oxima ely
2.5 ± 0.4 nm. The uni o m and op imal hickness, low su ace ough-
ness, and s ong adhesion o he film o he subs a es a e significan
ac o s ha a o he a enua ion o he acous ic wa e p opaga ion and
in u n he senso sensi i i y [2b].
In o de o confi m he inco po a ion o he Au NPs in o he spin
coa ed guiding/sensi i e laye s, he samples (PPy, Au/PPy (1:10) and
(1:2)) we e in es iga ed by TOF-SIMS echnique. SIMS is a semi-
Fig. 7. F equency shi s eco ded on he non-modified PPy and modified PPy L-
SAW senso s wi h low (1:10) and high (1:2) gold loadings a 2, 5 and 10 ppm o
(a) ammonia and (b) e hylene.
M. Še ka, e al. Senso s & Ac ua o s: B. Chemical 304 (2020) 127337
5

quan i a i e me hod, which allows o ob ain in o ma ion o solids by
spu e ing he solid su ace and collec ing ejec ed seconda y ions om
he opmos su ace. Fig. 5a shows he compa a i e SIMS spec a o
Au
−
molecula ion wi hin he samples. These esul s demons a e he
p esence o cha ac e is ic agmen ed ions o Au
-
a 196.97 m/z
(ma ked a ea) in he Au/PPy samples, in con as o he ba e PPy
samples. Mo eo e , he in ensi y o he coun s o Au
−
ions is consis en
wi h he amoun o Au NPs used o each sample; no ice he sha pe and
mo e in ense Au
-
peak o Au/PPy (1:2) compa ed o Au/PPy (1:10).
The co ela ion o he Au
-
ion in ensi y (collec ed in he dep h p ofile o
200 nm) and Au NPs loadings in he samples (Fig. 5b) confi med he
p opo ional inc ease o Au
-
signal wi h espec o he Au NPs amoun s
in oduced o he samples. Addi ionally, he p esence o cha ac e is ic
agmen s o PPy (e.g., C
x
H
y
N
-
), PVA (e.g., C
x
H
y
O
z
) and FeCl
3
(e.g.,
FeClN
-
, FeCN
-
) we e confi med in he dep h p ofile o samples by SIMS
analysis.
Fig. 6 shows he cha ac e is ic signals ob ained by measu ing he
ansmission sca e ing pa ame e (S
21
) o he L-SAW senso s be o e
(only SiO
2
guiding laye ) and a e in eg a ion o second guiding/sen-
si i e laye (PPy). Ve y simila elec ical esponse has been obse ed o
all es ed senso s (PPy, Au/PPy (1:10) and (1:2)), wi h he equency
and he inse ion loss o 161.6 ± 0.4 MHz and 22.4 ± 0.5 dB, e-
spec i ely. The dec ease in he equencies o he PPy o Au/PPy L-
SAW senso s wi h espec o he e e ence (165.2 Hz and -18.2 dB) is
consis en wi h he inc ease o weigh on he piezoelec ic subs a e
(mass loading effec ). Addi ionally, iscoelas ic p ope ies o PPy also
can con ibu e o equency changes and lead o changes in de ice a -
enua ion.
In summa y, he inco po a ion o he second guiding/sensi i e
laye s wi h he piezoelec ic subs a es demons a es simila mo pho-
logical and elec ical p ope ies o he non-modified and gold modified
PPy laye s, despi e he wo diffe en gold loadings inco po a ed in he
modified laye s.
3.3. L-SAW gas sensing es s
The ammonia and e hylene gas sensing es s o he L-SAW senso s
based on PPy and Au-modified PPy NPs (1:10 and 1:2) a oom em-
pe a u e a e p esen ed in Fig. 7. In gene al, all senso s egis e ed po-
si i e esponses upon exposu e o diffe en concen a ions o a ge
analy es. The senso s based on Au/PPy NPs demons a ed enhanced
sensing p ope ies owa ds bo h es ed gases compa ed o he senso s
based on non-modified PPy NPs. We obse ed u he ha he senso s
based on low Au loadings (i.e., 1:10) p o ided be e esponses o
ammonia (Fig. 7a) compa ed o hose based on high Au loadings (i.e.,
1:2). Namely, Au/PPy (1:10) senso s showed highe equency shi s
and an inc ease o he esponse by app oxima ely 5, 4 and 3 imes o 2,
5 and 10 ppm o ammonia, espec i ely, as compa ed o PPy senso s. In
con as , he esul s ob ained o e hylene (Fig. 7b) egis e ed imp o ed
esponses o Au/PPy (1:2) senso (highe Au loading) compa ed o Au/
PPy (1:10) senso , as opposi e o ha obse ed o he ammonia es s.
The equency shi s o Au/PPy (1:2) senso s wi h ega d o non-mod-
ified PPy senso s is inc eased app oxima ely by 4 imes o 2, 5 and
10 ppm o e hylene. The enhanced esponse o he Au/PPy (1:2) senso s
o e hylene could be ela ed o he highe loading o Au NPs in his
sample and he p o ed ca aly ic ac i i y o gold, which encou ages he
oxida ion o e hylene a oom empe a u e [23].
