molecules
Re iew
Fab ica ion o G aphene/Molybdenum Disul ide
Composi es and Thei Usage as Ac ua o s o
Elec ochemical Senso s and Biosenso s
Ji i Kud 1, Voj ech Adam 1,2 and Ond ej Zi ka 1,2,*
1Depa men o Chemis y and Biochemis y, Mendel Uni e si y in B no, Zemedelska 1, B no CZ-613 00,
Czech Republic; [email p o ec ed] (J.K.); [email p o ec ed] (V.A.)
2Cen al Eu opean Ins i u e o Technology, B no Uni e si y o Technology, B no CZ-616 00, Czech Republic
*Co espondence: [email p o ec ed]
Academic Edi o : C is ina F ei e
Recei ed: 22 Augus 2019; Accep ed: 11 Sep embe 2019; Published: 17 Sep embe 2019


Abs ac :
F om he edisco e y o g aphene in 2004, he in e es in laye ed g aphene analogs has
been exponen ially g owing h ough a ious ields o science. Due o hei unique p ope ies,
no el wo-dimensional amily o ma e ials and especially ansi ion me al dichalcogenides a e
p omising o de elopmen o ad anced ma e ials o unp eceden ed unc ions. P og ess in 2D
ma e ials syn hesis pa ed he way o he s udies on hei hyb idiza ion wi h o he ma e ials o
c ea e unc ional composi es, whose elec onic, physical o chemical p ope ies can be enginee ed
o special applica ions. In his e iew we ocused on ecen p og ess in g aphene-based and
MoS
2
hyb id nanos uc u es. We summa ized and discussed a ious ab ica ion app oaches and
men ioned di e en 2D and 3D s uc u es o composi e ma e ials wi h emphasis on hei ad ances
o elec oanaly ical chemis y. The majo pa o his e iew p o ides a comp ehensi e o e iew o
he applica ion o g aphene-based ma e ials and MoS
2
composi es in he ields o elec ochemical
senso s and biosenso s.
Keywo ds: 2D ma e ials; bioanalysis; bioma ke ; ca bon; elec ode
1. In oduc ion
In he las decade we we e wi nesses o a apid de elopmen o ma e ials science esea ch.
Inspi ed and mo i a ed by he legenda y Feynman’s lec u e, many scien is s a e wa ching o “ he
bo om” and ocusing on he unique physicochemical and mechanical p ope ies o nanoma e ials.
In he 1960’s, a simple sco ch ape echnique was used o mechanically ex olia e bulk MoS
2
o a
ew-laye s s a e; his also enabled he isola ion o o he laye ed ma e ials decades la e , including
g aphene [
1
–
3
]. A e p is ine g aphene isola ion in 2004, bu geoning esea ch in he ield o laye ed 2D
ma e ials began [
2
]. Nowadays, we can use se e al op-down and bo om-up syn he ic p ocedu es o
ob ain ma e ials wi h exac numbe s o laye s and speci ic p ope ies. In addi ion, s acking o laye ed
ma e ials on each o he due o an de Waals o ces can be used o enginee he e os uc u ed solids
wi h unp eceden ed p ope ies [4].
2D laye ed ma e ials ep esen he hinnes (a omically hin) unsuppo ed c ys alline solids
wi hou dangling bonds hus p o iding supe io in alaye anspo o ligh , hea , spin and
cha ge [
5
]. G aphene, a single laye o ca bon a oms bound in hexagonal honeycomb la ice, is
a p ominen membe o he 2D laye ed ma e ials g oup. I possesses se e al ex ao dina y p ope ies
ex ensi ely desc ibed elsewhe e [
6
]. The eno e al. desc ibed an elec ochemical biosenso as an
in eg a ed ecep o – ansduce de ice which p o ides selec i e quan i a i e o semi-quan i a i e
analy ical in o ma ion using a biological ecogni ion elemen and an elec ochemical ansduce [
7
].
Molecules 2019,24, 3374; doi:10.3390/molecules24183374 www.mdpi.com/jou nal/molecules
Molecules 2019,24, 3374 2 o 14
The in eg a ion o g aphene-based ma e ials wi h an elec ochemical ansduce p o ides se e al
ad an ages, such as inc eased conduc i i y, elec on ans e a e and/o inc eased su ace- o- olume
a io o ansduce hanks o g aphene’s ul a hin s uc u e [
8
–
11
]. Fu he , g aphene’s abili y o be
unc ionalized wi h he e oa oms, a ious molecules o unc ional g oups is pa o he supe io p ope y
o his unique ma e ial. The elec onic and chemical p ope ies o g aphene-based ma e ials a e highly
in luenced by he con en o oxygen unc ional g oups. G aphene oxide (GO) and educed g aphene
oxide ( GO), as oxygena ed monolaye s o ca bon a oms a e widely applied in bioelec onics and
biosenso s due o highe hyd ophilici y (compa ed o g aphene) and he p esence o oxygen-con aining
g oups, which enable b oad possibili ies o unc ionaliza ion. I is wo h no ing ha conduc i i y o
g aphene dec eases wi h inc easing oxygen con en , hus a ma e ial o op imal C/O a io is needed o
indi idual applica ions.
T ansi ion me al dichalcogenides (TMDs) a e g aphene analogs o med by s acking o
sul u - ansi ion me al–sul u shee s h ough an de Waals o ces. As a consequence, indi idual
laye s can be ex olia ed om bulk ma e ial o single-laye o m. Molybdenum disul ide (MoS
2
)
is a ypical membe o TMDs. I is composed o a s ack o hexagonal laye s o Mo a oms
sandwiched be ween wo laye s o S a oms and possesses p- ype semiconduc ing p ope ies wi h
poo elec ical conduc i i y. MoS
2
has wo main ad an ages in elec ochemical (bio)senso s. Fi s ly,
i p o ides addi ional elec ochemically ac i e si es. Secondly, i can imp o e ansduce p ope ies by
accommoda ing addi ional elemen s such as me al nanopa icles o bio ecogni ion (e.g., an ibodies,
enzymes, ap ame s) [
12
]. Simila o g aphene, MoS
2
possesses di e en a ini ies owa ds ssDNA
and dsDNA [
13
]. Such beha io enables in eg a ion o MoS
2
wi h b oadly used ap ame echnology.
Howe e , 2D MoS
2
s ill su e s om se e al d awbacks. Res acking o 2D ma e ials due high su ace
ene gy can dec ease he amoun o elec ochemically ac i e si es, and poo elec ical conduc i i y limi s
i s use as ansduc ion enhance . The e o e, he hyb idiza ion o 2D MoS
2
wi h highly conduc i e
ma e ials such as g aphene can help o o e come men ioned d awbacks and can esul in ma e ials
wi h ascina ing elec oanaly ical p ope ies.
Se e al e iews showing he use o MoS
2
o he g oup o TMDs in he ield o elec ochemical
(bio)senso s ha e been published [
14
–
17
], howe e he e we ocus s ic ly on g aphene-based composi e
ma e ials wi h MoS
2
(G /MoS
2
). We b ie ly summa ize he mos impo an syn he ic p ocedu es
p o iding men ioned ma e ial. The as majo i y o his e iew ocuses on he elec oanaly ical
pe o mance o de ices and di e en s a e-o -a elec ochemical biosensing app oaches bene i ing
om he unique p ope ies o g aphene/MoS2composi es.
2. Syn hesis o G /2D MoS2Composi es
Many di e en me hods ha e been de eloped o ab ica ion o G /MoS
2
hyb id ma e ials o
exac p ope ies such as hickness, mo phology, numbe o elec oac i e si es. Desi ed p ope ies o
ma e ials co espond wi h hei applica ion pu poses and o his eason a signi ican pa o his
e iew is ocused on G /MoS2syn hesis.
2.1. Hyd o he mal and Sol o he mal Syn hesis
These me hods a e based on g ow h o MoS
2
s uc u es o e g aphene/GO/ GO suppo . MoS
2
molecula p ecu so s (e.g., Na
2
MoO
4
and hioace amide) a e dissol ed in aqueous (hyd o he mal) o
o ganic sol en s (sol o he mal syn hesis) and hey a e he mally ea ed in s ainless s eel eac o s o an
exac ime and a a speci ic empe a u e abo e boiling poin o sol en . P oduc s o a ious p ope ies can
be ob ained by op imiza ion o hea ing empe a u e, eac ion ime and p esence o addi ional compounds
such as su ac an s. Ad an ages o hese me hods a e high yields, simple p ocedu es and ela i ely low
cos o equipmen . Howe e , he bigges d awback is low con ol o he syn hesis p ocess.
A ew-laye MoS
2
hyb id wi h GO was syn hesized by Yu e al. [
18
]. They used N-me hylimidazole
wa e -soluble pilla [
5
] a ene as a su ac an o imp o e dis ibu ion o MoS
2
shee s on comme cial
GO. They hea ed a solu ion con aining 7 mg
·
mL
−1
o GO, 1.5 mmol Na
2
MoO
4
, 7.5 mmol L-cys eine
Molecules 2019,24, 3374 3 o 14
dissol ed in 40 mL deionized wa e a 240
◦
C o 24 h. The eeze-d ied p oduc was annealed in a
ube u nace a 500
◦
C o 2 h in low o 10% hyd ogen in ni ogen. This app oach p o ided la e ally
(in-plane) s acked MoS
2
on G /GO/ GO subs a es as epo ed in o he publica ions wi h al e na i e
su ac an s o wi hou su ac an [
19
–
21
]. On he con a y, wi hou su ac an , MoS
2
e ically
s acked on elec ochemically ex olia ed g aphi e (EG) as a subs a e was epo ed by Wang e al. [
22
].
They mixed EG wi h (NH
4
)
2
MoS
4
in weigh a ios om 1:1 o 1:13 in he p esence o hyd azine and
ea ed hese mix u es in s ainless s eel eac o s a 200
◦
C o 15 h and ob ained G /MoS
2
wi h 95 w %
MoS
2
con en . The p oduc o his epo ed syn hesis can be seen in Figu e 1A,B. Hyd o he mal g ow h
o MoS
2
on GO in he p esence o poly inylpy olidone (PVP) and oxala e dihyd a e was epo ed
by Teng e al. [
23
]. As a MoS
2
p ecu so s, hey used ammonium pa amolybda e (NH
4
)
6
Mo
7
O
24
and
hiou ea and hea ed hei mix u e wi h GO a 180 ◦C o 12 h in 100 mL au ocla e. Then he ma e ial
was annealed a 800
◦
C in a gon a mosphe e o ob ain GO/MoS
2
. Finally, hey co e ed GO/MoS
2
wi h amo phous ca bon using chemical apo deposi ion (CVD) o enhance cha ge ans e h ough
composi e (Figu e 1C). Hyd o he mal and sol o he mal me hods a e able o ab ica e g aphene and
MoS
2
hyb id ma e ials wi h a ious 2D and 3D s uc u es. As epo ed Sun e al., jus by changing
he GO amoun in he eac ion, 3D assembly o MoS
2
can be uned om nano lowe s o c osslinked
nanoshee s la e ally s acked on GO [
24
]. They used mixed sol o he mal syn hesis in an e hanol and
oc ylamine mix u e. Mixed sol en s o deionized wa e and dime hyl o mamide (DMF) in a 1:2 a io
we e used by Zhao e al. [
25
]. They obse ed he e ec o NH
3·
H
2
O concen a ion in he eac ion eac o
on he inal p oduc and compa ed he esul s wi h solu ion wi h pH adjus ed wi h NaOH. When
NH
3·
H
2
O was added o eac ion mix u e, he 3D po ous amewo k cons uc ed by in e connec ed
lamella nanoshee s o G /MoS
2
hyd ogel became mo e homogeneous wi h po e sizes om hund eds
o nanome e s o mic ome e s. In addi ion, he p esence o NH
3·
H
2
O esul ed in g aphene N-doping.
Sol o he mal and hyd o he mal app oaches we e also used o modi y he 1D ca bon ibe , ca bon
nano ubes o mac oscopic ca bon pape [
26
–
29
]. MoS
2
s acked on ca bon nano ibe as was epo ed by
Li e al. can be seen in Figu e 1D,E.
Molecules 2019, 24, x FOR PEER REVIEW 3 o 14
mmol L-cys eine dissol ed in 40 mL deionized wa e a 240 °C o 24 h. The eeze-d ied p oduc was
annealed in a ube u nace a 500 °C o 2 h in low o 10% hyd ogen in ni ogen. This app oach
p o ided la e ally (in-plane) s acked MoS
2
on G /GO/ GO subs a es as epo ed in o he
publica ions wi h al e na i e su ac an s o wi hou su ac an [19–21]. On he con a y, wi hou
su ac an , MoS
2
e ically s acked on elec ochemically ex olia ed g aphi e (EG) as a subs a e was
epo ed by Wang e al. [22]. They mixed EG wi h (NH
4
)
2
MoS
4
in weigh a ios om 1:1 o 1:13 in he
p esence o hyd azine and ea ed hese mix u es in s ainless s eel eac o s a 200 °C o 15 h and
ob ained G /MoS
2
wi h 95 w % MoS
2
con en . The p oduc o his epo ed syn hesis can be seen in
Figu e 1A,B. Hyd o he mal g ow h o MoS
2
on GO in he p esence o poly inylpy olidone (PVP)
and oxala e dihyd a e was epo ed by Teng e al. [23]. As a MoS
2
p ecu so s, hey used ammonium
pa amolybda e (NH
4
)
6
Mo
7
O
24
and hiou ea and hea ed hei mix u e wi h GO a 180 °C o 12 h in
100 mL au ocla e. Then he ma e ial was annealed a 800 °C in a gon a mosphe e o ob ain GO/MoS
2
.