Fig. 8a and b show he esponse o Au/PPy (1:10) and Au/PPy (1:2)
L-SAW senso s o a ious concen a ions o ammonia and e hylene,
espec i ely, wi h he equency changes o he senso s showing p o-
po ional inc emen o gas concen a ion. The dec ease o equency
(nega i e equency shi ) ob ained du ing he exposu e o he L-SAW
senso s o ammonia and e hylene a e mos likely connec ed o he
dominance o mass loading effec s, a he han he elec ical effec s,
Fig. 8. (a) Response o he Au/PPy (1:10) based L-SAW senso o 2, 5 and 10 ppm o ammonia. (b) Response o he Au/PPy (1:2) based L-SAW senso o 2, 5 and
10 ppm o e hylene. Time-dependen esponse cu e o (c) Au/PPy (1:10) senso o 5 ppm o ammonia and (d) Au/PPy (1:2) senso o 5 ppm o e hylene.
M. Še ka, e al. Senso s & Ac ua o s: B. Chemical 304 (2020) 127337
6
which a e expec ed o cause posi i e equency shi du ing he in e -
ac ion o PPy and hese educing analy es [24]. This ac is connec ed
wi h he low conduc i i y (elec ical esis ance be ween 500 MΩ–1
GΩ) o he second guiding/sensi i e laye and he insignifican e-
sis ance changes eco ded du ing i s exposu e o gases such as ammonia
and e hylene ( his was p o ed by es ing he PPy and Au/PPy laye s
deposi ed di ec ly on he op o he elec odes o bo h a ge analy es).
Simila ly, he elas ic effec s in he esponse o he L-SAW senso s can
also be dis ega ded, as gene ally he elas ic changes in he sensi i e
ma e ial a e associa ed wi h a equency inc ease (a posi i e equency
shi ) [24b]. The e o e, he nega i e equency shi s eco ded on he L-
SAW senso s a e associa ed o he changes in he p opaga ion pa h o
he su ace wa es induced by he mass loading o he analy es a he
sensi i e laye ; whe e he mass loading e e s o physical/chemical
so p ion o a ge gas molecules a /in he sensi i e laye .
Fig. 8c and d show a de ailed iew o he esponse and he ime
equi ed o each 90 % o he esponse and eco e y. In gene al, he
non-modified and gold-modified L-SAW senso s showed simila e-
sponse and eco e y imes o he same analy e and concen a ion. The
esponse and eco e y imes owa d e hylene we e longe han o
ammonia. Fo ins ance, esul s show ha he esponse and eco e y
imes we e 59 s and 72 s o Au/PPy (1:10) senso s o 5 ppm o am-
monia, espec i ely, and 81 s and 142 s o Au/PPy (1:2) senso s o
5 ppm o e hylene. This may be ela ed o he diffe ence in molecula
size o hese gases (kine ic diame e o e hylene molecule o 0.42 nm
[25] and ammonia molecule 0.36 nm [26]), which slows down he
diffusion o e hylene molecules wi hin he sensi i e laye espec o
ammonia [26], making he esponse and eco e y ime longe o
e hylene.
Fig. 9a shows he sensi i i y o PPy, Au/PPy (1:10) and Au/PPy
(1:2) L-SAW senso s o ammonia and e hylene o concen a ion be-
ween 2 ppm and 10 ppm. The sensi i i y is defined as he a io be ween
he change in senso s esponse (Δ equency shi ) and a fixed analy e
concen a ion change (ΔC). The sensi i i y o he Au/PPy (1:10) senso s
o ammonia and e hylene was ound o be ∼1.8 imes highe han ha
o non-modified PPy senso s. The sensi i i y o he Au/PPy (1:2) sen-
so s wi h espec o he PPy senso s was imp o ed ∼2.2 and ∼3.2
imes o ammonia and e hylene, espec i ely. The sco e plo ob ained
by p incipal componen analysis (PCA) o he non-modified and Au-
modified PPy senso s (Fig. 9b) shows an app aisal o he selec i i y and
he possibili y o disc imina e ammonia and e hylene by concen a ions
using and a ay o he non-modified and gold-modified L-SAW senso s.