Finally, hey co e ed GO/MoS
2
wi h amo phous ca bon using chemical apo deposi ion (CVD) o
enhance cha ge ans e h ough composi e (Figu e 1C). Hyd o he mal and sol o he mal me hods
a e able o ab ica e g aphene and MoS
2
hyb id ma e ials wi h a ious 2D and 3D s uc u es. As
epo ed Sun e al., jus by changing he GO amoun in he eac ion, 3D assembly o MoS
2
can be
uned om nano lowe s o c osslinked nanoshee s la e ally s acked on GO [24]. They used mixed
sol o he mal syn hesis in an e hanol and oc ylamine mix u e. Mixed sol en s o deionized wa e and
dime hyl o mamide (DMF) in a 1:2 a io we e used by Zhao e al. [25]. They obse ed he e ec o
NH
3
∙H
2
O concen a ion in he eac ion eac o on he inal p oduc and compa ed he esul s wi h
solu ion wi h pH adjus ed wi h NaOH. When NH
3
∙H
2
O was added o eac ion mix u e, he 3D po ous
amewo k cons uc ed by in e connec ed lamella nanoshee s o G /MoS
2
hyd ogel became mo e
homogeneous wi h po e sizes om hund eds o nanome e s o mic ome e s. In addi ion, he p esence
o NH
3
∙H
2
O esul ed in g aphene N-doping. Sol o he mal and hyd o he mal app oaches we e also
used o modi y he 1D ca bon ibe , ca bon nano ubes o mac oscopic ca bon pape [26–29]. MoS
2
s acked on ca bon nano ibe as was epo ed by Li e al. can be seen in Figu e 1D,E.
Figu e 1. (A) TEM images and (B) HRTEM images o e ically aligned ex ollia ed g aphi e and MoS
2
composi e. F om Wang e al. [22]. (C) Schema ic illus a ion o he o ma ion o he
g aphene/MoS
2
/amo phous ca bon composi e. F om Teng e al. [23]. (D) FE-SEM and (E) TEM images
o he MoS
2
and ca bon nano ibe composi e. The inse shows he TEM image o a single MoS
2
and
ca bon nano ibe nanos uc u e. F om Li e al. [29].
2.2. The mal and Chemical Reduc ion
These me hods o G /MoS
2
syn hesis a e e en mo e acile han hyd o he mal and sol o he mal
ones. In case o he mal educ ion, he he mal ene gy is used o con e MoS
2
molecula p ecu so s
o MoS
2
solid ma e ials which a e s uck on g aphene-based suppo . In case o chemical educ ion,
chemical educ an s a e used o educe MoS
2
p ecu so s o 2D MoS
2
. Al hough hese me hods can
easily p oduce G /MoS
2
in g am-scale, he main d awback is he con ol o e syn hesis p ocess and
ha he p ope ies o he p oduc can ha dly be p edic ed. The common p ocedu e o G /MoS
2
Figu e 1.
(
A
) TEM images and (
B
) HRTEM images o e ically aligned ex ollia ed g aphi e
and MoS
2
composi e. F om Wang e al. [
22
]. (
C
) Schema ic illus a ion o he o ma ion o he
g aphene/MoS
2
/amo phous ca bon composi e. F om Teng e al. [
23
]. (
D
) FE-SEM and (
E
) TEM images
o he MoS
2
and ca bon nano ibe composi e. The inse shows he TEM image o a single MoS
2
and
ca bon nano ibe nanos uc u e. F om Li e al. [29].
2.2. The mal and Chemical Reduc ion
These me hods o G /MoS
2
syn hesis a e e en mo e acile han hyd o he mal and sol o he mal ones.
In case o he mal educ ion, he he mal ene gy is used o con e MoS
2
molecula p ecu so s o MoS
2
solid ma e ials which a e s uck on g aphene-based suppo . In case o chemical educ ion, chemical
educ an s a e used o educe MoS
2
p ecu so s o 2D MoS
2
. Al hough hese me hods can easily p oduce
G /MoS
2
in g am-scale, he main d awback is he con ol o e syn hesis p ocess and ha he p ope ies
o he p oduc can ha dly be p edic ed. The common p ocedu e o G /MoS
2
ab ica ion using he mal
Molecules 2019,24, 3374 4 o 14
educ ion is o dissol e he Mo sal wi h S sou ce o c ea e homogeneous solu ion which is subsequen ly
d ied and he mally ea ed a se e al hund ed
◦
C in ine a mosphe e. S i as a a e al. ab ica ed MoS
2
and g aphene oxide composi e by he mal ex olia ion and educ ion [
30
]. They g ound ammonium
hiomolybda e and g aphi e oxide and ea ed he powde o 6 h a 400
◦
C and inally o 15 min a
1200
◦
C unde low o ni ogen gas. Ko o ee e al. ab ica ed G /MoS
2
composi e by imp egna ion o
g aphene wi h Mo-con aining compound ollowed by he mal decomposi ion [
31
]. They dispe sed
g aphene lakes in wa e –e hanol mixed solu ion wi h addi ion o ammonium hiomolybda e. Be o e
he mal con e sion (500–800
◦
C o 1 h) o MoS
3
o MoS
2
a acuum, hiomolybda e was decomposed
using HCl and d ied a ai a mosphe e. Ins ead o he mal educ ion in ine gas o acuum, syn hesis
in he p esence o CS
2
esul s in S-doping o g aphene-based ma e ials (Figu e 2A) [
32
]. F eeze-d ying
o g aphene-based ma e ials wi h MoS
2
p ecu so s p o ides bene i s o sponge-like 3D p oduc s be o e
he mal educ ion [
33
]. As Jiang e al. men ioned, hese 3D s uc u es can help o p e en g aphene o
MoS
2
es acking p oblems du ing syn hesis and u he p ocessing [
34
]. They ab ica ed G /MoS
2
o
s able 3D s uc u e using a combina ion o hyd o he mal and chemical educ ion me hods. Fi s ly,
hey ab ica ed monolaye MoS
2
and g aphene oxide. They mixed GO and MoS
2
in isop opanol/wa e
solu ion whe e unc ional g oups o GO a ac ed MoS
2
. The solu ion was hyd o he mally ea ed
o c ea e po ous 3D a chi ec u e. Subsequen ly he composi e, o mo e p ecisely GO, was educed
using hyd azine. Ji e al. ab ica ed GO/MoS
2
by d y ball-milling o MoS
2
and bulk GO a a a io
o 1:1 o 5 h [
35
]. The p oduc was subsequen ly chemically educed wi h hyd azine. Wang e al.
used hyd azine o educe (NH
4
)
2
MoS
4
oo. In addi ion, hey used ce yl ime hylammonium b omide
(CTAB) as ca ionic su ac an o p omo e in e ac ion be ween nega i ely cha ged GO and MoS
42−
[
36
].