Table 1 compa es he key cha ac e is ics and esul s o ou L-SAW
senso s wi h o he piezoelec ic senso s epo ed in he li e a u e. The
esul s show ha he senso s desc ibed in his wo k possess highe
equency shi s (i.e., esponse) o he lowes es ed analy e con-
cen a ion (2 ppm) han o he piezoelec ic de ices such as Rayleigh
and Shea Ho izon al SAW o BAW (e.g., qua z c ys al mic obalance)
senso s. The enhanced sensi i i y o ou L-SAW senso s, compa ed o
o he ype o SAW senso s, is a ibu ed in pa o he mul iguiding
laye s uc u e o hese senso s, which combines he p ope ies o he
SiO
2
and he gas sensi i e PPy laye s o ap he wa e ene gy nea he
su ace. This s uc u e slows down he wa e p opaga ion eloci y and
makes he L-SAW senso s sensi i e owa ds any changes occu ing on
he su ace [2a,27]. Addi ionally, he imp o ed ammonia and e hylene
sensing pe o mances o Au/PPy senso s, wi h espec o he non-
modified PPy, can be a ibu ed o he ca aly ic effec o he Au NPs and
he subsequen en ichmen o PPy su ace by spill-o e o eac i e
species h ough ca alysis [28]. The influences o he PPy modifica ion
by diffe en Au NPs loadings on he L-SAW senso esponses o am-
monia and e hylene a e sligh ly diffe en . The highe densi y o Au NPs
on PPy L-SAW senso s (Au/PPy (1:2)) a o s he sensi i i y o e hylene.
P e iously was desc ibed ha he oxida ion o e hylene is inc eased by
he inc ease o Au loadings a oom empe a u e [23] in con as o
Fig. 9. (a) Sensi i i y (Hz/ppm) o he L-SAW senso based on PPy NPs and Au-
modified PPy films (Au/PPy 1:10 and Au/PPy 1:2) o ammonia and e hylene
(calcula ed o concen a ions be ween 2 ppm and 10 ppm). (b) Sco es o p o-
jec ions o measu emen s in an o hogonal base o p incipal componen s ana-
lysed o he PPy, Au/PPy (1:10) and (1:2) L-SAW senso s.
Table 1
The compa ison o sensing cha ac e is ics o ammonia and e hylene gas senso s based on diffe en piezoelec ic ansducing pla o ms.
Type o senso S uc u e Sensi i e laye Gas RH (%) Temp. (ºC) Response (Hz) LTC (ppm) LOD (ppm) Re .
L-SAW ST-Qua z/SiO
2
Au/PPy Ammonia 0 24 898 2 0.067 This wo k
L-SAW ST-Qua z/SiO
2
Fe
2
O
3
/WO
3
Ammonia NR NR 627 25 1 [30]
R-SAW ST-Qua z PPy Ammonia NR NR 20 10 NR [7b]
SH-SAW ST -Qua z ZnO Ammonia 25 25 110 10 NR [31]
QCM AT- Qua z c ys al PDA/HMSSs Ammonia 50 25 250 10 NR [32]
L-SAW ST-Qua z/SiO
2
Au/PPy E hylene 0 24 690 2 0.087 This wo k
R-SAW XY LiNbO
3
ZnO E hylene NR NR 200 100 NR [33]
QCM AT- PC AgBF
4
/PVP E hylene NR NR 115 1 0.42 [34]
RH: Rela i e humidi y, Temp.: Tempe a u e, LTC: Lowes es ed concen a ion, LOD: Limi o de ec ion, Response: F equency shi , L-SAW: Lo e wa e SAW; R-SAW:
Rayleigh SAW; SH-SAW: shea ho izon al SAW; ST, XY, AT: e e o c ys al cu ; QCM: qua z c ys al mic obalance; PC: piezoelec ic c ys al; PDA/HMSSs: poly-
dopamine/hollow mesopo ous silica sphe es; AgBF
4
/PVP: AgBF
4
/ poly inylpy olidone, NR: Non- epo ed.
M. Še ka, e al. Senso s & Ac ua o s: B. Chemical 304 (2020) 127337
7
ammonia, which equi ed a empe a u e ac i a ion [29].
The high esponses o ou L-SAW senso s also con ibu e o lowe
LODs han hose o o he de ices. Fo ins ance, he LOD o ammonia
was 67 ppb using Au/PPy (1:10) and o e hylene 87 ppb using Au/PPy
(1:2) senso s, conside ing ha he minimum signal in ensi y is 3 imes
highe han noise. These LODs a e wi hin he limi s equi ed in he
ea ly diagnosis o OS dependan diseases (e.g. schizoph enia, diabe es).