2.3. Mic owa e and Elec ochemical Syn hesis
Mic owa e syn hesis is an e ec i e me hod o G /MoS
2
ab ica ion and ep esen s an al e na i e
o he mal me hods. I can induce apid decomposi ion o MoS
2
p ecu so s and hence lowe s he
ene gy consump ion and does no need any chemical educ an . E ec i e one-po mic owa e-assis ed
sol o he mal syn hesis was epo ed by Li e al. [
37
]. They dispe sed liquid-ex olia ed g aphene
(0.71 mg
·
mL
−1
) in N-me hylpy olidone wi h addi ion o 1-dodecane hiol, Na
2
MoO
4·
2H
2
O and
hiou ea. Such solu ion was hea ed in a specialized glass eac o using mic owa e a 200
◦
C o 12 h.
Pos -syn hesis ea men in ube u nace a 800
◦
C o 2 h was used o emo e sul u esidues and
imp o e p oduc c ys allini y (composi e can be seen in Figu e 2B,C). Xiang e al. deco a ed chemical
apo deposi ed g aphene oam wi h MoS
2
nano lowe s using a mic owa e eac o [
38
]. Mo e p ecisely,
hey i adia ed an aqueous solu ion o Na
2
MoO
4·
2H
2
O, hioace amide and g aphene oam in glass
ube and kep i a 180
◦
C o 12 h. Fa sho e i adia ion o he eac ion mix u e was epo ed by
Li e al. [
39
]. They kep a solu ion o GO, phosphomolybdic acid hyd a e and hioace amide adjus ed
o pH 7 a 150 ◦C and 150 W o 10 min.
The elec ochemical app oach o ab ica e G /MoS
2
composi es ep esen s a low-cos and as
me hod wi hou he use o oxic compounds. Fu he , i seems o be he mos sui able app oach o
applica ion in elec ochemical (bio)senso s since hey can be ab ica ed di ec ly by he elec ochemis s
who a e enabled o op imize p oduc p ope ies by using deposi ion condi ions. Fab ica ion o
G /MoS
2
-modi ied elec ode wi hou he need o any pos - ab ica ion ea men was epo ed by
Li e al. [
40
]. Fi s ly, hey deposi ed GO laye on luo ine-doped in oxide (FTO) by elec ochemical
educ ion o GO om aqueous solu ion a
−
1.2 V. MoS
2
nanopa icles we e subsequen ly deposi ed on
he conduc i e su ace o GO laye h ough elec ochemical deposi ion o ammonium hiomolybda e
in KCl elec oly e a
−
1.0 V o 5 min. Wan e al. epo ed cons an cu en deposi ion o e ical
MoS
2
s uc u es o e a CVD-co e ed g aphene elec ode [
41
]. They used a wo-elec ode sys em and
(NH
4
)
2
MoS
4
as an elec oly e. Two-elec on educ ion occu ed a he ca bon od ca hode which was
co e ed wi h MoS
2
. On he g aphene anode a hin ilm o MoS
3
was oxida i ely elec odeposi ed
(Figu e 2D). A highly c ys alline G /MoS
2
-co e ed anode was ob ained by ea ing anode in qua z
ube a 800 ◦C.
Molecules 2019,24, 3374 5 o 14
2.4. Chemical Vapo Deposi ion
CVD is an e ec i e me hod o high quali y G /MoS
2
composi e ab ica ion which p o ides excellen
con ol o e he ab ica ion p ocess. In gene al, he subs a e (o en me al) is exposed in a acuum
chambe o gaseous p ecu so s which eac and/o decompose o c ea e he desi ed deposi ed ma e ial,
and ca ie gas emo es byp oduc s. CVD o g aphene is a well-es ablished echnique, howe e i s ill
aces many p oblems hampe ing he u he use o g aphene in undamen al esea ch and p ac ice [
42
].
In addi ion, i equi es expensi e equipmen and he p ocess needs o be s ingen ly coo dina ed,
hus i seems o be mo e sui able o FET-based (bio)senso s [
43
]. Fab ica ion o e ically aligned
MoS
2
nanoshee s on g aphene using CVD was epo ed by Gnanaseca e al. [
44
]. They ab ica ed
g aphene using a mosphe ic p essu e CVD o ace ylene on Cu oil, and he g aphene was ans e ed
on o a SiO
2
wa e using poly(me hyl me hac yla e) (PMMA) ilm. F ees anding g aphene on wa e
was ob ained by chemical e ching o Cu and PMMA ilm. Fo MoS
2
s uc u es g owing on g aphene
hey used a home-made wo-zone CVD eac o (Figu e 2E). MoO
3
and sul u p ecu so s we e placed
in sepa a ely con olled hea ing zones unde he low o A . The hea ing zone wi h MoO
3
was amped
up o 650
◦
C (15
◦
C
·
min
−1
), hen slowly hea ed o 750
◦
C (2
◦
C
·
min
−1
) and kep a 750
◦
C o 10 min.
Fo sul u iza ion, he sul u zone was apidly hea ed o 200
◦
C (20
◦
C
·
min
−1
). Bi oju e al. used he
mechanical ans e me hod o MoS
2
on g aphene [
45
]. They sepa a ely ab ica ed la ge a ea g aphene
and MoS
2
using CVD and MoS
2
on SiO
2
wa e was uni o mly p essed on g aphene using a hyd aulic
p essu ize . Chen e al. ab ica ed MoS
x
composi e wi h CVD g aphene by dispe sing g aphene in
(NH4)2MoS4DMF solu ion and ea ing i in a qua z ube u nace a 120 ◦C and 500 ◦C o 1h[46].
Molecules 2019, 24, x FOR PEER REVIEW 5 o 14
2.4. Chemical Vapo Deposi ion
CVD is an e ec i e me hod o high quali y G /MoS
2
composi e ab ica ion which p o ides
excellen con ol o e he ab ica ion p ocess. In gene al, he subs a e (o en me al) is exposed in a
acuum chambe o gaseous p ecu so s which eac and/o decompose o c ea e he desi ed
deposi ed ma e ial, and ca ie gas emo es byp oduc s. CVD o g aphene is a well-es ablished
echnique, howe e i s ill aces many p oblems hampe ing he u he use o g aphene in
undamen al esea ch and p ac ice [42]. In addi ion, i equi es expensi e equipmen and he p ocess
needs o be s ingen ly coo dina ed, hus i seems o be mo e sui able o FET-based (bio)senso s [43].
Fab ica ion o e ically aligned MoS
2
nanoshee s on g aphene using CVD was epo ed by
Gnanaseca e al. [44]. They ab ica ed g aphene using a mosphe ic p essu e CVD o ace ylene on Cu
oil, and he g aphene was ans e ed on o a SiO
2
wa e using poly(me hyl me hac yla e) (PMMA)
ilm. F ees anding g aphene on wa e was ob ained by chemical e ching o Cu and PMMA ilm. Fo
MoS
2
s uc u es g owing on g aphene hey used a home-made wo-zone CVD eac o (Figu e 2E).
MoO
3
and sul u p ecu so s we e placed in sepa a ely con olled hea ing zones unde he low o A .