Acco ding o he li e a u e, he concen a ions o gaseous bioma ke s
ound in heal hy con ols and pa ien s wi h OS dependen diseases os-
cilla e om 8 o 246 ppb o e hylene and om 290 o 2020 ppb o
ammonia [14b,35]. Fu he es s o he senso s o e hylene and am-
monia in humid ambien egis e ed a loss o he esponse o app oxi-
ma ely 2 imes a 10 % RH and 5 imes a 30 % RH. Addi ionally, he
humidi y in oduced ins abili y o he signal, making he esponses less
ep oducible and eliable, pa icula ly a he low es ed concen a ion
(2 ppm). Thus, he sensi i i y o he senso s was also affec ed. Fo in-
s ance, a 30% RH he sensi i i y o he Au/PPy (1:10) senso s o am-
monia dec eased om 92 in d y ai o 40. Simila ly, he sensi i i y o
he Au/PPy (1:2) senso s o e hylene dec eased om 270 in d y ai o
72. These significan changes in he esponse o he senso s in humid
ambien may be connec ed wi h he swelling o he polyme ic guiding/
sensi i e laye by wa e apo . In humid ambien , wa e molecules fill
he ee olume in he polyme ic laye , making i una ailable o he
gas so p ion and, hus, less esponsi e o he a ge analy e [36]. A
compa ison o hese esul s and hose o he li e a u e is a he complex
as mos o he epo s (e.g., hose lis ed in Table 1) do no make e-
e ence o he humidi y le els du ing he es s and/o he deg ee o
humidi y in e e ence in senso esponse. Howe e , based on he e-
po s in Table 1 ( ow 4 and 5) o 25% and 50% RH one can no ice ha
he lowes measu ed concen a ions o ammonia in d y and humid
condi ions a e ye lowe o ou senso s. Humidi y in e e ence is an
undesi ed and ecu en effec a RT ope a ion ha needs he im-
plemen a ion o addi ional s a egies o be compensa ed. These s a e-
gies may include u he uning o he polyme p ope ies using o he
addi i es (hyd ophobic ino ganic ma e ials o o ganic molecules) [37]
o coupling fil e s o p econdi ioning elemen s o he senso s as o e-
cas ed o nex gene a ion o po able b ea h analyse [20].
In summa y, he Au-modified PPy L-SAW senso s demons a e en-
hanced sensing esponses compa ed o he non-modified PPy senso s in
d y condi ions, wi h be e sensi i i y and lowe LOD o e hylene and
ammonia han hose epo ed ea lie in he li e a u e o o he SAW-
based gas sensing elemen s a RT. The es s in humid ambien affec he
senso pe o mance modi ying he LOD o highe concen a ion le els
han hose ob ained in d y ambien , hus, indica ing he need o u he
s a egies o compensa e he in e e ence o humidi y on he senso
esponse.
4. Conclusion
Lo e wa e gas senso s based on a mul iguiding laye s uc u e
consis ing o SiO
2
and ei he non-modified o gold modified polypy ole
we e de eloped in his wo k. Resul s demons a ed he inco po a ion o
dispe sed c ys alline gold nanopa icles in o he modified polypy ole
based senso s and he enhanced pe o mance o hese senso s, com-
pa ed o he non-modified polypy ole based senso s, o e hylene and
ammonia. Gas sensing es s in d y condi ions showed ha he de ec ion
limi o he gold modified senso s eaches lowe ppb le el o bo h
es ed gases (67 ppb o ammonia and 87 ppb o e hylene) as compa ed
o o he simila sys ems in he li e a u e. These imp o emen s a e a -
ibu ed in pa o he mul iguiding s uc u e and o he inco po a ion
o gold nanopa icles in o he gas sensi i e polypy ole laye , which
po en ially p omo es he so p ion o eac i e species h ough ca alysis.
The inco po a ion o humidi y o he es s changed significan ly he
esponse magni udes o he gold modified and non-modified senso s
and in u n he sensi i i y, which dec eased app oxima ely 2 imes o
he Au/PPy (1:10) senso s o ammonia and 4 imes o he Au/PPy (1:2)
o e hylene. Gene ally, hese esul s sugges he need o u he im-
p o emen s a he ma e ial and/o fil e ing le el o es ic he hu-
midi y effec in he senso esponse. Despi e hese weaknesses, he e-
la i ely easy and scalable ab ica ion o hese senso s, as well as hei
sensing pe o mance owa ds low e hylene and ammonia concen a-
ions make he modified s uc u es a ac i e o u u e s udies and
applica ions whe e gases and/o VOCs a e in ol ed.
Decla a ion o Compe ing In e es
The au ho s decla e ha hey ha e no known compe ing financial
in e es s o pe sonal ela ionships ha could ha e appea ed o influ-
ence he wo k epo ed in his pape .
The au ho s decla e he ollowing financial in e es s/pe sonal e-
la ionships which may be conside ed as po en ial compe ing in e es s.
Acknowledgmen s
This wo k has been suppo ed in pa by he Czech Science
Founda ion (GAČR) ia G an no. 17-16531S, he Spanish Minis y o
Economy and Compe i i eness ia p ojec s TEC2015-74329-JIN-(AEI/
FEDER,EU), and TEC2016-79898-C6-1-R (AEI/FEDER, EU) and by
Uni e sidad Nacional Au ónoma de México ia G an DGAPA-UNAM-
PAPIIT TA100118. The suppo o he In e nal G an Agency (IGA)
s uden junio p ojec no. STI-J-18-5559 and he Ramón y Cajal a e also
acknowledged. This esea ch has made use o he in as uc u es he
Spanish ICTS Ne wo k MICRONANOFABS, pa ially suppo ed by
MINECO, and CEITEC Nano Resea ch In as uc u e, suppo ed by
MEYS (2016-2019). We also acknowledge he suppo ecei ed om
Ondřej Chmela o Scanning P obe Mic oscope analysis and om Selena
Islas in he UV– is Spec opho ome e .