The hea ing zone wi h MoO
3
was amped up o 650 °C (15 °C∙min
−1
), hen slowly hea ed o 750 °C (2
°C∙min
−1
) and kep a 750 °C o 10 min. Fo sul u iza ion, he sul u zone was apidly hea ed o 200
°C (20 °C∙min
−1
). Bi oju e al. used he mechanical ans e me hod o MoS
2
on g aphene [45]. They
sepa a ely ab ica ed la ge a ea g aphene and MoS
2
using CVD and MoS
2
on SiO
2
wa e was
uni o mly p essed on g aphene using a hyd aulic p essu ize . Chen e al. ab ica ed MoS
x
composi e
wi h CVD g aphene by dispe sing g aphene in (NH
4
)
2
MoS
4
DMF solu ion and ea ing i in a qua z
ube u nace a 120 °C and 500 °C o 1 h [46].
Figu e 2. (A) Schema ic ep esen a ion showing syn hesis o S-doped educed g aphene oxide
( GO)/MoS
2
composi e. F om Wang e al. [32]. (B) Low-magni ica ion and (C) high-magni ica ion
TEM images o GO/MoS
2
composi e ab ica ed by one-po mic owa e syn hesis. F om Li e al. [37].
(D) Schema ic diag am o he chemical ba h deposi ion o MoS
2
on g aphene as he anode and ca bon
od as he ca hode. F om Wan e al. [41]. (E) Schema ic o he wo-zone chemical apo deposi ion
(CVD) u nace u ilized o he syn hesis o e ical MoS
2
on g aphene. F om Gnanaseka e al. [44].
2.5. Al e na i e App oaches
Figu e 2.
(
A
) Schema ic ep esen a ion showing syn hesis o S-doped educed g aphene oxide
( GO)/MoS
2
composi e. F om Wang e al. [
32
]. (
B
) Low-magni ica ion and (
C
) high-magni ica ion TEM
images o GO/MoS
2
composi e ab ica ed by one-po mic owa e syn hesis. F om Li e al. [
37
]. (
D
)
Schema ic diag am o he chemical ba h deposi ion o MoS
2
on g aphene as he anode and ca bon od
as he ca hode. F om Wan e al. [
41
]. (
E
) Schema ic o he wo-zone chemical apo deposi ion (CVD)
u nace u ilized o he syn hesis o e ical MoS2on g aphene. F om Gnanaseka e al. [44].
2.5. Al e na i e App oaches
Some al e na i e app oaches which canno be placed wi hin abo e-men ioned ca ego ies we e
de eloped. A e y acile me hod o G /MoS
2
ab ica ion was de eloped by Kuma e al. [
47
]. Fi s ,
hey p epa ed g aphi e oxide solu ion by con inuous magne ic s i ing and sonica ion o g aphi e

Molecules 2019,24, 3374 6 o 14
oxide in e hanol. A e addi ion o bulk MoS
2
in o g aphi e oxide solu ion, e hanol was e apo a ed.
D y powde was ea ed wi h mic owa e i adia ion (800 W, 130 s) o comple e ex olia ion o g aphi e
oxide. Simple mixing o GO solu ion wi h MoS
2
nanopa icles and annealing a 400
◦
C was epo ed
by Venka esan e al. [48].
3. Applica ions o G /2D MoS2Composi es
G aphene-based ma e ials and MoS
2
composi es possess speci ic p ope ies depending on hei
mo phology and s uc u e. The p ope ies a e mos ly in luenced by numbe o MoS
2
laye s, g aphene
deg ee o oxida ion, composi e plane o 3D s uc u e. Thus hey ep esen e sa ile ma e ials, which
we e ecognized as p omising o se e al ields o science. Among o he s, elec ochemical senso s and
biosenso s can bene i om G /MoS
2
ad ances by imp o ed analy ical pe o mance such as highe
sensi i i y, inc eased analy e selec i i y, be e peak- o-peak sepa a ion and/o a b oade linea dynamic
ange. In his chap e , elec oanaly ical de ices bene i ing om G /MoS
2
p ope ies a e di ided in o
senso s and biosenso s applica ions, which di ec ly educe/oxidize analy e and which use biological
ecogni ion elemen s, espec i ely.
3.1. G /2D MoS2Composi es in Elec ochemical Senso s
Elec ochemis y ep esen s a acile echnique o de ec small molecules wi h high sensi i i y, low
de ec ion limi s, easonable cos and sho ime consump ion. U ic acid (UA), dopamine (DA) and
asco bic acid (AA) a e small biological molecules, which a e p esen ed in human physiological luids
and can help o de e mine human s a es, including se e al diseases. Howe e hei simul aneous
de e mina ion is s ill challenging due o elec ode ouling and hei oxida ion a almos he same
po en ials. The imp o emen o elec ode sensi i i y owa ds u ic acid (UA), dopamine (DA) and
asco bic acid (AA) and di e en ial pulse ol amme y (DPV) peak- o-peak sepa a ion ia elec ode
modi ica ion wi h educed g aphene oxide composi e wi h MoS
2
was demons a ed by Xing e al. [
49
].
They showed ha po ous nanos uc u e o he composi e inc eased speci ic su ace o he elec ode
by nea ly 4- old compa ed wi h MoS
2
modi ica ion, p o ided mo e ac i e si es o a ge molecules
adso p ion and as a esul imp o ed elec ode ca aly ic pe o mance. The same conclusions we e
also made by Huang e al. in case o ace aminophen sensing in he p esence o AA and DA wi h a
simila elec ode [
50
]. Di ec oxida ion o ni i e ions on con en ional elec odes is s ill challenging
due o he high o e po en ials equi ed. Thus, di e en modi ied elec odes we e epo ed o ni i e
sensing [
51
–
54
]. G /MoS
2
can be used o dec ease ni i e ions educ ion po en ials o +0.8 V s.
Ag/AgCl and inc ease sensi i i y (Figu e 3A,B) [
55
]. Th ee-dimensional nanos uc u ed g aphene,
MoS
2
lowe s and mul iwall ca bon nano ubes (MWCNTs) composi e was p e iously used o
sensi i e enzymeless de e mina ion o hyd ogen pe oxide [
56
]. An ampe ome ic senso based on
modi ied glassy ca bon elec ode (GCE) showed excellen elec oca aly ic ac i i y owa ds educ ion
o H
2
O
2
, wi h a de ec ion limi (LOD) o 0.83
µ
M, linea ange o 5
µ
M–145
µ
M and sensi i i y o
5.184
µ
A
·µ
M
·
cm
−2
. Di ec educ ion o me hyl pa a hion (i s ni o unc ional g oup) was epo ed [
57
].