Re e ences
[1] a) A. B yan , D.L. Lee, J.F. Ve elino, A su ace acous ic wa e gas de ec o , IEEE
T ans. Sonics Ul ason. 29 (1982) 167-167;
b) A. A zal, N. Iqbal, A. Mujahid, R. Schi hagl, Ad anced apo ecogni ion ma-
e ials o selec i e and as esponsi e su ace acous ic wa e senso s: a e iew,
Anal. Chim. Ac a 787 (2013) 36–49.
[2] a) S.J. Ippoli o, A. T inchi, D.A. Powell, W. Wloda ski, Acous ic wa e gas and
apo senso s, in: E. Comini, G. Faglia, G. Sbe eglie i (Eds.), Solid S a e Gas
Sensing, Sp inge US, Bos on, MA, 2009, pp. 1–44;
b) J. De ko a, P.R. Ohodnicki, D.W. G e e, SAW senso s o chemical apo s and
gases, Senso s, (2017), p. 28.
[3] J.R. F agoso-Mo a, D. Ma a agui, F.A. Bahos, J. Fon echa, M.J. Fe nandez,
J.P. San os, I. Sayago, I. G àcia, M.C. Ho illo, Gas senso s based on elas ici y
changes o nanopa icle laye s, Sens. Ac ua o s B Chem. 268 (2018) 93–99.
[4] A.L. Zou, L.Z. Hu, Y. Qiu, G.Y. Cao, J.J. Yu, L.N. Wang, H.Q. Zhang, B. Yin, L.L. Xu,
High pe o mance o 1-D ZnO mic owi e wi h cu e-side hexagon as e hanol gas
senso , J. Ma e . Sci.: Ma e . Elec on. 26 (2015) 4908–4912.
[5] J.S. Liu, L.J. Wang, Y.Y. Lu, S.T. He, P ope ies o Lo e wa es in a piezoelec ic
laye ed s uc u e wi h a iscoelas ic guiding laye , Sma Ma e . S uc . 22
(2013) 8.
[6] M. Še ka, J. D bohla o á, J. Hubálek, Nanos uc u ed polypy ole-based ammonia
and ola ile o ganic compound senso s, Senso s 17 (2017) 28.
[7] a) M. Penza, E. Milella, V.I. Anisimkin, Moni o ing o NH
3
gas by LB polypy ole-
based SAW senso , Sens. Ac ua o s B Chem. 47 (1998) 218–224;
b) X. Chen, D.M. Li, S.F. Liang, S. Zhan, M. Liu, Gas sensing p ope ies o su ace
acous ic wa e NH
3
gas senso based on P doped polypy ole sensi i e film, Sens.
Ac ua o s B Chem. 177 (2013) 364–369;
c) F. Li, H. Li, H. Jiang, K. Zhang, K. Chang, S. Jia, W. Jiang, Y. Shang, W. Lu,
S. Deng, M. Chen, Polypy ole nanopa icles ab ica ed ia T i on X-100 micelles
empla e app oach and hei ace one gas sensing p ope y, Appl. Su . Sci. 280
(2013) 212–218.
[8] X.F. Yan, D.M. Li, C.C. Hou, X. Wang, W. Zhou, M. Liu, T.C. Ye, Compa ison o
esponse owa ds NO
2
and H
2
S o PPy and PPy/TiO
2
as SAW sensi i e films, Sens.
Ac ua o s B Chem. 161 (2012) 329–333.
[9] L. Al-Masha , H.D. T an, W. Wloda ski, R.B. Kane , K. Kalan a -zadeh, Polypy ole
nanofibe su ace acous ic wa e gas senso s, Sens. Ac ua o s B Chem. 134 (2008)
826–831.
[10] M. Še ka, F.A. Bahos, D. Ma a agui, Z. K al, I. G àcia, J. D bohla o á, S. Vallejos,
Polypy ole based lo e-wa e gas senso de ices wi h enhanced p ope ies o am-
monia, P oceedings 2 (2018) 786.
[11] S.J. Kim, S.J. Choi, J.S. Jang, H.J. Cho, I.D. Kima, Inno a i e nanosenso o disease
diagnosis, Acc. Chem. Res. 50 (2017) 1587–1596.
M. Še ka, e al. Senso s & Ac ua o s: B. Chemical 304 (2020) 127337
8
[12] a) B. U a a, A.V. Singh, P. Zamboni, R.T. Mahajan, Oxida i e s ess and neu o-
degene a i e diseases: a e iew o ups eam and downs eam an ioxidan he -
apeu ic op ions, Cu . Neu opha macol. 7 (2009) 65–74;
b) E. Ozbek, Induc ion o oxida i e s ess in kidney, In . J. Neph ol. 2012 (2012)
465897-465897.
[13] a) K. Kolanjiappan, S. Manoha an, M. Kayal izhi, Measu emen o e y h ocy e li-
pids, lipid pe oxida ion, an ioxidan s and osmo ic agili y in ce ical cance pa-
ien s, Clin. Chim. Ac a 326 (2002) 143–149;
b) Z. Ni, G. Angelidou, G. Coli a, M. Lange, M. Fedo o a, Analy ical s a egies o
unco e he di e si y o lipid pe oxida ion p oduc s and hei biological effec s,
F ee Radic. Biol. Med. 124 (2018) 560–561.
[14] a) L.M. Paa dekoope , G. an den Bogaa , M. Kox, I. Dingjan, A.H. Nee incx,
M.B. Bendix, M. e Bees , F.J.M. Ha en, T. Risby, P. Pickke s, N. Ma czin,
S.M. C is escu, E hylene, an ea ly ma ke o sys emic inflamma ion in humans, Sci.
Rep. 7 (2017) 10;
b) M. Pe us, A.-M. B a u, C. Popa, Spec oscopic analysis o b ea h e hylene and
oxida i e s ess ela ion wi h glycaemic s a us in ype 2 diabe es, Op . Quan um
Elec on. 49 (2016) 2;
c) S.M. C is escu, R. Kiss, S.T. Hekke , M. Dalby, F.J.M. Ha en, T.H. Risby,
N. Ma czin, B.S.I. Ha efield, Real- ime moni o ing o endogenous lipid pe oxida ion
by exhaled e hylene in pa ien s unde going ca diac su ge y, Am. J. Physiol.-Lung
Cell. Mol. Physiol. 307 (2014) 509–515.
[15] a) F. Nuhu, S. Bhanda i, Oxida i e s ess and ca dio ascula complica ions in
ch onic kidney disease, he impac o anaemia, Pha maceu icals 11 (2018) 15;
b) S. Pas o , L. Rod íguez-Ribe a, Z. Co edo , M.I. da Sil a Filho, K. Hemminki,
E. Coll, A. Fö s i, R. Ma cos, Le els o DNA damage (Mic onuclei) in pa ien s su -
e ing om ch onic kidney disease. Role o GST polymo phisms, Mu a . Res./Gene .
Toxicol. En i on. Mu agen. 836 (2018) 41–46;
c) C. Popa, D.C.A. Du u, R. Ce na , C. Ma ei, A.M. B a u, S. Bani a, D.C. Dumi as,
E hylene and ammonia aces measu emen s om he pa ien s’b ea h wi h enal
ailu e ia LPAS me hod, Appl. Phys. B-Lase s Op . 105 (2011) 669–674;
d) J. Obe meie , P. T e z, J. Happ, J.K. Schube , H. S aude, D.C. Fische ,
W. Miekisch, Exhaled ola ile subs ances mi o clinical condi ions in pedia ic
ch onic kidney disease, PLoS One 12 (2017) 18.
[16] O.S. Kwon, J.Y. Hong, S.J. Pa k, Y. Jang, J. Jang, Resis i e gas senso s based on
p ecisely size-con olled polypy ole nanopa icles: effec s o pa icle size and de-
posi ion me hod, J. Phys. Chem. C 114 (2010) 18874–18879.
[17] J. Tu ke ich, P.C. S e enson, J. Hillie , A s udy o he nuclea ion and g ow h
p ocesses in he syn hesis o colloidal gold, Discuss. Fa aday Soc. 11 (1951) 55–75.
[18] D. Ma a agui, O. Kolokol se , J.M. Sanige , I. G acia, M.J. Fe nandez, J.L. Fon echa,
M.D. Ho illo, Acous ic senso s based on amino- unc ionalized nanopa icles o
de ec ola ile o ganic sol en s, Senso s 17 (2017) 9.
[19] B. Hagenhoff, High esolu ion su ace analysis by TOF-SIMS, Mic ochim. Ichnoanal.
Ac a 132 (2000) 259–271.
[20] A. P abhaka , R.A. Iglesias, X.N. Shan, X.J. Xian, L.H. Zhang, F. Tsow, E.S. Fo zani,
N.J. Tao, Online sample condi ioning o po able b ea h analyze s, Anal. Chem. 84
(2012) 7172–7178.
[21] a) Y. Li, P. Bobe , D.H. Apaydin, T. Sy o ý, N.S. Sa ici ci, J. H omádko á,
I. Sapu ina, M. T cho á, J. S ejskal, Colloids o polypy ole nano ubes/nano ods: a
p omising conduc ing ink, Syn h. Me . 221 (2016) 67–74;
b) M. Rahaman, A. Aldalbahi, M. Almoiqli, S. Alzahly, Chemical and elec o-
chemical syn hesis o polypy ole using ca ageenan as a dopan : polypy ole/
mul i-walled ca bon nano ube nanocomposi es, Polyme s 10 (2018) 20.
[22] X.H.N. Xu, S. Huang, W. B ownlow, K. Salai a, R.B. Jeffe s, Size and empe a u e
dependence o su ace plasmon abso p ion o gold nanopa icles induced by is
(2,2′-bipy idine) u henium(II), J. Phys. Chem. B 108 (2004) 15543–15551.