Me hyl pa a hion belongs o he g oup o o ganophospho us pes icides which gene a e conce ns
in ood sa e y, wa e managemen and public heal h. Hyd o he mally ab ica ed g aphene MoS
2
nanocomposi e was used o modi y GCE, and ampe ome y a
−
0.6 V s. Ag/AgCl was used o
compa e he pe o mance o ba e, MoS
2
-modi ied and g aphene-modi ied elec odes. A senso was
shown wi h pa ame e s compe i i e o enzyme based de ec ion—LOD 3.2 nM and linea dynamic
ange om 10 nM o 1.9 mM [
58
]. Good claimed selec i i y o he senso was asc ibed o
π
-s acking
o me hyl pa a hion phenyl g oup on G /MoS
2
composi e, howe e disc imina ion was no possible
be ween pa a hion and me hyl pa a hion. Good pe o mance o he senso in spiked eal ui and
ege able samples was shown. A lexible elec ochemical senso o olic acid (FA) based on MoS
2
nanoshee -modi ied GO pape was designed by Ki ansan e al. [
59
]. Thei elec odes we e ab ica ed
by a wo-s ep p ocess. A i s , he acuum il a ion o MoS
2
and GO solu ion h ough polyca bona e
memb ane c ea ed a ee-s anding ilm o composi e. Secondly, he ilm was educed in HI solu ion
Molecules 2019,24, 3374 7 o 14
o 1 h and hen hey cu he memb ane o pieces o 5
×
10 mm. To ob ain he bes pe o mance hey
op imized he a io o GO and MoS
2
in il a ed solu ion, inding ha a 3:1 a io was op imal. Oxida ion
o FA in 0.1 M PBS bu e (pH 7) ook place a +0.73 mV s. Ag/AgCl (Figu e 3C). Ampe ome ic
de ec ion esul ed in LOD o 37 nM and he senso showed good selec i i y e en in he se um and he
p esence o 1.0 mM AA and 0.5 mM UA (Figu e 3D).
Molecules 2019, 24, x FOR PEER REVIEW 7 o 14
memb ane c ea ed a ee-s anding ilm o composi e. Secondly, he ilm was educed in HI solu ion
o 1 h and hen hey cu he memb ane o pieces o 5 × 10 mm. To ob ain he bes pe o mance hey
op imized he a io o GO and MoS
2
in il a ed solu ion, inding ha a 3:1 a io was op imal.
Oxida ion o FA in 0.1 M PBS bu e (pH 7) ook place a +0.73 mV s. Ag/AgCl (Figu e 3C).
Ampe ome ic de ec ion esul ed in LOD o 37 nM and he senso showed good selec i i y e en in
he se um and he p esence o 1.0 mM AA and 0.5 mM UA (Figu e 3D).
Figu e 3. (A) Cyclic ol amme y CV cu es o he glassy ca bon elec ode (GCE), GCE modi ied wi h
GO, MoS
2
and GO/MoS
2
in 0.1 M PBS (pH = 7.0) wi h 500 μM ni i e. (B) CV cu es o he GCE
modi ied wi h GO/MoS
2
in 0.1 M PBS (pH = 7.0) unde di e en concen a ions o ni i e: 100, 300,
500, 700, and 1000 μM (scan a e: 50 mV∙s
−1
). Bo h om Hu e al. [55]. (C) CV cu es o GO (black)
and GO/MoS
2
pape elec odes in 0.1 M PBS (pH 7.0) wi h (blue) and wi hou ( ed) 2.0 mM olic acid
(FA). Scan a e: 50 mV∙s
−1
. Inse : S uc u e o FA. (D) The CVs o he same concen a ions o asco bic
acid (AA, blue line), u ic acid (UA, g een line) and FA (black line) and 1.0 mM AA, 0.5 mM UA and
0.5 mM FA con aining solu ion ( ed line) a he GO/MoS
2
composi e pape elec ode in pH 7.0 PBS.
Scan a e: 50 mV∙ s
−1
. Bo h om Ki ansan e al. [59].
3.2. G /2D MoS
2
Composi es in Elec ochemical Biosenso s
Good biocompa ibili y o G /2D MoS
2
ma e ials has led many esea che s o modi y hese
ma e ials wi h biological mac omolecules such as nucleic acid ap ame s, enzymes o an ibodies. In
case o enzymes, i was demons a ed ha laye ed 3D s uc u es help o inc ease enzymes’ s abili y
and p o ec hem om loss o ac i i y. Se e al media o - ee enzyme-based biosenso s bene i ing
om G /MoS
2
p ope ies we e desc ibed. Among o he s, Yoon e al. designed he H
2
O
2
biosenso
based on myoglobin (Mb) edox ac i i y [60]. In de ail, hey encapsula ed MoS
2
nanopa icles wi hin
GO and used his composi e ma e ial o modi y gold elec odes ia chemical linke ( he p inciple can
be seen in Figu e 4A). Mb is able o media e elec ochemical educ ion o H
2
O
2
due o he p esence o
i on wi hin i s co e [61]. They compa ed he pe o mance o he designed elec ode wi h Mb/MoS
2
and Mb/GO. Mb/GO/MoS
2
showed an enhanced elec ochemical signal e en in he p esence o AA,
NaNO
2
and NaHCO
3
. The ampe ome ic ead-ou a −0.3 V s. Ag/AgCl eached a LOD o 20 nM
H
2
O
2
. The same app oach wi h immobiliza ion o Mb was used o biosensing o ni ic oxide and
ni i e ions [62,63]. Al e na i ely, hemoglobin can be used ins ead o Mb as showed by Liu e al. [64].
Jeong e al. compa ed he pe o mance o plana G /MoS
2
and G /MoS
2
wi h 3D s uc u e as
Figu e 3.
(
A
) Cyclic ol amme y CV cu es o he glassy ca bon elec ode (GCE), GCE modi ied wi h
GO, MoS
2
and GO/MoS
2
in 0.1 M PBS (pH =7.0) wi h 500
µ
M ni i e. (
B
) CV cu es o he GCE
modi ied wi h GO/MoS
2
in 0.1 M PBS (pH =7.0) unde di e en concen a ions o ni i e: 100, 300,
500, 700, and 1000
µ
M (scan a e: 50 mV
·
s
−1
). Bo h om Hu e al. [
55
]. (
C
) CV cu es o GO (black)
and GO/MoS
2
pape elec odes in 0.1M PBS (pH 7.0) wi h (blue) and wi hou ( ed) 2.0 mM olic acid
(FA). Scan a e: 50 mV
·
s
−1
. Inse : S uc u e o FA. (
D
) The CVs o he same concen a ions o asco bic
acid (AA, blue line), u ic acid (UA, g een line) and FA (black line) and 1.0 mM AA, 0.5 mM UA and
0.5 mM FA con aining solu ion ( ed line) a he GO/MoS
2
composi e pape elec ode in pH7.0 PBS.
Scan a e: 50 mV·s−1. Bo h om Ki ansan e al. [59].