[23] J.J. Li, C.Y. Ma, X.Y. Xu, J.J. Yu, Z.P. Hao, S.Z. Qiao, Efficien elimina ion o ace
e hylene o e nano-gold ca alys unde ambien condi ions, En i on. Sci. Technol.
42 (2008) 8947–8951.
[24] a) X.L. Qi, J.S. Liu, Y. Liang, J.H. Li, S.T. He, The esponse mechanism o su ace
acous ic wa e gas senso s in eal ime, J. Appl. Phys. 58 (2019) 7;
b) V.B. Raj, H. Singh, A.T. Nimal, M.U. Sha ma, M. Toma , V. Gup a, Dis inc
de ec ion o liquo ammonia by ZnO/SAW senso : s udy o comple e sensing me-
chanism, Sens. Ac ua o s B: Chem. 238 (2017) 83–90;
c) Q.B. Tang, Y.J. Guo, Y.L. Tang, G.D. Long, J.L. Wang, D.J. Li, X.T. Zu, J.Y. Ma,
L. Wang, H. To un, Y.Q. Fu, Highly sensi i e and selec i e Lo e mode su ace
acous ic wa e ammonia senso based on g aphene oxides ope a ed a oom em-
pe a u e, J. Ma e . Sci. 54 (2019) 11925–11935.
[25] R.B. Lin, L.B. Li, H.L. Zhou, H. Wu, C.H. He, S. Li, R. K ishna, J.P. Li, W. Zhou,
B.L. Chen, Molecula sie ing o e hylene om e hane using a igid me al-o ganic
amewo k, Na . Ma e . 17 (2018) 1128–1133.
[26] R. Sanka ganesh, M. Na anee han, G.K. Mani, S. Ponnusamy, K. Tsuchiya,
C. Mu hamizhchel an, S. Kawasaki, Y. Hayakawa, Influence o Al doping on he
s uc u al, mo phological, op ical, and gas sensing p ope ies o ZnO nano ods, J.
Alloys Compd. 698 (2017) 555–564.
[27] F. He mann, M. Weihnach , S. Bu genbach, P ope ies o senso s based on shea -
ho izon al su ace acous ic wa es in LiTaO
3
/SiO
2
and qua z/SiO
2
s uc u es, IEEE
T ans. Ul ason. Fe oelec . F eq. Con ol 48 (2001) 268–273.
[28] H.G. Moon, Y. Jung, S.D. Han, Y.S. Shim, B. Shin, T. Lee, J.S. Kim, S. Lee, S.C. Jun,
H.H. Pa k, C. Kim, C.Y. Kang, Chemi esis i e elec onic nose owa d de ec ion o
bioma ke s in exhaled b ea h, ACS Appl. Ma e . In e aces 8 (2016) 20969–20976.
[29] M.J. Lippi s, A.C. Gluhoi, B.E. Nieuwenhuys, A compa a i e s udy o he selec i e
oxida ion o NH
3
o N
2
o e gold, sil e and coppe ca alys s and he effec o ad-
di ion o Li
2
O and CeO
x
, Ca al. Today 137 (2008) 446–452.
[30] F.A. Bahos, S. Vallejos, I. G àcia, C. Cané, M.J. Fe nández, M.C. Ho illo,
D. Ma a agui, High-pe o mance ammonia senso a oom empe a u e based on a
lo e-wa e de ice wi h Fe
2
O
3
@WO
3
−x nanoneedles, P oceedings 1 (2017) 484.
[31] W. Li, Y.J. Guo, Y.L. Tang, X.T. Zu, J.Y. Ma, L. Wang, Y.Q. Fu, Room- empe a u e
ammonia senso based on ZnO nano ods deposi ed on ST-Cu qua z su ace
acous ic wa e de ices, Senso s 17 (2017) 10.
[32] J. Zong, Y.S. Zhang, Y. Zhu, Y. Zhao, W. Zhang, Y. Zhu, Rapid and highly selec i e
de ec ion o o maldehyde in ood using qua z c ys al mic obalance senso s based
on biomime ic poly-dopamine unc ionalized hollow mesopo ous silica sphe es,
Sens. Ac ua o s B Chem. 271 (2018) 311–320.
[33] N.H. Hasanuddin, M.H.A. Wahid, M.M. Shahimin, N. Hambali, N.R. Yuso ,
N.S. Nazi , N.Z. Khai uddin, M.A.M. Azidin, Ieee, Me al oxide based su ace
acous ic wa e senso s o ui s ma u i y de ec ion, 3
Rd
In e na ional Con e ence on
Elec onic Design, ed, New Yo k: Ieee, 2016, pp. 52–55.
[34] M.A.K.P. Tolen ino, D.R.B. Albano, F.B. Se illa, Piezoelec ic senso o e hylene
based on sil e (I)/polyme composi e, Sens. Ac ua o s B Chem. 254 (2018)
299–306.
[35] C. Popa, M. Pe us, A.M. B a u, Ammonia and e hylene bioma ke s in he espi a-
ion o he people wi h schizoph enia using pho oacous ic spec oscopy, J. Biomed.
Op . 20 (2015) 8.