3.2. G /2D MoS2Composi es in Elec ochemical Biosenso s
Good biocompa ibili y o G /2D MoS
2
ma e ials has led many esea che s o modi y hese ma e ials
wi h biological mac omolecules such as nucleic acid ap ame s, enzymes o an ibodies. In case o
enzymes, i was demons a ed ha laye ed 3D s uc u es help o inc ease enzymes’ s abili y and
p o ec hem om loss o ac i i y. Se e al media o - ee enzyme-based biosenso s bene i ing om
G /MoS
2
p ope ies we e desc ibed. Among o he s, Yoon e al. designed he H
2
O
2
biosenso based
on myoglobin (Mb) edox ac i i y [
60
]. In de ail, hey encapsula ed MoS
2
nanopa icles wi hin GO
and used his composi e ma e ial o modi y gold elec odes ia chemical linke ( he p inciple can be
seen in Figu e 4A). Mb is able o media e elec ochemical educ ion o H
2
O
2
due o he p esence o
i on wi hin i s co e [
61
]. They compa ed he pe o mance o he designed elec ode wi h Mb/MoS
2
and Mb/GO. Mb/GO/MoS
2
showed an enhanced elec ochemical signal e en in he p esence o AA,
NaNO
2
and NaHCO
3
. The ampe ome ic ead-ou a
−
0.3 V s. Ag/AgCl eached a LOD o 20 nM
H
2
O
2
. The same app oach wi h immobiliza ion o Mb was used o biosensing o ni ic oxide and
ni i e ions [
62
,
63
]. Al e na i ely, hemoglobin can be used ins ead o Mb as showed by Liu e al. [
64
].
Jeong e al. compa ed he pe o mance o plana G /MoS
2
and G /MoS
2
wi h 3D s uc u e as enzyma ic
glucose biosenso s [
65
]. They immobilized glucose oxidase (GOx) on glassy ca bon elec odes modi ied
wi h he men ioned composi es and e alua ed hem wi h ampe ome ic de ec ion using low-injec ion
analysis. In gene al, glucose enzyma ic biosenso s sense H
2
O
2
gene a ed by oxida ion o glucose
Molecules 2019,24, 3374 8 o 14
by GOx. They summa ized ha he 3D-based biosenso possessed conside ably highe sensi i i y
(3.36
µ
A
·
mM
−1
) han a biosenso using he same bu plana ma e ial (0.11
µ
A
·
mM
−1
). A he H
2
O
2
oxida ion po en ial o
−
0.45 V he minimal in luence o common in e e ences such as AA, DA o
UA was obse ed. G aphene pape suppo ed MoS
2
nanoc ys als monolaye wi h Cu submic on
buds o biosensing o lac a e and sensing o glucose in swea , as epo ed by Wang e al. [
66
]. In his
app oach Cu buds enabled di ec oxida ion o glucose a +0.42 V s. sa u a ed calomel elec ode (SCE)
as was epo ed be o e [
67
,
68
]. Fo glucose, hey eached LOD o 500 nM and linea dynamic ange o
5–1775
µ
M wi h minimal in luence o ions abundan in swea such as Na
+
, Cl
−
, K
+
, Ca
2+
and Mg
2+
.
Fu he , hey modi ied he men ioned elec ode wi h lac a e oxidase. Lac a e oxidase is able o con e
lac ic acid o py u a e and H
2
O
2,
which enabled he indi ec quan i ica ion o he concen a ion o
lac ic acid. LOD o 0.1
µ
M was ob ained o lac a e bu as au ho s poin ou , low de ec ion limi s a e
no manda o y o swea analysis and s abili y, selec i i y and wide linea ange a e p e e ed. To al
concen a ion o phenolic compounds in ed wine samples based on ca bon sc een-p in ed elec ode
modi ied wi h g aphene quan um do s, MoS
2
and T ame es e sicolo laccase (T L) was epo ed by
Vasilescu e al. (Figu e 4B) [69].
Apa om nucleic acid hyb idiza ion senso s, elec ochemical signal ansduc ion is highly
sui able o de ec ion o ap ame –p o ein in e ac ion. Ap ame s a e single-s anded nucleic acid (DNA
o RNA) which possess high a ini y o a ge molecules, compa able o o e en highe han an ibodies.
In compa ison wi h an ibodies, which a e s ill aken as a golden s anda d in bio ecogni ion elemen s,
ap ame s a e abou 10- imes smalle , mo e he mally s able and cheape . Since ap ame s a e selec ed
in i o
, hei sequence can be selec ed o p ese e desi ed unc ion e en in non-physiological pH
o high sal concen a ion (impo an o elec oanalysis). Since no animals a e used o ap ame
p oduc ion, molecules which do no cause immune esponse such as oxic compounds o small
molecules such as ions can be used o p oduce ap ame s. In esponse o hese ac s, ap ame s a e
equen ly used as bio ecogni ion elemen s in many di e en analy ical applica ions [
70
]. Among
o he s, elec ochemical ap asensing is apidly de eloping and co e s se e al ields such as ood sa e y,
en i onmen al haza ds, medical diagnosis, e c.
A ol amme ic lipopolysaccha ides (LPS) ap asenso bene i ing om ad anced p ope ies o
g aphene and MoS
2
composi e was epo ed by Yuan e al. [
71
]. They used la ge speci ic su ace o
polye hyleneimine (PEI) unc ionalized GO and MoS
2
composi e (PEI– GO–MoS
2
) as a ca ie o an
elec ochemical label— oluidine blue (TB). Mo e p ecisely, hey modi ied GCE wi h PEI– GO–MoS
2
and loaded i wi h TB. Nex , hey used gold nanopa icles (AuNPs) o a ach hiola ed LPS ap ame
on he elec ode and used bo ine se um albumin (BSA) o block he elec ode agains unspeci ied
binding o LPS. In he p esence o LPS in analyzed samples he TB educ ion signal (
−
0.35 V s.
SCE) g adually dec eased. The esponse o he ap asenso linea ly dec eased wi h loga i hm o LPS
concen a ion in he ange o 5.0
×
10
−5
ng
·
mL
−1
o 2.0
×
10
2
ng
·
mL
−1
wi h he LOD o 3.01
×
10
−5
ng
·
mL
−1
. Thei senso showed good pe o mance in he p esence o common se um in e e en s such
as BSA, AA, DA o glucose and showed eco e ies in he ange 101–103% in spiked se um samples.
A la oxin B
1
(AFB
1
) was a ge o he ap asenso designed by Gele a e al. [
72
]. They syn hesized GO,
MoS
2
and polyaniline (PANI) composi e co e ed wi h chi osan (CS). GCE modi ied as men ioned was
used o immobilize hiola ed AFB
1
ap ame ia AuNPs (Figu e 4C). A e ap ame immobiliza ion, he
su ace excessi e ac i e si es we e blocked wi h 6-me cap o-1-hexanol. They used [Fe(CN)
6
]
3−/4−
as an
elec ochemical epo e and obse ed a dec ease o i s DPV signal wi h inc easing concen a ion o
AFB
1
in analyzed samples. They ob ained a ema kable LOD o 0.002 g
·
mL
−1
and a calib a ion cu e
wi h a linea ange o 0.01 g·mL−1 o 1.0 g·mL−1(Figu e 4D).
Human papilloma i us (HPV) ap asenso was epo ed by Chekin e al. [
73
]. HPV is
non-en eloped dsDNA i us ha in ec s he epi helium and is associa ed wi h oncogenic isk. Since
his i us is essen ial o he de elopmen o ce ical cance i is accep ed as i s molecula bioma ke .
They decided o de ec HPV-16 ia i s L1 capsid p o ein. They d op-cas ed po ous GO on GCE and
subsequen ly d op-cas ed MoS
2
on GO-modi ied GCE. GCE/ GO/MoS
2
elec ode was chemically
Molecules 2019,24, 3374 9 o 14
unc ionalized using physiso p ion o hiol ligands (mix u e o PEG and 11-me cap oundecanoic acid
(MUA)). NH
2
unc ionalized L1 p o ein ap ame was subsequen ly immobilized on he elec ode
using ca bodiimide chemis y (EDC/NHS). They used DPV o de ec (Fe(CN)
6
)
4−
as a media o whose
signal showed a cons an dec ease in he L1 p o ein concen a ion ange o 0.2–2ng
·
mL
−1
and LOD
0.1–2ng
·
mL
−1
. GO/MoS
2
nanoshee s and Fe
3
O
4
NPs nanozyme syne gic ca aly ic ac i i y was used
o ampli y he signal o a MCF-7 cy osenso [
74
]. They used GO/MoS
2
composi e o elec ode
modi ica ion due o i s high su ace a ea, as elec on ans e and good biocompa ibili y. Fo MCF-7
cells p econcen a ion, hey used ap ame -modi ied supe pa amagne ic Fe
3
O
4
nanopa icles which
we e a ac ed by including a ached cells o he su ace o GCE ia magne ic ield (Figu e 4E). Bo h
ma e ials, GO/MoS
2
and Fe
3
O
4
NPs, possessed a syne ge ic e ec in abili y o educe H
2
O
2
, and hus
media e 3,3
0
,5,5
0
- e ame hylbenzidine (TMB) oxida ion (+0.3 V s. SCE). TMB oxida ion p oduc was
analyzed using DPV and he concen a ion o MCF-7 cells in samples was epo ed. They ob ained a
LOD o 6 cells·mL−1and a linea ange o e 15–45 cells·mL−1(Figu e 4F).
Molecules 2019, 24, x FOR PEER REVIEW 9 o 14
subsequen ly d op-cas ed MoS
2
on GO-modi ied GCE. GCE/ GO/MoS
2
elec ode was chemically
unc ionalized using physiso p ion o hiol ligands (mix u e o PEG and 11-me cap oundecanoic acid
(MUA)). NH
2
unc ionalized L1 p o ein ap ame was subsequen ly immobilized on he elec ode
using ca bodiimide chemis y (EDC/NHS). They used DPV o de ec (Fe(CN)
6
)
4−
as a media o whose
signal showed a cons an dec ease in he L1 p o ein concen a ion ange o 0.2–2 ng∙mL
−1
and LOD
0.1–2 ng∙mL
−1
. GO/MoS
2
nanoshee s and Fe
3
O
4
NPs nanozyme syne gic ca aly ic ac i i y was used
o ampli y he signal o a MCF-7 cy osenso [74]. They used GO/MoS
2
composi e o elec ode
modi ica ion due o i s high su ace a ea, as elec on ans e and good biocompa ibili y. Fo MCF-
7 cells p econcen a ion, hey used ap ame -modi ied supe pa amagne ic Fe
3
O
4
nanopa icles which
we e a ac ed by including a ached cells o he su ace o GCE ia magne ic ield (Figu e 4E). Bo h
ma e ials, GO/MoS
2
and Fe
3
O
4
NPs, possessed a syne ge ic e ec in abili y o educe H
2
O
2
, and hus
media e 3,3′,5,5′- e ame hylbenzidine (TMB) oxida ion (+0.3 V s. SCE). TMB oxida ion p oduc was
analyzed using DPV and he concen a ion o MCF-7 cells in samples was epo ed. They ob ained a
LOD o 6 cells∙mL
−1
and a linea ange o e 15–45 cells∙mL
−1
(Figu e 4F).
Figu e 4. (A) Schema ic o elec ochemical biosenso s composed o myoglobin (Mb) and o GO/MoS
2
wi h elec ochemical enhancemen o H
2
O
2
de ec ion. F om Yoon e al. [60]. (B) Schema ic
ep esen a ion o cons uc ion and he de ec ion p inciple o sc een-p in ed ca bon elec ode modi ied
wi h g aphene quan um do s, MoS
2
and laccase as a ca eic acid biosenso . F om Vasilescu e al. [69].
(C) Schema ic ep esen a ion o he educed g aphene oxide/molybdenum disul ide/polyaniline
nanocomposi e-based elec ochemical ap asenso o de ec ion o a la oxin B
1
ab ica ion. (D)
Di e en ial pulse ol amme y (DPV) esponses o he ap asenso a e 20 min incuba ion wi h 0.0100,
0.0156, 0.0313, 0.0625, 0.125, and 1.00 g∙mL
−1
AFB
1
. Bo h om Gele a e al. [72]. (E) Schema ic
illus a ion o magne ic beads assis ed bi-nanozyme signal ampli ica ion o de ec ion o ci cula ing
Figu e 4.
(
A
) Schema ic o elec ochemical biosenso s composed o myoglobin (Mb) and o GO/MoS
2
wi h elec ochemical enhancemen o H
2
O
2
de ec ion. F om Yoon e al. [
60
]. (
B
) Schema ic
ep esen a ion o cons uc ion and he de ec ion p inciple o sc een-p in ed ca bon elec ode
modi ied wi h g aphene quan um do s, MoS
2
and laccase as a ca eic acid biosenso . F om
Vasilescu e al. [
69
]. (
C
) Schema ic ep esen a ion o he educed g aphene oxide/molybdenum
disul ide/polyaniline nanocomposi e-based elec ochemical ap asenso o de ec ion o a la oxin B
1
ab ica ion. (
D
) Di e en ial pulse ol amme y (DPV) esponses o he ap asenso a e 20 min
incuba ion wi h 0.0100, 0.0156, 0.0313, 0.0625, 0.125, and 1.00 g
·
mL
−1
AFB
1
. Bo h om Gele a e al. [
72
].
(
E
) Schema ic illus a ion o magne ic beads assis ed bi-nanozyme signal ampli ica ion o de ec ion o
ci cula ing umo cells. (
F
) DPV esponses o MCF-7/ap ame /Fe
3
O
4
NPs/ GO/MoS
2
/GCE- ab ica ed
cy osenso a e cap u ing di e en concen a ions o MCF-7 cells om (a) o (h): 0, 15, 20, 25, 30, 35,
40 and 45 cells
·
mL
−1
in 0.01M PBS (pH=5.0) wi h 0.1mM o H
2
O
2
and 0.2mM o TMB. Bo h om
Tian e al. [74].