[36] J.D. Moon, M. Galizia, H. Bo jigin, R. Liu, J.S. Riffle, B.D. F eeman, D.R. Paul,
Wa e apo so p ion, diffusion, and dila ion in polybenzimidazoles,
Mac omolecules 51 (2018) 7197–7208.
[37] J. Zhang, X.H. Liu, G. Ne i, N. Pinna, Nanos uc u ed ma e ials o oom- em-
pe a u e gas senso s, Ad . Ma e . 28 (2016) 795–831.
M. Še ka ecei ed he B.Sc. and M.Sc. deg ee in chemical enginee ing om he Uni e si y
o Belg ade, Se bia, in 2013 and 2015, espec i ely. She is cu en ly PhD s uden a he
Cen al Eu opean Ins i u e o Technology (CEITEC) in B no, Czech Republic. He esea ch
in e es s include syn hesis and cha ac e iza ion o he gas sensi i e polyme s and de el-
opmen o gas senso s de ices.
F. Bahos ecei ed he B.Sc deg ee in Enginee ing Physics in 2011 om he Cauca
Uni e si y. He ecei ed his MEng. deg ee in Elec ical Enginee ing in 2018 and wo ked
on gas senso s and RF signal condi ioning a Ins i u o de Ciencias Aplicadas y Tecnología
o he Uni e sidad Nacional Au ónoma de México (ICAT –UNAM). Now, he is wo king a
Sis ema de In es igación, Desa ollo Tecnológico e Inno ación (Senno a –SENA) on
elec ical senso s and in e ne o hings.
D. Ma a agui is g adua ed in physics in 2007, ecei ed his M.Sc. in Ad anced Ma e ials
and Nano echnology in 2008 and his Ph.D. deg ee in physics in 2012 om he
Uni e sidad Au ónoma de Mad id. F om 2008 o 2013 he was wo king in he GRIDSEN
g oup a he CSIC (Spain) on I + D + i o bio-chemical mic osenso s and elec onic noses
o en i onmen al p o ec ion. He was a Resea ch P o esso a he Na ional Au onomous
Uni e si y o Mexico (UNAM), in he Biomedical De ices G oup a he CCADET on he
de elopmen o chemical senso s and biosenso s. Cu en ly, he is wo king a he Ins i u o
de Tecnologías Físicas y de la In o mación (CSIC) de eloping new senso echnologies.
M. Po oček ecei ed his PhD in Physics in 2010. He is cu en ly wo king as esea che a
he Cen al Eu opean Ins i u e o Technology CEITEC and as assis an p o esso a he
Ins i u e o Physical Enginee ing, Facul y o Mechanical Enginee ing, B no Uni e si y o
Technology, B no, Czech Republic. His esea ch is ocused on su ace analysis o ul a-
hin laye s su ace using Time-o -ligh Seconda y Ion Mass Spec ome y (TOF-SIMS) and
The mal deso p ion spec oscopy (TDS).
Z. K al ecei ed his PhD deg ee in Elec onic Enginee ing om he Uni e si y Ro i a i
Vi gili, Spain, wo king on cha ac e iza ion o no el op oelec onic s uc u es like pho-
onic c ys als. Sho ly a e academic ca ee he s a ed in a p i a e echnology company
ocused on de elopmen and ab ica ion o scanning elec on mic oscopes. Cu en ly, he
is wo king o The mo Fishe Scien ific as a senio applica ions scien is expe ienced in
analy ical ins umen s and ailu e analysis echniques.
J. D bohla o a ecei ed he PhD deg ee in physical chemis y in 2008. She wo ks as
senio esea che and associa e p o esso a B no Uni e si y o Technology in he field o
syn hesis and cha ac e iza ion o nanoma e ials o sensing in medical and en i onmen al
applica ions. F om 2017 she also wo ks as Seconded Na ional Expe in he Eu opean
Commission o nanoma e ials s anda diza ion, egula ion and go e nance.
I. G acia ecei ed he PhD deg ee in physics in 1993 om he Au onomous Uni e si y 18
o Ba celona, Spain, wo king on chemical senso s. She joined he Na ional
Mic oelec onics Cen e (CNM) wo king on pho oli hog aphy, cu en ly she is ull ime 20
senio esea che in he Mic o-Nano Sys ems depa men o he CNM and he wo k is
ocused on gas sensing echnologies and MEMS eliabili y.
S. Vallejos ecei ed he PhD deg ee in Elec onic Enginee ing om he Uni e si a
Ro i a i Vi gili, Spain. Cu en ly, she holds a Ramón y Cajal ellowship and he esea ch is
ocused on gas sensing echnologies and nanoma e ials. She is in e es ed in explo ing
scalable syn hesis me hods o ailo and enginee he sensing p ope ies o nanoma e ials,
as well as in he de elopmen o gas sensing mic osys ems o applica ions in sa e y,
medicine, and en i onmen .
M. Še ka, e al. Senso s & Ac ua o s: B. Chemical 304 (2020) 127337
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